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SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. The advertiser is no longer in business: www.optionalpower.com.au Contents Vol.13, No.5; May 2000 FEATURES 4 What’s Inside A Furby? A lot of smart electronics, that’s what. We peel back the fur and take a peek inside. And if you want to start hacking, there’s lots of web sites to look at – by Julian Edgar 34 Dolby Headphone: Five Channels Of Surround Sound Just how do you get five channels from normal stereo headphones? An Australian company, Lake Technology Ltd, made it happen – by Leo Simpson Building The Ultra-LD Stereo Amplifier – Page 16. PROJECTS TO BUILD 16 Building The Ultra-LD Stereo Amplifier; Pt.2 It fits nicely inside an ATX computer tower case, complete with a fan-cooled tunnel heatsink plus selector switch and volume control – by Leo Simpson 56 Build A LED Dice A PIC microcontroller makes the circuit really simple. We tell you how it was designed and show you how to build it – by Doug Jackson 72 A Low-Cost AT Keyboard Translator This low-cost project takes the complex scan codes from a PC keyboard and spits out standard ASCII codes. It’s just the shot for use with the BASIC Stamp and PIC series of microcontrollers but has lots of other uses as well – by Steve Carroll & Bob Nicol LED Dice – Page 56. 78 50A Motor Speed Controller For Models It fits in a tiny plastic case, can handle motor currents up to 50A and is compatible with existing radio control gear – by Ross Tester & Branco Justic SPECIAL COLUMNS 40 Serviceman’s Log When is a fault not a fault – by the TV Serviceman 64 Vintage Radio Keyboard Translator – Page 72. Making the obsolete useful again – by Rodney Champness DEPARTMENTS 2 10 33 53 Publisher’s Letter Mailbag Subscriptions Form Product Showcase 85 90 94 96 Electronics Showcase Ask Silicon Chip Market Centre Advertising Index 50A Motor Speed Controller – Page 78. May 2000  1 PUBLISHER’S LETTER www.siliconchip.com.au Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Production Manager Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Peter Smith Ross Tester Rick Walters Reader Services Ann Jenkinson Advertising Enquiries Rick Winkler Phone (02) 9979 5644 Fax (02) 9979 6503 Mobile: 0414 34 6669 Regular Contributors Brendan Akhurst Louis Challis Rodney Champness Garry Cratt, VK2YBX Julian Edgar, Dip.T.(Sec.), B.Ed Mike Sheriff, B.Sc, VK2YFK Philip Watson, MIREE, VK2ZPW Bob Young 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: Hannanprint, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $69.50 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 8, 101 Darley St, Mona Vale, NSW 2103. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9979 5644. Fax (02) 9979 6503. E-mail: silchip<at>siliconchip.com.au ISSN 1030-2662 * Recommended and maximum price only. 2  Silicon Chip Do-it-yourself amplifiers: a new approach This month we have taken quite a different approach to the construction of a high-performance amplifier, starting on page 16. As indicated in the March 2000 issue, we have housed the amplifier in a computer case rather than a conventional amplifier chassis. We have taken this approach for two reasons. First, custom metalwork for large projects like stereo amplifiers is now quite expensive and is the major cost in a kit for a project like this. Second, there are tens of thousands of computer cases going begging as people upgrade to ever faster machines. These computer cases are often beautifully made and I hate the thought of them being wasted, as so many of them are. Admittedly, we did not actually recycle a case for this project because we decided that the case we had in mind was a bit tatty and might not photograph all that well. But I hope you will agree that the finished project really does look the part and shows what can be done. Of course, if you don’t like the idea of a beige computer case, you can always check the spray paint shelves at your local auto accessory shop – fancy a metallic gold finish? By the way, I apologise to all those readers who were disappointed about the article not appearing in April but the sheer size of the article and the number of detailed diagrams prevented it happening in time. I hope you find that the wait was worthwhile. If you have comments on the presentation, don’t hesitate to drop us a line, by email or conventional mail. The Dolby Headphone story Another unusual story in this month’s issue is the feature on Dolby Headphone. When I first read about Dolby Headphone it sounded like an April Fool story, except that it wasn’t April. Until you hear the simulation of five channels of surround sound on headphones it is just not possible to conceive that it works but it certainly does. The really gratifying aspect of this story is that the whole process was developed by a small Australian company, Lake Technology Ltd, based in Sydney. And not only have they licensed the concept to Dolby but they have taken it to the airlines as well and if you travel overseas on Qantas or Singapore Airlines you will experience recent release movies with Dolby Headphone surround sound – a big feather in their caps. In fact, this story gives the lie to the recent softness in the Australian dollar which has been ascribed to overseas curren­cy dealers regarding Australia as an “old economy” not strong in new technology. What rubbish! These people wouldn’t know where to look when it comes to old or new technology and they are just not aware of how Australian companies are “punching well above their weight” on world markets. And when it comes to companies adopting new technology to obtain productivity benefits, Australian companies are generally far ahead of their counterparts in the USA or Europe – but the currency dealers wouldn’t know about that! Leo Simpson    PS/2 Keyboard & Mouse Adapter Turns your laptop into a desktop with a single, pocket size adapter. It allows the use of a keyboard and a mouse from a single port! Cat. 15093 Cat. 15094 PS/2 Keyboard & Mouse Adapter USB Keyboard & Mouse Adapter $179 $149 Dual PS/2 Mouse Adapter Use 2 Pointing Devices from 1 PC ! Left and right handed mice, trackballs, touch pads, etc. Each has its strengths. Now you can maximize your computing experience by connecting your two favourites and switching instantly between them as you work. Cat. 15090 Dual PS/2 Mouse Adapter $119 Dual Keyboard Adapter Need input from two locations or need a specialized and standard keyboard? Here is the answer! Cat. 15091 Dual PS/2 Keyboard Adapter $119 Dual Monitor Adapter The best way to attach two monitors to one computer. Not only does this adapter split the (S)VGA video signal, it boosts it for optimum image quality. It will support resolutions up to 1280 x 1024 and up to 32-bit color (4 billion colors). Perfect for presentations - use one monitor for the presenter and the other for the audience. Cat. 15092 Dual Monitor Adapter $229 Point-of-Sale GST Bundle Our Point of Sale bundle includes a Citizen parallel printer (as required by Digitill & Attache) or a Citizen serial printer (required by QuickPOS), a cash drawer and our very popular CCD bar code scanner. The printer (Cat 5667) connects to a parallel port on a PC, while the printer (Cat. 5668) connects to the serial port on a PC. The cash drawer (Cat 8897) connects to, and is triggered from the printer. Finally, the CCD scanner (Cat 8196) connects between keyboard and computer. Cat. 8903 Point-of-Sale GST Bundle - Digitill/Attache $879 Cat. 8902 Point-of-Sale GST Bundle - QuickPOS $879 Web-Based Training - Unlimited access to all courses in Group 1 from only $14.95 per month* New courses now available! Including Windows 98, Quicken 98, Lotus Notes, Internet Tools (Netscape) and more courses on TCP / IP. *Full details at www.tol.com.au Compact Keyboard Now over 300 courses to choose from Bar Code Laser Omni-Direct. Serial Cat. 8573 $2119 POS Customer Display When desk space is at a premium an 80 key keyboard with full 101 key functionality will come in handy. It has dimensions of only 297(W) x 152(L) x 30(D) mm. This POS customer display is driven from the serial port and has a vacuum fluorescent display with Compact 80 Key PS/2 Cat. 8403 $73 two lines of 20 characters. It is ergonomically designed with a 55 Key Programmable POS Keyboard 270 degree viewing angle . Our top of the line POS keyPOS Customer Display Cat. 8728 $369 board featuring very robust POS Touch Systems & Peripherals construction, compact size, Get ready for GST! Start with a down loadable key assigncompact all-in-one terminal with ments (eg switch menus), 12.1” TFT colour touch screen multi-level programming, ability to download entire 55 key and add the peripherals you template into internal non-volatile memory in 7 secs!, keyneed to customize your requireboard wedge interface with optional RS-232 interface and ments. The basic system coninternal 2KB non-volatile memory. 55 Key POS Keyboard Cat. 8356 $309 sists of a Pentium motherboard with 133MHz MMX CPU, 16MB RAM, 4 serial ports, 2 parallel ports, 2 Hi- Scan Bar Code Readers USB ports, VGA port, cash drawer port, 10Base-T High resolution CCD scanners Ethernet port, 1 free PCI slot, KB/mouse. which feature multi-interface POS Touch System Cat. 8755 $4,490 communication with RS-232C, & Optional add-ons include a magKeyboard Emulation in one unit. netic card reader, a magnetic ISimply release the RJ-45 jack to Button reader with 5 operator keys change cables! Offering optical performance with a minium for security access, an external resolution of 0.125 mm & maximum reading distance of 20 FDD kit, Customer Display & cash drawers. mm they can read high-density, laminated & acrylic-covered Cat. 8756 POS Touch System MCR Track 2 $299 bar codes. Magnetic I-Button Reader /5 keys Cat. 8757 $190 Cat. 8458 / 59 Hi Scan Bar BCR KB Wedge AT or PS/2 Cat. 8489 / 8704 Cat. 8675 CCD BC Scanner Long Range KB AT or PS/2 CCD BC Scanner Long Range KB Stand Cat. 8758 $469 $69 Intelligent Network tester with LCD Display As well as our standard range. Cat. 8196 CCD BC Scanner KB Wedge 80mm $259 Or pick from our Manual / Auto Trigger laser range. Cat. 8770 / 8767 Cat. 8771 Cat. 8772 Laser BCR Gun KB Wedge AT or PS/2 Laser BCR Gun Serial Laser BCR Gun Stand External FDD Kit $699 Also available, Long Range CCD bar code scanners. $599 $599 $35 Omni-Directional Laser Scanner An intelligent continuity tester for LAN cables that saves time on the job. It tests a range of Modular cables including 10Base-T (Category 3-5). Four numbered remote terminators allow testing, tracing and identification of in situ cables. The LCD display shows the pin connections as well as the wiring scheme detected. An affordable, vertically mounted, OmniDirectional laser scanner, suited to reading bar coded products at supermarket checkCat. 11518 outs. Depth of field is 300mm. Cat. 11519 Cat. 8521 Bar Code Laser Omni-Direct. KB Wedge $1999 $219 E & OE Intelligent Network Tester Network Tester with LCD $229 $239 All prices include sales tax MICROGRAM 0500 Come and visit our online catalogue & shop at www.mgram.com.au Phone: (02) 4389 8444 Dealer Enquiries Welcome sales<at>mgram.com.au info<at>mgram.com.au Australia-Wide Express Courier (To 3kg) $10 FreeFax 1 800 625 777 We welcome Bankcard Mastercard VISA Unit 1, 14 Bon Mace Close, Berkeley Vale NSW 2261 Vamtest Pty Ltd trading as MicroGram Computers ACN 003 062 100 Fax: (02) 4389 8388 Web site: www.mgram.com.au FreeFax 1 800 625 777 There’s a lot of smart electronics INSIDE A FURBY There’s some very smart electronic technology hidden beneath the cute fur-covered exterior of a Furby. So let’s peel back the fur and take a look at what’s inside. in response to the preferences of the child who owns it. Yes, the Furby can adaptively learn! Throw in a spoken vocabulary of 160 words (capable of being incorporated into no less than 1000 different phrases), the ability of Furbys to automatically communicate with one another via an inbuilt infrared port and then consider the retail cost – around $69 in Australia and just US$30 in the United States! It’s state-of-the-art in a very unassuming package indeed. By JULIAN EDGAR The Furby is a fur-covered pseudo-animal with fixed feet and a movable mouth, ears, and eyes. In addition, the Furby can rock forward on its base platform. The movable parts of the toy are mechanically driven by an internal electric motor (more on this in a moment) which The subject of a child’s toy might seem to be a strange choice for an electronics magazine like SILICON CHIP. But as you’ll soon see, it isn’t. Packed inside a Furby’s 130mm-high furry body is an amazing complexity of mechanical and electronic components – and software. Unconvinced? How’s this then – the software boasts the ability to actually change the toy’s output behaviour 4  Silicon Chip The toy TOP OF PAGE: Furbys come in different colours but internally they are all the same. A smart package of electronics and mechanicals, the Furby shows that not all electronic advances are confined to the esoteric. Furby, stripped of his furry coat and internal plastic carapace. Located between the eyes are the light sensor (centre) and a pair of infrared transmitter and receiver LEDs. Furbys can automatically communicate with one another via this infrared link. operates the eyelids, opens and closes the mouth, and waggles the ears up and down. Also hidden under the fur are press-switches on the front and back and a switch inside the mouth that is triggered whenever the mouth is opened manually. A big factor in the toy’s success is its language skills, with an internal speaker able to clearly communicate “spoken” words and phrases. There are also additional inputs and outputs but more about these later. A short description of the toy doesn’t do it justice; it is the way in which it works which is so interesting. For example, as I write, my Furby (yes, I bought one as part of the research for this story!) is “asleep”. How do I know? – well, it made snoring noises, then rocked forward and closed its eyes. Loud noises or changes in light or other stimuli will not wake it. To rouse the beast, it must be picked up and tilted to trigger an internal tilt switch. By the way, early Furbys were apparently much harder to put to sleep, requiring a certain sequence of events including lots of pats on the back. However, Furby manufacturer Tiger There are entire websites devoted to Furbys and hacking techniques. One of the best is “Blank Frank’s Furby Stimulation Page” at www.veg.nildram.co.uk/furby.htm This photo shows just how jam-packed Furby is inside. A semicircular PC board is located just above the battery box, with the mechanical module mounted on top of that. The sound-sensing microphone is hanging on its lead closest to the camera. Electronics Ltd changed the design, fearing a backlash from exasperated parents. Furby doesn’t have an on/off switch, you see. As an example of its behaviour, I have just picked up This website at http://www.geocities.com/SiliconValley/ Pines/7438/furby.html includes a program that lets you record, save and play back a Furby’s infrared signals. May 2000  5 In this view, the horizontal axis camshaft can be seen, with plastic cranks moved by the cam lobes connecting to the eyes, ears and mouth. The cam position switch is located in the middle of this picture, with the reset switch at the bottom. The wiring harness is held in place with many globs of hot-melt glue. the toy and it has said “Mmmmmmm, me love you”. However, the last time I roused it from its sleep, it said “Sun’s up”. This lack of predictability in response to stimuli lifts the personality realism to a totally different plane compared to most toys. When woken it may have alternatively said, “Me sleep again” or “Cock a doodle do, big light”! Or it might have sneezed, giggled, or made one of many other sounds. Each Furby picks its own name from its available list of sounds (mine says “Me Too Loo”) and individual Furbys have differently pitched voices. If left unstimulated for a few minutes (no noises, no changes in light intensity, or no switches pressed), a Furby will sometimes say “Mmmmm – boring!”. If still ignored, it will go to sleep. When taken for a ride in a car, a Furby will say “Wheeeeee!” whenever the car corners and suggest that it wants to play hide and seek when the intensity of the light suddenly changes. Holding it upside down will initially provoke giggles, changing sometimes to “I’m scared” if it is held in this position for too long. Games There are several games built into the toy. For exam6  Silicon Chip ple, to place a Furby into the “Hide and Seek” mode, the light sensor located between the eyes needs to be covered and uncovered three times and then the front pressure switch activated (“tummy tickled” in Furby-speak). The beast then needs to be hidden within a minute, following which it will be quiet for three minutes. Once this time has elapsed it will start saying “nah, nah, nah” at intervals until it is found. When batteries are first inserted into it, a Furby speaks no English words or phrases. Instead it speaks in “Furbish” and a dictionary with 44 entries lists the English translations. However, after a few hours of stimulation, the toy starts to speak some English and after a day or two, it speaks mostly English. Note, however, that English words are not actually being learned; instead, it would appear that after Furbish phrases and words have been “spoken” a set number of times, that word or phrase is replaced by English. The developmental stage that the Furby has reached is maintained when the batteries are changed. However, there is a reset mechanism that can be activated to return a Furby to infanthood! If a Furby initiates a pattern of behaviour (for example, it makes kissing sounds when the front “tickle” switch is activated), patting it on the back (ie, activating the rear switch twice) will reinforce this behaviour. Consequently, individual Furbys can adopt slightly different behaviours on the basis of their owner’s preferences. So you can see that, from a child’s perspective, a Furby is a very attractive toy indeed. It has a distinct personality (sometimes with negative character traits like belching and breaking wind!), initially has its own language but soon learns English, and has its own demands – if it isn’t fed, a Furby becomes ill and sneezes a lot. It’s easy to see why Furbys have become so popular. The mechanicals As mentioned earlier, an internal motor is used to drive the movable parts of a Furby. This reversible DC motor is mounted to one side of a “movement module” which is positioned inside the top half of the toy. The motor drives a series of reduction spur gears which rotate a worm drive. A 40mm diameter speaker is used. It is capable of quite clear reproduction. The worm drive, in turn, acts on a large cog attached to a shaft which has series of cam lobes. These lobes bear on connecting rods that move the eyelids, mouth and ears and rock the Furby backwards and forwards. Rotating the shaft in a single direction causes each moving part to be operated in sequence. However, because each movable item has its own cam and they are each arranged such that their lobe centre angles do not overlap one another, each movable item can be operated independently if the camshaft is rotated back and forth within a narrow rotational angle. For example, during “dancing” (where the Furby rocks back and forth), the shaft is rotated so that only the rocking motion lobe is operated. This position of the camshaft behaves as a “dead spot” for the lobes that drive the eyelids and ears – so during dancing, the eyes and ears stay still. Because the main worm drive cannot transmit torque in the opposite direction (eg, the motor cannot be turned by moving the ears), a slip mechanism is built into each movable body part. This allows these parts to be manually moved without causing damage. The motor uses sprung copper leaves to transfer power to the commutator. Carbon brushes aren’t used – instead there appears to be some type of conductive grease spread over the relevant area. This probably explains the strong “electric motor” smell that occurs if the toy has been operating continuously (eg, by being held upside down) for some time. The main PC board contains most of the electronic circuit-ry. The position sensor is at top-left, while two daughter boards (each with a custom COB microprocessor) are located at left. The electronics comprises a main, double-sided PC board with surface mount and conventional components on it. Additionally, there are two small daughter PC boards mounted on the main board at rightangles, each carrying a custom COB microcontroller. Serial data is transferred between these two microcontrollers, which are run at 3.58MHz. A 1K 93C46 non-volatile EEPROM is mounted on the main board and this probably contains Furby’s name, developmental state and adaptive memory. It would appear that a separate chip is solely responsible for generating the sound output – perhaps this approach has been taken to allow easy implementation of Furbys that speak other languages. The system’s inputs and sensors are as follows: (1) A reset switch (located adjacent to the battery compartment under the toy); (2) A back switch (senses back pats); (3) A front switch (senses tickling); (4) A cam position sensor (consists of a small leaf switch); (5) A gear speed sensor consisting of a LED which shines at a receptor through four slots cut in a black plastic gear; (6) A ball tilt switch (used to detect level, tilt and upside down orientations); (7) A light sensor positioned behind a panel between the eyes; (8) An infrared receiver LED (positioned near the light sensor); and (9) A feed sensor consisting of a microswitch behind the mouth. The outputs are as follows: What do you do if your Furby “dies”? Tie a toe-tag to him and conduct a thorough autopsy of course. You can find out the cause of Toh Loo-Kah’s untimely death on http:// www.phobe.com/furby/cause.html Furby includes an infrared port for communicating with other Furby’s and can often be tricked into responding to IR remote controls. There’s lots of information on this at http://www.homestead.com/hackfurby/files/FURBYIR.html The electronics May 2000  7 while a pair of diodes is used to provide 5.3V and 4.8V rails for the rest of the circuitry. Infrared communications The microprocessors are “blob” types, custom-made for this application. With the Furby manufactured literally by the million, this approach is very cost effective. The small reversible DC motor works hard for its living; if the toy is used for extended periods a strong “electric motor” smell is emitted! (1) A loudspeaker (40mm diameter with clear plastic cone); (2) An infrared transmitter LED (positioned near the light sensor in the forehead); and (3) Motor forward and reverse operations. The motor is driven at battery voltage (6V nominal) One interesting aspect of the toy is its ability to use infrared transmissions to communicate with other Furbys. Furbys can normally communicate with each other when placed in close proximity, although my sample Furby steadfastly refused to communicate with another Furby whose access was arranged for just that purpose. Apparently, they are capable of transferring colds (the healthy Furby starts to sneeze as well) and developmental stages – a Furby can speak more English after being in contact with a more advanced Furby! For the hackers, the infrared port also allows another pursuit – fooling Furby into doing odd things by stimulating it with foreign infrared signals! IR-emitting devices that people have used for confusing Furbys include PC IRDA ports, purpose-built standalone Furby IR transmitters, the Palm III handheld computer with OmniRemote software, TV and VCR remote controls and even a Nokia 9110 mobile phone! If you want to find out how to do this, refer to the websites listed at the end of this article – that’s right, there are entire websites devoted to Furbys and hacking techniques. Take a look at “Blank Frank’s Furby Stimulation Page” (www.veg.nildram.co.uk/furby.htm), for example. Among other things, he shows you how to control a Furby using a computer’s IRDA port. What, no IRDA port? Blank Frank’s got that covered as well, with a simple circuit that you can build yourself. For the technically-minded, Furbys communicate using IR pulses approximately 150-200ms wide with a bit time of 2ms. The communication packets consist of nine bits sent six times, with silence between each set of nine bits, giving a repeat rate of about 100ms. The nine bits consist of a start bit, four data bits and then the same four data bits inverted. There are 16 different signals that can be communicated. Conclusion A few years ago a self-learning toy that talked, communicated “intelligently” with other toys of the same type and contained internal software that gave a very real sim-ulation of “personality” would have been the stuff of dreams – especially at this price! It shows that not all SC electronic advances are confined to esoteric areas. There’s Lots More Info On The Furby On These Websites Much of the information for this article was derived from the many websites devoted to the history, dissection, hacking and electronics of the Furby. These sites include: (1) http://www.veg.nildram.co.uk/furby.htm (2) http://www.blueneptune.com/~maznliz/marius/furby.shtml (3) http://www.geocities.com/SiliconValley/Pines/7438/furby.html (4) http://ai.tqn.com/compute/ai/library/weekly/aa101398.htm (5) http://www.wired.com/wired/archive/6.09/furby_pr.html (6) http://www.homestead.com/hackfurby/files/FURBYIR.html (7) http://freeload.homestead.com/_ksi0701961574651052/hackfurby/files/furby.pdf (8) http://www.phobe.com/furby/faq2.html 8  Silicon Chip May 2000  9 MAILBAG Computers should be turned off I agree with your Publisher’s Letter in the January 2000 issue on the issue of turning computer equipment off. Running at elevated temperatures reduces the lifetimes of equipment. In fact I thought that the manufacturers establish the MTBF of new equipment by running a sample of units at elevated temperature, noting the failure rate and extrapolating the expected lifetime from that data. I have dimmers installed on several of my room lights at home and I rarely have the lights up full and the light bulbs rarely blow. I was once told that if you run an incandescent light at about one third of its rated voltage its lifetime is indefinite. Equipment often fails at turnon but that doesn’t mean that it failed solely due to power cycling. Sure, the final power-up broke the camel’s back but not without the effects of ageing accumulated through various means. Just last year I was asked to repair the power supply of a work-station that had not worked after a power down. It was fairly old and inspection showed that the filter capacitor in the switcher was as dry as a bone; in fact, the can rattled on its innards. This did not occur through power cycling; it was caused by years of running in a hot environment and when the unit was eventually switched off, it couldn’t handle the stress of being turned back on. I always turn my PCs off if I am leaving the house for more than 30 minutes and when I go to bed. Nor do I leave my PC on at work when I go home. At the same time I don’t think it is good to be cycling the power unnecessarily, so if I am working on a PC that I have to power up and down frequently I try to connect the monitor so it is always on. I also reckon it is false economy to turn the room lights off but leave the computer on, as 10  Silicon Chip most PCs use more power than the lights. If a PC is not going to be used overnight then it should be turned off. Another issue with PCs left running is the fan. The bearings tend to dry out and seize, then the temperature can rise beyond the endurance of parts and they start dying. There is always a risk of fire when electrical equipment is left turned on. Just a few years ago I heard in the news of a woman who died in Melbourne in a house fire started by a faulty monitor. I expect that the risk of this is probably quite low, especially with equipment made by reputable manufacturers, however we should not ignore the consequences. In the end we need to strike a balance: we need to get good lifetime from the equipment and we need to not waste energy for several reasons. I think that if you turn your PC on you should leave it on for an hour, and if you are not going to use if for a couple of hours, then turn it off. One should also bear in mind that on hot days a PC would make the room less comfortable but it can help warm a cold room in winter. Stipulating that PCs should be left on all the time is a simplistic approach; one that can prove fatal in extreme cases. P. Denniss, Sydney, NSW. Neons don’t like the dark I noted the letter in “Ask Silicon Chip” in the April issue about an electric fence tester which works only when there is some ambient light. For some time now, I have been intending to write a short note about this problem, or rather the basis of it. When we moved to our present address, in late 1966, there were no street lights. I was working night shift and noticed that sometimes the fluorescent light in the bathroom failed to light until I turned on a battery-powered torch. Eventually, I came to recognise that it was only under very dark conditions that the fluorescent light failed to strike. Later, I noticed that the neon indicator on the controller for an electric blanket showed much the same phenomenon. The blanket was a commercially-produced device with a “thermostat” and a neon indicator which should have lit whenever power was switched through to heat the blanket. In this case, the neon indicator did not glow at first (sometimes) but lit normally after a few minutes. At first I suspected a loose connection, such as a dry-soldered joint, but eventually came to the conclusion that it was similar to the problem with the fluorescent light. My younger son has been an electronics engineer for quite a few years and when I mentioned the two examples above, he was able to relate it to a machine he had to fix. It used a neon lamp as part of a timer circuit. After he had made the necessary repairs, the control was adjusted to the desired time and everything worked OK until the covers were replaced. This caused the time-out to change. After a few trials, he came to the conclusion that light was affecting the striking voltage of the neon gas discharge device. A. Brooks, North Mackay, Qld. Hot wire cutter can be simplified I just read the article on making a hot wire cutter in the April 2000 issue and I thought I’d let you know how I made mine; I think it’s a fair bit simpler. For the power supply I used a dimmable 12V lamp transformer. You can an usually buy a complete down-light kit for $20 at the hardware stores and occasionally a transformer on its own for $15. For the temperature control I used a standard lamp dimmer - I bought a dimmer, switch and switch-plate for $10 at K-Mart. For the cutter wire I bought nichrome resistance wire from Dick Smith Electronics. David Truett, via email. Switching off computers I read your January 2000 editorial about “turning computers off when not in use” and agreed totally. I was therefore astounded to read the letter of rebuttal in the Mailbag pages of the March issue. I completed an apprenticeship as a “Radio & TV Mechanic” and have spent the past 25 years repairing and designing new electronic equipment from consumer gear to industrial products and even pinball machines. I am flabbergasted that a person from a TAFE college can assert with total confidence that monitors will not catch fire. This is head-in-the-sand stuff. Actually my pet hate is cheap equipment with shonky switchmode power supplies and dubious mains wiring. This gear includes TV sets, computer monitors and VCRs. I have seen dozens of units that have either caught fire or were very close to doing so and this troubles me. When I build any piece of mains-powered equipment my first concern is that it is correctly wired, earthed and fused, according to good 240VAC practice. This seems to be little followed in some very popular and well known makes of consumer goods. I am sure that some house fires could be traced to dodgy TV sets running in “stand­by” mode”. To conclude, I agree 100% with your comments – “if it’s not being used, pull the plug”. Mike Kalinowski, via email. May 2000  11 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.dse.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.dse.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.dse.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.dse.com.au Building the Ul Stereo Amplifi In March 2000, we described the circuit of the Ultra-LD 100W amplifier module. In this article, we describe the construction of a complete stereo amplifier using two amplifier modules. It has input facilities for three program sources and a stereo volume control so no preamplifier is required. By LEO SIMPSON A S PRESENTED, this Ultra-LD 100W per channel stereo amplifier can be the basis of a very fine “no-frills” stereo sound system. You can plug in a CD player, tuner or tape deck and the selected program source is switched straight through to the volume control and then to the power amplifiers. This is equivalent to the “CD-Direct” mode on some stereo amplifiers. The Ultra-LD stereo amplifier takes the purist approach – no preamplifiers, no tone controls, no balance control or anything else to affect the signal quality before it goes to the power amplifiers. The result is the cleanest possible sound quality, rivalling that of the very best commercial amplifiers, regardless of price. In the “Publisher’s Letter” for the March 2000 issue we indicated our intention of building the new stereo 16  Silicon Chip amplifier into a computer case. In fact, we mentioned that we intended using a “clam-shell” desk-top computer case. Well, when we came to do the job we decided that the selected case looked a bit tatty and so we purchased a brand new ATX tower case for the princely sum of $66. This actually came with a power supply which is not needed for this project but which will be pressed into service elsewhere. Appearance aside, the clam-shell desktop case would have been adequate for the job but the tower case has substantially more room and has the bonus of slide-on top and side panels and effectively a sub-chassis inside with channels at the top and sides. These channels make it easier to tuck the mains wiring neatly away and the space between the sub-chassis and one of the side panels means that ltra-LD Ultra-LD fier Part 2 May 2000  17 they will be completely enclosed in the tower case and if you are playing music such as pipe organ at high levels, the dissipation can run as much as 50 watts per channel or more and this cannot be handled for more than a few minutes without forced air cooling. Very conveniently, just as we were going to press with the March 2000 issue, a neat tunnel heatsink extrusion to suit an 80mm fan became available from Jaycar Electronics and we elected to incorporate this into the design, as you can see. With the fan running at a low speed, the heatsink is very effective. Interestingly, 80mm heatsink tunnels now appear to be the standard cooling approach in 100W+ 5-channel home theatre receivers. All of the foregoing explains the assembly approach and also is the reason for the delay in presentation of this article which was originally intended for last month’s issue. Performance of stereo version The finished amplifier in the ATX computer case. If you really want to dress it up you could place a dress panel over the plastic in-fill panels and perhaps use much more upmarket knobs. Maybe you could spray the case champagne gold or . . . you can run wiring between them, for better shielding and a neater layout. Another bonus of buying a completely new case is that you get matching in-fill panels for the disk drive openings and this gives a neater finished appearance. In fact, we mounted the selector switch and volume control on one of the in-fill panels and the headphone socket on another. Using the tower case also gives more options in the way the power transformer is mounted although, 18  Silicon Chip as it turned out, that did not present a problem. As you can see from the photos, most of the power supply components are mounted on the base of the case. Fan cooling As part of our approach in using a computer case, it was always our intention to use a small fan to cool the heatsinks for the two amplifier modules. While normal running may not produce a lot of heat in the modules, We published a number of graphs which showed the performance of the prototype module in the March 2000 issue. However, for the stereo version we built two completely new modules and when they were finally installed in the tower case we ran the whole battery of tests again. It’s nice to confirm the results but in some instances the performance was even better with the new modules. Fig.1 shows the total harmonic distortion (THD) versus power at 1kHz when both channels are driven simultaneously into 8Ω loads. Power tops out (the onset of clipping) at just on 90W in both channels and you can see that one channel (right) was slightly lower in distortion at the higher powers. This measurement was taken with a bandwidth of 10Hz to 22kHz. Fig.2 shows the THD versus frequency for both channels driven into 8Ω loads at a power level of 90W. Here, one channel is slightly better at the midrange frequencies but it is higher in distortion at 5kHz and above. This is a result of the wiring layout. This is always a very careful compromise and here you will need to duplicate the power supply wiring details that we will discuss later in the article. The measurements of Fig.2 were taken with a bandwidth of 10Hz to 80kHz. Interestingly, Fig.2 stands up very well by comparison to our benchmark 15W Class-A amplifier when driven at 15 watts (see Fig.3, page 57, July 1998). We’re not going to claim the Ultra-LD stereo amplifier is better than the 15W Class-A design (that’s just not possible) but it indicates that the 100W amplifier is pretty good in this department. And of course, it has a great deal more power. Finally, Fig.3 shows the separation between channels across the frequency range from 20Hz to 20kHz, with both channels connected and alternately driven from the Audio Precision System One test set. This gives a result of better than -60dB over the whole audible spectrum for both channels. While this is a fair way short of the 90dB (typical) separation of a CD player, it is a good “real world” measurement, not the artificially enhanced result produced by the standard IHF-201 separation test. All other performance parameters of the Ultra-LD stereo amplifier are the same as published in the March 2000 issue. Now let us discuss the assembly of the amplifier module and then we will proceed to the power supply details and the rest of the amplifier assembly. Amplifier board assembly The component overlay diagram of the PC board is shown in Fig.4. Before starting the board assembly, it is wise to check the board carefully for open or shorted tracks or undrilled lead holes. Fix any defects before fitting the components. Start by inserting the PC pins and the resistors. When installing the 3.3V zener diode, make sure that it is inserted with the correct polarity. Also take care when installing the electrolytic capacitors to make sure that they are installed the right way around. Note that the 100pF compensation capacitor from the collector of Q8 to the base of Q7 should have a voltage rating of at least 100V while the 0.15µF capacitor in the output filter should have a rating of 400V. Another point to be noted is that if the amplifier is intended for continuous high power delivery at frequencies above 10kHz, then the 6.8Ω resistor in the output filter should be a wirewound type with a rating of at least 5W, otherwise it may burn out. Choke L1 is wound with 23.5 turns With the fan mounted at one end, this is what the two modules look like before they are mounted in the case. The inset shows how the two heatsink extrusions slide together to form a tunnel heatsink with the fins on the inside. May 2000  19 AUDIO PRECISION SCTHD-W THD+N(%) vs measured LEVEL(W) 10 28 MAR 100 16:42:57 AUDIO PRECISION SCTHD-HZ THD+N(%) vs FREQ(Hz) 5 1 1 0.1 0.1 0.010 0.010 0.001 0.001 .0005 .0005 0.5 1 10 100 200 Fig.1: total harmonic distortion (THD) versus power at 1kHz when both channels are driven simultaneously into 8Ω loads. The onset of clipping is just on 90W in both channels. This measurement was taken with a bandwidth of 10Hz to 22kHz. of 1mm enamelled copper wire on a 13mm plastic former. Alternatively, some kitset suppliers will provide this choke as a finished component. When installing the fuse clips, note that they each have little lugs on one end which stop the fuse from moving. If you install the clips the wrong way, you will not be able to fit the fuses. The 220Ω 5W wirewound resistors 20 100 Fig.2: THD versus frequency for both channels driven into 8Ω loads at 90W. can also be installed at this stage; they are wired to PC stakes adjacent to each fuseholder and are used during the setting of quiescent current. Next, mount the smaller transistors; Fig.4: the component overlay for the PC board. Note that the resistor feeding ZD1 has been changed to 2.7kΩ 5W wirewound. 20  Silicon Chip ) 28 MAR 100 20:19:46 AUDIO PRECISION SCCRSTK XTALK(dBr) & XTALK(dBr) vs FREQ(Hz) 0.0 28 MAR 100 20:45:48 -20.00 -40.00 -60.00 -80.00 -100.0 -120.0 1k 10k 20k 20 100 1k 10k 20k Fig.3: separation between channels across the frequency range from 20Hz to 20kHz. When you’ve finished assembling the first PC board and mounted it to the heatsink (see overleaf), it should look exactly like this! Now repeat the assembly procedure for the other channel . . . May 2000  21 Fig.5: the drilling and tapping details for the tunnel heatsink extrusions (not to scale). All holes above left are tapped for M3 screws while the base (above right) is tapped for M4 screws. Note these are not same size! Fig.6: these diagrams show how the transistors are mounted to their respective heatsinks. 22  Silicon Chip Fig.7: this the component overlay for the regulator PC board. Make sure you don’t inadvertently swap REG1 and REG2. ie, BC546, BC556, BF469 and BF470. The transistor pairs Q1 & Q2 and Q5 and Q6 are mounted so that their flat faces actually touch each other. Since we want each pair to thermally track each other, put a dab of heatsink compound on the flat faces and squeeze them together. Both Q8 & Q9 need to be fitted with U-shaped heatsinks, as shown in Fig.4. The four output transistors, the driver transistors (Q11 & Q12) and the Vbe multiplier Q10 are mounted vertically on one side of the board and are secured to one section of the tunnel heatsink with M3 and M4 machine screws. The heatsink needs to be drilled and tapped to take the screws. Fig.5 (not full-scale) shows the drilling and tapping details for mounting the transistors to the heatsink and the heatsink to the chassis. Alternatively, if you are building this amplifier from a kit, the heatsink may already be drilled and tapped. At this stage, you can temporarily attach the transistors to the heatsink but don’t bother with heatsink compound or washers at this stage. This done, poke all the transistor leads through their corresponding holes in the board and line up the board so that its bottom edge is 15mm above the bottom edge of the heatsink. This ensures that the board will be horizontal when fitted with 15mm tapped spacers at its front corners. Note that you will have to bend out all the transistor leads by about 20°, to poke them through the PC board. You can now solder all the transistor leads to the PC board. Having done that, undo the screws attaching the transistors to the heatsink and then fit mica washers and apply heatsink compound to the transistor mounting surfaces and the heatsink areas covered by the mica washers. The This view and the inset above shows how the two transformers were stacked and their primaries and secondaries terminated to an insulated terminal block (as shown in Fig.8). After this photo was taken we rewired the speaker terminals with much heavier figure-8 cables (2 x 79 strands 0.2mm). This made a significant difference to the power output and damping factor. Note that all power and output wiring to the amplifier modules is tightly twisted to provide maximum AC field cancellation. May 2000  23 PARTS LIST Amplifier Case 1 ATX tower PC case (available from CAM1 Computers; phone 02 9975 2919) 2 225mm tunnel heatsink extrusions (Jaycar Cat. HH-8530) 1 12V 80mm fan (see text) 1 toroidal power transformer, 300VA, 2 x 35V and 2 x 50V secondaries OR 1 300VA toroidal power transformer with 2 x 35V secondaries (Altronics Cat. M-5535) and 1 20VA or 30VA toroidal power transformer with 2 x 12V secondaries (Altronics Cat M-4912 or Jaycar Cat. MT-2112) 1 long bolt, nut, and washers to suit transformers 1 pushbutton DPST 250VAC switch to suit case (Jaycar Cat. SP-0746) 4 insulated female spade connectors (to suit DPST switch) 1 3-pole, 4-position rotary switch (adjust to 3 positions) 1 10kΩ dual-ganged log potentiometer 2 knobs, to suit rotary switch and potentiometer 1 IEC male power socket 1 IEC female power socket 2 insulating boots, to suit IEC power sockets 1 panel-mount 3AG safety fuse-holder (Jaycar Cat. SZ-2025 or equiv.) 1 5A 3AG fuse 2 gold-plated binding post terminal pairs (Jaycar Cat. PT-3008) 1 6-way RCA phono terminal panel (Jaycar Cat. PS-0265) 1 stereo headphone socket 1 12-way insulated terminal block 16 adhesive cable twist-ties 2 solder lugs 1 400V 35A bridge rectifier (BR1) 1 1N4001 1A silicon diode (D1) 4 8000µF 63VW chassis-mount electrolytic capacitors 1 470µF 25VW electrolytic capacitor 2 8.2kΩ 1W resistors 1 1kΩ 0.25W resistor 2 330Ω 1W resistors (to connect headphone socket) 24  Silicon Chip 1 120Ω 5W resistor (to suit fan; see text) Cable & Hardware 1m 250VAC 7.5A figure-8 flex 2m 2 x 79/0.2mm heavy-duty figure-8 speaker cable 2m red 7.5A hook-up wire 2m white 7.5A hook-up wire 2m black 7.5A hook-up wire 1m green 7.5A hook-up wire 1m rainbow cable 1m figure-8 shielded cable 2m red light-duty hook-wire 2m black light-duty hook-up wire 8 15mm tapped spacers 16 M3 x 6mm screws 35 M3 x 10mm screws 2 M3 x 15mm screws 24 M3 nuts 45 M3 flat washers 8 M4 x 10mm screws 1 M4 x 15mm screw 1 M4 nut 9 M4 flat washers 4 No.6 x 15mm self-tappers Amplifier Boards 2 PC boards, code 01103001, 105mm x 176mm 8 M205 PC mounting fuse clips 4 M205 5A fuses 2 coil formers, 24mm OD x 13.7mm ID x 12.8mm long, Philips 4322 021 30362 2 200Ω multi-turn trimpot Bourns 3296W series (VR1) 3 metres 1mm diameter enamelled copper wire 26 PC board pins 4 TO-126 heatsinks, Altronics Cat. H-0504 or equivalent 8 TO-3P insulating washers (for output transistors – see text) 6 TO-126 insulating washers Miscellaneous Heatshrink sleeving, heatsink compound, tinned copper wire, solder, insulation tape Semiconductors 4 MJL1302A PNP power transistors (Q13, Q14) 4 MJL3281A NPN power transistors (Q15, Q16) 2 MJE15030 NPN transistors (Q11) 2 MJE15031 PNP transistors (Q12) 2 MJE340 NPN power transistors (Q10) 2 BF469 NPN transistors (Q8) 2 BF470 PNP transistors (Q9) 6 BC546 NPN transistors (Q5-Q7) 8 BC556 PNP transistors (Q1-Q4) 2 3.3V 0.5W zener diodes (ZD1) Capacitors 4 1000µF 63VW electrolytic 4 100µF 63VW electrolytic 2 100µF 16VW electrolytic 2 2.2µF 25VW electrolytic 2 0.15µF 400VW MKC, Philips 2222 344 51154 or Wima MKC 4 10 0.1µF 63V MKT polyester 2 .0012µF 63V MKT polyester 2 100pF 100V ceramic Resistors (0.25W, 1%) 4 18kΩ 2 330Ω 2 12kΩ 1W 4 150Ω 2 3.3kΩ 6 120Ω 2 2.7kΩ 5W 8 100Ω 2 1.2kΩ 4 47Ω 2 1kΩ 2 6.8Ω 1W 2 390Ω 16 1.5Ω 1W 4 220Ω 5W (for current setting) Regulator Board 1 PC board, code 01103002, 61 x 92mm 6 PC pins 2 2kΩ multi-turn trimpots Bourns 3296W series (VR2,VR3) Semiconductors 2 TIP33B NPN power transistors (Q17, Q18) 1 LM317 adjustable positive 3-terminal regulator (REG1) 1 LM337 adjustable negative 3-terminal regulator (REG2) 1 BR610 bridge rectifier (BR2) 2 1N4004 silicon diodes (D1,D2) 2 33V 5W zener diodes (ZD2, ZD3) Capacitors 2 470µF 100VW electrolytics 1 220µF 63VW electrolytic 1 100µF 63VW electrolytic Resistors (0.25W, 1%) 2 6.8kΩ 2 47Ω 2 180Ω 6 15Ω 1W Fig.8: this diagram shows the details of the mains wiring and all the transformer secondary terminations at the insulated terminal block. details for mounting these transistors are shown in Fig.6. Alternatively, you can dispense with mica washers and heatsink compound and use silicone impregnated thermal washers instead, as can be seen in the photos. Whichever method you use, do not over-tighten the mounting screws. Now check with your multimeter, switched to a high Ohms range, that there are no shorts between the heatsink and any of the transistor collector leads. If you do find a short, undo each transistor mounting screw until the short disappears. It is then a matter of locating the cause of the short and remounting the offending transistor. Double-check all your soldering and assembly work against the circuit published last month and the component layout diagram of Fig.4. Set trimpot VR1 fully anticlockwise so that it is at minimum resistance. Remove both fuses and ensure that the 220Ω 5W resistors are wired across both fuse-holders, as described above. Power supply & case Assuming that you have built two amplifier modules you can now set them aside and proceed to build the regulated power supply board. Its component overlay is shown in While we elected to wire both IEC sockets and switch the female socket, most builders will probably take the simpler approach and not wire the female socket. May 2000  25 options for wiring these and we will come to those in a moment. We also elected to use the front panel power switch and if you are using an older computer case you can use the standard DPST (double-pole, single-throw) switch. However, if you are using a newer ATX case, its power switch will be a momentary contact type which is not suitable. If that is the case, you will be need a push-on push-off DPST switch to mate with the pushbutton on the front panel of the case. Again, you may able to obtain that from an older PC or you can purchase a suitable replacement from Jaycar (Cat. SP-0746). Now to the 240VAC mains wiring options. As far as the female IEC power (output) socket is concerned, you can either leave it unwired (and just use it to blank off the hole) or wire it in parallel with the male IEC power (input) socket. Alternatively, if you decide to switch the IEC female socket, you will need to run two lengths of figure-8 250VAC cable (to run from the IEC sockets to the switch and back). We took this approach but the wiring diagram of Fig.8 shows the simpler approach with the IEC female socket unswitched and just one length of figure-8 250VAC cable running from the IEC male socket to the DPST switch and then to the multi-way insulated terminal block. Note also that a panel-mount safety fuseholder is required and its contacts should be sleeved with heat­ shrink tubing. Similarly, the two IEC sockets should have insulating boots fitted over them to prevent accidental contact with the wiring terminals. Another point to note is that the IEC female socket is larger than its male counterpart and therefore requires a larger boot. Drilling the case Before you can start doing any wiring on the case, all the holes must be drilled for the hardware and any cutouts made. For simplicity, we won’t mention all the holes that are required and we’ll only talk about specific hardware as we discuss the wiring but you have to do all drilling and metal-bashing first. For example, you have to drill all the holes to mount the tunnel The rear panel has an extra cutout for the tunnel fan and has gold plated speaker terminals as well as a 6-way RCA input socket panel. Fig.7. This is quite straightforward to assemble but don’t make the mistake of inadvertently swapping REG1 & REG2, the positive and negative regulators. And make sure that the zener diodes and electrolytic capacitors are inserted the right way around. The next step is to work on the tower case for the amplifier. As stated previously, we purchased a new ATX tower computer case for $66 (from CAM1 Computer Wholesale Pty Ltd; phone (02) 9975 2919. This came with a power supply which we removed and that leaves quite a few metal working details to be sorted out. First, the opening where the power supply was needs to be filled in and to do that we cut off the rear panel of a non-working PC power supply. That gave us a panel with a fan cut-out (for ventilation) and two IEC power sockets – male and female. There are two 26  Silicon Chip An advantage of this case is that you can run some of the wiring between the chassis and one of the side panels. This improves shielding as well as giving a neater result. Note the ribbon cable for the input signal wiring – this is much easier to run than shielded cable. Fig.9: this is the alternative power supply arrangement using two power transformers with their secondaries added together. heatsink and the amplifier modules, regulated power supply board, the power transformers, the multi-way insulated terminal block, bridge rectifier, chassis-mount electrolytic capacitors and the chassis-mount fuseholder. You also have to make the cutouts in the rear panel for the 12V fan, loudspeaker terminals and RCA phono terminal panel. Make sure that all holes and cutouts are de-burred and that the chassis is completely clean of all metal swarf. It is also a good idea to wipe the entire chassis clean with a cloth moistened with methylated spirits or kerosene. This will remove grease and finger-pints which eventually become a site for surface corrosion in these (normally) bright zinc-plated chassis. We also had to remove the 3.5-inch disk drive cage but elected to leave the 5.25-inch drive cage where it was as it was spot-welded in place. Power transformer wiring There are two options for the power transformer. The power supply circuit on page 22 of the March 2000 issue shows a single transformer with two 35V windings and two 50V windings. The prototype 225VA transformer was made by Harbuch Transformers Pty Ltd (phone 02 9476 5854) and they will no doubt be able to supply a 300VA version for this stereo amplifier. As an alternative, we decided to power our prototype with two off-theshelf toroidal transformers: a 300VA unit with two 35V windings and a 30VA unit with two 12V windings. These are wired so that they effec- tively provide two 35V AC windings (from the 300VA unit) and two 47V windings, with the 35V and 12V windings added together, as shown in the circuit of Fig.9. One of the 12V windings is also used to power the front panel LED and the 12V DC fan; more on that in a moment. The two transformers were stacked, with a neoprene washer under the 300VA transformer, a washer between the two transformers and another neoprene washer underneath the steel cup washer for the 30VA transformer. One bolt passes through both transformers and secures them to the case, as can be seen in the photos. So the first steps in wiring the power supply are to stack the transformers together and terminate their primary May 2000  27 This underside view of the finished modules mounted on the heatsink shows how the extrusions have been drilled for M4 screws to secure it in the case. and secondary windings to the multi-way insulated terminal block, as shown in the diagram of Fig.8. Run the 240VAC mains wiring around the top and sides of the case, as shown. Do not connect any of the other power supply components yet until the phasing of the two transformers is confirmed as correct. To do this you connect the unit to the 240VAC mains, switch on and use your multimeter (switched to a 100VAC range or higher) and check that you have the two 35V windings delivering around 37VAC (unloaded) and the summed windings delivering around 50VAC unloaded. If the phasing is incorrect, you may find that the summed wind- Resistor Colour Codes                   No. 4 2 2 2 2 2 2 2 2 2 2 4 6 8 6 6 2 16 Value 18kΩ 12kΩ 8.2kΩ 6.8kΩ 3.3kΩ 2.7kΩ 1.2kΩ 1kΩ 390Ω 330Ω 180Ω 150Ω 120Ω 100Ω 47Ω 15Ω 6.8Ω 1.5Ω 28  Silicon Chip 4-Band Code (1%) brown grey orange brown brown red orange brown grey red red brown blue grey red brown orange orange red brown red purple red brown brown red red brown brown black red brown orange white brown brown orange orange brown brown brown grey brown brown brown green brown brown brown red brown brown brown black brown brown yellow purple black brown brown green black brown blue grey gold brown brown green gold brown 5-Band Code (1%) brown grey black red brown brown red black red brown grey red black brown brown blue grey black brown brown orange orange black brown brown red purple black brown brown brown red black brown brown brown black black brown brown orange white black black brown orange orange black black brown brown grey black black brown brown green black black brown brown red black black brown brown black black black brown yellow purple black goldbrown brown green black gold brown blue grey black silver brown brown green black silver brown ings actually deliver around 24VAC. If this happens, you will need to swap the connections from the two 12V windings. Note that while the wiring diagram of Fig.8 shows the colour-coding of the transformer wires to acheive the circuit shown in Fig.9, you will still have to check the output voltages, as noted above. In fact, while our prototype was wired as shown in Fig.8, we still had to swap one of the transformers secondaries to achieve the correct result; so don’t take it for granted. Next, install the four chassis-mount 8000µF filter capacitors and the bridge rectifier and the regulated power supply board and complete the wiring, as shown in Fig.8. Then apply power again and check the resulting ±55V regulated rails and the unregulated ±52.5V rails. For the regulated supply rails you will need to adjust trimpots VR2 & VR3 to obtain exactly ±55V DC. As far as the main unregulated supply rails are concerned, they will probably deliver around ±53V as they are completely unloaded. These measurements were made with an AC supply voltage of 240VAC. If your mains voltage is higher, and this will normally be the case, then the amplifier supply rails will be increased accordingly. Note that when you switch the unit off, the 8000µF capacitors will take a very long time to discharge. Hence, you should use a resistor of, say, 470Ω 5W to safely discharge each supply rail after your initial tests have been done. Testing the amplifier modules Before the amplifier modules are installed in the case, they must be tested. To do this, you need a steel or aluminium baseplate which can be earth­ed back to the tower case. This becomes a temporary chassis for the amplifiers. Place a piece of cardboard over the base-plate to reduce the Capacitor Codes     Value IEC Code EIA Code 0.15µF  150n  154 0.1µF  100n  104 .0012µF   12n  121 100pF 100pF  100 Fig.10: use this diagram when running all the signal wiring and power wiring to the amplifier modules. Note that the routing of the ±52.5V wiring is critical if you want to obtain the very best harmonic distortion performance. May 2000  29 Fig.11: the full-size PC board pattern for the amplifier power supply. Only one of these boards is required. chance of any shorts from the modules. Test one module at a time. You need to run the five power supply leads from the tower case to the amplifier module: ±52.5V (unregulated), ±55V (regulated) and 0V. Now apply power. No loudspeaker or resistive load should be connected at this stage. Now measure the voltage at the output of the amplifier module. It should be less than ±30mV of 0V. If it is not close to zero, switch off the power as you have a fault. Check over your work very carefully. Check the base-emitter voltages of each transistor; they should all be in the range of 0.6V to 0.7V. Also check for missed solder connections, solder splashes between tracks, incorrectly connected transistors, incorrect transistor types, parts in the wrong way around, etc. Check the voltage across the 3.3V zener diode. Our examples proved to be low as they were 1W types and they needed more current through them. Accordingly we changed the 8.2kΩ 1W bias resistor to 2.7kΩ 5W to increase the zener current to around 20mA. We recommend this change. Now monitor the voltage across one of the 220Ω 5W resistors. With VR1 fully anticlockwise, the voltage should be close to zero since there is no quiescent current in the output stage. Now slowly wind VR1 clockwise until the voltage starts to rise. Set VR1 for a voltage of 4.4V across the 220Ω resistor. This is equivalent to a quiescent current of 20mA or 10mA through each output transistor. You can check this by measuring the voltage drop across any of the eight 1.5Ω 1W emitter resistors. The average value across the resistors should be 7.5mV. Leave the amplifier to run for 10 minutes or so and then retouch the setting of VR1 if necessary. Finally, fit the 5A fuses and the module is finished. Repeat the procedure for the second amplifier module. Wiring up There remains quite a bit of wiring to be done. First, you need to run the rainbow cabling between the RCA phono sockets and the selector switch on the front panel. Note that the white phono sockets are for the left channel; red for the right channel. The wiring from the selector switch to the volume control and then to amplifier inputs is run in figure-8 shielded cable. The details are shown in the wiring diagram of Fig.10. Using ribbon cable for the signal wiring is much easier than running Fig.12: the full-size etching pattern for the amplifier PC board. Two boards are required for the stereo amplifier. 30  Silicon Chip shielded cable. It must be laid flat on the chassis and kept away, as much as possible, from power wiring. Using our tower case, we were able to run the ribbon cable between the chassis and one of the side covers to improve the shielding. The cables for the power supplies must be run exactly as shown in the diagram of Fig.10. First, run three leads, using 7.5A-rated hookup wire, from the regulator board to both modules. These leads must be tightly twisted as shown. Second, run three leads, again using 7.5A hookup wire, from the unregulated ±52.5V rails to both modules and again, tightly twisted. Particularly critical is the way in which these three leads are routed underneath the centre of both amplifier boards and then having the positive and negative leads radiating out to the respective PC stakes on the boards. The routing shown is critical because the heavy class-B currents produce a magnetic field which partially cancels the fields produced by the same class-B currents in the PC board tracks. Note the positioning of these wires carefully; see how they align with the tracks carrying the class-B currents from the paralleled 1.5Ω resistors on each side of the board. A change in position by as little as 5mm can make quite a significant difference to the resulting high frequency distortion performance of the amplifier. This photo shows the detail of wiring to the headphone socket (top left) and power switch. Note the insulating sleeves on the power switch: they’re essential! Output connections Again, this is a critical aspect. For the output leads from the amplifier modules to the output terminals we used a heavy-duty figure-8 speaker cable (Jaycar Cat. WB-1712 or WB1713; 2 x 79/0.2mm). Do not use lighter gauge cables as they do have a significant effect on the ultimate performance. These cables must be tightly twisted for effective field cancellation. The speaker terminals themselves should be heavy-duty solid metal units such as the gold-plated types from Jaycar (Cat. PT-3008). These are another essential item – do not use cheaper plastic or spring-loaded speaker terminals; they do not make reliable low resistance connections and they can make a large difference (like 10 times worse) to the distortion. The recommended terminals will The selector switch and the 10kΩ dual ganged log volume control are mounted on one of the plastic in-fill panels. also take the largest of jumbo speaker cables. You also need to run light duty hookup wire for the wiring to the headphone socket although you may decide to dispense with the head­ phone facility altogether. Assuming that you do wire the headphone socket, you need to run the twisted-wire pair from both channel outputs to the socket but only one earth return is connected while the other remains unconnected, as shown on Fig.8. Two more points about the head­ phone socket: first, do not earth the headphone socket, otherwise you will end up with an earth loop (they cause hum and distortion). Hence, the head­phone socket is mounted on one of the plastic infill panels, as shown. Second, do not use the headphone socket to switch the loudspeakers on and off. While we did this in the above-mentioned Class-A amplifier, the much higher speaker currents involved in this 100W amplifier are too much for the headphone switch contacts to handle and give a low distortion result. In a future issue, we will address the May 2000  31 Fig.13: the existing badge can be removed from the front panel of the case and this one used instead. Finally, here is the whole rear panel of the assembled amplifier. As previously noted, we replaced the cabling to the speaker terminals with much heavier wire – with very worthwhile results. problem of speaker protection, muting and headphone switching. Fan control As mentioned above, the fan is run at low speed and it runs continuously. We were able to salvage an 80mm 32  Silicon Chip fan from a defunct computer supply although they are readily available from electronic parts retailers. If you are buying a fan, purchase the one with the lowest noise rating. These days such 12V fans are brushless (ie, electronically commutated) which means that they are polarised; if you connect them the wrong way around they won’t run. The fan we used is rated at 12V <at> 200mA but we throttled it right back to around 5.8V by using a 120Ω 5W resistor in series with the half-wave rectified DC supply (see Fig.9). While you may be able to run your fan at lower than 5.8V and thereby make it even quieter, you will need to check that it runs properly; if the voltage to the fan is too low, it may not start reliably. Note that while the fan will run much quieter than if it was being powered by the full 12V, it will still make a low level hum which may still be a problem, depending on your listening room and how close you are to the amplifier. In our situation, we found that while ever music was playing, even at very low levels, the fan was not audible but when the program stopped, the fan could be heard as a very muted hum. We’ve taken this approach for simplicity. If fan noise is a problem in your situation, you may need to position the amplifier well away from your listening position or even put it in a cupboard. The DC supply for the fan also runs the front panel LED. Wiring for this LED will already be present in the computer case and it is simply a matter of connecting the wires to the DC supply at the multi-way insulated terminal block. When all your wiring is complete, you need to check all your work very carefully. Then apply power and recheck the voltages on the amplifier. Readjust trimpot VR1 on the amplifier modules if necessary. Finally, place the covers on the case, connect your CD player and loudspeakers. Have a listen close to the loudspeakers without any music playing. There should be only a very low level hiss coming from the speakers. Now place your favourite CD in the machine and sit back to enjoy the SC sound. 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. e & Get Subscrib count is D A 10% on ther Silic e O ll A n O is d n a h rc Chip Me $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. 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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 May 2000  33 5 channels of home theatre sound in headphones Is it nonsense or does it really work? TM Just recently there have been stories in the daily press about Dolby Headphone, a new system for reproducing home theatre sound in headphones. Is such a system possible or is it another marketing gimmick? By LEO SIMPSON I recently had the chance to talk to the developers of the Dolby Headphone system and experience a demonstration. To be honest, I did not know what to expect. On the one hand, how can it be possible to provide or simulate five separate channels of audio in stereo-phonic headphones? On the other hand, it is called “Dolby Headphone” and with a brand like 34  Silicon Chip that, it must be a genuine innovation. So I went along with an open mind (sort of). The demonstration was in a typical home theatre set-up: large screen for the video side of things and five speakers for the surround sound: left and right front, centre front and two rear speakers. There was no sub-woofer though, as far as I was aware, although that would normally be tucked away out of sight. I sat on the lounge in front of the video monitor and was handed a pair of normal stereo headphones to put on but I was told that the sound would come from the five speakers. The demo consisted of a spoken commentary, along the lines of “this is my voice coming from the left front speaker... This is my voice coming from the right front speaker... This is my voice coming from the left rear Dolby Digital speaker layout for cinema surround sound systems (above) and for the home theatre 5.1 system (below). speaker... and so on”. The demo starts with the sound clearly coming from the speakers arrayed around the room but part-way during the narrative I was told that I could now take the headphones off. As I did I realised that at some point in the narrative, the sound had stopped coming from the speakers and was now coming solely from the headphones. And yes, there was no doubt about it; there really were five discrete channels of audio, each strongly located where they were supposed to be. After the short demo and listening to some specially recorded material, I was convinced. It was no longer a question of whether Dolby Headphone works but “How is it done?” In effect, the Dolby Headphone system creates up to five virtual loudspeakers in a virtual room. Not only that, but the system can model the sound of surround sound playback in up to three different listening “rooms”: • DH1 is a small, well-damped room, ie, with carpet, curtains and soft furnishings, suitable for both movies and music-only recordings. It is the socalled Dolby Headphone “Reference Room” and is provided on all Dolby Headphone equipped products. • DH2 is a more acoustically live room particularly suited to music listening. • DH3 is a larger room, more like a concert hall or movie theatre. DH2 and DH3 are optional and may not be offered on some Dolby Headphone products. How it was done Normally, when you listen to a stereo program via headphones, the localisation of sound is quite unrealistic. Left channel sounds appear intimately in your left ear, right channels sounds in your right ear and sounds diffused over the stereo stage appear to come from right inside your head or for many listeners, over the top of May 2000  35 must be performed for all five channels simultaneously; with all the necessary acoustic delays for the direct sounds and the multiple reflections. While a number of companies have attempted to simulate surround sound via headphones, none have really caught on in the marketplace. Part of the problem has been that the simulations have not be able to cope with the huge number of signal For each speaker placed in a room a unique combination of direct and reflected sounds reaches the listener. Dolby Headphone simulates the acoustic effects for a complete surround experience over stereo headphones. your head. There is no “front” or “rear” localisation and if you have listened to stereo headphones over the years and understand the normal processes of audio recording, it is difficult to imagine how front and rear localisation could be provided, let alone left front, right front, centre front and so on. Think about how our ears and brain let us strongly localise sound. The process of localisation depends on the brain perceiving the difference in time of a arrival for a sound to reach our ears. But not only do we hear and perceive the sounds arriving via the shortest path to our ears, we also perceive all the reflections off walls and other objects to gain a sense of space, height and so on. Furthermore, our ears also provide a different frequency response to sounds coming from the front than they do from the rear. So much so, that even if we are blindfolded, we usually have no trouble knowing from where a sound originates. For example, if you were blind-folded or in a completely dark room, you would instantly be able to locate the source of most sounds, such an object falling to the floor, knocking on the wall and so on, even if the room was quite unfamiliar. This wonderful system of sound localisation, whereby our brain and ears work together, has been evolved over millions of years. It has enabled us to escape being eaten by predators because we could tell which direction they were coming from – and incidentally, allowed us to successfully hunt 36  Silicon Chip and survive. But the whole process of sound localisation by our ears had to be thoroughly understood before five channels of audio could be simulated electronically. Acoustic delays If you are going to simulate a sound arriving from the left front speaker at the left and right ears on a person’s head, you must provide acoustic delays which not only produce the direct path difference but also the delays for multiple reflections for any sound from the left front speaker off the walls, ceiling and floor. If you think in terms of computing power, the encoding and recording system becomes exceedingly complex, just to precisely locate the left front speaker via a set of headphones. But consider that the same process reflections involved for a period of perhaps half a second – the sort of reverberation time that can be experienced in a large listening room. Naturally, all of the simulation and filtering processes referred to above are done using DSP (digital signal processing). And that is where the Australian company Lake Technology Ltd, the developer of the Dolby Headphone system, comes into the picture. Lake Technology are experts in “convolution”, a mathematical operation used in the mixing of signals with applications in the processing of audio signals, radar signals and even in radio astronomy. Using their experience in convolution and DSP, Lake Technology developed algorithms to simulate the surround sound experience in head- phones using an FIR (finite impulse response) filter with low latency (meaning it’s very fast) and with 278,244 taps of convolution (meaning it can simulate vast numbers of room reflections). As part of their research, they went to the trouble of setting up a typical listening room with a home theatre setup of five loudspeakers and then recorded all sorts of signals as heard by a typical listener when seated in the “sweet-spot”. Real, live dummies! But they did not use a dummy head for the recordings; they used a real person and they fitted microphones in the ear canals of that person (must have been uncomfortable). Using their Huron acoustic virtual reality simulation platform, they then went on to produce a simulation of the recordings and subsequently, the algorithms. Such was the success of Lake Technology that the system is now licensed to Dolby Laboratories for full commercialisation. Already a number of semiconductor manufacturers, such as Motorola, Analog Devices and Sanyo, have produced chipsets for Dolby Headphone and the first commercial product, the Hitachi Prius computer, incorporating a DVD player and Dolby Headphone, has been released in Japan. Not only is it envisaged that Dolby Headphone will be incorporated into products such as DVD players and surround sound amplifiers but also into portable CD and MP3 players. As the release of the Hitachi Prius system proves, possibly the biggest market will be in computers and computer games, allowing users to enjoy full surround sound without the need for an array of tiny speakers. Standard headphones One of the beauties of the Dolby Headphone system is that any pair of stereo headphones can be used although naturally, the better the quality of the headphones, the better will be results. So while it can produce very good results for movie sound tracks with just average headphones, it will be even better with good quality phones and should be tops for music discs recorded with surround sound en- coding. Lake Inflight Theatre Nor are the benefits of surround sound confined to home users; there is a very big potential market in the airlines. Recognising this, Lake Technology and Dolby Laboratories Inc have acted to provide the system for in-flight movies. In this system, the sound portion of the program is not encoded as Dolby Digital with six channels but as two channels with the full surround sound simulation. This means that no decoders are required on the plane and all existing equipment can be used whether it is based on VCRs or DVD players. This system is already available on Qantas and Singapore Airlines and is available to all airlines. In fact, the LIFT program provides testing and accreditation for the entire inflight entertainment installation, including all the headsets. Further information on Dolby Headphone and related products is available from the following websites: www.dolby.com/headphone/ www.lake.com.au SC May 2000  37 Silicon Chip Back Issues September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High-Performance AC Millivoltmeter, Pt.2; Build The Vader Voice. April 1989: Auxiliary Brake Light Flasher; What You Need to Know About Capacitors; 32-Band Graphic Equaliser, Pt.2; The Story Of Amtrak Passenger Services. May 1989: Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; The Burlington Northern Railroad. July 1989: Exhaust Gas Monitor; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm; The NSW 86 Class Electrics. 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. October 1989: FM Radio Intercom For Motorbikes Pt.1; GaAsFet Preamplifier For Amateur TV; 2-Chip Portable AM Stereo Radio, Pt.2; A Look At Australian Monorails. 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. January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Phone Patch For Radio Amateurs; Active Antenna Kit; Designing UHF Transmitter Stages. February 1990: A 16-Channel Mixing Desk; Build A High Quality Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2. March 1990: Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC; The Australian VFT Project. April 1990: Dual Tracking ±50V Power Supply; Voice-Operated Switch (VOX) With Delayed Audio; 16-Channel Mixing Desk, Pt.3; Active CW Filter; Servicing Your Microwave Oven. August 1992: Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; 1kW Dummy Load Box For Audio Amplifiers; Troubleshooting Vintage Radio Receivers; The MIDI Interface Explained. October 1992: 2kW 24VDC - 240VAC Sinewave Inverter; Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For Personal Stereos; A Regulated Lead-Acid Battery Charger. January 1993: 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. 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 of Servicing Microwave Ovens. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Low-Cost 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; Build A 4-Channel Lighting Desk, Pt.1; 13.5V 25A Power Supply For Transceivers, Pt.2; Active Filter For CW Reception; Tuning In To Satellite TV, Pt.1. July 1991: 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. September 1991: Digital Altimeter For Gliders & Ultralights; Ultrasonic Switch For Mains Appliances; The Basics Of A/D & D/A Conversion; Plotting The Course Of Thunderstorms. 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, Pt.2; Military Applications Of R/C Aircraft. February 1993: Three Projects For Model Railroads; Low Fuel Indicator For Cars; Audio Level/VU Meter (LED Readout); An Electronic Cockroach; 2kW 24VDC To 240VAC Sinewave Inverter, Pt.5. March 1993: Solar Charger For 12V Batteries; Alarm-Triggered Security Camera; Reaction Trainer; Audio Mixer for Camcorders; A 24-Hour Sidereal Clock For Astronomers. April 1993: Solar-Powered Electric Fence; Audio Power Meter; Three-Function Home Weather Station; 12VDC To 70VDC Converter; Digital Clock With Battery Back-Up. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Alphanumeric LCD Demonstration Board; The Story of Aluminium. June 1993: AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; Digital Voltmeter For Cars; Build A Windows-Based Logic Analyser. July 1993: Single Chip Message Recorder; Light Beam Relay Extender; AM Radio Trainer, Pt.2; Quiz Game Adjudicator; Windows-Based Logic Analyser, Pt.2; Antenna Tuners – Why They Are Useful. August 1993: Low-Cost Colour Video Fader; 60-LED Brake Light Array; Microprocessor-Based Sidereal Clock; Southern Cross Z80-Based Computer; A Look At Satellites & Their Orbits. September 1993: Automatic Nicad Battery Charger/Discharger; Stereo Preamplifier With IR Remote Control, Pt.1; In-Circuit Transistor Tester; +5V to ±15V DC Converter; Remote-Controlled Cockroach. 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. November 1993: High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier With IR Remote Control, Pt.3; Siren Sound Generator; Engine Management, Pt.2; Experiments For Games Cards. December 1993: Remote Controller For Garage Doors; Build A LED Stroboscope; Build A 25W Audio Amplifier Module; A 1-Chip Melody Generator; Engine Management, Pt.3; Index To Volume 6. June 1990: Multi-Sector Home Burglar Alarm; Build A Low-Noise Universal Stereo Preamplifier; Load Protector For Power Supplies; Speed Alarm For Your Car. November 1991: Build A Colour TV Pattern Generator, Pt.1; A Junkbox 2-Valve Receiver; Flashing Alarm Light For Cars; Digital Altimeter For Gliders, Pt.3; Build A Talking Voltmeter For Your PC, Pt.2; Build a Turnstile Antenna For Weather Satellite Reception. 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; Engine Management, Pt.4. July 1990: Digital Sine/Square Generator, Pt.1 (covers 0-500kHz); Burglar Alarm Keypad & Combination Lock; Build A Simple Electronic Die; A Low-Cost Dual Power Supply; Inside A Coal Burning Power Station. December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Colour TV Pattern Generator, Pt.2; Index To Volume 4. February 1994: Build A 90-Second Message Recorder; 12-240VAC 200W Inverter; 0.5W Audio Amplifier; 3A 40V Adjustable Power Supply; Engine Management, Pt.5; Airbags In Cars – How They Work. 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. 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 1994: Intelligent IR Remote Controller; 50W (LM3876) Audio Amplifier Module; Level Crossing Detector For Model Railways; Voice Activated Switch For FM Microphones; Engine Management, Pt.6. September 1990: A Low-Cost 3-Digit Counter Module; Build A Simple Shortwave Converter For The 2-Metre Band; The Bose Lifestyle Music System (Review); The Care & Feeding Of Nicad Battery Packs (Getting The Most From Nicad Batteries). March 1992: TV Transmitter For VHF VCRs; Thermostatic Switch For Car Radiator Fans; Coping With Damaged Computer Directories; Guide Valve Substitution In Vintage Radios. April 1994: Sound & Lights For Model Railway Level Crossings; Discrete Dual Supply Voltage Regulator; Universal Stereo Preamplifier; Digital Water Tank Gauge; Engine Management, Pt.7. April 1992: IR Remote Control For Model Railroads; Differential Input Buffer For CROs; Understanding Computer Memory; Aligning Vintage Radio Receivers, Pt.1. May 1994: Fast Charger For Nicad Batteries; Induction Balance Metal Locator; Multi-Channel Infrared Remote Control; Dual Electronic Dice; Simple Servo Driver Circuits; Engine Management, Pt.8. May 1992: Build A Telephone Intercom; Electronic Doorbell; Battery Eliminator For Personal Players; Infrared Remote Control For Model Railroads, Pt.2; Aligning Vintage Radio Receivers, Pt.2. June 1994: 200W/350W Mosfet Amplifier Module; A Coolant Level Alarm For Your Car; 80-Metre AM/CW Transmitter For Amateurs; Converting Phono Inputs To Line Inputs; PC-Based Nicad Battery Monitor; Engine Management, Pt.9. October 1990: The Dangers of PCBs; Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; NE602 Converter Circuits. November 1990: Connecting Two TV Sets To One VCR; Build An Egg Timer; Low-Cost Model Train Controller; 1.5V To 9V DC Converter; Introduction To Digital Electronics; 6-Metre Amateur Transmitter. December 1990: 100W DC-DC Converter For Car Amplifiers; Wiper Pulser For Rear Windows; 4-Digit Combination Lock; 5W Power ORDER FORM Please send thethe following back issues: Please send following back issues:    SPECIAL STOCK CLEAROUT: 4 ISSUES FOR $10 (incl. p&p)* June 1992: Multi-Station Headset Intercom, Pt.1; Video Switcher For Camcorders & VCRs; IR Remote Control For Model Railroads, Pt.3; July 1994: Build A 4-Bay Bow-Tie UHF Antenna; PreChamp 2-Tran15-Watt 12-240V Inverter; A Look At Hard Disc Drives. sistor Preamplifier; Train Diesel HornDecember Simulator; Po *Offer applies to allSteam issues upWhistle to and&including 1994. Applies to Australian orders only and subscriber discounts do not apply. Offer closes 31st May, 2000. ____________________________________________________________ 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 ___________ 38  Silicon Chip Note: prices include postage & packing Australia ....................... $A7.70 (incl. GST) Overseas (airmail) ............................ $A10 Detach and mail to: Silicon Chip Publications, PO Box 139, Collaroy, NSW, Australia 2097. Or call (02) 9979 5644 & quote your credit card details or fax the details to (02) 9979 6503. Email: silchip<at>siliconchip.com.au August 1994: High-Power Dimmer For Incandescent Lights; Microprocessor-Controlled Morse Keyer; Dual Diversity Tuner For FM Microphones, Pt.1; Nicad Zapper; Engine Management, Pt.11. September 1996: VGA Oscilloscope, Pt.3; IR Stereo Headphone Link, Pt.1; High Quality PA Loudspeaker; 3-Band HF Amateur Radio Receiver; Cathode Ray Oscilloscopes, Pt.5. September 1994: Automatic Discharger For Nicad Battery Packs; MiniVox Voice Operated Relay; Image Intensified Night Viewer; AM Radio For Weather Beacons; Dual Diversity Tuner For FM Microphones, Pt.2; Engine Management, Pt.12. October 1996: Send Video Signals Over Twisted Pair Cable; Power Control With A Light Dimmer; 600W DC-DC Converter For Car Hifi Systems, Pt.1; IR Stereo Headphone Link, Pt.2; Build A Multi-Media Sound System, Pt.1; Multi-Channel Radio Control Transmitter, Pt.8. October 1994: How Dolby Surround Sound Works; Dual Rail Variable Power Supply; Build A Talking Headlight Reminder; Electronic Ballast For Fluorescent Lights; Build A Temperature Controlled Soldering Station; Electronic Engine Management, Pt.13. November 1996: Adding A Parallel Port To Your Computer; 8-Channel Stereo Mixer, Pt.1; Low-Cost Fluorescent Light Inverter; How To Repair Domestic Light Dimmers; Build A Multi-Media Sound System, Pt.2; 600W DC-DC Converter For Car Hifi Systems, Pt.2. November 1994: Dry Cell Battery Rejuvenator; Novel Alphanumeric Clock; 80-Metre DSB Amateur Transmitter; Twin-Cell Nicad Discharger (See May 1993); How To Plot Patterns Direct to PC Boards. December 1996: Active Filter Cleans Up CW Reception; Fast Clock For Railway Modellers; Laser Pistol & Electronic Target; Build A Sound Level Meter; 8-Channel Stereo Mixer, Pt.2; Index To Volume 9. 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; Remote Control System for Models, Pt.1; Index to Vol.7. January 1997: How To Network Your PC; Control Panel For Multiple Smoke Alarms, Pt.1; Build A Pink Noise Source (For Sound Level Meter Calibration); Computer Controlled Dual Power Supply, Pt.1; Digi-Temp Monitors Eight Temperatures. 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. February 1997: Cathode Ray Oscilloscopes, Pt.6; PC-Controlled Moving Message Display; Computer Controlled Dual Power Supply, Pt.2; Alert-A-Phone Loud Sounding Alarm; Control Panel For Multiple Smoke Alarms, Pt.2. 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; Remote Control System For Models, Pt.2. March 1995: 50 Watt Per 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: FM Radio Trainer, Pt.1; Photographic Timer For Dark­ rooms; Balanced Microphone Preamp. & Line Filter; 50W/Channel Stereo Amplifier, Pt.2; Wide Range Electrostatic Loudspeakers, Pt.3; 8-Channel Decoder For Radio Remote Control. October 1998: CPU Upgrades & Overclocking; Lab Quality AC Millivoltmeter, Pt.1; PC-Controlled Stress-O-Meter; Versatile Electronic Guitar Limiter; 12V Trickle Charger For Float Conditions; Adding An External Battery Pack To Your Flashgun. November 1998: The Christmas Star (Microprocessor-Controlled Christmas Decoration); A Turbo Timer For Cars; Build A Poker Machine, Pt.1; FM Transmitter For Musicians; Lab Quality AC Millivoltmeter, Pt.2; Setting Up A LAN Using TCP/IP; Understanding Electric Lighting, Pt.9; Improving AM Radio Reception, Pt.1. December 1998: Protect Your Car With The Engine Immobiliser Mk.2; Thermocouple Adaptor For DMMs; A Regulated 12V DC Plugpack; Build Your Own Poker Machine, Pt.2; Improving AM Radio Reception, Pt.2; Mixer Module For F3B Glider Operations. January 1999: The Y2K Bug & A Few Other Worries; High-Voltage Megohm Tester; Getting Going With BASIC Stamp; LED Bargraph Ammeter For Cars; Keypad Engine Immobiliser; Improving AM Radio Reception, Pt.3; Electric Lighting, Pt.10 February 1999: Installing A Computer Network (Network Types, Hubs, Switches & Routers); Making Front Panels For Your Projects; Low Distortion Audio Signal Generator, Pt.1; Command Control Decoder For Model Railways; Build A Digital Capacitance Meter; Remote Control Tester; Electric Lighting, Pt.11. March 1997: Driving A Computer By Remote Control; Plastic Power PA Amplifier (175W); Signalling & Lighting For Model Railways; Build A Jumbo LED Clock; Cathode Ray Oscilloscopes, Pt.7. March 1999: Getting Started With Linux; Pt.1; Build A Digital Anemometer; 3-Channel Current Monitor With Data Logging; Simple DIY PIC Programmer; Easy-To-Build Audio Compressor; Low Distortion Audio Signal Generator, Pt.2; Electric Lighting, Pt.12. April 1997: Simple Timer With No ICs; Digital Voltmeter For Cars; Loudspeaker Protector For Stereo Amplifiers; Model Train Controller; A Look At Signal Tracing; Pt.1; Cathode Ray Oscilloscopes, Pt.8. April 1999: Getting Started With Linux; Pt.2; High-Power Electric Fence Controller; Bass Cube Subwoofer; Programmable Thermostat/ Thermometer; Build An Infrared Sentry; Rev Limiter For Cars; Electric Lighting, Pt.13; Autopilots For Radio-Controlled Model Aircraft. May 1997: Teletext Decoder For PCs; Build An NTSC-PAL Converter; Neon Tube Modulator For Light Systems; Traffic Lights For A Model Intersection; The Spacewriter – It Writes Messages In Thin Air; A Look At Signal Tracing; Pt.2; Cathode Ray Oscilloscopes, Pt.9. May 1999: The Line Dancer Robot; An X-Y Table With Stepper Motor Control, Pt.1; Three Electric Fence Testers; Heart Of LEDs; Build A Carbon Monoxide Alarm; Getting Started With Linux; Pt.3. May 1995: Build A Guitar Headphone Amplifier; FM Radio Trainer, Pt.2; Transistor/Mosfet Tester For DMMs; A 16-Channel Decoder For Radio Remote Control; Introduction to Satellite TV. June 1997: PC-Controlled Thermometer/Thermostat; Colour TV Pattern Generator, Pt.1; Build An Audio/RF Signal Tracer; High-Current Speed Controller For 12V/24V Motors; Manual Control Circuit For A Stepper Motor; Cathode Ray Oscilloscopes, Pt.10. June 1999: FM Radio Tuner Card For PCs; X-Y Table With Stepper Motor Control, Pt.2; Programmable Ignition Timing Module For Cars, Pt.1; Hard Disk Drive Upgrades Without Reinstalling Software; What Is A Groundplane Antenna?; Getting Started With Linux; Pt.4. June 1995: Build A Satellite TV Receiver; Train Detector For Model Railways; 1W Audio Amplifier Trainer; Low-Cost Video Security System; Multi-Channel Radio Control Transmitter For Models, Pt.1. July 1997: Infrared Remote Volume Control; A Flexible Interface Card For PCs; Points Controller For Model Railways; Simple Square/ Triangle Waveform Generator; Colour TV Pattern Generator, Pt.2; An In-Line Mixer For Radio Control Receivers. July 1999: Build The Dog Silencer; A 10µH to 19.99mH Inductance Meter; Build An Audio-Video Transmitter; Programmable Ignition Timing Module For Cars, Pt.2; XYZ Table With Stepper Motor Control, Pt.3; The Hexapod Robot. August 1997: The Bass Barrel Subwoofer; 500 Watt Audio Power Amplifier Module; A TENs Unit For Pain Relief; Addressable PC Card For Stepper Motor Control; Remote Controlled Gates For Your Home. August 1999: Remote Modem Controller; Daytime Running Lights For Cars; Build A PC Monitor Checker; Switching Temperature Controller; XYZ Table With Stepper Motor Control, Pt.4; Electric Lighting, Pt.14; DOS & Windows Utilities For Reversing Protel PC Board Files. July 1995: Electric Fence Controller; How To Run Two Trains On A Single Track (Incl. Lights & Sound); Setting Up A Satellite TV Ground Station; Build A Reliable Door Minder. August 1995: Fuel Injector Monitor For Cars; Gain Controlled Microphone Preamp; Audio Lab PC-Controlled Test Instrument, Pt.1; How To Identify IDE Hard Disk Drive Parameters. September 1995: Railpower Mk.2 Walkaround Throttle For Model Railways, Pt.1; Keypad Combination Lock; The Vader Voice; Jacob’s Ladder Display; Audio Lab PC-Controlled Test Instrument, Pt.2. October 1995: Geiger Counter; 3-Way Bass Reflex Loudspeaker System; Railpower Mk.2 Walkaround Throttle For Model Railways, Pt.2; Fast Charger For Nicad Batteries; Digital Speedometer & Fuel Gauge For Cars, Pt.1. November 1995: Mixture Display For Fuel Injected Cars; CB Trans­verter For The 80M Amateur Band, Pt.1; PIR Movement Detector; Dolby Pro Logic Surround Sound Decoder Mk.2, Pt.1; Digital Speedometer & Fuel Gauge For Cars, Pt.2. December 1995: Engine Immobiliser; 5-Band Equaliser; CB Transverter For The 80M Amateur Band, Pt.2; Subwoofer Controller; Dolby Pro Logic Surround Sound Decoder Mk.2, Pt.2; Knock Sensing In Cars; Index To Volume 8. January 1996: Surround Sound Mixer & Decoder, Pt.1; Magnetic Card Reader; Build An Automatic Sprinkler Controller; IR Remote Control For The Railpower Mk.2; Recharging Nicad Batteries For Long Life. February 1996: Three Remote Controls To Build; Woofer Stopper Mk.2; 10-Minute Kill Switch For Smoke Detectors; Basic Logic Trainer; Surround Sound Mixer & Decoder, Pt.2. March 1996: Programmable Electronic Ignition System; Zener Diode Tester For DMMs; Automatic Level Control For PA Systems; 20ms Delay For Surround Sound Decoders; Multi-Channel Radio Control Transmitter; Pt.2; Cathode Ray Oscilloscopes, Pt.1. April 1996: Cheap Battery Refills For Mobile Telephones; 125W Audio Power Amplifier Module; Knock Indicator For Leaded Petrol Engines; Multi-Channel Radio Control Transmitter; Pt.3; Cathode Ray Oscilloscopes, Pt.2. May 1996: Upgrading The CPU In Your PC; High Voltage Insulation Tester; Knightrider Bi-Directional LED Chaser; Simple Duplex Intercom Using Fibre Optic Cable; Cathode Ray Oscilloscopes, Pt.3. September 1997: Multi-Spark Capacitor Discharge Ignition; 500W Audio Power Amplifier, Pt.2; A Video Security System For Your Home; PC Card For Controlling Two Stepper Motors; HiFi On A Budget; Win95, MSDOS.SYS & The Registry. October 1997: Build A 5-Digit Tachometer; Add Central Locking To Your Car; PC-Controlled 6-Channel Voltmeter; 500W Audio Power Amplifier, Pt.3; Customising The Windows 95 Start Menu. November 1997: Heavy Duty 10A 240VAC Motor Speed Controller; Easy-To-Use Cable & Wiring Tester; Build A Musical Doorbell; Relocating Your CD-ROM Drive; Replacing Foam Speaker Surrounds; Understanding Electric Lighting Pt.1. December 1997: Build A Speed Alarm For Your Car; Two-Axis Robot With Gripper; Loudness Control For Car Hifi Systems; Stepper Motor Driver With Onboard Buffer; Power Supply For Stepper Motor Cards; Understanding Electric Lighting Pt.2; Index To Volume 10. September 1999: Automatic Addressing On TCP/IP Networks; Wireless Networking Without The Hassles; Autonomouse The Robot, Pt.1; Voice Direct Speech Recognition Module; Digital Electrolytic Capacitance Meter; XYZ Table With Stepper Motor Control, Pt.5; Peltier-Powered Can Cooler. October 1999: Sharing A Modem For Internet & Email Access (WinGate); Build The Railpower Model Train Controller, Pt.1; Semiconductor Curve Tracer; Autonomouse The Robot, Pt.2; XYZ Table With Stepper Motor Control, Pt.6; Introducing Home Theatre. November 1999: USB – Hassle-Free Connections TO Your PC; Electric Lighting, Pt.15; Setting Up An Email Server; Speed Alarm For Cars, Pt.1; Multi-Colour LED Christmas Tree; Build An Intercom Station Expander; Foldback Loudspeaker System For Musicians; Railpower Model Train Controller, Pt.2. January 1998: Build Your Own 4-Channel Lightshow, Pt.1 (runs off 12VDC or 12VAC); Command Control System For Model Railways, Pt.1; Pan Controller For CCD Cameras; Build A One Or Two-Lamp Flasher; Understanding Electric Lighting, Pt.3. December 1999: Internet Connection Sharing Using Hardware; Electric Lighting, Pt.16; Index To Volume 12; Build A Solar Panel Regulator; The PC Powerhouse (gives fixed +12V, +9V, +6V & +5V rails); The Fortune Finder Metal Locator; Speed Alarm For Cars, Pt.2; Railpower Model Train Controller, Pt.3. February 1998: Hot Web Sites For Surplus Bits; Multi-Purpose Fast Battery Charger, Pt.1; Telephone Exchange Simulator For Testing; Command Control System For Model Railways, Pt.2; Build Your Own 4-Channel Lightshow, Pt.2; Understanding Electric Lighting, Pt.4. January 2000: Spring Reverberation Module; An Audio-Video Test Generator; Build The Picman Programmable Robot; A Parallel Port Interface Card; Off-Hook Indicator For Telephone Lines; B&W Nautilus 801 Monitor Loudspeakers (Review). April 1998: Automatic Garage Door Opener, Pt.1; 40V 8A Adjustable Power Supply, Pt.1; PC-Controlled 0-30kHz Sinewave Generator; Build A Laser Light Show; Understanding Electric Lighting; Pt.6; Jet Engines In Model Aircraft. February 2000: Build A Multi-Sector Sprinkler Controller; A Digital Voltmeter For Your Car; An Ultrasonic Parking Radar; Build A Safety Switch Checker; A Sine/Square Wave Oscillator For Your Workbench; Marantz SR-18 Home Theatre Receiver (Review); The “Hot Chip” Starter Kit (Review). May 1998: Troubleshooting Your PC, Pt.1; Build A 3-LED Logic Probe; Automatic Garage Door Opener, Pt.2; Command Control For Model Railways, Pt.4; 40V 8A Adjustable Power Supply, Pt.2. June 1998: Troubleshooting Your PC, Pt.2; Understanding Electric Lighting, Pt.7; Universal High Energy Ignition System; The Roadies’ Friend Cable Tester; Universal Stepper Motor Controller; Command Control For Model Railways, Pt.5. June 1996: BassBox CAD Loudspeaker Software Reviewed; Stereo Simulator (uses delay chip); Rope Light Chaser; Low Ohms Tester For Your DMM; Automatic 10A Battery Charger. July 1998: Troubleshooting Your PC, Pt.3 (Installing A Modem And Sorting Out Problems); Build A Heat Controller; 15-Watt Class-A Audio Amplifier Module; Simple Charger For 6V & 12V SLA Batteries; Automatic Semiconductor Analyser; Understanding Electric Lighting, Pt.8. July 1996: Installing a Dual Boot Windows System On Your PC; Build A VGA Digital Oscilloscope, Pt.1; Remote Control Extender For VCRs; 2A SLA Battery Charger; 3-Band Parametric Equaliser; Single Channel 8-bit Data Logger. August 1998: Troubleshooting Your PC, Pt.4 (Adding Extra Memory To Your PC); Build The Opus One Loudspeaker System; Simple I/O Card With Automatic Data Logging; Build A Beat Triggered Strobe; A 15-Watt Per Channel Class-A Stereo Amplifier. August 1996: Electronics on the Internet; Customising the Windows Desktop; Introduction to IGBTs; Electronic Starter For Fluores­cent Lamps; VGA Oscilloscope, Pt.2; 350W Amplifier Module; Masthead Amplifier For TV & FM; Cathode Ray Oscilloscopes, Pt.4. September 1998: Troubleshooting Your PC, Pt.5 (Software Problems & DOS Games); A Blocked Air-Filter Alarm; A Waa-Waa Pedal For Your Guitar; Build A Plasma Display Or Jacob’s Ladder; Gear Change Indicator For Cars; Capacity Indicator For Rechargeable Batteries. March 2000: Doing A Lazarus On An Old Computer; Ultra Low Distortion 100W Amplifier Module, Pt.1; Electronic Wind Vane With 16-LED Display; Glowplug Driver For Powered Models; The OzTrip Car Computer, Pt.1; Multisim Circuit Design & Simulation Package (Review). April 2000: A Digital Tachometer For Your Car; RoomGuard – A LowCost Intruder Alarm; Build A Hot wire Cutter; The OzTrip Car Computer, Pt.2; Build A Temperature Logger; Atmel’s ICE 200 In-Circuit Emulator; How To Run A 3-Phase Induction Motor From 240VAC. PLEASE NOTE: November 1987 to August 1988, October 1988 to March 1989, June 1989, August 1989, December 1989, May 1990, August 1991, February 1992, July 1992, September 1992, November 1992, December 1992 and March 1998 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 tear sheets) 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. A complete index to all articles published to date is available on floppy disc for $10 including p&p, or can be downloaded free from our web site: www.siliconchip.com.au May 2000  39 SERVICEMAN'S LOG When is a fault not a fault? A common problem with some customers is that they don’t tell you all the symptoms of a fault or don’t mention some faults at all. The most obvious fault may be mentioned but when another one appears, the customer invariably shrugs his shoulders and says “Oh yes, it does that too”. It can be annoying at times. But first, to that heading; when is a fault not a fault? That comment is not as facetious as it may appear. This story is a secondhand one and I was involved as little more than a specta­tor. Nevertheless, it is a story well worth telling if only because the solution was quite unexpected. A friend of mine who is interested in computers decided to purchase two secondhand Pentium 133 computers on which to network his family business. He was assured that they were in good work­ing order but when he set them up at home, neither would boot up – there was just a blank screen. However, if he switched them off and then on again immediately they work­ed fine. This made him think that there was either something wrong with the setup or with hardware compatibility, so he started experimenting. First, he tried a succession of different monitors and found that some worked perfectly and others didn’t – even though none of the “faulty” monitors gave trouble on any other computer. So was there some incompatibility between the non-working SVGA monitors and the motherboards fitted in the two computers? If so, the problem could be either in the energy saver function or multisync resolution but he could find no correlation between these features or why some monitors worked and some didn’t. In the meantime he asked me and several other people he knew if we had a clue as to why this was happening. But although we suggested various things to try in the BIOS, plus checking the links on the motherboard, he wasn’t getting anywhere. Then, one day, he connected one of the computers to one of the monitors that originally wouldn’t work and suddenly it all worked perfectly. He repeated this test several times and it booted up every time. It was then he realised he had Sets Covered This Month • Pentium 133 Computer. • Sherwood Home Theatre RV-4070R • • • 40  Silicon Chip Amplifier. NEC N3419 TV set. Akai CT-21WA9AT Philips 2SSP1788/75R TV Set This speaker terminal panel came with an unusual manufacturing fault, as indicated by the yellow circle. accidentally forgotten to plug in the keyboard. No big deal – he plugged it in and the fault was back! Could it be a faulty keyboard? He acquired anoth­er keyboard and plugged it in and this time all was well. He checked the first keyboard on other computers and could find nothing wrong with it. So what was the difference between the keyboard that produced the fault and the one that didn’t? Well, the former was a 101-key keyboard, while the latter was a 105-key Windows 95 type. As he had plenty of others around he tried a variety of keyboards and established that the problem was entirely due to the computers being incompatible with the older 101 keyboards (pre-Windows 95). Naturally, he was relieved to have discovered a cure although, strictly speaking, it wasn’t really a fault at all. (Editor’s note: this problem is generally due to an incom­patibility between the keyboard controller chip on the mother­board and the microcontroller in the keyboard itself). Fig.1: part of the switchmode power supply in the NEC N3419. The 5-pin IC, Q801, is at lower right. It’s heatsink had been loaded with five extra heat­ sinks in an effort to control overheating. was narrowed down to the speaker connections. It applied to the right channel only, where wiggling the speaker leads even slightly was enough to cause the amplifier to close down. Curious, I placed an ohmmeter across the terminals with the set switched off and inserted a speaker lead in the negative terminal. As I did so, the multimeter showed a dead short. As shown in the accompanying photo, the spring-loaded speaker terminals were part of a panel, with the positive (red) terminals at the top and negative (black) terminals along the bottom. Initially, it was hard to see how this setup could possi­ bly produce an intermittent short circuit, as the two terminals are well spaced. Home theatre system Young David, a 17-year old, was very proud of his Sherwood Home Theatre RV-4070R amplifier but he had become very concerned that it was intermittently cutting off. He could not think why it was happening as he was sure he was taking good care of it. Eventually, he go fed up with it and decided to take his pride and joy to the “doctor’s” to get it fixed. To begin with, I had great difficulty in getting it to produce the fault and was about to dismiss it as being something external to the amplifier, when it finally failed. Eventually, after a lot of tapping, heating, cooling and various other tests, which young David really wouldn’t want to know about, the problem May 2000  41 It all became clear when I removed the terminal panel and took a close look at the back. As shown in the photo, the tin­plate connectors from the terminals are all brought out along a common edge. The connectors from the red (top) terminals are towards the rear, while the connectors from the black (bottom) terminals sit closer to the panel. Unfortunately, due to a manufacturing defect, the connector for the right channel negative terminal had not been pushed all the way down into the plastic moulding. Instead, it was loose and could easily come into contact with the positive terminal connec­tor behind it. And, as I quickly discovered, inserting the speaker lead only made things worse. When this was done, the spring-loaded plastic tab pushed against the lead which in turn pushed the metal connector backwards so that it came into contact with the positive connector. Fortunately, the cure was a simple 42  Silicon Chip one – I pushed the connector all the way into the plastic moulding using a flat-bladed screwdriver and used a dab of super glue to ensure it wouldn’t come loose again. It was a rather strange fault but at least the repair was easy and it didn’t take too long to track down. A set from the country There’s often quite a bit of difference between service work in the city as compared to the country and that was brought home to me recently by this story. City technicians generally have much better access to tech­nical information and spare parts than their country cousins. In the country, it really is a case of sometimes making do and inventing solutions from limited resources. Obviously, if a country serviceman only has a 100µF capacitor and the circuit calls for a 47µF, the 100µF capacitor will have to do. The Hayes lived in the country on a small farm and they had had a few problems with their 34cm NEC N3419 portable. This little set uses a Daewoo C43 chassis, is made in Korea, and is very popular with many brands. But it is getting a little ancient now. The set had been cutting out intermittently for quite some time and though the local technician had tried his best on several occasions, it was finally brought in on a trip to the city. When I removed the back cover, I was immediately aware of an array of four extra heatsinks which had been screwed onto the manufacturer’s original heatsink for Q801 (STR5412), 5-pin IC in the switchmode power supply. I also noticed several possible dry joints and there was brown goo everywhere, especially around IC 1502. Despite all the extra heatsinks, they still became extreme­ly hot when the set was running which explained why the set was intermittently cutting out. The reason wasn’t hard to find – the high tension was high at 120V instead of 103V, as shown on the circuit. And that brings me to the real point of this story. The manufacturer has issued some modifications for this circuit, a fact that would be unknown to many technicians in remote areas. These modifications involve two capacitors, C811 and C808, both originally specified as 4700pF. Anyway, I replaced the IC (Q801), removed the additional heatsinks, and changed C811 and C808 to 2200pF and .001µF respec­tively, as recommended by the manufacturer. I also attended to the suspect joints and cleaned up the brown goo. Anyway, the set was now delivering the correct 103V HT and was running cool. The height had to be readjusted but that was that. I don’t know how much extra life the additional heatsinks gave to this set but at least the bloke was trying with whatever came to hand. And he wouldn’t have known about the manufacturer’s modifications. Finally, I would remind all those who work on this chassis to always change C434, a 10µF 160VW electrolytic capacitor on pin 4 of the horizontal output transformer. This will help avoid expensive pyrotechnics. Akai TV receiver Mr Keenan brought in his 2-year old Akai CT-21WA9AT 53cm TV set, complaining that it would switch off by itself after a while and that there was a white line across the screen. Consid­ ering the set was so new, I asked him if it might still be under warranty but it wasn’t. With the back off, it didn’t take long to determine that the fault was in the vertical output stage, IC401. This stage takes its supply (Vcc3, pin 11) from pin 4 of the horizontal output transformer (T402) and was loading the horizontal output stage. The vertical stage was drawing too much current and this, in turn, caused Q403 to eventually turn the set off. Replacing the IC fixed the problem but I was a bit nervous as to what had caused it to fail in the first place. I started by replacing the two electrolytics (C910, C912) in the power supply. I also checked the HT which was correct at 110V and then had a chat with a friendly Akai service agent that I know. He got onto the Akai Service Guide CTV-042 Code 204 on the Internet. This suggested that three 0.1µF green mylar capaci­tors – C911, C424 and C351 – should be changed in the CT2119AT series, to which this set belongs. He also showed me a few other modifications which, at the time, were irrelevant to the symptoms at hand. I changed the three green capacitors but I must say I was rather surprised at the advice to do so as I haven’t previously had any problems with this type of capacitor. To be on the safe side, I also replaced a few suspect-looking electrolytic capaci­ tors around the vertical IC. By now, I was feeling pretty confid­ent, so I boxed it up and put it aside for soak testing. Some time later, I decided to check on the precarious state of some of my shares. “Why not use Teletext?”, I thought. The Akai was the nearest set to hand but when I hit the text button on Channel 7, it didn’t immediately show the Index on page 100. Instead, the display was a mixture of text from a variety of pages and the clock jumped from time to time instead of showing every second. Now Teletext can be a rather temperamental feature and is highly dependent on a good quality signal (preferably with no ghosting and not too strong). With this in mind, I checked the reception on Channel 7 and it looked great. Just to make sure, I tuned in a UHF translator station and check­ed the text there too but again the Teletext was quite poor. I then tried another TV set, which performed perfectly. Obviously there was a fault in the Teletext section of the Akai – but where to start? I thought I would begin with the easy things, like the RF AGC. To do this, it is necessary to put the set into the Test mode or Adjust Menu, by switching the set off and on again while holding the volume + and - buttons at the same time. Pressing 2 on the remote keyboard brings on the RF AGC adjust menu which I then adjusted with + and - on the remote control, until the snow on the screen just disappeared. I then turned the set off and on again. This made no difference to the Teletext reception, which was slowly getting worse, with the clock not appearing for a very long time. Mr Keenan then phoned to ask about the set’s progress and I told him that although I had fixed the two faults he had com­plained about, there was still a problem with the Teletext. My immediate impression was that Mr Keenan had known about this problem all along because he wasn’t the slightest bit surprised. Now Teletext hasn’t been a huge success in this country and most people can take it or leave it but not Mr Keenan – he definitely wanted it fixed. And so I delved back into the guts of the set. The Teletext circuit consists of only two ICs (IC801 and IC802) and two tran­sistors (Q801 and Q802). Surely it shouldn’t be that hard to fix! I began by checking the 5V rail to this circuit and it was spot on. I then checked that crystal X801 was oscillating at 13.875MHz, which it was. The CRO also told me that I had video all the way to pin 3 of IC801. Unfortunately, there is no further technical information on the Teletext circuit (no block diagram or voltages), except for the adjustment of variable inductor T801 – this should give 2.5V on pin 28 of IC801. And that was my first clue – this voltage was low at only 0.5V and adjusting T801 didn’t make much dif­ference, although the display became worse after losing its horizontal hold. I also noticed other problems with text – in the mix mode, the text characters would lose their horizontal sync and tear. By delicately setting T801 I could almost lock it, implying a loss May 2000  43 of some sort of sync. I checked the two transistors and all the diodes and they were all OK. Frankly, I was running out of ideas. I went back to my Akai mate and he found that there was a modification involving an extra 1µF capacitor between pin 21 of IC801 (the 5V supply) and chassis. Encouraged, I hastened back to fit it only to find the set had already been modified on the PC board side. There was nothing for it but to order and replace the com­ponents I couldn’t really check, namely the two ICs, the crystal, inductor T801 and varicap diode CD801. I decided to change the crystal because, although it may be oscillating, there could be something wrong with the amplitude. While I was waiting for the new parts, I experimented with heating and freezing all the relevant circuits. This made no difference except that the problem was gradually getting worse. Eventually over $100 worth of parts arrived and I fitted them one at a time to try to pinpoint the culprit. Unfortunately, they made no difference. Once again I pestered my Akai mate and this time he found a page of AASC Service Hints for this series with similar (but not exactly the same) symptoms. This suggested EEPROM IC602 – ST24CO4(SGS) – and the reader can imagine my frustration when it arrived and still didn’t fix the fault. There are only about 50 components 44  Silicon Chip in this circuit and I had already replaced five of the main items – only 45 to go. I started with the capacitors, especially the high capacity (104) brown ceramic types that often give trouble, and work­ ed down. I also replaced the two electrolytics (C803 and C811) but nothing made any difference. By now, this repair was no longer economic but I hated being beaten, especially after all my work. I now decided to measure all the resistors, starting with the highest values first and working my way down. Everything was fine until I came to R806 33kΩ. It measured high at nearly 1MΩ. By the time I had removed it, it was even higher. This, I felt sure, was it. I replaced the resistor, fitted everything back into position and switched it on. The first thing I had to do now was to retune T801 for 2.5V on pin 28. This time, the voltage was much healthier and it didn’t take much adjustment to reach the correct value. What’s more, the screen was display­ing the full index and the clock was updating every second. Even in mix mode, the text was perfect and locked solid. It is extremely unusual for a 33kΩ 0.5W resistor to go high in this manner. The problem now is what to charge for finding and fixing it. Whatever the figure is, it won’t be big enough! Different standards It is always interesting to see the varying approaches used by different countries to achieve the same result. With today’s multinational companies, it is not unusual to see European chip­sets fitted in Asian TV sets, though often without large chunks of the technology within those chips being used. Almost all Asian factories (Japan, Korea, Taiwan, Hong Kong and China) have the aquadag of the CRT connected to chassis, whereas Philips and other European sets use an above chassis design connecting to a beam limiting circuit. Aquadag, by the way, is the water-based metallic black paint on the exterior of the picture tube – it acts as a large capacitor plate, in con­ junction with the internal anode, to filter the EHT. One of the main problems when servicing TV sets is finding a convenient and reliable chassis reference point for the meter. However, one can depend on Asian manufacturers with their chassis connected tubes. R e c e n t l y, I h a d a P h i l i p s 2SSP1788/75R Symphobass come in with low contrast and brightness. The first problem was to work out what chassis was used and whether it was designed for Austra­lia standards. It was built around 1991 and for those familiar with the Philips nomenclature, these points can be worked out from the model number. I had to look it up and the Australian version is a G112S (a variant of the G110 series). Because Philips have used the above-chassis system in their colour TV sets since the K9 chassis in 1974, I knew from experience to expect approximately +15V on the tube aquadag with respect to chassis, depending on the beam current drawn at the time. Based on this background, I went straight to this point and was not surprised to find it measured 0V. Following the path back from the aquadag to the beam limiting circuit was not so easy. The lead goes onto the CRT socket board (circuit C) and out via plug and socket 4P2/1S7 to D63. This then goes to plug and socket 1M7 (circuit D) and to the chassis end of the EHT tripler (pin 7) inside the horizontal output transformer (5901). From there, the path follows the “AQUA” D103 line and this goes to TP43. A number of circuits are involved with the beam limiting. First, there is TR7911, a protection transistor, and then the east/west circuit and vertical outputs, which are connected to keep a constant picture size during changes in beam current. I was looking for a source for the 15V DC but with so many affiliated circuits, I wasn’t sure which was the significant one. A beam limiting line ran via plug and socket C74 back to the C circuit so I decided to start looking here first. To cut a long story sort, I finally found that resistor R3970 (22kΩ) between the +34V rail and the beam limit line (C74) was open circuit. Replacing it restored the brightness and con­trast – and the average 15V on the aquadag. One can be lucky sometimes. 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. 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 PRODUCT SHOWCASE Exceptional new Agilent scopes from HP Agilent Technologies Australia Pty Ltd, a subsidiary of Hewlett-Packard, has introduced a series of five oscilloscopes which combines the channel count, memory depth, display definition and triggering that design engineers need to debug mixed analog and digital designs. Users can now easily see more signal detail when debugging and verifying mixed analog and digital designs. The Agilent 54600 series now offers multiple-channel configurations: 2- and 4-scope channels or the mixed signal oscilloscope (MSO) with 2+16 channels (two analog channels plus 16 integrated digital channels); 2MB of MegaZoom deep memory that respond instantly to control inputs; a high‑definition display system and powerful triggering. These four attributes differentiate the Agilent 54600 series oscilloscopes from other 100MHz scopes and address the challenges of the digital designer. The 2+16 MSO models (60MHz 54621D and 100MHz 54622D) combine the detailed signal analysis of a ’scope with the multi‑channel timing measurements of a logic analyser. Users can view two analog and up to 16 digital signals simultaneously, to debug microcontroller problems that would stymie a conventional scope, such as triggering on a mix of digital bus states and analog signals. The 4‑channel, 100MHz scope (54624A) gives engineers the channel count and measurement power they need for designs that include heavy analog content. There are also budget 2-channel models (60MHz 54621A and 100MHz 54622A). All models have two megabytes of “MegaZoom” deep memory behind every channel which provide deep capture without the sluggish response and complex operation associated with some deep‑memory scopes. Because MegaZoom is not a special mode, it is always available to help find details buried in complex signals, to discover anomalies in the absence of good triggering events, and to correlate high‑speed digital control signals with slower analog signals. This, combined with the high‑ definition display system, provides unsurpassed horizontal screen resolution and the ability to map deep memory into 32 levels of gray scale at up to 25 million vectors per second. This combination enables users to view and understand complex signal details. It also greatly decreases the chance of missing a narrow, occasional transient, or overlooking a glitch or distorted edge that impacts circuit operation. Further information on these products may be found on the Web at www.agilent.com/find/MegaZoom For further information on pricing, availability and technical information, contact 1800 629 485 or email on info_tmo<at>agilent.com May 2000  53 Digital-ready TV signal analyser Matchmaster Communications has introduced the Italian-made RO.VE.R. TDA-4a, a lightweight, battery operated digital field strength meter for the TV installation and service industries. With a frequency range of 47MHz to 870MHz, the instrument covers both VHF and UHF TV as well as FM radio channels used in Australia. It can carry out the following measurements: video carrier level, digital package average power, audio carrier level, FM radio carrier level, audio/video carrier delta plus analog and digital TV carrier to noise ratios. All measurements are shown on a multi-mode LCD panel which gives a variety of readings. A switchable FM or AM universal audio demodulator is also tunable from 44MHz to 870MHz. Received au- Safer fume extractors dio can be heard through an inbuilt speaker. An inbuilt rechargeable NiCd battery pack gives up to 12 hours portable use. A 240V mains adaptor and 12V DC car cigarette lighter adapter are also included. These will power the unit as well as charge the battery. The meter is fitted with a male “F” style 75Ω RF input connector with male to female and F to IEC adaptors supplied. The instrument is housed in a heavy duty plastic carry case which also has provision for storing the test leads and power supply. For the TV antenna installer, the CATV cabler and related areas, a device such as this would save an enormous amount of time and trouble. Being able to read signal strengths directly over all the required channels would make antenna aiming a breeze and also the detection of faults much more simple. With a trade price of $1300, the RO.VE.R. TDA-4a is available through sole agent in Australia, Matchmaster Communications, 48-50 Belmore Rd, Punchbowl NSW 2196. Phone (02) 9153 6666, Fax (02) 9153 9099 . The Alsident System ESD 50 and ESD 100 series of fume exhaust arms from Pyrotek are the first to gain certification for use in electrostatic discharge sensitive and explosion sensitive applications. This certification is also good news for computer and other electronics manufacturers whose reject rates are lessened by any measure that lowers the risk of electrostatic discharge through sensitive components. It is equally important for laboratories or chemical, pharmaceutical and food industries facing the need to exhaust powders, combustible gases or dust/air mixtures or fumes which pose possible explosion hazards. Extracting solder fumes is another example. The systems can be mounted on a wall, worktable or ceiling and the three joints enable the operator to effortlessly position the mount anywhere within its 1350mm reach. Adhesive resins do not threaten the conductivity of the system. The entire pipe system displays a resistance of substantially less than 1MΩ. The ESD 50 extracts at 85 cubic metres per hour while the ESD 100 exhausts at 400 cubic metres per hour. Over 100 variations in seven models of fume extractors are available with details in a free 18-page booklet, available on request to Pyrotek, 147 Magowar Road, Girraween NSW 2145. Phone (02) 9361 1333. Telephone Technical Services imports new US range of phone test equipment One of the side-benefits to the deregulation of the Australian telephone industry is increased access to installation, service and maintenance work for approved personnel. However, the availability of suitable equipment has been something of a problem. A Brisbane company, Telephone Technical Services, recognised the need for a range of high quality telephone and line test equipment and so has recently started importing the US-made “Test-Um Inc” range. Of particular interest are the phone test sets (called “butt phones”) which offer a broad range of testing facilities. There 54  Silicon Chip are two in the range, the “Lil’ Buttie” LB100 and the “Lil’ Buttie Pro” LB200. The big difference between the two is an LCD panel on the Pro model which reveals even more information about the line under test – even caller ID information. Other equipment includes tone generators and tracers, tell-all testers for both phone and data lines and similar devices. For more information contact Telephone Technical Services on (07) 3286 6388, Fax (07) 3286 6399, or via their website at www. ttservices.com.au Security video recorder with time-lapse With the proliferation of miniature video cameras (see below), many organisations have linked video recordings into their security systems. Usually a standard VCR is pressed into service but these have several shortcomings in this application. Jaycar Electronics have addressed this problem with the release of a video recorder specifically designed for the purpose. Its major advantage is a variety of recording modes including the ability to store 24 hours of video and audio on a single E-180 (three hour) VHS tape. Recording times can be programmed for certain periods on a daily or weekly time frame, they can be continuous or they can be time-lapse. They can also be triggered by devices normally used to trigger an alarm (eg, PIRs, light beams, door switches, etc) or by the alarm unit itself. When an alarm event is triggered, the recorder will sound a buzzer and record for a predetermined period. Alarm event information is also recorded and up to eight events can be displayed, by date and time, on an external monitor. At the end of the tape the recorder can be set to rewind and re-record the same tape or it can eject the tape and wait for a new tape to be inserted. A further possibility is the use of additional recorders in series where at tape end the first signals the second to start recording and so on. Various playback modes are available including standard, slow, fieldby-field, reverse direction and slow reverse direction. Rear panel connectors are provided for video, audio, alarm in (trigger), alarm reset, alarm out, one shot trigger, trigger out, tape end, series in and series out. The recorder operates on 240V AC With a recommended retail price of $995.00, the QV-3050 Time-Lapse VCR is available from Jaycar Electronics stores throughout Australia or via the Jaycar Mail Order service (Phone 02 9745 3222) or their website: www. jaycar.com.au Mini video cameras to suit Two miniature video cameras, one colour and one monochrome (b&w), which would mate perfectly with the above Time-lapse VCR are also available through Jaycar Stores. Both are pinhole models, meaning a hole only a couple of millimetres in diameter is needed to view through. Camera size is just 36mm square x 30mm including lens. Both feature audio and video outputs, the audio via an RCA connector and video via a BNC connector. Power (12V DC <at> 120mA b&w, 130mA colour) is via a standard 2.1mm DC jack. Video output is 1V pk-pk <at> 75Ω and the B&W model operates down to 0.1 Lux (that equates to a scene lit by dim moonlight!). These cameras also respond well to infrared (invisible) light. The colour camera requires 2 Lux. A tiny swivel mounting bracket is also supplied which would enable the camera to be permanently mounted and aimed. The B&W model has a 1/3-inch Sony CCD image sensor giving 400 line resolution while the colour camera features a 1/4-inch CCD sensor and 330 line resolution. The monochrome camera (QC3476) has a recommended retail price of $149.00 and the colour version (QC3486) sells for $229.00. For more information see page 127 of the new Jaycar catalog, visit any Jaycar Electronics store or visit the website, www. jaycar.com.au TOROIDAL TRANSFORMERS FOR SILICON CHIP AMPLIFIERS 13W CLASS A AMPLIFIER 80VA for single channel monoblock 240:2x21V/1.9A 160VA for amplifier as published 240:2x21V/3.8A 160VA low flux design + flux band 240:2x21V/3.8A 160VA low flux design + flux band 240:2x42Vct/1.9A ULTRA LOW THD 100W AMPLIFIER 160VA for single channel monoblock 240:2x35V/2.25A + 2x50V/0.1A 300VA for dual channel amplifier 240:2x35V/4.5A + 2x50V/0.1A $35.45 $42.50 $65.90 $74.40 $50.70 $60.45 500W MONO AMPLIFIER, as published 800VA 240:2x57V/7A $134.50 All prices include WST. Freight extra HARBUCH ELECTRONICS PTY LTD Ph 02 9476 5854 Fx 02 9476 3231 DSE digital pH meter Dick Smith Electronics has released a high quality Digital Water pH Meter that is compact enough to fit into a pocket and gives a direct reading of pH on its liquid crystal display. The lightweight Digital Water pH Meter can be used in many different areas such as swimming pools, spas, aquariums, aquaculture, hydroponics, photographic processes, cooling towers, water and wastewater treatment, generators, car washes and many more applications. Accuracy is maintained by a pH7 buffer solution although for industrial or laboratory use, known buffers are recommended. The pH Meter comes complete with a protective carry case and batteries and has a retail price of $96.00. It is available from Dick Smith Electronics stores Australia wide or via mail order, or through the Dick Smith Electronics website www.dse.com.au May 2000  55 Over the years, many LED Dice circuits have been published – but none are as simple as this one! With just one PIC micro and a handful of other components it’s cheap and easy to build, too! By DOUG JACKSON F IRST OF ALL, let’s settle an argument before it starts. Die or Dice? Sure, the venerable Oxford would have us say one die, two dice. But every man and his dog uses the word “dice” for both singular and plural. So we’ll stick with Fido and use dice. But just in case you still want to argue, we’re correct either way with this circuit because it contains not one but two dice. So it’s perfect for all of those games which require the roll of two dice at once. By the way, if you only want a single version, that’s easy too: just leave out one set of LEDs and driver resistors. The PIC micro will never know! Ahh, the PIC micro. We were getting to that. Using a PIC allows us to significantly simplify our dice circuit. Previous designs have typically used at least two ICs, four or more transistors and many resistors and capacitors. And they’ve been fairly current 56  Silicon Chip hungry, discharging batteries far too quickly. Using a single microcontroller not only allows simplification, it also lets us add features that previously haven’t been available: the ability to recall the last roll, for example. This is the first in a short series of articles we hope to publish over the next few months which will use PICs in a variety of simple applications. What makes this series a little different is that we intend to guide you through the hardware and software design step-by-step so that you get a better idea of the design process. It’s an ideal way for a beginner in micros to get a grasp on the fundamentals. We are not planning to print de- tailed software descriptions, though – magazine space simply does not allow this. However, a web site has been set up to provide detailed software discussions of all the projects presented in the series. Before we start our design, let’s look at the basis for all of these projects, the PIC microcontroller. Pick a PIC The PIC microcontroller family covers a wide variety of devices incorporating embedded peripherals, such as: integrated timers; analog-to-digital converters; digital-to-analog converters; RAM and Electrically Erasable ROM (EEROM). Our project will use a Microchip PIC 16F84 microcontroller. This device has 1K of on-board flash programmable ROM, 68 bytes of RAM, 13 I/O lines and an internal counter/timer. Each I/O line can source or sink approxi- The PC board version of the LED Dice was housed in a zippy box with the LEDs and switch emerging through the front panel. The red LEDs form one dice while the orange LEDs form the second (yes, we know we said we used green ones!). The second version of the LED Dice is the same circuit but is built on Veroboard and this forms the lid of a zippy box. Some components are mounted on the other side of the board. Note that some component values have been altered. mately 50mA making it ideally suited terms are not interchangeable – a creep’ interfering with the completion to directly driving a LED display. microcontroller actually contains a of our project. The 16F84 has enjoyed significant microprocessor but it also contains The specifications for our project popularity in the hobbyist market re- memory, I/O (input/output) lines and are simple – we will design an eleccently. A major reason for this is that often other features. tronic simulation of two dice, using it has a flash ROM, making it easily 14 LEDs. A single pushbutton switch The project re-programmable. The advantage of will control the rolling of the dice in the flash ROM is that it doesn’t rethe following manner: Before we start designing our Dice, quire an ultraviolet eraser to erase we need to decide exactly what it does  When the button is pushed for a the device. and how it does it. In doing this, we short period (say less that 0.5 sec), the M i c r o c h i p ’ s w e b s i t e a t reduce the likelihood of ‘specification dice turn on and display the result of the last roll. (http://www.microchip.com)  If the button is pushed provides full documentation for greater than about for the entire range of PIC 0.5 seconds, both dice devices, as well as a full are cleared then roll indevelopment environment dependently, eventually (MPLAB). slowing and stopping afA simple PIC programmer ter the button is released. was published in the March  In all cases, the result 1999 issue of SILICON CHIP is displayed for 20 sec(back issues are available for onds and then the dice $7.00 including postage and turns itself off. packing [$7.70 after June]). It would be desirable to This programmer is suitable have no power switch, so for programming the devices we have to minimise curwe will use in this series. rent consumption while You may have noticed we the project is ‘off’. use the word “microconNow that we have detroller” where many people Fig.1: all six faces of a dice with the standard patterns cided (and written down) use “microprocessor”. The shown. May 2000  57 Fig.2: driving LEDs from a PIC is easy! All you need to do is limit the current from the PIC to a level which the LEDs can handle – and tell the PIC to light them up! what we will build, let’s start the fun stuff. The hardware Lets look at a good old-fashioned dice. As we all know, it has six sides, with one, two, three, four, five or six “spots” or dots on each. (Did you know that adding the opposite sides of a dice always equals 7?) If we analyse the various dot patterns in Fig.1, we can see that the following rules apply:  The central dot (7) operates inde-pendently.  Opposing corner dots (1) and (3) appear simultaneously.  Opposing corner dots (2) and (4) appear simultaneously.  Middle dots (5) and (6) appear simultaneously. Fig.3: providing an on/off switch is also simple with the right instructions in the program. Therefore we can actually drive all seven LEDs from only four I/O pins on the microcontroller. Remembering that our goal is to emulate the operation of a standard dice using LEDs, let’s start by connecting some LEDs to the microcontroller. Driving LEDs with a PIC microcontroller is a simple exercise. Because the PIC outputs can drive up to 50mA and LEDs typically require only 1020mA, we can drive each LED directly via a suitable series current limiting resistor. Fig. 2 shows typical connection details. But what are the values of the current limiting resistors? Ohm’s Law tells us that one: R = E/I We know that “I” is 20mA max. and that “E” in this case is the supply Fig.4: if timing accuracy is not important, a simple R/C circuit attached to the PIC’s “OSC” input is all you need. voltage (5.4V) less the forward voltage drop across each LED (typically 2.1V). So for a single LED: R = 3.3/.02 = 165Ω. Where there are two LEDs in series the forward voltage drop doubles so the formula becomes:      R = 1.2/.02 = 60Ω. To save drain on the battery (and therefore give it more life), we’ll be a bit conservative and go for slightly less current through the LEDs, resulting in resistor values of 220Ω for the single LEDs and 100Ω for the double LEDs. Now that we have designed the output, we need to consider our input; something to “roll” the dice. This can be done simply by connecting a pushbutton switch between the supply voltage (VCC) and one of the PIC inputs that provides an interrupt Fig.5: the PIC drives the LEDs for about 20 seconds and then goes to sleep to conserve the batteries. 58  Silicon Chip Parts List – PC Board Version 1 PC board, code 08105001, 58 x 73mm 1 130 x 67 x 44 plastic case (Jaycar HB-6013) 1 front panel label, 124.5 x 62mm 1 4 x AA square battery holder 1 PC-mount SPST pushbutton switch (Jaycar SP-0722) 4 9mm untapped spacers 4 M3 x 15mm CSK steel or nylon cheese-head screws 4 M3 nuts Fig.6: this code tells the PIC to determine a random number and store it in a certain location, then display the result. capability (we’ll look at interrupts later). Fig.3 shows an example. Note that the input is held low by a 4.7kΩ resistor to ensure that random noise picked up on the input pin does not cause an input to be recorded. Clock and power supply All that remains is to add a power supply and provide some sort of clock circuit to the microcontroller. A clock circuit, by the way, has little to do with telling the time. It provides pulses at a specific rate which cause the microcontroller to undertake certain tasks. First, though, the supply: the most simple power supply we can have is four AA batteries. This provides 6.0V (4 x 1.5V). If a series diode is placed between the batteries and the PIC, the available supply voltage drops to about 5.4V. This is due to the nominal 0.6V voltage drop across a forward-biased silicon diode. 5.4V is within the PIC’s rated input voltage range of 4-6V whereas 6V from the batteries would be right on the upper limit. The series diode also protects the PIC from damage if the battery is accidentally connected back to front. Traditionally, microcontroller systems have used some sort of 3-terminal voltage regulator to ensure that 5V is available to the CPU. We decided not to use a 78L05 or similar 3-terminal voltage regulator, as the 4mA standby current drawn by the regulator would swamp the sleep current of the PIC (about 7µA), giving poor battery life. So in theory, a set of four ‘AA’ alkaline batteries with a capacity of about 800mA.h should be able to last about 114,000 hours while in sleep mode. (That’s about 13 years . . . we suspect that the batteries will die of their own accord LONG before this time!). Of course, current consumption will increase to about 120mA during operation. PIC microcontrollers can use a variety of clock circuits, ranging from crystal controlled oscillators if accurate timing is required, through to simple RC (resistor/capacitor) networks. In our application, we are not concerned about speed and clock accuracy, so we use an RC oscillator. This is shown in Fig.4. This works simply by charging the 100pF capacitor through the 10kΩ resistor until the microcontroller’s threshold voltage is reached, at which time the capacitor discharges quickly through the microcontroller. When the voltage falls to the micro’s lower threshold it goes high, allowing the capacitor to start charging once again. The final circuit Tying all of this together, we come up with the circuit for the hardware of our LED Dice simulation. This is shown in Fig.5. Semiconductors 1 PIC16F84 programmed microcontroller (IC1) 1 1N4004 diode (D1) 7 5mm red LEDs (LED1 - LED7) 7 5mm LEDs, another colour (LED8 - LED14) Capacitors 1 10µF 16VW PC electrolytic 1 .001µF ceramic disc Resistors (0.25W, 5%) 2 10kΩ 1 4.7kΩ 6 100Ω 2 220Ω Parts List – Veroboard Version 1 piece of Veroboard or other strip board, 107 x 57mm 1 112 x 60 x 27mm plastic case 4 AA batteries 1 PC-mount SPST pushbutton switch (Jaycar SP-0722) Semiconductors 1 PIC16F84 programmed microcontroller (IC1) 1 1N4004 diode (D1) 7 5mm red LEDs (LED1 - LED7) 7 5mm LEDs, another colour (LED8 - LED14) Capacitors 1 10µF 16VW PC electrolytic 1 .001µF ceramic disc Resistors (0.25W, 5%) 2 10kΩ 1 4.7kΩ 6 100Ω 2 220Ω Miscellaneous Hook-up wire, bubble-wrap plastic or other suitable insulation. May 2000  59 Fig.7: here’s how to mount the PC board to the front panel. Note the distance from the board to the LEDs and also the fact that the electrolytic capacitor will need to be bent over to allow clearance. Now you can see the simplicity of using a single chip microcontroller. The total circuit contains just one IC and a handful of discrete components! Random numbers One item that we will look at from the software is the generation of a random number. Mathematically, generating a truly random number is a very complex exercise. In our simple PIC circuit, we can generate a random-enough number in a couple of ways:  A seemingly random number can be obtained by timing how long the button is held down, using a timer that is incremented VERY quickly. (It would be a very rare person who could hold the button down for exactly 2243ms every time).  Alternatively, we could imple­ment a mathematical pseudo-random number generator. This requires the use of multiplication and division. A pseudo-random generator generates a very long sequence of numbers that eventually repeats, after many cycles. In our project, we use the first method. We sample the internal timer (TMR0) which is constantly increment­ ing at one quarter of the clock speed (about 256kHz) and store the sample in a variable, as long as the button is held down. A short code routine to perform this function is shown in Fig.6. As previously mentioned, the microcontroller will be spending most of its time in sleep mode (especially while it is sitting majestically on the mantelpiece!). In sleep mode, the internal oscillator is stopped and the device consumes about 7µA. Interrupts In order to wake up from sleep mode, we need to have an ‘interrupt’ Fig.8: the front panel for the PC board occur. Interrupts can be effected from version mates with the PC board a variety of sources but they always underneath. signal some external change. The LED Dice project that we are building has the pushbutton connected to bit 1 of Port B (RB0). This pin also functions as an ‘interrupt’ input. When the voltage level on this pin changes, an interrupt is generated, causing the PIC to stop whatever it was doing and to do something else. It is this interrupt that causes the PIC to wake up from its sleep mode. Interrupts in the PIC can be ‘global’ in nature (Global Interrupt Enable [GIE] bit set) or localised. In our example, we would like to continue executing instructions immediately following the ‘sleep’ command, so we need to ensure that the GIE bit is clear. Global interrupts cause program execution to branch to location 4, which is useful for a more traditional Fig.9: this is the component overlay for the PC board version. Compare this with the vectored interrupt approach photograph alongside. Note that two of the LEDs (labelled LED3 and LED13) mount the which we will cover in later other way around to the rest. The second colour LEDs can be green, orange or yellow. 60  Silicon Chip articles. Code to implement the interrupt functionality would look like that shown in Fig.11. Note that once the microcontroller has received an interrupt, it wakes and immediately disables any further interrupts. Multiple levels of interrupts can cause unexpected program errors, so we stop any further interrupts from occurring. Now that we have examined how to implement input, output, random num­ber generation and interrupts, we can tie all of this together and produce the code that will actually run the dice. There is a small amount of ‘glue code’ around these functions to produce actual running code. I recommend that you obtain the program listings and study them for more information. When you study the listings, you may find that there are faster, more elegant ways to do what has been done. Remember that there are commercial realities as to the time spent on producing a particular solution and that some times, doing something the ‘no brain’, long way is actually faster to develop. This is an embedded system and in a simple system like this, the emphasis is on producing a result, not on producing the most elegant code available. (Have you actually looked at the code in your microwave oven controller? Believe it or not, many of these Fig.10: full-size PC board pattern for those wishing to make their own boards. Otherwise, use this pattern to check commercial boards before commencing construction. This photo of the Veroboard version is reproduced slightly larger than actual size, so you can see exactly where the components go. Note that some of the components are on the other side of the board. The black object below the IC is a header pin set with a shorting link, used as an on-off switch in the prototype. However, this is considered unnecessary and has not been specified in the parts list. contain microcontrollers!) As previously mentioned, in an article of this length it is not appropriate to include bulk source code listings, so the source code and corresponding hex file to supply to the PIC programmer are available on my web site (http://www.dougzone.com). PIC programming To make the LED Dice operate you need to load the LED Dice program into a PIC. You can either purchase a pre-programmed PIC or you can program one yourself. Programming one yourself allows you to enter the world of PIC software design. In order to program the PIC, you need some basic tools. First, you need the Microchip assembler and simulator (MPLAB), available as a 9MB download from the Microchip web site (http://www.micro-chip.com). This is a HUGE download but you only need it once. Remember to make a backup. In addition to the assembler, you need a programmer. The PIC programmer that I use is based on a design Fig.11: this code will implement the interrupt function. May 2000  61 with a multimeter to minimise errors. When bending component leads, remember that using a pair of needle nose pliers will minimise stress while performing the bend. Continue the assembly by soldering in the 18-pin IC socket, ensuring that the indentation on the socket agrees with the position shown on Fig.9. Next, solder in the 14 LEDs. Be careful with their orientation, as they will not operate if they are installed backwards. The short leg is the cathode. Note that two of the LEDs are mount­ ed the opposite way around to the rest! Mount the pushbutton switch directly to the PC board, ensuring its straight edge is aligned as shown. Finally, connect the battery holder, ensuring that the batteries are not installed. Veroboard version Here’s what it looks like assembled and opened out. The batteries were simply soldered together and placed in the bottom of the case, with a piece of bubblewrap plastic to stop them moving around or shorting to the copper tracks. by Michael Covington, which was described in the May 1999 issue of SILICON CHIP. Initially, I had a some trouble getting the published programmer to operate with my particular parallel port, so I built the NOPPP-2 (Experimental) version that used a 74HC08 in place of the diode logic that was present in the initial version. It work­ed flawlessly. The programmer software (noppp) is available from the SILICON CHIP web site or from Michael’s web site (http://www.covingtoninnovations. com/noppp/). Once you have the tools, you need to create a .hex file to feed to the programmer. Start by loading up the MPLAB software and creating a project by selecting ‘Project’, ‘New Project’ from the menu and typing the name of the project (LED Dice) into the file name box, ensuring that the default directory is in a reasonable location for your system. You need to add a source (.asm) file by clicking on the ‘Add files’ button in the ‘Edit Project’ menu. Now that the project has a source file associated with it, you can assemble it by pressing F10. The build 62  Silicon Chip process will start and a .hex file will be produced in the default directory specified above. Once the program has been assembled, exit the MPLAB environment and start the programmer (noppp). Specify the type of PIC (16F84) and load the .hex file. Insert the PIC into the programmer and select Program. The PIC will be programmed in about six seconds. Exit the programmer and remove the PIC from the socket. Construction Two versions are presented, one on a PC board and the other on Veroboard. In the first, all the components mount directly on the PC board, which measures 58 x 73mm. It is always wise to carefully examine any PC board prior to assembly to ensure that there are no shorts, or breaks present. It saves a significant amount of time to spot them now. A component layout for the board is shown in Fig.9. Start the assembly by installing the passive components first, such as the resistors and capacitors. You may find that it is beneficial to measure the values of the resistors The Veroboard version is designed to mount on the top of a medium sized plastic zippy box, replacing the lid. This is to allow the simplicity of the circuit to be displayed to any curious onlookers. If desired, the project can be mounted inside a slightly larger case, with the LEDs and pushbutton mounted on the lid in a more conventional manner. Building on Veroboard also allowed a fast development time to be achieved on the hardware. If you use Veroboard, be very careful to support the board while cutting the hole for the pushbutton switch, otherwise, the board will snap in half (been there, done that . . .). File the edges if the board is slightly too large (you will probably have to file the corners round, too). No component overlay is shown for the Veroboard version but the photographs will give a very good idea of component placement. Some of the components are mounted on the copper (strip) side of the board. Take care when cutting the Vero­ board tracks that the cut is complete and no copper swarf shorts to an adjacent track. The easiest way to cut Veroboard tracks is to take a twist drill bit about 5mm or so and simply twist it in the hole to be cut with your fingers. If the drill is sharp it results in a clean, quick hole. You may like to install a small piece of clear Perspex sheeting over the top of the project to protect it from small which incidentally, is where those 265 other dice went. Have fun. And remember, unless you create some code to allow you to cheat, it is very hard to force the dice to roll a particular way. Remember also that the one disadvantage of this project over the real dice is that it isn’t built to survive 20G’s of deceleration, so throwing it would be bad. Troubleshooting There wasn’t room for a battery hold­ er: a piece of bubble-wrap held the batteries in place and stopped any possibility of shorts. prying fingers. This can be mounted on 12mm brass standoffs on the top of the Veroboard, with a suitable hole for the pushbutton. Testing Examine the PC board or Veroboard to ensure there were no shorts created during assembly and then install the batteries. Note that the PIC microcontroller is NOT installed yet. Verify that +5.4V is present on pins 4 & 14 (with respect to pin 5 [GND]). Finally, disconnect the batteries, install the pre-programmed PIC (16F84) and re-install the batteries. (Don’t insert the PIC with the power applied!). You should be rewarded with a self-test pattern. Verify that the unit operates when the button is pressed as described earlier in this article. When you release the button, the display should ‘slow down’ and then display the result for approximately 20 seconds before turning itself off. Quickly pushing and releasing the pushbutton should recall the last roll. If the unit operates correctly, carefully mount the PC board in the top of the zippy box. All that remains now is to instruct the kids on how to operate it and to chain it to the table so that it doesn’t end up at the bottom of the toy box, If for some reason the project fails to work, check all soldering carefully. Verify that all the LEDs have been installed correctly. You can check the hardware by removing the PIC and placing a 10Ω resistor between pin 14 (VCC) and each of the LED drive lines (pins 1, 2, 10, 11, 12, 13, 17 and 18) one at a time. The LEDs should light. You can verify that the pushbutton switch operates correctly by monitoring pin 6 with a logic probe, or multimeter while pushing the button. It should go to +5.4V when the button is down. Finally, if you have a CRO, you can verify that the internal PIC oscillator is running by examining pin 15 (CLK­ OUT). This pin is not used by our circuit but from it you should see a 1MHz square wave for three seconds after the device is powered up and for 20 seconds after the button is pressed. Remember that the device spends most of its time in sleep mode, with the CPU clock turned off to conserve power. If all of the hardware checks out, you should try re-programming the PIC. Perhaps it has the wrong code installed. Good Luck. And remember that this SC is supposed to be fun! Want to know more? As mentioned in the text, source code for the PIC microcontroller and other information is available for those interested in this project. You can log in direct to: www.dougzone.com or you can access it via the SILICON CHIP website, www.siliconchip.com.au and follow the link from the selection bar on the left side of the opening page. May 2000  63 VINTAGE RADIO By RODNEY CHAMPNESS, VK3UG Making the obsolete useful again Radio receivers running off vibrator power supplies were common in many rural areas right up until the 1950s. Many of these sets were later converted to mains operations as 240V AC power became available but some sets were more difficult to convert than others. In many country areas of Australia and New Zealand, 240V AC mains power didn’t become available until the 1950s. Before that, all sorts of voltages were used in country towns, while those living on farms may not have had any source of power other than batteries for their radios. Where power did exist, voltages such as 12, 32, 50, 110, and 250V DC were common. Of course, some places had their own 110V or 240V AC supplies, although in general these sources only covered a small area and were rather limited in output, with frequent interruptions to the supply. Are you old enough to remember having to pay the “electric light bill”? Before the war, electricity was almost exclusively used for lighting with few or no power points in the home, hence the bayonet adaptor that went into the light bulb socket so that the radio could be powered. To cater for areas where there was no mains supply, radio sets were specifically designed to run off a 1.5V or 2V battery for the filaments and 90-135V dry cell batteries for the HT supply. Unfortunately, these were expensive to operate relative to the cost of running sets off the 240V AC mains. As a result, to keep costs down, many sets that used battery valves were designed to operate from a 4V or 6V wet cell battery via a vibrator power supply. The valve filaments were usually wired in a series-parallel configuration to minimise current drain. Suddenly, these sets became obsolete when mains reticulated power came to an area and homes were connected to it. As a result, many old sets were either stored in the garage or thrown onto the local garbage tip – vintage radio collection and restoration was not even thought of in the 1940s, 50s and 60s. This was a shame because these sets were generally very good performers as they were designed for rural areas where signals weren’t all that strong. I hate seeing things that are still in good working order go to waste and, along with many others during that era, converted many of those otherwise obsolete sets to 240V AC mains operation. Of course, you would­n’t do that today as there are few of these Left: this is the view inside the cabinet of the converted HMV 268 receiver. The conversion involved replacing the valve line-up and replacing the 6V vibrator circuitry with a mains-operated power supply. 64  Silicon Chip Vintage Radio Repairs Sales Valves Books Spare Parts See the specialists * Stock constantly changing. * Top prices paid for good quality vintage wireless and audio amps. * Friendly, reliable expert service. The HMV 268 came in a stylish wood veneer cabinet and featured both shortwave and medium-wave AM bands. receivers still around in original condition. At that time however, it was much better to convert the sets rather than have them go to the rubbish tip. It’s worth noting that “Radio & Hobbies” (later “Radio, TV & Hobbies”) ran articles on converting many of the common types of sets used in country areas to 240V AC mains operation. It was cheaper to convert than to buy a new set and, what’s more, the conversion was usually very successful. Often, a converted set worked better than before and was cheaper to run into the bargain. Ease of conversion Some sets were easily converted to mains operation, these being the 32V sets with vibrator power supplies and using “mains-type” valves, eg, 6AQ5, etc. All that was necessary with this type of set was to remove the vibrator power supply, replace it with a mains supply and rewire the heaters and dial lamps for 6V operation. And because they were designed for remote country areas, these sets usually outperformed the newer AC mains sets which invariably lacked an RF stage (as used in the vibrator-powered designs). Unfortunately, sets using “battery-type” valves were much more difficult to convert. This applied regardless as to whether the set used batteries to supply all the necessary voltages or whether it used a vibrator power supply to derive the necessary voltages from one battery. It really was much more of a challenge with the battery sets. First, it was necessary to change all the valves and this involved finding out which valves in the AC range had similar characteristics to the battery valves being replaced. Second, AC valves usually work on higher supply voltages (usually 200-250V), whereas the battery sets usually ran on 135V and some on only 90V. This meant that many of the paper capacitors had to be replaced with higher voltage types. Third, quite a bit of redesign was necessary in order to obtain good performance from the new valve lineups. However, many servicemen in country areas rose to the challenge and many fine conversions were made to radios otherwise destined for the local rubbish tip. Converting 32V sets that used only 32V of high tension was a challenge too. That’s because the valves, although AC types, run at very low voltage and have low gain. For starters, it was necessary to replace the 25L6 valves with 6V6GTs or similar but because of the large increase in gain with the increased supply voltage, considerable redesign was necessary – even to the point of removing some stages. The RF and IF sections were usually left running off 30-45V which meant that no modifications were necessary Call in or send SSAE for our current catalogue RESURRECTION RADIO 242 Chapel Street (PO Box 2029) PRAHRAN, VIC 3181 Tel (03) 9510 4486 Fax (03) 9529 5639 Truscott’s • RESELLER FOR MAJOR KIT RETAILERS • PROTOTYPING EQUIPMENT • COMPLETE CB RADIO SUPPLY HOUSE • TV ANTENNA ON SPECIAL (DIGITAL READY) • LARGE RANGE OF ELECTRONIC COMPONENTS Professional Mail Order Service Truscott’s Amidon Stockist ELECTRONIC WORLD Pty Ltd ACN 069 935 397 Ph (03) 9723 3860 Fax (03) 9725 9443 27 The Mall, South Croydon, Vic 3136 (Melway Map 50 G7) email: truscott<at>acepia.net.au www.electronicworld.aus.as May 2000  65 This end view shows the location of the “new” power transformer and audio output valve. The new supply was much simpler than the vibrator supply it replaced. to their operating conditions. This usually achieved a satisfactory result – after all it was only the audio section that needed beefing up. Converting an HMV 268 6V vibrator Receiver to 240V AC My parents owned an HMV 268 dual-wave table model, a 6V vibrator receiver using five 2V battery valves. The circuit is shown on page 193 of Volume 7 of the Australian Official Radio Service Manual. In its original format, the old HMV 268 was an excellent set. The short­ wave band extended from 6-18MHz but where I lived, the local emergency fire service used a frequency of 2.836MHz and we had no radio capable of listening to important fire calls. As a young and relatively new devotee to radio, I decided that I would modify the shortwave coils so that it tuned from around 1.7-5MHz, so that the fire calls and amateurs on the 1.8MHz and 3.5MHz bands could be heard. The receiver was duly modified and I had a lot of fun listening to these stations – when my parents weren’t using the set of course. Unfortunately, recharging the 6V battery that powered the receiver was something of a chore, requiring a trip to the local garage. However, my parents had a smart, young son 66  Silicon Chip who reckoned he could save them the trouble of this ritual. I decided that I could charge the unit directly from our 32V lighting plant by putting two 12V globes in series with the battery. The total calculated voltage added up to 30V, so the globes weren’t going to be drastically overloaded. What’s more, by only charging the battery at night, the two globes would become part of our home lighting system – waste not want not. I found out after I had installed the system that it was very effective, provided the 32V batteries were off charge. However, it was a different story when they were on charge, the 12V globes glowing brilliantly for a short while until they blew! The real test of my radio prowess came at the end of the 1950s, when we got 240V AC power after having had 32V DC for about 15 years. The set would either have to be converted to 240V AC operation or thrown out, as we no longer had a ready source to charge the battery. Fortunately, there was an article on converting receivers to mains operation in the December 1953 issue of “Radio & Hobbies” and this steered me in the right direction. Using the article as a guide, I started by checking out which AC valves had similar characteristics to those that were being replaced. I decided on a 12AH8 converter to replace the 1C7G but a 6J8G or a 6K8G may have been a better choice, as I wouldn’t have need­ed to change the valve socket. In addition, a couple of 6K7GT valves were wired in place of the 1M5G and 1K7G valves in the IF amplifier, as their mutual conductance is similar to the valves they replaced and I didn’t want any problems with instability. A 6B6G was used in place of a 1K7G for the second detector and first audio stage, the gain of a pentode being considered unnecessary in this position as the overall gain of the set would be higher with AC valves anyway. The audio output stage became a 6AM5 instead of a 1L5G. I would have liked to have used an octal output valve but I didn’t have one with a similar output impedance and the 6AM5 nearly matched the 1L5G. It was then necessary to look at the voltage ratings of the capacitors. The set ran on 135V but now it would run on about 250V. Most of the capacitors had a 200V rating and were replaced with 400V units where necessary. At this stage, the 6V vibrator power supply was taken out of the set and consigned to the junk box. A metal sheet was then bolted across where the vibrator supply had been and a power transformer and a selenium block rectifier fitted in its place. The electrolytic filter capacitors were wired into position under the chassis. The retrofitted power supply can be seen in the photographs. The new AC supply was certainly much simpler than the vibrator supply it replaced. Wiring the heaters of the new valves was straightforward, since it was no longer necessary to use a series-parallel arrangement. However, it was necessary to fit a resistor and capacitor between each cathode and earth to give the bias required and rewire the valve sockets to suit the new valves. In my enthusiasm to stabilise the screen voltages, I also wired in a VR105 105V gaseous regulator. This was really an overkill and quite unnecessary (at that time, I wasn’t as competent as I thought I was). Anyway, it all worked reasonably well and the old HMV once again took pride of place in the lounge room. Eventually, my sister took possession of it and it continued to work satisfactorily until a brush with lightning caused the shortwave aerial coil to This “under-chassis” view of the converted HMV 268 shows the wiring layout. The electrolytic capacitors for the new power supply are at left, adjacent to the socket for the audio output valve. go open circuit. After that, she didn’t want it any more so I got custody of it and decided to get it operating again. Being more knowledgeable now than I was then, I soon found a few problems with my original conversion which caused the set to be slightly unstable. After some investigation, I found that the automatic gain control (AGC) line was radiating a signal at the intermediate frequency (IF) and this was being picked up by the IF front end – hence the instability. Don’t assume that the AGC line is always “cold” with no signals on it –some have quite a lot of IF signal on them. The original valves in the old HMV didn’t have as much gain as their replacements, so this problem didn’t occur with the original circuit. Carefully re-routing the AGC lead and adding some extra bypassing solved the instability problem and the set now goes extremely well. It is one of the favourites in my collection and has quite a lot of sentimental value. Converting an AWA 532MF 32V receiver to 240V AC A number of these radios were going to be thrown out as the reticulated power mains snaked around the country area in which I lived. These sets used a 6BA6 RF amplifier, a 6BE6 converter, a 6BA6 in the IF stage, a 6AV6 detector and a 6AQ5 audio output stage. They also used a synchronous vibrator power supply which ran from a 32V DC supply. This valve line-up is the same as used in many high-performance AC sets, so they were well worth converting. And the conversion was even simpler than for the HMV 6V vibrator set described above. In brief, the vibrator power supply was removed from the set and the dial lamps and valves heaters all wired in parallel to run off 6.3V. A power transformer was also installed and solid-state diodes used to rectify the high-tension voltages. The electrolytic capacitors were reused since they were quite adequate for the job. These sets and similar 32V sets that had AC valves and a vibrator supply were very easy to convert and the sets performed better than before. That’s because there was no longer any residual vibrator hash. Should we convert sets now? My personal belief is no, we shouldn’t convert any more vibrator sets to mains operation. There are several reasons for this: these radios are now quite scarce, they are a part of our radio heritage and they are interesting receivers in their own right. Some collectors wrongly believe that these battery or vibrator-powered radios are useless because there is no easy way of powering them. However, suitable AC-operated power supplies are available to operate these sets and occasional advertisements can be seen in electronics magazines. Articles on making your own power supplies have featured in the magazines too, so there is no reason why these radios cannot be made fully operational. So why did I do conversions on these sets if I now believe that they shouldn’t be done? Well, it was a different era and the conversions were done to save good high-performance sets from the rubbish tip during the period that the 240V reticulated mains spread throughout the countryside. In the period from the mid-50s into the early 60s, these conversions were commonplace and made good economic sense. And even though those converted receivers are no longer ‘standard’ they are an example of what happened in that era. It was a short but interesting period in the history of radio in SC Australia. May 2000  67 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au DON’T UTER COMP MISS OMNIBUS THE ’BUS! www.siliconchip.com.au SILICON CHIP’S 132 Pages 9 $ 95 * ISBN 0 95852291 X 780958 522910 IN LINCLUDES FEA U TUR X E A collection of computer features from the pages of SILICON CHIP magazine Hints o Tips o Upgrades o Fixes Covers DOS, Windows 3.1, 95, 98, NT o RT Do you feel a little “left behind” by the latest advances and developments in computer hardware and software? Don’t miss the bus: get the ’bus! THIS IS IT: The computer reference you’ve been asking for! SILICON CHIP's Computer Omnibus is a valuable compendium of the most-requested computer hardware and software features from recent issues of SILICON CHIP magazine - all in one handy volume. Here's just a sample of the contents: Troubleshooting your PC: what to do when things go wrong NO Choosing, installing and taming computer networks AVA W Upgrading and overclocking CPUs DIRE ILABLE C Hard disk drive upgrades, tune-ups and tips SILIC T FROM Windows 3.1, 95, 98 and NT tips and tricks ON just $ CHIP The Y2K Bug - and how to swat it 125O* INC All about Linux GST & P& P And much more!!! ORDER NOW: Use the handy order form in this issue or call (02) 9979 5644, 9-5 Mon-Fri with your credit card details. * Price includes GST 09 9780958522910 09 9 By STEVE CARROLL & BOB NICOL Build this low-cost AT keyboard translator This simple device converts the complex scan-codes from an AT keyboard to standard ASCII character and control codes. It was originally designed for use with the BASIC Stamp, Counterfeit and PIC series of microcontrollers but has lots of other uses as well. The rapid progress of computer technology has resulted in many old, fully-functional IBM AT keyboards being thrown away in favour of newer, fancier ones. If you’ve ever wanted to connect one of those discarded keyboards to a project which accepts standard ASCII codes, this AT Keyboard Translator could be just what you’re looking for. In operation, the device connects directly to any 101/104-key AT key- board with a 5-pin DIN connector and converts the key scan-codes to standard ASCII “character” and “control” codes. It then outputs these codes in standard inverted asynchronous format at 300, 1200, 2400 or 9600 baud. The baud rate chosen depends on your “receiver” and is selected using a single jumper designated HDR2 on the PC board. The output data is compatible with the RS-232 serial port of many devic- Information On PC Keyboard Standards Want to find out more about PC keyboard standards? You’ll find lots of information at these two websites: (1) http://www.hth.com/filelibrary/txtfiles/keyboard.txt (2) http://linton.csie.ntu.edu.tw/design-reference/pc/keyboard_FAQ.html 72  Silicon Chip es, allowing you to send text or control codes to your application. It’s just the shot for interfacing with microcontrollers such as the BASIC Stamp, Counterfeit and PIC series (in fact, the device was originally designed to do just that). There really is no easier way to connect over 60 switches to one pin of a Stamp1, Counterfeit Stamp1, Stamp2 or PIC chip (the non-ASCII keys are not used). Of course, it’s not just limited for use with microcontrollers. It can also interface with other serial devices such as a serial printer (via a suitable RS232 driver interface) or LCD drivers. One of the photographs with this article shows the AT Keyboard Translator driving a 4-line alphanumeric LCD via an “LCD Serial Backpack” (designed by Scott Edwards Electronics). Other possible applications include use in an ASCII User Terminal, an RF/Infrared Keyboard Link, a Video Text Generator and a Moving Message Display. The accompanying panel lists 12 possible applications but there are lots more. By the way, if your keyboard has a PS/2 connector (six pins) rather than the 5-pin DIN type, an adaptor can be purchased from most electronics sup- Fig.1: the circuit uses a PIC microcontroller to decode the complex scan-codes from an AT keyboard and convert them to ASCII character and control codes. pliers. Alternatively, an “off-board” PS/2 socket on a short length of cable can be used to replace the standard 5-pin DIN socket on the PC board. Power for the keyboard (+5V) is provided via the keyboard socket – it’s just a matter of plugging the keyboard in and applying power (12V DC) to the adjacent DC power socket. 10kHz to 30kHz. Fig.1 shows the circuit details of the AT Keyboard Translator. It’s deceptively simple, with all the “magic” taking place inside a pre-programmed PIC series microcontroller (IC2), either a PIC16F84-10 or PIC16F84-20. These devices have 1KB of “flash” EEPROM program-memory, 68 bytes of RAM and 64 bytes of EEPROM data storage. In this application, we require only a handful of external components to make a complete working circuit. How it works The AT keyboard has a fairly complex two-way communications protocol that is quite a handful to decipher. There’s no logical mathematical pattern to the “scan-codes” sent by the keyboard and certainly no similarity to ASCII. These AT scan-codes can involve up to 13 bytes of data being sent for a single keypress and release. Just to make things difficult, even the simple act of pressing “Caps Lock” does not automatically light the “Caps Lock” LED on the keyboard. Instead, the keyboard sends a “Caps Lock” scancode to the host (normally a PC or, in this case, the Keyboard Translator itself), which then sends a “Light Caps Lock LED” message back to the keyboard. Finally, as if all that isn’t complicated enough, an AT keyboard can operate at anything from about The PC board should only take about 10 minutes to assemble. It really doesn’t get much simpler than this! May 2000  73 Parts List 1 PC board, 51mm x 61mm, 1 10MHz ceramic resonator (CR1) 1 18-pin DIL IC socket 1 2.1mm DC socket 1 5-pin DIN socket, PC-mount 1 2-way pin-header strip 2 4-way pin-header strips 1 5-way pin-header strip 1 pin header jumper 1 link wire Semiconductors 1 LM7805 3-terminal regulator (IC1) 1 PIC16F84-10/20 microcontroller with ATKB program (IC2) 1 1N4001 silicon diode (D1) 2 1N4148 signal diodes (D2, D3) Capacitors 1 100µF 25VW PC electrolytic (C1) 2 0.1µF ceramic (C2-C3) Resistors (0.25W, 5%) 3 10kΩ (R5-R7) 2 2.2kΩ (R1-R2) 2 1kΩ (R8, R9) 2 220Ω (R3-R4) Basically, the PIC microcontroller converts the complex IBM AT scancodes to standard ASCII codes. Much of the actual decoding function is achieved by the use of “lookup” tables. Each time a key is pressed, the keyboard sends the scan-code to pins 17 & 18 of IC2 via resistors R3 & R4. Pin 17 accepts the clock signal, while pin 18 accepts the data signal. The microcontroller separates the eight data bits and uses this value as a memory address offset to look up the appropriate ASCII value. Assum- ing that the code is a valid ASCII “character” or “control” code, the serial data appears on pin 13 and is fed to pin 4 of a 5-way pin header (HDR3) via resistor R8 (1kΩ). The CTS (clear to send) line (pin 8) is optional and in most cases only one pin on the receiver is needed to ensure clean communications. Note that communications between the keyboard and translator are almost exclusively one way. The only translator-to-keyboard commands involve turning the “Caps Lock” LED on or off as required. Optional CTS function Sometimes typing speeds can be too fast for the receiving device (Stamp, PIC, etc), so an optional CTS function has been programmed into the PIC microcontroller. In this circuit, the CTS output at pin 8 is normally tied to 0V by resistor R7. However, if necessary, it can be pulled high (+5V) by the receiver, taken low to receive the next byte, then immediately returned to the high state until the receiving device is ready again. A similar method of data flow control is used between the keyboard and the translator, utilising the keyboard’s inbuilt buffer to temporarily store key presses until the microcontroller is ready for them. Unfortunately, this buffer has a limited storage capacity so prolonged bursts of high-speed typing may cause some characters to be missed if the receiving device is too slow. The baud rate (ie, the rate at which data is transmitted from pin 13 of IC2) is set by placing a jumper across one of four pairs of header pins (HDR2). This can be set to either 300, 1200, 2400 or 9600 baud (bits per second) and must be set to match the receiving device. Specifications Supply voltage ����������������������7.5-15VDC Supply current ����������������������<1mA (idle). Note that a typical AT keyboard current of up to 300mA must be added to this. Keyboards supported �����������Most IBM-compatible 101/104/105-key AT keyboards with 5-pin DIN connector. A keyboard with a PS/2 connector can be used via a suitable adapter. Output data format ����������������Standard asynchronous (inverted) at 300, 1200, 2400 or 9600 baud (8N1). 74  Silicon Chip Fig.2: take care to ensure that all semi­ conductors and the electrolytic capacitor go in with the correct polarity. Depend­ ing on the keyboard, it may be necessary to fit a small heatsink to regulator IC1. For example, a “Stamp1” is limited to a maximum of 2400 baud, as is the LCD Serial Backpack, but many other devices will readily accept speeds up to the Keyboard Translator’s maximum 9600 baud rate. The logic levels on pins 6 & 7 of IC2 determine the baud rate. As shown in Fig.1, one side of the 4-way dual pin header is commoned and connected to the +5V rail. When the jumper is in the 300 baud position, pins 6 & 7 are both pulled low via R5 & R6. In the 1200 baud position, pin 6 is pulled high (+5V) and pin 7 is low, while for 2400 baud pin 6 is low and pin 7 is high. Finally, when the jumper is in the 9600 baud position, pins 6 & 7 are both pulled high via diodes D2 & D3. Clock signals for IC2 are derived from an internal oscillator between pins 15 & 16. Its frequency is set to 10MHz by ceramic resonator CR1. Power supply An AT keyboard requires 5V DC and typically draws a current of 100-300mA. This is provided by a 7805 regulator which also provides a regulated +5V rail for the rest of the circuit and to the 5-way “output” socket. The 78xx series of regulators can handle in excess of 1A and have internal current-limiting and thermal-protection circuitry, making them almost bullet-proof. Note that earlier keyboards may have higher power requirements than later models. For this reason, if you use an early keyboard, the regulator may get quite hot. If this happens, the answer is to fit a small heatsink. This view shows the AT Keyboard Translator driving a 4-line alphanumeric LCD (via the Scott Edwards LCD Serial Backpack). Note that the LCD Serial Backpack writes lines 1 & 3 first, then lines 2 & 4. The unit itself runs from 7.5-12V DC and this can come from a DC plugpack supply. The power can be applied via an on-board 2.1mm DC socket or to a nearby 2-pin header (HDR1). The centre pin on the DC input socket is positive, while the body contact has negative polarity. Building it The PC board is very easy to assemble and should cause no problems if the overlay illustration is carefully followed – see Fig.2. As with most boards, it’s a good idea to begin with the smallest parts and work up to the larger ones. Start by installing the wire link (this goes between the keyboard and DC power sockets), then install the resistors, diodes and capacitors. Take care also to ensure that the electrolytic capacitor and the diodes are mounted with the correct polarity. Note particularly that D1 is a 1N4004 power diode, while D2 & D3 are 1N4148 small signal diodes. The pin headers can now be installed, followed by the IC socket, the DC power socket and the keyboard socket. Make sure that the sockets are all seated correctly on the PC board before soldering their pins. The PIC16F84-10/20 is a static-sensitive device, so normal ESD (electrostatic discharge) precautions should be employed. This device should not be installed in its socket until all other assembly has been completed. Take care to ensure that it is installed the right way around. The 7805 3-terminal regulator (IC1) must be installed with its metal tab towards the centre of the board (see photo). Setup & testing Once the assembly has been com- pleted, carefully examine the rear of the PC board for solder bridges between pins, missed solder joints and vacant holes. You should also check that all the parts are in their correct positions and that all polarised parts are correctly oriented. If all appears OK, place the jumper across the appropriate pins to select the required baud rate and connect the +5V, DAT (Data), 0V and CTS pins to the receiver as required. Also ensure that the receiver is configured for 8,N,1 (ie, 8 data bits, no parity bit, 1 stop bit), inverted polarity. If using the AT Keyboard Translator with a BASIC Stamp1, the correct serial modes are N300, N1200 or N2400. The Stamp (or Where To Buy The Parts The Keyboard Translator is available pre-assembled or in kit form from two companies, as follows: (1) Control Electronics, 231D Timmsvale Rd, Timmsvale, NSW 2450. Phone (02) 6654 5458; email ctrl<at>mpx.com.au (2) Microzed Computers, PO Box 634, Armidale, NSW 2350. Phone (02) 6772 2777; fax (02) 6772 8987; email sales<at>microzed.com.au Fully assembled and tested PC board (no case)..............................$49.00 Short-form kit (PC board plus all on-board components)..................$39.00 Programmed PIC microcontroller and 10MHz ceramic resonator.....$18.00 The BASIC Stamp, 4-line alphanumeric display and the Scott Edwards LCD Serial Backpack are available from Microzed Computers. Further information is available by phone or from www.microzed.com.au May 2000  75 Suggested Applications For The Keyboard Translator (1) STAMP “SERIN” COMPATIBLE: the Keyboard Translator’s output is directly compatible with the Stamp, Counterfeit and PICBASIC “SERIN” function. You can use it at 300, 1200 or 2400 baud for Stamp1 or Counterfeit and also 9600 baud for faster devices (PIC, Stamp2, etc), making keyboard input a simple matter for a wide variety of applications. A short program listing that enables the Stamp1 or Counterfeit to receive data from the Keyboard Translator is shown in the accompanying panel. (2) >60 SWITCHES, ONE STAMP PIN: an AT keyboard and Keyboard Translator combination is equivalent to more than 60 switches on one pin of a Stamp, Counterfeit or PIC, etc (two pins if CTS used). red link or RF data transmitter and receiver, the Keyboard Translator could be used to remotely send data to a PC running a QBASIC or terminal program. LCD display could allow a Stamp, Counterfeit, etc to accept ASCII data from a keyboard. You could then edit it and print it to a serial printer. (5) TV TEXT OVERLAY: a video text overlay generator could be designed to display text on a television screen using the Keyboard Translator and a suitable IC such as the STV 5730A. (9) RS-232 ASCII: with the addition of an RS-232 driver, standard ASCII character and control codes could be transmitted via cable to many devices and applications (eg, a serial printer). (6) MOVING-MESSAGE DISPLAY: the Keyboard Translator could be used, along with a Stamp or some other microcontroller and a suitable display, to design a moving-message display without tying up a PC. (10) HOME AUTOMATION: the Keyboard Translator could be used with an LCD display and a Stamp to control a simple home automation system. (3) ASCII USER TERMINAL: ap­ plication notes for a Stamp-based “User Terminal” extend only to a 3 x 4 or 4 x 4 numeric keypad. The Keyboard Translator, along with an LCD, can be used to build a far more versatile terminal, with all ASCII character and control codes available. (7) MOTOR CONTROL: an LCD display, a Stamp (or similar) and the Keyboard Translator could be used to program a wide variety of motor-control systems, especially if an extra memory chip (a serial EEPROM or similar) was used to store additional data for longer sequences, etc. Again, this could be done without a dedicated PC. (4) RF/INFRARED KEYBOARD LINK: in conjunction with an infra- (8) DO-IT-YOURSELF TYPEWRITER: the Keyboard Translator and an (11) EASY MORSE CODE: a Stamp and the Keyboard Translator could be used to send the Morse code tones for each keypress, without the user needing to learn Morse code. (12) TEXT WRITER/PLOTTER: using a microcontroller, a serial EEPROM or other memory IC and the Keyboard Translator, a writer/ plotter system could be devised to write text onto objects such as signs, etc. Fig.3: if you want to use the Keyboard Translator to send data to a terminal program, you will need to wire the connector as shown here. This tricks the port into thinking that it is connected to a serial device with full handshaking. The LCD Serial Backback is mounted on the back of the alphanumeric display via a 14-way pin header. It accepts serial data in ASCII format and decodes it to drive the display. 76  Silicon Chip similar) can also be powered from the +5V and 0V pins on the 5-pin output header. In our example, we are using the AT Keyboard Translator to drive the Stamp/Counterfeit Program Listing ASCII Control Codes Following is a short BASIC Stamp1 (or Counterfeit) program to receive serial data from the AT Keyboard Translator and display it on a PC monitor. After typing in the listing exactly as it appears below and connecting the keyboard to the Keyboard Translator, connect the 0V pin on the Stamp to the 0V pin on the Keyboard Translator, then connect Pin 0 on the Stamp to the Data pin on the Keyboard Translator. Next connect Pin 1 on the Stamp to the CTS pin on the Keyboard Translator and ensure that the baud-rate jumper is set to the required bit-rate. Finally, connect the Stamp’s download cable and press <Alt><R> as usual to download the program and execute the DEBUG instruction. At this stage, pressing any ASCII keys on the keyboard should result in the corresponding characters appearing on the PC monitor. NUL Ctrl <at> Null SO H Ctrl A Start of heading S TX Ctrl B Start of text ETX Ctrl C End of text EO T Ctrl D End of transmission EN Q Ctrl E Enquiry LF Ctrl J Line feed ‘KB_READ.BAS ‘BS1 PROGRAM TO RECEIVE SERIAL ASCII DATA FROM THE “AT KEYBOARD ‘TRANSLATOR” AND DISPLAY IT ON THE PC MONITOR VIA “DEBUG”. ‘BAUD-RATES OF 300, 1200 AND 2400 ARE SELECTABLE. (PLACE ‘ AT BEGINNING ‘OF UNUSED LINES) ‘DATA FORMAT IS INVERTED, 8,N,1, (N300, N1200, N2400). VT Ctrl K Verti cal tab ‘NB: FALSE CHARACTERS WILL BE DISPLAYED BY THE STAMP1 “DEBUG” ‘FIRMWARE IF CONTROL-CODES ARE SENT. SYMBOL COMS=0 SYMBOL CTS=1 PAUSE 1000 LOOP: LOW CTS ‘SERIN COMS,N300,B2 ‘SERIN COMS,N1200,B2 SERIN COMS,N2400,B2 HIGH CTS DEBUG #<at>B2 GOTO LOOP ‘SERIAL COMS ON PIN0 ‘CTS ON PIN1 ‘WAIT FOR KEYBOARD AND TRANSLATOR ‘TO INITIALISE ‘ENABLE KEYBOARD TRANSLATOR TX ‘N300 ‘N1200 ‘N2400 ‘DISABLE KEYBOARD TRANSLATOR TX ‘DISPLAY ASCII CHARACTER ON PC MONITOR ‘GET NEXT CHARACTER LCD Serial Backback and this requires connections from the +5V, 0V and data (DAT) pins. These points respectively go to +5V, GND and SER (serial) on the LCD Serial Backpack. Note that this device does not write to lines 1-4 of the LCD in numerical order. Instead it writes to line 1 first, then line 3, then line 2 and finally line 4 (ie, the order is 1, 3, 2, 4). The keys As mentioned earlier, the keys that have no ASCII equivalent are unused. All ASCII character-codes, both shifted and unshifted, are generated in the usual way by pressing the appropriate key/s. The “Caps Lock” function operates as usual and lights the “Caps Lock” LED when it is enabled. The alternative characters on the numeric keypad are all non-ASCII, so these have been disabled and the keypad operates in numeric mode only. Similarly, all the arrow keys are disabled with the exception of the “Backspace” key, which sends 08 hex, the ASCII code for “BS”. Pressing either “Enter” key will generate an ASCII “Carriage-Return” (CR). The “control” codes are accessed by holding down the “Ctrl” key or “Ctrl” + “Shift” and the relevant key. The <Esc>, <Backspace>, <Del>, <Enter> and <Tab> keys also generate the corresponding ASCII control codes. You can refer to the accompanying “ASCII Control Codes” table for a full ACK Ctrl F B EL Ctrl G Bell Acknowledge BS Ctrl H Backspace HT Ctrl I Horizontal tab FF Ctrl L Form feed CR Ctrl M Carri age return SO Ctrl N Sh wt out SI Ctrl O Sh wt in D LE Ctrl P Data li nk escape D C1 Ctrl Q Devi ce control 1 D C2 Ctrl R Devi ce control 2 D C3 Ctrl S Devi ce control 3 D C4 Ctrl T Devi ce control 4 N AK Ctrl U Negati ve acknowledge SYN Ctrl V Synchronous idl e ETB Ctrl W End of transmission block CAN Ctrl X Cancel EM Ctrl Y End of medium SU B Ctrl Z Substi tute ES C Ctrl [ Escape FS Ctrl \ Fil e separator GS Ctrl ] Group separator RS Ctrl ^ Record separator US Ctrl _ Uni t separator listing of the control codes as defined in ANSI X3.4. Keyboard compatibility Finally, although the device works with the vast majority of keyboards, you will inevitably come across the odd keyboard that won’t work with the translator. Typically, if you press the caps lock key on these keyboards, the keyboard LED indicator comes on and the device appears to lock up. The current answer is to use a different keyboard, although further refinements to the ATKB PIC program to include a simple error handling routine (and still fit the program in the available space) may eliminate this problem further down the track. SC May 2000  77 50 Amp Mode Controller ­ – W Are you into large or powerful radio-controlled electricpowered models? The ones where battery life is measured in minutes, not hours? Here’s a controller which can handle motor currents of up to 50A and is compatible with your existing radio control equipment. Article by ROSS TESTER – Design by BRANCO JUSTIC* T he obvious question is who could possibly want a control ler capable of such huge currents? After all, your typical radio controlled model, say a race car or buggy, has only a 7.2V battery and a 75W motor – ergo, 10A. For this project, we’re not talking your typical off-the-shelf radio controlled car or buggy. We’re talking industrial-strength models powered by, say, 12V motorcycle or even car batteries. Large boats, electric-pow- ered planes and big cars and trucks, for example. At the opposite end of the scale are competition boats, cars and planes which may not be very big but have very powerful motors demanding a lot of electrical power. They might draw 10 or 20A or more on load and therefore need significantly more in the controller department. But 10 or 20A is a far cry short of 50A. Why the brute strength? Couldn’t we make it a bit simpler and save a few bob? Yes . . . and no! The problem lies not so much in the typical load current of the motor, nor even the start-up current (which can be high). It lies in the stall current. A motor loafing along at 10A might draw ten times as much if locked up – for example, when the car it is pushing hits an obstacle and before the wheels start slipping. Another scenario is when a boat runs through some underwater greenery and gets its prop snagged. Housed in a tiny plastic case the motor speed controller is small enough to fit into the vast majority of models. The 3-wire rainbow cable on the left connects to the radio control receiver servo output while the wires on the right connect to a battery and the motor. You will probably need thicker cables. Note the six MOSFET tabs emerging through the case lid. 78  Silicon Chip el Motor Speed With Brake Sometimes it will cut or power its way through; other times it will be locked up. (We make no comment about what happens when an electric plane’s prop is locked up...) That’s when you need a controller capable of significantly larger peak currents than you would otherwise think were necessary. Sure, you could take the risk and hope that you can cut power before any damage occurs – but that damage might occur in a few milliseconds and for the sake of a few extra MOSFETs valued at less than $10.00 total, why would you? Of course, if your application says that the motor can never be locked up, you can get away with fewer MOSFETs. Five MOSFETs handle 50A so it follows we’re rating each at about 10A. But we’ll look at this in more detail shortly. This controller is significantly cheaper than commercial units available and is also nice and small. Overall the assembled PC board is only about Three DC motors which would be ideal for this controller: the top one is one we had in the “junk box”and is rated at 12V and draws about 5A off load, rising quickly to 1520A under load. The two smaller motors are both from Oatley Electronics, the middle one rated at 4-8V DC while the bottom one is 12V DC. These motors sell for $8 each. For more info visit www. oatleyelectronics.com/ motors.html 25 x 35 x 60mm; even in its specified case it’s only 80 x 40 x 27mm, including mounting feet. So it should fit in the vast majority of models. Radio control compatibility This controller is compatible with typical radio control equipment which has servo outputs; ie, 99.99% of commercial radio controls. The radio control servo output (only one output – there are three wires but two of them are for power) gives a pulse train between 1ms and 2ms long, depending on the position of the radio control “stick”, on a frame Fig.1: the circuit uses a ZN409 servo driver IC not to drive a servo but to drive MOSFETs which control the motor speed. May 2000  79 Fig.2: the current standard for radio controls uses these wave-forms to achieve forward, stop and reverse in the servos. The 20ms repetition rate is usually not at all critical but the pulse width is. rate (or time between pulses) of about 20ms or so. At centre, or rest (in a ±stick), the pulses are 1.5ms long. This pulse stream results (or should result) in the servo adopting the centre or zero position. By the way, the frame rate isn’t usually at all critical but the pulse width is. We’ve seen frame rates of up to 50ms and they work fine. However, 20ms is the current “standard” for radio control systems so we’ll use that. Push the stick in the positive direction and the pulses lengthen – up to 2ms at maximum travel which should have the model’s servo in full forward position. Push the stick in the negative direction and the pulses shorten – 1ms pulses at full travel will have the servo in the full reverse position. Fig.2 shows the waveforms of these various pulse trains. In practice, a small amount of Fig.3: the component overlay, reproduced same size. Note the lengths of tinned copper wire soldered to the tracks under the MOSFETs to increase current capacity. Compare this diagram to the larger-thanlife photograph of the completed PC board below. Here you can also see the external connection wires are soldered to the back of the board, not the front. “trim” is usually required to achieve the correct positions – the trim tabs on the transmitter adjust the pulse width slightly to make sure the servo behaves as you intend (not as it sometimes wants to!). Note that no provision for reverse direction is made in this simple controller. It has only zero to maximum (or 1.5ms to 2ms) capability. However, moving the stick to the normal reverse direction actuates the controller’s braking circuit. No radio control? You’re one step ahead of us (or per80  Silicon Chip haps we’re one step ahead of you!). Because the controller’s input demands are relatively simple, a square-wave oscillator capable of producing a pulse between 1ms and 2ms every 20ms will give full-range (zero to maximum) control of the controller plus braking. Such an oscillator is quite simple to make with either discrete components or, say, a couple of 555 timer ICs. However, simple oscillators usually drift a little with temperature so this needs to be taken into account. A suitable oscillator which simulates a radio control receiver output is shown later in this article. This oscillator can not only be used as a “wired” controller but can also be used to set your controller up. The controller We’ve already discussed the reasons for the number of MOSFETs in the output but we haven’t yet explained what they do – or how they get the information they need. That information is all taken care of by IC1, a ZN409 servo driver IC. There are no servos in this circuit, of course, but this IC is ideal because it decodes the radio control receiver “servo” pulse signal described above. The ZN409 has its own reference oscillator, producing 1.5ms pulses every 20ms. The precise length of these pulses can be varied slightly by VR1. Incoming pulses from the receiver are fed to pin 14 and are compared to this reference. If the pulses are longer than the reference the pin 9 output is taken high and the pin 5 output is taken low. Pulses shorter than the reference have pin 9 low and pin 5 high. Pulses equal to the reference have both pin 9 and pin 5 high. Remember that all this is happening every 20ms or so. Pin 5 is connected to three Schmitt NAND gates wired as inverters in series, so a low on pin 5 will result in a high on the gates of parallel connected MOSFETs Q1-Q5 (and vice versa). Pin 9 controls the “brake” MOSFET, Q6, via another Schmitt NAND gate/ inverter and transistor Q7. A low on pin 9 will result in Q7 being turned fully on, turning on Q6 which is wired directly across the motor. This effectively shorts the motor terminals which in turn acts as a brake on the motor armature. If you don’t believe how effective this is, try spinning the shaft of a small, permanent-magnet DC motor with your fingers, then short the terminals together and try spinning it again. Notice the difference? The length of time that pin 9 or 5 is held low is in direct proportion to the difference between the incoming (receiver) and reference pulses. A pulse width equal to, or very close to, the reference will result in an extremely short “low” time on pin 5, so the MOSFETs will effectively be turned off. Increasing this incoming pulse width results in a longer and longer “low” time until the point is reached where at 2ms pulse width, pin 5 is low for almost all of the 20ms cycle, thus turning the MOSFETs fully on for virtually all of the cycle. Pin 9 operates in a similar manner except that it controls the brake MOSFET. When the pulse length is between 1.0 and 1.5ms pin 9 goes low, and the output of inverter IC2a (pin 3) goes high. This turns on Q7 which connects the Q6 gate to ground, turning it on. As the pulse length approaches 1.5ms, Q6 on time becomes shorter and shorter until at 1.5ms (centre stick) the brake MOSFET is fully off. MOSFET ratings We’ve mentioned that the output of the speed controller is handled by five N-channel power MOSFETs, all The completed project with the disassembled case in the background. The case “lid” is actually the larger piece – note the cut-out in the case lid for the MOSFETs. If space is a real problem the PC board could be simply insulated in heatshrink plastic and shoe-horned into a suitable area within the model. May 2000  81 Parts List 1 PC board, 60 x 33mm, with chamfered corners to fit case Semiconductors 1 ZN409 servo driver (IC1) 1 4093 quad NAND gate (IC2) 5 IRFZ44 N-channel Power MOSFETs (Q1-Q5) 1 MTP2955 P-channel Power MOSFET (Q6) 1 C8050 NPN transistor (Q7) Capacitors 2 10µF 25VW electrolytic 2 1µF 25VW electrolytic 4 0.1µF MKT polyester 1 .022µF MKT polyester Resistors (0.25W, 1%) 1 68kΩ   1 47kΩ 1 33kΩ 1 4.7kΩ   3 1kΩ Miscellaneous Suitable case (if required) Heavy duty hook-up wire (see text) Fuseholder and fuse to suit Short lengths heavy tinned copper wire connected in parallel. Like all semiconductors, MOSFETs have a variety of ratings but there are only a few which really concern us in this application. Of course, we must ensure that the voltage rating is sufficient for not only the battery voltage but also any back-emf generated by the motor. And this can be substantial. The IRFZ44 MOS-FETs specified have a VDS (ie, drain-source voltage rating) of 55V. Likewise, the current rating of the MOSFET must be considered. In fact, there are two ratings – a continuous current rating (ID cont) which is 41A and the pulsed current rating (IDM) which is significantly higher (160A). We are using the MOSFETS in a pulsed mode but the limiting factor in this speed control circuit is the heat dissipation in the MOSFETs. Most important of all, though, is the MOSFET’s “on” resistance. When turned on as hard as possible (ie, any increase in drive to the gate results in no further drain/source current) the MOSFETs still offer some resistance to current flow. It is tiny – MOSFETs are significantly better than bipolar transistors in this regard but even then, the Speed controller rating. . . should it be 200A? We have rated this speed controller at 50A and this is a continuous rating, to suit the very high current motors used in today’s electric flight models, as well as those used in high performance model cars and boats. As noted in the text, we base this rating on the drain-source resistance of the specified IRFZ44 Mosfets. This gives rise to two limitations in the speed control circuit: voltage drop and power dissipation. For a 50A load, the circuit would have a likely voltage drop of 240mV and that means not much loss in speed compared to running the motor directly off the battery. Secondly, the power dissipation for a 50A load would be around 2.4W for each Mosfet or a total of 12W. That is quite a significant amount of power to be dissipated in such a small package and it is going need good ventilation which is often difficult to provide inside the fuselage or body of the model. But if you purchased an equivalent 82  Silicon Chip speed control from your local model shop it would be rated at 200A or higher. This is based on the peak current ratings of the Mosfets. Could a speed control such as this withstand 200A? The answer is yes but only for a second or two, as the likely total dissipation of around 50W in such a small package would not only blow the Mosfets but would melt the solder off the back of the PC board. We should also note that some motors that are likely to draw around 50A continuous could also draw as much as 200A or more, at initial start and if the motor is accidentally stalled. Under those conditions, a speed control like this one could survive the very high current, provided the overload condition did not last any more than a second or two. So when you see those 200A speed controllers in model shops, remember that, at best, it is only an instantaneous rating. The continuous or “real” rating is likely to be 50A or less. small amount of resistance has to be considered. In fact, there are two important considerations: one is heat dissipation, the other voltage loss. The IRFZ44 has an on resistance (RDS (on)) of just 0.024Ω. But as you know, passing a current through any resistor causes that resistor to heat up. So it is with the “resistance” in the MOSFET. Our maximum current is about 10A per device, which equates to a dissipation of some 2.4W. (P = I2 x R). Even though well within the device ratings that’s a significant amount of heat for any component to get rid of and we have five of these devices all wired cheek-by-jowl. The second problem any significant resistance causes is voltage loss. Passing a current through a resistor causes a voltage to develop across that resistor – voltage which is then not available to the load. If for a moment we assumed a single MOSFET could handle the total 50A load, we would be losing almost 1.2V across it (E = I x R). That’s an intolerable loss from a 12V supply and will make the motor run significantly slower. But as you also know, when you connect resistors in parallel the resistance drops. We’re connecting five of these MOSFET “resistors” in parallel so the equivalent resistance is just .0048 ohms. Using Ohm’s law again, 50A x .0048 is just 0.24V loss – a much better proposition. Remember that’s the worst case; at say 20A the loss is only going to be about 50mV. The MTP3055 P-channel power MOSFET used as the brake doesn’t have to handle very high currents. That’s fortunate, because P-channel devices generally have a higher RDS than N-channel devices (in this case 0.3Ω). Its 60V, 12A rating should be more than adequate for this application. Construction All components are mounted on a small PC board, nominally 60 x 33mm. Before commencing construction, make the usual checks for defects in etching. Also, if you are not building this from the Oatley Electronics kit, you will need to file the corners off the board – to about 5mm in each direc- tion – so that it will fit in the specified case. The Oatley kit, by the way, includes the case, the wiring loom pictured including fuseholder and fuse and, of course, the PC board and components. After checking that the board fits the case, commence assembly with the smallest components first. Note that most of the resistors mount on end. Our prototype used sockets for both ICs but this is left up to you. Use two of the resistor lead cut-offs to form the two links required on the board – both under where the MOSFETs mount. The final components to be mounted should be the MOSFETs. Note particularly their orientation – all go the same way but they must be the right way around – and also the location of Q6, the P-channel MOSFET. It mounts closest to the BAT + and MOTOR terminals. To keep the MOSFETs straight and in position we lined them up with a 3.2mm drill bit through all their holes and then soldered them in position. Because of the significant current drawn by the MOSFETs some short lengths of heavy tinned copper wire should be soldered along the appropriate PC board tracks (ie, under the MOSFETs) to increase the current carrying capability significantly. Just remember that Q6 is not in parallel with the rest of the MOSFETs! Speaking of current capability, the wiring used in the prototype for battery connection was certainly not rated at 50A! Our application called for only a fraction of this capacity so we used standard 10A hookup wire and a 4A in-line fuse. If you are powering anything larger, not only will greater capacity cabling be needed but you will also have to think seriously about connections to the PC board – soldered connections may be inadequate. Some form of busbar may be required. Some model shops sell silicone-coated hookup wire which is specifically intended for high-current applications such as this. It could be worth a look. Fitting to the case The final step is to mount the complete assembly in its case. The case is in two sections with the larger section of the case actually the “lid”. The PC board mounts upside-down in the Where do you get it? This project, including the circuit and PC board pattern, is copyright © 2000 to Oatley Electronics. They can supply a complete kit of parts, including the case, for $35.00 They will also shortly have available a simulator (see next page) suitable for use with this circuit. Contact Oatley Electronics on (02) 9584 3561, fax (02) 9584 3563, by email at sales<at>oatleyelectronics.com, via mail at PO Box 89, Oatley NSW 2233, or via their website www.oatleyelectronics.com * Branco Justic is the Manager of Oatley Electronics. “lid” so that when you turn it over it’s the right way up. Double dutch? Not really, but the photos might give a better idea of what we’re saying. No screws are necessary to hold the PC board in place – it’s held captive by its leads and the MOSFETs. A hole needs to be cut through the top of the lid for the MOSFETs – ours was 27 x 10mm, centred 5mm from one edge – and also a small hole drilled to allow VR1 to be adjusted from outside the case with a fine screwdriver. A 3mm hole would be about right, lined up with VR1 underneath. With the external leads soldered to the underside of the PC board (ie, direct to the tracks) they emerge from the assembled case through the cable- ways provided. Significantly larger leads will of course need larger holes cut. One feature of the specified case worth noting is that no extra screws are required to hold it together. The two portions snap together and then the same screws which mount the case prevent it from coming apart. The centres for the mounting screws are 73mm apart. Testing You will need a radio control transmitter and a matching receiver with servo outputs, a suitable DC motor and a DC supply or battery equal to the task. If you don’t have a radio control you may wish to build the radio control servo pulse simulator described at the end of this article. We will assume you are using a radio control receiver but if not, simply connect the wires to the simulator the same way around. Connect the three servo wires to the radio control receiver output. The red and black wires go to + and - on the output while the brown wire goes to the data output – usually the middle pin and on “real” servos, usually coloured yellow. Set the radio control transmitter stick to either minimum if it is a single direction controller or to centre (off) in a dual-direction controller, with trimtabs set to the centre as well, and turn both transmitter and receiver on. Apply power to the controller. You’ll almost certainly find the motor starts to turn (be careful of the starting kick on a large motor if it is not secured in some way!) but when you adjust VR1 you should be able to stop the motor completely. If so, move the stick on the radio control transmitter and you should find the motor turns with its speed proportional to the stick position. Full stick should give you full motor speed, or very close to it. What if it doesn’t work? Obviously, there is an error somewhere. Perhaps as a starting point, eliminate the radio control transmitter and receiver by connecting a real servo to the receiver and make sure it works properly. That ensures you have the right sort of waveform coming from the receiver. If it works, check your wiring and component placement again – more than 95% of faults in kits are due to one or two wrongly placed or reversed components or poor soldering. Check that you have +5V coming to the ZN409 supply rail from the radio control unit. If you have an oscilloscope, view the waveforms at pins 14, 5 and 9 of IC1. If you get what looks like a correct waveform, look further along. Otherwise the error is somewhere around that IC. There should be a positive-going waveform at approx. 50Hz from pin 11 of IC2, its width varying with either the input signal or the position of VR2. Also check the inversion of signal between pins 1/2 and 3, 5/6 and 4, 8/9 and 10 and finally 12/13 and 11. May 2000  83 Manual motor control via a simulator Earlier we referred to the waveform from a radio control receiver – a square wave of 50Hz with a duty cycle dependent on the setting of the radio control transmitter stick. At rest the pulse should be 1.5ms wide and full forward it should be 2ms wide. It follows then that if a waveform of this type was fed into the input the system would operate as if it was attached to a radio control receiver. All we need do is simulate that waveform. Fortunately, that is quite simple to do. Two suitable circuits are shown below. The first consists of two 555 timers (actually a 556 which is two 555s in one package) – one connected as an astable oscillator running at 50Hz (ie, producing continuous 20ms-wide pulses). This triggers the second 555 wired as a monostable which has its pulse width variable from less than 1ms to more than 84  Silicon Chip 2ms by adjusting VR1. The output from pin 3 of IC2 then is a series of pulses, 20ms apart, which vary in length from less than one to greater than two milliseconds. Now where have we heard that before? A similar circuit was first described in SILICON CHIP in May 1994. It produced 30ms pulses – which should work fine – but we’ve adjusted the values to give approximately 20ms, just to be consistent. The second circuit, from the same issue, is even simpler and contains just one 4001 quad NOR gate and a few other components. Its drawback was that due to its simplicity the frame rate changed with the pulse width but apparently that didn’t cause any problems. For a full description of these circuits, refer to the May 1994 issue. Copies of that issue are still available from SILICON CHIP Publications for $7 each including postage & packing ($7.70 after July 1). We believe either could be used but we must say that we haven’t tried either with this circuit. PC board patterns are shown for both but as they are so simple these could just as easily be built on a small piece of Veroboard to save the cost of a PC board. You can use these simulators to either set up your controller in the absence of a radio control system or you can use it to “hard wire” control an electric motor (low voltage DC only!). That’s up to you. Note that you will have to arrange a 5V supply for both the simulator and the ZN409 circuitry in the speed controller. This could most easily be done with a 7805 regulator taking its input from the 12V supply. (When used with a radio control receiver the speed controller takes its 5V supply from the servo output of the SC receiver). T TRONICSHOWCASELECTRO SURPLUS ELECTRONIC COMPONENTS at CHEAP CHEAP CHEAP PRICES! ICs, LCD Displays,Transistors, Diodes, Leds, Books, Connectors, Switches, Transformers, Fans, Relays, Speakers,Terminals, Resistors, Buzzers, Leads, Knobs, Batteries, Computer Accs. etc. FOR A FREE MONTHLY MAILER PLEASE CONTACT ROCOM ELECTRONICS STORE ADDRESS: 56 RENVER ROAD, CLAYTON VIC. 3168 POSTAL ADDRESS: BAG 620 CLAYTON SOUTH, VIC. 3169 PH (03) 9543 7877 FAX (03) 9543 4871 Email: sales<at>rocom.com.au NEW! HC-5 hi-res Vi deo Distribution Amplifier DVS5 Video & Audio str Di ibution Amplifier Five identical Video and Stereo outputs plus h/phone & monitor out. S-Video & Composite versions available. Professional quality. For broadcast, audiovisual and film industries. Wide bandwidth, high output and unconditional stability with hum-cancelling circuitry, front-panel video gain and cable eq adjustments. 240V AC, 120V AC or 24V DC VGS2 Graphics Splitter High resolution 1in/2out VGA splitter. Comes with 1.5m HQ cable and 12V supply. Custom-length HQ VGA cables also available. Check our NEW website for latest prices and MONTHLY SPECIALS www.questronix.com.au Email: questav<at>questronix.com.au Video Processors, Colour Correctors, Stabilisers, TBC’s, Converters, etc. All mail: PO Box 548, Wahroonga NSW 2076 Ph (02) 9477 3596 Fax (02) 9477 3681 Visitors by appointment only QUESTRONIX MicroZed Computers GENUINE STAMP PRODUCTS FROM EMC Technologies' internationally recognised Electromagnetic Compatibility (EMC) test facilities are fully accredited for emissions, immunity and safety standards. EMC Technologies Melbourne: (03) 9335 3333 Sydney: (02) 9899 4599 3990 FULL RANGE $ ELECTROSTATIC Now you can afford the legendary clarity, transparency, depth and precision of an electrostatic speaker. The new Vass ELS-5 is a full range electrostatic speaker, able to faithfully reproduce frequencies from 40Hz-20kHz. • 5 Year Warranty • Wide range of custom finishes. • Individually hand built & tested. Scott Edwards Electronics microEngineering Labs & others Easy to learn, easy to use, sophisticated CPU based controllers & peripherals. PO Box 634, ARMIDALE 2350 (296 Cook’s Rd) Ph (02) 6772 2777 – may time out to Mobile 0409 036 775 Fax (02) 6772 8987 http://www.microzed.com.au Most Credit Cards OK Do you want YOUR product or service showcased to Australasia's most important electronics marketplace? CALL ME: RICK WINKLER on (02) 9979 5644 and let me explain how cost effective the 1/42-44 Garden Bvde, Dingley 3172 Pyramid subwoofer Ph 03 9558 0970 Fax 03 9558 0082 separately available email: vass<at>hotkey.net.au May 2000  85 SILICON CHIP ELECTRONICS SHOWCASE can be for YOU! NOW WITH 34 E and st ternet in h t i w s s acce 2. PER M  NO download limits  NO mysterious hidden charges  NO long-term contracts  NO fine print *POPS (Points of Presence) NOW IN ALL THESE CITIES AND TOWNS VIC Bacchus Marsh, Ballarat, Balliang, Bendigo, Cranbourne, Emerald, Geelong, Gisborne, Healesville, Kilmore, Kinglake, Lara, Melbourne, Mornington , Nunawading, Pakenham , Romsey, Shepparton, Warrnambool NSW Albury, Armidale, Bathurst, Bega, Camden, Campbelltown, Coffs Harbour, Dubbo, Gosford, Grafton, Lismore, Mulgoa, Newcastle, Nowra, Orange, Penrith, Port Macquarie, Richmond, Sydney, Tamworth, Taree, Wagga Wagga, Windsor, Wisemans Ferry, Wollongong QLD Brisbane, Bundaberg, Cairns, Gladstone, Gold Coast, Mackay , Maroochydore, Maryborough, Mt Isa, Rockhampton, Toowoomba, Townsville WA Broome, Bunbury, Geraldton, Kalgoorlie, Katanning, Perth, Rockingham SA Adelaide, Gawler, Mt Gambier, Port Augusta ACT Canberra NT Darwin TAS Hobart EXTRA POPS* . . . till only COUNTRY .7c READERS TAKE NOT E! MINUTE     YES YES YES YES - your own email address your own website space 100% peace-of-mind 100% satisfaction g'tee You’ve seen all those other low-cost Internet access offers? The ones which look great until you read the fine print? Well, here's one without fine print! The only restriction to this service is a $10 minimum per month (5 hours included free) and payment may only be made by credit card. All capitals and many larger cities covered. INTERESTED? Call SILICON CHIP, totally obligation free, on (02) 9979 5644, 9am - 5pm Mon-Fri for more details. (We'll even call you back if STD). Or fax us on (02) 9979 6503. Or if you already have web access, email silchip<at>siliconchip.com.au or www.silchip.com.au REFERENCE GREAT BOOKS FOR NEW NEW NEW NEW AUDIO POWER AMPLIFIER DESIGN HANDBOOK 77 $ By Douglas Self. 2nd Edition Published 2000 A uniquely detailed and practical text on the design of audio amplifiers from one of the world’s most respected audio authorities. The new 2nd edition is even more comprehensive, includes sections on load-invariant power amps, distortion residuals, diagnosis of amplifier problems, reactive loads on amplifiers, how to make speakers draw higher currents and the practical side of variable temperature coefficient bias generators. 368 pages in paperback. 95 NEW VIDEO SCRAMBLING AND DESCRAMBLING for SETTING UP A WEB SERVER If you've ever wondered how they scramble video on cable and satellite TV, this book tells you! Encoding/decoding systems (analog and digital systems), encryption, even schematics and details of several encoder and decoder circuits for experimentation. Intended for both the hobbyist and the professional. 290 pages in paperback. NEW 2nd Covers all major platforms, software, links and web techniques. It details each step required to choose, install and configure the hardware and software elements, create an effective site and promote it successfully. 273 pages, in paperback. Satellite & Cable TV by Graf & Sheets By Simon Collin. Published 1997. 59 $ Edition 1998 TCP/IP EXPLAINED 95 90 Assumes no prior knowledge of TCP/IP, only a basic understanding of LAN access protocols, explaining all the elements and alternatives. Combines study questions with reference material. Examples of network designs and implementations are given. 518 pages, in paperback. By Tim Williams. First published 1991 (reprinted 1997). $ 59 Includes grounding, printed circuit design and layout, the characteristics of practical active and passive components, cables, linear ICs, logic circuits and their interfaces, power supplies, electromagnetic compatibility, safety and thermal management.302 pages, in paperback. 95 LOCAL AREA NETWORKS: An Introduction to the Technology ELECTRIC MOTORS AND DRIVES Want to become more familiar with local area networks (LANs) without facing the challenge of a 400-page text? . Gives familiarity with the concepts involved and provides a start for reading more detailed texts. 191 pages, in paperback. For non-specialist users – explores most of the widely-used modern types of motor and drive, including conventional and brushless DC, induction, stepping, synchronous and reluctance motors. 339 pages, in paperback. By Austin Hughes. Second edition published 1993 (reprinted 1997). By John E. McNamara. 2nd edition 1996. O R D E R H E R E                65 $ THE CIRCUIT DESIGNER’S COMPANION By Philip Miller. Published 1997. $ NEW NEW NEW 65 $ AUDIO POWER AMPLIFIER DESIGN..................$77.95 VIDEO SCRAMBLING/DESCRAMBLING.............$59.95 TCP/IP EXPLAINED.............................................$90.00 LOCAL AREA NETWORKS..................................$65.00 SETTING UP A WEB SERVER.............................$65.00 THE CIRCUIT DESIGNER’S COMPANION...........$59.95 ELECTRIC MOTORS AND DRIVES......................$59.95 UNDERSTANDING TELEPHONE ELECTRONICS....$55.00 AUDIO ELECTRONICS........................................$79.00 GUIDE TO TV & VIDEO TECHNOLOGY...............$55.00 EMC FOR PRODUCT DESIGNERS.......................$95.00 THE ART OF LINEAR ELECTRONICS..................$80.00 INTERNET HOME PAGES MADE SIMPLE...........$24.95 DIGITAL ELECTRONICS .....................................$59.95 ESSENTIAL LINUX..............................................$85.00               ORDER TOTAL: $............. 5995 $ Your Name_________________________________________________ PLEASE PRINT Address ___________________________________________________ ___________________________________ Postcode_______________ Daytime Phone No. (______) __________________________________ STD Email___________________<at>_________________________________  Cheque/Money Order enclosed OR  Charge my credit card –  Bankcard  Visa Card  MasterCard Signature____________________ Card expiry date PLUS P&P (if applic.): $.............. TOTAL$ AU.................... ALL TITLES SUBJECT TO AVAILABILITY. PRICES VALID FOR MONTH OF MAGAZINE ISSUE ONLY. BOOKSHOP WANT TO SAVE 10%? SILICON CHIP SUBSCRIBERS AUTOMATICALLY QUALIFY FOR A 10% DISCOUNT ON ALL BOOK PURCHASES! ENQUIRING MINDS! (To subscribe, see page 65) UNDERSTANDING TELEPHONE ELECTRONICS THE ART OF LINEAR ELECTRONICS By Stephen J. Bigelow. Third edition published 1997 by Butterworth-Heinemann. $ By John Linsley Hood. First published 1993. NEW SECOND EDITION 1998. A very useful text for anyone wanting to become familiar with the basics of telephone technology. The 10 chapters explore telephone fundamentals, speech signal processing, telephone line interfacing, tone and pulse generation, ringers, digital transmission techniques (modems & fax machines) and much more. Ideal for students. 367 pages, in soft cover at $55.00. 55 80 DESIGNING INTERNET HOME PAGES MADE SIMPLE AUDIO ELECTRONICS By John Linsley Hood. First published 1995. Second edition 1999. This book is for anyone involved in designing, adapting and using analog and digital audio equipment. It covers tape recording, tuners and radio receivers, preamplifiers, voltage amplifiers, audio power amplifiers, compact disc technology and digital audio, test and measurement, loudspeaker crossover systems, power supplies and noise reduction systems. 375 pages in soft cover at $79.00. $ By Lilian Hobbs. First published 1996. Second edition 1999. All you need to get started. Create and design your own Internet home pages that include both text and graphics, using this practical, easy to follow, jargon free guide. This edition has been enhanced and updated and now covers HTML 4.0. 182 pages, in paperback, at $24.95. 79 $   GUIDE TO TV & VIDEO TECHNOLOGY Eugene Trundle has written for many years in Television magazine and his latest book is right up to date on TV and video technology. The book includes both theory and practical servicing information and is ideal for both students and technicians. 382 pages, in paperback, at $55.00. 55 EMC FOR PRODUCT DESIGNERS By Richard Monk. Published 1998. 59 95 By Steve Heath. Published 1997. Widely regarded as the standard text on EMC, this book provides all the information necessary to meet the requirements of the EMC Directive. It includes chapters on standards, measurement techniques and design principles, including layout and grounding, digital and analog circuit design, filtering and shielding and interference sources. The four appendices give a design checklist and include useful tables, data and formulae. 299 pages, in soft cover at $95.00. 95 $ P&P $ With this book you can learn the principles and practice of digital electronics without leaving your desk, through the popular simulation applications, EASY-PC Pro XM and Pulsar. Alternatively, if you want to discover the applications through a thoroughly practical exploration of digital electronics, this is the book for you. A free floppy disk is included, featuring limited function versions of EASY-PC Professional XM and Pulsar. 249 pages, in paperback, at $59.95. ESSENTIAL LINUX By Tim Williams. First pub­­lished 1992. Second edition 1996. Add $A5.00 per book – Orders over $100 P&P free in Australia. NZ: Add $A10 per book, $A15 elsewhere 24 95 $ DIGITAL ELECTRONICS – A PRACTICAL APPROACH By Eugene Trundle. First pub­­lished 1988. Second edition 1996. $ This practical handbook from one of the world’s most prolific audio designers has been updated and amended to make it the leading practical source of information for those interested in linear electronics and its applications, particularly in the world of audio design. 348 pages, in paperback, at $80.00. Provides all the information and software that is necessary for a PC user to install and use the freeware Linux operating system. It details, setp-by-step, how to obtain and configure the operating system and utilities. It also explains all of the key commands. The text is generously illustrated with screen shots and examples that show how the commands work. Includes a CD-ROM containing Linux version 1.3 and including all the interim updates, basic utilities and compilers with their associated documentation. 257 pages, in paperback, at $85.00. 85 $ POST 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 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. Charging 4.8V batteries I want to build the Multi-Purpose Fast Charger featured in the February & March 1998 issues of SILICON CHIP. My problem is that I want to be able to charge 4.8V NiCd battery packs (for R/C model aircraft) of 600-1200mA.h. Have there been any updates to the circuit to allow this? If not, what modifications would need to be done? (B. V., Tindal, NT). • The value of divider resistance for a 4.8V battery pack will be 33.3kΩ and will need to be used instead of the dividers used for a different voltage selection. For example, you could remove the 150kΩ and 12kΩ paralleled resistors for the 12V NiCd position and place the 33.3kΩ value in their places. This will change the 12V NiCd setting to 4.8V. A 47kΩ and 120kΩ resistor in parallel will be close enough to the correct value. 13.8V regulated power supply I have the November 1997 issue which describes the Regulat­ed Supply for Darkroom Lamps. It has very good regulation but I am interested in making a 13.8V version. Can you suggest what modifications will be Rear projection TV picture rotation I recently purchased a Toshiba 43-inch rear projection TV. I have only had it for a week and have noticed that the picture is rotated clockwise by a small angle. The hifi shop tell me that a manufacturing tolerance of 10% is allowed on picture quality. They could not tell me what the 10% applied to – rotation or linear dimension. They just said it was a general tolerance that applied to all aspects of the picture. The rotation equates to about 12mm 90  Silicon Chip required? (I. S., via email). The circuit should provide 13.8V with no modifications being necessary. Just set trimpot VR1 for 13.8V instead of 12V. By the way, you do realise that the output is not smooth DC but pulsed. It is OK for driving motors or lamps but not suitable for other loads. • Connecting a mini stereo amplifier I would like to connect the 100W amplifier module described in the March 2000 issue to my Akai TX250 mini stereo system. It’s maximum output is 10W. (J. C., via email). • Does your mini stereo have a tape output? If so, the best way to drive the 100W amplifier is to connect the tape signal via a volume control potentiometer of, say, 25kΩ. Alternatively, if your system only has speaker outputs, the way to do it is to disconnect the speakers and feed each of the outputs to 1kΩ resistors and then to the 100W amplifier inputs. In this way, you can use the volume control on the mini stereo to control the volume from the 100W amplifier. Mind you, by feeding the signal from your mini stereo to the 100W module you will not be getting the best performance from it. in vertical distance, sloping down from left to right. I have looked at the store’s demo unit and it has a simi­lar rotation. The rotation is most visible when viewing a “letterboxed” or widescreen movie, as the black bars top and bottom highlight the effect. The problem is not with the DVD or DVD player, as the rotation is visible with Teletext too. I may be being too fussy but now that I’ve noticed it, I see it all the time; it’s a bit like looking at a framed picture on the wall that isn’t straight. Considering the cost of the Power supply blows Mosfets I have built the 40V 8A power supply described in April & May 1998 but I have a problem. I am blowing the BUK436s when the unit is short circuited, although the current limit is OK. Any ideas on the possible fault? Why is there no drain to source protection to stop the reflected transients under heavy reactive loads? (G. L., via email). • The BUK436 Mosfets do have drain to source protection by way of zeners ZD1 and ZD2. These conduct if the drain voltage exceeds the zener voltage plus the gate voltage. The Mosfet is then switched to conduct any transients. The Mosfets could be upgraded to higher rated devices if required. Devices such as the IRFP250 rated at 33A and IRFP260 rated at 46A would be more rugged. These are available from Farnell Electronic Components Pty Ltd. Phone 1300 361 005. Driving piezo transducers at high levels The publication in March of the high-power class-AB amplifier could not have come at a better time. My son is build­ing a sono-luminescence unit (just under $5000), I expect better. I was very surprised that there was no mechanical adjustment, or for that matter, an electronic adjustment via the menu system (red and blue tube convergence can be adjusted however). Is there anywhere I can find out the real manufacturing tolerance on picture rotation? Should I push for a replacement? (P. F. Mount Eliza, Vic). • As far as we’re concerned, the picture should be exactly horizontal. You should ask for it to be adjusted or replaced. Address http://www.oatleyelectronics.com Ph ( 02 ) 9584 3563 or 9584 3564 PO Box 89 Oatley NSW 2223 Fax 9584 3561 e-mail orders: sales<at>oatleyelectronics.com 1st FOR AUSTRALIAN MADE KITS NEW INCREDIBLE BARGAIN !!! DEVELOPED IN AUSTRALIA!!! K001...1.5 to 9V D.C. 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Prices subject to change M without notice ay 2000  91 ACN 068 740 081 ABN18068 740 081 EA_MAR_00 Questions on the PIC digital voltmeter I’ve just built the Digital Voltmeter Febru­ary 2000) and it works very well, calibrating to within 0.02V of my Fluke DMM. I’ll now build one for the auxiliary battery as well. I do have a couple of queries though, the first of which concerns regulator REG1. My car’s charging system was upgrad­ed two years ago to include an 85A alternator and the biggest battery I can fit. This combination solved the problems I was having with the charging system on a 15-year old vehicle. However, after starting and until the battery is fully recharged, I’ve noticed the voltage will occasionally peak at up to 15.2V and usually holds at about 14.6V during daylight driving and is never below 13.8V even with everything on, including driving and auxiliary lamps. This is great for my peace of mind but I notice that REG1 becomes very hot, to the point where it’s uncom­fortable to hold your finger on the outer case and impossible to touch REG1 itself. I’ve made a small heatsink that fits under the lower cir­cuit board and I think this helps but I wonder if it would be wise to limit the input voltage? generator and was looking for a high power amplifier to drive piezo-ceram­ ic ultrasonic transducers at 25kHz. High power ultrasound, when injected into water and some other fluids, will create tiny bubbles which emit blue-white light at a temperature hotter than the surface of the Sun. The effect is not well understood but some researchers believe that it may be connected with the Casimir Effect (Zero Point Energy). Nevertheless, with some perseverance and a little tinkering, single and multi-bubble sonoluminescence equipment can easily be built by amateurs. However, there is a problem. The amplifier is designed to roll off the high frequencies. Your article noted that, “At the high frequency end, the .0012µF capacitor and the 1kΩ resistor feeding the base of Q1 form 92  Silicon Chip Can you advise how much current the unit draws during full operation? When I connect my DMM to measure it the voltmeter doesn’t work. I want to be able to connect the voltmeter directly to the battery so I can monitor voltages at any time (without switching on the car’s systems) with just a simple on-off switch directly from the battery. Finally, could this unit be adapt­ ed to run a 3.5-digit LCD? (M. H., via email). • The Digital Voltmeter does operate with the regulator hot but it is well within its temperature ratings. If you wish, you could make up a small heatsink to be wrapped around the brass standoff connecting to the regulator tab. You can reduce the input voltage applied to the regulator using the resistor locations provided on the display board for the 24V version. Two 100Ω 1W resistors in parallel in place of the five 820Ω resistors would do for the 12V version. Connect the 12V supply to the 24V input on the board so the current flows through these dropping resistors. The only problem with doing this is that the low battery voltage may not be measured correct­ly if the resistance provides too much of a voltage drop. The circuit would have to be redesigned to suit an LCD panel. a low- pass filter which rolls off frequencies above 130kHz (-3dB)”. However, if one refers to Fig.1 on page 17, it appears that the -3dB point is around 65kHz. Is the frequency rolloff controlled elsewhere in the circuit, or can the value of the .0012µF capacitor be reduced to give an improved response at 25kHz? The equipment will not be operated in the house, so EMI and extraneous high frequency signals are not important. Since piezo-ceramic devices are voltage driven, in order to increase the voltage output, we were wondering if there may be an easy way to invert the input signal to one of the amplifier modules so that the output voltage can be doubled? (A. L., Whit­by, NZ). • There are a number of problems associated with driving piezo transducers. First, they are a pure capacitance so their im­pedance drops as the frequency rises. At frequencies of 25kHz and above, the impedance could easily be less than 8Ω and this would be unsuitable for the new amplifier. Most of the high frequency rolloff in the amplifier is due to the output RLC filter which ensures unconditional stability with capacitive loads. Without it, the amplifier would be un­stable with pure capacitive loads, as most amplifiers are without some output decoupling network. If you want to drive piezo transducers, you would be better off using a variant of the circuit used for the Dog Silencer (July 1999) or the Woofer Stopper (February 1996). By the way, we tried some experiments with sono-lumines­cence several years ago and had no success. DC-DC converter for car sound In October & November 1996 you published a 600W DC-DC con­verter for car stereo systems. Would it be possible to use this for the power supply for the 100W amplifier published in the March 2000 edition so that it could be used in a car? (D. J., via email). • The 600W DC-DC converter is really far too big for your needs. You would be better off looking at the 100W design we published in the December 1990 issue. However, there is another consideration and that is that our new 100W amplifier module is not recommended for driving 4Ω speakers which is what most car sound systems use. You might be better off looking at a commercial car ampli­fier such as some of those available from Jaycar Electronics. Cockroft-Walton voltage multipliers If possible, could you advise me what projects you have done, and in which issues they were published, that used a Cock­roft-Walton voltage multiplier (probably also called a voltage tripler)? My tech teacher apparently has not come across these devices before. (L. H., via email). • We have published only one project featuring a Cockroft-Walton multiplier and that was a wide range electrostatic loud­speaker (February, March & April 1995), with the circuit being in April 1995. However, a better version of the circuit was pub­lished in “Ask Silicon Chip” page 93, March 1994 issue. Overheating problem in turbo car I have a turbo-charged Mazda MX6 and the under-bonnet tem­peratures get extremely high when idling at traffic lights. This is due to the fact that the thermo fans are controlled by the water temperature which is quite slow to rise. The heat from the turbo combined with more than five minutes of no air flow allows the air temperature to rise significantly before the fans click in. What I would like to achieve is a system whereby the thermo fans come on automatically when the car is stationary and the standard water thermo switch can otherwise operate normally. I would also like to incorporate a cool-down timer (similar to a turbo timer but with the engine off and fans on). I have consid­ered several methods to do this but due to my lack off knowledge of electronics and my concerns about affecting the car electron­ics, I have not been able to come up with a solution. The system I would envisage is as follows: an idle switch activates a delay timer of about 10 seconds which sends power to an adjustable ambient thermo switch capable of reading temperatures above 60°C. When the air temperature rises above the set level, the factory water thermo switch is overridden by opening its circuit and this would turn on the fans. The fans would continue to run until the idle switch is opened. I hope Off-Hook Indicator LED is invisible I recently constructed the OffHook Indicator for Tele­phones as described in the January 2000 issue and it is much appreciated in my house. Inter­net interference from the kitchen phone is significantly reduced and I know when the phone is available. My complaint is that the flashing LED indicator is virtual­ly invisible at about 20-30° off the direct axis which turns out to be the angle where it is normally viewed. What do you suggest? I’d also like to add the Speed Alarm (November 1999) to my Subaru L-series 4WD. The rear drive to have the fans come on quite soon after stopping at the lights and turn off immediately when the throttle is pressed. The delay timer would allow for normal driving condi­tions and for slowing down to a stop. I would also like to incorporate a timer that allows the fans to continue to run for about 30-40 seconds after the ignition is turned off. (S. B., via email). • Your first requirement to ensure the fans will run at idle is an rpm switch. This will measure the engine rpm and only switch at idle. This will drive a relay to then drive the fans via a thermal switch. Thermal switches are available from Jaycar and Altron­ ics. These switches close a contact at the preset temperature. 60°C types are available. The rpm switch could be a variation of the tachometer (as described in the April 2000 issue). Use the shaft is not used on the highway so I must connect to the front drive shafts. Does this present any fitting problems? (M. T., Ringwood, Vic). • The LED indicator for the Off Hook Indicator for telephones is a high brightness type and they always have a narrow axis. The easiest way out of the problem is to angle the LED to the posi­tion you normally view it from. Alternatively, use a conventional LED which has a wider viewing angle. You can fit the speed sensor to the front wheel drive shaft without problems. It is best to locate the magnets on the un­sprung section of the shaft so that the gap to the sensor will remain fixed. limiter output to drive the base of a BC337 transistor via a 2.2kΩ resistor. Con­nect the emitter to ground and the collector to the coil of a 12V relay. The other end of the relay coil connects to the +12V supply. Connect a 1N4004 diode across the relay coil with the cathode (striped end) to the positive supply. The relay will be switched when the revolutions per minute go below a set value. This value can be set at just above idle, say 1000 RPM. Thus the idle can be detected which then switches the relay. The thermal switch (a normally open type) can connect in series with the normally closed contact on the relay. This can then drive the fans. The requirement for the fans to run after ignition switch off can be achiev­ed with the Turbo Timer as described in the November 1998 SC issue of SILICON CHIP. 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. May 2000  93 MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. FRWEEBE YES! Place your classified advertisement in SILICON CHIP Market Centre and your advert will also appear FREE in the Classifieds-on-the-Web page of the SILICON CHIP website, www.siliconchip.com.au And if you include an email address or your website URL in you classified advert, the links will be LIVE in your classified-on-the-web! S! D E I F I S C LAS EXCLUSIVE TO SILICON CHIP! CLASSIFIED ADVERTISING RATES Advertising rates for this page: Classified ads: $11.00 (incl. GST) for up to 12 words plus 55 cents for each additional word. Display ads: $27.50 (incl. GST) 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) 9979 6503. Taxation Invoice ABN 49 003 205 490 _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ FOR SALE ELECTRONIC/MECHANICAL DESIGN AND CONSTRUCTION: we offer a complete design service for electronic and mechanical devices. Most work is done in house and you deal directly with the designers. No job is too small and can be to prototype or “turn key” stage, in one offs or for future production. Simply send us an email at vladimir<at> u030.aone.net.au with your questions or requirements and we will get back to you. CAMERAS Quality Colour Dome $159. Colour Camera in case with Bracket/ Audio $165. Night Vision Camera $115. 8 Input Switcher $179. Wholesale Prices in SECURITY & ELECTRONIC Supplies 0410 73 9317. FUNCTION GENERATORS, BWD 170A 2MHz, sin, sq, Evi, pulse, Vco, w/ manual. No exotic parts, 3 off at $70 ea inc. freight. email jcd<at>c031.aone.net.au or (03) 9836 6494. WEATHER STATIONS: Windspeed & direction, inside temperature, outside temperature & windchill. Records highs & lows with time and date as they occur. $420.00 complete plus sales tax if appli­ cable. Optional rainfall and PC interface. Used by Government Departments, farmers, pilots, and weather enthusiasts. _____________ _____________ _____________ _____________ _____________ Enclosed is my cheque/money order for $­__________ or please debit my Circuit Ideas Wanted ❏ Bankcard   ❏ Do you have a good circuit idea. If so, sketch it out, write a brief description of its operation & send it to us. Visa Card   ❏ Master Card Card No. Name _____________________________________________________ Provided your idea is workable & original, we’ll publish it in Circuit Notebook & you’ll make some money. Street _____________________________________________________ We pay up to $60 for a good circuit so send your idea to: Suburb/town _________________________ Postcode______________ Silicon Chip Publications, PO Box 139, Collaroy, 2097. Signature­­­­­­­­­­­­ ________________________ Card expiry date______/______ 94  Silicon Chip Other models with barometric pressure, humidity, dew point, solar radiation, UV, leaf wetness, etc. Just phone, fax or write for our FREE catalogue and price list. Solar Flair/Ecowatch ph: (03) 5968 4863 fax: (03) 5968 5810, PO Box 18, Emerald, Vic., 3782. ACN 006 399 480. RAIN BRAIN AND DIGI-TEMP KITS: 8 station sprinkler controllers, 60 channel temp monitor uses DS1820s over 500 metres. Has PC Data logging. Mantis Micro Products, http://www.home.aone.net.au/mantismp COVERT Camera in PIR or Smoke Detector case from $94 * HI-RES better than SUPER-VHS Quality QUADS 4 Pix 1 screen from $208 * DOME CAMERAS from $88 - SONY CCD $107 - COLOUR $164 * Video BALUNS from $7 * DIY PAKS 4 Cameras, Switcher & Supply from $461 with 12" Monitor from $575 * 4 COLOUR CAMERAS, SWITCHER & POWER SUPPLY from $769 - with COLOUR QUAD 4 Pix 1 Screen from $1168 * COLOUR QUADS from $474 * COLOUR DUPLEX MUX from $1329 * 14" MONITORS from $203 - with Inbuilt 4 Ch SWITCHER from $236 * SEE-in-the-DARK CAMERAS & INFRARED 120 mW LED ILLUMINATOR Kits from $19 * FREE PC VIDEO RECORDER - TIME LAPSE - MOTION DETECTION Software with 4 Ch Capture Card from $113 * Video Transmitter KitSets & Systems from $142 * Camera, Microphone & Timer/ Controller in PIR DETECTOR from $129 * BULLET 480 Line 0.05 lux SONY CCD or DSP COLOUR from $132 * PCB Modules from $76 COLOUR Pinhole from $155 * MINI CAMERAS 36 x 36 from $85 - SONY CCD $102 COLOUR $162 www.allthings.com.au * 08 9349 9413. C COMPILERS: everything you need to develop C and ASM software for 68­HC08, 6809, 68HC11, 68HC12, 68­ HC16, 8051/52, 8080/85, 8086, 8096 or AVR: $155.00 each. Macro Cross Assemblers and Disassemblers for above CPUs + 6800/01/03/05, 6502 and 68­HC12 for $78. Debug monitors: $78 for 6 CPUs. All compilers, XASMs and monitors: $480. 8051/52 Simulator (fast, now incl. 80C320): $78. Try the C-FLEA Virtual Machine for small CPUs, build a “C-Stamp”. Demo desk: FREE. All prices + $5 p&p. Atmel Flash CPU Programmer: Handles the 89Cx051, 89C5x and 89Sxx ROLA Australia (08) 8270 3175 www.bettanet.net.au/GTD Silvertone’s RC Receiver Still the best little performer available! MP3-CD Player: $699 Plays standard CDs & MP3s as well. Plays MP3 CDs made with a CD writer. Up to 2200 songs per CD. Car adapter available. ROLA 15U & 15UX: $325 Size: 15" (380mm). Freqency response: 30-3,000Hz (15U); 30-12,000Hz (15UX). Power handling: 250 watts RMS. SPL: 97db/1 metre. FS (resonant frequency) 30Hz. Satellite TV Reception International satellite TV reception in your home is now affordable. Send for your free info pack containing equipment catalog, satellite lists, etc or call for appointment to view. We can display all satellites from 76.5° to 180°. Still only $129.50 AM or $149.50 FM. May be used with most ppm transmitters. This and many other radio control products available from: Silvertone Electronics, PO Box 580, Riverwood 2210. Phone/Fax (02) 9533 3517. www.silvertone.com.au AV-COMM P/L, 24/9 Powells Rd, Brookvale, NSW 2100. Tel: 02 9939 4377 or 9939 4378. Fax: 9939 4376; www.avcomm.com.au Need prototype PC boards? We have the solutions – we print electronics! Four-day turnaround, less if urgent; Artwork from your own positive or file; Through hole plating; Prompt postal service; 29 years technical experience; Inexpensive; Superb quality. Printed Electronics, 12A Aristoc Rd, Glen Waverley, Vic 3150. Phone: (03) 9545 3722; Fax: (03) 9545 3561 Call Mike Lynch and check us out! We are the best for low cost, small runs. Positions At Jaycar We are often looking for enthusiastic staff for positions in our retail stores and head office at Rhodes in Sydney. A genuine interest in electronics is a necessity. Phone 02 9743 5222 for current vacancies. series, and the new AVRs in both DIP and PLCC44. Also does most 8-pin EEPROMs. Includes socket for serial ISP cable. $199, $37 tax, $10 p&p. SOIC adaptors: 20-pin $90, 14-pin $85, 8-pin $80. Credit cards accepted. GRAN­TRONICS PTY LTD, PO Box 275, Wentworthville 2145. Ph (02) 9896 7150; Fax (02) 9631 1236; or Internet: http://www.grantronics.com.au er/chargers, mod. Sinewave inverters, call with requirements. AUST­RALIA WIDE DELIVERY (Free on orders over $500.00). TASMAN ENERGY: (03) 6362 3050 Fax (03) 6362 3054. PCBs for all older magazine projects can be obtained from 0408-613-300 or http://www.cia.com.au/rcsradio KITS KITS AND MORE KITS! Check ‘em out at www.ozitronics.com SOLAR PANELS: 120 watt $995.00, 80 watt $650.00, 60 watt $510.00, 40 watt $395.00 (all with 25 year guarantee). UNBREAKABLE PANELS: 64 watt $550.00, 42 watt $420.00, 32 watt $340.00, 11 watt $190.00, 5 watt $120.00, 1.25 watt $80.00. WIND GENERATORS: 400 watt $950.00. INVERTERS: sinewave inverters, invert- TELEPHONE EXCHANGE SIMULATOR, SC February 1998. Test equipment without the cost of telephone lines. Melbourne 9806 0110. KIT ASSEMBLY ANY KITS assembled/repaired: professional, speedy service. Phone Nev­ille Walker (07) 3857 2752. WANTED Operating manual or copy for HP54601A CRO. Phone (07) 5491 6988. May 2000  95 Silicon Chip Binders Keep your copies safe, secure and always available with SILICON CHIP binders: they’re cheap insurance! Advertising Index Altronics................................. 68-70 REAL VALUE AT Av-Comm Pty Ltd.........................95 PLUS P &P DPI Aerosol.................................41 $12.95  Heavy board covers with 2-tone green vinyl covering Dick Smith Electronics........... 12-15 EMC Technologies.......................85 Futurlec.......................................37  Each binder holds up to 14 issues so that you can include catalogs Harbuch Electronics....................55 Instant PCBs................................95  SILICON CHIP logo printed in gold-coloured lettering on spine & cover Jamo Australia.........................OBC Jaycar ................................... 45-52 Kits-R-Us.....................................95 Price: $12.95 plus $5 p&p each (available Aust. only) Microgram Computers................3,9 Order by phoning (02) 9979 5644 & quoting your credit card number; or fax the details to (02) 9979 6503; or mail your order with cheque or credit card details to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. MicroZed Computers..............63,85 Oatley Electronics........................91 Optional Power..........................IFC PowerQwest................................11 Premier Batteries.......................IBC DON’T MISS THE ’BUS Do you feel left behind by the latest advances in com­puter technology? Don’t miss the bus: get the ’bus! Includes articles on troubleshooting your PC, installing and setting up computer networks, hard disk drive upgrades, clean installing Windows 98, CPU upgrades, a basic introduction to Linux plus much more. Preston Electronics......................85 Printed Electronics...................... 95 www.siliconchip.com.au SILICON CHIP’S 132 Pages 9 $ 95 * ISBN 0 95852291 X 780958 522910 COMPUTER OMNIBUS Rocom Electronics.......................85 LIN UX R.T.N............................................11 Silicon Chip Back Issues....... 38-39 A collection of computer features from the pages of SILICON CHIP magazine Silicon Chip Binders....................96 Hints o Tips o Upgrades o Fixes NOW Covers DOS, Windows 3.1, 95, 98,ANT V o A DIRE ILABLE C SILIC T FROM ON just $ CHIP 125 ORDER NOW: Use the handy order form in this issue or call (02) 9979 5644, 8.30-5.30 Mon-Fri with your credit card details. RT P&P Resurrection Radio......................65 Robotic Education Products........85 INC LUD ES FEA TUR E INC Rall Electronics............................85 09 9780958522910 09 9 Questronix...................................85 O Silicon Chip Bookshop........... 88-89 SC Internet Access................ 86-87 SC Computer Omnibus...............71 Silicon Chip Subscriptions...........33 Silvertone Electronics..................95 Smart Fastchargers.....................35 Solar Flair/Ecowatch....................95 HELP SAVE THE NIGHT SKY! We are losing our heritage of starry night skies. Poor, inefficient outdoor lighting is causing glare and “light pollution”. This wastes energy and increases greenhouse gas emissions. You can help by joining SYDNEY OUTDOOR LIGHTING IMPROVEMENT SOCIETY (SOLIS). SOLIS aims to educate and inform about quality outdoor lighting and its benefits. We also lobby councils, government and other bodies to promote good lighting practice. SOLIS meetings are held third Monday night of each month at Sydney Observatory. Individual membership is $20 pa. Donations are also welcome. Cheques payable to “SOLIS c/- NSAS”, PO Box 214, West Ryde 2114. Email: tpeters<at>pip.elm.mq.edu.au 96  Silicon Chip Telephone Technical Services.....43 Truscott’s Electronic World...........65 Vass Electronics..........................85 _____________________________ PC Boards Printed circuit boards for SILICON CHIP projects are made by: • RCS Radio Pty Ltd. Phone 0408- 613-300. • Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730. 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.premierbatteries.com.au