Fullscreen HTML5Med Res (??MB)HTML4

Building The 40V 8A Power Supply SILICON CHIP MAY 1998 $5.50* NZ $6.50 INCL GST C I M A N Y D 'S A I L AUSTRA E N I Z A G A M S C ELECTRONI SERVICING - VINTAGE RADIO - COMPUTERS - SATELLITE TV - PROJECTS TO BUILD PRINT POST APPROVED - PP255003/01272 How to solve problems and stay out of trouble Garage Door Opener: Mechanical Details ISSN 1030-2662 05 Simple Logic Probe May 1998  1 9 771030 266001 Decoder Modules For Command Control SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings.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 Contents Vol.11, No.5; May 1998 FEATURES   4  Australia’s Revolutionary Concept Car Unique body, unique instruments and a 2.3-litre 2-stroke 6-cylinder engine with supercharging – by Ross Tester 12  Special Feature: Troubleshooting Your PC; Pt.1 How to solve problems and stay out of trouble – by Bob Dyball 84  Special Subscriptions Offer Buy a subscription before June 1998 and get a bonus data wallchart Australia’s Revolutionary Concept Car – Page 4 PROJECTS TO BUILD 32  Build A 3-LED Logic Probe A simple test instrument for digital fault-finding – by Rick Walters 36  A Detector For Metal Objects Build it and learn how metal detectors work – by John Clarke 54  An Automatic Garage Door Opener; Pt.2 Second article gives you the mechanical details – by Rick Walters Build A 3-LED Logic Probe – Page 32 60  Command Control For Model Railways; Pt.4 Building the receiver/decoder modules – by Barry Grieger 74  40V 8A Adjustable Power Supply; Pt.2 The full constructional and adjustment details – by John Clarke SPECIAL COLUMNS 27  Serviceman’s Log Lightning didn’t strike this time – by the TV Serviceman 70  Radio Control Radio-controlled gliders and launch winches – by Bob Young Garage Door Opener Mechanical Details – Page 54 86  Vintage Radio Safety with vintage radios – by Rodney Champness DEPARTMENTS  2  Publisher’s Letter 20  Circuit Notebook 42  Product Showcase 53  Order Form 90  Ask Silicon Chip 94  Market Centre 96  Advertising Index 92  Notes & Errata Receiver/Decoder Modules For Command Control – Page 60 May 1998  1 PUBLISHER'S LETTER Don’t take voluntary redundancy Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Production Manager Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Rick Walters Reader Services Ann Jenkinson Advertising Manager Brendon Sheridan Phone (03) 9720 9198 Mobile 0416 009 217 Regular Contributors Brendan Akhurst Rodney Champness Garry Cratt, VK2YBX Julian Edgar, Dip.T.(Sec.), B.Ed Mike Sheriff, B.Sc, VK2YFK Ross Tester 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: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $59 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9979 5644. Fax (02) 9979 6503. ISSN 1030-2662 and maximum * Recommended price only. 2  Silicon Chip It is a sad fact that in today’s leaner and meaner economy, many large commercial and government-run organisations are get­ting rid of their staff. The way that it is sold to the public and to the unions is that there “will be no compulsory layoffs” or that the reduction will come about by “natural wastage”. The people concerned then apply pressure to the staff they want to get rid of by offering what seem to be attractive redundancy packages. Many people take the money and run and unfortunately, they soon regret it. It is surprising, when I have been talking to technical people from universities and other public organisations, just how often this scenario has been mentioned recently. They will say that they have been offered an “attractive package” and that they are seriously considering it. Well, if you are in that situation I strongly advise you not to take it. Stay where you are and that applies particularly if you are over 45 years old with a long record of service in the one job. What inevitably happens, when somebody who is more than 45 years old takes a redundancy package, is that they immediately take a well-deserved holiday. They probably had this coming to them as long-service leave, anyway. Then, after a period of six or maybe even 12 months, the attraction of continuous leisure starts to pall and the money starts to run out. They hanker for the technical stimulation of the old job. But it is no longer available and so they start to apply for jobs. Several months later, reality dawns with a vengeance – there are virtually no permanent full-time jobs available for people 45 years or older. This is the nasty aspect of today’s so-called “lean and efficient” corporations. They don’t recognise the merits of someone who has been employed for all his life, has good practi­cal experience in a specialised technical field and importantly, wants to work for another 15 to 20 or more years. This is a sad but brutal fact. There is another factor which needs to be considered. If you are working in a fast moving technical area and you take redundancy, in two years time your lifetime experience could be regarded as “out of date”. That might mean that you will be regarded as even less employable. If you’re employed and secure, be happy. If you’re out looking for a job, particularly in a specialised field, you could find that your prospects are quite grim. So take some well-meant advice. Unless your retrenchment package is enough to allow you to permanently retire or you have another guaranteed position to take up, don’t take the money, if you can avoid it. Stay with the job and let the hierarchy get rid of somebody else. Who knows, in 12 months’ time when the retrenchments are complete, you may find that they are so short of staff that they are having to hire some people back on short-term contracts. You will be in demand, secure and happy that you have done the right thing for the long term. Your long service entitlements and superannuation will be intact. So even if your company or government organisation is short-sighted, you don’t have to be as well. Stick with the job and work as long as you can. It could be the last full-time job you will ever have. Leo Simpson M croGram Computers Multi I/O ISA Card Converter SVGA to RGB Internal UPS & Power Supply It’s not just a UPS but also a 300W power supply. The UPS is actually built into a standard size power supply and the batteries & front panel occupy a 5.25in drive bay. The UPS is rated at 500VA. Apart from power failure, the UPS also protects against over voltage, under voltage, overload & DC short circuit. The unit is available in two sizes - PS/2 or ATX. Optional software provides for automatic shutdown. Allows the use of an RGB monitor with either VGA or SVGA output. It is designed for high resolution graphics monitors and has the H and V synch signals added to the Green video channel. RGB to SVGA converters are also available. Cat. No. 15063 Cat. No. 15064 SVGA to RGB Converter RGB to SVGA Converter $189 $189 PCI Video Capture Card Cat. No. 12014 Switch Box Parallel 4 to 1 Auto $51 The PCI Video Capture card is PCI Plug & Play Printer Cards WIN 95 Plug & Play compatible Available in either 1, or 2 port verfor easy installation & setup. sions, these PCI bus PnP bi-direcUtility software provides full tional parallel ports have an 83 byte screen (640 x 480) or any size window live video FIFO buffer and are able to replace display. It includes an API to enable developers to faulty motherboard printer ports as integrate it into their applications. Connections on LPT 1/2. Support is provided for DOS, Win 95 & NT. the card are Composite Video-In (RCA Phono-Plug), Cat. No. 2618 1 Port Printer PCI PnP $185 S-Video In and an 8 pole mini DIN connector. Cat. No. 2619 2 Port Printer PCI PnP $225 PCI Video Capture Card $179 Headset and Microphone Combined Hands free operation makes this lightweight & compact headset a must for Internet phone & MicroSoft’s Netmeeting, etc. Comprises a condenser microphone & stereo headset which attaches to a standard sound card. Cat. No. 3310 Headset & Microphone combined $19 VGA Monitor Splitters These splitter modules enable up to 8 monitors to simultaneousy share the information of a host computer. The ideal way of providing multiple displays in training rooms, airport terminals, stock rooms, clubs, etc. The splitter may be up to 15m from the computer while the monitor may be up to 100m from the splitter for the 2 way module and up to 50m for the 4 and 8 way modules. Cat. No. 3070 Cat. No. 3055 Cat. No. 3056 Cat. No. 2055 Multi I/O Card ISA $45 Long Range CCD Bar Code Scanner Scan from contact to 100 mm! A low cost, high performance CCD Automatic Parallel Switch Box scanner offering variable width & Connects 2 computers to 1 printdepth of field as well as a superior er and automatically switches scanning rate. Equipped with according to requirements. No focus illumination, it enables you external power supply is to read marginal density & coloured labels with $429 required. All connectors are very flexible reading angles. It supports most $399 DB25 female. A four way model is also available common symbologies & the keyboard wedge $99 Cat. No. 12013 Switch Box Parallel 2 to 1 Auto $26 cable is easily detachable. Cat. No. 8498 UPS / PS (PS/2) Int 500VA/300W Cat. No. 8588 UPS / PS (ATX) Int 500VA/300W Cat. No. 8499 UPS / PS Internal RUPS S’ware Cat. No. 3358 A versatile interface card that supports 2 FDD, 2 HDD As well as 2 16550 compatible serial ports, 1 ECP/EPP printer port and 1 games port. $574 $469 Ultra High Speed Serial Card Break the barrier with this two port card featuring 16650 UART chips with 32 byte FIFO buffers. It provides interrupts 3, 4, 5, 7, 9, 10, 11, 12 & 15 as well as being configurable as COM 1,2, 3, 4, 5, 6, 7 or 8. Cat. No. 2333 Cat. No. 2239 Two Port 16650 Serial Card Two Port 16550 Serial Card $159 $99 Two Port USB Card PCI Provides 2 USB ports with a bandwidth up to 12Mb/s. Supports real time dynamic insertion Designed for multimedia, video-editing and advanced and removal of up to 127 devices. graphics applications. A low cost, flexible, and Cat. No. 2622 Two Port USB Card PCI $99 powerful bootable storage solution that links up to Cat. No. 9093 Universal Serial Bus Cable $12.95 four (expandable to eight) high capacity Ultra ATA or EIDE drives together as one huge drive C: on a PCI VGA to Video Converter High quality at an affordable price, system Features include: this external unit does not require • Provides “on-the-fly” data protection software drivers & supports up to • Supports up to 50MB/sec burst and 20MB/sec 1024 x 768 with true colour for sustained data transfers PAL & NTSC systems. Connect to IBM, Macintosh • Provides RAID levels 0, 1, and 0/1 support or NEC computers. The output can be viewed on a • Supports Windows 3.11, 95 & NT, OS/2, etc monitor & TV simultaneously. Connections are comCat. No. 2638 Multimedia Disk Accelerator $285 posite video, S-VHS and Analog RGB (15kHz). Multimedia Disk Accelerator Calculator Keypad Ideal for POS and industrial applications! This 26 key calculator keypad has an LCD display allowing entered digits to be visually verified before “sending” the data to the PC. It connects via the standard keyboard socket. Features include: • Operates as a stand alone calculator & clock when off-line $269 • “RND” key for full, cut, round 4/5 decimal display $336 • “Send” key to send calculated results to PC Two Output Four Output Eight Output Cat. No. 8489 Bar Code Scanner Long Range KB Cat. No. 8486 Calculator-keypad $155 Cat. No. 3102 VGA to Video Converter - External $499 SIMM RAM Tester Quickly identify the size & configuration of memory as well as identifying true or fake parity. This RAM tester incorporates a microprocessor & a programmable delay line to auto test & display information. SIMM size may be 64K to 16Mb in 30-pin format, or 1Mb to 32Mb in 72-pin format. The test speed can be adjusted from 40-120 ns with a resolution of 1ns. Cat. No.3174 RAM Tester E & OE All prices include sales tax $1499 MICROGRAM 0598 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 We welcome Bankcard Mastercard VISA Amex Unit 1, 14 Bon Mace Close, Berkeley Vale NSW 2261 FreeFax 1 800 625 777 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  – At its launch earlier this year, it was described as “the most innovative and technologically advanced car ever produced in Australia . . .” Without any doubt, the pundits were right. Equally without any doubt, the aXcessaustralia Concept Car will never roll off the production line. By ROSS TESTER Love it or hate it, you cannot ignore the aXcessaustralia concept car. Nor can you ignore the amazing range of Aussie ingenuity and expertise which has gone into making this dream a reality! 4  Silicon Chip Australia’s Concept Car That’s because the aXcessaustralia Concept Car is just that, a concept. It demonstrates what could be the future of motor vehicles given the right economic, political and industrial conditions – and showcases more than 140 Australian component companies and service suppliers. In other words, the aXcess­a ustralia Concept Car is more a component showroom on wheels than the family car of the future; a showroom for the ideas and innovations which Australian components companies can produce right now. They’re hoping that the big car makers will be impressed and will sign some lucrative contracts. That’s one of the things that makes this concept unique – it didn’t come from the drawing boards of General Motors or Ford (or any of their global affiliates or com- Great car –ll but you wiit never buy petitors), as virtually all new vehicles currently do. The aXcessaustralia Concept Car was designed and built by the component companies themselves as a means of showcasing the industry’s capabilities to the world. And it has been done at a cost the major manufacturers simply wouldn’t believe: around $13 million worth of goods, services and expertise supplied by those 140+ companies. By contrast, a major car manufacturer would have a budget ten times that amount to get to concept car stage! Designed and co-ordinated by specialists Millard Design Australia, from original concept to finished concept car (if you’ll pardon the pun) took just twelve months. That is some achievement! We will have a look at just some of the features of the aXcessaustralia Concept Car which make it so unusual; not just the electronics, though there is a huge variety included, but also the car body, chassis and power plant, all of which are purpose designed and built. Body construction The most striking feature of the car – love it or hate it – is the body. It’s quite unlike anything you’ve seen before. The X-shaped frame is actually on the outside of the car and is a single piece carbon fibre construction. Weighing a tiny 69kg but incredibly strong, the frame is attached to a precision metal chassis by a series of bolts and adhesive at key points. A revolutionary riveting system was used in the chassis, eliminating the need for spot-welding. The rivet makes its own hole and fastens in one neat operation. The 2mm thick carbon-fibre body panels and doors are also mounted on the X-frame. Each of the panels is one piece, making removal and replacement easy if required. There are no bumper bars as such but bonded twopiece moulded front and rear bumper reinforcement beams are included. One noticeable feature is the lack of a “B-Pillar” – the vertical pillar between the front and rear doors. Instead, the “clamshell” power doors are mounted on the front and rear of the May 1998  5 frame and close on themselves, interlocking as they do. The single-hinged doors are all operated by electric linear motors which also engage the locking mechanisms. As a safety measure, the rear doors cannot be opened until the front doors are slight­ly ajar. Keys are not required to open or lock the doors: they are activated from the outside by touch pads and by voice commands or fingertip controls on the inside. In fact, keys are not required at all – but more of that anon. While the door windows are made from conventional toughened safety glass, the front and rear windscreens and roof panels are made from Lexan Polycarbonate, protected from UV light, abrasion and chemicals by a flow-coated layer of silicone hardcoat. Not only do these reduce weight by 40%, they give a high resistance to forced entry or impact. Still outside the car, solar panels in the roof generate enough electricity to power an air extractor fan, keeping the car cool while parked in the sun. The mirrors also bear special mention because they are much more than mirrors! They incorporate a signal lamp, temperature sensor and the antenna for the passive entry system. The drive-train The engine chosen for the concept car is a supercharged, 2.3-litre twostroke inline six, made by the Orbital Engine Corporation. It’s only about three quarters the weight of a conven- No less than five prototype mock-ups were made during the design stage but despite this, the whole project took less than a year to complete. While this photo shows the traditional method of clay modelling for aXcessaustralia, extensive use was also made of computer modelling and design. tional (four-stroke) 6-cylinder engine. The block is aluminium while the bore is nickel-silicon carbide to give high wear resistance. It’s a small engine but delivers peak power of 160kW and 250Nm of torque. Unlike conventional two-stroke engines, it uses a wet sump lubrication system (similar to four-strokes). With a view to export, it meets the strict 1998 California ULEV emission requirements. The engine mates with a fully computer-controlled and programmable “intelligent” four-speed automatic transmission. Gear selection can be made by voice control or by the “Touchtronic” control system, allowing manual operation. In normal operation, a computer selects the appropriate gear depending on the driving style. And in case you forget, the handbrake is automatically applied when you place the transmission in “park”. A specially designed lightweight aluminium propellor shaft and fluid-coupled limited slip differential complete the power train. Suspension, brakes, wheels and tyres have all been specially selected or designed for the concept car using advanced components. The large 18x8 magnesium alloy wheels, for example, were directly cast from the original computer design. Incidentally, the anti-lock brakes feature their own microprocessor ECU module with self-diagnosis and a “limp home” mode – a feature previously found in EFI systems but certainly not in braking systems! Estimated top speed of the concept car is close to 240km/h. Interior features This impression of the interior of the car (with the frame and roof panels removed for clarity) was drawn by the car's interior designer, Yan Hong Huang. Everywhere you look, aXcessaustralia represents the very latest in design and technology. 6  Silicon Chip Even if the outside appearance hadn’t fazed you, your first glance inside would convince you this is no ordinary car! From the revolutionary instrument pod to the entertainment modules in the rear, the concept car has everything in electronics that one could wish for with an open order The highly innovative instrument pod is designed to mount on the steering column rather than a “dashboard”. This makes it an easy switch to left-handdrive – again, keeping the concept car’s main purpose of a showcase for the world market. All switches are finger-tip operated membrane types. book and Australia’s best suppliers. Let’s look at that instrument pod first. Mounted on the steering column (making it suitable for left or right hand drive), it is less than 60mm thick and weighs less than 1kg, yet incorporates all the controls and instruments usually found on the dash and steering column combined. The gauges and speedo use ultra thin stepper motors while a liquid crystal display shows distance travelled (odometer) and current gear engaged. A single LED and light ducting provides illumination to all pointers. You can even have your choice of illumination colour, thanks to bi-colour LEDs. All conventional switches have been replaced by membrane (touch pad) controls within easy fingertip reach of the driver, hands never having to leave the wheel. Turn indicators, light switches, windscreen wipers (though both headlamp and wipers can be set to automatic operation) and even the dimming for the display are immediately accessible. Many of the controls can also be voice-activated. Also integrated into the instrument cluster is another innovation, the hazard warning system. A pulsing LED and audible warning is activated when the vehicle approaches a range of hazards – emergency vehicles, rail crossings, even accident black spots where safety transmitters have been installed. To keep back-seat passengers amused, there’s an entertainment centre housed in an automatic-opening rear seat centre console with such goodies as a Sony Playstation and video payer, connected to colour monitors set into the rear of each front seat. Naturally, there’s also a complete audio system for the driver/front passenger too, much of it operated by voice control. Voice activation We’ve mentioned that voice control a few times. Developed by Robert Bosch Australia, the system recog- nises up to 40 commands which not only activate those items already mentioned but will also set individual driver and passenger temperature controls, open and close the doors, dial the telephone, and even start and stop the engine! The system also has the capability of giving speech warnings and information such as open doors or headlights left on, vehicle diagnostics, road alerts and navigation information. Navigation information? Of course, the vehicle is fitted with GPS navigation. Another nice feature (albeit also already found on some high price cars) is the memory keycard system where the car “remembers” a driver’s personal information – seat and mirror positions, entertainment centre settings and so on. There is a lot more to the aXcess­ australia car than we can cover here. However, it does have its own web site (www.axcessaustralia.accp.net.au) for more information. If you want to see the vehicle “in the flesh”, unfortunately you’re too late, at least for the present. Since its release in February it has travelled to the US, appeared at the Melbourne Motor Show and the Australian Grand Prix and most recently left for a tour through south-east Asia, commencing with the Automechanika Asia show in Singapore in late April. The web site will probably give you the best idea of when aXcessaustralia is coming “home”. SC Never again would Dad get “Are we there yet?” from the back seat! Not with individual Sony Playstations, video player and full entertainment system to choose from. Individual colour monitors are fitted to the rear of the front seats with the entertainment system mounted between the rear seats. May 1998  7 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 COMPUTERS Troubleshooting Your PC; Pt.1 A PC can be a frustrating beast when things go wrong. Here’s some good advice on problem solving & staying out of trouble in the first place. By BOB DYBALL Most people will, at some time or another, have problems with their PC. Unfortunately, when it comes to fixing those prob­lems, they often make things a lot worse before a “doctor” is finally called in. And that’s where the expense starts – computer technicians cost time and money. It doesn’t have to be like that, though. A little careful diagnosis will usually eliminate the need for a service call and save your valuable time, data and money. Provided you adopt a logical approach to troubleshooting, 12  Silicon Chip you can easily prevent minor prob­lems from becoming major headaches. In this first article on computer troubleshooting, we’ll take a look at common software and hardware problems. We’ll also tell you how to fix them and give some tips to prevent them from happening in the first place. Don’t panic Remember Corporal Jones from Dad’s Army? His reaction to a crisis was to always shout “don’t panic, don’t panic”; this while he flapped about in absolute panic. It’s good advice when it comes to PC problems as well but unlike Corporal Jones, you should remain calm when things go wrong. If your PC suddenly stops responding, for example, don’t immediately switch it off or press the reset button on impulse. The problem is unlikely to get any worse if you leave the comput­er on and you might even be able to recover some data that would otherwise be lost. Of course, if you smell something “cooking” inside the PC or if you see smoke erupting from under the bonnet, then switch off immediately. Most chips don’t work too well after their magic smoke escapes! Software problems Sometimes there can be an inordinately long delay before Windows responds. When it finally does, you Fig.1 (above): you can usually shut down a program that’s not responding in Windows 95 by pressing Ctrl-AltDel. This is far better than just pressing the Reset button on the PC. Fig.2 (right) shows the options you should choose to format a floppy disc for virus checking on another PC. may find that a “blue screen” error message appears. If this happens, just follow the on-screen prompts to shut down the offending program. If the screen goes black or the system has been very slow for some time, check to see if the hard disc light is still flashing. If it is, try waiting it out. Even with a truckload of RAM, occasional long delays can occur while your programs argue about whose turn it is to write data to the hard disc drive. In short, be patient and give the machine sufficient time to complete its tasks. Exporting large files from several popular drawing packages can take quite some time, for example, with lengthy periods of apparent inactivity. If, after a lengthy wait, you are satisfied that the ma­chine has “hung”, hold down the “Ctrl” and “Alt” keys and then press the Delete (Del) key (ie, press Ctrl-Alt-Del). If you are running Windows 95, this will bring up the “Close Program” window – see Fig.1. As shown in Fig.1, this dialog box lists the programs that are open. It even shows “Systray” which is the System Tray at the far right of the taskbar. Look through this list for anything with [Not Responding] after the program name. You can then close down any program that is not responding by clicking on it (to highlight the entry) and then clicking the “End Task” button. This will close down the offending program, after which you should be able to return to the operating system. Although data may be lost when you close a program in this way, it is usually only back to where you last saved your work. At the same time, there is usually no affect on other programs that may be open or on the operating system itself. Any other files that may be open in other programs can now be saved and the system shut down and re-booted in an orderly fashion. This is certainly much better than hitting reset if the system has gone on strike. Pressing reset or turning off a PC without properly shutting down Windows can result in directory problems, lost clusters and cross-linked files. And these prob­lems, in turn, result in lost data. Occasionally, even when a program is no longer responding, you might find that some of your most recent work is still vis­ible on the screen. In this case, you could try hitting the Print Scrn key and pasting the resulting screen capture into the Paint program. This can then be printed out and used as a guide when you later re-enter the information. Alternatively, you can use something as crude as a pencil to jot down vital details. For example, if your browser crashes after you’ve spent ages searching for a vital web site, jotting down the URL (ie, the website address) before closing the program down can save you a lot of searching later on. Intermittent problems Software problems that occur intermittently can easily be confused with hardware problems. If you find that a particular problem occurs in just one program or in one part of DOS or Windows, try running ScanDisk to see if there are any directory or file errors on the hard disc. Sometimes, you will find that a file has been damaged, or even the swap­file used by Windows may be corrupted. Running ScanDisk will usually fix such problems but note that there are a couple of precautions to take when running ScanDisk (see “Setting ScanDisk To Run Automatically”). In some cases, a file may be damaged in a program you are using or in some other part of the system. This can give rise to ob­scure errors such as illegal OPCodes or General Protection Faults (GPFs). Tracking down the offending program is not always easy. That’s because the program that’s affected by the problem is not always the cause of the problem itself. In this sort of case, it’s generally best to follow the procedure listed below: May 1998  13 COMPUTERS: Troubleshooting Your PC (1). Run ScanDisk (or Chkdsk on older computers). (2). Uninstall and then reinstall the offending program. (3). Double check that you are running the latest video drivers, mouse drivers (if you have a non-standard mouse), sound drivers, network card drivers and so on. Up-to-date drivers can usually be downloaded from the manufacturer’s web site. (4). Install any service packs, patches or updates that might be available for your software (again, check the web sites for these). There are service packs for Windows 95 (OSR1), Windows NT, Microsoft Office 97 and Visual Studio, for example. (5). If you are having trouble with a game, check to see if you have the latest Direct X drivers installed and that there are no updates to the game itself. (6). If problems still exist, reinstall Windows. Although reinstalling Windows and Windows applications can be time consuming, it is usually quite a safe procedure. However, some applications can reset things like templates and macros, so try to make backups of these just in case (back up your data files as well). A potential problem here is that some install programs will not over­ write existing files that have the same name. This means that if a file has become corrupted, reinstalling the software will not fix the problem. The answer here, of course, is to remove the offending pro­ gram by uninstalling it. Any remnants of the program that have been left behind after the uninstall procedure should be manually deleted. For this reason, it always pays to check on the program location before uninstalling it, so that you will know where to look for anything that’s been left behind. Only rarely should you have to reformat the lot and start again. This rather drastic procedure usually means a lot more work but sometimes there’s just no other choice, particularly if you suspect that the hard drive has a defect. Reformatting the lot When ever I hear of someone doing this to a Windows 95 installation, I always try to discover their reasons. And in most cases, I’ve found that reformatting the drive wasn’t really necessary or only became necessary because the user didn’t know what he or she was doing. If you don’t have an up-to-date virus checker, then get one – now! If you do have a virus checker, be sure to use it regularly. 14  Silicon Chip Consider, for example, one of my friends who owns an old 486DX4/100. He was playing around in the CMOS one day, when he came across the >504Mb setting. Thinking that this looked like a good thing because he had a 1GB drive, he turned it on only to find that his computer would no longer boot up. Unfortunately, he didn’t put two and two together at the time. Thinking that the problem was due to a virus, he decided to use FDISK /mbr (to rewrite the master boot record) which only made things worse. His problems only ended a few days later after he asked me what the >504Mb setting really meant. By then, of course, it was too late, as he’d completely upset his system – so much so that it was now necessary to reformat the drive and reinstall all his software. Basically, there are two places to be very careful of when exploring your system: (1) the partition table, which is usually accessed through the FDISK.EXE program; and (2) the CMOS set­tings, usually accessed by pressing Del or Ctrl-Alt-Esc during initial boot up. I think I have a virus! If you think you might have a virus, again don’t panic. Most viruses will simply make your system crash more often but some can corrupt or even delete files on your hard disc drive. Apart from a few rather nasty viruses, most do not normally format your hard disk drive – well not immediately! A virus would not spread very far if it was made too obvious. There is also no way that a virus can cause hardware damage – at least, not that I know of. Having said that, most older viruses tend to be quite obvi­ous under Windows 95 because they make it unstable. And quite often, they only allow an infected machine to be booted into safe mode with some obscure error or another. However, a virus is not the only reason why a machine will only boot into safe mode. If you have installed old CD-ROM drivers, for example, then don’t be surprised if you are stuck in safe mode until you remove them and go back to 32-bit Windows 95 drivers. Of course, the way to prevent viruses is to install an up-to-date virus scanner on your computer and use it If a scanner or some other piece of hardware is not responding properly, check that its interface card is properly seated in its slot on the motherboard and that all the cables to it are correctly plugged in. Check also for IRQ conflicts. regularly. If you don’t have a virus checker and you suspect a virus, you can diagnose the problem by formatting a blank floppy disc and plac­ing the system files on it. To do this, insert a floppy disc into the drive, go to the DOS prompt and type format a:/s/u (assuming that the disc is in the A: drive). Alternatively, if you are using Windows 95, you can right click the A: drive in My Computer (or Windows Explorer), click the Format option, and then click the buttons as shown in Fig.2. This will create a bootable floppy disc. Now copy over a couple of .EXE files, a couple of .COM files and, if you think you have a “Macro Virus”, a couple of .DOC files – try to select files that you think may be infected or have been used recently. If you have a virus, then this disk should be well and truly infected. Now ask someone with an up-to-date virus checker on another (uninfected) PC to check this diskette for you. This should give you a reliable idea of what is there. If you are going to check your own system out, make sure you do so with the latest version of a good virus checker. A check each time the system boots up is a good idea in many cases, particularly if you download a lot of material off the net or regularly receive files from other sources. CMOS setup Most problems here usually fall into one of two catego­ries: (1) either someone has fiddled with the CMOS settings; or (2) the backup battery has gone flat and the settings have been lost. Only rarely do CMOS settings become scrambled of their own accord. If you want to try different CMOS settings, be sure you try only one thing at a time. That way, you can easily restore the setup if the machine no longer functions correctly. There are excellent guides on the internet for both AMI BIOS (www.ami.com) and Award BIOS (www.award.com), with both giving detailed expla­nations of each function in the CMOS setup. If you wish to reinstall a hard disk drive, make sure you note the original settings as it might not be using the default mode listed under auto-detect. Sometimes, the bus speed setting can be quite critical, particularly in older ISA bus computers. I remember coming across more than one computer where 7.15MHz worked but 6MHz or 8MHz did not. Apart from rare quirks due to different I/O cards, mother­boards and VGA cards not working together, most older 16bit ISA cards don’t like going above 8MHz, while older 8-bit ISA cards should be run at 4.77MHz If the backup battery is on the way out, you’ll usually find that the PC’s clock no longer keeps good time. This fact can be used as a warning that the battery is about to fail and that now might be a good time to check the CMOS settings and jot them down on a piece of paper. In particular, you should note the settings for the hard disc drive. In fact, it’s always a good idea to record the CMOS set­tings on paper when you first get your computer. This piece of paper should then be kept in a safe place, so that it can be easily found when required. A good trick is to tape it to the bottom of the case. Replacing the backup battery is usually a straightforward exercise. If the battery is soldered in, check (in your mother­board manual) to see if you can run an external battery and if so, what voltage is needed. Three or four AA alkaline batteries in a holder are often all you need to get going again. Note that there is often a jumper on the motherboard to disable the on­board battery and enable the external battery, so check the manual carefully. Also, be sure to remove the May 1998  15 COMPUTERS: Troubleshooting Your PC old bat­tery from the motherboard. If it’s left there, it will eventually leak and cause damage. You don’t have to de-solder the battery; just use a pair of sidecutters to cut the leads. CMOS setup & the hard disc The first thing to realise here is that an IDE hard disc drive might not always be set up according to the par­ ameters on its sticker. For example, a drive with 2000 cylinders, 4 heads and 32 sectors per track might have been “mapped” to 1000 cylin­ders, 8 heads and 32 sectors per track to allow it to work with DOS which can only handle a maximum of 1024 cylinders, 16 heads and 64 sectors. Although drive manager software can extend DOS to provide access for larger hard disc drives, these factors mean that auto-detecting the hard disc in CMOS at some later stage can cause problems. Often, the machine won’t even boot or, if it does, data may be missing or corrupted. Typically, this might happen in a system if you had been running DOS and Windows 3.1x and then later upgraded to Windows 95. If you have lost your CMOS setup and don’t know the head, cylinder and sector settings for your hard disc drive, try auto-detecting it first. Often you will get two or three options for the mode setting. For larger hard disc drives, try picking the one labelled LBA mode, then reboot and rather than go into Wind­ows, press shift-F5 to drop to the DOS prompt. Now try running ScanDisk to see if there are directory structure problems. If you get lots of directory errors, then DO NOT use ScanDisk to fix the problems. Instead, go back into the CMOS setup and try one of the alternative mode selections. (Important: do not write to the hard disk during Fdisk, The Partition Table & Virus Basics The partition table is stored on the very first sector of the hard disc. It consists of the table itself (which is really just a few bytes) plus the partition loader. Because the system loads the partition loader from the first sector of the hard disc, you can boot different operating systems (eg, you can have a dual-boot Windows NT/Windows 95 system). This same feature also allows patches to the operating system to be loaded. A typical example here is a device driver to allow the operating system to handle a hard disc drive that’s larger than it was originally designed to handle. The downside of this is that the same tricks are used by some virus writers to get a virus running before your anti-virus software gets started. Some viruses are even smart enough to piggy-back onto some anti-virus programs and infect everything in sight while a virus scan is actually under way. If you use a disc manager of some sort, use a utility such as Norton Utilities Disk Edit to make a backup copy of the parti­tion loader and partition table in case of problems. If you don’t have a disc manager program running and you suspect a boot sector virus, it’s quite easy to restore the master boot record. Simply boot from a clean floppy disc that also contains the Fdisk.exe utility and, at the DOS A: prompt, type: Fdisk /MBR This undocumented command writes a fresh copy of the parti­tion loader program to your hard drive but leaves the data table as it was. It effectively removes simple partition infectors such as the Stoned and Michelangelo viruses. Note that this procedure will not work on systems with special partition loaders. In particular, do not use it if your system uses a disc manager to provide large hard disc access or if you use an encryption or security program. Some anti-virus programs might also get upset when you first reboot but this is not usually a problem. 16  Silicon Chip this procedure. If ScanDisk were to write back to the hard disc, chances are you could lose data when it started correcting things like the FAT table). Another way of checking that you have the correct settings is to run FDISK at the DOS prompt (boot from a floppy), then pick 4 to display the partition and look for it using 100% of the drive. Preventing software problems Some of the following tips might seem obvious after you’ve “broken” things a few times. However, by taking a few simple precautions, you will minimise down-time and often eliminate crashes altogether. (1). Don’t run too many programs at once without either adding extra RAM or waiting for things to happen. It is quite possible to run a good number of large programs at the same time under Windows 95 but you must be patient. So how much is too much to expect from your PC? Well, until fairly recently, I ran an old 486 DX2-66 machine at home with just 8Mb of RAM. It wasn’t all that quick running Windows 95 but I was still able to cook up some huge spreadsheets and do some pretty nifty programming. If you are short on RAM or have a slow PC, then wait it out – watch the hard disc light and don’t get too impatient if noth­ i ng happens for some time. All those open programs and data files have to fit somewhere and that somewhere if you don’t have enough real RAM is the “swapfile” on the hard disc. And writing to the hard disc is much, much slower than writing to RAM. (2). Systray “widgets” are programs too, so don’t load too many of these into your machine. Remember that “programs” aren’t limited to just the larger ones such as MS Word, Excel or Quake II. Everyone with Windows 95 should be familiar with the System Tray, or “Systray”. This is the small indented region at the righthand edge of the taskbar. Typically, it will include the clock plus various other utilities such as a volume control (for the soundcard) and the System Agent from the MS Windows 95 Plus! pack. Now the trouble is that in the hands of some gadget freaks, it also becomes the home for all sorts of other programs. Each of these might not amount to much on their own but System Agent, which comes with the “Microsoft Plus!” pack, lets you schedule regular hard disc maintenance activities so that they run automatically at certain times or when the machine has not been used for some time. taken together, they can easily gobble up enough resources to make your system slow or unstable. DOS users should note that TSR programs or popup pro­grams amount to the same thing as Systray widgets, so go easy on them. Run too many and they will cause problems. (3). Follow on-screen prompts carefully when installing software. Be sure to let the system reboot when called for, to ensure that critical system files are installed. That’s because some files that are a part of the installa­tion are not ac- tually installed unless the system is rebooted. These are generally dll and vxd files that cannot be changed while Windows is actually running. (4). Install only one program at a time and check that it works correctly before attempting another installation. Installing lots of programs without checking each installation as you go can make troubleshooting more difficult later on if you strike problems. (5). Regularly run ScanDisk. Windows 95 users will find that there are two versions: Scandskw.exe (the Windows version) and Scandisk.exe (the “DOS” version). The Windows version should be used for routine checks (see panel) and it must be run from within Windows 95 (click Start, Programs, Accessories, System Tools, ScanDisk). (6). Run Defrag on a regular basis. This utility “defragments” your hard disk, speeding up access to your files and making the system more reliable. Windows 95 users can run the Defrag utility by clicking Start, Programs, Accessories, System Tools, Defrag. Users who have older DOS 6.x systems will need to exit Windows 3.x com­ pletely before running Defrag. Simply type Defrag at the DOS prompt to run it, or add /? for any program options (ie, Defrag /?). Setting ScanDisk To Run Automatically If a PC is often used by children or by someone who doesn’t know a lot about computers, it’s a good idea to set the system up so that ScanDisk runs automatically each time the machine is booted. For Windows 95, you do that by adding Scan­dskw.exe to the Start­up group, as follows: (1) right-click the Start button, click Open, dou­ble-click Programs, then double-click the StartUp Folder. (2) Click the File Menu (at the top), click New, then click short­cut. (3) In the box provided, type scan­ dskw.exe /a /n (4) Click Next and in the next box type Scandisk, then click the Finish button. The parameters for Scandskw. exe are: /a   to check all ordinary hard disks in your PC, /n   to start and close ScanDisk automatically (no keypresses need­ed), /p   to stop ScanDisk from automatically correcting any errors it finds. Don’t use the DOS version of ScanDisk (Scan­ disk.exe) to routinely scan for (and fix) errors on a Windows 95 machine and don’t place it into autoexec.bat. Scan­ disk.exe doesn’t recognise long filenames. If you do use it to fix errors on a Win95 machine, any long file names associated with problem files will be lost. Theres one more wrinkle here: Windows 95 OSR2 will automatically run Scan­disk.exe when the machine is rebooting after a system crash. It’s usually a good idea to let it fix any problems here before going into Windows 95, after which you should then also run the Windows version of ScanDisk (click Start, Programs, Accessories, System Tools, ScanDisk). Any files with truncated filenames can then be renamed, if necessary. On the other hand, Scandisk.exe can (and should) be used to routinely fix errors on DOS and Windows 3.1x machines. If you want it to run auto­matical­ly at bootup, just add the following line to the auto­exec.bat file: scandisk /all/autofix/nosummary/ nosave This will do an automatic test of the directory structure of all hard disk drives (no surface test), fix any errors that are found, and not bother saving any lost clusters – all this without you having to press any keys or respond to questions. Alternatively, you might like to leave the /nosave option off if you wish to be prompted to choose whether or not to save any lost information. Any “lost clusters” (file fragments) will be saved as files FILE0001.CHK, FILE0002.CHK and so on. It’s then up to you to determine what these are and recover any useful data. May 1998  17 Check the power supply and I/O cable connections if one of your drives fails to respond properly. Faulty lead crimping inside power supply connectors (especially Y connectors) is a common problem, so don’t take these for granted. (7). Windows 95 users should buy the Plus! pack. This handy pack­age has a scheduling program called System Agent, or “Sage” for short. What does it do? Well, it automatically checks your system according to a pre-programmed schedule (you set this) and au­tomatically runs the Scan­Disk and defrag utilities according to this schedule or when you haven’t used the computer for some time. It will also warn you if your hard disc drive is running short on space. If your hard disc fills up, there will be no room for the temporary files that Windows sets up, print jobs will no longer print and your system will grind to a halt or run extremely slowly. The Plus! pack is worth the extra dollars. In my own work situation, I have found that System Agent can dramatically reduce downtime, costs and support calls to a help desk when introduced to a system. (8). Extra RAM will help make your system faster and more stable. Going from 8Mb to 16Mb or from 16Mb to 32Mb can increase the effective speed of a PC by 50-100%. (9). Never ever use old drivers or utilities. Some people install Windows 3.x drivers for printers, video cards and so on when they should be using 18  Silicon Chip Windows 95 drivers. Often, the correct drivers will be on the Windows 95 CD-ROM so don’t make the mistake of installing any Windows 3.1x drivers that may have been included on a diskette with the device. If you don’t have the correct Windows 95 drivers, either contact the device manufacturer or download new drivers from their website. Older Windows 3.x drivers (or worse, DOS drivers) can slow your system down to half normal speed or less, as they were rarely designed for 32-bit access. These older drivers should only be used for DOS/Windows 3.x systems or in DOS mode under Windows 95. Hardware problems If a problem occurs immediately after you have installed some new hardware, then exit from the operating system, switch off, remove the new hardware and see if you can restart the sys­tem. If the system works, carefully replace the item and check your connections. This might seem a little obvious but incorrect connections are often all that is wrong. Be sure to check that all plug-in cards are correctly seated in their slots. Sometimes, a new card might not fit too well, or might not line up with the backplane correctly. Check the physical placement of the card with respect to the motherboard and case. One of the most common problems is a card that is sitting too high in its slot on the motherboard but cannot be pushed down any further because of interference with some other part or with the back panel. If a hard disc drive, CD-ROM drive or floppy drive appears to be dead, check its power connector. The connector may have come loose or you may have left it off when adding new hardware. Don’t take the integrity of power connectors for granted either. Incorrectly crimped leads inside power connectors (especially in Y-connectors) are a common problem. Finally, if you strike hardware problems, think about the last thing you did. It’s all too easy to come to grief by doing too many things at once and then not knowing what was responsi­ble. If you need to add, say, an extra hard disc drive, a new sound card and an internal modem, it’s best to do it one device at a time. Always make sure that each new device works correctly before adding the next. If you’ve added a few extra items of hardware all at once, remove all but one of them. The less new bits to worry about when debugging the SC better. NEW!!! CMOS VIDEO CAMERAS Smaller than CCD cameras, (24x24x24) They give lower quality image but are ideal for battery operation (7-18V) & draw about 13mA & would run on a 9V battery for around 2 days :$79 Colour version should be available soon MAY-JUNE REDUCED-CLEARANCE ITEMS NETWORK 2 PCs FOR $30!! New Win/95 compatible (DEC (DE101) etherworks LC/TP) DIGITAL brand Ethernet PC. cards, software and booklet in original box. Cards inc. boot ROM so one of the PCs does not even require a hard disc. We dont supply the commonly available PC. cable which can also be made up with RJ45 connectors and two twisted wire pairs: Diagram included. We have a qty. of these with soiled boxes, Clearance:(DE101) $30 pair 60 SECOND SOUND RECORDER. IC, Contains all the control circuitry, AGC, power amplifier, A-D/D-A converters and even a 256K Flash EPROM: Complete good quality 60 Sec. digital rec. IC that even has random / sequential access of fixed/ variable length messages. Only requires a few passive components, an electret mic. & a spkr. Special introductory price: $23 *** CCD CAMERA SPECIAL *** The best "value for money" CCD camera on the market! Tiny CCD camera, 0.1 lux, IR responsive, high resolution. It has a metal lens housing and glass lenses, & performs better than FIBER OPTIC CABLE ( COMS GRADE ) DIGITAL BAR CODE WANDS: New USA many cheaper models. approx. 0.6mm diam. $1 per Mtr. made wands fitted with 2.5m long WIRED IR EXTENDER KIT $18 curly cord terminated in a 5pin 240° WITH YOUR CHOICE OF DIN plug. Contain an optical sensor, ONE OF THE GEIGER COUNTER KIT + TUBE!!! $40 visible red LED, a photo IC detector FOLLOWING and precision aspheric optics. LENS OVER-SPEED MONITOR KIT Converts bar codes into a digital Pinhole (60deg.), +HALL SENSOR +BUZZER $22 pulse train as it is manually swept 78 deg.; 92 deg.; across the bar code. Employs a 120 deg.; $89 or UNIVERSAL SWIVEL BRACKET Sapphire tip, pot size is 0.19mm. $99 with a 150 deg. Very strong!! Heavy duty! Will rotate Output is open collector TTL/CMOS 360deg. & tilt 180deg: 10 for $15 compatible and the wand is needs CASE AND SWIVEL to be powered from 5V: (G61) $30 A small plastic case suitable for enclosing the CCD camera, plus a very strong multi angle and position adjustable universal joint swivel bracket plus screws, suitable DOG SILENCER NEW IMPROVED KIT We have a new improved high power for stereo speakers etc.: $4 swept ultrasonic generator kit that can drive up to 4 piezo tweeters. Works on UHF A-V MODULATOR dogs & most animals. PCB & all onProfessional stable deboard components and horn piezo sign PLL, tuneable UHF tweeter:(K112) $33, Additional A/V modulator with built in Antenna booster and a test pattern gen- tweeters (AP1) $7 ea. Suitable 13.8V erator: As used in VCR’s. Inc. parts for 1A DC plugpack: (PP12) $10. a 5V regulator (RM1) $18 PROFESSIONAL QUALITY 2/3/4 ch. (selectable) SEQUENTIAL A/V SWITCHER: Yes you can have up to 4 cameras and up to 4 microphone inputs! Uses UHF A-V TRANSMITTER . relay switches to produce much better bandwidth / picture quality than is Send video to TVs in your possible with C’MOS IC’s. Has many more features and is of better quality home. Inc. Stylish case than many commercial units costing much, much more. Circuitry includes telescopic antenna & leads: (G01) $35 a VCR Rec. / Stop switch (Relays) which can be used with standard PIR’s and other alarm det.’s. 32mm AUDIO PREAMPLIFIER Has A/V outputs for Small kit which inc. a microphone. Gives a monitor, Line level output for use with the above optional UHF A/V Modulator or transmitter: (K105) $6 mixer amp. can be inc: 32mm AUDIO AMPLIFIER KIT: Add a security LM380 based power amplifier can channel into your directly drive a speaker from a line existing TV system, in this Suitable plug-pack $10 output from above kit: (K106) $8 case use your TV set as the monitor! Mixer/Amp even includes a switchable test pattern generator for easy tuning. Low cost, PCB and all TIME LAPSE RECORDING INTERFACE onboard components kit!:(K118) $65...$18 Extra for the UHF mixer/amp.. New kit, now has relay contact outputs! *** SPECIAL *** Can be directly connected to a VCR or OPTICAL TACHOMETER KIT Measures RPM of prop. shafts etc. GRAB THEM BEFORE THEY GO!!! via a learning remote control:(K48) $35 without physical contact. similar to the STILL THE BEST LASER LIGHT FOR PIR MOVEMENT DETECTOR module kit published in SC. ( May 1988 ), but HOLIGRAPHY ETC. HELIUM - NEON to suit above kit, very small:(G66) $16 includes X-tal control calibrator. Use a LASER TUBE & POTTED SUPPLY: DMM on 200mV or a 3 1/2 digit panel Large 2-3mW laser head + compact LED IR ILLUMINATORS KITS meter as the display PCB + all on-board potted US made power supply. Head 10 LED:(K103) $14, 30 LED:(K102) $30 components:(K117) $25. plugs into the supply & connects to 240Vac.. Bargain: $65 WARNING!!! HIGH RESOLUTION MONITOR MOVING MESSAGE DISPLAY PCB: VERY BRIGHT NOT FOR USE BY Brand new 240V 30cm enclosed Used, complete assy. 20 bright 5x7 CHILDREN!!! ALL LASERS MUST BE computer monitor + a video conversion matrix LED displays ( 700 LEDs.) and USED UNDER COMPETENT kit. Gives driver. Inc. 20 x 74HC164 ICs. Display SUPERVISION. better ressize is 280 x 18mm LED’s, PCB 330 x olution than 75mm. Req. ext.l 5V supply. Inc. a NEW ! 4Ch. UHF TV’s!! Avail. sample program on disk & instructions LEARNING REMOTE early Feb. to scroll a #1 on all displays, via a PC Can be programed as Limited but parallel port. Limited quantity: (DL1) $19 a spare for your current good qty. remote or to replace up BARGAIN to 4 other units and PRICE. combine into 1:(TX1) $30 MINIATURE FM TRANSMITTER 3 LED LOGIC PROBE KIT. (33 x 23 x 10mm) enclosed in a small black metal case. Built in switch & LASER DIODE POINTER ( Key-chain ) (ref SC May) Ideal for tracing microphone. Specifications: 88 to 108- Very bright ( 650 nM ) pointer. supplied digital/logic faults & powered with 4 extra lens caps that by the circuit under test. MHz (adjustable), has a produce symbols; CUPID, Inc. Only PCB, all onwire ant. attached, bat. I LOVE YOU, LOVE board components, life 60 hrs, Range HEARTS & A LEDs, LED bezzels & 50M:(G14) $39 (Std. LADY. $29 Oatley’s special case watch battery LR44, inc.) (approx. 35x24x123): LASER DIODE MODULE (K119) $7 *** SPECIAL *** Same quality module that MASTHEAD AMPLIFIER KIT is used in the above ***SPECIAL***SPECIAL***SPECIAL*** Our famous MAR-6 based masthead FOR JUST ONE DOLLAR EXTRA amp. Up to 2Ghz. 2 section PCB (power laser pointer: $24 WITH EACH ORDER WE WILL SEND supply can be indoors): Inc. Plugpack: 12V/7Ah GEL BATTERY BARGAIN YOU A WIRING KIT !!! and 2 Weatherproof boxes: (K035) $24. Fresh stock NEW standard battery plus Also great for automotive installations, ( MAR-6 avail. separately ) 1 NEW INTELLIGENT GEL / LEAD- car radios mobile phones, fog lights etc. The kit contains the following: COMMAND CONTROL FOR MODEL ACID BATTERY CHARGER for: $30 4 different colours TRAINS. Control up to 16 trains on one 2 different guages of wire. NIGHT VISION TUBE + SUPPLY layout with very little wiring!: As per SC. Spade connectors. Jan-May 98. We have some hard to get Used 25mm fiber Spade type fuse holders. ZN409CE IC’s. We will also be supply optic tube plus an Spade type fuses. EHT power supply silk screened, solder masked PCB’s More than 17 meters of wire. kit to suit. With All together approx. 0.2 Kg. small side blemish. Limited offer!!! just $1 Only $50 KITS OF THE MONTH $65 $50 $7 $1 WE have tried to keep constant prices for the last few years but unfortunatly most of our prices must rise by 10 - 15% next month. Still very competitive prices! **** TWO GREAT SPECIALS **** ***STEPPER MOTOR DRIVER KITS*** NEW!!! COMPUTER CONTROLLED STEPPER MOTOR KIT New improved kit that can drive larger motors and has optoisolation between the circuit and the computer. DB25 connector provided on PCB. Needs a standard DB25 cable for connection to a PC, and a power supply for the motor drive section. PCB and all on board components kit plus software and notes: $40 or $50 with two used 1.8deg. motors !!! ( ONE ONLY NEW MOTOR OF SIMILAR QUALITY TO THE ONE SUPPLIED COSTS OVER $100 ) STEPPER MOTOR DRIVER KIT Kit includes a large used 1.8deg. (200 step / rev) motor & uses SAA1042A IC. ( ONE OF THESE CHIPS WOULD RETAIL FOR ALMOST $19 ) Can be driven by external or an on-board clock; has a variable frequency clock generator. Ext switches (not inc) or logic levels from a computer etc set CW or CCW rotation, half or full step operation, operation enable/disable, clock speed. PCB and onboard components:$20 with 1 motor, $30 with 2 motors. AUTOMATIC LASER LIGHT SHOW KIT The changes every 5-60 sec, adjustable. Countless displays single to multiple flowers, collapsing circles, rotating single & multi ellipses, stars, etc. PCB + all PCB components, 3 motors & mirrors :(K83) $65 With pointer kit for $79 MAGNETS: HIGH POWER NEODYMIUM RARE EARTH MAGNETS: Very strong You will not be able to separate two of these by pulling them apart directly away from each other. Zinc coated.---CYLINDRICAL 7 mm diameter x 3 mm thick: (G37) $2.50.---CYLINDRICAL 10mm diameter x 3 mm thick: (G38) $5.--TOROIDAL 50mm outer, 35mm inner, 5mm thick: (G39) $12.---ROD 10mm long, 4mm diameter: (G54) $2.50.--CYLINDRICAL 3mm diameter x1.5mm thick: (G58) 2 for $1 SOLID STATE 4-6A PELTIER EFFECT COOLER / HEATER 3.3A<at>14V PELTIER: $27, 6A <at>15VPeltier: $35, both are approx. 40X40X4mm, can be temperature controlled by reducing supply voltage/current, will even work from a 1.5V battery!! We supply Peltier Effect device, data sheet, diagram & circuit for a small fridge / heater.. Other requirements; Insulated box, 2 large heatsinks, & a small aluminium block. This device is used in the common 15Lr car fridge. Peltier effect Device + (G02) 12V DC Fan:(G11) MORE KITS Geiger counter:$40,...Breath tester: $40, Music box: $11,..Ding dong doorbell $3.50,...Siren using a 10cm speaker: $14,..Electric fence using used car coil: $25,..Ultrasonic car alarm: $35,..1ch UHF Central locking, Tx and Rx: $35,...4 door Central locking: $60,..2 Channel UHF Remote Control 1Tx + 1Rx: $45. UHF DATA TRANSMISSION Stamp sized Xtal locked 433.9MHz superhetrodyne receiver module $35 Small matching transmitter kit: $18 OATLEY ELECTRONICS PO Box 89 Oatley NSW 2223 Ph ( 02 ) 9584 3563 Fax 9584 3561 orders by e-mail: oatley<at>world.net May 1998  19 http://www.ozemail.com.au/~oatley major cards with ph. & fax orders, Post & Pack typically $6 CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions from readers are welcome and will be paid for at standard rates. Deluxe LED tester identifies leads This tester can check if a LED works or not and can also identify the Anode and Cathode leads. It has a constant current generator that can be set between 0-30mA and an oscillator that can be switched in to flash the LED. Op amp IC1b, transistor Q1 and a 47Ω resistor form a constant current generator. The current that flows into Q1’s collector (via the LED) is essentially that through the emitter and is equal to VR divided by 56Ω. By adjusting the voltage at pin 5 of IC1b (VR), we can vary the current flowing through the LED. With the values used in the circuit the current can be smoothly adjusted between 0-28mA. S2 is used to reverse the polarity of the LED. With the LED connected to the test points, the switch is moved between positions until the LED turns on. The switch positions are la­belled to indicate which lead is the Anode and which is the Cathode. If the LED Torch battery recharger This circuit was devised to save money on the high cost of dry cells for items such as torches, radios and so on. I have found that nicads usually only have a quarter of the capacity of equivalently sized alkaline cells and that they are not as satis­factory for uses involving long term idleness followed by inten­sive use. I have tried recharging dry cells of every description, with low current DC, with high current DC, with charging followed by rest and further charging, and with charging in a cycle four seconds on followed by 250ms discharge. In all cases, the results were poor retention for standard and 20  Silicon Chip doesn’t turn on in either position, it is faulty. Op amp IC1a and its associated components form a square wave oscillator with a frequency of around 2Hz. When the Flash button is pressed, the oscillator continually turns transistor Q2 on and off. When Q2 is turned on it shorts out the current setting potentiometer, forcing VR to almost 0V. As a result, the current through the LED drops to almost zero. Power is supplied by a nominal 9V DC supply, either from a plugpack or bench power supply. The supply is regulated to 5V by a 78L05 regulator for two reasons: (1) to ensure that the constant current generator is accurate if the main supply varies; and (2) so that the maximum reverse voltage across the LED is below the typical maximum of 5V when the polarity switch is in the reversed position. Leon Williams, Bungendore, ACT. ($30) heavy duty batteries and no retention for alkaline batteries. Eventually I obtained success using half-cycle charging followed by half-cycle discharging, In no case did a battery explode and end-of-life was determined when a battery leaked (fluid) while in the charger. The precaution was not to over­charge and not to wait until the battery was fully discharged. A fully discharged battery will not accept any charge and it will be noted that the voltage across the terminals rises within a few seconds by 30% of its nominal voltage. A battery accepting charge will only rise by 2% in that time. Standard and alkaline batteries will keep increasing their voltage under charging and should be disconnected when they reach an over-voltage of 20%. In other words, a 1.5V cell should be discon­nected when its charging voltage reaches 1.8V. Some heavy duty batteries do not show such a progression and should be disconnected by a timer after the estimated ampere hours used have been restored. This recharger charges during each mains 950Hz) half-cycle and discharges by about 1/4 in the following half-cycle. This seems to affect the cell depolarisation and permits it to accept a satisfactory charge. The transformer is from a 12V plugpack and measured 19V open circuit and the resistors were selected by measuring the charging and discharging currents. The values shown Linear voltage controlled oscillator Most varicap-tuned VCOs (voltage controlled oscillators) have a non-linear voltage-to-frequency response. However, in many applications, such as in linear sweep generators and tuners, a linear response is necessary or desirable. This circuit illustrates a simple technique for com­ pensat­ing for the normally non-linear response in a VCO to obtain a substantially linear response. This is accomplished by trimpot VR1 and its associated components. The linearising network cuts in when the input control voltage goes below a level set by VR1. In this case, R6 forms a voltage divider with R7, thereby compensating for the greater sensitivity of the VCO to low input voltages. Diode D2, biased by R5, compensates for the temperature drift in diode D3. The accompanying graph shows the measured responses of the VCO with and without these linearising components. The optimum value for R6 may be determined from the “uncompensated” response curve in the graph or by trial and error. An interesting feature of the circuit is the use of power Mosfets (CD1 & CD2) in place of varicap diodes. One reason for this choice is that I didn’t have suitable varicaps on hand. I had considered using ordinary rectifier or zener diodes as vari­cap substitutes but the data sheets usually do not publish infor­ m ation on their capacitance. By contrast, most data sheets on Mosfets include detailed voltage-capacitance curves which make selection much easier. After browsing through these data sheets, I found the 2SK679 Mosfet to be suitable. Possible Mosfet alternatives (which have not be been tried) might be BS170 or MSF910. Herman Nacinovich, Gulgong, NSW. ($40) on the selector switch are the actual final charging currents accumulat­ing in the battery. The relay (RLY1) disconnects the battery from the charger when the AC mains supply is interrupted and thus This graph shows the measured responses of the VCO with and without the linearising components permits the use of an external timer. V. Erdstein, Highett, Vic. ($40) May 1998  21 Silicon Chip Back Issues 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 Mk.II; Magnetic Field Strength Meter; Digital Altimeter For Gliders, Pt.2; Military Applications Of R/C Aircraft. September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice. July 1990: Digital Sine/Square Generator, Pt.1 (0-500kHz); Burglar Alarm Keypad & Combination Lock; Simple Electronic Die; LowCost Dual Power Supply; Inside A Coal Burning Power Station. 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. 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. May 1989: Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; The Burlington Northern Railroad. September 1990: Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band; the Bose Lifestyle Music System; The Care & Feeding Of Battery Packs; How To Make Dynamark Labels. 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. December 1989: Digital Voice Board; UHF Remote Switch; Balanced Input & Output Stages; Operating an R/C Transmitter; Index to Vol. 2. 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: How To Connect 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; Build A Simple 6-Metre Amateur Band Transmitter. December 1990: The CD Green Pen Controversy; 100W DC-DC Converter For Car Amplifiers; Wiper Pulser For Rear Windows; 4-Digit Combination Lock; 5W Power Amplifier For The 6-Metre Amateur Transmitter; Index To Volume 3. January 1991: Fast Charger For Nicad Batteries, Pt.1; Have Fun With The Fruit Machine; Two-Tone Alarm Module; LCD Readout For The Capacitance Meter; How Quartz Crystals Work; The Dangers of Servicing Microwave Ovens. 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. December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Colour TV Pattern Generator, Pt.2; Index To Volume 4. January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Experiments For Your Games Card. March 1992: TV Transmitter For VHF VCRs; Thermostatic Switch For Car Radiator Fans; Coping With Damaged Computer Directories; Guide Valve Substitution In Vintage Radios. April 1992: IR Remote Control For Model Railroads; Differential Input Buffer For CROs; Understanding Computer Memory; Aligning Vintage Radio Receivers, Pt.1. 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 1992: Multi-Station Headset Intercom, Pt.1; Video Switcher For Camcorders & VCRs; IR Remote Control For Model Railroads, Pt.3; 15-Watt 12-240V Inverter; A Look At Hard Disc Drives. August 1992: An Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; 1kW Dummy Load Box For Audio Amplifiers; Troubleshooting Vintage Radio Receivers; MIDI 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 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Phone Patch For Radio Amateurs; Active Antenna Kit; Designing UHF Transmitter Stages. 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. 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 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. 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 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. 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. 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. April 1993: Solar-Powered Electric Fence; Audio Power Meter; Three-Function Home Weather Station; 12VDC To 70VDC Converter; Digital Clock With Battery Back-Up. June 1990: Multi-Sector Home Burglar Alarm; Build A LowNoise Universal Stereo Preamplifier; Load Protector For Power Supplies; Speed Alarm For Your Car. 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. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Alphanumeric LCD Demonstration Board; The Microsoft Windows Sound System; The Story of Aluminium. 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. 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. ORDER FORM Please send me the following back issues: _____________________________________________________________________ _____________________________________________________________________________________________________________ _____________________________________________________________________________________________________________ Enclosed is my cheque/money order for $­______or please debit my:  ❏ Bankcard  ❏ Visa Card  ❏ Master Card Signature ___________________________ Card expiry date_____ /______ Name ______________________________ Phone No (___) ____________ PLEASE PRINT Street ______________________________________________________ Suburb/town _______________________________ Postcode ___________ 22  Silicon Chip Note: all prices include post & packing Australia (by return mail) ............................. $A7 NZ & PNG (airmail) ...................................... $A7 Overseas (airmail) ...................................... $A10 Detach and mail to: Silicon Chip Publications, PO Box 139, Collaroy, NSW, Australia 2097. Or call (02) 9979 5644 & quote your credit card details or fax the details to (02) 9979 6503.  Card No. June 1993: AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; Digital Voltmeter For Cars; 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; A +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: Jumbo Digital Clock; 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; LED Stroboscope; 25W Amplifier Module; 1-Chip Melody Generator; Engine Management, Pt.3; Index To Volume 6. 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. 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. 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. May 1995: What To Do When the Battery On Your PC’s Mother­board Goes Flat; 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. February 1997: Computer Problems: Sorting Out What’s At Fault; 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. 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; Build A $30 Digital Multimeter. 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 (Uses Pressure Sensing); Adding RAM To A Computer. August 1995: Fuel Injector Monitor For Cars; Gain Controlled Microphone Preamp; Audio Lab PC Controlled Test Instrument, Pt.1; Mighty-Mite Powered Loudspeaker; How To Identify IDE Hard Disc Drive Parameters. September 1995: Keypad Combination Lock; The Incredible Vader Voice; Railpower Mk.2 Walkaround Throttle For Model Railways, Pt.1; Jacob’s Ladder Display; The 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. 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 – How They Work. November 1995: Mixture Display For Fuel Injected Cars; CB Trans­ verter 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. March 1994: Intelligent IR Remote Controller; 50W (LM3876) Audio Amplifier Module; Level Crossing Detector For Model Railways; Voice Activated Switch For FM Microphones; Simple LED Chaser; Engine Management, Pt.6. 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. 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. 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. 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; Passive Rebroadcasting For TV Signals. 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. July 1994: Build A 4-Bay Bow-Tie UHF Antenna; PreChamp 2-Transistor Preamplifier; Steam Train Whistle & Diesel Horn Simulator; Portable 6V SLA Battery Charger; Electronic Engine Management, Pt.10. 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 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 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 1994: Dry Cell Battery Rejuvenator; Novel Alphanumeric Clock; 80-Metre DSB Amateur Transmitter; Twin-Cell Nicad Discharger (See May 1993); Anti-Lock Braking Systems; How To Plot Patterns Direct To PC Boards. December 1994: Dolby Pro-Logic Surround Sound Decoder, Pt.1; Easy-To-Build Car Burglar Alarm; Three-Spot Low Distortion Sinewave Oscillator; Clifford – A Pesky Electronic Cricket; Remote Control System for Models, Pt.1; Index to Vol.7. January 1995: Sun Tracker For Solar Panels; Battery Saver For Torches; Dolby Pro-Logic Surround Sound Decoder, Pt.2; Dual Channel UHF Remote Control; Stereo Microphone Pre­amp­lifier;The Latest Trends In Car Sound; Pt.1. February 1995: 50-Watt/Channel Stereo Amplifier Module; Digital Effects Unit For Musicians; 6-Channel Thermometer With LCD Readout; Wide Range Electrostatic Loudspeakers, Pt.1; Oil Change Timer For Cars; The Latest Trends In Car Sound; Pt.2; Remote Control System For Models, Pt.2. March 1995: 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. 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; Use your PC As A Reaction Timer. 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 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; Build A High Voltage Insulation Tester; Knightrider Bi-Directional LED Chaser; Simple Duplex Intercom Using Fibre Optic Cable; Cathode Ray Oscilloscopes, Pt.3. 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 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 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 1996: VGA Oscilloscope, Pt.3; Infrared Stereo Headphone Link, Pt.1; High Quality PA Loudspeaker; 3-Band HF Amateur Radio Receiver; Feedback On Pro­grammable Ignition (see March 1996); Cathode Ray Oscilloscopes, Pt.5. 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; Infrared Stereo Headphone Link, Pt.2; Multi-Media Sound System, Pt.1; Multi-Channel Radio Control Transmitter, Pt.8. November 1996: Adding An Extra 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. December 1996: CD Recorders ­– The Next Add-On For Your PC; 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. March 1997: Driving A Computer By Remote Control; Plastic Power PA Amplifier (175W); Signalling & Lighting For Model Railways; Build A Jumbo LED Clock; Audible Continuity Tester; Cathode Ray Oscilloscopes, Pt.7. April 1997: Avoiding Windows 95 Hassles With Motherboard Upgrades; Simple Timer With No ICs; Digital Voltmeter For Cars; Loudspeaker Protector For Stereo Amplifiers; Model Train Controller; Installing A PC-Compatible Floppy Drive In An Amiga 500; A Look At Signal Tracing; Pt.1; Cathode Ray Oscilloscopes, Pt.8. May 1997: Windows 95 – The Hardware Required; 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. June 1997: Tuning Up Your Hard Disc Drive; 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; Fail-Safe Module For The Throttle Servo; Cathode Ray Oscilloscopes, Pt.10. 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; How Holden’s Electronic Control Unit works, Pt.1. 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; How Holden’s Electronic Control Unit Works, Pt.2. 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; The Flickering Flame Stage Prop; 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; Regulated Supply For Darkroom Lamps; Build A Musical Doorbell; Relocating Your CD-ROM Drive; Replacing Foam Speaker Surrounds; Understanding Electric Lighting Pt.1. December 1997: A Heart Transplant For An Aging Computer; 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. 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. 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; Demonstration Board For Liquid Crystal Displays; Build Your Own 4-Channel Lightshow, Pt.2; Understanding Electric Lighting, Pt.4. March 1998: Sustain Unit For Electric Guitars; Inverter For Compact Fluorescent Lamps; Build A 5-Element FM Antenna; Multi-Purpose Fast Battery Charger, Pt.2; Command Control System For Model Railways, Pt.3; PC-Controlled LCD Demonstration Board; Feedback On The 500W Power Amplifier; Understanding Electric Lighting, Pt.5; Auto-detect & Hard Disc Drive Parameters. April 1998: Automatic Garage Door Opener; 40V 8A Adjustable Power Supply, Pt.1; PC-Controlled 0-30kHz Sinewave Generator; Build A Laser Light show; Understanding Electric Lighting, Pt.6; Philips DVD840 Digital Vide Disc Player (Review). PLEASE NOTE: November 1987 to August 1988, October 1988 to March 1989, June 1989, August 1989, May 1990, August 1991, February 1992, July 1992, September 1992, November 1992 and December 1992 are now sold out. All other issues are presently in stock. For readers wanting articles from sold-out issues, we can supply photostat copies (or 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. May 1998  23 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 SERVICEMAN'S LOG Lightning didn’t strike this time If a TV set stops working while there’s a storm around, many people assume that it has been struck by lightning. They automatically link the two phenomena together simply because they happen at the same time but it ain’t necessarily so. My first story this month concerns a 1990 Grundig 68cm TV set. According to the customer, it had gone off during a storm and so she immediately jumped to the conclusion that lightning was responsible. I suppose it’s a natural enough conclusion under the cir­cumstances but in this case, it turned out to be quite wrong. The set was fitted with a West German 2-pin plug (with an Australian adaptor added) and the lady had obviously brought it with her from Germany. As I very rarely see German television sets these days, I was intrigued to see what might be involved. The set modestly proclaimed itself to be a “Grundig Monolith Blackline Multisystem”. A European set of this age could present problems. For one thing, their power grid is 220V and the increase in heater vol­tage, without a modification for our 240V, could be a tube kill­er; the picture tube could very well be low in emission. Another problem concerns model identification. The number of models in the Grundig lineup is bewildering. In fact, identi­ fying this model set requires several numbers: model M70575/90, chassis series CUC5836, and main chassis part number 29701-057. Despite all this, when a service manual which I ordered arrived, it was only a supplement which covered the differences between this and the CUC 5820, 5835, 5860 and 5880 models. So it was very much incomplete and among other things, lacked all the information for the plug-in modules. Later, I acquired the main manual but even then, this was incomplete. The PC board component layouts were not included and there are many differences and modifications between part numbers and the component reference numbers, which aren’t marked on the board. The back was easily removed but access to the horizontal main chassis underside was not as easy as on earlier models. The service manual suggests it should be pulled out and lifted onto its righthand side on the bench. This didn’t work because the speakers are directly below the chassis and the leads weren’t long enough. There wasn’t much life in the set except a low level motor-boating, which suggested the power supply was functioning – at least in a fashion. What was more immediately obvious was rust and corrosion everywhere – definitely not something caused May 1998  27 Fig.1: part of the deflection module circuitry in the Grundig M70-575/90. IC7010 (TDA8146) had blown apart and had to be replaced along with IC7020 (TEA8170A), zener diode D7012 and resistor R7033. by lightning and storm damage! The set had obviously had a hard life in a damp environment or near the sea. A glance at the tripler revealed several telltale carbon track deposits leading from holes in its insulation where it had been sparking and burning. For the time being, I disconnected it and went to the horizontal output transistor T541, a BU508A. It measured short circuit and so I replaced it, hoping that might be all the damage. With power applied, the motor boating disappeared but not much more was happening. And then suddenly, I heard a slight click and it started motor boating again. Not only had transistor T541 become red hot but so had diode D546, a BY228, and both had failed. The overall damage looked pretty severe – two horizontal output transistors, two diodes (D546 and D547), the tripler, almost certainly the horizontal output transformer, and probably the horizontal drive IC (IC500 – TDA8140). I would have to give an estimate on these before proceed­ing; if there 28  Silicon Chip were any other problems they would probably be minor. The lady had no problem with this and so I ordered the parts which arrived promptly. I decided to replace them all at once, to eliminate the possibility of further damage due to faulty parts. On switch-on, I was disappointed to find only limited im­ provement. Granted, the EHT was now working, the HT rail measured 165V and there were no signs of distress or overheating in T541 and D546. However, there was still no sign of a raster or sound, apart from a few noises in the speakers. I checked all seven voltage rails and this quickly revealed that there was no voltage on the 29.5V rail. This was quickly traced to R525 (0.33Ω) which was open circuit. Replacing this produced some sound but it was garbled, although this could have been due to mistuning. And there was still no picture; just a blurred blob which was uncontrollable. The EHT meter confirmed 25kV on the picture tube final anode and there was a healthy spark from the CRT socket focus pin. There was also plenty of G2 volts but shorting the tube cathodes to chassis produced no intelligent raster or picture, other than the unfocussed blob (the focus control had no effect). I prayed the tube wasn’t U/S; shorting any cathode to chas­ sis should give an intense bright raster. The only thing left to check was the deflection circuit. The CRO showed that there was no vertical deflection on the yoke, while there was too much signal at the chassis end of the horizontal coils. It was time to unplug and examine the deflection module. Once the deflection module was on the bench, it was obvious it had sustained major damage – IC7010 (TDA­8146) had literally blown apart, leaving a blackened hole in its lower half. A lot of power would have been required to do this, which meant that there was bound to be collateral damage. And sure enough, a quick check soon revealed that D7012, a 36V zener diode, was short circuit, while R7033 (100Ω) had gone high. In addition, R546 (4.7Ω) was open circuit. Until now, I had managed to obtain all the parts easily and cheaply from my local supplier and so I ordered a replacement TDA8146 (IC7010) from them. But IC7020 (TEA8170A), which I also strongly suspected, had to be ordered from the Grundig agents. While waiting for these parts, I had the opportunity to clean up the corrosion and to check the other components around these circuits. Nothing else appeared to be amiss. The ICs duly arrived and, when fitted, restored the pic­ ture. After some tuning and setting the CCIR B/G system standard (which is actually a story in itself), I had a watchable picture with good colour, sound and focus. The only problem remaining was severe pincushion distortion. Adjusting the pincushion control (R7011) made no dif­ ference. Ditto for the width control (R7002) and the trapezoid control (R7007). In fact, no east-west correction controls were working around IC7010 (TDA8146). I tried two more TDA8146s for IC7010 but to no avail – a matter of some significance, as it turned out. After a lot of CRO measurements, the only two waveforms I could fault were waveform 10, which is the vertical input to pin 2 of IC7010, and waveform 9, which was slightly different on output pin J7 to the deflection coils. I was really stuck now, as I couldn’t determine whether the pincushion fault lay in the motherboard or in the deflection module. panied by a whistling noise. Close inspection revealed that though both sets were similar, the Blaupunkt mod­ ules had major differences. Because the Grundig was a multi-system, with picture-in-picture, the boards were larger and contained a lot more components. I was mainly interested in the deflection module and the only major difference between the two was that IC7010 in the Blaupunkt deflection module was a smaller 8-pin TDA8145 device instead of the 14-pin TDA8146 in the Grundig. Despite this, I decided it was worth the risk and swapped the modules over. Surprisingly, this fixed the Grundig’s pincushion distor­tion problem completely. I was somewhat taken aback at this because I was sure I had checked every component in the module. Conversely, the Grundig’s deflection module (29504-107.80) did down to the IF module, of all things. This was established by temporarily fitting the IF module from the Grundig set. Unfortunately, I ground to a com­ plete stop here after replacing IC2340 (TDA2579) in the IF modu­le, which made no difference. I now had two problem sets: the Grundig with pincushion distortion and the Blaupunkt with lack of height. It was then that my friendly leprechaun came to my rescue for the second time. By chance, I was talking to a colleague and happened to mention my problems with these two sets. And as luck would have it, he knew the answer to the lack of height in the Blaupunkt, as he had once spent a lot of time tracking down this very fault. In his case, it turned out to be diode D2334 (TD190) in the IF module. And he was spot on. I subsequently discovered that the diode in my set was slightly leaky and replacing it A friendly leprechaun not fix the height or width problems in the Blaupunkt, nor did it correct its east-west foldover problems. Well, at least I had localised the Grundig’s problem. However, I decided to leave this set for the time being and concentrate on the Blaupunkt instead. The first step, of course, was to reinstall its deflection module. The lack of width and the horizontal foldover turned out to be due to IC526 (TDA8140), C527 and C574, which were causing transistor T572 (BU508A) and resistor R574 (18Ω) to overheat. The exact sequence of events involved here is not clear; I could not determine which had failed first and what was damaged as a result. All I can tell you is that all these parts had failed and had to be replaced. The lack of height was tracked completely cured the problem. It was at this time that I was blessed with an surprising coincidence (and for this, I imagine I should thank some friendly leprechaun – I’m writing this on March 17 which is St Patrick’s Day). As stated before, I very rarely see German TV sets and yet, incredibly, it was just then that another customer brought in his Blaupunkt IS 70-39 VT (FM 500.40 chassis 7669 800) which is manufactured by – yes, you guessed it – Grundig. And the main chassis Grundig part number was 29701-056 – only one digit dif­ferent from the Monolith. Luck doesn’t often come like this. The problem with the Blaupunkt was a shrunken picture (both vertically and horizontally) which became folded after about 10 minutes, accom- Back to the Grundig My next problem was what to do about the faulty Grundig deflection module. One option was to send it back to the Grundig agents for servicing, a process that would take two or three weeks. Another option was to buy a new one but this was not readily available and, in any case, is rather expensive. In the end, I played a hunch. I had begun to suspect that the TDA8146s (IC7010) which I had purchased from my supplier might be the problem. And I became suspicious because of their price. They were only about $7.00 each from my supplier whereas they were closer to $20.00 each from the Grundig agents. May 1998  29 Fig.2: part of the IF module in the Grundig M70-575/90. Diode D2334 (TD190) at lower right had gone leaky. OK, that’s fine; I’ll buy in the cheapest market, all else being equal. But were these parts really equal? To test my theo­ry, I ordered a TDA8146 (part no 8305-358-146) directly from the Grundig agents and when it arrived, I noticed one obvious dif­ference in the batch number. The original Grundig number was W994A9409 but the ones I had fitted during testing were marked W994A9422. And that was the answer; it was all that was required to cure the problem completely and the east-west correction circuits now worked perfectly. Both customers were pleased that their sets were now work­ing properly but neither was nearly as pleased as I was. And what was the final verdict? Was the set struck by lightning? I dunno, please. I have no doubt that the Grundig set failed while a storm was in progress but that doesn’t necessarily mean that the two events are directly related. From the evidence before me, I would have to say that lightning was not the probable cause. However, the customer is firmly convinced that lightning caused the problem and the matter is still before her insurance company. Well, if she’s happy, who 30  Silicon Chip am I to disillusion her? For my part, I returned the three cheaper ICs to my local supplier with a please explain note and am awaiting their re­ sponse. Unfortunately, this wouldn’t be the first time that bodgie, off-tolerance components had found their way onto the local scene and been marketed quite innocently by local dealers. Yes, it’s a rough world out there. The JVC video JVC videos don’t seem to like me. This week, a lady brought in her JVC HR-D600 VCR and complained that the picture was “sort of distorted but only with some tapes some of the time”. Obvious­ ly, she imagined, I must know what the trouble was, so could I please tell her what it was, how much it would cost and how long would it take to get it fixed. Ironically, I had a sneaking suspicion as to what the trou­ble might be but I certainly wasn’t going to commit myself to a guess. Instead, I suggested she leave it with me and I would make an assessment after I had seen the fault. I put it on the soak bench with an E240 cassette in standard play and left it produc­ing an excellent picture. Every so often, I would check that it was going OK and restart the tape. After three days of this, I was beginning to despair and so, when she phoned to enquire about progress, I had to confess that there was none; it hadn’t missed a beat. Perhaps it was her tapes? Her answer to this question was an emphatic “no”, because it also happened with hire tapes. Not wishing to start an argument on that basis, I told her she might as well pick it up and try it again later. She didn’t call for two more days and when I took her to meet the monster, the tape had stopped. So I pressed play again to show her it was still going OK and would you believe it, the wretched machine started to do its trick (I told you they don’t like me). The picture had three or four sets of noise bars across the screen – permanently. Somewhat embarrassed, I did my best to assure her that this was the first time that the fault had ap­peared. I don’t know whether she believed this or not but, in any case, I could only mentally shrug my shoulders; after all, that was the true situation. “Leave it with me”, I said. “Now that the fault has shown up, I should be able to get at the problem”. The customer readily agreed to this, so my explanation must have been at least partially accepted. Despite being busy, I decided I would tackle it straight away while the fault persisted. The symptoms were typical of a misaligned tape path and the tape guides used in this deck do give a lot of trouble. The top cover comes off conveniently but the bottom is not only screwed in via the fancy feet but also clips in on the sides and centre. And it was while I was removing this cover that the so-and-so bit me, a sharp edge cutting one of my fingers and causing it to bleed. The next step is to move the top PC board into its service position. This involves removing a screw at the rear, then using a smaller Phillips screwdriver to remove five self-tapping screws that hold it. The board was then parked in a vertical position along the rear of the video. Next, three more screws had to be removed from the metal cover over the heads. With the tape in the play mode, everything looked OK except that the entry and exit tape guides hadn’t engaged properly at the end stops. By wiggling them, I could restore the picture. It was while I was wiggling these guides that the machine bit me again; it cut another finger, this time on the sharp edge of the cassette ejector housing. Things were bad and getting worse. I removed the tape and put in a dummy cassette (one with no insides, just the outside framework). I then pressed the play button and pulled the mains plug when the two arms were only half-way along their action. Now I could see how loose things really were. On the underside of the deck, the guides are held in place with a brass plug/collar assembly and a plastic pin. Both of these are just a snug push fit and the brass ones were not all the way home. I removed them and applied some superglue before pushing them all the way home while holding the guides in on the other side. This done, I cleaned the heads and tape path and checked that everything was shipshape before trying another tape in the play mode. Everything now worked OK, so I refitted everything and gave it one more final test. I couldn’t believe it – not only was the original problem still in evidence but there was now another even heavier noise bar at the top of the picture. I stopped and started it several times but it wouldn’t go away. There was nothing for it but to go back in again and access the tape guides. Well, the cause of the problem was immediately obvious – the pin in the input guide had fallen out, presumably when I turned the machine upside down to fit the bottom screws. The annoying thing was that I had originally checked it and it had appeared to be tight. I decided to superglue it in and put a few drops on the end of the pin before pushing it into its hole. Big mistake – the pin set hard in the socket but wouldn’t go all the way in. There was nothing for it but to remove it and start again. It took a lot of aggro to remove and clean it with acetone. Before starting again, I made sure the pin could slide all the way home in its socket and that it did so easily. Another drop of glue and once again it seized half way in. I was on the verge of chucking the whole thing out the window when common sense told me to try some lateral thinking. After removing and cleaning the pin, I refitted it in the hole and applied the glue around the edges afterwards. Sure enough, it finally locked in place and capillary action made the glue sink in. I did the other guide too and then after cleaning every­ thing, tested it again. I was dismayed to find that the original symptoms were still there, although they were now quite inter­ mit­tent. In desperation, I went in for the third time and after a very careful examination of the guide assembly, I found I had inadvertently pulled the plastic pin connecting it to the loading arm. Consequently, this arm was also loose. I glued this and its partner on the other side, and anything else that might possibly come loose. Fortunately, that was the end of the story because it now worked like a steam train and was still working when the lady called to pick it up. I just hope that I managed to wipe off all those bloodstains and that she won’t notice the dents in the sides! SC May 1998  31 3-LED LOGIC PROBE Ever been chasing a problem on a digital logic board and wasted a lot of time because you were too lazy to get the scope out and plug it in? What, you don’t even own one? This logic probe will prove invaluable in digital fault finding and only costs a few dollars. By RICK WALTERS All right. So what is a logic probe? A logic probe is a small hand-held device which indicates the logic state at its input probe. The logic level should only be ground (low) or at the positive supply (high) but a faulty device can have an output level somewhere around half the supply. Ideally, a logic probe should indicate all three circuit states and that is what this simple design does. The probe has three LEDs which are readily visible whether you are right 32  Silicon Chip or left-handed. The red one indicates a low level, the green one a high level and the yellow one is lit whenever the level changes from high to low. You may wonder why we bothered with the yellow indication. We have just stated that if the level is low, the red LED will light, if the level is high the green one will be lit, and if the level is changing from high to low then obviously both will light. The fault condition described above can sometimes cause both LEDs to come on and this would give us a false indication. The yellow LED needs a full high-low transition to light it, thus eliminating any false indication. How does it work? As you can see from the circuit of Fig.1 there is not much to it. A 4001 quad 2-input NOR gate is used as it lets us make a monostable by cross-coupling two gates. We’ll get to that in a moment, so let’s start at the input. The probe tip is connected directly to pins 5 & 6 of IC1b. The 10MΩ resistor holds those pins low and prevents the input capacitance being charged and staying high when the probe en­ counters a momentary high level. The output of IC1b is fed to pins 1 & 2 of IC1a which in turn, drives the LEDs. Note that since each gate effectively inverts its input and there are two signal inversions via these gates, the output of IC1a is in phase with the input. Thus when the input is low, the Fig.1: the circuit uses a 4001 quad 2-input NOR gate to indicate high, low or fault logic conditions. output of IC1a is low and the red LED will be lit. When the input goes high, the red LED will go out and the green one will light. The output of IC1b is also coupled through a .001µF capaci­ tor to one input of IC1c. This input is held low by the 10kΩ resistor to ground. IC1c’s output, pin 10, is coupled via the 0.18µF capacitor to the inputs of IC1d. These inputs are held high by the 100kΩ resistor which means the output at pin 11 will be low. A low to high transition at the output of IC1b will pull pin 8 of IC1c high and consequently pin 10 will go low. This will pull pins 12 & 13 low, taking pin 11 high and thus turning on LED3. As pin 11 is also connected to pin 9 of IC1c, it will hold the output of IC1c low even after the initial logic signal at pin 4 has charged the .001µF capacitor. The yellow LED will stay lit until the voltage on the 0.18µF capacitor, which is charging through the 100kΩ resistor, reaches the switching threshold of IC1d. When it is reached, the output of IC1d will go low, the yellow LED will extinguish and the output of IC1c will go high again. Thus each high to low input transition will flash the yellow LED for 18ms. At low frequencies this is readily apparent but as soon as the input frequency is high enough, the LED will appear to be lit continuously. So just to sum up, if the red or green LED is on, the logic circuit being measured is indicating a valid condition (ie, low or high), although if you want a high and you get a low you ob­viously have a problem. Power for the Logic Probe comes from the circuit being measured and can be anywhere between 5V and 15V DC. Diode D1 protects the logic probe if you accidentally make the wrong supply connections (ie, wrong polarity) to the circuit. PC board assembly We made the PC board as small as possible, so you could fit it into a smaller case than the one we used, if you have one. We would have preferred a slightly narrower rectangular case but the one we used is readily available and inexpensive. On the positive side, if you have large hands, the size and shape of the speci­fied case is quite convenient to handle. The assembly details for the Logic Probe are shown in Fig.2 and are quite straightforward. Don’t use an IC socket for the 4001 as there is Fig.2: not shown on this wiring diagram are the positive and negative supply leads which clip onto the circuit being measured. Fig.3: actual size artwork for the PC board. not much depth in the case we have specified. Use the PC stakes as they are a convenient connection for the LED leads. Keep the wires close to the PC board when you solder them and cut the top off the stakes or else they will prevent you from assem­bling the case properly. Drill the three holes in the case for May 1998  33 This is the view inside the Logic Probe case. Note that the leads to the three LEDs must be sleeved to avoid the possibility of shorts. the LEDs and file a notch in the end panel to bring the power wires out. Make it small enough so that the wires are lightly clamped when the case is screwed together. We secured the board inside the case by using a small self-tapping screw into one of the integral pillars. But the pillar is very short and you must be careful not to tighten the screw too much otherwise it will penetrate right through the case. If you look closely at the inside photo of the Logic Probe you will note that we have placed a black fibre washer underneath the screw head to avoid this problem. Another point to note about the inside photo is that the LEDs should have sleeving on their leads to avoid A slot is cut in one of the end pieces of the case for the power supply leads. 34  Silicon Chip the possibility of shorts. We used a probe from an old multimeter lead as the input prod but failing this, a nail or a small gauge screw with a filed point could be pressed into service. I’m sure your ingenuity won’t fail you here. Testing Connect the power leads to 5-12V and the red LED should immediately light. If it doesn’t, you probably have its leads reversed. Don’t worry though, just make the connections correctly and it should work properly. Use your multimeter to measure the voltage at pin 3 of IC1a. It should be at ground potential; ie 0V. Now put the probe on the positive supply. This should extinguish the red LED and light the green one. As you remove the probe from the supply, you should see the yellow LED flash briefly. Tap the probe on and off a few times until you see it. The beauty of this device is that if you connect it to a logic PC board with a 5V supply, all the functions work as de­scribed. But it can be connected to any supply up to 15V with safety and the logic thresholds will move to track the supply. It will work with all “C” & “HC” devices as well as the older TTL range. The upper frequency depends on the Parts List 1 PC board, code 04104981, 50 x 26mm 1 small plastic case, Jaycar HB6030 or equivalent 1 red crocodile clip 1 black crocodile clip 3 5mm LED bezel clips 8 PC stakes 1 6mm long self-tapping screw 1 fibre washer (see text) 0.5m red hookup wire 0.5m black hookup wire Semiconductors 1 4001 quad 2-input NOR gate (IC1) 1 1N914 small signal diode (D1) 1 5mm red LED (LED1) 1 5mm green LED (LED2) 1 5mm yellow LED (LED3) Capacitors 1 0.18µF MKT polyester 1 0.1µF MKT polyester or monolithic ceramic 1 .001µF MKT polyester Resistors (0.25W, 1%) 1 10MΩ 1 10kΩ 1 100kΩ 3 1kΩ supply vol­tage. With a 5V supply the 4001 should indicate up to 2-3MHz and around three times this frequency with a 15V supply. SC MORE FROM YOUR EFI CAR! Own an EFI car? Want to get the best from it? You’ll find all you need to know in this publication EFI TECH SPECIAL Here it is: a valuable collection of the best EFI features from ZOOM magazine, with all the tricks of the trade – and tricks the trade doesn’t know! Plus loads of do-it-yourself information to save you real $$$$ as well . . . HERE ARE JUST SOME OF THE CONTENTS . . . n Making Your EFI Car Go Harder n Building A Mixture Meter n D-I-Y Head Jobs n Fault Finding EFI Systems n $70 Boost Control For 23% More Grunt n All About Engine Management n Modifying Engine Management Systems n Water/Air Intercooling n How To Use A Multimeter n Wiring An Engine Transplant n And Much More including some Awesome Engines! AVAILABLE DIRECT FROM SILICON CHIP PUBLICATIONS PO BOX 139, COLLAROY NSW 2097 - $8.95 Inc GST & P&P To order your copy, call (02) 9979 5644 9-5 Mon-Fri with your credit card details! FROM THE PUBLISHERS OF “SILICON CHIP” It probably won’t find gold nuggets in the bush but it will demonstrate how a metal detector works. A Detector For Metal Objects This simple project will demonstrate how metal detectors work. It uses the principle whereby the inductance of an air-cored choke changes in the presence of metal. By JOHN CLARKE Metal detectors are used in many applications. These include motor vehicle detectors at traffic lights, detecting unwanted metal objects in food processing, as process counters in industry and as treasure locators for fossickers. As you might expect, they vary widely in circuit complexity and function. A vehicle detector can easily detect a large piece of metal (ie, a car or truck) above it but it is quite a lot harder to detect metal fragments in food or coins and other items such as 36  Silicon Chip ring pull tabs from drink cans buried in beach sand. Some metal detectors can even discriminate between ferrous metal (ie, those with iron such as steel, cast iron, wrought iron, etc) and non-ferrous metals (aluminium, zinc, tin, lead, copper, mer­cury, silver, platinum, gold, etc). The metal detector presented here is of the simple variety and it only detects large items of metal at close range. It does not discriminate between ferrous and non-ferrous metals. Most metal detectors depend on the principle that an air-cored choke will change its inductance when brought into close proximity with a piece of metal. If the metal is ferrous (ie, if it has magnetic properties), the change in inductance will be considerably greater than for a non-ferrous metal and this fact can be used in circuits which can discriminate between metals. In our circuit, we have used an aircored inductor (choke) as the variable element in an LC oscillator. Block diagram Fig.1 shows the block diagram of the Metal Detector. There are two frequency sources, called oscillator 1 and oscillator 2, which are monitored with a NAND comparator. Oscillator 1 is adjusted using VR1 so that its frequency is exactly the same as for oscillator 2 when no metal is close to ductance increases. When non-ferrous metals are in close proximity to L1, the inductance decreases and so the frequency increases. This is the basis of discriminating metal detectors, as mentioned above. Circuit diagram Fig.2 shows the circuit which is based on two CMOS logic ICs. NAND Fig.1: block diagram of the Metal Detector. gates IC2a and IC2b form The two oscilla­tors beat together in a NAND oscillator 1 while IC1a gate comparator which then drives a loud­forms oscillator 2. -speaker. Oscillator 1 is a standard two-gate circuit with the 390pF capacitor alternateinductor L1. When metal is brought in ly charged and discharged proximity to L1, the frequency of os- via the 1kΩ resistor and series concillator 2 changes and this is detected nected trimpot VR1. in the comparator. When power is first applied, IC2b’s The comparator produces a tone in output could be either low or high. the loudspeaker whenever it detects When its output is high, IC2a’s output a difference in frequency between is low and the 390pF capacitor charges the two oscillators. The tone varies so that the junction of the two 1kΩ depending upon how large the metal resistors drops toward 0V. When this item is and how close it is to induc- junction voltage reaches IC2a’s lower tor L1. threshold, its output at pin 11 goes An interesting property of this high and so IC2b’s output goes low. type of oscillator is that when metWhen this happens, the 390pF als containing iron (ie, ferrous) are capacitor charges in the op­ posite brought close to L1, the frequency direction via the 1kΩ resistor and of oscillation falls because the in- trimpot. When the upper threshold of IC2a’s input is reached, its output goes low again and the cycle repeats. The frequency is varied by means of trimpot VR1. LC oscillator The LC oscillator works by successively charging and dis­ charging a .022µF capacitor via inductor L1. When power is first applied, pins 1 & 2 of IC1a will be low (because the .022µF capacitor is discharged) and the pin 3 output of IC1a will be high. The capacitor is then charged through inductor L1. When the voltage at pins 1 & 2 reaches the upper threshold of IC1a, its output goes low and discharges the .022µF capacitor via L1. This cycle repeats endlessly. The 180pF capacitor at pin 3 of IC1a makes the oscillator immune to variations in capacitance across the inductor. This means that the oscillator is insensitive to hand capacitance. Without the capacitor, just moving your hand close to L1 would change the oscillator frequency. NAND gate comparator IC1b inverts and buffers oscillator 2 and then NAND gate IC2c monitors both oscillators. Pin 2 monitors pin 10 of IC2b while pin 1 of IC2c monitors IC1b. The output of IC2c is then inverted using IC2d. Fig.2: the circuit is based on two CMOS logic ICs. IC1a is an LC oscillator using an air-cored inductor. If metal is brought close to the inductor, the oscillator frequency changes. May 1998  37 Fig.3: the top trace is the oscillator waveform at pin 10 of IC2b (oscillator 1) while the second trace is the output of oscillator 2 at pin 4of IC1b. This is what happens when there is no metal close to the inductor. LOUDSPEAKER SALE Limited stocks Prices include sales tax Australian Audio Consultants PO Box 11 Stockport SA 5410 Phone or Fax 08 85 282 201 Vifa D25AG-35-06 Vifa D19SD-05-08 Vifa D19TD-05-08 SEAS ExcelT25-001 Vifa M11WG-09-08 Vifa P17WJ-00-08 Vifa M22WR-09-08 Vifa M26WR-09-08 SEAS Excel W11CY001 SEAS Excel W17CY001 SEAS Excel W21EX001 Scanspeak D3806/8200 Dynaudio 20W75 Dynaudio 15W75 Car Speakers Vifa M26WR-19-04 Vifa M26WR-29-04 DVC Vifa M22WR-19-04 Vifa M22WR-29-04 DVC $69.00 $45.00 $49.00 $25.00 $62.00 $20.00 $194.00 $110.00 $99.00 $50.00 $99.00 $75.00 $195.00 $110.00 $229.00 $135.00 $264.00 $125.00 $284.00 $140.00 $329.00 $250.00 $181.00 $50.00 $296.00 $150.00 $257.00 $120.00 $229.00 $150.00 $249.00 $159.00 $195.00 $120.00 $210.00 $125.00 Other Vifa car speakers available Call for full specs on any driver 38  Silicon Chip Fig.4: this is what happens when an metallic object is brought close to inductor L1. The upper trace frequency remains the same as expected at 299kHz, while oscillator 2 frequency shifts, as shown on the middle trace. The resulting inverted NAND com­parator output on the bottom trace is a varying pulse width waveform. A NAND gate has a high output unless both inputs are high. The oscilloscope waveforms of Figs.3, 4 & 5 show what happens. On Fig.3, the top trace is the oscillator waveform at pin 10 of IC2b (oscillator 1) while the second trace is the output of oscillator 2 at pin 4 of IC1b. The bottoms trace is an inverted NAND gate output at pin 4 of IC2d. Note how the oscillator frequencies and waveforms are virtually the same. Fig.4 shows what happens when a metallic object is brought close to inductor L1. The upper trace frequency remains the same as expected at 299kHz, while oscillator 2 frequency shifts, as shown on the middle trace. The resulting inverted NAND com­ parator output on the bottom trace is a varying pulse width waveform. “So what?”, you might say. Well, these waveforms do not tell the whole story because the oscillator frequencies of around 300kHz are totally inaudible from the loudspeaker. But when we wind down the timebase on the oscilloscope we see what is happen­ ing at audible frequencies. Fig.5 shows the output of IC2d with a metallic object near inductor L1. See how it consists of bursts of signal at a rate of about 1.5ms. This is equivalent to a signal of about 670Hz and is quite audible although the signal is a bit weak at this point in the circuit. Therefore the pulsed signal from IC2d drives the base of transistor Q1 via a 10kΩ resistor. The transistor in turn drives the 8Ω loudspeaker via a 100Ω resistor which provides current limiting. The circuit is shown as being powered from 12V DC but in practice it can be powered from a 9V battery or 9V DC plugpack. Diode D1 protects against reverse polarity connections while LED1 indicates when the power is on. Fig.5: this shows the output waveform from IC2d when a metallic object is brought near induc­tor L1. It consists of bursts of signal at a rate of about 1.5ms. This is equivalent to a signal of about 670Hz and is quite audi­ble through the loudspeaker. Construction All the parts are mounted on a PC board measuring 104 x 69mm and coded 04405981. If need be, the PC board can be mounted into a plastic Table 1: Capacitor Codes ❏ Value   IEC ❏ .022µF   22n ❏ 390pF 390p ❏ 180pF 180p EIA 223 391 181 Fig.6: this is the component layout for the PC board. The loudspea­ker’s magnet is fixed to the PC board using super glue. Table 2: Resistor Colour Codes ❏ No. ❏  1 ❏  1 ❏  2 ❏  1 Value 10kΩ 2.2kΩ 1kΩ 100Ω 4-Band Code (1%) brown black orange brown red red red brown brown black red brown brown black brown brown 5-Band Code (1%) brown black red brown brown red red black brown brown brown black black brown brown brown black black black brown May 1998  39 Parts List 1 PC board, code 04405981, 104 x 69mm 1 40mm diameter Mylar 8Ω loudspeaker 1 DPDT miniature slider switch (S1) 1 560µH (0.56mH) air-cored choke (L1) 1 4.7kΩ miniature horizontal trimpot (VR1) 6 PC stakes 1 40mm length of hookup wire Semiconductors 2 4011 CMOS NAND gates (IC1,IC2) 1 BC548 NPN transistor (Q1) 1 1N4004 1A 400V diode (D1) 1 5mm red LED (LED1) Fig.7: this is the full-size etching pattern for the PC board. utility case measuring 130 x 68 x 41mm but that won’t be large enough to accommodate the air-cored choke. Fig.6 shows the parts layout for the PC board. Begin construction by checking the board for shorts or broken tracks. This done, insert the PC stakes for the supply input (+12V and 0V), inductor L1 and for the loudspeaker. The resistors can be insert­ed next, using Table 2 as a guide to the values. Alternatively, check each resistor with your multi­meter before it is soldered into the board. The capacitors can be installed next. Take care with the 100µF electrolytic which must be inserted with the correct polar­ity. This done, insert the two ICs making sure that they are oriented correctly. Trimpot VR1, LED1, transistor Q1 and diode D1 can then be installed and soldered in place. When you mount switch S1 you will need to crimp its eyelet terminals so that they will fit into the PC board holes. The loudspeaker is wired to its terminals on the board and then secured with some super glue on the back of its magnet. Finally, connect the air-cored choke to the PC board. Capacitors 1 100µF 16VW PC electrolytic 1 .022µF MKT polyester 1 390pF ceramic 1 180pF ceramic Resistors (0.25W, 1%) 1 10kΩ 2 1kΩ 1 2.2kΩ 1 100Ω Testing Apply power to the circuit and check that LED1 lights when S1 is on. Adjust VR1 until no tone is heard from the loudspeaker. Now bring a metallic object close to the coil and check that a tone is heard. You may need to readjust VR1 for best results. You may also want to experiment with a larger search coil of say 150mm Miscellaneous Solder, super glue diameter and about 50 turns. With the larger diamet­er coil, the detector will be more sensitive to smaller SC metal items. 14 Model Railway Projects Our stocks of this book are now limited. All we have left are newsagents’ returns which means that they may be slightly shop soiled or have minor cover blemishes. Otherwise, they're undamaged and in good condition. Sh soile op d bu HALF PRIC E t SPECIAL CLEARANCE PRICE: $3.95 + $3 P&P (Aust. & NZ) Send your order to: Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number (Bankcard, Visa Card or MasterCard). This book will not be reprinted 40  Silicon Chip Silicon Chip Bookshop SUBSCRIBE   AND GET   10% OFF SEE PAGE 84 Guide to Satellite TV Installation, Recept­ion & Repair. By Derek J. Stephen­son. First published 1991, reprinted 1997 (4th edition). This is a practical guide on the installation and servicing of satellite television equipment. The coverage of the subject is extensive, without excessive theory or mathematics. 383 pages, in hard cover at $55.00. Servicing Personal Computers By Michael Tooley. First published 1985. 4th edition 1994. Computers are prone to failure from a number of common causes & some that are not so common. This book sets out the principles & practice of computer servicing (including disc drives, printers & monitors), describes some of the latest software diagnostic routines & includes program listings. 387 pages in hard cover at $90.00. Video Scrambling & Descrambling For Satellite & Cable TV By Rudolf F. Graf & William Sheets. First pub­lished 1987. This is an easy-to-understand book for those who want to scramble and unscramble video signals for their own use or just want to learn about the techniques involved. It begins with the basic techniques, then details the theory of video encryption and decryption. It also provides schematics and details for several encoder and decoder projects, has a chapter of relevant semiconductor data sheets, covers three relevant US patents on the subject of scrambling and concludes with a chapter of technical data. 246 pages, in soft cover at $50.00. The Art of Linear Electronics By John Linsley Hood. Pub­lished 1993. This is a practical handbook from one of the world’s most prolific audio designers, with many of his designs having been published in English technical magazines over the years. A great many practical circuits are featured – a must for anyone inter­ ested in audio design. 336 pages, in paperback at $70.00. Digital Audio & Compact Disc Technology Produced by the Sony Service Centre (Europe). 3rd edition, published 1995. Prepared by Sony’s technical staff, this is the best book on compact disc technology that we have ever come across. It covers digital audio in depth, including PCM adapters, the Video8 PCM format and R-DAT. If you want to understand digital audio, you need this reference book. 305 pages, in paperback at $90.00. Surface Mount Technology By Rudolph Strauss. First pub­lished 1994. This book will provide informative reading for anyone considering the assembly of PC boards with surface mounted devices. Includes chapters on wave soldering, reflow­soldering, component placement, cleaning & quality control. 361 pages, in hard cover at $99.00. Radio Frequency Transistors Principles & Practical Applications. By Norm Dye & Helge Granberg. Published 1993. This book strips away the mysteries of RF circuit design. Written by two Motorola engineers, it looks at RF transistor fundamentals before moving on to specific design examples; eg, amplifiers, oscillators and pulsed power systems. Also included are chapters on filtering, impedance matching & CAD. 235 pages, in hard cover at $95.00. Guide to TV & Video Technology By Eugene Trundle. First pub­lished 1988. Second edition 1996. Eugene Trundle has written for many years in Television magazine and his latest book is right up date on TV and video technology. 382 pages, in paperback, at $55.00. Electronics Engineer’s Reference Book Edited by F. F. Mazda. First published 1989. 6th edition. This just has to be the best refer­ ence book available for electronics engineers. Provides expert coverage of Your Name__________________________________________________ PLEASE PRINT Address____________________________________________________ _____________________________________Postcode_____________ Daytime Phone No.______________________Total Price $A _________ ❏ Cheque/Money Order  ❏ Bankcard  ❏ Visa Card  ❏ MasterCard Card No. Signature_________________________ Card expiry date_____/______ Return to: Silicon Chip Publications, PO Box 139, Collaroy NSW, Australia 2097. Or call (02) 9979 5644 & quote your credit card details; or fax to (02) 9979 6503. Prices valid until 31st May, 1998 all aspects of electronics in five parts: techniques, physical phenomena, material & components, electronic design, and applications. The sixth edition has been expanded to include chapters on surface mount technology, hardware & software design, semi­-custom electronics & data communications. 63 chapters, soft cover at $160.00. Audio Electronics By John Linsley Hood. Pub­lished 1995. This book is for anyone involved in designing, adapting and using analog and digital audio equipment. Covers tape recording, tuners & radio receivers, preamplifiers, voltage amplifiers, power amplifiers, the compact disc & digital audio, test & measurement, loudspeaker crossover systems and power supplies. 351 pages, in soft cover at $75.00. Understanding Telephone Electronics By Stephen J. Bigelow. Third edition published 1997 by Butterworth-Heinemann. This is 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. ✓ Title Price ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ Guide to Satellite TV $55.00 Servicing Personal Computers $90.00 Video Scrambling & Descrambling $50.00 The Ar t Of Linear Electronics $70.00 Digital Audio & Compact Disc Technology $90.00 Surface Mount Technology $99.00 Radio Frequency Transistors $95.00 Guide to TV & Video Technology $55.00 Electronic Engineer's Reference Book $160.00 Audio Electronics $75.00 Understanding Telephone Electronics $55.00 Postage: add $5.00 per book. Orders over $100 are post free within Australia. NZ add $10.00 per book; elsewhere add $15 per book. TOTAL $A May 1998  41 PRODUCT SHOWCASE Program uses flow charts Fischertechnik has developed a new machine control language using flow charts to describe the sequence of logic functions. The system has been used by universities and companies for the simulation and testing of control systems and their related software. The Fischertechnik software, called LLWIN, runs under Wind­ows 95 or 3.1 and provides a graphical depiction of the flow chart, including decision blocks for switch inputs, action blocks to control each output and other blocks to increment and test up to 99 variables. Other features include a terminal block to aid testing and debugging, time delay block, one-shot block, sub-program blocks and aids such as automatic routing and the ability to add com­ ments and graphics to the program page. The Fischertechnik interface units provide eight digital outputs, two analog inputs and four bidirectional motor outputs. The two analog inputs may be used with potentiometers (for posi­ tion control), light dependent resistors, thermistors or any resistive device between zero and 5kΩ. One interface unit (30566) plugs into the parallel port (LPT1 or LPT2) of any IBM PC-compatible computer. The other ‘intelligent’ unit (30402) connects to the serial port (COM1 or COM2) and allows passive control CPU voltage checker If you are in the business of assembling or upgrading com­ puters, you will have the need to check the voltages on mother­ boards before new microprocessors are installed. Doing this with a multi­meter is at best tedious and at worst, almost impossible. However, it needs to be done otherwise a wrong jumper setting could mean death to a CPU. 42  Silicon Chip where the PC reads the inputs and drives the outputs accordingly; or active control, where the program is downloaded to the interface and then operates indepen­ dently of the PC, allowing the serial cable to be disconnected. Two versions of LLWIN are available. Version 2.04E controls only the 30566 interface and costs $99. Version 2.10E controls both interfaces and costs $199. The 30566 parallel interface is priced at $144.80 while the 30402 interface is $351; these prices do not include sales tax. For further information on this program, contact Procon Technology, PO Box 655, Mount Waverley, Vic 3149. Phone (03) 9807 5660; fax (03) 9807 8220. The solution is this CPU voltage checker. You plug it into the CPU socket and it displays the voltage on the 7-segment LED readout. It will check Socket 5 & 7 voltage settings as well as MMX dual I/O core voltages. The CPU voltage checker is priced at $99 including sales tax and is available from Microgram Computers, 1/14 Bon-Mace Close, Berkeley Vale, NSW 2261. Phone (02) 4389 8444 or fax (02) 4389 8388. Charge alkaline & NiCd batteries with Lazer­Charge broadcast quality Designed and engineered in Australia by Digital Works Engi­neering, the LazerCharge can recharge nicad and alkaline batter­ ies, including AA, AAA, C, D and 9V types, as used in toys, audio equipment, cameras and other electronic equipment. It automatically detects the type of battery to be charged and is capable of charging different size batteries. Charging time can be as short as one hour but in some cases fully charging a very low battery could take up to six hours. Once a battery is fully charged, the unit automatically switches to trickle mode. The unit employs an AlkalineMax(TM) charge control- ler and microprocessor. Very reasonably priced at $69, you can buy the LazerCharge direct from Digital Works Engineering, 188 Victoria St, Footscray, Vic 3011. Phone (03) 9396 1079; fax (03) 9396 1080. Turn your hobby into your career Electronics Technology Certificate. This course is aimed at electronics enthusiasts who may not have formal qualifications in electronics yet have devel­oped their skills via their hobby and now wish to pursue a career in The Open Training and Education Network (OTEN) offers over 200 TAFE courses via mail, including the ACN 073 916 686 embedded computers designed for the real world Put some intelligence in your next project! MC112 - 68HC11 processor, 32k RAM, 32k EPROM, serial, parallel, timers, A/D converters, BUFFALO software with inbuilt assembler / disassembler and bootloader. $220 Postage and handling $10. Available soon - ARM-based RISC, DSP and PIC systems • RISC • DSP • Parallel • Microcontrollers • Ultra low power • High Performance • Data Acquisition • Control Systems • Neuro-fuzzy • 8, 16, 32 and 64 bit WE HAVE THE SOLUTION Embedded Pty Ltd Level 5 371 Queen St Brisbane GPO Box 2603 Brisbane 4001 Phone: Fax: AUDIO MODULES (07) 3236 5977 (07) 3221 0549 Manufactured in Australia Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 9476-5854 Fx (02) 9476-3231 electronics or telecommunications. Studying with OTEN enables students to complete most of their course at home or work, although practical sessions are necessary for some courses. Details are available at time of enrolment. The modules in the Electronics Technology Certificate are recognised by the National Metals and Engineer- NORBITON SYSTEMS NS_PC101 card for XT/AT/PCs allows access to 48 I/O lines. There are 5 groups (0 to 4) available on a de-facto industrial standard 50-way ribbon cable used in STEbus and VMEbus 19" rack mount control systems. The board uses 2 x 8255 ICs. Multiple boards can be used if more I/O lines are required. NS_LED PCB gives visual access to five groups (0 to 4) of the NS_PC1OX. There is a total of 40 status LEDs. The board offers a 25-way “D” type female socket. The lines are driven by 74244 ICs & configured as a parallel printer port. This socket gives access to printer port kits, eg, stepper motors, LCDs, direct digital synthesis. NS_16_8 PCB is a system conditioning card with 16 optically isolated inputs set up for either 12V or 24V operation. The board provides 8 single pole, double throw relays with 10 Amp contact rating. KITS & CARDS NS_DC_DC is a step down converter with an input range 11 to 35V DC and an output of 5 volts DC at 5 Amps, with an output ripple of approx 150mV. There is an IN/OUT 50-way connector isolating the 5V and 12V+ & 12V- rails of the PC power supply. This segregates PC’s power when working on prototypes. NSDC_DC1 module used with NS_DC_DC & NSDC_DC4 converters is a 5V to 12V(+/-) step- up converter. The board utilises 743 switch mode IC with 2 x 12V regulators, with output ripple of approx 200mV. NS_UTIL1 prototyping board has 1580 bread board holes access to any 3 groups (0 to 4) on the 50-way cable pinout. Power is available from the 50-way cable format 5 volts at 2 Amps & 12V+ 12V- at 1 Amp. There is provision for array resistors with either a ground or positive common connection. For brochure write to: Reply Paid 68, NORBITON SYSTEMS, PO Box 687, Rockingham WA 6968 Email: norbiton<at>bigpond.com May 1998  43 Piezoelectric tweeters For sheer efficiency, piezoelectric tweeters are unsur­passed and they are made in a range of models to suit a variety of applications, mainly for PA and music sound reinforcement. This LeSon range from Altronic Distributors has four models which range in efficiency from 95dB to 106dB at 1 metre for a 2V input and a maximum equivalent program input ranging from 150W to 1kW equivalent to 8Ω). The four models in the range are the C-6175, a 230 x 125mm horn tweeter selling at $39.00, the C-6180 160 x 116mm phase aligned cluster tweeter selling at $89.00, the C-6205 63mm auto­motive dome tweeter selling at $19.95 and the C-6215 74mm dome tweeter selling at $29.95. All are well finished and can be connected via a 4.7µF 63VW capacitor to serve as the crossover network. For further information, contact Altronics at 174 Roe St, Perth, WA 6000. Phone (08) 9328 2199; fax (08) 9328 4459. ing Training Advisory Board and the National Electrical and Electronics Industry Com­mittee. For further details, contact Flynn Henry, Senior Head Teacher, Electrical Engineering, OTEN Industry section. Phone (02) 9715 8467; fax (02) 9715 8492 AC clampmeter for DMMs Jaycar Electronics has released an AC clampmeter adaptor that plugs into a DMM to allow AC measurement up to 300 amps. The adaptor produces 1mV per every 0.1A measured, allowing a maximum of 200A on a typical 2V DMM range. DMMs with a 3V range or there­ abouts can take advantage of the adaptor’s full measuring capacity of 300A. The adaptor features a moulded hand guard for increased safety, a 3-metre extended curly cord and shroud­ ed 4mm banana plugs. The adaptor’s housing is a durable ABS 44  Silicon Chip C6215 C6175 C6180 C6205 plastic, with the meter’s overall weight coming in at just 220grams. The QM-1565 adaptor is available through all Jaycar stores for $39.95. Contact Jaycar’s head office on (02) 9743 5222 for a Jaycar store or dealer closest to you. Dual axis accelerometer The new ADXL202 from Analog Devices Inc is a low power (250µA Fluke 80 Series III multimeters First introduced in 1988, the Fluke 80 series multi­meters have recently been upgraded and are now able to withstand voltage surges to 8kV and are independently tested to meet IEC Category III 1kV safety standards. The 80 Series III multimeters also incorporate LED back­lighting for the LCD which has larger digits and improved viewing angle. Another improvement is a back access door which enables the user to change batteries without break- per axis) two axis accelerometer with a digital output which can be fed to a number of low cost microcontrollers. No D/A converter is required. The outputs are duty cycle modulated (DCM) signals with the ratio of pulse width to period proportional to the acceleration in each of the two sensitive axes. For further information, contact Analog Devices, PO Box 2098 Rosebud Plaza, Vic 3940. Phone (03) 5986 7755; SC fax (03) 5986 4688. ing the calibration seal. Models 87 and 87/E have a 4 1/2-digit display mode. Fluke 80 Series III multi­ meters come with a lifetime war­ ranty and are now available from Philips Test & Measurement dis­tributors. For further information, contact Philips Test & Meas­ urement, 34 Waterloo Road, North Ryde, NSW 2113. Phone (02) 9888 8 222; fax (02) 9888 0440. 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 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. cial See Spe – er Subs Off Page 84 $A SUBSCRIPTIONS  New subscription – month to start­­____________________________  Renewal – Sub. No.________________    Gift subscription  GIFT SUBSCRIPTION DETAILS RATES (please tick one) 2 years (24 issues) 1 year (12 issues) Australia (incl. GST)  $A135  $A69.50 Australia with binder(s) (incl. GST)**  $A159  $A83 New Zealand (airmail)  $A145  $A77 Overseas surface mail  $A160  $A85 Month to start__________________ Overseas airmail _____________________________  $A250  $A125 **1 binder with 1-year subscription; 2 binders with 2-year subscription YOUR DETAILS Your Name_________________________________________________ Message_____________________ _____________________________ Gift for: Name_________________________ (PLEASE PRINT) Address______________________ _____________________________ (PLEASE PRINT) Address___________________________________________________ State__________Postcode_______ ______________________________________Postcode_____________ Daytime Phone No.____________________Total Price $A __________ Signature  Cheque/Money Order   Bankcard   Visa Card   Master Card ______________________________ Card No. Card expiry date________/________ Phone (02) 9979 5644 9am-5pm Mon-Fri. Please have your credit card details ready OR Fax (02) 9979 6503 Fax the coupon with your credit card details 24 hours 7 days a week Mail order form to: OR Reply Paid 25 Silicon Chip Publications PO Box 139, Collaroy 2097 No postage stamp required in Australia May 1998  53 Do-It-Your Garage Do This view shows the motor drive with the control box mounted close by. Behind is the vane which is moved up or down when the door contacts the cord stops at top and bottom of the door. 54  Silicon Chip rself Automatic oor Opener; Pt.2 Last month we featured the electronic circuitry to con­trol the windscreen wiper motor which powers this chain drive system. This month we complete the job with the presentation of the mechanical details. By RICK WALTERS While there is a fair amount of mechanical work involved in the drive system it should not be beyond the ability of the average handyman with a reasonable array of tools. The garage door we fitted the drive to was about 4 years old but it should be suitable for any roll-up style door. Our door is apparently designed to take a drive pulley as the three bolts Fig.1: the mounting bracket for the motor was made out of a piece of angle iron, 40 x 40 x 200mm. A 15-tooth rear-wheel bicycle sprocket (62mm diameter) was mounted on the wiper motor shaft (see text). you can see in the photos are inserted directly into exist­ing holes in the door spider. Doors of this type always have a three-legged spider which rotates on the central support shaft which is typically a 2-inch pipe. Our first attempt at this drive system was to use a V-belt and pulleys; a large pulley attached to the door spider and a small pulley attached to the windscreen wiper motor. Modern windscreen wiper motors are ideal for this task as they use a ferrite permanent magnet with a very high flux density which gives lots of torque without needing lots of current. They also have a built-in worm-drive reduction gear which prevents the motor from being rotated by the output shaft. This effectively locks the door in position when the motor stops. The third benefit is the fact that the permanent magnet motor can be readily reversed by swapping the leads to the bat­tery; ie, by swapping the supply polarity. Unfortunately this original setup did not work satisfacto­rily. The belt needed a lot of tension and was still prone to slip when the going got tough. Our answer was to go to plan B which uses bike gears and a bike chain for the drive and this has proved to be entirely satisfactory. The pulley can still be seen fixed to the door spider in the photos and it was left there to provide a rigid support for the 46-tooth pedal sprocket. These days pedal sprockets are made from pressed steel and while they are adequate for pushbike use, when the central section is cut out to clear the central door support shaft, they are little on the flimsy side. Mind you, we certainly do not May 1998  55 still in place, with the bike sprocket attached to it. The small sprocket can be bolted or welded to the 60mm plate. It depends on the type you obtain. Drill the motor mounting bracket holes to suit your motor and mount the motor on it. The ends of the chain were joined to establish its length, then the motor bracket was secured to the door frame using two coach screws, allowing just a slight amount of slack in the chain. Make sure the sprockets are in vertical alignment. Just a trace of grease was applied to the chain, once everything was adjusted, to keep it running smoothly. Make sure that the chain you buy matches the sprockets as there are two different sizes. Initial tests Fig.2: a 46-tooth pedal sprocket (about 190mm in diameter) is bolted to a stiffening plate and to the door spider. Spacers are necessary to allow the bike sprocket and chain to clear the end of the roller door but they should not let the bolt threads and nuts get too close to the adjacent mounting bracket. advocate using a large pulley if you are building this project from scratch since the central section will have be cut out. A cheaper and easier solution would be to make a support plate from a round or hexagonal metal plate, say 3mm or thicker. The 46-tooth pedal sprocket (about 190mm in diameter) was bolted to the pulley with 10mm standoffs to give a little clearance for the chain. Fig.1 shows the general concept of how the support disc and bike sprocket is attached. Spacers are necessary to allow the bike sprocket and chain to clear the end of the roller door but they should 56  Silicon Chip not let the bolt threads and nuts get too close to the mounting bracket. The mounting bracket for the motor was made out of a piece of angle iron, 40 x 40 x 200mm. A 15-tooth rear- wheel bicycle sprocket (62mm dia­meter) was mounted on the wiper motor (see Fig.1). The wiper motor shaft was originally fitted with an angled bracket to drive the wiper arms. The bracket was keyed to the gearbox shaft with a D-shaped hole and this took a bit of drill­ing and filing to reproduce in the centre of a 60mm plate. This plate is retained on the shaft with a locking nut. Our photo shows the V-belt pulley Power the motor and run the door up and down a few times to ensure that everything is working smoothly. If the motor tends to labour excessively towards the top or bottom of the door’s travel, the door balance spring may need adjustment. Speaking from experience, this is definitely a two-person job. Disconnect the chain and then run the door up and down by hand to see whether the spring is set to pull the door up or drive it down. Ideally, you want the spring set so that it has no bias and the door is equally easy to push up or pull down. To adjust the spring you need two people, each with a pair of Stillsons to hold each end of the door shaft. Loosen the pipe U-bolts and twist the pipe so that the spring tension just bal­ ances the door. Re-tighten the U-bolts and then run the door up and down by hand to confirm that it is balanced. When you are satisfied, reconnect the chain and run the motor again to confirm your adjustment. Should the door drive motor or electronics fail for any reason, the nut holding the small sprocket to the motor shaft can be undone and the sprocket removed, allowing the door to be manually operated. Limit switches The item that caused the most brain strain was the limit switch system. As you will have noted from last month’s article, the circuit has provision for one or two limit switches. These may be microswitches, reed switches or any other type that comes to mind. For our prototype, we initially tried This view of the windscreen wiper motor shows the small pulley still fitted, in addition to the rear wheel bike sprocket. This general view of the chain drive shows the arrange­ment of the sprockets. The large pulley attached to the door spider is not necessary although you will need a circular plate to add rigidity to the bike sprocket. A chain guard is recommended, as a safety measure. microswitches that are readily available from the usual suppliers but they were found to be too flimsy for this type of application. After several trials and many impolite words the system shown in Fig.3 was evolved. Two pulleys were mount­ ed, top and bottom, on the door guide rail using a 25mm bolt and a 10mm unthreaded spacer. An aluminium bracket was mounted on the bottom rail of the door. The limit switch cord is threaded through this bracket and at the top and bottom of its travel it contacts the respective limit stop. The limit stops are single pieces of the connector strip with the cord threaded through them. The two screws are gently tightened once the correct limit position is found. Depending on which limit stop is contacted by the door bracket, the cord moves the aluminium blade up or down, to oper­ate a single reed switch. A steel strip, which is attached to the aluminium blade, acts as a magnetic shunt when it moves between the magnet and the reed switch, allowing the switch to open. The limit switch setup may have to be adapted slightly to suit your door or you may find it simpler to use an upper and a lower limit switch as shown in the circuit. These can be wired in parallel at the terminal block or looped at the door. Obviously if you use a single switch as we did, only one set of limit inputs will be used. The size of the magnetic shunt will have to be determined by trial and error, as it will depend on the strength of the magnet. When the blade is horizontal the reed switch should be open but as the blade moves up or down it should close. Too small a piece of steel will not let the switch open and too large a piece will never let it close. The piece we used was the width of the blade and 25mm long. This should be a good starting point. Limit switch indicator One additional feature which we found we needed when we were adjusting the limit stops was an indication of when the limit switch actually operated. This was easily added to the controller by soldering a wire to pin 2 of IC1 and another to pin 16, the +12V supply. A 5mm high brightness LED was mounted in a retaining clip on May 1998  57 Fig.3; details of the cord-operated limit switch devised for the door. Two pulleys are mounted, top and bottom, on the door guide rail using a 25mm bolt and a 10mm unthreaded spacer. An aluminium bracket is mounted on the bottom rail of the door. The limit switch cord is threaded through this bracket and at the top and bottom of its travel it contacts the respective limit stop. 58  Silicon Chip Parts List Mechanical 1 12V windscreen wiper motor and gearbox (available from most car wreckers) 1 3mm thick 220mm diameter round or hexagonal steel plate (refer text) 1 3mm thick 75mm diameter steel plate (refer text) 1 46-tooth pedal sprocket (refer text) 1 15-tooth rear wheel sprocket (refer text) 1 bike chain to suit sprockets 1 200mm x 40mm x 40mm x 10G steel angle 2 25mm curtain pulleys 7M curtain cord (for limit switch) Miscellaneous 16-gauge aluminium, bolts, nuts, washers, spacers etc. the front panel below the light. A 3.3kΩ resistor was soldered to the supply wire and the anode of the LED. Its cathode was soldered to the pin 2 wire. Whenever the motor is running pin 1 of IC1 goes high and consequently pin 2 goes low, lighting the LED. When the flipflop toggles, the motor stops and the LED goes out. This is a simple but useful addition. Installation You will need to mount the control box in a suitable loca­tion on the garage wall and connect the external leads. We fur­ther suggest that the control box be as close as possible to the drive motor and the battery should be close by as well, to mini­mise the length of the power leads. Ideally, it would be good to have a 240VAC power point nearby, to plug in the 12V DC plugpack to be used as the trickle charger for the battery. By the way, do not mount the battery on the garage floor and this especially applies if you are using a car battery. Car batteries deteriorate quick­ ly if they are left on a cold concrete floor. The battery should be mounted above ground on its own shelf and should have a cover over it to prevent any possibility of accidental shorts. The limit switch cord runs over a pulley at the top and bottom of the door. The cord is the same as used for curtain and blind pulls. The Local switch should be located in a hidden but conveni­ent position. You don’t want any burglars opening the door to let themselves out. The door should be set to the half open position. The first time the door is operated after power is initially applied it should open. If it closes, reverse the leads to the motor. Overcurrent setting The overcurrent control is wired so that it is most sensi­tive in the fully clockwise position. VR1 should be set anti­clockwise so that the door closes without reversing, but if additional restraint (placing your hand under it) is experienced, it will reverse. Chain guard Finally, we recommend that you fit a chain guard to cover the chain and sprockets to ensure safety. You can either fabricate this yourself from sheet metal or perhaps purchase a ready-made unit from a bicycle shop. Reference Remote Controlled Gates For Your Home, SILICON CHIP, August 1997. An aluminium bracket was mounted on the bottom rail of the door. The limit switch cord is threaded through this bracket and at the top and bottom of its travel it contacts the respective limit stop. May 1998  59 Big HO locomotives like this American outline unit present few problems in installation but smaller British, European and some Australian locomotives will be a real shoehorn job. Part 4: the receiver/decoder modules This month we present the receiver/decoder for the Protopower 16 Command Control system. Each locomotive on the layout needs one of these decoders and the circuit is laid out on two PC boards to enable it to be shoe-horned into the locomotive body. Design by BARRY GRIEGER As discussed in previous articles in this series, the Com­mand Control system impresses a serial data stream onto the track voltage. The serial data stream has blocks of 16 pulses, one pulse for each of the 16 locomotives which can be used on the system. These pulses have an amplitude of 5V peak-to-peak and so form a very “robust” data stream which will not be subject to interference from the commutator hash of typical model locomo­tives. The job of the receiver/decoder is to separate the particu­lar width-modulated pulse for its own locomotive from the block of 16 pulses and then turn that pulse into direction and voltage signals to drive the locomotive’s motor. Essentially, the receiver/decoder can be regarded as a speed and direction control built into each locomotive and get­ting its “throttle” settings from the serial data stream. The speed control part of the circuit will supply up to 1A to the locomotive motor at up to about 13-14V DC. To understand how the receiver/ decoder works, we need to refer to the block diagram of Fig.1 and then to the complete circuit of Fig.2. Fig.1 just shows the main circuit Run your model railway with Command 60  Silicon Chip Fig.1: this block diagram shows the major circuit functions of the receiver/decoder board. The data stream superimposed on the track voltage is demultiplexed by the up/down counter to recover the widthmodulat­ed pulse for the particular locomotive and this pulse is then fed to the servo decoder. functions. On the lefthand side at the top of the diagram you will see the track voltage being fed to a bridge rectifier. The data pulses pass through the bridge rectifier unchanged. The voltage from the bridge rectifier then goes in four separate directions. First, it feeds a 3-terminal 5V regulator (REG1) to drive the three ICs on the receiver board. Second, it is fed via diode D1 to the H-bridge circuit to drive the motor in either direction. Third and fourth, the pulses superimposed on the track voltage are fed in two directions, to the Sync Detector and a Schmitt trigger/buffer (IC1f). The Schmitt trigger/buffer squares and cleans up the signal before feeding it to the CD input of IC2, an up/ down counter which acts as a de­ multiplexer. If you remember, in the encoder described in the February 1998 issue, we had a multiplexer to insert the 16 throttle settings into the pulse waveform. Now, in the decoder circuit, we need the opposite form; a “demultiplexer” to get the throttle information out of the pulse signal. The sync detector, for its part, finds the sync “gap” bet­ween blocks of 16 pulses and feeds the detected sync pulse to the “load” input of IC2. By a mysterious process which we’ll describe later, the up/down counter (demultiplexer) then magically ex­tracts the wanted pulses for the particular locomotive and feeds it to IC3, the servo decoder. This servo decoder turns the width-modulated pulses into direction and speed signals which drive the H-bridge and this in turn, drives the locomotive motor forward or backward at any speed between stop and “flat chat”. Well, the broad overview is just that, a broad overview and it doesn’t really tell you how the same track voltage can provide the power for the motor and the ICs as well as the speed and direction information. To really understand the nitty-gritty of the circuit operation, we need to have a detailed look at Fig.2. Circuit description Again, you will see the bridge rectifier, BR1, on the lefthand side of the circuit and it is fed with the track vol­tage, via the wheels and current pickups of the locomotive. Remember that the track voltage is 11V DC with a 5.9V pulse signal superimposed on top, giving a total track voltage of about 16.9V peak. The track voltage passes through the bridge rectifier virtually unchanged, apart from the voltage losses in the bridge diodes of about 1.3V. So after the bridge rectifier we have about 10V DC with a 5.6V pulse signal still superimposed on top. This “composite” track voltage is then fed via diode D1 Control May 1998  61 Fig.2: three ICs perform the crucial functions to drive the locomotive motor with a pulse-width modulated (PWM) signal via the H-bridge transistors. These also provide forward and reverse operation. to the H-bridge circuit which drives the motor. There is a small amount of filtering provided by capacitor C13 but it is mainly there to remove commutator hash from the motor. At the same time, track voltage from BR1 is fed directly to REG1, the 78L05 3-terminal regulator, to provide 5V DC to power the three ICs. The fact that the 5.6V pulses are riding on top of the DC input to the regulator makes little difference to its performance. Counting the pulses As well as drawing DC power from the track voltage, the receiver circuit must decode the data stream. So, following the bridge rectifier, the track voltage is fed via a 10V zener diode which effectively removes the 10V DC and just leaves the 5.6V pulses to 62  Silicon Chip be fed to a voltage divider consisting of resistors R1 & R2. From there, the signal voltage goes to the inputs of two 40106 Schmitt trigger inverters, IC1a & IC1f. IC1f squares up the pulse signal and feeds it to the CD (count down) input of IC2, the 40193 pre­settable up/ down counter which functions as the demultiplexer. IC2 has four data inputs (pins 1, 9, 10 & 15) which can be hard-wired (high or low) to set the wanted channel. Upon the application of a “load” pulse to pin 11, IC2 counts down by 16 from the preset channel so that the decoded output is present at the Borrow terminal (pin 13). Now before we go too far, we’ll clear up a possible area of confusion. We have said that the Command Control system uses a serial data block of 16 pulses and so it does. But the 40193 is a binary counter so it counts up from 0 to 15 or down, from 15 to 0. So while we might be talking about the overall system having 16 channels, IC2 actually counts down from a count of 15 to as far as zero, if channel 1 is required for the particular receiver/ decoder. If we’re talking about a locomotive on channel 4 or the 4th pulse in the data stream, we preload the counter using the four data inputs so that IC2 gives an output when the 4th data pulse is reached. What actually happens is that IC2 counts down until it reaches a count of 4, whereupon the “Borrow” output at pin 13 goes low. It goes high again as soon as the input at pin 4 goes high. Hence the output pulse at pin 13 lasts as long as the relevant 4th pulse in the data stream fed to pin 4 and so we have recovered the wanted data pulse and it is inverted by IC1d before being fed to IC3, the servo decoder. Fig.3: these waveforms show how IC2 recovers the correct width modulated pulse from the data stream. The top trace shows the data signal fed to pin 4 of IC2. Below that, the wide negative-going pulse is the “load” signal fed to pin 11 of IC2. The bottom trace is the output of IC1d, at pin 8. Note that the narrow positive-going pulse of the bottom trace is an inverted version of the wanted 4th pulse in the data stream on the top trace. Fig.5: these waveforms show the operation of the servo decoder, IC3. The top trace shows the input pulse for forward motion. The middle trace shows pin 5 pulsing low at the same rate as the input pulse while the bottom trace, pin 9, stays high. We can see this sequence of events in the waveforms of Fig.3. The top trace shows the signal fed to pin 4 of IC2. Below that, the wide negative-going pulse is the “load” signal fed to pin 11 of IC2. The bottom trace is the output of IC1d, at pin 8. Note that the Fig.4: these waveforms show the operation of the sync detector or “sync stripper”. The top trace is the inverted data stream at pin 2 of IC1a. The middle trace is the integrated pulse waveform at pin 5 of IC1c with its series of little “teeth” followed by a big tooth. The bottom trace at pin 6 of IC1c shows how the little teeth have been completely erased while the big tooth becomes a wide negative-going pulse, somewhat narrower than the big sync pause in the top waveform but still wide enough for our purpose. Fig.6: these waveforms show IC3’s operation for reverse motion. The top trace is the input (note its greater width than in Fig.5). Pin 5 (middle trace) now stays high while pin 9 (bottom trace) pulses low. narrow positive-going pulse of the bottom trace is an inverted version of the 4th pulse in the data stream on the top trace. Sync pulse detection Before we can look at how IC3 works, we need to understand how the sync or “load” pulse fed to pin 11 is obtained from the pulse stream. This is achieved by inverter IC1a, diode D2, R3 & C3, together with inverter IC1c. We noted previously that the track May 1998  63 Fig.7 (above): this is the STOP condition for the receiver/ decoder. The input pulse (top trace) is close to the nominal neutral condition at 244µs wide so that both pin 5 (middle trace) and pin 9 (bottom trace) stay high and keep all the H-bridge transistors turned off. Fig.8 (right) shows some of the waveforms across the motor when it is driven signal is fed via zener diode ZD1 to a voltage divider consisting of resistors R1 & R2 and then to Schmitt trigger inverters IC1a & IC1f. IC1f does precisely the same job as IC1a but it then drives a network consisting of diode D2, resistor R3 and capacitor C3. R3 and C3 can be regarded as a pulse integrator, with R3 feeding a slight positive charge to C3 for each pulse on the data line but C3 is then discharged by diode D2 as each pulse drops to zero. However, when the much longer positive sync pulse arrives from IC1a, capacitor C3 is able to charge to a much higher vol­ tage before being discharged by diode D2. The result is a wave­form with 15 little “teeth” followed by a big “tooth” represented by the integrated sync pulse. This waveform is fed to Schmitt forwards. The top trace is the output pulse at pin 5 of IC3 and the middle trace is the waveform at the commoned collectors of Q5 & Q7. The bottom trace is the waveform on the other side of the motor, at the commoned collectors of Q4 & Q8. Note that the middle trace shows the remnant pulses which are superimposed on the track voltage. trigger IC1c which ignores the little teeth and squares up the big tooth to form the recon­stituted sync pulse which becomes the “load” signal for counter IC2. The waveforms of Fig.4 show the above process in action. The top trace is the inverted data stream at pin 2 of IC1a. The middle trace is the integrated pulse waveform at pin 5 of IC1c with its series of little “teeth” followed by a big tooth. The bottom trace at pin 6 of IC1c shows how the little teeth have been completely erased while the big tooth becomes a wide nega­tive-going pulse, somewhat narrower than the big sync pause in the top waveform but still wide enough for our purpose. The above process is sometimes referred to as “sync strip­ping” whereby the small pulses are “stripped out” of the wave­form, leaving just the sync pulse. The waveforms of Fig.4 give a graphic illustration of this process. Servo decoder So now we have the actual pulse information for the locomo­tive, it needs to be turned into speed and direction Capacitor Codes ❏ ❏ ❏ ❏ ❏ ❏ Value IEC Code EIA Code 0.1µF 100n  104 .015µF  15n  153 .01µF  10n  103 .0047µF  4n7  472 .001µF  1n0  102 Resistor Colour Codes ❏ No. ❏  1 ❏  1 ❏  1 ❏  1 ❏  1 ❏  7 ❏  2 ❏  2 64  Silicon Chip Value 1MΩ 100kΩ 68kΩ 3.3kΩ 2.2kΩ 1kΩ 620Ω 470Ω 4-Band Code (1%) brown black green brown brown black yellow brown blue grey orange brown orange orange red brown red red red brown brown black red brown blue red brown brown yellow violet brown brown 5-Band Code (1%) brown black black yellow brown brown black black orange brown blue grey black red brown orange orange black brown brown red red black brown brown brown black black brown brown blue red black black brown yellow violet black black brown This is the finished receiver/decoder board, shown here larger than actual size. Note the way in which all the resistors are mounted end-on. Some of the resistor pigtails then become convenient test points in case you have to troubleshoot the board. The H-bridge board has the four Darlington output transistors laid flat and stacked to minimise height. Fig.10: the artwork for the two PC boards, shown twice full size. Fig.9: the wiring details for the receiver/decoder and H-bridge PC boards. No not forget to install the links under IC1 & IC2 before soldering these chips in and take care to ensure that all polarised parts are correctly oriented. Note that the PC boards are shown twice actual size, for the sake of clarity. Fig.11: the four Darlington output transistors are laid flat and stacked on the H-bridge board to reduce the height. May 1998  65 The receiver/decoder and H-bridge boards are a neat fit inside the shell of this locomotive. Each loco will need the boards installed in a particular way to fit everything in. It is most important to make sure that there are no shorts to the motor or locomotive chassis. signals to drive the motor. This job is done by IC3, the ZN409CE servo decoder. There are no servos in this circuit but the ZN409CE was originally designed to drive the servo motors used in radio-controlled aircraft, cars, boats and so on. For those not familiar with how a servo drive circuit works, you can find a full description in Bob Young’s “Radio Control” column in the November 1997 issue of SILICON CHIP. You can also refer to a servo circuit employing the ZN409CE in the “Circuit Notebook” pages of the December 1997 issue. Now when the ZN409CE is used to drive a servo it compares the incoming pulse at pin 14 with an internally-generated pulse which is varied by a potentiometer driven by the servo motor. The potentiometer’s wiper is connected to pin 3. When the two pulses match, the servo comes to a stop in the desired position. Where our circuit varies is that the potentiometer (VR1) is not driven but is set to match the internally generated reference pulse to the incoming pulse when the throttle setting is for STOP. This corresponds to a nominal pulse 66  Silicon Chip width of 244µs which corresponds in turn to the crystal-derived pulse frequency of 2048Hz. Thus, when the input pulse is narrower than the reference pulse of 244µs, the locomotive motor is driven forward; when it is wider than 244µs, the locomotive motor is driven in reverse. Motor drive Pins 5 & 9 of IC3 are the outputs and these drive transis­tors Q2 & Q1 which provide level shifting and signal inversion to Q3 & Q6. In turn, Q3 & Q6 drive the H-bridge transistors Q4, Q5, Q7 & Q8. To drive the locomotive in the forward direction, pin 5 of IC3 pulses low at the same rate as the pulse train at pin 14 (the input) while pin 9 stays high. Tracing that through, this means that Q1, Q6, Q7 & Q8 stay off while Q2, Q3 & Q5 are pulsed on. Q4 is also turned on, by dint of the pulse signal from the collector of Q3 but Q4 is turned full on because of the 1µF filter capaci­tor at its base – see the waveforms of Fig.8. To drive the locomotive in the reverse direction, pin 5 of IC3 stays high while pin 9 pulses low. This means that Q2, Q3, Q4 & Q5 are turned off while Q1, Q6 & Q8 are pulsed on. Q7 turns on fully because of the 1µF filter capacitor at its base – see the waveforms of Fig.8. Finally, the waveforms of Fig.7 show the STOP condition. Here the top trace is the input pulse to pin 14 of IC3 and the other two traces are the outputs at pins 5 & 9. Both are high, leading to the condition where all the transistors in the H-bridge are off. Fig.8 shows some representative waveforms across the motor when it is being driven forwards. The top trace is the output pulse at pin 5 of IC3 and the middle trace is the waveform at the commoned collectors of Q5 & Q7. The bottom trace is the waveform on the other side of the motor, at the commoned collectors of Q4 & Q8. Note that the middle trace shows the remnant pulses which are superimposed on the track voltage. By the way, we have referred to pin 5 pulsing when the motor is going forward and pin 9 pulsing when the motor runs in reverse. At the same time, whenever the motor is being driven forward, Q9 and Q10 turn on to drive the locomotive’s headlight. No doubt some enterprising modellers will want to extend the headlight drive to drive the headlights and tail lights of diesel locomotives to cater for both directions. For the time being at least, this is beyond the scope of this article. PC board assembly Two PC boards are used to accommodate the receiver/decoder circuitry. The main board measures 53 x 30mm and is coded 09105981 while the smaller board for the H-bridge transistors measures 25 x 26mm and is coded 09105982. The main board is quite crowded and you will need to solder it carefully to avoid solder splashes shorting out adjacent conductors. Before installing any components on either board, check the copper patterns carefully for any open circuit tracks, bridges or undrilled holes. Fig.9 shows the component layout for both PC boards and the interconnecting wiring between them. Before soldering any components in, install the short links under IC1 & IC2. Then insert all the resistors which are in­ stalled “end on” to conserve space. The diagram of Fig.9 actually does show how the bodies of the resistors are oriented. For example, the body of resistor R10, from pin 5 of IC3, is nestled up to transistors Q2 and Q9. It is important to orient the resistor bodies in the same way as depicted on Fig.9 because the accessible resistor pigtails then become test points if you have to troubleshoot the receiv­er/ decoder. Hopefully, you won’t have to do any troubleshooting but if it comes to the crunch, it’s nice to have those test points accessible. Make sure that you check the value of each resistor as it is installed. Use your multimeter to physically check each value because it is almost impossible to check resistor colour codes once the resistors are all installed and obscured by other com­ponents. Next, install the zener diode, bridge rectifier, the two diodes and the capacitors. Note that all the polarised components must go in the right way otherwise the circuit won’t work or it may be damaged. All the electrolytic capacitors on the PC boards are tantalum types, specified because of their small size. C6, the .018µF capacitor connected to pins 1 & 2 of IC3, must be an NPO ceramic type. If you can’t obtain .018µF, you can use a value of .015µF but it still must be NPO. Do not substitute other capacitor types here, such as Fig.12: this diagram shows how to hook up a temporary throttle potentiometer and reversing switch to the encoder PC board (published in March 1998) so that the receiver/decoders can be tested. MKT polyesters, because their temperature coefficient is just not good enough. Next, insert the 78L05 regulator and the transistors. Finally, the three ICs may be inserted and soldered. Do not use sockets as there is not enough room on the board. Finally, there are two long insulated links to be installed, one on top and the other on the underside of the board. H-bridge board The H-bridge board has only a few components on it but there is a preferred order of assembly. First, insert May 1998  67 Another American HO locomotive installation. The receiver/decoder is at one end while the H-bridge board is at the other. Note that these are early prototype boards and differ from those shown in Fig.9. the end-on resistors, followed by the two tantalum capacitors and the three small-signal transistors. Then mount the four power transistors, Q4, Q5, Q7 & Q8. Mount Q4 & Q5 first. You will need to bend their leads at rightangles, close to their bodies. They should both sit flush with the PC board, with their metal mounting surfaces facing down. This done, bend the leads of Q7 & Q8 at rightangles in the same way and mount them so that they sit flush on top of Q5 & Q4, respectively. Q7 & Q8’s metal mounting surface should face up, as shown in the photos. Finally, mount the 2.2µF electrolytic capacitor. Testing To test the boards you will need to temporarily intercon­nect them with short lengths of hookup wire and you will need to program the receiver board so that it can be addressed by the Command/Power Station, described in the February and March 1998 issues. The programming involves tying four pins on IC2, the 40193 programmable up/down counter. Table 1 shows how the pins are tied high (H) or low (L) and we are using channel designations 1 to 16 rather than the coun­ter’s binary sequence of zero to 15 (as noted previously). If you are doing a batch of these receiver/decoder boards, you will need to make sure that each one is programmed with its own code. Most importantly, you need to label the board with its code as soon as it has been done otherwise you will become very confused later on. So either use a 68  Silicon Chip pencil to write the channel number on one of the ICs or use a little stick-on label to accom­plish the same thing. Once you have programmed the board, you need to hook it up to a locomotive motor. We strongly suggest that you do not in­stall the receiver/ decoder into a locomotive before it has been tested. That would be asking for trouble. Use a spare locomo­tive motor if you have one or any small permanent magnet motor which draws a few hundred milliamps or so. The motor should have a 0.1µF capacitor connected across it to suppress commutator hash, as shown in the circuit of Fig.2 and the wiring diagram of Fig.9. You also need to wire up a temporary “headlight” so that you know Table 1: Program Pins On IC2 C h. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Pin 9 Pin 10 Pin 1 Pin 15 L L L L L L L L H H H H H H H H L L L L H H H H L L L L H H H H L L H H L L H H L L H H L L H H L H L H L H L H L H L H L H L H which direction the motor is turning. We used a red LED in series with an 8.2kΩ resistor to simulate a headlight load for Q10. Using a temporary throttle Since we have not yet described the handheld throttles (that comes next month) it is now necessary to hook up a tempo­rary throttle to the Command/ Power Station, so that it can drive any of the receiver/decoder channels. Fig.12 shows how this is done. You will need a 10kΩ potentiometer and an SPDT switch, wired as shown to the encoder board. The wiper (centre tag) of the potentiometer is connected to the appropriate pin of the 16-pin header socket. We did this by wiring the pot wiper to a length of wire with a cutoff pin from a defunct IC. The pin can then be inserted into any pin socket on the 16-pin header. Table 2 shows the channel numbers and their respective pin numbers on the socket. Power station changes By the way, there are a couple of changes to be made to the Power Station wiring, as noted in the Errata at the end of this article. Having made the appropriate throttle connection and having programmed the receiver/decoder board and connected it across the track outputs of the Command/Power Station you are ready to proceed. Rotate the throttle potentiometer to its minimum setting and set the Forward/Reverse switch to forward. Turn on the Power Station. The motor may buzz or rotate. Don’t worry about that for a moment, just measure the voltage from the 3-terminal regu- lator. It should be close to +5V. This is most convenCh. Pin No. iently measured 1 6 across the three 2 4 ICs: between pins 3 2 7 & 14 of IC1, pins 4 8 8 & 16 of IC2 and 5 1 between pins 6 & 6 7 10 of IC3. 7 3 You should also be able to measure 8 5 about +2.2V be9 11 tween pin 6 (0V) 10 13 and pin 2 of IC3. 11 15 If the motor is ro12 9 tating or buzzing, 13 16 adjust trimpot VR1 14 10 until it stops. Then 15 14 flick the Forward/ 16 12 Reverse switch to reverse and check that the motor is still stationary. Now rotate the throttle potentiometer clockwise and the motor should start running and speed up as you rotate the pot further clockwise. Rotate the throttle pot fully anticlockwise and the motor should come to a complete stop. If it doesn’t, you may need to tweak VR1 again. Now flick the Forward/Reverse switch to forward and rotate the throttle pot clockwise. The motor should now run in the opposite direction to the reverse condition and the headlight LED should come on. Table 2 Troubleshooting What if it doesn’t work as it should? Then you have to put on your thinking cap and figure out why. First, check that the programming for IC2 matches the channel you have selected on the 16-pin header on the decoder board. Second, check that the outputs of IC3, at pins 5 & 9, are working as they should. For example, when forward motion is selected, pin 9 should high, (ie, close to +5V) while pin 5 should be pulsing low. If you don’t have an oscilloscope, you can measure the DC voltage at pin 5. As you advance the throttle, the voltage at pin 5 should gradually reduce. We had a fault with one of our receiver/decoders which demonstrates how easily a typical fault can occur. Regardless of which way the Forward/ Reverse switch was set, the motor always ran in the one direction while the headlight LED did come on correctly for the forward setting. When we checked pins 5 and 9 they performed as they should but the motor steadfastly ran in the same direction anyway. We then checked the voltage at the collectors of transistors Q1 and Q2. The collector of Q1 should be low when pin 9 is high and vice versa. Similarly, the collector of Q2 should be low when pin 5 is low and vice versa. The fault turned out to be a small sliver of solder between the base and emitter of Q1. With a small, tightly packed PC board like this, you need a good magnifying glass and good light to find faults like this. Installing the boards The most important aspect of installing the receiver/decod­er boards in the locomotive is that you must ensure that there are no shorts. The existing locomotive wiring must be removed so that the wheel wipers no longer connect to either side of the locomotive motor or to the locomotive chassis. This is doubly important for locomotives with metal shells. The second most important aspect of installation is to make sure that no part of the receiver/decoder circuit, including the motor itself, is shorted to the locomotive shell, any of the wheel pickups or anything else. In many, if not most, locomotives, you will need to sepa­rate the receiver/ decoder and H-bridge boards to fit them in. For example, the H-bridge board might mount at one end while the receiver/decoder mounts at the other end. It may be wise to sleeve the boards with heatshrink tubing to make installation easier and less subject to shorts. When each locomotive installation is complete, you will need to hook it up to the Command/Power Station again to ensure that it all works as it should. Be sure to label the underside of the locomotive with its channel number. Next month, we will continue with the wiring of the throt­tles and control panel. Errata Command Control Power Station, March 1998: a change should be made to the circuit of page 55 and the component overlay diagram on page 56. R4 should be changed to 2.2kΩ. R5 on page 56 should be 1.5kΩ to agree with SC the circuit on page 55. Parts List For Receiver/Decoder (one required for each locomotive) 1 PC board, 53 x 30mm, code 09105981 1 PC board, 25 x 26mm, code 09105982 1 1kΩ miniature sealed top adjust trimpot (VR1) Semiconductors 1 40106, 74C14 hex Schmitt trigger (IC1) 1 40193 programmable up/down counter (IC2) 1 ZN409CE servo decoder (IC3) 1 78L05 3-terminal 5V regulator (REG1) 3 PN100 NPN transistors (Q3, Q6,Q10) 3 PN200 PNP transistors (Q1, Q2,Q9) 2 BD681 NPN Darlington transistors (Q5,Q8) 2 BD682 PNP Darlington transistors (Q4,Q7) 1 WO4 bridge rectifier (BR1) 1 1N4936 fast recovery diode (D1) 1 1N4148 small signal diode (D2) 1 10V 400mW or 1W zener diode (ZD1) 1 red LED (for temporary headlight) Capacitors 1 2.2µF 63VW PC electrolytic 6 1µF 25VW or 35VW tantalum electrolytic 1 0.33µF 25VW or 35VW tantalum electrolytic 1 0.1µF MKT polyester or ceramic (across motor terminals) 1 .015µF or .018µF 100VW NP0 ceramic 2 .01µF MKT polyester 1 .0047µF MKT polyester 1 .001µF MKT polyester Resistors (0.25W, 1%) 1 1MΩ 1 2.2kΩ 1 100kΩ 7 1kΩ 1 68kΩ 2 620Ω 1 3.3kΩ 2 470Ω Miscellaneous Heatshrink tubing, tinned copper wire, hookup wire, solder May 1998  69 RADIO CONTROL BY BOB YOUNG Radio-controlled gliders While most people think of radio-controlled aircraft as powered models there is a whole branch of radio control devoted to gliders. These can be large, fast and very acrobatic models which are great to watch and even better to fly. In this series of articles we will look at the subtle art of glider flying, including slope and soaring models. As well, we will look at some of the technology used in this very demanding aspect of R/C modelling. We will begin with the two metre class of soaring glider and continue up through slope soaring to the exotic international F3B competition class. The two metre class glider is an officially recognised class of model which is sanctioned by the Model Aeronautical Association of Australia (MAAA). The rules are deliberately aimed at producing a simple model which is ideal for introducing mod­ ellers to the rigorous art of competition glider flying. As a result, clubs run regular competitions for this class) often with a yearly point score) and they are quite popular. The simple model places few demands on the radio equipment and a This close-up view of one of the home-made winches clearly shows the high standard of the workmanship involved. Long metal stakes are used to anchor the winch to the ground, while a car starter motor drives the pulley. Power comes from a heavy-duty 12V car battery. 70  Silicon Chip basic two-channel system will suffice. These simple models usually take little time to build, unlike their ultra-complex cousins, the F3B models. These place extraordinary demands on the radio and require a high level of manual skill and the innovative application of materials technology to produce a competitive model. The two metre and F3B models are primarily intended to be used on flat fields, using hand-tow, bungee or winch-launching and therefore must be designed to withstand the quite consider­ a ble launch stress. Thus these types of models are essentially thermal or soaring models, unlike the slope soaring models which are designed to ride the wave lift from hills. The two types of models have completely different design parameters and we will look at slope soarers in due course. There are various methods of scoring for soaring competi­tions but one simple and popular method is the MAAA thermal soaring point system. Under these rules, each pilot is allowed eleven minutes working time with a maximum eight-minute flight in this period. Thus, there is sufficient time for a re-launch if required. There is no limit to the number of re-launches. Landing points are scored by measuring the distance from the model’s nose to a marked spot after the model has come to rest. One point is given for each second of flight time up to the maximum eight minutes. If the flight exceeds eight minutes then the clock starts to run backwards with one point being deducted for each second over eight minutes. If the flight exceeds eleven minutes then there are no landing points allowed. If the model lands more than one hundred metres away from the marked spot, then the flight does not score at all. It’s not meant to be easy and contests are won on mar­gins of one or two points. Any reader wishing to know more about the fine points of the rules should refer to the MAAA rules book. Reading the sky Everyone has heard about thermals but what are they? Ther­mals are bubbles of hot air which originate on the ground due to local differences in heat absorption which may be due to ground texture, colour or composition. Thus a bitumen car park located in a field covered in moist green grass will generate a local hot spot. The air over the bitumen will gradually warm up and a hot bubble of air will form over the bitumen. This will increase in size until the bubble eventually becomes large enough to break away through the colder air above it. The bubble will start to rise, increasing in size as the air pressure drops with altitude. As the bubble leaves the ground, it often sucks up grass seeds and small insects along with it. Birds quickly find these bubbles and feed off the debris, thus signalling to the alert pilot that here is a thermal to be used when you are ready. Ultimately, the bubble reaches an altitude (and therefore a tempera­ture) at which the originally warm air can no longer hold its moisture and the familiar puffy little cumulus-nimbus cloud begins to form. Thus when you look across a clear blue sky and see those little cotton puffs scattered around, you are looking at the end of a great little thermal in each cotton puff. Flying soaring models requires a very high level of under­ standing on the part of the pilot in regards to the formation of thermals, weather patterns, local conditions and all of the very subtle information available on any one field at any given time. It is no accident that the same small group of pilots dominate soaring competitions. They are usually the very experienced pilots who have learned their craft well and can read the subtle signs available to all on the field but observed only by the few. For example, birds soaring in a thermal are a dead givea­way. Small birds zooming around feeding on the debris give anoth­er clue. Wind-puffs, changes in wind direction and lots of equal­ly subtle pointers are there like Taking the strain – Peter Abel about to launch an F3B model built by Phil Bird. Note that the winch line has been stretched over his shoulder in order to take the strain off the model. signposts in the sky for the experienced glider pilot, all pointing the way to victory at competition level. It takes years to absorb and you have enough learning to deal with just this aspect of glider flying without having to cope with a complex model as well. Thus the two-metre class competition uses simple models which are relatively easy to fly. Launch methods The original and simplest launch method is hand-tow. It requires one or more runners to run across the field, leaping ditches, fences and fallen trees while keeping an eye on the model at all times to ensure the tow speed is not too high. If the tow speed is too high, the model will try to move sideways, resulting in the familiar kite-type looping circle, often striking the ground in the process if the model cannot flick off the line beforehand. The strain of excessive launch speed can also tear the wings off the model. An additional hazard is stalling of the tailplane which will result in a frantic small looping circle which can wrap the towline around the model with no hope of it releasing. This can be a sad spectacle, as you might imagine. Obviously hand tow is only for the young at heart or the very fit. It can result in excellent launches as the tow team can move around the field, keeping the model on the line until a thermal comes through, at which time the model is released. The drawback with hand-tow is that it is difficult to fly the model and tow at the same time, which means that another person or persons are required. This can lead to inconsistency in the launch if the same people are not available each contest. It also requires May 1998  71 Bob Young (foreground) watches as his own-design glider is launched for round 5 of the Heathcote Cup. According to Bob, it was his “last chance” to redeem himself but as it turned out, this flight was no better than his previous efforts. a very skilled tow team to launch a large model and into a thermal to boot and skilled people of this order are not easy to find. A more popular method is the bungee launch in which a fixed length of nylon line is attached to a length of bungee rubber. This is drawn back to a suitable tension and the model is re­ leased. The rubber snaps back to its original length and the model climbs away to launch height. This method is simple and consistent and one man can operate the system quite comfortably. However, the most popular method for contest work is the winch launch. In this method a turn-around pulley is placed at one end of the field and the towline looped though the pulley and returned to the winch. Fig.1 shows the basic con­cept. The line is fitted with a small parachute and a tow ring. The tow-ring is attached to the top of the parachute so that, during the launch, the tension on the line keeps the parachute closed. When the model is released the chute opens, slowing the decent of the line and allowing the winch to wind in the line before it reaches the ground. The rules call for the turn-around pulley to be placed 200 metres from the winch, with a maximum of 400 metres of line on the drum. Winch launches are very spectacular, especially for the larger models, and the glider climbs away vertically at a speed that takes your breath away for the first few launches. Driving these powerful winches takes a deal of skill as it is very easy to rip the wings off the model if you launch too hard. However, used correctly, winch­es result in one-man launches of great consistency and excellent height. A typical winch system consists of an automotive starter motor with solenoid and foot switch, a winch drum with ratchet and a 12V car battery. The foot-switch applies voltage to the solenoid which in turn switches the starter motor. The motor drives the drum directly and the ratchet allows the line to be recovered after the launch. The footswitch is used by the pilot to power Fig.1: winch rules call for the turnaround pulley to be placed 200 metres from the winch with a maximum of 400 metres of line on the drum. 72  Silicon Chip the winch during launch and takes a little getting used to. Depending on the wind speed, the foot-switch may have to be pulsed on and off to adjust the launch speed. There are very strict rules governing the design of the winches for it is here that real advantages can be obtained by a lavish application of technology and money. In the late 1980s, those techno-junkies, the Germans, developed a series of winches for their F3B team which were microprocessor controlled. The winches were mounted on hydraulic rams and the microprocessor sensed the ram pressure which reflected the towline tension. It then adjusted the winch speed to compensate for the wind speed. The cost of these engineering marvels? – $10,000 each and the German team had four of them! The rules now call for a winch motor of no less than 15mΩ armature resistance powered by a 12V battery of a designated size and capacity. No electronics are permitted in the winch switch­ ing, only electromechanical switches. Most winches use a simple foot-switch to actuate one or more solenoids. Parallel solenoids are sometimes used for extra reliability. Once the glider has been launched it is incumbent upon the pilot or winch operator to wind in his line as quickly as possi­ble to prevent any crosswind component blowing the line across the other winch lines on the field. In a contest there may be many winch lines laid out in parallel and there is nothing worse than attempting a re-launch with the clock ticking away, only to find that someone has laid their line right across the top of your line. Once the model has left the line, the real work begins. In still air with no lift of any kind, or worse still sinking air, it is possible to be back on the ground inside three minutes, even from an excellent launch. This means a re-launch if the pilot considers that he can improve his position by doing so. In good conditions a glider can stay up for hours but this is of no benefit in a contest. The rules call for the model to be back on the ground in eight minutes or the clock starts to run backwards. So every trick in the book is used to milk eight minutes from each flight and it is a measure of the pilot’s skill to place the model on Another of the winches is shown here and once again the high standard of the workmanship is evident. The wheels and the handle at the top make it easy to move the unit from one place to another. The launch winches come in all shapes – it all depends on the ingenuity of the builder and the materials to hand. This was the line-up for the Heathcote Cup, held back in March. There are very strict rules governing the design of winches. the ground as close to eight minutes as possible and with the nose resting on the spot landing marker. If all has gone to plan and the pilot wins the round he is given the maximum number of points (1000) and the battle begins anew. There are usually four to six rounds flown in a contest, depending on the number of competitors and the time available. Contest glider flying is good fun and calls for a high level of team effort to ensure a successful day. It can be very physical, chasing towlines and retrieving gliders, and it’s all done against a ticking clock and in a spirit of good-natured competi­ t iveness. For those who enjoy the intelligent application of technology mixed with outdoors exercise and a real and subtle appreciation of nature, I can strongly recommend it. SC May 1998  73 40V 8A Adjustable Power Supply; Pt.2 Last month we provided the circuit details for this com­pletely revised 40V 8A adjustable power supply. This month, we cover the construction. Most of the parts are mounted on a large PC board and there are only two setting up adjustments. By JOHN CLARKE The new power supply is housed in a large plastic instru­ ment case measuring 355 x 250 x 122mm. Our prototype case is light blue in colour although currently available cases come in grey or black, The case uses an internal steel baseplate to provide adequate strength and requires the addition of aluminium front and rear panels rather than the plastic ones supplied. The case and baseplate are 74  Silicon Chip available from Altronics (see parts list from last month). Most of the circuit components mount onto a PC board meas­uring 80 x 94mm, code 04304981. The remaining components are either mounted on the steel baseplate or onto the front or rear panels. Begin assembly of the power supply by checking the copper pattern on the PC board. It should be free of any shorted, missing or open circuit tracks. Check the pattern against the published artwork of Fig.7 to be sure that the board has no faults. Fig.1 shows the component layout on the PC board. You can start by installing the PC stakes first and then the links which can be made from tinned copper wire or from component pigtails. Note that you need to use 1.25mm diameter tinned copper wire for the links between the drains of Q1 and Q2 and transformer T2. The other links can be made from the standard 0.8mm diameter tinned copper wire. Insert the resistors next. You can use the accompanying colour code in Table 1 to check each resistor value, or easier still, use your digital multimeter to measure them. The 5W resis­tors should be mounted with about a 2mm gap between the resistor body and the PC board. This will allow for free air Fig.1: the component overlay for the PC board. Take care to ensure that all polarised parts are correctly oriented. flow to assist cooling. Diodes D5 & D6 can be installed next, along with zener diodes ZD1 & ZD2 (top left of Fig.1). Take care with their orien­tation. The ICs can be inserted at this stage and be sure that each one is oriented as shown and with the correct type number, before it is soldered in place. Check that there are no solder bridges between the pins. By the way, IC sockets are a worthwhile option here. Next, the capacitors can be installed. The MKT polyester types are marked with a value code as shown in Table 2. When inserting the electro- lytic capacitors, make sure they have the correct polarity, as shown on Fig.1. Transistors Q3 & Q4 are installed by pushing them down so that the lower edge of each device body is about 8mm above the board. The trimpots can go in next. VR3, the 5kΩ trimpot, could be marked 502 rather than 5kΩ. Similarly, the 50kΩ trimpot (VR4) may be marked as 503 and the 500Ω trimpot (VR5) may be marked as May 1998  75 501 rather than 500Ω. This coding is similar in principle to the EIA coding on capacitors. The 3-terminal regulator REG1 is mounted on a small heat­sink. Loosely bolt the device and its heatsink to the PC board and bend the component leads at rightangles so that they can be inserted into the allocated holes. Once you have soldered the leads in place, tighten down the screw and nut. Winding the coils Inductor L1 uses the ETD34 transformer assembly and its winding details are shown in Fig.2. It comprises two 20-turn windings wound side-byside. Use 0.8mm diameter enamelled copper wire and terminate one end on pin 3 and the other end on pin 4. Now carefully wind both wires together for 20 turns. Terminate the wires onto pins 11 & 12. Check with your multimeter that there is continuity between pins 3 & 12 and between pins 4 & 11. One of the ferrite cores can be inserted into the bobbin and secured in place with the steel clip. Now place the 10 x 5 x 0.5mm spacers on the two outside core faces and insert the second core. Fit the clip in place to secure this ferrite core in place. The assembly of L1 is now complete with a 0.5mm gap between its core faces. Since the assembly is symmetrical, L1 can be inserted into the PC board either way around. Transformer T2 is a little more tricky to wind than L1. It is wound on the larger ETD44 bobbin and core Fig.2 (above): these diagrams shows the winding details for T2 and L1. Fig.3: the winding details for toroids L2 and L3. Note that the two windings on both cores are wound in different directions. Table 1: Resistor Colour Codes ❏ No. ❏  1 ❏  1 ❏  2 ❏  3 ❏  1 ❏  1 ❏  2 ❏  1 ❏  1 ❏  2 ❏  1 ❏  4 ❏  6 ❏  2 ❏  3 ❏  2 ❏  2 76  Silicon Chip Value 1MΩ 220kΩ 100kΩ 47kΩ 33kΩ 27kΩ 22kΩ 18kΩ 12kΩ 10kΩ 4.7kΩ 2.2kΩ 1kΩ 470Ω 100Ω 47Ω 10Ω 4-Band Code (1%) brown black green brown red red yellow brown brown black yellow brown yellow violet orange brown orange orange orange brown red violet orange brown red red orange brown brown grey orange brown brown red orange brown brown black orange brown yellow violet red brown red red red brown brown black red brown yellow violet brown brown brown black brown brown yellow violet black brown brown black black brown 5-Band Code (1%) brown black black yellow brown red red black orange brown brown black black orange brown yellow violet black red brown orange orange black red brown red violet black red brown red red black red brown brown grey black red brown brown red black red brown brown black black red brown yellow violet black brown brown red red black brown brown brown black black brown brown yellow violet black black brown brown black black black brown yellow violet black gold brown brown black black gold brown Fig.4: this diagram shows the physical layout and wiring of the power supply. For clarity, we have used a numbering system in­stead of showing every single wire interconnection. So, for example, points 1 & 2 on the PC board go to points 1 & 2 on LED1 on the front panel, points 7 & 8 on the board go to points 7 & 8 on potentiometer VR1, and so on. May 1998  77 Fig.5: the mounting details for the Mosfets (Q1, Q2) and fast recov­ery diodes (D1-D4). Table 2: Capacitor Codes ❏ Value ❏ 0.1µF ❏ .01µF ❏ .001µF IEC 100n 10n 1n0 EIA 104 103 102 enamelled copper wire, wind on 13 turns as shown in Fig.3. This winding should cover slightly less than one half of the core. The second winding is also 13 turns of the same gauge wire, wound on the second half of the core. Note the direction of the winding. This toroidal inductor is installed in place on the PC board and held in position with two cable ties, as can be seen in the photographs. Check that the coil wires are soldered correctly by checking for continuity with your multimeter. Inductor L3 is wound on a 33mm toroidal core, in a similar fashion to L2. Fig.3 shows the winding details. It uses 1.25mm diameter wire and has 8 turns per winding. Be sure to wind in the directions shown for each winding. L3 does not mount on the PC board but is connected to the power supply output terminals. We will refer to this later. Insulated links Fig.6: this is a load diagram of the power supply to show how much current is available at various voltages. The maximum power output available is 35V at 8A, corresponding to 280W. This is not much less than the 300VA rating of the power transformer. assembly. It has four quadrifilar (ie, 4 wires wound together) primary windings and a bifilar (2 wires) secondary. Again, the details are shown in Fig.2. Start by soldering four ends of 0.8mm enamelled copper wires onto pins 3, 4, 6 & 7. Now carefully wind all four wires together and each side by side for 15 turns. Terminate onto pins 12, 13, 15 & 16. Note that the wire starting at pin 3 must termi­nate on pin 16; pin 4 must connect to pin 15; pin 6 must connect to pin 13; and pin 7 must connect to pin 12. Check the continuity of each with your multi­meter to ensure that these connections are correct. The secondary is wound with two lengths of 0.8mm diameter enamelled 78  Silicon Chip copper wire, starting on pins 1 & 2. Wind both wires at the same time for 20 turns (the direction of winding is unimport­ant) and terminate at pins 17 & 18. Ensure that the winding starting on pin 1 finishes on pin 18 by measuring continuity with your multimeter. Insert the ferrite cores in through the bobbin and secure them in place with the steel clips. There is no spacer required between the cores for this assembly. T2 inserts into the PC board holes with pin 1 oriented as shown. Toroid coils Inductor L2 is wound on a 44mm toroidal core. Using 1.25mm diameter Two lengths of heavy duty hookup wire can now be connected from PC stakes just below pins 1 and 16 of T2 to the allocated pins above inductor L1. Finally, insert and solder in the two Mosfets (Q1 & Q2) and the four power diodes (D1-D4). The leads for these are inserted into the PC board so that there is about 1mm of lead length below the copper side of the board. Mounting the hardware Now that the PC board is complete, work can begin on the case. We will assume that you are building the power supply from a kit of parts which has all the necessary metalwork drilled out. If you are building the power supply up from blank metalwork, then all holes will need to be drilled and deburred or filed to shape before assembly of the components. Using the wiring diagram shown in Fig.4 as a guide, mount all the hardware onto the baseplate. This includes the transform­ er (T1), the This general view of the interior shows most of the wiring details on the PC board. Note that the two windings on the large toroidal core (L2) at right are wound in different directions. mains terminal block, bridge rectifier (BR1), the earth connections and PC board. The bridge rectifier is mounted with a smear of heatsink compound between the lower face and the baseplate before securing it with a 4mm screw and nut. Note: the baseplate cannot be installed in the case until all the hardware is mounted on it. The power transformer is mounted with a large neoprene washer between it and the baseplate and another neoprene washer between the transformer and the circular retaining plate. It is secured in place with a bolt and nut. Tighten the nut so that the transformer cannot slide around. The primary (orange wires) are terminated at the mains terminal block as shown. The secondary windings are paralleled, with the blue and red wires connecting to one AC (~) terminal of BR1 and the yellow and grey wires connecting to the other AC terminal. The solder lugs for the three earth connections on the baseplate are each secured with a 3mm machine screw, nut and star washer. The PC board is mounted on the baseplate with 6mm spacers and secured with machine screws and nuts. Do not forget the solder lug which is mounted adjacent to the three 1000µF electro­lytic capacitors. The baseplate can now be secured with eight self-tapping screws which tap into integral pillars in the base of the case. Rear panel assembly You can begin the rear panel assembly by attaching the fuseholder (F1) and securing the mains cord into the cord-grip grommet. The Earth wire (green/yellow striped wire) is attached to the solder lug as shown in Fig.4. Make sure that the Earth wire is attached properly to the solder lug and that it is not a dry joint. Alternatively, crimp lugs can be used in place of the solder lugs. Slide a length of heatshrink sleeving over the Active (brown wire) from the mains cord and solder the wire to the centre leg of the fuseholder. Solder another brown wire to the second fuse terminal and slide the heatshrink sleeving over the fuseholder body. This second brown wire and the Neutral (blue) wire attach to the insulated terminal block, as shown. Mosfets Q1 & Q2 and the four diodes (D1-D4) are attached to the rear panel with machine screws. Fig.5 shows the mounting details. Note that the large finned heatsink is secured to the back of the rear panel with the same screws. Apply a smear of heatsink compound between the heatsink and rear panel before mounting. If mica washers are used, these will require a smear of heatsink compound May 1998  79 Fig.7: check your PC board against this full-size etching pattern before installing any of the parts. on both sides of the washer before assembly. If silicone washers are used instead, heatsink compound is unnecessary. Check that the metal tabs of the Mosfets and diodes are isolated from the metal panel by measuring the resistance with a multimeter. The thermal cutout switch, TH1, 80  Silicon Chip is secured with two 3mm screws and nuts. Front panel assembly The front panel should be supplied with a screen printed label and with the cutouts for the meters and other components already provided. If the panel is not supplied with all holes drilled, the meter packaging provides a cardboard template for the necessary cutouts. New scales will need to be installed on the meters to show voltage and current. Firstly, remove the clear plastic escutcheon by undoing the screws on each side of the meter. The meter scale is removed by undoing the small screws on either side. Then carefully slide the scale away from the meter, taking care not to damage the pointer. Finally, install the new scale and replace the plastic cover. Before mounting the meters on the front panel, install the countersunk earth screws which are below the (-) terminal on the voltmeter and below the (+) terminal on the ammeter. Then attach the meters with the supplied spring washers and nuts. Mount the potentiometers (VR1 & VR2), switches S1-S4 and the output terminals on the front panel. Attach the earth solder lugs to the screws and secure these with a star washer and nut. Wiring it up Now the power supply can be wired up. When wiring the mains switch (S1), be sure to use 250VAC-rated wire and slide heatsh­ rink sleeving over the switch body to insulate the terminals. Shrink both the switch and fuseholder sleeving with a hot air gun to secure it in place. Use cable ties to neatly secure the wires together at the fuseholder, terminal block and switch. This is a safety measure, so that if one wire comes adrift, the other wire or wires will keep it in place and prevent it from shorting to the case. Complete the earth wiring from the rear panel to baseplate, baseplate to front panel and GND terminal to front panel using green/yellow mains-rated wire. Use heavy duty hookup wire where indicated to prevent excessive voltage drops and to prevent them fusing. The remaining wiring can be done using medium-duty hookup wire. For clarity on the diagram we have used a numbering system instead of showing every single wire interconnection. So, for example, points 1 & 2 on the PC board go to points 1 & 2 on LED1 on the front panel, points 7 & 8 on the board go to points 7 & 8 on potentio­ meter VR1, and so on. Use a variety of colours so that it will be easier to check the wiring once completed. Install insulating sleeving over the leads to the LEDs. Do not forget the wire from the earth lug on the right hand lower corner of the PC board to the PC stake on the board. The 0.1µF 250VAC capacitor solders across the (+) and (-) output terminals and inductor L3 mounts above this capacitor and is wired as shown. The two power Mosfets and four fast recovery diodes are mounted on the rear panel. Their mounting screws also retain the finned heatsink on the back of the rear panel. The wiring of the front panel is quite tight in parts so you will need to follow the diagram of Fig.4 quite closely. When the wiring is complete, check your work very carefully to ensure that all components are in their correct place on the PC board and that the wiring is correct. You can now bundle the wiring with cable ties where appropriate. Once you are sure everything is correct, insert the fuse into the fuseholder. Also check that there is continuity between the Earth pin on the mains plug and the aluminium front and rear panels and the baseplate. There should be a zero ohm reading on your multimeter when these connections are tested. Testing Attach the lid to the case and apply power to the circuit. If there are no May 1998  81 explosions, switch off the power and remove the lid of the case. Incidentally, when you are first powering up a big power supply or amplifier, it is a good idea to wear a pair of goggles. It is a very rare occurrence for an electrolytic ca­pacitor to fail at switch-on but when they do fail it can be pretty spectacular. Attach the negative lead of your multimeter to the negative (-) output terminal on the PC board located near trimpot VR4. Set your multimeter for 0-20VDC and switch on the supply. Check for +12V at the output of REG1 (the righthand pin), on pins 8, 11 & 12 of IC1, pin 1 of IC2 & IC3, pin 7 of IC4 and pin 4 of IC5. There should be +5V at pin 14 of IC1. If at any stage the readings are incorrect, switch off the power and find the fault before proceeding further. Measure the voltage on the output terminals and check that it can be adjusted from close to 0V up to about +45V. You may need to change ranges on your multimeter as you do this, if it is not an auto-ranging model. If the output voltage does not change when you vary the voltage control, check that the load switch is on and that switch S4 is set for the adjustable position. Calibration Fig.8: here are the full-size artworks for the two meter scales. They can be cut out and used direct if required. These analog oscilloscope waveform photos show the ripple and noise on the output of the power supply when it is delivering 8A. You can compare this with the equivalent digital oscilloscope waveforms published last month. Photo 82  Silicon Chip You can calibrate the voltmeter by comparing its readings against those from your digital multimeter. Typically, the accu­racy of an analog meter movement such as in this pow- 1 (left) shows the ripple at a high scope timebase speed (10µs/div), while photo 2 (right) shows the ripple at a low timebase speed (>2ms/div). Overall ripple is about 50mV RMS. The large finned heatsink is bolted to the rear panel to prevent the output devices from overheating and self-destructing. er supply is about ±3% of full scale deflection (F.S.D.) which is nowhere near as good as the typical digital voltmeter. For best results, you need an output voltage setting which is close to FSD and in this case, that means around +45V or so. Calibrate the voltmeter by adjusting VR4 until the reading on the voltmeter matches that on your digital multimeter. Note that when you make comparisons at lower voltages, there could be an error of 1V or more which is still within the specifications of an analog meter but pretty poor when compared to your digital multimeter. Now switch S4 to the 13.8V position and adjust VR3 for a reading of +13.8V on your digital multimeter. If you are lucky, the reading on the analog meter will be pretty close to 13.8V. If not, don’t worry about it. The ammeter is calibrated by setting your multimeter to its 5A range and connecting it in series with a 0.22Ω 5W resistor across the output terminals. Adjust the output voltage so that a reading of 4A is obtained on the multimeter. Now adjust trimpot VR5 for a reading of 4A. Note that the current adjust control should be rotated fully clockwise during the current calibration to avoid current limit­ing. Other methods Note that this is only one method of calibrating the ammet­ er. Other methods include connecting a known resistance, as measured by your multimeter, across the output terminals and measuring the voltage. The current flow is the voltage divided by the resistance. Now adjust VR5 for this calculated reading. You will need to ensure that the resistance can take the power and that the resistance does not change with current. Even high power resistors will change their resistance as they heat up so they do need to be kept cool, if accuracy is to be obtained. You can make a suitable load resistor from an electric jug element with a tapping taken part way along the wire coil. This coil can be immersed in water to provide adequate cooling. You can check the current limit facility by winding down the current adjust control when a load is connected. When in current limit mode, the overload LED should light. Also, check the operation of the current adjust feature when the set current switch is pressed. You should be able to wind down the current adjust knob until the overcurrent LED just lights. Press the current set switch with the load off to see if it has the same reading. Also pressing the current set switch with the load on should show close to 0A since this is the reserve current read­ing. Finally, we have produced a load diagram of the power supply to show how much current is available at various voltages – see Fig.6. The maximum power output available is 35V at 8A, corre­sponding to 280W which is not much less than the 300VA rating of the power transformer. For settings above 35V, the available current is less but it is still quite SC respectable at 6.5A at 41V. May 1998  83 3 1 2 GREAT REASO SUBSCRIBE NO Every new or renewing subscriber* between now and June 30 gets a FREE copy of the superb SILICON CHIP/JAYCAR Wall Data Chart. THAT’S WORTH $10.95 ALONE! Every new or renewing subscriber* between now and June 30 qualifies for an EXCLUSIVE 10% discount on ANY SILICON CHIP merchandise: books, software, EPROMS & microprocessors, binders, back issues, etc 84  Silicon Chip * This offer applies to Australian subscribers only ONS TO OW TO 3 The best reason of all: you’ll actually save money! Not only will you get your copy of SILICON CHIP BEFORE it’s on the news-stands – it’s cheaper getting your copy mailed direct to you – and you’ll never miss an issue! HURRY! TAKE ADVANTAGE OF THIS STRICTLY LIMITED OFFER TODAY! Yes Please! I want SILICON CHIP delivered every month to my letterbox and I want to take advantage of the exclusive subscribers’ offers. Name............................................................................................. PLEASE PRINT Address.......................................................................................... ....................................................................Postcode..................... ❑ New Subscription (month to start....................................) ❑ Renewal (Sub No from wrapper.......................................) I want ❑ One Year <at> $59 ❑ Two Years <at> $112 or ❑ 1Yr with binder <at> $72 ❑ 2 Yr with binders <at> $138 This is a YES! This offer also applies to GIFT SUBSCRIPTIONS: Call SILICON CHIP to place your order for a gift subscription. Here’s how to order: or or Fax this coupon (or a copy) to SILICON CHIP on (02) 9979 6503 – 24 hours a day Post this coupon (or a copy) to SILICON CHIP, PO Box 139, Collaroy, NSW 2097 You can even order by phone with your Bankcard, Mastercard or Visa Card: Call SILICON CHIP on (02) 9979 5644 9am-5pm, Monday to Friday FAX or POST ORDERS: Card No: Expiry Date:_______/_______ Signature:__________________________ (Yes, we do accept cheques or money orders by post!) May 1998  85 VINTAGE RADIO By RODNEY CHAMPNESS, VK3UG Safety with vintage radios If you don’t know what you are doing or become com­placent, a vintage radio receiver can be a very dangerous device. Here’s some advice to ensure your personal safety. Certainly, we now hear a lot about safety in our communi­ties. One example is road safety and this includes the condition of the roads, road signs, the weather, the amount of traffic, the time of day and traffic speed. We also hear about how cars are being made safer, with ABS brakes, airbags, seat belts, better lights, better tyres and so on. What has this to do with vintage radio you might ask. The only thing it has directly to do with vintage radio is that you and your newly-acquired treasure are more likely to arrive home safely. However, once you’re home, you should follow a few strict procedures when working on a vintage radio set to make sure you stay safe. No warnings Have you noticed all the safety warning signs on your vin­tage radios? No? – well that’s not surprising as there usually aren’t any. Can you pick up and turn over the set you are restor­ing while it is running and not run the risk of putting your fingers on some point that has a lethal voltage onto it? The answer is probably no. Obviously safety was not of much concern to the designers and builders of what are now vintage radios. Manufacturers would not get away with this careless attitude today. With this in mind, it was decided that the subject of safety in vintage radio restoration should be revisited. Some vintage radio buffs like to build replica sets and safety should be one of the prime considerations in the mechanical construction of these sets too. The older the set that is being restored, the more likely it is to have exposed mains and high tension leads and terminals. Some European sets are very bad in this respect, with exposed mains and HT terminals in very easy to touch locations. Take a careful look at the set that is about to be restored and see where the danger points are. Where will your hands go when you are moving the set around? Will your hands touch any of these danger points? It is very easy when concentrating on the job in hand to forget the danger points. Minimising the danger A typical core balance detector. These devices are cheap life insurance at $20-30 so there is no excuse for not having one. 86  Silicon Chip How do you minimise the danger? You could get someone else who is more experienced than you to restore the set! However, most restorers like to do the lot; to be able to proudly say “I did it all myself”. Having observed where the danger points are, it may be possible to put a cardboard or plastic sheet cover over them, or even to physically shift the danger point to a spot where it can not easily be touched. Where I haven’t been able to do any of the preceding things, I have put glue over the exposed terminal. This may not be the most foolproof method of approaching safety but with several layers of glue, your chances of escaping an electric shock or electrocution are much better if you touch something you shouldn’t in a moment of carelessness. Power transformer In many early mains-operated sets, there is the very real possibility that the power transformer insulation may not be as good as it had been in years gone by. It is possible that the mains winding or the wires to the transformer are defective and so a short or partial short to the frame of the transformer and hence the chassis may occur. And a live chassis is a very dan­gerous item indeed. An easy test here is to use the various ohms ranges on a multimeter to test for shorts or leakage between the transfor­mer’s mains winding and the frame or chassis. Any indication other than a momentary kick on the meter is to be treated as a possible dangerous circumstance. If the set has been stored in a damp environment it would be worthwhile putting the set chassis or the transformer alone into the oven in the kitchen. Heat the set for several hours at about 60°C to dry the transformer out and hopefully get rid of the leakage. If leakage is still evident, things are not looking good and a test with a high voltage insulation tester such as John Hill has described or as appeared in SILICON CHIP (May 1996) would be desirable. Note that an ohmmeter will only detect shorts and leakages that are not voltage dependent. An insulation tester, on the other hand, checks the transformer under stresses similar to when it is operating. Before applying any power to the set, it is important to check the insulation of all the various wires to ensure that no short circuits exist. That’s because insulation can deteriorate over the years – some types more than others. Any insulated wire that has badly deteriorated insulation must be replaced or the wire sleeved with insulation tubing. The mains cord must be replaced without further thought if it has cracked insulation. Up until the time that valve sets were being replaced by transistor sets, most sets used twin-core power lead. Ideally, the twin-core lead should be replaced by three-core lead, par­ ticularly where the chassis or other metal can be touched when the set is back in its cabinet (I am only referring to mains-operated sets here). For the sake of authenticity if the set had a fabric cov­ered mains lead it would be nice to replace it with one that looks the same. Burton Cables do produce an unfilled brown fabric 3-core mains cable that looks much the same as the cable being replaced. The 3-pin power plug should also be inspected. The Bakelite on old power plugs may be chipped and a strand of wire could extend beyond the side of the plug – and this could be the Active mains wire! Yes, it is nice to keep the set looking as authentic as possible but safety must be considered and it may mean you have to fit a modern plastic plug. So be it – at least you will be around to enjoy seeing and hearing your set. Core balance detectors These devices go under a variety of trade names and a typi­cal one is shown in the accompanying photograph. What they basi­cally do is detect when there is more current passing through the Active 240V lead than is returning via the Neutral lead. How can this be? If there is leakage or a short from the Active lead to Earth, some of the current will return via the Earth lead – or you, with possible deadly results, if there is no Earth lead. When the current on the Neutral lead is 30 milliamps (30mA) less than through the Active lead, a sensing circuit detects this and trips a small circuit breaker to remove the power. Fig.1 shows a simple diagram of the sensing circuit of a core balance detector. The Active and Neutral leads go through the centre of a toroid ring core. These act as 1-turn primaries of a transformer, while a third winding consists of many turns of wire to act as a step-up transformer. Because the currents through the two single-turn primaries flow in opposite directions and are normally equal, the two magnetic fields cancel each other out and no voltage is developed in the third winding. However, when there is leakage and not as much current flows through the neutral lead, the magnetic fields are not cancelled and so a voltage is developed in the third winding. This is detected in the device which trips the circuit breaker and removes the 240V AC from the lead. The response time for core balance detectors is very fast and your chance of being electrocuted is low, EVATCO TUBE SPECIALS While stocks last 12AT7WC JAN Philips ECG Mil Spec $12.00 12AU7A/5963 $11.00 12AX7WA JAN Philips ECG Mil Spec $14.00 12AX7WA Sovtek $10.00 300B Sovtek Dual Point Matched $125.00 807 AWV Australia E82CC/6189 Siemens Germany $19.00 $20.00 EL34/6CA7 Sovtek or Svetlana Matched $26.00 EL84/6BQ5 Sovtek Matched $17.00 GE Tube Data Manual 1973 473 pages $26.00 TUBE DATA 3.5 DOS Disk 27,000 tubes $53.00 SSAE DL size for CATALOGUE ELECTRONIC VALVE AND TUBE COMPANY PO Box 381, Chadstone Centre, Vic 3148 Tel/Fax: (03) 9571 1160   Mobile: 0411 856 171 Email: evatco<at>mira.net SILICON CHIP This advertisment is out of date and has been removed to prevent confusion. May 1998  87 Fig.1: the basic sensing circuit of a core balance detector. Fig.2: the tone control circuit shown at (a) can be made safer by wiring it as shown at (b). The capacitor voltage rating may need to be increased though. should there be a problem in the set with mains leakage to chassis. These devices are cheap life insurance at $20-30 so there is no excuse for not having one. They also have four power outlets with an overload trip as well. I’ve mounted mine on the back wall of the workbench and plug any devices that I am working on into it. Under some circumstances they will trip when no fault exists, mostly at switch on or switch off of the device being run on the detector. This possibly occurs because the interwinding to frame capacity of the power transformer is being charged or discharged, causing a momentary unequal current to flow through the sensing core. As wonderful as these core balance detectors are, they will not protect you against the effect of voltages after the power transformer. These are every bit as dangerous as the mains, so be vigilant. It is particularly important to be extremely cautious when endeavouring to restore a set that has been “butchered” by someone in its past. You may have picked the set up because it couldn’t be made to work or worse 88  Silicon Chip was even known to be dangerous! Some time ago, I had the task of restoring a commercially-made late 1920s TRF set. It had been considerably “got at” and required a complete redesign to make the set a goer. In the process, I nearly fell for one of the traps mentioned earlier in this article and could have been electrocuted. Now we all tend to believe that the shafts of volume and tone controls are earthed to the chassis, even when the moving arm is physically attached to the control shaft as did occur with some early controls. In this set, they weren’t earthed, having barely visible fibre washers insulating them from the chassis. One was about 50 volts plus above the chassis, while the other was at a whopping 400 volts! I broke out into a cold sweat when I realised how close I’d come to departing this world. Fig.2(a) shows the circuit that the tone control was wired into, while Fig.2(b) shows how it could have been wired and made quite safe. The capacitor voltage rating may have needed to be increased to cope with the DC plus the audio voltages across it. This is a small price to pay for a life possibly saved. One statement that is often made is to work with one hand and have the other in your pocket. It’s often not very practical but the thought is there to minimise your contact with lethal voltages. I often go part way there by clipping a short lead (with small alligator clips) between the set chassis and the negative lead of the multi­meter. The positive lead is the only one then that is being used, so one hand in the pocket is possi­ble. When changing components in a set, always turn the set off at the mains socket and remove the mains plug. You should also short the HT line to the chassis using an insulated lead in case any charge is left in the electro­lytics. It is advisable to show someone else in the home where the main power switch is so that it can be switched off should something untoward happen. And it isn’t a bad idea to have a rubber mat on the floor where you stand to work on your radios, as this will minimise the chance of electric shock. AC/DC sets There are some other rather frightening sets that you may come across from time to time. They are the rare AC/DC sets and the even rarer pure DC sets designed for 240 volts DC. Some of these sets even have one side of the mains lead (Active or Neutral) connected to the chassis. WOW! With care, these sets can be quite safely serviced once you make sure that the NEUTRAL lead is attached to the chassis, not the Active. It is easy enough to change the wiring of the plug over so the chassis is connected to the Neutral, which is also at the same potential as earth. However, this does not mean that all power points are wired correctly, so never assume that the chas­sis will be neutral when plugged into just any power point. These sets are usually quite well insulated so that you cannot touch the chassis when it is in the case. Even into the 1950s, a number of portable AC/DC sets were made like this. They had a 2-pin non-polarised socket that could be put onto the set plug either way so that a “cold” chassis could be obtained. Also when you opened up the set case, the power socket was automatically disconnected. The ones that I mostly serviced in those days were Astors Summary (1). Before applying power to any receiver, check that the trans­former insulation is in good condition, visually and by instru­ments. (2). Check other wiring to make sure no shorts exist in the wir­ing. (3). If the power cord is old and the insulation is at all sus­pect, replace it. The same goes for the plug if it is old and unsafe. (4). If the set is an AC/DC type, make sure that the Neutral is connected to the chassis or the negative bus. Also, do not take it for granted that the power point is wired correctly. The use of an isolation transformer is strongly recommended. (5). Use a core balance detector (CBD) on the mains. With all the above completed, remove the rectifier valve and try the set on power. Check for voltage on the chassis that should not be there, then connect an earth wire to it without touching it yourself. If there are no sparks and the core balance detector does not throw itself out, the chassis will be safe to touch. Run the set for some time like this while you are there to make sure nothing untoward happens to the transformer. Don’t leave the set during this time – it wouldn’t be much fun to come back a few hours later only to find that the set had started a fire. Finally, check and re-check everything at all times to prevent being electrocuted. And never rely on units like a CBD, even though you may have one in use – to do so is to become lazy and complacent. In conclusion, think safety (yours in particular) and you will be restoring SC sets for many years to come. SILICON CHIP SOFTWARE Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. Notes & Errata: this file lets you quickly check out the Notes & Errata for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate any item. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. OR D ER FOR M PRICE ❏ Fl oppy Index (i ncl . fi l e vi ewer): $A7 ❏ Notes & Errata (i ncl . fi l e vi ewer): $A7 ❏ Al phanumeri c LCD Demo Board Software (May 1993): $A7 ❏ Stepper Motor Control l er Software (January 1994): $A7 ❏ Gamesbvm.bas /obj /exe (Ni cad Battery Moni tor, June 1994): $A7 ❏ Di ski nfo.exe (Identi fi es IDE Hard Di sc Parameters, August 1995): $A7 ❏ Computer Control l ed Power Suppl y Software (Jan/Feb. 1997): $A7 ❏ Spacewri .exe & Spacewri .bas (for Spacewri ter, May 1997): $A7 ❏ I/O Card (Jul y 1997) + Stepper Motor Software (1997 seri es): $A7 ❏ Random Number Generator/Chook Raffl e (Apri l 1998): $7 POSTAGE & PACKING: Aust. & NZ add $A3 per order; elsewhere $A5 Disc size required:    ❏  3.5-inch disc   ❏ 5.25-inch disc TOTAL $A Enclosed is my cheque/money order for $­A__________ or please debit my ❏ Bankcard   ❏  Visa Card   ❏ MasterCard Card No. Signature­­­­­­­­­­­­_______________________________  Card expiry date______/______ Name ___________________________________________________________ PLEASE PRINT Street ___________________________________________________________ Suburb/town ________________________________ Postcode______________ Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number (Bankcard, Visa Card or MasterCard). ✂ and Healings. Ideally, if you want to service any of these AC/DC sets, you should use a 240VAC isolation transformer. Straight 240 volt DC sets are a real problem to service as there are probably no locations where 240 volts DC is even avail­able now. Sets like this should be just set aside to admire, unless you care to make a 240 volt DC power supply capable of supplying up to 300mA. My advice is to leave AC/DC and pure DC sets strictly alone, unless you know exactly what you are doing. (Editorial note: we think that they’re death traps). May 1998  89 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. EGO sensor may be dead I recently purchased a fuel mixture display kit (SILICON CHIP, November 1995) and installed it in my car, a 1986 Nissan Skyline with a 3-wire EGO sensor. Initially the readings showed a very lean mixture. Upon inspection, the EGO sensor had a vague white coating. I had the car’s mixture and idle checked and was told everything was fine. I then went on to calibrate the display as per the instructions in an on-road test at a constant throttle opening. For a brief period the display started to oscillate through the green LEDs. Then it started to peak in the yellow LEDs and after few seconds only the furthest yellow LED was illuminated. Further adjustment of the trimpot has had no effect. I replaced the IC but it has been of no help. (G. E., Sydney, NSW). •  From your description of the symptoms, we wonder if in fact your mixtures are correct or if your EGO sensor is faulty. Nor­mally, an EGO sensor will Vertical polarisation for FM antenna I want to build the 5-element FM antenna described in the March 1998 issue of SILICON CHIP. The article is great but I note there is no mention of how this unit could be mounted for optimum reception of vertically polarised signals. Here in Melbourne, and presumably elsewhere, many, if not all, local (low powered) community based broadcasters radiate their signals using vertical polarisation rather than horizontal or circular polarisation. The antenna described in your article would be of immense benefit to the many who listen to these stations and I would ask if a further 90  Silicon Chip have an output in the range from 0V to 1V, with normal mixtures giving a reading of 0.4V to 0.6V and rich mixtures giving a reading of 0.8V to 1V. You can check this with your digital multimeter, although the reading will tend to os­cillate around. If the EGO sensor is giving a reading of say, 0.8V or higher, then the Mixture Meter is doing the right thing by displaying a “rich” LED; ie, amber. If you floor the accelerator, the mixture should always revert to rich and this should be indicated by the Mixture Dis­play. If you have a Gregory’s manual, you should find a procedure in it for checking the EGO sensor. We are inclined to think that the sensor may be faulty. Electric fence has no bite I have a problem with your electric fence controller as it does not produce a high output from the coil. The circuit appears to be working correctly as the output pulses at approximately one second intervals but you can hold your hand to it. 1V can be detected article could be run at some date in the future describing how either your five element yagi or the three ele­ ment commercially produced units could be mounted to obtain optimum performance of these signals. (D. B., Balaclava, Vic). •  The 5-element FM antenna, or any other Yagi antenna for that matter, can be mounted in the vertical plane to receive vertically polar­ ised signals. However, the mast on which it is mounted must be non-metallic otherwise it will interfere with the electrical resonance of the various elements. In practice, you can use a mast made of timber or fibreglass. We would suggest a timber mast of 2-inch dowel and it should be painted to weather-proof it. at the base of Q2 as described in the instructions, however there is no high voltage anywhere in the circuit and the collector of Q2 measures 12V. I replaced the 1.2MΩ 1W resistor with a straight bridge and the 1.5kΩ resistor between pins 6 & 7 of the 555 with a 3.3kΩ resistor without any noticeable difference. The coil is a new one and is meant to be used with a ballast resistor. (J. H., Revesby, NSW). •  If there is insufficient spark from the high tension output of the coil when you have shorted the 1.2Ω resistor in series with the coil and increased the charge time by altering the 1.5kΩ resistor between pins 6 & 7 of IC1, then the only other problems could be that Q1 or Q2 are not functioning correctly. Check that there is a good connection from the case of Q2 to the tracks under the PC board via the mounting screws and nuts (use a multimeter to check this). Also check that zener diodes ZD1-ZD3 are mounted with the correct orientation as shown on the overlay diagram and are actually 75V types. Make sure that Q1 is a BC327 and not a BC337 type. Fast clock runs backwards I refer to the article “A Fast Clock For Railway Modellers” published in the December 1996 issue of SILICON CHIP. I have assembled the module as per instructions and checked the components and their positions. It works but the clock runs anti-clockwise! Swapping leads around does not make any difference; it just keeps running in the same direction. Any advice? (M. P., Surrey Downs, SA). •  We do not have an explanation why the clock should operate in the reverse direction unless it was a mechanism designed for an anti-clockwise movement; such clocks are available. The only way to check for this is to restore the original clock movement connections and check the direction of operation. I have a query regarding the MiniVox Voice Operated Relay described in the September 1994 issue of SILICON CHIP. It works OK but I wanted to use it for a different purpose. I replaced the electret microphone insert with a piezo element so I can use it as a shock detector for (say) a window. I connected four piezo elements (the ones like little watch speakers) in parallel to the ground and pin 3 of IC1a (LM358). I disconnected the 10kΩ resis­tor, as this seemed to improve the sensitivity. Anyway, surpris­ingly, the thing worked. The piezos were connected via shielded audio cable to a stereo audio cable. The runs were 1 metre. I kicked the piezo and the Vox tripped for some seconds. I was laughing! But then, I had another “sec­tor”, with runs of about (say) 6-7 metres. I connected the MiniVox, kicked one of the piezos and it worked. They all worked in fact, but, after about 10-20 minutes, suddenly the MiniVox becomes less and less sensitive to the signal and then I had Earphone amplifier mystery On a number of occasions I have needed to amplify the output from the “earphone” sockets of transistor radios, etc, so that I can directly feed a speaker. It seems like a simple job. Why not connect the “earphone” output into the base of a BC337 or similar transistor (say via a 4.7kΩ resistor) and feed the col­lector output into the speaker, using (say) a +3V supply. Similar circuitry is used to accept the output from CMOS devices to feed a speaker; eg, page 247 of the 1997/98 Dick Smith Electronics catalog, which describes a “UM66T Series Melody Generator”. But when I try the same trick with the “earphone” socket, it just doesn’t work! In contrast, when I use an LM386 based circuit (eg, “Little Champ”), I can obtain useful output from the to really “beat up the piezo” to get a response. Playing with the 150kΩ feedback resistor (I used a 200kΩ trimpot) for IC1a gave no result. So what could be the problem? Why is it working in the first 1020 minutes and then suddenly becomes “half deaf”? Is there some capacitance, etc, building up in the cable? Should I reconnect the 10kΩ resistor or connect the piezos in another way? (O. N., Calamvale, Qld). SMART ® FASTCHARGERS Brings you advanced technology at affordable prices As featured in ‘Silicon Chip’ Jan. ’96 This REFLEX® charger charges single cells or battery packs from 1.2V to 13.2V and 110mAh to 7Ah. VERY FAST CHARGING. Standard batteries in maximum 1 hour, fast charge batteries in max. 15 minutes AVOID THE WELL KNOWN MEMORY EFFECT. •  The reason your MiniVox circuit is not working properly is that IC1a is operating with no bias to pin 3. It needs to be biased to about half the supply voltage; ie, +6V. How it works at all in the condition you have it is a mystery. The diagram of Fig.1 shows a suggested method for biasing IC1a. The two 10kΩ resistors provide a +6V bias supply while the 100kΩ resistor connected to pin 3 provides a high input impedance for the piezo sensors. speaker even with the relatively low output from the “earphone” socket. But this is more complex than my BC337 version and draws heaps more cur­rent! Where have I gone astray? I guess it is something to do with impedance matching, gain, offset, or unlike the “earphone” output, pre-amplification existing within the UM66T (or similar) device. I have attempted to provide a suitable load for the “earphone” output (say 10kΩ), again without success. My approach is unashamedly unscientific, but as a “lash-up” it should work in some sort of fashion. Please help! (B. G., Mt Waverley, Vic). •  Whole books have been written on this subject but we will try to answer you briefly. When you connect a single transistor to enable a CMOS chip to drive a loudspeaker (we have done the same thing with the Metal Detector circuit featured on page 36 of NO NEED TO DISCHARGE. Just top up. This saves time and also extends the life of the batteries. SAVE MONEY. Restore most Nicads with memory effect to remaining capacity and rejuvenate many 0V worn-out Nicads EXTEND THE LIFE OF YOUR BATTERIES Recharge them up to 3000 times. DESIGNED AND MADE IN AUSTRALIA 12V-24V Converters, P. supplies and dedicated, fully automatic chargers for industrial applications are also available. For a FREE detailed technical description please Ph: (03) 6492 1368 or Fax: (03) 6492 1329 2567 Wilmot Rd, Devenport, TAS 7310 ELECTRONIC COMPONENTS & ACCESSORIES •  RESELLER FOR MAJOR KIT RETAILERS •  PROTOTYPING EQUIPMENT •  CB RADIO SALES AND ACCESSORIES •  FULL ON-SITE SERVICE AND REPAIR FACILITIES •  LARGE RANGE OF ELECTRONIC DISPOSALS (COME IN AND BROWSE) Croydon Ph (03) 9723 3860 Fax (03) 9725 9443 Mildura Ph (03) 5023 8138 Fax (03) 5023 8511 M W OR A EL D IL C ER O M E Using the MiniVox with piezo sensors Truscott’s ELECTRONIC WORLD Pty Ltd ACN 069 935 397 30 Lacey St Croydon Vic 3136 24 Langtree Ave Mildura Vic 3500 May 1998  91 Notes and Errata Multi-Purpose Fast Battery Charg­ er; February and March 1998: After testing three prototypes, we have found that a few component changes are required to produce reliable charging characteristics. The 0.47µF capacitor between pin 19 of IC1 and 0V should be replaced with a 100µF 16VW electrolytic type. The polarity of the component should be with the (-) toward the outside of the PC board and the (+) lead connecting to pin 19. This capacitance increase improves the detection of the NiCd & NiMH fall in vol­tage at full charge. The 0.18µF MKT capacitor at pin 17 of IC1 should be reduced to .0018µF. Its markings will either show 1n8 or 182. The number of turns on inductor L1 should be reduced from 20 to 10. The 1kΩ 0.5W resistor on the cathode of ZD1 should be re­placed with a 2.2kΩ 0.5W type. Also the 470Ω 1W resistor between the cathode of D3 and pin 12 of IC1 should be replaced with two 1kΩ 1W resistors in parallel. Charging current is best determined by checking the charg­ ing this issue), you have not produced an audio amplifier although it may well produce an audible signal. The normal output signal from a CMOS chip is a switching waveform with an amplitude almost equal to the supply voltage of the circuit. A 5V CMOS circuit will have 5V switching pulses. The CMOS chip cannot deliver enough output current to effectively drive an 8Ω loudspeaker so the usual practice is to connect a small time of a discharged battery. If charging time is too long, a slight adjustment can be made to increase the current by using a larger value resistor at pin 2 of IC1. A 3.9kΩ resistor should increase the current by about 10%. If charging time is too short, the battery is probably suffering from memory effect. Try running the battery through a few discharge (refresh) and charge cycles to bring it up to full performance. The timeout period can be increased to suit larger amp hour batteries by increasing the value of the 820pF oscillator capaci­tor at pin 14 of IC1. The wiring diagram on page 47 has two errors. The 1000µF adjacent to L1, between THS1 and -VOUT should be 100µF 25VW. The 470µF capacitor between ZD1 and D3 should be 1000µF 63VW (note increase in voltage rating compared to the circuit diagram). On the circuit diagram, the 2.2kΩ resistor at pins 12 & 13 of IC2a should be 22kΩ to agree with the wiring diagram. The 1kΩ resistor feeding ZD1 should be 1/2W. There should also be a 33kΩ pulldown resistor at pin 6 to ground (this resistor is on the wiring diagram). transistor to boost the current. In fact, the current through the loudspeaker is generally limited by a resistor of about 100Ω or so, to avoid destroying the transistor. Such a crude “amplifier” works well when fed with CMOS or TTL output signals but as you have found, it doesn’t work at all, when asked to amplify the small analog signal from an earphone output or other source. Not only does the amplifier need to increase the voltage and current swing (amplitude) of the signal, it must do so without noticeable distortion. This generally requires three or four transistors, at the very least, together with correct biasing networks, feedback and frequency compensation and so on, in a practical audio amplifier. Or you can do it with an IC. Either way, the circuit will draw lots more current than a single transistor switching stage. There just isn’t any simple way around the problem if you want a satisfactory audio amplifier. Phantom power wanted I have a condenser microphone but it needs phantom power to run. My multi-track recorder has none. I wonder if you have any project that will give phantom power and con­nect it to your mixer. A few months ago I bought and built the Digital Effects Unit described in the February 1995 issue but I can’t use it because when you talk or sing into it, the delay has distortion. Any help would be much appreciated. (N. M., Fairy Meadow, NSW). •  A preamplifier circuit featuring “phantom power” for a microphone was described in the May 1995 issue of SILICON CHIP. This is available for $7.00 including postage. The Digital Effects Unit should not suffer from distortion. Perhaps one of the op amps is oscillating or the half supply bias at pin 10 of IC1b, pin 12 of IC1a, pin 3 of IC1c and pin 5 of IC1d is not correct. Check for about +8V on each of these pins. Also try 100pF capacitors across the feedback resistors of IC1a, IC1c and IC1d and a 10pF capacitor for IC1b. These should be placed between pins 9 and 8 of IC1b, pins 13 and 14 of IC1a, pins 2 and 1 of SC IC1c and pins 6 and 7 of IC1d. 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. 92  Silicon Chip MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. FOR SALE CLASSIFIED ADVERTISING RATES Advertising rates for this page: Classified ads: $10.00 for up to 12 words plus 50 cents for each additional word. Display ads (casual rate): $25 per column centimetre (Max. 10cm). Closing date: five weeks prior to month of sale. To run your classified ad, print it clearly on a separate sheet of paper, fill out the form below & 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. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ ❏ Bankcard   ❏ Visa Card   ❏ Master Card Card No. ✂ Enclosed is my cheque/money order for $­__________ or please debit my Signature­­­­­­­­­­­­__________________________  Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ 94  Silicon Chip C COMPILERS: everything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC12, 68HC16, 8051/52, 8080/85, 8086 or 8096: $145.00 each. Macro Cross Assemblers and Disassemblers for above CPUs + 6800/01/03/05, 6502 and 68HC12 now combined at the new low price of $75. Debug monitors: $75 for 6 CPUs. All compilers, XASMs and monitors: $480. 8051/52 Simulator (fast, now incl. 80C320): $75. 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, the 89C5x and 89Sxx series, and the new AVRs in both DIP and PLCC44. Also does most 8-pin EEPROMs. Includes socket for serial ISP cable. $189, $35 tax, $10 p&p. 20-pin SOIC adaptor only $70. Credit cards accepted. GRAN­ TRONICS PTY LTD, PO Box 275, Wentworthville 2145. Ph (02) 9896 7150 or Internet: http://www.grantronics.com.au MPEG-2 DIGITAL SATELLITE RECEIVERS, Nokia 9500 S e3 $795 O.N.O., Panasat 520 $495 O.N.O. Also digital vidiplexer decoder includes Nexus satellite receiver card and adjustable I.F. bandpass filter $300 O.N.O. Phone 08 8387 5972. FLUKE 105B SCOPEMETER, cost $5680 sell $3100. Hitachi 674 plot­ter, emulates HP75 series, 4-pen A0 $500 O.N.O. Cassiopeia A11A Plus, 6Meg with extras $450. Phone Scott on 9610 8475 A.H. or email: scottdb<at>speednet.com.au ELECTRONIC ENGINEERING SOLUTIONS: No matter what problem what industry we will find you a solution that meets your needs. Specialising in schematic & PCB design, custom Windows based software, embedded control, Windows/PC based test HOMEBUILT DYNAMO, engineering dreams into reality. “An absolutely marvellous book for the true ex­ perimentalist!” Elektor Electronics. (www.onekw.co.nz) SIMPLE PIC84 PROGRAMMER: various models available. Also PIC-driven moving message and digital displays. EST (02) 9789 3616. www.nettrade.com.au/sesame/ ! MAY SALE ! MAY SALE ! Limited Quantities - Be Quick! 32 x 32 PCB Module $69. SONY Chipset 400 x 0.05 lux PCB $89. 36 x 36 Mini Camera $89. DOME Ceiling Camera $89. DUMMY CEILING DOME Mono or TINY 32 x 32 Colour PCB modules could be fitted into these $25. QUAD 4 pix - 1 Screen $249. QUAD/Multiplexer Full Frame Full Resolution Recording $749. Tiny 32 x 32 DSP Colour PCB Module $169. DSP Colour PCB 330 TVL $199. DSP Colour 450 TVL $319. Colour DSP 450 TVL C/CS Mount Camera, Comp / S-VHS O/Ps, Audio, Title, OnScreen Set-Up Menu, Manual Control of BLC, AES & Colour Temp $349. PACKAGED SETS! QUAD + FOUR CAMERAS + Power Supplies ONLY $625 just add cabling! CCTV - TV/ VCR Interface Module $15. Infra-Red 50 LED 52mm Round Illuminators $19. Wire­less Video/Audio Transmitter - Receiver Module/PCB pairs Last Chance! Sellout! Not Available Again $59. GREENCELL Battery Regenerator 4 x AA or AAA suit Alkaline, Heavy/Super Duty Zinc Chloride & Nicads with Mains Plug Pack $15. Our Camera Range includes 380 - 570 Line Resolution, 0.05 lux Low Light & Infra-Red Sensitive with 1/4" & 1/3" HI RESOLUTION HI SENSITIVITY SILICON (not low res, low sens CMOS) CCD Sensors from SONY, SHARP & SAMSUNG, 28 x 28 PCBs, Digital Signal Processing Colour. UP TO 24 MONTH WARRANTY! Before you buy ask for our ILLUSTRATED CATA­ LOGUE/PRICE LIST with Application Notes. Allthings Sales & Serv­ices 08 9349 9413 Fax 08 9344 5905. continued next page KITS-R-US PO Box 314 Blackwood S.A. Ph/fax 08 8270 3175 FMTX2A Universal Stereo Coder $49 FMTX2B 30mW Xtal Locked 100MHz Transmitter $49 FMTX1 1-3 Watt Free Running Transmitter $49 FMX1 200mW Full Broadcast Transmitter, built & tested $499 FM220 10-18 Watt FM BGY133 Philips Linear $499 FM1525 25 Watt Discrete Linear FM Band $499 FM2100 110 Watt Discrete Linear FM Band $699 FM3000 300 Watt Discrete Linear FM Band $1499 Philips 828E/A VHF Receiver Boards (6 metres) $9 AWA 721 VHF Receiver Boards (2 metres) $9 AWA 721 VHF transmitter boards 1 watt (2 metres) $19 Philips 323 UHF transmitter boards 500mW (70cm) $19 AEM 35 Watt Little Brick Audio Power Amp $15 Digi-125 200W RMS Audio Power Amp $39 CA Clipper Compiler, new in box $49 6dBd Gain Colinear FM Band Antenna $999 Roll Smart-1 FM Station Audio Processor $999 Free catalog on disk of discounted surplus components Same day shipping, credit cards OK, circuits supplied. MicroZed Computers BASIC STAMPS & PIC Tools SPECIAL STEAM BOAT KITS $14 equipment, turnkey solutions. Fast turn around with competitive rates. DAMUE PTY LTD, 46 Whitby Road, Kings Langley NSW 2147. Phone (02) 9624 2802. Fax (02) 9624 2651 or E-mail alovell<at>ibm.net Scott Edwards Electronics microEngineering Labs & others Easy to learn, easy to use, sophisticated CPU based controllers & peripherals. SX Key Ver 1.0 now in stock. PO Box 634, ARMIDALE 2350 (296 Cook’s Rd) Ph (02) 6772 2777 – may time out to Mobile 014 036775 Fax (02) 6772 8987 http://www.microzed.com.au/~microzed Most Credit Cards OK 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. FREQUENCY COUNTER High performance to 3GHz Compact Handheld Easy to use From $98.00 (FC1001) to $220 (FC2002 pictured) PRESTON ELECTRONIC COMPONENTS Now at 172 HIGH STREET, PRESTON, VIC (Corner of Bell and High Streets) Phone: (03) 9484 0191 Specialising in a wide range of: TV Antennas – Resistors – Cables – Circuit Boards – Capacitors – Sprays – PCB Artwork – Instrument Cases – Relays – Kit Sets – Semiconductors (all types) – Trimpots – Photo Sensitive – Transformers – Switches – Alarm/Security Equipment – CB Radios & Accessories. We are approved resellers for Altronics, DSE and RPG Products! 651 Forest Rd, Bexley 2207 makes all the project PCBs published in SILICON CHIP and other Australian magazines Tel +61 2 9587 3491 Fax 9587 5385 E-mail rcsradio<at>cia.com.au Prices do not include sales tax Computronics Corporation Ltd 6 Sarich Way, Technology Park, Bentley, WA, 6102 Ph. 08 9470 1177 Fax 08 9470 2844 Specifications at www.computronics.com.au Silicon Chip Binders ★  Heavy board covers with 2-tone green vinyl covering ★  Each binder holds up to 14 issues ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover REAL VALUE AT $12.95 PLUS P &P Price: $12.95 plus $5 p&p each (Aust. only) Just fill in & mail the handy order form in this issue; or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. May 1998  95 14 Model Railway Projects Shop soiled but HALF PRICE! Advertising Index Altronics................................. 24-26 Aust. Audio Consultants...............38 Computronics..............................95 Dick Smith Electronics..................... .................................. IFC,OBC,8-11 Electronic Valve & Tube Co..........87 Our stocks of this book are now limited. All we have left are newsagents’ returns which means that they may be slightly shop soiled or have minor cover blemishes. Otherwise, they're undamaged and in good condition. Embedded Pty Ltd.......................43 SPECIAL CLEARANCE PRICE: $3.95 + $3 P&P (Aust. & NZ) Microgram Computers...................3 Harbuch Electronics....................42 Instant PCBs................................95 Jaycar ................................... 45-52 MicroZed Computers...................95 This book will not be reprinted Norbiton Systems........................43 Yes! Please send me _____ copies of 14 Model Railway Projects at the special price of $A3.95 + $A3 p&p (p&p outside Aust. & NZ $A6). Enclosed is my cheque/money order for $­A__________ or please debit my Preston Electronics......................95 ❏ Bankcard   ❏  Visa Card   ❏ MasterCard Procon Technology......................95 Oatley Electronics........................19 Printed Electronics.......................95 Quest Electronics........................38 Card No. RCS Radio...................................95 Signature­­­­­­­­­­­­___________________________  Card expiry date______/______ Rola Australia..............................95 Name Scan Audio..................................87 ______________________________________________________ PLEASE PRINT ______________________________________________________ Silicon Chip Back Issues....... 22-23 Suburb/town_________________________________ Postcode_________ Silicon Chip Bookshop.................41 Street Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number (Bankcard, Visa Card or MasterCard). Silicon Chip Binders/Wallcht........93 Silicon Chip Software..................89 Silicon Chip Subscriptions..... 84-85 Smart Fastchargers.....................91 Truscott’s Electronic World...........91 A HOT SPOT FOR CHEAP PCB SUPPLIES, raw stock, drills etc plus quality manufactured boards is located at http://www.accsoft.com.au/~acetronics or phone 02 9743 9235. R.T.N. Parallax AUS/NZ distributor. Special on till July 98, a complete StampBus motherboard which holds the Basic Stamp1 chip­set a serial LCD driver module and a 2*8 LCD module. Ideal ex­pandable starter kit for $110.00 includes tax. and postage to any location in AUS/NZ. Programming software and examples supplied also. Now also carry the FerretTronics range of R/C servo 96  Silicon Chip control chips. Email: nollet<at>mail.enternet.com.au http://people.enternet.com.au/~nollet Ph/fax/ans (03) 9338 3306. PCBs MADE, ONE OR MANY. Low prices, hobbyists welcome. Sesame Electronics Ph/fax (02) 9554 9760. sesame<at>nettrade.com.au http://nettrade.com.au/sesame/ WANTED APRIL 1988 ISSUE of SILICON CHIP. Phone Doug (08) 9398 7718. Zoom EFI Special........................35 Zoom Magazine.........................IBC _____________________________ PC Boards Printed circuit boards for SILICON CHIP projects are made by: •  RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 9587 3491. •  Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730. R AUSTRALIA’S BEST AUTO TECH MAGAZINE It’s a great mag... but could you be disappointed? If you’re looking for a magazine just filled with lots of beautiful cars, you could be disappointed. Sure, ZOOM has plenty of outstanding pictorials of superb cars, but it’s much more than that. If you’re looking for a magazine just filled with “how to” features, you could be disappointed. Sure, ZOOM has probably more “how to” features than any other car magazine, but it’s much more than that. If you’re looking for a magazine just filled with technical descriptions in layman’s language, you could be disappointed. Sure, ZOOM tells it in language you can understand . . . but it’s much more than that. If you’re looking for a magazine just filled with no-punches-pulled product comparisons, you could be disappointed . Sure, ZOOM has Australia’s best car-related comparisons . . . but it’s much more than that If you’re looking for a magazine just filled with car sound that you can afford, you could be disappointed. Sure, ZOOM has car hifi that will make your hair stand on end for low $$$$ . . . but it’s much more than that. If you’re looking for a magazine just filled with great products, ideas and sources for bits and pieces you’d only dreamed about, you could be disappointed. Sure, ZOOM has all these . . . but it’s much more than that. But if you’re looking for one magazine that has all this and much, much more crammed between the covers every issue, there is no way you’re going to be disappointed with ZOOM. Look for the June/July 1998 issue in your newsagent From the publishers of “SILICON CHIP”