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Especially For Model Railway Enthusiasts Order Direct From SILICON CHIP Order today by phoning (02) 9979 5644 & quoting your credit card number; or fill in the form below & fax it to (02) 9979 6503; or mail the form to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. This book has 14 model railway projects for you to build, including pulse power throttle controllers, a level crossing detector with matching lights & sound effects, & diesel sound & steam sound simulators. If you are a model railway enthusiast, then this collection of projects from SILICON CHIP is a must. Price: $7.95 plus $3 p&p Yes! Please send me _______ copies of 14 Model Railway Projects Enclosed is my cheque/money order for $­_________ or please debit my  Bankcard    Visa Card    Master Card Card No. Signature­­­­­­­­­­­­_________________________ Card expiry date_____/_____ Name _________________________Phone No (____)_____________ PLEASE PRINT Street ___________________________________________________ Suburb/town __________________________ Postcode____________ Vol.9, No.1; January 1996 Contents FEATURES 4 Living With Engine-Managed Cars We take a look at some of the do’s and don’ts when it comes to maintaining a modern engine-managed car. Also, is it worthwhile changing the chip or are there better ways of increasing engine performance? – by Julian Edgar 10 Recharging Nicad Batteries For Long Life Nickel cadmium and nickel metal hydride batteries often don’t last very long before requiring replacement. One solution is to use “burp charging” which is claimed to greatly extend battery life – by Horst Reuter 53 Satellite Watch THE DO’S AND DON’TS OF LIVING WITH ENGINE-MANAGED CARS – PAGE 4 A new column that gives you satellite reception reports for Australia and New Zealand – by Garry Cratt PROJECTS TO BUILD 22 Surround Sound Mixer & Decoder Build this unit and add depth and realism to your home videos. It provides realistic surround sound mixing and even includes a simple decoder – by John Clarke 40 Build A Magnetic Card Reader & Display Check out what’s written on the magnetic stripe on your credit card. This unit could also be used as the basis for an electronic door lock, restricting access to those with “authorised” cards – by Mike Zenere 54 The Rain Brain Automatic Sprinkler Controller BUILD A MAGNETIC CARD READER & DISPLAY – PAGE 40 Comes as a kit and controls up to eight solenoids plus a master solenoid. You program it yourself to selectively water any area of your garden as little or as often as you like – by Graham Blowes 70 IR Remote Control For The Railpower Mk.2 Provides complete freedom of operation and has pushbutton control for everything. An optional speed meter is also included – by Rick Walters SPECIAL COLUMNS 32 Computer Bits Upgrading your PC; is it worthwhile? – by Geoff Cohen 80 Serviceman’s Log The complaint seemed simple enough – by the TV Serviceman 8-STATION SPRINKLER CONTROLLER – PAGE 54 86 Vintage Radio Converting from anode bend to diode detection – by John Hill DEPARTMENTS 2 Publisher’s Letter 3 Mailbag 16 Circuit Notebook 63 Product Showcase 69 Order Form 92 Ask Silicon Chip 94 Notes & Errata 95 Market Centre 96 Advertising Index IR REMOTE CONTROL FOR THE RAILPOWER MK.2 – PAGE 70 January 1996  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Rick Walters Reader Services Ann Jenkinson Advertising Enquiries Leo Simpson Phone (02) 9979 5644 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Marque Crozman, VK2ZLZ Julian Edgar, Dip.T.(Sec.), B.Ed John Hill Jim Lawler, MTETIA Philip Watson, MIREE, VK2ZPW Jim Yalden, VK2YGY 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: $49 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 Crystal balling the telephone With the advent of the new year and the new century being not far away, it is timely to think about products that could appear in the near future. After all, with people being so con­scious of computers, cellular phones, video and pay TV, the Internet and so on, it is common topic of conversation: “what will be next big consumer product?” No-one really predicted that cellular phones would be as popular as they have become and it is my opinion that another telephone derived product will be the next big seller. An obvious derivative, to my mind, is a small computer combined with a fax machine. Perhaps it would be called a “fax terminal” or something similar. This would have a typewriter keyboard and LCD screen and probably not much storage but you could type a message on the screen and then send it to another person’s fax machine. It could also receive fax messages but would not normally print them out, unless you wanted it to. Perhaps it would send a short voice message as well. You could also use it to pay bills and do all the things that a fax machine can do now. Such a machine is feasible now. It could be in many homes within five years. Another more expensive product would be a home telephone exchange and burglar alarm system. Most small businesses have a phone system now, with three or four incoming lines and up to eight extensions. They can transfer calls, allow conferencing and operate as an intercom. Currently priced at around $2000 to $4000, such systems are becoming cheaper all the time. Five years ago, equivalent systems were priced at around $8000 or more and are now just starting to be installed in larger homes where their convenience is really appreciated – no more shouting to call people to the phone, no more running to answer the phone and so on. Such a system could be extended to provide a full home security system, with computer interfacing as well. You could be able to connect a computer modem to any handset so that any member of the household could connect to the outside world. How long before we see such a product marketed I wonder? Further into the future, with the advent of highly com­pressed video and optical fibres, it seems likely that video phones are just a matter of time. It is not hard to envisage several or most rooms of a household having a video terminal which will do everything: provide entertainment, phone and com­ puter services, the whole bit. There are more variants on this theme but essentially they are all derivatives of the humble telephone. Who would have thought we want or need more telephones? 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 Old house wiring is often dangerous I would like to comment on your Publisher’s Letter, Novem­ber 1995, on the subject of house wiring safety. Congratulations for raising this subject. You state the house was built before 1950. This is significant. You express surprise that the study power point was not earthed. At the time the house was wired, unless the room was considered an earthed situation, the wiring regulations did not require earthing of the power point. This would also apply to most bedrooms. It was not until the 1960 wiring rules that earthing was mandatory. I was employed as a Supply Authority Inspector from 1966 until retirement. While working in a country power station in the 1950s, we received pages of interpretations on the wiring rules, including three pages explaining where earthing was re­quired or not. I could never understand the type of thinking that permit­ted and perpetuated non-earthing of power points. It is virtually a booby trap for someone. The installation of a circuit breaker switchboard with old wiring would have been a good first move towards a complete rewire. R. Brownjohn, Charlton, Vic. Pinking vs pinging: which is correct? I notice that in his article on “Knock Sensing” (SILI­CON CHIP, December 1995), Julian Edgar refers to the term “ping­ing” as “a light, barely observable knock”. Although this term is widely used, it is not correct. In a package put out by the ABC a few years ago, called “Know Your Car”, the speaker refers to this phenomenon as “pinking”. I thought that this was a language problem at the time, so I checked and found that he was correct. I double checked today in the Macquarie Dictionary and see that it seems to be still right. This may not be real- ly important but I feel that Julian would appreciate the point. I would also like to thank him for his many interesting and informative articles. L. Cook, Numurkah, Vic. Comment: the Macquarie Dictionary gives both terms as descriptive of knocking. We prefer “pinging” as it seems to be the most widely used in the trade. “Pinging” is also more precise in terms of onomatopoeia – it imitates the actual sound. SATELLITE SUPPLIES Aussat systems from under $850 SATELLITE RECEIVERS FROM .$280 LNB’s Ku FROM ..............................$229 LNB’s C FROM .................................$330 FEEDHORNS Ku BAND FROM ......$45 FEEDHORNS C.BAND FROM .........$95 DISHES 60m to 3.7m FROM ...........$130 Oxygen sensor is the hard way Your fuel injector article in November was interesting but, given the simple way the mixture or “burn” of the typical air­craft piston engine is sensed, controlling it by exhaust oxygen seems to be the hard way. Especially with lower-powered, carbur­ etted mills, exhaust gas temperature (EGT), metered with a simple thermocouple, is often used to gauge the burn. The latter is leaned out until EGT peaks, indicating maximum combustion heat and least fuel flow at the extant throttle setting. If cylinder head temperature, sensed by a couple on the hottest jug, is too high, the burn is richened to cool it down. (On larger mills, the mixture control is usually set to auto lean). Jug temperature alone can be used but either ploy optimis­es shaft horsepower for the fuel used. Although such a mill may run with near-constant parameters for some hours (easing the problem), why wouldn’t EGT controllers work as well for autos? G. Lindley, Redfern, NSW. Comment: your remarks about the ease of monitoring exhaust tem­ perature are no doubt correct but the reason for monitoring exhaust oxygen content is to obtain the best compromise between carbon mon­ oxide on the one hand and nitrogen oxides (NOx) on the other. Simply maximising exhaust temperature will lead to exces­sive nitrogen oxide production. LOTS OF OTHER ITEMS FROM COAXIAL CABLE, DECODERS, ANGLE METERS, IN-LINE COAX AMPS, PAY-TV DECODER FOR JAPANESE, NTSC TO PAL TRANSCODERS, E-PAL DECODERS, PLUS MANY MORE For a free catalogue, fill in & mail or fax this coupon. ✍     Please send me a free catalog on your satellite systems. Name:____________________________ Street:____________________________ Suburb:_________________________ P/code________Phone_____________ L&M Satellite Supplies 33-35 Wickham Rd, Moorabin 3189 Ph (03) 9553 1763; Fax (03) 9532 2957 January 1996  3 The do’s & don’ts of Living with engine-managed While over the last few years we’ve covered in detail the technical make-up of current cars’ electronic engine control systems, a more general treatment of what the average owner should and should not do with their car has been lacking. Here’s the remedy! By JULIAN EDGAR In general, the engineers employed by the car manufacturers really do know best – they’re the people who have worked with the investment of millions of dollars in developing the technology. This means that the maintenance schedule laid out in the owners’ manual should be followed to the letter. It doesn’t, however, necessarily mean that the official dealer needs to do the servic­ing of the car. Many dealer mechanics in my experience are quite ignorant about the cars for which they’re supposed to be experts and do quite illogical things in response to perceived problems. Injector blockage can be avoided by regularly re­placing the fuel filter. In addition, injector removal and back-flushing every 50,000km or so can be a worthwhile service precaution. 4  Silicon Chip An example of this is where, during a routine service, a dealer-trained mechanic instigated an ECU self-check investigation because he thought that the exhaust note of my car ‘sounded funny’. Given that the car runs a modified 75cm diameter ex­haust with free-flow mufflers, it wasn’t surprising that the exhaust note was non-standard! But checking this by using the self-diagnosis function of the ECU...? Having said this, there are some mechanics who really do take their marque to heart and have an incredibly detailed knowl­edge about their cars. If you find such a mechanic stick with him (or her) but unfortunately they are few and far between. General maintenance The frequently advertised invitations to use oil additives or “upper cylinder lubricant” can generally be ignored – unless specified in the official maintenance schedule. However, the occasional use of an in-tank injector cleaning additive can be a worthwhile addition to the manufacturer’s recommendations. Also, about every 50,000km or so, the injectors can be removed and back-flushed to clean their inbuilt filters. However, note that injector problems are much more likely to occur if the fuel filter is not changed at the recommended service intervals. I’ve not bothered having the injectors removed for cleaning in any of my six EFI cars (some with more than 170,000km on the clock) but note that I have regularly changed the fuel filter. Most engine-managed cars use high combustion pressures to achieve efficiency (and so fuel economy) gains. d cars Firing the spark with high cylinder pressures requires a high-energy ignition system and these do not respond happily to high tension leads which are losing their insulation integrity. The best replace­ments for worn leads are usually the original equipment products – unless they are terribly expensive. But surely a set drawn from the plethora of aftermarket leads would give better results? An example tells an interesting story. I once covered the building of a very powerful Nissan FJ20 turbo four cylinder engine. Having a standard power of 200bhp, this particular race unit used a new turbo, was run on methanol using fully-programmable Many current cars require a spark plug change only every 50,000 or 100,000 kilometres. Reducing the quality of the replacement plug will result in poor performance. Changing the ECU’s main memory chip is unlikely to give any noticeable improvement in power, with independent tests showing that losses are as likely as gains. engine management and ended up producing just over 400bhp! Some very high-tech spark plug leads were initially tried but were soon discarded High energy ignition systems place great demands on the ignition leads. Experience has shown that the original equipment leads are often the best. January 1996  5 A modified exhaust system using free-flow mufflers will result in power gains in electronically managed cars, with the average peak-power benefit being about 10%. when the dyno-mounted engine put on a full display of pyrotechnics when it came on boost! The replacements were the old original Nissan leads which went on to perform faultlessly. Likewise, be careful when replacing spark-plugs. Some manu­facturers specify platinum-tipped plugs, with a service interval of 50,000 or 100,000 kilometres. When they come due for replace­ment they will be expensive but they will also go on to perform for the next 50,000 or 100,000 kilometres without problems! Electrical system Because engine-managed cars place a larger-than-convention­ al demand on the electrical system, make sure that the alternator and battery remain in good condition. Corrosion on the battery terminals can result in more than just poor headlight performance and it can be illuminating to feel the temperature of the battery terminals af- One reason that frequent tune-ups are no longer required in modern cars is the presence of an exhaust gas oxygen sensor. This constantly indi­cates the air/ fuel mixture strength to the ECU. The changes made to injector pulse widths as the result of this information allows the system to take into account changing parameters such as engine wear. 6  Silicon Chip ter the car has been running for some time. When it comes time for the battery to be replaced, it’s advantageous to replace it with a similar-sized package which has a larger capacity – especially if you live in a cold environment where starting loads will be high. If your car does not have an on-dash indication that the ECU has logged a problem (that is, if there is no “Check Engine” or equivalent warning light), make sure that you perform an ECU self-diagnosis each time the oil is changed. In the situation where it has a problem, this prevents the car from being con­ stantly driven in limp-home mode – which may be un­detectable unless you regularly check fuel economy or performance figures. Engine mods Everyone likes getting a little additional oomph under the bonnet – or its corollary, better fuel consumption at smaller throttle openings. However, this area is fraught with traps for naive players. Basically, modification of electronically engine managed cars can be divided into four different categories: (1) chip changes in otherwise standard engines; (2) inlet and exhaust changes; (3) turbocharger boost pressure changes (obviously, only in turbo engines); and (4) major mechanical modifications (port­ing, cams, compression ratio and so on). The last item on the list can result in substantial gains in engine power but its detailed examination is beyond the scope of this magazine. Chip changes (which give different ignition and fuel maps to that which exist as standard) may look attractive but in general give little or no real benefit. In fact, in some cases the performance can actually be worsened! Chassis dynamometer testing of a variety of ECU chips installed in a VR V6 Commodore gives a good guide to the changes made by installing a new chip alone. In this case, the power gains or losses at each 500 RPM step in the engine’s rev range were recorded and then averaged. The results are shown in Table 1, the comparison being against the standard Holden chip. As can be seen, there was a greater Table 1: Chip Substitution Results Chip Average Gain Or Loss Across New Range A 1.6% loss B 1.7% loss C 1.0% gain D 1.9% loss E 0.6% gain Standard Chip + PULP 1.9% gain overall power gain (1.9%) made by simply filling the tank with premium un­leaded petrol (PULP) while retaining the standard chip! And a gain of just 1.9% is quite trivial. In short, making just a chip change (in a car which doesn’t use forced induction) is likely to make no discernible difference to its performance. This is not the case when mechanical modifications have been made, where the fuel and ignition requirements may well have changed from standard. Intake and exhaust changes can improve power and economy. Fitting extractors and a larger exhaust system will improve peak power output by approximately 10% in most late-model cars. Fuel economy will also be improved, with a gain of 10-20% realisable in country running. Inci­dentally, the noise output of the exhaust will also increase but this may not be discernible from within the cabin. Changing the air filter in the standard box – as is advo­cated in numerous magazine advertisements – will gain very little power and in some cases will actually reduce power. Chassis dyno tests undertaken on both a late-model Falcon and a late-model Commodore showed, if anything, power reductions with a top aftermarket filter installed in the box. And that was in comparison with a dirty standard filter! Ducting cold outside air to the filter’s air box will improve power in many EFI cars. Using plastic storm­ water pipe and fittings (painted black) is an efficient and cost-effective way of doing this. If a new air pick-up point is used, more frequent changing of the air filter element may be needed, as a greater quantity of dust is ingested. However, power gains of 5% are easily achieved in this way for under $50. Lifting turbo boost pressure by 20- Ducting cold air into the standard air filter box can result in power gains of 5% for less than $50. The trade-off is the requirement for more frequent air filter changes as more dust is usually ingested. A cold air intake duct can be made from plastic stormwater pipe and fittings, painted black with a spray-can. The hole saw was used to cut a path through the inner guard. 30% in turbo cars will invariably result in an increase in engine power, with no nega­tives to speak of. If you undertake this course of action, fuel with an appropriate octane rating (for example, premium unleaded) will usual­ly need to be used but there will be no other costs while an agreeable increase in power will be realised. Note that there is usually no need for ECU software changes – sufficient latitude has been built into the fuel system to cope with this type of increase in power. Conclusion The electronic side of current cars is usually much more reliable than the old-tech equivalent systems. This generalisa­tion isn’t always the case, of course but most engine-managed cars will run reliably for 150,000km+ without even the need for a traditional tune-up. Incidentally, if paying large amounts for a tune, ask what is actually being done. In most current cars there’s no need for plug changes, points re-gapping, mixture adjustment and so on and so a “full tune” can sometimes involve just an oil and filter change, together with a quick visual once-over. In terms of gaining more power easily, in non-turbo cars the fitting of a good exhaust and extractors will give the best cost/benefit. In turbo cars, fit the modified exhaust and also lift turbo SC boost a little. January 1996  7 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 8  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 January 1996  9 New from Smart Fastchargers, this nicad and NiMH charg­er caters for a wide range of battery voltages and capacities and uses the patented Reflex charging method. It has eight buttons to set the rate of charge, a rotary switch to select the battery voltage and a LED bargraph to indicate the cell voltage. An audible beep, at one second intervals, gives an indication that the main charge is still in progress. Recharging nicad batteries for long life Nickel cadmium and nickel metal hydride batteries are widely used in all sorts of portable equipment but they often don’t last long before they must be replaced. One solution is to use “burp charging” which is claimed to provide many thousands of charge/discharge cycles. By HORST REUTER* Battery powered equipment is undeniably practical – lightweight, portable and small, with no cables to drag around. But there is a price to pay for that convenience. Rechargeable bat­ teries are costly to buy and often don’t last long. The problem can usually be traced back to the type of charger used. Unfortunately, most of the nicad chargers supplied with ap­pliances at 10  Silicon Chip present require manual termination; ie, the user has to switch off the charger and disconnect the battery. This makes it practically impossible to avoid overcharging the batteries, thereby reducing their life expectancy. The key to long life lies in the charging method. In this article, a battery is defined as consisting of one cell or several cells connected in series. Internal cell im­ pedance is defined as the sum of the resistance of the internal connections and plates (both constant) and the degree of diffi­culty the ions encounter passing through the separators and electrolyte (variable). Nicad or NiMH? From an environmental point of view it would be an advan­ tage to change to NiMH batteries. Nickel Metal Hydride (NiMH) batteries are made without cadmium and are therefore less damag­ing to biological systems. At present, they have about 20% higher energy density than nicad cells (AA) and produce no memory effect (more about memory effect later). However, typical NiMH cells have a higher internal im­ pedance than nicad cells; 50mΩ instead of 10mΩ for 1200mAh cells. As a consequence, NiMH batteries have lower maximum discharge currents. This means they are only suitable for low current ap­ pliances like handheld radios. The maximum discharge current is 3C for NiMH AA cells and 2C for NiMH button cells, whereupon the cell voltage drops to approximately 1.1V. “C” is defined as the current that equals the rated battery capacity. For example, charging a 1.2Ah battery with a 4.8A current is a 4C charge. The same 4.8A current applied to a 4.8Ah battery is a 1C charge. In practice, the useful discharge currents for NiMH batteries are limited to less than 1C (the cell voltage remains above 1.2V). For currents above 1C, nicad batteries are superior. Fig.1 is a comparison of the load characteristics of one 1200mAh AA size NiMH cell, one 600mAh AA size nicad and one 1200mAh sub-C size nicad cell. The load was only applied for 5 milliseconds. The tests showed that a fully charg­ ed 12V 1200mAh nicad battery as used in power drills delivers a maximum of 11.9V with a 10A load. Even a 12V 600mAh nicad battery delivers a maximum of 10.9V with a 10A load. However, a 1200mAh NiMH battery with the same load delivers only 7.65V. NiMH batteries also differ from nicad cells in that the chemical reaction during charge is exothermic; ie, the charging process produces heat. The chemical reaction in nicad cells is endothermic; the reaction absorbs heat. However both battery types produce some heat during the main charge cycle because of internal impedance and both produce heat when overcharged. Over­ charging creates heat and gas but does not produce any further energy storage in the cells. The heat produced during the main charge in nicad cells due to cell impedance is absorbed in the endo­ thermic reaction. In NiMH cells, the cell heating due to internal impedance is added to the heat of the exothermic reaction. When NiMH batteries reach the overcharge region, they are therefore hotter than nicads. All available NiMH cells I have tested vented at around 43-45°C case temperature – much lower than for nicads. This means that charge termination at high charge rates is criti­cal and cannot safely be achieved with delta V termination charg­ers. The case temperature should not exceed 40°C Fig.1: a comparison of the load characteristics of a 1200mAh AA size NiMH cell, a 600mAh AA size nicad and a 1200mAh sub-C size nicad cell. The load was only applied for 5 milliseconds. This clearly demonstrates that the higher internal impedance of NiMH batteries limits their usefulness in delivering high currents. for NiMH cells and 45°C for nicads. Delta V termination utilises the voltage drop at the begin­ning of the overcharge region of the cell voltage curve (see Fig.2). The magnitude of this voltage drop is generally not as well defined in NiMH cells as it is in nicad cells. It depends on factors like charge current, ambient temperature, cell impedance, cell capacity, etc. The situation can be worse in battery packs. Several unmatched cells may cause the battery voltage to reach only a very shallow peak if some cells reach their individual peaks while others are still charging. Even if the Fig.2: delta V termination utilises the voltage drop at the beginning of the overcharge region of the cell voltage curve. The magnitude of this voltage drop is generally not as well defined in NiMH cells as it is in nicad cells. It depends on factors like charge current, ambient temperature, cell impedance, cell capaci­ty, and so on. January 1996  11 the nickel hydroxide to nickel oxyhydroxide. This process is reversed during discharge. If each cell in the battery pack is discharged completely and then charged, the individual crystal sizes on the cell plates remain unaltered. However, if the cadmium is not completely converted back into cadmium hydroxide during partial discharge, on the following charge the cadmium hydroxide crystals will clump together, forming larger crystal structures. Although it is not yet fully understood how Fig.3: the patented Reflex or “burp” charge this happens, scanning method consists of a positive charge pulse followed by a high current, short duration electron micrographs discharge pulse. This is quite different from of batteries with and other chargers which have an essentially without memory effect pulsed output but no discharge pulses. clearly show the difference in crystal sizes. The net result is that we charger circuit is able to detect a very are left with a smaller, less reactive small voltage drop (<10mV) at the very surface area and therefore reduced start of the overcharge region, the fact capacity. remains that we are already operating The clumping of crystals is mostly in the overcharge region. a slow process but is cumulative. Overcharging is not acceptable if we However, as we will see later, it is want to achieve maxi­mum battery life reversible. for nicad cells. For NiMH cells it can End point voltage be dan­gerous if used in combination with high charge currents. It can lead The usual strategy to prevent memto venting and consequent loss of ory effect is to discharge each cell to capacity and in extreme cases to cell 1.1V or 1.0V, a level where very little explosion, due to a build up of gas useful energy is left. This is only partly pressure. effective with single cells and with If NiMH cells are charged with new and well matched cells in battery delta V termination char­ gers, then this has to be done at the rate the manufacturer recommends, typically C/10 (120mA) for 1200mAh cells. At this rate, any heat produced during charging and overcharging will be safely dissipated. packs. Not all cells in a battery pack will age equally or charge and discharge equally at different operating temperatures. In the end, some cells will only be partly discharged when others are deep dis­charged. At the final stage of the battery discharge, a sudden sub­stantial voltage drop occurs. This can lead to reverse charging of the weakest cell in a battery pack of more than 12 cells and will still cause a clumping of crystals in all cells (except the weakest cell) during the next charge. The magnitude of memory effect in each cell depends on the depth of discharge. Unlike some other types of cells, nicads can be totally discharged and then even shorted to avoid the memory effect but not without reducing life expectancy. The life expectancy of all types of batteries, including nicads, is partly dependent on the depth of discharge. Hence, a total discharge will reduce life expectancy (up to a factor of 10 in cases of frequent total discharge). Totally discharging a battery to 0V – unlike discharging a single cell – is a sure recipe for extremely short battery life due to cell voltage reversal. Shallow discharge, less than 25% of total capacity, makes for long battery life but creates the conditions for memory effect. A 1.1V or 1.0V discharge voltage is only a compromise, not a magic value. Freezing cells Another strategy to combat memory effect, the practice of freezing batteries to break up the clumping of the crystals, creates mechanical stresses in the cells. This can also lead to Memory effect Let’s look at the major problem of nicad cells: memory effect. This is caused by charging a partially discharged battery and enhanced by slow charging and high operating temperatures. During charging, the negative plate loses oxygen and converts cadmi­um hydroxide to metallic cadmium, while the positive plate goes to a higher state of oxidation, changing 12  Silicon Chip Fig.4: the essential characteristic of the Reflex charging method is a high current charge pulse, followed by a short rest period and then an even higher discharge pulse for 5ms. The battery voltage is then measured before the next charge pulse. This is the view inside the prototype from Smart Fastchargers. It uses a total of three PC boards and can charge batteries at a rate of up to 9A. reduced life expectancy since a high degree of mechanical preci­sion goes into the production of today’s high capacity cells. It is also a time consuming method, since all cells in the battery have to be slowly warmed to above 10°C after freezing for efficient fast charging. All these are makeshift solutions. The problem should be tackled at the roots, by using a charge method that will reduce crystal size in batteries where crystal clumping has occurred and avoids crystal clumping during the charging of partially dis­charged batteries. Another area that needs improvement is the small number of recharge cycles suggested for most nicad batteries. In the case of some hand-held radios, the batteries are supposed to have only 300 recharge cycles. Batteries for other appliances are rated for 500 and 1000 cycles. Theoretically, 5000 charge/discharge cycles are possible over a minimum life span of 10 years. One power hand tool manu­ facturer advertises 3000 cycles and 10 minutes charging time. This is achieved by using advanced charger technology and fast charge batteries. 3000 cycles represent approximately 6.5 cents per cycle as compared to 55 cents per cycle for the hand-held radio batteries (at presently quoted prices). Another problem is the excessive time required to charge nicad and NiMH batteries with delta V termination chargers: generally between one hour for fast charge nicad batteries and 15 hours for standard nicad batteries and NiMH batteries. Only in exceptional cases, as with some chargers for battery powered tools, is it possible to achieve charge rates of less than one hour for nicad batteries. Burp charging One overseas company has designed a fast charger that achieves an amount of recharge cycles close to the theoretical limit. This patented charger, well proven in industrial and military applications, is used to charge aircraft batteries, emergency standby batteries for hospitals, etc and operates fully automatically. It automatically detects the type of battery (nicad, NiMH, lead-acid, etc), battery capacity and voltage and adjusts itself accordingly. These complex chargers use the patented Reflex or BURP charge method. This consists of a positive charge pulse followed by a high current, short duration discharge pulse. This should not be confused with pulse or switchmode chargers which switch the charge current on and off but do not apply a discharge cur­rent – see Fig.3. By using a charger circuit with the patented Reflex method incorporated in a licensed integrated circuit, it is possible to obtain a dramatic increase in the charge/discharge cycles of nicad batteries, to at least 3000 cycles if reasonable care is exercised. There is no need to run appliances until the batteries are flat to avoid the mem­ory effect. It is now possible to recharge the batteries after each use. Partial dis­­ charge, as opposed to full discharge, will significantly increase the life of the batteries. A microprocessor calculates and accurately terminates the applied charge by evaluating the inflection points on the charge voltage curve. The termination point varies according to the charging characteristic of the battery; it occurs just prior to the transition into overcharge (see Fig.2). The circuit provides a fast charge, preceded by a series of soft start charge pulses. Then, if the battery is left in January 1996  13 Fig.5: the timing for soft start, fast, topping and maintenance charges. The charge/discharge pulse combination for the topping and maintenance modes remain the same as for the fast charge cycle; only the rest time is changed. the charger, the fast charge will be followed by a topping charge and a non-destructive indefinite maintenance charge. All of the above can be done by one charger with an adjust­able output current sufficient for batteries of 7000mAh capacity at the 1C (1 hour) charge rate or for 1900mAh capacity batteries at the 4C (15 minute) charge rate, taking the charge efficiency into account. To fully charge a battery, approximately 20% more charge than has been withdrawn has to be put back into the bat­tery if charged at or above C/10 at 20°C. The charge efficiency of batteries depends on charge cur­rent and ambient temperature. High or very low ambient temper­ atures and/or low charge currents decrease the charge efficiency; in extreme cases to a point where the battery cannot be fully charged. Soft start Batteries can exhibit a high impedance during the initial stages of charging. The resulting voltage peak can be interpreted by the processor as a fully charged battery. However, with the soft start cycle, at first only short duration current pulses are applied to the battery. Starting at 200ms, the pulse width is gradually increased to approximately one second in duration. This gradual increase in pulse width takes place over a period of two minutes to avoid voltage peaks. Fast charge During the main charge cycle, each positive current pulse is followed by a discharge pulse, as shown in Fig.4. The dis­charge pulse is 2.5 times the amplitude of the charge pulse. After the main charge, if the battery is left on the charger, it will be fed a topping 14  Silicon Chip charge. This charge is at a current low enough to prevent cell heating but high enough to convert all active material in the cells to the charged state. Due to higher temperatures and gas bubbles (see explanation further on), 100% charge cannot be achieved with fast chargers. Standard constant current chargers create heat and gas bubbles on the cell plates during charging. This results in less than 90% efficiency. This version of the Reflex charger is approximately 95% efficient, since the termination method largely avoids cell heating and the charge/discharge pulse sequence removes most of the gas bubbles from the cell plates. The 2-hour C/10 charge tops up the battery if the time is available or 100% capacity is required. Maintenance charge After the full charge and topping charge, the C/40 charge compensates for the internal self-discharge of the battery, at the same time preventing dendrite formation and maintaining the crystal structure. The battery can remain on the charger until used – there is no time limit. This charge cycle can be useful in standby applications, as in security installations. Fig.5 shows the timing for soft start, fast, topping and maintenance charges. The charge/discharge pulse combination for the topping and maintenance modes remain the same as for the fast charge cycle; only the rest time is changed. The removal of gas bubbles from the cell plates during charge keeps the cell impedance low, reduces operating tempera­ture and allows higher charge currents for nicad and NiMH batter­ies. The following charge times can be achieved: fast-charge nicad batteries in less than 15 minutes at the 4C rate, standard nicad and NiMH batteries in less than one hour. As well, memory effect in batteries can be eliminated. This works even when the battery no longer holds any charge. It re­quires a minimum of three complete charge/discharge cycles. A typical case in practice involved a 4.8V 600mAh cellular phone battery pack. This had only 20% of its stated capacity, after it had been used over a period of six months with the supplied charger. After five charge/discharge cycles, it had recovered to approximately 95% of capacity. The possibility to rejuvenate shorted nicad batteries is also a feature. Whenever a nicad battery has been stored charged and has then slowly self-discharged over a very long period of time at an elevated temperature, or has been charged at a low current over a long period, as in constant current trickle charging in standby applications, crystals on the cell plates can form crystalline fingers, or dendrites, which can propagate through the plate separators and across the cell plates. In extreme cases, these crystalline dendrites can partially or completely short-circuit a cell. Such cells can be rejuvenated by this charger. Charger circuit Fig.6 shows the block diagram of a charger using the pat­ented Reflex charging method. The charger covers a battery vol­tage range from 1.2V to 13.2V at charge currents from 0.1A to 9.0A. The central part of the battery charger is basically a reduced instruction set microprocessor (RISC) to handle the complex calculations for the charge termination point. The microprocessor uses an analog-to-digital converter (ADC) with 300µV resolution to convert the battery voltage, normalised to one cell by the input attenuator VR1. The ADC is followed by a filter to limit the effects caused by battery voltage jumps and ADC noise and to eliminate Fig.6: the block diagram of a charger using a RISC microprocessor programmed with the patented Reflex charging method. The charger covers a battery voltage range from 1.2V to 13.2V at charge currents from 0.1A to 9.0A. any large aberra­tions in the battery voltage curve. The microprocessor controls the charge, topping and main­ tenance modes. One input of the microprocessor controls the charge rates (1C or 4C) and is linked to the bank of push- buttons for selection of charge current. One input resets the microprocessor to repeat a charge cycle or to charge shorted cells. In this case, the reset button has to be activated until the LED “cell voltage” display indi­cates acceptance of the charge current. A battery voltage guard circuit avoids au­tomatic charging of shorted batteries. This is necessary since the current required to kick start a shorted battery varies from case to case and should be controlled manually. Another detect circuit avoids the automatic charging of batteries with a voltage or more than 2V per cell. This condition is due to high internal impedance, as found in new batteries that have not been cycled and in some batteries which have been stored for several months. Charging these batteries would cause exces­sive heating. The DC input to the charger can range from 11.5V to 28V, depending on the number of cells in the battery to be charged. Essentially, this is a minimum of 2V per cell plus an additional 2V. Hence a 6V battery (5 cells) requires a minimum of 12VDC to the charger while a 12V battery (10 cells) requires a minimum of 22VDC. Safety cut-off In case the voltage sensing for end of charge does not work there is a timeout circuit which is set for 72 minutes at the 1C rate and 18 minutes for the 4C rate. In addition, there is a heatsink temperature sensor to interrupt the charge as a safety measure in extreme hot weather conditions. The microprocessor controls three output circuits and two LED indicators. The charge circuit is a switch­ mode current source, adjustable from 0.1A to 9A with VR2 (a bank of pushbutton switches). The discharge circuit is a pulsed constant current sink adjusted to between 0.25A and 22.5A (2.5 times the charge current). During the main charge cycle, a small piezo speaker emits a brief tone once a second, synchronised to the discharge pulses. This is a convenient audio cue to tell the user the battery is still in the main charge sequence. The tone control on the front panel actually adjusts the volume, so that the tone is not obtru­sive. Other details of the operation can be gleaned from the block diagram. By this time this issue goes on sale, the charger will have been released for sale. For information concerning availability and price, contact Smart Fastchargers, R.S.D. 540, Devonport, Tas 7310. Phone/fax (004) 921 368. *Horst Reuter is Technical Manager of Smart Fastchargers. January 1996  15 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. Automatic level control for line signals This circuit adapts the Plessey Sl6270 gain control chip to line levels. Intended for automatic level control of balanced microphones, the SL6270 was featured in the August 1995 issue. In this circuit, it will accept up to 1V RMS of signal before clip­ping and will provide a constant output level for input signals between 14mV and 1V. The 1.5kΩ and 1kΩ resistors at the input provide the neces­sary attenuation of the signal to prevent clipping within IC2. IC1 is simply used to buffer the signal and drive the 150Ω input impedance at pin 4. The 470Ω resistor in IC1’s feedback path increases the impedance seen by the op amp to 600Ω to prevent distortion. The signal output at pin 2 of IC2 is AC-coupled to buffer amplifier IC3a. By virtue of feedback action, pin 2 of IC3a applies signal to the pin 7 input of IC2 where it is rectified and filtered to determine the gain. VR1 sets the output level. SILICON CHIP. to turn on transistor Q1 which drives the relay. After two minutes or so, as determined by the 470kΩ resistor and 220µF capacitor at pin 6, the output at pin 3 will go low and Q1 will turn off. The relay must have adequate ratings to handle the current drawn by the pump. If you need a longer pumping time, increase the value of the 470kΩ resistor and vice versa. SILICON CHIP. Bilge pump timer uses a mercury switch This circuit was designed to enable a mercury switch to replace the contacts in a float switch for a bilge pump. The mercury switch can be expected to last indefinitely compared with the limited life of mechanical contacts in a float switch. Howev­er, the mercury switch cannot be used to control the pump direct­ly. Therefore it is used to initiate a 2-minute timer based on a 7555. The mercury switch is mounted on the float switch lever in such a way that it closes when the water reaches a preset level. This momentarily pulls the trigger input (pin 2) low to start the timer. This takes pin 3 high 16  Silicon Chip PWM speed controller This circuit can be used to provide a wide range of speed control for a 6V DC motor, with very little power dissipation in the controlling transistor. Op amp IC1a forms a Schmitt trigger oscillator with a 45% duty cycle, as set by the voltage divider resistors at pin 3. The frequency is varied between 47Hz and 500Hz by VR1. The wave­ form at pin 6 of IC1b is a sawtooth and this is compared with the DC threshold voltage set by VR2 at pin 5. With VR2 set for a low voltage, IC1b delivers short pulses; for a high setting, long pulses are delivered. IC1b drives a Darlington transistor (Q1) to switch the motor. Diode D1 clips the back EMF, while the .047µF capacitor helps suppress EMI from the motor’s brushes. The circuit can also be used with higher supply voltages whereupon the bipolar transistor can be substituted with a Mosfet such as an MTP-3055E or BUZ71. M. Schmidt, Edgewater, WA. ($30) DC amplifier for a centre-zero meter Moisture monitor for pot plants This circuit will sound a piezo beeper when your plants need a drink. IC1a is a free-running Schmitt trigger oscillator which produces a brief positive pulse once every three minutes. This is fed to pin 8 of IC1b and to pins 5 & 6 of IC1d via a 470kΩ resis­tor and the pot­plant pot. IC1d is connected to invert the pulses fed to pin 9 of IC1b. This gate’s output remains high and inhib­its an oscillator comprising IC1c, as long as the soil is moist and conducts. When the soil is dry, IC1d’s output goes high so that IC1b enables IC1c and the beeper sounds. VR1 acts as a sensitivity control. B. Avi, Rose Bay, NSW. ($30) This circuit will allow a 5mA FSD centre-zero meter to be used where a 50µA meter movement would otherwise be required. The circuit is based on an LF411 op amp which has been specified for its low drift. It operates as a current amplifier. VR1 is used to zero the meter when the input signal is zero, while VR2 adjusts the full scale deflection. SILICON CHIP. Circuit Ideas Wanted Do you have a good circuit idea? If so, sketch it out, write a brief description & send it to us. Provided your idea is original, we’ll publish it & you’ll make some money. Send your idea to: Silicon Chip Publications, PO Box 139, Collaroy, 2097. January 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 Surround Sound MIXER & DECODER PART 1 – By JOHN CLARKE Build this unit and add depth, realism and effects to your home videos. It provides realistic surround sound mixing, while an inbuilt decoder provides the rear channel signal during playback if a surround sound processor is unavailable. 22  Silicon Chip W HILE HOME VIDEOS usu- ally provide fairly bland viewing for all but a few doting grandparents and close relatives, this does not have to be so. Surround sound can capture the audience so that they become part of the action. Adding surround sound will add a new dimension to your video recordings. It may even stir you into creating bigger and better movie productions, as you experiment with surround mixing. As well as surround mixing, this Surround Sound Mixer & Decoder can also be used to mix normal stereo signals; ie, by using just the Left and Right channels. You can also mix in signals from two other sources via the A and B channels. By adding the Centre and Surround channels, you will have surround processing. Signals from the A and B inputs can be mixed into any of the Left, Centre, Right and Surround channels using the L-R and the C-S pan controls. The resulting surround sound signal is encoded into the Left and Right channels and is subsequently decoded on replay. To simplify the task of mixing, signal level meters are fitted to all four Main Features • • • Surround sound encoding and decoding. • • Compatible with normal stereo and mono outputs. • • • • • • A-channel panning between L-R and C-S. Encoding similar to 4-channel Dolby® surround format. Encoded signals can be decoded by Dolby Pro Logic® and passive surround sound units, or by using the internal decoder in the mixer. Separate Left, Centre, Right and Surround inputs, plus A and B channel inputs. B-channel panning between L-R and C-S. Separate level controls for all inputs. Balanced or unbalanced microphone and line input options. Single output level control. LED level meters for the L, C, R & S channels (-24dB to +3dB). output (L, C, R & S) channels. They comprise 10-LED displays with a -24dB to +3dB range in 3dB steps. In operation, they monitor the encoded Left and Right channel sign­als and the Centre and Surround channels. Surround sound playback The encoded signals can be played back in stereo or mono but in order to obtain surround sound, they must be re­ played through a stereo VCR and decoder. While the mixer does incorporate a simple decoder, its main purpose is to provide the meter signals. Ideally, for best sound effects, the L & R outputs from the VCR should be fed through a Dolby Pro Logic surround sound decod­ er. This could be a commercial unit or you could use either of the two units described in SILICON CHIP (see Dec.94-Jan.95 and Nov.95-Dec.95). Fig.1(a) shows the basic scheme. If you don’t have a Dolby Pro Logic decoder, the basic decoder built into the Surround Sound Mixer & Decoder can be used instead. In this case, the L & R outputs from the VCR connect to the Left Fig.1: the encoded signals on the video tape can either be decoded using a Dolby Pro Logic unit as shown at (a), or fed through an internal decoder in the mixer itself as shown at (b). In the case of (b), the Centre (C) channel is not normally used, while the Surround (S) channel should ideally pass through a 20ms delay before being fed to its power amplifier. January 1996  23 Fig.2: block diagram of the Surround Sound Mixer and Decoder. The various inputs are mixed in summing amplifier stages before being fed to the Left and Right outputs via level controls VR11a and VR11b. On playback, IC9a sums the Left and Right channels to provide the Centre output, while IC9b produces a difference output which is then filtered to provide the Surround output. and Right channel inputs of the unit in the line mode – see Fig.1(b). The overall volume can then be controlled by the Output Level control, while the balance is adjustable using the individual Left and Right level pots. Note that, ideally, the Surround channel output from the mixer unit should be passed through a 20ms delay (a suitable 20ms delay unit will be described in the February 1996 issue of SILI­CON CHIP). The Centre output is best left disconnected here, since it will have poor separation from the Left and Right chan­nels. Note also that the decoded sound will be nowhere near as realistic as from a Dolby Pro Logic unit. The decoder built into the mixer is very much a “poor man’s” approach to surround sound, although it can still give good effects. In either case, separate amplifiers are required for the Left, Right, Surround and Centre channels in order to drive the loudspeakers. The Left 24  Silicon Chip and Right channels are normally fed to an existing stereo amplifier, while a second stereo amplifier can be used for the Surround and Centre channels. Alternatively, some Dolby Pro Logic decoders have several audio amplifiers built in. Inputs & outputs As shown on the main circuit diagram (Fig.3), each input has a stereo jack socket which can accept either a microphone or a line level signal, as selected by a toggle switch. Either a balanced or an unbalanced source can be used for the microphone input, while line level inputs must be unbalanced. If necessary, unbalancing can be achieved by using either a mono plug or a stereo plug wired with the ring connection to ground. At the other end, the outputs are run to RCA sockets to provide the Left, Centre, Right and Surround (L, C, R & S) signals. For recording purposes, the Left and Right channels only connect to the tape recorder (or VCR). Although making a stereo recording is fairly straightfor­ ward, 4-channel recordings will require a fair degree of prac­ tice. Fairly obviously, you will need four microphones – one for each channel. For a concert, the Left, Centre and Right micro­phones should be spread across the stage. The rear channel micro­phone can either be placed behind the stage or within the audi­ence, depending on the effect you want. The A and B inputs can be used to add background sounds or music to one or more channels. And, if desired, you can produce the effect of movement between one channel and another by pan­ ning. There are four panning controls in all (two for the A input and two for the B input) and these provide panning between the Left and Right channels (Pan L-R) and between the Centre and Surround channels (Pan C-S). Block diagram Fig.2 shows the block diagram of the unit. Starting at the left, there are six amplifiers for the Left, Centre, Right, Surround, A and B inputs. The output Output level control The SUM3 and SUM4 outputs are now fed to output level con­trols VR11a and VR11b, respectively. These are sections of a dual-ganged pot and are used to adjust the encoded Left and Right channel output levels. From there, the encoded signals are fed to the Left and Right channel output sockets. They are also used to drive the Left and Right signal strength meters. In addition, the encoded Left and Right channel outputs drive summing circuit SUM6 and difference circuit DIFFERENCE 1. The SUM 6 output provides the Centre channel and is inverted (IC10a) before being fed to the output socket and to the Centre meter. PARTS LIST 1 sloping front console cabinet, 170 x 213 x 31 x 82mm 1 PC board, code 02302961, 144 x 194mm 1 PC board, code 02302962, 76 x 105mm 1 PC board, code 02302963, 72 x 82mm 1 self-adhesive front panel label, 166 x 215mm 1 self-adhesive rear panel label, 165 x 78mm 6 10kΩ log pots (VR1-VR6) 4 10kΩ linear pots (VR7-VR10) 1 10kΩ dual ganged pot (VR11) 1 1kΩ horizontal trimpot (VR12) 7 SPDT toggle switches (S1-S7) 6 6.35mm stereo PC board mount switched sockets 1 2 x 2-way PC-mount RCA panel socket (Altronics P0211) 1 DC panel socket (to suit plugpack) 1 12VAC 300mA plugpack 4 knobs with blue insets 2 knobs with red insets 2 knobs with purple insets 3 knobs with black insets 15 cable ties 1 15m length of single shielded cable 1 1.5m length of yellow hook-up wire 1 500mm length of red hook-up wire 1 500mm length of green hookup wire 1 800mm length of blue hook-up wire 4 9mm tapped spacers 4 6mm untapped spacers 4 3mm dia. x 12mm screws 5 3mm dia. x 6mm screws The DIFFERENCE1 output provides the Surround signal. This is rolled off above 7kHz by low pass filter stage IC10b before being applied to the output socket and metering circuitry. Circuit Refer now to Fig.3 for the complete circuit details. Although it may appear quite complicated at first glance, there is in fact a considerable amount of duplication for the various inputs. Let’s begin by taking a look at the 1 3mm nut 74 PC stakes 4 11-way pin headers (13mm long pins) Semiconductors 10 LM833 dual op amps (IC1IC10) 1 TL071, LF351 single op amp (IC11) 4 LM3915 log. display drivers (IC12-IC15) 1 7812T 3-terminal regulator (REG1) 1 B104 1A bridge rectifier (BR1) 4 BC328 PNP transistors (Q1Q4) 4 1N914 signal diodes (D1-D4) 40 3mm red LEDs (LED1-40) Capacitors 1 2200µF 25VW PC electrolytic 1 100µF 16VW PC electrolytic 12 47µF 16VW PC electrolytic 6 10µF 16VW PC electrolytic 20 2.2µF 16VW PC electrolytic 19 0.1µF MKT polyester 2 .0027µF MKT polyester 2 680pF ceramic 6 220pF ceramic 1 180pF ceramic 1 100pF ceramic Resistors (0.25W, 1%) 4 1MΩ 8 4.7kΩ 4 100kΩ 12 2.2kΩ 19 22kΩ 4 1.2kΩ 4 16kΩ 8 1kΩ 2 20kΩ 4 680Ω 4 13kΩ 6 220Ω 1 12kΩ 4 150Ω 30 10kΩ 5 100Ω 2 8.2kΩ input circuitry for the Left signal. This circuit is based on op amp IC1a which is wired in the balanced configuration. Fig.3 (following pages): the input and summing circuitry is based on LM833 dual op amps (IC1-8), and these are also used in the decoding circuitry (IC9-10). IC11 is used to derive the split supply, while the four signal level meters are based on LM3915 display driver ICs. January 1996  25 ▼ levels from these stages are set by potentiometers VR1-VR6 re­spect­ively. The Left amplifier output connects to summing junction SUM1 which comprises IC4a. This mixes in the Centre amplifier output after it has been attenuated by 3dB. Similarly, the Right ampli­fier output connects to summing junction SUM2 (formed by IC5a) and this also mixes in a -3dB Centre signal. The A and B amplifier outputs are each amplified by two, using IC7a and IC7b respectively. This is done to compensate for losses in the following L-R pan circuit stages. The resulting L-R pan signals are then mixed into the SUM1 and SUM2 junctions. Similarly, the Surround amplifier output is summed at SUM5 with the C-S (Centre to Surround) pan control outputs. The summed output is then filtered using low-pass filter stage IC6a, so that only signals below about 7kHz are fed to the following stages. Following IC6a, the Surround signal is fed in two different directions. In one direction, it is first phase shifted by 180° (ie, inverted), then attenuated by 3dB and mixed at SUM3 with the signal from SUM1. In the other direction, it is fed straight to a 3dB attenuator (ie, no phase shifting) and then mixed at SUM4 with the signal from SUM2. The process so far is similar to the encoding process used for Dolby Surround Sound recording, except that no noise reduc­tion is used in the Surround signal path. This lack of noise reduction encoding circuitry is not important in this applica­tion, particularly as we wanted to keep costs down. 26  Silicon Chip January 1996  27 Assuming that S1 is closed (LINE), the input signal is attenuated by the 220Ω resistor and the overall stage gain is +1. The output from IC1a appears at pin 1 and is fed to level control VR1. IC1b, IC2a, IC2b, IC3a & IC3b are the input amplifiers for the Centre, Right, Surround, A and B channel inputs respectively. These stages are all identical to IC1a and their outputs feed level controls VR2-VR6. Following VR1, the Left signal is fed to summing amplifier IC4a via a 10kΩ resistor. Similarly, the Right signal is fed via a 10kΩ resistor to summing amplifier IC5a. The Centre channel output at the wiper of VR2 is buffered using IC4b before being applied to each of these summing junctions via a 14kΩ resistance (made up of 13kΩ and 1kΩ resistors in series). This arrangement effectively attenuates the Centre channel signal by 3dB with respect to the Left and Right signals. That’s because IC4a & IC5a operate with a gain of -1 for the Left and Right signals, and a gain of -0.714 for the Centre signal. Moving now to the Surround channel, the signal on the wiper of VR4 is coupled to pin 6 of IC5b, where it is summed with the Centre-Surround (CS) pan signals (more on these shortly). The output of IC5b then drives IC6a. This op amp is wired as a 2-pole lowpass filter stage and rolls off frequencies above 7kHz. Performance of Prototype Signal-To-Noise Ratio Better than 84dB with respect to 1V output Frequency Response: L, C, & R Channels: -1dB at 10Hz & 40kHz A & B Channels: -3dB at 40Hz & -1dB at 40kHz S Channel: -3dB at 7kHz Total Harmonic Distortion 0.01% at 1kHz and 300mV input Decoder Separation Surround to Centre Channels: 42dB minimum at 1kHz Left to Right Channels: 76dB at 1kHz Left & Right to Centre Channel: 12dB Left & Right to Surround Channel: 15dB Signal Handling 2V RMS maximum for line input Sensitivity: Mic Input: 30mV for 300mV out. Line Input: 300mV for 300mV out. Assuming that S1 is in the MIC position, it has a gain of -10 for signals fed to its inverting input and +11 for signals fed to its non-inverting input (as set by the 22kΩ feedback resistor and the 2.2kΩ input resistors). However, signals applied to the non-inverting input are first attenuated by 0.909 using a resistive divider (2.2kΩ & 22kΩ) before being amplified. As a result, the overall stage gain for signals applied to the non-inverting input is +10, which matches the gain for the inverting input. This gives good common mode rejection for balanced signals (eg, from a microphone). For unbalanced signals, the inverting socket connection must be ground­ ed externally by a mono plug (or by earthing the ring terminal of a stereo plug). This means that only signals at the socket tip will be amplified, with IC1a now operating as a non-inverting amplifier. TABLE 1: RESISTOR COLOUR CODES ❏ No. ❏   4 ❏   4 ❏ 19 ❏   4 ❏   2 ❏   4 ❏   1 ❏ 30 ❏   2 ❏   8 ❏ 12 ❏   4 ❏   8 ❏   4 ❏   6 ❏   4 ❏   5 28  Silicon Chip Value 1MΩ 100kΩ 22kΩ 16kΩ 20kΩ 13kΩ 12kΩ 10kΩ 8.2kΩ 4.7kΩ 2.2kΩ 1.2kΩ 1kΩ 680Ω 220Ω 150Ω 100Ω 4-Band Code (1%) brown black green brown brown black yellow brown red red orange brown brown blue orange brown red black orange brown brown orange orange brown brown red orange brown brown black orange brown grey red red brown yellow violet red brown red red red brown brown red red brown brown black red brown blue grey brown brown red red brown brown brown green brown brown brown black brown brown 5-Band Code (1%) brown black black yellow brown brown black black orange brown red red black red brown brown blue black red brown red black black red brown brown orange black red brown brown red black red brown brown black black red brown grey red black brown brown yellow violet black brown brown red red black brown brown brown red black brown brown brown black black brown brown blue grey black black brown red red black black brown brown green black black brown brown black black black brown Fig.4: install the parts on the main PC board as shown here. Note particularly that IC11 is a TL071. The filtered output from IC6a is summed in IC8b with the signal from IC5a. It is also inverted by IC6b (ie, phase shifted by 180°) and summed in IC8a with the signal from IC4a. Note that, in both cases, the filtered Surround signal is attenu­ated by 3dB in the summing amplifiers due to the 14kΩ input resistances (again made up of 13kΩ and 1kΩ resistors). Following these two summing amplifiers, the signals are fed to output January 1996  29 The Surround Sound Mixer and Decoder is built into a compact console case with a sloping front panel. Note that there is a fair amount of internal wiring to be run, most of it between the main board and the front panel controls. level controls VR11a and VR11b. The encoded Left and Right signals are then coupled to their respective output sockets via 2.2µF capacitors. Panning Now let’s take a look at how the pan signals are derived. In the case of the A input, the signal at the wiper of VR5 is first buffered and amplified by IC7a. This stage functions as a non-inverting amplifier with a gain of two. The output from IC7a is then applied to pan control VR8 via a 4.7kΩ resistor and to pan control VR7 via a second 4.7kΩ resistor and two 10kΩ isolating resistors. VR7 is used to pan the “A” signals between the Left and Right channel summing amplifiers (IC4a and IC5a), while VR9 does the same for the “B” signals. Similarly, VR8 and VR10 (Pan C-S) pan the “A” and “B” signals between the Pan L-R controls and the input to IC5b. In theory, VR7 and VR9 pan between the Left and Right chan­nels, while VR8 and VR10 pan between the Centre and Surround channels. In practice, however, there is some interaction between these controls. Surround sound decoding The internal decoding circuitry is 30  Silicon Chip based on IC9a, IC9b, IC10a & IC10b and is normally only used on playback – see Fig.1(b). IC9a and IC10a are used to derive the Centre channel. This is achieved by first adding the Left and Right channel outputs together in summing amplifier IC9a. The output of IC9a is then buffered by unity gain inverter IC10a and coupled to the Centre output socket. A different technique is used to derive the Surround out­put. In this case, the encoded Left and Right channel outputs are fed to IC9b which is configured as a difference amplifier. This configuration is arrived at by feeding the Left channel to the inverting (pin 6) input and the Right channel to the non-inverting (pin 5) input. The output from IC9b is simply the difference between the two input TABLE 2: CAPACITOR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ Value IEC Code EIA Code 0.1µF   100n   104 .0027µF   2n7   272 680pF   680p   681 220pF   220p   221 180pF   180p   181 100pF   100p   101 signals. This signal is filtered and invert­ed by low-pass filter stage IC10b and fed to the Surround output sock­et. Signal meters As mentioned previously, the circuit contains four signal level meters which monitor the Left, Right, Centre and Surround outputs. These four meters are all identical, so we’ll just look at the meter that monitors the Left output. The circuit is based on IC12 which is a 10-LED display driver wired in dot mode. In operation, the incoming signal is first buffered by emitter follower stage Q1. It is then recti­fied by D1, filtered and applied to pin 5 of IC12. The filter components on pin 5 consist of a 0.1µF capacitor and a 1MΩ resistor, connected in parallel. These give the meter a fast attack time and a slow decay response, so the meter effectively displays the peak average value. As well as acting as a buffer, Q1 also compensates for the voltage drop across D1, since its emitter is always approximately 0.6V above its base. While this compensates fairly well, the balance is not perfect since there is more current through Q1’s base-emitter junction than through D1. This slight imbalance is taken care of by using VR12 to set an offset voltage on pin 3 (RLO) of IC12. This jacks the pin 3 voltage up so that it equals the voltage at pin 5 when the input signal is tied to ground. The full scale deflection value for the meter depends on the voltage on pin 7 and is set by the 4.7kΩ and 680Ω resistors. In this case, the voltage on pin 7 is set to 1.64V, which corre­ sponds to a peak value of 3dB above 774mV RMS (ie, LEDs 1-10 lit). As a result, the meter is calibrated for 0dBm, which corre­ sponds to 1mW into 600Ω. Power supply Power for the circuit is derived from a 12VAC plugpack. This is fullwave rectified using BR1, filtered by a 2200µF ca­pacitor and applied to REG1 to derive a regulated +12V output. IC11 is used to provide the circuit ground, so that the op amps are effectively fed from split supply rails. It does this by buffering the 5.45V output from a voltage divider (12kΩ & 10kΩ) wired across the regulator output. The 100Ω resistor at IC11’s output isolates the op amp from the following 100µF capacitive load and prevents oscillation. As a result, the +12V rail is 6.55V above ground, while the 0V rail is 5.45V below ground; ie we effectively have split supply rails of +6.55V and -5.45V. Construction Despite the circuit complexity, building this unit is quite straightforward. Most of the circuitry is contained on three PC boards: (1) a main board coded 02302961 (144 x 194mm); (2) a display driver board coded 02302962 (76 x 105mm); and (3) a LED display board coded 02302963 (72 x 82mm). Begin the construction by checking the PC boards. In particular, check for any breaks in the tracks and for shorts between adjacent tracks. The board mounting holes should all be drilled to 3mm, while a 3mm hole is also required on the main board for the regulator (REG1) mounting screw. Fig.4 shows the parts layout on the main PC board. Start by installing PC stakes at all external wiring points, then install the wire links (using tinned copper wire). The next step is to install the ICs. Note that these must all be oriented in the same direction. Note too that IC11 is a TL071 while the rest are all Make sure that all polarised parts are correctly oriented when building the main PC board. The 2200µF capacitor (bottom, right) is installed on its side and is secured to the board using silicone sealant to prevent lead breakage. LM833s, so don’t get them mixed up. The bridge rectifier (BR1) can also now be installed (orient it as shown), followed by 3-terminal regulator REG1. Secure REG1’s metal tab to the PC board using a screw and nut. The resistors and capacitors can now be mounted. Table 1 lists the resistor colour codes but it is also a good idea to check them with a multimeter, as some colours can be difficult to decipher. Table 2 lists the capacitor codes. Make sure that the electrolytic capacitors are all correctly oriented and note that the 2200µF capacitor is mounted on its side. Use silicone sealant to secure the body of the 2200µF ca­pacitor to the board, to prevent its leads from flexing and eventually breaking. As shown on Fig.4, three of the 6.35mm stereo sockets are mounted directly on the main board. Install these now, along with the 2 x 2 RCA socket package. The mounting clips on the underside of RCA socket package will have to be removed using side cutters before it is installed on the board. That's all we have space for this month. Next month, we will resume with the parts layout diagrams for the display driver and display boards and give the complete wiring and testing details. We will also publish the full-size PC board patterns and the front-panel layout. Note: “Dolby”, “Pro Logic” and the Double-D symbol are trademarks of Dolby Laboratories Licensing Corporation, San Francisco, CA 94103-4813 USA. January 1996  31 COMPUTER BITS BY GEOFF COHEN gcohen<at>pcug.org.au Upgrading your old PC – is it worthwhile? Is it worthwhile upgrading your old PC or should you put the money towards a new one? The answer depends on the state of your old PC and the applications you wish to run. There are a swags of old 286, 386 and even 486SX PCs float­ing around now and a question I often get asked is “is it worth­while upgrading my old PC to run Windows, or should I buy a new one?”. The answer depends, of course, on what sort of PC you have and how much you want to increase the performance – and thus how much you are prepared to spend on the upgrade. The options are: (1) do a minimal upgrade and recycle the old PC so the kids can run Windows (word processing and games); or (2) go for a full upgrade by replacing the motherboard, CPU and hard disc. Is it worth it? First, you have to decide if it is worthwhile upgrading your PC. If you have a PC with a mono screen, a hard disc smaller than 80Mb and less than 4Mb of RAM, upgrading the PC to run Windows (especially Windows 95) is not really an economic propo­sition. In addition, if you have a major brandname PC (IBM, Compaq, etc), you will need to check if the beast uses a standard size motherboard, with normal plug in cards. Many brand- name computers use specialised components and cannot accommodate some of the standard parts used in clone PCs. However, if you your PC has a minimum of a VGA card, a colour monitor and at least 4Mb of RAM, it may be worthwhile upgrading it. At the time of writing (November 1995), Fig.1: the SimmVerter from Cameleon Technology accepts four 30-pin memory modules (either 4 x 1Mb or 4 x 4Mb) and effectively converts them to a single 4Mb or 16Mb 72-pin memory module that plugs into the latest motherboards. 32  Silicon Chip the cost of upgrading to a 486DX2-66 mother­board (including the CPU) is around $300.00, while a 545Mb hard disc drive and controller can be had for just $280.00. The cost of RAM is not too bad either, with the price of a 4Mb 72-pin RAM module currently around $230. What should I upgrade to? The answer to this question depends on what you want to do. Here are a couple of alternatives to consider: (1) Windows/games PC. If you only want to run Windows 3.1 at a reasonable speed – eg, so that the kids can run Word and a few games – I would recommend upgrading to: (i) a 486DX2-66 CPU (these are so cheap it’s not worthwhile using a slower CPU); (ii) 4Mb RAM; and (iii) an 80Mb or preferably bigger hard disc. (2) Microsoft Office/Windows 95 PC. These programs require a bit more firepower than the system listed above. To run Microsoft Office the minimum system would be: (i) a 486DX2-66 or 486DX4-100/120 CPU, a Pentium being even better; (ii) 8Mb RAM for Windows 3.1 or 16Mb for Windows 95; (iii) a 540Mb, 850Mb or even a 1Gb hard disc. In addition, a CD ROM drive is handy for installing pro­ grams like Office and Windows 95 , as it saves having to install from multiple flopp­ ies. I have noticed that there are still suppliers advertising Windows 95 systems with only 8Mb of RAM. I have tried this and it is very slow with Office 95. In fact, you need at least 16Mb for better performance and allow more programs to be opened. 16Mb is a good size for Windows 3.1 and 32Mb for Windows 95. Parity or non-parity RAM Most new motherboards have a CMOS option to enable or dis­ able parity RAM, the default option being non parity in the motherboards I have tried. Unless the PC is going to be used as a network server, non parity RAM should be adequate, as a RAM test is performed every time the PC is switched on. In any case, I cannot remember the last time I had a faulty RAM chip – it was, at least, several years ago. Disc controllers Some motherboards have two sets of 72-pin RAM sockets and four sets of 30-pin sockets. This photo shows a SimmVerter module, itself carrying four 30pin SIMMs, plugged into one of the 72-pin sockets at the rear. a Windows 95 system if it is to operate at a reasonable speed. Using your old memory A major problem used to be that while older motherboards used 30-pin SIMM RAM, the latest 486 and Pentium motherboards only have sockets for the new 72-pin SIMM RAM. This meant that upgrading to a new motherboard with 72-pin sockets necessitated throwing out (or selling cheaply) any existing 30-pin RAM, which was a tad annoying. Fortunately, a new device in now available which overcomes this problem. It’s called a “SimmVerter” and it effectively allows four 30-pin SIMMs (1Mb or 4Mb) to be converted to one 4Mb or 16Mb 72-pin SIMM module. All you have to do is plug four 30-pin SIMMs into the sockets on the SimmVerter. The SimmVerter itself then plugs into a 72-pin RAM socket on the motherboard. SimmVerters cost around $30 each, which is far less than the cost of having to replace 4Mb of RAM. They are available in four different shapes so that you can easily accommodate four SimmVerter modules adjacent to each other, if necessary – see Fig.2. Another approach is to see if there is any secondhand RAM available, either on the Net (eg, aus.ads.for­sale. computers) or in the Saturday paper. An important difference with the Pen- tium is the need to fit 72-pin SIMMs in groups of two. I won’t mention who fell for that trap the first time he installed a Pentium motherboard and used a single 8Mb SIMM, instead of two 4Mb SIMMs, and then complained that the !<at>#$%^&* thing wouldn’t work. If you want to improve Windows performance, the cheapest option is to increase your RAM. Upgrading from 4Mb to 8Mb makes the biggest difference and Word 6, for example, loads many times faster with this simple upgrade. Increasing the memory even further will provide even MODEL B MODEL A MODEL C MODEL D Fig.2: SimmVerters come in four models (A, B, C and D) so that they can be fitted to adjacent memory sockets. An upgraded disc controller card may be necessary if you are upgrading the hard disc. Assuming that you are going to stick with an IDE disc, you can purchase a multi-I/O card for around $25. As well as running your floppy drives and two IDE hard discs, this will also generally provide two serial ports, a parallel printer port and a games port. If you have (or are upgrading to) a VESA motherboard, then you should buy a VESA multi-I/O card, as they are much faster than a standard ISA card. Note, however, that most new Pentium PCI motherboards will already have the floppy, hard disc and I/O controllers on board. In that case, you don’t have to worry about a separate I/O card. Hard discs Depending on your requirements, you could stay with an existing 80200Mb hard disc and buy a used 100200Mb drive. However, a new 500Mb hard disc is only around $200 and a minimum of 150Mb is needed to run the full Windows 3.1 and Microsoft Office suite of software. If you are fitting a hard disc of 500Mb or above and have thousands of files, you need to consider how to partition it. For drives under 512Mb, a one byte file will take 8192 bytes. This increases to 16,384 bytes for 5121024Mb drives, and so on. In other words, the larger the logical drive, the larger the space that a one byte file effectively takes up and this wastes space. For example, if you have an 850Mb disc with 10,000 files, this will waste (on average) 10,000 x January 1996  33 The ZIP Drive – 100Mb On A $33 Disc speed at which Windows updates the screen may not be all that fast if an old ISA video card is fitted. Starting at around $120, a VESA or PCI video card will speed things up considerably. Typical examples, using ATPERF for relative performance details, are:      Old ISA  2       VESA 12      PCI 20 Another item to consider, if you want to use high resolu­tion (ie, 1024 x 768 or larger), is the amount of video RAM. A new video card should have a minimum 1Mb of RAM (preferably with sockets to accept more), or you can just bite the bullet and get a video card with 2Mb of RAM for even better performance. Installation Most computer users don’t consider backing up the large hard discs that are now being sold. There’s an old saying that there are only two types of computer users: those who have lost data and those who will lose data. The truth is that backing up onto floppy discs is often too cumbersome, while tape drives have the capacity but are quite slow when it comes to retrieving files (unless you have a DAT tape drive). External drive An external drive is the answer to backup problems. One interesting new device is the Zip drive which has recently been released by Iomega. This is a (relatively) cheap 100Mb removable disk drive which retails for around $370, with the 100Mb discs selling for around $99 for a pack of three. When installed, it is assigned a drive letter and is treated just like any other disc drive. I have been using the parallel port version for several weeks now. It really is quite nifty – you just plug it into a parallel port, run GUEST. 16,384/2 bytes, or around 80Mb. However, if this disk was configured into two 425Mb parti­tions, you would save over 40Mb of space. So consider carefully how you should partition the 34  Silicon Chip EXE and copy to/from the ZIP disc. A SCSI version is also available for the same price and is reported to be three times faster than the parallel version. On the down­side, the SCSI version isn’t as portable and you have to buy a SCSI controller for it. Testing I did some testing and found that large database files copied to the Zip drive at about 4.5Mb per minute. Alternatively, by using Norton Back­up and saving to a logical disc drive, I was able to copy at an effective 8-10Mb per minute and fit over 250Mb (before compression) on one 100Mb disc. So, at just $33 per disc, the Zip drive is good for archiving applications. Assuming that it stands up to prolonged use, the Zip drive is a good product. I tested mine by copying files to and from it for over 20 hours without any problems. Zip drives are imported by Polaroid Australia (1800 066 021) and are available from computer dealers and from Harvey Norman retail stores. disc (using FDISK), before you actu­ally start using it. Video cards Even with a Pentium processor, the For timid souls, there are many computer shops and techni­cians who will upgrade your PC for a reasonable labour cost. If you are more adventurous, replacing a motherboard is a relatively straightforward job. First, remove all cables from the PC (including the power cord) and remove the cover (this is usually done by removing a number of self-tapping screws). Once inside the PC, remove all the plug-in cards from the mother­ board. Depending on the age of the PC, the motherboard itself will probably be secured by two or more screws that will need to be removed. Once this has been done, the motherboard will then either lift or slide out. The next step is to swap the nylon clips from the old to the new mother­ board, after which the new mother­board can be installed in the case and the plug-in cards reinstalled. An important point to note here is that if you have two connectors that go to the power connector on the mother­board, the black wires should be next to each other when they are plugged in. Another option that you may want to consider is a new case, especially if the old one is looking a bit tacky. A complete mini-tower case and power supply can be purchased for less than $100 and would certainly improve the value of the PC if you wanted to sell it. Finally, if you have any problems locating a SimmVerter, I purchased mine from The Logical Approach in Canberra – phone (06) 251 6511. SC 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 By MIKE ZENERE Build a magnetic card reader & display Have you ever wanted to find out what’s written on your credit card or other magnetic stripe cards? Now you can do it. This unit will enable you to read and display the contents of track two on any magnetic card and could be used as the basis for an electronic door lock. Magnetic cards have been around for many years and have found their way into many fields such as banking, security and vending machines. Most cards follow defined guidelines as to their con­struction and layout and are therefore very flexible to the designer. 40  Silicon Chip Each card has three tracks but the most commonly used is track two. Recalling data from the card has become relatively simple in the last few years with modern card readers. These generally have a single on-board chip to decipher the raw data from the read head. This looks much like the record/play head in a cas­sette deck. The on-board chip generally contains conditioning circuitry to pick up the signal, reject noise and provide a digital output. Most card readers interface via three wires which are Clock, Data and Card Valid. Assuming that a microprocessor is hooked up to the card reader, a typical card read takes place as follows. When a card is swiped through the card reader, the Card Valid line goes low after eight or nine flux reversals, indicating that a valid card is present. The microprocessor monitors the clock line and waits until the Clock Magnetic Card Standards Most magnetic cards adhere to defined standards that de­scribe the physical as well as electrical layout. The standards outline card size, magnetic stripe and track positioning, and format information. The information is recorded onto the card using a technique known as Two Frequency Coherent Phase Recording or F/2F. This allows for serial recording of self-clocking data on each track. The data consists of data and clocking bits together. When a flux transition occurs between Fig.1: the track layout on a magnetic card. Track 1 can record alphanumeric data, clock cycles, a “one” is while tracks 2 and 3 provide only numeric data. obtained and when there is an absence of flux between encoded using 4-bit BCD with odd start of the actual data to be read, cycles a “zero” is obtained. parity. followed by the data, the end sentiStandard magnetic cards have nel, LRC and finally, trailing zeros to All tracks are recorded with the three data tracks and each has its the end of the card. The term LRC least significant bit first and the parity own subtle differences. Track 1 has stands for “longitudinal redundancy bit last. The higher density track three a bit density of 210 bits per inch, check” and is used for horizontal holds up to 107 numerics while track giving it the ability to hold a total of error detection. two holds only 40. The necessity for 79 charac­ters over the entire length start and end sentinels and other By far the most commonly used of the card. Each character on this separating char­acters reduces the track is track two. Although holding track is made up of six data bits and above storage capabilities to a cerless information than the others, this one parity bit, providing 64 differtain ext­ent. track has all the data required to do ent alphanumeric combinations to a banking transaction. If there is a choose from. The card and track Reading or writing of data to the need for the customer’s name to be layout is shown in Fig.1. card generally follows the same present, then track one is used as it is path for all three tracks. First, leadThe remaining tracks, two and the only one that holds alphabetical ing zeros are encoded to indicate three, provide only numeric data characters. The third track is special the presence of data and to provide and have a bit recording density of in that data may be written or read synchro­ n isation. Next, the start 75 bpi and 210 bpi respectively. The during a transaction. sentinel is encoded to indicate the character set for these two tracks is line goes low, indicating that data is present on the data line. The data bit is collected and temporarily stored until a succession of bits is gathered to make a 5-bit word, with four data bits and one parity bit. When the 5-bit word is obtained and stored, the cycle repeats itself until all the 5-bit characters have been read into memory. The processor can now go back over the data and analyse it for parity. Date rate & swipe direction The data rate even for the high density tracks is quite low, allowing almost any microprocessor to sample and collect the data. Let’s assume that the card is passed through the reader at around one metre per second. This translates to around 9983 bps or 1426 7-bit characters per second, meaning that a new data bit is presented about every 100µs. Most card readers are capable of reading two of the three tracks in one swipe. Even allowing for this extra load, most microprocessors running at 1MHz or more will handle this with ease. Although data is written onto the card in a particular format, there being a start and end sentinel, this does not limit the programmer to write software to read a card when swiped forwards or backwards. In a “backward read”, the card data is simply read as usual and stored in memory but this time the last character is first and the first character is last. The program simply detects this by looking for the start and end sentinels and then corrects itself. Card reader The card reader and display unit to be presented here is self-contained on January 1996  41 42  Silicon Chip Fig.2: the circuit is based on a magnetic card reader module with its own on-board decoding. The data from this module is fed via three lines to the microprocessor (IC1) and this in turn drives a multiplexed 4-digit display. The track 2 contents of four cards can be stored in the EEPROM (IC2) and this data can be used as the basis of an electronic door lock. IC3 and its associated parts form a watchdog timer circuit and this automatically resets the microprocessor if signal activity from pin 11 ceases, indicating that the processor has “crashed”. a PC board measuring 128 x 101mm. As well as the card reader module with its integral PC board, there is a 4-digit display, a 28-pin 68705P3 microprocessor (IC1), a piezo buzzer and three pushbuttons. The circuit is shown in Fig.2. The card reader and its integral PC board has all the cir­cuitry necessary to decode and convert the raw data coming from the card being read. The data is transformed into logic levels and is then sent out via three serial lines to the processor. The card reader is connected to the logic board via a 5-way cable, with three of the lines for data and the other two for power. The recording function of the circuit is performed by a small serial EEPROM, IC2. Once the unit is placed in the record mode and a card is swiped through, the data will be saved in the EEPROM. Because timing is not critical in this project, a crystal for the microprocessor is not necessary. Instead, by placing an 18kΩ resistor from pin 5 to the +5V rail, an inbuilt oscillator is enabled, causing the processor to run at near full speed. Beeper & relay driver A DC self-oscillating beeper is connected to port B, pin 12, on the processor. Port B can sink up to 10mA which is suffi­cient for this application and is pulled low to turn on the beeper. The relay is driven by transistor Q1 which is controlled by the line from pin 24. This line is normally low and the relay is off. When a valid card is swiped through the reader, the proces­ sor port pin 24 goes high for a period of time and turns on Q1 which operates the relay. The display consists of four 7-segment common anode dis­plays multi­ plexed together. The cathodes are driven directly by port lines from the processor, while each display anode is driven by its respective PNP driver transistor (Q2-Q5). The processor receives an interrupt every 5ms from an internal timer. Each time an interrupt is received, the processor switches off the current display digit that it is driving and turns on the next. In this manner, each digit is only on for 5ms before the next digit is updated. This gives each digit a total on-time of around 250ms per second; ie, a duty cycle of 25%. The SHIFT LEFT and SHIFT RIGHT buttons are used to move the display laterally to enable the user to view the entire number. Construction Begin assembly of the PC board by mounting the four stand­offs, one at each corner. This done, install the diodes, resistors, links and capacitors. Note the polarity of the electrolytic capacitors and the diodes. Install the 7805 regulator and fit it with a small heatsink. Next, install the transistors, the two small ICs and the socket for IC1 but do not install the processor until after the unit has been powered up and a voltage check performed. When in­stall­ing the four 7-segment displays, their decimal points should be close to the edge of the PC board. The remainder of the components can now be mounted, noting the orientation of the pushbutton switches. The card reader module is attached to the PC board with screws fitted from the underside. The back of the read head should face the outside edge of the board. When all the assembly work is complete, apply 12V DC to the board and check that +5V is present at pins 3 & 6 of the socket for IC1, at pin 8 of IC2, pins 4 & 8 of IC3 and at the emitters of Q2-Q5. If this checks out, remove the power, plug in the pro­cessor and connect the card reader module. Reapply power – the buzzer should beep four times and the display should read “OPEr”. The unit is now ready for a test drive. Before you start, here are a few tips. The mode button is used to cycle through the various available modes. Each time you press this button, the next option appears on the display. The modes are OPEr (operate), rEC (record), d EL (delete), p LAY and rEAd. When in the operate mode, the display blanks out after about 30 seconds to conserve power. If any button is pressed after this time the display will light and programming may con­tinue. Initial set up If this is the first power-up you will need to reset the memory of the EEPROM and this is done by holding down SHIFT LEFT and SHIFT RIGHT and applying power. The EEPROM will be cleared and the relay on-time will be set to three seconds. PARTS LIST 1 PC board, 128 x 101mm 1 magnetic card reader module 1 piezo buzzer 1 12V miniature SPDT relay 3 momentary contact pushbutton switches 1 5-way connector 1 2-way connector 2 3-way PC-mount insulated terminal blocks 4 PC standoffs Semiconductors 1 MC68705P3 programmed microprocessor (IC1) 1 93C46 EEPROM (IC2) 1 555 timer (IC3) 1 7805 5V 3-terminal regulator (REG1) 4 HD11310 7-segment red LED displays (DISP1-4) 3 1N4004 silicon diodes (D1-D3) 2 PN100 NPN transistors (Q1,Q6) 4 PN200 PNP transistors (Q2-Q5) Capacitors 2 100µF 16VW electrolytic 1 1µF 16VW electrolytic 4 0.1µF monolithic Resistors (0.25W, 5%) 1 1MΩ 1 1kΩ 1 33kΩ 7 330Ω 1 18kΩ 1 22Ω 0.5W 11 10kΩ Miscellaneous Screws, nuts, shakeproof washers, solder. Where to buy the parts A complete kit of parts for the magnetic card reader is available from the author. This includes all electronic compon­ents except for the 12VDC power supply and a case. The price is $75.00 plus $7.50 for postage and packing. Completely assembled and tested units are also available at an extra cost of $20.00. The documented source code is a further $8.00 for the print out. Please make postal money orders payable to Mike Zenere, 83 Head­ ingley Road, Mt. Waverley, Vic 3149. Phone (03) 9803 3535. Note: copyright© of the PC board is retained by the author. January 1996  43 Fig.3: install the parts on the PC board as shown here, taking care to ensure that the displays, switches and other polarised parts are correctly oriented. The card reader module is connected to the main PC board via a 5-way cable. The unit can be used in two modes which enable the user to: (1) read and display cards; and (2) operate the relay. Let’s initially talk about the first option. After power-up, the unit should be showing “OPEr” indicating that it is in the door access mode. To change this, push the mode button until the display shows “rEAd”, indicating that if a card is swiped, its track 2 cont­ents will be displayed. Swipe any card through and you should see some digits or letters on the display. These will correspond to the digits stored on the magnetic card with the start sentinel (b) being the first character. The display can only show four numerics at a time so to view the rest, push the SHIFT LEFT button once to view the next character to the right. Keep doing this until the display shows the end sentinel (F) or until the display shifts no further . While doing this, look at the front of the card and its embossed number. You should see this number appear in the display as you move along. If you wish, you can move the display to the right by pushing the SHIFT RIGHT button. To view another card, simply swipe it through the slot. Door lock applications The following functions relate to the operate mode which is when the 44  Silicon Chip unit is used as a door lock. After going through the functions listed below, place the unit in the operate mode by hitting the mode button until “OPEr” is displayed. After a short time, the display will blank out and the unit will now be ready to compare swiped cards with its memory contents. If a match is found, the door release relay will operate for a set time and a single beep will be heard. If no match is found, two beeps will be heard. Recording a card The unit can store up to four cards in the serially fed EEPROM. The MODE button is hit until the “rEC” message is dis­played. If the memory is full, there being four cards stored already, the display will alternate between “FULL” and “rEC” and you will not be able to store any more cards until you have used the delete function. Each time a card is entered, the unit jumps back to the operate mode until the function key is once again hit. Deleting a card You can delete a previously entered card by first hitting the mode button until “dEL” is displayed. Swipe the card to be delet­ed through the slot and if the card is found and deleted from mem­ory, a single beep is heard. If the card is not found the unit will beep twice. Relay operation When a card has been successfully recognised by the unit, it will operate the relay for a set time which will be between one and nine seconds. To set this time, hit the MODE button until the “rLAY” message is shown. Hit either of the SHIFT buttons to display the current setting. Using the SHIFT LEFT and SHIFT RIGHT buttons, set the relay on-time in the display to the desired number; eg, the display may show something like 0002, indicating that the relay will operate for about two seconds. Hit the mode button again to save the new number in memory. If using the unit as a door lock, you can remove the mag­netic card reader module from the PC board and extend its con­ necting cables to enable the two sections to be housed separate­ly. The two separated units can then be mounted on either side of the wall to provide greater security. Battery back-up Provision has been made for battery back-up in case of a power failure. The battery GND is commoned to the power supply ground and the battery +12V SC is connected via D2. 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 SATELLITE WATCH Welcome to the first Satellite Watch column, where we will keep you updated with satellite signal reception reports for Australia and NZ. • INTELSAT – 70-66° E longitude, C band: This satellite is visible only from the west coast of Australia and carries World­net programming from the USA, CFI from Paris and various other itinerant signals. • GORIZONT – 19 - 96.5° E longitude, C band: This satellite carries the Russian “Network 1” programming on 1475MHz, with audio at 7.02MHz. An additional radio service is also carried at 7.5MHz. CCTV 4 Chinese television can be seen at 1325MHz and now carries a new English News service. Az Tv from Azerbaijan can be seen on an irregular basis at around 1800AEST and can be found at IF 1425MHz. • ASIASAT II – 100.5° E longitude, C band: Scheduled for launch last November, this will provide new programming for satellite enthusiasts. After months of delay caused by previous failures aboard the Long March launcher, this is the launch that will make or break Great Wall. Mooted to carry similar programming to ASIASAT I, this satellite will be visible over Australia and New Zealand with a small (2m) dish. At least five channels will be free to air, according to prelaunch press releases. • GORIZONT 25 – 103° E longitude, C band: Another Russian satellite carrying Network 1 programming, for a different time zone to Gorizont 19. • ASIASAT 1 – 105.5° E longitude, C band: Visible in the northern and north western parts of Australia, this satellite has a poten­tial northern hemisphere audience of over a billion viewers and covers from India to the Middle East. Reports as far south as Albury (NSW) and the Barossa Valley area indicate sidelobe signals are visible in some parts of southern Australia. Program­ming carried includes Prime Sports, Star Movies, Zee TV and other pay *Garry Cratt is Managing Director of Av-Comm Pty Ltd, suppliers of satellite TV reception systems. services. Transponder frequencies can be obtained by dialling the Hong Kong Info service number: 0011 852 172 777 01. Call charges are at normal IDD rates. • PALAPA B2P – 113° E longitude, C band: Presently visible only in the Northern part of Australia, this satellite was placed in an inclined orbit in November, to conserve station keeping fuel, whilst waiting the launch and subsequent replacement by PALAPA C1, a higher powered satellite covering all of Australia and New Zealand. Palapa C1 will now be launched by Lockheed Martin of the USA. Prior to this announcement in October, the launch was scheduled with Arianne­ space but the launch company was unable to keep to the original schedule. It is expected that all current users will transfer to the new satellite, now scheduled for launch in January 1996. Amongst signals on the B2P satellite is Australia’s ATVI, the interna­tional arm of the ABC. Weekly program data can be obtained by polling fax # 055 29900. • JCSAT 3: First observed early in October, this satellite has the capability to cover Australia and New Zealand with strong sign­als. Reports from the east coast of Australia, Japan, Hawaii and Noumea indicate the testing phase of this satellite is almost complete. It is expected that some programming could become available early in 1996. • RIMSAT G1 – 130° E longitude, C band: The orbit of this Russian Gorizont class satellite is only slightly inclined, making 24-hour small dish reception of RAJ TV, a Tamill language broadcast, a reality. RAJ TV operates at 1475MHz. • RIMSAT G2 – 142.5° E longitude, C band: Until September 12, this satellite carried the ATN network from India. Due to unresolved difficulties involving the satellite operator RIMSAT, the Russian government space agency and ATN, this transponder ceased opera­tions temporarily during September but now appears to be operat­ing on a permanent basis. The other full time transponder, oper­ ating Compiled by GARRY CRATT* at 1265MHz, carries EM TV from Papua New Guinea. This transponder operates LHCP (left hand circular polarisation) and carries a mix of Nine network (Australia) and local programming. During late November, ATN changed format to two adjacent half transponders. Whilst continuing with the regular ATN broad­casts on IF 1465MHz, ATN PRIME will commence early December using an IF of 1480MHz. • OPTUS B1 - 160° E longitude, K band: This satellite carries outback TV in BMAC, as well as up to five interchange services in PAL. Interchange IF frequencies are: 1219, 1155, 1425 (all verti­cally polarised) and 1249MHz horizontal. • OPTUS B3 – 156° E longitude, K band: The latest Optus satellite came into operation last August. Presently, it carries several closed user group BMAC services, as well as the OTEN network (Victorian and NSW education departments) and several interchange services. IF frequencies are 1233, 1361 and 1094MHz. The Optus A3 satellite, until recently co-located at 156° E, is most likely part way through a planned drift back to 164°, where it could be used to replace the ageing A2 satellite, now in an inclined orbit. • PANAMSAT PAS-2 – 169° E longitude, C band: Although many services on this bird use either secure BMAC or MPEG 2, there are still some analog services that can be viewed by enthusiasts. CNN, NHK and CNBC Asia operate on 1153, 1113 and 1035MHz IFs. Recent itinerant users include the American ABC network and a number of news feeds from Osaka, Japan, during the recent ASEAN conference. • INTELSAT 511 – 180° E longitude, C band: This ageing satellite, now in an inclined orbit but due to be replaced during 1996, carries Deutsche Welle programming from Germany, RFO from Tahiti and Worldnet from the USA. In the last few months several servic­ es have migrated from Intelsat to other satellites, whilst some previous analog services (CNN, NBC) SC have gone to digital format. January 1996  53 n i a R n i a Br By GRAHAM BLOWES This automatic sprinkler controller allows you to selec­tively water any area of a garden or nursery as little or as often as you like. It can control up to eight solenoids plus an optional master solenoid. T HE FIRST VERSION of this de- sign was published in the July 1992 edition of SILICON CHIP. It was a popular project and I still get enquires from the original article. About a year ago, I decided that an update was due. The most obvious thing that needed replacing was the microcontroller, as the NMOS 68705­P3 microcontroller was to be discontinued. The controller now uses a PLCC version of the popular 68HC­705­C8. There was also some changes made 54  Silicon Chip to the power supply, which now uses a switching IC. While I was at it, I also decided to make a couple of changes to the front panel layout. First, I deleted the row of green LEDs that were used to indicate which solenoids were on. This function is now taken care of by the row of red LEDs – when a solenoid turns on, the appropriate LED flashes at a fast rate to provide the “on” indication. I also added an extra button to the front panel to make it easier to get back to the default mode. Apart from that, the layout of the front panel worked pretty well, so I kept it that way. The PC board is also now a lot easier to put together than before. And finally, I’ve added three inputs –designated Rain 1, Rain 2 and Frost 1 – that enable almost complete automation of your garden! Two of the inputs are for optional rain switches that enable the controller to turn off selected cycles if it is rain­ing. This facility is especially important in a country like Australia, where many parts of the country suffer from low rain­fall. Wasting water costs money, especially these days with the in-vogue user-pays principle, so turning off the sprinklers when it rains makes economical (and ecological) sense. The third input is for a temperature sensor (again option­al). This enables the controller to switch in extra cycles on a hot day. It even works in reverse; an extra cycle can be switched in if the temperature falls below a set trip point. The con­troller even stores the MIN and MAX temperatures (time stamped) for today and yesterday. Each rain switch and temperature trip point can be set on a cycle by cycle basis. The default mode can display the time and date, or the time and current temperature. This facility n Main Features (1). Uses a 16 x 1 liquid crystal display (LCD) to show time, date and sprinkler settings, plus all the various system menus. (2). Controls up to eight solenoids plus a master solenoid. (3). Each station can have up to four cycles on Program A and Program B, or eight cycles on Program C (Program C = Program A + B). Each cycle can operate with either the three-week built-in calendar or on a continuous schedule for up to 99 days (4). Each station (and cycle) is completely autonomous, providing a possible 64 programmable start times per day (Program C). (5). LED indication of station status. Continuously lit = auto mode on; fast flash = solenoid on; 1Hz flash = Rain Off mode. (6). Manual on/off control for each solenoid. The run time of cycle 4 can be used to provide an automatic cutoff feature. This lets you manually is pro­ grammable via the “CONFIG” menu. More about that later. Main features The original version allowed sprinklers to turn on every day, every second day, every third day, etc. While this system worked OK, it was a bit difficult to nail down exactly which days the sprinklers would turn on. To rectify this, the Rain Brain now has a 3-week cycle as well as the original method – the original method being useful for plants that require watering at a set interval, regardless of whether it is a weekend or not. The “3-week cycle” method is based on a built-in calendar. It lets you choose exactly which days the sprinklers will turn on up to three weeks in advance! For example, you could program the unit so that solenoid 1 turned for two 1-hour cycles on Monday of the first week, Wednesday of the second week and Thursday of the third week. All the facilities mentioned above are available to every single cycle, and are programmable via the “AUXILIARY FUNCTIONS” menu. To cater for the extra facilities, the Rain Brain has twice the EEPROM capacity of the previous version. Each switch on a sprinkler and forget it. The sprinkler will then automatically turn off after the run time of cycle 4 has expired. (7). Run time (per cycle): 1-99 minutes. The cycles can be joined so the maximum run-time (per solenoid) is: 8 x 99 minutes = 13 hrs, 10 mins. (8). An EEPROM stores all settings, so settings are not lost if the backup battery fails. Battery backup is provided by a 3V lithium battery. (9). A “Rain Mode” deactivates all automatic cycles while saving program settings. (10). Two fully programmable Rain Switches (optional) allow any/all of the 64 cycles to be controlled by the immediate weather conditions automatically. (11). An optional Temperature Sensor enables any/all of the 32 cycles of Program A (or B ) to switch to another cycle if the programmed trip temperature is exceeded. This allows extra cycles to of the eight stations can switch on as often as eight times a day (ie, there are up to eight daily cycles), or as little as once every 99 days! As before, each cycle can be programmed for an “on time” of 1-99 minutes. A new feature allows you to choose from three standard programs, designated A, B and C. Programs A and B allow each station to programmed for four cycles per day, while program C combines programs A and B to provide up to eight cycles per station per day. If this isn’t enough, you can add optional extra memory plus a switch to select an alternative group of A, B and C pro­grams. The row of eight LEDs beneath the LCD indicates the status of the solenoids at a glance. If a LED is flashing quickly, this indicates that the solenoid is turned on. If a LED is steady, the station is active, meaning that it will switch on automatically once its “turn on” conditions are satisfied. And if all enabled LEDs are flashing slowly (1s on, 1s off), a rain switch has been activat­ed. A flash rate of 0.5s on, 0.5s off indicates the “RAIN OFF” mode. This means that all automatic cycles have been globally disabled (see later). This mode has precedence over the rain be automatically added; eg, so that plants get extra water on a hot day! The sensor is accurate to ±0.1°C and has a range from -20°C +60°C. (12). The controller stores the maximum and minimum temperatures sensed that day and the time at which these extremes occurred is also recorded. This information is accessed by pressing the “Cursor” button while in the Default Mode. The previous day’s temperature extremes can also be displayed, as well as the current temperature! (13). Uses the well proven MC68HC­ 705C8 microcontroller. A watch dog circuit ensures a proper reset is issued to the microcontroller if it “crashes” due to a mains glitch. (14). All appropriate solenoids are enabled and the various cycles completed after a reset, or when power is restored after a power failure. (15). Runs from a 10-24VAC or a 1035V DC 1A plugpack supply. switch inputs and the fast flash rate has precedence over them all. Although these different flash rates may seem initially confusing, it all makes perfect sense when you start using the unit. Power requirements The unit is powered by the usual 24V AC plugpacks associat­ ed with watering systems, or from voltages as low as 10V DC. As with the first version, flat batteries are not a problem, as all settings are stored securely inside an EEPROM. The controller reads the EEPROM when it is first turned on, so it knows exactly which mode it should be in (RAIN OFF or DEFAULT) and which sprin­klers are active. Other uses By this stage, you are probably already thinking of other uses for this versatile controller, apart from its primary use as a sprinkler solenoid controller. For example, those of you who have an interest in satellites can set the controller to switch on a tape recorder at the time it is due to pass overhead, even though you may be on holidays for a few weeks. Alternatively, the unit could be used as a security light controller or January 1996  55 56  Silicon Chip Fig.1 (left): the circuit is based on IC4, a 68HC705C8 microcontroller. IC3 is a real-time clock (RTC), while IC1 is an EEPROM and is used to store the programmed settings. as a general-purpose timer. In these applications, the on-board relays can act as slaves to appropriately rated offboard relays, so that other equipment can be controlled. How it works The circuit is fairly straightforward (Fig.1), with all the heavy work being done by the software in the micro­ controller (IC4). Starting with the power supply, diodes D1-D4 rectify the 24V AC input, which results in about 35V DC across C1. IC8 (LM2574-5) is from the “simple switcher” series from National Semiconductor and provides a very efficient method of providing a 5V rail to power the circuitry. The resultant 5V across C2 is further decoupled by L1 and L2. These inductors attenuate any spikes generated by the sole­noids as they switch on and off. Note that the relay driver (ULN2804, IC5) is supplied from the “noisier” 5V across C2. C16, C17 and C18 are spread around the PC board to decou­ple the power supply. The circuit draws the following currents from a 24V AC plugpack under the following conditions: (1) all LEDs off = 26mA; (2) all LEDs on = 32mA; and (3) all LEDs and relays on = 88mA. The microcontroller (IC4) uses a standard 3.58MHz crystal (Xtal2) as a timebase. A feature of this micro­ controller is an internal watchdog function, called the Computer Operating Proper­ly (or COP). I tried to get this to work but the maximum timeout period with this crystal is a bit over one second. This is a bit short and I eventually opted for a tried and tested alternative built around timer stage IC2. The time function is supplied by real time clock stage IC3 (PCF8573), hereafter referred to as the RTC. This RTC chip inter­ rupts the micro­ con­ troller every minute. Each time it receives an interrupt, the micro­con­ troller reads the RTC and stores the time in an internal RAM buffer. After this, it reads 12 bytes of January 1996  57 set if any of these inputs are activated. The temperature input (PD4) is read every minute, for one second exactly. During this time, writes to the LCD and LED flashing routines are disallowed, so as to prev­ent incorrect temperature measurements. Button switches The button switches are connected directly to the microcon­troller (PD0-PD4 & TCAP). An RC network attached to each pin provides a small amount of debounce, while the software does the rest. Buttons S1-S4 (Menu, Cursor, Up, Down) are polled during the main loop, whereas button S5 (Exit) is connected to the TCAP input. The TCAP pin is an interrupt pin associated with the internal timer function. In this application, it is simply used to notify the micro­controller that the button was pressed in a manner similar to how a normal interrupt would be used. Watchdog timer This circuit comprises a CMOS 7555 IC (IC2), configured as an astable multivibrator but normally prevented from oscillating. If IC4 is functioning correctly, PA7 (pin 5) is set to a logic 1 within the timer interrupt routine and cleared in the mainloop. The resulting waveform continually charges and discharges C14. This means that Q1 is continually turned on and off, which prev­ents C4 from charging up and thus disables IC2. However, if the pulses from PA7 stop due to a spike causing the program to stop and/or crash, IC2 will begin to oscillate. After about 10 seconds, its pin 3 output will pull IC4’s reset pin (pin 1) low via D16, thereby resetting the microcontroller. Note that the time-out period is set to 10 seconds to allow for the “dead time” during the EEPROM read cycle every minute. The timer interrupt interval is set to 5ms. Fig.2: install the parts on the PC board as shown here. Note that IC1, IC3, IC4 & IC11, the relays and the LCD should not be mounted until after an initial “smoke” test has been carried out (see text). EEPROM (IC1 or IC11) asso­ciated with cycle 1 of solenoid 8 and compares the stored start times with the current time and date. It then repeats the process 31 more times for the other cycles and solenoids (this process takes twice as long when program C is selected). The LCD and the two 8-bit latches IC6 & IC7 (74HC573) share port B as a common data bus. When the micro­ con­troller needs to send data to either latch, pin 11 of the re­quired latch is pulsed high (by either PA5 or PA6). At reset, all port pins are initialised as inputs (high Z), therefore the OE pin (pin 1) of IC7 is held high by R18 until the latch is cleared and PA2 is made an output. This stops inadvertent operation of any relays until initialisation is complete. The LCD data is validated by the E pin (pin 6, LCD connec­tor). As the microcontroller is not required to read the internal RAM of the LCD display, the R\W pin can be tied low, which is write mode. VR1 is used to adjust the contrast of the display. The two Rain Switch inputs (PD7 & PD5) are tested during the timer interrupt routine. Appropriate flags are 58  Silicon Chip The EEPROM The EEPROM is an 8Kb device, internally organised as 1024 x 8 bits. Each cycle of each solenoid is allocated 12 bytes of the EEPROM (11 of these are used, with one spare). Another part of the EEPROM is set aside for storing “global” variables like the current year, the LED status, and whether “Rain Mode” is active or not. Pin 3 (A2) of IC1 and IC11 is an address pin, which allows two of these chips to be connected onto the same I2C bus. The A2 pins are connected to either side of S6, which allows either of the EEPROMs to be switched into circuit. The selected EEPROM is read at power up, to determine which mode it should be in (ie, “RAIN OFF” mode or just the Default mode) and which LEDs are active. At the next interrupt from the RTC (IC3), any cycle that satisfies the “On Time” conditions will be switched on. No settings will ever be lost! Real time clock The RTC chip (IC3) interrupts the microcontroller every minute, causing it to read the time. IC3 re­quires a 32.768kHz crystal (commonly called a “watch” crystal) for its internal dividers. The oscillator can be trimmed using C12 to provide very accurate time keeping. Note that the FSET pin (frequency SET) is brought out to a The switches, the eight station indicator LEDs and the LCD are all installed on the reverse side of the board. PC board pin to facilitate easy tuning using a frequency meter. When power is lost from the main circuit, a 3V lithium battery (B1) cuts in and keeps IC3’s oscillator going. The bat­tery is held off via D14 and D13 when normal power is applied to the circuit. IC3 draws about 7µA when the power is off. Note that if the HOURS or MINUTES setting is altered when setting the time, the seconds counter in the RTC will be reset. The DAY and MONTH settings do not cause the seconds counter to reset but the HOUR and MINUTE settings are written to. The YEAR and (P)rogram settings have no effect on the RTC. Rain/temperature inputs The three input circuits are identical and are based on LM393 comparator ICs. VR2-VR4 are used to adjust the trip voltag­es, which can vary from about 0.9V to about 2V. Resistors R3, R15 & R16 (1MΩ) provide hysteresis to prevent the outputs from oscillating. R8, R9 and R10 provide the current The programmed data in the EEPROM is backed up by a 3V lithium cell. Take care with the orientation of IC4. feed to the rain switch­es and temperature sensor circuit. The output circuits of the rain switch and temperature sensor act as constant current sinks. If the probes are wet, then the Rain Switch draws an extra 13mA compared to when the probes are dry. The current flows to ground via 68Ω resistors R4, R14 & R17. The extra current flowing when the probes are wet causes the voltage across these resistors to increase, which in turn causes the comparator to trip. Normally, the open collector outputs of the comparators are held high by 10kΩ pullup resis­tors. When they trip, the outputs turn on, thereby presenting a logic 0 to the micro­controller port pins (PD7, PD5 & PD4). The temperature input requires a frequency that is directly proportional to the temperature at a resolution of 50Hz/°C. 1000Hz corresponds to 0°C, 2000Hz corresponds to 20°C and so on. When the temperature sensor is not connected, the temperature display will be -19.9°C. Relay drivers & relays IC7 drives IC5, a ULN2804 relay driver IC. This device has open collector outputs and can therefore be used to drive relays with an operating voltage different to that specified. To do this, the component side track marked “*” (above the battery holder) must be cut. A wire running off to a separate power supply is then soldered into the via on the solder side, about 10mm below the “*”. The controller can operate all of the specified relays at once if need be. Each relay draws about 41mA at 5V. This does not mean that all solenoids should be operated at once, however. This very much depends on the transformer that is used to power your sprinkler system. Most solenoids draw around 300mA when supplied by 24V AC. Diodes D5-D12 form an 8-input diode AND gate. If any of the relays (RLY1-RLY8) is (are) switched on, then the associated diode(s) will also be forward biased, thereby switching on RLY9 (the master relay). This relay January 1996  59 The PC board is mounted on the front panel using 12mm spacers and machine screws and nuts. Similarly, the lower edge of the LCD module (near the LEDs) is secured to the PC board using 5mm spacers and machine screws and nuts. can be used to switch on the master solenoid in a sprinkler system, or to start a pump in a rural situation. Manual operation In addition to automatic operation, the solenoids can also be switched on manually. To do this, you simply select the solenoid with the Menu button, then press the Down button; the select­ed solenoid will immediately turn on, as indicated by the fast flashing LED. It will subsequently automatically switch off after the “Run Time” of cycle 4 (cycle 8 if program C) for that sole­noid has expired. If the “Run Time” is set to “00”, then the solenoid will switch off at the next interrupt from the RTC. Note that this facility works whether the “RAIN OFF” mode is active or not. Construction Construction of the Rain Brain is straightforward, since it is supplied as a complete kit. All the parts mount on a double-sided PC board with plated-through holes and a screened layout overlay, so that you can see at a glance where the parts go. As always, eyeball the PC board for any obvious faults before starting assembly. Begin by fitting all the ICs and sockets (except the PLCC socket for IC4). The RTC IC (IC3) and the EEPROM(s) (IC1 & IC11) are the only ICs that require sockets. Do not use sockets for the other ICs. In particular, IC8 (LM2574-5) absolutely must be sol­ dered to the PC board This done, fit the PLCC socket. This socket has one corner chamfered and this must match up with the screened 60  Silicon Chip The five pushbutton switches are all mounted in modified 6-pin DIP sockets on the track side of the board. Note that two pins of each socket are removed – see text. overlay on the PC board. Also pin 1 on the PC board is square, and you will see a little ridge on the side of the socket that denotes pin 1. Do not plug the microcontroller in yet! The three SIL resistor networks (R1, R2 and R7) should be installed next, noting that the pin with the dot goes into the square hole. Note that two of these resistor networks are 10kΩ types, while the other is a 1kΩ type so don’t get them confused. All three can be either 9-pin or 10-pin types. The following parts are mounted on the solder side of the board: LEDs 1-8 (discussed later), the five 6-pin DIP sockets, and the 14-pin SIL connector for the liquid crystal display. Pins 2 & 5 of the 6-pin DIP sockets (used to mount the push buttons) have to be cut out so that they won’t interfere with the PC board (pushing the pins out with the hot soldering iron re­sults a neater job). Solder in all five sockets, then turn the board over and fit the battery holder (don’t fit the battery yet). This done, solder in the 14-pin LCD connector, remembering that it goes onto the solder side of the board (along with the five switch sockets). Next, fit the four trimpots (VR1VR4) and the trimmer ca­pacitor (C12). Set VR2, VR3 and VR4 to midway, then install power supply components IC8, C1, C2, D15 and L3. Note that the cathode of D15 goes into the square hole. The resistors can now all be installed. In particular, install R15 (1MΩ near pin 1 of IC10) so that its long lead goes into the top hole. The same goes for R16 (1MΩ below IC10), while R3 (1MΩ near pin 1 of IC9) should have its long lead to the left. The reason for this is that these long leads are used as test points when adjusting the comparator trip points. The capacitors, diodes, the transistor and the two crystals can be fitted now. You will notice that all the diode cathode pads have square holes, as do all the positive pads of the elec­trolytic capacitors. L1 and L2 have small lengths (23mm) of spaghetti sleeving fitted over their mounting leads so that they stand proud of the board. If only one EEPROM is to be installed, solder a link between the bottom two holes of S6 (marked SW1 on the screened overlay). This links the A2 pin of IC1 to ground. Installing the LEDs As mentioned earlier, the LEDs are mounted on the solder side of the board, so that they match up with clearance holes in the front panel. Insert each LED into its position, remembering that the cathode (short lead) goes into the square hole but do not solder any yet. This done, carefully fix the front panel to the PC board using 12mm spacers and machine screws and nuts – just install two spacers diagonally opposite each other, as this is only a temporary operation. Once the panel is on, manipulate the LEDs so that they fit into the appropriate holes, then solder These two photos show typical displays for the Auxiliary Functions menu. At left, rain sensor 1 has been enabled (1R), the temperature trip point is 10°C, the three-week cycle mode (W) has been selected, week 1 has been selected (—), and the sprinkler will turn on every day of this week. In the photo at right, the continuous schedule (D) mode has been selected and the sprinkler will turn on every day (01). them in from the component side and remove the front panel. Now fit the fuse clips and the connector blocks to the PC board. Don’t fit the LCD or the relays yet, as a smoke test needs to be done first! Smoke test Before applying power, ensure that IC3, IC4, IC1, IC11 (if supplied) and the LCD have not been fitted. This done, connect a suitable power supply to the designated connectors and switch on. Now check that 5V is present across the power supply pins of IC6 (or IC7); ie, between pins 20 & 10. If so, touch the top of each IC for a few seconds, particularly IC8. All the ICs should be cool to the touch. If all is well, switch off and plug in the rest of the ICs. Make sure that you install the microcontroller around the right way. The chamfered corner of the IC must match the chamfered corner of the socket. the connec­tor on the main board and force it down slightly so that it firmly grips the pins. Now turn the power on, while making sure that nothing on the LCD board can short against the main board. You should be greeted with a message telling you to check the battery, a soft­ware version message for a second or two, and then the time and date display. Assuming that all is well, the LCD can be permanently mounted. The lower edge of the LCD (near the LEDs) is secured to the main board using 5mm spacers and machine screws and nuts. Once these are fitted, judge the gap at the connector edge and solder tack a pin. This done, check that the LCD board is paral­lel to the controller board, adjust it as necessary, then solder the rest of the pins. By the way, all the LCDs are tested before they are packed into the kits, as are the microcontrollers. However, it is still nice to know that it works before soldering it in as it is an unpleasant job trying to unsolder them. The five pushbutton switches can now be installed by fit­ting them to the previously installed DIP sockets (there’s no need to solder them). Once they’re in, the plastic switch caps can be clipped into position. If you have purchased the additional memory kit, solder the wires to the toggle switch, then mount the switch in a convenient loca­tion on the side of the case. Make sure that this switch can not foul other parts on the main board when it is installed in the case. Now the front panel can be refitted using the four 12mm spacers provided. This done, clip the lithium battery into its holder (positive side up), connect a power supply and switch on. The LCD should go through the same routine as above. Once the time has been programmed into the RTC, the battery flat message should not show at power up unless the battery is flat. Note that, at this stage, the time display will have mis­cellaneous characters in the time and date fields. Memory initialisation The next step is to put the memory Where To Buy The Parts Parts for the Rain Brain Sprinkler Controller are available as follows: ITEM Rain Brain Kit (excludes relays) Relays – FBR211D005M (Price ea.; specify number required) PRICE P&P $175.00 $10.00 $4.50 Installing the LCD Built & tested (relays extra) $225.00 $10.00 Before installing the LCD, the six tabs that secure the metal frame to the LCD board should be bent over slightly. This is to prevent possible contact with any of the leads protruding through the main PC board. Also check that none of the tabs is shorting to any of the fine tracks around the edges of the tab holes. Next, turn VR1 clockwise until it stops, so that it is in the full contrast position. This done, fit the LCD to Rain switch kit (Price ea.; specify number required) $25.00 $2.00 Temperature probe kit $33.00 $2.00 Optional memory kit $12.00 $2.00 Optional super twist LCD with LED backlight upgrade $8.00 Note 1: p&p is $10.00 for Rain Brain kit plus any combination of other kits. Individual parts are also available (POA). Note 2: Payments by cheque or money order to Mantis Micro Products. Send order to Graham Blowers, 38 Garnet St, Niddrie, 3402 Vic. Phone/fax (03) 9337 1917. For COD orders, you pay $4.75 COD charge plus postage at the destination post office. The Post Office will notify you when the parcel arrives. January 1996  61 PARTS LIST 1 double-sided PC board, code SPV6 1 plastic case with screened front panel 1 P1601 liquid crystal display (H1) 1 BH800 battery holder (BH1) 1 3V lithium battery (B1) 9 5V SPDT relays, FBR211CD005M (RLY1-9) 2 M205 fuse clips (FH1,FH2) 11A M205 fuse (F1) 2 ferrite (6-hole) inductors (L1,L2) 1 470µH inductor (L3) 1 50kΩ miniature horizontal trimpot (VR1) 3 10kΩ miniature horizontal trimpots (VR2-VR4) 1 44-pin PLCC IC socket 1 8-pin DIP socket 1 16-pin IC socket 5 momentary contact pushbutton switches plus plastic caps (S1S5) 5 6-pin DIP sockets (for switches) 4 15mm x 3mm dia. machine screws plus nuts 4 12mm x 3mm dia. spacers 2 5mm x 3mm dia. spacers 1 14-way connector (X1, for LCD) 1 6-way terminal block (X2) 4 3-way terminal blocks (X3-X6) 2 PC pins (X7,X8) Semiconductors 1 CAT24C08P EEPROM (IC1) 1 LM7555 CMOS timer (IC2) 1 PCF8573P real time clock (IC3) 1 MC68HC705C8FN microcontroller (IC4) into a known state. To do this, turn off the power, hold down the Menu and Cursor (⇒) buttons, and turn the power back on. This time, the LCD will tell you to press the Menu button. Once this is done, the “Config” menu will be displayed. This consists of three options: (1). “M” is memory initialisation. Press the Down (⇓) button to ini­ tialise the memory. As each block of 16 bytes is initialised, a LED lights. The LEDs chase each other from left to right, eight times. This routine also acts as a fault locater. If more than one LED lights at the same time, then there is a short circuit on the port B 62  Silicon Chip 1 ULN2804 8-channel driver (IC5) 2 74HC573 latches (IC6,IC7) 1 LM2574-5 5V switching regulator (IC8) 2 LM393 dual op amps (IC9,IC10) 1 BC548 transistor (Q1) 4 1N4004 silicon diodes (D1-D4) 11 1N4148 silicon diodes (D5D14,D16) 1 MUR120RL fast recovery diode (D15) 8 3mm red LEDs (LED1-8) 1 32.768kHz crystal (Xtal1) 1 3.579545MHz crystal (Xtal2) Capacitors 1 1000µF 16VW electrolytic (C2) 1 220µF 63VW electrolytic (C1) 4 10µF 10VW electrolytic (C3,C4,C10,C11) 1 1µF 10VW electrolytic (C13) 10 0.1µF monolithic (C5-8,C1418,C20) 2 27pF monolithic (C9,C19) 1 3-40pF trimmer capacitor (C12) Resistors (0.25W, 1%) 1 10MΩ 5 2.2kΩ 4 1MΩ 1 1kΩ 1 33kΩ 3 470Ω 1W 5 10kΩ 3 68Ω 1 4.7kΩ 2 10kΩ SIL resistor networks 1 1kΩ SIL resistor network Optional memory kit 1 CAT24C08P EEPROM (IC11) 1 8-pin DIP IC socket 1 SPDT switch (S6) data bus. Each cycle is set to 00:00:00 which is actually a start time of midnight, with a run time of 00 minutes. All cycles and both rain switches are enabled. The temperature trip point is off. The 3-week cycle is active, with all days set to on (upper­case). (2). Press the Cursor (⇒) button to move to the next option (A) which is the VR4 adjusting mode. This mode continually reads the tem­perature and displays the result. If VR4 is adjusted correctly, the display will show a steady temperature. How to do this is included as part of the temperature sensor kit. (3). D is the default display setting. A “D” indicates that the date will be displayed in the default display. A “T” means that the temperature will be displayed instead of the date. Press the Down (⇓) button to toggle from “D” to “T”. Adjustments The contrast pot (VR1) should already be set up. The range isn’t very broad, so maximum is probably the best to start with (fully clockwise). The other pots (VR2-VR4) were originally set during construction. Assuming that you are using the optional Mantis Rain Switches (available from the author), VR2 and VR3 can be further adjusted to set the trip voltages to 1.5V. This can be monitored by connecting the positive lead of your meter to the top lead of R15 for Rain Switch 1 (VR2), or to the top lead of R16 for Rain Switch 2 (VR3). To adjust IC3’s oscillator, connect a frequency meter to the pin marked “128Hz” (X7) and the ground lead to the GND pin (X8) nearby. Now tune C12 until a display of “128.0000 Hz” is ob­tained. Note that the frequency counters built into some multi­meters will probably prove unsuitable, as they do not have the resolution required. If a frequency meter is unavailable, check the time against a known good source and tweak the trimmer until the unit keeps good time. Installation The case is not waterproof, so mount it on a wall in the garage or in some other sheltered location. If you must have it outside, the controller will have to be installed in a waterproof case. You will have to drill two rows of five holes (5mm dia.) in the bottom of the case to provide access for the external wiring. Position one row close to the back of the case and the other row about 5mm away. Programming At first sight, programming this controller may seem a little daunting but it only takes about 20 minutes to get the hang of things. If you can program a VCR, you can program this device. We don’t have space to include the programming instructions here but full instructions will be supplied SC with the kit. PRODUCT SHOWCASE Tektronix P5200 high-voltage differential probe The measurement of high voltage or AC mains voltage signals presents problems that are not easily overcome with standard dual channel oscilloscopes. One solution is to use a Tektronix P5200 high voltage differential probe. The attenuators of most general purpose oscilloscopes pro­ v ide a maximum input sensitivity of 5V/ division. With the screen displaying eight vertical divisions this means that the maximum input signal can only be 40V peak-to-peak with a direct probe or 400V peak-to-peak using a 10:1 divider probe. Larger signals can be displayed using the variable input control but then the ampli­tude measurement facility is lost. If the signal to be measured is a mains AC wave­form or other higher voltage which is not ground referenced then it can be displayed using a dual trace oscilloscope in the Add mode. Once again the maximum calibrated display voltage will be 400V peak to peak. As an alternative, some organisations adopt the practice of using an oscilloscope with its mains earth dis­connected to display floating and mains voltages. This is a highly dangerous procedure with nothing to recommend it. Displaying the mains voltage waveform using a regular probe with the tip connected to the active lead and the earth clip connected to the neutral is also a dangerous procedure. Trans­po­sition of the live and neutral connections to the probe is always a possibility and if this mistake is made then the best that can happen is a blown fuse and the worst is electrocution. What is really required is an instrument with a differen­tial input, some level of signal attenuation and a single ended output signal to apply to the following measuring equipment. To cater for signals with fast rising wave fronts – eg; SCR circuits, switchmode supplies, etc – it should also have a wide bandwidth and fast rise time. The Tektronix P5200 high voltage differential probe meets all these requirements and allows the aforementioned measurements to be made easily and safely. It is supplied with two sets of connectors and a 9VDC 1A plugpack power supply. One Table 1: Specifications Maximum applied voltage between either input and ground............ 1kV (DC + peak AC) Maximum applied voltage between inputs.................................... 1.3kV (DC + peak AC) Rise time .........................................................................................<14ns in 1/50 range DC CMRR .........................................................................................>5000:1 at 500VDC AC CMRR................................................ 60Hz >10000:1; 100kHz >300:1; 1MHz >300:1 Bandwidth ..................................................................DC to 25MHz (-3dB) in 1/50 range Maximum operating input voltage.................... 1/500 differential 1.3kV (DC + AC peak); 1/500 common mode, 1kV (DC + AC peak); 1/50 differen­tial, 130V (DC + AC peak); 1/50 common mode, 1kV (DC + AC peak) Range accuracy................................... ±3% between 20-30°C after 20 minute warmup. Input impedance........... 8MΩ + 3.5pF between inputs; 4MΩ +7pF each input to ground DC output drift............................................................................................... ±0.5mV/°C Propagation delay.................................................................................................... 20ns Operating temperature range ............................................................................... 0-40°C January 1996  63 pair of connectors are long reach plunger probes and the other pair are heavy duty, double insulated crocodile clips. Its dimensions are 185mm (L) x 66mm (W) x 32mm (H). Two 500mm long input connectors are at one end of the case and these are terminated with shrouded plugs to fit the probe connectors. At the other end of the case is a 1500mm long output lead termi­ n ated with a moulded plug that carries an input socket for the plugpack and a 300mm long coaxial lead terminated with a BNC male plug to supply output to the measuring instrument which will usually be an oscilloscope. The face of the probe case features a pushbutton switch which provides 1/500 or 1/50 attenuation to the input signal. There are also LEDs for Power and Over Range and a table showing the effective volts/division of the combined probe plus oscillo­scope for different settings of the oscilloscope’s input attenua­tor. Output level from the probe is a maximum of 2.6V. The specifications for the P5200 are shown in Table 1. We used a sample P5200 in our laboratory and found that it does all that is claimed for it. It enables safe and accurate measurements when the source is not referenced to ground, par­ t icularly where mains voltage signals are concerned. In addition, it offers a much higher common mode rejection ratio than any typical dual channel oscilloscope when used in the “Add” mode – an important advantage. The Tektronix P5200 is priced at $658 plus sales tax where applicable. For further information, contact Tek­ tron­ix Australia Pty Ltd, 80 Waterloo Rd, North Ryde, NSW 2113. Phone (02) 888 7066 or fax (02) 888 0125. Fast-charger IC for lead-acid batteries Reptechnic has introduced the Benchmarq bq2031 lead acid fast charge IC. This incorporates current and voltage regulation with fast charge control to produce a highly cost effective fast charge system. Available in a 16-pin narrow DIP or SOIC package, the bq2031 is designed for controlling constant voltage and constant current charging of lead acid batteries in emergency lighting, backup power, industrial equipment and consumer elec­tronics applications. It can be configured for linear or gated current regulation applications. The bq2031 meets the battery manufacturers’ charge recom­mendations for both cyclic and float/maintenance charge. It includes a flexible pulse width modulation regulator which is suitable for high efficiency switch­ mode designs. Direct LED control outputs are featured for displaying charge status and fault conditions. Pre-charge qualification tests have been per­ formed on the device for shorted, open or damaged cells, allow­ ing it to condition the battery for fast charge. Charging is also qualified by selectable temperature and voltage 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. 64  Silicon Chip AV-COMM PTY LTD www.avcomm.com.au PCB POWER TRANSFORMERS 1VA to 25VA allow designers to experiment with the bq2031. For further information, contact Reptechnic, 3/36 Bydown St, Neutral Bay, NSW 2089. Phone (02) 9953 9844. Jaycar kits now made under AS9002 Manufactured in Australia Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 476-5854 Fx (02) 476-3231 limits. Key specifications include temperature, float voltage reference, pin select­able charge and maintenance modes, and pin selectable charge termination by maximum threshold voltage, minimum current and maximum time. A switchmode development system, the DV2031S1, is available to Pocket-sized fax machine & organiser Now available at Dick Smith Electronics, the Handifax 1000 is a 256K electronic personal organiser and fax machine in one. In a lightweight, compact 72 x 198mm unit, Handifax 1000 gives you the capability of faxing your colleagues and clients any­where, any time, by simply using it in conjunction with a stan­dard touch tone tele­phone or analog mobile phone. Simply type the message you want to fax, place the handset of the tele­ phone or mobile phone on the acoustic The head office, warehouse and kit department of Jaycar Electronics has successfully passed all requirements and has been accredited to AS/NZ ISO 9002:1994. “We realised that sooner or later we would have to seek this level of quality of management, documentation and quality control,” commented Managing Director, Gary Johnston. “As it turned out, our existing organisation was close to the high standards required anyway, so achieving the AS9002 level of quality was not particularly difficult. Our kits have always been very high quality. Now we have independent proof that they are.” According to Mr Johnston, the quality accreditation is part of an ongoing commitment by Jaycar to provide a high standard of service in the indus­try. YOU CAN AFFORD AN INTERNATIONAL SATELLITE TV SYSTEM SATELLITE ENTHUSIASTS STARTER KIT YOUR OWN INTERNATIONAL SYSTEM FROM ONLY: FREE RECEPTION FROM Asiasat II, Gorizont, Palapa, Panamsat, Intelsat coupler speaker and microphone, dial the fax machine you are calling and press SEND. Handifax 1000 can communicate with any standard fax machine at speeds of up to 9600 bps. Quick and simple to use, it will hold up to 120 faxable pages and its auto dialling facility ensures that there is no need to manually dial numbers or access codes. The unit has built-in fax cover pages and the ability to customise fax headers, standard orders, invoices, etc. With a 256K memory, Handifax 1000 also doubles as a person­al organiser, capable of storing more than 3500 entries. A 7-digit password can be used to protect all data. An optional PC interface allows users to back up and store information on any standard IBM compatible PC. The Handifax comes complete with an operation manual, an instruction video and is available at all Dick Smith Electronics stores for just SC $699. 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 January 1996  65 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 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 January 1996  69 IR remote control for the Railpower Mk.2 This remote control gives you complete freedom of opera­tion for the Railpower Mk.2 train controller. It has pushbutton control for everything & pulls negligible current when not in use. By RICK WALTERS As presented in the September & October 1995 issues, the Railpower Mk.2 is a walkaround throttle. It allows you to follow your trains as they go around the layout. As such, it performs very well. But perhaps you don’t like being tethered by a remote control cable. If so, you will want this infrared remote control. It operates just like any other remote and is based on 70  Silicon Chip the same microprocessor used in the Railpower Mk.2. The remote control handpiece has six pushbuttons but does not have the meter which was included in the walkaround hand control. Instead, we have designed a small PC board which has an array of 10 LEDs, to give an indication of train speed. This is mounted inside the main unit, along with a small PC board for the infrared receiver. The remote control uses the same plastic case as for the walkaround hand control. It contains a small PC board (coded 09101961) and a battery. The board contains six pushbuttons, three transistors, one IC, one crystal and a few other compon­ents. As you can see from the circuit of Fig.1, the battery is connected all the time, as is standard practice in all infrared remote controls. But instead of a dedicated IC as found in most remote controls, we have used a Z86E08 microprocessor. To conserve the battery, we have used a feature which was not previously exploited. The Z86E08 is a CMOS device and normal­ly does not draw much current but for battery operation, it can be put into a “sleep” mode, whereby the current it draws Fig.1: the transmitter circuit. This uses a Z86E08 microprocessor to produce coded IR pulses when the buttons are being pressed. When the buttons are not being pressed, the micro­processor goes into sleep mode to conserve the battery. is only 10µA. This greatly increases the battery life. When IC1 is put to sleep. it takes pins 16, 17 & 18 high (ie, to the battery positive line, +4.5V). Later, when any button is pressed, R0 or R1 (ie, row zero or row one of the pushbutton matrix) will go high, turning on transistor Q1 via diode D1 or D2. Q1 pulls pin 4 of IC1 low, to “wake it up”, after which it takes pins 16, 17 & 18 low and scans the buttons to see which one was pressed. C3 (column 3), the input to the INERTIA button, is high and if this is pressed, pin 9 of IC1 will go high. If this button is not pressed the processor then takes pin 16 (C2) high. As you can see from the circuit, the STOP or FASTER button, if pressed, will take pin 8 or pin 9 of IC1 high and the code for this button will be sent. Pins 17 and 18 are taken high in sequence and if any of the remaining buttons are pressed, their code will be trans­mit­ted. The pulse code appears on pin 3 of IC1 and turns Q2 and thus Q3 on and off. Q3 pulses two infrared LEDs (LED1 and LED2). Remember, only one button is press­ ed at a time and the code for this button will be sent many times before you can release it. With the jumpers set on 1,1 a burst of code takes 20 milli­seconds to be sent. Each time the processor finishes a scan, it takes all column outputs high (C0-C3) and looks at the collector of Q1. If it is low, indicating a button is pressed, it will scan the buttons again; if high, it will go into sleep mode to conserve the batteries. The RATE links A and B must be the same in the transmitter and the Below: this photo shows the completed IR receiver board being installed in the Railpower case. Note the mounting details for the Acknowledge LED and the LT536 infrared diode (PD1). January 1996  71 Fig.2: the IR receiver circuit. This uses two cascode transistor stages (Q1, Q2 and Q4, Q5) with AGC to provide the necessary large gain for the photodiode signal. The signal decoding is done by IC4, a Z86E08 microcontroller programmed for this purpose. receiver. These links could allow you to have one hand control with a 3-position selector switch and this could control three Railpower IR receivers, each with a different rate setting. Infrared receiver The infrared receiver consists of photodiode PD1, cur­ rent-to-voltage converter IC1, two cascode transistor amplifiers (Q1, Q2 and Q4, Q5) with AGC (automatic gain control), a comparator and AGC detector (IC2), a pulse stretcher (IC3) and a data decoder, IC4. These are all mounted on a PC board (coded 09101962) which is housed in the case of the 72  Silicon Chip Railpower controller. The circuit is shown in Fig.2. Photodiode PD1 sees the IR pulses emitted by the remote control and varies its current accordingly. This variation in current is converted to voltage pulses by op amp IC1 which drives the base of Q1 via a .015µF capacitor. The pulses from IC1 can vary from around 0.2V peak-peak when the remote control is close to PD1 to being lost in the noise when it is some distance away. For this reason, we need a lot of gain for weak signals but not very much for the stronger ones. We obtain lots of gain by using cascode circuits and then we use automatic gain control (AGC) on both to cope with large signals. Gain control The two cascode circuits are similar, the first using PNP transistors Q1 & Q2, the second using NPN transistors Q4 & Q5. AGC is applied to the first pair by FET Q3, while FET Q6 applies AGC to the second cascode pair. The gain of the first cascode stage, with Q3 turned off, is around 3.3 while the gain of the second stage, with Q6 turned off, is 2.2 giving an overall gain of 7.3 (3.3 x 2.2). With Q3 & Q6 turned on fully, the gain of each cascode stage can be in excess of 200, giving an overall gain of 40,000 or more for very small input signals. PARTS LIST Remote Control Transmitter 1 PC board, code 09101961, 85 x 50mm 1 plastic case (Jaycar HB-6032 or equivalent) 1 4MHz crystal (HC18, HC49) 2 yellow PC mount momentary switches (Jaycar SP-0722 or equival­ent) 1 red PC mount momentary switch (Jaycar SP-0720 or equivalent) 1 black PC mount momentary switch (Jaycar SP-0721 or equivalent) 1 white PC mount momentary switch (Jaycar SP-0723 or equivalent) 1 green PC mount momentary switch (Jaycar SP-0722 or equivalent) 1 single AA cell holder (see text) 3 L1154 alkaline batteries 1 18 pin IC socket (optional) 4 #8 x 10mm self-tapping screws 4 5mm untapped spacers 1 100mm-length red wire 1 100mm-length black wire 1 50mm-length 1mm sleeving Semiconductors 1 Z86E08 programmed TXA (IC1) 2 1N914 signal diodes (D1,D2) 2 BC338 NPN transistors (Q1,Q2) 1 BC640 PNP transistor (Q3) 2 CQY89A LED (or equivalent) Capacitors 1 100µF 16VW electrolytic 2 0.1µF 50VW monolithic 2 22pF ceramic In practice, the output signal from the collector of Q5 is monitored by IC2b which is connected as a peak rectifier. With no input signal present, pin 2 of IC2b is pulled high by the 47kΩ resistor connected to the +5V rail. Negative-going pulse signals at the collector of Q5 cause IC2b and its associated diode D1 to pull pin 2 towards 0V and hence discharge the 100µF capacitor. Thus, the gates of Q3 & Q6 tend to be taken high for small sign­als, to increase the gain. Conversely, large signals tend to result in the gates of Q3 & Q6 going toward 0V, to Resistors (0.25W, 1%) 4 100kΩ 1 470Ω 1 22kΩ 1 100Ω 1 10kΩ 2 1Ω 1 1kΩ IR Receiver Board 1 PC board, code 0911X951, 120 x 50mm 1 4MHz crystal (HC18,HC49) 1 18-pin IC socket (optional) 2 3mm x 15mm threaded spacer 2 3mm x 10mm screw 2 3mm x 6mm screw 1 200mm-length black hook-up wire 1 200mm-length red hook-up wire 1 200mm-length orange hook-up wire 1 200mm-length yellow hook-up wire 1 200mm-length green hook-up wire Semiconductors 1 TL071 op amp (IC1) 1 TL072 dual op amp (IC2) 1 74HC132 quad 2-input NAND gate (IC3) 1 Z86E08 programmed RXB (IC4) 2 2N2907 PNP transistors (Q1,Q2) 2 BC549 NPN transistors (Q4,Q5) 2 BS170 FET (Q3,Q6) 1 LT536 photodiode (PD1) 1 1N914 signal diode (D1) 1 5mm red LED (LED1) Capacitors 1 100µF 16VW electrolytic 3 10µF 50VW electrolytic turn them off and reduce the gain. In practice, the circuit continuously varies its gain so that the signal amplitude at the collector of Q5 is more or less constant. Q3 & Q6 are connected to the emitters of their respective cascode stages via 0.1µF capacitors. This means that the gain of the cascodes increases at high frequencies but not at 50Hz or 100Hz, to reduce any interference from incandescent or fluores­cent lights. IC2a is connected as a comparator and compares the signal from the collector of Q5 with the DC voltage at 6 0.1µF 50VW monolithic 1 .015µF 100VW MKT polyester 1 .01µF 100VW MKT polyester 1 .001µF 100VW MKT polyester 1 820pF disc ceramic 1 680pF disc ceramic 2 22pF capacitors Resistors (0.25W, 1%) 1 220kΩ 1 18kΩ 3 100kΩ 3 10kΩ 1 68kΩ 1 3.3kΩ 2 56kΩ 1 2.2kΩ 2 47kΩ 2 1kΩ 3 33kΩ 1 470Ω 3 22kΩ Speed Display Board 1 PC board, code 09101963, 65 x 50mm 1 5kΩ horizontal trimpot (VR1) 1 1kΩ horizontal trimpot (VR2) Semiconductors 1 LM3914 bargraph driver (IC1) 1 10-LED display (Jaycar ZD1700) Capacitors 1 10µF 50VW electrolytic 1 1µF 16VW electrolytic 1 0.1µF monolithic Resistors (0.25W, 1%) 1 100kΩ 1 4.7kΩ 1 15kΩ 1 820Ω 1 15kΩ 9-resistor array (10-pin SIP) Miscellaneous Hookup wire, PC stakes. its pin 5. It effectively squares up the signal pulses and removes any residual noise. IC2a drives IC3, a CMOS quad NAND gate which is used as a pulse stretcher. This allows us to supply a consistent pulse width to IC4, regardless of the output of IC2a. Data decoder IC4 is another Z86E08 microprocessor which has been pro­grammed to accept the IR data transmitted by the hand control and convert it to the correct code on pins 15, 16 & 17 to operate the Railpower functions. The January 1996  73 This topside view of the remote control transmitter board shows how the crystal is laid flat. Make sure that the two IR LEDs are correctly oriented. Fig.3: the component layout for the transmitter PC board. Note the three capacitors mounted on the underside of the board. These are shown dotted within the outline for IC1. microprocessor stores two consecutive codes from the transmitter and compares them. If they are identi­cal, it will send the information to the Railpower; if they differ, it will ignore them and compare the next two codes received. As mentioned previously, the rate links on the receiver must be the same as those on the transmitter. The three output lines from IC4 are This view inside the completed transmitter shows the mounting details for the three capacitors on the copper side of the board. Note the modified AA cell holder for the three button cells. Fig.4: the component overlay for the IR receiver board. Note that the rate links on this board must match the rate link settings on the transmitter PC board. 74  Silicon Chip This view shows how the IR receiver board is mounted vertically along one side of the Railpower Mk.2 case, while the speed board is mounted upside down, with the LEDs protruding through the front panel. RESISTOR COLOUR CODES ❏ No. ❏  1 ❏  8 ❏  1 ❏  2 ❏  2 ❏  3 ❏  4 ❏  1 ❏  1 ❏  4 ❏  1 ❏  1 ❏  1 ❏  3 ❏  1 ❏  2 ❏  1 ❏  2 Value 220kΩ 100kΩ 68kΩ 56kΩ 47kΩ 33kΩ 22kΩ 18kΩ 15kΩ 10kΩ 4.7kΩ 3.3kΩ 2.2kΩ 1kΩ 820Ω 470Ω 100Ω 1Ω 4-Band Code (1%) red red yellow brown brown black yellow brown blue grey orange brown green blue orange brown yellow violet orange brown orange orange orange brown red red orange brown brown grey orange brown brown green orange brown brown black orange brown yellow violet red brown orange orange red brown red red red brown brown black red brown grey red brown brown yellow violet brown brown brown black brown brown brown black gold gold 5-Band Code (1%) red red black orange brown brown black black orange brown blue grey black red brown green blue black red brown yellow violet black red brown orange orange black red brown red red black red brown brown grey black red brown brown green black red brown brown black black red brown yellow violet black brown brown orange orange black brown brown red red black brown brown brown black black brown brown grey red black black brown yellow violet black black brown brown black black black brown brown black black silver brown January 1996  75 Adding A Speed Meter To The Railpower Mk.2 Fig.5: the speed meter is a conventional LM3914 LED bargraph circuit. It takes the place of the analog meter in the original walkaround control for the Railpower Mk.2. If you wish to add a speed meter to the Railpower Mk.2, then use the LED bargraph display we have designed. It sits above the LED indicators on the front panel of the main unit and con­sists of a bar of 10 red LEDs. It is a standard circuit employing an LM3914 LED bar­graph display driver. The two preset potentiome­ters on this board are adjusted in a similar manner to the meter setup in the hand control. The circuit is shown in Fig.5 while the component overlay for the PC board (coded 09101963) is shown in Fig.6. Fit the IC, SIP and resistors, then the capacitors and potentiometers. If you wish, you can solder the potentiometers on the copper side of the board, as we have done, to make them easy to adjust. Connect a red wire to the +17V, orange to the +5V, black to the ground and yellow to the input terminal, as shown on the layout. The other end of the red wire connects to +17V on the main board (REG1 input), the orange to +5V (REG1 output) and the black wire to ground. The other end of the yellow wire should be sol­dered to pin 4 of IC1 (top of VR5). connected to IC1 in the Railpower unit. handpiece and the IR receiver board. As mentioned previously, we have also designed an optional LED bar­ graph speed indicator which takes the place of the speed meter in the original walkaround hand control. Let’s start with the remote control transmitter PC board. Its component layout is shown in Fig.3. Check the board for open circuit tracks or shorts, especially the track that passes between pins 7 and 8 of IC1. While you’re at it, check the other two boards for any etching problems and make any fixes as required. The first step is to mount the blank board in the plastic case. It goes in the half with the brass inserts (the front), with the copper side of the PC board facing up. A small hole has been drilled at the centre of each group of four pushbutton pads to allow you to drill pilot holes through into the case front for the six pushbuttons. When you have drilled them, remove the board from the case. (By the way, these pilot holes are not present in the photo of our prototype). Fit the two long and two short links Construction In discussing the construction, we will assume that you have already built the Railpower Mk.2, as described in the Sep­ tember & October 1995 issues. We will also assume that you have built up the original wired hand control and have made everything function as described in the setup procedure. To add the infrared remote control, you need to build the remote control 76  Silicon Chip Calibration Once the maximum and minimum speeds have been set satisfac­ torily on the main Railpower PC board, FORWARD should be se- This assembled speed meter shows nine discrete resistors instead of the specified SIP resistor array. lected and the minimum pot (VR2) on this board set so that the first LED lights. The controller should then be taken to full speed and the maximum pot (VR1) adjusted so that LED number 10 is lit. There is a small amount of interaction and the adjustments may have to be made several times to get it right. As an alternative to the speed bargraph, there is no reason why you could not mount the original walkaround control meter in the front panel, fitting a meter zero adjust control the same as in the handpiece and taking the positive meter wire to pin 2 on the DIN socket. at the LED end of the board and the two rate links. We suggest you initially code it 1,1 as shown on the overlay, as this gives the fastest transmis­sion rate. Next, fit and solder the diodes and resistors, followed by the transistors, capacitors and crystal. Push the transistors well down so that they are only about 2mm off the board. Bend the crystal’s leads at right angles and lie it down flat. The electrolytic capacitor should also lie flat on the board. Lastly, fit the pushbuttons, noting that all the flats face in the same direction (towards the rate links). Do not The two adjustment pots are mounted on the underside of the speed meter board for easy access. Fig.6 (right): install the parts on the speed meter PC board as shown in this wiring diagram. Check that all the LEDs are correctly oriented and note the mounting details for VR1 and VR2 (see photo above right). fit the LEDs as this will be done later. If you elected not to use an IC socket, fit and solder the IC marked TXA (this Z86E08 has been programmed as the transmitter); otherwise, solder in the IC socket. In either case, be sure to check the orientation of pin 1. As the PC board is rather small, we elected to mount three capacitors on the copper side. These can be fitted now. The 0.1µF monolithic type is soldered from pin 5 to pin 14, then laid flat against the board towards the pin 1 end. The two 22pF capacitors are soldered from pin 6 to pin 13 and from pin 7 to the pad on the copper track between pin 13 and pin 10. Both are laid flat, facing towards the other end of the socket. These details can be checked in the relevant photo. Battery holder The battery consists of three 1.5V button cells in series. These are held in a half-sized holder made out of a single AA cell holder. Cut the battery holder in half with a saw or sharp knife about 28mm from the spring end. Our holder had a moulded ridge at this point. Carefully cut the non-spring January 1996  77 plastic end out of the holder and locate it in the piece with the spring to make a half-size unit. The easiest way to retain the end is to melt the plastic with your soldering iron. If you do this inside and out, the end will be held firmly in place. Alternatively, you can do a neater job if you have access to ACC adhesive as used in plastic model making). Solder a red wire to the spring end and a black wire to the other end, then connect the red to the positive supply terminal on the PC board and the black wire to the nega­ tive terminal. Now drill one of the case end pieces to take the IR LEDs. Drill two 5mm holes on the horizontal centreline and 7.5mm either side of the vertical centreline. Slip 10mm of 1mm-dia. sleev­ing over each long LED lead, sit the PC board and LEDs in the case and bend the leads so that 2-3mm of each LED protrudes through the end piece. The longer sleeved lead should be on the right when viewed from the component side. Once you are satisfied, solder in the LEDs, insert the IC if you used a socket and fit the board in the case using the self-tapping screws and spacers. The battery holder can be kept in place with a dab of BLU-TACK® adhesive. Receiver board The component layout for the receiver board is shown in Fig.4. Start by fitting the one link and the resistors. Next, fit the ICs, using a socket for IC4 if you prefer. Make sure that all the ICs are correctly oriented. This done, solder in the MKT capaci­ tors, the transistors, electrolytic capacitors and finally the crystal. Don’t mount PD1 or the acknowledge LED yet. RAILPOWER SLOWER FASTER REVERSE FORWARD leads so that it protrudes satisfactorily through the front panel. Locate the sensor centrally behind the rectangular cutout. Both anodes (longer lead) are towards the top of the PC board. When you are satisfied with their positions, solder them both in place. Solder the black wire to the centre pin of REG1 (ground) and the red wire to the output pin of REG1 (+5V). The orange wire should be soldered to pin 1 of IC1, the yellow to pin 2 and the green to pin 3. Reassemble the unit and after applying power, check that the walkaround control still operates. If it doesn’t, the most likely cause is a short between pins 1, 2 or 3 on IC1. Testing INERTIA STOP Fig.7: the full-size artwork for the remote control front panel. Fit 200mm lengths of hook-up wire to the board, in the wire colours as shown in Fig.4, for the signal output and supply connections. This done, mount the PC board in the righthand side of the Railpower case, using two tapped metal spacers. Drill two 5mm holes in the front panel for the photodiode and acknowledge LED. File the hole for the photodiode to a 5 x 7.5mm rectangle, then replace the panel and bend the LED Clip the three cells into the holder on the IR remote con­trol unit, observing their polarity. They are back-to-front compared to standard cells, the small cap being the negative connection. Point the remote control at the receiver and press a button. If all is well, the acknowledge LED on the Rail­power should light and the corresponding function should be indicated by the Railpower LED. If it doesn’t work, the problem is knowing which unit is not operating correctly, the transmitter or the receiver. First, check that the battery voltage is around 4.5V on the transmitter. If you have an oscilloscope, hold a button down and check pin 7 of IC1 to see that the crystal is oscillating at 4MHz. Now check at the anode of one of the transmitter LEDs. There should be a pulse train output whenever a button is pressed. If the pulses are being sent continuously, RAILPOWER Fig.8: this is the full-size front panel artwork for the remote control version of the Railpower Mk.2. 78  Silicon Chip AC K ER PO W ST OP FO RW AR D RE VE IN RS ER E TI A OF F OV E RL OA D CUTOUT Fig.9: here are the full size etching patters for the IR receiver board (right), transmitter PC board (bottom right) and the speed meter PC board (below). Check the etched boards carefully before installing any of the parts. then one of the pushbut­tons has been inserted incorrectly. If an oscilloscope is not available, remove the batteries and connect a DC power supply set to 4.5V. When a button is pressed, the current should be around 9mA. As soon as the button is re­leased, the current should drop to about 5mA and after one second drop to 100µA. If this occurs, you can assume that the transmitter is working satisfactorily. If not check the capacitors on the crystal pins. IR receiver board On the receiver, check that pin 14 of IC3 is at +5V with re­spect to pin 7. If you have an oscilloscope, check pin 7 of the processor to confirm that the crystal is oscillating at 4MHz. Hold the transmitter close to the receiver with a button pressed. The output at pin 6 of IC1 should be a negative-going pulse of several hundred millivolts. It should be positive-going at Q2’s collector and 3-4V negative-going at Q5’s collector. The output of IC2a (pin 7) should be positive-going, while the signal into pin 9 of IC4 should be a negative-going 5V pulse 33µs wide. This close-up view shows how the leads of the infrared photodiode (PD1) on the receiver are bent over, so that the active surface of the device faces the hole in the front panel. If you don’t have an oscilloscope, the best approach is to compare the DC volt­ages measured in your receiver with those shown on the circuit. They should be within 10% of each other. If there is a discrepancy, check the component values around the relevant stage and also your soldering. Check also that the A and B rate links on the transmitter and re­ceiver match each other. If they don’t, the SC remote control won’t work. January 1996  79 SERVICEMAN'S LOG The complaint seemed simple enough Yes, it did sound simple. And, relatively speaking, it was. The trouble was, it didn’t stop there – it had brought all its gremlin mates along with it. By the time I’d knocked them all over, it was a major exercise. This story concerns a Sanyo colour TV set, model 6627 (79P chassis), which lead me a merry dance with a succession of faults – these in addition to the original complaint. The set belongs to a pensioner, one of several among my regular customers, and whom I regard as being in something of a special category. In general, their equipment tends to be older than average, for the very simple reason that, for many, the cost of new equipment is almost prohibitive. So they keep their old units and call on me to keep them going for as long as possible. Of course, I do my best to help them, even though at times it taxes one’s ingenuity and patience. (After all, I’ll be old myself someday – and no editorial comment, please). Anyway, this case was a classic example of this sort of job and, as is typi­cal, involved a set that was over 10 years old. But the owner’s complaint seemed simple enough – distorted sound. And a quick check while he was there confirmed the com­plaint; the distortion was quite bad. Even so, I reckoned it should be a snack; that I would be able to knock the job over in no time. And that, as the reader has doubtless guessed, was where I came a gutser. Sound circuitry The sound section in this set is quite straightforward – see Fig.1. It consists of a sound IF amplifier and demodulator IC (IC151), the latter feeding two output transistors, Q151 and Q152. These are both specified as 2SC2568 or 2SC2456. 80  Silicon Chip My first step was to check the 220V main HT rail, which came up spot on, as did several secondary rails derived from it. OK, so where to in the sound section? My first inclination was to suspect one of the two output transistors and, with more haste than wisdom, I whipped them out and tested them. They both tested OK, which served me right for rushing in. I then did what I should have done first – checked the voltages around these transistors. And, yes there was something wrong. The base voltage of Q151 is shown on the circuit as “80V-106V”, which seemed an unusually large spread. But that was largely academic anyhow, because the actual voltage was way down on even the lower figure. And this was where I encountered the first of several discrepancies between the set on the bench and the circuit. And I don’t meant bodgie repairs; I’m referring to original components. The bias resistor for Q151 (R151) is shown as 39kΩ but the one in the set was 27kΩ. Or, more correctly, it was coded 27kΩ. In fact, it measured over 100kΩ. Well that seemed like the answer and I promptly fitted a new 27kΩ resistor. That brought the voltages back to within tolerance of those on the circuit and wiped out most of the distortion. And I say “most” because there remained a niggling level. It was noth­ing like the original but it was enough to indicate that there was still something wrong. And that’s just about the nastiest kind of fault I can imagine. It was at such a level that, at times, on certain pro­ g ram material, one could kid oneself that it wasn’t there. Then the program would change and it was all too obvious. There was nothing for it; it had to be found. So, with all the stage’s operating voltages restored to normal, where should I go from here? The IC seemed the next most likely culprit. I had one on hand and changing it was not a particularly difficult job. But, alas, I drew another blank. Down to basics It was time to really get down to basics. I went right over the output stage and, by one means or another, checked each component in turn. And in the process, I encountered another circuit discrepancy; a diode, D153, which was in the set but not on the circuit. It has been drawn in on the circuit shown here. I paid particular attention to electrolytic capacitors C151 (1µF) and C157 (2.2µF on the circuit, 4.7µF in the set). Low value electrolytics are always suspect. But these and all the other components, except one, were cleared. That one component was C153, a 5600pF capacitor connecting to pin 13 of the IC. And I had left it until last because, ini­tially, I couldn’t identify it. I had been looking for a small ceramic capacitor or something similar but without success. In the end, I had to trace the copper pattern and, when I found it, it was quite a surprise. It wasn’t a ceramic capacitor and it wasn’t 5600pF. It was an electrolytic and it was 0.47µF; the biggest change from the original circuit I had found so far. More to the point, being an electrolytic – and of very low value to boot – it was a prime suspect and I lost no time in reefing it out and fitting a new one. And that was the answer, with the set now producing clean sound. And to confirm it, the suspect electrolytic showed sub­ stantial leakage when tested. So that looked like the end of the exercise. I gave the set the usual once over for general perfor­mance and minor adjustments, then set it up on the end of the bench and let it run. The set carks it Initially, it ran for several hours and then, suddenly, I was aware that it was completely dead, with no picture and no sound. Well, I took another punt: the horizontal output transis­tor (2SD838 on the circuit, 2SD621L in the set). And I picked it in one; it was short circuit. This failure, in itself, did not present any real problem, except that the 2SD838 was cheaper – at around $30 – than the 2SD621L ($42) but was no longer available. It was something of a slug for a pensioner but that’s life. More importantly, I was concerned as to why the transistor had failed. It has a pretty hard life in this set. The waveform shown on the collector is 1900V p-p which is high by any stan­ dards. That means that the stage is vulnerable to any spikes or rubbish on the driving waveform. And from experience, the most likely cause is a failure in C483, a 1µF electrolytic, which decouples the 220V rail to the horizontal drive transistor, Q481. Again, experience has shown that this capacitor dries out, allowing all kinds of rubbish to reach the driver. So I pulled it and replaced it. And, as an attempt at insurance, I upped the value to 10µF. I can’t guarantee how much it will help but it won’t do any harm. When I switched the set on again, there was sound but no picture. So what on earth could be wrong now? My first reaction was to suspect the operating voltages on the picture tube. I fished out the probe and checked the EHT. There were plenty of volts there, something over 25kV, and so I checked the screen voltage, focus voltage and the RGB drive transistors. All seemed OK. I have experienced trouble in the past around transistor Q191. This forms part of the ACL (Automatic Contrast Limiter) circuit and the problem concerns resistor R197 (220kΩ) which goes high. And while the trouble had never been anything like this, I checked it, found it somewhat high January 1996  81 Fig.1: the audio output stage in the Sanyo 6627. Note the additional diode (D153) which has been drawn in between the base and emitter of Q151. As well, R151 is now 27kΩ, C157 is now 4.7µF and C153 (top left) is now a 0.47µF electrolytic. and replaced it. But I wasn’t surprised when it had no effect. Next I did a waveform check, right through the video chain, but could find nothing wrong. I stopped and had a think and a caffeine fix and went over the checks I had made. And suddenly I became suspicious. I realised that all the voltages I had measured – EHT, screen, focus, RGB, etc – had all been marginally high. I hadn’t taken as much notice of this as I should have, the complete picture failure suggesting a total loss of voltage somewhere. Now I went back to taws – the main HT rail. And there was the answer, or part of it. Instead of the previous spoton 220V, it was now 275V. It was only a symptom but it was a start. I went straight to the power supply and, after a few preliminary checks, attacked Q901, the power regulator. And that was it; it was short circuit. I fitted a new one and switched on. And everything came up roses; 220V on the HT rail and a picture on the screen. And that was the end of the drama. But why did the exces­sive HT rail voltage create the effect it did? Frankly, I don’t know. I considered a number of likely reasons – including the possible action of an over-voltage protection circuit somewhere in the system – but I’m afraid I was too fed 82  Silicon Chip up with the set to want to spend any more time trying to find out. I let it run for another day or so, then called the customer to come and collect it. And I was glad to see the back of it. Granted, I was lucky in one way. At least those secondary faults occurred while the set was still on the bench. If I had returned the set immediately after fixing the first fault – as I might have done had the customer been in hurry – then I would have had it bounce. And that can generate bad will on the part of the customer. So let’s be thankful for small mercies. The crook Telefunken My next story is about a Telefunken colour set. It used an ICC4 chassis and while it had its problems, it wasn’t quite the headache of the previous story. The set came from a colleague. He passed it over to me for a couple of reasons. First, he is not particularly keen on serv­icing European sets and, second, he was rather snowed under at the time and didn’t want to be caught with something that might take up a lot of time. And I gathered that it had been through several other organisations before it came to him. The complaint was quite straightforward; it was completely dead. Fortunately, my colleague had a circuit, although it was a trifle grotty in places. And so I let myself be saddled with the monster. It was quite an elaborate set, with most of the modern features: a very impressive remote control system, Teletext, and so on. As with any dead set, the first thing to check is the rail voltages and, by implication, the power supply. So I went straight to the power supply. And, yes, it was completely dead. The supply itself is a fairly standard switchmode arrange­ ment, the main difference being that, in order to accommodate the remote control on-off function, the supply runs continuously while ever the power point is on. The set itself is turned on or off via its 12V rail and this comes from IP61, an LM317T adjust­able 3-terminal regulator. This regulator is in turn controlled by a signal from pin 7 of IR25. In addition to the aforementioned 12V rail, there is also a 13V rail, a 22V rail and a 90V rail, the latter being the main supply rail. And, at first glance, there also appears to be a 17V rail emanating from the chopper transformer (UP40). In fact, this is something of a furphy; the 17V rail is actually generated at pin 10 of the horizontal output transformer and this apparently takes over from the 13V rail (which feeds the regulator) once the horizontal stage fires up. (Note the arrow configuration on the 17V block). No voltage More to the point, there was no voltage on any of these rails. I moved over to the primary side of the chopper transform­ er (UP40). There was voltage out of the bridge rectifier and, in fact, this was applying some 350V across the main filter capaci­tor (CP11 – 100µF). I traced this through the primary winding, pins 9 & 1, of the transformer to the collector of the chopper transistor, TP32. I subsequently spent some time checking likely components around this stage but could find nothing wrong. But I did make one useful observation. With the CRO connected to the waveform points indicated on the circuit, I found that, at the moment of switching on, there was a very brief indication of activity but the waveforms vanished almost immediately. The stage was trying to oscillate but couldn’t continue. Fig.2: part of the switchmode power supply in the Telefunken ICC4. IP61 is an LM317 adjustable 3-terminal regulator which produces a +12V rail. This +12V rail is switched off (to turn the set off) when the main control IC pulls pin 2 of the regulator low (via a transistor). This started a different train of thought. Perhaps there was a short circuit or overload on one of the rails which was placing an unacceptable load on the power supply? First, I checked each rail with the ohmmeter but found nothing suspicious. This was not conclusive of course – there could still be a breakdown or leakage at the operating voltage, which would not show up with an ohmmeter check. I also checked the diodes supplying each of the rails. Again I drew a blank. Next, I checked the horizontal output transistor, TL37 (BU508A), which connects to pin 2 of the horizontal output trans­former (UL65) and thence to the 90V rail via pin 6. This checked out OK. On the basis of all these tests, and assuming that the overload theory was still a valid suspicion, the next obvious step was to disconnect each of the rails in turn. I started with the 90V rail by disconnecting the 0.22Ω safety resistor, RP51, at pin 2 of UP40. As it turned out, this was the wrong way to do the right thing. It was right because the power supply now show­ ed signs of life. Each of the other rails now came up, partially and briefly, and then died away. (On reflection, I suspect that the aforementioned weird 17V rail configuration had something to do with this strange behaviour). Unfortunately, disconnecting the rail at that point was the wrong way to do it, because it was directly on the transformer pin and did not allow me to check the 90V rail itself. I restored the 0.22Ω resistor and went back to the horizon­tal stage. This is a very complex arrangement and difficult to follow, both in the set and on the circuit. But the 90V rail goes to a choke (LL54), through diode DL56, and thence to pin 6 of the horizontal output transformer via LL57. And LL54 provided a convenient place to break the 90V rail and check it. In fact, it did come good, in a similar manner to the way the other rails had responded. The trail was getting Fig.3: part of the horizontal output stage in the Telefunken ICC4. The 90V rail connects (via LL54, DL57 & LL57) to pin 6 of the horizontal output transformer, while pin 2 connects to the horizontal output transistor (TL37 – not shown). January 1996  83 SERVICEMAN’S LOG – CTD warmer now. I restored the connection at LL54, then disconnected the rail at pin 6 of the transformer – same result. So the fault was either somewhere on the other side of this transformer winding, in a circuit connected to one of the other windings, or in the winding itself. I restored the pin 6 connec­tion and lifted the pin 2 connection. And it was a different story this time. I was now back to the original fault, with no voltage on any of the rails. By now, I was becoming more and more suspicious of the transformer itself – so much so that I went for broke and pulled it out. My idea was to check it for shorted turns, which I felt was the most likely explanation. But first I made a routine check of each winding with an ohmmeter. Well, they were all intact individually but when I happened to check between winding 2-6 and winding 1-5, I struck oil; there was a dead short between them. Naturally, there was only one answer to a fault like that; I needed a new transformer. But that had me worried initially because I knew of no current Australian agency for Tele­ funken. Fortunately, a few enquiries revealed that Hitachi use the same transformer, a type 243445. In fact, as I understand it, they actually make it and Telefunken buys it from them. Anyway, they are readily available, and one was obtained and fitted. End of story? Not quite. Oh, the switchmode supply leapt into life alright at switch-on but there was one little snag – the set was still dead. A quick check with the voltmeter provided the first clue; all the rails were up and spot on, at least out of the power supply. But there was no 12V rail out of pin 3 of regulator IP61. The reason wasn’t hard to track down. As mentioned earlier, IP61 is controlled by pin 7 of the remote control IC, IR25. This control signal is fed to pin 2 of IP61 via transistor TR74 (BC547B). And TR74 was shot – it was as simple as that. A replacement BC547B was fitted and I finally had every­thing running at full bore. And a very nice result it was too. I gave the set the usual routine adjustment check, let it run for a day or so, and then passed it back to my colleague to return to his customer. It wasn’t going to be cheap, of course, taking into account the new transformer. But that’s the way it goes SC and I hope he was happy. 20 Electronic Projects For Cars 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. 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 the coupon to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. 84  Silicon Chip Signature­­­­­­­­­­­­________________________ Card expiry date_____/______ Name _______________________Phone No (_____)____________ Street PLEASE PRINT _________________________________________________ Suburb/town _____________________________ Postcode_________ SILICON CHIP BOOK SHOP Newnes Guide to Satellite TV 336 pages, in paperback at $49.95. 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. Servicing Personal Computers By Michael Tooley. First pub­ lished 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. 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. Optoelectronics: An Introduction By J. C. A. Chaimowicz. First published 1989, reprinted 1992. This particular field is about to explode and it is most important for engineers and technicians to bring themselves up to date. The subject is comprehensively covered, starting with optics and then moving into all aspects of fibre optic communications. 361 pages, in paperback at $55.95. Digital Audio & Compact Disc Technology 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 format and R-DAT. If you want to understand digital audio, you need this reference book. 305 pages, in paperback at $55.95. Power Electronics Handbook 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. Surface Mount Technology By Rudolph Strauss. First pub­ lish-ed 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. Electronics Engineer’s Reference Book Edited by F. F. Mazda. First pub­ lished 1989. 6th edition 1994. This just has to be the best reference book available for electronics engineers. Provides expert coverage of all aspects of electronics in five parts: techniques, physical phenomena, material & components, electronic design, and applications. The sixth edition has been expanded to include chapters on surface mount technology, hardware & software design, Your Name__________________________________________________ PLEASE PRINT Address____________________________________________________ _____________________________________Postcode_____________ Daytime Phone No.______________________Total Price $A _________ ❏ Cheque/Money Order ❏ Bankcard ❏ Visa Card ❏ MasterCard Card No. Signature_________________________ Card expiry date_____/______ Return to: Silicon Chip Publications, PO Box 139, Collaroy NSW, Australia 2097. Or call (02) 9979 5644 & quote your credit card details; or fax to (02) 9979 6503. semicustom electronics & data communications. 63 chapters, in paperback at $140.00. Radio Frequency Transistors Principles & Practical Appli­ cations. By Norm Dye & Helge Granberg. Published 1993. This timely 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 techniques, impedance matching & CAD. 235 pages, in hard cover at $85.00. Newnes Guide to TV & Video Technology By Eugene Trundle. First pub­ lish-ed 1988, reprinted 1990, 1992. Eugene Trundle has written for many years in Television magazine and his latest book is right up date on TV and video technology. 432 pages, in paperback, at $39.95.  Title Price  Newnes Guide to Satellite TV  Servicing Personal Computers  The Art Of Linear Electronics  Optoelectronics: An Introduction  Digital Audio & Compact Disc Technology  Power Electronics Handbook  Surface Mount Technology  Electronic Engineer's Reference Book  Radio Frequency Transistors  Newnes Guide to TV & Video Technology $55.95 $59.95 $49.95 $55.95 $55.95 $59.95 $99.00 $140.00 $85.00 $39.95 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 January 1996  85 VINTAGE RADIO By JOHN HILL Anode bend to diode detection During the early to mid-1930s era, the low priced 5-valve superhet console radio was very popular. Many employed anode bend detection but they can be easily converted to diode detection for improved audio performance. The early ’30s were the tough times of the Great Depression years, when about 25% of the workforce was out of work. And, of course, they were without the back-up support that the unemployed have today. This meant that any radio manufacturer who wanted to stay in business had to produce a range of receivers that were affordable. The formula, in most cases, was to keep things fairly basic. The usual format for these cheaper radios was the autodyne superhet – a 5-valve receiver with an autodyne mixer, IF stage, anode bend detector and a single output stage. Some designs used a 175kHz IF and this necessitated a pre-selector stage, using a 3-gang Fig.1: the circuit of a typical anode bend detector. The valve type shown is a 24A tetrode or similar sharp cutoff tetrode. Later circuits used a type 57 pentode, although the basic arrangement remained the same. Fig.2: this is what the circuit looked like after conversion to diode detection. The original type 24A tetrode was replaced by a type 27 triode valve. 86  Silicon Chip tuning capacitor, in order to control the double spot problem created by of such a low value. Other makers chose a 455kHz IF, which was rapidly gaining popularity, and which solved the double spot problem automatical­ly. This allowed the use of a cheaper 2-gang capacitor. Either way, this broad design concept was a compromise between price and quality and while these sets work­ ed reasonably well, they had several disadvantages. Design drawbacks One problem was the lack of automatic gain control. This circuit innovation came into existence in the early 1930s but was only found on the more up-market receivers. Another difficulty with the auto­ dyne setup was that, while it worked OK on broadcast band frequencies, its performance on short­ wave was not so good. And finally, the anode bend detector used in these sets created a level of audio distortion that left something to be desired. While this distortion may have been acceptable in the 1930s, by today’s standards it is not very good and can be quite distracting. It may have been fairly distracting in the 1930s too, because by the middle of that decade most manufacturers had changed to diode detection. Some of those old receivers with anode bend detection sound better than others and in many instances the loudspeaker must play a part. The moving coil loudspeaker had been in existence for only a few years at that stage of radio development and there were still things to learn and manufacturing techniques to mas­ter. While an early ’30s moving coil loudspeaker was a remarkable improvement on a ’20s horn speaker, there was still quite a lot of developmental work ahead of it. Basic circuit Fig.1 shows the circuit of a typical anode bend detector. The valve type shown is a 24A or similar sharp cutoff tetrode. When the type 57 valve (a pentode) was developed, it replaced the radio frequency tetrode, although the circuit arrangements for anode bend detection were still the same. The main aspect of the anode bend detection method is the very high cathode bias resistor, which operates the valve at close to cutoff. The term “cutoff” simply means that the anode or plate current will be at or near zero when no signal is being received. When a modulated radio frequency (RF) signal is applied to the control grid, there will be pulses of anode current during the positive half cycles and little or no anode current during the negative half cycles. Therefore, the anode current is a rectified version of the signal waveform at the grid. Filtering of the RF component after detection is achieved by a small plate bypass capacitor (typically around 250pF) to chassis and an RF choke in series with the plate load. Anode bend detection has some odd characteristics and the distortion it produces can be minimised by varying the value of the cathode bias resistor. However, if the cathode bias is selected to give good low distortion sound with a strong signal at the control grid, then the performance is not as good on a weak signal and vice versa. So, after much experimenting, the cathode circuit is often re­turned to its original form, as the manufacturer’s setup was probably a reasonable compromise. Detector conversion I have quite a number of old auto­ dyne/anode bend console radios and I find some of them quite irritating due to their high levels of distortion. There are times I like to listen to my radios for hours on end and if they sound crook, there is no listening pleasure at all. The last of these receivers to come off the restoration assembly line was an old 1932 Darelle (see June 1995). While the Darelle was no more annoying to listen to than any of the Shown here is the Darelle 5-valve superhet cabinet. It is affectionately known as the “tea chest on legs”. The Darelle’s chassis was converted from anode bend detection to diode detec­tion and this simple modification gave a significant improvement in sound quality. others, it was the one I selected to see if the sound reproduction could be improved by converting the set to diode detection. The experi­ment produced a surprisingly good result, so allow me to fill you in on the details. There are several choices when it comes to converting a set to diode detection. One can use either a valve with diodes in it, a triode connected as a diode, or do the unforgivable and use a germanium signal diode. As the old Darelle used tetrode valves, there was no appli­cable diode type valve apart from the 55 duo-diode triode. The use of this valve would require a valve socket change from 5-pin to 6-pin. Using a triode connected as a diode was not an option either because there was insufficient room to accommodate it. So that left the unthinkable – a germanium signal diode. Not being a modern electronics man, I was not really sure how to incorporate a solid state diode into a valve circuit. I mentioned what I planned to do to young David (a collector friend) and he drew up a circuit of what he thought I needed to make a solid state diode detector work in a valve receiver – see Fig.2. I might add that David’s January 1996  87 24A audio amplifier. It was tried as a tetrode, a triode, with high and low plate voltages, and with a variety of cathode bias setups. None proved to be really satisfactory, although the triode connection wasn’t too bad except for a drop in overall volume. It had to be consid­ered unsatisfactory for that reason alone. Valve replacement The original anode bend detector valve was a 24A, as shown at left. This was replaced with a 27 triode (right) and this worked well as an audio amplifier, something that the 24A could not do. circuit was a little more in­volved than what I had in mind. Another aspect of my conversion was to retain the existing 24A anode bend detector valve and use it as an audio amplifier – if that was at all possible. David was not confident that this could be done but as I wanted to keep the original valve line-up, I would try to do it anyway. Whether or not it would be success­ful was in doubt at that stage. Many radio frequency valves (the 57 and the 6J7 for exam­ple) can be used as audio valves when connected as either pen­todes or triodes. Hopefully, the 24A would perform likewise, although there is no mention of audio frequency application in the valve manual. (Editorial comment: the 24A, being a tetrode – as distinct from the above mentioned pentodes – is less suitable for use as a resistance/capacitor coupled audio amplifier. When it was used as an audio amplifier, it was usually in the choke/capacitor coupling mode. This permits a much greater plate voltage signal swing without distortion). The detector circuit was made up on a small piece of tag­strip to form a compact detector module (see photo). This module was then bolted to a convenient part of the chassis and wired to the second IF transformer and the control grid of what was the anode bend detector. But while the set worked, one could not say that it was working well. Actually, the sound quality was really good at moderate volume levels, but distorted badly as the volume increased. Various alterations were made to the The diode detector module was built from miscellaneous compon­ ents mounted on a tagstrip. The small size of the module allows it to be mounted in some out-of-sight location if so desired. 88  Silicon Chip It was time to do what should have been done in the first place and that is fit a valve that was more suitable for audio frequency work than a 24A. A 27 was a logical choice as its 5-pin base was compatible with the existing valve socket. Rewiring the socket to suit the triode valve required a couple of alterations, as the 27 has no top-cap grid connection. After fitting the 27, all the previous problems associated with the diode detection modification suddenly disappeared. Triode audio amplifiers were all the go in the early 1930s and a triode also proved to be most successful with this particular circuit arrangement. Once everything was working OK, it was time to experiment a little. The detection module was disconnected and another signal diode substituted. This setup used no grid leak, no coupling capacitor or anything else – just the diode between the IF trans­former and the grid of the valve. It made little difference apart from an ever so slight increase in volume. So it would appear as though there are many ways to incor­porate a signal diode into a valve circuit – and they will all probably work. However, if one decides to do this modification, remember that the second IF transformer will require realignment. That would be about the only inconvenience incurred. After this little experiment, the original detector module was reconnected into the circuit. Practicality vs originality No doubt some readers will have difficulty in understanding why I would want to modify an existing circuit and ruin the set’s originality! Well, in this case, I want to listen to the radio and not be annoyed by it. It is as simple as that! What’s more, if a receiver can be significantly improved by implementing such a simple modification, then why not do it? In this RESURRECTION RADIO VALVE EQUIPMENT SPECIALISTS Repairs to valve radios, guitar and audio amplifiers. Books for holiday reading: Efforts to use the original 24A valve failed miserably. Substi­tuting the 27 involved some socket rewiring and the removal of the top-cap connector. It was worth the effort, as it solved the problem of trying to use the 24A in a role for which it was never intended. Golden Age of Radio In the Home ..............$42.95 More Golden Age of Radio .........................$49.95 Old Time Radios Restoration & Repair .......$36.95 70 Years of Radio Tubes & Valves ...............$42.95 Crystal Sets ‘n’ Such ...................................$19.95 In Marconi’s Footsteps ................................$49.95 The Complete Talking Machine ...................$39.95 An Approach to Audio Frequency Design ...$39.95 The Audio Designer’s Tube Register ...........$36.95 Send SSAE for Catalogue Visit our Showroom at 242 Chapel Street (PO Box 2029) PRAHRAN, VIC 3181 Tel: (03) 9510 4486; Fax (03) 9529 5639 Silicon Chip Binders Buy subsc a & get a ription discou nt on the binder The missing top-cap and connector may look a bit odd but so be it! Removing the anode bend detector and replacing it with diode detection was an experiment that paid off with a cleaner audio output. instance, the improvement was well worth the effort. Should a future owner wish to convert the receiver back to original, it can easily be returned to its anode bend state. Why someone would want to do this I don’t know, but if they did, they may not be happy with the distortion that this detection method produces. The diode detector described here can be a completely invisible modification if so desired. Although I chose to mount the diode and accompanying components on a small tag strip under­neath the chassis, there is no reason why it cannot be housed inside the second IF transformer shield can or positioned in some other out-of-the-way place where it is out of sight. As far as I’m concerned, if everything looks OK then that’s all that matters. A few devious modifications here and there don’t upset me in the least, especially if they improve the set’s performance. The fact that the old Darelle sounds a bit better than most radios from that era must be worth SC something! These beautifully-made binders will protect your copies of SILICON CHIP. They are made from a dis­tinctive 2-tone green vinyl & will look great on your bookshelf. Price: $A11.95 plus $3 p&p each (NZ $8 p&p). Send your order to: Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. January 1996  89 Silicon Chip October 1990: Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; Using The NE602 In Home-Brew Converter Circuits. BACK ISSUES November 1990: How To Connect Two TV Sets To One VCR; A Really Snazzy Egg Timer; Low-Cost Model Train Controller; Battery Powered Laser Pointer; 1.5V To 9V DC Converter; Introduction To Digital Electronics; Simple 6-Metre Amateur Transmitter. September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice. Tips For Your VCR; Speed­ing Up Your PC; Phone Patch For Radio Amateurs; Active Antenna Kit; Speed Controller For Ceiling Fans; Designing UHF Transmitter Stages. April 1989: Auxiliary Brake Light Flasher; What You Need to Know About Capacitors; 32-Band Graphic Equaliser, Pt.2; LED Message Board, Pt.2. February 1990: 16-Channel Mixing Desk; High Quality Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2. May 1989: Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; LED Message Board, Pt.3. July 1989: Exhaust Gas Monitor (Uses TGS812 Gas Sensor); Extension For The Touch-Lamp Dimmer; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; High Or Low Fluid Level Detector; Studio Series 20-Band Stereo Equaliser, Pt.2; Auto-Zero Module for Audio Amplifiers (Uses LMC669). October 1989: FM Radio Intercom For Motorbikes Pt.1; GaAsFet Preamplifier For Amateur TV; 1Mb Printer Buffer; 2-Chip Portable AM Stereo Radio, Pt.2; Installing A Hard Disc In The PC. November 1989: Radfax Decoder For Your PC (Displays Fax, RTTY & Morse); FM Radio Intercom For Motorbikes, Pt.2; 2-Chip Portable AM Stereo Radio, Pt.3; Floppy Disc Drive Formats & Options; The Pilbara Iron Ore Railways. December 1989: Digital Voice Board; UHF Remote Switch; Balanced Input & Output Stages; Data For The LM831 Low Voltage Amplifier IC; Index to Volume 2. January 1990: High Quality Sine/Square Oscillator; Service March 1990: 6/12V Charger For Sealed Lead-Acid Batteries; Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC. April 1990: Dual Tracking ±50V Power Supply; Voice-Operated Switch (VOX) With Delayed Audio; 16-Channel Mixing Desk, Pt.3; Active CW Filter For Weak Signal Reception; How To Find Vintage Receivers From The 1920s. June 1990: Multi-Sector Home Burglar Alarm; Low-Noise Universal Stereo Preamplifier; Load Protection Switch For Power Supplies; A Speed Alarm For Your Car; Fitting A Fax Card To A Computer. July 1990: Digital Sine/Square Generator, Pt.1 (Covers 0-500kHz); Burglar Alarm Keypad & Combination Lock; Simple Electronic Die; Low-Cost Dual Power Supply; Inside A Coal Burning Power Station. August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/Square Generator, Pt.2. September 1990: Remote Control Extender For VCRs; Power Supply For Burglar Alarms; Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band. December 1990: DC-DC Converter For Car Amplifiers; The Big Escape – A Game Of Skill; Wiper Pulser For Rear Windows; A 4-Digit Combination Lock; 5W Power Amplifier For The 6-Metre Amateur Transmitter; Index To Volume 3. January 1991: Fast Charger For Nicad Batteries, Pt.1; Have Fun With The Fruit Machine; Two-Tone Alarm Module; LCD Readout For The Capacitance Meter; How Quartz Crystals Work; The Dangers When Servicing Microwave Ovens. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Inverters For Fluorescent Lights; Low-Cost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; A Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal Wideband RF Preamplifier For Amateur Radio & TV. April 1991: Steam Sound Simulator For Model Railroads; Remote Controller For Garage Doors, Pt.2; Simple 12/24V Light Chaser; Synthesised AM Stereo Tuner, Pt.3; A Practical Approach To Amplifier Design, Pt.2. May 1991: 13.5V 25A Power Supply For Transceivers; Stereo Audio Expander; Fluorescent Light Simulator For Model Railways; How To Install Multiple TV Outlets, Pt.1. June 1991: A Corner Reflector Antenna For UHF TV; 4-Channel Lighting Desk, Pt.1; 13.5V 25A Power Supply For Transceivers; Active Filter For CW Reception; Tuning In To Satellite TV, Pt.1. July 1991: Battery Discharge Pacer For Electric Vehicles; Loudspeaker Protector For Stereo Amplifiers; 4-Channel Lighting Desk, Pt.2; How To Install Multiple TV Outlets, Pt.2; Tuning In To Satellite TV, Pt.2. ORDER FORM Please send me a back issue for: ❏ July 1989 ❏ September 1989 ❏ January 1990 ❏ February 1990 ❏ July 1990 ❏ August 1990 ❏ December 1990 ❏ January 1991 ❏ May 1991 ❏ June 1991 ❏ October 1991 ❏ November 1991 ❏ April 1992 ❏ May 1992 ❏ September 1992 ❏ October 1992 ❏ April 1993 ❏ May 1993 ❏ September 1993 ❏ October 1993 ❏ February 1994 ❏ March 1994 ❏ July 1994 ❏ August 1994 ❏ December 1994 ❏ January 1995 ❏ May 1995 ❏ June 1995 ❏ October 1995 ❏ November 1995 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ September 1988 October 1989 March 1990 September 1990 February 1991 July 1991 December 1991 June 1992 January 1993 June 1993 November 1993 April 1994 September 1994 February 1995 July 1995 December 1995 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ April 1989 November 1989 April 1990 October 1990 March 1991 August 1991 January 1992 July 1992 February 1993 July 1993 December 1993 May 1994 October 1994 March 1995 August 1995 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ May 1989 December 1989 June 1990 November 1990 April 1991 September 1991 March 1992 August 1992 March 1993 August 1993 January 1994 June 1994 November 1994 April 1995 September 1995 Enclosed is my cheque/money order for $­______or please debit my: ❏ Bankcard ❏ Visa Card ❏ Master Card Signature ____________________________ Card expiry date_____ /______ Name _______________________________ Phone No (___) ____________ PLEASE PRINT Street ________________________________________________________ Suburb/town ________________________________ Postcode ___________ 90  Silicon Chip Note: all prices include post & packing Australia (by return mail) ............................. $A7 NZ & PNG (airmail) ...................................... $A7 Overseas (airmail) ...................................... $A10 Detach and mail to: Silicon Chip Publications, PO Box 139, Collaroy, NSW, Australia 2097. Or call (02) 979 5644 & quote your credit card details or fax the details to (02) 979 6503. ✂ Card No. August 1991: Build A Digital Tachometer; Masthead Amplifier For TV & FM; PC Voice Recorder; Tuning In To Satellite TV, Pt.3; Step-By-Step Vintage Radio Repairs. June 1993: Build An AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; Digital Voltmeter For Cars; Remote Volume Control For Hifi Systems, Pt.2. September 1991: Studio 3-55L 3-Way Loudspeaker System; Digital Altimeter For Gliders & Ultralights, Pt.1; The Basics Of A/D & D/A Conversion; Windows 3 Swapfiles, Program Groups & Icons. July 1993: Single Chip Message Recorder; Light Beam Relay Extender; AM Radio Trainer, Pt.2; Quiz Game Adjudicator; Programming The Motorola 68HC705C8 – Lesson 1; Antenna Tuners – Why They Are Useful. October 1991: Build A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator For Model Railways Mk.II; Magnetic Field Strength Meter; Digital Alti­meter For Gliders & Ultralights, Pt.2; Getting To Know The Windows PIF Editor. August 1993: Low-Cost Colour Video Fader; 60-LED Brake Light Array; A Microprocessor-Based Sidereal Clock; The Southern Cross Z80-Based Computer; A Look At Satellites & Their Orbits. November 1991: Colour TV Pattern Generator, Pt.1; Battery Charger For Solar Panels; Flashing Alarm Light For Cars; Digital Altimeter For Gliders & Ultralights, Pt.3; Build A Talking Voltmeter For Your PC, Pt.2. September 1993: Automatic Nicad Battery Charger/Discharger; Stereo Preamplifier With IR Remote Control, Pt.1; In-Circuit Transistor Tester; A +5V to ±15V DC Converter; Remote-Controlled Cockroach. December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Solid-State Laser Pointer; Colour TV Pattern Generator, Pt.2; Index To Volume 4. October 1993: Courtesy Light Switch-Off Timer For Cars; Wireless Microphone For Musicians; Stereo Preamplifier With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1; Programming The Motorola 68HC705C8 – Lesson 2. January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Experiments For Your Games Card. March 1992: TV Transmitter For VHF VCRs; Studio Twin Fifty Stereo Amplifier, Pt.1; Thermostatic Switch For Car Radiator Fans; Telephone Call Timer; Coping With Damaged Computer Direct­ories; Valve Substitution In Vintage Radios. April 1992: IR Remote Control For Model Railroads; Differential Input Buffer For CROs; Studio Twin Fifty Stereo Amplifier, Pt.2; Understanding Computer Memory; Aligning Vintage Radio Receivers, Pt.1. May 1992: Build A Telephone Intercom; Low-Cost Electronic Doorbell; Battery Eliminator For Personal Players; Infrared Remote Control For Model Railroads, Pt.2; Aligning Vintage Radio Receivers, Pt.2. June 1992: Multi-Station Headset Intercom, Pt.1; Video Switcher For Camcorders & VCRs; Infrared Remote Control For Model Railroads, Pt.3; 15-Watt 12-240V Inverter; A Look At Hard Disc Drives. July 1992: Build A Nicad Battery Discharger; 8-Station Automatic Sprinkler Timer; Portable 12V SLA Battery Charger; Multi-Station Headset Intercom, Pt.2. August 1992: Build An Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; Dummy Load Box For Large Audio Amplifiers; Troubleshooting Vintage Radio Receivers. September 1992: Multi-Sector Home Burglar Alarm; Heavy-Duty 5A Drill speed Controller (see errata Nov. 1992); General-Purpose 3½-Digit LCD Panel Meter; Track Tester For Model Railroads; Build A Relative Field Strength Meter. October 1992: 2kW 24VDC To 240VAC Sine­wave Inverter; Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For Personal Stereos; Build A Regulated Lead-Acid Battery Charger. January 1993: Peerless PSK60/2 2-Way Hifi Loudspeakers; Flea-Power AM Radio Transmitter; High Intensity LED Flasher For Bicycles; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.4; Speed Controller For Electric Models, Pt.3. February 1993: Three Projects For Model Railroads; Low Fuel Indicator For Cars; Audio Level/VU Meter (LED Readout); An Electronic Cockroach; MAL-4 Micro­controller Board, Pt.3; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.5. March 1993: Build A Solar Charger For 12V Batteries; Alarm-Triggered Security Camera; Low-Cost Audio Mixer for Camcorders;A 24-Hour Sidereal Clock For Astronomers. April 1993: Solar-Powered Electric Fence; Build An Audio Power Meter; Three-Function Home Weather Station; 12VDC To 70VDC Step-Up Voltage Converter; Digital Clock With Battery Back-Up. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Remote Volume Control For Hifi Systems, Pt.1; Alphanumeric LCD Demonstration Board; The Micro­soft Windows Sound System. November 1993: Jumbo Digital Clock; High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier With IR Remote Control, Pt.3; Siren Sound Generator; Electronic Engine Management, Pt.2; Experiments For Games Cards. December 1993: Remote Controller For Garage Doors; Low-Voltage LED Stroboscope; Low-Cost 25W Amplifier Module; Build A 1-Chip Melody Generator; Electronic Engine Management, Pt.3; Index To Volume 6. November 1994: Dry Cell Battery Rejuv­enator; A Novel Alphanumeric Clock; 80-Metre DSB Amateur Transmitter; Twin-Cell Nicad Discharger (See May 1993); Anti-Lock Braking Systems; How To Plot Patterns Direct To PC Boards. December 1994: Dolby Pro-Logic Surround Sound Decoder, Pt.1; Easy-To-Build Car Burglar Alarm; Three-Spot Low Distortion Sinewave Oscillator; Clifford – A Pesky Electronic Cricket; Cruise Control – How It Works; Remote Control System for Models, Pt.1; Index to Vol.7. January 1995: Sun Tracker For Solar Panels; Battery Saver For Torches; Dolby Pro-Logic Surround Sound Decoder, Pt.2; Dual Channel UHF Remote Control; Stereo Microphone Preamplifier; The Latest Trends In Car Sound; Pt.1. February 1995: 50-Watt/Channel Stereo Amplifier Module; Digital Effects Unit For Musicians; 6-Channel Thermometer With LCD Readout; Wide Range Electrostatic Loudspeakers, Pt.1; Oil Change Timer For Cars; The Latest Trends In Car Sound; Pt.2; Remote Control System For Models, Pt.2. March 1995: 50W/Channel Stereo Amplifier, Pt.1; Subcarrier Decoder For FM Receivers; Wide Range Electrostatic Loudspeakers, Pt.2; IR Illuminator For CCD Cameras; Remote Control System For Models, Pt.3; Simple CW Filter. April 1995: Build An FM Radio Trainer, Pt.1; Photographic Timer For Darkrooms; Balanced Microphone Preamplifier & Line Filter; 50W/Channel Stereo Amplifier, Pt.2; Wide Range Electrostatic Loudspeakers, Pt.3; 8-Channel Decoder For Radio Remote Control. January 1994: 3A 40V Adjustable Power Supply; Switching Regulator For Solar Panels; Printer Status Indicator; Mini Drill Speed Controller; Stepper Motor Controller; Active Filter Design; Electronic Engine Management, Pt.4. May 1995: Introduction To Satellite TV; CMOS Memory Settings – What To Do When the Battery On Your Mother­ board Goes Flat; Mains Music Transmitter & Receiver; Guitar Headphone Amplifier For Practice Sessions; Build An FM Radio Trainer, Pt.2; Low Cost Transistor & Mosfet Tester For DMMs; 16-Channel Decoder For Radio Remote Control. February 1994: 90-Second Message Recorder; Compact & Efficient 12-240VAC 200W Inverter; Single Chip 0.5W Audio Amplifier; 3A 40V Adjustable Power Supply; Electronic Engine Management, Pt.5; Airbags – How They Work. June 1995: Build A Satellite TV Receiver; Train Detector For Model Railways; A 1W Audio Amplifier Trainer; Low-Cost Video Security System; A Multi-Channel Radio Control Transmitter For Models, Pt.1; Build A $30 Digital Multimeter. March 1994: Intelligent IR Remote Controller; Build A 50W Audio Amplifier Module; Level Crossing Detector For Model Railways; Voice Activated Switch For FM Microphones; Simple LED Chaser; Electronic Engine Management, Pt.6. July 1995: Low-Power Electric Fence Controller; How To Run Two Trains On A Single Track (Plus Level Crossing Lights & Sound Effects); Setting Up A Satellite TV Ground Station; Build A Door Minder; Adding RAM To A Computer. April 1994: Remote Control Extender For VCRs; Sound & Lights For Model Railway Level Crossings; Discrete Dual Supply Voltage Regulator; Low-Noise Universal Stereo Preamplifier; Build A Digital Water Tank Gauge; Electronic Engine Management, Pt.7. August 1995: Vifa JV-60 2-Way Bass Reflex Loudspeaker System; A Fuel Injector Monitor For Cars; Gain Controlled Microphone Preamp; The Audio Lab PC Controlled Test Instrument, Pt.1; The Mighty-Mite Powered Loudspeaker; An Easy Way To Identify IDE Hard Disc Drive Parameters. May 1994: Fast Charger For Nicad Batteries; Induction Balance Metal Locator; Multi-Channel Infrared Remote Control; Dual Electronic Dice; Two Simple Servo Driver Circuits; Electronic Engine Management, Pt.8; Passive Rebroadcasting For TV Signals. September 1995: A Keypad Combination Lock; The Incredible Vader Voice; Railpower Mk.2 Walk-Around Throttle For Model Railways, Pt.1; Build A Jacob’s Ladder Display; The Audio Lab PC Controlled Test Instrument, Pt.2; Automotive Ignition Timing, Pt.1. June 1994: 200W/350W Mosfet Amplifier Module; A Coolant Level Alarm For Your Car; An 80-Metre AM/CW Transmitter For Amateurs; Converting Phono Inputs To Line Inputs; A PC-Based Nicad Battery Monitor; Electronic Engine Management, Pt.9 October 1995: Build A Compact Geiger Counter; 3-Way Bass Reflex Loudspeaker System; Railpower Mk.2 Walk-Around Throttle For Model Railways, Pt.2; Fast Charger For Nicad Batteries; Digital Speedometer & Fuel Gauge For Cars, Pt.1; Automotive Ignition Timing, Pt.2. July 1994: Build A 4-Bay Bow-Tie UHF Antenna; PreChamp 2-Transistor Preamplifier; Steam Train Whistle & Diesel Horn Simulator; Portable 6V SLA Battery Charger; Electronic Engine Management, Pt.10. November 1995: LANsmart – A LAN For Home Or A Small Office; Mixture Display For Fuel Injected Cars; CB Transverter For The 80M Amateur Band, Pt.1; Low Cost PIR Movement Detector; Dolby Pro Logic Surround Sound Decoder Mk.2, Pt.1; Digital Speedometer & Fuel Gauge For Cars, Pt.2. August 1994: High-Power Dimmer For Incandescent Lights; Microprocessor-Controlled Morse Keyer; Dual Diversity Tuner For FM Microphones, Pt.1; Build a Nicad Zapper; Simple Crystal Checker; Electronic Engine Management, Pt.11. September 1994: Automatic Discharger For Nicad Battery Packs; MiniVox Voice Operated Relay; Image Intensified Night Viewer; AM Radio For Aircraft Weather Beacons; Dual Diversity Tuner For FM Microphones, Pt.2; Electronic Engine Management, Pt.12. October 1994: Dolby Surround Sound – How It Works; Dual Rail Variable Power Supply (±1.25V to ±15V); Talking Headlight Reminder; Electronic Ballast For Fluorescent Lights; Temperature Controlled Soldering Station; Electronic Engine Management, Pt.13. December 1995: Engine Immobiliser For Cars; Five Band Equaliser For Musicians; CB Transverter For The 80M Amateur Band, Pt.2; Build A Subwoofer Controller; Dolby Pro Logic Surround Sound Decoder Mk.2, Pt.2; Knock Sensing In Cars; RAM Doubler Reviewed; Index To Volume 8. PLEASE NOTE: November 1987 to August 1988, October 1988 to March 1989, June 1989, Aug­ust 1989, May 1990, February 1992, November 1992 and December 1992 are now sold out. All other issues are presently in stock. For readers wanting articles from sold-out issues, we can supply photostat copies (or tear­sheets) at $7.00 per article (includes. p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. January 1996  91 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. Sins of omission in a preamplifier I recently constructed the Low Noise Universal Preamplifier as described in April 1994, for use with a pair of unbalanced binaural microphones. During construction, I decided to omit all components between the input pins and the op amp, as these seemed to relate largely to the phono preamp version. Any comments? It seems to work perfectly well. Would the omitted part of the circuit have made any difference or improvement? As part of the same project, I intend to build balanced outputs. The December 1989 issue of SILICON CHIP gives a design utilising a pair of LM833s per channel to provide balanced ins and outs. Is the PC board for this available anywhere? I also came across a design in “ETI” in the December 1982 issue for a Balanced Input Differential Preamp. This used a pair of 5534 op amps, one for each of the balanced line conductors, feeding a TL071. Any comments on the pros and cons of the two different approaches to producing balanced inputs? (D. M., Canton Beach, NSW). • Omitting all the components between the input pins and the op amp Speed controller for a 2hp router Have you produced a speed control for a 2hp router. I am using it with some large diameter bits and the recommendation is to reduce the speed for safety. I know you produced a 5A speed controller but I obviously need something bigger. By the way, the current rating for the router is 10A. Could I upgrade your 5A design by just using a bigger Triac? (N. M., Sey­ mour, Vic). • The 5A speed controller is the 92  Silicon Chip is not good practice, even though, as you have observed, the circuit will still work. The RF suppression components, consisting of the inductor L1, 150Ω resistor and the 100pF ca­pacitors, are desirable in order to prevent pickup of interfer­ence, particularly AM radio stations. Second, the 100kΩ resistor on the op amp side of the 47µF capacitor should be retained so that, if the microphone is unplugged, the op amp continues to be correctly biased; otherwise there will be a loud ‘pop’ whenever the microphone is plugged in or out. The 47µF capacitor is desirable to prevent the bias current of the LM833, typically around 0.5µA, from flowing through the microphone. This could lead to non-linearity or possibly de­ mag­­ netisation, over a long period. Finally, the second 100kΩ resis­tor is required to make sure that the 47µF capacitor is always charged and does not charge via the microphone when it is plugged in; if this happened, a loud ‘pop’ would result. The PC board for the balanced output circuit is available from RCS Radio Pty Ltd, 651 Forest Road, Bexley, NSW 2207. Phone (02) 587 3491. The ETI circuit for balanced inputs would certainly work but a superior highest rating we have pro­duced and it already uses a 40A Triac. As it stands, you could use the 5A design for your 2hp router provided you change the 10A fuse to a “slow-blow” type and you arrange for better heatsinking for the Triac. This would most easily be done by using a reason­able size diecast aluminium box. Note that at the full speed setting with any half-wave speed control, the maximum speed of the router will be reduced by about 20%. So a 20,000 RPM router would immediately be reduced to a maximum of 16,000 RPM. circuit using the special purpose SSM2017 was published in the April 1995 issue of SILICON CHIP. A kit for this project is available from Altronics, in Perth. Altering timer for burglar alarm I have just completed wiring up your Multi-Sector Home Burglar Alarm from the June 1990 edition and thankfully (for me) it worked straight away. My question is what do I alter to get a five minute alarm instead of the 10-minute period? And just as a query, why did you put the sector switches with the off position down? Thanking you for a really good magazine for novices as well as the brighter boys! (H. M., Ballina, NSW). • The 10-minute timer comprises IC4, IC6 & IC7. Halving the 10-minute period is simply a matter of using the Q5 output (pin 5) of IC6 to drive IC7. So disconnect pin 6 of IC6 and connect pin 5 instead. We’re not sure what you mean by your question about the sector switches being down in the Off position. The design was presented in the form of PC boards so the way in which it was built was up to the constructor. Combination AM/FM radio trainer wanted Could the AM Radio Trainer (June/ July 1993) and the FM Radio Trainer (April/May 1995) be combined to make an AM/FM Radio Trainer? Over the years I have built AM valve radio sets and AM transistor sets. I did not make the FM Radio Trainer because it only had the one section. Completely designing a radio trainer would be desirable so that a person could obtain experience aligning the AM/FM coils using a cheap oscilloscope, sweep generator or FM-AM generator. It would be a good idea if a sweep generator kit was developed for alignment of the FM section. By this method, one would learn Coolant alarm for plastic radiators I refer to the very successful coolant alarm project from the June 1994 issue. I have just purchased a new Mitsubishi Magna sedan and to my surprise, I find that the radiator appears to be of composite manufacture, with plastic head and bottom tanks moulded on to a metal heat exchanger. The metal heat exchanger is earthed to the car body, ac­cording to my ohmmeter, and as the plastic header tank is an insulator, it would appear that a suitable sensor probe could be made by just drilling and tapping a 1/8-inch brass metal thread into the header tank. However, I would like your comments please. (B. P., Port Macquarie, NSW). more alignment procedures experimentally. If possible, rather than IC1IC4 of the FM side being integrated circuits they should be completely transistorised. Then one could learn the internal structure of each circuit on the FM side. (L. F., North Bondi, NSW). • Although FM/AM radios and tuners are standard commercial products, frequently using only one or two ICs, there is no easy way of combining our radio trainer circuits onto one PC board. These discrete circuits are quite difficult to produce on a freestanding PC board and our final versions were only arrived at after quite a few prototypes had been built. Car burglar alarm malfunction I’m hoping you can help with a num­ber of problems I’m having with the Car Burglar Alarm featured in December 1994. I’ve obviously botched something somewhere and anything you can suggest to get the alarm working properly would be appreciated. After assembling the kit carefully and doing a neat solder­ ing job, I installed it in the car and no matter what I do to the trimpots it doesn’t seem to work properly at all. The car it is fitted in is a Volkswagen Beetle, • A large number of modern cars now use radiators with plastic header tanks. While a bolt attachment to the top tank would be a simple addition, we’re not keen on the idea of drilling and tapping the tank to fit a brass screw. A screw might work its way out after a time and then you really would have a loss of cool­ant. Nor are we keen on the idea of fitting a brass screw in close proximity to the aluminium radiator core. That seems like asking for corrosion problems. We think it would be preferable to fit a stainless steel bolt and nut to this type of radiator, together with flat washers and a lockwasher. Natural­ly, this would need to be installed close to the radiator cap, in order to attach the nut and washers to the bolt. not a very complicated car in terms of wiring, so installation was easy, even for an amateur like me. About the only extra items fitted to the kit are two pin switches under the bonnet and boot which are connected to the “Immediate Sense” circuit of the alarm and a key switch as op­posed to the toggle switch included in the kit. When I arm the alarm with the key switch the LED doesn’t “continuously light” as described in the assembly instructions. But after the set exit delay period, the LED starts flashing to indicate the alarm is set. When I then open a door or the bonnet or boot to set off the alarm/horn siren, the LED continues to flash instead of turning itself off to indicate it is going to sound the horn siren. However, the horn siren fails to go off at all. The LED continues to flash and switching the keyswitch to “disarm”, fails to have any effect on the LED (and obviously the alarm as well) and the only way to turn it off is to push in the door pin switch of the open door. So it appears I can arm the alarm (sort of) but not disarm it. (J. C., Melbourne, Vic). • As far as we can tell from your description, IC2 and the LED are operating normally. The LED does not start to flash until after the exit period. We suggest that you carefully check the voltages around the circuit and also 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.avico.com.au January 1996  93 Door minder is insensitive I have recently assembled the “Door Minder” kit as pub­lished in the July 1995 issue of SILICON CHIP. I find that it is not very sensitive and it only works in a small room with the windows shut and if I give the door a hefty pull. I would be most grateful if you could tell me how to make it more sensitive; the preset pot is adjusted to the most sensitive it will go. The article says it works with open windows in an adjoining room. Also, where can I purchase the Philips ETD49/25/16 trans­former components and the TEA100 nicad monitor IC for the Fast Nicad Charger, as published in the September 1995 issue? I refer to the letter on page 7 of the April 1995 issue, on making PC boards by photocopying the original back to front and rubbing with thinners mixture on the back. I have had limited success and find it is best if the photocopy is removed whilst still moist. I say moist and not wet, as too much thinners gets underneath and smudges the pattern. When dry, doing it a second time darkens the picture but use a fresh, new photocopy. monitor the output of IC1 to see that it delivers the correct signal from its output in re­sponse to the arm/disarm switch. How to reduce preamp gain I recently put together the preamp section of your 50W amplifier design and find it very satisfactory. My amplifier and speakers are of very high sensitivity so I need much less gain than is provided. Would you please advise the correct way of changing the feedback components around IC1 to achieve closer to unity gain? I prefer to do this rather than use atten­uators. (K. A., Moss Vale, NSW). • The gain of IC1 can be reduced by increasing the 4.7kΩ resistor at pins 6 & 2. To halve the gain, increase the 94  Silicon Chip However, the result produces a porous copper surface which has to be heavily layered with solder. An improvement can be made by going over the whole pattern with a fine felt tip pen which is water resistant. (D. S., Caloundra, Qld). • We are surprised that your Door Minder is so insensitive. You should check that the 0.1µF and 1µF capacitors on IC1a’s input are the correct values and that the 1µF capacitor is inserted with the correct polarity. Also confirm that the two resistors around IC1a are 47kΩ and 3.9MΩ – a wrong value may have been fitted. Also, did you ground the case of the electret insert? Check that the regulated DC is about 8V and the voltage on pin 1 of IC1a is 3.3V. As the circuit has a gain of 80 it only needs 10mV from the microphone to trigger the chimes. It should not be necessary to increase the gain of the circuit, as it is quite adequate. Perhaps the microphone insert is faulty. You can get some extra gain by decreasing the 47kΩ input resistor to 39kΩ but any more variation could alter the passband of the filter. Regarding the parts for the Fast Nicad Charger, these can be purchased from Jaycar Electronics. 4.7kΩ resistor to 10kΩ. To obtain unity gain, omit the 4.7kΩ resistor. Frigid remote control won’t respond I have just built the UHF remote switch from the December 1989 issue of SILICON CHIP. It is operating perfectly from a distance of 10 metres but only when the temperature is over 20°C. Can you advise how to overcome this problem as the temperature in Victoria is generally under 20°C. (P. L., Spring­ vale North, Vic). • Ever thought of moving to warmer climes? It appears as though one or more of the transistors or possibly one of the ICs is temperature sensitive. As a first step, we suggest you check all voltages in the circuit. Second, check all soldering on the PC boards. Cold solder joints can be temper­ature sensitive. Third, with a can of freezer spray, freeze each semiconductor component to see if it causes the problem. Alterna­ tively, replace the transistors one by one to see if you can effect a cure. Extended leads for a digital thermometer Recently, I bought a digital thermometer with indoor/outdoor display from Jaycar (Cat QM-7210). I intended to extend the outdoor twin lead by a further 12 metres to enable the probe to be sited in the foliage of a bushy tree for a genuine outdoor reading. Doing this increased the leads’ total resistance by about 0.3Ω which, in turn, increased the readout figure by 7°C. I tried counteracting this by adding 0.3Ω in parallel with the probe but then the readout for this probe disappears. I cannot see any internal adjustment to compensate for extra lead length. Have any readers had similar experience along these lines? (M. B., Taree, NSW). • We doubt whether the additional resistance in the probe leads has caused the increase in temperature reading. We are more inclined to think that the long leads may be picking up hash which is adding to the reading. Try connect­­ing a 0.1µF green­cap or MKT capacitor across the probe leads where they enter the case. Note & Errata Dolby Pro Logic Surround Sound Decoder, Pt.1, November 1995: the anode of diode D12 is shown incorrectly joined to the junction of the cathode of D14 and an associated 10kΩ resistor. Instead, D14 and the 10kΩ resistor should connect directly to pushbutton switch S7. Dolby Pro Logic Surround Sound Decoder, Pt.2, December 1995: the resistor connected to pin 21 of IC2 is marked “30O” on the layout diagram (Fig.4, p71). The correct value of this resistor is 30Ω. Five-Band Equaliser, December 1995: the supply pins for IC2 on the circuit diagram (Fig.5, p24) are shown reversed. Pin 4 should go to the +15V rail, while pin 11 should go to -15V. The parts layout diagram (Fig.6, p25) SC is correct. MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. FOR SALE BUSINESS FOR SALE: electronic service and repair business for sale in the fastest growing inland city in NSW. Plenty of fresh air, sunshine and country hospitality. At present servicing mainly audio gear, specialising in car audio. Service agent for leading car audio brands. Regular, wide customer base. Plenty of room to expand 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. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ in premises and business, including into retail. Good lease available. This business is offered for genuine urgent sale due to the owner’s ill health. Price $45,000 WIWO. Enquiries phone (068) 84 1158. MicroZed are supplying BS2 upgrade kits free with purchase of BS2 and carrier, regardless of where you bought your legit BS1. Proof of purchase required. NEW SPRINKLER CONTROLLER KITS: RAIN BRAIN version uses ‘C8 and switch mode supply. Features galore!! Contact Mantis Micro Pro­ducts, 38 Garnet St, Niddrie 3042. Phone/fax (03) 337 1917. EDUCATIONAL ELECTRONIC KITS: Easy to build. Guaranteed to work. Good quality. Latest technology. Cheap. Good selection. LESSON PLANS FOR TEACHERS. Send $2 stamp for catalogue and price list. Log onto our bulletin board for full details. DIY Elect­ ron­ ics, 22 McGregor St, Numurkah 3636. Ph/Fax (058) 62 1915. E-Mail: laurie.c<at>cnl.com.au BBS (058) 62 3303. SATELLITE DISHES: international reception of Intelsat, Panamsat, Gorizont, 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. ❏ Bankcard   ❏ Visa Card   ❏ Master Card ✂ Enclosed is my cheque/money order for $­__________ or please debit my RCS RADIO PTY LTD Card No. Signature­­­­­­­­­­­­__________________________ Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ 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 January 1996  95 MicroZed Computers Specialist in controllers with on-chip interpreters Boards, Software, Chipsets, Books. Easy to learn. Fast prototyping Low cost. Chipsets available for volume production Easy to use – get going in hours, not months Raw PIC chips available too, JW & OTP Send 2 x 45c postage stamps for information package. PO Box 634 (296 Cook’s Rd), ARMIDALE 2350. Ph (067) 722 777       Fax (067) 728 987 Mobile (014) 036 775 Advertising Index BASIC Stamp I 8 I/O; and BSII 16 I/O Altronics ................................ 66-68 Scott Edwards Electronics Av-Comm................................64,65 Accessories for Stamp and second source for Stamp I Avico Electronics.........................93 Versa Tech Car Projects Book....................OBC TICkit – a 21 I/O PIC based controller NEW Micro 68HC11 F1 boards with resident FORTH. Other languages supplied, ASM. Small C & BASIC Dick Smith Electronics........... 18-21 Harbuch Electronics....................65 Instant PCBs................................96 Jaycar ................................... 45-52 MEMORY * DRIVES * MODEMS SPECIAL! (Incl Tax) 1Mbx9 – 70ns Simm $60 1Mbx9 – 80ns Simm $45 SIMMS (Parity/No Parity) 4MB 30 PIN-70 $179 $185 4MB 72 PIN-70 $177 $148 8MB 72 PIN-70 $353 $303 16MB 72 PIN-70 $695 $605 32MB 72 PIN-70 $1389 $1210 EDO SIMMS 4MB (1Mbx32)-70ns $198 8MB (2Mbx32)-70ns $370 MAC 8MB P’BOOK $437 VIDEO MEMORY 256KX16 70ns (SOJ) $24 256KX16 70ns (ZIP) $58 Kits-R-US.....................................64 L & M Satellite Supplies.................3 LASER PRINTER MEMORY HP 2MB UPGRADE $156 CO-PROCESSORS 80387SX/DX to 40MHz $90 COMPAQ 8MB CONTURA AERO $445 TOSHIBA PORTEGE/SATELLITE 8MB / 16MB $650 / $1218 DRIVES SEAGATE 850MB EIDE 11ms 3yr $325 1080MB EIDE 10.5ms 3yr $360 2150MB SCSI 9ms 5yr $1033 MODEMS (Includes Sales Tax) 14,400 BANKSIA 5yr W $283 14,400 SPIRIT 2yr W $203 28,800 BANKSIA V.FC $321 28,800 SPIRIT V.34/V.FC $410 Phone for other products not listed EX TAX PRICING AS AT JANUARY ‘96 MicroZed Computers...................96 Oatley Electronics...................... 8-9 Pelham........................................96 Railway Projects Book...............IFC RCS Radio ..................................95 Resurrection Radio......................89 Rod Irving Electronics .......... 35-39 Scan Audio Pty Ltd Silicon Chip Bookshop.................85 PELHAM Ph: (02) 9980 6988 Fax: (02) 9980 6991 Suite 6, 2 Hillcrest Rd, Pennant Hills, 2120. ETI PIC Basic Interpreter: BASIC57/ XT/P $45, BASIC84/04/P $45. 2K EEPROM $8, 8K EEPROM $16. PC serial port driven. 18 and 28-pin PCB $20, 4MHz Xtl $5. Windows Software free. InfoFax: Voice then Fax, (03) 9338 2935 Password ‘# 1111’. Don McKenzie, 29 Ellesmere Crescent, Tullamarine 3043. Phone (03) 9338 6286. 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 96  Silicon Chip Scan Audio..................................96 Silicon Chip Back Issues.............90 Sales Tax 22%, O/Night Delivery $8. Ring For Latest Prices. Credit Cards Welcome. We Also Buy And Trade-In Memory. Silicon Chip Walchart.................IBC _________________________________ PC Boards Printed circuit boards for SILICON CHIP projects are made by: $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. 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. C COMPILERS: Dunfield compilers are now even better value. Everything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC16, 8051/52, 8080/85, 8086 or 8096: $140.00 each. Macro Cross Assemblers for these CPUs + 6800/01/03/05 and 6502: $140 for the set. Debug monitors: • RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 587 3491. • Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730. $70 for 6 CPUs. All compilers, XASMs and monitors: $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. HC11s AND ICs - http://worf.albany­is. com.au/bobhome.html. SOUND TECHNOLOGY 3100A/3200A programmable transmission/audio test system, operating manual, $9500. (03) 9499 1524.