10193 lines
357 KiB
Plaintext
10193 lines
357 KiB
Plaintext
Beginners' corner -design your own Colpitts oscillator
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ELECTRON ICS
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WORLD 111 09>
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INCORPORATING WIRELESS WORLD
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9 770959 833066
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A REED BUSINESS PUBLICATION SOR DISTRIBUTION
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SEPTEMBER 2000 £2.65
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New rf mixer design
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Make better buffers
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Evaluate capacitors for SMPS
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Light controller for dynamic art
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Eye flicker fusion meter
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Global clock synchronisation
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Circuit ideas
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Jingle softener New use for cycle computer Liquid level sensor Glitch simulator NiCd & lead-acid charger
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PC stepper interface
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Te net Quality second-user test 8. measurement equipment
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Tel: 02476 650702 NEW PHONE CODE FOR COVENTRY 02476
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Hewlett Packard
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8642A —high performance R/1: snthesiser
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(04-1050MHz)
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£4750
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3335A —synthesiser (200Hz-81MHz)
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£2400
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Hewlett Packard
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436A power meter and sensor (various) from £750
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437B power meter and sensor (various) from £1100
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Hewlett Packard
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8753A network analyser (3GHz)
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from £2500
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8753B network analyser (3GHz)
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from £3250
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'S' parameter test sets 85046A and 85047A
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available at
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£2000 & £3000
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Wandel & Goltermann
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SPECIAL OFFER
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PCM-4 PCM Channel measurement set
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(various options available)
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from £5500
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Marconi 2305 —modulation meter
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£999
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Marconi 6310 —programmable sweep generator
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(2 to 20GHz) —new Hewlett Packard
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£3250
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5342A —microwave frequency counter
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(500MHz-18GHz) ops 1& 3
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5370B —universal time interval counter
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£1500
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OSCILLOSCOPES • *.'Hz 4channel DSO , .-,4201A -300MHz Digitizing Hewlett Packard 54600A -100MHz -2channel
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Hitachi V152N212N222N302B/V302FN353F V5508 V650F Hitachi VI 100A -100MHZ •4channel Intron 2020 -20MHz Dual channel D.S.O. (new) lwatstu SS 5710/SS 5702 Kikusui COS 5100 -100MHz -Dual Channel
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Lecroy 9450A -300MHz/400 MS/s D.S.O. 2channel Meguro MSO 1270A -20MHz -D.S.O. (new) Philips PM3094 -200MHz -4channel Philips 3295A -400MHz -Dual channel
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Philips PM3392 -200MHz-200Ms:s -4channel Tektronix 465 -100MHZ -Dual channel Tektronix 464/466 -100MHZ -(with AN storage) Tektronix 475/475A -200MHz250MHz • Tektronix 468 -100MHZ •D S.0 Tektronix 2213/2215 -60MHz •Dual channel Tektronix 2220 -60MHZ -Dual channel D S 0 Tektronix 2235 -100MHZ -Dual channel Tektronix 2221 -60MHz -Dual channel D S.0
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Tektronix 2245A -100MHZ -4channel Tektronix 2440 -300MHz/500 MS/s D.S.O. Tektronix 2445A -150MHz -4channel Tektronix 2445 -150MHZ •4channel. OMM Tektronix TAS 475 -100MHZ •4channel Tektronix 7000 Series (100MHZ to 500MHZ)
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Tektronix 7104 - 1GHz Real Time
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Tektronix 2465/2465A24658 -300MHz,350MHz 4channel Tektronix 2430/2430A - Digital storage -150MHz
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Tektronix 2467B -400MHz -4channel high writing speed Tektronix TOS 320 100MHz 2channel
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Tektronix TOS 540 500MHz 4channel Tektronix 544A 500MHz 4channel
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£1500 £1250
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£750 from £125
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£900 £450 from £125 £350 £2250 £450 £1750 £1600 £1995
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£350 £350 from £450 £650 £350 £1250 £600 £1250 £900 £2950
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£1250 £1200
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£995 from £200 from £25130 from £1250 from £1250
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£4750 £850
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£4500 £4950
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SPECTRUM ANALYSERS
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Ande AC 8211 -1i'i.ahtz
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Avcom PSA-65A -2to 1000MHz Anntsu MS 2663A -9KHz •8.1GHz Anntsu MS 628 -50Hz to 1700MHz Anntsu MS 6108 10KHz -2GHz -as new Anntsu MS 710F -100KHz -23GHz
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AdvanteeTAKEDA RIKEN -4132- 100KHz •1000MHz Hewlett Packard 3562A Dual channel dynamic signal analyser 64pHz •100KHz Hewlett Packard 8505A -1.3GHz -Network Analyser Hewlett Packard 8756A/8757A Scaler Network Analyser
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Hewlett Packard 853A Mainframe •8559A Spec. An. (0.01 to 21GHz) Hewlett Packard 182T Mainframe •8559A Spec. An. (0.01 to 21GHz) Hewlett Packard 85688 -100Hz -1500MHz Hewlett Packard 8567A -100Hz -1500MHz Hewlett Packard 8754A - Network Analyser 4MHz-1300MHz Hewlett Packard 8591E 9K1-1z-1 8GHz Hewlett Packard 8594E 9KHz-2 9GHz Hewlett Packard 3561A Dynamic signal analyser Hewlett Packard 35660A Dynamic signal analyser IFR A7550 -10KHz-IGHz -Portable Meguro -MSA 4901 -30MHz -Spec Analyser Meguro -MSA 4912 -1 MHz -IGHZ Spec Analyser Tektmnoi 2712 9KHz-1 8GHz (with tr.-Jung generato,r and video money mryie,
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£1500 £7£080500 ££13455000
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£ £51250500
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£5500 £1995 from £1000 ££22725500 £5250 £3195 0 90 5
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£4250 £6.750 ££33299505 £1£975000
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f995 £5503
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All equipment is used -with 30 days guarantee and 90 days in some cases Add carriage and VAT to all goods.
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Telnet, 8Cavans Way, Binley Industrial Estate,
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Coventry CV3 2SF.
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CIRCLE NO. 701 ON REPLY CARD
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Radio Communications Test Sets
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Marconi 2955 Marconi 2958/2960 Antritsu MS555A2 Hewlett Packard 8922B (GSM) Schlumberger Stabilock 4031 Schlumberger Stabilock 4040 Racal 6111 (GSM) Racal 6115 (GSM) Rhode & Schwarz CMTA 94 (GSM) IFR 1200S
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£2000 £2250 £1200 £6950 £3995 £1500 £1750 £3995 £5950 £2995
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Fax 02476 650 773
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. termann TSA-1 system a . Minor, 6439 -10-2000MHz R/F Analyser
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Hz-180M Hz)
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MISCELLANEOUS
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Eaton 2075-2A -Noise Gain Analyser FFlluukkee 25612000ADa5t1a00Bu8c5ke2t0s0A -Calibration Units (various available)
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a2100 from: £57050
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Fluke 8842A -Digital Multimeter Hewlett Packard 339A Distortion measuring set Hewlett Packard 435A •4358 Power meters Hewlett Packard 7780 Dual-Directional Couplers Hewlett Packard 3488A -Switch Control unit Hewlett Packard 3784A -Digital Transmission Analyser Hewlett Packard 3785A -Jitter Generator & Receiver Hewlett Packard 5343A -Frequency counter 26 5GHz Hewlett Packard 5385A -1GHZ Frequency counter Hewlett Packard 6033A -Autoranging System PSU (20v-30a)
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Hewlett Packard 66223A - DTruiaplle0o/Pp ssyysstteemm pp..ss..uu..
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£600 £1200 from £10(
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6
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£4££45075 05C £1250 £2070005000
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£ 6
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££1132 055000
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Hewlett Packard 6624A -Quad Output Power Supply
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£2000
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Hewlett Packard 6632A -System Power Supply (20v-5A)
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|
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Hewlett Packard 6652A -20V-25A System PSU Hewlett Packard 8112A -50MHz Pulse Generator
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£278° 5°0 £2250
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Hewlett Packard 83508 - Sweep Generator Mainframe
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£2000
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Hewlett Packard 8656A Synthesised signal generator
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£850
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Hewlett Packard 86568 Synthesised signal generator
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£1450
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||
|
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Hewlett Packard 86600 -Synthd Sig Gen (10 KHz-2600MHz)
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|
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£3250
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||
|
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Hewlett Packard 8901B -Modulation Analyser
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||
|
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Hewlett Packard 8903A. B and E •Distortion Analyser
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from £ £21275500
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||
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Hewlett Packard 16500A • B -Logic Analyser Mainframes
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||
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||
from £1000
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||
|
||
Hewlett Packard 16500C -Logic Analyser Mainframe
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||
|
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£3250
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||
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Hewlett Packard 16501A/B & C •Logic Analyser System Expander Frame from £2000
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|
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Hewlett Packard 379000 -Signalling test set
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||
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£3750
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Hewlett Packard 75000 VXI Bus Controllers
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||
|
||
Hewlett Packard 4193A -Vector Impedence Meter Hewlett Packard 5350B -20Hz Frequency Counter
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|
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fC4P7°5A0 £1950
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Hewlett Packard 86578 •100KHz-2060 MHz Sig Gen
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|
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Hewlett Packard 86570 -XX DOPSK Sig Gen
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||
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££43959 005
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|
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Hewlett Packard 8130A -300 MHz High speed pulse generator Hewlett Packard 8116A -50MHz Pulse/Function generator
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£5250 £2250
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||
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Hewlett Packard 1660A-136 channel Logic Analyser£9
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||
|
||
Keytek MZ-15,EC Minizap ESO Simulator (151,5 •hand held)
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££317550
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|
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Marconi 1066B -Demultiplexer & Frame Alignment Monitor (140MBIT to 64KBIT)
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NEW
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£1750
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||
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Marconi 2610 True RMS Voltmeter
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||
|
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Marconi 6950,6960/6960B Power Meters & Sensors
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from ££450500
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Philips 5515 -TN -Colour TV pattern generator£1400
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||
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Philips PM 5193 -50MHz Function generator
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££1570905
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Leader 3216 Signal generator 100KHz -140MHz -AM/FM/CW with built in FM stereo
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modulator (as new) asnip at
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Racal 1992 - 13GHz Frequency Counter
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£500
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RRoohhddee && SScchhwwaarrzz SNMRYV-0d1ualSicghnaanlnGeelnpeorwateorrm(e9tKerHz&-1N0A4V0MZH2z)Sensor Systron Donner 6030 -26 5GHz Microwave Freq Counter Tektronix ASG100 -Audio Signal Generator Wayne Kerr 3245 - Precision Inductance Analyser »Won 6747A-20 -10MHz•20GHz •Swept Frequency Synthes ise r
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£2250 ££ 112 95 9 50
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£750 ££419 99505
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||
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Tel: 02476 650 70'À
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Fax: 02476 650 77
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CONTENTS
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Oià COMMENT
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Wither Wap?
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674
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NEWS
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• UK videophone setback • Internet on TV available this year • Display technology uses ink-jet printing • Electronic product gazumping? • UK lags Europe with Internet
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broadband • Isolated drivers made by
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micromachining • South Korea scraps phones subsidies • Modulator scheme for 25Tbit/s • BSkyB must free up encryption
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Is the opto-coupler dead? Find out what the benefits of an alternative coupler using micro-machined inductors are on page 677.
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704
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DYNAMIC ART
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Douglas Clarkson argues that electronics engineers and artists should work
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together to produce dynamic works of art, and makes suggestions for simple artistic lighting effects using opto-mechanics.
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709 NEW PRODUCTS
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720 SPEAKERS' CORNER Loudspeaker crossover networks: constant voltage or constant power' John Watkinson's answer might surprise you.
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722
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SPECIAL RELATIVITY: RIGHT OR WRONG?
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In telecomms, synchronising clocks around the Earth is an important issue. Al Kelly believes that the correction applied to such clocks is not explained properly by existing theories.
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725 BETTER BUFFERS
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Having been unsuccessful in looking for
|
||
information to help him design
|
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|
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680
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|
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A NEW LOW-IMD MIXER
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Chris Trask's new series-shunt feedback active mixer offers clear advantages over
|
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both the common Gilbert Cell active mixer and diode-ring mixers. Yet it's possible to implement the design on the kitchen table!
|
||
|
||
686
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|
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FLICKER-FUSION METER
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The maximum rate of flicker that a person can perceive relates to how tired that person is. It is also affected by age, by whether or not you've been drinking coffee and even on whether you're introvert or extrovert. Peter Naish describes how to measures it.
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|
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694
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|
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OPTOELECTRONICS SPOTS CANCER CELLS
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A new technique called light-scattering
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spectroscopy' helps detect pre-cancerous cells in afraction of asecond using just an endoscope, light beam and some DSP. Pete Mitchell reports.
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|
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696
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EVALUATE CAPACITORS FOR SMPS DESIGNS
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When choosing acapacitor for amodern switch-mode power supply, high
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frequencies, complex waveforms and the demand for ever increasing efficiency make life difficult. Cyril Bateman explains what the problems are, and how to sort them out.
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complementary compound emitter followers, Dave Kimber set about developing his own guidelines.
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730
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BEGINNERS' CORNER
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RF oscillators play an important role in
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wireless communications. One is required in every transmitter, and there is also at least one in most receivers. Ian Hickman explains how to design your own Colpitts oscillator.
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734
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CIRCUIT IDEAS
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• Bike computer reads amps, amp.hours • One-at-a-time phone switch • Economical level sensor needs just 7pA • Circuit simulates glitches • PC-controlled bipolar stepper motor • Simple charger for NiCds and lead acid • Jingle softener
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742 WEB DIRECTIONS Useful web addresses for the electronics designer.
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|
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747 LETTERS THD. Hard-drive failures, Thoughts from along-standing reader
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Illustration Mark Oldroyd
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Ever-changing light patterns: electronics adds anew dimension to art. Read how. on page 706.
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ogidight.
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Optoelectronics spots cancer cells in seconds using anew technique involving just an endoscope, light beam and some DSP. Dave Mitchell reports on page 694.
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To evaluate acapacitor for amodern switched-mode power supply, agood test jig is vital. Find out what Cyril Bateman uses on page 696.
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October issue on sale 7 September
|
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|
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September 2000 ELECTRONICS WORLD
|
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|
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Pie BaMÇR, Write your PIC programs in BASIC! -No STAMP EQUIRED!
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PIC Micro CIO-ROM
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over 1.26b el info £10 Inc PaP and VAT
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•
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Quicker and easier than C or assembler PIC BASIC is a true compiler providing faster execution and shorter programs than BASIC stamp interpreters, built in I2C routines and serial cornms upto 115K Baud and full BASIC STAMP compatibility make writing for the Microchip PICrnicroS easy! PIC BASIC compiles your basic language programs to Microchip Hex format for use with In-circuit emualtors or for programming directly into the PIC CHIP Supports PIC12C67x. PIC14Cxxx, PIC16C55x, 6xx. dxs.84, 92xand 16F87x Full documentation with syntax examples are provided in the 168 page user manual. A
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technical support mailing list is provided for life time support.
|
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• RIM Illa% -07411%
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The PIC BASIC Pro compiler instruction set is compatible with the Basic Stamp II providing additional functionality over PIC BASIC. feature like LCD read Write, fully customisable Sonal in I out (Create a senal LCD display driver In modules) Full de-bug facilities, compile with debug to produce assembly commented with your Basic commands PIC BASIC and PIC BASIC PRO compile tight efficient code without the use of a basic interpreter Supplied with a 168Page manual, explaining each command and worked examples FREE PIC Macro compiler FREE Programmers File Editor. FREE Windows Front End PIC BASIC PRO Includes samples programs and code to support Smart card readeiwnte
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Download the full 168 page PIC BASIC MANUAL and sample programs
|
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http://www.picbasic.co.uk Order Online via our secure server
|
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http://www.crownhill.co.uk
|
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• Low cost programmer for PIC12Cxxx. PIC12CEiocc. PIC14Ctoot. PIC10C505. 65x. a.. 7xx,84. 9xxPIC 18CE82x and PIC18F87x
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•ZIF adaptors are available for 8/18 in 40/28Pln OIL. 8.18 and 28 SOIC. 44 Pin MOFP, 44 and 88 Pin PLCC
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• Powered by 2e 9V bananas or AC adapter • Connects to PC PareIle P.M • Upgredable software is supplied for future PIC Micro s • FREE 8051 style PIC Macro compiler
|
||
£35withWhPIeCnBpAu$rJcChased <
|
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Parallel port extension cable -£5.95 40Pln ZIF socket -£22.50 8/18Pin ZIF Socket -£22.50 PIC8 Prototype board -£4.50 PIC18 Prototype board -£5.50 PIC64 Prototype board -£8.50
|
||
PIC Real-time Emulat afin Programmei k;i4e9
|
||
|
||
Packed with information, data sheets, application notes, programs diagrams and tutorials. Includes TETRIS and PING PONG with sound and video out of a single PIC 16F84. Basic language assembly routines and macros for hundreds of commands. Data sheets on thousands of devices, micro's, memory and support chips
|
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WO DISPLAYS
|
||
16x2 line super twist displays -£7.50 ea
|
||
RIM awl Resonators
|
||
4Mhz and 2,10111Av from 45p
|
||
PIC16x84 programmer Kit
|
||
WINDOWS Driver -£15.00 inc PaP 4- VAT
|
||
Programs the popular PIC1684 and 24 series serial memory devices. Cennects to the serial port ol PC unto pentium (not P2 or P3) and requires
|
||
NI External power supply. The KIT Includes Diagram. layout. High Quality PCB
|
||
INK all componenets. software on 3.5" FO
|
||
SMARTCARD DEVELOPMENT SYSTEM
|
||
Reim:1*i daax &meat *rat PC& careele ! Paige Indies. Professional card Reader Writer (Chien Micro), Asserted Smart Cards (3 pars), Undies of settee code r) VB3,4,5+6, Cand Delphi Exarrçês Agst Read While lo Srital Cards and DJ zes Doceetc, aY!detàled ',11,:icoe DLL
|
||
Www.towitoko.co.uk
|
||
|
||
=
|
||
|
||
4 9$
|
||
|
||
7, , 7 1
|
||
|
||
16F871 In Cite«
|
||
aller %if% %haft
|
||
|
||
EFor PIC16F8111 [emulates most PIC16C6Kflidevicesi El In-Circuit run time debugging
|
||
Real Time code execution 32Klu to 20Miu real time operation E High Speed Parallel port interlace z2.5V to 6.V operating range izBulh in device programmer [Ann. Step. Run to Cursor etc EConditlonal Animation Break FSollware animation trace captures 3user defined variables
|
||
in addition to encode. W. Status, ESA registers and corresponding instructions FSource Level and symbolic debugging
|
||
Runs under PICICD IDE twin95/98 or DTI or MPLAB rz Supplied with ICD debug module, Prom board,
|
||
40Pin and Min emulator headers. Cables WE software and user guide
|
||
|
||
, _LabProg 48LV (4 Low Cost -High Performance
|
||
|
||
Includes:
|
||
|
||
-eee-
|
||
|
||
Intelligent Universal Device Programmer
|
||
Plugs into parallel port of your PC Adaptors for TSOP, PSOP. UP, SOIC, PtCC
|
||
|
||
Connection cable
|
||
|
||
True No Adapter Programming upto 48 Pins
|
||
|
||
Diagnostic POD User Manual PC Sotware Driver
|
||
|
||
11! CE certified
|
||
|
||
Programs and Verifies 2,2.7,3,3.3 a. 5V devices FREE sollviare updates 3Year Warranty
|
||
|
||
240VAC/12V adaptor
|
||
|
||
Universal Serial [[prom programmer
|
||
|
||
PreProm UNIVERSAL (mom Programmer
|
||
Adaptors tor TSOP PSOP, QFP, SOIC, PECC
|
||
|
||
E49
|
||
|
||
Adaptors tor Microprocesors Adaptors tor Eeprom Emulator ulster,
|
||
|
||
WWI>
|
||
|
||
*a plow me sew, to
|
||
|
||
ea2.00
|
||
|
||
Crownhill Associates Limited
|
||
|
||
VISA
|
||
|
||
32 Broad Street Ely Cambridge Cb7 4PW Tel: 01353 666709 Fax: 01353 666710
|
||
|
||
ORDER ON-LINE
|
||
|
||
WWW.Crownhill.co.uk
|
||
|
||
CIRCLE NO. 104 ON RI
|
||
|
||
%kJ
|
||
|
||
Whither WAP?
|
||
|
||
EDITOR
|
||
Martin Eccles 020 8652 3614
|
||
CONSULTANTS
|
||
Ian Hickman Philip Darrington Frank Ogden
|
||
EDITORIAL ADMINISTRATION
|
||
Jackie Lowe 020 8652 3614
|
||
EDITORIAL E-MAILS
|
||
jackie.lowe@rbi.co.uk
|
||
GROUP SALES EXECUTIVE
|
||
Pat Bunce 020 8652 8339
|
||
ADVERTISEMENT E-MAILS
|
||
pat.bunce@rbi.co.uk
|
||
ADVERTISING PRODUCTION
|
||
020 8652 8339
|
||
PUBLISHER
|
||
Mick Elliott
|
||
EDITORIAL FAX
|
||
020 8652 8111
|
||
CLASSIFIED FAX
|
||
020 8652 8938
|
||
NEWSTRADE ENQUIRIES
|
||
020 7907 7777
|
||
ISSN 0939-8332
|
||
For afull listing of RBI magazines: http/Avww.reedbusiness.com
|
||
eff41l4,„•.• REED fair BUSINESS M.- INFORMATION
|
||
|
||
5hock, horror, hold the front page... sales in the UK of WAP-capable mobile phones —you know, the ones that work as Internet terminals as well —have achieved just 200 000 instead of the projected half million.
|
||
But perhaps you didn't know —or didn't even care? That seems to be the reaction of the public at large, even if dealers, manufacturers and pundits are wailing and gnashing their teeth. Building societies and mobile dealers are reduced to giving away WAP phones as acome-on, while the prophets of
|
||
doom and desperation portray WAP as abigger techno-flop than the Millennium Dome —as if that were possible. But is WAP really aclick too far?
|
||
It depends on your outlook. Undoubtedly the product has been oversold if the following nonsense is typical of the sales pitch for WAP —and no, I won't embarrass the perpetrator!
|
||
"I'm in the pub, where Iorder around of drinks, paying for them from my mobile and join my friends.
|
||
"We gather round one mobile to watch highlights of what movies are currently playing at the local cinema. We make areservation through the mobile and check out the view from our seats on line.
|
||
"I also order some food to be ready for me to pick up when Iarrive. Ilike the film so much that Ibuy and download the soundtrack to my mobile while I am watching.
|
||
"After the movie Iam too tired to walk home so I call ataxi. Iallow the taxi company to find my location and Iwatch the taxi approach on amap on my mobile. The taxi is paid automatically when I get out and the lights in the house come on as I approach.
|
||
"As Isettle down with aglass of wine, the soundtrack Ibought at the cinema is transferred to my hi-fi to end agreat night out!"
|
||
Perhaps life really is like that on planet WAP — but not down here.
|
||
Clues to WAP's poor performance to date are not hard to find. While many people find the ability to make phone calls on the move convenient and reassuring, it's less clear whether they have the enthusiasm, requirement or the patience to download stock quotes or e-mail or make travel bookings and other transactions over aconnection that's slow — at 9600 bit's —expensive — at 5p or 10p aminute —and hardly ashowpiece of legibility
|
||
or graphic presentation. For WAP browsing online, content must be
|
||
redesigned from scratch, without even the benefit of open standards. WAP technology is proprietary and sold under licence, controlled by agroup called the
|
||
|
||
WAP Forum embracing the main companies involved.
|
||
The marketing of WAP has been less than scintillating too. There's abundant evidence that successful extraction of customers' money demands
|
||
creating an awareness of need or desire; few products sell themselves.
|
||
Even when the merchandise itself is appealing, a price that's pitched higher than the public is prepared to pay will restrict sales to all but 'must have' early adopters. Pocket calculators, microwave
|
||
ovens, video recorders, home computers, CD players —the list is endless of new technologies that
|
||
took awhile to catch on. It doesn't help that today's offerings are less than
|
||
compelling. Even the Carphone Warehouse —
|
||
arguably Britain's most successful independent purveyor of mobile communication —is forced to concede:
|
||
"There is alot of current hype in the media about what WAP is, and while the possibilities in the very near future are exciting and limited only by the imagination, WAP is currently apredominantly text-based view of the Internet. Improvements to the current mobile networks and in screen and battery technology will all enhance the WAP experience, eventually delivering rich multi-media content in the not too distant future."
|
||
Full marks for honesty! To write off WAP entirely would be wrong, though —its time will eventually come when prices fall and product specifications improve. Combining aWAP-enabled phone with an electronic organiser, palmtop PC, portable FM radio, MP3 player and TV would make afar more compelling proposition. And then, finally, amass market could be born. Mobile phones are aclassic examplar; those clumsy featureless 'bricks' that cost £1000 back in 1985 were scarcely arunaway success, yet fifteen years on more than half the population now owns acellphone and a sleek, highly featured and affordable one to boot. Commoditisation is the name of the game. And that's it. Sorry, what's WAP? Yes, Ishould have defined the term at the outset but nobody else bothers to. It stands for Wireless Application Protocol, aname that conveys precisely nothing to the world at large. Years ago, successful marketeers knew that to sell an obscurely titled technology, you had to give it a meaningful name. Touch-Tone, Video Plus and Walkman all give aclue to their function —but not WAP. Time for are-launch with anew name perhaps? Andrew Emmerson
|
||
|
||
SUBSCRIPTION HOTUNE
|
||
Tel (0) 1444 475662 Fax (0) 1444 445447
|
||
SUBSCRIPTION QUERIES
|
||
rbp.subscriptions@rbi.co.uk Tel (0) 1444 445566 Fax (0) 1444 445447
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||
|
||
Electronics World is published monthly. By post, current issue £2.65, back issues (if available £3.00). Orders, payments and general correspondence to L333, Eleorenks Woild, Quadrant House, The Quadrant, Sutton, Surrey SM2 SAS. Tlx: 892984 REED BP G. Cheques should be made payable to Reed Business Information Ltd Newstrade: Distributed by Morketforce (UK) Ltd, 247 Tottenham Court Road London WI POAU, tel 020 7907 7777. Subscriptions: Quadrant Subscription Services, Ookfield House Perrymount Road, Haywords Heath, Sussex RH16 3DH. Telephone 01444 445566. Please notify change of address. Subscription rates 1year UK £36.00 2years £58.00 3years £72.00. Europe/Eu 1year £51.00 2years £82.00 3years £103.00 ROW 1year £61.00 2years £98.00 3years £123
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||
|
||
Overseas advertising agents: France and Belgium: Pierre Mussard,
|
||
18-20 Place de la Madeleine, Paris 75008. United States of America:
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||
Ray Barnes, Reed Business Publishing Ltd, 475 Park Avenue South, 2nd Fl New York, NY 10016 Tel; (212) 679 8888 Fax; (212) 679 9455 USA mailing agents: Mercury Airfreight International Ltd Inc, 10(b) Englehard Ave, Avenel NJ 07001. Periodicles Postage Paid at Rahway NJ Postmaster. Send address changes to above. Printed by Polestar (Colchester) Ltd, Filmsetting by.11Typogrophics Ltd, Unit 4Boron Court, Chandlers Way, Southend-on-Sea, Essex SS2 SSE.
|
||
CD Reed Business Information Ltd 1997 ISSN 0959 8332
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
673
|
||
|
||
[111111DATE
|
||
|
||
UK videophone setback
|
||
|
||
The launch of the world's first GSM mobile videophone has been delayed for up to six months, according to the UK companies behind the project.
|
||
The videophone from Orange was most recently scheduled for launch this summer but is now not expected to see the light of day until the last quarter of this year.
|
||
"The launch date is set for sometime in Q4," said an Orange spokeswoman, who refused to comment on why the project was delayed.
|
||
According to another member of the entirely UK-based project team, working prototypes of the videophone were delivered to Orange earlier this year and have also been on display at last week's Tomorrow's World Live exhibition in London. • In May of this year the company was still saying it would launch in the summer when high-speed data capability was added to the network in the form of HSCSD (high speed circuit switched data). HSCSD is set to roll-out at the end of July when corporate trials are completed.
|
||
A group of UK technology companies was chosen to work on the design and manufacture of the videophone last year and Spring 2000 was set as the date for
|
||
|
||
launching the innovative product. Cambridge Consultants has led the
|
||
overall technical project management including both the industrial and mechanical design of the handset and creating the user interface.
|
||
ISDN videophone firm Motion Media, Microsoft system integrator NMI and the University of Strathclyde have been working on
|
||
|
||
various different aspects of the project, with manufacturer Celestica.
|
||
The development work has included video compression software,
|
||
video specific application software, control protocols, implementation of
|
||
the user interface and the design, development and integration of the electronics.
|
||
HSCSD achieves 57.6kbitis data
|
||
|
||
Internet on TV available this year
|
||
|
||
Digital terrestrial TV company ONdigital
|
||
will be offering Internet on TV to its
|
||
subscribers this year.
|
||
An Internet box, around the size of alarge paperback book, which connects to the digital set-top box and atelephone line is needed to receive the service.
|
||
French company Netgem has been chosen as atechnology partner and will be providing the Internet box which uses asystem based on the Linux operating system.
|
||
Pace Micro Technology, which supplies ONdigital's set-top boxes, already has an Internet TV product on the market, but an ONdigital spokesman said the French supplier was chosen because its, "technology seems to work particularly well."
|
||
The Internet pages are instantly reconfigured and the system apparently makes the pages readable on aTV screen from 10-15 feet away.
|
||
|
||
"I haven't seen anything else like it," said the spokesman. Viewers will be able to click straight from programmes to the Internet while
|
||
the TV picture remains in the corner of their screen.
|
||
"ONdigital will offer the easiest and most cost effective way of getting on to the Internet," said Stuart Prebble, ONdigital's CEO. "No dish, no cable, no computer. Simply atelevision and an ONdigital subscription."
|
||
The box will initially connect to the telephone line via a56k modem but will be capable of connection to ADSL technology later. Details of price and the launch date will be made available in the next few weeks. There are plans to integrate the Internet box inside the digital set-top box.
|
||
Pace licensed its Web technology to Alba for use in its Internet browsing TV in March this year.
|
||
|
||
Display technology relies on ink-jet printing
|
||
|
||
Seiko-Epson and Cambridge Display Technology (CDT) have demonstrated afullcolour, active-matrix light-emitting polymer (LEP) display.
|
||
The display, which is a prototype, measures 64 by 64mm, has 200 by 150 pixels and 16 levels of grey scale — achieved through acombination of time modulation and the use of sub-pixels.
|
||
The display is notable, not only for being the first of its kind, but for being the first display made using ink-jet printing techniques. In fact, the relationship between the two companies was started when Seiko-Epson approached CDT realising that LEP
|
||
|
||
technology would be anew outlet for Epson's printing expertise.
|
||
Producing the display has pushed ink-jet technology to its current limit. Printing 30µm features with 301im droplets has required special treatment of the printable surface as well as custom print heads.
|
||
Our reporter present at the
|
||
demonstration reports that the display had no problems with fast action, was acceptably bright for shaded viewing, could be viewed easily from the side and had good LCD-like colours, but not as well saturated as CRT colours.
|
||
"The display uses our previous generation of polymers," explained CDT
|
||
|
||
technical director Jeremy Burroughs, "We now have polymers that can match PAL television colours, but they are not suitable for ink-jet printing yet."
|
||
The companies are aiming the displays firmly at the mobile-phone
|
||
and PDA markets, and expect production within two years. Beyond this, the companies are confident they have the technology to push into all other display areas, including TVs. "We can make 20 or 30in, no problem," said Mr Shimoda, head of R&D at Epson, "the feasibility is very high, the advantage of light emitting polymer is high."
|
||
|
||
674
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
TiePieScope HS801 PORTABLE MOST
|
||
war»
|
||
ABRITARY WAVEFORM GENERATORSTORAGE OSCILLOSCOPESPECTRUM ANALYZERMULTIMETERTRANSIENT RECORDER-
|
||
|
||
•The sophisticated cursor read outs have 21 possible read outs. Besides the usual read outs, like voltage and time. also quantities like rise time and frequency are displayed.
|
||
|
||
The HS801: the first 100 Mega samples per second measuring instrument that consists of aMOST (Multimeter, Oscilloscope. Spectrum analyzer and Transient recorder) and an AVVG (abritary waveform generator). This new MOST portable and compact measuring instrument can solve almost every measurement problem. With the integrated AVVG you can generate every signal you want.
|
||
The versatile software has auser-defined toolbar with which over 50 instrument settings quick and easy can be accessed. An intelligent auto setup allows the inexperienced user to perform measurements immediately. Through the use of asetting file, the user has the possibility to save an instrument setup and recall it at alater moment. The setup time of the instrument is hereby reduced to aminimum.
|
||
When aquick indication of the input signal is required, asimple click on the auto setup button will immediately give a good overview of the signal. The auto setup function ensures aproper setup of the time base, the trigger levels and the input sensitivities.
|
||
|
||
• Measured signals and instrument settings can be saved on disk.This enables the creation of alibrary of measured signals. Text balloons can be added to asignal, for special comments. The (colour) print outs can be supplied with three common text lines (e.g. company info) en three lines with measurement specific information.
|
||
•The HS801 has an 8bit resolution and a maximum sampling speed of 100 MHz. The input range is 0.1 volt full scale to 80 volt full scale. The record length is 32K/64K samples. The AVVG has a 10 bit resolution and asample speed of 25 MHz.The HS801 is connected to the parallel printer port of acomputer.
|
||
The minimum system requirement is a PC with a486 processor and 8Mbyte RAM available. The software runs in Windows 3.xx /95 /98 or Windows NT and DOS 3.3 or higher.
|
||
TiePie engineering (UK), 28 Stephenson Road, Industrial Estate, St. Ives, Cambridgeshire, PE17 4VVJ. UK Tel: 01480-460028; Fax: 01480-460340
|
||
TiePie engineering (NL), Koperslagersstraat 37. 8601 VVL SNEEK The Netherlands Tel: +31 515 415 416: Fax +31 515 418 819
|
||
Web: http://www.tiepie.n1
|
||
|
||
CIRCLE NO. 150 ON REPLY CARD
|
||
|
||
UPDATE
|
||
|
||
Is electronic product gazumping back due to scarcities?
|
||
|
||
Gazumping could be back in the semiconductor market after aperiod in which shortages have — surprisingly —not translated into higher prices.
|
||
Normally, when the silicon cycle turns up, prices increase sharply. However, in the present up-cycle prices have stayed broadly flat.
|
||
Asked last week why this is so, Motorola Semiconductor CEO Fred Tucker, replied: "I wish Icould figure that out".
|
||
Tucker added: "Price increases can be so detrimental to acustomer relationship. Could you give them a price increase and get away with it? Yes —but boy would it affect the
|
||
|
||
relationship". Four bad years have made chip
|
||
manufacturers nervous about offending customers. But there are anecdotal signs from the industry (not related to Motorola) that things may be changing.
|
||
"We placed an order for 5000 serial EPROMs back in March for delivery in 22 weeks. Confirmed, acknowledged, everything," our reporter was told by Drew Hoggatt, managing director of access control system manufacturer Paxton Access, "We got to around week 19, and were told by the franchised distributor that we would not receive our EPROMs —ever."
|
||
|
||
Giving art aplug... The annual design showcase at the Royal College of Art came round recently. Among the things of beauty there were things with practicality as well —particularly
|
||
in the industrial design section. This Ergo Plug concept comes from Stephen Waldron who worked at Dyson Appliances last year. Waldron is on sj.waldron«,virgin.net. You can read more about the exhibition at www.rca.ac.uk.
|
||
|
||
The distributor told Hoggatt there was asupply shortage. "The supply shortage was of course aeuphemism for 'You've been gazumped'," commented Hoggatt.
|
||
The suspicion was that someone in the supply chain had allocated the devices elsewhere —quite possibly at a
|
||
better price. "To add insult to injury," added
|
||
Hoggatt, "the distributor offered us some devices which 'they found on the grey market' at five times the price on our purchase order to them. We could
|
||
of course address the same market ourselves and we bought 10k devices at a40 per cent premium on our original order unit price."
|
||
UK lags Europe with Internet broadband
|
||
The UK is slipping well behind Europe, and Europe slipping behind the US and Asia in upgrading the Internet to broadband capability, it appears from speakers at the DSL Summit in Colorado Springs.
|
||
The UK could be the last country in Europe to open up to free competition for the upgraded products. Whereas the EC has recommended that all countries in the EU should have free competition by the end of the year, the UK won't have it until July 2001.
|
||
While BT has the field to itself, for the next 12 months, it will charge £40 amonth for the service, on top of the BT line rental charge, whereas speakers at the DSL Summit agreed that $40 (£25) amonth was the figure which would actively encourage consumers to pay for broadband services.
|
||
Korea, Taiwan, Singapore and Hong Kong expect 4.5 million users in 12 months.
|
||
|
||
BSkyB must free up encryption technology
|
||
|
||
In amove to further open up the digital TV market, watchdog Oftel has decreed that encryption technology used by satellite TV company BSkyB should be made openly available.
|
||
The encryption technology is provided
|
||
by Sky Subscribers Services (SSSL) and is used in BSkyB's digital set-top boxes to provide interactive services over digital televisions.
|
||
The watchdog has decided that SSSL is in adominant position in the market and so in the interests of competition it must allow other companies to have fair access to its
|
||
|
||
services so they can provide interactive
|
||
|
||
services to their customers.
|
||
|
||
"As digital TV becomes more
|
||
|
||
widespread, it is important that different
|
||
|
||
companies can provide new and exciting
|
||
|
||
interactive services to consumers," said
|
||
|
||
David Edmonds, Oftel's director general.
|
||
|
||
"But it is also important to ensure
|
||
|
||
regulation in this area is only imposed
|
||
|
||
when justified, otherwise competition and
|
||
|
||
innovation in afast-moving market could
|
||
|
||
be stifled."
|
||
|
||
•
|
||
|
||
The ruling will be reviewed in the first
|
||
|
||
half of 2001.
|
||
|
||
•The UK is leading the world in converting to digital TV, according to analyst company Strategy Analytics.
|
||
By the end of the year it, expects 29% of
|
||
homes to have switched to digital. The US will follow with 24% while in France and Spain 15% will have converted.
|
||
The company forecasts there will be 56 million homes around the world watching digital TV by the end of this year. By the end of last year the figure was 34.4 million homes with satellite taking the major share of 77%. Cable achieved 21% and terrestrial just 2%.
|
||
|
||
676
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
UPDATE
|
||
|
||
Isolated drivers made by nu•cromachining
|
||
|
||
A magnetic alternative to optocouplers has been announced by Analog Devices.
|
||
The 'fflIsolation technology' uses micromachining —hence 'gm' —to add coils to the die, isolating driver and receiver circuitry.
|
||
"We use what's called set-reset technology," said Ronn Kliger, business development manager at Analog Devices. The driver side of the chip looks for edges on the input. "Whenever it sees an edge it sends a short pulse to the top coils," said Kliger.
|
||
The receiver side of the die measures pulses using acomparator for detection. In order to distinguish between rising and falling edges there are two pairs of coils.
|
||
"With two pairs of coils we can send two bits of information," said Kliger.
|
||
Pulses sent to the coils are around 2ns long —agood achievement from the 0.6gm CMOS process. This length enables the isolator to cope with input data rates above 100Mbit/s.
|
||
|
||
Data rate (Mbit/s) Propagation delay (ns) Transient immunity (kV/ps) 25Mbit/s consumption (mW)
|
||
|
||
Optocoupler 25 40 10 95
|
||
|
||
umlsolator 100 10 25 30
|
||
|
||
To successfully couple the 2ns pulses across the coils, Analog Devices had to achieve ahigh inductance. To do this the firm uses a separate process for the tnicromachining.
|
||
|
||
A standard CMOS process can only manage coil depths of 2gm, while the firm's process can manage 8to lOpm. Thus the 300gm diameter copper coils have an inductance of around 100nH.
|
||
|
||
South Korea scraps mobile phones subsidies
|
||
|
||
Mobile phone operators in South Korea have thought the unthinkable and agreed to government plans to scrap the subsidises on mobile phones in the
|
||
country. •Faced with the enormous cost of investment in third-generation
|
||
mobile phone services, the Korean operators have said they can no longer afford the subsidies which keep handset prices down and cost them 30 per cent of sales.
|
||
Korean plans to scrap subsidies on mobile phones could send shock
|
||
|
||
waves through the world's mobile phone markets.
|
||
Low-cost mobile phones, which
|
||
are heavily subsidised by network operators, are away of life in most of the world's mobile phone markets, but South Korea has
|
||
broken ranks by scrapping handset subsidies this month.
|
||
But similar moves are seen as
|
||
highly unlikely in this country. "It is in no one's interest to stop subsidies," said aspokeswoman for UK operator Vodafone. "We are certainly not considering it."
|
||
|
||
What seems to worry the Korean government is the high level of foreign silicon in each subsidised mobile phone. It believes too high aproportion of the financial benefit of the subsidies paid by Korean operators is going to foreign chip suppliers.
|
||
For example, atrendy new handset valued at $200 is made of $100 to $120 worth of imported components, including $30 to $40 worth from Qualcomm's Mobile Station Modem 3000 chip and $10 worth of Intel flash memory.
|
||
|
||
Hairing aid... Micro-via PCB technology called DYCOstrate has been used to implement a
|
||
programmable hearing aid by Swiss firm Sulzer Microelectronics. This hearing aid is the smallest of its type, the firm claims. The extreme packaging needs of ahearing aid led the firm to use the flexible substrate which can be folded up
|
||
after manufacture. DYCOstrate is available in the UK through Rigid
|
||
and Flex.
|
||
|
||
Wage rises
|
||
for engineers
|
||
stay low
|
||
Engineering pay settlements have remained low with the average pay settlement being 2.5 per cent over the last three months. The latest survey findings from the Engineering Employers' Federation (EEF) shows that nearly one in seven settlements were pay freezes in the three months to the end of May 2000. The EEF puts the low level down to companies facing "difficult economic conditions".
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
677
|
||
|
||
UPDATE
|
||
|
||
Modulator scheme for 25Tbitis involves time-domain and wavelength multiplexing
|
||
|
||
Researchers in an inter-university project have accumulated £12.5m in grants and investment to develop 100Tbit/s fibre-based data communication techniques.
|
||
Behind the project is amodulation scheme that combines both time domain and wavelength-division multiplexing.
|
||
The modulator requires asource of 'hyper-short' 10fs pulses of 800nm light, although slightly broadened pulses of 1500nm light are also being considered.
|
||
Being so short, these pulses have a wide spectral content and can therefore be broken into individual 'colours' using aprism. This process is called 'spectral slicing'.
|
||
The sliced components —and you may have to get out your book of Fourier transforms here —are longer than the original pulse. The new width depends on how thinly the spectrum is sliced, but ten ways yields pulses of around 100fs, according to the
|
||
|
||
University of St Andrews which is heading the project.
|
||
The wavefront of the spectrally separated 100fs pulses impinges on a multi-channel high speed modulator block featuring one channel per colour. The individual modulators block or pass the 100fs pulses to add digital bits to the wave front.
|
||
The multicolored, modulated wavefront is recombined into asingle pulse with asecond prism and alens. The spectral content and duration of this pulse depends on the data content for any given pulse.
|
||
"These pulses," says Dr Tom Brown, assistant programme director at the University of St Andrews, "are suitable for transmission over local and metropolitan networks, but not transatlantic communication", adding "It could also be used between two adjacent computers or even within a PC'.
|
||
At the receiving end, athird prism splits the pulse again and the re-sliced
|
||
|
||
Spatially separated modulators
|
||
|
||
Lens
|
||
|
||
10 fs pulse
|
||
|
||
Prism to spread pulse spectrum
|
||
|
||
Modulated data stream
|
||
|
||
Prism to recombine
|
||
pulse spectrum
|
||
|
||
Streams of 100 fs pulses
|
||
|
||
Optical fibre for transmission
|
||
|
||
multi-coloured wave front hits an array
|
||
|
||
of photodetectors which recover the
|
||
|
||
original data.
|
||
|
||
It is reasonable to predict, says the
|
||
|
||
university, that this modulator will
|
||
|
||
provide the potential for ten separate
|
||
|
||
2.5Tbit/s channels, thus constituting a
|
||
|
||
total transmission rate of 25Tbit/s. "We
|
||
|
||
therefore believe that it will be
|
||
|
||
necessary to develop advanced
|
||
|
||
femtosecond-based technologies if data
|
||
|
||
rates up to 100Tbit/s are to be made
|
||
|
||
available," said the University in a
|
||
|
||
statement —and this is what the six
|
||
|
||
year project is all about.
|
||
|
||
There are two choices for the source
|
||
|
||
of 10fs pulses. "We have some ideas
|
||
|
||
for asemiconductor laser. The other
|
||
|
||
option is asolid-state crystal laser
|
||
|
||
pumped with asemiconductor laser.
|
||
|
||
We can do the solid-state laser now."
|
||
|
||
The technology challenge here,
|
||
|
||
according to Brown, is to get the pulse
|
||
|
||
repetition rate for the system under
|
||
|
||
control, "then miniaturise the whole
|
||
|
||
thing and make it rugged and cheap".
|
||
|
||
The prisms are acting as 'dispersive
|
||
|
||
elements' and could in practice be
|
||
|
||
diffraction gratings or, according to
|
||
|
||
Brown, exotic structures in photonic
|
||
|
||
bandgap materials.
|
||
|
||
The spatially-separated modulator
|
||
|
||
idea is brand new according to Brown,
|
||
|
||
but applicable technology already
|
||
|
||
exists. Marconi already has suitable
|
||
|
||
lithium-niobate modulators, "well into
|
||
|
||
development, running at high bit rates.
|
||
|
||
This is not hugely exotic technology,"
|
||
|
||
he said.
|
||
|
||
Photodetector technology for the
|
||
|
||
receiver does not exist yet. But, says
|
||
|
||
Brown, "Detectors are running at
|
||
|
||
40GHz now, but they need good
|
||
|
||
quality pulses that have not been
|
||
|
||
messed about."
|
||
|
||
Brown says that all of the
|
||
|
||
components can be miniaturised and
|
||
|
||
could be put on asingle chip.
|
||
|
||
•
|
||
|
||
Government faces tax legal challenge
|
||
|
||
The government is facing alegal
|
||
challenge over its controversial IR35 tax crackdown on contract employees which affects many self-employed electronics engineers and IT professionals.
|
||
The Professional Contractors Group (PCG), an industry body, is preparing papers to go before the court in the next few weeks requesting ajudicial review of the case. The PCG believes IR35 contravenes European law and so has astrong case.
|
||
"We believed all along it [IR35] was
|
||
|
||
unfair, wrong and would never work," said aPCG spokeswoman. "We're now
|
||
following it up because the government looks intent on pushing this through. The challenge in the courts is because we think
|
||
it is legally wrong too." The PCG has also urged the
|
||
government to abandon IR35 after a loophole was discovered which would allow large foreign-owned companies to gain atax advantage over their smaller UK competitors by employing cheap,
|
||
|
||
foreign labour. It is claimed that foreign workers brought
|
||
here on 'fast-track visas' to tackle the skills shortage are being paid alow wage and then
|
||
rented to clients for an inflated fee. The difference can be treated as pre-tax profit and re-invested by big companies whereas small UK consultants must treat any profit as salary and cannot re-invest it in their business.
|
||
The legislation is intended to tackle tax avoidance by some self-employed staff working for larger electronics firms on temporary contracts.
|
||
|
||
678
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
The Balance Box
|
||
Microphone or line level amplifier for balanced or unbalanced signal lines
|
||
Professional portable units operating from an internal PP3 battery or external mains adaptor
|
||
|
||
* Precision true floating transformerless balanced input and output at microphone or line level * Simple interfacing and
|
||
conversion between balanced and unbalanced signal lines * Low noise and distortion * High common mode rejection
|
||
* Switchable gain selection * Extensive RFI protection
|
||
The Phantom Power Box —The Headphone Amplifier Box -The OneStop DIN rail mounting radio
|
||
frequency interference filter and voltage transient protector for voltage and current loop process signal lines
|
||
Conford Electronics Conford Liphook Hants GU30 7QW
|
||
Information line 01428 751469 Fax 751223 E-mail contact@confordelec.co.uk Web: www.confordelec.co.uk/
|
||
(IRCI FNO. 106 Ox RI PI 1 (,1110
|
||
|
||
New concept in data logging
|
||
|
||
MiniLC
|
||
|
||
PC-based data logging and control are combined in one tiny package!
|
||
|
||
- Connected to printer port
|
||
•
|
||
• - 8 12-bit ana. inputs (0-2.5V) •- 8digital outputs (TTL level)
|
||
|
||
£79.99 + Vat
|
||
|
||
.- Terminal board - DOS and Win programs - I/O drivers for TP6 and Win - Various sensors available
|
||
|
||
Solid State Sound Recorder
|
||
|
||
- 10 second, 1sound track
|
||
- 20 second, 1or 4tracks - Small size: 42 x24 mm
|
||
10 sec. £7.00 + Vat
|
||
20 sec. £7.90 + Vat
|
||
|
||
We also supply other sound loggers, and...
|
||
|
||
Centronic port I/O Card
|
||
|
||
£40 + Vat
|
||
|
||
Expand aprinter port into 24 programmable I/0s
|
||
|
||
RS232 port I/O Card
|
||
|
||
£37 + Vat
|
||
|
||
Expand an RS232 port into 8inputs and 8outputs
|
||
|
||
www.intec-group.co.uk
|
||
|
||
Intec Associates Limited Tel: 44(0) 161 477 5855 Fax: 44(0) 161 477 5755
|
||
Email: mail @ intec-group.co.uk
|
||
|
||
II V OL
|
||
|
||
Mai VISA
|
||
|
||
V 1,1
|
||
btre-trae
|
||
|
||
MI!
|
||
|
||
CIRCLE NO.107 ON 11E101 (ARI)
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
Our
|
||
|
||
ete
|
||
|
||
eeffIC in a uaríciy ofinodefe
|
||
|
||
Antex thermally balanced soldering irons are fast, easy to handle and
|
||
very safe. Plus you get awide range of different voltages and wattages.
|
||
So race off with a fixed temperature' iron or try the 'In Handle'
|
||
temperature controlled model. Each one comes with achoice of a
|
||
PVC or aburn-proof silicon lead, has been manufactured in the UK and meets CE conformity. And with
|
||
Antex you get abig choice of soldering bits to suit every need.
|
||
But while our irons sell faster than adragster, they come at
|
||
aprice that won't burn a hole in your pocket.
|
||
So visit our web site or your electronics retailer and
|
||
take one for atest drive
|
||
|
||
ALknI_mN_I_TJuEuX
|
||
NOT JUST ANY OLD IRON
|
||
|
||
YOU CAN NOW BUY ANTEX EQUIPMENT ON-LINE
|
||
ALL ON-LINE ORDERS OVER £.20 TAKEN IN AUGUST
|
||
AND SEPTEMBER WILL RECEIVE A 25% DISCOUNT
|
||
www.antex.co.uk
|
||
|
||
(WC! FNO.108 ON REPLY CARD
|
||
|
||
679
|
||
|
||
Anew low-IMD mixer
|
||
|
||
Chris Trask's new series-shunt feedback active mixer offers clear advantages over both the common Gilbert Cell active mixer and diode-ring mixers. With lower local-oscillator power requirements, low distortion, and higher saturable output power, this new mixer is highly suitable for low-power high-performance communications systems. Yet it's possible to implement the design on the kitchen table!
|
||
|
||
ivi ixers are essential building blocks of radio communications systems, being used for
|
||
|
||
modulation, demodulation, and signal
|
||
|
||
frequency conversion. Among the var-
|
||
|
||
ious forms have been transconductance
|
||
|
||
multiplication —dual-gate FETs, pen-
|
||
|
||
tagrid and heptode vacuum tubes, etc. —
|
||
|
||
diode and switching FET rings, and the
|
||
|
||
transistor tree — also know as the
|
||
|
||
Gilbert Cell.
|
||
|
||
An inherent undesirable property of
|
||
|
||
mixers has been —and continues to be
|
||
|
||
— intermodulation
|
||
|
||
distortion.
|
||
|
||
Commonly abbreviated to IMD, inter-
|
||
|
||
modulation distortion is caused by two
|
||
|
||
adjacent signals interacting. This inter-
|
||
|
||
action creates spurious signals that can
|
||
|
||
interfere with adjacent smaller signals.
|
||
|
||
In some cases, IMD can actually cause
|
||
|
||
interference within wideband commu-
|
||
|
||
nications systems themselves.
|
||
|
||
Eliminating IMD
|
||
Overcoming this unwanted character-
|
||
istic is no small task. Traditionally, the efforts at improving IMD have included using Class III diode ring and
|
||
switching FET ring mixers that generally require local oscillator signal levels
|
||
of +I7dBm or more. This is an unsuitable solution for field-portable equipment though, where power consump-
|
||
tion is an important parameter.
|
||
Active mixers, such as Plessey's SL6440 and the Motorola's MC 1496, make use of the six-transistor double-
|
||
balanced transistor tree. Emitter degen-
|
||
eration is applied to the driver transistors to provide some degree of linearisation.
|
||
Still more recent methods regulate the leg currents using negative feed-
|
||
back, but they do not encompass all sources of distortion in the mixer.
|
||
|
||
680
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
RF DESIGN
|
||
|
||
These sources must include the switching transistors as well if the correction is to be truly effective.
|
||
Until now, it has been generally considered that the mixer is an open-
|
||
ended device. This means that there is
|
||
no obvious opportunity to apply the traditional linearisation techniques such as feedback.
|
||
Notable exceptions have been Plessey's SL6440, devised by Phil
|
||
Moon, which originally used aclever negative feedback amplifier for lin-
|
||
earising the leg currentsI•2. This linearisation amplifier
|
||
required p-n-p transistors. Because of the difficulties involved in making
|
||
suitable p-n-p transistors though, the original circuit was sadly dropped in favour of the more easily fabricated version with emitter degeneration
|
||
resistors 2. In more recent years, aUS patent
|
||
by Joseph Heck describes an active mixer in which the leg currents are linearised by way of using transconductance amplifiers3.A later circuit by Barrie Gilbert uses Norton current input amplifiers to achieve the same
|
||
results& These last two are specific embodiments of an earlier gener-
|
||
alised method patented by Daniel Talbot5.All of these methods produce an appreciable improvement,
|
||
but they fall short of the mark in terms of complete linearisation.
|
||
Presented here is an active mixer circuit that produces substantial IMD improvement. At the same time, it
|
||
uses far less local oscillator (LO)
|
||
power than a diode ring mixer of comparable performance.
|
||
|
||
lah/t. I. ,11t.a.ureduerforman« ,data for the nett Ini‘er configuration.
|
||
|
||
Circuit configuration
|
||
|
||
Gain
|
||
|
||
Input
|
||
|
||
intermodulation
|
||
|
||
intercept point
|
||
|
||
(I1P 3)
|
||
|
||
Mini-Circuits SBL-1 Typical Gilbert-cell mixer, see text. 1st-generation series-shunt feedback mixer, Fig. 3. 2nd-generation series-shunt feedback mixer, Fig. 4.
|
||
|
||
—5.0dB —1.5dB —7.0dB —3.0dB
|
||
|
||
+19.0dBm +17.5dBm +21.5dBm +29.5dBm
|
||
|
||
By using amore detailed method of combining the four signal currents in a transistor tree mixer, the amplified intermediate-frequency (IF) signal voltage can be recovered at the mixer output and then used in atraditional feedback topology, thereby including all sources of IMD in the feedback scheme 6.7.8.
|
||
In addition, the radio-frequency output is derived from the combiner as well, and with agood degree of IF-RF and LO-RF isolation. Moreover, the circuit can be made to operate from the baseband modulator and demodulator level to VHF frequencies using components that are readily obtainable from common hobbyist sources.
|
||
Active mixer basics Before Iget into specifics, to help you appreciate this new concept, I'll examine the currents within ageneralised transistor tree active mixer with the aid of Fig. 1.
|
||
Driver transistors Tr3 and Tr6 generate collector currents /3 and /6, respectively. These currents each con: tain aquiescent DC bias current and a differential signal current.
|
||
|
||
Signal currents of /3 and 16 are a direct consequence of the input differential IF signal voltage. Both are chopped, or modulated, by switching transistor pairs Tri/Tr2 and Tr41Tr5, respectively. This results in afoursome
|
||
of output currents I. 12,/4,and /5.
|
||
These contain components of DC, IF, LO, and RF signals, each with aunique phase relationship. The accompanying panel on double-balanced active mixers gives amore detailed explanation for those so interested.
|
||
In the traditional double-balanced active mixer, the currents /1and 15 are combined by connecting the collectors of Tri and Tr5together, and the currents /2and /4are combined by connecting the collectors of Tr2and Tr4.
|
||
Combining currents in this way leaves an output differential RF current and effectively cancels the output LO and IF currents. This last cancellation deprives us of the signals needed for the implementation of a feedback linearisation scheme.
|
||
Signal combining and recovery
|
||
Now consider other combinations of the four output currents, using Fig. 2as
|
||
|
||
RF LO+ IF-
|
||
|
||
RF LO IF+
|
||
|
||
RF+ LO+ IF+
|
||
|
||
RF
|
||
Combiner
|
||
|
||
Compression point (Pida)
|
||
—4.5dBm +4.5dBm +5.5dBm +10.5dBm
|
||
|
||
12 •
|
||
|
||
•14
|
||
|
||
• 15
|
||
|
||
IF-
|
||
|
||
V14
|
||
|
||
• 15
|
||
|
||
Tr4
|
||
|
||
LO- LO+
|
||
|
||
Tri
|
||
|
||
Tr2
|
||
|
||
Tr4
|
||
|
||
Tr5 •
|
||
|
||
LO-
|
||
|
||
•
|
||
|
||
16 • •
|
||
|
||
IF- IF+
|
||
|
||
Tr3
|
||
|
||
13
|
||
|
||
2RE
|
||
|
||
Tre
|
||
|
||
7
|
||
|
||
IF -
|
||
|
||
IQ •
|
||
|
||
IQ •
|
||
|
||
Fig. 1. Currents involved in the basic transistor tree mixer.
|
||
|
||
Fig. 2. Feedback mixer signal combining and recovery configuration.
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
681
|
||
|
||
RF DESIGN
|
||
|
||
aguide. In ageneral sense, the desired outcome of the mixer is to have an output RF signal that is alinear combination of the input intermediate-frequency and local-oscillator signals.
|
||
By using asaturating LO signal for the switching transistors, you are left with the burden of ensuring that the amplified IF currents at the four switch-
|
||
|
||
ing transistor collectors are afaithful linear reproduction of the input signal voltages. Therefore, an output feedback signal needs to be provided for each input signal to be used in comparison and subsequently correct for any errors.
|
||
First, if /I with /2 are summed, the amplified and inverted IF signal current for the left side can be recovered.
|
||
|
||
Similarly, by summing /4 and I. the amplified IF signal for the right side can be recovered. This can be accomplished in avariety of ways. Two of these are described in detail later, after the preliminaries are taken care of.
|
||
Once the amplified IF signals are recovered, they can be used as feedback signals for use in the linearisation of the
|
||
|
||
The double-balanced active mixer
|
||
Here, I'll briefly examine of the core element of adoublebalanced active mixer, as in Fig. A.
|
||
Drive transistors Tr3 and Tr6 convert the input IF voltage into a
|
||
pair of differential currents /3 and 16,
|
||
|
||
= IQ + Acos(ay) RE +r,
|
||
|
||
(1)
|
||
|
||
I, = '
|
||
|
||
10 -
|
||
|
||
Acos(cost) R,+r,
|
||
|
||
(2)
|
||
|
||
Here, A is the amplitude of the input IF voltage, /Q,is the
|
||
quiescent bias current for each leg, and re is the nonlinear emitter resistance of Tr3 and Tr6,assumed to be equal for both devices.
|
||
Fixed resistance RE is used to establish the mixer signal (and conversion) gain as well as degenerate the driver transistors to provide for some stability over temperature and asmall degree of linearisation. These two currents are then passed on to apair of differential switching transistor pairs, Tri/Tr2 and Trer5,where an applied LO signal causes each of these currents to be divided into two differential currents. Ignoring the higher-order terms, these currents are:
|
||
|
||
/,=/Q+Acos(wsr) /Qcos(a),r)
|
||
|
||
" 2 2( R,+
|
||
|
||
2
|
||
|
||
(3)
|
||
|
||
A[cos(cos—co, +cos(ws+co, )t]
|
||
|
||
2( RE +
|
||
|
||
I, = I +Acos(cost) 1Qcos(coLt),
|
||
|
||
2 2( R,+
|
||
|
||
2
|
||
|
||
(4)
|
||
|
||
A[cos(u), —0'L )t +cos(cos+co,
|
||
|
||
2( RE +
|
||
|
||
— Q Acos(cost) + cos(w,t)
|
||
|
||
2 2( RE +
|
||
|
||
2
|
||
|
||
(5)
|
||
|
||
A[cosfros — +cos(ws+ )t]
|
||
|
||
2( RE +r,
|
||
|
||
/,= lQ Acos(cost) /Q cos(co,r)
|
||
|
||
" 2 2( RE +
|
||
|
||
2
|
||
|
||
(6)
|
||
|
||
A[cosfros — +cos(o), +roL)t]
|
||
|
||
2( RE +
|
||
There's agreat deal of information contained in these four currents. No two are alike, all four containing elements of RF, LO, and IF signals each with aunique variety of phase relationships.
|
||
In equations 3to 6, the first term is the quiescent bias current, the second is the amplified IF signal current, the third is the LO current, and the fourth is the mixing product RF current. By making various combinations we can recover one and eliminate the other two, the most obvious of which is the combining of Ii with 15 and 12 with 14,illustrated in Figure 1, which creates a differential pair of RF output currents 17and 18,cancelling both
|
||
|
||
LO +
|
||
|
||
RF+
|
||
17 • •
|
||
|
||
12 •
|
||
|
||
• Tri
|
||
|
||
Tr2
|
||
|
||
•• •
|
||
|
||
RF-
|
||
|
||
• 18
|
||
|
||
0
|
||
|
||
• 14
|
||
|
||
• 15
|
||
|
||
Tr4
|
||
|
||
Tr5 •
|
||
|
||
LO-
|
||
|
||
4• *
|
||
|
||
• 13
|
||
|
||
16 •
|
||
|
||
IF+
|
||
|
||
Tr3
|
||
|
||
Tr6
|
||
|
||
IF-
|
||
|
||
•
|
||
|
||
2RE
|
||
|
||
e
|
||
|
||
•
|
||
|
||
•
|
||
|
||
Fig. A. Conventional double-balanced active mixer.
|
||
|
||
10 •
|
||
|
||
the IF and LO signals currents:
|
||
|
||
= /Q +A[cos(cos —u),.)t +cos(cos +cojt1 2( RE +
|
||
|
||
(7)
|
||
|
||
—
|
||
|
||
)tj A[cos(cos —(0,)t +cos(ws +0L
|
||
2( RE +r,
|
||
|
||
(8)
|
||
|
||
This is the very basis of the double-balanced active mixer, which
|
||
|
||
was originally patented in the form of asynchronous demodulator
|
||
|
||
by Howard Jones in 1966 1.It was later given the name Gilbert Cell after its subsequent use in alater patent for an analogue multiplier in 1972 by Barrie Gilbert2.
|
||
The obscurity of the work by Jones has been detrimental in his being recognised as the original inventor of this circuit. A more detailed explanation can be found in references 3and 4below, as well as numerous other works on semiconductor circuit theory and design.
|
||
|
||
References
|
||
1. Jones, Howard E., 'Dual Output Synchronous Detector Utilising Transistorised Differential Amplifiers,' US Patent 3,241,078, 15 March 1966.
|
||
2. Gilbert, Barrie, 'Four-Quadrant Multiplier Circuit,' US Patent 3,689,752, 5September 1972.
|
||
3. Gray, Paul R. and Robert G. Meyer, 'Analysis and Design of Analog
|
||
Integrated Circuits, 2nd ed,' Wiley, 1984, pp. 590-605. 4. Burns, Stanley G. and Paul R. Bond, 'Principles of Electronic
|
||
Circuits,' West Publishing Co., 1987, pp. 737-746.
|
||
|
||
682
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
RF DESIGN
|
||
|
||
mixer as awhole. The earlier combining of /I with 15
|
||
and /2 with /4 is still apractical choice for recovering an output RF signal while at the same time cancelling the undesired IF and LO signals at the output. But it would be preferable to do this and still accommodate the recovery of the amplified IF signals.
|
||
|
||
An alternative method is to take the difference of /I and /2.This yields a positive RF signal and anegative LO signal on the left side. A similar difference between /5 and /4 on the right side also yields apositive RF signal, but now the LO signal is positive.
|
||
By adding these two signals together you arrive at apositive RF output and a
|
||
|
||
cancellation of the LO signal, which is the desired outcome.
|
||
With the amplified IF signals recovered, you can now consider an appropriate feedback amplifier topology. For baseband modulation, apair of operational amplifiers can be used to compare the input IF signal with the feedback IF signals. Then, the amplified
|
||
|
||
The series-shunt feedback amplifier
|
||
There's ahandful of circuit topologies that are suitable for RF feedback amplifiers. Perhaps the most straightforward of these is the series-shunt feedback amplifieru.
|
||
|
||
RCB •
|
||
|
||
VOUT
|
||
|
||
VIN
|
||
|
||
•
|
||
|
||
Tr RE
|
||
|
||
Fig. B. Basic seriesshunt feedback amplifier.
|
||
|
||
VA. RA 11A
|
||
|
||
VD• RD
|
||
|
||
1 VB.
|
||
|
||
ID VG.
|
||
|
||
Fig. C. Hybrid transformer -originally used in telephony to enable two-way communication over a single pair of wires.
|
||
|
||
RB1B
|
||
|
||
RC 'IC
|
||
|
||
This circuit, shown in Fig. B, is agood example of how the
|
||
|
||
simplest of inventions can be the most profound. These simple
|
||
|
||
wide-band amplifiers are easily designed using the following
|
||
|
||
simple relationships for input/output resistance and gain:
|
||
|
||
R,„ =R„„, =\IR„ x(R, r,)
|
||
|
||
(1)
|
||
|
||
R, + G=1 f It,8
|
||
|
||
(2)
|
||
|
||
where Rcg is the collector-base feedback resistance, RE is the emitter feedback resistance, and re is the incremental nonlinear emitter resistance of the transistor.
|
||
|
||
References 1. Seader, Leonard D. and James E. Sterrett, 'Unit Transistor
|
||
Amplifier with Matched Input and Output Impedances,' US Patent 3,493,882, 3February 1970.
|
||
|
||
2. Meyer, Robert G., Ralph Eschenbach, and Robert Chin, 'Wide-Band Ultralinear Amplifier from 3to 300 MHz,' IEEE Journal on Solid-State Circuits, Vol. SC-9, No. 4, August 1974, pp. 167-195.
|
||
|
||
Hybrid transformer
|
||
|
||
The hybrid -or bridge -transformer1•2 has been with us for
|
||
|
||
well over acentury. It was originally used in telephony to
|
||
|
||
enable two-way communication over asingle pair of wires,
|
||
|
||
with earth being the required third connection.
|
||
|
||
As shown in Fig. C, the hybrid transformer is simply atwo-
|
||
|
||
winding transformer with acentre-tapped primary winding.
|
||
|
||
The various currents and voltages conform to the following
|
||
|
||
relationships,
|
||
|
||
= +
|
||
|
||
(1)
|
||
|
||
(2) (3)
|
||
|
||
(4)
|
||
|
||
In other words, the common-mode voltage and current appears
|
||
|
||
at the centre-tap while the differential voltage and current is at
|
||
|
||
the secondary. The differential voltage and current are scaled
|
||
|
||
=R, =2R. by the turns ratio K. It also follows that, RA
|
||
|
||
(5)
|
||
|
||
R=—c-
|
||
|
||
(6)
|
||
|
||
D K2
|
||
|
||
The hybrid transformer can be found in numerous applications in telecommunications, including repeater amplifiers, crystal lattice filters, amplifier neutralisation, and frequency multiplexing.
|
||
|
||
References 1. Sartori, Eugene F., 'Hybrid Transformers,' IEEE Transactions
|
||
on Parts, Materials, and Packaging, Vol. 4, No 3, September 1968, pp. 59-66. 2. Gross, Tom, 'Hybrid Transformers Prove Versatile in HighFrequency Applications,' Electronics, 3Mar. 1977, pp. 113115.
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
683
|
||
|
||
RF DESIGN
|
||
|
||
Fig. 3. Firstgeneration series-
|
||
shunt feedback mixer. Test
|
||
results show that this circuit gives
|
||
amarked improvement over the Gilbert
|
||
cell.
|
||
+12V
|
||
LO
|
||
IF T2
|
||
|
||
difference can be applied to the driver transistors.
|
||
For high-frequency mixer applications, the use of an operational amplifier becomes impracticable. Instead, a very simple feedback amplifier topology commonly referred to as seriesshunt can be used. These simple yet effective amplifiers require two additional resistors to the common-emitter transistor amplifier. A detailed discussion is provided in the accompanying panel.
|
||
First-generation series-shunt feedback active mixer
|
||
Figure 3illugrates the first generation of what has become known as the series-shunt feedback active mixer6.7. Resistors Rm.') serve as both IF feedback signal combiners and as the shunt feedback resistances for the IF feedback amplifier.
|
||
The combining takes place at their common junction with the bases of the driver transistors. Since each of these carries only half of the total IF feedback signal current, they are of the same value as would be derived for asingle amplifier stage.
|
||
Resistors R7A.c perform the series feedback function for the IF feedback amplifier as well as establishing the quiescent bias currents in lieu of using dedicated current sources, and with a
|
||
|
||
value of 100i1 each they produce an RE of 33e, giving the mixer an IF signal amplification factor of around —2.16, or 6.7dB All capacitors shown are lOnF.
|
||
Resistors R4A_D provide collector biasing pull-ups. The resistors R4_7 are in the form of SIP networks in order that the physical design be somewhat elegant and providing for the practical purpose of tracking over temperature.
|
||
Transformers T1_3 are identical, being of a 1:1:1 ratio, in which case
|
||
the centre tap of T3 is not used. A commercially available transformer
|
||
such as Mini-Circuits' T4-1 may be used here, or you can make one by twisting three wires together on asuitable ferrite core.
|
||
It is best to use transistors in the form of an array so that parameter
|
||
matching doesn't become an issue. Intersil's (née Harris, née RCA) CA3054 and CA3102 arrays come to mind, the former being less costly and more plentiful.
|
||
The 3102 should be used where higher frequency performance is needed. Other transistor arrays, such as the series of dual transistors made by Panasonic and NEC, are equally suitable.
|
||
Performance in practice
|
||
We built an example circuit using
|
||
|
||
R1 1k5
|
||
R5A
|
||
330
|
||
|
||
R4A 470
|
||
|
||
•
|
||
|
||
R4B
|
||
|
||
470
|
||
|
||
R6C
|
||
|
||
100
|
||
|
||
•
|
||
|
||
R6A 100
|
||
|
||
• R4C 470
|
||
|
||
R6D 100
|
||
|
||
R4D 470
|
||
'R5D 330
|
||
RF R5C 330
|
||
|
||
the CA3054 for the transistor array using the components values shown in Fig. 3. For T1, T2, and T3, we used the Mini-Circuits T4-1 transformer.
|
||
With asupply of 12V, the resulting
|
||
quiescent bias current was approximately 12mA for each of the driver transistors Tr3 and Tr6.In addition,
|
||
we made acomparable Gilbert Cell mixer. Its circuit was essentially that
|
||
of Fig. 3 with the shunt feedback resistors R5 and the associated DC blocking capacitors removed.
|
||
For the test signals, alocal-oscillator signal of 10.0MHz at alevel of 0.0dBm was used, although the cir-
|
||
cuit performs equally well at levels as low as —10dBm. For intermodulation measurements, the IF input sig-
|
||
nals were set at 500kHz and 510kHz. For conversion gain measurements, the first of these was used.
|
||
Mini-Circuits' • popular SBL:1 diode ring mixer was also tested for
|
||
comparison. The signals used were as for the active mixers, except that the local oscillator signal level was
|
||
set at +7.0dBm to ensure proper operation.
|
||
Test results, listed in Table 1. indicated that there is amarked improvement in the distortion characteristics over the comparable Gilbert Cell mixer. Input intermodulation intercept point, IIP3, is increased by 4.0dB. The ldB compression point, Pin,is also improved by ldB.
|
||
Closing the series feedback loop, however, decreases the conversion
|
||
gain by 5.5dB. Even so, this is a considerable improvement over the SBL-1 —particularly in regard to the Pia compression point.
|
||
Using resistors in the output signal
|
||
combiner of the first generation series-shunt feedback mixer was a matter of convenience. It was necessary in order to create acircuit that was suitable for possible future MMIC implementation. Their use
|
||
does not impair the linearisation qualities of the mixer, but they do result in a decrease in conversion
|
||
gain and in the apparent IIP3 and
|
||
Plat.
|
||
|
||
2nd-generation series-shunt feedback active mixer
|
||
By applying apair of hybrid transformers as ameans of combining the four switching transistor collector currents, as shown in Fig. 4, the compromises of the first generation series-shunt feedback mixer are decisively dealt with.
|
||
The result is aseries-shunt active mixer with markedly improved performance7.8.This represents the sec-
|
||
ond method discussed earlier in the
|
||
|
||
684
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
RF DESIGN
|
||
|
||
combining and recovery of signal voltages.
|
||
Simply stated, the hybrid trans-
|
||
|
||
+12V
|
||
|
||
7
|
||
|
||
former combines the two pairs of collector currents in the following manner. Collector currents of switch-
|
||
ing transistors Tri and Tr2 are applied to the primary winding of hybrid transformer T3. As aresult, the common-mode components are
|
||
|
||
R1
|
||
|
||
L1
|
||
|
||
1k5
|
||
|
||
100&H
|
||
|
||
•
|
||
|
||
RF
|
||
|
||
T4
|
||
u
|
||
100H
|
||
|
||
added together at the centre-tap, while the odd-mode terms cancel.
|
||
|
||
R4 < 330
|
||
|
||
Conversely, the odd-mode terms of are added together at the secondary
|
||
|
||
winding, while the even-mode terms are cancelled. At the same time, the
|
||
collector currents of switching transistors Tr4 and Tr5 are processed by
|
||
hybrid transformer T4 in a similar way.
|
||
Clearly, the LO signal appears at the secondary windings of T3 and T4.
|
||
But the windings are respectively
|
||
180° out of phase, and therefore can-
|
||
|
||
LO T1
|
||
|
||
Tri
|
||
|
||
Tr2
|
||
|
||
Tr4
|
||
|
||
Tr5
|
||
|
||
Tr3
|
||
|
||
T113
|
||
|
||
R6B 100
|
||
|
||
cel, as was discussed earlier. With the minor exception of bulk
|
||
and induced losses in the transformer
|
||
windings, the process of combining and recovering the signals is virtual-
|
||
|
||
R6A
|
||
|
||
R6C
|
||
|
||
100
|
||
|
||
100
|
||
|
||
ly lossless. This is ahighly desirable
|
||
|
||
circumstance. The components shown in Fig. 4
|
||
|
||
follow very much with those of Fig. 3. However, there is now a single feedback resistor for each half of the
|
||
|
||
Fig. 4. Second-generation series-shunt feedback mixer. Adding apair of hybrid transformers to combine the four collector currents eliminates the compromises of this circuit's
|
||
|
||
mixer, these being resistors R4 and predecessor.
|
||
|
||
R5.
|
||
Hybrid transformers T3 and T4 are the same Mini-Circuits T4-1 transformers as used for T1and T2 earlier. And as before, all capacitors are lOnF. All testing conditions remain
|
||
as before. Referring again to Table 1, the
|
||
performance of the second-generation series-shunt feedback mixer greatly exceeds that of the earlier version. By replacing the lossy resistive combiner network with apair of hybrid transformers, the conversion gain has been improved by 4.0dB, the IIP3 by 8dB, and the Pin compression point by 5.0dB.
|
||
Although the open-loop Gilbert Cell mixer still has the advantage of slightly higher conversion gain, the second-generation series-shunt feedback mixer excels in all other respects. And it is a substantial improvement over the SBL-1.
|
||
In summary
|
||
The series-shunt feedback active mixer offers definite advantages over both the common Gilbert Cell active mixer and diode ring mixers.
|
||
With lower local-oscillator power requirements, low distortion, and higher saturable output power, the
|
||
|
||
series-shunt feedback mixer is high-
|
||
|
||
ly suitable for low-power high-per-
|
||
|
||
formance communications systems.
|
||
|
||
Using resistors in the output signal
|
||
|
||
combiner is straightforward and con-
|
||
|
||
venient, rendering the series-shunt
|
||
|
||
feedback mixer suitable for MMIC
|
||
|
||
implementation. With hybrid trans-
|
||
|
||
formers used in lieu of the resistors,
|
||
|
||
the results are amixer of incompara-
|
||
|
||
ble performance.
|
||
|
||
Noise figure —another important
|
||
|
||
factor in mixers — was not
|
||
|
||
addressed in these designs. This
|
||
|
||
was because the mechanism that
|
||
|
||
causes current-commutating mixers
|
||
|
||
such as these to be noisy is still
|
||
|
||
present9.
|
||
|
||
It is entirely feasible that other
|
||
|
||
topologies can be employed that
|
||
|
||
will allow this characteristic to be
|
||
|
||
improved, while at the same time
|
||
|
||
retaining the desirable linear char-
|
||
|
||
acteristics shown here.
|
||
|
||
For now though, the series-shunt
|
||
|
||
feedback mixers presented here rep-
|
||
|
||
resent amethod by which the dynam-
|
||
|
||
ic range of this important element in
|
||
|
||
radio design can be greatly improved,
|
||
|
||
without excessive local-oscillator
|
||
|
||
power generation or DC power con-
|
||
|
||
sumption increases.
|
||
|
||
•
|
||
|
||
References I. Chadwick, Peter E.. "Ile SL6440 High
|
||
Performance Integrated Circuit Mixer,' WESCON 81 Conference Record, Session 24, No 2, pp. 1-9 2. Peter Chadwick (private communication). 3. Heck, Joseph P.. Balanced Mixer Circuit with Improved Linearity,' US Patent 5,548,840,20 Aug. 1996. 4. Gilbert, Barrie, "rhe MICROMIXER: A Highly Linear Variant of the Gilbert Mixer Using aBisymmetric Class-AB Input Stage.' IEEE Journal of Solid-State Circuits. Vol. 32, No 9, Sept. 1997, pp. 1412-1423. 5. Talbot, Daniel B.. 'Amplitude Modulator Having Substantially Zero Modulation Distortion,' US Patent 4,485,359, 27 Nov. 1984. 6. Trask. Chris, 'Feedback Technique Improves Active Mixer Performance.' RF Design, Sept. 1997. pp. 46-52. 7. US patent pending. 8. Trask, Chris, A Linearised Active Mixer,' Proceedings RF Design 98. San Jose., California, Oct. 1998. pp. 13-23. 9. Fong, Keng Leong and Robert G. Meyer,
|
||
'Monolithic RF Active Mixer Design. IEEE Transactions on Circuits and Systems. Part 2, Vol. 46, No. 3, Mar. 1999, pp. 231-239.
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
685
|
||
|
||
MEDICAL ELECTRONICS
|
||
|
||
Flicker fusion meter
|
||
|
||
.i. he photoreceptors of the eye and the neurons of the visual system are relatively sluggish transducers. This is particularly true for the cones —the receptors that are colour sensitive, and respond in bright light. Rods on the other hand have faster responses. They signal intensity only —not colour —and are principally active in dim light.
|
||
The cones are largely clustered in the centre region of the retina, while the rods predominate around the periphery. The rods' faster responses and peripheral location explain why many people are able to detect the flicker of fluorescent lighting out of the corners of their eyes.
|
||
To the slower acting cones, this flicker is imperceptible. But there is of course afrequency below which flashing can be detected —even by the cones.
|
||
The flash rate at which the illumination just appears to be continuous is termed the critical flicker fusion frequency, which is frequently shortened to CFF. For many people the critical frequency is in the region of 20 to 40Hz.
|
||
Factors affecting fusion frequency
|
||
A number of factors affect CFF. These include, as indicated above, whether the light is viewed directly or with the eye slightly averted, so that the image is perceived peripherally. Brightness has an impact, since the visual system responds more quickly in bright light.
|
||
The receptors are :photon gatherers'. Once they have captured sufficient photons a neural impulse is generated. Since bright light has a higher photon rate, the neural response is more rapid. In poor light
|
||
|
||
there is an appreciable integration time, which is recognised in the game of cricket, when bad light is allowed to stop play. A fast moving cricket ball could hit aplayer, before its location had been recognised.
|
||
The panel entitled, 'A dim view is aslow view' describes aparticularly compelling demonstration of the relatively slower processing of dim light.
|
||
Not only do characteristics of the light stimulus modify CFF; so also do factors relating to the viewer. There is, for example, aclear impact of age. Older viewers exhibit alower fusion frequency. In other words, their visual system is unable to resolve such high rate flashes as can younger people I.
|
||
The stimulating effects of coffee and tea raise CFF2,but there is some indication that this effect is influenced by personality. Extroverts are said to have lower base-line neural reactivity than introverts3.This is claimed to explain why, with their greater 'head-room', extroverts enjoy raising their activation by engaging in exciting activities. Consistent with this description, it is extroverts rather than introverts who appear to show the CFF speed-up effect of caffeine4
|
||
Sensitive to fatigue
|
||
Of particular interest, CFF has been shown to be sensitive to fatigue, and can serve as ameasure of workers' general 'sharpness' levels. It has been used in this way to research the effects of shift working, for example with air traffic controllers5.
|
||
As you would expect, afatigued operator has alower fusion frequency. To detect the change, portable light-flashing devices, sometimes referred to as fatigue meters, have
|
||
|
||
The maximum rate of flicker that a person can perceive relates to how tired that person is. This rate is affected by age and such things as whether you're introvert or extrovert. It is even affected by whether or not you've been drinking coffee. Peter Naish describes a meter that measures the 'critical flicker fusion frequency', and describes how to get the most from it.
|
||
Dr Peter L. N. Naish, B.Sc., D.Phil., C.Psychol. is with the Department of Psychology at the The Open University in Milton Keynes.
|
||
|
||
686
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
MEDICAL ELECTRONICS
|
||
|
||
O +6volts
|
||
0 to 7-segment common anode
|
||
Tr2
|
||
|
||
0
|
||
|
||
To 7-segment common cathode
|
||
|
||
Tri
|
||
|
||
To segments of both displays
|
||
|
||
Lj\AF3)\A rci
|
||
|
||
— V\AA,-0 e
|
||
|
||
— VV0 d —1\AAA/-ci c
|
||
|
||
rt_ot —M AAro b a
|
||
re\AR/7\Ar°
|
||
|
||
e\MAI-1 0
|
||
|
||
j
|
||
|
||
R12
|
||
|
||
Jack tip LED
|
||
|
||
Jac shaft
|
||
|
||
S1
|
||
|
||
S2
|
||
|
||
S3
|
||
|
||
S4
|
||
|
||
0 volts skt
|
||
|
||
Fig. 1. Complete circuit
|
||
of the flicker fusion meter, apart from the display. All 13 i/o lines
|
||
of the PIC16C84 are used. The controller can be set to work with acrystal, resonator or RC network, depending on the accuracy you
|
||
need. In this application, aceramic
|
||
resonator is the best compromise.
|
||
|
||
been designed to measure CFF in the workplace6.
|
||
This measurement is particularly sensitive to fatigue in the visual system. A comparison of manual workers and vdu operators showed that it was only the latter whose CFF dropped significantly over aworking day 7.
|
||
If aworker's fusion frequency does fall off appreciably over the day, it is likely that he/she will be feeling weary, will not be working as effectively, and may be more accident prone. The situation can be ameliorated if the worker takes adequate breaks or changes the task from time to time.
|
||
A number of different types of flicker-fusion meter have been used; the one to be described here, like that in reference 6, employs a flashing LED, but has more flexible control of the flash rate than the referenced device. It is based on aPIC microcontroller.
|
||
Circuit details
|
||
Shown in Fig. 1, the circuit uses a PIC 16C84, although the newer 16F84 could equally have been used. The device has thirteen i/o lines, all of which are used in this design. It also has an on-chip timer, which is used in setting the flash rate.
|
||
|
||
Frequency is displayed on two seven-segment LED devices, which,
|
||
to conserve the battery, are normally turned off. Four push buttons are used. Respectively, these permit stepwise increases or decreases in frequency, cause asteady ramping (up or down) of flash rate, or 'freeze' the LED in the on state (without visible flashing).
|
||
Uses of these functions will be described later.
|
||
Two ports represent the PIC's i/o
|
||
lines internally; Port A addresses five lines while Port B addresses the
|
||
remaining eight. Full details of the PIC can be found on the data sheet, which may be downloaded in pdf format
|
||
from the Arizona Microchip website, at http://www.microchip.com.
|
||
Input/output lines can be config-
|
||
ured individually in software to act as inputs or outputs. When used as inputs, the pins associated with Port B can also be programmed to have internal weak pull-up resistors.
|
||
Using the internal pull-ups can lead to auseful reduction in external component count. It was simpler not to take advantage of it in this design though, as all the Port B pins are configured as outputs, to drive two 7segment displays.
|
||
Inside the PIC, this port is repre-
|
||
sented as asingle eight-bit register,
|
||
|
||
so writing an appropriate bit pattern to this register drives corresponding pins high or low, turning on and off the various segments of the displays.
|
||
Bits 0through 6are used for segment control. Bit 7, on pin 13, permits amultiplexing action, so that the seven pins can drive fourteen segments in total, via current limiting
|
||
D resistors R1.7. This is achieved by
|
||
using one common anode display, I (for the `tens') and one common cathode, D2 ('units').
|
||
The common pins are respectively
|
||
taken to positive and ground via nand p-channel field effect transistors Tiand T2. These transistors are driven by the eighth pin of Port B, which when high turns on one, and when
|
||
low turns on the other. By alternating rapidly between the
|
||
two displays, at arate greater than
|
||
twice the flicker fusion frequency, the tens and units of the frequency display appear to be on simultaneously and steadily.
|
||
The bit patterns required to turn on the appropriate combinations of display segments are stored in alook-up table in the PIC. So, to display the digit 8, which has all seven segments on, the bit pattern is such as to switch every pin high, i.e. it is seven Is, or 7F in the hexadecimal notation of the PIC, i.e. 7F 16 .
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
687
|
||
|
||
MEDICAL ELECTRONICS
|
||
|
||
To produce an 8, the pattern sent to the port is 01111111, which you will notice leaves bit 7 off, i.e. at zero. This is the multiplexing bit. When the corresponding pin is low, as in this example, T2 is turned on, which in this case means that 8would be displayed in the units.
|
||
If the same bit pattern is inverted before sending to the port the result will be 801 16,or 100000002.With the multiplex bit high this turns on 7). By
|
||
taking every cathode of DIlow — i.e.
|
||
with bits 0through 6all zeros—all its segments are lit. Again this displays an 8, this time in the 'tens' position.
|
||
In this way, the same bit pattern can be used for agiven digit. Whether or not it is inverted determines whether the tens or units display shows it.
|
||
Fusion frequency LED
|
||
With the Port B pins fully utilised for the frequency read out, one pin from Port A has to be used to drive the flashing LED that establishes the fusion frequency. The remaining four pins of this port are configured as inputs. But since the port does not have an internal pull-up facility, external resistors R8_11 are required. The pins therefore normally sit high, and are pulled low when acorresponding single pole, normally open, push button is depressed.
|
||
By polling this port, button presses are detected and acted on. Momentary closure of Si or S3 respectively increments or decrements the flash frequency by 1Hz.
|
||
Holding S4 down causes the frequency gradually to ramp up or down. This is auseful facility, when trying quickly to get to a testee's fusion frequency. Once he/she says that the light seems continuous the one-step up and down buttons can be used to make finer adjustments.
|
||
For afinal judgement, it is useful to be able to make an A/B comparison.
|
||
For this purpose, freeze switch S2 has been added. Holding this down stops visible flashing of the LED, while releasing S2 returns it to the former rate. If the viewer can see the difference between these, the CFF point has not been reached.
|
||
Invisible flashing
|
||
Notice that the freeze option stops visible flashing: in fact this is achieved by turning on and off at
|
||
|
||
approximately 1kHz, which is far above the CFF. The reason for adopting this approach is that the normal flashing is via asquare wave, with
|
||
50% duty cycle. If the 'frozen' LED were in fact permanently on — i.e.
|
||
100% of the time —it would appear twice as bright. This would confuse the A/B comparison process.
|
||
Switch S2 has asecond role of turning on the frequency display: while the LED is in freeze mode the sevensegment displays are active. The default ramping direction is up —i.e. the rate gets faster while the button is depressed. But the direction depends upon which of the single-step buttons was previously depressed. If S3 (down) is used before ramping, then
|
||
the direction will be down, until SI
|
||
(up) is next pressed. The flashing LED, driven via cur-
|
||
rent-limiting resistor, R12 ,could be mounted directly on the board carrying the other components. This is effectively the approach adopted for the fatigue meter described in refer-
|
||
ence 6. However, leaving the LED exposed in this way leaves measure-
|
||
ments open to the effects of ambient lighting, viewing angle and viewing
|
||
distance; reproducibility is difficult to maintain.
|
||
I recommend that the LED is mounted at the base of atube, about 25cm long and fitted with an eyepiece at the other end Fig. 2. This can take the form of aplug, with asmall, say 5mm, axial hole, through which the LED is observed.
|
||
The viewing end of the tube should be fitted with an eye cup. This cup serves to limit interference
|
||
from extraneous light and can be cut from foam rubber.
|
||
Paint the inside of the tube matt black to reduce reflections which would tend to enter the eye more obliquely and stimulate the rods.
|
||
In the prototype, the tube-mounted LED is connected to aflexible lead, so that the viewer can hold it at a comfortable distance from the control board. The lead is terminated with a 3.5mm jack plug; on the board acor-
|
||
responding stereo socket is used. By using astereo component the plug can act as apower switch, by shorting the
|
||
'spare' contact to ground. The PIC can be configured to be
|
||
externally clocked, or to use acrystal or RC oscillator. In this application the
|
||
|
||
Components Microcontroller Ti
|
||
T2
|
||
LED DI
|
||
02
|
||
R1-7 12
|
||
R8-11
|
||
Resonator S1-4 Skt Jack plug Battery box
|
||
|
||
PIC 16C84 ZVN 2106A ZVP 2106A Standard red device 7.6mm common anode display, e.g. 5082-7731 7.6mm common cathode display, e.g. 5082-7740 56os2 100kí2 680nF 4MHz with integral capacitors, CST4.00MGW
|
||
SPNO push button switches, Parnell code: 535-916 3.5mm stereo jack socket, RS code: 476-328 3.5mm mono, or stereo with poles shorted 4xAA, pcb mounting. Maplin code: CL19V
|
||
|
||
crystal option was chosen for greater stability, although rather than acrystal, Iopted for a4MHz ceramic resonator. This particular device has built-in capacitors, eliminating the need for additional components.
|
||
Four AA cells power the unit, capacitor C reducing transients from the rapidly switched Tiand 7.2.In the prototype, the components are mounted on apcb, cut to the same dimensions as afour-cell battery holder. The holder attaches to the track side of the pcb and, as explained above, power is switched on by inserting the jack plug of the flashing LED.
|
||
Power consumption is low, being less than 5mA during flashing, and 14mA while displaying the frequency.
|
||
Programming the PIC
|
||
List 1is afully-commented program listing so only the salient details need be given here.
|
||
Within the PIC are configuration bits. These are set as required during programming. This aspect is not shown in the listing, since the compiling-programming software available from Arizona Microchip — and
|
||
freely downloaded from their web site — offers the user the opportunity to select required parameters at the time of 'blowing' the chip.
|
||
Two parameters are of interest here: the clock oscillator and the watchdog timer. As already stated, the oscillator is configured to be crystal controlled. The watchdog timer is based around a separate, internal RC oscillator, which increments an 8-bit register. When the
|
||
register overflows the device is reset. To prevent the program from reset-
|
||
ting it is necessary to include com-
|
||
|
||
Fig. 2. Mounting the flicker LED in atube in this way helps eliminate reading errors due to ambient light and movement.
|
||
|
||
688
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
MEDICAL ELECTRONICS
|
||
|
||
A dim view is aslow view The separation between the two eyes affords them slightly different views of the same scene. The size of this binocular disparity depends on the distance of a perceived object, and is used by the brain to make distance judgements.
|
||
In effect, the eyes are used to triangulate. Each reveals the direction in which an object lies; where the two direction lines intersect the object is to be found.
|
||
If an object is moving, its perceived location will be slightly outdated, due to the finite time taken by the visual system to respond. The delay is greater when the
|
||
light is less bright. This delay results in mis-triangulation,
|
||
when one eye receives adimmer view than the other - an effect that can be demonstrated by viewing a swinging pendulum through half a pair of sunglasses.
|
||
Make along pendulum, for example by pinning athread to the ceiling and tying on an object near to the floor. Set the pendulum swinging, then stand back some distance, say 2m.
|
||
The direction of swing should be across the field of view, not towards and away from the viewer; be sure that the swing is in astraight line. While observing with both eyes, cover one eye with asunglass
|
||
lens. The pendulum weight should no longer
|
||
seem to swing in astraight line, but in an ellipse, closer to the viewer when moving in one direction, then further away on the return swing.
|
||
This phenomenon's mechanism is illustrated in the diagram, which assumes that the sunglass filter is placed over the right
|
||
eye. When the pendulum weight moves
|
||
from left to right, diagram i, the 'bright' left eye perceives it at point a. But the slow-responding right eye represents the weight as being further back along the path, at position b.
|
||
The two direction lines cross at c, which is where the brain decides the object actually is; the position is in front of the true line of swing. When movement is in the opposite direction, diagram ii, the corresponding positions become a', b' and c', so that the swinging weight is
|
||
perceived to be behind the actual posi-
|
||
tion. When the pendulum is moving fastest,
|
||
i.e. at the mid-point of its swing, the discrepancy is greatest. At either extreme the pendulum momentarily comes to rest, the slow eye catches up, and the weight is perceived in its true position. Consequently, the entire cycle appears to trace an ellipse, which is widest at the
|
||
pendulum's mid-point. It is interesting to note that this phe-
|
||
nomenon was first predicted by aman
|
||
|
||
who never witnessed it, as he was blind in one eye. In his honour it bears his name: the Pulfrich pendulum.
|
||
|
||
Estimating the eye's speed
|
||
|
||
It is possible to estimate the relative slow-
|
||
|
||
ness of the darker eye. Stand an object under the pendulum
|
||
|
||
weight, high enough that the pendulum only just clears it at the lowest point of the
|
||
|
||
swing. This object acts as apointer to indi-
|
||
|
||
cate the pendulum position; it will facili-
|
||
|
||
tate adjustments if it is attached to along stick that can be reached from the viewing position.
|
||
With the pendulum seeming to make its
|
||
|
||
elliptical path, move the pointer to and fro, until it seems to be immediately below the
|
||
|
||
pendulum when at its furthest point -
|
||
|
||
either in front or behind -from the true
|
||
|
||
line. Measure the magnitude of this displace-
|
||
|
||
ment -shown as don the diagram. It is
|
||
|
||
also necessary to measure the viewing distance from the pendulum, D, and the separation of the eyes, s. By similar triangles,
|
||
|
||
you will find tharthe distance of point b
|
||
|
||
behind a-or b' behind a' -is given by,
|
||
|
||
sx—Dd
|
||
|
||
(1)
|
||
|
||
Strictly, D should be replaced by D-d, for the case where the displacement is in
|
||
front. But if the viewing distance is large compared with the size of displacement, then the approximation is reasonable.
|
||
|
||
Calculating temporal lag From the distance of b behind a it is possible to calculate the temporal lag, provided the velocity of the pendulum weight is known, at the centre of its swing.
|
||
To calculate the velopity it is necessary to measure the length, L, of the pendulum thread, and the half-amplitude, A, of its swing. Length A is the distance from the rest position of the pendulum to the widest point of its swing, making sure that this was the width of swing used when the viewing measurements were taken.
|
||
From the equations of simple harmonic motion, to aclose approximation the velocity is,
|
||
|
||
Ax L
|
||
|
||
(2)
|
||
|
||
Here, g is the acceleration due to gravity. If the measurements have been made in centimetres, then the appropriate value for gis 981 cm s-2 . Using the familiar expression distance
|
||
=speed xtime, equations 1and 2can be combined to provide an estimate of the difference in response times, .àt, between the eyes.
|
||
|
||
= s .dL. L A D \g
|
||
|
||
(3)
|
||
|
||
The value found is likely to be of the order of 10ms.
|
||
|
||
These diagrams show how aperson visually perceives apendulum with one eye filtered.
|
||
|
||
C,
|
||
|
||
a'
|
||
|
||
lento 11 ,2111
|
||
|
||
o
|
||
|
||
September 2000 ELECTRONICS WORLD I
|
||
|
||
MEDICAL ELECTRONICS
|
||
|
||
mands in the code that regularly clear
|
||
the watchdog timer. The watchdog facility can be auseful means of auto-
|
||
matically resetting the device, should it become stuck in aloop. It is not used in this application though, so the configuration is set to disable the watchdog timer.
|
||
Initialisation of the PIC takes place
|
||
in the first part of the program, setting
|
||
i/o pins to the desired input or output. It also assigns a prescaler to the watchdog timer. This assignment is
|
||
concerned with the flash rate timing, which uses an on-chip timer.
|
||
The flash-rate timer is another 8-bit counter that can be incremented by an external clock, or by the internal sys-
|
||
tem clock. In this design the system clock is used.
|
||
The clock runs at aquarter of the oscillator rate, so with the 4MHz res-
|
||
onator this design clocks at 1MHz. For some applications, such arapid tick rate may be too fast for the timer, so the PIC offers the option of prescaling the tick rate by any power of 2, up to 2s.
|
||
Alternatively, this same prescaler can be assigned to the watchdog
|
||
timer, so that it does not have to be cleared as frequently: the prescaler has to be assigned to one or other timer.
|
||
For timing the flicker rate, this program uses the ips tick length, so to avoid lengthening this period the prescaler is assigned to the watchdog
|
||
timer. Although the watchdog is dis-
|
||
abled in the design, it is legitimate to make this assignment.
|
||
The flashing LED turns on and off with a50% duty cycle, the duration of
|
||
each half being determined by waiting an appropriate number of timer
|
||
cycles. How many timer cycles are required is determined by the selected flicker frequency. which is propor-
|
||
tional to the reciprocal of the frequency.
|
||
Rather than implement asoftware calculation to determine the necessary timer delay. Iused alook-up table. The subroutine RATEFIX incorporates this table. Instead of the usual, single return-from-subroutine instruction at the end, this routine has multi-
|
||
ple return instructions, in fact as many as there are elements in the table.
|
||
The 'returns' are also alittle more complex than normal: the mnemonic RETLW represents 'return with literal (i.e. anumber) in the W (working) register'. Each RETLW instruction is followed by anumber, in hexadecimal. It is this value that is contained in the W register on returning from the routine.
|
||
In its second line, the routine adds
|
||
a value, n say, representing the
|
||
|
||
List1.Pherannlisfingforthe flk*erfusionfalipmenteten
|
||
|
||
; Hexadecimal values for variable names
|
||
|
||
PortA
|
||
|
||
equ
|
||
|
||
Ox05
|
||
|
||
;five bits wide - LED and control switches
|
||
|
||
PortB
|
||
|
||
equ
|
||
|
||
Ox06
|
||
|
||
;eight bits for mux 7-seg F readout
|
||
|
||
Rate
|
||
|
||
equ
|
||
|
||
Ox0C
|
||
|
||
;Register for frequency
|
||
|
||
timeCount
|
||
|
||
equ
|
||
|
||
Ox0D
|
||
|
||
;reg for no. of cycles in delay
|
||
|
||
HiDig
|
||
|
||
equ
|
||
|
||
Ox0E
|
||
|
||
;reg for bit pattern for freq readout - hi
|
||
|
||
LoDig
|
||
|
||
equ
|
||
|
||
OxOF
|
||
|
||
;reg for lo digit 7-segment bit pattern
|
||
|
||
DecRate
|
||
|
||
equ
|
||
|
||
Ox10
|
||
|
||
;reg for bcd of rate
|
||
|
||
GPReg
|
||
|
||
equ
|
||
|
||
Ox11
|
||
|
||
;general purpose register
|
||
|
||
TenReg
|
||
|
||
equ
|
||
|
||
Ox12
|
||
|
||
;reg used in hex to dec conversion
|
||
|
||
SpeedReg
|
||
|
||
equ
|
||
|
||
Ox13
|
||
|
||
;reg for delay between ramp-up/down steps
|
||
|
||
SpeeDirect
|
||
|
||
equ
|
||
|
||
Ox14
|
||
|
||
;reg for ramp direction
|
||
|
||
RampStart
|
||
|
||
equ
|
||
|
||
Ox15
|
||
|
||
;reg for start value for ramping
|
||
|
||
TRISA
|
||
|
||
equ
|
||
|
||
Ox05
|
||
|
||
;Page 1, reg 5 is data direction reg
|
||
|
||
TRISB
|
||
|
||
equ
|
||
|
||
Ox06
|
||
|
||
;and same for port B
|
||
|
||
TIMER
|
||
|
||
equ
|
||
|
||
Ox01
|
||
|
||
;Timer0 address
|
||
|
||
Opt
|
||
|
||
equ
|
||
|
||
Ox01
|
||
|
||
;Option reg in page 1)
|
||
|
||
PCL
|
||
|
||
equ
|
||
|
||
Ox02
|
||
|
||
;program counter (lower bits)
|
||
|
||
Status
|
||
|
||
equ
|
||
|
||
Ox03
|
||
|
||
;Status reg
|
||
|
||
Carry
|
||
|
||
equ
|
||
|
||
Ox00
|
||
|
||
;carry bit is bit 0
|
||
|
||
equ
|
||
|
||
Ox02
|
||
|
||
;zero flag
|
||
|
||
pBit
|
||
|
||
equ
|
||
|
||
Ox05
|
||
|
||
;Page select bit in status reg
|
||
|
||
Intcon
|
||
|
||
equ
|
||
|
||
Ox0B
|
||
|
||
;Interrupt control reg
|
||
|
||
GIE
|
||
|
||
equ
|
||
|
||
Ox07
|
||
|
||
;Global interrupt enable bit
|
||
|
||
TF
|
||
|
||
equ
|
||
|
||
Ox02
|
||
|
||
;Timer overflow flag
|
||
|
||
; First have to set up IO ports etc, for when initially powered up
|
||
|
||
ORG
|
||
|
||
0
|
||
|
||
;Start address
|
||
|
||
SETUP
|
||
|
||
BSF
|
||
|
||
Status,pBit ;Get to page 1, for setting port masks
|
||
|
||
MOVLW
|
||
|
||
Ox00
|
||
|
||
;IO mask for port B. It's 0000 0000 ...
|
||
|
||
MOVWF
|
||
|
||
TRISB
|
||
|
||
;all bits output for 7-segments
|
||
|
||
MOVLW
|
||
|
||
Ox17
|
||
|
||
;0001 0111
|
||
|
||
MOVWF
|
||
|
||
TRISA
|
||
|
||
;One output for LED, rest input switches
|
||
|
||
CLRF
|
||
|
||
Opt
|
||
|
||
;Zero OPTION, then set desired bits
|
||
|
||
BSF
|
||
|
||
Opt,7
|
||
|
||
;Setting bit disables pull-ups
|
||
|
||
BSF
|
||
|
||
Opt,3
|
||
|
||
;prescaler to WDT, so no dividing
|
||
|
||
BCF
|
||
|
||
Status,pBit ;Back to page 0
|
||
|
||
BCF
|
||
|
||
Intcon,GIE ;Disable global interrupts
|
||
|
||
MOVLW
|
||
|
||
OxDO
|
||
|
||
;208 dec
|
||
|
||
MOVWF
|
||
|
||
SpeedReg
|
||
|
||
;... so takes 48 steps before ramping
|
||
|
||
MOVWF
|
||
|
||
RampStart
|
||
|
||
;Put value here too
|
||
|
||
MOVLW
|
||
|
||
Ox01
|
||
|
||
;+1 to add from ...
|
||
|
||
MOVWF
|
||
|
||
SpeeDirect
|
||
|
||
up/down direction reg
|
||
|
||
MOVLW
|
||
|
||
Ox0A
|
||
|
||
;10 down the list of 10 - 60 ...
|
||
|
||
MOVWF
|
||
|
||
Rate
|
||
|
||
;... to start at 20 Hz
|
||
|
||
CLRF
|
||
|
||
PortB
|
||
|
||
;turn off 7-segment displays at star'
|
||
|
||
CALL
|
||
|
||
BUTTONS
|
||
|
||
;button not pressed, but need rate et
|
||
|
||
; Now everything in place, go into main monitoring loop
|
||
|
||
MAIN
|
||
|
||
MOVLW
|
||
|
||
Ox07
|
||
|
||
;0111 to mask off main button bits
|
||
|
||
ANDWF
|
||
|
||
PortA,0
|
||
|
||
;get button state
|
||
|
||
XORLW BTFSS
|
||
|
||
Ox07 Status,2
|
||
|
||
;should leave zero if no button down ;if zero get on with displaying
|
||
|
||
CALL
|
||
|
||
BUTTONS
|
||
|
||
;non-zero;see what's pressed
|
||
|
||
MOVF
|
||
|
||
timeCount,0 ;get current delay setting
|
||
|
||
MOVWF
|
||
|
||
GPReg
|
||
|
||
;put in general counter
|
||
|
||
MOVLW
|
||
|
||
Ox08
|
||
|
||
;1000 bit pattern
|
||
|
||
XORWF
|
||
|
||
PortA
|
||
|
||
;toggle bit 3 for flashing LED
|
||
|
||
TIMING
|
||
|
||
BTFSS CALL MOVLW
|
||
|
||
PortA,4 SPEEDUP Ox3E
|
||
|
||
;will be clear if ;go and deal with ;62 dec, which is
|
||
|
||
speed-up button depressed speed-up - 190 off a roll-over
|
||
|
||
MOVWF BCF
|
||
|
||
TIMER Intcon,TF
|
||
|
||
;start timer at preset value ;clear timeout flag
|
||
|
||
WAIT
|
||
|
||
BTFSS
|
||
|
||
Intcon,TF
|
||
|
||
;time out yet?
|
||
|
||
GOTO
|
||
|
||
WAIT
|
||
|
||
;keep showing frequency
|
||
|
||
DOWNTIM
|
||
|
||
DECFSZ
|
||
|
||
GPReg
|
||
|
||
;go through the delay steps
|
||
|
||
GOTO
|
||
|
||
TIMING
|
||
|
||
;off for next step
|
||
|
||
GOTO
|
||
|
||
MAIN
|
||
|
||
;all steps done: go toggle LED and repeat
|
||
|
||
; Next section used when ramp button depressed
|
||
|
||
SPEEDUP
|
||
|
||
BCF
|
||
|
||
Status,Z
|
||
|
||
;make sure zero flag is clear
|
||
|
||
MOVF
|
||
|
||
SpeeDirect,O;get either +1 or -1
|
||
|
||
ADD MF
|
||
|
||
SpeedReg
|
||
|
||
;increment or decrement
|
||
|
||
BTFSS
|
||
|
||
Status,Z
|
||
|
||
;result a zero?
|
||
|
||
RETURN ADDWF
|
||
|
||
Rate
|
||
|
||
;if not just return ;add xl to inc/dec rate
|
||
|
||
MOVF MOVWF CALL
|
||
|
||
RampStart,0 SpeedReg OVERRUN
|
||
|
||
;start value for ramp; don't wait 256 steps ;to give 48 delay steps in either direction ;make sure rate is in usable range
|
||
|
||
CALL
|
||
|
||
RATEFIX
|
||
|
||
;get required time delay for rate ...
|
||
|
||
MOVWF
|
||
|
||
timeCount
|
||
|
||
;... and store it
|
||
|
||
RETURN ; Following handles button presses
|
||
|
||
;now flash at new rate
|
||
|
||
Continued over page...
|
||
|
||
690
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
MEDICAL ELECTRONICS
|
||
|
||
desired flicker frequency, to the PIC's program counter. The effect is to make the program jump forward by n instructions, to encounter one of the RETLWs. The returned number is the timer delay appropriate to the frequency.
|
||
A similar principle is used in the subroutine PATTERN, which uses avalue between 0and 9to return with acorresponding 7-segment bit pattern, to send to Port B.
|
||
Implementing the design Layout is not critical, but at the breadboard stage the capacitor C was found to be necessary, to avoid spurious frequency jumps and unwanted device resets.
|
||
As Iexplained earlier, it is preferable to mount the flashing LED in aviewing tube, but adequate results are likely to be obtained if the LED is mounted directly on the main circuit board. Notice, though, that the frequency readout would then also be in view of the person being tested.
|
||
It is likely that knowledge of their CFF would influence some people's judgments — attempting to 'beat' their last score for example. For this reason, Irecommend that the read-out be covered during use, if aboardmounted LED is used. In this configuration. without the jack socket, an on-off power switch would be required.
|
||
The jack socket, switches and battery holder stipulated in the component list fit my pcb design.
|
||
Evaluating and using the meter On connecting power, it will be immediately apparent whether the device is functioning, with LED flashing and frequency displayed when the freeze switch is closed.
|
||
The quickest way of making ameasurement is to use the ramp-up switch, stopping when the flicker is no longer perceptible. A better result will be obtained by finding amean; after ramping up, take the flicker rate well above the CFF, then ramp down until the flicker is just perceptible.
|
||
An average of the two scores will be areasonable estimate of the CFF. A more accurate result may be achieved by following ramping with finer adjustments, by means of the up and down switches.
|
||
Even this technique can be influenced by the testee's judgement criteria; for example atendency to say 'Yes' to the slightest glimmer of aflicker will lead to ahigher CFF than astrategy of saying 'No' to anything but the clearest blinking.
|
||
Eliminating false readings If atruly criterion-free measure is required, and speed of measurement-taking is not important, then the two-interval forced-choice, or 2IFC, method should be used. To carry out the 2IFC procedure A/B comparisons are conducted, using the freeze button; it is important that the testee cannot see whether the button is depressed or not.
|
||
Pairs of presentations are given, one 'frozen' the other flashing. The testee should be asked to look away from the LED during the transi-
|
||
|
||
tion between switch positions; he/she looks only when the flash/no-flash conditions are established, and with agap of afew seconds
|
||
between the two. In this case, the testee is required to state —
|
||
|
||
even if unsure —which of the two intervals was flashing. The operator should arrange that sometimes it is the first of the pair that flashes, sometimes the second. If the viewer's hit rate
|
||
is only 50%, then he/she must be guessing, so
|
||
|
||
BUTTONS
|
||
|
||
BTFSC
|
||
|
||
PortA,0
|
||
|
||
;up button - will use pull-ups
|
||
|
||
GOTO
|
||
|
||
TRY2
|
||
|
||
;if up, try other button
|
||
|
||
INCF
|
||
|
||
Rate
|
||
|
||
;go faster
|
||
|
||
MOVLW
|
||
|
||
Ox01
|
||
|
||
;+1
|
||
|
||
MOVWF
|
||
|
||
SpeeDirect ;for adding when speed ramping
|
||
|
||
MOVLW
|
||
|
||
OxDO
|
||
|
||
;208
|
||
|
||
MOVWF
|
||
|
||
RampStart
|
||
|
||
48 off roll-over
|
||
|
||
TRY2
|
||
|
||
BTFSC
|
||
|
||
PortA,2
|
||
|
||
;down button
|
||
|
||
GOTO
|
||
|
||
GETON
|
||
|
||
;if not down get on with setting params
|
||
|
||
DECF
|
||
|
||
Rate
|
||
|
||
;go slower
|
||
|
||
MOVLW
|
||
|
||
OxFF
|
||
|
||
; equiv to -1
|
||
|
||
MOVWF
|
||
|
||
SpeeDirect ;for adding when ramping speed down
|
||
|
||
MOVLW
|
||
|
||
Ox30
|
||
|
||
;48
|
||
|
||
MOVWF
|
||
|
||
RampStart
|
||
|
||
;decrement from 48 when ramping down
|
||
|
||
GETON
|
||
|
||
CALL
|
||
|
||
OVERRUN
|
||
|
||
;check rate still in range
|
||
|
||
CALL
|
||
|
||
DECIM
|
||
|
||
;go and decimalise rate
|
||
|
||
CALL
|
||
|
||
SEGPAT
|
||
|
||
;use dec values to get 7-seg patterns
|
||
|
||
CALL
|
||
|
||
RATEFIX
|
||
|
||
;go and get delay for current frequency
|
||
|
||
MOVWF
|
||
|
||
timeCount
|
||
|
||
;... and put in counter
|
||
|
||
BTFSS
|
||
|
||
PortA,1
|
||
|
||
;freeze button
|
||
|
||
CALL
|
||
|
||
FREEZE
|
||
|
||
;make LED look steady
|
||
|
||
DEBOUNCE
|
||
|
||
MOVLW
|
||
|
||
Ox07
|
||
|
||
;0111 to mask off button bits
|
||
|
||
ANDWF
|
||
|
||
PortA,0
|
||
|
||
;is button still down?
|
||
|
||
XORLW
|
||
|
||
Ox07
|
||
|
||
;should leave zero if no button down
|
||
|
||
BTFSS
|
||
|
||
Status,Z
|
||
|
||
;if zero get on with displaying
|
||
|
||
GOTO
|
||
|
||
DEBOUNCE
|
||
|
||
;wait until button up
|
||
|
||
RETURN
|
||
|
||
;all done
|
||
|
||
; Next lolt flashes v. fast, to look permanently on
|
||
|
||
FREEZE
|
||
|
||
MOVLW
|
||
|
||
Ox08
|
||
|
||
;1000
|
||
|
||
XORWF
|
||
|
||
PortA
|
||
|
||
;toggle LED
|
||
|
||
MOVE
|
||
|
||
LoDig,0
|
||
|
||
;get units value of frequency
|
||
|
||
MOVWF
|
||
|
||
PortB
|
||
|
||
;display the value
|
||
|
||
BCE
|
||
|
||
Intcon,TF
|
||
|
||
;make sure timer not overflowed
|
||
|
||
CLRF
|
||
|
||
TIMER
|
||
|
||
;zero timer, ready to wait ...
|
||
|
||
UnitCycle
|
||
|
||
BTFSS
|
||
|
||
Intcon,TF
|
||
|
||
;... 256 ps
|
||
|
||
GOTO
|
||
|
||
UnitCycle
|
||
|
||
;keep waiting
|
||
|
||
COME
|
||
|
||
HiDig,0
|
||
|
||
;get lOs frequency value, invert for readout
|
||
|
||
MOVWF
|
||
|
||
PortB
|
||
|
||
;display the value
|
||
|
||
BCE
|
||
|
||
Intcon,TF
|
||
|
||
;clear it again
|
||
|
||
CLRF
|
||
|
||
TIMER
|
||
|
||
;start another ...
|
||
|
||
TenCycle
|
||
|
||
BTFSS
|
||
|
||
Intcon,TF
|
||
|
||
;... 256 us
|
||
|
||
GOTO
|
||
|
||
TenCycle
|
||
|
||
;keep waiting
|
||
|
||
BTFSS
|
||
|
||
PortA,1
|
||
|
||
;freeze button still down?
|
||
|
||
GOTO
|
||
|
||
FREEZE
|
||
|
||
;yes - repeat
|
||
|
||
CLRF
|
||
|
||
PortB
|
||
|
||
;turn off 7-segs before leaving
|
||
|
||
RETURN
|
||
|
||
;all done
|
||
|
||
; Routine to stop rate value going beyond length of look-up table
|
||
|
||
OVERRUN
|
||
|
||
MOVLW SUBWF
|
||
|
||
Ox32 Rate,0
|
||
|
||
;max value Rate should contain ;take from actual value
|
||
|
||
BTFSC
|
||
|
||
Status,Carry;will be clear if Rate has not gone over max
|
||
|
||
CLRF
|
||
|
||
Rate
|
||
|
||
;if over, wrap round to zero
|
||
|
||
RETURN
|
||
|
||
RATEFIX
|
||
|
||
Following is table with Nos, of delay steps to get required rate
|
||
|
||
MOVE
|
||
|
||
Rate, O
|
||
|
||
;get the rate (0=10 Hz, 50=60 Hz)
|
||
|
||
ADDWF
|
||
|
||
PCL
|
||
|
||
;jump forward in table
|
||
|
||
RETLW
|
||
|
||
OxFF
|
||
|
||
;255 dec for 10 Hz
|
||
|
||
RETLW
|
||
|
||
OxE8
|
||
|
||
RETLW
|
||
|
||
OxD5
|
||
|
||
RETLW
|
||
|
||
OxC4
|
||
|
||
RETLW
|
||
|
||
OxB6
|
||
|
||
RETLW
|
||
|
||
OxAA
|
||
|
||
RETLW
|
||
|
||
Ox9F
|
||
|
||
RETLW
|
||
|
||
Ox96
|
||
|
||
RETLW
|
||
|
||
Ox8E
|
||
|
||
RETLW
|
||
|
||
Ox86
|
||
|
||
RETLW
|
||
|
||
Ox80
|
||
|
||
RETLW
|
||
|
||
Ox79
|
||
|
||
RETLW
|
||
|
||
Ox74
|
||
|
||
RETLW
|
||
|
||
Ox6F
|
||
|
||
RETLW
|
||
|
||
Ox6A
|
||
|
||
RETLW
|
||
|
||
Ox66
|
||
|
||
RETLW
|
||
|
||
Ox62
|
||
|
||
RETLW
|
||
|
||
Ox5E
|
||
|
||
RETLW
|
||
|
||
Ox5B
|
||
|
||
RETLW
|
||
|
||
Ox58
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
691
|
||
|
||
MEDICAL ELECTRONICS
|
||
|
||
the flash rate is above the CFF. Start with the rate alittle below fusion, then
|
||
gradually increment it, giving several pairs of presentations at each stage. Continue, until the 50% criterion is just reached; this will be the
|
||
|
||
unbiased critical frequency. Variation in CFF is most easily tested by find-
|
||
ing the fusion frequency first without, then while wearing sunglasses. When the testee is wearing sunglasses, the frequency should be lower.
|
||
|
||
RETLW
|
||
|
||
Ox55
|
||
|
||
RETLW
|
||
|
||
Ox52
|
||
|
||
RETLW
|
||
|
||
Ox50
|
||
|
||
RETLW
|
||
|
||
Ox4D
|
||
|
||
RETLW
|
||
|
||
Ox4B
|
||
|
||
RETLW
|
||
|
||
Ox49
|
||
|
||
RETLW
|
||
|
||
Ox47
|
||
|
||
RETLW
|
||
|
||
Ox45
|
||
|
||
RETLW
|
||
|
||
Ox43
|
||
|
||
RETLW
|
||
|
||
Ox41
|
||
|
||
RETLW
|
||
|
||
Ox40
|
||
|
||
RETLW
|
||
|
||
Ox3E
|
||
|
||
RETLW
|
||
|
||
Ox3D
|
||
|
||
RETLW
|
||
|
||
Ox3B
|
||
|
||
RETLW
|
||
|
||
Ox3A
|
||
|
||
RETLW
|
||
|
||
Ox39
|
||
|
||
RETLW
|
||
|
||
Ox37
|
||
|
||
RETLW
|
||
|
||
Ox36
|
||
|
||
RETLW
|
||
|
||
Ox35
|
||
|
||
RETLW
|
||
|
||
Ox34
|
||
|
||
RETLW
|
||
|
||
Ox33
|
||
|
||
RETLW
|
||
|
||
Ox32
|
||
|
||
RETLW
|
||
|
||
Ox31
|
||
|
||
RETLW
|
||
|
||
0x30
|
||
|
||
RETLW
|
||
|
||
Ox2F
|
||
|
||
RETLW
|
||
|
||
Ox2E
|
||
|
||
RETLW
|
||
|
||
Ox2E
|
||
|
||
RETLW
|
||
|
||
Ox2D
|
||
|
||
RETLW
|
||
|
||
Ox2C
|
||
|
||
RETLW
|
||
|
||
Ox2B
|
||
|
||
RETLW
|
||
|
||
Ox2A;
|
||
|
||
60Hz
|
||
|
||
; Following changes to decimal format - nibbles = tens & units
|
||
|
||
DECIM
|
||
|
||
CLRF
|
||
|
||
DecRate
|
||
|
||
;zero current value
|
||
|
||
MOVLW
|
||
|
||
Ox0A
|
||
|
||
;10 as frequency starts at 10 Hz
|
||
|
||
ADDWF
|
||
|
||
Rate,0
|
||
|
||
;get actual frequency ...
|
||
|
||
MOVWF
|
||
|
||
GPReg
|
||
|
||
;... and save it
|
||
|
||
MOVLW
|
||
|
||
Ox0A
|
||
|
||
;a counter for ten operations
|
||
|
||
MOVWF
|
||
|
||
TenReg
|
||
|
||
;store in register
|
||
|
||
DECUP
|
||
|
||
INCF
|
||
|
||
DecRate
|
||
|
||
;start incrementing the register
|
||
|
||
DECFSZ
|
||
|
||
TenReg
|
||
|
||
;do up to ten additions
|
||
|
||
GOTO
|
||
|
||
MAINDEC
|
||
|
||
;if not ten yet, nothing to correct
|
||
|
||
MOVLW
|
||
|
||
Ox0A
|
||
|
||
;if ten, reset counter
|
||
|
||
MOVWF MOVLW
|
||
|
||
TenReg Ox06
|
||
|
||
;to count next ten ;add another 6 ...
|
||
|
||
ADDWF
|
||
|
||
DecRate
|
||
|
||
;... to rollover to tens nibble
|
||
|
||
MAINDEC
|
||
|
||
DECFSZ
|
||
|
||
GPReg
|
||
|
||
;working through entire No
|
||
|
||
GOTO RETURN
|
||
|
||
DECUP
|
||
|
||
;repeat ;all done
|
||
|
||
SEGPAT
|
||
|
||
following gets correct 7-segment patterns from digits
|
||
|
||
MOVF
|
||
|
||
DecRate,0
|
||
|
||
;get the BCD value
|
||
|
||
ANDLW
|
||
|
||
OxOF
|
||
|
||
;mask off lower nibble
|
||
|
||
CALL
|
||
|
||
PATTERN
|
||
|
||
;get the pattern
|
||
|
||
MOVWF
|
||
|
||
LoDig
|
||
|
||
;and put in units store
|
||
|
||
SWAPF
|
||
|
||
DecRate,0
|
||
|
||
;get other nibble at lower end
|
||
|
||
ANDLW CALL
|
||
|
||
OxOF PATTERN
|
||
|
||
;mask again ;find its 7-seg pattern
|
||
|
||
MOVWF
|
||
|
||
HiDig
|
||
|
||
;and store it
|
||
|
||
PATTERN
|
||
|
||
RETURN ADDWF
|
||
|
||
PCL
|
||
|
||
;all done ;jump ahead
|
||
|
||
RETLW
|
||
|
||
Ox3F
|
||
|
||
;pattern for zero
|
||
|
||
RETLW
|
||
|
||
Ox06
|
||
|
||
;1
|
||
|
||
RETLW
|
||
|
||
Ox5B
|
||
|
||
RETLW
|
||
|
||
Ox4F
|
||
|
||
RETLW
|
||
|
||
Ox66
|
||
|
||
RETLW
|
||
|
||
Ox6D
|
||
|
||
RETLW
|
||
|
||
Ox7D
|
||
|
||
RETLW
|
||
|
||
Ox07
|
||
|
||
RETLW
|
||
|
||
Ox7F
|
||
|
||
RETLW RETLW END
|
||
|
||
Ox6F Ox40
|
||
|
||
;9 ;minus
|
||
|
||
The difference in inter-flash intervals repre-
|
||
|
||
sented by the frequency difference may be
|
||
|
||
compared with the timing difference calculat-
|
||
|
||
ed by the method detailed in the panel entitled,
|
||
|
||
'A dim view is aslow view'. The two are
|
||
|
||
unlikely to be identical, since each depends on
|
||
|
||
brightness levels; however, the values should
|
||
|
||
be of the same order of magnitude.
|
||
|
||
Testing arange of people should show aten-
|
||
|
||
dency for CFF to fall with age and with tired-
|
||
|
||
ness. In women, some variation may be found
|
||
|
||
over the menstrual cycle.
|
||
|
||
In the workplace, the device can be used as
|
||
|
||
afatigue meter, testing at the start and end of
|
||
|
||
the working day. If avdu operator shows an
|
||
|
||
appreciable drop in CFF of, say, 10% over the
|
||
|
||
day, then it would be appropriate to examine
|
||
|
||
the working practice and ergonomical layout
|
||
|
||
of the workstation.
|
||
|
||
Standard health and safety practices should
|
||
|
||
be employed, checking that there is no glare or
|
||
|
||
reflection from monitor screens, that the mate-
|
||
|
||
rial displayed is easily legible and that the
|
||
|
||
worker wears appropriate glasses if required.
|
||
|
||
Ambient lighting levels must be adequate.
|
||
|
||
There is some evidence8 that the flickering
|
||
|
||
of standard fluorescent lighting can lead to an
|
||
|
||
experience of stress, particularly for those with
|
||
|
||
high CFF thresholds; driving the tubes at high
|
||
|
||
frequency leads to greater comfort.
|
||
|
||
As ageneral rule, workers should take reg-
|
||
|
||
ular breaks, which not only relieve the
|
||
|
||
demands of the task, but also give aperiod
|
||
|
||
when the eyes can take in scenes of different
|
||
|
||
brightness and at different distances.
|
||
|
||
•
|
||
|
||
References 1. Mendelson, J.R. & Wells, E.F. 1999, 'The neu-
|
||
rophysiological effects of aging on the ability of the visual cortex to process temporal information', Brain and Cognition 39, 55-57. 2. Hindmarch, 1., Quinlan, PT., Moore, K.L. & Parkin, C. 1998. 'The effects of black tea, and other beverages on aspects of cognition and psychomotor performance,' Psychopharmacology 3, 230-238. 3. Eysenck, H.J. 1970, Readings in extraversionintroversion: bearings on basic pschological processes, Vol. 3, New York: Wiley. 4. Corr, P.J., Pickering, A.D. & Gray, J.A. 1995, 'Sociability, impulsivity and caffeine-induced arousal —Critical flicker fusion frequency and procedural learning', Personality and Individual Differences 18, 713-730. 5. Costa, G. 1993, 'Evaluation of workload in airtraffic-controllers', Ergonomics 36, 1111-1120. 6. Hosokawa, T., Mikami, K. & Saito, K. 1997, 'Basic study of the portable fatigue meter: effects of illumination, distance from eyes and age', Ergonomics 40, 887-894. 7. Murata, K., Araki, S., Yokoyama, K., Yamashita, K., Okumatsu, T. & Sakou, S. 1996, 'Accumulation of VDT work-related visual fatigue assessed by visual evoked potential, near point distance and critical flicker fusion', Industrial Health 34, 61-69. 8. KuIler, R. & Laike, T. 1998, 'The impact of flicker from fluorescent lighting on well-being, performance and physiological arousal', Ergonomics 41, 433-447.
|
||
|
||
692 ELECTRONICS WORLD September 2000
|
||
|
||
SMALL SELECTION ONLY LISTED -EXPORT TRADE AND QUANTITY DISCOUNTS -RING US FOR YOUR REQUIREMENTS WHICH MAY BE IN STOCK
|
||
|
||
HP New Colour Spectrum Analyser: LAST FEW ONLY
|
||
|
||
HP1417.85528 IF. 8553B RF -1KHZ -nomes -£500.
|
||
|
||
ueo. HP141T. 85528 IF •85548 RF -100KHz -1250M -£00.
|
||
HP141T. 85528 IF •8556A RF -20Hz-300KHz -
|
||
|
||
HP141T. 85528 IF 8555A 10 MC/S•18GlizS -C1000.
|
||
|
||
HP8443A Tracking Gen Counter 100KHz-110Mc/s E200
|
||
|
||
HP8445B Tracking Preselector DC to 18GHz £250.
|
||
|
||
HP8444A Tracking Generator •5-1300Mc/s -050.
|
||
|
||
HP8444A OPT 059 Tracking Gen •5-1500Mc/s •£50.
|
||
|
||
HP35601A Spectrum Ant Interface -f300.
|
||
|
||
HP4953A Protocol Ant •£400.
|
||
|
||
HP13970A Noise Figure Meter •3468 Noise Head -C3k.
|
||
|
||
HP8755A+B+C Scalar Network Ant PI -C250 .MF 180C -Heads
|
||
|
||
11664 Extra -050 each.
|
||
|
||
HP37098 Constellation ANZ £1,000.
|
||
|
||
HP11715A AM-FM Test Source -£350.
|
||
|
||
FARAELL TVS70MKII PU 0-70V 10 amps E150.
|
||
|
||
MARCONI 6500 Network Scaler Ant -£00. Heads available to
|
||
|
||
40GHz many types in stock.
|
||
|
||
Mixers are available forANZs to 60Gilz.
|
||
|
||
HP6131C Digital Voltage Source +-1001/*/, Amp.
|
||
|
||
HP5316A Universal Counter A.13.
|
||
|
||
Marconi TF2374 Zero Loss Probe -£200.
|
||
|
||
Racal/Dana 2101 Microwave Counter 10Hz•20GH: -with book
|
||
|
||
as new C2k.
|
||
|
||
Racal/Dana 1250-1261 Universal Switch Controller •200Mds PI
|
||
|
||
Cards and other types.
|
||
|
||
Racal/Dana 9303 True RMS Levelmeter Head -£450.
|
||
|
||
TEKA6902A also A69028 Isolator 000-C400.
|
||
|
||
TEK CT-5 High Current Transformer Probe -E.250.
|
||
|
||
HP Frequency comb generator type 8406 £400.
|
||
|
||
HP Sweep Oscillators type 8690 A.B .plug-in
|
||
|
||
18GHz also 18.40GHz.
|
||
|
||
HP Network Analyser type 8407A •8
|
||
|
||
110Mcis -£00 -£1000.
|
||
|
||
HP 8410-A-8-C Network Ana
|
||
|
||
18 GHz
|
||
|
||
-plus most other units a i
|
||
|
||
t-up -8411a-
|
||
|
||
8412-8413-8414-841
|
||
|
||
6-8650. F Elk.
|
||
|
||
Racal/Dana 9301
|
||
|
||
F
|
||
|
||
•1.5-2GHz
|
||
|
||
stock E250-E
|
||
|
||
Recel/Deus M
|
||
|
||
pe 9009-9008
|
||
|
||
E
|
||
|
||
50- 9
|
||
|
||
FICLIki type TF2700 -E150.
|
||
|
||
croweve 6600A 1sweep ose., mainfra
|
||
|
||
ith
|
||
|
||
6.5 GHz or 6651 PI -26.5-40GHz-E750 or Pl on
|
||
|
||
nly £250.
|
||
|
||
GouI23B test oscillator .manuel -E150.
|
||
|
||
Marconi 6155A Signal Source-1 to 2GHz •LE
|
||
|
||
Barr & Stroud Variable filter EF3 0.1Hz-1
|
||
|
||
O. pass -E150, other makes in stoc
|
||
|
||
Racal/Dana 9300 RMS voltmeter •
|
||
|
||
HP 8750A storage normalizer 400
|
||
|
||
N. A
|
||
|
||
Marconi mod meters ty
|
||
|
||
f2
|
||
|
||
5-£1,000.
|
||
|
||
Racal/Dana counters
|
||
|
||
16-9917-
|
||
|
||
50Mcfs.3Gliz -C100 -
|
||
|
||
fi
|
||
|
||
FX standards.
|
||
|
||
HP180TR. HP181T, HP1
|
||
|
||
es C300 -£500.
|
||
|
||
HP432A-435A or 8-436A-
|
||
|
||
eters .powerheads to 60
|
||
|
||
E150 E1750 -spare heu. available.
|
||
|
||
HP3586A or Cselective level meter -£00.
|
||
|
||
HP86222A443 Sweep Pl -01.2.4GHz •ATT C1000-C1250.
|
||
|
||
HP86290A+8 Sweep PI-2 -18GHz -£1000 -0250.
|
||
|
||
HP8620C Mainframe -£250.1EEE £50.
|
||
|
||
HP8165A Programmable signal source 1MHZ •50M
|
||
|
||
HP3455/3456A Digital voltmeter -£400.
|
||
|
||
HP5370A Universal time interval counter -C1
|
||
|
||
HP5335A Universal counter 200Mc/s-E1
|
||
|
||
HP3552A Transmission test set -£50.
|
||
|
||
TEKTRONIX 577 Curve tracer •adapt
|
||
|
||
TEKTRONIX 1502/1503 TDR cable test
|
||
|
||
HP8699B Sweep Pl VIO oscillator .01
|
||
|
||
86908 MF -
|
||
|
||
E250. Both £00.
|
||
|
||
Dummy Loads & Power att up to 2.5 kilowatts FX up to 18GHz -
|
||
|
||
microwave parts new and ex equipt -relays •attenuators -
|
||
|
||
switches -waveguides Yigs SMA •APC7 plugs -adaptors
|
||
|
||
etc. qty. in stock.
|
||
|
||
B&K barns in stock ask for list.
|
||
|
||
Power Supplies Heavy duty • bench in stock -Farnell •HP -
|
||
|
||
Weir -Thurtby -Racal etc. Ask for list. Large quantity in stock,
|
||
|
||
all types to 400 amp -100Kv.
|
||
|
||
HP8405A Vector voltmeter •late colour -£00.
|
||
|
||
HP8508A Vector voltmeter -£500.
|
||
|
||
HP8505A Network Ant 500KHz-1.3GHz -£1000.
|
||
|
||
HP8505A .8502A or 8503A test sets- f12
|
||
|
||
HP8505A •8502A or 8503A •8501A
|
||
|
||
Phillips 3217 50Mc/s oscillosco
|
||
|
||
Wavetek-Schlumberger 4031 R
|
||
|
||
mu
|
||
|
||
ionWst set
|
||
|
||
LIGHT AND OPTICAL E
|
||
|
||
Anritsu ML93A & Optical L
|
||
|
||
eter •£250.
|
||
|
||
Anritsu ML938 & Optical L Power Sensors for above M
|
||
|
||
Meter -£50. MASSA -MA913A Battery
|
||
|
||
Pack M295A.
|
||
|
||
Anritsu MW97A Pulse Echo Tester.
|
||
|
||
Pl available -MH914C 1.3 -MH9158 1.3 •MH91313 0.85 • MH925A 1.3 •MH929A 1.55 •MH925A 1.301 •MH914C 1.3SM -
|
||
|
||
£500 •one P.I. Anritsu MW98A Mme Domain Reflector.
|
||
|
||
Pl available MH914C 1.3 -MH9158 1.3 -MM9138 0.85 MH925A 1.3 •MH929A 155 MH925A 1.301- MH914C 1.3SM •
|
||
|
||
£S00 .one PL
|
||
|
||
Anritsu M2100A E0 Converter.
|
||
|
||
MG91213 ILD 1.351 UgM Source yMG928 ILD 0.851
|
||
|
||
Light Source £350.
|
||
|
||
Anritsu M2118A 0/E Converter.
|
||
|
||
.MFt922A 0.8 0/E unit •MH923 A1.3 0/E unit £50. Anritsu ML968 Power Meter & Charger £450.
|
||
|
||
Anritsu MN958 Variable Att, 1300 £1 90.
|
||
|
||
Photo Dyne 1950 KR Continuous Att. 1300 -1500 £100.
|
||
|
||
Photo Dyne 1800 FA. Att £100.
|
||
|
||
Cossor-Raytheon 108L Optical Cable Fault Locator
|
||
|
||
0 1000M 0•10kM £300. TEK P6701 Optical Converter 700 MG/S-850 £250.
|
||
|
||
TEK OF150 Fibre Optic TDR -£750.
|
||
|
||
HP81512A Head 150MC/S 950-1700 £250.
|
||
|
||
HP84801A Fibre Power Sensor 600-1200 £250
|
||
|
||
HP81588 ATE OPT 002.011 1300-1550 000. HP81519A RX DC-400MC/S 550-950 £250. STC OFR10 Reflectometer -f250.
|
||
STC OFSK15 Machine jointing n eye magnifier -C250.
|
||
|
||
COMMUNICATION EQUIPMENT
|
||
|
||
Anritsu ME453L AX Microwave ANZ -£350.
|
||
|
||
Anritsu ME453L TX Microwave ANZ -£350.
|
||
|
||
Anritsu MH370A Jitter Mod Oscillator -£350.
|
||
|
||
Anritsu MG642A Pulse Pitt Gen. £350.
|
||
|
||
System MS02A Timer & Digital Printer -£500.
|
||
|
||
Complete MS65A Error Detector.
|
||
|
||
Anritsu ML612A Sel Level Meter -£400.
|
||
|
||
Anritsu ML244A Sel Level Meter -000.
|
||
|
||
W&G PCM3 Auto Measuring Set -000.
|
||
|
||
W&G SPM14 Sel Level Meter -000.
|
||
|
||
W&G SPM15 Sel Level Mater -050.
|
||
|
||
W&G P519 Level Gen -£00.
|
||
|
||
W&G DA20+0A1 Data ANZ £400
|
||
|
||
W&G PMG3 Transmissio
|
||
|
||
W&G PSS16 Generator
|
||
|
||
W&G PS14 Level
|
||
|
||
W&G EPM-1 P
|
||
|
||
wer Meter
|
||
|
||
W&G DLM3 Pb e r&
|
||
|
||
£50
|
||
|
||
W&G DLM4 Dm Li
|
||
|
||
st Set -£400
|
||
|
||
W&G PS10 & PM10 L Gen -E250.
|
||
|
||
ELLANMIUS ITEM
|
||
|
||
2A Data Acq
|
||
|
||
on
|
||
|
||
nit n
|
||
|
||
1A 16ch
|
||
|
||
4261 LCR mete
|
||
|
||
HP 4274 FR me
|
||
|
||
HP 4951A HP 3488 Se.
|
||
|
||
olA ontro
|
||
|
||
t PI
|
||
|
||
HP 75 632 IS
|
||
1
|
||
|
||
Controllers
|
||
|
||
S/PCS 1805-
|
||
|
||
-£2.060.
|
||
|
||
631-1650
|
||
|
||
in
|
||
|
||
tY. for use
|
||
|
||
8754A Net, nrk A 4-1 8754ft Net» it
|
||
|
||
MC/S 502A cabl 600MC/S.8
|
||
|
||
E2,0001
|
||
|
||
per
|
||
|
||
83540A Pl
|
||
|
||
-C3,50 .
|
||
|
||
4GH
|
||
|
||
ETWT AM
|
||
|
||
2GH
|
||
|
||
-(400.
|
||
|
||
IFIER 8447 MPLIFIER 8447
|
||
|
||
Dual -£300.
|
||
|
||
POWER ampuREN
|
||
|
||
-(400.
|
||
|
||
PPRE •P
|
||
|
||
PLIE
|
||
|
||
0.01-1.30H
|
||
|
||
HP 3574 Go*
|
||
|
||
h Meter 1 3MC/S 0
|
||
|
||
'm'on Meter-50
|
||
|
||
Tru
|
||
|
||
SMeter -
|
||
|
||
AF Power Met
|
||
|
||
d fi
|
||
|
||
e's-
|
||
|
||
C350. E900.
|
||
|
||
SIGNAL SOU
|
||
|
||
4-18GHZ-
|
||
|
||
E
|
||
|
||
1712 •
|
||
|
||
'NICA
|
||
|
||
early -
|
||
|
||
-FX
|
||
|
||
modal we RAC
|
||
|
||
g and
|
||
|
||
test.
|
||
|
||
M_ fi
|
||
|
||
PLIS le TEX M
|
||
r.'5003 96. nbOlf-M1 -Prog
|
||
|
||
$ -
|
||
|
||
rog 20M
|
||
|
||
Gen -
|
||
|
||
50 -DM Prog
|
||
|
||
M -(400. K 7000 7834-7
|
||
4
|
||
|
||
S -760
|
||
|
||
4- i £1,000
|
||
|
||
-7A13-7A18-
|
||
|
||
53A-7
|
||
|
||
7
|
||
|
||
7633-
|
||
|
||
2-7514-7M
|
||
|
||
S
|
||
|
||
S
|
||
|
||
Otys vailable. Al
|
||
|
||
RADIO COMMUNICATI
|
||
|
||
SETS
|
||
|
||
BULK
|
||
|
||
CHASE
|
||
|
||
JOHNS RA
|
||
|
||
Comm
|
||
|
||
lion Test S -Opt
|
||
|
||
ble
|
||
|
||
1 4113-K -£1.500-U,71
|
||
|
||
opt 002 Spec
|
||
-3-4-5-11 or •digital ose
|
||
|
||
us tracking Werator H includes syn sig r•mod met
|
||
|
||
power meter
|
||
|
||
£2,
|
||
|
||
¡fl OFFERS
|
||
|
||
plus RLN42
|
||
|
||
F tSet -f1,a0
|
||
|
||
Test Sets-1000M
|
||
|
||
00 inch.
|
||
|
||
RF Test Sets-1000M
|
||
|
||
4300.ech
|
||
|
||
0 2960 RF Test Sets-1000
|
||
|
||
1,250 each.
|
||
|
||
MARCONI 29550 RF Test Sets-1000
|
||
|
||
£1,500 each
|
||
|
||
MARCONI 2960A RF Test Sets-1000MC)S -£1,500 each.
|
||
|
||
ANRITSU MS555A2 Radio Comm Anz-1000M/Cs -f750
|
||
|
||
each.
|
||
|
||
MARCONI 2019A SYNTHESIZED SIGNAL GENERATORS -
|
||
|
||
80KC S loemc s-AM-FM -£400 inc. instruction book -
|
||
|
||
tested
|
||
|
||
MARCONI 2022E SYNTHESIZED SIGNAL GENERATOR -
|
||
|
||
10KC/S-1.01GHZ AM-FM -C500 inc. instruction bol:* -
|
||
|
||
tested.
|
||
|
||
R&S APN 62 LF Si Gen 0.1Hz -260KHz chu book -E250
|
||
|
||
WE KEEP IN STOCK HP and other makes of RF Frequency doublersswhich when fined to the RF output socket of a S/Generator doubles the output frequency EG.50-1300MC/S to
|
||
50•2600MC/S price from £250 -£450 each.
|
||
|
||
SPECTRUM ANALYZERS
|
||
HP 3580A 5HZ-50KHZ -C750. HP 3582A Dual 0.2HZ-25.5KHZ -£1,500. HP 3585A 20HZ-40MC/S -C3,500. HP 3588A 10HZ-150MC/S -C7.500. HP 8568A 100HZ•1.5GHZ -0,500.
|
||
HP 85688 100H2-1.5GHZ -[4,500. HP 859013 9KC/S-1.8GHZ -C4,500. HP 856913 10MC/S (0.01-22GHZ) -E3,500. HP 3581A Sgnal Analyzer 15HZ-50KHZ -E400.
|
||
|
||
TEK491 10MC,S-12.4GHZ .12.4-40GHZ -£00.
|
||
|
||
TEK492 50KHZ-21GHZ OPT 2-C.2
|
||
|
||
TEK492P 50KHZ-21GHZ OPT 1-2
|
||
|
||
TEK492AP 50KHZ-21GHZ
|
||
|
||
TEK4928P 50KHZ•21GHZ
|
||
|
||
TEK495 100KHZ-1.8
|
||
|
||
HP 8557A 0.0 C/S-
|
||
|
||
F180T cr 180C -£150
|
||
|
||
1827 -ESO
|
||
|
||
HP 85588 0
|
||
|
||
MF1807 cr 180C - 15C
|
||
|
||
1 -000
|
||
|
||
A 0.0
|
||
|
||
E1,000 -MF180T or 180C E150 -182T
|
||
|
||
M FM Modulation ANZ Meter -£00
|
||
|
||
AM FM Modulation ANZ Meter -C1,750.
|
||
|
||
P A Audio Analyzer -C1,000.
|
||
|
||
P890313 Audio Analyzer -£1,500.
|
||
|
||
MARCONI 2370 SPECTRUM ANALYZERS -HIGH QUALITY -
|
||
|
||
IGITAL STORAGE -30H2•110MC/S Large qty to clear as
|
||
|
||
eived from Gov -all sold as • from pile complete or add
|
||
|
||
100 for basic testing and
|
||
|
||
ont -callers preferred - pick
|
||
|
||
rown from over si
|
||
|
||
discount on qtys of five.
|
||
|
||
EARLY MODEL GR
|
||
|
||
hor
|
||
|
||
al alloy cooling fins -
|
||
|
||
LATE MODEL
|
||
|
||
ica
|
||
|
||
ycooling fins -000.
|
||
|
||
C LATE MOOEL BROWN
|
||
|
||
ab lfew onlyl- 500.
|
||
|
||
OSCIU.OSCOPE81 ,. TEK 465-4803 100MC/S .2probes -E250-C300.
|
||
|
||
K 41118,111MC.S storage .2probes -f200.
|
||
|
||
EK 4711175A 200MC/S-250MC/S •2probes -OW -(350
|
||
|
||
TEK 2213.221314.2215-2215A-2224-2225-2235-2236-2245-60-
|
||
|
||
100MC/S -uso-mo.
|
||
|
||
TEK 2445 Ich 150MC/S .2probes -E450.
|
||
|
||
TEK 2445A Ich 150MC/S •2probes -000.
|
||
|
||
TEK 24458 4ch 150MCPS +2probes -£750.
|
||
|
||
TEK ID.S.O. 100MC/S 2probes -£500.
|
||
|
||
'NeVEK
|
||
|
||
350MC/S .2 probe
|
||
|
||
50.
|
||
|
||
TEK 2 4ch-300MC/S -
|
||
|
||
TEK 2465A 4ch-350M
|
||
|
||
TEK 2465ACT 4e
|
||
|
||
TEK DSOgel
|
||
|
||
s-£1,000.
|
||
|
||
TEK DSO.
|
||
|
||
probes -C1,250.
|
||
|
||
TEK CLELO.
|
||
|
||
C. 2probes -E1,750.
|
||
|
||
K
|
||
|
||
TS 2probes -£2,000.
|
||
|
||
MC/S-20MC/S-4 ch n2probes -000-(1.1K
|
||
|
||
17
|
||
|
||
C/S .2probes -E250.
|
||
|
||
P174
|
||
|
||
100MCTS storage .2probes -E200.
|
||
|
||
1720A -1722A -1725A -275MC/S •2probes -
|
||
|
||
1744A -100MCTS storage -large screen -C250
|
||
|
||
HP1745A -1746A -100MCS •large screen -
|
||
|
||
HPS 00A -1GHz digitizing -000.
|
||
|
||
A -50MC/S digitizing -E500.
|
||
|
||
-100MC/S digitizing -
|
||
|
||
1GHZ digitizing -f
|
||
|
||
AVE C
|
||
|
||
El 351D Au
|
||
|
||
EIP 371
|
||
|
||
z-18GHz -C850.
|
||
|
||
£EIP 45
|
||
|
||
Pu
|
||
|
||
300MC/S-18GHz -C700.
|
||
|
||
545
|
||
|
||
uency Counter -10H1•186Hz -E1K.
|
||
|
||
548A Mie
|
||
|
||
ve requency Counter -10HZ-26.5GHz -E1.5k
|
||
|
||
Micro eSource Locking -10Hz-18GHz -E1.2K.
|
||
|
||
Microwave Pulse Counter -300MC/S-26.5GHz -C1.4K.
|
||
|
||
Micro Co ter 20HZ•24GHZ -SMA Socket -000.
|
||
|
||
Micro C
|
||
|
||
r20HZ•18GHZ -N Socket -
|
||
|
||
SD 60540 fiD Co
|
||
|
||
C/S-18GHz -000.
|
||
|
||
SD 62
|
||
|
||
260H1 -E1.2K.
|
||
|
||
SD 6
|
||
|
||
ii
|
||
|
||
z.4.5GHz -000.
|
||
|
||
HP53
|
||
|
||
rOPT 010-005-46GHz -new in box -f5k
|
||
|
||
HP53
|
||
|
||
nter 10HZ-18GHz -Nixey -£00.
|
||
|
||
P53
|
||
|
||
Counter 10HZ-18-24GHz -C800-C1K -OPTS
|
||
|
||
3-005-011 available.
|
||
|
||
342A •5344$ Source Synchronizer -C1.5K.
|
||
|
||
45A 500MC/S 11 Digit LED Readout -C400.
|
||
|
||
HP5345A •5354A Plugin -4GHz -C700.
|
||
|
||
HM-345A y5355A Plugin with 5356A 18GHz Head -(1K.
|
||
|
||
HP5385A 1GHz 5386A-5386A 3GHz Counter -(1K-(2K.
|
||
|
||
Racal/Dana Counter 1991-160MC/S -C200.
|
||
|
||
RacaliDana Counter 1992-1.3GHz -000.
|
||
|
||
Racal/Dana Counter 9921-3GHz -050.
|
||
|
||
NAL GENERATORS HPE1640A -AM-FM 0.5-512-1024MC/S -C200-C400.
|
||
HP86408 -Phase locked -AM-FM-0.5-512•1024MC/S -C500C1 2K. Opts 1-2-3 available.
|
||
HP8654A -BAM-FM 10MCS-520MCÍS -000. HP8656A SYN AM-FM 0.1•990MC/S -000.
|
||
HP86568 SYN AM-FM 0.1-990MC/S -E1.5K. HP8657A SYN AM-FM 0.1•1040K4C/S -C2K. HP86578 SYN AM-FM 0.1-2060MC-S -f3K. HP8660C SYN AM.FM-PM-0.01-1300MC/S•2600MC/S -E2K.
|
||
HP8660D SYN AM-FM-PM-0.01-1300MC/S-2600MC/S -C3K.
|
||
HP136730 SYN AM-FM-PM-0.01-26.5 GHz -C12K.
|
||
HP3312A Function Generator AM-FM 13MC/S-Dual -000. HP3314A Function Generator AM-FM-VC0•20MC/S -C600
|
||
HP3325A SYN Function Generator 21MC/S -£800. HP3325B SYN Function Generator 21MC/S -E2K. HP8673•B SYN AM-FM-PH 2-26.5 GHz -0.5K.
|
||
HP3326A SYN 2CH Function Generator 13MC/S-IEEE -C1.4K. HP3336A-8-C SYN Func/Level Gen 21MC/S -0100-000000.
|
||
Racal/Dana 9081 SYN S/G AM-FM-PH-5-520MC/S -000. Racal/Dana 9082 SYN SA AM-FM-PH-1.5•520MC/S -E400. Racal/Dana 9084 SYN S/G AM-FM-PH-.001-104MCS -000.
|
||
Racal/Dana 9087 SYN S/G AM-FM-PH-.001-1300MCS -E1K. Marconi TF2008 AM-FM-Sweep 10KC/S•510MC/S -(200 Fully Tested to £300, as new •book «probe kit in wooden box. Marconi TF2015 AM-FM-10-520MC/S -(100. Marconi TF2016A AM-FM 10KC/S-120MC/S -£100.
|
||
Marconi TF2171/3 Digital Synchronizer for 2015/20165 Marconi TE2018A AM-FM SYN 80KC/S•520MC/S -000.
|
||
Marconi TF2019A AM-FM SYN 80KC/S•1040MC/S -E650-E1K. Marconi TF2022E AM-FM SYN 10KCS-1.016Hz -C1K-E1.2K.
|
||
R& SSMPD AM-FM-PH 5KHz-2720MC/S -E3K. Anritsu MG3601A SYN AM-FM 0.1-1040M0S -E1.2K.
|
||
|
||
ITEMS VAT
|
||
|
||
BOUGHT FROM ANO CARRIAGE
|
||
|
||
HM GOVERNMENT BEING SURPLUS PRICE IS EXTRA ITEMS MARKED TESTED HAVE 30 DAY
|
||
|
||
EX WORKS SAE FOR ENQUIRIES PHONE FOR APPOINTMENT OR FOR DEMONSTRATION OF ANY ITEMS, AVAILABILITY OR PRICE CHANGE WARRANTY WANTED TEST EQUIPMENT-VALVES-PLUGS AND SOCKETS-SYNCROS-TRANSMITTING AND RECEIVING IQUIPMENT ETC
|
||
|
||
MEDICAL ELECTRONICS
|
||
|
||
Optoelectronics spots cancer cells in seconds
|
||
|
||
A new technique called 'lightscattering spectroscopy' helps detect precancerous cells in a fraction of a second using just an endoscope, light beam and some DSP. Mitchell reports.
|
||
|
||
Cancers are much more curable if spotted early, before malignant cells have spread elsewhere. So doctors are always looking for new ways of
|
||
detecting early-stage tumours or "dysplasias", preferably before they even become visible.
|
||
But it's not easy: the usual method of
|
||
extracting atissue sample by biopsy and then examining it microscopically is timeconsuming, invasive, and sometimes painful.
|
||
Now, groups of US researchers have developed optolectronic methods that need just an endoscope and alight beam —no needles or aspirators —and produce results in afraction of asecond.
|
||
Both methods are based on atechnique called light-scattering spectroscopy. LSS
|
||
has been used for some years in chemistry to study the size and shape of small spheres such as droplets. More recently, the MIT Laser Biomedical Research Centre, run by
|
||
|
||
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|
||
|
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|
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||
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|
||
|
||
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|
||
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|
||
|
||
physics professor Michael Feld, has been
|
||
applying it to measure the spheroid nuclei of body cells. The key fact is that cancer precursor cells are different from normal ones —they are closely packed, with unusually large nuclei crammed full of DNA.
|
||
In the LSS method, the clinician shines light through the probe onto the patient's tissue, and the probe collects the light that bounces back. The spectrum of this scattered light is slightly different from that of the original beam, in away that depends on the size and refraction properties of the nuclei. Examining this characteristic
|
||
'signature' of the tissue can reveal a dysplasia.
|
||
The probe is designed for use on epithelial tissue —the material that lines cavities of the body such as the mouth, bladder wall and colon. The epithelium is often the body's first line of defence against cancer-causing substances, and many tumours originate there —including
|
||
lung, stomach, breast and cervical cancer. Such cancers are virtually invisible at the early stages, even through an endoscope.
|
||
Gastroenterologist Jacques Van Dam is working with Feld to test the LSS probe clinically. "Being able to see the changes while actually there with the patient has not been possible before," said Van Dam. "If these very subtle changes are detected before they become cancerous, we can prevent cancer from forming."
|
||
The lab has also developed amore
|
||
advanced LSS imaging device that scans areas of tissue several centimetres across.
|
||
This instrument produces aseries of light beams formed from white light with coloured filters and apolarizer. An electronic camera records apair of images
|
||
at each wavelength of the reflected light in two separate polarizations. The two images
|
||
are then subtracted, which cuts out scattered background light and leaves behind only images relating to the cell nuclei.
|
||
|
||
694
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
MEDICAL ELECTRONICS
|
||
|
||
Using digital signal processing, this analysis can be done in afraction of a second and the results displayed in away that is easy for the doctor to interpret. "By analyzing the intensity variations in this back-scattered component from colour to colour, the nuclear size and density can be
|
||
mapped," says Feld. He predicts that, within two years, these
|
||
new devices will lead to anew class of endoscopes and other diagnostic instruments that allow physicians to obtain high-resolution images. These easy-to-read images will map out normal, pre-cancerous and cancerous tissue the way acontour map highlights elevations in reds, yellows and greens.
|
||
In clinical tests, the probe accurately distinguished dysplasias in the bowel and
|
||
oesophagus (gullet), where simple endoscopy would not have worked. For the oesophagus, even biopsies are very hard to interpret, and experienced pathologists often disagree on biopsy results.
|
||
The stakes are high: if adysplasia is present, the usual treatment is surgical removal of the whole gullet. Feld believes the LSS method would be agreat improvement.
|
||
Other people are exploring infra-red technology, created by the military and
|
||
|
||
aerospace electronics sectors, to detect more advanced tumours non-invasively. One such instrument is BioScan, developed by the New York company OmniCorder.
|
||
BioScan senses and records heat patterns radiated by the human body. Body heat is closely associated with blood flow (technically called perfusion), and tumours are notoriously good at keeping themselves well supplied with blood.
|
||
So mapping 'hot spots' on, say, abreast, can often reveal where asolid tumour is forming. Traditional mammograms (breast X-rays) often give uncertain results because the transparency of breast tissue to X-rays
|
||
varies sharply between women, depending on their age and physiological state. Mammograms are also very uncomfortable and pose the usual risk from ionizing radiation.
|
||
But the heat differences are so small that only the most sensitive of IR detectors will do. Omnicorder uses QWIP (quantum well infra-red photodetection) technology
|
||
developed by NASA and Lockheed Martin, to which it has obtained the biomedical rights. The technology relies on hybrid circuits cooled to very low temperatures to reduce thermal noise.
|
||
In the BioScan, adigital infrared camera containing the QWIP sensor measures the
|
||
|
||
very small changes in heat energy caused by perfusion changes. The camera is sensitive to temperature changes of less than 0.015°C and has aspeed of more than 200 frames per second.
|
||
This data is analysed using apowerful workstation and aproprietary technique called dynamic area telethermometry, invented by Dr Michael Anbar, the founding scientist of OmniCorder.
|
||
This generates an image of the target area and points out the presence and size of atumour.
|
||
As well as screening, this can also check the effectiveness of radiotherapy or chemotherapy on aknown tumour. Some new therapies also attempt to interfere with the flow of blood to tumours, so BioScan can give feedback on how well this is working.
|
||
The BioScan underwent extensive testing at the Dana-Farber cancer institute in Boston, and was licensed for sale in the US in December. OmniCorder says it is "inundated" with orders for the device.
|
||
The company has now contracted AEG Infrarot-Module to manufacture its QWIP cameras modules in volume, using a technology developed by the German company in conjunction with the Fraunhofer Institute in Freiburg.
|
||
|
||
Professional PCB Layout for Windows at
|
||
|
||
From
|
||
£97
|
||
|
||
Computer Store Prices!!
|
||
|
||
Easy-PC For Windows
|
||
Version 3.0 of this outstanding product is the latest evolution of one of the most popular affordable CAD systems available. With powerful new features and a true Windows graphical user interface, it is also one of the easiest to learn and use. With full manufacturing outputs using Gerber, Windows printers, N.C. Drill and pen plotters it is one of the most complete systems for the casual to the professional user. Run multisheet Schematics, PCB layouts and library manager all at the same time in the same interface. Switching between each is simply case of selecting the window with the mouse without running a new program. Now with our new autorouter option. Runs under Windows 95/98/NT'm & Win2000
|
||
|
||
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|
||
Ptil Design: Stuiege.pcb
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||
|
||
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||
|
||
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||
|
||
Number One Systems
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||
|
||
Call 01684 773662 or Fax 01684 773664 Email info@numberone.com
|
||
|
||
www.numberone.com... For afree demo disk, visit our web site
|
||
|
||
Number One Systems. Oak Lane.Bredon, Tewkesbury. Glos. GL20 7LR. UK
|
||
|
||
CIRCLE NO. 110 ON REPLY CARD
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
I
|
||
|
||
Evaluate capacitors for
|
||
|
||
designs
|
||
|
||
When choosing a capacitor for a linear power supply, you don't need to know much more than capacitance value, working voltage and ripple rating. For modern switch-mode power supplies though, high frequencies, complex waveforms and the demand for ever increasing efficiency make the choice significantly more difficult. Cyril Bateman explains what the problems are, and how to sort them out.
|
||
|
||
The ever-increasing demand for small, lightweight, efficient equipment has resulted in an explosion in the number and•variety of switched-mode power supply integrated circuits. Many of the latest designs are available only in minute surface mount packages, encouraging designers to use physically small capacitors and inductors.
|
||
Increase in switching frequency can reduce the theoretical capacitance value needed —hence the physical size of the component. Since almost all practical capacitors differ considerably from these theoretical ideals, trading off size for frequency introduces many pitfalls for the unwary designer.
|
||
For agiven capacitance and working voltage, the smallest physical size usually results from using either high-K
|
||
|
||
ceramic chips, or tantalum or aluminium electrolytic capacitors. These possess three undesirable attributes'.
|
||
• As frequency increases, their apparent, measurable capacitance reduces. It can become much smaller than the marked, low frequency, nominal value.
|
||
• For agiven CV product, case size reduction invariably increases the ESR of the capacitor.
|
||
• Measurable self-inductance.
|
||
At high frequencies, the equivalent series resistance of an electrolytic capacitor can exceed its capacitive reactance. When this happens, the capacitor's measured phase angles become small —afew degrees only. The measured impedance curve then appears
|
||
|
||
flat-bottomed over awide frequency
|
||
band. At some frequency, the capacitive and
|
||
inductive reactances are equal and cancel. Measured impedance is then equal to the capacitor's ESR. Above resonance, the capacitor's measured impedance increases with frequency, Fig. 1.
|
||
Some manufacturers provide nominal impedance or ESR values for their ranges, usually at 100kHz and at room temperature. High frequency capacitance and inductance values are rarely stated though.
|
||
Using asuitable, variable-frequency LCR meter, these parameter changes with frequency can be accurately measured. Since even aused meter can be extremely expensive, one may not be available.
|
||
These measurements are also possi-
|
||
|
||
696
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
ANALOGUE DESIGN
|
||
|
||
ble using simple methods and low-cost laboratory instruments. Taken with with care, such measurements can provide useful accuracy.
|
||
Impedance is traditionally measured by passing aknown AC current through the capacitor, and measuring the resulting voltage drop. Impedance is equal to voltage drop divided by the through current2.
|
||
Measurement basics At switching power supply frequencies, the capacitor becomes avery low impedance. Four-wire test lead connections are essential. For consistency and accuracy the capacitor should be mounted in asuitable test jig.
|
||
When an AC current is passed through the ideal, or perfect capacitor, having neither inductance nor resistance, the voltage waveform lags that of the current by 90°. The capacitor produces an impedance with aphase angle of —90°.
|
||
At any one frequency, a practical capacitor can be represented by a series combination of inductance, capacitance and resistance. These combine to produce an impedance with a much reduced phase angle. Depending on frequency, phase can be either positive or negative.
|
||
An LCR meter converts this measured impedance and phase angle into two components only,
|
||
IZIZO= R±JX
|
||
representing ESR (resistance) and reactance.
|
||
If the measured phase angle is negative, the meter calculates acapacitance value, if positive, an inductance value. Because only asingle frequency has been measured, the meter cannot segregate this reactance into its inductive and capacitive components.
|
||
IZIZO=R±j7(=-RX2
|
||
Here, R is capacitor ESR at the measured frequency while X is reactance at that frequency.
|
||
With practical capacitors, this net reactance has both a capacitive and inductive component. In principle, provided impedance and phase angle are measured at no fewer than two frequencies, it is feasible to extract these components from the values of Xmeasured. There's more on this in the panel entitled, 'Three-component modelling'.
|
||
|
||
Attenuation dB o
|
||
|
||
—20
|
||
|
||
—40
|
||
|
||
—60
|
||
|
||
—80
|
||
|
||
—100
|
||
|
||
01
|
||
|
||
1
|
||
|
||
Phase +100 —100 ciegres
|
||
|
||
10
|
||
|
||
100
|
||
|
||
Frequency kHz
|
||
|
||
1,000
|
||
|
||
1000µF 25V Philips 135 Capacitor.
|
||
|
||
limiting resistor. This resistance's value must be much greater than the impedance of the capacitor being measured, so that any change in current due to change in the capacitor's impedance can be ignored.
|
||
Measurements of electrolytic capacitors can be made using the internal source resistance of asignal generator to limit current. Accuracy of this method can be poor though, since the current can vary with frequency. Also, the voltage drop across the capacitor may be extremely small —at best afew millivolts.
|
||
Measuring impedance: Method 1 Accurate impedance measurements can be made, based on the techniques used to measure the insertion loss, or
|
||
|
||
attenuation, of EMC filters. Such a procedure was originally defined in MIL-STD-220.
|
||
Using aspectrum analyser and track-
|
||
ing generator, apicture of the capacitor's performance can be obtained —
|
||
even to very high frequencies. This allows very quick comparisons between capacitor types.
|
||
Actual impedance values of the capacitor by frequency can be calculated from these attenuation measurements, as detailed in the panel entitled, 'Implementing Method 1'.
|
||
With the capacitor mounted in asuitable test jig, such measurements can be carried out using low-cost laboratory equipment. You need only a50f2 low distortion signal generator, ahigh input impedance RF millivoltmeter, a
|
||
10dB isolating attenuator and a50S2
|
||
|
||
Impedance Generating aknown alternating current at various frequencies can be difficult.
|
||
One common method is to apply a constant voltage via aknown current-
|
||
|
||
Impedance 2
|
||
1.6
|
||
1.2
|
||
0.8
|
||
0.4
|
||
o
|
||
10,000
|
||
Fig. 1. Measured insertion loss, blue curve, of a 1000pF 25V Philips 135 capacitor using test jig 1, Method 1. Impedance, in red, is calculated using,
|
||
Z= 25 xA I—A
|
||
where,
|
||
A=10 1
|
||
Self inductance was calculated as 8.75nH, impedance at 100kHz measured
|
||
Fig. 2. Impedance measurement method, using test jig 1, Method 1, with ahigh inputimpedance meter. The capacitor lead wires were soldered to the stripline and ground plane. The 10d13 attenuator isolating the signal generator from line reflections is connected to one jig connector, the terminating 50i2 load to the other.
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
697
|
||
|
||
ANALOGUE DESIGN
|
||
|
||
non-inductive termination. Fig. 2. The test jig shown, test jig has
|
||
other uses. It was used with afunction generator and oscilloscope to provide
|
||
the measurements shown in Figs 6a), 6b), and 6c) in the June 2000 issue3.
|
||
A true four-terminal measurement method, it can provide extremely accu-
|
||
rate measurements of impedances rang-
|
||
ing from 51.2to socia Accuracy
|
||
depends on the signal generator source,
|
||
the terminating load's actual impedances and your ability to measure small voltages.
|
||
Lower impedances require very small voltages be measured. Ideally aspec-
|
||
trum analyser or atuned narrow band-
|
||
|
||
width receiver would be used here, to minimise contributions from noise and distortion.
|
||
Although the voltage being measured is in fact complex -i.e. avector having both magnitude and phase -to calculate impedance, you need only measure voltage magnitude using a conventional voltmeter or spectrum analyser.
|
||
This method can provide accurate measurements of impedance and phase angle. However using only common laboratory equipment, the small capacitor voltages complicate phase angle measurements. An accurate phase angle reference must also be established, Fig. 1.
|
||
|
||
Capacitor performance in practice
|
||
|
||
Capacitance and inductance values, calculated from measured RtjX for typical 220pF/10V capacitors. One random sample only of each style was measured.
|
||
|
||
Unit/parameter 220pF/10V Philips 037 IZI ESRLI Capacitance
|
||
|
||
10kHz Aluminium 0.824 0.818
|
||
129pF
|
||
|
||
30kHz
|
||
0.785 0.783 68.4pF
|
||
|
||
100kHz
|
||
0.738 0.74 27.1pF
|
||
|
||
300kHz
|
||
0.706 0.71 9.1pF
|
||
|
||
1MHz
|
||
0.671 0.67 2.0pF
|
||
|
||
220pF/10V Rubycon YXF IZIS1 ES131-1 Capacitance
|
||
|
||
Aluminium 0.404 0.394 153pF
|
||
|
||
0.372 0.372 94pF
|
||
|
||
0.341 0.34
|
||
44pF
|
||
|
||
0.322 0.32 20.7pF
|
||
|
||
0.308 0.32 9.2pF
|
||
|
||
220pF/10V Rubycon ZL lZl ESKI Capacitance
|
||
|
||
Aluminium
|
||
0.122 0.10 187.5pF
|
||
|
||
0.091 0.09 169.5pF
|
||
|
||
0.082 0.09 122.3pF
|
||
|
||
0.076 0.08 104.5pF
|
||
|
||
0.073 0.08 1.21nH
|
||
|
||
220pF/10V Rubycon ZA IZISI ESRQ Capacitance
|
||
|
||
Aluminium 0.087 0.04 189.8pF
|
||
|
||
0.041 0.04 185.4pF
|
||
|
||
0.030 0.03 200.9pF
|
||
|
||
0.028 0.03 0.69nH
|
||
|
||
0.035 0.03 2.39nH
|
||
|
||
220pF/10V Elna RSH IZILI ESRSI Capacitance
|
||
|
||
Aluminium 0.313 0.31 171.7pF
|
||
|
||
0.290 0.29 119.7pF
|
||
|
||
0.270 0.27 55.0pF
|
||
|
||
0.254 0.26 27.6pF
|
||
|
||
0.242 0.25 19.33pF
|
||
|
||
220pF/10V AVX TPS IZIS2 ESRS1 Capacitance
|
||
|
||
Tantalum 0.143
|
||
0.10 149.2pF
|
||
|
||
0.089 0.08 100.9pF
|
||
|
||
0.06 0.06 62.3pF
|
||
|
||
0.045 0.05 45.7pF
|
||
|
||
0.040 0.05 0.83nH
|
||
|
||
220pF/10V Sanyo Oscon IZIS2 ESRO Capacitance
|
||
|
||
Oscon 0.077 0.02 201.3pF
|
||
|
||
0.027 0.02 192.0pF
|
||
|
||
0.01 0.01 230.9pF
|
||
|
||
0.01 0.01 2.13nH
|
||
|
||
0.029 0.01 4.23nH
|
||
|
||
These values were derived using my dedicated meter, switched to Method 3for impedance then Method 2for ESR and capacitance. Many other suitable capacitors are available, from
|
||
other stockists. ESR cannot exceed 14. Where this occurs in the table, it is caused by insufficient resolution in my phase angle measurement.
|
||
While the rapid increase in capacitance of the 220pF/10V Rubycon ZA and the
|
||
220pF/10V Sanyo Oscon may look odd, this is simply areflection of the effect self-
|
||
inductance has on apparent capacitance when approaching series resonance. A notable impedance null is frequently found at resonance with low-loss capacitors. With
|
||
electrolytics, series resistance usually dominates, so the effect is not there.
|
||
|
||
Three-component modelling
|
||
The results table was calculated
|
||
using the two-component capacitor
|
||
model. For best accuracy, athreecomponent evaluation is needed, as indicated by,
|
||
=.\/EsR2 +(xc-xj
|
||
Here Xc is capacitive reactance and XL the inductive reactance at
|
||
the measured frequency. Solving for three unknowns
|
||
requires aminimum of two
|
||
measurements at differing
|
||
frequencies. Ideally, aswept measurement at several frequencies is used.
|
||
Some recent swept-frequency component analysers, such as the HP4194 and HP4195, are provided with internal software routines, which automatically calculate the three-component mode1 7.
|
||
These evaluate parameters at frequencies where the measured impedance is afactor of Ni2 smaller and larger than the maximum and minimum values measured8.
|
||
This works well for many stable components, but not for electrolytic capacitors, having ESR and capacitance values that change with frequency. Self inductance for these however is relatively constant with frequency.
|
||
Iprefer to estimate this inductive component by taking aseries of impedance measurements at frequencies well above resonance. But why bother?
|
||
Taking the Oscon capacitor which resonated at 190kHz as an example, Imeasured impedance at 1MHz intervals up to 10MHz. Above 2MHz its apparent measured inductance stabilised close to 5nH, its impedance then increasing linearly with frequency.
|
||
A capacitor that measures as an
|
||
inductive impedance can still act as acapacitor to decouple noise or
|
||
store and discharge energy. It has an inductive behaviour simply because at that frequency its inductive reactance exceeds its capacitive reactance. At high switching frequencies, it will
|
||
exhibit an inductive overshoot as in Fig. 6a) in the June issue3.
|
||
Having areasonable estimate for self-inductance, using the above three-component equation can produce abetter estimate of the true capacitance value at any frequency.
|
||
|
||
698
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
ANALOGUE DESIGN
|
||
|
||
Even at 100kHz though, it can be difficult to guarantee similar path lengths and phase delays between the reference and measurement channels.
|
||
Simplified measurements: Method 2
|
||
In Method I, when measuring lowimpedance electrolytic capacitors, there's awide ratio between the 50Q source and loads used as references, and the capacitor's impedance. This requires voltage measurements over a wide dynamic range.
|
||
A lower-value reference resistor can dramatically reduce these voltage differences, simplifying the measurement and improving accuracy using low-cost instruments.
|
||
In this method, the test capacitor is
|
||
mounted in ason microstrip line, on a
|
||
double sided board, in series with the signal generator. The reference resistor forms the ground return.
|
||
Complex voltages, V(1) and V(2), at levels suitable for impedance and phase angle measurements, are found on each of the capacitor lead wires, Fig. 3.
|
||
By these means, alow-cost RF millivoltmeter4 can be used with aphase meter5 to characterise the test capacitor. While anumber of calculations are needed to convert the measured voltages and phase angle into the required impedance, ESR and capacitanceinductance values, the method is quick and easy to apply —and cheap to carry out. To facilitate these calculations, I use a small program written for my programmable calculator.
|
||
In practice, the main difficulty is providing aknown value, non-inductive resistor. I needed to measure impedances at 100kHz from 0.01 to
|
||
Lon, increasing to 2.on at lower fre-
|
||
quencies. A reference resistor around 0.5 to 1.0Q would be suitable.
|
||
|
||
Implementing Method 1
|
||
For consistent measurements, ajig that maintains agood 50£1 impedance up to and beyond the insertion point of the capacitor being tested is essential. Capacitors should be soldered to this jig using the same lead lengths as you will use in your application, Fig. 2.
|
||
Iuse a3mm-wide stripline on doublesided FR4 circuit board. The capacitor is connected in shunt with this line, to the ground plane. This ground plane covers the reverse side of this jig, except for acircular area where the capacitor mounts.
|
||
The jig is suitable for leaded and surfacemount components. Both sides of the printed board are linked together at the capacitor ground connection using vias and asoldered copper foil wrap.
|
||
As with all 5012 measurement systems, reflections caused by mounting acapacitor across the line must be minimised. A 10dB attenuator should be inserted in the signalgenerator cable, as close as possible to the test jig.
|
||
is Iuf saedh,igahs-iomnpetdhraonucgeh-mteearsmuirniantginignrsetsriustmoern,t
|
||
or aterminating 50Q load and 'T' piece, should be placed at the jig output, Fig. 2.
|
||
If acoaxial cable is necessary between the test jig and the measuring instrument, a second 10dB attenuator should be connected to the test jig output. The coaxial
|
||
cable should be terminated in son at the
|
||
measuring instrument.
|
||
|
||
While each 10dB attenuator reduces the signal level by 10dB, reflected signals are twice attenuated, so are reduced by 20dB.
|
||
A measurement of attenuation, either as a voltage ratio or decibels, is taken for each measurement frequency. At each frequency, the 'jig out' voltage, with the measurement test jig replaced by an empty jig, should be noted.
|
||
With no other change in set-up, the measurement test jig with capacitor, should then be inserted into position, and the 'jig in' voltage measured, Fig. 1.
|
||
|
||
V„,
|
||
|
||
Attenuation ratio —
|
||
|
||
= A
|
||
|
||
Vmm.)
|
||
|
||
Attenuation in dB =20log —VkenVftagm,
|
||
Convert any decibel readings to attenuation ratio,
|
||
a
|
||
A =1Oro-
|
||
Impedance — 25A I—A
|
||
|
||
This equation holds good provided both
|
||
source and load impedances are son. In the
|
||
above, the figure '25' represents the Thévénin equivalent of the source/load impedances.
|
||
This method can provide very accurate results, but because of the wide dynamic range voltage measurements needed, it is
|
||
|
||
Making anon-inductive resistor
|
||
Conventional Lon I% resistors are
|
||
readily available, but these usually have aspiral 'cut', used to trim to final value. Combined with the resistor's physical length, this results in sufficient self-inductance that the resistor's impedance is measurably increased at 100kHz — degrading measurements. For accuracy, a spiralled reference resistor should not be used.
|
||
Surface-mounted chip resistors offer less inductance for two reasons. Firstly, astraight 'L' cut is often used to trim to value and their physical lengths can be shorter. Even better, certain types are available that are wider than they are long. Sometimes, these are effectively three 1206 resistors in parallel.
|
||
A typical 1206 chip has some 1to 1.5nH inductance, so with three in parallel, this construction provides mini-
|
||
|
||
Fig. 3. Using test jig 2, Method 2, to measure impedance, with ahigh input-impedance meter. My stack of three 1218 surface mount chip resistors, total resistance 0.4989n, are visible near the test-probe ground clip. Compared with Fig. 1, the test voltages, VM(1) and VM(2) have larger magnitudes. This facilitates both voltage and phase measurement.
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
699
|
||
|
||
ANALOGUE DESIGN
|
||
|
||
1222200m.1)
|
||
|
||
28d
|
||
|
||
-r
|
||
|
||
Probe -[Impedance of capacitor stac Phase in degrees (10.000K,-3 11
|
||
|
||
-5d
|
||
|
||
Fig. 4. Simulation used to verify
|
||
Method 2. Astack of 10pF plastic-film
|
||
capacitors, each accurately pre.
|
||
measured at 10kHz, was assembled and measured. These
|
||
pre-measured values were simulated. ESR and capacitance was
|
||
calculated from
|
||
simulated results and confirm the
|
||
calculation method. Both sets of
|
||
measured values agreed, with less
|
||
than 5% error.
|
||
|
||
200aU
|
||
|
||
-10d
|
||
|
||
180eU
|
||
|
||
-15d
|
||
|
||
1680
|
||
|
||
-20d
|
||
|
||
N. •
|
||
|
||
VII(1) (10.000K,193 357.) -
|
||
|
||
Act al values used in simulation
|
||
|
||
Values calculated from simulation plot
|
||
|
||
Rsense=4 75 Ohms. ESR = 1.02 Ohms Capacitance = 50,633 uF
|
||
VII(2) (10.000X.158.940.)
|
||
|
||
121 total = Rsense*VM(1)/VM(2) = 5 77856 ESR = ((Cos-3.1182)*IZItotal)-Rsense = 1.02 Xc = (Sin-3.1182)*IZItotal = -3.1433 Capacitance = 50 633 uF
|
||
Values calculated from stack measurement.
|
||
Phase = -3.22 .1egrees E>SA = 1..01 Ohms Capacitance = 49,114 uF
|
||
|
||
140mU
|
||
|
||
1.0DKoHz
|
||
|
||
3.0KHz
|
||
|
||
IM(l)
|
||
|
||
Wt(2) M
|
||
|
||
10kHz
|
||
|
||
30KHz
|
||
|
||
• (UP(1) -UP(2))
|
||
|
||
Frequency
|
||
|
||
100KHz
|
||
|
||
380KHz
|
||
|
||
1.0MHz
|
||
|
||
Implementing Method 2
|
||
By comparing the voltages at the unknown capacitor, now placed in series with the test signal, with those on alow value, noninductive, current sensing resistor, the voltage range that needs to be measured, is minimised.
|
||
This smaller jig again uses a3mm wide stripline on double sided FR4 circuit board. The current sense resistor, connected between one capacitor lead and ground, terminates this jig.
|
||
The value of the current sensing resistor should approximate the mean impedances to be measured. It must be non-inductive and its true resistance accurately known.
|
||
To minimise line reflections to the signal generator, a10dB attenuator should be inserted in the signal coaxial cable, immediately adjacent to the test jig.
|
||
The basis of this measurement is clear from Fig. 3. Two ground-referred voltage measurements at each frequency are needed. These are easily made using ahigh input-impedance millivoltmeter with a conventional high-impedance oscilloscope probe, contacting each capacitor lead wire in turn, Fig. 3.
|
||
Voltage measured at the capacitor lead nearest the signal generator is V(1). The voltage measured at the capacitor lead near the current sensing resistor is V(2).
|
||
Both voltage magnitudes will be similar, simplifying voltage and phase angle measurements.
|
||
A measurement of phase angle difference across the capacitor, is also required. A high input-impedance phase meter with two identical oscilloscope probes can be used.
|
||
|
||
The reference probe connects to the V(1) capacitor lead wire while the measurement channel probe connects to the V(2) lead. Both probe earth leads are grounded.
|
||
Using normal laboratory instruments, this method can measure impedance and phase angle of acapacitor with good accuracy. This is because relatively high and similar voltages are measured.
|
||
Using 'IZI totafto describe the combined impedance of the test capacitor and sense resistor,
|
||
|
||
171
|
||
=
|
||
|
||
WNW
|
||
MV(2)
|
||
|
||
where VM(1) and VM(2) are voltage magnitudes measured at V(1) and V(2) using anormal voltmeter.
|
||
ESR =(cos phase angle x14.0- R„.„
|
||
|
||
Here, phase angle is VP(1)-VP(2). X. =sin phase angle xZL
|
||
|
||
See reference 5for more on the above equation. If phase angle is negative,
|
||
C- 1
|
||
|
||
Or if phase angle is positive, L= -2Xsxf-
|
||
=NIESFR X:
|
||
Voltages V(1) and V(2) are complex, having both magnitude and phase. But for this method you only need to measure their voltage magnitudes, Fig. 4.
|
||
|
||
mal self inductance6. Ibought anumber of 1.511 resistors,
|
||
Philips type PRC201. These are 1218 size, comprising three 1206 resistors in parallel. Measuring voltage drop while passing a 100mA DC, Iwas able to
|
||
select a number of identical sets of three, effectively nine 1206 resistors in parallel. Each set makes anon-inductive, near 0.5i2 value, for my test jigs.
|
||
The selected group of three 1218 chip resistors were stacked together then soldered in place on my jig. This assembly can be seen in the photo-
|
||
graph, Fig. 3. To validate my reference resistor, I
|
||
mounted aconventional 1% 10 resistor rated at 0.6W on this jig. At 100mA DC, it measured 0.9960. At 1kHz it measured 0.998e while at 5MHz it
|
||
measured Lome— equivalent to some 5nH inductance. This confirmed that my reference resistors have minimal
|
||
inductance. As with all self-built measurement
|
||
systems, the remaining problem was to test its measurement accuracy when measuring capacitors.
|
||
At 10kHz and above, the largest capacitance Ican accurately measure on my 0.1% bridge is 11µF. Iassem-
|
||
bled astack of five 10pF metallised PET capacitors, which Ifirst carefully measured at 10kHz.
|
||
To increase this stack's ESR to represent atypical electrolytic capacitor, I
|
||
added ala, 1% series resistor. Using a 1%, 4.70 resistor as the reference resistor and Method 2, Imeasured this stack, then ran aPSpice simulation.
|
||
|
||
700
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
z
|
||
|
||
Probe [Method 3proof.]
|
||
|
||
1 1.8- 2 Od-r
|
||
|
||
Phase angle degrees (10 000K,-8 2402)
|
||
|
||
-18d 8.6-
|
||
|
||
Actual values used in simulation Rsense = 0 4995 Ohms ESR = 0 05 Ohms Capacitance = 200 uF
|
||
\\
|
||
co 499iive(1) /VM(2) (10 000K,555 232m)
|
||
. .
|
||
|
||
ANALOGUE DESIGN
|
||
DUu
|
||
Fig. 5. Simulation used to verify Method 3. Impedance was plotted in two ways. Both curves overlay exactly in the plot. The Method 2ratio needed to calculate ESR and capacitance is also plotted.
|
||
|
||
-3ed
|
||
|
||
8.4-
|
||
|
||
-48d,
|
||
|
||
0.2-
|
||
|
||
-50d ,
|
||
|
||
Values calculated from simulation
|
||
|
||
(V(1)-V(2))/1(Rs
|
||
|
||
e) (10.000K,93 982m)
|
||
|
||
IZI total = 0 4995*(VM(1)/VM(2) = 0.555232
|
||
ESR= ((Cos-82402) * IZI tots)) -04995 =004999
|
||
xc = (Sin -8 2402) * 121 total = 0 07958 Capacitance = 199 99 uF
|
||
IZI = SORT(ESR*ESR+Xc*Xc) = 0 09398
|
||
= (0 4995*(V(1)-V(2)))/VM2 = 0 093982
|
||
|
||
(0 4995*(V(1)-V(2)))/VM(2) (10 000K,93 982m)
|
||
|
||
-60d+
|
||
|
||
,
|
||
|
||
r
|
||
|
||
,
|
||
|
||
,
|
||
|
||
,
|
||
|
||
1
|
||
|
||
rn
|
||
|
||
1.0KHz
|
||
|
||
3. OKHz
|
||
|
||
10KHz
|
||
|
||
36KHz
|
||
|
||
168KHz
|
||
|
||
368KHz
|
||
|
||
1.6MHz
|
||
|
||
(U(1)-U(2))/ I(Reenee) - (8.4995u(U(1)-U(2)))/UM(2) • (0.4995NUM(1))/UM(2) Gfl •(UP(1)-UP(2))
|
||
|
||
Frequency
|
||
|
||
Measured voltage and phase angle agreed closely with the simulation. The ESR and capacitance values obtained from my measurements were within 5% of the capacitance and ESR for the assembly. Fig. 4.
|
||
This accuracy is more than sufficient for my electrolytic capacitor measurement needs. There's more on this method in the panel entitled, 'Implementing method 2'.
|
||
()tiler methods At the self-resonant frequency of the capacitor, its measured impedance exactly equals its ESR. This frequency is determined by the capacitor's effective capacitance and self inductance.
|
||
Using this resonance technique and inserting additional inductance external to the capacitor, ESR can be measured at lower frequencies. This inductance can be provided either by extending the capacitor leads or by adding alow loss inductor.
|
||
A small additional inductance —even that from lcm length leads —can significantly reduce the resonance frequency, allowing ESR measurements over arange of frequencies.
|
||
Method 3—impedance meter In method 2, both voltage measurements are ground referred, allowing easy measurement of voltage magnitude using conventional instruments. Using these complex voltages, you can derive ameasurement method, giving a direct digital readout of impedance
|
||
|
||
magnitude and phase of the unknown. Suppose you have an unknown resis-
|
||
tor in series with aknown resistor to ground. Because they each pass the same current, the unknown resistor value can be calculated by measuring the voltage drop across the unknown, and the voltage drop across the reference resistor.
|
||
|
||
x
|
||
|
||
&Wm« =
|
||
|
||
V
|
||
ibet,e)
|
||
|
||
If you look at the PSpice plots in Fig.
|
||
|
||
5, you will see that V1 and V2 have
|
||
|
||
both magnitude and phase. They are
|
||
|
||
complex voltages. Using the vector dif-
|
||
|
||
ference of these two voltages, you can
|
||
|
||
calculate the impedance of the capaci-
|
||
|
||
tor. Fig. 5.
|
||
|
||
W1) -- 11(2)
|
||
|
||
=
|
||
|
||
VM(2)
|
||
|
||
At km frequency, you could 'float' a conventional battery powered multimeter to measure this difference vector. For higher frequencies, a high input
|
||
|
||
Implementing Method 3
|
||
|
||
Using the jig outlined in Method 2, both voltages 141) and 142) are complex.
|
||
If you take the vector difference of these two and divide by the current passing through the reference sensing resistor, you have adirect measurement of the capacitor's impedance, Fig. 5.
|
||
V(1)— V(2) IA— R
|
||
sourlaarrent)
|
||
Voltages V(1) and V(2) are complex. VM(2)
|
||
R
|
||
|
||
where VM(2) is the
|
||
|
||
= R
|
||
|
||
V(1)— V(2) VM(2)
|
||
|
||
voltage drop and,
|
||
|
||
At very low frequencies, the easiest way to measure this vector difference is by using a conventional battery powered multimeter, connected between 141) and 142).
|
||
|
||
At higher frequencies, atrue differential voltmeter reading is needed. This can be provided by using ahigh input-impedance, instrumentation amplifier having high common-mode rejection to the highest frequencies measured.
|
||
Noted that this differential voltage can be very small, compared with the commonmode voltages at 141) and 142), so the instrumentation amplifier must also have a small output offset voltage.
|
||
The differential voltage is easily divided by VM(2) using amodified PM128 meter, exactly as used for my tan8 meter design.
|
||
This method provides adirect reading impedance meter, usable over awide frequency range. It iS a ratio method. Since both ratio-ed voltages are measured concurrently, accuracy does not depend on signal source impedance or amplitude. It can even be used with asignal generator whose output changes with load and frequency.
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
701
|
||
|
||
ANALOGUE DESIGN
|
||
|
||
Fig. 6. My prototype test meter with
|
||
special jig, developed for the Method 3
|
||
differential voltage measurements. Both
|
||
are usable from 10kHz to 10MHz. This meter outputs a
|
||
direct reading of capacitor impedance,
|
||
from 0.001 to 1.99%1, on a
|
||
modified PM128 meter. A switch provides adirect
|
||
reading of the 'llse„sexVM(1)/VM(2)'
|
||
ratio, simplifying calculations needed
|
||
for ESR and capacitance. A buffered, phaseequalised output, suitable for aphase meter is provided.
|
||
|
||
impedance, differential instrumentation amplifier with aflat response and good common-mode rejection up to the
|
||
highest measurement frequency is required.
|
||
Idecided to investigate this approach using two identical high-impedance input channels, similar to my RF millivoltmeter'. These would be followed by two identical rectifying stages, as used in this meter. The rectified DC outputs
|
||
were divided using a PM128 meter modified to ratio mode, as used for my
|
||
tans meter, in the January 2000 issue.
|
||
|
||
A relay could be used to select
|
||
|
||
between measuring the two input chan-
|
||
|
||
nels or the differential measurement, as
|
||
|
||
required. This new meter could then
|
||
|
||
directly display either measured
|
||
|
||
impedance, as the vector result of
|
||
|
||
(V1—V2)/VM2. Alternatively it could be
|
||
|
||
switched to display VM(1)/VM(2) as
|
||
|
||
needed for method 2. See the panel
|
||
|
||
entitled, 'Implementing Method 3'.
|
||
|
||
Ihave designed and implemented a
|
||
|
||
suitable dedicated meter Fig. 6. Its
|
||
|
||
design, construction and use form the
|
||
|
||
subject of my next article.
|
||
|
||
•
|
||
|
||
References 1. Bateman C, 'Understanding
|
||
capacitors', Electronics World, June 1998. 2. The Impedance Measurement Handbook. Agilent Technologies (HP), USA. 3. Bateman C. 'Efficient battery power supplies', Electronics World, June 2000. 4. Bateman C. 'Measure AC millivolts to
|
||
5MHz', Electronics World, April 2000. 5. Bateman C, 'Fazed by phase?', Electronics World, November 1997.
|
||
6. Bateman C, 'Understanding Capacitors', Electronics Wor/d, April 1998.
|
||
7. 'Parametric Analysis for Electronic Components and Circuit Evaluation,' — AN339 Agilent Technologies (HP), USA.
|
||
8. 'Practical Design & Evaluation of High Frequency Circuits' —AN317, Agilent Technologies (HP), USA.
|
||
|
||
The science lab in aPC
|
||
|
||
LI=
|
||
|
||
—
|
||
|
||
.... .-0
|
||
|
||
Ex periments Ideas for DrDAQ
|
||
|
||
fadieelneUght.
|
||
|
||
Dawn c.,.
|
||
|
||
„
|
||
|
||
r
|
||
|
||
Ye WWI« •114......m.1
|
||
• t. a "•
|
||
LI Li LJ
|
||
|
||
Yb .
|
||
|
||
-495.2nts.• --59.5ens.àso
|
||
|
||
Sound wa.e ,,,n• of an Light decry Mauna ed
|
||
|
||
Acid Base /nod Raw.
|
||
Exedwenn, Reactors Enclothern. R•actona Day Nd MØt
|
||
Fanneal...en &Begs,
|
||
|
||
Cap.*. crutgadnach
|
||
|
||
Ht. nod rernota control
|
||
|
||
ouse of •sole,
|
||
|
||
•
|
||
|
||
Claps Wn..g
|
||
|
||
I .1H111 1
|
||
|
||
Output Voltage Resistance Light level
|
||
Temperature
|
||
|
||
Only £59!
|
||
|
||
+VAT
|
||
|
||
PH
|
||
|
||
The DrDAQ is alow cost data logger from Pico Technology. It is supplied ready to use with all cables, software and example science experiments.
|
||
|
||
DrDAQ represents a breakthrough in data logging. Simply plug DrDAQ into any Windows PC, run the supplied software and you are ready to collect and display data. DrDAQ draws its power from the parallel port, so no batteries or power supplies are required.
|
||
Tel: 01480 396395, Fax: 01480 396296, E:mail: post@
|
||
|
||
Microphone External sensors
|
||
Very low cost
|
||
Built in sensors for light, sound (level and waveforms) and temperature Use DrDAQ to capture fast signals (eg sound waveforms) Outputs for control experiments Supplied with both PicoScope (oscilloscope) and PicoLog (data logging) software
|
||
|
||
CIRCLE NO. 111 ON REPLY CARO
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
ELECTRONICS
|
||
Subscribe for 3 years, pay for just 2 WORLD
|
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Ye
|
||
|
||
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|
||
ELECTRONICS WORLD
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|
||
Please enter my subscription for one of the following terms.When Isubscribe for three years, Ipay the price for just two years.
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|
||
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||
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|
||
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||
|
||
In Pvpry içti
|
||
Detailed circuit diagrams New product news Informative design-oriented explanations CAE software
|
||
Ut2i1vL rcu u‘rect to your uour each mor
|
||
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|
||
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•
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|
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|
||
|
||
Tel: +44 (0)1444 475662
|
||
|
||
15,000 semiconductor data sheets on two CDs
|
||
|
||
Farnell, well known throughout industry as the catalogue distributor with the broadest range of semiconductors, has teamed up with Intersil to bring you a pair of CD-ROMs -The Farnell Semiconductor Data CD-ROM set.
|
||
This unique offering features more than 15,000 data sheets -from over 80 major manufacturers -together with detailed applications notes. You can now have access to the largest collection of data sheets available anywhere.
|
||
All of the data sheets are complete and accurate renditions of the original manufacturers' literature; to allow the user to view or print the data sheets an installable version of Adobe Acrobat reader (in both 16- and 32-bit) is included. A built-in browsable search engine assists the user in finding the desired data sheet.
|
||
Nine volumes of application notes are available, detailing both typical and innovative uses of components. Some volumes are dedicated to certain suppliers such as ST, Philips and Infineon, whereas others are multisupplier based
|
||
The Farnell Semiconductor CD-ROM database is asearch engine containing thousands of full manufacturers' data sheets. Once you have found the part you are interested in, you can browse the PDF datasheet on screen or print it out. You can place your order online or ring Farnell on the number below.
|
||
Using the CD Catalogue In order to use the Semiconductor Data CD-ROM you will need to have aPC running Windows 3.11 TM , Windows 95 1^^ or Windows NT4Tm, with the following minimum specification:
|
||
|
||
24 hour, all year round sales hotline: tel 0870 1200 200 fax 0870 1200 201 e-mail sales@farnell.com
|
||
Online catalogue: http://www.farnell.com/uk Farnell, Canal Road, Leeds 1512 2TU
|
||
|
||
• 486 25MHz processor • 8Mb RAM (WIN 3.11 &'95) • 16Mb (WIN NT) • 10Mb free on hard disk drive • Dual speed CD-ROM drive • VGA monitor
|
||
|
||
In association with Intersil
|
||
intersji
|
||
|
||
The 15,000 semiconductors covered by the datasheets are just asmall part of the total Farnell product offering, which spans over 100,000 lines in asix-volume catalogue. All products are available ex-stock and are backed by free technical support. Orders can be placed 24 hours aday, 365 days ayear, with free next day delivery on orders placed before 8:00pm.
|
||
|
||
To request your free copy of the catalogue simply call 0870 1227 725 or visit Farnell's web site & Online Catalogue at http://www.farnell.com/uk
|
||
|
||
f. fze.aeit ?
|
||
|
||
Farnell
|
||
|
||
Mailt U11138 7821828
|
||
2113212 7,3788 UO/98 50202 482121 116804 203750 271329 121253 291717 21U3I
|
||
7883M
|
||
781312
|
||
|
||
HUE-7610143 HUE 71171P3 HUF76121P3 HUF75112P3 HUÍ 76149'3 11 1/121014 1416014 141124 14Y1/0 HY534256AS 70 11150 HY6225EALLP 10 HY1225641110 HY6225fAlP70 HY62256811170 NY8284ALF1 0 11914591000•00 IM15948008M 70 OO1 I/07
|
||
|
||
TRANSISTOR MOSEET TO 220 IFIANSIS TOR 110SFE TTO 220 1RANSISTOR MOSFET 10-220 TRANSISTOR MOSFET 10220 IRANSIS TOR 1109E1 T0220
|
||
P0WTH SI1P111Y IHIP 64" LCD MONITOR IC 611.1 BIPOLAR POWER AMP 40H1.1 IC 6014 BIPOLAR POWER AMP 801111 IC 1118 CMOS DRAW IC 304, BIPOLAR POWER AMP IC 1561 C1405 SRAM IC MU CMOS SRAM IC 2561 CMOS SRAM IC 259 CMOS SRAM IC fa CMOS SRAM MODULE 1MX9 DRAM IC MODULE 440(9 DRAM RELAY OPTO ISOLATOR MODULE RS212 INTERFACE SWII CH PUSH •POT MODULE
|
||
|
||
Data Shull
|
||
501000 507001 181181
|
||
|
||
3
|
||
|
||
Dais II 4 81 •,*
|
||
|
||
- A
|
||
|
||
FIV-2405E
|
||
|
||
Application Information ,cone”....e,
|
||
|
||
compome• i••••
|
||
|
||
et •ma.... Mau. ell
|
||
|
||
PAD Um. le au
|
||
|
||
155•510.10•11,
|
||
|
||
•Se. tele
|
||
|
||
c. •AAA AP 8•15151
|
||
|
||
•
|
||
|
||
Pee. PLAC ,POL•
|
||
|
||
:rep
|
||
|
||
UPPVIlaync
|
||
|
||
a •e- lee
|
||
|
||
11. V., •Olt eel
|
||
|
||
.9•• ••• /v. lloearee.e.rALM
|
||
|
||
flat.« If DUAL WPM.
|
||
|
||
Dual Supply
|
||
|
||
:kw. Geer., voltage* au era» tr, mew", tee te PM 5V
|
||
5 ...woe al an Iry •••••• SPoe tea», an•nu mule Mt e50M acme 'menu', cApad And fl 110 p,Apà mow1 b fue 5v ...ye •den•no Kan ee ...we Pe aner Mee Tee Mpg ca.:aim la re
|
||
IaA ed. ttonOJ, I,
|
||
|
||
043.0 • ,
|
||
|
||
,
|
||
|
||
• >" ^
|
||
|
||
General Precautions
|
||
|
||
.1
|
||
|
||
.1 • •
|
||
|
||
.4 v
|
||
|
||
Pprat•rna• Ci tO OS •••••5« 1,0,05,5 5^ 5
|
||
10_105 t, Am01t re eel equa•ent ¡pare p•d5e an done ke pm, •de
|
||
|
||
410., on ape* metal betere• of AC pave0 Ob opeprnord
|
||
AC arm. EOM. Baegmund
|
||
|
||
e.•••••
|
||
|
||
e• VANIArA fola,n pap-
|
||
|
||
ELECTRONICS WORLD September 1999
|
||
|
||
Dynanïic art
|
||
|
||
argues that electronics engineers and artists should work together to produce dynamic works of art, and makes suggestions for simple artistic lighting effects using opto -mechanics.
|
||
|
||
4111 ust as an artist can call up awide selection of hues and colours to complete acreative commission, so the electronics engineer has available awide range of products and devices that can be used to develop systems for 'creative' visual effects.
|
||
In stage effects, computers interfaced to complex production systems have allowed new heights of technical achievement. Also, once acomplex lighting sequence has been set up, it can be easily replicated on successive performances.
|
||
Most electronic systems are designed with functionality in mind. But there is increasing interest not just in constructing electronic systems that perform anecessary task but in exploring the creative potential of abroad spectrum of physical systems. The aim is to basically make life more varied and stimulating.
|
||
Moving art For avariety of reasons, most works of art are static. These predominantly consist of images frozen in two/three dimensions. It may be that artists would want to use time-varying effects, but they do not have the technical ability to implement them. Likewise it may be that those competent in electronics have the ability to bring dynamism into art, but have little interest in doing so.
|
||
When we perceive aconventional image on display,
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
OPTOELECTRONICS
|
||
|
||
we subconsciously move in relation to it to change our perspective. In doing so, we make sense of the image's lines, colours and forms. This tells us in part how we naturally observe objects.
|
||
We discriminate boundaries between areas. We register the specific details of aparticular focus of the visual field. Our brain scans for moving images. In the final product, the brain integrates all these processes seamlessly together. The process of visual perception is complex and so successful that we appear to observe effortlessly.
|
||
There is something, however, more attention seeking about images that change their appearance in time. In the supermarket aisle, attention seeking devices attract the eye of the shopper with asingle pulse of ared LED every few seconds. This indicates that we have the potential to discriminate a relatively small change out of alarge and complex static visual field.
|
||
If avisual display has elements that change over aspecific time frame, it will receive more attention than one that is static. Perhaps one of the reasons why television is so compulsive is that it presents avisual field that is always changing. It is latching onto those receptors in the visual field that would instinctively direct us to movement.
|
||
|
||
the light sources described can be modified.
|
||
For the time being though, Iwill outline asystem that runs essentially on a9V DC supply.
|
||
|
||
Ways and means
|
||
|
||
Considering the full range of analogue
|
||
|
||
and digital circuits at your disposal,
|
||
|
||
there is abewildering number of ways
|
||
|
||
that such aprocess can be implement-
|
||
|
||
ed. Computers make the number of
|
||
|
||
options boundless. This article though
|
||
|
||
outlines an effective artistic light con-
|
||
|
||
troller, made simple by using an opto-
|
||
|
||
mechanical system.
|
||
|
||
Consider nlight sources as having a
|
||
|
||
function, fl,f2,f3... fn.Each function
|
||
|
||
varies independently with time in a
|
||
|
||
cyclic manner and with uniquely
|
||
|
||
defined amplitude, phase relationship
|
||
|
||
and frequency.
|
||
|
||
To make such asystem interesting,
|
||
|
||
around twelve or more separate light-
|
||
|
||
ing
|
||
|
||
channels
|
||
|
||
are
|
||
|
||
needed.
|
||
|
||
Implementing this would require 12
|
||
|
||
distinct oscillator and drive systems. It
|
||
|
||
is likely that this would lead to alack
|
||
|
||
of spatial co-ordination between the
|
||
|
||
elements of the display. It is also
|
||
|
||
unlikely that there would any co-ordi-
|
||
|
||
nated relationships between the com-
|
||
|
||
ponents.
|
||
|
||
A less complex option would be to
|
||
|
||
have asmaller number of oscillators,
|
||
|
||
say four. These oscillators, designated
|
||
|
||
#1
|
||
10
|
||
Number of rotations Fig. 1. Notional variation of sensor parameter as afunction of degree of rotation and with the cycle repeating itself every revolution.
|
||
Photodiode/transistor positions Wheel with reflective and non-reflective areas
|
||
Fig. 2. Positioning of the reflective detectors under the rotating disc.
|
||
|
||
Design objectives
|
||
|
||
This discussion revolves around using
|
||
|
||
electronics to introduce cyclic varia-
|
||
|
||
+9V
|
||
|
||
tion into a discrete number of light
|
||
|
||
sources. One option for the suggested
|
||
|
||
scheme is to use the light sources as
|
||
|
||
directly-visible elements in adisplay.
|
||
|
||
Alternatively, they can be used in
|
||
|
||
association with apiece of art to pro-
|
||
|
||
duce reflective or refractive enhance-
|
||
|
||
ments.
|
||
|
||
While this approach introduces elec-
|
||
|
||
tronics into art, it does not restrict the
|
||
|
||
input of the artist. He or she still has
|
||
|
||
the task of setting up the actual nature
|
||
|
||
of the 'time dependent' profile and the
|
||
|
||
medium in which the lights are used.
|
||
|
||
The end product can be considered as
|
||
|
||
a sub-system for incorporating into
|
||
|
||
appropriate works of art.
|
||
|
||
One example of how the lights can
|
||
|
||
be applied involves a series of
|
||
|
||
coloured panels. Each panel can be
|
||
|
||
back lit by alamp, which is part of
|
||
|
||
such acontrolled sequence. This is an
|
||
|
||
approach that can be cascaded, adding
|
||
|
||
complexity, and the output power of
|
||
|
||
R1 10k
|
||
+9V
|
||
|
||
R2 W50vk
|
||
+9V
|
||
Tri
|
||
|
||
R3
|
||
|
||
LED1/Lamp
|
||
|
||
10k
|
||
|
||
I _
|
||
|
||
R6 150R (short if lamp:
|
||
|
||
Motor
|
||
|
||
Fig. 3. Basic single channel system
|
||
showing photodiode/phototransistor detector and output drive system. When areflective area of the disc is over an opto device, its associated lamp turns on gradually. In the lower part of the diagram is the simple
|
||
motor-speed adjustment buffer.
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
705
|
||
|
||
OPTOELECTRONICS
|
||
|
||
A, B, C and D, could be arranged to produce sum and difference effects, A—B, A—C, A—D, B—C, C—D, A+B, A+C, A+D, B+C and B+D. This would again tend to produce alack of spatial co-ordination between the elements though, and we are not really in control of the combinations.
|
||
Fig. 6. Aseries of photographs taken using acyclic pattern change on painted glass and six channels of variable light output.
|
||
|
||
Also, these options would require more than afew analogue/logic chips to implement effectively.
|
||
|
||
Towards coherence
|
||
It is possible to have aPC provide the ultimate solution. A computer with 12
|
||
a-to-d channels could output appropriate analogue voltages under software control. As a design problem, though, this is beginning to look daunting and expensive. Are there more practicable ways of achieving the same end point?
|
||
A more attractive option is to main-
|
||
tain the same 'cyclic period' for all elements but to introduce independent phase and amplitude modulation for all elements. Figure 1 shows some
|
||
notional variations of sensed parameter as afunction of degree of rotation. The cycle essentially repeats itself
|
||
after each cycle. A novel way to establish this
|
||
phase/amplitude relationship across say twelve discrete signals is to encode optical reflectivity/transmission parameters onto acircularly rotating disc and use phototransistors/photodiodes. This is done in association with variation of optical properties of the disc surface to provide the phase and amplitude relationships. A complete cycle of signals will thus be replicated in one revolution of the encoded disc, but each channel can have its own identity.
|
||
Some element for synchronising the variation in levels of the illumination channels is needed. But remember that the goal is for visual effect only —not for precise control and processing.
|
||
Figure 2 shows adisc for such a system, involving twelve photodiode/phototransistor elements in reflective mode.
|
||
In my design, the small optical units are actually positioned flush with the circuit board. The rotating disc — reflective side face down —blocks out stray light. As the disc rotates, it passes under units of reflective detector pairs.
|
||
As an alternative, it would be possi-
|
||
|
||
%out SG-2BC (Base view)
|
||
Fig. 4. Pin out of photorefkctive device used in the author's prototype (SG-28C -Famell code 441-566). Device diameter is 4mm.
|
||
bic to use the system Iam proposing in 'transmission' mode using ambient light to modulate the detector array.
|
||
The optical modulator
|
||
Each detector pair comprises an integral phototransistor and photodiode. In this way, avoltage is produced that is proportional to the degree of reflection of the surface. Thus the sequence of areas to be illuminated can be carefully selected to take advantage of the known sequence derived from the rotation of the encoded wheel.
|
||
It may also be possible to introduce an element of randomness into the display. This could be done by building some eccentricity into the circular disc, which rotates under the phototransistor/photodiode heads.
|
||
This module is intended to be self contained. After being powered up it will operate as an integral part of an item of art with aminimum of controls. A different 'template' of the disc produces adifferent series of voltage signals from each of the channels.
|
||
My prototype consumes very little power. Its motor only consumes around 50mA at 6V. It would also be possible to use RGB LEDs so that the variation of sensed voltage was also translated to colour changes.
|
||
The concept of a relatively slow rotating disc maps well into the visual changes that may be expected. Thus a typical repeat interval of 15 seconds requires low levels of rotation of around 4rev/min. This requires either aDC motor with very high gearing or astepper motor with small step intervals.
|
||
|
||
Table 1. Table of rotational speed of iron core motor as afunction of drive voltage. Rotational speed (rev/min) Drive voltage
|
||
|
||
2.9
|
||
|
||
2.8
|
||
|
||
4.8
|
||
|
||
4.0
|
||
|
||
5.7
|
||
|
||
5.0
|
||
|
||
8.4
|
||
|
||
7.5
|
||
|
||
706
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
A stepper motor with control of input frequency from 1to 50Hz would be appropriate. But a stepper motor with 48 steps per revolution is alittle too coarse relative to the true continuous movement of the DC motor. A 1.8° stepper would provide adequate resolution, but they tend to require more complex drive systems and consequently more power consumption.
|
||
In my prototype, Iused a small geared iron-core motor. With variation in voltage control, this gives a range of rotational speed as indicated in Table 1. The motor is essentially operating in unloaded mode.
|
||
Elements of circuit design
|
||
The elements of detection/amplification of aspecific channel are indicated in Fig. 3. Nominally, the system is adjusted so that full reflection outputs 6V and zero reflection, 1V.
|
||
Power transistors are included in the output drive elements to allow either LEDs or conventional filament bulbs to be used. Resistors in the output circuit can be included as needed. The maximum current per channel is around 100mA. Figure 4 shows the pin-out of the photoreflective device I used.
|
||
A simple potentiometer controls the motor's rotational speed. The motor can be switched to rotate either clockwise or anticlockwise. A conventional quad operational amp carries out the simple electronic signal processing.
|
||
Enter the artist
|
||
After establishing the core 12-channel unit, outlined in Fig. 5, there is then the creative challenge to create the 'reflection template' to control the series of changes with rotation. This is where the artist changes place with the electronics designer in order to communicate an idea or effect to the audience.
|
||
Why not cover the underside of the
|
||
|
||
array with 4mm diameter ball bearings and use the physics of light reflection to provide ahighly complex
|
||
level of variation? Bearings are only one of many such 'translational devices' for transforming achange in some physical parameter to a more visible set of parameters — which is part of a separate aspect of artistic expression.
|
||
Figure 6 indicates aseries of photographs taken of an 'installation' where cyclic pattern change on painted glass operates on six channels of variable light output.
|
||
|
||
Final thoughts
|
||
|
||
In my view, the step from an elec-
|
||
|
||
tronic device with an everyday func-
|
||
|
||
tion to one that is promoted as aphe-
|
||
|
||
nomenon of artistic expression could
|
||
|
||
double the end value of the system.
|
||
|
||
Surely there is scope for serious and
|
||
|
||
committed 'wired' artists, who could
|
||
|
||
produce devices and constructions that
|
||
|
||
would be gladly accepted with pride
|
||
|
||
in a21st-century habitation, organisa-
|
||
|
||
tion or institute?
|
||
|
||
Such devices must of course be con-
|
||
|
||
structed carefully, to good standards
|
||
|
||
of safety, design and functionality.
|
||
|
||
They would give satisfaction to their
|
||
|
||
designer. But they would also satisfy
|
||
|
||
the customer that there is evidence of
|
||
|
||
careful thought tempered with rational
|
||
|
||
design and construction. This would
|
||
|
||
produce apracticable contrast to the
|
||
|
||
splendidly vacant collections of con-
|
||
|
||
temporary art.
|
||
|
||
Are there artists who would wel-
|
||
|
||
come assistance in translating effects
|
||
|
||
into reality using electronic tech-
|
||
|
||
niques? Conversely, are there are elec-
|
||
|
||
tronics engineers who could work
|
||
|
||
with 'artists'.
|
||
|
||
Every self respecting electronics
|
||
|
||
engineer should ask himself/herself
|
||
|
||
the question, "If Iam so creative with
|
||
|
||
electronic components and circuits,
|
||
|
||
are there areas of creative endeavour
|
||
|
||
that might Iturn my hand to?"
|
||
|
||
•
|
||
|
||
Op-amps Output transistors
|
||
|
||
Reflective wheel
|
||
Fig. 5. Outline layout of the author's twelve-channel system.
|
||
|
||
To LEDs/Lamps
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
OPTOELECTRONICS
|
||
|
||
•
|
||
|
||
e
|
||
|
||
•
|
||
|
||
Virtual System Modelling
|
||
•
|
||
|
||
Adirr
|
||
|
||
Build It In Cyberspace
|
||
www.labcenter.co.uk
|
||
CIRCLE NO. 112 ON REPLY CARD
|
||
|
||
Develop and test complete micro-controller designs without building a physical prototype. PROTEUS VSM simulates the CPU and any additional electronics used in your designs. And it does so in real time. *
|
||
|
||
• CPU models for PIC and 8051 and series
|
||
|
||
micro-controllers available now. 68HC11
|
||
|
||
comming soon. More CPU models under
|
||
|
||
development. See website for latest info. • Interactive device models include LCD
|
||
displays, RS232 terminal, universal keypad
|
||
|
||
e• I, • 11 e ir
|
||
Nita
|
||
ill 1r III
|
||
|
||
plus arange of switches, buttons, pots,
|
||
|
||
LEDs, 7segment displays and much more. • Extensive debugging facilities including
|
||
register and memory contents, breakpoints and single step modes.
|
||
|
||
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|
||
e •Ls. 1•...• rue u•• mom,
|
||
|
||
e
|
||
|
||
ea ram
|
||
|
||
• Source level debugging supported for selected development tools.
|
||
• Integrated make' utility -compile and simulate with one keystroke.
|
||
|
||
•e'..'; aq....es. •••••••••••.i.
|
||
|
||
• Over 4000 standard SPICE models included. Fully compatible with manufacturers' SPICE models.
|
||
• DLL interfaces provided for application specific models.
|
||
|
||
• Based on SPICE3F5 mixed mode circuit simulator. • CPU and interactive device models are sold separately -
|
||
build up your VSM system in affordable stages. • ARES Lite PCB Layout also available.
|
||
|
||
cbcenLJen
|
||
|
||
"E g PROTEUS VSM can simulate an 8051 clocked at 12MHz on a300MHz Pentium II
|
||
|
||
Electronics
|
||
|
||
Write, phone or fax for your free demo CD -or email info@labcenter.co.uk. Tel: 01756 753440. Fax: 01756 752857. 53-55 Main St, Grassington BD23 5AA.
|
||
|
||
PRODUCTS
|
||
Please quote Electronics World when seeking further information
|
||
|
||
Data acquisition
|
||
software
|
||
Version 5.5 of Adept's Dasylab data acquisition software lets users monitor test stands, development rigs and processes on screen. It also alerts users to predefined events remotely, via networks, the web, email or SMS-enabled mobile phones. Its point-and-click interface lets the user set up, see and document data acquisition applications without programming or command-line instructions. The software is for applications that link sensors and instrumentation to aPC. On-screen displays and controls, triggering and signal processing are set by dragging icons into place and connecting them with amouse click.
|
||
Adept Scientific
|
||
Tel. 01462 480055
|
||
P-channel HEXFET
|
||
power MOSFETs
|
||
International Rectifier has introduced four 12 and 20V p-channel HEXFET power MOSFETs for portable applications. They come in TSSOP-8 packages. The 12V IRF7701 has RDS— at 4.5V. Applications include cell phones, digital cameras and notebook computers. The other three products are
|
||
|
||
MOSFET for 42V automotive
|
||
Intersil's latest power MOSFET is designed for the new automotive 42V battery systems currently being developed for the next generation of vehicles. The HUFA7510S3S UltraFET is a75V, 75A MOSFET with an on-resistance of lOmfl, which the company says gives one of the lowest resistances per area of silicon available. In addition the FET features a75V drain-source breakdown voltage, giving it the ruggedness required for higher-voltage automotive systems. The device is engineered to withstand high energy in avalanche mode and features a combination of low gate charge, fast recovery
|
||
|
||
time, and alower reverse body-diode charge (QRR) for applications that require fast switching speeds and improved power efficiency. Intersil's UltraFe. Iprocess technology achieves the lowest possible onresistance per silicon area, lower gate charge and improved dynamic switching characteristics. UltraFET devices withstand high peak currents
|
||
and energy in the avalanche mode, important when switching inductive loads. The
|
||
HUFA7510S3S is immediately available for volume production in the10263 package.
|
||
Intersil
|
||
Tel: 01344 350250
|
||
|
||
the IRF7702. IRF7750 and IRF7700.
|
||
International Rectifier Tel: 020 8645 8001
|
||
Development environment
|
||
Netsilicon has announced Net+OS —an out-of-the-box product that integrates an embedded development environment, real-time operating system and the firm's Net+Works architecture. It contains the development tools,
|
||
|
||
networking software and hardware needed to begin application development using system-
|
||
on-chip technology to design
|
||
interne and Ethernet connected devices. It includes Green Hills Software's Multi2000 IDE for Windows, ThreadX RTOS from Express Logic and Net+Works drivers, protocols and services for web, email, FTP, flash and SNMP applications. It comes with aNet+Arm development board including an integral 10/100 Ethernet,
|
||
two serial ports, two parallel
|
||
|
||
ports, RAM, ROM and aJTag port. The package also includes adebug tool that connects the JTag port to the parallel port of the development PC and is used for code downloading.
|
||
Netsilicon Tel: 00 1781 398 4548
|
||
Reprogrammable FPGA memories
|
||
Atmel has introduced the AT17 reprogrammable FPGA configuration memories in eight-pin narrow-bodied SOIC packages
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
709
|
||
|
||
NEW PRODUCT
|
||
Please quote Electronics World when seeking further information
|
||
|
||
and 65k, 128k and 256k densities. These nonvolatile memories can be used to load program data into any SRAM based FPGA during power-up. Atmel Tel: 00 1408 441 0311
|
||
Quad 10-bit transceivers
|
||
Vitesse has introduced the VSC7182 and VSC7186 quad 10-bit Gigabit Ethernet and Fibre Channel transceivers for switches, routers, hubs, host adapters, backplane connectors and test equipment. These 3.3V ICs allow full duplex operation at 1.05 to 1.36Gbit/s. Each of the four transmitters serialises 10-bit input (8B and 10B encoded) for transmission, while the four receivers perform the reverse on incoming serial data. They have integrated JTag access ports. Each device dissipates 2.2W typical and they come in 208-pin, 23mm BGA packages. Vitesse Semiconductor Tel: 01634 683393
|
||
|
||
3V transceiver
|
||
Fairchild has introduced the 74LVTH16500 18-bit universal bus transceiver for 3V systems. It has tri-state outputs and operates at 3.7ns maximum at 3.3V Vœ .There is input and output interface capability to 5V Vc, systems. For off-board driving applications, such as backplanes, memory arrays, telecoms switches and networking, the device has outputs rated at +64 to —32mA. Latchup performance exceeds 500mA. It is fabricated using BiCMOS. Fairchild Semiconductor Tel: 01793 856856
|
||
Optical encoders
|
||
Optical encoders are available from Tecan through abespoke service for the supply of discs and similar components in control, positioning and measurement applications. Different manufacturing techniques are used. Photochemical machining, for example, will produce burr and
|
||
|
||
stress-free results typically with accuracies of ±10 per cent of the thickness of the metal used from 1.5 to 0.01mm. For more accuracy, electrofonning techniques are used, atypical tolerance being ±81.1m and, in some cases, ±2mm can be achieved. Tecan Components Tel: 01305 765432
|
||
Six-channel audio d-to-a converter
|
||
Burr-Brown's PCM1604 is a six-channel audio d-to-a converter with 24-bit resolution and 1921(Hz sampling for multi-channel audio applications such as DVD. It contains six 24-bit 1921cHz converters on amonolithic IC and can be used in AV or HDTV receivers, car audio, multi-channel home theatre, surround-sound processors and digital mixing consoles. The device uses multi-level deltasigma modulation to improve audio dynamic performance and reduce jitter sensitivity. Dynamic range is 105dB and it has —95dB THD+N on each channel. The internal digital filter operates at 8times oversampling for a96kHz sampling rate or 4times for 192kHz, with selectable sharp or slow roll-off. The filter has 82dB stopband attenuation and ±0.002dB passband ripple. Functions include digital attenuation, mute and zero flag for each channel. The device accepts standard audio data formats of 16, 18, 20 and 24-bit
|
||
|
||
and can be used with 128, 192, 256, 384, 512 or 768f, system clocks. It has single-ended analogue outputs and operates on dual +3.3 and +5V power supplies. Burr Brown Tel 01923 233837
|
||
Programmable buzzer
|
||
Dau has introduced an audible buzzer with achoice of 16 outputs. The output can be set to be constant, swept tone or one of 16 options. It can be reset. For use in vehicles or buildings as an alarm, it has a sound output of 90dB at lm. It can be hard wired or connected with spade terminals to the power source. The unit can be run from 12 to 35V DC or 12 to 24V AC. The AC can be applied directly to the unit and is astandard in the licensed trade. The DC option is standard for vehicles. The choice of tone can be set by a code switch, which the user can change. The device measures 61 by 43mni and is 28mm high. Dau Components Tel: 01243 553031
|
||
BDM tools for Motorola
|
||
Comsol has been appointed European distributor of background debug mode (BDM) tools from P&E Microcomputer Systems. DOS versions are used as the development environment in Motorola evaluation board packages. The Windows
|
||
|
||
Tuning fork
|
||
oscillator
|
||
Flint has introduced a surface-mount tuning-fork crystal from Raltron for time of day clock applications in portable communication equipment and other compact appliances. The RSE comes in an SMD package and 16mm tape packaging, suitable for automatic and HD surface mounting. It is available in A, B. C and D options, with A and B having afootprint of 10.41
|
||
|
||
by 4.06mm and C and D 8.7 by 3.7mm. A and C come with single I/O lead connections and B and D with dual connections. Available with 6or 12.5pF load capacitance, it has a nominal frequency of 32.768kHz and afrequency
|
||
tolerance a±2Oppm
|
||
maximum. Operating range is —40 to +85°C, and the device can withstand up to 230°C for 20s in solder reflow conditions. Flint Tel: 01530 510333
|
||
|
||
710
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
Test & Measurement Instruments
|
||
|
||
The NEW HF -08 Analog to Serial Converter
|
||
|
||
8 brt resolution Windows and DOS software available
|
||
MAI, Scope Spectrum, Logging ranges .1.25V to .5 OV, -2 5V and ±2.5V
|
||
/ Crystal controlled timing for accurate OSP
|
||
Simple to interface to your own software / Low Cost -Just f$9.33 incl vat
|
||
12 bit module coming soon
|
||
|
||
RF Instruments
|
||
EMC Equipment
|
||
|
||
FIF
|
||
Instruments
|
||
|
||
Data Logging & Acquisition
|
||
|
||
Phone: 01420 590000 e-mail sales@hf-inst.co.uk
|
||
|
||
Metered bench power supplies Up to 60V and 6A
|
||
Prices from £127 inc. VAT
|
||
|
||
Handy Wet IScope Counter/Timer TTL Sig. Gen. £199 inc. VAT
|
||
|
||
Visit our Web Site for full details:
|
||
www.hf-inst.co.uk
|
||
CIRCLE NO.1 H ON REPLY CARD
|
||
!Mediae'
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||
W40/iftPCie e POOktcOM
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||
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||
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||
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||
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||
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||
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||
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||
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||
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||
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||
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||
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||
•
|
||
|
||
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|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
t(CeDtI. •'O .
|
||
|
||
Are
|
||
|
||
02
|
||
|
||
rp .
|
||
|
||
z'i
|
||
.710),
|
||
|
||
there
|
||
|
||
black
|
||
|
||
o o
|
||
|
||
holes
|
||
|
||
v+
|
||
|
||
•3 o0 0•ins•ide
|
||
|
||
0 ou?*
|
||
|
||
="
|
||
Ft;
|
||
rs
|
||
|
||
issue date 1April 2000
|
||
|
||
Smart people know where to look
|
||
NewScientist
|
||
|
||
CIRCLE NO.115 ON REPLY CARD
|
||
|
||
711
|
||
|
||
NEW PRODUCT Please quote Electronics World when seeking further information
|
||
|
||
versions include in-circuit debugger, BDM programmer, register editor, direct BDM control libraries and BDM cables. Comsol Tel: 01932 829460
|
||
|
||
4Mbit SRAMS
|
||
Memotech has announced 4Mbit SRAMs from Brilliance Semiconductor for battery powered applications such as digital set-top boxes. Available in 256k by 16 or 512k by 8 configurations, they are made on 0.25pm CMOS. Based on a six-transistor memory cell design, they have adata retention voltage of 1.5V with an operating current of 30mA for the 5I2k by 8device and a standby current of 3pA. They come in Jedec standard TSOP, TSOP2, STSOP and CSP packages. Memotech Tel: 01223 370060
|
||
|
||
DC power supplies
|
||
The PQ range of current-fed DC power supplies from Kingshill includes 44 models supplying 10 to 625V DC and 5to 600A DC, with powers up to 10kW. The units function as voltage or current sources. In voltage-source mode, if the load increases above the current command setting, automatic crossover to current mode occurs. Differential amplifiers isolate programming lines from DC output, enabling remote programming at any distance from the load. The units are programmable by
|
||
|
||
Í The Distributor with
|
||
|
||
20,000 hard-to-find lines
|
||
|
||
EX STOCK!!!
|
||
|
||
Semiconductors
|
||
We have one of the largest ranges of discrete parts in the UK, both new and obsolete types and, if we do not have it in
|
||
stock, we can usually source it for you. Call or fax for our latest Semiconductor stock list.
|
||
Computer products
|
||
We carry in stock everything to make a Personal Computer. CPUs - Memory - Motherboards - Cards - Scanners -
|
||
Modems -Sound Cards - Speakers - All types of Drives Cases - PSUs - Monitors etc
|
||
Call or fax for our latest Semiconductor stock list.
|
||
Components & equipment
|
||
|
||
Capacitors - Resistors -Connectors - Potentiometers Cables - Batteries -Speakers -Amplifiers - Lamps -
|
||
Microphones - Fans - Power supplies -Transformers Buzzers - Sirens - Fuses and Holders - LEDs - LCDs -
|
||
Relays - PA Systems -Tools -Test Equipment -etc Fax or write to us for our latest catalogue
|
||
|
||
EEI
|
||
|
||
Semiconductor Supplies International Ltd
|
||
Dawson House, 128 -130 Carshatton Road, Sutton, Surrey, England, UK. SM1 4TW 020-8643 1126 (Sales and Technical Queries) Fax: 020-8643 3937 (For International use +4420) e-mail: sales@ssi-uk.com Web ssi-uk.com
|
||
|
||
resistance, voltage, current or optional IEEE488 and RS232. Diagnostic functions are integral to the control loop, while circuits identify the control function. There are three levels of overvoltage and overcurrent protection. They have start and stop pushbuttons. Kingshill Tel: 01634 821200
|
||
|
||
WDM application for measuring and recording channel power, wavelength and optical signal-to-noise ratio (OSNR). Applications include testing WDM passive components such as filters, multiplexers and Bragg gratings. Agitent Technologies Tel: 07004 666 666
|
||
Transistor array in 0605 packaging
|
||
Rohm has introduced surface mount small-signal bipolar and digital transistor arrays in 0605 equivalent packaging for mobile phones, camcorders and personal stereo equipment. More than 30 transistor devices
|
||
|
||
Optical spectrum analyser
|
||
Agilent has introduced an optical spectrum analyser for characterising WDM optical components and systems. The 86140B provides awavelength accuracy of lOpm from 1480 to 1570nm. It includes abuilt-in
|
||
|
||
GPIB and Ethernet Interface for PCI
|
||
National Instruments has introduced the GPIB-ENET/I00 Ethernet-to-GPIB controller and the PCI-8212 combination GPIB and Ethernet interface for PCI. The interface is for connecting, sharing or controlling GPIB instruments on Ethernet networks. Both are HS488 compliant. With the controller, users can access remote test equipment from anywhere in the world via TCP/IP protocols on 10baseT and 100baseT networks. It is shipped with NI-488.2 and NI-Visa API software for Windows 2000, NT and 9x. Any program previously written in either API runs unmodified on the controller. NI488.2 and NI-Visa can be integrated with Labview and Measurement Studio. The controller can be configured with DHCP or with aconfiguration utility. No dip switches or jumpers are required and it has installation options including rack mounting, Din rail mounting, wall mounting and stackable standalone. National Instruments Tel: 01635 572400
|
||
|
||
-I2
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
7.1ectronics,, Electrical & Mathematics
|
||
|
||
inciples V6'
|
||
If you are looking for an easy and enjoyable way of studying or improving
|
||
|
||
CD-ROM
|
||
|
||
your knowledge of electronics then this is the software for you.
|
||
Li Electronics, Electrical and Mathematics Principles VG
|
||
DC AC Electrical SetriCand OpAmps Malta Digital Measure Micro RC e Toolbox II
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||
|
||
Students and Hobbyists the complete package for
|
||
£49.95* ($82.17) normally £99.95*
|
||
Colleges and universities including
|
||
|
||
Dee:tics &Electrical INeon/ActI Components1 Took &Eceipreent ICs
|
||
|
||
unlimited user site licence.
|
||
|
||
Categ 1 DC VOLTAGE Loading aVoltage Divider.
|
||
|
||
£299.95* normally £595.95*
|
||
|
||
Boolean &DeMc
|
||
|
||
*+VAT if applicable
|
||
|
||
Binary Numbers
|
||
|
||
=23m4
|
||
|
||
Loaded Vout = 7 268V
|
||
|
||
R1
|
||
|
||
Load = 10k
|
||
|
||
10k
|
||
|
||
R2 II Load =3.1973k
|
||
|
||
Postage FREE
|
||
R1 10k
|
||
|
||
4 7k 7268\
|
||
|
||
RLoad Ira
|
||
|
||
R2
|
||
|
||
inarti Arithmetic Analogue Muki-n
|
||
|
||
Vout -Vin 3, ,R2,-, ,
|
||
|
||
Effect of connecting a load across 02.
|
||
|
||
Vout =Vin x
|
||
|
||
iz II Load
|
||
|
||
Bi + (R2 Il Load)
|
||
|
||
mean> in parallel
|
||
|
||
.A•sea aupati
|
||
|
||
• 33 •Tre:1n,*-rmy • 9591837 •95919v
|
||
|
||
laded out. 3197 279
|
||
3) '1 MOD • '3197279
|
||
|
||
73333,1 •729N
|
||
|
||
Original Outp
|
||
|
||
Calculations. t Topic Noble I
|
||
|
||
Feedback vo
|
||
|
||
New Av
|
||
|
||
A-v 1 +(Av x8)
|
||
|
||
Effective Input =Input voltage -(8
|
||
|
||
New Output voltage = Input voltag
|
||
|
||
Printing
|
||
|
||
'Loading aVoltage Divider
|
||
|
||
'.7 Crystal/Resonator 'HS' High Speed Crystal/Reiriaioi
|
||
|
||
Load 110k
|
||
|
||
Remove Load RS
|
||
|
||
ection for ullatou
|
||
OSC2/C2 I ES -1 00pF
|
||
5-33pF
|
||
150pF I5-33pF 15-33pF
|
||
15-33pF ' 33pF
|
||
|
||
eatures.
|
||
nalogue. igital. lectrical. Microprocessors. PIC Microcontrollers. Mathematics. Electronics Toolbox. Components and Equipment Dictionary. Fully interactive graphics, graphs and calculations. Single page colour printing.
|
||
|
||
Explanatory text. Hundreds of Electronics & Maths formulae with worked examples using your inputs. All calculations are shown. Default values on startup. Easy to use, no prior knowledge assumed. Comprehensive menu an indexing. Covers college courses fro
|
||
rursity level.
|
||
|
||
"Electronics Principles is a well thought out and comprehensive program that is also easy to install and stable in operation. It can be wholeheartedly recommended." Robert Penfold. Everyday Practical Electronics magazine.
|
||
www.eptsoft.com
|
||
|
||
Codes.
|
||
|
||
mar
|
||
|
||
Please telephone or visit our web site
|
||
for alist of over 900 topics from Ohm's Law to PIC' microcontrollers.
|
||
|
||
Colour Values
|
||
|
||
Tolerance
|
||
|
||
• Mack
|
||
|
||
• Blue .6
|
||
|
||
Red .25
|
||
|
||
• Brawl .1
|
||
|
||
It Valet .7
|
||
|
||
Gold -5k
|
||
|
||
▪ Red .2
|
||
|
||
Grey .8
|
||
|
||
Sim .10k
|
||
|
||
• Orange.3
|
||
|
||
\else .9
|
||
|
||
11
|
||
|
||
Valor. Green
|
||
|
||
.4 .5
|
||
|
||
Bends 103. numeral valuer. fourth -matrix or metier or nought's Fa values <10ohor Forrth bole
|
||
|
||
gold. moire« .01 or river. nisi. •1101
|
||
|
||
LOloponent Ilope
|
||
%laird
|
||
Reran Five Band Rewire
|
||
|
||
eptsoft limited. Pump House, Lockram Lane, Witham, Essex. UK. CM8 2BJ.
|
||
Tel: 01376 514008. Fax: 0870 0509660 infoeeptsoft.com Switch, Delta, Visa and MasterCard payments accepted -
|
||
please give card number and expiry date. Cheques and P.O. made payable to e tsoft limited.
|
||
|
||
voie... Violet. Black. Red .
|
||
|
||
Calmed Banda.
|
||
|
||
Second Bard
|
||
|
||
Yellà•
|
||
|
||
. 'vole
|
||
|
||
Fire Band ilealshe Vale.
|
||
47k
|
||
Tolerance 55
|
||
|
||
Thrd Bard
|
||
|
||
I
|
||
|
||
Fought:land
|
||
|
||
teed
|
||
|
||
Red
|
||
|
||
(U) PreFerted value F12 Swim 471
|
||
Preferred value E24 Sane. 47k
|
||
|
||
CIRCLE NO. 116 ON REPLY CARO
|
||
|
||
Please quote Electronics World when seeking further information
|
||
|
||
are available in five and sixpin EMT packages including dual small-signal bipolar and dual digital transistor arrays. The latter have built-in bias resistors and optional diodes to simplify circuit design and reduce the need for external components. Suitable for operating voltages up to 50V, the transistors are rated for currents up to 150mA. Rohm Electronics Tel: 01908 282666
|
||
One-chip RS232 transmit/receive
|
||
Intersil has introduced singlechip RS232 transmitters and receivers for PCs, peripherals and portable, battery operated appliances. The ICL3241 and ICL3243 have atransmitter circuit that converts ITL and CMOS signal levels to RS232 levels at minimum data rates of 250kbit/s. Applications include laptops, palmtops, printers, terminals, barcode readers, scanners and high-speed modems. These 3V products require 0.3mA supply current during normal operation. A manual and automatic powerdown features increase battery life by reducing standby supply current to a1µA trickle. A shutdown mode conserves
|
||
|
||
energy in battery powered applications. The receivers remain active during shutdown. The ICL3243 detects when the receiver inputs go to ground from, say, adisconnected RS232 cable, and automatically places itself into shutdown mode. Intersil Tel: 01344 350250
|
||
Humidity sensor
|
||
Panametrics makes ageneral purpose thin film polymer capacitive type RH sensor for OEMs. The Minicap 2sensor has aTO-18 configuration. The dielectric constant of the polymer thin film changes with the atmospheric RH, resulting in linear capacitance changes as afunction of relative humidity. It is
|
||
|
||
unaffected by water condensate, is immune to most reagent vapours and can handle temperatures up to 180°C. It can measure RH from 5to 95 per cent with a linearity of ±1 per cent RH and atypical response time of less than 60s for 90 per cent of total range, or faster for small step changes. It requires a+1V excitation and returns atypical signal between 170 and 230pF from 0to 100 per cent RH. Panametrics Tel 020 8643 5150
|
||
CompactPCI processor
|
||
Teknor Applicom has introduced the Raptor RAPC810 CompactPCI processor in a3U footprint. The board is available from Wordsworth: Celeron-powered with up to 500MHz CPU speed, 66MHz front side bus and 128kbyte level two cache, the board is for test and measurement, in-vehicle transportable and automation applications. Features include integrated 2D and 3D graphics and up to 128Mbyte of synchronous SDRAM on a144-pin SODIMM socket. Wordsworth Technology Tel: 01732 861000
|
||
|
||
135 MHz oscillator
|
||
Epson has developed the SG-W oscillators with output frequencies up to 135MHz. They use CPLL technology to reduce longterm jitter levels. They are for networking applications, PCs and peripherals. The SG531xxW and SG-615xxW each come in three versions with output frequencies of 66.7 to 135, 55 to 135 and 26 to 135MHz. The SG-636xxW comes in 41 to 135 and 32 to 135MHz, and the SG-710xxW in 67 to 135 and 80 to 135MHz versions. Frequency stability is ±100 or ±5Oppm. Supply voltage is 3.3 ±-0.3V or 5.0 ±-0.5V. Epson Electronics Tel: 00 49 89 14005 363
|
||
Full-brick DC-to-DC
|
||
Artesyn has launched full-brick, DC-to-DC converters. The BXF300 and 400 are for
|
||
|
||
Micros takes Riscs with DSPS
|
||
Hyundai is launching Rise and DSP microcontrollers. The GMS30C2216/32 embedded microprocessors are for applications that handle digital and
|
||
|
||
analogue signals such as DVDs, flash cards, digital cameras, PDAs and multimedia electronic systems. Based on an architecture from Hyperstone, the EI-
|
||
|
||
32x core combines a32-bit Risc core with a16 to 32-bit fixed point DSP, using an integrated instruction set to provide aunified programming model. The 32-bit wide 96-way register set supports parallel operation of the ALU, DSP and load-store units, delivering 2.4Gop/W. The 8kbyte of on-chip DRAM runs at CPU clock speed. Operating at 108MHz, power consumption is 180mW at 3.3V.
|
||
On-chip peripheral support includes DRAM controller, software programmable PLL, 32-bit timer, three serial I/0 lines, interrupt controller and a16 to 32-bit bus interface addressing 4Gbyte of memory. It has power-down and sleep modes. Power-down halts instruction execution, while DRAM refresh and the internal timer are maintained. Sleep stops everything, drawing 30pA until awake-up signal is received. Hyundai Electronics Tel: 00 49 02131 754170
|
||
|
||
714
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
SPECIAL OFFERS
|
||
|
||
SPECTRUM ANALYSERS
|
||
HP 8562A 1KHz-22GHz
|
||
|
||
TEKTRONIX 2445A
|
||
|
||
SINAD
|
||
|
||
ADVANTEST R3261A 9KHz-2
|
||
|
||
àe
|
||
04000
|
||
|
||
Channel 150Mf-f: .veep CUISOYS
|
||
£750
|
||
|
||
TEKTRONIX 475
|
||
|
||
f• T:
|
||
|
||
I•
|
||
•
|
||
|
||
Trace 200MHz delay sweep
|
||
|
||
te:
|
||
|
||
£400
|
||
|
||
MARCONI 2610 TRUE WS VOLTMETER
|
||
|
||
C.M
|
||
|
||
Digital LCD •ana ogue meter 5Hz -
|
||
|
||
25MHz •DC
|
||
|
||
MEASUREMENTS
|
||
|
||
MARCONI 8930 AF POWER METER 300u watts-30 watts. 20Hz-35KHz 25 Ohm -20K Ohms
|
||
|
||
for only
|
||
|
||
Marconi 893C unused, boxed
|
||
|
||
Marconi 8936 -to 10 watts max. 41) NO SINAD
|
||
|
||
GOULD J3B SINE/S0 OSCILLATOR
|
||
|
||
10Hz-1200KHz.Low
|
||
|
||
distortion. Balanced
|
||
|
||
metered output.
|
||
|
||
••••4
|
||
|
||
Attenuator
|
||
|
||
MARCONI 2022E
|
||
|
||
SYN AM/FM SIG GEN fOKHz •1.010th
|
||
|
||
Up to .1040
|
||
|
||
.
|
||
|
||
,_CD display,
|
||
|
||
keyboard ere.,elc
|
||
|
||
iigntweight
|
||
|
||
RADIO COMMUNICATIONS TEST SETS
|
||
|
||
KARCC441 2955
|
||
|
||
£2iX0
|
||
|
||
0500
|
||
|
||
ILIRCCNI 2019 See etdfu Sg Gen SOKRz-101LIFtz
|
||
|
||
£475
|
||
|
||
EATON/AILTECH 757 0.001-22GHz TEKTRONIX 492 50KHz-18GHz
|
||
|
||
£2500 £3500
|
||
|
||
H.P. 85588 with Main frame 100KHz.1500MHz.£1250
|
||
|
||
H.P. 8534 (Dig Frame) with 8559A 100Khz-21GHz
|
||
|
||
£2750 MARCONI 2382 100Hz-400MHz High Resolution £2000
|
||
|
||
B K2033R Signal Analyser ACA/ANTESTTR4131 10KHz-3.5GHz
|
||
|
||
£1500 f2750
|
||
|
||
MARCONI 2370 3014Z-110MHz
|
||
|
||
from £500
|
||
|
||
HP141 Systems 8553 1KHz-110MHz from
|
||
|
||
£500,
|
||
|
||
8554 500KHz-1250MHz from £750; 8555 10MHz-
|
||
|
||
18Gliz
|
||
|
||
from £1000
|
||
|
||
UNUSED OSCILLOSCOPES
|
||
|
||
TEKTRONIX 105350 Dual Trace 200MHz 1GS/Sec.f1500 TEKTRONIX TAS485 4Channel 2001Aliz etc............f1103 H.P. 546008 Dual Trace 1001Aeiz 20149/s..£1003
|
||
|
||
autoranging
|
||
AVO 8Mk 6MULTIMETER
|
||
In Ever Ready case eth CD> leads and Danenes
|
||
Other AVOSs from (ED
|
||
|
||
RACAL/UM 9343M LCR Databridge Meal
|
||
|
||
£200
|
||
|
||
Auto measurements of R. C. L. Q D
|
||
|
||
HUNTRON TRACKER Model 1000.................£125
|
||
|
||
HP5315A Universal Counter 1GHz 2Ch.................£80
|
||
|
||
FLUKE 80504 DMM 4.digit 2A True WAS ...............£75
|
||
|
||
FLUKE 80104 DM1.13 digit 10A
|
||
|
||
£50
|
||
|
||
FLUKE 80120 DMM 3 digit 2A
|
||
|
||
RACAL TRUE RMS
|
||
|
||
SOLARTRON 7150
|
||
DMM 6 1. f:* TRUE RMS Hr .facy IEEE
|
||
£95-£150 HIGH QUALITY
|
||
RACAL COUNTERS
|
||
9904 Universal timer counter 50M-
|
||
9916 Counter 10Hz-520MHz
|
||
9918 Counter 10Hz-560MHz 9cl,git
|
||
|
||
HP 6657A Syne) Sg Gen 1001041-10401Ahlz
|
||
|
||
f2500
|
||
|
||
HP 86568 SKIM Sig Gen 10014Hz-990*D
|
||
|
||
£1350
|
||
|
||
P8656A Synth Sg Gen 100KHz-99:#111.1.
|
||
|
||
£995
|
||
|
||
GGITRONIC 7100 Seal Sg Gen 1014Ftz-20Géti
|
||
|
||
£5000
|
||
|
||
19ARCON1 2017 AWN Rose inclied Sig Gen 1010(z-1024MHz. ...
|
||
|
||
£1200
|
||
|
||
Good SO Rift&
|
||
|
||
- 8640A AURA Sg Gen 50301z-10244Hz
|
||
|
||
£400
|
||
|
||
8640A MAFIA Sg Gen 500Iütz-513artz
|
||
|
||
£250
|
||
|
||
PHILIPS MA5328 Sg Gen 19900-19948299.1Hz
|
||
|
||
£650
|
||
|
||
Freg Canter IEEE
|
||
|
||
RACAL 9081 Sy* PURA Sig Gen 5-5204kg
|
||
|
||
£350
|
||
|
||
P3325A Syre FundeonGen 211.1Hz
|
||
|
||
0600
|
||
|
||
MARCONI 6500 Ampltde Arklyse
|
||
|
||
f1509
|
||
|
||
HP 427511CA Meier 101ütz-101Atlz
|
||
|
||
£2750
|
||
|
||
liPf033E Datorbon Meser
|
||
|
||
crso
|
||
|
||
WAYNE KERR Inlidence Analyser 3245
|
||
|
||
£2000
|
||
|
||
H.P 8112A Pulse Generator eat
|
||
|
||
£1250
|
||
|
||
OSCILLOSCOPES
|
||
|
||
PHILIPS PM3092 2.2 Ch 200MHZ Delay TB etc..... £950
|
||
|
||
PHILIPS PIA3082 2+2 Ch 1031.41-2 Delay etc
|
||
|
||
£800
|
||
|
||
TEKTRONIX TAS465 Cual Trace 100MHz Delay etc £800
|
||
|
||
TEKTRONIX 24654 Ch 300MHz Delay Sweep Cursors....
|
||
|
||
£1250
|
||
|
||
TEKTRONIX 2433 Dual Trace 150L4Hz 1001ASS Cursors
|
||
|
||
etc
|
||
|
||
£800
|
||
|
||
TEKTRONIX 2232 Dual Trace 100MHz 100MS/s Cursors
|
||
|
||
etc
|
||
|
||
.£800
|
||
|
||
TEKTRONIX 2212 Dual Trace 60MHz 201es Cursors etc
|
||
|
||
................£650
|
||
|
||
TEKTRONIX 2210 Dual Trace 500MHz
|
||
|
||
£450
|
||
|
||
HP 54200A Digitising 50MHz 203MS/s...................... £600
|
||
|
||
PHILIPS PM3217 -veiqnd9u'di4ngm2iplr°obeecsee
|
||
|
||
Dual Trace 50MHz Delay
|
||
|
||
Pouch and Fro,.
|
||
|
||
VOLTMETERS
|
||
|
||
9300 5HZ-20MHZ usable to 60MHZ 10 volts 3160
|
||
|
||
ED
|
||
|
||
93008 version
|
||
|
||
MIMI !MI e
|
||
|
||
FARNELL AMM255
|
||
|
||
DATROel kloCal Multrneler 5HT, rie 1065'1061k 1071 . .
|
||
|
||
Iran £370-£603
|
||
|
||
IletCOM 2440 Frequency Carle 20GHz...
|
||
|
||
£1003
|
||
|
||
HP53508 Freguency Ccuter 20Gliz
|
||
|
||
£2000
|
||
|
||
HP 5342A 13h-lfIGHz Freq Cowie
|
||
|
||
£250-£300
|
||
|
||
Automatic Mod Meter AM FL'
|
||
|
||
FARRELL 6010999 Pear Sag ..£1000
|
||
|
||
GOODWILL
|
||
|
||
2GHz 3.5 digit LCD Display Unused
|
||
|
||
FARPELL AP70130 Peff Sigiey
|
||
|
||
£800
|
||
|
||
THIS IS THE
|
||
|
||
GVT427 DUAL CHANNEL AC
|
||
|
||
MILLIVOLTMETER
|
||
|
||
10/0 3000 in 12 ranges
|
||
|
||
Frequency 10H.7-1MHz
|
||
|
||
Used £100
|
||
|
||
Unused£125
|
||
|
||
Also available. FARNELL AMM2000 Automatic Mod Mel ,E.' 10Hz-2.4GHz Unused MARCONI 2305 Mod Meter 500KHz-20I-f:
|
||
|
||
ED)
|
||
|
||
PrIAJPS P116418TN Cdout TV Pattern Generator PrItUPS FIA5418TX1 Cobs TV PAM Generale 60KAccelw'are0rWe4399
|
||
P11692D Dual Dreamed Coupler 2lifkg-18614z HP116910 Dual pre:Odra C4upler 21//42-186Hz.
|
||
|
||
£1750 £2000 £300 £1600
|
||
|
||
BEST CHEAP SCOPE YOU WILL
|
||
EVER BUY!!!
|
||
|
||
£1250
|
||
|
||
GOULD 051100 Dual trace. 30MHz
|
||
|
||
IC1111/4 I OT ricauuui.a
|
||
110 WYKEHAM ROAD, READING, BERKS RG6 1PL Telephone: (01 18) 9268041 Fax. (01 18) 9351696
|
||
|
||
J VISA
|
||
|
||
TEXTRDMX P61098 Probe 1004Hz Readoe Unused îcclwwix IDÉVKIP,./..14111,4, xs.x I
|
||
|
||
£60
|
||
|
||
delay, very bright Supplied wiln
|
||
|
||
ro‘
|
||
|
||
USED EQUIPMENT -GUARANTEED. Manuals supplied
|
||
|
||
irr17.7)
|
||
|
||
This is VERY SMALL SAMPLE OF STOCK SAE or telephone for lists Please check availability before
|
||
|
||
Callers welcome 9am-5.30pm Monday to Friday (other times by arrangement)
|
||
|
||
ordering CARRIAGE all units £16 VAT to be added to total of goods and carnage.
|
||
|
||
I CIRCLE NO.117 ON REPLY CARD
|
||
|
||
el', !I
|
||
|
||
ADVANCED ACTIVE AERIAL
|
||
• 0 0 0 1-
|
||
The aerial consists of an outdoor head unit with acontrol and power unit and offers exceptional intermodulation performance: SOIP +90dBM, TOIP +55dBm. For the first time this permits full use of an active system around the If and mf broadcast bands where products found are only those radiated from transmitter sites • General purpose professional reception 4kHz-30MHz. • -10dB gain, field strength in volts/metre to 50 Ohms. • Preselector and attenuators allow full dynamic range to
|
||
be realised on practical receivers and spectrum analysers. • Noise - 150dBm in 1Hz. Clipping 16 volts/metre. Also 50 volts/metre version. • Broadcast Monitor Receiver 150kHz-30MHz. * Stabilizer and Frequency Shifters for Howl Reduction * Stereo Variable Emphasis Limiter 3 * PPM10 In-vision PPM and chart recorder * Twin PPM Rack and Box Units. * PPM5 hybrid, PPM9 microprocessor and PPM8 IEC/DIN -50/+6dB drives and meter movements * Broadcast stereo coders *
|
||
SURREY ELECTRONICS LTD
|
||
The Forge, Lucks Green, Cranleigh, Surrey GU6 7BG. Telephone: 01483 275997. Fax: 276477.
|
||
Sepember 2000 ELECTRONICS WORLD
|
||
|
||
WATCH SLIDES ON TV MAKE VIDEOS OF YOUR SLIDES DIGITISE YOUR SLIDES
|
||
(using a video capture card)
|
||
|
||
"Liesgang chat,/ automatic slide viewer with built in high quality colour TV camera. It has
|
||
|
||
acomposite video output to aphono plug (SCART & BNC adaptors are available). They
|
||
|
||
are in very good condition with few signs of use
|
||
|
||
£91.91+ vat =£108.00
|
||
|
||
Board cameras all with 51 2x582 pixels 8.5mm 1/3 inch sensor and composite video out All need to be housed in your own enclosure and have fragile exposed surface mount parts. They all require apower supply of between 10 and 12v DC 150mA.
|
||
|
||
47MIR size 60x36x27mm with 6 infra red LEDs (gives the same illumination as a small
|
||
|
||
torch but is not visible to the human eye)
|
||
|
||
£37.00 +vat =£43.48
|
||
|
||
30MP size 32x32x14mm spy camera with afixed focus pin hole lens for hiding behind a
|
||
|
||
very small hole
|
||
|
||
£35.00 +vat =£41.1 3
|
||
|
||
40MC size 39x38x27mm camera for c mount lens these give a much sharper image
|
||
|
||
than with the smaller lenses
|
||
|
||
£32.00 +vat =£37.60
|
||
|
||
Economy C mount lenses all fixed focus & fixed iris
|
||
|
||
VSL1 220F 12mm F1.6 12x1 5degrees viewing angle
|
||
|
||
£15.97 +vat =£18.76
|
||
|
||
VSL4022F 4mm F1.22 63x47 degrees viewing angle
|
||
|
||
£17.65 +vat =£20.74
|
||
|
||
VSL6022F 6mm F1.22 42x32 degrees viewing angle
|
||
|
||
£19.05 +vat =£22.38
|
||
|
||
VSL8020F 8mm F1.22 32x24 degrees viewing angle
|
||
|
||
£19.90 +vat =£23.38
|
||
|
||
Better quality C Mount lenses
|
||
|
||
VSL161 4F 16rnm F1.6 30x24 degrees viewing angle
|
||
|
||
£26.43 +vat =£31.06
|
||
|
||
VWL813M 8mm F1.3 with iris 56x42 degrees viewing angle
|
||
|
||
£77.45 +vat =£91.00
|
||
|
||
1206 surface mount resistors E12 values 10 ohm to 1M ohm 100 of 1value £1.00 «vat
|
||
|
||
1000 of 1value £5.00 +vat
|
||
|
||
866 battery pack originally intended to be used with an orbitel
|
||
|
||
mobile telephone it contains 10 1.6Ah sub C batteries
|
||
|
||
(42x22dia the size usually used in cordless screwdrivers etc.)
|
||
|
||
the pack is new and unused and can be broken open quite
|
||
|
||
easily
|
||
|
||
£7.46+vat =£8.77
|
||
|
||
M1ar4-1 .
|
||
|
||
Please add 1.66 +vat =£1.95 postage &packing per order
|
||
|
||
JPG ELECTRONICS
|
||
276-278 Chatsworth Road, Chesterfield, S40 2BH.
|
||
Tel 01246 211202 Fax 01246 550959 MastercardNisa/Switch Callers welcome 9:30 am .to 5:30 p.m. Monday to Saturday
|
||
|
||
CIRCLE NO.118 ON REPLY CARD
|
||
|
||
715
|
||
|
||
Please quote Electronics World when seeking further information
|
||
|
||
distributed power applications in computing and communications. The single-
|
||
output units have output voltages of 3.3, 2.5, 2, 1.8 and 1.5V, with anominal input of 48V and an input range of 36 to
|
||
|
||
75V. Users can draw up to 60A from the BXF300 and 80A from the BXF400. Both include short-circuit, overvoltage and over-temperature protection, remote sensing and remote onoff. Artesyn Technologies Tel: 00 353 24 25572
|
||
Frame grabber
|
||
Matrox has introduced aPCI version of its Orion frame grabber. It supports colour and monochrome video capture and uses the MGA G400 graphics controllej. The unit can capture analog composite (CVBS) and Y/C in NTSC and PAL formats and composite RS-170 and CCIR video formats. It includes discrete analogue-todigital converters for capturing component RGB in NTSC and
|
||
|
||
PAL. A separate trigger input is provided for synchronising video capture to external events. The graphics controller has two independent CRT controllers. The primary controller handles the main VGA display output and the other handles secondary TV display output. It provides arbitrary video scaling and nondestructive graphics overlay of live video without host CPU intervention. Matrox Imaging Tel: 01753 665500
|
||
Inductors with
|
||
shields
|
||
Meggitt has introduced shielded and unshielded power inductors and signal line chokes for industrial applications. The unshielded range includes
|
||
|
||
twelve sizes with different height to size to current ratios.
|
||
The 3622's package is 5mm in diameter, with up to 1mH inductance. Lower values carry
|
||
|
||
BOOK TO BUY
|
||
Low-Power CMOS VLSI Circuit Design
|
||
A comprehensive look at the rapidly growing field of low-power VLSI design
|
||
|
||
LOW-POWER
|
||
CMOS VLSI
|
||
CIRCUIT DESIGN
|
||
|
||
Return to Jackie Lowe, Room L333, Quadrant House, The Quadrant, Sutton, Surrey, SM2 SAS
|
||
Please supply the following title: Low-Power CMOS VLSI Circuit Design
|
||
Total Name Address
|
||
|
||
Low-power VLSI circuit design is a
|
||
|
||
dynamic research area driven by the
|
||
|
||
growing reliance on battery-powered
|
||
|
||
portable computing and wireless
|
||
|
||
communications products. In addi-
|
||
|
||
tion, it has become critical to the continued progress of high-performance and reliable microelectronic systems.
|
||
|
||
111 SLual CPra-ul
|
||
|
||
This self-contained volume clearly
|
||
|
||
introduces each topic, incorporates dozens of illustrations, and
|
||
|
||
concludes chapters with summaries and references. VLSI circuit
|
||
|
||
and CAD engineers as well as researchers in universities and
|
||
|
||
industry will find ample information on tools and techniques for
|
||
|
||
design and optimisation of low-power electronic systems.
|
||
|
||
Postcode Telephone Method of payment (please circle) Access/Mastercard/Visa/Cheque/PO
|
||
Cheques should be made payable to Reed Business Information
|
||
Credit card no
|
||
Card expiry date
|
||
Signed
|
||
|
||
Topics include: • Fundamentals of power dissipation in microelectronic devices • Estimation of power dissipation due to switching, short
|
||
circuit, subthreshold leakage, and diode leakage currents • Design and test of low-voltage CMOS circuits • Power-conscious logic and high-level synthesis • Low-power static RAM architecture • Energy recovery techniques • Software power estimation and optimisation
|
||
** Price includes delivery and package **
|
||
|
||
716
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
PROFESSIONAL
|
||
Development Tools
|
||
|
||
'from Milford Instruments
|
||
Milford Instruments Tel 01977 683665, Fax 01977 681465
|
||
www.milinst.demon.co.uk info@milinst.demon.co.uk Milford House, 120 High Street, South Milford, LEEDS LS25 5AQ
|
||
|
||
PIC Emulators from Tech Tools
|
||
Mathias In-Circuit Emulator • 16C5X to 20MHz • 16CXX to 25MHz and data breakpoints •Modular design •True Integrated Windows Environment •Supports standard assemblers and compilers •True Prondout Chip set based •Programmers and adaptors also available Full details at www tech-tools corn
|
||
|
||
BASIC Stamps
|
||
Still the easiest and fastest way to get your project up and going. 8or 16 I/O pins, easy-to-read BASIC instructions plus on-board comms and simple interfacing to peripheral chips.
|
||
Scenix Emulators from Parallax
|
||
|
||
ROM Emulators from TechTools
|
||
|
||
EconoROM, FlexROM and UniROM
|
||
|
||
Fast 9Ons, 45ns and 35ns access times Fast download (up ta 2.5Mbitisecondl Read-back, Verify and Self-test modes Full editor and utilities included
|
||
|
||
Live editing ilJniROM only1
|
||
8bit &I6bit up to 32Mbit
|
||
EPROM. FIA,SH and SRAAA emulation '•
|
||
|
||
Il details and demo software at www.tech-tools.com
|
||
|
||
New to PICs or just wanting to learn new tricks?
|
||
We stock the excellent Squa series of PIC primers. See our web site for contents.
|
||
|
||
SX-Key Emulator SX chips ore EERROM based, PIC 16C5x pin compatible micros with up to 100mip• performance. •Full speed debugging on production chips •Integrated Windows environment •Software configured oscillator • 18 to 52 pin reprogrammable devices •SX Blitz low cost programmer also
|
||
available Full detail sand software at nc.com
|
||
|
||
LOW POWer, Piled
|
||
serial interface
|
||
SERIAL LCDs reduce display hassle'
|
||
We stock arange of alphanumeric and graphic displays all fined with serial RS232 interface boards- 2x16 to 4x40 and up b 128x64 graphics size. RS232 data entry terminal unit also available
|
||
|
||
CIRCLE NO.I 19 ON REPLY CARD
|
||
30% discount for EW readers
|
||
on dmm with frequency, capacitance & inductance
|
||
|
||
Features
|
||
3.5 digit 43 ranges 0.25% AC & DC voltage &. current Resistance to 20Mohm Capacitance to 2000uF Frequency to 20MHz Inductance to 20H Diode, continuity & logic test Auto pwr off, data & peak hold Overload protection Input warning beeper Rubber holster
|
||
Vann Draper is offering the professional quality LP300 digital multimeter to readers of Electronics World at a30% discount. The LP300 normally sells at an already low price of £81.08 but is available to readers for only £59 fully inclusive of vat & delivery.
|
||
|
||
Vann Draper Electronics Ltd
|
||
The test & measurement specialists
|
||
www.vanndraper.co.uk Equipment from Grundig, Kenwood, Hameg, Tektronix, Hitachi, Fluke, Avo and many more.
|
||
Use this coupon for your order Please supply me
|
||
LP300 multimeter(s) at £59 00 inc vat &del
|
||
Narre
|
||
Address
|
||
|
||
The meter is supplied ready to use complete with test leads, rubber holster, battery, operating instructions and a 12 month guarantee.
|
||
Data sheets for all products are published on our web site at www vanndraper co uk including the new pc based 20MHz 40Ms/s digital scope & spectrum analyser for £159
|
||
To order your meter simply post the coupon to •
|
||
Vann Draper Electronics Ltd, Stenson House, Stenson, Derby DE73 1HL. Or Tel 01283 704706 Fax 01283 704707 Email sales@vanndraper.co.uk
|
||
|
||
DC volts AC volts DC current AC current Resistance Capacitance Inductance Frequency Size and weight
|
||
|
||
Key Specifications
|
||
200m. 2V. 20V. 200V. 1000V -basic accuracy 0.25% 200m, 2V, 20V, 200V, 750V -basic accuracy 10% 200uA, 2mA. 200mA, 10A -200mA & 10A fuse protection 200uA, 2mA, 200mA, 10A -200mA & 10A fuse protection 200ohm, 2k, 20k, 200k, 2M, 20M -protection to 500Vrms 20nF, 200nF, 2uF, 20uF, 2000uF -by test leads or socket 2mH, 20mH. 200mH, 2H, 20H -by test leads or socket 2kHz, 20kHz, 200kHz. 2MHz. 20MHz -auto ranging 200 x95 x55mm. 500g (with holster)
|
||
CIRCLE NO.120 ON REPLY CARD
|
||
|
||
Tel No Total £ Cheques payable to Vann Draper Electronics Ltd
|
||
or debit my visa mastercard or switch card
|
||
card type Card No
|
||
|
||
Expiry date
|
||
|
||
Switch iss No
|
||
|
||
Signature
|
||
Overseas readers can still obtain this discount but carriage charges vary according to country Please telephone fax email or write to Vann Draper
|
||
|
||
BOOK TO BUY
|
||
|
||
Valve Radio and Audio Repair Handbook
|
||
•Apractical manual for collectors, owners, dealers and service engineers •Essential information for all radio and audio enthusiasts Valve technology is ahot topic
|
||
This book is not only an essential read for every professional working with antique radio and gramophone equipment, but also dealers, collectors and valve technology enthusiasts the world over. The emphasis is firmly on the practicalities of repairing and restoring, so technical content is kept to a minimum, and always explained in away that can be followed by readers with no background in electronics. Those who have agood grounding in electronics, but wish to learn more about the practical aspects, will benefit from the emphasis given to hands-on repair work, covering mechanical as well as electrical aspects of servicing. Repair techniques are also illustrated throughout. This book is an expanded and updated version of Chas Miller's classic Practical Handbook of Valve Radio Repair. Full coverage of valve amplifiers will add to its appeal to all audio enthusiasts who appreciate the sound quality of valve equipment.
|
||
Contents: INCLUDES: Electricity and magnetism; Voltage, current, resistance and Ohm's Law; Real life resistors; Condensers; Tuning; Valves; Principles of transmission and reception; Practical receiver design; Mains valves and power supplies; Special features of superhets; Battery and mains battery portable receivers; Automobile receivers; Frequency modulation; Tools for servicing radio receivers; Safety precautions; Fault finding; Repairing power supply stages, Finding faults on output stages; Faults on detector/AVC/AF amplifier stages; Finding faults on IF amplifiers; Faults on frequency-changer circuits; Repairing American 'midget' receivers; Repairing faults on automobile radios; Repairing battery operated receivers; Repairing FM and AM/FM receivers; Public address and high fidelity amplifiers.
|
||
UK Price: £22..50 Europe £25.00 ROW £27.00
|
||
** Price includes delivery and package
|
||
Return to Jackie Lowe, Room 1333, Quadrant House,
|
||
The Quadrant, Sutton, Surrey, SM2 5AS
|
||
|
||
Please supply the following title: Valve Radio and Audio Repair Handbook
|
||
|
||
Name Address
|
||
|
||
Total
|
||
|
||
NEW PRODUCTS
|
||
Please quote Electronics World when seeking further information
|
||
|
||
up to 7.5A. Shielded devices range from the 3630 with inductance to 820µH and maximum current of 3.1A (3.7mm diameter) to the 12.7mm high 3621 at 1000tH and 7.5A in asquare case. Meggit Electronic Component Tel: 01793 487301
|
||
Development kit for TCP/IP
|
||
Rabbit Semiconductor has released the Rabbit 2000 TCP/IP development kit containing the hardware and software to design a microprocessor-based application that networks via Ethernet and uses intemet protocols. The kit contains a TCP/IP development board with an 8-bit microprocessor, Dynamic C software development system, power supply and PC serial cable for real-time debugging. The software includes integrated editor, compiler and debugger, so no in-circuit emulator is required. Sample demonstration programs include HT!? Web server and SMTP mail client. Hardware reference schematics help with development. Executable code can be downloaded into flash memory or optional battery-backed RAM. Two communication
|
||
|
||
ports are available —an RS232 port and afactory configurable port for either RS485 or RS232. Features include four highcurrent outputs, four digital inputs, seven timers. real time battery-backable clock and 10baseT Ethernet interface. TCP/IP source code is provided. Rabbit Semiconductor Tel: 00 1530 757 8400
|
||
Ultra low-profile keytops
|
||
Devlin Electronics has developed the ML family of .keytops to match the Cherry ML key switches. The keytops are
|
||
5.3mm high and available in 1 by 1, 1by 1with bar, 1by 2 horizontal and 2by 1vertical sizes. There is achoice of standard colours with either two-pack printing or laser engraving. Also available are keypad and keyboard assemblies. Devlin Electronics Tel: 01256 467367
|
||
|
||
Postcode Telephone
|
||
Method of payment (please circle) Access/Mastercard/Visa/Cheque/PO Cheques should be made payable to Reed Business Information
|
||
Credit card no Card expiry date
|
||
Signed
|
||
|
||
U series signal relays for telecoms
|
||
NEC is shipping two U-series signal relays for telecoms and industrial equipment and consumer appliances. Consisting of a slim type UA2 and UB2 relay with amount area of 60mm2, through-hole type and flat type UC2 and UD2 relay with a height of 5.45mm, the range uses the firm's magnetic circuit design, simulation and processing technologies.
|
||
NEC Electronics
|
||
Tel: 01908 691133
|
||
|
||
718
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
Test Equipment Price Blitz!
|
||
|
||
While Stocks last:
|
||
PHILIPS PM3217 Oscilloscopes
|
||
DC-50MHz Dual beam, Dual Timebase (inc Delay). Ind NEW probes and Cover...
|
||
an Un -Beatable £199 Wiltr .n Sc.l.r-
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||
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||
-
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||
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-4.% .. ,,
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||
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-. ..: -.-4:«,,t: af..4': - .., '...
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||
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4. ,•:* ;
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||
|
||
. £n.l ys .r
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||
|
||
j
|
||
|
||
.
|
||
|
||
10MHz to 20GHz comprising: Model 560 SNA, 6647B sweeper and
|
||
|
||
1722A Touch Screen Controller...all fitted into one 19" rack cab with
|
||
|
||
covers. Complete with Manuals, Leads, Sensors and Software.
|
||
|
||
ONE ONLY £2995
|
||
|
||
LAST FEW Available:
|
||
MARCONI 2019A Signal Generators
|
||
80KHz to 1040MHz AM-FM...Synthesised...3x LCD readouts.
|
||
STILL ONLY £475
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||
|
||
r.......,,„.ger
|
||
|
||
*xi Id MO ••• Ill
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'"
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JUST ARRIVED:
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||
HP 8569B opt H02 Spectrum Analyser. 10MHz-22GHz...Storage, On Screen Displays.
|
||
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||
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RACAL 9475 Rubidium Frequency Standard.
|
||
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|
||
|
||
EIP 575 Source Locking Microwave Counter...10Hz to 18GHz...1 2 digit LED
|
||
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|
||
|
||
Sorensen DCA 300-9
|
||
0-300V @ 9A DC Regulated and
|
||
Stabilised Power supply. Twin meters One Only £195
|
||
|
||
Marconi TK 2373 Frequency Extenders for 2370
|
||
(1250MHz)... Only £375
|
||
|
||
Wavetek 155 Programmable VCG 0.01 Hz to
|
||
1MHz.sine,sq,tri...
|
||
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||
|
||
Rohde +Schwarz APN62 Sig gens 0.1Hz-260Hhz...sine,
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square, triangle, sawtooth. LCD display.. Only £399
|
||
SMLH Sig Gens...10KHz-40MHz...AMFM
|
||
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|
||
|
||
TEK 2205 Oscilloscopes... DC-20MHz Unbeatable Value at
|
||
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|
||
High Power 50ohm attenuators 2x 10db @ 100W in one... Only £25
|
||
|
||
FLUKE 80-40K High Voltage Probe for DMM's...40kV
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||
rated...
|
||
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|
||
|
||
Farnell DSG2...Synthesised Sig Gens...
|
||
0.1MHz-110kHz...sine+square...
|
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||
|
||
Last FEW.. As-New DTA20 20M Hz dual beam scopes
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||
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||
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|
||
|
||
HP 8445B 18GHz Pre-Selectors for 141T spectrum
|
||
analyser system...
|
||
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|
||
|
||
Marconi 6311
|
||
Programmable Sweep Gen...
|
||
10MHz-20GHz Now Only £2995
|
||
|
||
Rolleiflex TTLR Cameras incl leather case
|
||
Few left at £175
|
||
|
||
ANCHOR SUPPLIES LTD
|
||
|
||
MasterCard
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||
|
||
All prices are plus VAT and Delivery
|
||
|
||
The Cattle Market, Nottingham NG2 3GY, UK
|
||
|
||
Tel: +44 (0) 115 986 4902
|
||
|
||
Fax: +44 (0) 115 986 4667
|
||
|
||
Also at Ripley, Derbys (01773) 570137 and Coalville, Leicestershire (01530) 811800
|
||
|
||
Visit our web site: www.anchorsupplies.com email: electronics@anchorsupplies.com
|
||
|
||
Sepember 2000 ELECTRONICS WORLD
|
||
|
||
71()
|
||
|
||
Loudspeaker crossover networks: constant voltage or constant power? John Watkinson's answer might surprise you.
|
||
SPEAKERS' CORNEKR
|
||
|
||
II nthe last few issues of this magazine there has been a significant number of constant-voltage crossover circuits published, not to mention acertain amount of debate. It is heartening to see such aresurgence of interest in this subject, but there does appear to be asome confusion over the question of constant voltage or constant power operation.
|
||
In an ideal loudspeaker, the use of more than one drive unit and the
|
||
|
||
resulting crossover would be transparent to the listener. The internal operation of the loudspeaker is the designer's problem. But the sound it produces should be afunction of the audio waveform and by definition should not reveal anything about that construction.
|
||
At this point, the conventional speaker designer will state that theory is all very well but it can't be achieved in practice and so there is no point in
|
||
|
||
trying. The only reply Ican make is to point out that active loudspeakers with inaudible crossovers are commercially available. And they really do sound
|
||
more realistic. Clearly the ideal is apractical pos-
|
||
sibility. But how is it done? Quite simply the answer is to do what acoustics allows, with the degree of precision the ear demands. This means that the crossover design, the crossover frequency and the directivity and positioning of the drive units all have to meet certain criteria. If all are not met, the result is unsatisfacto-
|
||
|
||
Fig. 1. The criterion for accuracy in atwo-way
|
||
speaker is that the waveform created in the
|
||
air at microphone a) is identical to the input
|
||
waveform. This is difficult enough, but it is also a requirement to achieve
|
||
the same result with offaxis microphone at b).
|
||
|
||
For example, an ideal crossover topology used with an inappropriate mix of drive units or an inappropriate crossover frequency won't sound
|
||
much better than a conventional crossover. This would lead to the false conclusion that the ideal crossover is
|
||
unnecessary. Figure 1a) shows one of the criteria
|
||
we are trying to meet. This is that the radiation from the two drive units should sum to the original waveform at the listener. However, this isn't the only issue. Figure lb) shows that another requirement is for this condition to be met off-axis as well. Then the reverberant field will also carry no evidence of the use of two drive units.
|
||
|
||
720
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
AUDIO DESIGN
|
||
|
||
If we meet only the first criterion, we
|
||
could get awonderful on-axis frequency and time response. But the power response —i.e. the power radiated in all directions —could be unsatisfactory in the vicinity of the crossover. This symptom is only too obvious on most two-way loudspeakers.
|
||
The only solution is that the directivity functions of the two drive units must be similar in the crossover region. In traditional speaker design this criterion is seldom met.
|
||
Figure 2 shows that to obtain an inaudible crossover, the two drive units must be acoustically close at the crossover frequency. This means that the distance between them must be smaller than the crossover wavelength.
|
||
If this requirement is met, then it doesn't matter which drive unit contributes to the sound, so that the two
|
||
contributions can add up in front of the two drivers. In practice, this requires arelatively low crossover frequency assuming typical woofer dimensions.
|
||
Once the drivers are acoustically close, something wonderful happens. Once in awhile, amidst the struggle which is high quality audio, physics gives the designer abreak. Figure 3 shows that if a constant voltage
|
||
crossover is used, in which the high and low frequency waveforms add back to the original, we can get both a flat voltage response and aflat acoustic power response through the
|
||
crossover frequency. This defies conventional logic.
|
||
Figure 3a) shows that both outputs of aconstant voltage crossover are —by definition — 6dB down, i.e. half the
|
||
midband voltage, at the crossover frequency.
|
||
As power ordinarily goes as the square of the voltage, one would conclude that each driver is receiving one quarter of its midband power, and so it is. However, it is completely incorrect to assume that the radiated power at the crossover frequency is then half the midband power.
|
||
What happens at the crossover frequency is that there are two acoustically close drive units radiating the
|
||
|
||
same signal. These drive units are in one another's close field. So what happens is that the radiation from one
|
||
doubles the radiation impedance seen by the other and vice versa, Fig. 3b).
|
||
The result of the doubling of the acoustic impedance is that the output of each driver is only 3dB down (half power) at the crossover so the sum of the two contributions is OdB down, or flat, as in Fig. 3c).
|
||
Imust stress that to make this work requires suitable drive units. Don't think that ablameless constant-voltage crossover will transform the performance of the average two-way bookshelf travesty because the dome tweeters won't work at a low enough frequency. If the transducers aren't up to it and the crossover frequency has to be raised, the technique doesn't work.
|
||
Once the two drive units are no longer acoustically close they don't augment one another's impedance at the crossover and aconstant-voltage crossover doesn't give the required results. Instead a constant power crossover is needed.
|
||
In general, the spacing between the
|
||
|
||
drive units will be alarge part of a
|
||
|
||
wavelength and the directivity func-
|
||
|
||
tion when both drivers are working at
|
||
|
||
the crossover will be seriously lobed
|
||
|
||
and audible as acoloured reverbera-
|
||
|
||
tion.
|
||
|
||
All that can be done is to narrow the
|
||
|
||
crossover region by using steep filters.
|
||
|
||
The trouble is that they almost invari-
|
||
|
||
ably sound pretty grim because they
|
||
|
||
impair the time or step response.
|
||
|
||
As far as Ican see, achieving an
|
||
|
||
inaudible crossover to adome tweeter
|
||
|
||
isn't possible theoretically, nor have I
|
||
|
||
heard it done. The poor directivity
|
||
|
||
function of domes makes them funda-
|
||
|
||
mentally narrow bandwidth drivers
|
||
|
||
and pushes crossover designers into
|
||
|
||
corners that they wouldn't be in with
|
||
|
||
wider band transducers.
|
||
|
||
The result is the characteristic
|
||
|
||
'dome sound' which restilts from a
|
||
|
||
combination of the poor directivity
|
||
|
||
characteristic of the driver itself along
|
||
|
||
with the poor phase characteristics of
|
||
|
||
the necessarily steep crossovers.
|
||
|
||
I personally prefer the 'original
|
||
|
||
waveform sound' where the loud-
|
||
|
||
speaker hasn't put hoofprints in the
|
||
|
||
acoustic output.
|
||
|
||
•
|
||
|
||
HF
|
||
d
|
||
Fig. 2. Distance between speakers d must be small compared to wavelength of sound d at crossover frequency. This suggests closest possible mechanical coupling and low crossover frequency.
|
||
|
||
(a) LF signal
|
||
|
||
Crossover frequency
|
||
•
|
||
|
||
6dB
|
||
|
||
HF signal L
|
||
6dB •
|
||
|
||
Fig. 3. Acoustic coupling between drive units doubles the impedance at the crossover frequency. This makes up perfectly for the power falling to one quarter when the drive voltage is halved. Thus an inaudible crossover is a possibility.
|
||
|
||
(b) Acoustic Radiation
|
||
Impedance
|
||
Pressure response
|
||
(C) Power response
|
||
|
||
,Both are flat
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
721
|
||
|
||
COMMUNICATIONS
|
||
|
||
SPECIAL RELATIVITY
|
||
|
||
In telecomms, synchronising clocks around the Earth is an
|
||
important issue. Al Kelly believes that the correction applied to such clocks is not explained properly by existing theories because they rely on
|
||
the notion that light has a constant velocity.
|
||
|
||
Light travels around the Earth faster eastward than westward. Does not the Special Theory of Relativity claim that the speed of light is aconstant?
|
||
The standard answer to this conundrum is that the Special Relativity applies solely to uniform straight line motion. It is claimed that, no matter how big the circle, motion along its periphery cannot be said to approach straight line motion. This is said to be so even if the best measuring instruments devised cannot pick up the divergence from straight line motion over the portion of circumference being used.
|
||
In his paper launching the theory in 1905, having applied his theory to straight line motion, Einstein then applied it to a closed curve of any shape. This rather undermines the popular explanation!
|
||
The circuit does not have to be as large as the cross section of the Earth to detect this effect. A Frenchman, Sagnac, found in 1914 that light signals go around adisc of 1m diameter faster against the spin of the disc than in the direction of the spin, Fig. 1.
|
||
By ameasurement made solely upon the spinning disc, he recorded the difference in the time of the signals sent in
|
||
|
||
Fig. 1. Sagnac test. Michaelson and
|
||
Gale used such a test to show that the
|
||
speed of light is different depending
|
||
on whether it is
|
||
travelling eastward or westward.
|
||
|
||
o
|
||
|
||
right or wrong?
|
||
|
||
the opposing directions. As shown in the diagram, the time for the signal to
|
||
traverse from the light source at A via C-D-E-F-C is less than the time in the opposite direction A-C-F-E-D-C.
|
||
The light source was fixed to the spinning disc; the measurement of the time difference was at an interferometer at C also fixed to the spinning disc. Sagnac produced aformula that exactly matches the difference in the times taken in opposing directions.
|
||
This formula can be derived, by assuming that the light travels in relation to the fixed laboratory. But, the measurement of the time difference is done solely aboard the disc. What can this mean? The only explanation possible is that the time aboard the spinning disc and in the fixed laboratory is the very same. This is not in accord with Special Relativity.
|
||
Another defence of Relativity theory is the claim that the light path upon the disc is longer in one direction than the other. But, the circumference of the disc, as measured by someone upon it, is surely the very same in both directions.
|
||
In a test in which signals are sent around the Earth from afixed position, the light signal is emitted upon the spinning Earth, and the record of the time difference taken by the opposing light paths is solely upon the Earth. To claim, in this case, that the circumferential distances east and west are different is bizarre.
|
||
A test done in 1926, by Michelson & Gale, first showed that the speed of light was not the same eastward and westward around the Earth. They constructed arectangular circuit of over amile in periphery. This was aSagnac test on a disc of diameter 9500000m diameter — the diameter of the Earth at that latitude.
|
||
In the case of the Earth at the equator, the difference between the times taken in opposing directions is 414.8ns. This result is enormous when considered against the accuracy —one million times better than that — required to-day of
|
||
|
||
standard clock-stations. The difference between the times going northward and southward around the globe is zero.
|
||
The International Telecommunications Union (ITU) sets the rules for synchro-
|
||
nising clock stations. A signal sent eastward around the globe has to allow for the fact that it travels at the speed of light cplus the rotational speed of the Earth at that latitude 1,,giving c+v.
|
||
A signal sent westward has to allow for the fact that the speed of the signal is c—v. According to Special Relativity theory, the speed of light is aconstant. Not only that, but the direction is not supposed to matter to Special Relativity; going east, west or north should have
|
||
the very same speed. As shown in the Fig. 2, a ground
|
||
clock station at A is to be synchronised with aground station at B, via asatellite S. The signal sent from A to B travelling in the same direction as the spin of the Earth takes more time than in the reverse direction.
|
||
A third defence that is used is that the c+v and c—v are only average figures and that the instantaneous velocity of the light signal is always equal to c. On aperfectly circular circuit the c+v in one direction is the velocity that would be measured at amillion spots on the circumference; how then can the average become c?
|
||
Take yas 250 0001cm/s. In amillion measurements the speed of the signal is 550 000km/s while the claim is that the instantaneous speed is 300 000km/s. Bunkum.
|
||
The ITU apply the necessary correction and call it 'a relativistic correction, for the rotation of the Earth'. But it is not arelativistic correction. A person at afixed position sends signals eastward and westward around the globe.
|
||
There is no relative motion concerned. How then is it that the signals arrive back at different times? There is only one sensible explanation. The signals are travelling at different speeds around the globe. Taking the speeds to be ctv in the opposing directions agrees exact-
|
||
|
||
722
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
COMMUNICATIONS
|
||
|
||
ly with the experimental result. A test was done in 1976 in which an
|
||
atomic clock was transported on an aeroplane from Washington (USA) to Tokyo. Also, asignal was sent between the two clock-stations. A correction had to be applied to the signal exactly as described above, while the transported clock needed no correction.
|
||
Despite this, the ITU claims that a correction of 207.4 nanoseconds has to be applied to the time on a clock brought around the Earth at zero height and very slowly; these stipulations ensure that there can be no correction due to General Relativity (height over sea level) or to Special Relativity (speed). This correction is anonsense.
|
||
The President of the organisation in Paris which oversees these rules wrote to the author 'you are right stating that the Sagnac effect is not relativistic'. That is an honest answer.
|
||
For the sending of signals from one site to another, their rules work fine. Saying the correction is 'relativistic' is amisnomer. The rules are wrong in the case of physical transportation of a clock from one site to another, but that is very rarely done, and can conveniently be overlooked.
|
||
There is also acorrection applied to the clocks that ride on a satellite, to
|
||
|
||
keep them in synchronisation with clocks on the ground. This is also supposed to be a relativistic correction. But, there is virtually no relative motion between the satellite clock and the ground station; the only relative motion is caused by the slight variation in the orbit of the satellite from an ideal orbit.
|
||
The correction applied is huge; it can amount to as much as 750Ons per day in atypical case; the clock is preset to alter by this amount each day, so that it will keep the same time as the clock fixed to the ground. It is calculated from the absolute velocity of the satellite compared with the absolute velocity of the ground station clock, in relation to the centre of the Earth, as it orbits around the Sun.
|
||
This correction is due to this absolute velocity, and not to the relative velocities of the satellite clock and the ground clock.
|
||
A very simple assumption would fit all of the these necessary corrections. If we assume that the signals travel with the Earth, on its orbit around the Sun, but do not adapt to the daily spin of the Earth, this fits the facts. In this case, the absolute velocity of the satellite versus the ground station accounts for the correction applied to the satellite
|
||
|
||
S
|
||
Fig. 2. Synchronising clocks on Earth. A and 8are ground stations, while Sis asatellite.
|
||
clock; the c±v of the signals sent around the Earth is explained simply by the spin of the Earth affecting the speed of the signal.
|
||
What could cause the signals to behave in this fashion? If light and gravity went together, on the Earth's orbit around the Sun, then the result would be fully explained.
|
||
We must then take it that the Special Theory of Relativity is not correct and that time and space are absolute, not relative. The speed of light is no longer sacrosanct.
|
||
But, what about the many many experiments that fit Relativity theory? A thousand things may fit atheory but, if one fact does not, the theory fails. In the words of Huxley 'the great tragedy of science —the slaying of abeautiful hypothesis by an ugly fact'.
|
||
|
||
TV Fault Finding Guide
|
||
Peter Marlow Contents: Introduction; A-Z of manufacturers and models Readership: Professional service engineers, some college courses.
|
||
Pages: 400pp
|
||
Price: £22.50
|
||
|
||
(
|
||
|
||
Unique expert authorship and trusted Television How to pay
|
||
|
||
magazine identity real repair and troubleshooting info —not just cribs from
|
||
|
||
(TV Foul? Finding Guide) paperback
|
||
|
||
manufacturers' data sheets. Ease of reference — this book is an essential repair tool, not just another volume for the shelf, Television
|
||
|
||
Ienclose acheque/bank draft for £ (payable to Reed Business Information)
|
||
|
||
magazine's TV Fault Finding column is aunique
|
||
|
||
forum for practical servicing tips, with the UK's
|
||
|
||
Please charge my credit/charge card
|
||
|
||
leading service engineers and servicing writers contributing their observations and recommendations month by month. But try
|
||
|
||
CI Mastercard JAmerican Express JVisa JDiners Club
|
||
|
||
Credit Card No:
|
||
|
||
Expiry Date:
|
||
|
||
finding those faults reports for the Amstrad
|
||
|
||
CTV2200 that's on your bench. Even with an
|
||
|
||
index you will be chasing through apile of magazines.., until now. Peter Marlow's TV Fault
|
||
|
||
Signature of Cardholder
|
||
|
||
Finding Guide is adistillation of the most used
|
||
|
||
fault reports from 11 years of Television magazine. Arranged by make and model the
|
||
|
||
Cardholder's statement address: (please use capitals)
|
||
|
||
information is extremely easy to access, and the book is aconvenient size for the bench or to
|
||
|
||
Name
|
||
|
||
carry with you. This will undoubtedly become one of the service engineer's most useful tools.
|
||
|
||
Address
|
||
|
||
Unlike other fault guides, this one is based on
|
||
|
||
top quality information from leading authorities,
|
||
|
||
and genuine repair case studies. This is real-life
|
||
|
||
servicing information, not just acompilation of
|
||
|
||
manufacturers' manuals.
|
||
|
||
Over 2,000 reports covering over 300 models Instant on-the-spot diagnosis and repair advice
|
||
|
||
Post Code
|
||
|
||
Tel:
|
||
|
||
Television magazine's leading writers' wit and
|
||
|
||
wisdom available for the first time in book form.
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
;
|
||
|
||
Unique 15% reader discount on Crownhill's range of versatile programmers
|
||
|
||
LabProg 48
|
||
Flagship universal programmer, for Microprocessors, EEproms, [proms, Flash memory etc.
|
||
Normal selling price exclusive of VAT and delivery £356.00, discount price £302.60.
|
||
UK delivery £15.00 — next day courier EC delivery £45 —DHL or UPS normally 1-2 working days Delivery outside EC £55 —DHL or UPS 2-3 working days VAT 017.5% is applicable only to UK and EC orders.
|
||
Company orders in EC (not UK) where the company is VAT registered and the VAT number is produced at the time of order, can be shipped exclusive of VAT.
|
||
SEE PROG
|
||
Serial EEprom programmer with enhanced facilities. Normal selling price exclusive of VAT and delivery £49.95,
|
||
discount price £42.46. UK delivery £7.00 (Royal Mail special next day delivery) EC delivery £10.00 (Swift Registered air mail 5-7 working
|
||
days) Delivery outside EC £12 (Swift Registered air mail 5-7
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||
working days) USA £45 (DHL or UPS 2-3 working days) VAT 017.5% is applicable only to UK and EC orders.
|
||
Company orders in EC (NOT UK) where the company is VAT registered and the VAT number is produced at the time of order, can be shipped exclusive of VAT
|
||
PIC Prog
|
||
Universal Pic Programmer Normal selling price exclusive of VAT and delivery £99.95,
|
||
discount price £84.96. UK delivery £7.00 (Royal Mail special next day delivery) EC delivery £10.00 (Swift Registered air mail 5-7 working
|
||
days) Delivery outside EC £12 (Swift Registered air mail 5-7
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working days) USA £45 (DHL or UPS 2-3 working days) VAT 017.5% is applicable only to UK and EC orders.
|
||
Company orders in EC (not UK) where the company is VAT registered and the VAT number is produced at the time of order, can be shipped exclusive of VAT
|
||
|
||
Programmers for all occasions
|
||
Crownhill Associates is offering an exclusive 15% discount on any product in the company's programmer range to any reader of Electronics World until 31 August 2000. This unique reader discount is of particular interest in that the range of programmers on offer is competitivley priced even without the discount.
|
||
For more details on the of range programmers, see Crownhill's web site, detailed below, and the company's advertisement on page 551 of this issue.
|
||
Crownhill Associates Limited, 32 Broad Street, Ely,
|
||
Cambridge CB7 4AH England, UK.
|
||
Tel: +44 (0) 1353 66 67 09 Fax +44 (0) 1353 66 67 10
|
||
sales@crownhill.co.uk
|
||
http://www.crown hiII.co. uk
|
||
http://www.edsim2000.com http://www.picbasic.co.uk
|
||
http://www.cambsnet.co.uk for your FREE Internet account
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||
|
||
r oder coupon
|
||
|
||
Please send me.
|
||
|
||
LabProg 48
|
||
|
||
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||
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||
PIC Prog
|
||
|
||
For which Ienclose aacheque made payable to Crownhill
|
||
|
||
Associates Limited for £. or my credit card details as follows:
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||
|
||
Card type (please tick) Visa Cl
|
||
|
||
Master LI
|
||
|
||
Card number
|
||
|
||
Expiry date
|
||
|
||
Name of cardholder
|
||
|
||
Address of cardholder
|
||
|
||
Please post this coupon to Crownhill Associates Limited 32 Broad Street Ely, Cambridge CB7 4AH England, UK.
|
||
|
||
ETTER BUFFERS
|
||
|
||
.r he complementary compound emitter follower is a useful building block. When compared with the ordinary emitter follower, it can have higher input
|
||
impedance, lower output impedance and lower distortion, so it makes asuperior buffer. In addition, there is avariant that
|
||
can provide some voltage gain. Although the textbooks mention this circuit block, not
|
||
much guidance is given on suitable component values. Idis-
|
||
covered this when designing an FM tuner. Iwanted to use a
|
||
complementary compound emitter follower —CCEF from now on —as abuffer for the birdy filter between the FM discrirninator and the stereo decoder. Ifound that Ididn't know
|
||
how to pick component values; then Ifound that none of the
|
||
books Ihad was much help either. Iwas also prompted to investigate CCEF when reading
|
||
Selfs book on audio power amplifier design'. He found that acomplementary pair of CCEF made an excellent Class-B output stage, but with aquiescent current set at what seemed to me avery low figure in the region of 7-15 mA.
|
||
Everybody `knows' that quiescent currents in Class B output stages are somewhere between 30 and 100mA and rel-
|
||
atively non-critical. It turns out that while this may be the case for aDarlington-pair output it is certainly not true for a CCEF output. Self also found that the quiescent current set-
|
||
|
||
Having been unsuccessful in looking for information to help him design complementary compound emitter followers, Dave Kimber set about developing his own guidelines. These include easy-to-use approximations for distortion components. This first article is an introduction to the subject and a discussion of how to predict Class-A followers at currents up to audio power-amp levels.
|
||
|
||
David P. Kimber B.Sc.
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
ANALOGUE DESIGN
|
||
|
||
ting was quite critical if crossover distortion is to be min-
|
||
imised. If you are not familiar with the emitter follower, there's
|
||
more background in the panel below.
|
||
|
||
Fig. 1. The simplest complementary compound emitter follower is abasic emitter follower with
|
||
atransistor added. Input impedance is much higher, but output impedance and distortion remain the same.
|
||
|
||
Fig. 2. This variant of the complementary
|
||
compound emitter follower provides voltage and current gain.
|
||
|
||
Simple complementary compound emitter follower
|
||
The simplest CCEF just adds asecond transistor, Fig. 1.
|
||
Total current gain is then roughly PIx(32,which provides a
|
||
much higher input impedance. However, other things being equal, the simple CCEF does
|
||
not reduce output impedance or distortion. This is because the input transistor, Tr', runs at areduced current, approxi-
|
||
mately /0„/132,so has much lower g. This counteracts the current gain provided by the output transistor Tr2.
|
||
However, by running at a higher current, the output impedance can be reduced while still leaving the input impedance above what it would be for aplain emitter fol-
|
||
lower. A variant of the simple CCEF is the simple complemen-
|
||
tary feedback pair, Fig. 2, which provides voltage gain.
|
||
|
||
The emitter follower
|
||
|
||
The basic emitter follower, Fig. A, can be analysed as follows. This analysis assumes that the transistor follows the Ebers-Moll model, which relates collector current /, to base-emitter voltage Vbe,and can be written as:
|
||
|
||
=exp(40(Vb,—1/0)) (rnA)
|
||
|
||
(1)
|
||
|
||
This will be reduced if, as is usually the case, there is an additional AC
|
||
load in parallel with the DC load. Output impedance is approximately equal to r, if the input signal source impedance is low.
|
||
So far we have ignored the base current /b. For small signal transis-
|
||
tors this is usually proportional to 4,
|
||
|
||
p
|
||
|
||
(7)
|
||
|
||
where V, is the base-emitter voltage which produces acollector current
|
||
of lmA, and is normally somewhere around 0.6V. Collector current 4
|
||
is in milliamps. Differentiating this gives the transconductance, or g„,:
|
||
|
||
g,„ =40 exp(40(K, —Vo)) =40 x/, (rnA/V)
|
||
|
||
(2)
|
||
|
||
Another way of looking at this is that asmall change in Vbe produces a
|
||
change in 4which, is equal to the current change that voltage change
|
||
would cause across asmall resistor rwith avalue given by:
|
||
|
||
r(i)) =—25
|
||
|
||
(3)
|
||
|
||
Here, I. is in milliamps again. For small signals you can treat atransistor as if it had an infmite g,,
|
||
but with this small resistor rin the emitter circuit, Fig. B. Now the voltage gain of an emitter follower can be found by treating rand R, as a voltage divider network:
|
||
|
||
gain = R1 1
|
||
|
||
(4)
|
||
|
||
R, +r
|
||
|
||
R,
|
||
|
||
For maximum output voltage swing, you would normally arrange the quiescent conditions such that the output sits at about half the supply voltage, i.e.,
|
||
|
||
R,
|
||
|
||
=0.5 ÷1`
|
||
|
||
(5)
|
||
|
||
Substituting equations (3) and (5) into (4), you will find that the gain is given by
|
||
|
||
gain 1— 0.05
|
||
|
||
(6)
|
||
|
||
The input impedance is approximately given by, (8)
|
||
|
||
Finally, you can estimate the distortion. The proportion of the input signal that appears across the base-emitter junction is, from equation (6),
|
||
0.05/V,. It can be shown that for smallish signals, the percentage of second-harmonic distortion generated by abase-emitter junction is equal to the peak signal amplitude in mV. See reference 2for more information on this.
|
||
The dominant distortion for the emitter-follower will be second-harmonic, although higher harmonics are likely to be significant too. The distortion will be reduced by the 100% negative feedback, to give a final figure,
|
||
|
||
Distortion
|
||
|
||
(2nd%)
|
||
|
||
=1.414
|
||
|
||
xV.t
|
||
|
||
x(—0.05 1in,.
|
||
|
||
2
|
||
)
|
||
|
||
ling
|
||
280 xtic':
|
||
|
||
(9 )
|
||
|
||
where Vng is the RMS signal voltage in millivolts and V, is the supply voltage in volts. For a2V signal and a 10V supply, this comes to 0.07%.
|
||
However, this increases quadratically as the AC load increases. For example, an AC load in parallel with aDC load of the same value will give four times as much distortion. This is because the base-emitter signal voltage is increased and the available negative feedback is reduced.
|
||
To achieve low distortion the DC load must be low compared with the AC load, i.e. the quiescent current must be high.
|
||
This treatment of the emitter follower may seem laborious, but it is a good introduction to the techniques used for the CCEF. The emitter follower can be improved in other ways —for example by introducing an active load —but this is outside the scope of this article.
|
||
|
||
Fig. A. Basic emitter follower has no voltage gain and is widely used as a buffer, to prevent loading on the stage before it and increase its output current capability.
|
||
|
||
Fig. B. For small signals, it is possible to treat the transistor of an emitter follower as though it had infinite gain, provided you also assume that there's alow-value resistor, r, in series with the emitter.
|
||
|
||
726
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
ANALOGUE DESIGN
|
||
|
||
Improving the CCEF Adding asingle resistor across the base and emitter of Tr2 as in Fig. 3, brings much more flexibility. But this simple change makes analysis more complicated.
|
||
The main advantage is that Tri runs increased current, so has ahigher gm than for the simple CCEF. This reduces distortion, but at the expense of lower input impedance — although still higher than for the plain emitter follower.
|
||
The circuit can be considered to operate in three regions. In the low current region, the voltage drop across R is too low to turn on Tr2 so effectively the CCEF degenerates into aplain emitter follower consisting of Tri only.
|
||
In the medium current region, both transistors are active, but the current in Tr2 is sufficiently low that its input impedance does not unduly load R. In other words, Tr2 is voltage driven.
|
||
At high currents, Tr2'sinput impedance now swamps R, i.e. Tr2 is current driven. Resistor R still boosts the current in Tri, so increases gm,but this effect becomes less important
|
||
|
||
24000 +960 x
|
||
|
||
(mA/V)
|
||
|
||
(13)
|
||
|
||
At the upper end of the region Tr2 begins to load R which
|
||
|
||
reduces the gain. A better approximation is then,
|
||
|
||
(1+ ) 24000
|
||
gek,w) — R
|
||
|
||
960 x42
|
||
|
||
(mA/V)
|
||
|
||
(14)
|
||
|
||
where 42( „.h) is the current for the medium-high transition, given by equation (10).
|
||
|
||
Low-medium transition. It is instructive to compare the transconductance just below and just above the low-medium transition. Assume R equals lkfl, which might be asuitable value for asmall signal CCEF. Then the transition occurs at 0.6mA. For g„,(0.5,„A),41=0.5mA and 42=0mA, while for g„,(1„„t),41=0.6mA and 1,2=0.4rriA,
|
||
|
||
•
|
||
|
||
=40 x0.5 =20mAN
|
||
|
||
using eqn (2)
|
||
|
||
Fig. 3. Adding aresistor across the base and emitter of Tr2 increases the operating current of Tri,and with it, the transistor's gm.
|
||
as the total current rises. A Class-A CCEF will operate in the medium current
|
||
region or the lower end of the high current region. A Class-B CCEF —to be considered in athird article on
|
||
this topic —will operate in all three regions. In each case the critical feature is the effective transconductance, because this determines distortion and output impedance.
|
||
|
||
24000
|
||
|
||
•
|
||
|
||
= 1000 +960 x0.4 =408rnA/V using eqn (13)
|
||
|
||
Thus aratio of 2in current has given rise to aratio of 20 in g„. This transition has avery sharp knee. Iwill be returning to this issue in the third article.
|
||
Note that when 1, 1 is 0.5mA, /c2 will actually be about 18pA. This adds 17.6rnA/V to the 20mA/V calculated above, so the approximations are not too good just below the transition.
|
||
|
||
High-current region. Current in Tr' still has not increased very much at the lower end of this region. Transconductance in this region is dominated by Tr2 current gain amplifying g„, of Tri. Transconductance is still given by equation (14), although it can be rewritten as,
|
||
f
|
||
|
||
Low-current region. Tr2 begins to turn on when its baseemitter voltage reaches somewhere around 600mV. Thus the low current region is the range 0 to 600/R mA. Transconductance, g„„ is given by equation (2) in the separate panel, and so increases linearly with current from 0to
|
||
approximately 24 000/R mA/V.
|
||
|
||
Medium-current region. This region is bounded at the lower end by the low current region at 600/R mA. The transition to the high-current region can be considered to occur when the input impedance of Tr2 is equal to R. This happens at,
|
||
|
||
42,„,_„ )=25 x
|
||
|
||
(mA)
|
||
|
||
(10)
|
||
|
||
The total current is /c2 plus /c i,but ici will change only slightly from the current at the top of the low current region. This is because it only has to provide some base current for
|
||
Tr2 and allow for asmall rise in the voltage across R. Thus the size of the medium current region, expressed as aratio of the total current, is,
|
||
|
||
(25 x +600) =1+ (A
|
||
|
||
(11)
|
||
|
||
600
|
||
|
||
24 )
|
||
|
||
The transconductance in this region has two contributions.
|
||
|
||
One comes directly from Tr, and is approximately 24000/R
|
||
|
||
mA/V, as for the top of the low current region. The second
|
||
|
||
contribution is the transconductance of Tr2 multiplied by the
|
||
|
||
voltage gain of Tr 'and R—with care over units!
|
||
|
||
g ff
|
||
|
||
40 x
|
||
|
||
x
|
||
|
||
000
|
||
24R
|
||
|
||
x10R00
|
||
|
||
(12)
|
||
|
||
g„,(mA/V)=
|
||
|
||
x
|
||
|
||
(15)
|
||
|
||
This makes the mechanism more explicit. Equations (14) and (15) really are equivalent, although they look very dif-
|
||
ferent. For higher currents it is necessary to add in /62 to /e l:
|
||
|
||
0, 1+ g(mAN) =40 x(6°-° + R
|
||
|
||
x 1+
|
||
|
||
,e2
|
||
|
||
(16)
|
||
|
||
For very high currents, /c2 is much greater than 132x600/R. This can be reduced to the approximation,
|
||
g„,(mAN) 40 x4„,
|
||
which is the same as the equation for very small currents! Thus the effect of R is to greatly boost transconductance in
|
||
the middle region by increasing the current through Tri.But at very low and very high currents the simple formula for an emitter follower applies.
|
||
|
||
Medium-high transition. With the medium-high transition,
|
||
as before, assume R is 11c.0 and also assume 132 is 240. Then from equation (10), the medium-high transition occurs when 42 is 6mA. Assume total currents of 5mA and 10mA.
|
||
|
||
•
|
||
|
||
=24 +960 x
|
||
|
||
4.4 4.4
|
||
|
||
— 2461rnA/V
|
||
|
||
6
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
727
|
||
|
||
ANALOGUE DESIGN
|
||
|
||
gm(10mA)= 24 +960 x
|
||
|
||
9.4 9.4
|
||
|
||
—3540mA/V
|
||
|
||
1+ 6
|
||
|
||
In the first instance, 41=0.6mA and 42=4.4mA, while in the second, 4. 1=0.6mA and 42=9.4mA.
|
||
This transition is much softer than the low-to-medium one. A ratio of 2in current has given rise to aratio of only 1.4 in transconductance.
|
||
Figure 4shows the overall picture. There is asharp knee into the medium current region, with steeply rising transconductance. This then gradually moves into the high current region where transconductance slowly rises until the simple emitter follower has caught up with it again.
|
||
Current gain of Tr2 determines the size of the boost while R sets the position of the boost.
|
||
|
||
Fig. 4. There's aknee in the medium-current region, which then rises slowly into the highcurrent region, where the simple emitter follower catches up with
|
||
the CCEF.
|
||
|
||
Current
|
||
|
||
Distortion Now we can consider signal distortion. For low distortion, the transconductance of the CCEF should be high when compared with the reciprocal of total load impedance, and should not vary much with current. So it is important to steer well clear of the low-medium transition and the lower part of the medium current region if low distortion is required. This is because in these areas g„, is low and strongly dependent on current.
|
||
As for the simple emitter follower, distortion will be mainly second harmonic but with higher harmonics not far behind. To estimate distortion you can use two tricks.
|
||
The first is Baxandall's 'reverse distortion' method 3.If distortion is not too high, then the distortion produced by an amplifier fed with adistortionless signal is approximately equal —phase reversal aside —to the pre-distortion required in the input signal in order to generate adistortionless output.
|
||
This trick is useful when, as is the case here, we have a means of calculating the required input to an amplifier in order to achieve the desired output but the converse would become intractable.
|
||
The second trick is that the amount of second-harmonic distortion can be estimated if the gain of the amplifier at the signal peaks can be calculated. There's more on this in the panel entitled, 'Estimating second-harmonic distortion'.
|
||
I'll continue to use the same example CCEF, with 132=240, and as before asupply of 10V with the quiescent output at half this voltage. For acurrent of 5mA, R1is then 1Ica A 2VRMS signal would swing the current from 2.17mA to 7.83mA if no distortion was present.
|
||
You can find the transconductance for these two currents, then estimate the distortion,
|
||
|
||
Estimating second-harmonic distortion Assume that the gain of an amplifier varies linearly with input voltage i.e.,
|
||
gain = gaino + a x
|
||
Then the amplifier will generate pure second harmonic distortion. Integrating the above gives,
|
||
=gain,, x +—21 xa x
|
||
plus aconstant, which can be ignored. Then if asinusoidal signal with peak voltage Vpk is applied, the output positive and negative peak voltages will be,
|
||
|
||
gain_ = gain„ - a X Vs
|
||
Then
|
||
|
||
a xVPk
|
||
|
||
=—1 x(gain, 2
|
||
|
||
- gai&)
|
||
|
||
gaino = -I x(gain, +gain,) 2
|
||
So,
|
||
distortion„,, — 1x(gain., - gai&) 4 (gain. +gain_)
|
||
|
||
= gain, xV1.4 +—1 xa X Vi,2 2
|
||
|
||
=
|
||
|
||
x
|
||
|
||
+—21 xa xvp2,
|
||
|
||
The first term in each case is the fundamental signal, amplified by the gain, and the second term contains equal amounts of the second harmonic distortion and aDC level shift.
|
||
=gain() xVp,
|
||
|
||
1 1 Vo.,(211d) = 2x—2xax Vp2, As afraction:
|
||
|
||
1 distortion,,,, = - X a X
|
||
|
||
Vp2k
|
||
|
||
4
|
||
|
||
gain, x
|
||
|
||
You can rewrite this in terms of peak gains by noting that,
|
||
|
||
This result is exact if gain varies linearly with input voltage. It pro-
|
||
vides auseful estimate if this is not the case, but second harmonic distortion is the dominant one. It breaks down completely if higher even harmonics are dominant. Iam sure this result is not original, but Idon't recall seeing it in print before.
|
||
If third harmonic distortion is dominant then an analogous result is,
|
||
|
||
distortion, d = 1 x(gain, —gaino)
|
||
|
||
12
|
||
|
||
gain,,
|
||
|
||
If both second and third harmonics are present, but higher ones
|
||
|
||
are smaller, then these results can still be used but in amodified
|
||
|
||
form,
|
||
|
||
distortion,„, = 1x(gain, - gai&)
|
||
|
||
8
|
||
|
||
gain,,
|
||
|
||
distortion3rd
|
||
|
||
=
|
||
|
||
1 x 12
|
||
|
||
(gain. + gain_)
|
||
2
|
||
gain,,
|
||
|
||
gaino )
|
||
|
||
728
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
ANALOGUE DESIGN
|
||
|
||
=24 +960 x
|
||
|
||
1.57 1.57
|
||
|
||
—1219mA/V
|
||
|
||
1+ 6
|
||
|
||
7.23 =24 +960 x 7.23 =3172mA/V
|
||
1+ 6
|
||
|
||
distortion,g. ,— 41 x
|
||
|
||
eg."_- =0.111
|
||
|
||
distortion
|
||
|
||
= 0.111 =0.005% g„,„ XR,
|
||
|
||
This is over ten times better than the emitter follower. Most of the advantage comes from the higher gn,of the CCEF, but g„, is also changing more slowly with current.
|
||
Adding an AC load would have the same effect as for the emitter follower, i.e. the distortion would vary roughly as the square of the ratio of the DC load to the total load.
|
||
|
||
Circuit design
|
||
We now have the necessary knowledge to return to the original question. How can we choose suitable component val-
|
||
ues for aCCEF, given the environment —e.g. supply voltage
|
||
—and requirements —e.g. signal level, load? The first step is to work out the peak signal current and
|
||
choose aTr2quiescent current that is alittle higher than this, so we keep clear of the low current region. At this stage it may be worth doing aquick calculation to see if an ordinary emitter follower can provide sufficient performance.
|
||
The value of the DC load resistor is found using Ohm's law. This leaves Rto be chosen. The best value would seem to be the one that maximises the transconductance boost, and hence minimises distortion and output impedance. This
|
||
|
||
means placing the operating point somewhere in the region of the medium-high current transition.
|
||
Unfortunately this depends on the current gain of Tr2, which is apoorly controlled parameter, but fortunately this transition has asmooth knee so accuracy is not too impor-
|
||
tant. So, we invert equation (10),
|
||
|
||
R=25 x
|
||
|
||
(17)
|
||
|
||
Here, R is in ohms and 4.2 in milliamps. Slightly higher values of R may reduce distortion because
|
||
the operating point is moved into the low end of the highcurrent region, where transconductance changes only slow-
|
||
ly with current. Slightly lower values of R may help highfrequency performance.
|
||
Given R, the performance of the circuit can be calculated. If not quite good enough, try an increase in quiescent current and recalculate. If the CCEF still does not meet the requirements, then at least you have pushed it as far as it will go.
|
||
My second article considers the complementary feedback pair, as aspecial case of the CCEF. A third article will look at using the CCEF in aClass Boutput stage.
|
||
|
||
References I. •Audio Power Amplifier Design Handbook,' Douglas Self,
|
||
Newnes 1996, Chapter 5. 2. Baxandall, Peter J. 'Audio power amplifier design,' Wireless
|
||
World, February 1979, p. 72.
|
||
3. Baxandall, op di, p. 71.
|
||
|
||
How to pay
|
||
(VCR Fault Finding Guide) paperback
|
||
|
||
0 Ienclose acheque/bank draft for £ (payable to Reed Business Information)
|
||
|
||
Please charge my credit/charge card 0Mastercard IAmerican Express 0Visa 0 Diners Club
|
||
|
||
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|
||
|
||
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|
||
|
||
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|
||
|
||
Television magazine's VCR Clinic column is a unique forum for practical servicing tips, with the UK's leading service engineers and servicing writers contributing their observations and recommendations month by month. But try finding those faults reports for the Amstrad XYZ123 that's on your bench. Even with an index you will be chasing through apile of magazines.., until now. Peter Marlow's VCR Fault Finding Guide is adistillation of the most used fault reports from 11 years of Television magazine. Arranged by make and model the information is extremely easy to access, and the book is aconvenient size for the bench or to carry with you. This will undoubtedly become one of the service engineer's most useful tools. Unlike other fault guides, this one is based on top quality information from leading authorities, and genuine repair case studies. This is real-life servicing information, not lust acompilation of manufacturers' manuals. Approximately 2,000 reports on 193 models from 35 different manufacturers. Instant on-thespot diagnosis and repair advice. Television magazine's leading writers' wit and wisdom available for the first time in book form
|
||
|
||
VCR Fault Finding Guide
|
||
Peter Marlow This book is an essential repair tool, not just another volume for the shelf
|
||
Pages: 464pp
|
||
Price: £22.50
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
729
|
||
|
||
Design your own Colpitts oscillators
|
||
|
||
Radio-frequency oscillators play an important role in wireless communications. One is required in every transmitter, and there is also at least one in most receivers. Here, as an aid to giving students and beginners practical experience of building circuits, Ian Hickman describes one of the widely used types the Colpitts oscillator.
|
||
|
||
W
|
||
|
||
hite light contains awide range of visible frequencies, but yellow light from
|
||
|
||
asodium lamp contains amuch nar-
|
||
|
||
rower range. A laser, on the other hand
|
||
|
||
produces monochromatic light, con-
|
||
|
||
taining just asingle frequency compo-
|
||
|
||
nent.
|
||
|
||
In asimilar way, the earliest wireless
|
||
|
||
transmitters, using aspark gap as the
|
||
|
||
Fig. 1. Two types of source of radio frequency energy, pro-
|
||
|
||
oscillator; a) using a duced a broad band of frequencies.
|
||
|
||
maintaining This was soon reduced to arather nar-
|
||
|
||
amplifier, bl rower band using aresonant circuit,
|
||
|
||
negative resistance more analogous to the sodium lamp
|
||
|
||
oscillator. than white light.
|
||
|
||
a)
|
||
|
||
b)
|
||
|
||
As the art progressed, it was desirable to produce radio-frequency energy comprising just asingle spectral line — analogous to the output of a laser. Subsequent modulation would then spread the energy over just the necessary bandwidth to communicate the message to be transmitted, rather than spraying it all over awider range like a spark transmitter.
|
||
So instead of producing broadband energy, and then using atuned circuit to select just apart of it, oscillators using valves were invented. Here, a continuous oscillation in atuned circuit was maintained by an active device — the valve — which made up the inevitable losses due to dissipation in the tuned circuit.
|
||
If the valve were disabled, the oscillation would die away to nothing in a few cycles, or tens of cycles at most.
|
||
Two sorts of oscillator One way to make an oscillator is to connect asuitable RF amplifier to the circuit, and then feed its output back into the tuned circuit, in the same
|
||
phase. If the gain around the circuit, from the input to the amplifier, to its output, through the tuned circuit and back again to its input, exceeds unity, then rather than dying away, the oscillation will build up in amplitude. Eventually, the amplitude will reach a stable limit, as the energy the amplifier can supply is itself limited, by its supply voltage and its standing current.
|
||
This type of oscillator is illustrated in Fig. la). Depending on whether the amplifier is inverting or non-inverting, the coupling winding used to feed its output energy back into the tuned circuit will have to be connected one way round or the other, to ensure that the feedback is positive. Thus the amplifier's output is areplica of the oscillating voltage in the tuned circuit, and con-
|
||
|
||
tinually makes up the losses. These losses are due to the finite Q —
|
||
or quality factor —of the capacitor, and more particularly the inductor. The Q of the latter may be afew hundred at most, but probably less than ahundred, while that of the capacitor will usually be ten or more times better. Operating Q will also be affected by the loading of the active device's input and output impedances upon the circuit.
|
||
There is another sort of oscillator, as illustrated in Fig. 1b). At first glance, it looks as though the circuit can never
|
||
In this series
|
||
As explained in apreliminary article in the May 2000 issue, this series is intended to help students —and anyone interested in getting to grips with RF design —as abackground in practical electronic circuitry and troubleshooting.
|
||
The series was originally developed in response to the government's RF Engineering Education Initiative. Below is a list of the three tutorials that have already appeared, together with my plans for future articles in the series — 'Beginners' corner'.
|
||
• Timer circuit using the 555, June issue.
|
||
• Audio oscillator —Wien bridge based, July issue.
|
||
• hie tester, August issue. • Radio-frequency oscillator,
|
||
Colpitts type. • Audio filter and oscillator —
|
||
state-variable based. • Capacitance meter. • Radio-frequency
|
||
oscillator/receiver involving negative resistance.
|
||
|
||
730
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
RF DESIGN
|
||
|
||
work, as there is no way of coupling the output of the oscillator back into the tuned circuit. But it can work, if the amplifier is suitably designed.
|
||
The trick is to make the impedance, seen looking into the amplifier's input, anegative resistance. This then cancels output losses in the tuned circuit,
|
||
resulting in astable level of oscillation, of amplitude determined by the particular circuit design.
|
||
This type of oscillator can be very useful, and will be featured in alater
|
||
article in this series. But for the present, let's look at aversion of the Fig. la) variety.
|
||
Amplifier-maintained oscillation
|
||
The circuit of Fig Ia) uses acoupling winding to inject the 'make-up' energy
|
||
from the amplifier, back into the tuned circuit.
|
||
Designers often prefer a circuit arrangement that dispenses with the separate winding, for anumber of rea-
|
||
sons. Taking technical considerations first, an RF oscillator does not usually use aclosed flux path for the inductor.
|
||
It may be purely air cored, or have a 'tuning slug' of ferrite usually, dust iron, or sometimes brass.
|
||
Either way though, the coupling between the two windings will be somewhat unpredictable. It is not simply determined by the turns ratio, as would be the case in atransformer with
|
||
aclosed flux path, such as amains transformer. And from the point of view of practical economics, both component and labour costs are increased.
|
||
So an arrangement where both input and output of the maintaining amplifier are directly connected to the tuned circuit will often be preferred. Now the amplifier is a three-terminal device; input, common and output, so there must be three connection points on the tuned circuit. Consequently, asingle capacitor and inductor, as in Fig. 1, will not suffice, and the arrangement of
|
||
Fig. 2is employed. With three connection points avail-
|
||
able on the tuned circuit, an active device, be it valve, transistor or FET, can be connected as shown. An interesting property of this circuit is that Z2 and Z3 must be impedances of the same type, either both capacitors or both inductors, while Z1 must be the other type. Furthermore, the common terminal of the active device, cathode, emitter or source, must be connected to the junction of Z2 and Z3.
|
||
If Z/2 and Z3are inductors —or, more likely asingle, tapped inductor —the circuit is known as aHartley oscillator, while if Z2 and Z3 are capacitors, it is known as a Colpitts oscillator. The Colpitts arrangement is often preferred,
|
||
|
||
as an untapped inductor is cheaper to
|
||
make, test and assemble than atapped component.
|
||
The Colpitts oscillator
|
||
Within the basic 'tapped capacitor' arrangement — actually two separate capacitors —several variants are possible. Figure 3a) shows one of these.
|
||
The base of the transistor is referenced to ground DC-wise, so the average emitter current is determined by the value of R1and the voltage of the negative rail. Effectively, the large decoupling capacitor C3 connects the collector to the junction of L1and C2, exactly as in Fig. 2, where Zi is the inductor L1and Z2the capacitor C2.
|
||
The amplitude of the oscillation builds up, resulting in the transistor being cut off for much of each cycle, due to abias voltage being built up across C2.Collector current thus flows in narrow pulses, the transistor operating in 'class C'. The fundamental component of these pulses, at the resonant frequency of the tuned circuit, maintains the oscillation.
|
||
Making an oscillator useful
|
||
It is all very well making an oscillator, but to be useful, it must be possible to bleed off some of the signal, for use say as alocal oscillator in asuperhet
|
||
receiver, or as the exciter in atransmitter.
|
||
The signal should be bled off in such away as not to impose excessive further loading on the oscillator. If it does load the oscillator, the Q of the tuned circuit would be reduced, degrading the oscillator's stability and purity.
|
||
Various pick-off arrangements are possible. One possibility is to draw off alittle current from the emitter, via a small capacitor of afew picofarads, or asingle turn coupling winding on Li could be used. Another popular arrangement is to draw off the signal across alarge capacitor in series with the earthy end of C2.In the case of Fig. 3, where the oscillator runs at about
|
||
5MHz, its value might be afew nanofarads.
|
||
Figure 36) shows another variation on the theme, this time requiring only a single supply rail. With the emitter dc referenced to ground via L2,base current is supplied via RI.Capacitor C3
|
||
couples the tuned circuit to the base of the transistor, while preventing the current via R1 being simply shunted to ground via LI.
|
||
At the operating frequency, the reactance of L2 is very high. So as far as the emitter circuit is concerned, it is, like R1 in Fig. 3a), virtually an open circuit —just aconvenient way of supplying the emitter current.
|
||
|
||
Or 9- or
|
||
|
||
Z1=
|
||
|
||
or er-
|
||
|
||
Z2, Z3 =# or
|
||
|
||
Fig. 2. Varieties of Fig. la) type oscillator based
|
||
on amaintaining amplifier. No separate feedback winding is involved here.
|
||
|
||
Inductor L2can be acommercial RF choke, as can L1—at least for experimental purposes.
|
||
Magnitude of the emitter current is
|
||
determined by RI,the current gain of the transistor and the voltage of the positive rail. In fact, if R1 is low enough and the Q high enough, the amplitude may increase to the point
|
||
where on positive peaks, the base voltage actually rises above the positive rail. This is not adesirable condition, as severe damping is applied to the tuned circuit, to the detriment of the purity of the waveform and the stability of the frequency.
|
||
Given the considerable device-todevice variation in current gain ha., the circuit of Fig. 3b) is thus not as 'designable' as that in a). There, the average emitter current is determined principally by the value of R1 and the voltage of the negative rail.
|
||
Emitter current can be set at alevel such that the transistor does not bottom, removing one of the causes of close-in phase noise and resulting in a purer output waveform. The advantages of this were appreciated long
|
||
ago'.
|
||
Might it squeg?
|
||
Choosing the value of C3 in Fig. 3b) also needs care. If it is too small, the circuit will not oscillate; too large and the circuit will `squeg'.
|
||
Squegging is when the amplitude rises up so fast that anegative voltage builds up on the base end of C3,cutting off the transistor completely. The oscillation across the tuned circuit dies away, but the base of Tr' is left at a negative voltage, charging only slowly towards +15V via RI,on the time-con-
|
||
stant RixC3. When the base reaches about +0.6V,
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
731
|
||
|
||
RF DESIGN
|
||
|
||
Fig. 3a). AColpitts oscillator, and b),
|
||
another variant, which may -or may not -squeg.
|
||
|
||
Li 10pH
|
||
|
||
R1 1M
|
||
Cl 680p
|
||
C2 120p7
|
||
|
||
Tri BC184
|
||
|
||
+15V
|
||
|
||
Tri BC184
|
||
L2 150pH
|
||
|
||
C4 10n
|
||
C3 =82pF. CW C3 =680pF. squegging
|
||
(super-regen RX)
|
||
|
||
b) a)
|
||
|
||
the transistor begins to conduct, the RF oscillation rapidly builds up again, resulting in the next cycle of the squeg frequency -amuch lower frequency than the r.f. oscillation frequency.
|
||
A squegging oscillator forms the basis of a'super-regenerative' receiver -atype of receiver that saw extensive military use in the Second World War. If ashort whip antenna is connected to the tuned circuit, as indicated in Fig. 3b), then any energy incoming at the resonant frequency of the tuned circuit causes an increase in the squeg frequency. It also causes acorresponding small change in collector current.
|
||
This current change can be monitored by the drop across aresistor, connected in series with the +I5V supply.
|
||
|
||
Thus the received signal is demodulated and available at the collector of Tri - you have a simple 'super-regen' receiver.
|
||
In Figs 3a) and b), the ratio of C1to C2 is one of the many design choices. Generally, the ratio is between 2to 1 and 5to I. Increasing the value of C1, while reducing that of C2 to maintain the desired oscillator frequency reduces the loading of the transistor's input circuit on the tuned circuit. It also demands ahigher gain from the transistor.
|
||
If the ratio of C1 to C2 is made too large, the circuit will not oscillate. Conversely, making C2 larger, and reducing CI to maintain the desired
|
||
oscillator frequency reduces the load-
|
||
|
||
ing of the transistor's output circuit on the tuned circuit.
|
||
Again, go too far, and the circuit will not oscillate. Thus there are limits to the ratio, at both ends of the range, as discussed in reference 2.
|
||
References 1. Sutcliffe, H, 'Transistor L.C. oscil-
|
||
lator circuits with amplitude controlled by mean current', Electronic Engineering July 1968, Vol. 40 No 485, 0. 388. 2. Shahzadi, B, Two distinct boundaries for feedback transistor oscillators', Electronic Engineering Jan. 1965, pp. 32-34.
|
||
|
||
Too good for words
|
||
|
||
The Complete Integrated Schematic PCB Layout
|
||
Package
|
||
|
||
sales@seetrax.com
|
||
|
||
www.seetrax.corn
|
||
|
||
.17:c• ma,
|
||
|
||
The New Ranger
|
||
XL Series
|
||
|
||
1:,01:,•1 2for Windows
|
||
|
||
t:I70
|
||
|
||
NEW Ranger 2XL
|
||
|
||
£00
|
||
|
||
NEW Ranger XL from
|
||
|
||
£50
|
||
|
||
FREE Website Download Demo
|
||
|
||
—IIIfIrene
|
||
Advanced Systems & Technology for PCB Manufacturers Oh] Bunion lime Work., Buriton. Petersfield. Hants. UK GU31 5S.1
|
||
Tel: (44) 01730 260062 Fax: (44) 01730 207273
|
||
|
||
CIRCLE NO. 121 ON REPLY CARL)
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
BOOK TO BUY
|
||
|
||
Completely updated, this comprehensive dictionary contains over 28,000 electronic terms, phrases, acronyms, and abbreviations from the everexpanding worlds of consumer electronics, optics, microelectronics, computers, communications, and medical electronics. This dictionary is a valuable resource for professionals in the field, hobbyists, students, or anyone interested in electronics. Poptronics
|
||
|
||
Included in this fully revised classic are well over 28,000 terms, phrases, acronyms, and abbreviations from the ever-expanding worlds of consumer electronics, optics, microelectronics, computers, communications, and medical electronics. From the basic elements of theory to the most cutting-edge circuit technology, this book explains it all in both words and pictures. For easy reference, the author has provided definitions for standard abbreviations and equations as well as tables of SI (International System of Units) units, measurements, and schematic symbols.
|
||
Modern Dictionary of Electronics is the bible of technology reference for readers around the world. Now fully updated by the original author, this essential, comprehensive reference book should be in the library of every engineer, technician, technical writer, hobbyist, and student.
|
||
|
||
Post your completed order form to:Jackie Lowe, Room 1514, Quadrant House, The Quadrant, Sutton, Surrey, SM2 5AS
|
||
Fax your completed order form to 020 8652 8111 UK Price: £42.50 Europe £45.00 ROW £47.50 Price includes delivery
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||
|
||
How to pay
|
||
Modern Dictionary of Electronics
|
||
|
||
a Ienclose acheque/bank draft for £ (payable to Reed Business Information)
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||
|
||
Please charge my credit/charge card J Mastercard J American Express a Visa J Diners Club
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||
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||
Credit Card No:
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||
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||
Expiry Date:
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||
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||
Signature of Cardholder Cardholder's statement address: (please use capitals) Name Address
|
||
|
||
Post Code
|
||
|
||
Tel:
|
||
|
||
IDEAS
|
||
|
||
Fact: most circuit ideas sent to Electronics World get published
|
||
The best circuit ideas are ones that save time or money, or stimulate the thought process. This includes the odd solution looking for aproblem —provided it has adegree of ingenuity.
|
||
Your submissions are judged mainly on their originality and usefulness. Interesting modifications to existing circuits are strong contenders too —provided that you clearly acknowledge the circuit you have modified. Never send us anything that you believe has been published before though.
|
||
Don't forget to say why you think your idea is worthy. Clear hand-written notes on paper are aminimum requirement: disks with separate drawing and text files in apopular form are best —but please label the disk clearly.
|
||
|
||
Bike computer reads amps, amp.hours
|
||
|
||
Abicycle computer counts wheel revolutions, and displays speed and distance travelled. Depending on the model, it may also show the maximum and average speeds achieved.
|
||
The user has to program the computer with the wheel circumference C in metres, since velocity yin km/h is related to the frequency of wheel rotation, Frps, by (v÷3.6)/C=F. Usually, amagnet attached to awheel operates areed relay to provide the count pulses, but in this application, a transistor switch is used.
|
||
|
||
Such abicycle computer can be used for other purposes, such as measuring the charge rate and total charge stored in asolar panel accumulator charging set-up, Fig. 1. To achieve this, the charging current is monitored by a current shunt R, controlling avoltagecontrolled oscillator.
|
||
The voltage controlled oscillator produces an output frequency such that abicycle computer velocity reading of 120km/h indicates acurrent of 12A, and atrip reading of 2998.9 km indicates acharge of 299.89A/h.
|
||
The programmable value of C on the
|
||
|
||
7 PV solar
|
||
panels —T1—
|
||
|
||
I 7
|
||
|
||
Battery charge
|
||
|
||
-IL- regulator
|
||
|
||
Rs
|
||
|
||
+12V
|
||
VCO +Vin
|
||
|
||
BicYcle computer
|
||
|
||
712V lead-acid accumulator
|
||
|
||
(E10a)
|
||
|
||
Fig. 1. Block diagram of charger metering system in asolar energy system, using àbicycle computer to monitor amps and A/h.
|
||
|
||
computer used was up to 2.999m. The VCO was designed to produce an output frequency of up to I3.7Hz for a 140mV input, corresponding to a14A charging current. With this design of oscillator. Fig. 2, acircumference setting C of 2.671m worked well.
|
||
This application is limited by the lowest and highest frequencies that the bicycle computer can count, and by VCO offset and linearity errors.
|
||
A minimum output frequency of 0.1Hz is produced by the VCO, even when the drop across R, is zero. But ,linearity errors up to the designed maximum, checked with aDVM and DSO, proved to be generally insignificant. There is aslight increase in error at the high frequency end of the range, due to the finite discharge time of Ci. Heinz Zanke GR-24002 Messenias Greece El 0
|
||
|
||
+12V •
|
||
OV
|
||
|
||
F1
|
||
0.2A IN
|
||
4002
|
||
|
||
TL317LP
|
||
|
||
6VT1:17p
|
||
|
||
226R 1k2
|
||
|
||
+8V stab 10p 16V
|
||
|
||
Fig. 2. Circuit of charger metering system, using abicycle computer. A voltage-controlled oscillator produces the pulses that would normally be derived using areed switch controlled by amagnet on the bicycle wheel.
|
||
|
||
IN
|
||
|
||
Vin
|
||
|
||
4148
|
||
|
||
0..150mV
|
||
|
||
100R
|
||
OV 1
|
||
4148
|
||
|
||
3 IC1
|
||
|
||
2p2 MkT
|
||
BC 82
|
||
|
||
1k MF
|
||
|
||
1k
|
||
8V 0.5x8V ---
|
||
|
||
^
|
||
20ps discharge pulse
|
||
|
||
EiC177
|
||
|
||
Hl
|
||
|
||
Bicycle computer
|
||
|
||
km/h
|
||
|
||
A
|
||
|
||
LO
|
||
|
||
km -3. Ah
|
||
|
||
IC1, LM358
|
||
|
||
1N4148
|
||
|
||
IC2, 74C14/CD40106
|
||
|
||
T on
|
||
|
||
(E10b)
|
||
|
||
734
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
National Instruments sponsors Circuit Ideas
|
||
|
||
National Instruments is awarding over £3500 worth of equipment for the best circuit ideas.
|
||
Once every two months throughout 2000, National Instruments is awarding an NI4050 digital multimeter worth over £500 each for the best circuit idea published over each two-month period. At the end of the 12 months, National is awarding aLabVIEW package worth over £700 to the best circuit idea of the year.*
|
||
|
||
About National Instruments National Instruments offers hundreds of software and hardware products for data acquisition and control, data analysis, and presentation. By utilising industry-standard computers, our virtual instrument products empower users in a wide variety of industries to easily automate their test, measurement, and industrial processes at afraction of the cost of traditional approaches.
|
||
Software
|
||
Our company is best known for our innovative software products. The National Instruments charter is to offer a software solution for every application, ranging from very simple to very sophisticated. We also span the needs of users, from advanced research to development, production, and service. Our flagship LabVIEW product, with its revolutionary, patented graphical programming technology, continues to be an industry leader. Additional software products, such as LabWindows/CVI, Component Works, Measure and VirtualBench, are chosen by users who prefer C programming, Visual Basic, Excel spreadsheets, and no programming at all, respectively.
|
||
Hardware
|
||
Our software products are complemented by our broad selection of hardware to connect computers to real-world signals and devices. We manufacture data acquisition hardware for portable, notebook, desktop, and industrial computers. These products, when combined with our software, can directly replace.a wide variety of traditional instruments at afraction of the cost. In 1996 we expanded our high-performance ESeries product line in PCI. ISA and PCMCIA form factors, shipped our first VXI data acquisition products, and added remote (long-distance) capabilities to our SCXI signal conditioning and data acquisition product line.
|
||
Our virtual instrumentation vision keeps us at the forefront of computer and instrumentation technology. National Instruments staff works actively with industry to promote international technological standards such as IEEE 488, PCMCIA, PCI, VXI plug&play, Windows 95/NT, and the Internet. More importantly, we integrate these technologies into innovative new products for our users.
|
||
,'All published circuit ideas that are not eligible for the prizes detailed here will earn their authors aminimum of £35 and up to £100.
|
||
|
||
NI4050 The NI 4050 is afull-feature digital multimeter (DMM) for hand-held and notebook computers with aType II PC Card (PCMCIA) slot. The NI 4050 features accurate 51/2digit DC voltage, true-rms AC voltage, and resistance (ohms) measurements. Its size, weight, and low power consumption make it ideal for portable measurements and data logging with hand-held and notebook computers.
|
||
• DC Measurements: 20mV to 250V DC; 20mA to 10A • AC Measurements: 20mV rrns to 250V nns; 20mA nns to 10A nns; • True rms, 20Hz to 251cHz • Up to 60 readings/s • UL Listed • 51/2 Digit Multimeter for PCMCIA
|
||
LabVIEW LabVIEW is ahighly productive graphical programming environment that combines easy-to-use graphical development with the flexibility of apowerful programming language. It offers an intuitive environment, tightly integrated with measurement hardware, for engineers and scientists to quickly produce solutions for data acquisition, data analysis, and data presentation.
|
||
• Graphical programming development environment • Rapid application development • Seamless integration with DAQ, GPIB, RS-232, and VXI • Full, open network connectivity • Built-in display and file I/O
|
||
|
||
National Instruments —computer-based measurement and automation
|
||
National Instruments, 11 Kingfisher Court, Hambridge Road, Newbury, Berkshire, RG14 551. Tel (01635 523545), Fax (01635) 524395 info.ukeni.com www.ni.com.
|
||
..)
|
||
|
||
CIRCUIT IDEAS
|
||
|
||
One-at-a-time phones
|
||
Normally, where two or more phone share asingle line, someone picking up another, when the first is in use, can overhear the other party. This circuit allows only one of the phones to be used at any given time.
|
||
One circuit must be connected in series with each phone. This idea relies on the fact that the off-hook line voltage is 48V. but
|
||
|
||
only 10V on-hook. Incoming calls will ring all phones. as the ringing voltage is 80V
|
||
RMS. /M Brassart
|
||
Saint-Laurent-Du -Var France
|
||
D68
|
||
In some countries, you are not allowed to connect any equipment that has not been formally approved by the service provider to telephone outlet -Ed.
|
||
|
||
2 Thyristors 2N5062
|
||
2 15V zener diodes
|
||
(D681
|
||
Connected in series with each phone on aline, this circuit permits only one to be used at atime.
|
||
|
||
Economical liquid level sensor needs just 7pA
|
||
3 to 15V
|
||
|
||
100p
|
||
|
||
/7177
|
||
|
||
Piezo sounder
|
||
|
||
(E9)
|
||
|
||
Low cost, long battery life and adjustable sensitivity are features of th's liquid level sensor circuit. If you want alogic-level output, tie pin 13 to tit,and omit components Aand 13.
|
||
|
||
This simple sensor circuit consumes only 71.1A at 3V supply, and is ideal for battery operation. There is no dc through the sensing electrodes, minimising corrosion.
|
||
Sensitivity may be adjusted for different electrode sizes and fluid conductivities by means of the 1001(12 potentiometer. The circuit's cost is considerably less than the LM183, which is in any case currently unavailable. David Tayler
|
||
Sheffield UK
|
||
E9
|
||
|
||
Ten year inde new upd te
|
||
Hard copies and floppy-disk databases both available
|
||
Whether as aPC data base or as hard copy, SoftCopy can supply acomplete index of Electronics World articles going back over the past nine years.
|
||
The computerised index of Electronics World magazine covers the nine years from 1988 to 1996, volumes 94 to 102 inclusive and is available now. It contains almost 2000 references to articles. circuit ideas and applications -including asynopsis for each.
|
||
The EW index data base is easy to use and very fast. It runs on any IBM or compatible PC with 512K ram and ahard disk.
|
||
The disk-based index price is still only £20 inclusive. Please specify whether you need 5.25in, 3.5in DD or 3.5in HD format. Existing users can obtain an upgrade for £15 by quoting their serial number with their order.
|
||
Photo copies of Electronics World articles from b issues are available at a flat rate of £3.50 per article, £1 per circuit idea, excluding postage.
|
||
Hard copy Electronics World index Indexes on paper for volumes 100,101, and 102 are available at £2 each, excluding postage.
|
||
|
||
TABLE OF CONTENTS
|
||
|
||
Applications Applications by description Applications by pad numbers Com an addresses
|
||
|
||
Books
|
||
|
||
Circuit Ideas
|
||
|
||
Information
|
||
|
||
Subject Index
|
||
|
||
Analogue Design
|
||
|
||
Audio
|
||
|
||
Avionics
|
||
|
||
Broadcast
|
||
|
||
Communications
|
||
|
||
Components
|
||
|
||
Computing
|
||
|
||
Consumer Electronics
|
||
|
||
Control Electronics
|
||
|
||
Digital & DSP Design
|
||
|
||
History
|
||
|
||
— .
|
||
|
||
The Electronics World SoftIndex runs from
|
||
|
||
January 1989 to May 1996 and contains
|
||
|
||
references to 1300 articles and 800 circuit ideas
|
||
|
||
There is aseparate author index with full cross
|
||
|
||
references Reprints can be obtained for all the
|
||
|
||
articles in this index -see the Information
|
||
|
||
section for more details For up to date
|
||
|
||
information about Electronics World see our
|
||
|
||
websrte at http
|
||
|
||
sperm co uk
|
||
|
||
1:1
|
||
|
||
"ur
|
||
|
||
ww.softcopy.co.uk
|
||
|
||
Ordering details
|
||
The EW index data base price of £20 includes UK postage and VAT. Add an extra £1 for overseas EC orders or £5 for non-EC overseas orders Postal charges on hard copy indexes and on photocopies are 50p UK, £1 for the rest of the EC or £2 worldwide. For enquires about photocopies etc please send an sae to SoftCopy Ltd. Send your orders to SoftCopy Ltd, 1Vineries Close, Cheltenham GL53 ONU. Cheques payable to SoftCopy Ltd, please allow 28 days for delivery.
|
||
e-mail at SoftCopy@compuserve.com, tel 01242 241455
|
||
|
||
736
|
||
|
||
ELECTRONICS WORLD September '2000
|
||
|
||
CIRCUIT IDEAS
|
||
|
||
Measuring femtofarads on traditional AC bridges
|
||
|
||
Ineeded to check the matching of two Inominally 1pF capacitors, but all Ihad was aMarconi Instruments TF868B universal
|
||
bridge having alowest capacitance range of
|
||
0-100pF. Icould have made atransformer bridge, but
|
||
this was not justifiable for the job in hand, given the extensive screening and construc-
|
||
tional work required. The possibility of using the AC source and tuned detector in the TF868B was then considered; ideally without any alterations. Bridge resolution would have
|
||
been adequate at 0.1 % at the top end of a range.
|
||
Figure 1shows the basic bridge circuit for
|
||
capacitance measurements; the earthing of one side of the detector allows three-terminal
|
||
capacitance measurement to exclude strays. These are either across the detector or across
|
||
C2+R i;so of insignificant effect at null. If the voltage across C2+R Iwere multiplied
|
||
by afactor of, say 10, then areduction in the unknown capacitor by afactor of 10 is needed to preserve bridge balance.
|
||
Amplification only need be applied to the voltage across the standard capacitor, since the magnified voltage is in phase with the
|
||
original voltage across the capacitor, preserv-
|
||
|
||
raRn2ge
|
||
|
||
resistor
|
||
|
||
to'
|
||
|
||
Unknown
|
||
|
||
ing phase balance to the detector, Fig. 2. No modifications are needed inside the TF868B.
|
||
Figure 3shows the first circuit tried; to give arange of 0-10pF. The signal on 'Hi' never exceeded 1.2V pk-pk, so an op-amp
|
||
with again of 10 could be used when driven from two 9V batteries in series; batteries were used to prevent earth loops and null offsets.
|
||
Op-amp /CIA is abuffer —not strictly necessary —and R5 protects the TL082 FET inputs against static build-up when the circuit
|
||
is disconnected. Components RI,R2 and C1gave adecou-
|
||
pled reference for the signal to swing about, R4 and R3 defining the gain. It worked as expected, giving asharp null with atest 2.2pF
|
||
capacitor at the 22pF dial reading. Figure 4showed the circuit tried to give 0-
|
||
lpF range —with aresolution of IfF at the top end; stray capacitances Ci and Cs2 are
|
||
shown. Iconsidered atransformer to be the easiest method for giving the voltage step-up needed. A tightly-coupled toroid transformer was found with the characteristics shown —
|
||
and aself-resonant frequency well above the IkHz of the bridge source.
|
||
Two op-amps — used as unity gain buffers
|
||
—were connected in parallel to give the peak
|
||
|
||
drive current of around 13mA. Individual and
|
||
|
||
differential DC offsets, giving inter-amplifier
|
||
|
||
and primary DC currents, were <1mV on the
|
||
|
||
device used; should this be thought aproblem
|
||
|
||
capacitive coupling from the outputs to the
|
||
|
||
transformer could be used at the risk of some
|
||
|
||
phase shift; adding series resistance would
|
||
|
||
also give significant phase shifts.
|
||
|
||
Supply current was around 11mA and the
|
||
|
||
circuit worked well. Nulled 'tan-delta' setting
|
||
|
||
was non-zero, due to phase shift from op-amp
|
||
|
||
output impedance and primary inductance,
|
||
|
||
but asharp capacitive null was obtained.
|
||
|
||
Output voltage from the transformer was
|
||
|
||
5120V pk-pk and at high impedance, but take
|
||
|
||
care to avoid electric shock. Hand-capaci-
|
||
|
||
tance effects were very significant and the
|
||
|
||
high voltage output of the transformer
|
||
|
||
secondary was placed at least 2inches away
|
||
|
||
from the `Lo' terminal of the bridge. Even so,
|
||
|
||
null readings of over 80fF were obtained, but
|
||
|
||
use of ametallic screen between the high-
|
||
|
||
voltage terminal and the 'Lo' terminal
|
||
|
||
reduced this further. Low battery voltage is
|
||
|
||
shown by adrifting null.
|
||
|
||
D. Sweetman
|
||
|
||
Surbiton
|
||
|
||
Surrey
|
||
|
||
D20
|
||
|
||
(D20c)
|
||
|
||
From batteries +18V
|
||
|
||
Fig. 3. An implementation of Fig. 2 that results in a range of 0-10pF.
|
||
|
||
TL082CP 1/10C x
|
||
|
||
AC source
|
||
|
||
Balance pot. R3
|
||
|
||
Standard cap.
|
||
tan-delta Ri C
|
||
|
||
(D20a)
|
||
|
||
PE
|
||
|
||
Fig. 1. Showing the basic bridge circuit for capacitance measurements.
|
||
|
||
raR n2gae resistor
|
||
|
||
,Lo ,1/10C x
|
||
|
||
Detector
|
||
|
||
AC source
|
||
|
||
Standard cap.
|
||
|
||
Balance pot. tan-delta
|
||
|
||
R3a
|
||
|
||
Ria C3a
|
||
|
||
(D20b)
|
||
|
||
PE
|
||
|
||
Fig. 2. Outline arrangement to extend the smallest range from 100pF maximum to 10pF maximum.
|
||
|
||
'Earth'
|
||
|
||
From batteries +9V
|
||
|
||
›; R9 >>10M
|
||
|
||
R7
|
||
:2k7 R6 10k yvy1,
|
||
|
||
OV From batteries
|
||
|
||
IC 2b
|
||
|
||
7
|
||
|
||
Winner of the National Instruments digital multimeter worth over £500
|
||
|
||
TL082CP
|
||
|
||
Fig. 4. Final circuit with aresolution
|
||
|
||
of 11F at the top end of its range and
|
||
|
||
1pF full scale.
|
||
|
||
IC 2a
|
||
2
|
||
|
||
T, ITcs,
|
||
|
||
TL082CP/ 1:100
|
||
|
||
ITcs0,10.
|
||
|
||
10 2k7 7 1 C2
|
||
|
||
R8
|
||
|
||
OV
|
||
|
||
From batteries
|
||
|
||
7mH:70H Primary inductance was
|
||
0.6pH with secondary short-circuited
|
||
|
||
(D20d)
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
CIRCUITS IDEAS
|
||
|
||
Simple charger for NiCd and lead acid batteries
|
||
|
||
£50 Winner
|
||
|
||
This circuit is suitable for charging and discharging — i.e. refreshing —NiCd and lead-acid batteries. Despite being simple, it also pro-
|
||
motes long battery life. Charging current /2 is constant. In
|
||
switch position 'NiCd' the current flows for aperiod of 20ms, deter-
|
||
mined by R7 and Ci.The next charge pulse will follow if the off-load voltage of the battery falls below
|
||
|
||
1.4V/cell.
|
||
Charging of NiCd cell with pulsed current has some advantages. Measuring the off-load voltage works well with old batteries having a higher internal resistance. The charging current used may be up to
|
||
the C capacity of the battery; this permits ashort charge time. On the other hand, the battery cannot be
|
||
overcharged by a20ms pulse.
|
||
|
||
+ 47011 •
|
||
|
||
24V
|
||
|
||
0-
|
||
|
||
V3 11 0.85mA
|
||
|
||
R9
|
||
|
||
1/VVN.,
|
||
|
||
IC3
|
||
|
||
100k
|
||
|
||
R3
|
||
|
||
6R8
|
||
|
||
12 02A
|
||
R8
|
||
|
||
(E19)
|
||
Start discharge
|
||
|
||
Charge P1 4k7
|
||
Discharge P2 4k7
|
||
R2 4k7
|
||
|
||
IC2A
|
||
|
||
1N4148 R4
|
||
6k8
|
||
|
||
1 k
|
||
1N4002
|
||
|
||
'Charge' green low current LED
|
||
|
||
R10 100k *MA,
|
||
|
||
R11 100k
|
||
|
||
VVVN.,
|
||
|
||
R6
|
||
|
||
13
|
||
|
||
1N4148
|
||
|
||
IC2B
|
||
|
||
• 47p
|
||
|
||
•
|
||
R12
|
||
|
||
Hi =Charge 1N4148
|
||
R5
|
||
|
||
4148
|
||
|
||
6k8 'Discharge' red low
|
||
current LED
|
||
|
||
3311
|
||
|
||
0.2A
|
||
|
||
2.5W
|
||
|
||
rue 100n
|
||
|
||
Tri BD139
|
||
|
||
Battery 8-cell NiCd C=250mAh
|
||
|
||
/7177
|
||
|
||
Analogue flop-flop
|
||
|
||
Discharge circuit
|
||
|
||
With experience, the flash rate of the green LED can indicate the state of charge of the battery. With new and fully charged batteries, the period between flashes is several seconds. Use of high current pulses up to C avoids the memory effect in NiCd cells.
|
||
The semi-automatic discharge circuit is optional. Discharge is initiated by the push button, and the red LED lights, discharging the battery to, for example, 0.9V/cell. The circuit then automatically switches to the charge function.
|
||
In switch position 'Pb' for lead-acid batteries, aconstant charge current is employed, until the battery voltage reaches, for example, 2.4V/cell. Current is then reduced and the green LED fades, indicating achange to constant voltage operation.
|
||
For correct operation, good battery contacts are required. In the event of asupply interruption, the battery will not be discharged. Heinz Zanke D-10829 Berlin Germany El 9
|
||
This charger uses pulse charging for NiCds, constant current/constant voltage for lead acid. Supply voltage needs to be 3.4 Vhigher than the highest expected battery voltage. Current 1, is about amilliamp. Resistor R3 is 1.35 V/12.For lead-acid cells, VIis between 2.25 and 2.5 Vper cell and 12 is less than C. For NiCd alternatives, VIis 1.4 Vper cell while V2 is between 0.9 and 1.1V per cell. Current 12 is roughly equal to both 13 and C.
|
||
|
||
Jingle softner
|
||
W hen v, ¡itching TV, have you ever been annoyed by the increase in sound level during the advertisements? One way to deal with it is to press the mute key of the remote control unit. Another way is to plug this little unit into the Scart/Peritel socket at the back of your TV.
|
||
The schematic is given Fig. 1. The heart of this circuit is the MC3340P from Motorola, which is avoltagecontrolled attenuator. This circuit offers a80dB range attenuation when driven with a3.5V control voltage range, but in order to obtain areasonable THD (distortion) of less than 3%, the attenuatioa range must be limited to 40dB.
|
||
The input signal is reduced by afactor of 2by resistors RIand R2 because the maximum input voltage of /CIis 500mV. The signal attenuated by ICIappears at point B. The value of C2 is not critical and limits the bandpass to
|
||
|
||
20kHz. Capacitors Ciand C3 DC block ICE.Values given for R3 and C3produce alow-frequency cut-off close to 10Hz.
|
||
The signal at point B is amplified by IC2a and P1 permits the sound level to be adjusted as required. At point B, the signal follows asecond path and is amplified
|
||
by ./C28. R8 protects the output of /C2b. Components C'4, Cs, DIand D2 form adoubler-rectifi-
|
||
er, producing at point D ameasure of the average value for the signal amplitude. The value of R9 has been chosen to give atime constant big enough to avoid low frequency distortion. At point D, the voltage is equal to the
|
||
average value of the signal amplitude at point C. Op-amp 1C3acts as avoltage follower and R10 and C8
|
||
form an additional low-pass filter. The time constant is fixed at 50ms.
|
||
Voltage at point Econtrols the attenuation value of /CI.
|
||
|
||
738
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
CIRCUIT IDEAS
|
||
|
||
21(2
|
||
|
||
PI 0
|
||
TC6 22pF
|
||
|
||
1C3 Cf1311SE
|
||
|
||
ONO
|
||
|
||
Input
|
||
|
||
SCART-P ug Output
|
||
|
||
End
|
||
|
||
TOM
|
||
|
||
ONO 0
|
||
[il P111 47K
|
||
|
||
1N 4148 02
|
||
|
||
C4
|
||
F4-
|
||
22),
|
||
|
||
C5 22pF
|
||
|
||
E DI
|
||
|
||
1N41 42
|
||
|
||
Re
|
||
0
|
||
isoc
|
||
—
|
||
|
||
TL872111 1C2B
|
||
|
||
_
|
||
P7 1=1
|
||
561C
|
||
|
||
n R6
|
||
U 4k 7
|
||
|
||
UCC IC2
|
||
|
||
ONO 15E
|
||
O'g
|
||
i7ta,F-.FT—.--P= l 1
|
||
TORNCB
|
||
Cif
|
||
ORD
|
||
|
||
1OpF +
|
||
|
||
UCc
|
||
|
||
Ctrl
|
||
|
||
Uout
|
||
|
||
ICI
|
||
|
||
-
|
||
|
||
-5.
|
||
|
||
11C33111P
|
||
|
||
C3 476 nF
|
||
|
||
Uin 8N0 Po
|
||
|
||
1C2 4711 pF
|
||
|
||
-I3
|
||
L 47K
|
||
|
||
n 114 U 1K2
|
||
|
||
19 OUT
|
||
|
||
CI é ISSN
|
||
|
||
GNO
|
||
7014.08
|
||
|
||
C14 lOSN
|
||
|
||
C11 10011
|
||
|
||
ICS 791.118 'AD UT IN
|
||
|
||
de IBON
|
||
|
||
+12U C16 470pF
|
||
• SU CI 7 47OpF
|
||
-I 2U
|
||
|
||
C2111 1
|
||
TL072P 1KS
|
||
P5
|
||
|
||
Fig. 1. Circuit of advert sound leveller.
|
||
O
|
||
IIIK pl
|
||
|
||
ONO
|
||
|
||
When the sound becomes louder, voltage at D increases, increasing the attenuation. Thus the sound level at B remains constant.
|
||
The functional block diagram is given in Fig. 2and the attenuation curve of the MC3340 in Fig. 3. An 8V supply is used, so the attenuation curve gives a40dBN attenuation factor for control voltages greater than 2V.
|
||
Gain variation of the device can be derived from the curve,
|
||
G =—40 x(V, —2) =20 log
|
||
|
||
Static gain for /CIis 13dB and amplification is 4.5x. When V, is under 2V, /C i's amplification value is close
|
||
to 4and Vb is 4xlia.As Ve=1/cy„,,,x) and V, is 13xVb, you can work out, Ve=13x4.5x1/„(,„„,)=58xV,",„,).
|
||
When V, is less than 2V, Va(„, )is less than 35mV and )is less than 70mV (50mV RMS). Thus, when Vin
|
||
is under 50mV RMS, the circuit doesn't limit and the value of Vf is given by the linear expression,
|
||
Vf=0.5x4.5x2.25xVin=5xV„
|
||
Gain is I4dB. When V is greater than 50mV RMS, V, increases in
|
||
order to maintain VI,at the same value. Voltage V1 keeps its former value, Vf=5xVin=250mV RMS. Voltage V, can be adjusted between 0and 250 mV RMS.
|
||
Note that if another value of the starting point for limitation, currently 50mV RMS, is needed, this can be achieved by changing the values of R7 and/or R6,
|
||
|
||
R, R9
|
||
|
||
2000
|
||
4.5x 0.5 xy„, Rms ,x1.14
|
||
|
||
1
|
||
|
||
M Terrade 63100 Clermont-Ferrand France D51
|
||
|
||
Rectification
|
||
Low -pass filter
|
||
•.11c•ex
|
||
|
||
o Amplification 4—
|
||
A.13 G.+ 22 dB
|
||
|
||
Fuctionnal bloc enema
|
||
|
||
For to ar3343 tat• 13 -MO .(17.2)1
|
||
45 Ault -10-(7m.
|
||
|
||
0.10 V•in lulu
|
||
|
||
G
|
||
|
||
Level edema:xi
|
||
A . 1/2 G. -6dB
|
||
|
||
0 Gain variation >
|
||
Alto 10". G = 0to -8C4B
|
||
|
||
Internal • amplification
|
||
A.4 5
|
||
|
||
Amplification A.2 25
|
||
|
||
1.1C3340
|
||
Fig. 2. Block diagram of advert sound leveller.
|
||
|
||
Level erkstment
|
||
A to 1
|
||
|
||
ATTENUATION (dB)
|
||
|
||
Attenuation versus DC control voltage u
|
||
|
||
Vcc =
|
||
|
||
Vcc =
|
||
|
||
Vcc =
|
||
|
||
20
|
||
|
||
8Vd e
|
||
|
||
12Vde
|
||
|
||
16Vdc
|
||
|
||
40
|
||
|
||
60
|
||
|
||
80
|
||
|
||
2
|
||
|
||
3
|
||
|
||
4
|
||
|
||
5
|
||
|
||
6
|
||
|
||
CONTROL VOLTAGE (V)
|
||
|
||
Fig. 3. Attenuation characteristic of Motorola MC3340
|
||
|
||
September 2000 ELECTRONICS WORLD
|
||
|
||
739
|
||
|
||
CIRCUIT IDEAS
|
||
|
||
Circuit simulates glitches
|
||
|
||
ircult Fig. 1a) can he used to simulate glitches and waveforms encountered in electronic circuits during operation. Glitches can arise due to various causes such as bouncing of mechanical switch contacts, switching transients, timing mismatch, electromagnetic interference, etc. Digital logic can interpret glitches as valid logic level transitions and erroneous operation can
|
||
OCCUr.
|
||
To avoid such spurious operation, glitch detectors and glitch elimination
|
||
|
||
glitches is needed. Ihe circuit described here can be used to produce such aglitch-simulating test waveform.
|
||
The circuit consists of a556 dual timer, both halves of which are configured as astable multivibrators.
|
||
The frequency of the A half is kept very low, at around 1Hz. On the other hand, the frequency of the second half, B, is kept high so that Bproduces narrow short-duration pulses.
|
||
Output of A is connected to the reset input of B so that when the
|
||
|
||
This generator simulates glitches,
|
||
contact bounce,
|
||
etc., as an aid to making sure that a
|
||
circuit is glitch proof.
|
||
|
||
+5V
|
||
|
||
4M7
|
||
|
||
9
|
||
|
||
3k3
|
||
|
||
(D15)
|
||
|
||
,G„ich fry waveforms
|
||
(015b)
|
||
techniques are used. Nonetheless, glitches find away into digital circuits and false operations do occur in some situations.
|
||
To test and validate aglitch detector or aglitch eliminator, or even a circuit designed to be immune to glitches, atest circuit that simulates
|
||
|
||
output of A is high, the astable B oscillates and when the output of A is low, the reset input of B is kept
|
||
low and it does not oscillate. The duty-cycle of the output of B
|
||
can be adjusted by varying the resistor R4. Waveforms involved are shown in Fig. 1b). Output at
|
||
point Y consists of asequence of short-duration pulses coming in
|
||
bursts and this can be used to test logic circuits. Output at Y is differentiated by aC-R differentiator and rectified by diode D to get
|
||
|
||
positive going spikes at point Z. The output of the differentiator can
|
||
also be used to test the immunity of a digital logic circuit to voltage spike type of glitches. Note that the reset function is asynchronous, so that R4 can be set to make the last pulse in a train very short or glitch like.
|
||
Frequencies of the astable multivibrators are given by,
|
||
1.44
|
||
|
||
and, 1.44
|
||
f» = (R3+2R )c
|
||
|
||
Duty-cycle of the astable B is given
|
||
|
||
by,
|
||
|
||
w =
|
||
|
||
124
|
||
|
||
(R, +2R4)
|
||
|
||
To simulate different types of glitches, the duty-cycle can be altered. For example, to simulate contact bounce, you can make waround 10ms.
|
||
Making R4 variable will enable change of pulse-width as required. The time-constant of the differentiator should be chosen such that RC<T/10 where Rand Care the
|
||
values of the differentiator's resistor and capacitor and Tis the time period of the input waveform of the differentiator i.e., at Y.
|
||
Since the circuit is quite simple, it can be packaged in the form of a handy testing tool. Usage of alowpower timer such as XR-L556, or equivalent, will enable operation on batteries.
|
||
V. Lakshminarayanan Bangalore India D15
|
||
|
||
£50 Winner
|
||
|
||
PC controlled bipolar stepper motor
|
||
|
||
APC can control the speed and direction of abipolar, i.e. twophase, stepper motor, in asimple
|
||
way as described below. Circuit Fig. 1interfaces abipolar
|
||
stepper-motor to the parallel LPT
|
||
port of an IBM-compatible PC. It consists of complimentary transistors connected in bridges. One bridge is required for each phase winding of the stepper
|
||
motor.
|
||
Each bridge transistor should be installed on 5W rated heat sink. Diodes in each bridge are used to
|
||
provide free-wheeling action. Two 2N2222-type transistors interface
|
||
|
||
each bridge to the parallel port of the PC.
|
||
Data bits Do and DIon pins 2
|
||
and 3of the parallel port, are used to drive abridge circuit. Bits D2 and D3, pins 3and 4, drive the second bridge. Pin 25 of the parallel port connects to the ground of the bridge power supply.
|
||
Manufacturers data on a3.6V, 4A/phase, 1.8°, two-phase stepper motor is provided in Fig. 2. A
|
||
power-supply design, capable of driving two similar motors is provided in Fig. 3.
|
||
Figure 4 gives the data sequence
|
||
required at the parallel port to
|
||
|
||
drive the stepper motor in one direction. When alow on data bit Do and ahigh on data bit DIis sent, this switches transistors Tr1.3 on.
|
||
The result is acurrent flow through the motor's R-Y phase in one direction. When ahigh on data bit Do and alow on data bit Diis sent this switches transistor Tr2 and transistor Tr4 on. The result is acurrent flow through the motor's R-Y phase in the opposite direction.
|
||
Continued on page 745...
|
||
|
||
740
|
||
|
||
ELECTRONICS WORLD September 2000
|
||
|
||
Visit our website I THE ORIGINAL SURPLUS WONDERLAND!
|
||
|
||
www.distel.co.uk
|
||
|
||
THIS MONTH'S SELECTION FROM OUR VAST EVER CHANGING STOCKS
|
||
|
||
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|
||
|
||
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||
|
||
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|
||
|
||
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|
||
|
||
Converts your colour monitor Into aQUALITY COLOUR TV!!
|
||
TV SOUND &
|
||
VIDEO TUNER
|
||
CABLE COMPATIBLE
|
||
|
||
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|
||
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||
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|
||
|
||
Superb quality 6foot 40U Virtually New, Ultra Smart
|
||
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|
||
Top quality 19" rack cabinets made in UK by Optima Enclosures Ltd. Units feature
|
||
|
||
designer, smoked acrylic lockable front door,
|
||
|
||
One of the highest specification The TELEBOX is an attractive hilly cased mans powered unit, ccntahing at monitors you will ever see - etdrones ready to plug into ahost of vdeo mentors or AV equioment istich
|
||
|
||
full height lockable half louvered back door and louvered removable side panels. Fully
|
||
|
||
are fitted wIth acomposite video or SCART rout. The composite vice° output
|
||
At this price -Don't miss it!! an also plug directly into most vdeo recorders, alowing receptron ol TV chan-
|
||
nets not normally receivable on most television receivers' (TELEBOX MB). Push button oontrols on the front panel allow reception of 8hey tuneable 'off an UHF colour termite«, channels. TELEBOX MB covers vritually al televison kequences VHF and UHF including the HYPERBAND as used by most cabie TV operators. Ideal fa desktop computer video systems 8PIP (picture ri picture) setups. For complete compatblity -even for mentors without sound -an ntegral 4wan audio amplifier and law level Hi Fi audio output are provided as stanciard Brand new -fully guaranteed.
|
||
|
||
Mitsubishi FA3415ETKL 14" SVGA Multisync colour monitor with fine 028 dot pitch tube and resolution of 1024 x768. A varety or inputs allows ccnnecticn to ahost oh computers ncludng BM PCs in CG", EGA VGA & SVGA modes, BBC, COMMODORE (including Amiga 1200), ARCHSVIEDES and APPLE Many features: Etched faceplate. tee sivitchng and LOW RADIATION MPR
|
||
specification. Fully guaranteed, n EXCELLENT little
|
||
|
||
adjustable internal fixing struts, ready punched for any configuration of equipment mounting ,plus ready mounted integral 12 way 13 amp socket switched mains distribution strip make
|
||
|
||
these racks some of the most versatile we have ever sold. Racks may be stacked side by side and therefore require only two side panels to stand singly or in multiple bays.
|
||
|
||
Overall dimensions are: 77W H x32W ID x22* W. Order as:
|
||
|
||
OPT Rack 1Complete with removable side panels. £345.00 (G)
|
||
|
||
OPT Rack 2Rack. Less side panels
|
||
|
||
£245.00 IG!
|
||
|
||
TELEBOX ST for composite video input type monitors
|
||
|
||
£36.95
|
||
|
||
TELEBOX STL as ST but fitted with integral speaker
|
||
|
||
£39.50
|
||
|
||
TELEBOX MB Multiband VHF/UHF/Cable/Hyperband tuner £69.95
|
||
|
||
used careen. Tilt &Swivel Base £4.75
|
||
|
||
Only £119 (n pAOrrreesrvee.A
|
||
|
||
VGA cable for IBM PC Included.
|
||
|
||
Over 1000 racks, shelves, accessories 19" 22" & 24" wide 3to 46 U high.
|
||
|
||
For overseas PAL versions state 5.5 or 6mHz sound specification. 'For cable /hyperband signal reception Telebox MB should be con-
|
||
|
||
External (*Wes for other types of computers available -CALL
|
||
|
||
Available from stock!!
|
||
|
||
nected tg acable type service. Shipping on all Telebox's, code (B)
|
||
|
||
Ex demo 17" 0.28 SVGA Mitsubishi Diamond Pro
|
||
|
||
State of the art PAL (UK spec) UHF TV tuner module
|
||
|
||
monitors, Full multisync etc.
|
||
|
||
32U -High Quality -All steel RakCab
|
||
|
||
.with composite 1V pp video & RICAN hi ti stereo sound
|
||
|
||
Outputs. Micro electronics all on one small PCB only 73 x160
|
||
|
||
. 52 mm enable full tuning control via a simple 3 wire link to an
|
||
|
||
IBM pc type computer. Supplied complete with simple working pro-
|
||
|
||
gram and documentation. BRAND NEW -Order
|
||
|
||
asRewquoior.es
|
||
|
||
+12OVnl&y+£459V.D95C
|
||
|
||
to
|
||
|
||
operate. code (B)
|
||
|
||
See vAvw.dishel.co.uk/data_my00.htm for picture +full details
|
||
|
||
Full 90 day guarantee. Only £199.00 (E)
|
||
Just In -MicrovItec 20" VGA (800 x600 res.) colour monitors. Good SH condition-from £299 -CALL for Into
|
||
PHILIPS HCS35 (same style as CM8833) attractively styled 14" colour monitor with Deb RGB and standard composite 15.625 Khz video inputs via SCART socket and separate phono jacks.
|
||
|
||
Made by Eurocraft Enclosures Ltd to the highest possible spec, rack features all steel construction with removable side, front and back doors. Front and back doors are hinged for easy access and all are lockable with five secure 5 lever barrel locks. The front door is constructed of double walled steel with a 'designer style' smoked acrylic front panel to
|
||
|
||
FLOPPY DISK DRIVES 21/2"-8"
|
||
|
||
Integral audio power amp and speaker for all audio visual uses. enable status indicators to be seen through the Will connect direct to Amiga and Atari BBC computers. Ideal for all panel, yet remain unobtrusive. Internally the rack
|
||
|
||
All units (unless stated) are BRAND NEW or removed from often brand new equipment and are fully tested, aligned and shipped to you with a full 90 day guarantee. Call or see our web site www.distel.co.uk for over 2000 unlisted drives for spares or repair.
|
||
|
||
31/2 "Mitsubishi MF355C-L. 1.4 Meg. Laptops only
|
||
|
||
£25.95(B)
|
||
|
||
31/2 "Mitsubishi MF355C-D. 1.4 Meg. Non laptop
|
||
|
||
£18.95(B)
|
||
|
||
51/4 "Teac FD-55GFR 1.2 Meg (for IBM pes) RFE
|
||
|
||
£18.95(B)
|
||
|
||
51/4 "Teac FD-55F-03-U 720K 40/80 (for BBC's etc) RFE £29.95(B)
|
||
|
||
51/4 "BRAND NEW Mitsubishi MF501B 360K
|
||
|
||
£22.95(B)
|
||
|
||
Table top case with integral PSU for HH 514' Floppy /HD £29.95(B)
|
||
|
||
8" Shugart 80W801 8' SS refurbished 8 tested
|
||
|
||
£210.00(E)
|
||
|
||
8 Shugart 810 8 SS HH Brand New
|
||
|
||
£195.00(E)
|
||
|
||
8" Shugart 851 8' double sided refurbished & tested
|
||
|
||
£260.00(E)
|
||
|
||
8" Mitsubishi M2894-63 double sided NEW
|
||
|
||
£295.00(E)
|
||
|
||
8" Mitsubishi M2896-63-02U DS slimline NEW
|
||
|
||
£295.00(E)
|
||
|
||
Dual 8" cased drives with integral power supply 2Mb
|
||
|
||
£499.00(E)
|
||
|
||
HARD DISK DRIVES 21/ 2 "-14"
|
||
|
||
214' TOSHIBA MK1002MAV 1.1Gb laptop(12.5 mm H) New £79.95
|
||
|
||
214* TOSHIBA MK2101MAN 2.16 Gb laptop (19 mm H) New £89.50
|
||
|
||
21/2 "TOSHIBA MK4309MAT 4.3Gb laptop (8.2 mm H) New £105.00
|
||
|
||
214' TOSHIBAMK6409MAV ".i.1Gb laptop (12.7 mm H) New 190.00
|
||
|
||
2W to 31/2 "conversion kit fcr Pc's, complete with connectors £14.95
|
||
|
||
3W FUJI FK-309-26 20mb MFM I/F RFE
|
||
|
||
£59.95
|
||
|
||
3W CONNER CP3024 20 mb IDE I/F (or equiv.) RFE
|
||
|
||
£59.95
|
||
|
||
314' CONNER CP3044 40 mb IDE I/F (or equiv.) RFE
|
||
|
||
£69.00
|
||
|
||
3W QUANTUM 40S Prodri ve 42mb SCSI I/F, New RFE £49.00
|
||
|
||
5W MINISCRIBE 3425 20mb MFM I/F (or equiv.) RFE
|
||
|
||
£49.95
|
||
|
||
5)4' SEAGATE ST-238R 30 mb RLL I/F Refurb
|
||
|
||
£69.95
|
||
|
||
5W CDC 94205-51 40mb HH MFM I/F RFE tested
|
||
|
||
£69.95
|
||
|
||
514' HP 97548 850 Mb SCSI RFE tested
|
||
|
||
video monitoring /security applications with direct connection
|
||
|
||
to most colour cameras. High quality with many features such as
|
||
|
||
front concealed flap controls, VCR correction button etc. Good
|
||
|
||
used condition-fully tested -guaranteed o n ly rag, nn
|
||
|
||
Dimensions: W14' xH1214" x15W D.
|
||
|
||
(E)
|
||
|
||
PHIUPS HCS31 Ultra compact 9" colour video monitor with stan-
|
||
|
||
dard compost* 15.625 Khz video input via SCART socket. Ideal
|
||
|
||
for all monitoring /security applications. High quality, ex-equipment
|
||
|
||
fully tested & guaranteed (possible minor screen bums). In attrac-
|
||
|
||
tive square black plastic case 240 V AC mains powered.
|
||
|
||
measuring
|
||
|
||
W1O0n'lxyH1£07' 9x.10301/2 "(DD).
|
||
|
||
KME 10" 15M10009 high definition colour monitors with 0.28' dot
|
||
|
||
pitch. Superb clarity and modern styling.............
|
||
|
||
Operates from any 15.625 khz sync RGB video .
|
||
|
||
source, with RGB analog and composite sync
|
||
|
||
such as Atari, Commodore Amiga, Acorn
|
||
|
||
Archimedes & BBC. Measures only 1314' x 12' x
|
||
|
||
11". Good used condition.
|
||
|
||
Only £125 (E)
|
||
|
||
20" 22" and 26" AV SPECIALS
|
||
Superbly made UK manufacture. PIL all solid state colour monitors, complete with composite video & optional sound input. Attractive teak style case. Perfect for Schools, Shops, Disco, Clubs, etc.In EXCELLENT little used condition with full 90 day guarantee.
|
||
20"....£135 22"....£155 26"....£185(F)
|
||
We probably have the largest range of video monitors in Europe, All sizes and types from 4' to 42" call for info.
|
||
|
||
DC POWER SUPPLIES
|
||
|
||
features fully slotted reinforced vertical fixing members to take the heaviest of 19" rack equipment. The two movable vertical fixing struts (extras available) are pre punched for standard 'cage nuts'. A mains distribution panel internally mounted to the bottom rear, provides 8xIEC 3 pin Euro sockets and 1x 13 amp 3 pin switched utility socket. Overall ventilation is provided by fully louvered back door and double skinned top section with top and side louvres. The top panel may be removed for fitting of integral fans to the sub plate etc. Other features include: fitted castors and floor levelers, prepunched utility panel at lower rear for cable /connector access etc. Supplied in excellent, slightly used condition with keys. Colour Royal blue. External dimensions mm=1625H x6350 x603 W. (64" H x25" D x23'4" W )
|
||
Sold at LESS than athird of makers price Il
|
||
A superb buy at only £245.00 (G)
|
||
42U version of the above only £345 -CALL
|
||
12V BATTERY SCOOP -60% off!!
|
||
A special bulk purchase from acancelled export order brings you the most amazing savings on these ultra high spec 12v DC 14 Ah rechargeable batteries. Made by Hawker Energy Ltd, type SBS15 featuring pure lead plates which offer afar superior shelf & guaranteed 15 year service life. Fully BT & BS6290 approved. Supplied BRAND NEW and boxed. Dimensions 200 wide, 137 high, 77 deep. M6 bolt terminals. Fully guaranteed. Current makers price over £70
|
||
each Our Price £5 each (C)or 4for £99 (E)
|
||
|
||
514' HP C3010 2Gbyte SCSI differential RFE tested
|
||
|
||
£195.00
|
||
|
||
8 NEC D2246 85 Mb SMD interface. New
|
||
|
||
£199.00
|
||
|
||
8' FUJITSU M2322K 160Mb SMD I/F RFE tested
|
||
|
||
£195.00
|
||
|
||
8' FUJITSU M2392K 2Gb SMD I/F RFE tested
|
||
|
||
£345.00
|
||
|
||
Many other drives in stock -Shipping on all drives is code (Cl)
|
||
|
||
Virtually every type of power supply you can imagine. Over 10,0 0 0 Power Supplies Ex Stock
|
||
Call or see our web site.
|
||
|
||
RELAYS -200,000 FROM STOCK
|
||
Save tiff's by choosing your next relay from our Massive Stocks covering types such as Military, Octal, Cradle, Hermetically Sealed, Continental, Contactors, Time Delay, Reed, Mercury Wetted, Solid
|
||
|
||
TEST EQUIPMENT & SPECIAL INTEREST ITEMS
|
||
|
||
State, Printed Circuit Mounting, etc. ,CALL or see our web site www.distel.co.uk for more information. Many obsolete types from
|
||
|
||
MITS.J.FA3445ETKL 14" Industrial spec SVGA monitors FARNELL 0-60V DC 0 50 Amps. bench Power Supplies FARNELL AP3080 0-30V DC 080 Amps, bench Suppy lkW to 400 kW -400 Hz 3phase power sources -ex stock IBM 8230 Type 1. Token ring base unit driver Wayne Kerr RA200 Audio frequency response analyser IBM 53F5501 Token Ring ICS 20 port lobe modules IBM MAU Token ring distribution panel 8228-23-5050N
|
||
|
||
£245 £995 £1850 £P0A £760 £2500 £750
|
||
£95
|
||
|
||
HP6030A 0-200V DC 0 17 Amps bench power supply
|
||
|
||
£1950
|
||
|
||
Intel SBC 486/125C08 Enhanced Multibus (MSA) New
|
||
|
||
£1150
|
||
|
||
Nikon HFX-11 (Ephiphot) exposure control unit
|
||
|
||
£1450
|
||
|
||
PHILIPS PM5518 pro. TV signal generator
|
||
|
||
£1250
|
||
|
||
Motorola VME Bus Boards & Components List. SAE /CALL £P0A
|
||
|
||
Trio 0-18 vdc linear, metered 30 amp bench PSU. New
|
||
|
||
£550
|
||
|
||
Fujitsu M3041R 600 LPM high speed band printer
|
||
|
||
£1950
|
||
|
||
Fujitsu M30410 600 LPM printer with network interface
|
||
|
||
£1250
|
||
|
||
stock. Save fTa's
|
||
|
||
COLOUR CCD CAMERAS
|
||
Undoubtedly a miracle of modern technology 8.
|
||
|
||
aINrt
|
||
|
||
our special buying power !A quality product fea-
|
||
|
||
turing a fully cased COLOUR CCD camera at a
|
||
|
||
give away price !Unit features full autolight sensing for
|
||
|
||
use in low light 8 high light
|
||
|
||
AIM 501 Low distortion Oscillator 9Hz to 330Khz, IEEE
|
||
|
||
£550 Perkin Elmer 299B Infrared spectrophotometer
|
||
|
||
£500
|
||
|
||
applications. A 10 mm fixed focus
|
||
|
||
ALLGON 8360.11805-1880 MHz hybrid power combiners
|
||
|
||
£250 Perkin Elmer 597 Infrared spectrophotometer
|
||
|
||
£3500
|
||
|
||
wide angle lens gives excellent focus
|
||
|
||
Trend DSA 274 Data Analyser with G703(2M) 64 i/o
|
||
|
||
£P0A VG Electronics 1035 TELETEXT Decoding Margin Meter £3250
|
||
|
||
and resolution from close up to long
|
||
|
||
Marconi 6310 Programmable 2to 22 GHz sweep generator £6500 Ligh1Band 60 output high spec 2u rack mount Video VDA's £495
|
||
|
||
range. The composite video output will
|
||
|
||
Marconi 2022C 10KHz-1GHz RF signal generator
|
||
|
||
£1550 Sekonic SD 150H 18 channel digital Hybrid chart recorder £1995
|
||
|
||
connect to any composite monitor or TV
|
||
|
||
Marconi 2030 opt 03 10KHz-1.3 GHz signal generator,New £4995
|
||
|
||
HP1650B Logic Analyser
|
||
|
||
£3750
|
||
|
||
HP3781A Pattern generator & HP3782A Error Detector
|
||
|
||
£P0A
|
||
|
||
HP6621A Dual Programmable GPIB PSU 0-7 V 160 watts £1800
|
||
|
||
HP6264 Rack mount variable 0-20V 0 20A metered PSU
|
||
|
||
£675
|
||
|
||
HP54121A DC to 22 GHz four channel test set
|
||
|
||
£P0A
|
||
|
||
HP8130A opt 020 300 MHz pulse generator. GPIB etc
|
||
|
||
£7900
|
||
|
||
B&K 2633 Microphone pre amp
|
||
|
||
£300
|
||
|
||
Taylor Hobson Tallysurf amplifier /recorder
|
||
|
||
£750
|
||
|
||
ADC SS200 Carbon dioxide gas detector /monitor
|
||
|
||
£1450
|
||
|
||
BBC AM20/3 PPM Meter (Ernest Turner) +drive electronics £75
|
||
|
||
ANRITSU 9654A Optical DC-2.5G/b waveform monitor
|
||
|
||
£5650
|
||
|
||
ANRITSU MS9001B1 0.6-1.7 uM optical spectrum analyser £P0A
|
||
|
||
ANRITSU ML93A optical power meter
|
||
|
||
£990
|
||
|
||
(via SCART socket) and most video recorders. Unit runs from 12V DC so ideal for security & portable applications where mains power not available. Overall dimensions 66 mm wide x 117 deep x 43 high. Supplied BRAND NEW & fully guaranteed with user data, 100's of applications including Security. Home Video, Web TV, Web Cams etc. etc.
|
||
|
||
HP Al, AO 8pen HPGL high speed drum plotters -from HP DRAFTMASTER 18pen high speed plotter
|
||
|
||
£550 £750
|
||
|
||
ANRITSU Fibre optic characteristic test set R&S FTDZ Dual sound unit
|
||
|
||
£P0A £650
|
||
|
||
Web ref =1.833
|
||
|
||
ONLY £99.00 or 2 for £180.00 (13)
|
||
|
||
EG+G Brookdeal 95035C Precision lock in amp View Eng. Mod 1200 computerised inspection system
|
||
|
||
£1800 £P0A
|
||
|
||
R&S SBUF-E1 Vision modulator WILTRON 6630B 12.4 /20GHz RF sweep generator
|
||
|
||
£775 £5750
|
||
|
||
SOFTWARE SPECIALS
|
||
|
||
Sony DXC-3000A High quality CCD colour TV camera Keithley 590 CV capacitor /voltage analyser Racal ICR40 dual 40 channel voice recorder system
|
||
|
||
£995 £P0A £3750
|
||
|
||
TEK 2445 150 MHz 4trace oscilloscope TEK 2465 300 Mhz 300 MHz oscilloscope rack mount TEK TDS380 400Mhz digital realtime +disk drive. FFT etc
|
||
|
||
£1250 £1955 £2900
|
||
|
||
NT4 WorkStation, complete with service pack 3 and licence -OEM packaged. ONLY £89.00 (13)
|
||
|
||
Fiskers 45KVA 3ph On Line UPS -New batteries
|
||
|
||
£9500 TEK TDS524A 500Mhz digital reattime +colour display etc £5100 ENCARTA 95 -CDROM, Not the latest -but at this price! £7.95
|
||
|
||
Emerson AP130 2.5KVA industrial spec.UPS Mann Tally MT645 High speed line printer
|
||
|
||
£2100 f2200
|
||
|
||
HP3585A Opt 907 20Hz to 40 Mhz spectrum analyser
|
||
|
||
£3950 DOS 5.0 on 354" disks with concise books cJw °Basic
|
||
|
||
£14.95
|
||
|
||
PHILIPS PW1730/10 60KV XRAY generator & accessories £P0A Windows for Workgroups 3.11+ Dos 6.22 on 3.5" disks £55.00
|
||
|
||
Intel SBC 48611335E Multibus 486 system. 8Mb Ram Siemens K4400 64Kb to 140Mb demux analyser
|
||
DisTEL on the web !I
|
||
|
||
£945 CLAUDE LYONS 12A 240V single phase auto, volt. regs
|
||
|
||
£325 Wordperfect 6for DOS supplied on 314" disks with manual £24.95
|
||
|
||
£2950 CLAUDE LYONS 100A 240/415V 3phase auto, volt. regs £2900
|
||
|
||
shipping charges for software is code B
|
||
|
||
-Over 16,000,000 Items from stock -www.distel.co.uk
|
||
|
||
• • •
|
||
•
|
||
• • • •
|
||
|
||
• • •
|
||
|
||
• ••
|
||
|
||
• • •
|
||
|
||
•
|
||
|
||
•
|
||
|
||
• ••
|
||
|
||
• •• •
|
||
|
||
."*.
|
||
|
||
•
|
||
|
||
•
|
||
|
||
•
|
||
|
||
•
|
||
|
||
•
|
||
|
||
•
|
||
|
||
•
|
||
|
||
• ••
|
||
|
||
•
|
||
|
||
-ELECTRONI(S-
|
||
|
||
real OD
|
||
|
||
EST Yf 6
|
||
|
||
ALL MAIL TO
|
||
Dept WW, 29/35 Osborne Rd Thornton Heath
|
||
Surrey CR7 8PD Open Mon -Fri 9.00 -5:30
|
||
|
||
LONDON SHOP
|
||
Open Mon -Sat 9:00 -5:30 215 Whitehorse Lane South Norwood
|
||
On 68A Rut Rout* Pe. Thornton Heath a. Selhurst Park SR Rail Stations
|
||
|
||
DISTEL©
|
||
Visit our web site www.distel.co.uk
|
||
email =admintadistel.co.uk
|
||
|
||
ALL
|
||
|
||
ENQUIRIES
|
||
|
||
0208 653 3333
|
||
|
||
FAX 0208 653 8888
|
||
|
||
All prices for UK Manland. UK customers add 17 5°. VAT to TOTAL order arnount. Minimum order £10. Bona Fide account orders accepted horn Government Schack, Universities and Local Authorites -minimum account order £50. Cheques over £100 are wiped to 10 working clays clearance. Carriage charges (AS£3.00, (A1>£4.00, (B)=£5.50, (C)=£8.50. (Cl) £1250, (DS£15.CO. (E£18.00, (F)=£20.00, (GSCALL Allow approx 6days le sheçrnig -taster CALL Al goods supplied to our Standard Conditions of Sale and unites stated guaranteed Icx 90 days. All guarantees on areturn to base base. Al tilts reserved to change prizes /specrfications iverout prior notice. Orders subtract to stedr. Discounts ay volume. Top CASH paces pad for surplus goods Al trademarks. tradenames etc aderoiviedged Display Electrenics 1999. E&0 E. 0799.
|
||
|
||
CIRCLE NO. 122 ON REPLY CARD
|
||
|
||
WEB
|
||
|
||
1
|
||
IL
|
||
|
||
AQUILA VISION http://www.aguila-vision.co.uk
|
||
Aquila Vision specialises in supplying and supporting Embedded Microprocessor Development products from PICs to DSPs. We also stock robotics boards, Linux and general interest CD-ROM's.
|
||
1.111aUdie
|
||
Mom nd•ruo
|
||
•mon.
|
||
ALCATEL COMPONENTS http://www.components ©alcatel.de ASHWELL ELECTRONICS http://www.ashwell-hg.com
|
||
Ashwell provide technical support for Apex Microtechnology op-amps and DC/DC'S; Aeroflex; EMP filtered connectors: M SKennedy: Mintech obsolescence; NSC Mil/Aero; Teledyne Relays and isocom mil/optocouplers.
|
||
ARCOM http://www.arcomcontrols.com/ew'
|
||
_UM!
|
||
oeenw. Wu.
|
||
ww..wiere
|
||
Aleading international supplier of
|
||
communication and control technology to industry. Arcom provides leading edge solutions through a comprehensive range of market leading products.
|
||
BROADERCASTING COMMUNICATIONS SYSTEMS www.broadercasting.co.uk
|
||
WINRADIO now brings you acomplete choice in personnel computer controlled radio scanning and reception solutions • Broadcast • Media • Monitoring • Professional Amateur Radio communications
|
||
BEDFORD OPTO TECHNOLOGY LTD http://www.bot.co.uk
|
||
Optoelectronic products UK design development manufacture standard and
|
||
|
||
custom, LED bargraphs, circuit board indicators, stand offs, transmissive/reflective switches, baseefa optocouplers tubular and surfacemount. pannel mount LED assemblies.
|
||
CONCEPT ELECTRONICS http://www.conceptkey.co.uk
|
||
Concept Keyboards are specialists in the design and manufacture of customer specified membrane panels and keyboards, and electronic design. Concept's membrane manufacture is supported by afull electronic production facility to provide a complete turnkey keyboard and electronics service, fully accredited to IS09001.
|
||
CONTROL SOLUTIONS www.controlsolutions.co.uk
|
||
Data acquisition and control for beginners, hobbyists, and professionals. Perform mathematical and logical operations on data in real time. Email: info4controlsolutions.co.uk,
|
||
COOKE INTERNATIONAL http://www.cooke-int.corn e-mail: info©cooke-int.com
|
||
Stockists of Quality Used Electronic Test Instruments and Operating 8 Service Manuals.
|
||
CROWNHILL ASSOCIATES LTD http://www.crownhill.co.uk
|
||
Crownhill supply low cost development tools for use with Micro-Controllers and Smart Cards. Products include Smart Card development tools. Smart cards, Micro Development tools and Bespoke Design Services.
|
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DANIEL MCBREARTY http://www.danmcb.demon.co.0 k/eng.html
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Experienced engineer based in London, specialist in audio and control systems. Available for design, project engineering or general consultancy. Background of high-quality work.
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DESIGNER SYSTEMS CO. http://www.designersystems.co. uk
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Electronic product design company with over adecade of experience promoting it's own product range and designing and manufacturing innovative products
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„la for client companies/individuals. fitie
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=
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Welcome to One ham pop of
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FELLER UK http://www.feller-at.corn
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Feller (UK) Ltd. manufacture Fully approved cordsets (Moulded mains plugs and connectors) and Power Supply Cables for all industrial Countries to National and International Standards
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FLASH DESIGNS LTD http://www.flash.co.uk
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Flash supply low cost AVR ISP programmers (£39), MINI-ICE starter kits (from £69), Portable Easy-ICE emulators (from £199), ICE Adapters
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HSPS LTD
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http://dspace.dial.pipex.com/hsps/
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LEVY/LATHAM GLOBAL http://www.levylatham.com
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111 11•Wele.••••• rboom %tn.. ne
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Equinox Technologies UK Ltd.. specialise in development tools for the embedded microcontroller market.
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ECM SELECTION http:// www.ecmsel.co.uk
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http://www.lprs.co.uk
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LPRS markets low power radio transmitters, receivers and transceiver modules manufactured by ourselves, Radiometrix, Circuit Designs, ROT and Micrel. Applications for telemetry, video and remote control.
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MATTHEY MICROFILTERS
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http://www.microfilters.net
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30 years experience in the design and manufacture of high quality passive filters and delay lines. Used in Broadcast, Telecommunications. Medical, Multimedia. and Computer industries.
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742
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ELECTRONICS WORLD September 2000
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OMEGA RESEARCH LTD http://www.omega-research .co.uk
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'SAID prototyping adapters. Unique, flexible, low cost adapters to allow bench working with SM devices. Range suits most devices down to 0.5mm pitch."
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PCA:PHILIP COLLINS & ASSOCIATES PTY. LTD http://www.pca.cc
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POLY-FLEX CIRCUITS LTD http://www.polyflex.com
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Design, manufacture and population of printed polyester flexible circuits, including Flip Chip on Flex providing practical, low cost. reliable solutions for today's small lightweight products.
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RADIOMETRIX http://www.radiometrix.co.uk
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RADIO-TECH LIMITED http://www.radio-tech.co.uk
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Radio modules. modems, telemetry, audio transmitters, pagers, antenna, remote controls and much more. All UK designed and manufactured.
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RALFE ELECTRONICS professional test &measurement www.ralfe-electronics.co.uk
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-110,000+ products available -Technical data library -Stock availability check -Integrated on-line purchasing -Order by 8pm -with you tomorrow.
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As aPC data base or hard copy. SoftCopy can supply acomplete index of Electronics World articles over the past ten years. Photo copies of articles from back issues are also available.
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SESCOM, INC. http://www.sescom.com
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SESCOM, INC. is a30-year manufacturer of audio problem solvers and
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RS COMPONENTS LTD http://rswww.com
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The award winning on-line service from RS
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STAFFORDSHIRE WIRELESS COMPANY http://www.staffs-wireless.corn
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Wireless, communication, test equipment, bought and sold for very competitive prices visit our web site or telephone John on 01889 569928 or 0973 296461.
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Continued over page
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September 2000 ELECTRONICS WORLD
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743
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THOSE ENGINEERS LTD http://www.spiceage.com
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TEMWELL CORPORATION http://www.temwell.com.tw
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Manufacturer 8 Exporter of Heelical BPF Filter, 30 Watts BPF Power Filter and Handset/Base Station Duplexers
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TRIDENT MICROSYSTEMS LTD http://www.trident-uk.co.uk
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Visit the Trident website for details and datasheets on their entire LCD and printer product range. Download data and subscribe for our regularly updated newsleter.
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TOWER HILL TECHNICAL SERVICES http://www.towerhillaerials.com
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Everything you need for DIY Satellite 8 TV aerial installation. The one stop shop for TV, FM, Satellite, Amateur
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-Scientific books and catalogues -Manuals and data sheets
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VANN DRAPER ELECTRONICS LTD http://www.vanndraper.co.uk
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Test equipment from Grundig. Kenwood, Hitachi. Fluke. Ayo. Glassman, Advance in acomprehensive site including oscilloscopes, multimeters, power supplies, generators, counters, soldering, digital tv etc.
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Following on from the newsgroup discussion last month there is aUK Email group for TV technicians where you can send an Email to everyone in the group. There's just over 30 people in the group at present. For more details and how to register look at the egroup home page. Just ageneral comment though -you do have to be careful who you give your Email address to so that you can avoid 'spamming -that is getting lots of unwanted Email about dubious Russian site (amongst others).
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http://www.reedconnect.net/
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Another free internet access site, this time from Reed Business Information. However the site possesses auseful UK People and Business Finder, with an email search. There's also business news and local information, and some good links to directory sites.
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WOOD & DOUGLAS http://www.woodanddouglas.co.uk
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Wood 8 Douglas Ltd is the leading independent British designer and manufacturer of quality radio products for International telemetry. data.voice video wireless communications.
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UK ELECTRICAL DIRECT http: //www. uked .com
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For acomprehensive on-line directory. buyers guide and resource locator for the UK Electrical Industry look at this site. Many of the companies listed have links to their own web sites, making this aone-stop shop for ahuge amount of information.
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UK MAILING LIST GROUP
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http://www.repairworld.com
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Repairworld is asophisticated US based fault report database which is updated biweekly. It operates on asubscription basis and describes itself as an 'affordable solution for all technicians". There is apparently no minimum number of months for which you have to subscribe. You can see some samples of the material for free, monitors, VCR. DVD
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and Camcorders being of particular relevance to UK users. The site even provides a'chat room' where you can talk via your keyboard to others 'in the
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room'.
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To reserve your web site space contact Pat Bunce
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Tel: 020 8652 8339 Fax: 020 8652 3981
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||
|
||
CIRCUIT IDEAS
|
||
|
||
PC controlled bipolar stepper motor
|
||
|
||
...continued from page 740
|
||
|
||
A simple QuickBasic program to run the stepper motor at any speed and in any direction is given. The parallel port's address is 378 16 . Duration of execution of four FOR TO NEXT' loops in subroutines CW and CCW determines the speed of the motor. If the duration of these loops is increased, by increasing the variable D, the motor speed will reduce.
|
||
|
||
Pressing function key FI should move the motor in aclockwise direction, while the motor should move in counter clockwise
|
||
direction by pressing F2. This circuit can be used to drive
|
||
two-phase stepper motors of various sizes. M T lqbal Rawalpindi Pakistan. E23
|
||
|
||
Orange
|
||
|
||
Step Red Blue Yellow Orange
|
||
|
||
1 —
|
||
|
||
2 +
|
||
|
||
++
|
||
|
||
3 +
|
||
|
||
Blue
|
||
|
||
•
|
||
|
||
4 —
|
||
|
||
Red
|
||
|
||
Yellow
|
||
|
||
Stepper motor Sanyo Denshi model 103H8223-5141, 3.6V, 4A/phase, 1.8°/step
|
||
|
||
Fig. 2. Connections for the stepper motor used in the author's prototype.
|
||
|
||
26SWG 660T
|
||
|
||
13SWG 23T
|
||
|
||
(E23d)
|
||
|
||
DO D1 D2 D3
|
||
|
||
e1HL 2LH
|
||
C,, 3L H
|
||
|
||
L H L H H L
|
||
|
||
4HL H L
|
||
|
||
Fig. 4. Data sequence on parallel port for clockwise rotation.
|
||
|
||
Fig. 1. Drive bridges, interface transistors and LPT connections for the PC-controlled stepper motor driver.
|
||
|
||
LN E
|
||
220Vec 50Hz
|
||
|
||
13SWG 36T
|
||
Core area =2.5in2 =1.25M by 2mn
|
||
C1: 10 000p, 16V C2: 22 000p, 25V This supply will drive two motors
|
||
|
||
Fig. 3. Power supply for the drive circuits.
|
||
|
||
+5.6V
|
||
|
||
BDX53B +12V Tr i
|
||
|
||
Listing. Quick Basic program for driving astepper motor from aPC.
|
||
CLS:D=1000 PRINT "Press Fl for clockwise rotation PRINT "Press F2 for counter clockwise" PRINT "Press F3 to change speed" ON KEY(1) GOSUB CW ON KEY(2) GOSUB CCW ON KEY(3) GOSUB Direction KEY(1) ON KEY(2) ON KEY(3) ON 10 GOTO 10 END
|
||
|
||
CW: OUT &H378,9 FOR I=1 TO D : NEXT I OUT &H378,10 FOR I=1 TO D : NEXT I OUT &H378, 6 FOR I=1 TO D : NEXT I OUT &H378, 5 FOR I=1 TO D: NEXT I RETURN
|
||
|
||
CCW OUT &H378, FOR I=1 TO OUT &H378, FOR I=1 TO OUT &H378, FOR I=1 TO OUT &H378, FOR I=1 TO RETURN
|
||
|
||
5 D : NEXT 6 D : NEXT 10 D : NEXT 9 D : NEXT
|
||
|
||
Direction: INPUT "Please enter new speed"; D RETURN
|
||
|
||
+5.6V
|
||
|
||
All diodes type 1N5401
|
||
September 2000 ELECTRONICS WORLD
|
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|
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745
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Pico ADC42
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Virtual oscilloscope
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a Net Ls to
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ote 10
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Phone number/fax Total amount £ Ienclose acheque
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Please charge to my credit/debit card. Card type (MasterNisa/Switch etc)
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Card No
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Expiry date
|
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Please mail this coupon to Electronics World, together with payment. Alternatively fax credit card details with order on 0181 652 8111. Address orders and all correspondence relating to this order to Pico Offer, Electronics World, Quadrant House, The Quadrant, Sutton, Surrey SM2 5AS. email jackie.lowe@rbi.co.uk
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Make cheques payable to Reed Business Information Group.
|
||
|
||
Letters to the editor
|
||
|
||
Letters to "Electronics World" Quadrant House, The Quadrant, Sutton, Surrey, SM2 5AS e-mail jackie.lowe@rbi.co.uk using subject heading 'Letters'.
|
||
|
||
THD is meaningless
|
||
Anthony New's article in the June issue has much merit. It
|
||
would be easy to pick up and make much of afew errors, but
|
||
that would do the matter agreat injustice.
|
||
What, however, is worthy of comment, Ithink, is that the
|
||
criticisms of current practices are actually well-known to many audio designers, but nevertheless to far too few.
|
||
Mr New stands to receive similar criticism to that levelled at Matti Otala when he published his first paper in English on transient
|
||
intermodulation distortion. Top designers said, more or less, 'This is all old stuff, we know all about it and any claims of novelty are false.' But lots of designers didn't know about it, and designed amplifiers that
|
||
exhibited it in various degrees. A limited defence of harmonic
|
||
distortion measurements is that
|
||
the object of design is to achieve linearity. A design exhibiting no
|
||
THD must be completely linear and cannot produce intermodulation distortion either.
|
||
Simple theory can show that there is astrict numerical relationship between the
|
||
amounts of THD and IMD produced by agiven nonlinearity. But simple theory is too simple: there are many conditions necessary if the numerical relationship is to be preserved.
|
||
These conditions are rarely
|
||
fulfiled. This is discussed in BS EN 60268-2, which is identical to IEC 60268-2. But if designers don't read these standards...
|
||
Reliance on THD control, regardless of its psychoacoustic significance, if any, worked quite well in historical times, when linearity was not very good, but it is indeed too 'broadbrush' now that linearity is excellent.
|
||
Having said that, an authoritative source of information on measurements of audio amplifiers is BS EN 60268-3, which is identical to LEC 60268-3. This has,
|
||
|
||
throughout its editions -athird is imminent -included standard methods of measurement for intermodulation distortion.
|
||
The fact that designers don't use these methods, or, at least, IMD does not feature in published specifications, is regrettable. Ican demonstrate the relative inaudibility of harmonics compared with even low-order intermodulation products, using contrived circuits that can produce one without the other. John Woodgate Via e-mail
|
||
Ihad intended to present acrosssection of responses to Anthony's article on IMD, but Iran out of space again, sorry. I'll try to find space again next month. Ed
|
||
Thoughts from a long-standing reader
|
||
1have been areader of Wireless World since 1943 and asubscriber since 1949. During my working life, mainly in engineering research and development, Ifound the magazine an invaluable source of technical information.
|
||
Now Iam well retired, Istill read it with interest, though not having the hardware available, I do not find the computer articles very much help. Obviously they help other people in the way that earlier articles helped me.
|
||
Ihave always had astrong practical interest in audio and sound recording. Since Ido quite alot of headphone listening, for various reasons, Iwas very interested in John Waticinson's article in the November 1999 issue, particularly in the headphone shuffler circuit. Ihad hoped that he would produce apractical circuit for this, but since he did not, Idecided to try it myself.
|
||
As Iam in my mid-seventies and my maths is well on the way to rusting up solid, Iadapted the group delay circuit from Bill Hardman's 'Precise active crossover' in the August issue. I based the system on the equilateral triangle spacing of speakers and listener. This required a delay of around 200kts. This was easy to obtain up to about 21cHz,
|
||
|
||
Sizzling hard drives
|
||
The interesting correspondence regarding hard-drive failures due to overheating, and Ed Dell's "fridge" remedy, suggest that the problem is bearing-related.
|
||
A number of years ago, Iencountered aregular failure, on very hot days, in the drive of aTranstec HD2 machine. It was similarly cured by lowering the ambient temperature around the unit and giving it a'nudge'.
|
||
Our office had alarge plate-glass window facing on to the street. Close to high-noon, the programmers' desk used to get alarmingly hot. Invariably, the HD2 would fail at around 2pm!
|
||
A quick burst with the office fan and atap on the casing of the computer got it healthy again.
|
||
Many drives rely on the precise alignment of ashaft in aset of precision agate, ruby, or similar bearings. These have built in
|
||
compensation for temperature changes. If this sensitive equilibrium is upset, the shaft can expand
|
||
axially and produce heat in the bearing surfaces. This then
|
||
compounds the problem because some of the heat is transferred to the shaft, which then expands even more, and so on.
|
||
If the overheating continues unchecked, radial carrier-shaft expansion can become significant and lead to bearing failure.
|
||
The drive is usually unusable after this point has been reached. In what we laughingly call 'The-Good-Old-Days', mainframe
|
||
rooms were air-conditioned and temperature-controlled.
|
||
However, with the proliferation of PCs, we seem to have overlooked the fact that computers, like people, have aoptimum
|
||
temperature at which they are most comfortable. Chris Ecdes Research Director Gardner Watts Ltd
|
||
|
||
but the delay fell off to about 80ps at 10kHz.
|
||
Imade ashade attenuator
|
||
within ±1dB of the graph given by John Watkinson. This contributed to the delay that now ranged between 260 and 95s.
|
||
By recording short sections with and without the shuffler in circuit on acassette recorder, I was able to assess its effect. First impressions were that the bass was increased, as you would expect from the response of the shader attenuator.
|
||
The 'in-head' effect was
|
||
reduced, but the sound only seemed to be shifted about three inches forward, not comparable with actual loudspeaker listening. However, it was an interesting experiment. Iwould welcome seeing aproper circuit from John Watkinson. Ifear my circuit is not up to the standard I expect from Electronics World.
|
||
Iwas also very interested in Anthony New's article in the June issue; Ithink he was abit too sweeping in dismissing THD measurements. Ihave
|
||
|
||
always regarded THD and IMD as two interdependent facets of non-linearity in amplifiers, IMD being the worst effect of the two.
|
||
In valve technology, as Iused it in the 1950s, there was a commonly held view that IMD values had asimple relationship to THD, so that knowledge of THD gave an index of IMD. No
|
||
doubt the incidence of higherorder distortions than we had in those days has affected this relationship and possibly led to the disregard for IMD that • Anthony New is trying to redress.
|
||
Ialso enjoyed reading John Linsley Hood's reminiscences. They reminded me in places of my own experiences in electronics; though Iwas more interested in sound recording, building my own disc recorder on ashoe-string in the 1950s.
|
||
Ilook forward to reading EW each month. A TGranger Ledbury Herefordshire
|
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|
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September 2000 ELECTRONICS WORLD
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|
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Rack Enclosures
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New and Used most sizes 16U to 50U side and rear panels mains distribution 19" Panel mounts optima eurocraft. Prices from £45 •vat
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Designer :**-- ESystems
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FOR SALE
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RF DESIGN SERVICES
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All aspects of RF
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WATERREACH ELECTRONICS m‘i %%.rlas er.dial.pipex.com
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TEL: 01223 862550 FAX: 01223 440853
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FOR VALVES, eg KT88, PX25 EL37. DA100 — CASH WAITING!
|
||
Wide range of valves purchased and supplied
|
||
Visitors please phone for an appointment BillIngton Export Ltd, BIllingshurst, Sussex RH14 9EZ billingtonexportlitd@blinternet corn Tel 01403 784961 Fax: 01403 783519
|
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LINEAGE
|
||
PRINTED CIRCUIT BOARDS - Quick Service. Design and Manufacture for Prototypes or Production. Agar Circuits. Unit 5, 308 Albedbridge Road. Belfast BTS 4GX. Tel: 02890 738897. Fax: 02890 731802. E-mail: agareargonet.co.uk
|
||
|
||
FARNELL CiS600 SMPS I2V adju.tahle :n 50A. unused. complete, £250 ono. Phone Leeds 0113 249 8661.
|
||
MSI 868 C-V plotter measures capacitance MO/200/2000pr over fixed or swept bias voltage between I99.9V at IMHz £400. 01476 550826.
|
||
P&P Electronics, design and analogue and digital systems, phone and fax: 01924 402931.
|
||
NICOLET 4094 DSO two independent plugins each with 12 bit twin channel differential amplifiers timebase 0.5p5-200s/point user manual RS232/GP1B, £200. 01476 550826.
|
||
ANRITSU MS62D spectrum analyser with storage display two ranges 50Hz- 1700kHz 10kHz- I700MHz with MH628A tracking generator 100khz-1700MHz with manuals £00. 01476 550826.
|
||
WANTED
|
||
Valves & Semiconductors All types e.g. Discrete & IC's
|
||
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|
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CHELMER VALVE CO.
|
||
130 New London Road, Chelmsford. Esse,
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Tel: 01245 265865 Fas: 01245 490064
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D. S. G. SPEDITION LIMITED
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For further information plea ie contact
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Tel: 01277 812337 Fax: 01277 812359 Email: DSGSPED@aol.com
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HPI744A storage scope with manual £30C inclusive. Many other scopes and items and test equipment and components available. Mayflowei Electronics, 48 Brendon Road, Watchet, Somerse. TA23 OHT. Tel: 01984 631825.
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WIRELESS WORLD magazines for sale, 197f to 1999, please telephone/fax S. Jacovides 0207272 7139 or e-mail: jacovides@btintemet.com
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QTY Electronic Equipment, Components. 041. Books etc. £550 ono. Tel/Fax 01280 848626.
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CCD weather proof camera and monitor fou transport vehicle with lights, connecting cable etc, 24v dc, unused. £00 ono. 01522 751942.
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Call Pat Bunce Tel: 020 8652 8339 Fax: 020 8652 3981
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September 2000 ELECTRONICS WORLD
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Contact Pat Bunce on 020 8652 8339
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ELECTRONICUPDATE
|
||
|
||
A regular advertising feature enabling readers to obtain more
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information on companies' products or services.
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|
||
These compact, light recorders
|
||
|
||
have 2 or 4 analogue channels
|
||
|
||
with isolated inputs, PC card
|
||
|
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slot, fax/modem communication
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function,
|
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|
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versatile
|
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|
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trigger
|
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|
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functions and 3-way power.
|
||
|
||
They are ideal for a variety of
|
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|
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CIRCLE NO.128 ON REPLY CARD
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|
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PXI Solutions 2000/01 Product Guide CompactPCI for Measurement and Automation
|
||
MISS
|
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liu101
|
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ni.com
|
||
|
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National Instruments' PXI Solutions
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|
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Product Guide features detailed
|
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|
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information
|
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|
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on
|
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the
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latest
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PXVCompactPCI
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solutions
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|
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applications. The 224-page catalogue
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and technical reference guide details
|
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|
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|
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|
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compliant
|
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|
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chassis,
|
||
|
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controllers,
|
||
|
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|
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provides a complete tutorial on the
|
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|
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information on the PXI Systems
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Alliance, and a PXI systems
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configuration guide.
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Phone 01635 523545 Fax 01635 524395
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||
|
||
A range of truly portable, Universal and EPROM/Flash programmers for every need
|
||
•Support for all types of devices including 8and 16-hit memory, up to 128Mbit, PLDs, CPLCrs, and over 300 microcontrollers
|
||
•Uses the parallel port of any PC or laptop •Program and verify low voltage devices down to 1.8V •Low cost package adapters available for PLCC, PSOP, TSOP, QFP, SDIP, SOIC and BGA •No additional modules or adapters required for any DIP device •Compatible with DOS, Windows 95/98, Windows' NT •Powerful and comprehensive software interface is easy to use •Uses PSU/Recharger supplied, or batteries for real portability •Includes Chiptester for TTL/CMOS, DRAM and SRAM devices •Optional EPROM/RAM emulators also available
|
||
|
||
55oilt•I EPMaster LV48
|
||
|
||
,upp, I. 48-pin support tor EPROM, EEPROM, Flash 8 Serial PROM
|
||
|
||
Speedmaster LV48 As EPMaster LV48, plus 13PROMs, PALs, GALs, CPU)', and 8748/51 microcontrollers
|
||
|
||
Micromaster LV48
|
||
|
||
As Speedmaster LV48, plus over 300 microcontrolle, including 87C48/51/196, PIC',, AVRs, 89Cxxxx, SIT, MC705/711, SA13-05xx, TMS320/370, Z86, COP et,.
|
||
FULLY UNIVERSAL
|
||
|
||
LV40 Portable
|
||
|
||
40-pin version M Micromaster LV48 + LCD 8 Keypad
|
||
|
||
Price L495
|
||
|
||
...the be
|
||
|
||
L695 programmers
|
||
L'I'li
|
||
are here...
|
||
|
||
The new Matrix Programming System offers the most complete,
|
||
flexible gang programmer you will ever need for production
|
||
applications at an extremely competitive price from £1,995
|
||
•Two levels of device support: Memory only, or Universal support for memory
|
||
devices up to 128Mbit, PLDs, CPLDs and over 300 Microcontrollers •4or 8independent programming sites per box •Daisy-chaining allows up to 48 centrally controlled sites •Very high throughput (program/verify time in seconds): 28E400 =4/2.5,
|
||
28E16083 = 18/12, 28E64015 = 155/60 •Low cost passive socket modules give support for DIP, PLCC, PSOP, TSOP, QFP etc. •Modules are not device specific giving major savings in cost of ownership •True low voltage support down to 1.8V, plus marginal verification •Intelligent auto-sensing of sockets eliminates need to continually access keyboard •Powerful and comprehensive software, with easy-to-use interface •Manufacturer approved algorithms for accurate programming and maximum yield •Full on-board diagnostics •Compatible with Windows' 95/98 and Windows NT •Universal input power supply -90-260V, 50/60Hz
|
||
|
||
Matrix From
|
||
£1995
|
||
|
||
All ICE Technology programmers come with lifetime FREE software
|
||
updatest and technical support, 12 month warranty and 30-day moneyback guarantee. For complete Device Support lists, FREE software
|
||
updates, Demo software and full product information,
|
||
just visit our website at www.icetech.com
|
||
|
||
...and here, wwwwicetech.com
|
||
|
||
ILL
|
||
|
||
Penistone Court, Sheffield Road, Penistone, Sheffield. S36 6HP. UK
|
||
|
||
tel: +44 (0)1226 767404 •fax: +44(0)1226 370434 •email: salesgicetech.com
|
||
|
||
ICE Ti
|
||
|
||
5370 Gulf of Mexico Drive, Suite 204B, Longboat Key. FL 34228. USA
|
||
|
||
tel: 1(941) 387 8166 •fax: 1(941)387 9305 •email: icetechuseïicetech.com
|
||
|
||
ORDER NOW VIA OUR CREDIT CARD HOTLINE :+44 (0) 1226 767404 ALL PRODUCTS IN STOCK
|
||
|
||
tCustom software and enhanced priority device support is also available for all programmer platforms. All prices are exclusive of carriage and VAT All trademarks are recognised as belonging to their respective owners.
|
||
CIRCLE NO. 102 ON REPLY (•IR1)
|
||
|
||
STILL THE WORLD' POWERFUL PORTABLE PROGRAMMERS?
|
||
495
|
||
CE
|
||
|
||
7g 5+VAT
|
||
|
||
L
|
||
DATAMAN-48LV
|
||
•Plugs straight into parallel port of PC or laptop
|
||
•Programs and verifies at 2, 2.7, 3.3 &5V •True no-adaptor programming up to 48
|
||
pin DIL devices •Free universal 44 pin PLCC adaptor •Built-in world standard PSU -for go-
|
||
anywhere programming •Package adaptors available for TSOP,
|
||
PSOP, QFP, SOIC and PLCC •Optional EPROM emulator
|
||
DATAMAN S4
|
||
•Programs 8and 16 bit EPROMs, EEPROMs, PEROMs, 5and 12V FLASH, Boot-Block FLASH, PICs, 8751 microcontrollers and more
|
||
•EPROM emulation as standard •Rechargeable battery power for total
|
||
portability •All-in-one price includes emulation
|
||
leads, AC charger, PC software, spare library ROM, user-friendly manual •Supplied fully charged and ready to use
|
||
|
||
SURELY NOT. SURELY SOMEONE SOMEWHERE HAS DEVELOPED A PORTABLE PROGRAMMER THAT HAS EVEN MORE FEATURES, EVEN GREATER FLEXIBILITY AND IS EVEN BETTER VALUE FOR MONEY, ACTUALLY, NO. BUT DON'T TAKE OUR WORD FOR IT. USE THE FEATURE SUMMARY BELOW TO SEE HOW OTHER MANUFACTURERS' PRODUCTS COMPARE.
|
||
|
||
S4 GAL MODULE
|
||
•Programs wide range of 20 and 24 pin logic devices from the major GAL vendors
|
||
•Supports JEDEC files from all popular compilers
|
||
SUPPORT
|
||
|
||
MONEY-BACK 30 DAY TRIAL
|
||
If you do not agree that these truly are the most powerful portable programmers you can
|
||
buy, simply return your Dataman product within 30 days for afull refund
|
||
|
||
•3year parts and labour guarantee •Windows/DOS software included •Free technical support for life •Next day delivery -always in stock •Dedicated UK supplier, established 1978
|
||
|
||
me' • MI !ale. 4i,
|
||
Orders received by 4pm will normally be despatched same day. Order today, get it tomorrow!
|
||
|
||
Still as unbeatable as ever. Beware of cheap imitations. Beware of false promises. Beware of hidden extras. If you want the best, there's still only one choice -Dataman.
|
||
Order via credit card hotline -phone today, use tomorrow.
|
||
Alternatively, request more detailed information on these and other marketleading programming solutions.
|
||
|