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SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.tek.com Vol.9, No.4; April 1996 Contents FEATURES 6 Dead Phone Battery? – Refill It With Standard AA Rechargeable Cells & Save Big Dollars Fed up with paying big dollars to replace the battery for your mobile phone. Here’s how to refurbish it with standard rechargeable cells that together cost must less than the price of a new battery – by Ross Tester 14 Traction Control In Motor Racing; Pt.2 Traction control was permitted in Formula 1 racing in 1993. We take a look at how the technology was applied – by Julian Edgar REPLACE DEAD PHONE BATTERIES WITH LOW-COST RECHARGEABLE AA CELLS & SAVE MONEY – PAGE 6 56 Cathode Ray Oscilloscopes, Pt.2 Find out how cathode ray oscilloscopes work. This month, we look at deflection options, blanking circuits and triggering methods – by Bryan Maher PROJECTS TO BUILD 22 A High-Power Hifi Amplifier Module This rugged new power amplifier will deliver 175W into a 4-ohm load or 125W into an 8-ohm load. It uses the latest plastic power transistors and is suitable for use with musical instruments or for hifi applications – by Leo Simpson & Bob Flynn 53 Replacement Module For The SL486 & MV601 Remote Control Receiver ICs A new IR receiver subsystem and a specially programmed Z86 microcontroller make this module easy to build. It replaces two obsolescent Plessey ICs – by Rick Walters HIGH-POWER 125-WATT AMPLIFIER MODULE – PAGE 22 72 Avoid Expensive Repairs – Build A Knock Indicator For Leaded-Petrol Engines Knocking (or pinging) can cause serious engine damage and many older cars are now starting to knock because of the reduced lead content in super grade petrol. This simple circuit will warn you when engine knock is occurring so that you can ease up and avoid costly engine damage – by John Clarke SPECIAL COLUMNS 38 Serviceman’s Log When I switch it on, nothing happens – by the TV Serviceman 65 Radio Control Multi-channel radio control transmitter; Pt.3 – by Bob Young REPLACEMENT MODULE FOR THE SL486 & MV601 ICs – PAGE 42 84 Vintage Radio A look back at transistor radios – by John Hill DEPARTMENTS 2 Publisher’s Letter 3 Mailbag 13 Order Form 80 Circuit Notebook 88 Product Showcase 91 Ask Silicon Chip 94 Market Centre 96 Advertising Index KNOCK INDICATOR FOR CAR ENGINES – PAGE 72 April 1996  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Rick Walters Reader Services Ann Jenkinson Advertising Manager Christopher Wilson Phone (02) 9979 5644 Mobile 0419 23 9375 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Julian Edgar, Dip.T.(Sec.), B.Ed John Hill Mike Sheriff, B.Sc, VK2YFK Philip Watson, MIREE, VK2ZPW Bob Young Photography Stuart Bryce SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $54 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 34, 1-3 Jubilee Avenue, Warrie­ wood, NSW 2102. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9979 5644. Fax (02) 9979 6503. PUBLISHER'S LETTER Pay TV cables are not a pretty sight By now, Pay TV is available to several hundred thousand people in the major capital cities via the cables of Optus and Telstra. For the most part, Telstra cable is undergound in exist­ing ducts while Optus cable is being strung from power poles. The latter process is currently under legal challenge by a number of municipal councils in Melbourne. I can well understand why. When cables are strung from power poles, they are about 1.5 metres below the existing mains supply wires. As well, they are quite thick, about 16mm in diameter by my estimation. To make matters worse, they are black (naturally) rather than the soft weathered green of the copper mains wires. In some streets, two or more cables may be bundled together, making a very substantial rope which sticks out like a sore thumb. So far I have just described Telstra cables. “What’s that?” you say, “aren’t Telstra cables underground?”. Well, they are but in hilly rocky areas where existing telephone services are strung from pole to pole, the Pay TV cables go up there too. Optus cables are worse. While Telstra cables are self-supporting, strung at high tension, Optus cables are supported from a steel catenary and have a stress loop at each pole, so they are even uglier. In the often scenic areas I am referring too, you have telephone and power wires plus Optus and Telstra cables all strung from the same poles. It can make an otherwise pleasant suburb look like a hick town in a third world country. What I have just described is the cabling as it is now being strung. When there are lots of customers, there will natu­rally be even more cables in the streets; each customer will have a cable from the closest power pole to their residence. Frankly, in view of the visual mess of these cables, it is surprising that there has been so little public outcry. These cables are far uglier than mobile tele­phone transmitting towers and ultimately, Optus cables will be seen in virtually every subur­ban street that has power poles. Under existing legislation, it appears than municipal councils are virtually powerless to stop their suburbs from being cabled. Is this for the good of the community? As cabling becomes more widespread (and more dense) I pre­dict that some residents could eventually become so annoyed with the ugliness of it that they will take matters into their own hands and attempt sabotage. It is stating the obvious but all these cables must ul­timately be placed underground. If the companies and their cus­tomers cannot afford this condition, then clearly Pay TV from two competing suppliers is not viable. Leo Simpson ISSN 1030-2662 WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. 2  Silicon Chip MAILBAG Maglev article was enjoyable I enjoyed your article on the “Maglev” in the February 1996 issue as it brought to mind the “Benny Rail Car” circa 1935. This had a speed of 120 knots, the same as commercial aircraft of the period and being a suspended monorail, could have been installed above existing railways, obviating expensive real estate. The demonstration prototype was torn down for steel in the 1939-1945 war and was not, possibly due to death or financial problems, resumed at war’s end. No mention was made in your magazine of three major advantages of rail surface transport: (1) The ability of the rail system to bring the train into the destination in the densest fog, instead of having to divert to another, possibly distant, facility; (2) the ability to spread the arriving traffic over a large number of platforms and using a flyover system similar to Sydney’s Central Suburban distributor, not interfering with outgoing traffic on any platform. As an aside, when this distributor was installed, railway engineers from all over the world came to see this major step forward. (3) More particularly, the train may come into the centre of the destination town, no matter how big (London, New York, Paris, Berlin, etc) without causing undue noise and pollution, instead of being situated at a place remote from the intended destination and then using second- ary surface transport to complete the journey. The Benny Rail Car had one advantage over the “Maglev” of not being disrupted by snow, the open steel supports allowing the snow to fall through while large drifts could form on the “Ma­glev” track, impeding the system. All this is academic as “Ma­glev” will probably, like so many radical ideas, never be imple­mented beyond the demonstration stage or possibly, a small com­ mercial line as a showcase opposed by airlines and aircraft manufacturers and other business interests and therefore never progressing beyond the curiosity stage. As you can see, I am a pessimist but an optimist can only be horribly disappointed where a pessimist may be agreeably sur­prised. L. Cross, Newtown, NSW. Cartoons are superb In the “Mailbag” column of the February 1996 issue, I read a letter from John Beyers congratulating the artist who draws the illustrations that accompany the “Serviceman” articles. I support John in his comments. Whilst the majority are just extremely good, there are some that deserve higher grading. The sketches published in October 1995 on page 41 and in February 1995 on page 65 (to name just two), I consider to be superb. It is not so much the content of the sketch itself, as the relevance to the specif­ic situation highlighted in the article that they accompany. Congratulations on maintaining an entertaining/educational column that teaches a sense of clear thinking and logic. A. Mott, Blackburn, Vic. Maglev article half missing As a reader of your excellent magazine, may I make a sug­gestion? In the February 1996 issue, in an article on “Maglev” trains, about half (to say the least) was left out. I found myself, at the conclusion, wondering where all the rest of the article was. Some years ago, Brian Maher had a series of articles in SILICON CHIP on iron-ore trains, old power stations, hydro-electrics, etc. They were absolutely interesting and obviously well researched. He sure did his homework on those articles but there again, half the details were left out. Couldn’t you run 12 articles a year on that sort of interest? Well I guess that’s enough growling for one letter. Keep up the standard of SILICON CHIP. Bob Graham, Korumburra, Vic. Comment: we would have preferred to provide more technical infor­mation on the Maglev article but that was all that was available at the time. If more information comes to hand to present a worthwhile follow-up article, it will be published. Coming Next Month* (1). High-Power Blue Laser with motor generated patterns. Build it and generate complex patterns like the one shown in the photograph at right (note: held over from this month due to lack of space). ON SALE DATE : April 27th (2). 10A Automotive Battery Charger: do you need a fast battery charger . . . something with a bit more “oomph” than run-of-the mill commercial products? This new automatic multi-range 10-amp charger should fit the bill. It features automatic selection for 6, 12 or 24V batteries; 10A maximum charging current; and automatic changeover from high through medium to trickle charge. In addition, it’s short circuit and reverse polarity protected. *Note: these features are well advanced in production for the May issue but unforeseen circumstances could force a change in the editorial content. April 1996  3 ALL REFURBISHED PRODUCTS CARRY MINIMUM 90-DAY WARRANTY ● COUNTRY/INTERSTATE: FREE CALL 1800 680680 ● ALL REFURBISHED PRODUCTS CARRY A MINIMUM 90-DAY WARRANTY ● CONTACT MA HEWLETT PACKARD 334A Distortion Analyser HEWLETT PACKARD 200CD Audio Oscillator • measures distortion 5Hz600kHz • harmonics up to 3MHz • auto nulling mode • high pass filter • high impedance AM • 5Hz to 600kHz • 5 ranges • 10V out • balanced output detector HEWLETT PACKARD 8614A UHF Sig. Gen. HEWLETT PACKARD 8640B Sig. Generator HEWLETT PACKARD 654A Test Oscillator • 0.5-1024MHz freq. range • int. audio osc. 20Hz-600kHz • 800-2400MHz freq. range • select. functions: CW, lev­elled • reverse power protection • internal phase lock/synch. output, sq. wave mod., ext. • +19 to -145 dBm output AM, FM & pulse mod. power range • output attenuation 0 to -127 • low SSB phase noise dBm • sig. gen. can be phase locked • digital frequency readout • 10Hz - 10MHz freq. range • +11dBm to -90dBm output level in 1dB steps • calibrated impedance 50Ω • + 75Ω unblanced; 135Ω, 150Ω + 600Ω balanced distortion <at> 1-10MHz > 34dB below fundamental $795 $79 $525 $3995 $695 HEWLETT PACKARD 3336B Synthesizer/ Level Generator HEWLETT PACKARD 3586B Selective Level Meter HEWLETT PACKARD 1740A Oscilloscope HEWLETT PACKARD 1710A Oscilloscope HEWLETT PACKARD 141T/8552/8555A Spectrum Analyser • variable • Frequency coverage 10Hz- • Frequency coverage 50Hz20.9MHz 32.5MHz • Precise frequency & spectral • Excellent measurement purity 1 Microhertz res up accuracy ±.2dB to 100kHz • Autoranging & automatic • Absolute amplitude accuracy calibration ±.05dB at 10kHz • SSB mode provides • Unique levelled sweep demodulation capability capabilities • HPIB programmable $1650 Austron 2010B Oscillator 1MHz........................... $400 AWA A215-2 Transmission Measuring Set .......... $175 AWA E221 Level Meter ........................................ $650 AWA F240 Distortion & Noise Meter ................... $375 AWA G231 Audio 10Hz-30KHz ............................ $495 AWA G250 Test Oscillator 10Hz-610kHz .............. $525 AWA G251 Level Oscillator 50Hz-2MHz .............. $600 BECKMAN L10A Megohmeter ........................... $1400 EATON 2075 Noise Gain Analyser ...................... $6500 ESI DB62 Decade Box ......................................... $350 EUROCARD 6 Slot Frames ..................................... $40 FLUKE 408B 6kV 20mA Power Supply................. $800 GR 1381 Random Noise Generators .................... $160 HP 204C Oscillator............................................... $225 HP 332A Distortion & Noise Meter ...................... $495 HP 353 Audio Attenuator...................................... $170 HP 400EL AC Voltmeter ....................................... $195 HP 403B AC Voltmeter......................................... $150 HP410C Multimeter ............................................. $295 HP 427A Voltmeter ................................................ $95 HP 432A Power Meter C/W Head & Cable ........... $825 HP 435A Power Meter.......................................... $495 HP 652A Test Oscillator ....................................... $375 HP 1200B Oscilloscope DC-500kHz..................... $425 HP 3400A RMS Voltmeter (1mV - 300V)............. $475 HP 3406A Broadband Sampling Voltmeter .......... $575 HP 3455A 61/2 Digit DVM ................................... $650 HP 3490A 51/2 Digit Digital Multimeter ............... $295 HP 3555B Transmission & Noise Meas. Set......... $325 HP 4204A Oscillator 10Hz-1MHz ......................... $350 HP 4260 LCR Bridge............................................ $295 HP 5245L/5253/5255 Electronic Counter ............ $550 HP 5300/5302A Universal Counter to 50MHz ...... $195 HP 5326B Universal Timer/Counter/DVM ............ $295 HP 5328A Universal Counter to 500MHz.............. $695 HP 5335A 200MHz Universal Counter ............... $4500 HP 6002 50V/10A Power Supply........................ $1495 HP 8005A Pulse Gen. 20MHz 3-Channel ............. $350 HP 8690B/8698/8699 400KHz-4GHz Sweep Osc ..................................................... $2450 HP 8690B/8707A/8706A 4GHz-18GHz Sweep Osc ..................................................... $1500 MARCONI TF2006 FM Sig. Gen. 1000MHz........... $800 MARCONI TF2300A FM/AM Mod Meter 500kHz-1000MHz ............................................ $450 MARCONI TF2500 AF Power/Volt Meter .............. $180 MOTOROLA Sinad Meter ..................................... $325 NORTHEAST 4002A Transmission Meas. Set ...... $600 RACAL DANA 9500 Universal Timer/Counter ...... $350 SD 6054B Freq. Counter 20Hz-18GHz ............... $2500 SD 6054C Microwave Freq Counter 1-18GHz .... $2000 SD 6152A 512MHz Counter/Timer....................... $350 TEKTRONIX CFC 100MHz Freq. Counter.............. $270 TEKTRONIX CDC 175MHz Univ. Counter.............. $405 TEKTRONIX FG504/TM503 40MHz Fun. Gen...... $1290 TEKTRONIX 067-0502-01 Scope Calibrator......... $550 TEKTRONIX 464 Storage Scope DC-100MHz..... $1400 TEKTRONIX 465 Oscilloscope DC-100MHz ....... $1190 TEKTRONIX 475 Oscilloscope DC-200MHz ....... $1550 TEKTRONIX 485 Oscilloscope DC-350MHz........ $2400 TEKTRONIX 602 XY Display ................................ $350 TEKTRONIX 7603NIIS Scope DC-65MHz ............ $650 TEKTRONIX 7904 Oscilloscope DC-500MHz ..... $2800 W&G SPM3 Selective Level Meter C/W; W&G PS3 Signal Generator 300Hz-612kHz (pr)........ $450 WAVETEK 143 Function Generator 20MHz .......... $475 WAVETEK 907 Signal Generator 7-11GHz.......... $1600 • DC-100MHz bandwidth • 2-channel display mode • trigger - main/delay sweep • coupling AC, DC, LF & HF rej $990 • HP 1741A var. persistence expansion to full screen model available $1325 $1250 $3995 BALLANTINE 323 AC Voltmeter BALLANTINE 6310A Test Oscillator BALLANTINE 3440A Millivoltmeter $1450 BALL EFRATOM M100 Rubidium Frequency • factory cal certs • perfect for ISO accreditation • GPS applications • ruggedised military design • • • • • • • • • • • • • bandwidth DC-150MHz • trigger source channel A, B or composite • delay timebase with single sweep • main intensify timebase persistence storage mainframe internal graticule eliminates parallax error IF section 10Hz minimum bandwidth log & linear sens. control absolute amplitude accuracy to ±1.6dB direct coax input to 18GHz high res. 100Hz bandwidth true RMS response including harmonics + crest factors 300µV to 300V full scale 1% basic accuracy freq. range 2Hz - 25MHz full field portability fast response without thermal lag $2950 • true RMS • • • • • 2Hz-1MHz freq. range • digital counter with 5 digit LED display • output impedance switch selectable • output terminals fuse protected $425 response to 30mV frequency coverage 10kHz-1.2GHz measurement from 100µV to 300V accuracy ±1% full scale to 150MHz list price elsewhere over $5500 $350 $795 NEW EQUIPMENT Affordable Laboratory Instruments The name that means quality PS305 Single Output Supply • • • • • • • • SSI-2360 60MHz Scope 60MHz dual trace, dual trigger Vertical sens. 1mV/div. Maximum sweep rate 5ns/div. Component tester Delay sweep, single sweep Two high quality probes $1110 + Tax • • • • PS8203 Digital Dual Supply 0-30V & 0-5A Load & line regulation <=0.01%+3mV Ind. & tracking modes Low ripple output Constant current voltage 2 x 3.5 dual purpose digital voltmeters • PS303D Dual Output Supply • 0-30V & 0-3A • • Four separate output meters • Independent or Tracking modes • Low ripple output $420 + Tax PS305D Dual Output Supply 0-30V and 0-5A $470 + Tax 0-30V & 0-5A $300 + Tax PS303 Single Output Supply PS8112 Single • 0-30V & 0-3A Output Supply • Two output meters • Constant I/V • 0-60V & 0-5A $490 + Tax $265 + Tax Audio Generator AG2601A Pattern Generator CPG1367A $640 + Tax PS8201 Digital Single Supply digital display • 0-30V & 0-5A • Load & line regulation • Constant current analog display <=0.01%+3mV • Constant voltage $320 + Tax • 10Hz-1MHz 5 bands • Colour pattern to test PAL • High frequency system TV circuit stability • Dot, cross hatch, vertical, • Sine/Square output horizontal, raster, colour $245 + Tax $275 + Tax ● ALL REFURBISHED PRODUCTS CARRY A MINIMUM 90-DAY WARRANTY ● CONTACT TEKTRONIX 100kHz to 1800MHz Spectrum Analyser System Consisting of: 7613 7L12 7A17 TR501 TM503 WAVETEK Signal Generator/Deviation Meter Model 3000-200 incorporates a complete 1 to 520MHz FM, AM and CW Signal Generator with an FM Deviation Meter in one convenient instrument. Storage Mainframe 1.8GHz Spectrum Analyser Plug-In Amplifier 1.8GHz Tracking Generator 3 Slot Mainframe $4250 Please phone or fax today for a full specification sheet incorporating all the system’s features. SPECIAL OFFER: DM501 MULTIMETER ONLY $100 EXTRA Frequency Range: 1-520MHz selectable in 1kHz steps; 1kHz resolution; frequency programmable via rear-panel connector. RF Output Level: +13dBm to -137dBm (1V to .03µV RMS); output level continuously adjustable in 10dB steps and with an 11dB vernier; impedance = 50 ohms. RF Output Protection: resettable RF circuit breaker; RF trip voltage = 5V RMS nominal; maximum reverse power = 50W. Spectral Purity: harmonic output > 30dB below fundamental from 10-520MHz; residual AM > 55dB below carrier in a 50Hz to 15kHz post-detection bandwidth; residual FM <200Hz in a 50Hz to 15kHz post-detection bandwidth (100Hz typical). Amplitude Modulation: internal 400Hz and 1kHz ±10%; external DC to 20kHz; range 0-90%; distortion 3% to 70% AM at 1kHz. Frequency Modulation: internal 400Hz and 1kHz (±10%); 50Hz to 25kHz; accuracy ±500Hz on x1 range, ±5kHz on x10 range; distortion 4% at 1kHz. FM Deviation Meter: frequency range 30-500MHz; input level range 10mV to 5V RMS; impedance 50 ohms; deviation range 0 to ±5kHz, 0 to ±50kHz $1250 IMPORTANT: GARAGE SALE! This is our first ever Garage Sale and represents an opportunity to purchase a whole range of “as traded” and imported stock that has been accumulated over years. Some equipment is tested, others “as is” . . . You’re sure to find a bit of everything mechanical, etc. INTERSTATE/COUNTRY BUYERS: Send or phone for lists . . . All interstate lists returned to us for this sale will be opened on 1st May 1996 and drawn from a hat. First opened letter gets whatever – it could not be fairer for people out of town. All successful customers will be notified. PRICES START FROM $1.00 LOCAL BUYERS: LOCAL SALE SUNDAY 5TH MAY 1996 – 9AM to 3PM. Located at warehouse 26 Fulton St, South Oakleigh. Phone for further details. 100MHz Tektronix 465M Oscilloscope 2-Channel, Delayed Timebase VERTICAL SYSTEM Bandwidth & Rise Time: DC to 100MHz (-3dB) and 3.5ns or less for DC coupling and -15°C to +55°C. Bandwidth Limit Mode: Bandwidth limited to 20MHz. Deflection Factor: 5mV/div to 5V/div in 10 steps (1-2-5 sequence). DC accuracy: ±2% 0-40°C; ±3% -15-0°C, 40-55°C. Uncalibrated, continuously variable between settings, and to at least 12.5V/div. Common-Mode Rejection Ratio: 25:1 to 10MHz; 10:1 from 10-50MHz, 6cm sinewave. (ADD Mode with Ch 2 inverted.) Display Modes: Ch 1, Ch 2 (normal or inverted), alternate, chopped (250kHz rate), added, X-Y. Input R and C: 1MΩ ±2%; approx 20pF. Max Input Voltage: DC or AC coupled ±250VDC + peak AC at 50kHz, derated above 50KHz. HORIZONTAL DEFLECTION Timebase A: 0.5s/div to 0.05µs/div in 22 steps (1-25 sequence). X10 mag extends fastest sweep rate to 5ns/div. Timebase B: 50ms/div to 0.05µs/div in 19 steps (1-2-5 sequence). X10 mag extends maximum sweep rate to 5ns/div. Horizontal Display Modes: A, A Intensified by B, B delayed by A, and mixed. CALIBRATED SWEEP DELAY Calibrated Delay Time: Continuous from 0.1µs to at least 5s after the start of the delaying A sweep. Differential Time Measurement Accuracy: for measurements of two or more major dial divisions: +15°C to +35°C 1% + 0.1% of full scale; 0°C to +55°C additional 1% allowed. TRIGGERING A & B A Trigger Modes: Normal Sweep is triggered by an internal vertical amplifier signal, external signal, or internal power line signal. A bright baseline is provided only in presence of trigger signal. Automatic: a bright baseline is displayed in the absence of input signals. Triggering is the same as normal-mode above 40Hz. Single (main timebase only): The sweep occurs once with the same triggering as normal. The capability to re-arm the sweep and illuminate the reset lamp is provided. The sweep activates when the next trigger is applied for rearming. A Trigger Holdoff: Increases A sweep holdoff time to at least 10X the TIME/DIV settings, except at 0.2s and 0.5s. Trigger View: View external and internal trigger signals; Ext X1, 100mV/div, Ext -: 10, 1V/div. Level and Slope: Internal, permits triggering at any point on the positive or negative slopes of the displayed waveform. External, permits continuously variable triggering on any level between +1.0V and -1.0V on either slope of the trigger signal. A Sources: Ch 1, Ch 2, NORM (all display modes triggered by the combined waveforms from Ch 1 and 2), LINE, EXT, EXT :-10. B Sources: B starts after delay time; Ch 1, Ch 2, NORM, EXT, EXT :-10. X-Y OPERATION Sensitivity: 5mV/div to 5V/div in 10 steps (1-2-5 sequence) through the vertical system. Continuously variable between steps and to at least 12.5V/div. MACSERVICE PTY LTD $900 Optional cover for CRT screen – $35 X Axis Bandwidth: DC to at least 4MHz; Y Axis Bandwidth: DC to 100MHz; X-Y Phase: Less than 3° from DC to 50kHz. DISPLAY CRT: 5-inch, rectangular tube; 8 x 10cm display; P31 phosphor. Graticule: Internal, non-parallax; illuminated. 8 x 10cm markings with horizontal and vertical centerlines further marked in 0.2cm increments. 10% and 90% markings for rise time measurements. Graticule Illumination: variable. Beam Finder: Limits the display to within the graticule area and provides a visible display when pushed. Australia’s Largest Remarketer of Test & Measurement Equipment 20 Fulton Street, Oakleigh Sth, Vic, 3167. Tel: (03) 9562 9500; Fax: (03) 9562 9590 **All illustrations are representative only. Products listed are refurbished unless otherwise stated. Countr Interstate y & Call Free Ca ers 1800 680 ll 680 T MACSERVICE P/L FOR ALL YOUR FLUKE REQUIREMENTS ●   FREE CALL: 1800 680680 REFURBISHED PRODUCTS: MINIMUM 90-DAY WARRANTY ● CONTACT MACSERVICE FOR ALL YOUR FLUKE REQUIREMENTS ACSERVICE FOR ALL YOUR FLUKE REQUIREMENTS ●   FREE CALL 1800 680680 ● ALL Mobile phone batteries are way over the odds. You can buy this NEC Sportz phone for $299 with $1000 worth of free weekend calls but the battery will set you back anywhere up to $100 or so. The open battery in this photo has just had its cells replaced for $25! DEAD PHONE BATTERY? Don’t toss it – refill it with standard AA rechargeable cells Dead battery in your bat-phone again? Getting sick of paying out big dollars to replace it? Well cheer up. In this article, we show you how to replace the cells in your mobile phone batteries with standard AA-size nicad cells and save heaps of dollars. By ROSS TESTER 6  Silicon Chip If you’re one of the million plus Australians who owns a mobile phone, chances are you have already discovered one of the negative aspects: the price of replacement batteries. Sure, mobile phones themselves have dropped in price dramatically in recent years. The phone shown above, an NEC Sportz, is a classic example. When purchased two years ago it cost me the best part of a thousand dollars – $899 to be precise. Yesterday, I saw an advertisement for the same phone for just $299, with a thousand dollar’s worth of weekend calls thrown in for nothing! That’s progress, I guess. Fig.1: reproduced from the August 1994 issue, this Nicad Zapper circuit charg­es two 1000µF capacitors to 33V. This charge is then dumped through the dud cell by Mosfet Q7 when the ZAP button is pressed. It’s a pity that the same thing hasn’t happened to mobile phone batteries. Unfortunately, this is the one “expendable” where they can really get at you. Or at least they could until now. Typical replacement mobile phone batteries will set you back anywhere from about $50 up to more than $100. And that’s for the “ordinary” models which give you minimum talk time. If you want the “super” batteries which last a lot longer, be prepared to pay significantly more. In addition, buying genuine (ie, branded) phone batteries will set you back even more. The service life of mobile phone batteries leaves a lot to be desired, mainly due to the way we treat (or mistreat) them. Manufacturers normally rate their nicad cells for at least 1000 charge/discharge cycles but most mobile phone users find that their batteries last a year or less. Last time we checked, there were less that 1000 days in a year, so it follows we are doing something wrong! Nicad problems Many readers would be aware of the various problems which befall nickel cadmium batteries but to briefly recap, here are just some of them: (1) Memory effect – the battery loses capacity by being constant­ ly discharged only partially and then recharged. For example, you take your phone out for the day, then you come home and bung it on the charger so it’s ready for next day. The problem, of course, is that the battery is only par­tially discharged and never receives a full charge. Over time, it “remembers” this amount of charge, and this becomes its total capacity. Memory effect can be cured by a few cycles of complete discharge and recharge but you need to know when your batteries are discharged. Generally, if you wait until your phone starts beeping with its low battery signal you can be sure it is dis­charged but that brings us to another problem. (2) Reverse polarity cells – all phone batteries are composed of a number of individual cells connected in series. In a typical 6V phone battery, there will be five nicad cells, each rated at 1.2V (5 x 1.2 = 6V). However, not all nicad cells in a pack are born equal. Some may discharge further than others, and the charge/discharge patterns may actually cause one or more cells to be discharged “below zero” so that they become reverse polari­ty. This is a prime reason for battery failure. (3) Dendrites – the ideal battery would never lose its charge while waiting to be used. Unfortunately, this is not the case – all cells discharge over time. Also over time, crystalline growths may occur inside the cell which has the effect of in­ creasing the internal leakage current dramatically. These growths, called dendrites, will eventually short out a cell and are another major reason for battery failure. (4) Overcharging – all batteries have Fig.2: if you have a DC power supply which can deliver more than 30V, you can use this circuit to zap dud nicad cells. April 1996  7 The battery on the left, from an Ericsson GH198, was given a new lease of life by “zapping” bad cells. The battery on the right, from an NEC Sportz, was completely renewed. This photo shows the Ericsson and NEC batteries with their cases disassembled. The Ericsson was delightfully simple, the NEC took a little more work! a correct charge rate and a correct time to be charged. Exceed either of these, and you risk overcharging. Usually, this means a build-up of heat which will ultimately cause irreparable damage inside the cell. Often it will cause the cell to start leaking fluid and that leads to corrosion and general degradation. Occasionally, this heat build up is so dramatic that it blows the cell apart. Many phones have smart chargers which monitor the state of charge and adjust automatically. Many do not –they rely on the user to remove the battery once it is charged. And that doesn’t always happen! (5) Corrosion – surprising though it may seem, many users fail to recognise the need to keep battery contacts (both charging con­tacts and 8  Silicon Chip phone contacts) clean. This can lead to a battery not charging properly, or not being able to deliver power to the phone. Resurrecting a dead battery There are three steps to breathing new life into an appar­ently dead battery. The first is quite simple – clean the con­tacts on the battery, the phone and on the charger. For people living near the sea or in industrial areas, this is an all-too-common problem and one which many people seem blissfully unaware of. You might find that after cleaning the contacts, the battery accepts charge and works quite satisfactorily. The second is a little more complex, involving the opening of the battery case and checking the individual cells with a multimeter. You may well find that one, two or even most cells are quite OK, each measuring around 1.2V. However, it is quite likely that at least one cell and maybe a couple are showing either very low or no voltage. These cells need to be zapped or replaced. We have talked about zapping nicad cells in past issues of SILICON CHIP. If cells are low in charge due to den­drites, you can often fix them by zapping. This literally blows up the den­drites by applying a very brief but powerful charge to the cell. This technique was covered, along with a Nicad Zapper to build, in the August 1994 issue. This circuit is shown as Fig.1. Don’t be tempted to apply a high voltage directly from a power supply to the cell in the hope that this will blow the dendrites away. All you will succeed in doing is permanently cooking the cell and you might even damage your power supply in the process. However, if you have a suitable power supply, you can use the circuit of Fig.2 to make a cut-down version of a Nicad Zapper which is just as effective. We were able to fully restore an apparently dead phone battery to life using the Nicad Zapper. The technique is to “zap” individual cells, not the whole battery at once. To do this, the battery case must be opened and we will show you how to do this shortly. As luck would have it, the battery concerned (for an Erics­son phone) was one of the easier ones to disassemble. Once this was achieved, we had to zap one particularly difficult cell half a dozen times but eventually it said “I give up” and ac­cepted charge. In this battery, there was only one cell apparently dead, with only a couple of hundred millivolts across it instead of more than 1.1V for each of the rest. It was the obvious target for “zapping.” You don’t need to disconnect the cell to be zapped from the other cells. Instead, you simply connect the leads from the zapper across the cell concerned (taking care of polarity) and press the button. It’s easy to check whether your “zapping” has worked, simply by measuring the voltage across the suspect cell after the whole battery has been on charge for a few hours. Take the bat­tery off charge and measure each Corrosion is a major cause of rechargeable battery problems. These contacts clearly show a bad case of oxidisation – no wonder it wouldn’t charge properly. cell. Depending on how long they have been on the charger, they should all be somewhere between 1.1V and 1.2V (or maybe higher if they are almost fully charged). If the zapped cell looks OK, put the battery back on to fully charge it and then leave it for a day or so. This done, check all the cells again. If they are all close to the same voltage (ie, 1.2V), then you cured it. On the other hand, if the suspect cell has dropped to below 1V, you can assume it still has a few problems! Try zapping it again – you’ve got nothing to lose. You may cure it or if the cell is really dead, you’re not going to do any more damage by over-zapping it! Ultimately, nicads do wear out; the chemical components become exhausted and will no longer support the reaction neces­ sary to recharge a cell. Again, cell voltage is a good check of this. Cell strategy So what if you have one or more dead cells in your battery? Do you just replace dead cells or replace the lot? The answer is to replace the lot. This might seem like overkill but is the only practical approach. For a start, if you place one or two new cells into a bat­tery, the new cells will almost certainly have more capacity than the old cells, even if their label ratings are identical. It stands to reason that a brand new cell will always have more capacity than an old cell. If you have cells of different ages in a battery, its capacity will always be limited to that of the weakest cell in the pack – it’s like the weakest link in the chain. So if you put one or two new cells in a battery, you will be wasting your money. Do the job properly and fit all new cells – you will still be saving heaps of money over the cost of a new sealed battery! Just as importantly, instead of the measly 700mAh battery which came with your phone, you will end up with at least a 1000mAh battery, which will give you hours more standby and talk time! YOU CAN AFFORD AN INTERNATIONAL SATELLITE TV SYSTEM Nicads or NiMH? SATELLITE ENTHUSIASTS STARTER KIT Throughout this feature, we have talked about nickel cadmi­um (nicad) batteries as if they were the only types used. One of the more recent batteries to come onto the consumer market is the nickel metal hydride, or NiMH, type. These offer some advantages over nicads. For a start, NiMH batteries do not develop a memory. They are much more forgiving of the type of charge/ discharge cycles we consumers inflict on them, and they are much more environmen­tally friendly in manufacture and disposal. Most importantly, size for size NiMH batteries offer sig­ nificantly better capacity than their nicad counterparts. For example, the AA types we feature in this article offer a 1000mAh capacity in nicad form and 1100mAh capacity in NiMH form. On the downside, they are more expensive and they are not suitable for high discharge applications such as in battery-powered tools and radiocontrolled toys. There is also the question of whether chargers, especially smart chargers, designed for nicads would be suitable for NiMH batteries. It’s a question that we have not been able to get firm answers for. Experience, though, suggests that every charger we have tried has no problem whatsoever with NiMH batteries. We have used both types in preparing a number of batteries for this article. All original batteries were nicads, as would be expected, but when replaced all have performed at least as well as the original (and usually much better), whether fitted with nicads or NiMH cells. Note that which ever cell you choose, make sure it has solder tags. It is possible to solder to cells but it is not easy and when they are available with solder tags already on, why not take advantage of them? You place YOUR OWN INTERNATIONAL SYSTEM FROM ONLY: FREE RECEPTION FROM Asiasat II, Gorizont, Palapa, Panamsat, Intelsat HERE'S WHAT YOU GET: ● ● ● ● ● ● 400 channel dual input receiver preprogrammed for all viewable satellites 1.8m solid ground mount dish 20°K LNBF 25m coaxial cable easy set up instructions regular customer newsletters BEWARE OF IMITATORS Direct Importer: AV-COMM PTY. LTD. PO BOX 225, Balgowlah NSW 2093 Tel: (02) 9949 7417 / 9948 2667 Fax: (02) 9949 7095 VISIT OUR INTERNET SITE http://www.avcomm.com.au YES GARRY, please send me more information on international band satellite systems. Name: __________________________________ Address: ________________________________ ____________________P'code: __________ Phone: (_______) ________________________ ACN 002 174 478 April 1996  9 This photo shows how to open up the battery. If it is gripped along an edge as shown and the vise slowly tightened, eventually the weld or glue will give. Suitable tools (eg, a table knife) can then be used to open up the crack. To fully open the case, continue working slowly around the edge with the knife. The screwdriver prevents the case from closing again. the cells under much less stress by soldering to tags. Opening the case The manufacturers don’t want you to replace cells. They want you to buy a new battery! Because of this, they don’t make it easy to open up the case, usually welding it or seamlessly gluing it. But if you know the secret, it’s not too hard to defeat this. The technique for opening any welded plastic battery case is to apply 10  Silicon Chip just enough pressure in the right place to make it give. This is most easily achieved in a bench vise, because the pressure is very easily controlled. Sometimes, it is not even necessary to go to this level. The battery for the Ericsson, for example, came apart very easily once we removed the label covering the back of the battery. Examine the case carefully – it should be possible to make a reasonable guess as to where the halves of the case join. Place the battery so that this seam runs lengthwise from one jaw to the other in the vise (as shown in the accompanying photo). The battery should be positioned so that it is just gripped along the very edge to be broken. Now very slowly tighten the vise so that pressure is ap­plied to the seam. If all goes well, before too long you should hear a reassuring “crack” as the first seam gives way. Sometimes, I have found it necessary to give a little extra help by tapping lightly along the seam with a small hammer, or even a knife handle. Eventually, you should hear that “crack” and you’re on your way. Don’t be too concerned if the seam doesn’t break completely cleanly – after all, you are breaking a weld. Besides, it will be glued together later anyway. It is also possible that the plastic may crack in the wrong place –again, a dab of super glue later will generally fix this up. The best tool for expanding the seam is an ordinary table knife. It doesn’t need to be sharp (in fact, it’s safer if it’s blunt) – just as long as it’s thin enough to work into the seam, and wide enough to give a little leverage. Use a second knife or a thin blade screwdriver to keep working your way around the seam until you have lifted it on all four sides. Before opening up the battery completely, prise it apart slightly and see how the cells are assembled inside. You might find that they have used some glue, double sided tape, wax or other gunk to hold the batteries together or in place. Just take your time, prising the case apart slowly until you’re sure you can see what goes where. Inside the case, you’re likely to find a polarity protection diode, perhaps a thermistor or some other components. Make a note (or drawing) of how and where these are placed and connected. Incidentally, we did find one slightly disturbing thing when breaking apart several batteries for the NEC Sportz phone. The genuine NEC battery contained protection components, while the significantly cheaper non-genuine “equivalent” replaced these with lengths of wire! Once you have the case apart, you might have to carefully remove some insulation to gain access to the individual cells. At this point, you can decide wheth- the replacement cells, keep your solder joints as thin as possible. We found that tucking a negative-end tag under the positive-end tag achieved the minimum bulk. You might find that some solder tags need to be trimmed a little shorter if space is very tight in your battery but so far we haven’t had to do that. You might also find it necessary, as we did in one battery, to solder the tags at approximately 15° angles to each other in order to get the cells to fit. Experiment with your cells before soldering. If using the connecting straps from the original cells leave them until last. Double and triple check your positive and negative terminals before soldering the straps into place. Reassembly This battery is from the surf club transceiver pictured on the next page. Unlike mobile phone batteries, this is rated at 7.2V and therefore required six new cells. As you can see, there is plenty of room inside the case. er you want to persevere and “zap” cells, or simply replace the lot. In many ways, the second option is the best, because you know you have a brand new battery when it’s done. It’s obviously the only route to follow if you don’t have a zapper. Removing cells In all batteries that we have disassembled, the cells themselves are welded together. This is a pity, because if at all possible, we want to use the same connecting straps on the new cells. These were made to fit the case. The straps are usually spot-welded to the first and last cell in the string but they usually come free with a little coaxing (ie, with pliers). In the case of the NEC Sportz battery, the connecting straps also form the connection to the charging contacts as well as the phone power contacts, so it was imperative to get the straps off in one piece. Other batteries have separate contacts moulded onto the case and are connected by flying leads. Remember if soldering or unsoldering to a moulded contact, apply heat for as short a time as possible. Any insulation or other material removed should be kept as intact as possible for reuse. In some cases, due to the method of original manufacture, this may be impossible. However, keep any broken pieces to make fabrication of new pieces easier. Replacing cells The major difference between original cells and replacement cells is that, in most cases, the original cells don’t have a raised “dimple” on top which marks the positive end; they may not even have positive or negative markings on them, so be careful when identifying which end is which! That dimple on the replacement cells could create a space problem but so far we haven’t found any cases that can’t accommodate the slightly longer replacement cells. Because the cells are connected in series, it’s simply a matter of soldering positive to negative in the right position – use the cells which came out as a guide. It’s always wise to pre-tin the solder tags and, contrary to what you might imagine, a good, hot iron is better than a lukewarm one. It gets the job done quicker, before the battery has a chance to think “Hey, I’m getting hot!”. Check and double check your solder connections. Keeping in mind our comments about the extra length of Refit any protection diodes, therm­ istors, etc, to exactly the same positions and cells as they were originally. Your charg­er might rely on certain connections to sense charge levels and cell temperature to avoid overcharging. Be sure also to replace any insulation (preferably the original insulation). In many batteries we have seen, the con­ necting straps are separated from the battery terminals by a thin piece of insulation – if this is creased or bent out of shape, shorts are almost inevitable. We have found that in some cases the replacement cells are smaller in diameter than the original cells. In this case, it may be necessary to provide a small amount of packing (eg, cardboard) inside the case to prevent cell movement. Naturally, any packing material that was used in the origi­nal cells should be re-packed if possible. Where cells are a tight fit, we found the kitchen knife a handy tool to help slightly expand the case as cells were re-inserted. If possible, you should do a “dummy run” of the new battery before final assembly. With it held together as far as possible, check with a multimeter that voltage appears at the phone termi­ nals. Check that the charging contacts make contact with the charger (most chargers have some form of indication) and that the battery still clips on to the phone. If all appears well, reassemble the case with a tiny drop of super glue at April 1996  11 each of the four corners. Ensure that the case is clamped together for five minutes or so, until the glue dries. You don’t want to use more glue that necessary – after all, in a year or so, you might want to replace the cells again! It will be so much easier the next time around because you will know exactly what to do. Transceiver batteries We mentioned before that mobile phone batteries aren’t the only ones which can be refurbished. In fact, The techniques are not limited to mobile phone batteries. This UHF transceiver belongs to a surf life saving club and their batteries are even more expensive. Six new NiMH cells and an hour’s work saved them more than $80 for a new battery! while this article was in preparation we received a call from the local Narrabeen Beach Surf Life Saving Club. They had just been told that the batteries for their hand-held UHF radio transceivers had gone up to more than $100 plus tax (or more than $130). As volunteers, their finances were already stretched beyond the limit. Using the techniques described in this article, we cracked open two of their defunct batteries and replaced the cells – one with NiMH cells and the other with nicads. Probably the only real difference between these batteries and mobile phone batteries was that they took six cells (7.2V) and there was still plenty of room inside the cases. The chargers used by the Surf Club are very sophisticated models, offering a switched choice of standard trickle charge or a 1-hour rapid charge with au­tomatic switch-over to trickle charge. Without wanting to delve too much into the charger elec­tronics, we want­ ed to know if there was any difference between the NiMH and the nicad batteries. As far as we can tell, both new batteries behave identically. Charging times appeared similar, switch over to trickle charge is identical and radio operation is the same except for the slightly longer operation of the NiMH battery. What about other transceivers, such as handheld units for the CB or amateur bands? As far as we can tell, the process described here still applies and you can save heaps of money. Special offer from Jaycar High capacity rechargeable cells are not normally all that easy to buy, especially at a reasonable price, but Jaycar Elec­tronics has made a huge purchase of them and is offering them at very good prices. For example, 1000mAh AA nicad batteries, with solder tags, are just $5 each and 1100mAh AA NiMH batteries, also with solder tags, are just $6.25 each. But exclusively for SILICON CHIP readers, Jaycar has agreed to a bargain offer: buy four cells and get the fifth one free! And for the vast majority of readers wishing to refurbish phone batteries, five cells just happens to be exactly what they need. So for AA nicads, you pay just $20.00 for five (instead of $25) and for AA NiMH cells you pay $25 (instead of $31.25). To take advantage of the offer, fill in the coupon below (or a photocopy) and take it with you to your near­est Jaycar Electronics store (offer also available through Jaycar mail order). Note: this offer is available for two months only, until 31st May 1996. References For additional reading on the care of nicad batteries, these articles will be of use: (1). An Automatic Nicad Battery Discharger; SILICON CHIP, Novem­ber 1992. (2) Single Nicad Cell Discharger; SILICON CHIP, May 1993. (3) Nicad Zapper; SILICON CHIP, August 1994. (4) Automatic Discharger For Nicad Battery Packs; SILICON CHIP, September 1994. (5) A Fast Charger For Nicad Batteries; SILICON CHIP, October 1995. (6) Reflex (“Burp”) Charging Nicad Batteries For Long Life; SILICON CHIP, SC January 1996. Jaycar Nicad/NiMH AA Battery Offer For the months of April & May 1996 only, Jaycar Electronics is making the following special offer to SILICON CHIP readers: buy four AA 1000mAh nicad cells with solder tags (Cat. SB-2441) or four AA 1100mAh NiMH cells with solder tags (Cat. SB-2457) and get a 5th cell for free. That's represents a saving of $5 for the nicad cells and $6.25 for the NiMH cells. You can take advantage of this offer only by filling in this coupon and taking it to your nearest Jaycar store; or fax or mail the coupon to Jaycar’s mail order department. Yes! please supply: ❏ 5 1000mAh nicad cells ($20)   ❏ 5 1100mAh NiMH cells ($25) Name ___________________________________________ Street ___________________________________________ Suburb/town_______________________ Postcode _______ 12  Silicon Chip Note: please include credit card details for mail order & add $4 for p&p. Offer expires 31st May, 1996. ORDER FORM BACK ISSUES MONTH YEAR MONTH YEAR PR ICE EACH (includes p&p) TOTAL Australi a $A7.00; NZ $A8.00 (airmail ); Elsewhere $A10 (airmail ). Buy 10 or more and get a 10% discount. Note: Nov 87-Aug 88; Oct 88-Mar 89; June 89; Aug 89; Dec 89; May 90; Aug 91; Feb 92; July 92; Sept 92; NovDec 92; & March 98 are sol d out. All other issues are currently i n stock. $A B INDERS Pl ease send me _______ SILICON CHIP bi nder(s) at $A12.95 + $5.00 p&p each (Australi a only). N ot avail abl e elsewhere. Buy five and get them postage free. $A SUBSCRIPTIONS  New subscription – month to start­­____________________________  Renewal – Sub. No.________________    Gift subscription  RATES (please tick one) 2 years (24 issues) 1 year (12 issues) Australia (incl. GST)  $A135  $A69.50 Australia with binder(s) (incl. GST)**  $A159  $A83 New Zealand (airmail)  $A145  $A77 Overseas surface mail  $A160  $A85  $A250 Overseas airmail  $A125 **1 binder with 1-year subscription; 2 binders with 2-year subscription YOUR DETAILS Your Name_________________________________________________ GIFT SUBSCRIPTION DETAILS Month to start__________________ Message_____________________ _____________________________ _____________________________ Gift for: Name_________________________ (PLEASE PRINT) Address______________________ _____________________________ (PLEASE PRINT) Address___________________________________________________ State__________Postcode_______ ______________________________________Postcode_____________ Daytime Phone No.____________________Total Price $A __________ Signature  Cheque/Money Order  Bankcard  Visa Card  Master Card ______________________________ Card No. Card expiry date________/________ Phone (02) 9979 5644 9am-5pm Mon-Fri. Please have your credit card details ready OR Fax (02) 9979 6503 Fax the coupon with your credit card details 24 hours 7 days a week Mail order form to: OR Reply Paid 25 Silicon Chip Publications PO Box 139, Collaroy 2097 No postage stamp required in Australia April 1996  13 One of the Larrousse-Lamborghini cars in action at the Adelaide Grand Prix. A sophisticated traction control system was used to allow greater acceleration and cornering speeds and to improve the start-line performance. Traction Control Last month, we examined the traction control systems now used in some road vehicles. This time we look at how the technology has been used in motor racing. During 1993, electronic aids were permitted in the highest form of motor sport: Formula 1. This meant that, together with electronically-controlled gearboxes and active suspension, electronic traction control was used. In addition to preventing unwanted wheel-spin during normal acceleration, the system was also used during Grand Prix starts to give the best possible results. All electronic driver aids were banned from the 1994 season onwards and so the technology was seen largely for just the one year. PART 2: By JULIAN EDGAR 14  Silicon Chip The system examined here was fitted to the Lamborghini V12 engine of the Larrousse-Lamborghini cars, driven by Philippe Alliot and Erik Comas. It was developed by Bosch Motorsport in conjunction with Lam­ bor­ghini Engineering. System requirements The requirements of the traction control system were to control slip with precision; capable of subtle levels of control, yet able to be quickly recalibrated. It also needed to be easy to use, allowing driver interaction, yet not being driver dependent. Engine power was controlled in such a way that drive wheel slip was limited to a value which ensured maximum straight-line acceleration and cornering stability. Unlike normal Fig.1: the appropriate goal value of wheel slip was dependent on car speed and throttle position, the gear being used and the lateral (cornering) acceleration. road-vehicle traction control systems, the system did not use braking to control wheel-spin but relied entirely on engine torque control. This was achieved by progressive injector cut-off. System details A closed loop PID (proportional, integrating, differentiat­ing) controller was chosen to minimise racetrack setup of the traction control algorithm. In addition, fuzzy logic control elements from racing ABS systems were added. This control ap­proach gave the following set up advantages which were independ­ent of tyre wear characteristics and independent of the slip-goal target value. Only a simple ‘wet/dry’ driver-selectable goal-offset switch was required. The digital control process was handled by one of the existing engine management microcomputers which, as well as using engine sensor information, Fig.2: a PID controller was used to calculate the desired was fed with speed data from each wheel. per­centage reduction in engine torque output to reduce The procedure taken for the calculation of the wheel slip to an optimal value. rear wheel slip is shown in Fig.1. The basic goal value was derived from a map using the functions of car speed and throttle position, with an offset provided by the cockpit wet/dry switch. The value derived from a gear-dependent curve was added and this in engine torque, compensated by the current gear ratio is multi­plied by a factor based on the lateral acceleromand the differential ratio. eter input. The calculation of wheel slip was made by Should the driver have sensed that slip was occurring comparing the speed of each of the rear wheels with the and had lifted his foot during traction-controlled slip, reference speed of the car, which was derived from the problems could have occurred. To counteract this, a drivfront (non-driven) wheels. er-initiated torque reduction was also compensated for as The deviation between the desired slip and the actual a function of engine RPM and throttle position. slip values was fed to the PID controller, as shown in Fig.2. The calculated engine torque reduction was convertThe gain and time delay factors of each of the P, I and D ed to a corresponding injector cut-off pattern by dyna­ components were stored in maps as functions of the car mometer-derived data held in a 24-point curve. The speed/throttle position operating points. The output of encoded steps of injector shut-off ranged from “half” a the PID controller was the per­centage reduction required cylinder (one every other 720° cycle) to a full 12-cylinder April 1996  15 10 5 40 30 20 OSITIO N 70 60 50 THRO TTLE P CYLINDER CUT-OFF NUMBER 90 80 10 0 0 12000 10000 8000 6000 4000 0 2000 Fig.3: the maximum number of injectors which could be cut off was dependent on throttle position and engine RPM. This provided safety against engine stalling should the PID controller be programmed incorrectly or if part of the system failed. cut-off. An absolute limit calibration was incorporated, fixing the maximum number of cylin­ders which could be cut off at a given RPM and throttle position. This acted as a safeguard against engine die-outs at low RPM and also allowed rapid recalibration of the PID controller without upsetting overall vehicle dynamics. Fig.3 shows this overall cut-off limiting calibration. A completely separate algorithm was used during the stand­ing starts which occur in this form of racing. It used two dis­tinct control strategies. In part 1, the system allowed the driver to maintain full throttle prior to clutch engagement, with the ECU holding the engine RPM at the desired level. Once the clutch was engaged by the driver and the car exceeded a certain speed, part 2 of the system was enabled. This modulated the continued full throttle by means of injector cut-off, allowing control of wheel slip to the desired level. Normal PID control was activated once the car had reached a second, higher speed threshold. Fig.4 shows the telemetry record from a Grand Prix start. Note that the throttle is held fully open for the majority of the time and the rear wheel speed increase as the clutch is engaged in part 1. In part 2, a constant slip ratio is maintained, as indicated by the difference in the front and rear wheel speeds. Testing & development Calibrating the system to give the optimal level of slip proved very difficult. This was firstly because only limited traction control testing was undertaken, with the testing com­pleted only during normal chassis set-up procedures. Second, the preferences of the THR RPM CUTOFF PATTERN PART ONE REAR SPEED PART TWO FRONT SPEED Fig.4: the Grand Prix ‘start’ strategy, as shown by the telemetry data from an actual race. Note the small amount of wheel spin achieved, even though the throttle is being held fully-open most of the time! 16  Silicon Chip THR GOAL SLIP ACTUAL SLIP REAR WHEEL SPEED CUTOFF PATTERN Fig.5: the telemetry record from a wet track, with the system programmed to be very responsive to wheel slip. two drivers using the system varied: the amount of slip which suited one driver did not always suit the other! Extensive testing on a smooth, dry track revealed that 4-6% slip gave the best results but the engineers were unsure whether this would apply to all racing circuits. But while 4-6% longitudinal slip gave good acceleration, this amount of slip during cornering slowed the car. Although a lateral accelerometer input was available, it was found that a driver would not exceed a certain throttle threshold unless the car was within his ‘comfort’ yaw zone and so throttle position was able to be used to predict when more or less system intervention was required. However, driver comment and track side observation revealed that the optimal slip level wasn’t the test-derived 4-6%. In fact, the slip level which gave the best results varied from 1215% at low speeds, to less than 2% at very high speed. Rather than the percentage slip being the relevant factor, it was concluded that a slip which corresponded to a difference in wheel speed of 4-5km/h between the front and rear wheels at 90km/h was the critical value. This relative difference in rotational speed gave the car its characteristic feel in yaw and was what the driver was actu­ally feeling and describing. Once this was understood a spread­ sheet program was created to allow the new calibration of delta speed to be converted into percentage slip, FRONT WHEEL SPEED allowing the continued use of the existing software. Results Fig.5 shows the system, programm­ ed to be very responsive to slip, in action on a wet track. The car speed is shown by the “front wheel speed”, with the difference between front and rear wheel speeds being the amount of slippage, highlighted by the “actual slip” line. It can also be seen that when the throttle is closed briefly, slip ceases to occur and so momentarily drops below the “goal slip”. Acknowledgment: thanks to the Society of Automotive En­ g ineers for permission to use material from the “SAE Australasia” journals of September/October and November/ SC December 1995. Especially For Model Railway Enthusiasts Includes 14 projects for model railway layouts, including throttle controllers, sound simulators (diesel & steam) & a level crossing detector. Price: $7.95 plus $3 for postage. Order today by phoning (02) 9979 5644 & quoting your credit card number; or fax the details to (02) 9979 6503; or send cheque, money order or credit card details to: Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. April 1996  17 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au Plastic Pow 175 watts into 4 ohms; 125 watts into 8 ohms This new amplifier module is a real powerhouse. It will deliver 175 watts into a 4Ω load or 125 watts into 8Ω loads for a rated distortion of .01%. It is very quiet, very stable and suitable for musical instruments or any hifi application. W E HAVE HAD THIS amplifier under development for a long time and now that the new Motorola MJL21193/94 series transistors have become available, we can finally publish it. These new bipolar power transistors can be considered to be the plastic replacements for the very popular MJ15003/4 TO-3 metal encapsu­lated transistors. As we see it, all TO-3 power transistors will eventually be phased out and so these new plastic transistors will become one of the standard power transistors in the future. And while plastic power transistors are usually not as rugged as their metal equivalents, these new 22  Silicon Chip Motorola MJL21193/94 transistors are exceptional in this regard. They are rated at 200 watts (<at> Tcase 25°C), 16 amps continuous collector cur­rent (30 amps peak) and 250 volts (Vceo). This compares with the MJ15003/4 series which are rated at 250 watts, 20 amps and 140 volts. This simple comparison might suggest that the latter devices are still more rugged but when you look at “second break­ down” characteristics, the ability of a transistor to handle high currents at high voltage, the new plastic transistors are clearly superior. Not only do they have a much higher collector voltage rat­ing, 200V versus 140V, they have Vcbo (collec- tor base voltage, open emitter) and Vcex (collector emitter voltage, base reverse biased) ratings of 400V and can deliver considerably more current than the TO-3 types when high voltage is applied. For example, with 100V between collector and emitter, the MJ15003/4 series can deliver 1A. By contrast, with the same voltage applied, the MJL21193/4 series can deliver about 1.7A, a considerable in­ crease. (Note: both these figures refer to a one-second non-repetitive pulse condition). As well, the new plastic power transistors feature higher current gain, a better current gain-bandwidth product (4MHz versus 2MHz) and wer! By LEO SIMPSON & BOB FLYNN lower distortion when used in class-B amplifier stages. All of these factors combine to enable an improved power amplifier design. In fact, when compared to our previous design featuring MJ15003/4 transistors – the Studio 200 published in the February 1988 issue – this new design delivers considerably more power. Fig.1 shows the load lines for 4Ω and 8Ω resistive loads in the new amplifier, together with reactive load lines for (2.83Ω + j2.83Ω) and (5.6Ω + j5.6Ω). Also shown on Fig.1 are concave maximum power hyperbolas showing the 400W rating for two Motorola MJL21193/4 transistors and the one-second SOAR curve. Actually, we have not shown Motorola’s full SOAR curve; it extends to 250V. As well as the performance advantage, the new plastic power transistors feature single hole mounting to a flat heatsink surface; there is no need for a heatsink flange or bracket as is the case with TO-3 power transistors. Performance Full details of performance are shown in the separate panel and the various power and frequency response plots. As noted above, the power rating is 175 watts into 4Ω and 125 watts into 8Ω at a rated total harmonic distortion of less than .01%. The music power outputs are 230 watts and 140 watts respectively, giving a headroom of 1.1dB for 4Ω loads and 0.4dB for 8Ω loads. However, this parameter is really a measure of the regulation of the power transformer and can be ignored. For a really good power supply, the music power and the continuous power ratings of any amplifier will be almost equal. As can be seen from the distortion curves of Figs.2, 3, 4 & 5, while we have quoted a rated distortion of .01%, the typical distortion of the amplifier is actually below .002%, depending on the frequency and power output. Also, for frequencies above 10kHz, and approaching full power, the distortion April 1996  23 rises above .01% to as high as .03%. The effects of this are inaudible though, since harmonics of 10kHz are above the range of human hearing. While we have rated the amplifier fairly conservatively, using .01% harmonic distortion as the benchmark for full power, if you drive the amplifier just to the point of clipping, say where the curve reaches 0.3% on Fig.5, the amplifier will deliver over 200 watts. This will naturally be boosted if the mains voltage is above 240VAC, as it normally is in urban areas. This amplifier module is also very quiet, as is expected from modern circuit design. The residual noise is better than -114dB unweighted (20Hz to 20kHz filter) or -122dB A-weighted. That is much quieter than any CD player! Fig.1: load lines for 4Ω and 8Ω resistive loads in the new ampli­fier, together with the arched reactive load lines for (2.83Ω + j2.83Ω) and (5.6Ω + j5.6Ω). The concave curves show the 400W power hyperbola (dotted) and the one-second SOAR curve, for two Motorola MJL21193/4 transistors. The module As can be seen from the photos, this amplifier module is assembled onto a reasonably compact PC board measuring 100 x 165mm, with the four output power transistors and three smaller power devices mounted along one edge for easy mounting to a vertical heatsink. The PC board has two supply fuses on board and provi­ sion for temporary mounting of two 5W wirewound resistors which are used for setting the quiescent current. We’ll have more to say about that later in the article. AUDIO PRECISION SCTHD-HZ THD+N(%) vs FREQ(Hz) 5 21 FEB 96 10:02:08 1 0.1 0.010 0.001 T T .0005 20 100 1k 10k 20k Fig.2: THD (total harmonic distortion plus noise) versus frequen­cy at 150W RMS into a 4Ω load. 24  Silicon Chip Circuit details The full circuit of the amplifier mod­ule is shown in Fig.7. For those who are familiar with previous power amplifier circuits we have published, this design is similar to the configuration of the 120W Mosfet amplifier we featured in November and December 1988. Superficially, all we have done is substitute bipolar output transistors for the Mosfets. In fact, there is a lot more to it than that as will become apparent as we describe the vari­ous circuit features. Which brings us to the point: why use bipolar transistors instead of Mos­ fets? The reasons are quite straightforward. While Mosfet output stages in amplifiers have the virtue of being rugged they are generally more expensive than equivalent bipolar power transistors. For a given circuit configuration and power supply, bipolars will always deliver more power. As well, they don’t need such large quiescent AUDIO PRECISION SCTHD-HZ THD+N(%) vs FREQ(Hz) 5 21 FEB 96 09:56:03 1 Model Railway Projects 0.1 0.010 0.001 T .0005 20 100 1k 10k 20k Fig.3: THD distortion versus frequency at 110W RMS into an 8Ω load. current in the output stage and that translates to less heat and again, more audio power output. Inevitably, some readers may question why we used the con­figuration of the November 1988 circuit rather than the well-proven Hitachi configuration featured in our December 1987 & February 1988 issues. In fact, we built up prototypes with both circuits. Both performed very well with the Hitachi circuit giving slightly less harmonic distortion at frequencies above 10kHz. However, the circuit featured in Fig.7 gave substantially more power before the onset of clipping and so it won out. Fifteen transistors and three diodes make up the semicon­ductor count of the circuit of Fig.7. The input signal is coupled by a 2.2µF capacitor and 1kΩ resistor to the base of Q1 which AUDIO PRECISION SCTHD-W THD+N(%) vs measured 10 LEVEL(W) 21 FEB 96 09:45:00 Available only from Silicon Chip Price: $7.95 (plus $3 for postage). Order by phoning (02) 979 5644 & quoting your credit card number; or fax the details to (02) 979 6503; or mail your order with cheque or credit card details to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. ➦ Use this handy form 1 Enclosed is my cheque/money order for $________ or please debit my 0.1 ❏ Bankcard   ❏ Visa   ❏ Mastercard Card No: ______________________________ 0.010 Card Expiry Date ____/____ Signature ________________________ Name ___________________________ 0.001 Address__________________________ .0005 0.5 1 10 100 300 __________________ P/code_______ Fig.4: THD versus power at 1kHz into an 8Ω load. April 1996  25 AUDIO PRECISION SCTHD-W THD+N(%) vs measured 10 LEVEL(W) 21 FEB 96 09:47:03 1 0.1 0.010 0.001 .0005 0.5 1 10 100 300 Fig.5: THD versus power at 1kHz into a 4Ω load. AUDIO PRECISION SCFRQRES AMPL(dBr) vs FREQ(Hz) 5.0000 Vbe multiplier 21 FEB 96 09:51:55 4.0000 3.0000 2.0000 1.0000 0.0 -1.000 -2.000 -3.000 -4.000 -5.000 20 100 1k 10k 50k Fig.6: frequency response at 4W into an 8Ω load. to­gether with Q2 makes up a differential pair. Q3 is a constant current tail which sets the current through Q1 & Q2 and thereby makes the amplifier insensitive to variations in the power supply rails (this is known as PSRR; power supply rejection ratio). The collector loads of Q1 & Q2 are provided by current mirror tran­sistors Q4 & Q5. Commonly used 26  Silicon Chip of Q1 connects to the base of Q7, part of a cascode stage comprising Q7 & Q8, with Q6 pro­viding a constant current load to Q8. A 3.3V zener diode, ZD1, provides the reference bias to the base of Q8 (to see how a cascode circuit works, see the separate panel in this article). A 100pF capacitor from the collector of Q8 to the base of Q7 rolls off the open-loop gain of the amplifier to ensure a good margin of stability. The output signal from the cascode stage is coupled directly to the output stage, comprising driver transistors Q10 & Q11 and the four output transistors, Q12-Q13. Actually, it may look as though the collector of Q6 drives Q10 and that Q8 drives Q11, and indeed they do, but in reality, the signals to the bases of Q10 and Q11 are identical, apart from the DC offset provided by Q9. in operational amplifier ICs, current mirrors provide increased gain and improved linearity in differential amplifier stages. In a conventional direct-coupled amplifier, the signal from the collector of Q1 would be connected directly to the base of the following class-A driver stage transistor. In our circuit though, the signal from the collector Q9 is a “Vbe multiplier”. It can be thought of as a temper­ a turecompensated floating voltage source of about 2V. Q9 multi­plies the voltage between its base and emitter, as set by VR1, by the ratio of the total resistance between its collector and emitter (470Ω + 100Ω + VR1) to the resistance between its base and emitter (100Ω + VR1). In a typical setting, if VR1 is 100Ω (note: VR1 is wired as a variable resistor), the voltage between collector and emitter will be:     Vce = Vbe x 670/200 = (0.6 x 670)/200 = 2.01V In practice, VR1 is adjusted not to produce a particular voltage across Q9 but to set the quiescent current through the output stage transistors. We’ll describe setting the quiescent current later in this article. Because Q9 is mounted on the same heatsink as the driver and output transistors, its temperature is much the same as the output devices. This means that its base-emitter voltage drops as the temperature of the output devices rises and so it throttles back the quiescent current if the devices become very hot, and vice versa. Before leaving the cascode stage, we should mention the bias arrangements. As already noted, zener diode ZD1 sets the bias on the base of Q8, however the current through the cascode transistors is set by constant current source Q6 which has its base-emitter Fig.7: this direct coupled amplifier module uses a differential input stage (Q1,Q2) with a constant current tail (Q3) and current mirror load (Q4,Q5). This drives a cascode stage (Q7,Q8) with constant current load (Q6). Quiescent current in the output stage is set by VR1 and Q9. The output stage is a complementary class-AB Darlington configuration using Q10 and Q11 as the drivers and Q12 to Q15 as the power devices. bias set by the two diodes, D1 & D2. Because of D1 & D2, Q6 applies 0.62V to its emitter resistor and this thereby sets the current through Q6, Q8 & Q9 to 13mA. Note that D1 & D2 also provide the base-emitter bias to Q3 which sets the current through Q1 & Q2. Note too that although D1 & D2 provide identical bias to Q3 & Q6, Q3 applies a higher vol­ tage, 0.69V, to its 220Ω resistor. How can this be? The answer is partly that Q3 is operating at a slightly lower current (3mA rather than 13mA) but mainly because the BC556 transistors require less base-emitter voltage to turn them on than the BF470 used for Q6. Driver & output stages As already mentioned, Q10 & Q11 are the driver stages and they, like the output transistors, operate in classAB mode (ie, class B with a small quiescent current). Resistors of 100Ω are connected in series with the bases of these transistors as “stoppers” and they reduce any tendency of the output stages to oscillate supersonically. In order to deliver the high output currents required, four output transistors are used, essentially as paralleled pairs. Each pair, Q12/Q13 and Q14/ Q15, has its bases and collectors connected together and the emitters connected to the common­ed output via 0.47Ω 5W resistors. The resistors are includ­ed mainly to ensure a degree of current sharing between the transistors in each paralleled pair. For example, if the output stage was delivering 9 amps (possible at full power into a 4Ω load) and one transistor say, Q12, had twice the gain of Q13. The initial effect of this would be for Q12 to take twice as much current as Q13; ie, 6A versus 3A. However, if Q12 had 6A through it, its emitter resistor would have 2.82V across it and Q13’s emitter resistor would only have 1.41V across it. The net effect would be that the bias to Q12 would be throttled back substantially and so while Q12 would still take more current, the sharing would be April 1996  27 Cascode Operation Explained A cascode stage is one where two transistors are connected in series, as shown in Fig.8. This shows an idealised circuit with a precise reference voltage (Vref) applied to the base of Q2. In one sense, Q2 acts like an emitter follower and applies a fixed DC voltage (Vref - Vbe) to the collector of Q1. This con­stant supply voltage at the collector of Q1 eliminates any gain variations which would otherwise occur if Q1’s collector voltage was able to vary. The varying current drawn by Q1 due to its input signal then becomes the signal drive to the emitter of Q2. Because of the constant voltage at its base, Q2 is effectively connected much more even and so Q12 would not overheat. The emitter resistors also help to stabilise the quiescent current to a small degree and slightly improve the frequency response of the output stage by adding local current feedback. Negative feedback is applied from the output stage back to the base of Q2 via an 18kΩ resistor. The amount of feedback and therefore the gain, is set by the ratio of the 18kΩ resistor to the 820Ω value at the base of Q2. Thus the gain is 23. The low frequency rolloff is mainly set by the ratio of the 820Ω resistor to the impedance of the associated 100µF capacitor. This has a -3dB point of about 2Hz. The 2.2µF input capacitor and 18kΩ base bias resistor feed­ ing Q1 have a more important effect and have a -3dB point at about 4Hz. The two time-constants combined give an overall roll­off of -3dB at about 6Hz. Fig.8: an idealised cascode circuit. This has a precise reference voltage (Vref) applied to the base of Q2. At the high frequency end, the 820pF capacitor and the 1kΩ resistor feeding the base of Q1 form a low pass filter which rolls off frequencies above 195kHz (-3dB). The overall amplifier fre­quency response can be seen in the diagram of Fig.6. An output RLC filter comprising a 6.8µH choke, a 6.8Ω resistor and a 0.15µF capacitor couples the output signal of the amplifier to the loudspeaker. It isolates the amplifier from any large capacitive reactances in the load and thus ensures stabili­ty. It also helps attenuate RF signals picked up by the loud­speaker leads and stops them being fed back to the early stages of the amplifier where they could cause RF breakthrough. The low pass filter at the input is also there to prevent RF signal breakthrough. Finally, before leaving the circuit description, we should note that the PC board itself is an integral part of Fig.9: suggested power supply for the amplifier. This should be upgraded if the amplifier is to be used with 4Ω loads, with 20,000µF (2 x 10,000µF) on each supply rail. 28  Silicon Chip as a “grounded base” stage and it converts the varying signal current at its emitter to a signal voltage at its collector. The combined effect of operating Q1 with a constant collec­tor voltage and Q2 in grounded base mode gives a stage with much improved linearity and bandwidth compared with a single common emitter stage. Cascode stages are a common feature of RF circuitry where their wide bandwidth is desirable. Cas­ code stages were originally designed around valves and the word “cas­code” is derived from the phrase “cas­­cad­ed via the cathode”, a reference to the cathode of a valve. the circuit and is a major factor in the overall performance. The board features star earthing, for minimum interaction between signal, supply and output currents. Note that the small signal components are clustered at the front of the board while all the heavy current stuff is mostly at the back and sides. For good tempera­ ture compensation of the quiescent current, all the output tran­sistors, the driver transistors and the Vbe multiplier, Q9, are mounted on the same heatsink. Suggested power supply Fig.9 shows the circuit of a suggested power supply for the amplifier. Note that we regard this as a “minimum spec” power supply and one which should be upgraded if the amplifier is to be used with 4Ω loads. If this is the case, we suggest that 20,000µF (2 x 10,000µF) on each supply rail would be the minimum required, in order to satisfy the ripple current demands when the amplifier is delivering high power. The power transformer is a 300VA toroidal type which may seem rather large but remember that this amplifier will easily deliver more than 200 watts at the onset of clipping and there­fore needs a 300VA transformer, particularly if it is to be used in professional sound reinforcement applications. The power supply and the amplifier module will need to be mounted in Fig.10: install the components as shown here, taking care to ensure that all polarised parts are correctly oriented. Note that the 5W resistors are mounted slightly proud of the board. a substantial metal case with a large heatsink. The bridge rectifier will need to be mounted on the metal chassis because it will dissipate quite a large amount of heat when the amplifier is delivering high power. the amplifier is in­tended for continuous full power delivery at frequencies above 10kHz, then the 6.8Ω resistor in the output filter should be a wire­ wound type with a rating of at least 5W, otherwise it will burn out. Choke L1 is wound with 24.5 turns of 0.8mm enamelled copper wire on a 13mm plastic former. Alternatively, some kitset suppliers will provide this choke as a finished component. When installing the fuse clips, note that they each have little lugs on one end which stop the fuse from moving. If you install the clips the wrong way, you will not be able to fit the fuses. Board assembly The component overlay diagram of the PC board is shown in Fig.10. Before starting board assembly, it is wise to check the board carefully for open or shorted tracks or undrilled lead holes. Fix any defects before fitting the components. Start by inserting the PC pins and the resistors. When in­stalling the diodes, make sure that they are inserted with the cor­rect polarity and that you don’t confuse D1 & D2 (1N914 or 1N4148) with the 3.3V zener diode (BZX79-C3V3 or equivalent). Take care when installing the electrolytic capacitors to make sure that they are installed the right way around. Note that the 100pF compensation capacitor from the collec­tor of Q8 to the base of Q7 should have a voltage rating of at least 100V while the 0.15µF capacitor in the output filter should have a rating of 400V. Another point to be noted is that if Both Q6 and Q8, which are BF470 and BF469 respectively, are fitted with U-shaped flag heatsinks, as shown here. April 1996  29 Fig.11: this diagram shows the heatsink mounting details for the power transistors. After mounting, use an ohmmeter to confirm that each device has been correctly isolated from the heatsink (there should be an open circuit between the heatsink and the device collectors). The 560Ω 5W wirewound resistors can also be installed at this stage; they are wired to PC stakes next to each fuseholder and are used during the setting of quiescent current. Next, mount the smaller transistors; ie, BC546, BC556, BF469 and BF470. Both Q6 & Q8 need to be fitted with U-shaped heat­ sinks, as shown in Fig.10. The four output transistors, the driver transistors (Q10 & Q11) and the Vbe multiplier Q9 are mounted vertically on one side of the board and are secured to the heatsink with 3mm machine screws. Perhaps the best way of lining up the transistors before they are soldered to the board is to temporarily attach them to the heatsink (don’t bother with heatsink compound or washers at this stage). This done, poke all the transistor leads through their corresponding holes in the board and line up the board so that its bottom edge is 10mm above the bottom edge of the heatsink. This ensures that the board will be horizontal when fitted with 10mm spacers at its front corners. Note that you will have to bend out all the transistor leads by about 30°, in order to poke them through the PC board. The heatsink will need to be drilled and tapped to suit 3mm machine screws. The relevant drilling details are shown in Fig.12. You can now solder all the transistor leads to the PC board. Having done that, undo the screws attaching the transis­tors to the heatsink and then fit mica washers and apply heatsink compound to the transistor mounting surfaces and the heatsink areas covered by the mica washers. The details for mounting these transistors are shown in Fig.11 . Alternatively, you can dispense with mica washers and heatsink compound and use silicone impregnated thermal washers instead, as can be seen in the pho­tos. Whichever method you use, do not over-tighten the mount­­ing screws. PARTS LIST 1 PC board, code 01104961, 100mm x 165mm 4 20mm fuse clips 2 20mm 5A fuses 1 coil former, 24mm OD x 13.7mm ID x 12.8mm long, Philips 4322 021 30362 2 metres 0.8mm diameter enamelled copper wire 7 PC board pins 1 large single sided heatsink, Jaycar Cat. HH-8546 or equivalent 2 TO-126 heatsinks, Altronics Cat. H-0504 or equivalent 4 TO-3P insulating washers (for output transistors – see text) 3 TO-126 insulating washers 4 3mm x 20mm screws 3 3mm x 15mm screws 7 3mm nuts 1 200Ω trimpot Bourns 3296W series (VR1) 30  Silicon Chip Semiconductors 2 MJL21194 NPN power transistors (Q12,Q13) 2 MJL21193 PNP power transistors (Q14,Q15) 2 MJE340 NPN driver transistors (Q9,Q10) 1 MJE350 PNP driver transistor (Q11) 1 BF469 NPN transistor (Q8) 1 BF470 PNP transistor (Q6) 3 BC546 NPN transistors (Q4, Q5,Q7) 3 BC556 PNP transistors (Q1, Q2,Q3) 2 1N914 diodes (D1,D2) 1 3.3V 0.5W zener diode (ZD1) Capacitors 4 100µF 63VW electrolytic 1 100µF 16VW electrolytic 1 2.2µF 16VW electrolytic 1 0.15µF 400V MKC, Philips 2222 344 51154 or Wima MKC 4 5 0.1µF 63V MKT 1 820pF 50V ceramic 1 100pF 100V ceramic Resistors 4 0.47Ω 5W 2 560Ω 5W (for current setting) 1 15kΩ 1W 1 5.6kΩ 1W 1 6.8Ω 1W 2 18kΩ 0.25W 1 6.8kΩ 0.25W 1 1kΩ 0.25W 1 820Ω 0.25W 1 470Ω 0.25W 3 220Ω 0.25W 1 180Ω 0.25W 2 150Ω 0.25W 3 100Ω 0.25W 1 68Ω 0.25W 1 47Ω 0.25W Fig.12: this diagram shows the drilling details for the large finned heatsink. April 1996  31 Fig.13: this is the full-size etching pattern for the PC board. Check the board carefully for defects before installing any parts. Now check with your multimeter, switched to a high Ohms range, that there are no shorts between the heatsink and any of the transistor collector leads. If you do find a short, undo each transistor mounting screw until the short disappears. It is then a matter of locating the cause of the short and re­mounting the offending transistor. Double-check all your soldering and assembly work against the circuit of Fig.7 and the component layout diagram of Fig.10. Set trimpot VR1 fully anticlockwise so that it is at minimum resistance. Remove both fuses and ensure that the 560Ω 5W resis­ tors are wired across both fuseholders, as described above. Testing We will assume that you have made or have access to a suit­ able power supply which is already working. That being the case, connect the supply rails and apply power. No loudspeaker or resistive load should be connected at this stage. Check the voltages shown on the circuit of Fig.7. These measurements were made with an AC supply voltage of 240VAC. If your mains voltage is PERFORMANCE Output power....................... 125 watts into 8Ω; 175 watts into 4Ω Music power........................ 140 watts into 8Ω; 230 watts into 4Ω Frequency response............ -0.3dB down at 20Hz and 20kHz (see Fig.6) Input sensitivity.................... 1.37V RMS (for full power into 8Ω) Harmonic distortion............. <.03% from 20Hz to 20kHz; typically <.003% Signal-to-noise ratio ����������� 114dB unweighted (20Hz - 20kHz); 122dB A-weighted Damping factor.................... >95 at 100Hz & 1kHz; >50 at 10kHz. Stability................................ Unconditional 32  Silicon Chip higher, and this will normally be the case, then the amplifier supply rails will be increased accordingly. Now measure the voltage at the output of the amplifier. It should be within ±50mV of 0V. If it is not close to zero, switch off the power as you have a fault. Check the voltages in the early stages as this should give you a guide to where the fault lies. The things to look for include: missed solder connections; solder splashes between tracks; incorrectly connected transistors; incorrect transistor types; and parts in the wrong way around, etc. Now monitor the voltage across one of the 560Ω 5W resis­tors. With VR1 fully anticlockwise, the voltage should be close to zero since there is no quiescent current in the output stage. Now slowly wind VR1 clockwise until the voltage starts to rise. Set VR1 for a voltage of 14V across the 560Ω resistor. This is equivalent to a quiescent current of 25mA or 12.5mA through each output transistor. You can check this by measuring the voltage drop across any of the 0.47Ω 5W emitter resistors. The average value across all four resistors should be 11mV. Leave the amplifier to run for 10 minutes or so and then retouch the setting of VR1 if necessary. Finally, fit the 5A fuses and the SC module is finished. SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SERVICEMAN'S LOG When I switch it on, nothing happens The old gag about the power switch being at fault be­cause the set won’t work when you turn it on is taking on a new twist these days. And it’s no longer a gag – these days, when the remote control system fails, the set won’t work. That was the situation I faced recently, involving a Super­star brand remote control colour TV set – 34cm model 1401R made in China. It was another repair for a colleague, so I had only a secondhand version of the fault. But the complaint was straight­forward enough; the set was completely dead. This is one of those sets which can only be switched on or off by the remote control and that was the first problem. The set came in with the remote control but this was in a rather grotty state. It had obviously had a hard life, judging by its external appearance, and was even worse inside. For starters, the batteries were flat. And although they hadn’t leaked, a previous set of batteries had, as was all too obvious from the badly corroded contacts. In fact, the corrosion was so bad that one of the contacts broke off as I was removing the dead batteries. The next problem was that I didn’t have a circuit or manu­al and so I had to track down the agents to get one. And when I did finally get a manual, the circuit turned out to about the worst quality copy I have ever encountered. I would defy anyone to decipher any of the values at anything more than a guesstima­tion level – and then only by cross referencing to the set it­self. This not an unusual state of affairs these days, unfor­tunately. I don’t know who is to blame but I do know that the service industry is being given a pretty raw deal. Anyway, back to the set itself. One of the first things to determine in situations like this is whether there is a fault in the set itself or a fault in the remote control system. Initial­ly, I set about familiarising myself with the layout and making some preliminary checks which might suggest where the fault lay. And, in order that the reader can follow the story, it is neces­sary to convey some idea of the circuitry – something which is made all the more difficult by reason of the poor circuit quality which I’ve already mentioned (the only other justification for reprinting it would be as an ‘orrible example). Voltage checks My first step was to identify and check the main voltage rails. As far as I could see, there were three: a 120V rail and two 12V rails, which I will call “A” and “B”. The 120V rail is derived from a switchmode power supply. This involves the usual bridge rectifier (D121) across the mains, a chopper transformer (EM110), and IC104, which provides the oscillator and Fig.1: the power supply circuitry in the Superstar 1401R TV receiver. The bridge rectifier is at lower left, the chopper components (EM110 & IC104) centre and right, and transformer EM112 above the bridge rectifier. Connector CN201 is at top left. 38  Silicon Chip K ALEX The UV People ETCH TANKS ● Bubble Etch ● Circulating LIGHT BOXES ● Portuvee 4 ● Portuvee 6 ● Dual Level TRIMMER ● Ideal PCB DRILL ● Toyo HiSpeed MATERIALS ● PC Board: Riston, Dynachem ● 3M Label/Panel Stock ● Dynamark: Metal, Plastic ✸ AUSTRALIA’S NO.1 STOCKIST ✸ K ALEX 40 Wallis Ave, East Ivanhoe 3079. Phone (03) 9497 3422, Fax (03) 9499 2381 TRANSFORMERS control functions for the transformer. The output from D121 is around 340V and this is smoothed by a 100µF 400V capacitor (C101). This is applied to pin 1 of IC104 via the primary winding of EM110 (pins 2 & 4). The 120V rail comes off pin 9. The 12V “A” rail is derived from another winding on trans­former EM110 (pins 12 & 13), via diode D108 and voltage regulator IC103. The 12V “B” rail, on the other hand, comes from a small 50Hz power transformer (EM112), via diode D107 and two filter capacitors (C127 & C128). It is used to power the remote control receiver and its associated circuitry, ensuring that this is functional at all times, even when the main part of the set is shut down. In general terms, this is all fairly conventional. More importantly, it enabled me to make the first assessment as to the broad nature of the fault. At first switch-on, there was no 120V rail and no 12V “A” rail. However, there was output from the bridge rectifier and there was 12V on the “B” rail. In other words, the switchmode supply wasn’t working. The switchmode supply is turned on and off – from the remote control board – via a chain of three transistors: Q116, Q117 and Q118. In simple terms, to turn the set on, a positive voltage is applied to Q116’s base from the remote control board (via pin 4 of plug/socket CN201). This turns on Q116 which then turns off Q117 and Q118. Q118 is connected between pins 2 & 4 of IC104. From this, it appears that the set is held off by connecting pins 2 & 4 together via Q118, when this is turned on. Conversely, when this transistor turns off, the set turns on. And since there was no positive voltage applied to Q116’s base when the Power button on the remote control was pressed, it • TOROIDAL • CONVENTIONAL • POWER • OUTPUT • CURRENT • INVERTER • PLUGPACKS • CHOKES STOCK RANGE TOROIDALS BEST PRICES APPROVED TO AS 3108-1990 SPECIALS DESIGNED & MADE 15VA to 7.5kVA Tortech Pty Ltd 24/31 Wentworth St, Greenacre 2190 Phone (02) 642 6003 Fax (02) 642 6127 April 1996  39 Serviceman’s Log – continued was obvious that the set could not turn on – quite apart from any other reason why it may not work. I pulled a swifty here – I set the analog multimeter switch to the low ohms range and connected the positive probe to the chassis and the negative one to Q116’s base. Like most such meters, mine applies reverse voltages to the probes when in the ohms range, which meant that I was applying a positive voltage to the base of the transistor. And it worked; the set burst into life. Well, that was a major step forward. The fault was quite clearly in some part of the remote control system. I still had to find out where but the search had been narrowed considerably. Remote control section The remote control section consists of a photo receiver module, two ICs (IC1 & IC3), a few transistors, and the 40  Silicon Chip usual array of switches, diodes and pots in the channel selection network. Fig.2 shows part of this circuit. At this point I had to get the remote control unit itself working. Apart from its grotty external appearance and the broken battery contact, there wasn’t a great deal wrong with it and I was able to get it working on a temporary basis. More permanent repairs could come later. The next thing was to determine whether the photo receiver was functioning. When a valid signal is received, this should deliver pulses to transistor Q4, which in turn drives pin 13 of IC3. In fact, the CRO confirmed that all this was happening. However, there was no positive voltage produced at pin 6 of IC3, which ultimately connects to the base of Q116. And that seemed to throw suspicion on either IC3 itself or its associated circuitry. I checked that 12V was being applied to pin 12 and that the clock crystal (Z1) was functioning (the frequency meter confirmed that this was oscillating at 455kHz). I made a few more checks of the other associated parts but could find nothing wrong. In short, it all came back to the IC. I didn’t have a replacement, so I ordered a new one from the agents (price $30 trade). And while I waited for it, I tried something else; I fitted a socket in place of IC3. Now I know that sockets have not enjoyed a very good reputation in the past and with good reason. Some of the early attempts were pretty woeful. Fig.2: part of the remote control receiver in the Superstar 1401R. Q4 buffers signals from the photo receiver module and drives pin 13 of IC3. The output from this IC appears at pin 6 and goes to pin 4 of connector CN201. But the scene has changed for the better and there are now some very good quality units available. And there is no doubt that a socket makes things a lot easier where there may be some doubt about the fault. On the other hand, space around or above the site often makes such a modification impossible. But there was room in this case, so I went ahead. And as if to justify what I had done, I suddenly found a spare IC that I’d had all the time. It wasn’t a new unit, having been removed some time previously from another set. Nevertheless, I pushed it straight into the socket, switched on and everything came good, with all remote control functions fully operative. This not only confirmed that it was the IC at fault but, in the process, cleared everything else, including the remote con­trol unit itself. I let the set run for the rest of the day and all next day and it never missed a beat. But on the third day it died. I wasn’t particularly worried; the IC was suspect, so I simply assumed that it had failed and waited for the new one to arrive. When it did a couple of days later, I pushed it in and the set came good again. I let it run as before but took the oppor­tunity to go over the various adjustments and make sure that everything was up to scratch. So the job was virtually finished, or so I thought until, a couple of days later, the set suddenly died again. Can something “die again”? Well this set did and it came as a rude shock. I had a horrible feeling that there was a “nasty” lurking in there somewhere, causing the set to fail every few days. A simple explanation In fact, it was a simpler explanation than that. A few meter checks revealed that the 12V “B” rail had failed and that this was due, in turn, to the failure of the EM112 transformer. In fact, its primary winding measured open circuit. And that created a difficult situation. While I hadn’t quoted for the job, I had given an estimate. A new transformer would be expensive and, when added to what had already been chalked up, it wasn’t going to make a very nice figure. Then I had an idea – many of these transformers feature an internal thermal fuse and I was prepared to bet long odds that this was what had failed (it wouldn’t be the first time). So was it worth trying to fix? Well, I didn’t have much to loose. The winding was wrapped in yellow plastic tape and, armed with a razor blade, I very carefully cut through it near the winding terminals, where I judged it was clear of the winding. In fact it was and, working very carefully, I was able to peel back the tape to give a good view of the winding. That was fine but Murphy had seen to it that the thermal fuse was on the opposite side to where I had started. When I finally did reach it, a quick check revealed that it was open circuit. The failure was not due to any normal fuse action; rather it appeared to be a simple structural failure. More to the point, what should I do about it? In theory, I suppose, I should have aimed to replace it. However, I didn’t fancy the time and trauma that would be involved in getting a replacement. Nor could I see the justification for it in the first place. The set is adequately fused in the mains lead, which should surely take care of any fault which could occur anywhere in the set. Why pick on this component? I simply bridged it, then rewrapped the winding in new tape, refitted the transformer and gave the set another soak test. This lasted several days and passed without further incid­ent. I handed the set back to my colleague, filled him in on the thermal fuse situation, and left him to deal with his customer. By all accounts, everyone was satisfied. Postscript: having done all the above and written about it, I suddenly acquired another version of the circuit. It is a quite different drawing but exactly the same circuit and, while not perfect, a far better quality print (most of it is readable). This is the one used to illustrate this article. The distorted Toshiba My next story is about a Toshiba 48cm colour set, model 207E9A, April 1996  41 electronic design, and applications. The sixth edition has been expanded to include chapters on surface mount technology, hardware & software design, semicustom electronics & data communications. 63 chapters, in hard cover at $120.00. Silicon Chip Bookshop Radio Frequency Transistors Newnes Guide to Satellite TV Installation, Recept­ion & Repair. By Derek J. Stephen­son. First published 1991, reprinted 1994 (3rd edition). This is a practical guide on the installation and servicing of satellite television equipment. The coverage of the subject is extensive, without excessive theory or mathematics. 371 pages, in hard cover at $55.95. Guide to TV & Video Technology By Eugene Trundle. First pub­lish-­ ed 1988. Second edition 1996. Eugene Trundle has written for many years in Television magazine and his latest book is right up date on TV and video technology. 382 pages, in paperback, at $39.95. Servicing Personal Computers By Michael Tooley. First published 1985. 4th edition 1994. Computers are prone to failure from a number of common causes & some that are not so common. This book sets out the principles & practice of computer servicing (including disc drives, printers & monitors), describes some of the latest software diagnostic routines & includes program listings. 387 pages in hard cover at $59.95. format and R-DAT. If you want to understand digital audio, you need this reference book. 305 pages, in paperback at $55.95. The Art of Linear Electronics By John Linsley Hood. Pub­lished 1993. This is a practical handbook from one of the world’s most prolific audio designers, with many of his designs having been published in English technical magazines over the years. A great many practical circuits are featured – a must for anyone inter­ested in audio design. 336 pages, in paperback at $49.95. Components, Circuits & Applica­ tions, by F. F. Mazda. Published 1990. Previously a neglected field, power electronics has come into its own, particularly in the areas of traction and electric vehicles. F. F. Mazda is an acknowledged authority on the subject and he writes mainly on the many uses of thyristors & Triacs in single and three phase circuits. 417 pages, in soft cover at $59.95. Digital Audio & Compact Disc Technology Electronics Engineer’s Reference Book Hard cove Produced by the Sony Service Centre (Europe). 3rd edition, published 1995. Prepared by Sony’s technical staff, this is the best book on compact disc technology that we have ever come across. It covers digital audio in depth, including PCM adapters, the Video8 PCM Power Electronics Handbook Your Name__________________________________________________ PLEASE PRINT Address____________________________________________________ _____________________________________Postcode_____________ Daytime Phone No.______________________Total Price $A _________ ❏ Cheque/Money Order r Edited by F. F. Mazda. version now available First published 1989. 6th edition. This just has to be the best refer­ ence book available for electronics engineers. Provides expert coverage of all aspects of electronics in five parts: techniques, physical phenomena, material & components, ❏ Bankcard ❏ Visa Card ❏ MasterCard Card No. Signature_________________________ Card expiry date_____/______ Principles & Practical Applications. By Norm Dye & Helge Granberg. Published 1993. This book strips away the mysteries of RF circuit design. Written by two Motorola engineers, it looks at RF transistor fundamentals before moving on to specific design examples; eg, amplifiers, oscillators and pulsed power systems. Also included are chapters on filtering, impedance matching & CAD. 235 pages, in hard cover at $85.00. Surface Mount Technology By Rudolph Strauss. First pub­ lished 1994. This book will provide informative reading for anyone considering the assembly of PC boards with surface mounted devices. Includes chapters on wave soldering, reflow­ soldering, component placement, cleaning & quality control. 361 pages, in hard cover at $99.00. Audio Electronics By John Linsley Hood. Pub­lished 1995. This book is for anyone involved in designing, adapting and using analog and digital audio equipment. Covers tape recording, tuners & radio receivers, preamplifiers, voltage amplifiers, power amplifiers, the compact disc & digital audio, test & measurement, loudspeaker crossover systems and power supplies. 351 pages, in soft cover at $52.95.   Title  Newnes Guide to Satellite TV  Guide to TV & Video Technology  Servicing Personal Computers  The Art Of Linear Electronics  Digital Audio & Compact Disc Technology  Power Electronics Handbook  Electronic Engineer's Reference Book  Radio Frequency Transistors  Surface Mount Technology  Audio Electronics Postage: add $5.00 per book. Orders over $100 are post free within Australia. NZ & PNG add $10.00 per book, elsewhere add $15 per book. TOTAL $A Price $55.95 $39.95 $59.95 $49.95 $55.95 $59.95 $120.00 $85.00 $99.00 $52.95 Fig.3: the vertical output stage of the Toshiba 147R9E. IC303 at left provides the vertical output signal to the deflection yoke (note the input and output waveforms). Capacitor C317 is at centre, while the deflection coils (L462) are at the extreme right. made in Singapore, vintage 1989. The complaint was gross vertical scan distortion. Only the top half of the screen had any recognisable image, while the bottom half was compressed in the centre. A colleague has a theory about vertical distortion. His rule of thumb is that if the problem is at the top of the screen, it is a power supply problem; if it is at the bottom, it is a feedback problem. Frankly, I’m always rather suspicious about general state­ments of that nature but I have to agree that it has some merit. Did it apply in this case? I leave the reader to judge for him­self. The relevant sections of the circuit involve two ICs: IC501 and IC303. IC501 is a TA8718N, a 30-pin multi-purpose chip which provides most of the front-end processing. This includes colour decoding and the derivation of the vertical and horizontal sign­als. The vertical signal comes out on pin 11 and goes to pin 4 of IC303 (AN5515). This is the vertical output stage and the signal from pin 11 goes into it on pin 4, comes out on pin 2, and goes to terminal 7 of the vertical deflection yoke. My first step was to check the voltages on IC303 and they came up virtually spot on. Next, assuming that it was a signal path fault, possibly in the feedback network, I decided to check out the various electrolytic capacitors, particularly the lower value ones, which are notorious for poor reliability. And no sooner had I made that decision, than I found one staring me in the face. It was a red Elna 2.2µF unit (C317) in what appeared to be part of the feedback path from terminal 8 of the yoke. It had leaked its inside outside, all over the board around it. Bingo, I thought. Picked it in one; I’ll knock this one over in no time. Alas it was not to be. I removed the sick unit, cleaned up the board, fitted a new one, and switched on. Result: exactly as before. Circuit waveforms So it wasn’t going to be easy after all; I would have to tackle it stage by stage. The circuit shows two waveforms; the input to IC303 on pin 4 and its output on pin 2 – see Fig.3. I reached for the CRO leads and checked pin 4. It was virtually spot on, its amplitude and shape exactly as shown. But pin 2 was a different story. The waveform was nothing like that on the circuit. I followed the signal through to the yoke (terminal 7) and then to the other side of the yoke (termi­nal 8), speculating on the remote possibility of shorted turns in the yoke. This check didn’t tell me much. For some strange reason, the waveform on terminal 8 was more like the circuit pattern than the one direct from IC303 at terminal 7. If it meant anything at all, it seemed to rule out the shorted turns theory. And that, in turn, put suspicion back on IC303 and its sur­ rounding components. With one crook electro already encountered, I first proceeded to check all the electros around the IC. And by checking, I really mean replacing, because I felt this was the only sure test when chasing a weird fault like this one. That achieved nothing. To cut a long story short, I fin­ished up checking or replacing every component around that IC – even the diodes. Nothing made any difference, which left the IC itself. It is a common type and I had stock on hand so I changed it. Again I drew a blank. I was feeling pretty desperate by April 1996  43 ning from terminal 8 of the yoke to pin 14 of this IC (via R304). And the circuit indicates 6.7V on pin 14, which was exactly what it measured. Was the fault in IC501? I didn’t fancy the time and expense involved in changing this – I would have had to order one – and looked around desperately in this part of the circuit for further inspiration. And I found it in the most unexpected place. Connected to the adjacent pin 13 of IC501 is the height control (R351), a 50kΩ pot to chassis. Now I probably would never have suspected this part of the circuit in a month of Sundays but what caught my eye was a bypass capacitor, C303, from pin 13 to chassis – it was a red Elna 2.2µF electrolytic, identical to the one I had already replaced in the yoke circuit. I should have spotted it sooner; it was the only other red electro on the board. But having spotted it, I didn’t stop to ponder the technical implications – I reefed it out and replaced it. And that was it; problem solved. Still a mystery now and came back to the idea of a fault in the yoke winding. Not surprisingly, I didn’t have another yoke of that type on hand but I did have a somewhat similar one from another set. I decided to temporarily substitute that, at least electrically, and note whether it made any drastic difference to the faulty waveform at pin 2. It didn’t, so I finally ruled out that theory. So what was there left to check? At this stage, I remem­bered my colleague’s theory about the feedback circuit. I hadn’t consciously checked this, as such, assuming that checking all obvious components would include it. But it hadn’t. The feedback circuit also involves IC501, with a line run- I’m still at a complete loss to explain just how the height control came to be involved in this particular fault. But then, without knowing the exact circuit details within the IC by which the height is controlled, who can say. Is the height control part of the feed­ back circuit? And what is the function of the 2.2µF ca­pacitor which caused the fault? But those questions aside, the story reinforces what I’ve said so many times before and with which all my colleagues agree; never trust a low SC value electrolytic capacitor. 20 Electronic Projects For Cars Available only from Silicon Chip Price: $8.95 (plus $3 for postage). Order by phoning (02) 9979 5644 & quoting your credit card number; or fax the details to (02) 9979 6503; or mail your order with cheque or credit card details to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. 44  Silicon Chip SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au Replacement module for the SL486 & MV601 remote control receiver ICs This simple module is a replacement for the Plessey SL486 & MV601 infrared preamplifier & receiver ICs. It’s based on a new IR receiver subsystem plus a specially programmed Z86 microcontroller. By RICK WALTERS Over the years, SILICON CHIP has described a number of projects that included infrared remote control. Several of these were based on the Plessey SL486 & MV601 infrared preamplifier and receiver ICs but unfortunately these devices are no longer avail­able. There are three projects involved, as follows: (1). Infrared Remote Control For Model Railroads, April-May 1992; (2). Remote Volume Control For Hifi Systems, May-June 1993; and (3). Stereo Preamplifier With IR Remote Control, Sept-Nov 1993. For a while, it looked as though these circuits would all become obsolete, or that readers would not be able to get re­placements if either of the two Plessey devices failed. Fortu­nately, a new infrared (IR) receiver subsystem recently became available and so we’ve been able to come up with a module that’s a complete replacement for the two Plessey devices. Of course, the module is not a dropin replacement since two separate ICs were originally used. Instead, the board has to be mounted separately and flying leads used to make the connec­ tions after the two Plessey devices have been removed. This is quite straightforward, since the outputs from the module are labelled exactly the same as for the original MV601 device. Before we take a closer look at the new circuit, let’s briefly recap on the roles of the original devices. The SL486 was basically an infrared preamplifier IC that processed IR signals picked up by an external photodiode. It included a differential input to reduce noise pick-up, several amplifier stages and an AGC circuit. Its output was then fed to the MV601 “remote control receiver” IC. Fig.1: the circuit is based on a Z1954 (or equivalent) IR receiver subsystem (IC1) and a Z86E08 microcontroller (IC2). IC1 takes the place of the original SL486 preamplifier IC and its external photodiode, while IC2 does the job of the MV601. April 1996  53 PARTS LIST 1 PC board, code 09103961, 50 x 50mm 1 Z1954 (DSE) or PIC12043 (Oatley Electronics) – (IC1) 1 Z86E08 programmed microcontroller (available from Silicon Chip) – (IC2) 1 18-pin IC socket (optional) 1 4MHz crystal (X1) 1 5mm LED (LED1) Fig.2: install the parts on the PC board as shown here. Leave the two links (shown dotted) out if you intend using the device in SILICON CHIP projects. Fig.3: this is the full-size etching pattern for the PC board. Check your board carefully for any defects before installing the parts. Capacitors 1 47µF 16VW electrolytic 1 0.1µF MKT polyester 1 680pF ceramic 2 22pF NPO ceramic Resistors (0.25W, 1%) 4 100kΩ 1 47Ω 1 470Ω This larger-than-life-size view shows the completed PC board. Make sure that the microcontroller carries an RXD label. The MV601 decoded the signal from the SL486 and provided five BCD outputs (labelled A-E). These could be either momentary or latched, depending on whether pin 5 was high or low. In addi­tion, the MV601 provided a “data ready” output at pin 10. This output was normally high but would go low whenever a valid code was present on the A-E outputs. Finally, pins 3 & 4 were the “rate” inputs and these were connected to match the transmitter rate connections. IR receiver subsystem The new IR receiver subsystem carries the type designation Z1954 and is available from Dick Smith Electronics. An equivalent device, designated PIC12043, is also available from Oatley Elec­tronics. We’ve tested both devices in this circuit and found that they offer similar performance. In each case, the device looks a bit like a small 3-terminal regulator but has a plastic bubble on the front which is the lens for the IR receiver diode. The Z1954 is actually a lot simpler to use than the SL486 it replaces, as it needs no external components around it. As well as the IR receiver diode, the TO-220 style package contains an amplifier, a limiter, a bandpass filter and a demodulator. Its on-axis reception distance is quoted as eight metres but this will obviously depend on the light output from the source. Circuit details Fig.1 shows the circuit of the replacement module. IC1 is the Z1954 IR receiver subsystem. Its output appears at pin 1 and is fed to pin 9 of IC2, the Z86 IC. Note that the output of IC1 is actually inverted, compared to the transmitted signal, but this is compensated for in IC2. RESISTOR COLOUR CODES ❏ No. ❏  4 ❏  1 ❏  1 54  Silicon Chip Value 100kΩ 470Ω 47Ω 4-Band Code (1%) brown black yellow brown yellow violet brown brown yellow violet black brown 5-Band Code (1%) brown black black orange brown yellow violet black black brown yellow violet black gold brown The Z86E08 microcontroller used for IC2 is the same type of device used in the recent Railpower Mk.2 project (Sep-Oct 1995 & Jan 1996). This time, however, it has been programmed to emulate the MV601 codes. The processor needs a crystal, a couple of capacitors and four resistors to do the emulation. An acknowledge LED has also been included to indicate the reception of a valid code. When power is first applied to the microprocessor, it checks the A & B rate inputs and, depending on the linking, sets the internal timer to the correct frequency. It then waits until two pulses with a 6T period between them appear at pin 9 (P32) of IC2. This is the synchronising pulse time. Once a sync pulse has been recognised, the next five bits of data are decoded as zeros or ones and stored. This data string will be repeated a number of times before the transmitter button is released. The next string is also decoded and compared with the first one. If they are identical, the data is made available at P20-P24 and the DATA READY line is pulled low, thereby illuminating LED1. Finally, linking options have been provided to latch the output data (output 5 low) and Tristate the outputs (output 9 high). These functions were provided to allow complete compa­tibility with the MV601. Note: Tristate outputs were not used in the SILICON CHIP designs. Construction A small PC board coded 09103961 (50 x 50mm) has been de­signed to hold all the parts. Fig.2 shows the wiring details. As shown on this diagram, some of the pads have numbers next to them. These numbers refer to the equivalent pin on the MV601. The two optional links are shown dotted – leave them off the board if you intend using the module in the aforementioned SILICON CHIP projects. This will ensure momentary operation of the A-E outputs (ie, the decoded outputs will only go high while the transmitter button is being press­ed). Alternatively, install the link at output 5 if you want latched outputs and the link at 9 for Tristate out­puts. The remaining parts can be installed on the board in any order although its best to leave the microcontroller (IC2) until last. A socket can be used for this IC or you can solder it directly to the PC board. Both the acknowledge LED (LED1) and the IR receiver subsystem (IC1) can be connected to the PC board via flying leads if that makes for more convenient mounting arrangements. Testing Being such a simple board, it should work first go without any problems. The only way to confirm its operation is to illu­minate it with one of our previous remote controls which uses an MV500 remote control IC and a 500kHz resonator. The acknowledge LED should light whenever a valid code is received. If it doesn’t, make sure that the A and B rate programming in the transmitter and receiver are the same. If you do have a problem, look for dry solder joints and for solder bridges between the IC pins. Footnote: the programmed Z86E08 microprocessor (RXD) is available from Silicon Chip Publications for $18 SC (incl. p&p). X-ON ELECTRONIC SERVICES WHOLESALE TO THE PUBLIC SEMICONDUCTORS ULN2804A 1N914 1N4004 1N4148 1N4936 1N5404 78L05 BB119 BC327 BC328 BC337 BC338 BC548 BC549 BC558 BC639 BC640 BD139 BD140 BD649 BD650 BS170 BZV85C16 BZV85C75 BZW03C75 BZV85C16 BZX79C5V6 C7805H HEF4046BP HEF4053BP HEF4066BP ICM7555CN IRF540 LF347N LM317T LM358N LM386N-1 LM393N LM833N LM1875T $2.82 $0.04 $0.10 $0.04 $0.39 $0.27 $0.95 $0.52 $0.31 $0.31 $0.31 $0.31 $0.18 $0.18 $0.18 $0.57 $0.57 $1.16 $1.16 $1.71 $1.71 $0.88 $0.37 $0.49 $1.83 $0.37 $0.18 $1.53 $1.34 $1.10 $0.82 $1.34 $8.54 $4.09 $2.14 $1.10 $1.71 $1.16 $2.14 $7.32 LM3914N LM7805CT LM7808CT LM7812CT LM7815CT LM7915CT MC68HC705C8P MTP3055E NE555N NE571N NE602AN NM93C46N PC74HC11P PC74HC42P PC74HC132P PC74HC573P PC74HC4051P PC74HC4040P PCF8573P TDA1074A TEA1100 TL071CP TL072CP TL074 W04M CRYSTALS HC-38C-32.76800-kHz HC-49/U-2.000000-MHz HC-49/U-3.579545-MHz HC-49/U-4.000000-MHz HC-49/U-10.00000-MHz CAPACITORS CERAMIC 2222-681-09688 6P 10P/5MM 22P/5MM 33P/5MM 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PKT 250 035941R 5mm SPACER $10.48 PKT 50 403375H 6mm SPACER $11.33 PKT 50 403377D 8mm SPACER $12.96 PKT 50 403378B 12mm SPACER $16.60 PKT 50 403380C HTLP3050-08 $12.18 PKT 50 403381A HTLP3050-12 $16.07 PKT 50 HARDWARE CV100 CABLE TIE 100*2.5MM $0.05 $4.88 $1.53 $1.53 $1.53 $1.53 $1.53 $28.06 $2.56 $0.73 $7.20 $4.27 $3.42 $0.73 $1.34 $1.10 $1.83 $1.34 $1.34 $11.71 $15.49 $15.49 $1.83 $2.32 $3.05 $0.98 $1.27 $4.60 $2.44 $2.44 $2.44 $0.12 $0.12 $0.12 $0.12 $0.12 $0.12 $0.12 $0.12 $0.12 180P/5MM $0.12 220P/5MM $0.12 270P/5MM $0.12 470P/5MM $0.12 680P/5MM $0.12 820P/5MM $0.12 GREENCAPS GC0.001uF $0.18 GC0.0027uF $0.18 GC0.01uF $0.18 GC0.022uF $0.18 GC0.039uF $0.18 GC0.082uF $0.18 GC0.1uF-100V $0.24 ELECTROLYTIC CAPACITORS LL10/50 $0.31 RB1/63 $0.18 RB2.2/50 $0.18 RB4.7/63 $0.18 RB10/50 $0.18 RB22/25 $0.18 RB33/35 $0.24 RB47/25 $0.24 RB100/16 $0.31 RB100/25 $0.31 RB220/16 $0.31 RB220/63 $0.73 RB470/16 $0.55 RB470/25 $0.61 RB1000/16 $0.67 RB1000/25 $0.85 RB2200/25 $1.22 RB4700/16 $2.32 RB4700/50 $4.64 RB10000/25 $5.86 80x80x25mm 12V FANS B802512BL $12.00 HEATSINKS 5mm 274-2 HEATSINK TO220 LEDS AND OPTO ELECTRONICS CSL-300E1DT 3MM ORANGE ROUND CSL-300G1DT 3MM GREEN CSL-300H1GT 3MM RED CSL-300Y1BT 3MM YELLOW CSL-500E1DT 5MM ORANGE CSL-500G1DT 5MM GREEN CSL-500H1DT 5MM RED CSL-500Y1DT 5MM YELLOW CSL-620E1DT 5MM*2MM ORANGE CSL-620G1DT 5MM*2MM GREEN CSL-620H1DT 5MM*2MM RED CSL-620Y1DT 5MM*2MM YELLOW POTENTIOMETERS VG067TH1 SIDE ADJUST TRIMMERS VG067TL1 TOP ADJUST TRIMMER RELAYS R729/DC12-1C SPDT 12VDC 10AMP H100S24-1-C PCB RELAY SPDT RESISTORS MRS25 SERIES 1% 0.6 WATT MF25 SERIES 1% 1/4 WATT CR25 SERIES 5% 1/4 WATT SIP10A-102G 1K 10P 9RES RESNET SIP10A-103G 10K 10P 9R RESNET SIP10A-153G 15K 10P 9R RESNET SQP5-0R1 0R1 5W RESISTOR SQP5-82R 82R 5W RESISTOR SQP5-100R 100R 5W RESISTOR SWITCHES EDS-1-4-S DIP 4-WAY PCB 8222/RED RED PUSH BUTTON 8222/BLACK BLACK PUSH BUTTON BUZZERS TDB-12PN BUZZER 12MM PIEZO 7S3240-LA BUZZER 1.5-28VDC BATTERIES 9 VOLT BATTERY SNAP CABLES AND WIRE 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THIS IS A SAMPLE OF OUR MASSIVE RANGE TAKEN FROM RECENT PROJECTS PUBLISHED. DEL CHARGE $8.00 FREE DELIVERY FOR ORDERS OVER $200. 10% DISCOUNT FOR 10+ SAME ITEM PRICES TAX INCLUDED MASTER/VISA/BANK/AMEX CARD X-ON ELECTRONIC SERVICES 1161 ALBANY HWY, BENTLEY PHONE: 09 351 9202; FAX: 09 458 5545 IF ITS NOT HERE JUST ASK. OVER 200,000 LINES AVAILABLE! April 1996  55 In this chapter, we will deal with oscilloscopes using monoacceleration tubes and up to 20MHz bandwidth. High voltage circuits, DC coupled blanking/ unblanking and triggering methods are investigated in some detail. By BRYAN MAHER If you are puzzled by some strange fault in any electronic equipment and your voltmeter gives no clear evidence, your first question should be “what does the oscilloscope show?” It can reveal at a glance more information than all the voltmeters in the world can demonstrate. Maybe you have subtle supersonic oscillations. To see some faults, even in audio equipment, your CRO may need a bandwidth of 20MHz or more but whatever the band­width, a CRO is a very handy instrument. Last month, we saw the basic configuration of a cathode ray tube (CRT), as shown in Fig.1. The heated cathode emits electrons which are attracted forward by the (relatively) positive poten­tial on the acceleration grid (G3) and the conductive aquadag coating inside the tube, near the screen. When these fast electrons hit the fluorescent phosphor coating on the inside of the front glass screen, light is emitted. The resulting trace on the screen is a graph of the voltage signal we apply to vertical deflection plates Y1 and Y2 via the vertical amplifier. The electron beam current is determined by the tube, its acceleration voltage and your setting of brightness; typically between 10 and several hundred microamperes. In the simplest arrangement, as in Fig.1, after hitting the screen, the electrons must leak across the phosphor to the conducting aquadag and then to ground. G3 is called the acceleration grid. In this simple tube, it has the highest positive potential. The word grid is used here (even though it is posi- This photo shows the base ends of two elementary CRO tubes with the glass envelope removed. In each, nearest the base is the electron gun, consisting of heater, cathode, control grid G1 and hollow tubes we call focus grid G2 and acceleration grid G3. Further from the base, ceramic insulator pillars separate and support the pair of vertical deflection plates. Farthest out are the two horizontal deflection plates. 56  Silicon Chip Fig.1: this sort of CRO tube is a monoaccelera­tion type because all electron beam acceleration occurs before deflection. Therefore this type of tube requires high voltage signals of up to 250 volts swing applied to the deflection plates. tive) because electrons pass straight through it. The term anode is reserved for electrodes which collect electrons. The CRO tube shown in Fig.1 is known as a monoacceleration type, because all acceleration of the electrons is achieved before beam deflection occurs. We will see how this fact limits the realisable bandwidth to about 20MHz and acceleration voltages to the 2kV to 5kV range. In Fig.1, to prevent deceleration of the electron stream, G3, the deflection plates and the screen are all maintained at about the same potential. But the deflection plates are low voltage circuits. Therefore, we choose to ground the high voltage supply at the G3-screen end; ie, its positive side. The heater, cathode K, control grid G1, focus grid G2 and acceleration grid G3 are collectively known as the electron gun. Because the high voltage supply in Fig.1 is positive grounded, the cathode K is at a high negative potential with respect to earth. But an even greater negative potential is applied to control grid G1. This negative bias (ie, the K-G1 potential difference) determines the beam current and thereby varies the brightness of the trace on the screen. The high voltage supply usually consists of a high frequen­cy oscillator driving a ferrite core step-up transformer, fol­lowed by high voltage rectifier(s) and filter capacitors. High frequencies are chosen for four reasons: (1) any sounds from the transformer core are supersonic, above human hearing; (2) a high volts-per-turn ratio is easily achieved; (3) the trans­former can be small and light; and (4) only small filter capaci­tors are required to smooth the rectified current to DC. Deflection options An electron beam can be deflected by an electrostatic field between two deflection plates or by a magnetic field at right angles to the path of the electron beam. Almost all analog oscilloscopes use electrostatic deflection, as in Fig.1. There are two reasons for this: (1) deflection of the electron beam is linearly proportional to the voltage applied to the deflection plates; and (2) the low capacitance between the vertical deflec­tion plates (about 2pF) can be easily driven over a very wide range of frequencies, from DC to 1200MHz (1.2GHz) or even higher, assuming suitable amplifiers. By contrast, magnetic deflection requires large signal currents flowing in coils (the yoke) wrapped around the neck of the CRO tube. This is unsuitable for analog oscilloscopes for the main reason that the inductance of the yoke windings severely limits the current as the frequency rises. Magnetic deflection is universally used in TV and computer monitor CRTs but here the deflection frequencies are fortunately quite low and fixed: 50Hz vertical and 15625Hz horizontal, in the case of PAL TV. This allows each deflection circuit to be optimised for its particular frequency. Electrostatic deflection For parallel deflection plates, the distance across the CRO screen (vertically or horizontally) that the electron beam is deflected is directly proportional to: (1) the potential difference Vd between deflection plates; (2) the dis­tance Ls from the deflection plates to the screen; and (3) the length Lp of the deflection plates. In addition, April 1996  57 Fig.2: simplified diagram of the high voltage circuits suitable for a small analog oscilloscope. Transformer T1, operating at 60kHz, provides two independent negative DC supplies. The -1.5kV supply at TP3 provides the electron beam current from cathode K to screen. The -1.6kV supply at TP2 is dedicated to providing the control grid G1 potential. it is inversely proportional to the accelerating voltage VHT between the cathode and the deflection plates and the spacing “d” between them. These factors come together in the following equation for Deflection Factor which gives the deflection voltage required for one centimetre of trace length on screen: Deflection Factor = Vd/cm = (2d.VHT)/ (Ls.Ld) volts/cm This equation dictates that the vertical deflection plates should be placed as far from the screen as possible. Why? To correctly display the signals, the frequency response of the vertical system needs be much higher (often 20 times more) than the horizontal. Therefore, the design of the vertical ampli­fiers is much more critical, in terms of bandwidth, than the horizontal amplifiers. And it is easier to obtain high frequency response from any amplifier if less output voltage is required. From the equation we see that, for a given length of trace across the screen, less voltage is required at the deflection plates farthest from the screen. Therefore, the vertical plates are always furthest from the screen. Of course that means more deflection voltage is needed at the horizontal 58  Silicon Chip deflection plates as their distance to the screen is less. This is usually not a problem, due to the lower band­width demanded of the horizontal sweep system. The above equation also indicates that by lengthening the vertical deflection plates, we could achieve deflection with less output voltage from the vertical amplifier. That certainly is practised but cannot be overdone because longer plates mean greater inter-plate capacitance which must be driven by the vertical amplifier without loss of frequency response. Furthermore, long plates mean that at high enough frequen­cies the signal will cycle to the opposite phase while any one elec­tron is still between the plates, partly cancelling the deflec­tion achieved and increasing the plate current. In modern CRO tubes, the vertical deflection plates are commonly long and curved, as a compromise between these conflicting factors. For a really bright, sharp trace on the screen, high accelera­tion voltages must be used but the above equation says that higher VHT results in smaller deflection angles. This is because faster electrons are more difficult to deflect. Typical deflec­tion angles for CRO tubes are only 10-30°. Because of this, typical CRO tubes tend to be much longer than their diamet­er. Diameters commonly range from 50-135mm, with lengths from 200-600mm. Magnetic shielding In all equipment using CRO tubes, the power transformer should be carefully positioned to avoid accidental deflection of the beam by 50Hz magnetic fields. As well, electrostatic CRO tubes are usually shrouded in a shield of mu-metal, to prevent interference to the electron beam by stray magnetic fields. TABLE 1 Acceleration Pot. Electron Velocity 2kV 26,400km/s 5kV 41,600km/s 10kV 58,400km/s 20kV 81,500km/s 75kV 147,000km/s 120kV 176,000km/s Electron speeds Electrons accelerate all the way from the cathode to the region of highest positive potential. In monoacceleration tubes, this means electrons continuously gaining velocity between K and G3. They then coast at constant speed to the front screen. Great­er velocity Fig.3: timing diagram for the CRO tube horizontal deflection and trace brightness control. Sections of the repetitive input sinew­ave signal actually displayed on screen during the forward sweep are from t1 to t3, t11 to t13 and so on. During the remainder of time the screen is blanked to conceal the retrace and holdoff and wait times. results from using a higher accelerating voltage. Table 1 shows some examples. Deflection factor The design of any analog oscilloscope must start with the vertical deflection factor of the tube; ie, the number of volts that must be applied between the deflection plates to produce one centimetre of trace on screen. The lower this value, the easier is the design of the vertical amplifier and the wider the bandwidth that can be achieved. One of the earliest CRO tubes, famous in Australian Radar sets during World War 2, was the ubiquitous 5BP1 (125mm in dia­meter). Cheap in postwar disposals stores, this tube found its way into many home constructors’ projects. It had the disadvantage of a high deflection factor value. With 2.2kV acceleration voltage, the 5BP1 required a 320V peak-to-peak signal between the vertical deflection plates to draw a line 8cm high; a vertical deflection factor of 40V/cm. If the acceleration potential on similar tubes was raised to 5kV to produce a brighter trace on the screen, then a deflec­tion voltage swing of about 700V would be required to pro­duce an 8cm trace; ie, 88V/cm. A deflection amplifier capable of producing such a large output voltage swing, even at only 2MHz bandwith, would be very difficult to design. Later tubes progressively reduced this demand for high deflection voltages. The European types 30C3 and 30E7, with 4kV acceleration potential, had a deflection factor of 50V/cm. Today, to keep the deflection factor low, monoacceleration CRO tubes are sometimes limited to a high voltage of around 2kV. For example, the Tektronix TAS220 oscilloscope uses 2kV between cathode and accel­erator grid. Careful design of the vertical deflection plates optimised their curved shape, their length (Ld) and the spacing (d) between them. That, together with a high accuracy wideband solid state vertical amplifier, achieves a working bandwidth of DC to 20MHz. In the next chapter of this series, we April 1996  59 Fig.4: a simplified circuit diagram of an oscilloscope showing the vertical and horizontal deflection amplifiers. will see how post deflection acceleration (PDA) voltages up to 26kV can be used to give a very bright, sharp trace, yet achieve a very low deflec­tion factor of 6.5V/cm and bandwidths up to one gigahertz! A practical oscilloscope Fig.2 shows a simplified high voltage circuit for a small CRO tube, operating at 1.5kV. On a 75mm diameter tube this moder­ate voltage will produce a bright enough trace when Fig.5 (below): a trigger point control circuit. This gives trigger pulse signals at outputs 1 and 2 each time the input signal V(in) passes through some nominated voltage level, V(shift), which you select by potentiometer VR1. 60  Silicon Chip seen in subdued room lighting. The deflection factor is reduced by lower­ ing the acceleration voltage from 2kV to 1.5kV but it is in­creased by using a shorter tube. So we would expect a deflection factor of about 30V/cm. CRO vertical bandwidth is decided by the question: can your vertical amplifier provide enough volts to the deflection plates at the highest frequency you desire? To achieve a screen display 4cm high and 5cm wide, your vertical deflection amplifier must provide a 120V signal swing and the horizontal amplifier must provide a 150V excursion. The author has used a 75mm diameter disposals CRO tube with only 600V acceleration potential, with moderate success. On such a low voltage, the screen trace is less bright or sharp than you desire, yet better than none. A more satisfactory project used a 125mm tube operating on 2.2kV accel­eration, with vertical amplifiers of 5MHz bandwidth – quite useful for TV servicing. In Fig.2 a 60kHz power oscillator excites the primary wind­ing of transformer T1. Secondary winding 1, together with diode D2 and smoothing capacitor C2, generates a 1.5kV DC supply which has its positive end grounded at point F. Its negative end connects through R1 to test point TP3, providing the negative 1.5kV DC supply for the cathode K. The 4V drop across R1 sets the heater slightly more negative than the cathode K, to prevent electron flow from cathode to heater. The resistor string to ground provides a 285V drop across the focus potentiometer VR2. Transformer T2 provides the 6.3 VAC heater supply for the tube. The secondary of T2 is elevated to the neg- ative 1.5kV potential, so it must have at least 2kV insulation rating. Brightness control There are two essential aspects to controlling the bright­ness of the waveforms on the screen. First, the manual brightness control potentiometer VR1 sets the trace to the level to suit the ambient room lighting. Fast rising voltages may need extra brightness to be visible. Second, the timebase sweep circuits must blank out that trace during every retrace (flyback) of the presentation, to prevent confusing patterns. Both these functions are provided by the upper half of Fig.2. Control grid G1 has a 1mm diameter hole through which elec­trons emitted by the cathode may pass. G1 is held more negative than the cathode to control the number of electrons passing through G1 to the screen. Thus, the G1-K bias voltage controls the beam current and thereby sets the trace brightness on screen. In many CRO tubes, a bright (unblanked) trace on screen results when G1 is 10V more negative than the cathode. To block off the electron beam to achieve a dark (blanked) screen, the K-G1 bias must exceed 50V. Secondary winding 2 of transformer T1, together with rectifier D1 and storage capacitor C1, provides an isolated -1.6kV supply (measured between test point TP2 and point A). This nega­tive system finds its ground return via point A, through R2 and a separate +230V supply. For a blanked or dark screen condition, the drive at B to Q1 is made low (around 0V). This cuts off Q1 and causes Q2 to fully conduct, pulling point A down to nearly 0V. That is equival­ent to point A being grounded, so TP2 rests at -1.6kV and test point TP4 at -1.5kV. The brightness control pot. (VR1) has 100V across it. In Fig.2, we set VR1 so that it taps off -1585V, to control grid G1. This potential is 85V more negative than the cathode. With such a large negative bias, the electron beam is completely cut off and the screen is blanked. To unblank the screen, a positive signal of about +5V is applied to point B, making Q1 fully conducting and cutting off Q2. Thus, point A rises to the +75V from zener diode ZD1 and this lifts the complete L2-D1-C1R1-R27 system up by +75V. VR1 still has a 100V drop across it but both ends Fig:6: timing diagram for the trigger point control circuit of Fig.5. are raised by the same amount. Hence TP2 becomes (-1.6kV + 75V) = -1525V; TP4 becomes (-1.5kV + 75V) = -1425V; and G1 becomes (-1585V + 75V) = -1510V. Thus, the G1-K bias is reduced to only -10V, which allows a bright trace on screen. By this means, you set VR1 for the brightness you want on screen. The timebase sweep system then generates a 0-5V control signal at B which automatically blanks out the return (flyback) trace. Note that all these circuits are DC coupled, so that the blanking/unblanking works correctly, even at very slow sweep speeds. At very fast sweep rates, C3 is a speed-up capacitor to overcome delay due to the time constant formed by R27 and stray circuit capacitance to ground. Screen focus To focus a beam of electrons, we pass them through hollow electrostatic fields. This is analogous to the focusing of beams of light by glass lenses. So similar are these two processes that both exhibit the same defects, such as astigmatism and geometri­cal aberrations. In Figs.1 & 2, G2 is the focus grid; sometimes called a focus ring. The small electrostatic field between K/G1 April 1996  61 Fig.7: a rise differentiator based on a 74S00 AND gate package. input signal V(in) passes through the zero axis or at some other point on the cycle. You can adjust the period of the horizontal timebase sweep generator (time/division switch) to display any number (or fraction) of cycles of the input signal. Fig.3a shows about one and a quarter cycles of signal being displayed. The trace is visible on screen from times t1 to t3, from times t11 to t13, and so on. Notice that we do not display every cycle of V(in), because time must be allowed for the beam retrace (flyback) and for holdoff and wait times. In Fig.3, retrace occurs between times t3 to t5 and from t13 to t15. Holdoff Fig.8: this is the timing diagram for the rise differentiator of Fig.7. and G2 acts as a divergent lens. The stronger field (about 1kV) between G2 and G3 brings the electron beam back to a small point on the screen. Thus, you focus the electron beam by adjusting VR2. Potentiometers VR1 and VR2 are elevated to dangerously high voltages and so they are operated by long insulated shafts from their front panel knobs. Astigmatism Astigmatism is the tendency of the beam to come to an elliptical rather than a circular spot on the screen. This is minimised by slightly adjusting the potential on the acceleration grid 62  Silicon Chip G3, by adjusting VR3. That alters the difference between G3 and the average voltage at the deflection plates. G3 rests at about +100V, 1.6kV more positive than the cathode. Triggering To view repetitive signals (ie, a continuous waveform) on the CRO, we superimpose many cycles of the input signal on the screen as shown in Fig.3. To produce a clear display, the hori­ zontal timebase must repeatedly begin its forward sweep across the screen when V(in) passes through the same nominated voltage level each time, as at t1, t11, t21, etc. You may wish the dis­played pattern to commence as the After each retrace is completed, a deliberate holdoff time is incorporated into the system, between times t5 to t6, t15 to 16, etc. The purpose of holdoff is to give the horizontal genera­ tor time to settle and to avoid confused traces when the input signals have a complex period. After the holdoff time, the horizontal timebase waits for the next occurrence of a trigger signal (t11, t21), which ini­ tiates the subsequent forward sweep. The length of holdoff time is dictated by the horizontal generator circuit. It is compara­tively short at slow sweep speeds but relatively long at very high sweep speeds. The duration of wait time is not specified by the circuits; it just depends on how long before V(in) again passes through the trigger voltage level you have selected. Deflection amplifiers Fig.4 is a simplified circuit of an oscilloscope showing the vertical and horizontal deflection amplifiers, trigger point control and rise differentiator. Also shown are the triggered time­base generator and the front panel controls: trigger source selector S2, trigger point control potentiometer VR1, and slope selector switch S1. We’ll start our discussion with the timebase generator which consists of sweep logic circuits controlling a Miller integrator. This generates the rising ramp horizontal deflection signal, by using a selected constant current to charge a low-loss capacitor. The slope of the rising ramp in volts/ second is directly propor­tional to the value of constant current chosen by the time/divi­sion front panel switch, and inversely proportional to the ca­ pacitance value. For very fast sweeps, a small value capacitor is used; larger values of C are switched in for slow sweep speeds. Discharging the capacitor results in the much faster falling retrace (or flyback) signal. The display sequence starts when the trigger signal in Fig.3e triggers the timebase generator. That begins the forward sweep at time t1. Simultaneously, the timebase also generates the blanking signal, Fig.3d, which is fed to point B on Fig.2. At the end of each retrace (t5, t15), the timebase spaces out the holdoff time until t6 (or t16). The system then sits and waits for the next occurrence of a valid trigger signal. The trigger point control unit naturally generates more trigger signals than are used – once each time your input signal V(in) passes through the chosen voltage level. But during forward sweep, retrace and holdoff time, the timebase generator will not respond to those invalid triggers, shown dotted in Fig.3e. Trigger point control Stable triggering of the display is an absolutely essential property of any oscilloscope. To trigger the CRO from your input signal, first set front panel trigger source selector S2 to the INT or Internal position. That will feed amplified input signal from point H to the trigger point control unit. You then set trigger point control potentiometer VR1 to the voltage level at which you want your display to begin. Fig.5 is a circuit which could form the block called trig­ger point control unit in Fig.4. IC1 & IC2 operate on ±15V rails, while Q1 & Q2 work from a single +5V rail for TTL compa­tibility with following circuits. Fig.6 is a timing diagram for Fig.5. In Fig.5, waveform (a) is V(in). Suppose you wish the trace to commence when V(in) passes through voltage level M, on the rising part of the cycle. On the front panel, you adjust potentiometer VR1 to select a DC voltage called V(shift). This is added to V(in) in IC1, an operational adder. Waveform (b) indi­cates the sum of V(in) and V(shift); where we have chosen V(shift) as a negative voltage about half the amplitude of V(in). Thus we call IC1 a level shifter. IC1 is inverting so its output, shown at (c), is just (b) inverted. This signal Because of the small deflection angles achieved by electrostatic means, monoacceleration analog oscilloscope tubes tend to be much longer than their diameter; typically 200-600mm from base to screen. is passed to IC2, an inverting Schmitt trigger. In this condition, IC2 has enormous gain – at least 30,000. So the moment its input, waveform (c), goes the slightest bit negative at time M, IC2’s output saturates to almost the positive rail voltage, about +14V, as shown by waveform (d). IC2 remains in this condition while waveform (c) has any negative value. The moment the input to IC2 (wave- form (c)) becomes posi­tive, at time W, its output switches back to saturation near its negative rail voltage. Any noise on V(in) could make the change over at M and W jittery. To prevent this we add a small amount of positive feedback to IC2. The 100#/10k# voltage divider feeds one hundredth of the output back to the non-inverting input, pin 3. Thus, the moment waveform (c) crosses the zero line, the rise of waveform (d) locks Shown here is a highvoltage DC low-current power supply for the acceleration potential of an oscilloscope. The ferrite core transformer is excited by high frequency drive from a low voltage power oscillator. The high voltage secondary current is rectified and filtered to DC, the large 10kV rated ceramic filter capaci­ tors can be seen at top rear. High frequency primary drive allows the transformer to be light and compact. April 1996  63 Cathode Ray Oscilloscopes – continued If the triggering is switched off, or selected from unrelated sources, the oscilloscope display of a simple sinewave signal can be quite useless, because successive timebase sweeps start with V(in) at different voltage levels. With correct triggering this picture unscrambles to a single trace of six cycles of a sinew­ave. Q2 into saturation, until time W. Q1 is an inverter and level shifter, changing the signal level to a swing between +5V and nearly zero, as at (e). Q2 inverts again to waveform (f). The output of Q1 or Q2 is compat­ible with the following TTL circuits in the rise differentiator. The circuit of Fig.5 is intended only to show the princi­ples of operation. Used with faster integrated circuits, it would work from DC up to moderate frequencies but for a wider passband (eg, 20, 100 or 500MHz) the circuit would be condensed to minimise time delays. Fewer semiconductor junctions, extremely fast tran­sistors and very short leads would be employed. Rise differentiator You have chosen point M on the rising phase of V(in) to be the trigger point. So you want the output of Fig.5, waveform (f), to be changed to a short pulse beginning at time M. Such a pulse can then trigger the timebase generator to begin the forward sweep. But you might change your mind and 64  Silicon Chip decide to trigger the timebase at time W in Fig.6, the same voltage level but on the falling phase. How can the circuits follow your wish? The answer is differentiate waveforms (e) or (f). That can pick off just the +5V rising edge, at time M in (f), or at time W in (e). Fig.7 is a suitable TTL circuit called a rise differentia­tor which actually works by integration, a safe noise-defeating mechanism. This simple circuit uses three sections of a 74S00 quad NAND gate. Its output is a very short pulse coincident with the rising edge of whatever TTL signal is fed to it. Suppose we switch S1 in Fig.5 to output 1, waveform (f) in Fig.6. That signal from the trigger point control unit now feeds ICa in Fig.7 (called waveform L in Fig.8). This is inverted in IC3a to waveform N, which is integrated by R1 and C1, forming waveform P. IC3b then has both waveforms P and L as its inputs. IC3b is a NAND gate, so it gives a low output only when both its inputs are high. But observe in the timing diagram that, due to the R1C1 time constant, P does not drop immediately when waveform N does, at time M. Rather, P takes a small time after time M to fall from its +4V output. So depending on the values of R1 & C1, P is still above the TTL threshold level (+2V) for a brief period Delta(t) after time M. During that very short interval, Delta(t), P and L are simul­ taneously high (in TTL terms). That is, (P.AND.L) is a logical high signal for that brief time, as the timing diagram shows. IC3b promptly inverts this to a logical low (waveform U). IC3c inverts again, giving waveform Z, a signal at TTL high level for a short period from time M to M + Delta(t). This is wave­ form (g) in Fig.6, a pulse suitable for triggering the timebase generator. Suppose now you change your mind and wish to trigger the oscilloscope at that same voltage level of V(in) but on the falling phase, as at W in Fig.6. In this case, you just switch S1 in Fig.5 down to output 2, selecting waveform (e) in Fig.6. This now becomes input signal L to IC3a in the rise differentiator, which detects the rise of waveform (e) at time W. As a result, it gives forth its trigger pulse every time V(in) passes through the chosen voltage level but on the falling phase. Most oscilloscopes provide a wealth of trigger sources such as External, 50Hz Line, Single Sweep and Auto, triggered by an internal free-running flipflop, so there is always some display on screen, with or without vertical input. Others commonly found include TV Horizontal, TV Vertical, DC/AC Coupling and Noise Rejection. Next month we will look at post deflection acceleration (PDA), calibrated screens, deflection amplifiers, probes, time­base generators, shift controls and dual timebases. Acknowledgements Thanks to Philips Scientific & Industrial and to Tektronix Australia for data and illustrations; also to Professor David Curtis, Ian Hartshorn, Ian Marx and Dennis Cobley. References “ABC’s of Oscilloscopes”; Philips/ Fluke USA. “Solid State Physical Electronics”; Van der Ziel, Prentice Hall NJ. “XYZ’s of Oscilloscopes” and AppliSC cation Notes; Tektronix Aust. RADIO CONTROL BY BOB YOUNG Multi-channel radio control transmitter; Pt.3 Following the description of the encoder module last month, we present the long-awaited AM transmitter circuit. This has been carefully designed to keep harmonic content and third order intermodulation to an absolute minimum. Modern radio control transmitters place enormous demands on their designers due to the wide range of (often conflicting) features expected by the users and the standards required by the various watchdogs responsible for the safe and harmonious appli­cation of technology. This is particularly true of the transmitter module. Here the operator can cause a third (innocent) party to bore neat little holes in the ground. We treated this subject in some detail in the July 1995 issue of SILICON CHIP. Thus the designer of a modern transmitter module is charged with serious responsibilities. With this in mind the design of the RF module presented has proceeded slowly and cautiously. This has been far too slow for some, judging Interference takes on a very serious meaning for model fliers. If they allow their trans­mitter antennas to come in close proximity with their neighbours, they can cause a third (innocent) party to bore neat little holes in the ground. can intrude into the domain of his neighbour in a very big way. We are all familiar with broadcast and television interference but a new dimension has been added recently in R/C circles, at least in the form of 3rd order inter­ modulation inter­ference. This aspect of the interference spectrum takes on a very serious meaning for model fliers, for if they allow their trans­mitter antennas to come in close proximity with their neighbours, they by some of the letters and comments we have received in the period since the publication of the AM receiver. However, as they say, all good things come to those who wait, and so here at last is the long awaited transmitter module. Design philosophy Those who remember the discussion in the June 1995 issue may recall that at the time, I concluded that the best approach for an RF module with reduced third-order intermodulation would be a class-B push-pull unit. Initially, I proceeded to design a transmitter along those lines. I quickly discovered several important aspects of third order intermod­ ulation. First, direct injection can play an im­portant part in the process. Direct injection occurs where the interfering RF gets directly into the coils and PC board tracks as opposed to being picked up by the transmitter antenna. This form of injection has been minimised by the use of an aluminium transmitter case, a ground plane on the PC board, shielded coils and most important of all, by having the minimum number of stages in the transmitter. Secondly, I discovered that yes, the push-pull circuit did give good results but it had to be very carefully designed and was very tedious and expensive to build. What finally sunk this very promising development was the discovery that if the bias was set incorrectly the third order intermodulation was much worse than a class C output stage. This was a great disappointment since the class B stage proved to be extremely efficient and one module that we had out flying drew only 18mA and gave excellent results. I cried tears of blood over losing that 18mA output stage, especially when I had to wrestle with this new design to bring the current drain down to reasonable limits. More on that later but I still weep when I think of a transmitter with 12 hours of flying time on a 600mA.h battery pack, especially when you listen carefully to one of the modern computer radios and you can hear virtually the electrons roaring as April 1996  65 Fig.1: the circuit consists of a Hartley oscillator, Q1, driving Q3, a VMOS Mosfet critically biased by trimpot VR1. Modulation is applied to the output stage by transistor Q2 which varies the supply to Q3. they are sucked through the wires to keep up with the demand for current. At this point my attention was focused on the encoder design which took many months, leading to its presentation last month. In the intervening period I was able to formulate the approach presented in this article. The key aspect is the oscillator which delivers a very high drive level with good stability. In fact, you could almost hang an antenna off this oscillator and fly with it but it wouldn't really be practical. You would need to amplitude modulate the oscillator and the subsequent frequency modulation and pulling that with AM would cause all sorts of problems – not a good practice. So that meant an RF power amplifier (PA) with modulation. Here I ran into serious problems as the isolation between stages was poor – there was oscillator breakthrough and only 90% modulation. At this stage the project looked to be in serious jeopardy. The standard cure is to use a diode to set the bias threshold but this meant more non-lineari­ ty in the PA. This was completely contrary to the design philoso­phy which called for the output stage to be biased to the point of acting as a perfect transistor in order to reduce third order intermodulation. 66  Silicon Chip I could have used a buffer stage but again I ran foul of my own design requirements, set out above. At this point I realised that the emitter resistor was the main culprit in the third order intermodulation process and I set out on a search for transistors with diffused emitter resistors. The data books are full of them but you try buying one in this country. Up until then I had been concentrating on bipolar tran­sistors. I then had an inspiration and decided to use one of the VN series V-MOS FETs and lo and behold all problems vanished; well, almost. These FETs make ideal output transistors for transmitters, being almost indestructible and with good gain at 30MHz. Once the change was made to a FET PA, the problem of oscillator break­ through was minimised but it still remains in a very mild form, so care is need in this area during setup. The circuit presented also features some degree of latitude to make it useful in non-modelling applications. To this end I have indicated which components are not used for R/C work and those needed for matching into a 50Ω coax cable. As presented, the transmitter delivers close to 500mW into a 1.5 metre (60-inch) telescopic antenna with a total current of ap­proximately 120mA. This includes the oscillator, PA and encoder current. Useful operating time from a 600mAh battery pack should be in the order of four hours. Circuit description This photo shows the transmitter in early prototype form. The construction starts next month. Transistor Q1, coil L5, crystal X1 and associated compon­ents comprise a Hartley oscillator which is transformer coupled into the PA transistor, Q3. R6 and C5 are for decoupling and C4 is used to shunt any inductance in C5. This type of oscillator provides a high level of drive combined with good depending on the coupling bet­ween the oscillator and PA, too much bias can drive the FET into a very high current mode. Capacitor C7 provides a ground return for the RF flowing in the secondary of L5. In the early stages of development of this circuit, I had terrible problems with strong harmonics on 90MHz coupled with very high levels of current in the FET. This resulted in the FET almost steaming. Yet despite this maltreatment the five original FETs used in the prototypes are all still working very happily and I have yet to see one fail. As an added precaution, I have designed the PC board so that the ground plane and the transmit­ter case form a substantial heatsink. More power possible This spectrum sweep tells the story of how this new circuit is successful in suppressing third order intermodulation. The two large spikes represent the transmitter fundamentals of the Mk.22 at 29.745MHz and a standard imported Tx at 29.805MHz. The subsid­iary spike at right shows how the imported unit has substantial third order intermod­ulation at 29.865MHz but the intermodulation pro­duct of the Mk.22 Tx is well down, almost in the noise. Reproduced from the July 1995 issue, this spectrum sweep shows two conventional class C transmitters spaced 20kHz apart at 27.175MHz and 27.195MHz. The interfering signals, spaced 20kHz away at 27.155MHz and 27.215MHz, are only 30dB down on the wanted signals. stability. The 22pF capacitor C2 is used for fine tuning the crystal, if re­quired. Increasing C2 will pull the crystal lower in frequency although there is a limit to this. Bias for Q3 is provided by trimpot VR1, resistor R8 and diode D1 and is the core of the intermodulation solution. The setting of VR1 is fairly critical and the third order products can actually be tuned out when setting this trimpot. By watching the spectrum analyser and tuning VR1, the third order can be reduced to its absolute minimum. As this point is theoretically the point at which the FET is behaving as a perfect transistor, this point also corresponds closely to the point which gives the best harmonic suppression results. One word of warning here: This circuit is capable of further development and could eventually deliver up to 1W with care in regard to harmonic output. Coil L6 and capacitor C8 form a trap for 90MHz which can prove troublesome at high drive levels. These are not mounted in the R/C system but the PC board does provide for them. 1W is far too much power for R/C work but readers with non-R/C applications may find this of interest. The 10Ω resistor R5 is a “stopper” to prevent high frequen­cy parasitics while resistor R7 is there to discharge the gate. Q3 is loaded in the R/C circuit with L4. While provision is made for L3, it is not used in this circuit. Capacitor C10 swamps the Mosfet capacitance and provides some stability to the output stage. It also provides production repeatability and tunes L4 to 29MHz. The amplified RF is then matched to the antenna by an LC network consisting of capacitor C13 and coil L2. For those wishing to use a 50Ω coax output, C6 will provide adequate matching. This capacitor is quite critical and would probably be best made up of a fixed capacitor in parallel with a smaller variable type. Provision is also provided on the PC board for an additional base loading coil should the application re­quire it. These components are not used in the R/C system. This coil would be required, for example, if a short antenna was to be used. TB1 is the transmitter module connector and provides power, antenna and modulation connections. Transistor Q2 is the modulation transistor and is config­ ured as an emitter follower. Capacitors C11 and C15 provide RF bypassing and assist in the final shaping of the modulation waveform. This shaping is absolutely critical if the system bandwidth is to be held inside the ±20kHz allowed under current MAAA guidelines. At this stage of development, the Mk.22 Tx is rated at ±15kHz at 60dB. This is a little higher than I would have liked but well within the guidelines. Capacitors C16 and C14 are DC filters for the supply rail. This module will tune across the range of frequencies al­lowed for R/C work and should tune to 50MHz for non- modelling applications. The table presented in the circuit diagram gives some idea of the capacitor changes required for different operat­ing frequencies. The coils do not need to be changed. So there you have it. I promised you a module with reduced third intermodulation and if you look at the spectrum sweep in the accompanying photo you will see that this aim has been met. Next month, we will discuss construction SC of the transmitter module. See you then. April 1996  67 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au Knocking can cause serious damage to an engine. This simple circuit warns you when engine knock is occurring, so that you can ease up and avoid costly engine damage. Do you drive an old car? If so, build this . . . Knock indicator for leaded-petrol engines By JOHN CLARKE D RIVERS OF OLD CARS are facing an increasing problem. With the progressive decrease in the lead content of super grade petrol, many older engines are starting to “ping” (or knock) when called on to deliver the goods. This pinging effect typically occurs when the engine is under load (eg, when lugging up a hill), or during periods of moderate to heavy accel­eration. Even fairly light engine loads can cause pinging in severe cases. The reason for this is that the reduced lead content in super grade petrol has lowered its octane rating. And that in turn means that the fuel is more disposed to pre-detonation, particularly in high-compression en- gines. Modern engines designed to run on lead-free petrol avoid this problem by running lower compression ratios than the old leaded engines. In addition, modern engines use devices known as knock sensors. These sensors typically screw into the engine block and listen for the onset of knocking. If knocking is detected, they feed a signal to the engine management system which then retards Fig.1: block diagram of the Engine Knock Indicator. Signals picked up by the knock sensor are amplified, filtered and fed to a rectifier to derive a DC voltage. This voltage is then fed to a LED bargraph display, which indicates the knock severity. 72  Silicon Chip Fig.2: the final circuit diagram. IC1a, IC1b & IC1c are the amplifier and filter stages, D1 is the rectifier and IC2 is the LED bargraph display driver. IC1d and Q1 ensure that the circuit only “listens” for engine knock while the coil is firing. the ignition timing so that knocking ceases. On older cars, knocking can sometimes be alleviated by retarding the static ignition timing and/or by altering the weights in the distributor to change the centrifugal advance curve. On some leaded cars, however, the ignition timing was controlled electronically and could not be altered, so this is not option. The VK Commodore is one such example. Another problem with older cars is that most are now well past the 100,000km mark and are no longer carefully maintained. Often, the ignition system will be in need of adjustment or the head could do with a decoke. The build up of carbon deposits on the head of an old engine can be a major cause of pinging, because it gets hot and pre-ignites the fuel. Stopping an old engine from ping- ing is usually easier said than done. Although it’s sometimes possible to have the engine modified, such modifications are usually expensive and not re­garded as economically viable. As a result, drivers of older cars either ignore the problem or, if they are aware of it, drive so that engine knock is minimised. More often than not, however, the problem is one of igno­rance. Many drivers do not know what pinging is and just com­ pletely ignore the characteristic noise coming from the engine. Unfortunately, this can April 1996  73 The LED bargraph display was mounted with its top surface 27mm above the PC board, so that it would protrude through a matching slot in the lid of the case. Note that shielded cable is used to connect to the knock sensor. cause severe engine damage and lead to costly repairs. Pinging can cause piston and valve damage, blown head gaskets, excessive bearing wear and overheating (which in turn can distort the head). In severe cases, holes can even be burnt through the piston crowns. Knock indicator Although it cannot stop an engine from pinging, this simple Engine Knock Indicator can warn a driver when pinging is occur­ring so that the appropriate action can be taken. This can be as simple as easing off on the accelerator or changing back a gear to reduce the engine load. As in modern cars, the circuit monitors the output of a piezoelectric knock sensor which is attached to the engine block. This sensor connects to a dash-mounted unit that carries a bargraph display. When pinging occurs, the bargraph display indicates the severity of the problem on a scale of 1-10 (minor to severe). In addition, the unit sounds a buzzer 74  Silicon Chip to provide an audible warning when the bargraph reaches step 6. This sort of easily understandable feedback allows the driver to quickly adjust his driving technique so that engine knock ceases. So if you own an old “bomb” and you suspect that it is pinging, take a close look at this circuit. It could save you a packet in engine repairs. There’s just one proviso here – this circuit is designed to pick up engine knock under everyday driving conditions. It will not reliably detect Main Features • LED bargraph shows knock intensity • • Preset sensitivity control • Knock severity depends on repetition rate and intensity Audible warning when bargraph reaches threshold level engine knock at very high revs or on a high-performance engine that makes a lot of noise. In these situations, the noise from the engine simply swamps out the knock frequencies that this circuit is designed to detect (note: some modern cars get around this by using special filtering techniques plus a second sensor that’s specially tuned to detect knock at high revs). What is knock? Before we take a look at the circuit, let’s take a closer look at what causes engine knocking. In simple terms, knocking is caused by the irregular burning or explosion of the fuel-air mixture in the combustion chamber of the engine. The result is widely varying cylinder pressures that vibrate the engine components. By contrast, a correctly burning mixture within the combustion chamber produces a smooth pressure that causes a steady increase in the acceleration of the piston. When an engine knocks it does so at a particular frequency and this can be calculated as follows:      F = 900/πr where F is the frequency in hertz and Fig.3a (right): the parts layout on the PC board. Make sure that you don’t get ZD1 and ZD2 mixed up and note that they face in opposite directions to each other, as do the ICs. Fig.3b (far right) shows the full-size etching pattern. r is the cylinder radius in metres. For most cars, this equates to a frequency somewhere between 800Hz and 5kHz. In addition, the major knock sounds become audible from 0-60° after top dead centre. Designing an engine knock indicator can be difficult since it must be able to discriminate between knock and all the other noises produced by the mechanical action of the engine. These noises include those produced by the valve operation, chain drives, pumps, camshaft and crankshaft, plus any other mechanical noise makers which can mask the knock. One way to filter out these unwanted sounds is to only “listen” for knock during the time that it occurs. suffi­cient level and then fed to highpass and low-pass filter stages. These effectively select only the frequency band of interest (800Hz to 5kHz). Following the filters, the signal is rectified and fil­tered. It is then fed to a LED bargraph display. The number of lit LEDs in the bargraph depends on the knock intensity and repetition rate. The audible warning is provided when LED 6 on the bargraph lights. This is detected by Q2 and Q3 which in turn drive a buzzer. Block diagram Fig.1 shows a block diagram of the circuit arrangement. The knock sensor consists of a piezo element which is attached to the engine block. The resulting signal is first amplified to a TABLE 1: RESISTOR COLOUR CODES ❏ No. ❏  1 ❏  1 ❏  1 ❏  2 ❏  3 ❏  1 ❏  8 ❏  1 ❏  1 ❏  1 ❏  1 ❏  2 ❏  1 Value 1MΩ 100kΩ 27kΩ 18kΩ 15kΩ 12kΩ 10kΩ 9.1kΩ 6.2kΩ 2.2kΩ 1.2kΩ 1kΩ 10Ω 4-Band Code (1%) brown black green brown brown black yellow brown red violet orange brown brown grey orange brown brown green orange brown brown red orange brown brown black orange brown white brown red brown blue red red brown red red red brown brown red red brown brown black red brown brown black black brown 5-Band Code (1%) brown black black yellow brown brown black black orange brown red violet black red brown brown grey black red brown brown green black red brown brown red black red brown brown black black red brown white brown black brown brown blue red black brown brown red red black brown brown brown red black brown brown brown black black brown brown brown black black gold brown April 1996  75 Fig.4: basic detail for a do-it-yourself knock sensor. The piezo element is scrounged from a crystal earpiece. The piezo element is removed from the earpiece by first carefully cutting the housing at the glued joint. Schmitt trigger stage IC1d monitors the ignition coil prim­ary to provide a dwell gate signal for the rectifier/filter stage. This ensures that the rectifier/filter stage only receives signal from the low pass filter during the time that the ignition coil is firing; ie, when there is a high voltage on the switched side of the ignition coil primary. This measure effectively restricts the “listening” time of the circuit to the coil firing period, when knock is most likely to occur. At other times, signals from the low pass filter are “blocked”, to prevent false alarms which may be generated during the remainder of the ignition cycle. Circuit details Refer now to Fig.2 for the full circuit details. There are two ICs, 10 LEDs, 76  Silicon Chip This close-up view shows how the piezo element is mounted on the baseplate. The cover comes from a 16mm pot. Use shielded cable to make the connections to the knock sensor before the cover is fitted. three transistors, a regulator and a few other minor parts. IC1 is an LM324 quad op amp package which performs the signal processing. IC1a amplifies the signal generated by the piezo transducer. Its gain can be varied from one to 201, as set by 200kΩ trimpot VR1 and the 1kΩ resistor on pin 9. Its frequency response is rolled off below about 600Hz by the associated 0.27µF capacitor, while the 120pF capacitor across VR1 restricts the high frequency response. The output from IC1a appears at pin 8 and is fed to high-pass filter stage IC1b. This stage rolls off frequencies below 800Hz, as set by the RC filter network on the input. The signal is then fed to 5kHz low-pass filter stage IC1c. As a result, IC1b & IC1c together form a bandpass filter which passes signals only in the range from 800Hz to 5kHz. Note that IC1a, IC1b and IC1c are all biased at about half supply using common 12kΩ and 10kΩ voltage divider resistors. This bias voltage is filtered using a 100µF capacitor. The bandpass filtered signal appears at pin 1 of IC1c and is rectified and filtered using diode D1 and its associated 1µF capacitor. The charging time is set by a 1.2kΩ resistor which prevents transient signals from providing false indications on the meter. IC1d and Q1 provide the gating signal. In operation, the ignition coil input is fed to a voltage divider network and clamped to 6.8V using zener diode ZD2. The ignition coil signal is then fed to pin 6 of IC1d. Op amp IC1d is wired as an in- This commercial knock sensor is from a Daihatsu Mira and worked quite well with the circuit described here. verting Schmitt trigger. This means that when the ignition coil input is at ground (ie, when the points close or the coil switching transistor turns on), IC1d’s pin 7 output is high. This turns on transistor Q1 which then shunts the signal output from IC1c to ground. Conversely, when the ignition coil is firing, pin 6 of IC1d is high (+6.8V) and so pin 7 goes low. Transistor Q1 is now off and so the signal from IC1c is fed to the rectifier and filter stage. The output from the rectifier/filter stage is fed to IC2, a 10-LED dot/ bargraph display driver wired here in bargraph mode (pin 9 high). This device provides a linear output for signals ranging from RLO (ie, approximately half supply) to RHI. In other words, the voltage between RLO and RHI sets the full-scale vol­tage of the display. In operation, the REF OUT voltage (pin 7) sits 1.25V above the voltage at REF ADJ (and RLO). The voltage on RHI is then set by an internal 10kΩ resistor string (to RLO) and the external 15kΩ resistor. As a result, RHI sits about 0.5V above RLO which means that the display has a full-scale voltage of 0.5V. The 2.2kΩ resistor between pin 7 and ground sets the LED brightness. Transistors Q2 and Q3 monitor pin 14 (LED 6) of IC2. When LED 6 lights, pin 14 goes low and Q2 turns on. This then turns on Q3, which drives the buzzer to provide an audible warning. D2 protects Q3 from high back-EMF voltages when the buzzer turns off. Power for the circuit is derived via the ignition switch. The +12V supply is fed to 3-terminal regulator REG1 which provides an 8V rail for the ICs. The buzzer is powered from the +12V rail at the input of REG1. ZD1 and the 10Ω resistor protect the PARTS LIST 1 PC board, code 05302961, 102 x 59mm 1 plastic case, 130 x 67 x 43mm 1 self-adhesive front panel label, 123 x 60mm 1 10-LED bargraph display (LED1-LED10) 1 12V buzzer 1 200kΩ miniature trimpot (VR1) 1 3mm screw and nut 6 PC stakes 1 large grommet regulator against high voltage transients which may be pres­ent on the ignition supply. Construction The prototype Engine Knock Sensor was built on a PC board coded 05302961 and measuring 102 x 59mm. This board clips neatly into a standard plastic case (130 x 67 x 43mm). Fig.3a shows the parts layout on the board. Before starting the assembly, check the board carefully for any defects in the etching pattern. This done, install PC stakes at the six external wiring points, then install the links and resistors. Table 1 shows the resistor colour code but it is also a good idea to check each value on a digital multimeter, as some colours can be difficult to decipher. The diodes and zener diodes can go in next. Note that ZD1 and ZD2 face in opposite directions and that they have different values, so be careful not to mix them up. Similarly, note that D1 is a 1N4148, while D2 is a more rugged 1N4004 type. Take care when installing the ICs, as they also face in opposite directions (pin 1 is adjacent to a notch or dot in the body of the IC – see Fig.3). Once the ICs are in, the capacitors and transistors can be installed. Note that Q2 is a BC558 PNP type, while the others are BC338 NPN types. The 3-terminal regulator (REG1) is mounted with its metal tab flat against the PC board and is secured with a screw and nut. Bend its leads through 90°, so that they pass through their designated holes. This done, fit trim­pot VR1 to the board. The LED bargraph array must be installed with its anode (A) adjacent to the 1MΩ resistor – see Fig.3. It should be mounted so that the top surface of Sensor 1 crystal earpiece, DSE Cat. C-2765 1 cheap TO-3 transistor or equivalent baseplate (to make sensor) 1 16mm pot (for sensor cover) 1 solder lug 1 3mm screw and nut Semiconductors 1 LM324 quad op amp (IC1) 1 LM3914 10-LED bargraph driver (IC2) 2 BC338 NPN transistors (Q1,Q3) 1 BC558 PNP transistor (Q2) 1 7808 regulator (REG1) 1 16V 1W zener diode (ZD1) 1 6.8V 1W zener diode (ZD2) 1 1N4148 signal diode (D1) 1 1N4004 diode (D2) Capacitors 2 100µF 16VW PC electrolytic 2 10µF 16VW PC electrolytic 1 1µF 16VW PC electrolytic 1 0.27µF MKT polyester 3 .015µF MKT polyester 1 .0047µF MKT polyester 1 .0015µF MKT polyester 1 .0012µF MKT polyester 1 120pF ceramic Resistors (0.25W 1%) 1 1MΩ 1 9.1kΩ 1 100kΩ 1 6.2kΩ 1 27kΩ 1 2.2kΩ 2 18kΩ 1 1.2kΩ 3 15kΩ 2 1kΩ 1 12kΩ 1 10Ω 8 10kΩ Miscellaneous Automotive hook-up wire, shielded cable, tinned copper wire, heat­ shrink tubing, bullet terminals, solder, etc. April 1996  77 1 2 3 4 5 6 7 8 9 10 MINOR SEVERE ENGINE KNOCK INDICATOR Fig.5: this full-size artwork can be used as a template when making the notch for the LED bargraph display. the display is 27mm above the board, so that it will later fit into a matching slot cut into the lid of the case. Once completed, the PC board can be installed inside the case and flying leads connected to the power supply, ignition coil, buzzer and knock sensor wiring points. These leads pass through a grommeted hole drilled in one end of the case. The slot in the front panel for the bargraph display is made by first attaching the label and then using this as a drilling template to give a rough knockout. The slot can then be carefully filed to shape. Knock sensor The easiest way of obtaining a knock sensor is to scrounge a commercial unit from a wrecking yard. The commercial knock sensor shown in one of the photos is from a Daihatsu and this worked quite well with the circuit. Alternatively, you can make your own knock sensor. We made ours using a piezo transducer taken from an earpiece. This was mounted on a TO-3 transistor baseplate and clamped in posi­tion using the rear enclosure from a 16mm pot. If you don’t have a transistor baseplate, or don’t want to destroy a perfectly good transistor, you can make up your own baseplate using 3mm steel or brass. Fig.4 shows the details of our home-made sensor. The pot cover is secured by soldering its lugs to the TO-3 baseplate. The transistor package is modified by first cutting the cap off the baseplate using a hacksaw. The two leads are then removed by breaking them 78  Silicon Chip Fig.6: basic scheme for connecting multiple coils to the ignition input. An extra diode should be added for each additional coil. off with pliers and the baseplate filed to a smooth finish. Warning – transistors can use dangerous materials inside. Use rubber gloves during this process and a facemask and goggles when cutting and filing the baseplate. Wash both the transistor baseplate and your hands after the work has been completed. Next, one of the transistor mounting holes is enlarged to accept the mounting bolt (the prototype sensor was mounted on the edge of the rocker cover using an existing bolt into the head). The piezo element is removed from the earpiece by first carefully cutting around the outside of the housing at the glued joint. This done, carefully prise the element from the plastic housing using a knife. You should leave the wire attached to the top of the element intact and remove the wire from the larger lower plate. The piezo element is now centred on the baseplate (larger plate down) and secured using the pot cover – see Fig.4. Be sure to pass the lead under the pot enclosure and protect it with heatshrink tubing before soldering the tangs of the pot cover to the baseplate. Finally, bolt a solder lug to one of the baseplate mounting holes and connect a suitable length of shielded cable to the transducer, so that is can be wired back to the circuit board. We used heatshrink tubing to help secure the wiring. Testing To test the circuit, first apply power and check that pin 4 of IC1 and pin 3 of IC3 are at 8V. If this is correct, switch off and connect the knock sensor wire to the sensor input on the PC board. You should also connect the case of the sensor to the GND terminal (via the shielded cable braid). Next, short the base and emitter terminals of Q1 using a clip lead, set VR1 fully clockwise and apply power. If you now lightly tap the knock sensor with a screwdriver, the LEDs in the bargraph display should light. Adjust VR1, so that the display just reaches the 10th LED each time the sensor is tapped. Assuming everything is operating correctly, remove the short between the base and emitter of Q1. Installation Be sure to install this unit in a professional manner. The display should be mounted where it can be easily seen by the driver, while the buzzer can be either mounted inside the case (drill a few holes to let the sound out) or installed under the dashboard. The GND connection can be made via an eyelet lug screwed to the chassis, while the +12V ignition supply rail should be de­rived from the fusebox using automotive connectors. Make sure that this rail is fused and only goes to +12V when the ignition is switched on. In most cases, the only wires passing through the firewall will be to the ignition coil and to the piezo sensor. Be sure to connect the ignition coil lead to the switched side of the coil (ie, to the negative terminal). Do not connect to the coil lead to the EHT terminal. If your car uses multiple-coil ignition, use the circuit shown in Fig.6 to make the connections (add an extra diode for each extra coil). The PC board clips into a standard plastic case and the leads brought out through a grommeted hole. These leads go to the negative side of the ignition coil, to the power supply (+12V & ground), to the buzzer and to the sensor. Important: the ignition coil lead will have up to 500V on it when the coil is firing and so must be well insulated from the chassis. It would also be wise to insulate the ignition coil terminal on the PC board to prevent accidental contact. The piezo sensor is best mounted on the engine block using an existing bolt. As a second preference, it can be attached to the head. As mentioned above, we secured our sensor using one of the rocker cover securing bolts. Once the unit has been installed, start the engine and adjust VR1 so that the display is just off for all engine revs while the car is in neutral. This effectively provides maximum sensitivity for knock signals without also detecting normal engine noise. Finally, the unit can be tested by deliberately provoking engine knock on the road (don’t overdo this though). This can be done by lugging up a steep hill in a higher gear than normal. If the unit fails to respond to knocking or is overly sensitive, then it’s simply a matter of slightly adjusting VR1 for the correct response. Now you will always be warned when engine knock is occurring, regardless of how loud your kids are screaming or how far your sound sysSC tem is cranked up. 20 Electronic Projects For Cars $8.9s5 plu $3 p&p Yes! Please send me ___ copies of 20 Electronic Projects For Cars Enclosed is my cheque/money order for $­________ or please debit my ❏ Bankcard   ❏ Visa Card   ❏ Master Card Card No. Signature­­­­­­­­­­­­________________________ Card expiry date_____/______ Order by phoning (02) 979 5644 & quoting your credit card number; or fax the details to (02) 9979 6503; or mail the coupon to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. Name _______________________Phone No (_____)____________ Street PLEASE PRINT _________________________________________________ Suburb/town _____________________________ Postcode_________ April 1996  79 CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions from readers are welcome and will be paid for at standard rates. Body filler depth detector This circuit detects the absence of metal in automotive panels. It is essentially an inductive proximity switch with variable sensitivity. A LED will light when sheet metal is close to the coil. The sensitivity can be adjusted by VR1 so that the LED lights when the sheet metal is anywhere between zero and about 3mm from the coil surface. It could be used for map­ping the depth and extent of plastic body filler (bog) in vehicle bodywork. Large areas of body filler with a depth of over 3mm are prone to cracking or lifting, while shallower areas of body filler are considered acceptable. Q1 operates as a tuned oscillator using a coil (L1) which is encapsulat- ed in plastic and has no metal or ferrite core. Normally, in the absence of metal, the circuit oscillates weakly in the region of several hundred kilohertz. In the presence of metal, the inductance of L1 increases, causing the oscillation to stop. Trimpot VR1 is used to adjust the onset of oscillation while VR2 sets the oscillator current, to suit the transistor used. Q2 acts as a buffer circuit for the oscillator and drives a diode pump consisting of D1 & D2. These diodes develop a negative bias which turns off Q3. At other times, Q3 is turned on by the 1MΩ resistor feeding its base. Hence Q3 turns on the LED when no metal is present. ZD1 regulates the oscillator sup- Micropower low-voltage indicator 80  Silicon Chip ply voltage to stabilise the oscillator against changes in battery voltage. Current con­sumption is about 1mA when the oscillator is operating. The circuit is available as a kit (includes PC board) for $12 (plus $2 for the optional buzzer) from Oatley Electron­ics, PO Box 89, Oatley, NSW 2223. Phone (02) 579 4985; fax (02) 570 7910. This low voltage indicator consists of two parts: (1) a voltage sensor; and (2) a visible indicator. The first function is provided by a Darlington transistor, while the second is provided by a low-frequency oscillator driving a LED. Q1, a Darlington transistor, has its bias voltage adjusted by trimpot VR1. This is set so that Q1 stops conducting at a preset voltage level. Typically, this could be +11V for a 12V battery or +5.5V for 6V. When Q1 is conducting, its collector will be low and when it stops, its collector voltage will be low. The latter condition enables an oscillator comprised of two 2-input NAND gates. This runs at about 2Hz and drives the LED. Standby current is about 120µA for a 6V battery input and around 1.5mA when the LED is flashing. M. Schmidt, Edgewater, WA. ($30) RS232 modem switcher This circuit was designed to remotely read two electricity consumption meters via one phone line and one modem. As can be seen from the circuit, the RS232 pins RX data, TX data, data terminal ready and request to send, are connected to 4066 analog switch IC4 & IC4. These 4066s are turned on or off alternately by the IC3, a 4027 flipflop. IC3 is clocked via IC2, a CA3140 op amp which senses the changing voltage on the collector of the opto transistor in IC1. The LED of the optocoupler 4N25/4N28 is connected in series with the “off hook” LED of the Avtek modem used in this metering situation. When the JEM-2 meter (consumption meter model name) is required to be read, the modem reads the meter via the 4066, then the modem hangs up, the “off hook” LED changes state, causing the 4027 flipflop to switch on the other 4066 ready for the data from the other meter. LEDs A and B indicate which 4066 is turned on, thus which RS232 socket is active. The 7812 regulator and full bridge rectifier is fed +12V DC from same plug­ pack that powers the modem. P. Howarth, Gunnedah, NSW. ($40) Single rail operation for the TDA1514 Most circuits employing the TDA­ 1514 power amplifier IC use balanced supply operation. This circuit uses single rail opera­tion instead. A voltage divider consisting of two 15kΩ resistors holds virtual ground at half the supply voltage. Signal freq­ uen­cies are bypassed over the range of interest with 100µF and .047µF capacitors, while the gain is adjusted by the ratio of the 220kΩ and 680Ω resis­tors at pin 9. The 1000µF capacitor blocks DC from the loud­speaker. E. Ferrier, West Hobart, Tas. ($25) April 1996  81 NICS O R T 2223 LEC 7910 y, NSW EY E OATLBox 89, Oa8t5leFax (02) 5s7a0 C a rd MANY OF THE PRICES LISTED APPLY DURING APRIL AND MAY ONLY Vi PO 49 fax ) 579 e r C a rd , 2 0 ( ne & rs: choice for a special price. Choose motors from e o t n s h o a p h P M17 / M18 / M35. $44. , M ith rde d o w r a d d c e You can also purchase this kit with the B a n k x accepte most mix 0. Orders stepper motor pack described above: $65. e r 1 o m $ f A ) l i P Kit without motors is also available: $32. & & ma r i P a ( . s order 4-$10; NZ world.net FLUORESCENT TAPE $ <at> High quality Mitsubishi brand all weather Aust. IL: oatley 50mm wide red reflective tape with self A by EM adhesive backing: 3 metres for $5. MISCELLANEOUS ITEMS LED BRAKE LIGHT INDICATOR: make a 600mm long high intensity line display, includes 60 high intensity LEDs plus two PCBs plus 10 resistors: $20 (K14). AC MOTOR: 1RPM geared 24V-5W synchronous motor plus a 0.1 to 1RPM driver kit to vary speed; works from 12V DC: $12 (K38 + M30). TOMINON SYMMETRICAL LENS: 230mm focal length - f1:4.5, approximately 100mm diameter an 100mm long: $25 (O14). SPRING REVERB: 30cm long with three springs: $30 (A10). MICROSONIC MICRO RECORD PLAYER: includes amplifier: $4 (A11). MOTOR DRIVEN POTENTIOMETER: dual 20k with PCB: $9. ANGLED TELEPHONE STANDS: Angled, smoky perspex: 4 for $10 (G47). LARGE METER MOVEMENTS: moving iron, 150 x 150mm square face, with mounting hardware: $10. New ARLEC brand 24VDC-500mA approved plugpacks: $9. One FARAD 5.5V capacitors: $3. SPECIALS – POLLING FAX LINE Poll our 579 3955 fax number for new items and some very limited quantity specials. ALCOHOL TESTER KIT Based on a high quality Japanese thick film alcohol sensor. The kit includes a PCB, all on board components and a meter movement: $30. The circuitry includes a latching alarm output that can be used to drive a buzzer, siren etc. We should also have other gas sensors available for this kit. WIND POWER GENERATOR KIT In late April we will have available a low cost kit that employs a low cost electric motor, as used in car radiator cooling systems, to serve as a wind powered electricity generator. Construction drawings for an 800mm 2 blade propeller are supplied. The combination puts out up to 30W of power in high winds. Electronic kit price should be approximately $30. Price of a used suitable motor (available from car wreckers) should be under $40. We will have a limited quantity available for $35. LED FLASHER KIT 3V operated 3 pin IC that can flash 1 or two 2 high intensity LEDs. Very bright and efficient. IC plus 2 high intensity LEDs plus small PCB: $1.30. SIMPLE MUSIC KIT 3V operated 3-pin ICs that play a single tune. Two ICs that play different tunes plus a speaker plus a small PCB: $2.50. CD MECHANISMS AND CD HEADS Used CD mechanisms that have a small motor with geared worm drive assy. Popular with model railway enthusiasts: $5. Also new CD heads that include a laser diode, lenses etc: $3. STEPPER MOTOR PACK Buy a pack of 7 of our stepper motors and save 50%!! Includes 2XM17, 2XM18, 2XM35 and 1 used motor. Six new motors and one used motor for a total of: $36. COMPUTER CONTROLLED STEPPER MOTOR DRIVER KIT This kit will drive two 4, 5, 6 or 8-wire stepper motors from an IBM computer parallel port. The motors require a separate power supply (not included). A detailed manual on the computer control of motors plus circuit diagrams and descriptions are provided. Software is also supplied, on a 3.5" disk. NEW SOFTWARE WILL DRIVE UP TO 4 MOTORS (2 kits required), with LINEAR INTERPOLATION ACROSS FOUR AXES. PCB: 153 x 45mm. Great low cost educational kit. We provide the PCB and all on-board components kit, manual, disk with software, plus two stepper motors of your 82  Silicon Chip UHF REMOTE VOLUME CONTROL SPECIAL As published in EA Dec 95-Jan 96. We supply two UHF transmitters, plus a complete receiver kit, including the case and the motorised volume control potentiometer: $60. PC CONTROLLED PROGRAMMABLE POWER SWITCH MODULE This module is a four channel programmable on/off timer switch for high power relays. The timer software application is included with the module. Using this software the operator can program the on/off status of four independent devices in a period of a week within a resolution of 10 minutes. The module can be controlled through the Centronics or RS232 port. The computer is opto isolated from the unit. Although the high power relays included are designed for 240V operation, they have not been approved by the electrical authorities for attachment to the mains. Main module: 146 x 53 x 40mm. Display panel: 146 x 15mm. We supply: two fully assembled and tested PCBs (main plus control panel), four relays (each with 3 x 10A / 240V AC relay contacts), and software on 3.5" disk. We do not supply a casing or front panels: $92. (Cat G20) STOP THAT DOG BARK Troubles with barking dogs?? Muffle the mongrels and restore your sanity with the WOOFER STOPPER MK2, as published in the Feb 96 edition of Silicon Chip. A high power ultrasonic sweep generator which can be triggered by a barking dog. We supply a kit which includes a PCB and all the on-board components: all the resistors, capacitors, semiconductors, trimpotentiometers, heatsinks, and the transformer. We will also include the electret microphone. Note that our kit is supplied with a solder masked and silk screened PCB, and a pre-wound transformer!: $39. Single Motorola piezo horn speakers to suit (one is good, but up to four can be used): $14. Approved 12VDC-1A plugpack to suit: $14. UHF REMOTE CONTROL FOR THE DE-BARKER OF ANNOYING DOGS Operate your Woofer Stopper remotely from anywhere in your house, even your bedside. Allows you to remotely trigger your Woofer Stopper at any time. Nothing beats a randomly timed “human touch”. We supply one single channel UHF transmitter, one suitable UHF receiver and very simple interfacing instructions: $28. Based on the single channel transmitter and a slightly modified version of the 2 channel receiver, as published in the Feb 96 edition of Silicon Chip. Note that the article features 3 low cost remote controls: 1 ch UHF with central locking, 1-2 ch UHF, and an 8 ch IR remote. MOTOR DRIVEN VOLUME CONTROL/POT New high quality motor driven potentiometer, intended for use in commercial stereo sound systems. Includes clutch, so can also be manually adjusted. Standard 1/4" shaft, stereo (dual 20k pots) with 5V/20mA motor: $12 (Cat A13). MINI HIGH VOLTAGE POWER SUPPLY Miniature potted EHT power supply (17 x 27 x 56mm) that was originally designed to power small He-Ne Laser tubes. Produces a potent 10mm spark when powered from 8-12V / 500mA DC source. Great for experimentation, small portable Jacobs Ladder displays, and cattle prods. Use on humans is dangerous and illegal. A unit constructed for this purpose would be would be considered an offensive weapon. Inverter only: $25. CCD CAMERA SPECIAL Very small PCB CCD camera including auto iris lens: 0.1 Lux, 320K pixels, IR responsive; overall dimensions: 38 x 38 x 25mm. We will include a free VHF modulator kit with every camera purchase. Enables the viewing of the picture on any standard TV on a VHF Channel. Each camera is supplied with instructions and a 6 IR LED illuminator kit. $170. CCD CAMERA - TIME LAPSE VCR RECORDING SYSTEM This kit plus ready made PIR detector module and “learning remote control” combination can trigger any domestic IR remote controlled VCR to RECORD human activity within a 6M range and with an 180 deg angle of view! Starts VCR recording at first movement and ceases recording a few minutes after the last movement has stopped: just like commercial CCD/TIME LAPSE RECORDING systems costing thousands of dollars!! CCD camera not supplied. No connection is required to your existing domestic VCR as the system employs an “IR learning remote control”: $90 for an PIR detector module, plus control kit, plus a suitable “lR learning remote” control and instructions: $65 when purchased in conjunction with our CCD camera. Previous CCD camera purchasers may claim the reduced price with proof of purchase. SOUND FOR CCD CAMERAS/UNIVERSAL AMPLIFIER (To be published, EA). Uses an LM386 audio amplifier IC and a BC548 pre-amp. Signals picked up from an electret microphone are amplified and drives a speaker. Intended for use for listening to sound in the location of a CCD camera installation, but this kit could be used as a simple utility amplifier. Very high audio gain (adjustable) makes this unit suitable for use with directional parabolic reflectors etc. PCB: 63 x 37mm: $10. (K64) LOW COST IR ILLUMINATOR Illuminates night viewers or CCD cameras using 42 of our 880nm/30mW/12 degrees IR LEDs. Power output (and power consumption) is variable, using a trimpotentiometer. Operates from 10 to 15V and consumes from 5mA up to 0.6A (at maximum power). The LEDs are arranged into 6 strings of 7 series LEDs with each string controlled by an adjustable constant current source. PCB: 83 x 52mm: $40 (K36). MASTHEAD AMPLIFIER SPECIAL High performance low noise masthead amplifier covers VHF - FM UHF and is based on a MAR-6 IC. Includes two PCBs, all on-board components. For a limited time we will also include a suitable plugpack to power the amplifier from mains for a total price of: $25. VISIBLE LASER DIODE KIT A 5mW/660nM visible laser diode plus a collimating lens, plus a housing, plus an APC driver kit (Sept 94 EA). UNBELIEVABLE PRICE: $40. Suitable case and battery holder to make pointer as in EA Nov 95 $5 extra. SOLID STATE “PELTIER EFFECT” DEVICES We have reduced the price of our peltiers! These can be used to make a solid state thermoelectric cooler/heater. Basic information supplied. 12V-4.4A PELTIER: $25. We can also provide two thermal cut-out switches and a 12V DC fan to suit the above, for an additional price of $10. PLASMA EFFECTS SPECIAL Ref: EA Jan. 1994. This kit will produce a fascinating colourful changing high voltage discharge in a standard domestic light bulb. Light up any old fluorescent tube or any other gas filled bulb. Fascinating! The EHT circuit is powered from a 12V to 15V supply and draws a low 0.7A. Output is about 10kV AC peak. PCB: 130 x 32mm. PCB and all the on-board components (flyback transformer included) and the instructions: $28 (K16). Note: we do not supply any bulbs or casing. Hint: connect the AC output to one of the pins on a fluorescent tube or a non-functional but gassed laser tube for fascinating results! The SPECIAL???: We will supply a non-functional laser tube for an additional $5 but only when purchased with the above plasma kit: TOTAL PRICE: $33. 400 x 128 LCD DISPLAY MODULE - HITACHI These are silver grey Hitachi LM215 dot matrix displays. They are installed in an attractive housing. Housing dimensions: 340 x 125 x 30mm. Weight: 1.3kg. Effective display size is 65 x 235mm. Basic data for the display is provided. Driver ICs are fitted but require an external controller. New, unused units. $25 ea. (Cat D02) 3 for $60. VISIBLE LASER DIODE MODULE SPECIAL Industrial quality 5mW/670nM laser diode modules. Consists of a visible laser diode, diode housing, driver circuit, and collimation lens all factory assembled in one small module. APC control circuit assures. Features an automatic power control circuit (APC) driver, so brightness varies little with changes in supply voltage or temperature. Requires 3 to 5V to operate. Overall dimensions: 12mm diameter by 43mm long. Assembled into an anodised aluminium casing. This module has a superior collimating optic. Divergence angle is less than 1 milliradian. Spot size is typically 20mm in diameter at 30 metres: $65 (Cat L10). This unit may also be available with a 635nm laser diode fitted. dimensions: 25 x 43mm. Construction is easy and no coil winding is necessary as the coil is pre-assembled in a shielded metal can. The solder masked and screened PCB also makes for easy construction. The kit includes a PCB and all the on-board components, an electret microphone, and a 9V battery clip: $12 ea. or 3 for $33 (K11). CYCLE/VEHICLE COMPUTERS BRAND NEW SOLAR POWERED MODEL! Intended for bicycles, but with some ingenuity these could be adapted to any moving vehicle that has a rotating wheel. Could also be used with an old bicycle wheel to make a distance measuring wheel. Top of the range model. Weather and shock resistant. Functions: speedometer, average speed, maximum speed, tripmeter, odometer, auto trip timer, scan, freeze frame memory, clock. Programmable to allow operation with almost any wheel diameter. Uses a small spoke-mounted magnet, with a Hall effect switch fixed to the forks which detects each time the magnet passes. The Hall effect switch is linked to the small main unit mounted on the handlebars via a cable. Readout at main unit is via an LCD display. Main unit can be unclipped from the handlebar mounting to prevent it being stolen, and weighs only 30g. Maximum speed reading: 160km/h. Maximum odometer reading: 9999km. Maximum tripmeter reading: 999.9km. Dimensions of main unit: 64 x 50 x 19mm: $32 (Cat G16). FM TX MK 3 This kit has the most range of our kits (to around 200m). Uses a pre-wound RF coil. The design limits the deviation, so the volume control on the receiver will have to be set higher than normal. 6V operation only, at approx 20mA. PCB: 46 x 33mm: $18 (K33). PASSIVE TUBE - SUPPLY SPECIAL Russian passive tube plus supply combination at an unbelievable SPECIAL REDUCED PRICE: $70 for the pair! Ring or fax for more information. 27MHZ RECEIVERS Brand new military grade 27MHz single channel telemetry receivers. Enclosed in waterproof die cast metal boxes, telescopic antenna supplied. 270 x 145 x 65mm 2.8KG. Two separate PCBs: receiver PCB has audio output; signal filter/squelch PCB is used to detect various tones. Circuit provided: $20. BATTERY CHARGER WITH MECHANICAL TIMER A simple kit which is based on a commercial twelve-hour mechanical timer switch which sets the battery charging period from 0 to 12 hours. Employs a power transistor and five additional components. It can easily be “hard wired”. Information that shows how to select the charging current is included. We supply the information, a circuit and the wiring diagram, a hobby box with an aluminium cover that doubles up as a heatsink, a timer switch with knob, a power transistor and a few other small components to give you a wide selection of charge current. You will also need a DC supply with an output voltage which is greater by about 2V than the highest battery voltage you intend to charge. As an example, a cheap standard car battery charger could be used as the power source to charge any chargeable battery with a voltage range of 0 to 15V. Or you could use it in your car. No current is drawn at the end of the charging period: $15. SIREN USING SPEAKER Uses the same siren driver circuit as in the “Protect anything alarm kit”. 4" cone / 8 ohm speaker is included. Generates a very loud and irritating sound that is useful to far greater distances than expensive piezo screamers. Has penetrating high and low frequency components and the sound is similar to a Police siren. Output has frequency components between 500Hz and 4KHz. Current consumption is about 0.5A at 12V. PCB: 46 x 40mm. As a bonus, we include all the extra PCBs as used in the “Protect anything alarm kit”: $12. FM TRANSMITTER KIT - MKII Ref: SC Oct 93. This low cost FM transmitter features preemphasis, high audio sensitivity (easily picks up normal conversation in a large room), a range of around 100 metres, and excellent frequency stability. Specifications: tuning range: 88-108MHz; supply voltage 6-12V; current consumption <at> 9V: 3.5mA; pre-emphasis: 75uS; frequency response: 40Hz to greater than 15KHz; S/N ratio: greater than 60dB; sensitivity for full deviation: 20mV; frequency stability with extreme antenna movements: 0.03%; PCB MOTOR SPEED CONTROLLER PCB Simple circuit controls small DC powered motors which take up to around 2 amps. Uses variable duty cycle oscillator controlled by trimpot. Duty cycle is adjustable from almost 0 - 100%. Oscillator switches P222 MOSFET. PCB: 46 x 28mm. $11 (K67). For larger power motors use a BUZ11A MOSFET: $3. ELECTROCARDIOGRAM PCB + DISK The software disk and a silk screened and solder masked PCB (PCB size: 105 x 53mm) for the ECG kit published in EA July 95. No further components supplied: $10 (K47). DC MOTORS We have good stocks of the following high quality DC motors. These should suit many industrial, hobby, robotics and other applications. Types: Type M9: 12V. I no load = 0.52A <at> 15800 RPM at 12V. Weight: 150g. Main body is 36mm diameter. 67mm long: $7 (Cat M9). Type M14: made for slot cars. 4 to 8V. I no load = 0.84A at 6V. At max. efficiency I = 5.7A <at> 7500 RPM. Weight: 220g. Main body diameter is 30mm. 57mm long: $7 (Cat M14). MAGNETS: HIGH POWER RARE EARTH MAGNETS Very strong. You will not be able to separate two of these by pulling them apart directly away from each other. Zinc coated. CYLINDRICAL 7 x 3 mm: $2 (Cat G37) CYLINDRICAL 10 x 3 mm: $4 (Cat G38) TOROIDAL 50mm outer, 35mm inner, 5mm thick: $9.50 (Cat G39) CRYSTAL OSCILLATOR MODULES Small hermetically sealed, crystal oscillator modules. Used in computers. Operate from 5V and draw about 30mA. TTL logic level clock output. Available in 4MHz, 4.032MHz, 5.0688MHz, 20MHz, 20.2752MHz, 24.74MHz, 40MHz, and 50MHz.: $7 ea. (Cat G45) 5 for $25. XENON FLASH BOARDS Flash units with small (2cm long) xenon tube, as used in disposable cameras. Power from one AA 1.5V battery. Approx 7 joules energy: $3 (Cat G48). INDUCTIVE PICKUP KIT Ref: EA Oct 95. Kit includes coil pre-wound. Use receiver in conjunction with a transmit loop of wire which is plugged in in place of where a speaker is normally used. This wire loop is run around the perimeter of the room / house you wish to use the induction loop in. We do not supply the transmit loop wire. Also excellent for tracing AC magnetic fields. PCB: 61 x 32mm. Kit contains PCB and all on board components: $10 (K55). SLAVE FLASH TRIGGER Very simple, but very effective design using only a few components. Based on an ETI design. This kit activates a second flash unit when the master, or camera mounted, flash unit is activated. This is useful to fill in shadows and improve the evenness of the lighting. It works by picking up the bright flash with a phototransistor and triggering an SCR. The SCR is used as a switch across the flash contacts. This circuit does not false trigger even in strongly lit rooms, but is sensitive enough to operate almost anywhere within even a quite large room. Of course, by making more of these and fitting them to more slave flash units even better lighting and more shadow reduction is obtained. PCB: 21 x 21mm: $7 (K60). SOUND ACTIVATED FLASH TRIGGER Based on ETI project 514. Triggers a flash gun using an SCR, when sound level received by an electret microphone exceeds a certain level. This sound level is adjustable. The delay between the sound being received and operation of the flash is adjustable between 5 and 200 milliseconds. A red LED lights up every time the sound is loud enough to trigger the flash. This is handy when setting the unit up to suit the scene, without waiting for the flash unit to recharge or flatten its batteries in the process. This kit allows you take interesting pictures such as a light bulb breaking. PCB: 62 x 40mm: $14 (K61). OPTO PHOTO INTERRUPTER (SLOTTED): an IR LED and an phototransistor in a slotted PCB mounting assembly. The phototransistor responds to visible and IR light. The discrete components are easy to separate from the clip together assembly. Great for IR experiments: $2 ea. or 10 for $15. IR PHOTODIODE: similar to BPW50. Used in IR remote control receivers. Peak response is at 940nm. Use with 940nm LEDs: $1.50 ea. or 10 for $10. VISIBLE PHOTODIODE: this is the same diode element as used in our IR photodiode but with clear encapsulation, so it responds better to visible and IR spectrum: $1.50 ea. or 10 for $10. LDRs: large, 12mm diameter, <20ohm very bright conditions, >20Mohm very dark conditions: $1. LEDs BRIGHTNESS RATING: Normal, Bright, Superbright, Ultrabright. BLUE: 5mm, 20mA max, 3.0V typical forward voltage drop. $2.50 RED SUPERBRIGHT: 5mm, 0.6 to 1.0 Cd, 30mA max, forward voltage 1.7V, 12 degrees view angle, clear encapsulation: 10 for $4 or 100 for $30. BRIGHT: 5mm. Colours available: red, green, orange, yellow. Encapsulation colour is the same as the emitted colour. 30mA max.: 10 for $2 or 100 for $14. BRIGHT NARROW ANGLE: 5mm, clear encapsulation, 30mA. Colours available: yellow, green: 10 for $2.50 or 100 for $20. TWO COLOUR: 5mm, milky encapsulation, 3 pins, red plus green, yellow by switching both on: $0.60. ULTRABRIGHT YELLOW: Make a LED torch!: $2.50. PACK OF 2mm LEDs: 10 each of the following colours: red, green, amber. We include 30 1.0K ohm resistors for use as current limiting. Great for model train layouts using HO gauge rails: $10. IR LEDs: 800nm. Motorola type SFOE1025. Output 1mW <at> 48mA. Forward voltage 1.7V. Suitable for use with a focussing lens. At verge of IR and visible, so has some visible output. Illuminates Russian and second generation viewers: $2. HIGH POWER IR LEDs: 880nm/30mW output <at> 100mA. Forward voltage: 1.5V. The best 880nm LEDs available. Excellent for IR illumination of most night viewers and CCD cameras. We use these LEDs in our IR illuminator kit K36. Emits only a negligible visible output. Both wide angle (60 degrees) and narrow angle (12 degrees) versions of these LEDs are available. Specify type required: 10 for $9 or 100 for $80. IR LEDs: 940nm. Commonly used in IR remote control transmitters. Good for IR viewers with a deeper IR response. No visible output. 16mW output. 100mA max. Forward voltage is 1.5V: 10 for $5. 18V AC <at> 0.83A PLUGPACKS Also include a diecast box (100 x 50 x 25mm): Ferguson brand. Australian made and approved plugpacks. Output lead goes to diecast box with a few components inside. Holes drilled in box where LED and 2 RF connectors are secured: $8 (Cat P05). CASED TRANSFORMERS 230Vac to 11.7Vac <at> 300mA. New Italian transformers in small plastic case with separate input and output leads, each is over 2m long. European mains plug fitted; just cut it off and fit the local plug. This would be called a plugpack if it sat on the powerpoint: $6 (Cat P06). FREE CATALOGUE WITH YOUR ORDER Ask us to send you a copy of our FREE catalogue with your next order. Different items and kits with illustrations and ordering information. And don’t forget our website at: http://www.hk.super.net/~diykit April 1996  83 VINTAGE RADIO By JOHN HILL A look back at transistor radios About 35 years ago, I bought my very first transistor radio. It was a 7-transistor AWA with a black leatherette case. I wanted a tan leather model at the time but they were unavailable. Of course, it wasn’t long before the steel chassis was replaced with a printed wiring board and many of the components were greatly reduced in size. Some, like the output transformer, were eliminated from the circuit altogether. Although many radio collectors do not look upon transistor radios as collectible, I beg to differ. I believe that some transistor radios are very collectible, particularly those early receivers made here in Australia back in the days when we still had a radio manufacturing industry. Many transistor radios from the early 1960s era were not built along what might now be considered conventional lines. Those first generation transistor radios clearly showed the manufacturing techniques of their day in that they were often constructed on I recently acquired an early Kriesler transistor radio, a plastic-cased print­ed wiring board type that was in exceptionally good condition, apart from a millimetre thick layer of dust. It restored quite well. As I was cleaning up the old Kriesler, I thought that this could be the ideal introduction into radio collecting. The idea is to start with something that is cheap to buy and has minimum repair problems and expenses. If a new collector can gather together a few old transistor radios and get them going again, then it may provide the necessary incentive to move onto bigger and better things. I know of one particular lad who collects transistor ra­dios while his father collects valve radios. Between the two of them, they now have quite an interesting collection of old receivers. a steel chassis with the metal-cased transistors mounted in rubber grommets. They also used many normal size radio parts such as IF transformers, paper capacitors and air-dielec­ tric tuning capacitors. And they used point-to-point wiring through­out. Add to this the use of germanium transistors, a transformer coupled loudspeaker and battery only operation, and we surely have a collectible radio receiver that differs considerably from anything that is available today. My early Kriesler Obsolete batteries This early Kriesler transistor radio is small mantel model which comes in a plastic case. It is a battery only model and has a large (4 x 6-inch) oval speaker which gives the set a good sound. 84  Silicon Chip The most common problem with many early transistor radios is not that they no longer function but the special dry cell batteries used to power them are no longer available. In the past, several different battery types were made in a variety of shapes and sizes. All are no longer made with the exception of the very small 9V battery. This battery problem isn’t really a problem at all, as all of them can be replaced with an “AA” battery pack of the appro­priate size (6, 9 or 12V), The Kriesler radio uses quite large components, such as an air dielectric tuning capacitor. Later transistor radio receivers used much smaller components. While on the subject of dials, the Kriesler is similar to many valve radio dial mechanisms in that there are pulleys and cords to work the dial pointer. What is different, however, is a little reduction gear box between the dial knob and the tuning capacitor. It is unlikely that you would find anything like that on a modern receiver. One small problem with the Kriesler restoration was the fact that the tone and volume controls were noisy. This was remedied simply by cleaning the tracks and wiper arms with a cotton bud dipped in WD40. A particularly good aspect of the Kriesler is that it uses a 4 x 6-inch oval loudspeaker which is equivalent to a 5-inch (125mm) round speaker. That is a considerably larger speaker than is usually used in battery-operated transistor radios and, as a result, the Kriesler has a fairly good sound. The HMV Capri The volume and tone controls of the Kriesler are also full-sized components. Both were noisy and required cleaning. or with a standard 9V battery. While such a substitute may not have the capacity of the original battery, this can be overcome to a large extent by using heavy-duty alkaline cells. If these are used, then the replacement battery will have a long and useful life – far in excess of what its size may in­dicate. What’s more, alkaline cells are not expensive compared with the price of the original batteries used to power these radios. The price had risen to $24 in some instances before production ceased. Note that when switching to an AA pack, it is often neces­sary to change the battery connector to a 9V snap-on type. The old Kriesler that I acquired was converted to an AA power supply and it worked immediately without any other repairs or modifica­tions. One good aspect of the Kriesler is the fact that it is built on a printed board and the components used are modern types (no paper capacitors) that should last forever – well almost. The electrolytic capacitors may eventually prove trouble­some but they are all working OK at present, even after many years of inactivity. As with most locally-made receivers, the Kriesler has its dial marked with station call signs. This isn’t a great help these days, as many stations have changed their call sign and frequency, or moved to the FM band. I recently collected an HMV “Capri” transistor radio which is a small, almost pocket-size, receiver with six transistors. Once again, it is Australian-made and although it has a plastic cabinet, it fits into a neat leather carrying case. The Capri was designed to take an Eveready 2662 battery which is about twice as long as a standard 9V battery and has a single snap connector at each end. Receivers of this size are too small to accommodate AA holders and the only alternative is to alter the battery connec­tors so that the radio will take a standard 9V battery. Although the replacement battery is considerably smaller than the origi­nal, if a heavy duty alkaline battery is used it will possibly outlast the original. A few pieces of foam plastic will prevent the smaller battery from rattling around inside the case. As previously stated, many of these old transistor radios are often in quite good working order and the only reason they have been discarded is because the batteries needed to run them are no longer available. Substitute those batteries and you have a working receiver once again. The 13-transistor Hitachi Perhaps one of the better transistor radios in my collec­tion would be a 5-band, 13-transistor model KH-1325 Hitachi. Once again, it is a relatively April 1996  85 The HMV Capri is shown here with its leather case. Like the Kriesler, this receiver was Australian made. This photo shows two of the now unobtainable 9V batteries which were used in old transistor radio receivers. Also shown is a 9V AA battery holder (left). While the AA setup may be considerably smaller in capacity, alkaline cells will give reasonable battery life. early transistor radio. I have had this receiver for 15 years and it was secondhand when I inherited it. The Hitachi was a very up-market radio in its day and is capable of world wide reception. Its two shortwave bands cover a 6-18MHz frequency range. It also boasts FM, MW and LW reception and band selection is by pushbuttons. In addition, the Hitachi has a dial light, a tuning light and a loudspeaker of generous proportions. In short, it is a very good receiver. One big advantage with the Hitachi is that it uses 5 D-size cells for its power source. These will keep the set operating for quite some time. Comparing the 13-transistor Hitachi to the 6-transistor HMV Capri clearly shows the superiority of the former. The Hitachi will pull in stations that the HMV can only raise to a whisper. It’s the old story of getting what you pay for and in this case the two receivers are worlds apart. Radio-cassette players Perhaps it’s also time that some of the early cassette radios became collectible? I have, for example, a small Japanese “Silver” which has 3-band reception plus a built-in cassette player. At a guess, it must be getting close to 20 years old and is Considered up-market in its day, the Hitachi KH-1325 is a 4-band Japanese receiver. Most collec­tors are not particularly interested in collecting transistor radios but attitudes are slowly changing. 86  Silicon Chip again working well after receiving a major overhaul. The repairs were mainly to the cassette player which re­ q uired a new electric motor and some work on a worn tape head. This work on the tape head was done using a fine file and emery cloth. While such an operation may sound a bit severe, it was a completely successful repair and cured the distorted sound prob­ lem caused by a deeply grooved playing head. How long before the head wears through is anyone’s guess but it’s working OK at the moment! My Sony Walkman® may not be old enough to be declared a rare collectible just yet but it will, in time, be just that. With its FM/AM stereo reception, It will not be long before some of the early model radio cas­sette players become suitable for collecting. This Silver model radio-cassette player is close to 20 years old and is still working well. Silicon Chip BINDERS This view inside the HMV Capri clearly shows the extent of the miniaturisation that had taken place since the Kriesler radio was made. Note the substitute 9V battery and the extra space provided for the longer original battery. These beautifully-made binders will protect your copies of SILICON CHIP. They feature heavy-board covers & are made from a dis­ tinctive 2-tone green vinyl. They hold up to 14 issues & will look great on your bookshelf. ★ High quality ★ Hold up to 14 issues ★ 80mm internal width ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A14.95 (includes postage in Australia). NZ & PNG orders please add $A5 each for postage. Not available elsewhere. Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. it certainly differs from most other Walkmans. When I bought it, it was the only pocket-sized radio that featured AM stereo. We don’t hear much about AM stereo any more do we? Maybe it’s a bit like high definition TV. Most people aren’t very interested – particularly if it’s going to cost heaps of money. Will they be serviceable? In this throwaway world we are forced to live in, it is unlikely that the radio receivers of today will survive like those of yesterday. It is not that difficult or expensive to restore a 50-60 year old radio. But whether the radios of today will be serv­iceable in the year 2050 is fairly debatable. Fancy trying to substitute a 50-year old chip – now that could be difficult! Perhaps the receivers of today will not have the necessary appeal to become truly collectible tomorrow. Only SC time will tell. Use this handy form ➦ Getting together a collection of Walkman® radios may sound a bit extreme today but it may only be a matter of time. However, will these wonders of the plastic age have collector appeal and what are the chances of servicing them 50 years from now? Enclosed is my cheque/money order for $________ or please debit my ❏ Bankcard   ❏ Visa   ❏ Mastercard Card No: ______________________________ Card Expiry Date ____/____ Signature ________________________ Name ___________________________ Address__________________________ __________________ P/code_______ April 1996  87 PRODUCT SHOWCASE Night vision viewer from DSE While SILICON CHIP has published build-it-yourself night viewers in the past, Dick Smith Electronics now have Apple Nighteyes as a commercial product. It is envisaged that it will be popular with boat users venturing out after dark. Other people who may be interested include hunters, wildlife and bird watch­ers, caving enthusiasts and security companies. The unit is manufactured by Zenit who are well-known for photo­graphic lenses. Apple Nighteyes has a lens magnification of 3.8 times while the internal photomultiplier gives a light amplifica­tion of 10,000 times. It also comes with an IR LED illuminator to allow observation in total darkness. Apple Nighteyes is priced at $999, comes with a 12-month replacement warranty and is available from all Dick Smith Elec­tronics stores. Macservice garage sale How can a business have a garage sale? There is one way to find out and that is to visit the premises of Mac­service Pty Ltd. They are having a ware­house sale of “as traded” and imported stock on Sunday, 5th May from 9.00 AM to 5.00 PM. Prices start from a dollar! Interstate and country buyers do not need to miss out as they can phone for a list of gear on sale. The sale will be at the Macservice warehouse, 20 Fulton St, South Oakleigh, Vic 3167. Phone (03) 9562 9500; fax (03) 9562 9590. Digital multimeter has computer interface The Nilsen BX-905AC digital multimeter offers voltage, cur­ rent, resistance, frequency and capacitance measurement, as well as dB calculation. It features manual or auto-ranging modes and is provided with an RS-232 serial output to connect it to a comput­ er. Software is provided to enable it to 88  Silicon Chip be used for data logging and in manufacturing. dB calculation is presented as dBm; ie, relative to 0.775V RMS into a 600-ohm load. The BX-905AC has relative value display and a memory capable of storing and recalling five data points. Other features include min/ max value storage, low/high/ pass display, and automatic power off after 20 minutes of non-use. Voltage measurements can range up to 1000V DC or 750V AC, current up to 20A AC/DC, resistance to 40MΩ, capacitance to 100µF and frequency to 1.999MHz. For further information, contact Nilsen Technologies, 150 Oxford St, Colling­wood, Vic 3066. Phone (03) 9419 9999; fax (03) 9416 1312. Fluke RLC meter tests at up to 1MHz This new RLC meter from Fluke, the PM 6306, can test components at any frequency between 50Hz and 1MHz. This is desirable for testing a wide range of components, particularly those used in switchmode power supplies, and low value capacitors and inductors. In addition, the PM 6306 features continuously variable AC and DC voltage scales so voltage behaviour of components can be analysed. An internal bias source can provide up to 10V DC for testing electrolytic capacitors and semiconductor junctions or up to 40V DC can be applied from an external source. A deviation mode makes component comparisons quick and efficient, providing a percentage readout of the different between the measured component and the initial reference. Fully automated testing with up to 10 measurements per second can be handled when the PM 6306 is April 1996  89 AUDIO MODULES Over-temperature alarm from Hypec Manufactured in Australia Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 476-5854 Fx (02) 476-3231 The Alert 110 is an over temperature alarm that warns of inadequate cooling before damage occurs to a computer. It sets off an alarm when the internal temperature reaches 43°C (110°F), allowing the user to shut the system down before damage occurs. It is simple to install, only requiring to be plugged into a spare power connector. It is fixed inside the lid of the case with double-sided tape. Three versions are available: with over temperature alarm; with over temperature and cooling fan failure alarm; and the TwinAlert with over broadcast quality connected to a PC via an IEEE-488 interface. An RS-232 interface is also available and Windows-based Component View software will shortly be available. For further information contact Philips Scientific & Indus­ trial, 34 Waterloo Rd, North Ryde, NSW 2113. Phone (02) 888 8222; fax (02) 888 0440. Instrumentation CD-ROM is free National Instruments has announc­ ed a free CD-ROM containing information for engineers with an interest in measurement and control applications. The Windows-compatible CDROM, entitled “Instru­pedia”, features more than 60 tutorial and application KITS-R-US PO Box 314 Blackwood SA 5051 Ph 018 806794 TRANSMITTER KITS $49: a simple to build 2.5 watt free running CD level input, FM band runs from 12-24VDC. •• FMTX1 FMTX2B $49: the best transmitter on the market, FM-Band XTAL locked on 100MHz. CD level input 3 stage design, very stable up to 30mW RF output. $49: a universal digital stereo encoder for use on either of our transmitters. XTAL locked. •• FMTX2A FMTX5 $99: both FMTX2A & FMTX2B on one PCB. FMTX10 $599: a complete FMTX5 built and tested, enclosed in a quality case with plugpack, DIN input •connector for audio and a 1/2mtr internal antenna, also available in 1U rack mount with balanced cannon input sockets, dual VU meter and BNC RF $1299. Ideal for cable FM or broadcast transmission over distances of up to 300 mtrs, i.e. drive-in theatres, sports arenas, football grounds up to 50mW RF out. FMTX10B $2599: same as rack mount version but also includes dual SCA coder with 67 & 92kHz subcarriers. • AUDIO Audio Power Amp: this has been the most popular kit of all time with some 24,000 PCBs being •soldDIGI-125 since 1987. Easy to build, small in size, high power, clever design, uses KISS principle. Manufacturing rights available with full technical support and PCB CAD artwork available to companies for a small royalty. 200 Watt Kit $29, PCB only $4.95. AEM 35 Watt Single Chip Audio Power Amp $19.95: this is an ideal amp for the beginner to construct; uses an LM1875 chip and a few parts on a 1 inch square PCB. Low Distortion Balanced Line Audio Oscillator Kit $69: designed to pump out line up tone around studio complexes at 400Hz or any other audio frequency you wish to us. Maximum output +21dBm. MONO Audio DA Amp Kit, 15 splits: $69. Universal BALUN Balanced Line Converter Kit $69: converts what you have to what you want, unbalanced to balanced or vice versa. Adjustable gain. Stereo. • • •• COMPUTERS I/O Card for PCs Kit $169: originally published in Silicon Chip, this is a real low cost way to interface •to Max the outside world from your PC, 7 relays, 8 TTL inputs, ADC & DAC, stepper motor drive/open collector 1 amp outputs. Sample software in basic supplied on disk. PC 8255 24 Line I/O Card Kit $69, PCB $39: described in ETI, this board is easy to construct with •onlyIBM3 chips and a double sided plated through hole PCB. Any of the 24 lines can be used as an input or output. Good value. 19" Rack Mount PC Case: $999. •• Professional All-In-One 486SLC-33 CPU Board $799: includes dual serial, games, printer floppy & IDE hard disk drive interface, up to 4Mb RAM 1/2 size card. PC104 486SLC CPU Board with 2Mb RAM included: 2 serial, printer, floppy & IDE hard disk $999; VGA •PC104 card $399. KIT WARRANTY – CHECK THIS OUT!!! If your kit does not work, provided good workmanship has been applied in assembly and all original parts have been correctly assembled, we will repair your kit FREE if returned within 14 days of purchase. Your only cost is postage both ways. Now, that’s a WARRANTY! KITS-R-US sell the entire range of designs by Graham Dicker. The designer has not extended his agreement with the previous distributor, PC Computers, in Adelaide. All products can be purchased with Visa/Bankcard by phone and shipped overnight via Australia EXPRESS POST for $6.80 per order. You can speak to the designer Mon-Fri direct from 6-7pm or place orders 24 hours a day on: PH 018 80 6794; FAX 08 270 3175. 90  Silicon Chip temperature alarm at 43°C followed by system shutdown at 48°C. The Alert 110 is priced at $32.50 plus sales tax while the other versions are priced at $52.50 plus sales tax. For further information, contact Hypec Technology Group, PO Box 438, West Ryde, NSW 2112. notes on computer based systems for instrument con­trol, data acquisition, analysis and pres­ent­ation. Also featured are more than 500 hardware and software pro­ducts for 20 industry standard computers. For more information, contact Nilsen Instruments Australia Corporation, PO Box 466, Ringwood, Vic 3134. Phone (03) 9879 9422. Micro inspection camera with light source How many times have you wished you had a tiny CCD camera so you could look into inaccessible places in equipment, down pipes or in cavity walls. Now there is the Dyna Image DM 340C micro head CCD video camera which comes with a 3m cable. This has an illuminated head and is fitted with a 5mm focal length F5 lens. This has a 38mm best focus and a minimum working distance of 15mm. Magnification on a 14-inch monitor is about seven times. Illumination is provided by built-in LEDs which may be switched off. A 12mm diameter 45° mirror adaptor is available for side viewing. The DM340C consists of a main case which connects to the CCD sensor/lens head via a 5mm dia­ meter 3-metre long cable The camera head is 12mm in diameter and 50mm long. Power requirements are 12V DC at 160mA, rising to 240mA with the LEDs on. The video output is 1V p-p standard CCIR composite video at 75-ohm impedance. For further information, contact Allthings Sales & Service, PO Box 25, Westminster, WA 6061. Phone (09) 349 9413; fax (09) 5905. ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097. Cockatoo stopper wanted I read your article on the Woofer Stopper in the February 1996 issue of SILICON CHIP and wondered if I could take up the slightly broader topic of electronic pest control. My particular problem is cockatoos in walnut groves. Whilst a permit can be obtained to shoot them, it’s only granted after they have de­stroyed half your crop! Seeing most birds that prey on fruit and nut groves are protected, the problem is far from academic. I had thought of developing some sort of biological deterrent along the lines of a microphone to pick up their screeching, a voice recognition circuit to verify it’s a cocky not a car, and then playback of a digitised recording of sounds made by a cocky in distress. Would your magazine feature something on voice recognition, as the other components of the setup seem to have been covered? (C. S., Ferntree Gully, Vic). • Your application is a little specialised for us to design a project in SILICON CHIP but you could use the 16-second voice storage module described in our July 1993 issue to provide the Command control is desirable On page 99 of the September 1995 edition, G. S. of Es­perance, WA, writes with respect to “Command Control for Model Railways”. From his letter, G. S. is interested in moving towards Command Control and I believe that I can help him with such a system. This system which I call CTS 16C is my completely revised edition of the old American CTC 16 system. In my many years of experience with this form of Command Control, I have found that CTC 16C works well as the system is stable and most importantly can be built distressed cockatoo sounds. However, in our experience, when cockatoos are feeding they make very little sound at all, so using voice recognition might not work. Instead, a PIR detector might be more useful. 50Hz source for alarm clock I have an old LED clock/radio (AWA B110) which has every accessory needed with a couple of features not found on most modern clocks. It lacks the 9V battery backup after power failure which I have tried to overcome by adding a 9V rail to the IC. However, it only keeps the time from when the power is turned off and does not keep clocking; eg, if it was 1.45 AM at power off, it stays at that time until power is resumed. Could you tell me of a way to wire it so it will keep clocking when mains power is turned off? My second question is can you tell me of some simple 12V fluorescent circuits, preferably with a prewound transformer, as I have a fluorescent light 12V system (car wand) but some parts on the circuit are damaged; a transistor is burnt out (3882 – NEC) but by hobbyists themselves from the ground up with electronic parts that are commonly available in Australia. I’m sure that G. S., with his experience, could easily build such a system and enjoy the benefits that Command Control can so easily control. (B. G., Flinders Park, SA). • We are aware of the CTC 16 system described in “Model Rail­ roader” about 10 years ago. However, this circuit was based on the NE544 and NE5044 encoder and decoder chips. These devices are no longer made so unless the circuit was changed to take this into account, it is no longer a viable option. I cannot come up with an equivalent one. It also has two greencaps, one electrolytic capacitor, one resistor, a 1N1004 diode and miniature transformer. (B. B., Sebastopol, Vic). • The reason why your clock does not keep time while the power is off is that its 50Hz source of clock pulses is absent. In order to keep time whether the 50Hz mains is present or not, you need an independent clock. This could be based on an MM5369EYR divider chip which uses a 3.579545MHz crystal to derive a precise 50Hz source. The 60Hz version of this chip (MM5369AA) was featured in a circuit notebook item on page 41 of the March 1996 issue. We published a series of compact fluorescent driver cir­ c uits in the February 1991 issue but they would not be small enough to replace your damaged module. It would be better to fix it. In general, the simple block oscillator inverters used for these small fluorescent lights use an NPN transistor with a rating of around 100V. Try using a BF469. Current adjustment in 300W module I’ve been having trouble with a 300 watt amplifier de­scribed in another magazine more than 10 years ago. Construction of the kit was without problems but during the initial set up proce­ dure the amplifier would not come within its specifications. When adjusting the offset trimpot to get the voltage between the output and common ground as near as possible to zero, the trimpot had to be wound right over in one direction. Even then, it could only get as close to zero as approximately -50mV. When adjusting the voltage across the fuseclips to 50V with the bias trimpot (about mid-position), the voltage difference between the two fuse- clips was 0.2V (negative fuseclip: -50V). After 30 seconds, the resistors across the fuseclips were too hot to touch. April 1996  91 Alarm clock modifications A couple of days ago, I had an idea for my existing alarm clock. The idea is to connect an infrared LED across the speaker in my alarm clock, so when the alarm goes off in the morning it would also activate the LED. The resulting infrared signal would then trigger a solenoid across the room, to operate a light switch. I started out thinking that this would be easy, but to my dismay I cannot figure out how to get the infrared signal to switch anything. I have since bought your February 1996 edition and have seen the 8-button IR controller but all I need is a 1-button version. With the fuses in position, the current through the output transistors was about 100-140mA, whereas it should be only 25-40mA. There is no audio output available after 3-4 minutes. The heatsink gets very hot (approximately 50°C). I removed the main output transistors and tested them with a multi­meter – all were OK. I then refitted them to the heatsink and tested for insulation leakage – OK. Next, I removed and tested all other transistors and diodes with the multimeter – OK. Finally, I triple-checked the component positions and values – all OK. Despite this, it still will not come to within specs or even work for that matter. Could you please point me in the right direction, or should I discard the PC board and start with a new kit? (H. C., Tomerong, NSW). • While we cannot be sure about the faults, we suspect that there is a component malfunction associated with the Vbe multi­plier transistor which is biased by the quiescent current adjust­ ing trimpot. This can be confirmed by using a clip lead to short between its collector and emitter. If the current drops to zero, the malfunction is in this transistor or its associated bias components. As far as the problem in adjusting the offset trimpot is concerned, we suspect that one of the associated emitter resis­ tors for the differential pair is incorrect in value. 92  Silicon Chip I would be very grateful if you could refer me to a basic circuit diagram for a 1-button transmitter and the circuit diagram for a receiver that would switch momentarily and one that would latch. I would be capable of adding the relay driver. (P. R., Albury, NSW). • Unfortunately, the system suggested by you, having the IR LED across the speaker, is not workable. In practice, an IR transmission system needs to have a coded pulse stream sent by the IR LED. We have not published a 1-button IR remote control system however you may be able to adapt the IR light beam relay, published in our December 1991 issue, to your needs. We have stocks of this issue available at $7 including postage. Heart transplant for Fisher amplifier I found a Fisher amplifier in a secondhand shop. When I checked it out, I found that the power amplifier section was not very good, so I pulled it out and replaced it with two of your 50W modules using the LM3876 chip. I found these modules to be excellent value, producing beautiful sound. My problem is that the preamplifier section of this ampli­fier is not loud enough to run the power amplifier section to full power. At full volume, the output is only about 8W RMS. Rather than try to boost up the preamp section, is it possible to increase the input gain to the LM3876 chip? What would the modifications be? I also thought of purchasing a universal stereo preamp (SILICON CHIP, April 1994) and using this to boost up the short­fall on the preamp signal before the power amplifier. Would this work? If so, what version of this universal preamp should I build? What modifications would I need to do to get this preamp kit to deliver enough overall gain to drive the LM3876 chips to full power of 50W with the volume control about halfway? I also have another amplifier, with the power amplifier section blown. Rather than repairing it, I also plan to install two 50W LM3876 modules. The problem is that the power supply rails are ±50V DC. Is there a way of reducing these supply rails to ±37.5V DC to suit the LM3876? Because of the limited room inside the cabinet, these modules are a good substitute. I really love using these modules as they are cheap com­pared with the overall cost of other kits. The performance and the fact that the modules have built-in protection make them the best power amplifier module on the market today, I believe. I have built up eight complete stereo power amplifiers in the last 12 months, so I speak from experience. Most of them were used with your first Dolby Prologic Decoder, to drive the centre and the surround channels. With my Dolby Prologic kit (your design), I took the mono surround output from the PC board and connected it to a stereo simulator with left and right surround outputs and used this stereo signal to drive two 50W modules with very pleasing re­ sults. Because of its small size, the stereo simulator fitted snugly inside the supplied cabinet. Maybe SILICON CHIP could design a new one that has better separation figures. I have also experimented with the simulator by using it with a mono video. This could be a future project for people who cannot afford a stereo VCR. (K. S., Morphett Vale, SA). • Increasing the gain of the LM­3876 module is simply a matter of reducing the 1kΩ resistor at pin 9 to 470Ω. This will increase the gain by a factor of slightly more than two, which should be sufficient. As far as using the modules with ±50V rails is concerned, the only safe way is to regulate the supplies down to below ±40V. The most efficient way to do this would be to use switching regulators from the LM2576 series, as described in the March 1994 issue. We do plan to design a new stereo simulator, using one of the Mitsubishi delay chips. Frequency display for radios Is there some way of making up an add-on LCD display to show the frequency that a radio receiver is receiving on? This would make life much easier than trying to figure out just what the pointer on the dial is trying to tell us. (J. R., West Pym­ble, NSW). • It is certainly possible to produce such a circuit. In fact, a LED readout SILICON CHIP SOFTWARE Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands are listed on the screen, so you’ll always know what to do next. Notes & Errata also now available: this file lets you quickly check out the Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate the item of interest. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. ORDER FORM PRICE ❏ Floppy Index (incl. file viewer): $A7 Smoke detector beeps ❏ Notes & Errata (incl. file viewer): $A7 ❏ Alphanumeric LCD Demo Board Software (May 1993): $A7 I have a small problem that you may be able to help me with. I have a smoke detector which is working fine but it gives a low beep at regular intervals at night time. I don’t hear it during the day. I have tested the unit by pushing the button and the alarm works in its usual loud and raucous fashion. What’s wrong with it? (D. S., Berala, NSW). • This is a common problem with smoke detectors but it is entirely normal. As we pointed out in our February 1996 article entitled “Fit A Kill Switch To Your Smoke Detector”, these units produce an audible beep to tell you when the battery is low. So the answer is simple: replace the battery. Use an alkaline type because these have a longer life than normal carbon-zinc batter­ies. ❏ Stepper Motor Controller Software (January 1994): $A7 ❏ Gamesbvm.bas /obj /exe (Nicad Battery Monitor, June 1994): $A7 ❏ Diskinfo.exe (Identifies IDE Hard Disc Parameters, August 1995): $A7 ❏ Computer Controlled Power Supply Software (Jan/Feb. 1997): $A7 ❏ Spacewri.exe & Spacewri.bas (for Spacewriter, May 1997): $A7 ❏ I/O Card (July 1997) + Stepper Motor Software (1997 series): $A7 Notes & Errata Radio Control 8-Channel Encoder; March 1996: in the circuit on pages 56 & 57, R19, the 10kΩ resistor at pin 6 of IC3b, should connect to pin 5 instead. It comprises a voltage divider with R13, a 22kΩ resistor. POSTAGE & PACKING: Aust. & NZ add $A3 per order; elsewhere $A5 Disc size required:    ❏ 3.5-inch disc   ❏ 5.25-inch disc TOTAL $A Enclosed is my cheque/money order for $­A__________ or please debit my ❏ Bankcard   ❏ Visa Card   ❏ MasterCard Card No. Signature­­­­­­­­­­­­_______________________________ Card expiry date______/______ Name ___________________________________________________________ PLEASE PRINT Street ___________________________________________________________ Suburb/town ________________________________ Postcode______________ Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number (Bankcard, Visa Card or MasterCard). ✂ along these lines was published in another Australian electronics magazine many years ago. In principle, the circuit needs to measure the frequency of the local oscillator in the radio and then offset the reading by the intermediate frequency, to get the actual incoming frequency. In an AM broadcast radio with digital readout, the local oscilla­tor usually covers the range from about 1MHz to just over 2MHz and the intermediate frequency is 450kHz (not 455kHz as in older AM radios). By contrast, the local oscillator in an FM radio covers from 93.5MHz to 113.5MHz while the intermediate frequency is 5.5MHz. Since the FM local oscillator is such a high frequency, a prescaler IC is generally used to divide the frequencies down to a more manageable frequency in the region of about 1MHz. In practice, digital radios solve the problems of pushbutton tuning, frequency readout and so on by using a dedi­cated microprocessor. It is unlikely that we will publish a project along these lines in SILICON CHIP. April 1996  93 MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. FOR SALE CLASSIFIED ADVERTISING RATES Advertising rates for this page: Classified ads: $10.00 for up to 12 words plus 50 cents for each additional word. Display ads (casual rate): $25 per column centimetre (Max. 10cm). Closing date: five weeks prior to month of sale. To run your classified ad, print it clearly in the space below or on a separate sheet of paper, fill out the form & send it with your cheque or credit card details to: Silicon Chip Classifieds, PO Box 139, Collaroy, NSW 2097. Or fax the details to (02) 979 6503. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ DonTronics HAS MICROCHIP PIC GEAR: Programmers from $20 to $225, PICBASIC: 64 $47, 57 $33, 84 $33, EEPROM: 93LC56 $5, 24LC16B $8, 24LC65 $16, CPU: 84/04/P $12, 57/04/P $12, 64/04/P $17. Serial and parallel I/F kits and lots of other stuff. VISA-MC-BC. Ask for free Promo Disk. http://www.labyrinth.net.au/home/~donmck –29 Ellesmere Crescent, Tulla­ marine 3043. (03) 9338 6286. Fax (03) 9338 2935. KITS KITS KITS: Electronic kits for enthusiasts of all ages and abilities. Top quality. Large range. Free catalog and price list available. Call Ozitronics, 24 Ballandry Crescent, Greensborough 3088. Tel/Fax: (03) 9434 3806 email: ozitronics<at>c031.aone.net.au. _____________ _____________ _____________ _____________ _____________ MicroZed HAVE stocks of PIC chips including PIC 16C84. Ring for prices. _____________ _____________ _____________ _____________ _____________ SATELLITE DISHES: international reception of Intelsat, Panamsat, Gori­ zont,Rimsat. Warehouse Sale – 4.6m dish & pole $1499; LNB $50; Feed $75. All accessories available. Videosat, 2/28 Salisbury Rd, Hornsby. Phone (02) 482 3100 8.30-5.00 M-F. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ A REAL BARGAIN: Riston type copper clad laminate. Develop cold, no toxic fumes, easy to use. Excellent results. Single sided 610x304 $34; 305 x 304 Enclosed is my cheque/money order for $­__________ or please debit my Card No. ✂ ❏ Bankcard   ❏ Visa Card   ❏ Master Card RCS RADIO PTY LTD Signature­­­­­­­­­­­­__________________________ Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ 94  Silicon Chip RCS Radio Pty Ltd is the only company that manufactures and sells every PC board and front panel published in SILICON CHIP, ETI and EA. RCS Radio Pty Ltd, 651 Forest Rd, Bexley 2207. Phone (02) 587 3491 START WITH A MICROZED KIT then when your "test the market", small run project hits the big league MicroZed can help you with alternative schemes and quantities ex stock at the right pricing. MicroZed Computers To order or enquire: PO Box 634, ARMIDALE 2350. (296 Cook’s Rd) Ph (067) 722 777 – may time out to Mobile 014 036 775 Fax (067) 728 987    (Credit Cards OK) RAIN BRAIN 8 STATION SPRINKLER KIT: Ultra reliable & versatile Hi Q kit. Rain switch & LED B/L Free!!! (SC JAN ’96). Mantis Micro Products, 38 Garnet St, Niddrie, 3042 P/F/A (03) 9337 1917 man­tismp<at>c031.aone.net.au SATELLITE EQUIPMENT DEMO SALE: 1m dish Echostar Lt730 low threshold receiver 1.1dB voltage switching Ku Band LNB works VERY well 1 only $850. 1.1dB voltage switching with built in feedhorn Ku Band LNB $130. C Band 25 deg LNB $120. Nokia dual LNB input receiver $190. 1.3dB voltage switching with built in feedhorn Ku Band LNB $115. Signal strength meter for sat $320. Sexton for finding satellites $400. Fax/phone (03) 9803 0215. Circuit Ideas Wanted Do you have a good circuit idea. If so, why not sketch it out, write a brief description of its operation & send it to us. Provided your idea is workable & original, we’ll publish it in Circuit Notebook & you’ll make some money. We’ll pay up to $60 for a really good circuit but don’t make them too big please. Send your idea to: Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. NEW Micro 68HC11 F1 boards and now 80535 (up spec 8051), both boards with BASIC, FORTH, ASM, Small C Accessories for Stamp and second source for Stamp 1 80535 board has 8052AH INTEL BASIC installed. W Data Collection Proto Board now available. NE 24 I/O expansion board now in stock for both boards. 2-input, 12-bit A>D, real time clock and EEPROM. Also prototype expansion board, addressing only. Up to 32K for data storage, example programs and book software. Switchable power on board and 8 I/O Get your project on the way in hours, not months. left for other jobs. Uses Parallax BS2-IC. Send two 45c stamps for information package Scott Edwards Electronics LASER LIGHT SHOW EQUIPMENT: scanners, controllers, soft­ware. Lasers, optoelectronics. Laser Dynamics. Phone (03) 532 1981. Fax (03) 9555 7449. STOPWATCH MODULE: UHF radio start/stop, optocoupled clock, lap, reset outputs and LCD display on 150 x 100 board. $165 kit. (06) 291 4911 (AH) or vladimir<at>ozemail.com.au BASIC Stamp I and II ➡ $17.50; 152 x 305 $9.95; 152 x 152 $6.50. Double-sided also available. 2 litre developer mix, worth $2.50, free this month. Add sales tax if applicable. Delivery $6.00. Money back guarantee. Ph (02) 743 9235. Fax (02) 644 2862. MEMORY * DRIVES * MODEMS SPECIAL! (ExTax) 1Mbx9 – 70ns $25 30-pin Simms 68HC705 DEVELOPMENT SYSTEM: Oztechnics, PO Box 38, Illawong, NSW 2234. Phone (02) 541 0310, fax (02) 541 0734. Email: info<at>oztechnics.­com.au WWW: http://www.hutch.com.­au./~ozt­ ech/index.htm. C COMPILERS: Dunfield compilers are now even better value. Everything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC16, 8051/2, 8080/85, 8086 or 8096: $140.00 each. Macro Cross Assemblers for these CPUs + 6800/01/03/05 amd 6502: $140 for the set. Debug monitors: $70 for 6 CPUs. All compilers, XASMs and moni- SIMMS (Parity/No Parity) 4Mb 30 PIN-70 $71 $90 4Mb 72 PIN-70 $75 $53 8Mb 72 PIN-70 $133 $100 16Mb 72 PIN-70 $230 $192 32Mb 72 PIN-70 $456 $378 EDO SIMMS 8Mb (1Mbx32) – 60ns $118 16Mb (2Mbx32) – 60ns $210 MAC MEMORY 8Mb P’BOOK 190 $240 VIDEO MEMORY 256K x 16 70ns (SOJ) $17 256K x 16 70ns (ZIP) $48 LASER PRINTER MEMORY 2Mb UPGRADE $140 CO-PROCESSORS 80387SX/DX to 40MHz $100 COMPAQ 8Mb CONTURA AERO $240 All other models available $Call TOSHIBA PORTEGE/SATELLITE 8Mb / 16Mb EDO $294 / $550 All other models available $Call IDE DRIVES: SEAGATE/CONNER 1080Mb EIDE 10.5ms 3yr $283 1620Mb EIDE 14ms 3yr $360 2113Mb EIDE 10.5ms 3yr $384 MODEMS: BANKSIA / SPIRIT 28,800 BANKSIA V.34 $360* 28,800 SPIRIT V.34/V.FC $350* *Plus 14% sales tax on modems Ex Tax Pricing – Delivery $8. Pricing as at 26/6/96. Phone for latest. Sales Tax On Modems 14%. Everything Else 22%. Credit Cards Welcome. We Also Buy And Trade-In Memory. PELHAM Memory Pty Ltd Suite 6, 2 Hillcrest Rd, Ph: (02) 9980 6988 Pennant Hills, 2120. Fax: (02) 9980 6991 Email: pelham1<at>ozemail.com.au tors: $400. 8051/52 or 80C320 simulator (fast): $70. Demo disk: FREE. All prices + $5 p&p. GRANTRONICS PTY LTD, PO Box 275, Wentworthville 2145. Ph/ Fax (02) 631 1236 or Internet: lgrant<at> mpx.com.au SILICON CHIP FLOPPY INDEX WITH FILE VIEWER Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands are listed on the screen, so you’ll always know what to do next. Notes & Errata also now available: this file lets you quickly check out the Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate the item of interest. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. Price $7.00 each + $3 p&p. Send your order to: Silicon Chip Publications, PO Box 139, Collaroy 2097; or phone (02) 979 5644 & quote your credit card number; or fax the details to (02) 979 6503. Please specify 3.5-inch or 5.25-inch disc. April 1996  95 Microprocessors For Silicon Chip Circuits We have stocks of the 68HC705-C8P pre-programmed micro­pro­cessor ICs for the Digital Effects Unit (Feb­ruary 1995) and the Remote Controlled Stereo Preamplifier (Sept.-Oct. 1993). Also available is the pre-programmed Z86E08 microprocessor for the Railpower Mk.2 Model Railway Controller. Advertising Index Altronics ................................ 68-71 Av-Comm.......................................9 68HC705-C8P – $45 ea; Z86E08 $18 ea. Prices include p&p. Car Projects Book....................OBC Payment by cheque, money order or credit card to: Silicon Chip Pub­lica­tions, PO Box 139, Collaroy, NSW 2097. Phone (02) 9979 5644; Fax (02) 9979 6503. Dick Smith Electronics........... 18-21 Emona.........................................89 MICROCRAFT PRESENTS: Dunfield (DDS) products are now available exstock at a new low price; please ask for our catalogue. Micro C, the affordable “C” compiler for embedded applications. Versions for 8051/52, 8086, 8096, 68HC08, 6809, 68HC11 or 68HC16 $139.95 each + $3 p&h • Now on special is the SDK, a package of ALL the DDS “C” compilers for $399 + $6 p&h • EMILY52 is a PC based 8051/52 high speed simulator $69.95 + $3 p&h • DDS demo disks $7 + $3 p&h • VHS VIDEO from the USA (PAL) “CNC X-Y-Z using car alter­nators” (uses car alternators as cheap power stepper motors!) $49.95 + $6 p&h (includes diagrams) • Device programming EPROMs/PALs etc from $1.50 • Fixed price electronic design and PCB layout • Credit cards accepted • All goods sent certified mail • Call Bob for more de­tails. MICROCRAFT, PO Box 514, Concord NSW 2137. Phone (02) 744 5440 or fax (02) 744 9280. TEACH­ERS. Send $2 stamp for catalogue and price list. Log onto our bulletin board for full details. DIY Elect­ron­ics, 22 McGregor St, Numurkah 3636. Ph/Fax (058) 62 1915. E-Mail: laurie.c<at>cnl.com .au BBS (058) 62 3303 EDUCATIONAL ELECTRONIC KITS: Easy to build. Guaranteed to work. Good quality. Latest technology. Cheap. Good selection. LESSON PLANS FOR Instant PCBs................................95 Jaycar ................................... 45-52 Kalex............................................39 COMPLETE WORKSHOP PROGRAM: suit IBM compatible 386 or better computer. Handles: Stock Control, Sales, Service Records, Debits, Credits, Faults, Service Manuals and Phone Directory. Full price $399.00. For demo disk, phone or fax your details to (045) 71 1640. Jack Albers Electronics & Software Development. Kits-R-US.....................................90 VALVES: TRANSMITTING, RECEIVING, collectibles, parts, catalogue 85c stamp. Hadgraft, 17 Paxton Street, Holland Park, Qld, 4121. Phone (03) 3397 3751. Railway Projects Book.................25 SERVICE & REPAIRS Scan Audio..................................88 PATRA ELECTRONICS: assembly and repairs of all kits. Repairs of electronic equipment. Call Peter on (02) 718 1202 or 015 215957. Silicon Chip Bookshop.................42 SILICON CHIP BINDERS These binders will protect your copies of SILICON CHIP. ★ Heavy board covers with 2-tone green vinyl covering Macservice................................ 4-5 MicroZed Computers...................95 Oatley Electronics.................. 82-83 Pelham........................................95 RCS Radio ..................................94 Rod Irving Electronics .......... 33-37 Silicon Chip Software..................93 Tektronix....................................IFC Tortech.........................................39 X-On Electronic Services............55 Zoom.........................................IBC _________________________________ PC Boards ★ Each binder holds up to 14 issues Printed circuit boards for SILICON CHIP projects are made by: ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover • RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 587 3491. Price: $A14.95 each (incl. postage in Aust). NZ & PNG orders please add $A5 each for p&p. To order, just fill in & mail the order form in this issue to: Silicon Chip Publications, PO Box 139, Collaroy 2097; Or phone (02) 9979 5644 & quote your credit card details or fax (02) 9979 6503. 96  Silicon Chip Harbuch Electronics....................90 • Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730. BUMPER PREMIERE EDITION NOW AT YOUR NEWSAGENT