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SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au Contents Vol.10, No.5; May 1997 FEATURES 4 Toyota’s Advanced Safety Vehicle We take a brief look at some of the features that could become standard in tomorrow’s cars – by Julian Edgar 16 Windows 95: The Hardware That’s Required What sort of PC do you need to run Windows 95? How much RAM do you need? This article tells you what’s required – by Jason Cole 78 Cathode Ray Oscilloscopes; Pt.9 The new breed of sampling scopes operate at bandwidths up to 50GHz. Here’s a look at how they work – by Bryan Maher Build This Teletext Decoder For Your PC – Page 6 PROJECTS TO BUILD 6 A Teletext Decoder For Your PC Easy-to-build card plugs into the motherboard & lets you display Teletext pages on your PC screen – by Chris Schach & Braden Phillips 18 Build an NTSC-PAL Converter Use this converter to watch NTSC programs in full colour on a PAL-standard TV set or video monitor. It’s based on a pre-built module – by John Clarke 24 Neon Tube Modulator For Cars & Light Systems It connects to the subwoofer signal and modulates a neon light to the beat of the bass – by Rick Walters 40 Traffic Lights For A Model Intersection NTSC-To-PAL Converter Uses A Pre-Built Module – Page 18 Add realism to your model railway with this simple project. It drives red, green & orange LEDs to simulate real traffic lights – by Rick Walters 54 The Spacewriter: It Writes Messages In Thin Air Here’s a really novel project. Just wave it back and forth to write messages that seemingly appear out of thin air – by John Clarke SPECIAL COLUMNS 28 Serviceman’s Log Two VCRs, a TV & a computer – by the TV Serviceman Neon Tube Modulator For SoundOff Competitions – Page 24 53 Satellite Watch The latest news on satellite TV – by Garry Cratt 72 Radio Control Transmitter interference on the 36MHz band – by Bob Young 84 Vintage Radio A look at signal tracing, Pt.2 – by John Hill DEPARTMENTS 2 38 67 68 77 Publisher’s Letter Circuit Notebook Mailbag Product Showcase Bookshelf 83 88 90 94 96 Order Form Back Issues Ask Silicon Chip Market Centre Advertising Index Write Messages In Thin Air With The Spacewriter – Page 54 May 1997  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Rick Walters Reader Services Ann Jenkinson Advertising Manager Brendon Sheridan Phone (03) 9720 9198 Mobile 0416 009 217 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Julian Edgar, Dip.T.(Sec.), B.Ed John Hill Mike Sheriff, B.Sc, VK2YFK Ross Tester Philip Watson, MIREE, VK2ZPW Bob Young Photography Glenn A. Keep SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $54 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 34, 1-3 Jubilee Avenue, Warrie­ wood, NSW 2102. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9979 5644. Fax (02) 9979 6503. PUBLISHER'S LETTER Windows of opportunity in the kit business To a casual observer, the electronics business has been fairly static over the last few years. The pace at which new semiconductors are being introduced might seem to have slowed or at least, the semiconductor manufacturers appear to be making less noise about their new products. But in fact, while semicon­ ductor companies, with the exception of those such making micro­processors, don’t seem to promote their products much, the pace of change is rapidly accelerating. Two projects featured in this month’s issue highlight these changes. The first of these is the Teletext decoder for PCs and the second is the NTSC-to-PAL converter. Both of these use custom chips as the key devices rather than chips you can find in data books (or can’t find in data books, as they become harder to get). The same trend was evident last month with the Picture-in-Picture Adaptor. Why is this happening? The first point is that custom devices such as PGAs (pro­grammable gate arrays), PLAs (programmable logic arrays) and all their generic equivalents make it possible to design circuitry with far fewer chips than could be achieved with conventional logic chips. Second, the use of these custom devices and OTP (one-time programmable) ROMs makes it possible to protect a design from being copied. Third, designers and manufacturers are finding it impossible to rely on mainstream semiconductor manufacturers to provide the chips they want. And even if the manufacturers do make a particular device which could be of use, the reliability of delivery times is becoming increasingly in jeopardy. Fourth, and probably the most important factor of all, semiconductor manufacturers cannot be relied upon to keep manu­facturing the devices in their range. They seem to be increasing­ly capricious in deciding to discontinue semis, some of which may have been introduced only a few years ago. For the semiconductor manufacturers it does not matter that some of their smaller customers may be cut off without a second source for key devices; they have such a demand on their production that they can make these decisions with impunity. You can expect to see this trend increase. In one respect it is good because these customised chips do mean that designs are cheaper to make. The three projects mentioned above are pretty cheap after all and they would be much more involved and expensive if conventional chips had been used. On the other hand, they probably won’t be available for more than about 12 months or so because production runs are becoming much shorter, across the entire field of electronics. All of which means that if a high-tech project appeals to you, you should buy and build it soon. If you wait too long, the “window of opportunity” will close and you will miss out. Leo Simpson ISSN 1030-2662 WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. 2  Silicon Chip 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 Toyota’s Advanced Safety Vehicle features 17 systems designed to make motoring less hazardous. All the systems are electronically based. Toyota’s advanced safety vehicle Toyota has developed an experimental safety vehicle that relies heavily on electronic systems. Here’s a brief look at some of the systems that could become standard in the future. By JULIAN EDGAR It’s not generally realised, but around 20% of all road fatalities are pedestrians. To reduce the occurrence of pedes­ trian fatalities, the Toyota Advanced Safety Vehicle uses a bonnet-mounted airbag. In the event of an accident, it inflates to cushion the pedestrian’s head and body from the upper bonnet and windscreen area. To avoid the occurrence of blind spots, four on-board video cameras are used. An additional camera, sup4  Silicon Chip plemented by a milli­metre wave radar system, monitors road conditions and warns the driver to take evasive action as appropriate. This computer-based system measures the distance to and relative speed between vehi­ cles or obstacles ahead and can automatically brake the car if the driver does not respond. On a simpler level, an adjunct to the 40-year-old flashing indicator system is used. An “after you” light tells other motor­ists or pedestrians that the driver is giving way (Toyota does not mention what happens if another polite motorist is also equipped with the light)! Toyota’s Advanced Safety Vehicle also features an automatic fire extinguisher system. This is located in the engine bay and is automatically activated in the event of an engine fire. In addition, a thermal actuator automatically opens the bonnet lock, presumably to allow easier access for external extinguishers. Driver alertness Failing driver alertness is detected by a pulse rate moni­tor linked to a computer that monitors steering response. Should the driver start falling asleep, a dashboard warning display Silicon Chip BINDERS One of the new systems being trialled by Toyota is a bonnet airbag, designed to reduce injury to pedestrians in the event of a collision. is activated. If the driver still doesn’t respond, a seat vibrator is activated! Finally, an on-board accident reporting system automatical­ly calls police and emergency services in the event of an accid­ent or the driver collapsing. A black box recorder is also fitted to the car to provide evidence of driver behaviour in the event of a crash. In all, Toyota has fitted 17 new systems, all electronic based, to its experimental car. Although some of these features are unlikely to see production, a few at least will be seen in Toyota vehicles in the next SC few years. NSW POLICE SERVICE INVESTIGATIVE ELECTRONICS DESIGN (2 POSITIONS) ★ High quality ★ Hold up to 14 issues ★ 80mm internal width ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A14.95 (includes postage in Australia). NZ & PNG orders please add $A5 each for postage. Not available elsewhere. Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. Use this handy form  Two positions exist in the Research & Development Branch of the Special Services Group of the NSW Police Service for designers of Investigative Electronics. These professional jobs involve the concept, design, prototyping, testing, and product manufacture/assembly of equipment for use by Police in investigating crime. A wide range of technologies and deployment methods are involved, and applicants should be prepared to work in exciting and differing environments such as marine, aviation and intelligence areas. Interaction with like overseas agencies is involved, including personnel exchange, so applicants should be prepared to travel internationally, if necessary for extended periods. Demonstrated skills and experience in design and construction are required in two or more of the following disciplines:  Radio (HF, VHF, UHF and Microwave)  Video – origination, recording, transmission and reception and encryption  Audio – origination, transmission and recording, and encryption  Microprocessors (hardware and software development) Additionally, applicants should have had experience in one or more of the following fields:  Miniaturisation (surface mount technology)  GPS (Global Positioning System) technology  Video, Audio and Data encryption  Modern communications systems (satellite, data and fiberoptics)  Telephony (fixed and mobile, digital and analog) These positions represent an exciting and challenging prospect for people with the motivation and energy to be innovative and diligent in this rewarding field of activity. If you are interested in these positions please contact Mr Syd Griffith on (02) 9950 9344 or by letter to Building 4, 77 Portman Street, Zetland for further information about the job and advice on application requirements when these positions are formally advertised in around six weeks. These beautifully-made binders will protect your copies of SILICON CHIP. They feature heavy-board covers & are made from a dis­ tinctive 2-tone green vinyl. They hold up to 14 issues & will look great on your bookshelf. Enclosed is my cheque/money order for $________ or please debit my  Bankcard    Visa    Mastercard Card No: ______________________________ Card Expiry Date ____/____ Signature ________________________ Name ___________________________ Address__________________________ __________________ P/code_______ May 1997  5 By Chris Schach & Braden Phillips* *Chris Schach & Braden Phillips are the principals of Current Dynamics. A Teletext decoder for your PC If you haven’t looked at it lately, there’s a heap of information from all sorts of sources on Teletext. Now you can display these Teletext pages on your PC screen using this stan­dard card which plugs into your motherboard. The software is Windows 95 and 3.1x compatible. Imagine the scenario: you’re at your computer and suddenly you’d like to know the weather report on the Gold Coast tomorrow or you need to check some current share prices. Perhaps you’d like to know the current Sheffield Shield cricket scores or you are about to phone overseas and you’d like to check the time in Vancouver before you dial. Or maybe, perish the thought, 6  Silicon Chip you’ve had a little flutter on the horses and you’d like to check the results. You get the picture? Now if you are at home and you have Teletext on your TV, you can switch on the set and wait for it to bring up the screen you want. But there’s something a bit deca­dent about having the TV on while you are supposed to beavering away at the your computer, isn’t there? Wouldn’t it be so much more convenient to click on the Teletext icon and select the page you want from the control panel? Well, now you can do just that with this Teletext card for a PC. The Teletext card occupies a standard 8-bit slot in your computer and it comes with Windows software on a floppy disc. The only other hardware you need is a VCR – that feeds the offair video signal to the Teletext card for processing. By using a standard VCR as the source of off-air video, the Teletext card is much cheaper and less complicated since it does not need on-board TV tuners (VHF & UHF) and all the associated video circuitry. You need to set the VCR to the station you want (generally one of the Seven Network stations carrying Teletext) and then connect its video output to the Teletext card via a cable This Teletext decoder card plugs into a spare ISA slot on your PC. An interrupt is not required; instead, it communicates using polling over a small amount of I/O address space. fitted with an RCA phono socket. Your VCR’s video output may use a BNC or RCA socket so you will need a cable to match. By the way, the VCR you use only needs to have its video functions working; if it doesn’t work in playback or record that is unimportant. So you could use a VCR with a dud transport for the job. Noise-free TV signal We should point out that you will need a good TV antenna or at least, a good noise-free source of off-air TV signals other­wise you won’t get to first base. If your present TV reception is snowy, you will not get reliable Teletext reception, regardless of whether you are using this Teletext PC card or your TV itself has built-in Teletext facilities. Note that your PC doesn’t need to be a Pentium-based machine. The software runs under Windows 95 or 3.1x and can be on a 486 or 386 machine. All the Teletext processing is done on the card itself and does not involve the PC. Nor does the Teletext card require a PC hardware interrupt, something that can be hard to find on today’s feature-loaded machines. Instead, the Teletext card communicates using polling over a small amount of I/O address space. Nor does the PC need to store Teletext pages. The Teletext card captures and stores the pages, using an on-board micropro­cessor and static RAM (SRAM). The PC card itself is half-size. It is double-sided with plated-through holes and uses conventional ICs, transistors and passive components. One IC is mounted in a chip carrier socket. No surface-mount components are used so you don’t have to worry on that score. You will need a temperature controlled soldering iron with a small tip. On-screen features The software supplied with the Teletext card runs under Windows, as already mentioned. To install the software you run Setup.exe and then follow the bouncing ball. Actually, you don’t follow a bouncing ball; you follow the on-screen prompts. By default, the software is installed in a folder (directory) called “Teletext” and, for Windows 95, an appropriate entry is added to the Start menu. Alternatively, for Windows 3.1x, the relevant icons are added to the Program Manager. Launching the program brings up the Teletext control panel, as can be seen in one of the screen grabs accompanying this article. The control panel defaults to page 100 and it brings up a Teletext window with the message “The requested page has not yet been captured ...” Meanwhile, the page counter in the control panel ticks over to show its progress. By the way, as each page comes in, it is stored in the buffer which is virtual memory; ie, on the hard disc. Ultimately, all Teletext pages are stored in this way and so May 1997  7 any page can be accessed almost instantaneously. This is a big advance on Teletext in normal TV sets because they don’t have a buffer and you have to wait for the wanted page to be transmitted before you can see it on screen. Once the wanted pages are in the buffer, you can display as many Teletext windows as you want on screen. You can also print them out, on virtually any printer. You can also elect to save the buffer (to a directory on the hard disc) and you can thereby display those pages on screen at any time, long after they have ceased to be transmitted. So there you have it. This Teletext card enables you to access and display more pages than you could with a normal TV and you have the bonus of storing and printing out countless pages, if you wish. 8  Silicon Chip There are two differences to be noted between those Tele­text pages displayed on your PC’s screen and those displayed on a normal TV. First, because of the resolution of a VGA screen, the Teletext pages on your PC will be sharper than those on your TV. Not that there’s a real benefit but they are sharper. Second, while Teletext pages normally have the same 4:3 aspect ratio as a normal TV screen, when displayed on your PC, they are somewhat squarer. That too is immaterial and is an effect of the software. OK, so you now know what the Teletext card does. Let’s have a brief look at the circuit details. Circuit details As you may be aware, Teletext signals are sent during the vertical blanking interval of a normal off-air TV signal. If you roll the picture up, you will see several bright lines of ever-changing data embedded in the vertical blanking bar. The data is mainly text and single graphics. The data is normally decoded by the TV set and reconstitut­ed into pages on the screen. Up to 800 or so pages can be trans­mitted and they are sent in sequence. The time to access a par­ ticular page off air depends on where it is in the sequence and how recently it was sent. It can take several minutes for a page to be captured. The Teletext data signal comes in at high speed, with a serial bit rate of 6.9375MHz. This, coupled with Fig.1 (right): the Teletext decoder extracts ASCII text and graphics from an off-air composite video signal, usually from a VCR. The data is stripped from the video signal using video slicer U6 and then processed in U3 under the control of U1, the PIC microprocessor.  This screen capture shows how the Teletext Control Panel and the Teletext window appear on the Windows 95 desktop. You can open as many Teletext windows as you like and all incoming pages are stored in a buffer for quick access. The buffer can also be saved to the hard disk and the pages printed out. May 1997  9 Open a new teletext window Close the active teletext window Reveal hidden text the need for other high speed digital processing of the Teletext signal, requires specialised hardware so that the microprocessor only needs to take on a coordinating and hence relatively low-speed role. An XILINX FPGA, U3, was chosen to do the job. FPGA stands for Field Programmable Gate Array. U3 is controlled by the PIC16C57 microprocessor and stores its data in an HM62256 static RAM, U4. The interface between the PC and the card consists of a GAL20V8 logic array, U5, and two 74HC373 Tri-state buffers, U2 & U8 (note: GAL stands for Generic Array Logic). Data from the PC is latched into U8 when the PC writes to one of the four I/O addresses stored in the GAL and selected by the jumpers JP1 & JP2. The PIC1657 reads the data by enabling the outputs of U8 and it can write data to the PC by latching it into U2. The PC can read this latch at any time by reading from the correct I/O address. 10  Silicon Chip Display Capture the next page 100 sub page now Load a buffer from file Save the buffer to a file Empty the buffer The PIC16C57 microprocessor contains 2048 words of on-board program space and 72 bytes of on-board RAM. In addition, it contains 20 I/O lines and can operate at cycle times as low as 200ns. It is used as the interface between the data capture hardware and the PC. It accepts commands from the PC and responds appropriately with actions and/or data. For example, if the PC wants a specific page of Teletext, it will issue the appropriate command word to the PIC followed by the page number. The PIC will set the SRAM address to 0 and then initiate a Teletext line capture. When the line capture is com­plete, the PIC will check to see if the line was a valid header row, in which case it will check to see if it is from the re­quired page. If not, it will reset the SRAM address and continue look­ing. When the correct header line is found, the PIC will continue capturing and storing Print teletext page xxx Stop autocapture Quit the teletext viewer lines until it comes across another line 0. Another line 0 means that a full page has been received and the PC can be notified that the page capture is complete. Data slicer A Philips SAA5231 data-slicer, U6, is used to extract the Teletext clock and data signal from the incoming video signal. The clock and data outputs from this IC must be level shifted to produce TTL signals. This is accomplished using transis­tors Q1 & Q2 and a dual high-speed comparator, U7. The comparators use the average of the incoming clock signal as their reference, eliminating drift problems possible with a fixed reference. The level-shifted signals then go directly to the FPGA. The 5231 needs a “sandcastle” input which must stay low for 8.5µs after the start edge of a video sync pulse. This is generated via a counter in the FPGA. Fig.2: the parts are installed on the PC board and tested in stages, as detailed in the article. Make certain that all parts are correctly oriented before soldering their leads, as this is a double-sided board with plated-through holes. The FPGA uses volatile configuration data and must be reconfigured after each power up. The configuration data is sent from the PC to the FPGA via the PIC in a serial data stream. The whole configuration process takes a fraction of a second. The Teletext data signal is fed to an 8-bit shift register whose outputs can be enabled onto the SRAM’s data bus. An 8-bit comparator is also attached to the outputs which produces a sync signal whenever the line sync byte appears. This sync signal is used to reset both the bit counter and the byte counter at the start of a line and also to set the line capture process in motion. When a line capture is in progress, the SYNC REC output will indicate that fact to the PIC. As the bit counter clocks over each time, the byte currently in the shift register is written to the SRAM at the location pointed to by an address counter also contained in the FPGA and both the address counter and byte counter are in­crement­ed by 1. When the byte count reaches 43, the line capture is complete and SYNC REC will go low. The upper eight bits of the 11-bit May 1997  11 address counter can be set by the PIC before a line capture takes place. The PIC can read the contents of the SRAM by asserting _READ which enables both the SRAM output buffers and connects the microprocessor and memory data busses through the FPGA. The PIC increments the address counter by asserting the CLK signal. Construction Begin by inspecting the double sided PC board carefully for short circuits or broken tracks, being especially careful in areas that will be concealed by components. Fix any problems as necessary using solder or a sharp knife. The metal bracket can be mounted at this stage, adjusting the alignment as necessary to suit your computer’s expansion slot. The suggested way of assembly is to progressively populate the board, testing as you proceed. This is made easy though a program called TT_TEST included on the installation discs. Ensure that each of the test options are run in sequence each time the program is restarted to ensure that the Teletext card is properly initialised. The first components to install are the GAL20V8 (U5), C18, R9, R10 and JP1&2 which form a sub-circuit responsible for I/O address decoding. The first two test program options enable the reset line (U5 pin 21) to be toggled between 0V and +5V respec­ tively. Choose these options and use a multimeter to make sure the reset line behaves as expected. When this part of the circuit works, proceed to the next stage. The PIC16C57 microprocessor (U1), Where To Buy A Kit This Teletext decoder was designed by Current Dynamics who own the design and software copyright. The kit will include a high quali­ty double-sided PC board with plated-through holes, screen print­ed component overlay and green solder mask, all components, 3.5-inch 1.44MB installation discs and instructions. The discs will include the full Windows Teletext viewing software, a test pro­gram and some example C source code for those who wish to develop their own software. The complete kit is priced at $150 plus $5 for postage within Australia. For postage to New Zealand, add an extra $7.00 (Aus­tralian dollars). Remittances may be sent by bank cheque, money order, Visa, Bankcard or Mastercard. Current Dynamics can be contacted by phoning (08) 8303 3349 or by fax on (08) 8303 4363; email currentd<at>ozemail.com.au or http://www.ozemail.com. au/~currentd Send mail orders to Current Dynamics, 37 Queen Street, Thebarton, SA 5031. 12  Silicon Chip X1, C8, C22, R8, C17, C19 and the 74HC373s (U2 & U8) are next. Anoth­ er test option enables the function of this section to be verified by a simple command/echo sequence between the PC and the PIC. It also has the effect of ensuring that both the PC and the PIC have synchronised “clock” variables. Now for the XILINX2064-68PC (U3). Be careful to ensure correct device and socket orientation. The bevelled corners on the socket and overlay should be aligned. Also, the pin 1 dot on the IC should be aligned with the white legend dot on the PC board. Be warned that once the IC is inserted, it can be diffi­cult to remove without a special tool. Next, solder in C15, C16, R7 and the RAM (U4). To check this section of the circuit a test routine has been developed which sends a configuration to the FPGA. If this operation is completed successfully we can be fairly sure the FPGA is alive and well and communicating with the microprocessor and the PC. The next task is to test the RAM. A difficulty here is that the FPGA only writes to the RAM when it is receiving Teletext. Therefore, the best we can do is use a test routine to read the entire contents of the RAM and then check to see that it is stable by reading it again. The remaining components can now be inserted. At this point, a suitable video signal is required. For most construc­tors, this will mean access to the video output of a VCR tuned SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. to a channel with a Teletext service (Channel 7 or 10 in Australia). To be sure that the video signal is of sufficient quality, it is wise to monitor the picture quality on a TV while your computer is running. A computer can be a significant cause of noise input to an RF television signal, so it is important to keep your antenna and your computer well separated. Picture quality needs to be reason­ably good with little “snow”. Moderate ghosting does not usually cause many errors in Teletext pictures. The final test routine will verify that the Teletext data and clock lines are active. The test will look for sync charac­ters present at the start of each Teletext line. A video signal must be present for this test to pass. Acknowledgement: all Teletext screen grabs in this article SC reproduced courtesy Austext, Channel 7. May 1997  13 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 COMPUTER BITS BY JASON COLE Windows 95: what it really needs in terms of hardware What sort of hardware do you need to run Windows 95? How much RAM do you need? We take a look at what’s really needed to make the most of Windows 95. On the side of the Windows 95 upgrade box it states that it will work on a computer with a 386 processor, 4Mb of RAM and 40Mb of available space on the hard disc drive (HDD). That is correct – it will run on such a system but then my car will run on 50ml of petrol! It won’t go far but it will run and so will Windows 95. Unfortunately, any program that you want to run will be slow and tedious which is exactly what a computer is not meant to be. My personal minimum recommendation for running Windows 95 is a 486 DX4 100MHz CPU, 16Mb of RAM and a 500Mb HDD. It will work with 8Mb of RAM but you will still have trouble running programs. A nice Windows 95 system will have a 133MHz Pentium or equivalent processor, 32Mb of RAM and a 1.6 gigabyte (1.6Gb) HDD. That is what it really takes if you want real performance but why? Access Memory and is the area where the programs are loaded. If you have 8Mb of RAM, for example, then you can only load 8Mb worth of programs into memo­ry. When it comes to RAM, 8Mb is not a lot and indeed Windows 95, with all its associated Dynamic The microprocessor The CPU can be considered as the brains of the system. This is where all the calculations are done so it stands to reason that the higher its MHz rating (ie, 120, 133, 166 or 200MHz), the faster it can do these calculations. The term “RAM” stands for Random 16  Silicon Chip Link Libraries (DLLs), plus a program such as Word Ver.7 will actually gobble up more than 8Mb. In fact, the .exe file for Word alone is about 3.85Mb. The magical swapfile Of course, we can run both Win- dows 95 and Word Ver.7 on a system with just 8Mb of RAM, so how does Windows achieve this? It does it by means of a device called a swapfile, which is simply a reserved area on the hard disc that the system treats as memory when it runs out of real memory. When the computer wants to access a part of memory, it goes to the required memory location and reads or writes to it. Howev­er when it runs out of places to write the data, it grabs a segment of RAM, copies it to the swapfile, and uses the now free RAM for the new data. So, by using the hard disc, your system has much more memory available to it than just the amount of RAM. Unfortunate­ly, there’s a downside to swapping data from RAM to the hard disc and that’s speed. When the computer accesses the RAM, it typically only takes 70 nanoseconds (70ns). However, when it needs to write to the hard disc drive, it first has to find the swapfile in the file allocation table (FAT), then locate the actual sector on the drive, wait for the start of the sector, write to it and finally, update the FAT. And that can take quite some time. In fact, compared with the 70ns access time for RAM, it’s an eternity. That is why Windows, whether it be 3.x or 95, can be slow with only 8Mb RAM. The sweet spot for Windows 95 is 24Mb RAM. With 24Mb, Wind­ ows 95 is fully loaded into memory and therefore the only real thing slowing down the computer will be the speed of the CPU. With this much RAM, you can load Word and Excel and work at a nice rate. 32Mb enables you to load even more programs and run them in RAM at once, while having a few open Word and Excel Docu­ments. As a matter of fact, I run my computer with 64Mb of RAM and I rarely see the HDD light turn on except when I load a program or save a document. It takes me a few seconds to load Word but after that ini­tial loading the program is cached in memory so that if I close it and then load it again it will only take a couple of seconds Even if I quickly load a graphics program before reloading Word, it still takes only a couple of seconds because there is plenty of RAM to go around. Hard disc drives RAM is not the only thing that can slow down Windows 95. Windows is continually loading and unloading data in the back­ground and if you have a slow HDD then it’s going to take longer to do the job. Western Digital offer a series of drives that really do perform very well in terms of speed, reliability and price. I personally prefer the Western Digital Caviar series Enhanced IDE HDDs for a Windows system. These drives operate at 5200 rpm and are good, cost-effective units for both home and business sys­tems. Alternatively, if you have the money, you could go for a SCSI-based unit such as the Seagate Barracuda which operates at 7200 rpm but I will tell you more about HDDs another time. In summary, it’s really a matter of having the right ingre­dients – a reasonable amount of RAM, a fast CPU and a decent HDD. But that’s not all. A decent motherboard is also required and it also helps to have a “real” video card. Software updates A few changes have been made to Windows 95 since its offi­cial release to enhance its capabilities. These updates are available as Service Pack 1, which also has a couple of added extras such as an update information tool. There have also been a few updates to the Internet Explorer which retails for the lovely price of $0.00. That’s right, it costs nothing! We are now up to Version 3 (the Win95 Upgrade Pack has Version 2) and I recommend that you use the latest version if you intend exploring the internet. If you don’t have it, ask around or download it from www.microsoft.com. It is not really necessary to install the service pack on home systems that are generally used for games, as the areas it affects will seldom (if ever) be used. Conversely, it is always a good idea to install any service pack that comes out if the computer is used in a business environment. Service packs are often brought out not only to enhance current features but also to fix obscure bugs and to allow some new programs to work correct­ly. A new Win95 Recently, a new version of Windows 95 was released but this is only available as an OEM (original equipment manufacturer) product. This basically means that you can’t buy it unless you are buying a new computer. The new version is called Windows 95 Service Release 2 (SR2). It includes all the updates as part of the new system plus various other improvements, including the option of a 32-bit FAT system. In the older Windows 95, the 16-bit FAT is located at the edge of the drive and the cluster size is dependent on the drive size, although some third party programs allow you to change the cluster size to a certain extent. With the FAT 32 system, howev­er, the root directory can be located anywhere on the drive and the cluster size is just 4Kb for partitions up to 8Gb. In addition, the largest partition size available for a FAT 16 system is 2Gb, while for a FAT 32 system it can go as high as 2Tb (terabytes). If you want the features offered by the Service Release 2 version of Windows 95 but don’t want a new computer, you won’t have to wait long. The new features should all be included in Windows 97, due for release later this year. In summary, you will not get the most out of Windows 95 if your hardware is not good enough. It’s cruel how the best soft­ware packages require the best hardware but if you shop around and choose carefully, you can get a fast machine that can really handle Windows 95. Fortunately, computer prices have dropped dramatically in SC the last 12 months. 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. 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 SUNSHINE DEVICE PROGRAMMERS Power 100 Universal Programmer 48-pin Textool Socket para I/F ............$1371 HEP 101 Value for Money 8MB E(E)PROM - 1 slave socket ...................$283 HEP 808 High Speed 8MB E(E)PROM programmer 1 master 8 slave sockets .. $790 JET 08 Production Series E(E)PROM Programmer Stand alone or PC (para) .$1590 PEP01 Portable 8MB E(E)PROM Programmer, Parallel Port ....................$295 EML2M EPROM Emulator ....................$480 Picker 20 Stand Alone Dram, CMOS TTL IC Tester ........................................$199 RU20IT 16 Piece UV EPROM Eraser with timer .............................................$187 Plus converters, adapters & eproms. Contact us for other spe­cialised development tools or data acquisition, industrial elec­tronics, computer and electronic parts and service at: NUCLEUS Computer Services Pty. Ltd. 9b MORTON AVE, CARNEGIE, VICTORIA, 3163 TEL: (03) 9569 1388 FAX: (03) 9569 1540 Email: nucleus<at>ozemail.com.au May 1997  17 NTSC-to-PAL Converter Use this converter to watch NTSC programs in full colour on a PAL-standard TV set or video monitor. It is easy to put together because it is based on an assembled PC board and a standard video modulator module. By JOHN CLARKE These days there are quite a few video program sources which produce an American NTSC signal instead of the PAL standard signal used in Australia, New Zealand and much of Europe. These sources range from video disc players, NTSC VCRs and 18  Silicon Chip cam–corders and last, and perhaps most important, signals from some satellite TV channels. If you have tried it, you will probably realise that many PAL standard TVs and video monitors will actually work with an NTSC signal but it will always be in black and white instead of colour and the picture will probably not be the full screen height. This is not the most satisfying way to view a video program so the availability of this NTSC-to-PAL Converter pro­ject at a reasonable price is good news. Of course, some upmarket TVs can accept and display NTSC signals in colour but they are in the minority and some are quite costly. The unit described here is designed to be used for view­ing purposes only. It cannot be used for recording from NTSC to the PAL format. The unit is built into a small plastic case with audio and video input and output RCA sockets on the rear panel. Fig.1: this scope shot depicts a colour bar video signal. The top trace is an NTSC signal showing the negative going line sync pulse, the short colour burst and then stair-cased chroma and brightness video information. The second trace is the bypass output from the NTSCto-PAL Converter, while the lower trace shows the video signal after conversion to PAL. Fig.2: this shot shows the NTSC colour burst signals on the top trace and the PAL colour burst signals on the lower trace. The precise NTSC colour burst frequency is 3.579545MHz, while the PAL colour burst frequency is 4.433619MHz. These oscilloscope traces show that the NTSC-to-PAL converter does change the colour burst frequency. Features • • • • Fig.3: this shows what happens with the NTSC-to-PAL Converter when it is given a frame rate of 60Hz. It can be seen that the conversion process does not change the frame frequency The output is also avail­able as an RF modulated signal at VHF channel 0 or 1. Front panel controls are the power on/off switch and the NTSC-PAL/ Bypass switch. Inside there is little to the circuit since the conver­sion is all done on a small pre-built module. We have added a modulator and power supply to complete the converter. Before we go too much further, we should briefly explain what the terms “NTSC” and “PAL” actually mean. Contrary to what some smart alecks like to say, NTSC does not stand for “never twice the same colour”. Rather, it stands for National Television Sys- Uses a pre-built NTSC-PAL converter module Video or RF modulated output Bypass or NTSC-PAL conversion option Allows viewing of NTSC programs in colour on a PAL TV Warning! This NTSC-to-PAL converter does not alter the 60Hz frame rate to 50Hz. This means that some TV sets or monitors will not lock onto this frequency and will continuously roll. To test whether your PAL TV or monitor can be used with the NTSC-to-PAL converter, simply test it on an NTSC signal. It should produce a stable picture in black and white. tem Committee of the USA. This was the body that set the American colour TV standard in the first place. The “never twice” epithet alludes to the fact that the NTSC system has problems maintaining the correct colour due to drift in the circuitry. PAL stands for “phase alternate line” and refers to the changing phase of the colour burst signal on each alternate line of the picture. PAL is a German (Telefunken) development. How does it work? The NTSC and PAL video formats are similar in a number of re­spects. The NTSC horizontal line frequency is 15.750kHz while PAL operates at 15.625kHz. The sync levels and widths are also similar and a colour burst signal occurs after each line sync. By the way, the easy way to remember these line frequencies is to take the product of the number of picture lines, multiply by the field (or frame) rate and then divide by two. For NTSC, we multiply 525 lines by 60 Hz and divide by two to obtain 15.750kHz. Similarly, for PAL, we multiply 625 lines by 50Hz and divide by two to obtain 15.625kHz. It is because the line frequencies for May 1997  19 PARTS LIST 1 NTSC-PAL Converter (available from Av-Comm Pty Ltd) 1 PC board, code 02303971, 102 x 117mm 2 adhesive labels 132 x 28mm 1 plastic case, 140 x 110 x 35mm (Jaycar Cat. HB-5970) 1 ASTEC UM1285AUS 0/1 video modulator (DSE Cat. K-6043) 1 12VAC 500mA plugpack 1 TO-220 heatsink, 30 x 25 x 13mm 1 SPDT toggle switch (S1) 1 1kΩ horizontal trimpot (VR1) 3 panel-mount RCA sockets 1 DC panel socket 1 8mm ID grommet to insulate DC socket 1 400mm length of hook-up wire 1 3mm dia. x 6mm screw and nut 1 3mm dia. x 9mm screw and ut 1 3mm x 3mm spacer (TO220 insulating bush) 4 self-tappers to mount PC board 6 PC stakes Semiconductors 1 7805 5V regulator (REG1) 4 1N4004 1A diodes (D1-D4) 1 12V 400mW zener diode (ZD1) 1 3mm LED (LED1) Capacitors 1 1000µF 16VW PC electrolytic 2 470µF 16VW PC electrolytic 1 47µF 16VW PC electrolytic 3 10µF 16VW PC electrolytic Resistors (0.25W, 1%) 1 1kΩ 1 180Ω 1 560Ω 1 100Ω Where To Buy The Parts The major parts for this design are available as follows: (1) NTSC-PAL converter module plus main PC board: Av-Comm Pty Ltd, PO Box 225, Balgowlah, NSW 2093. Phone (02) 9949 7417; Fax (02) 9949 7095. Price: $89 plus $5 p&p. Cat. K1300. (2) Astec UM1285AUS 0/1 video modulator: Dick Smith Electronics. Cat. K-6043. (3) Complete kit: Jaycar Electronics. Price: $149.50 plus $8 p&p. Cat. KC-5223. 20  Silicon Chip Fig.4: the circuit consists of the NTSC-to-PAL converter board, a standard video modulator and a power supply (D1-D4 and REG1). The NTSC video input signal is applied to the converter board and it delivers a converted PAL output. This output can be taken direct and is also used to drive the modulator. both formats are so similar that many PAL TVs and video monitors will display an NTSC picture. However, some older sets may not be able to lock onto the higher frame rate of NTSC (60Hz) and so will display a rolling picture. If your set is among these, you can’t use this NTSC-to-PAL Converter. Fig.1 shows a colour bar video signal. The top trace is an NTSC signal showing the negative going line sync pulse, the short colour burst and then stair-cased chroma and brightness video information. The second trace is the bypass output from the NTSC-PAL Converter, while the lower trace shows the video signal after conversion to PAL. This demonstrates the different colour bursts of the NTSC and PAL formats. The phase of the PAL colour burst changes by 180° on every alternate line and this reversal cancels out drift in the circuits to maintain accurate colour locking. This is where the PAL signal derives its name: Phase Alternate Line. Fig.2 shows the NTSC colour burst signals on the top trace and the PAL colour burst signals on the lower trace. The precise NTSC colour burst frequency is 3.579545MHz and the PAL burst is 4.433619MHz. These oscilloscope traces show that the NTSC-to-PAL converter does change the colour burst frequency. Fig.3 shows what happens with the NTSC-to-PAL Converter when it is given a frame rate of 60Hz. It can be seen that the conversion process does not change the frame frequency. To sum up, the converter changes the colour burst signal but it does not change the number of picture lines or the frame rate. Circuit details The circuit for the NTSC-PAL Converter is shown in Fig.4 and it is about as simple as you get, bearing in mind the complex function it performs. It comprises the NTSC-PAL board, a video modulator and a power supply. The NTSC-PAL board comprises a number of inscrutable proprietary chips. It is an irregularly shaped board 73mm along its longest dimension and 46mm wide. The input, output and power connections to the board are made via a 5-pin header. The video input is coupled to the NTSC-PAL converter board via a 470µF capacitor. Similarly, the output signal is also coupled via a 470µF capacitor. Trimpot VR1 attenuates the video output before applying it to the video modulator via a 47µF coupling capacitor. The modulator input in- Fig.5: install the parts, including the NTSC-PAL board, on the main PC board as shown here. cludes a clamping circuit which sets the video level at around 2V. The 1kΩ resistor provides a discharge path for the 47µF capacitor. The video modulator produces an RF output on VHF channel 0 or channel 1. This option is selected by linking the channel input to ground for channel 0 or leaving it open circuit for channel 1. Power for the circuit is derived from a 12VAC 500mA plug­pack. Diodes D1D4 rectify the voltage and a 1000µF capacitor filters it to produce about 20V DC. Zener diode ZD1 provides RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ No. 1 1 1 1 Value 1kΩ 560Ω 180Ω 100Ω 4-Band Code (1%) brown black red brown green blue brown brown brown grey brown brown brown black brown brown 5-Band Code (1%) brown black black brown brown green blue black black brown brown grey black black brown brown black black black brown May 1997  21 Fig.6: this is the full-size etching pattern for the PC board. a regulated +12V supply to the video modulator via a 180Ω resistor. This limits the current to the 6.2V zener diode inside the modulator can. A 7805 3-terminal regulator (REG1) provides +5V to the NTSC-to-PAL Converter and drives the power indicator LED via a 560Ω resistor. and breaks in the copper pattern. You may need to drill out two holes; one for a 3mm screw to mount the NTSCPAL module and one for mounting REG1. Also check the hole sizes for the modulator earth mounting lugs and the four corner mount­ing holes for the PC board. Fig.5 shows the wiring details. Install the resistors first, followed by the diodes. Note that there are two types used: the 1N4004s which have a black body and the smaller zener diode, ZD1. Next mount the four PC stakes, followed by REG1. This mounts horizontally on a small U-shaped heatsink and is secured using a 3mm screw and Construction As already mentioned, the NTSC-toPAL Converter is based on a pre-assembled module. We mounted it on a PC board coded 02303971 (102 x 117mm). It is housed in a plastic case measuring 140 x 110 x 35mm. Begin construction by checking the PC board for shorts between tracks nut. Bend its leads so that they fit into the holes provided on the board. The capacitors can be inserted next, taking care to orient them with the correct polarity. LED1 is mounted with sufficient lead length to enable it to be bent over and inserted into the front panel hole. The video modulator can be mounted next. Solder the earth tags to the PC board and insert the four wires into the holes provided. You will have to decide whether you want the modulator to provide an RF signal on channel 0 or channel 1. The NTSC-PAL module is mounted with its 5-way pin header inserted into the main PC board. It is supported on a spacer using 3mm screws and nuts into the one mounting hole. Now fit the adhesive labels onto the front and rear panels and drill out the holes for the RCA sockets, DC socket and RF out socket on the rear panel. On the front panel, drill and file out the holes for the power switch, LED and Convert/Bypass slider. Attach the DC socket, RCA sockets and switch onto the panels and then complete the wiring, with the panels and board secured in place on the baseplate of the case. Note that if a metal panel label is used, the DC socket must be insulated from it with a rubber grommet otherwise the labelling will short one side of the AC power supply to ground via the RCA sockets. Testing The unit can now be tested. Apply power and check that there is 12V across zener diode ZD1 and that +5V is present at the output of 3-terminal regulator REG1. If these checks are OK, you can connect the converter to a standard PAL Fig.7: you can use these full-size artworks as drilling templates for the front and rear panels of the case. The larger holes are made by first drilling the hole with a small pilot drill and then carefully reaming them to size. NTSC TO PAL CONVERTER + + CONVERT BYPASS POWER + + VIDEO IN VIDEO OUT 22  Silicon Chip + AUDIO IN + + RF OUT 12VAC IN The PC board fits neatly inside a low-profile instrument case measuring 140 x 110 x 35mm. Note the small U-shaped heatsink fitted to regulator REG1 (top photo). Power comes from a 12V AC 500mA plugpack. audio/video source such as that from a VCR. This done, slide the Convert/ Bypass switch to Bypass, connect the RF output to the TV antenna input, and tune the TV set to channel 0 or 1 (if the RF output is used). VR1 is set to give the cor­rect contrast range and to prevent overmodulation. You are now ready to test its operation on an NTSC signal source. Switch the front panel slide switch to the “Convert” setting. The Hue and saturation trimpots on the NTSC-to-PAL module may then need adjusting for best colour and contrast. You may also need to adjust the height on the TV set so that there are no black strips at the top and bottom of the picture. Bear in mind, however, that when you switch back to a PAL signal (Bypass mode), you will need to readjust the height control to avoid SC vertical overscan. May 1997  23 For Sound-Off competitions, neon underbody car lighting is a fantastic visual effect. Now you can make it pulse on and off with the beat of the music. (Photo: Julian Edgar). Neon tube modulator for cars & light systems This little circuit will modulate the 12V neon tubes which are now available for lighting systems in cars. It connects to the subwoofer signal from the car sound system and the neon light is modulated by the bass signal. By RICK WALTERS These days it is impossible to miss the evidence that some cars are fitted with very fancy and expensive sound systems. Often, the sound systems are worth more than the cars and owners go to great lengths when competing in “Sound-Off” competitions. One of the more unusual ways to dress up a car is to use neon tubes to light up the under body, the cabin and the boot space of the car. The neon tubes we are talking about are 24  Silicon Chip 955mm long overall and are housed in a tough plastic pipe for protec­tion. At one end of the pipe is a plastic case housing a high voltage inverter running from 12V DC. These tubes are available from Jaycar Electronics at $49.95 (Cat. ST-3126). Connection is simple: you just connect the tube up to 12V DC and it runs. Well, pretty neon lights are OK but they’re a bit static aren’t they? We thought to ourselves, “Why not make them pulse in time to the bass beat of the music?” That should give the gawkers at Sound-Off shows something to look at! The solution is a small PC board which will drive one or two of these neon tubes. There is an onboard trimpot to set the sensitivity and that’s about it; set and forget. Circuit description The circuit of the Neon tube modulator is shown in Fig.1. The subwoofer audio signal from the car’s sound system is applied to the input level trimpot VR1. From there, the signal is coupled via a 10µF capacitor to the base of transistor Q1. Q1 is lightly biassed on by the 330kΩ resistor and this means that its collector voltage is normally close to 0V. Provid­ed that the audio signal is more than about 1V peak-to-peak, Fig.1: transistor Q1 is fed with the subwoofer signal and acts to trigger the 555 timer in 15ms bursts to extinguish the neon tube. PARTS LIST 1 PC board, code 05105971, 60 x 28mm 1 8-pin IC socket (optional) 5 PC stakes (optional) 1 10kΩ horizontal mount trimpot (VR1) it will be sufficient to turn transistor Q1 on and off. The resulting signal at the collector of Q1 will be a poor square wave with a rounded rising edge, due to the 0.1µF capaci­tor across the 6.8kΩ collector resistor, but with a much faster falling edge, as shown in the waveform of Fig.2. The capacitor rolls off any higher frequencies that may be present since we’re only interested in sub­woofer frequencies; ie, 100Hz and below. Q1 is used to control IC1, a good old reliable 555 timer wired as a triggered mono­stable oscillator. Its output, pin 3, will nor­mally be close to 0V and this will turn on transistor Q2 via its 1kΩ base resistor. Q2 will then feed the +12V battery voltage through the neon tube’s inverter and it will light up. This is the situation with no audio input. If a negative trigger pulse is applied to pin 2 of IC1, its output at pin 3 will go high, turning off Q2 and therefore the neon tube. The length of time the output is high is controlled by the 150kΩ resistor and 0.1µF capacitor connected to pins 6 and 7. With these values, the time the output is high is 15 millisec­onds, after which the output pin will go low again. This turns Q2 on again and the neon lights up once more. Semiconductors 1 555 timer (IC1) 1 BC549 or equivalent NPN transistor (Q1) 1 BD140 PNP power transistor (Q2) 1 1N4001 or 1N4004 power diode (D1) Capacitors 1 100µF 25VW PC electrolytic 1 10µF 25VW PC electrolytic 4 0.1µF MKT polyester 1 .01µF MKT polyester Resistors (0.25W, 1%) 1 330kΩ 2 6.8kΩ 1 150kΩ 1 1kΩ 1 10kΩ The PC board should only take a few minutes to assemble. It can be housed in a small plastic case. Fig.3: use this diagram when wiring up the PC board. Fig.4: actual size artwork for the PC board. May 1997  25 You simply hook the little PC board in series with a 12V neon tube to make the light pulse on and off in time to the bass beat of the music. PC board. Use one of these pig­tails for the link. If you wish to use an IC socket, fit it next along with trimpot VR1, then fit the MKT capacitors and transistor Q1. Finally, fit the electrolytic capacitors and transistor Q2. If you use PC pins solder them in now and if you used an IC socket, plug the IC into it, making sure it faces the right direction. Testing Fig.2: this is the waveform at the collector of Q1 when the circuit is fed with a low-frequency audio signal. This negative trigger pulse comes from Q1’s collector via a 0.1µF coupling capacitor. To recapitulate, audio signals from the subwoofer are shaped and clipped by Q1 then applied to the trigger input of IC1. The negative-going edge will trigger IC1, turning Q2 and therefore the neon tube off. After a short time IC1 will reset and the neon will ignite again. As the audio input is taken from the subwoofer feed, only the low frequencies are present and these tend to be a repetitive beat effect. If normal full range audio were to be applied, the 555 would be triggered continuously. Thus, Q2 would be permanently held 26  Silicon Chip off and the tube would never be lit. The circuit as shown is capable of driving two neon tubes in parallel at its output. Diode D1 provides protection against accidental reversing of the 12V supply. Board assembly It is always wise to check the etching of the PC board before you begin any assembly. Look for open circuits (breaks) in the tracks or areas where the copper pattern may not be fully etched away. Any repairs needed should be done first. Begin by fitting all the resistors and diode D1. Solder each lead in turn, then cut off all the pigtails below the You can use a 12V battery or a DC power supply for the test. Connect the supply negative wire to the PC board earth. Connect the tube’s red wire to the neon tube + terminal on the PC board and the tube’s black wire to the PC board earth. When you connect the 12V positive lead to the +12V battery input on the PC board the tube should light. If it doesn’t, check the orientation of IC1 and Q2, then double check the wiring as detailed above. Once you get the tube to light, connect your subwoofer signal to the audio terminals, making sure that the signal wire is connected to the top of VR1. This done, set your car stereo to the normal listening level and adjust VR1 until the neon pulsing effect suits you. Don’t turn the control up too far or the tube will spend most of its life turned off. Also heed the warning on the tube and don’t run it continuously for more than two hours and probably for even shorter periods in very hot SC weather. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. SERVICEMAN'S LOG Two VCRs, a TV & a computer Amongst the many services we offer nowadays, one is upgrading computers. This always sounds straightforward but it is easy to get caught with unforeseen problems. But first, a few of my more regular VCR and TV problems. The very nervous man who waltzed carefully into the shop was gently cradling his Panasonic video. “What’s it likely to cost?”, he whispered. “Well that depends on what’s actually wrong with it. What’s it not 28  Silicon Chip doing properly?”, I enquired. I tried to sound matter-of-fact so as not to frighten him too quickly. Mr Nervous fished around in his pocket and finally produced a small bit of folded paper which he passed to me. On it, he had written, in small neat writing, a short list of symptoms with the problems outlined very precisely. Summarising it, his Panasonic NV-G30 VCR was showing a noisy picture on playback and he could only tune in a channel if the antenna was plugged directly into his TV. He couldn’t watch TV whilst recording another channel. Oh dear, I thought, this could be a tricky one and the age of the video meant it wasn’t too far from its use-bydate. If, as I suspected, it was the RF modulator, this poor bloke could die from a coronary when told the likely cost. After all, the cost was obviously at the forefront of his mind. But then again, maybe he had misinterpreted the symptoms or perhaps it was only a dry joint. Who could tell? I decided the best course of action would be to come clean and tell him all the options and their likely cost, and hope he wouldn’t collapse on the floor. He was slightly taken aback with the worst option but he only wobbled and didn’t quite fall over. We finally settled on spending an hour’s labour on the machine to see what I could come up with. He made it to the door and I hoped he would make it all the way home. That afternoon when the bench was clear, I hooked up the video and switched on. My worst fears were confirmed – the symp­toms were precisely as listed, there were no intermittent dry joints, and the heads weren’t dirty. Obviously, the output from the video was low in gain, especially in the E-E mode (Electronic to Electronic mode or Tuner/RF modes). I stripped the unit down and removed the RF modulator which took quite a bit of effort. I then removed the covers and exam­ined the whole assembly carefully under a magnifying lamp. I could­ n’t discern any cracks, dry joints or obvious burn marks (of course, that just might be my age and sight) so, to be on the safe side, I reworked all the solder joints, reassembled the unit and switched it on. Unfortunately, that made no difference so it was back to the drawing board. Because the VCR is closest to the antenna, which is after all a near perfect lightning conductor, I considered that it might have suffered a small strike in a storm – enough to blow out the semiconductors in the front end while leaving everything else intact. With this in mind, my next step was to check all the diodes in the modulator. The multimeter unfortunately did not yield any secrets. I also measured the B+ to the modulator and checked the VTR/Antenna switch line but all was correct. At that point, I figured that I had gone as far as I could and that the worst-case scenario of a new modulator was inevi­ table. However, I decided to put the unit to one side for the rest of the day until I could gather the heart to break the bad news to Mr Nervous. And then came a stroke of luck. Later that afternoon, I got a call from a colleague wanting some technical support on a TV set he was working on. Fortunately, I was able to help him with his problem and then, because he is something of a National Pana­ sonic expert, I thought I would run my own problem past him in exchange. “Oh yeah, I know what your problem is – I thought everyone knew that symptom and its cure”. Obviously, everyone bar my humble self, that is. “It’s Q51, a 2SC2570 – just change it. You can’t measure it, apparently it’s gain changes”. My mind instantly went back to my college days when my tutor insisted that it wasn’t possible for a transistor to do this. “Er, thank you, of course I knew that – it just temporarily slipped my mind”. I couldn’t wait to test this wellknown cure. As it hap­pened, he was absolutely right on all counts. It was the transis­tor and I couldn’t measure anything untoward about it on the multimeter. And the VCR now worked perfectly. Anyway, I was certainly grateful to him, especially as it meant that Mr Nervous wouldn’t pass out at my counter. A Panasonic morning It must have been Panasonic day because the next job dropped in after Mr Nervous was yet another Pana­sonic VCR. The young man who came in was a completely different character from Mr Nervous and the NVL20A he was carrying was completely dead. And, he added, “it wasn’t just the fuse” because he had had a look at it and it was OK. I wasn’t too happy on learning that it wasn’t “just the fuse” because it meant that the young man had dismantled the switchmode power supply in order to gain access to it. Anyway, when I later I retraced his steps, I found that 240V was definitely going in and that +350V was appearing across the main electrolytic filter capacitor and was being applied to the switching IC. The power supply wasn’t making any noises at all but just to confirm that there were no shorts on the second­ary, I checked all the diodes using a multimeter to ground. Either the switching IC had carked it or the start-up circuitry wasn’t working. I considered the latter to be the more likely and concentrated on the electrolytics around the IC. C109 is a dirty grey/brown unit rated at 1µF 400V 105°C and it was definitely looking suspicious. I replaced it, reconnected everything, switched on and stood back. Nothing went bang and after one or two seconds I was rewarded with the clock display flashing and when I pressed the power button, everything sprang to life. Before putting it all back together, I carefully examined the rest of the electros in the power supply but they all looked pretty good. I boxed it up and soak tested it before phoning the young man to tell him the good news. I only wish all my jobs were that easy. The crook Blaupunkt Just before closing time, there was a lot of activity in shop as a large family tried to herd in their TV and plonk May 1997  29 it down on the counter. The story I pieced together from their various accounts, given in unison, was that a relative had given them the set and it wasn’t working. The set was a 56cm Blau­punkt Malta IP32 stereo TV in a wooden veneer cabinet. It looked in good condition but it made me nervous because it was a foreign TV and was over 10 years old. I identified the ringleader of this family fairly quickly because he was older and taller than the rest. When I mentioned problems about spare parts, their cost and availability, he was a little crestfallen as they were all so obviously proud of their new acquisition. And when one of them 30  Silicon Chip pointed out that one of my stickers was on the back (dated, I might add, in 1990), I felt honour-bound to at least have a look at it, which I agreed to do the next day. Before I removed the back, I looked up the last time I had serviced the set to find that the previous owner had lived very near the sea and I had replaced the flyback transformer seven years ago. When the back was un­clipped, I realised my worst fears because virtually all the metal surfaces were heavily rusted and parts of the PC board pattern had turned green. I gingerly connected the power and switched it on with the remote control. There were a few minor sparks as it tried to fire up but it didn’t quite make it, although the sound appeared to be working. Fortunately, when I had repaired it the last time, I had purchased the service manual for it. Now I was perusing the circuit for only the second time. Had it really been worth spend­ing all that money to store this manual for seven years? I wasn’t really sure but at least I had it for this job. Anyway, with the aid of the circuit diagram, I was able to identify and measure all the B+ rails. These were all OK, even to the collector of the line output transistor (V830). Next, I connected a CRO to the collector of this tran­sistor and switch­ed the set on. There was a brief flash of activ­ity on the screen before the trace went flat. More to the point, I could smell and see sparks everywhere. My immediate conclusion was that this was a very corroded old TV and that the EHT protection circuit was operating. And this in turn was preventing the line oscillator from delivering a signal to the output stages. Before going further, the set obviously had to be cleaned up. As a result, I sprayed, wiped and cleaned all the EHT stages with CRC2-26, including the ultor cap, the tube socket, the flyback transformer and the focus pot. After making sure that I had removed all the excess, I then heated all these parts with a hairdryer to make sure they were dry. When I switched on this time, there were no more sparks but still no EHT. It was time to go over the EHT protection circuit. A quick glance at the circuit soon established that the protection circuit is based on IC W700 and transistors V802 and V799. I overrode it by shorting pin 7 of W700 to ground and tried again. This time, smoke gushed from the flyback transformer and the job was starting to look expensive. Just in case something was loading it down, I disconnected the CRT ultor cap and also the CRT socket but there was still smoke. Finally, I disconnected the focus pot. This time there was a corona discharge from the flyback transformer to its nearest components so we had EHT. On examining the focus control, I could see that a carbon track had been etched on the board. Ob­viously, it had been arcing over for quite some time before it finally gave up. I cut, cleaned and filed this track away to stop the arcing but when it was all reconnected, smoke again erupted from the flyback transformer and, to a lesser extent, from the focus pot. I knew it was hopeless to try any more – these parts just had to be replaced. I phoned the agents in Melbourne to find that both parts were still available, although they were pretty expensive. I could only pass the news on to the family and advise them that I really didn’t think the set warranted this expense. Surprisingly, they didn’t agree with me. I suppose that because they got the set for free, my service cost really only represent­ ed the full purchase price to them. As a result, they decided to proceed and so the parts were ordered. The parts arrived about a week later and I quickly set about installing them. When I removed the old focus pot, a plas­tic clip on the case came off, the ceramic element fell out and I could see where it had been burning internally. I cleaned the PC board where the two parts had been located before soldering in the new ones. When I subsequently switched it on, I was rewarded with a blurred picture. This came good when the focus control was ad­ justed. I then checked all the functions and left it on to soak test. Despite its years, the picture was excellent and, after a couple of days, I felt confident that the set was going well. However, when the family clan reassembled to collect it, I told them that the set was old and corroded and that I could only guarantee the parts and labour I had supplied. I don’t know whether this sank in but I haven’t heard from them since. The computer upgrade No sooner had they departed than Mrs Brown brought in her son’s old 286 and wanted it upgraded. Despite his pathetic pleas for a new Pentium machine with all the bells and whistles, Mrs Brown was on a budget and after some heavy haggling settled for a secondhand 486 motherboard with 8Mb of RAM, a 1Gb IDE hard disc drive, and a new Microsoft mouse. She also supplied the upgraded software that was to be installed, namely DOS 6.22 and Windows 3.11. I allowed an hour’s labour to swap the hardware plus a further hour to load the software and quoted accordingly. All went well apart from the usual swearing and bad temper that goes with removing and fitting a new motherboard in under the power supply and drive bays. The other drama involves working out where to connect the leads from the front control panel and configuring the turbo speed display. It’s OK if you have a manual for the motherboard but in this case the manual had long ago disappeared. Anyway, the new 486 booted up OK and I was able to install DOS and Windows without any dramas. I then ran Memmaker to opti­mise the RAM and configured Windows for 32-bit file and disk access. I also set up a permanent swapfile, to ensure efficient operation. Altogether, it was a fairly satisfactory job even if it did take longer than expected. It’s amazing how the time disappears when working on a computer. The new mouse was a beauty and felt very positive. I installed MOUSE.EXE v. 9.01 through the usual setup disk and configured it as described in the manual. A secondhand pup? I was happy with the job and more importantly so was Mrs Brown and her son when I showed it to them. That is, until about a week later when they reappeared in the shop with a completely different attitude, namely that I had sold them a secondhand pup. After soothing down their ruffled feathers and reassuring them that it was all guaranteed, I finally got down to asking them what the real problem was Despite all the aspirations of the upgrade being an essen­ tial educational tool, it turned out that an old game now refused to work and the computer was hanging when he tried to get into it. “Look”, I said recklessly, “leave it with me and I will fix it”. Courageous but foolish words. That night, I set it all up and tried to figure out what was going wrong. The game was Battle Chess, circa 1988. This is a mouse-driven animatMay 1997  31 ed 3D game of chess. The graphics of this par­ticular version are now quite ordinary by modern day standards but it is still an excellent game and the fault was exactly as described. The easiest answer would have been to get an upgrade of the game but in the light of my rash promise, this was no longer an option. OK, so it worked all right on the old 286 but not since the upgrade, so what was it that it didn’t like? Was it the speed of the new machine, the graphics, a memory conflict, or something else? First, I checked the amount of free RAM by typing mem /c/p. This gave the largest executable program size as 613Kb, which was plenty. But was there perhaps an EMM386.EXE exclusion conflict in high memory? I re­boot­ed the computer, pressed F8 when it reached “Starting MS-DOS”, and said no to both the HIMEM.SYS and EMM386.EXE lines in the CONFIG.SYS file. This meant that every­ 32  Silicon Chip thing would be loaded low. When the bootup sequence was complete, I ran mem /c/p again and this reported that the largest executable program size was now only 530Kb. Was this too low to run this program? There was only one way to find out. When I typed C:\CHESS>CHESS, the opening screen came up as usual and when I pressed ENTER to start the game it hung just as before. And as before, the edge of the mouse was just visible on the righthand side of the screen. Strictly speaking, it wasn’t completely “hung” up in that the CAPS LOCK, NUM LOCK and SCROLL LOCK keys still functioned. However, no other keyboard or mouse commands made any difference apart from the three-fingered salute “ CTRL-ALTDEL”. By now, I was fairly sure that it wasn’t a memory conflict. Perhaps it was the faster motherboard or perhaps it was the driver for the hard disc. To test the latter theory, I decided to copy the Battle Chess program to a bootable floppy disc and try running it from there. This time, when the second ENTER was depressed, the game didn’t hang and instead one of the squares was flashing as if to start. The only problem was that there was no mouse; I had for­ gotten to load the driver. However, I quickly discovered that the game could be played using the keyboard, although I didn’t know all the commands. I did find, however, that the arrow keys and ENTER moved the pieces, while F1 brought down the menu bar. So the game worked OK when loaded from a floppy disc with­out the mouse. The fact that it was being loaded from a floppy disc was probably irrelevant; instead, I was beginning to suspect a rodent problem. To prove this point, I copied the mouse driver from the hard disc to the floppy, loaded it and tried loading the Battle Chess program again. This time, the game hung as before but I was getting closer. It seemed to me that the game didn’t like the new mouse on COM1. I tried plugging the mouse into the second COM port and even tried a different type of mouse before I realised that it wasn’t the mouse itself that it didn’t like but its driver (MOUSE.EXE). I was surprised at this turn of events because I have always found the Microsoft mouse to be excellent, with very few compatibility problems. Unfortunately, this particular driver wasn’t compatible with this early version of Battle Chess. So, what was the fix? I decided that the only course was to experiment with some older drivers. My first choice was another Microsoft Mouse driv­ e r, MOUSE. COM v8.2. I deleted MOUSE.EXE from the floppy disc and replaced it with MOUSE.COM (at this stage, I was sticking with the floppy disc to avoid any other unforeseen conflicts). This time, everything worked correctly. The Battle Chess game loaded without problems and the game could be played using the mouse. My next step was to see what could be done on the hard disc. Normally, when booted, MOUSE.EXE v9.01 is mainly loaded into high memory (272 bytes into conventional memory and <at>echo off cls mouse.exe off cd\chess lh mouse.com chess.exe mouse.com off cd \ lh mouse.exe I put the old mouse driver in the chess directory, so that it would be found when the time came to load it. Basically, the batch file cleans up the screen, turns off the MOUSE v9.01 driv­er, switches to the chess directory, loads the compatible MOUSE v8.2 driver, and starts the game. Then, when you quit Battle Chess, it turns off the old mouse driver, switches to the root directory and loads the new mouse driver. It all worked, so I left it at that. When Mrs Brown picked up the computer the next day, I pointed out that there was nothing really wrong with it. Instead, the problem was a software conflict that could have been fixed by upgrading to the latest version of Battle Chess. I think she might have suspected something like that all along, judging by the slightly detectable smirk on her lips as she and her boy disappeared out to the car. Or perhaps I’m becom­ ing oversensitive. Just in case you’re wondering, the above batch file will only work at DOS level. You cannot change mouse drivers within Windows without a lot more work. I have also been informed that Battle Chess was upgraded in 1992/1993 and was last available on CD with terrific new multimedia and VGA graphics. I don’t know whether it is still available but apparently this version worked fine with MOUSE. SC EXE v9.01. SILICON CHIP SOFTWARE Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands are listed on the screen, so you’ll always know what to do next. Notes & Errata also now available: this file lets you quickly check out the Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate the item of interest. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. ORDER FORM PRICE ❏ Floppy Index (incl. file viewer): $A7 ❏ Notes & Errata (incl. file viewer): $A7 ❏ Alphanumeric LCD Demo Board Software (May 1993): $A7 ❏ Stepper Motor Controller Software (January 1994): $A7 ❏ Gamesbvm.bas /obj /exe (Nicad Battery Monitor, June 1994): $A7 ❏ Diskinfo.exe (Identifies IDE Hard Disc Parameters, August 1995): $A7 ❏ Computer Controlled Power Supply Software (Jan/Feb. 1997): $A7 ❏ Spacewri.exe & Spacewri.bas (for Spacewriter, May 1997): $A7 ❏ I/O Card (July 1997) + Stepper Motor Software (1997 series): $A7 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). ✂ 24,336 into upper memory). I didn’t really want to stop using this driver as it worked so well in Windows. Fortunately, when I typed MOUSE/?, a whole host of options appeared, one of which was “off”. To save time and because I wasn’t actually making any money on this software problem (which wasn’t really my responsibility), I decided to write a simple batch file. This file, called CHESS.BAT, swaps the mouse drivers around as necessary and loads the game. This batch file went like this: May 1997  33 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 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. Passive network reduces DC offset effect DC offset voltages in audio power amplifiers can present a serious problem if the load is a transformer with a low resistance primary. The DC offset can cause large currents to flow which can lead to thermal runaway in the amplifier and damage to the trans­former. For this reason, the DC offset voltage is usually nulled to zero by a trimpot associated with the input differential transistor pair. However, unless the transistors are closely matched and are thermally bonded together, there is still the possibility of DC offset as the temperature changes. This DC offset increase can be made less of a problem if there is a low impedance load by the addition of a passive net­work involving four 5.6kΩ resistors and a 22µF bipolar capacitor. As depicted here, the network has been added to the output stage of the 150W PA amplifier featured in the March 1997 issue of SILICON CHIP. In effect, the four 5.6kΩ resistors sum the DC voltages across the upper SCR pre-regulator circuit Here is a way to make use of a transformer with a secondary voltage too high for the job in hand, without the need for a large heat­ sink. It is essentially a pre-regulator circuit using an SCR as a switching regulator. A bridge rectifier supplies raw DC to an SCR which is con­trolled to fire on the back part of each half cycle. D1 and zener diode D2 generate +5V for the control circuit which employs an LM324 quad op amp. IC1 is connected as a comparator. The normally high (+5V) output of IC1a falls to zero when the raw DC input is less than one diode drop above zero. The peak value of this 38  Silicon Chip and lower output transistor emitter resistors. The output offset current will pass through only the upper or lower pair of emitter resistors, depending on its polarity. Therefore, the net DC voltage due to the offset current is equal to the product of the offset current and the two 0.47Ω emitter resistors in parallel. This is divided by two (the mixer attenuation) and fed via the 18kΩ feedback resistor to the base of Q2. Meanwhile the AC signal feedback is coupled from the ampli­fier’s output via the 22µF bipolar capacitor The effect of this arrangement is equivalent (under DC conditions only) to placing a 0.12Ω resistor between the output of the amplifier and the load. The equivalent resistance is not present for AC signals, which means that there input must be less than Vcc; ie, no more than +5V. IC1b is connected as an integrator and generates a positive ramp voltage at its output. This ramp is reset to 0V at the beginning of each half cycle by the zero notch in the output of IC1a. The slope of the ramp is adjusted by 10kΩ multi­turn pot VR1. This pot should be set to midrange initially and adjust­ ed so that the ramp extends for each half cycle. This ramp voltage is fed to the non-inverting input of IC1c, the error amplifier. Its inverting input is fed with a control voltage and the two are compared. During any half cycle, when the ramp voltage exceeds the control voltage, the output of IC1c will go high and this will be no loss of output power. A value of 0.12Ω is not large enough to eliminate the need for static offset will, via optocoupler IC2, fire the SCR. This then charges the output capacitor via diode D3. Note that an increase in control voltage will trigger the SCR later in the half cycle so the output voltage will be lower. IC1d is arranged as a summing amplifier and its output is a function of the output voltage sample at pin 3 and the DC level from 5kΩ trimpot VR2. The 4.7µF capacitor connected to pin 3 pulls this input high for soft starting. The circuit will regulate the output to within ±1V of the desired setting. The 3A supply fuse is essential as the current demand under fault conditions can destroy the SCR. W. Jolly, Tranmere, SA. ($40) voltage nulling but it greatly improves its effectiveness. For a typical 0.1Ω output transformer primary, the effective DC load resistance will be in- creased to 0.22Ω, more than doubling the allowable input offset voltage. (Editorial note: this circuit does add a pole (extra time con­stant) to the amplifier’s AC response and may lead to instabili­ty.) Bret Hirshman, Pymble, NSW. ($30) Latched outputs for IR remote control have had a number of readers request a circuit to convert the momentary outputs to latched outputs; ie, one button push for on and another push for off. This circuit uses a 4013 D flipflop (IC3) to convert each momen­tary output to a latched output. A transistor driven from each Q output can then used to drive a relay for switching external circuitry. SILICON CHIP. The 8-channel IR remote control featured in the February 1996 issue has been a popular project but we May 1997  39 A quickie project for your model railway By RICK WALTERS Traffic lights for a model layout Most model railway layouts have a few roads wending their way around and often a small town with an intersection is included. A good way to add life to such a scene is to have working traffic lights at the intersection. Any working light system on a model railway will add real­ism and having working traffic lights – cycling through the green, amber, red sequence – is a nice touch that can be easily and cheap­ly achieved. While you will probably have at 40  Silicon Chip least two sets of traffic lights visible and perhaps up to four sets for one intersection, you only need one PC board to drive the lot. These lights will change in the normal green, amber, red sequence which most of us, as motorists, are used to. We have chosen a timing cycle which seems realistic but it can be changed, as described later. Circuit description Fig.1 shows the circuit details. IC1 is a 555 timer which is wired as a free-running oscil­lator with a frequency of about 5.3 seconds, as determined by the 220kΩ resistor and 10µF capacitor connected to pins 6 & 2. IC1’s output at pin 3 is used to clock pin 14 of IC2, a 4017 counter with 10 outputs, each of which goes high in turn. Each time pin 14 of IC2 is clocked, the next output goes from 0V to +12V (low to high). Thus, each of the 10 outputs is high for about 5.3 seconds and low for about 48 seconds. We use a diode gating system from these 10 outputs to turn on the respective green, amber (orange) and red lights for dif­ferent times. Hence, the amber lights are only on for one clock cycle (ie, 5.3 seconds), while the red and green lights are each on for just over 26 seconds. By the way, if this overall cycle of 53 seconds seems too long or too short, it is a simple matter to change it by changing the value of the 220kΩ resistor at pins 6 & 2 of IC1; higher values give longer times and vice versa. The outputs are shown sequentially on IC2, going from output zero on pin 3 through to output 9 on pin 11. Only one output at a time can be high, as already noted. Let’s look at the outcome when pin 3 is high. Transistor Q1 will be turned on via the 10kΩ resistor connected to its base. This will turn on the two orange LEDs wired to its collector. In addition, transistor Q4 will be turned on via D1 and its 10kΩ base resistor, causing the red LEDs in its collector circuit to light up. By the way, we will use amber and orange interchangeably as we go through this article. Most people refer to the middle light as “amber” instead of orange but LEDs are available in orange, not amber. Typical intersection Before we go any further, we need to explain how all the light emitting diodes (LEDs) are wired up to control a typical intersection. Have a look at Fig.2 which shows a typical inter­ section with four sets of traffic lights to control the four directions of traffic. We have named the horizontal road “Cross Street” while the vertical road is named “Down Street”. (We hope readers appreciate how much of a mental strain it was for us to come up with these imaginative names.) As can be seen from the labelling of the four traffic lights, LEDs 1-6 Fig.1 (right): the circuit is based on a 4017 decade counter (IC2) which drives transistors and LEDs in a fixed sequence lasting around 53 sec­onds. IC1, a 555 timer, provides the clock signals for the counter. May 1997  41 Fig.2: this diagram will help in visualising the circuit opera­tion and also when the time comes to wire the lights (LEDs) at the intersection. control the traffic along Cross Street while LEDs 7-12 control the traffic along Down Street. Furthermore, the LEDs are paired up so that, LEDs 3 & 4 are the orange (amber) lights for Cross Street and so on. Traffic light cycle Fig.3: these waveforms are taken at three points in the circuit, with operation speeded up by 2.7 times. The upper trace shows the output at pin 3 of IC1, the clock cycle. The middle trace shows the signal at pin 3 of IC2. When this is high, Q1 and the orange LEDs 3 & 4 are on. The bottom trace is the signal at the junction of diodes D2-D6 and represents the signal driving Q2. When this is high, Q2 and the red LEDs 1 & 2 are on and so are the green LEDs 11 & 12. 42  Silicon Chip Thinking about how traffic lights work in practice, when the lights are green for traffic in Cross Street, they will be red for traffic in Down Street. When the lights change to amber (orange) in Cross Street, they remain red in Down Street. Final­ly, after the lights change from amber to red in Cross Street, there is a short delay before the lights in Down Street change to green. This short delay gives a slight margin of safety for those fools who run through red lights. In our modelling version of traffic lights, we have the same sequence except that when the lights change from amber to red in Cross Street, they simultaneously change from red to green in Down Street. This slight variation from reality can be toler­ated in a model railway scene, because the road vehicles in a typical model railway layout don’t actually move! And even if you were using wire-guided moving road models, you wouldn’t have to worry about the dangers of any vehicle running red lights. So now let’s resume our description of the circuit opera­tion. As we said, pin 3 of IC1 is high, Q1 is on so that LEDs 3 & 4 are lit, and Q4 is still on as well, so that red LEDs 7 & 8 are on. Traffic in Cross Street is coming to a stop while traffic in Down Street is stopped and ready to go. When IC2 is next clocked, pin 3 will go low and pin 2 will go high. So Q1 will turn off, Q2 will turn on showing red lights in Cross Street, and Q4 will turn off, allowing green LEDs 11 & 12, to light. So traffic in Down Street gets the green light. Note that both sets of green LEDs, 5 & 6 and 11 & 12, are not turned on by transistors. This is possible because both sets of six LEDs (red, orange, green) are each fed via a common 470Ω resistor. When transistors Q3 and Q4 are off, green LEDs 11 & 12 will be fed via diode D11 and the 470Ω resistor. Whenever Q3 or Q4 is turned on, the green LEDs will be extinguished as the voltage drop across the red or orange LEDs and their transistor will be less than that You can increase the realism at a road intersection on a model railway layout by having the lights working. This board is shown assembled with 12 LEDs to check its opera­tion. In normal use, the LEDs will be installed in the traffic lights at the intersection. Fig.4: the component layout for the PC board. Note that the LEDs are only installed on the board for checking its operation. across the green LEDs and diode D11. A similar situation exists with Q1, Q2 and the green LEDs 5 & 6. Thus we have red lights in Cross Street and green lights in Down Street. This condition is maintained for the next four clock cycles or 21.2 seconds (5.3 x 4) at which point pin 1 of IC2 goes high to turn on Q3 and orange LEDs 9 & 10 (for Down Street). This extinguishes the green lights and diode D6 keeps Q2 turned on to maintain the red lights (LEDs 1 & 2) for Cross Street. In the next clock cycle, pin 5 (output 6) goes high and pin 1 goes low. So Q4 turns on to light LEDs 7 & 8 and Q3 turns off. Q1 also turns off and so green May 1997  43 PARTS LIST 1 PC board, code 09205971, 95 x 80mm 1 555 timer (IC1) 1 4017 counter (IC2) 1 7812 12V regulator (REG1) 5 BC548 or BC338 NPN transistors (Q1-Q5) 4 green LEDs (see text) 4 orange LEDs (see text) 4 red LEDs (see text) 12 1N914 silicon diodes (D1D12) 1 1N4004 silicon diode (D13) Capacitors 1 100µF 25VW electrolytic 2 10µF 25VW electrolytic 1 1µF 25VW electrolytic 1 0.1µF monolithic ceramic 1 .01µF MKT Resistors (0.25W, 1%) 1 220kΩ 2 470Ω 0.5W 1 100kΩ 1 100Ω 8 10kΩ Where to buy parts Note: Oatley Electronics can supply a pack of 2mm LEDs for installation in HO scale signals. Each pack contains 10 red, 10 orange and 10 green LEDs, plus 30 1kΩ resistors. The cost is $10 plus $3 for postage and packing. Oatley Electronics is located at 66 Lorraine Street, Peakhurst, NSW 2210. Phone (02) 9584 3563; fax (02) 9584 3561. LEDs 5 & 6 are lit, via D12. If you keep stepping through the outputs of IC2 you will see that the traffic lights cycle in the correct sequence. Scope waveforms The oscilloscope waveforms of Fig.3 show the sequence speeded up by about 2.7 times. The upper trace shows the output at pin 3 of IC1, the clock cycle. In this case, the clock cycle is 1.35 seconds. The middle trace shows the signal at pin 3 of IC2. When this is high, Q1 and the orange LEDs 3 & 4 are on. The bottom trace is the signal at the junction of diodes D2-D6 and represents the signal driving Q2. When this is high, Q2 and the red LEDs 1 & 2 are 44  Silicon Chip Fig.5: the actual size artwork for the PC board. Check your board carefully against this pattern before installing any of the parts. on and so are the green LEDs 11 & 12. Traffic lights override One additional feature we have included is the ability to set IC2 (and thus the traffic lights) to a known state. This is done by grounding the 100Ω resistor in the base circuit of tran­ sistor Q5. This will reset IC2, so that pin 3 (output 0) is high. This is the initial condition which we described, whereby Q1 is on and the orange LEDs 3 & 4 are lit. If the lights for Cross Street were also used to control the traffic over a railway level crossing, an approaching train could ground the 100Ω resistor. This would immediately show an orange light to the traffic, followed by red on the next clock pulse. This gives the train an ‘all clear’ though the intersec­tion. The only remaining aspect of the circuit to talk about is the power supply arrangement. A 3-terminal regulator REG1 is used to obtain a stable 12V supply for the circuit and diode D13 provides protection against reversed polarity. Building it The PC board for this design measures 95 x 80mm and is coded 0910-5971. After checking the copper pattern for any defects against the artwork of Fig.4 you can start assembly by inserting the resistors and diodes. Note that all the diodes on the board face the same way; ie, with their cathode bands away from IC2. Next, insert the transistors and capacitors, ensuring that the electrolytic capacitors and transistors are correctly orient­ed. This done, insert the ICs and the 3-terminal regulator, REG1. Finally, you can insert the LEDs. While our prototype has been wired with the correct coloured LEDs on the board, this is not necessary for checking the circuit operation. You could initially use LEDs that all have the same colour. Testing To test the board, apply +15V to the input and check that the LEDs turn on and off in pairs. The red and green pairs should alternate with each other and the orange pairs should only turn on for just over five seconds each time. The total cycle time should be around 53 seconds but the exact value will depend on the tolerance of the 10µF capacitor connected to pins 2 & 6 of IC1. When wiring the traffic lights on your layout, 2mm LEDs are the closest to correct scale for HO layouts (1:87 scale) while 3mm would be good for O scale layouts (1:43). If you’re into N scale, the only way to produce a correct scale traffic light set would be to use optical fibres. Use the diagram of Fig.2 to aid in wiring the traffic lights for your SC intersection. SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SATELLITE WATCH Compiled by GARRY CRATT* Intelsat satellite shuffling under way Some shuffling of the Intelsat satellites has . taken place in recent months, with Intelsat 801 now in orbit and Intelsat 802 slated for a June launch. At the same time, some of the earlier satellites are to be moved to new locations. Intelsat 801 was successfully launch­ ed by Ariane V.94 on March 1st, 1997. Despite earlier intentions of moving the satel­lite to 174°E and shuffling the present Pacific Ocean Region birds (including replacing I511), the spacecraft will now be positioned at either 62°E or 64°E, in the Indian Ocean Region. From either position, the satellite footprint will cover part of Australia and Indonesia, using a SE zone beam. Intelsat 802 will now be launched in June and will be posi­tioned at 174°E, replacing Intelsat 701 which will be moved to 180°E. Intelsat 511 at 180°E will be deployed to 157°E, whilst Intelsat 503, presently located at 157°E, will be de-orbited. Measat 2, 148°E longitude: March 5th saw the first identifiable tests from MEASAT 2 at 148°E, with colour bars being displayed at IF 1065MHz and audio at 6.8MHz. No doubt, the users of this satellite will be re­vealed after this testing phase is complete. By now, Asiasat 2 should be broadcasting another free-to-air MPEG signal. Myan­mar’s MYAWADDY TV, which was operating each morning on Asiasat 1, was due to commence digital transmissions during March, for both their morning and evening broadcasts. Optus B3, 156°E longitude: Meanwhile, to make room for OptusVision Pay TV on the Optus B3 satellite, the ABC Northern Territory, Imparja and the ABC South Australia services will change frequency over the next few months. Viewers will be notified by mail or can obtain details from satellite equipment dealers. Palapa C2: March 9th saw the Indonesian broadcaster SCTV testing BMAC format signals on the Palapa C2 satellite. RCTI, previously available at IF 1350MHz, has been moved to 3745MHz (IF 1405MHz). TV Brunei has commenced operations on Palapa C2 for 18 hours each day. The transponder is being shared with SITV (Singa­ pore International TV), who utilise the transponder for one hour each day. Gorizont 29, 161°E longitude: Those monitoring the orbital position of the old Rimsat G1 (Gorizont 29) satellite are no doubt puzzled as to why the space­craft is now located at 161°E. The satellite was origi­nally located at 130°E and is believed to have been sold to a new regional operator. The details are unknown. Net on Air-Asiasat 2: Despite two attempts to demonstrate the net on air system via the Asiasat 2 satellite in January and February, the com­mencement of the service is scheduled for this month. Effects of data stream testing on March 8th and 9th caused problems with Pace, Panasat and Grundig MPEG receivers. Deutsche Welle services were disrupted for two days. The other EEB servic­es were unaffected. It is now obvious that the system is not completely debugged. Intelsat 702, 177°E longitude: Space TV Systems Taiwan say they will soon release their 6-channel DBS service to Chinese residents in Australia. The foot­print we have been given shows 45.5dbw at beam centre, a very strong signal indeed. This equates to using a 90cm/1.2m dish. According to a company spokesperson, the service was to begin testing early March. The service will be MPEG-2 using non-IRDETO conditional access. The new Japanese broadcaster “Jet TV” is testing a 5-chan­nel digital service in PowerVu. The IF is 1188MHz. Present­ly, the service is free-to-air, although it is not known how long this will remain the case. The service is believed to be uplinked from SC Singapore. * Garry Cratt is Managing Director of AvComm Pty Ltd, suppliers of satellite TV reception systems. Phone (02) 9949 7417. http://www.avcomm.com.au May 1997  53 If you want others to notice what you have to say, try using the Spacewriter. Simply wave it from left to right to automatically display a message that appears to materialise out of thin air. By JOHN CLARKE This novel gadget is ideal for games nights, outdoor ev­ents, spy activities and for just having fun. Called the Space­ writer, it can display up to four separate messages, each up to 10 characters long. The messages are programmed in via the print­er port of a PC, after which the Spacewriter operates indepen­dently of any other equipment. The Spacewriter comprises a length of 32mm diameter conduit with a single column of seven LEDs at the top end. The lower end has two push­ button switches to select the message, while a switch on the bottom end cap selects between Record, Spacewrite and Off. By waving the Spacewriter from side to side the appropriate LEDs light up in sequence and a message magically appears to be writ­ ten in “space”. If you want to select a new message, no problem - just press one (or both) of the two pushbutton switches on the side. And if you tire of the existing messages, you can quickly program in a new batch using your PC. How it works Fig.1 shows how we can use a single column of seven LEDs to make up the first three characters of the alphabet. To display an “A”, the Spacewriter Fig.1: this diagram shows how a single column of seven LEDs can be used to make up the first three letters of the alphabet. It’s simply a matter of lighting the appropriate LEDs at the appropriate times as the column travels from left to right. 54  Silicon Chip momentarily lights LEDs 2-7 to form the left hand side of the letter. These then extinguish. A moment later, the LEDs are positioned further to the right and the next part of the letter is displayed by lighting LED1 and LED4. This process continues until the entire letter has been displayed, after which “B” and “C” are displayed in similar fashion. In practice, the display process relies on the Spacewriter being swung from left to right so that each successive part of the character is located just to the right of the last. Our observation of the complete display depends on persistence of vision where­by we continue to see an image for a short time after it has gone. Block diagram Take a look now at Fig.2 – this shows the block diagram of the Spacewriter. The basis of the circuit is the memory block, which stores the requisite LED codes to make up the messages. Each memory location stores the code for one column of each character. Each memory location is sequent­ ially accessed using coun­ters IC3 and IC4. These increment the address at a rate set by a clock circuit based on IC2. During this process, the memory data lines from IC1 switch the LEDs on and off via driver transistors Q1-Q7. Flipflop IC5 resets the counter and stops the clock (IC2) via its reset input when the counter (IC3 & IC4) reaches its end of count value. IC5, in turn, is reset via mercury switch S2 which closes when the Spacewriter begins travelling from left to right. This allows clock IC2 to start again and so the counter stage begins counting again to Features • • • • • • Writes messages of up to 10 alphabet characters in “space” Four separate messages can be stored & displayed Messages programmed via a PC printer port Operates independently from the computer once programmed Adjustable write speed Battery powered shuffle data out of the memory. For the display to be readable, the entire message must be spelt out during a single left-to-right sweep of the LEDs in space. This means that the clock rate must be set to suit the person using the Spacewriter. If the clock rate is too slow then the characters will appear to be stretched. Conversely, if it is too fast, the characters will appear squashed. Ultimately, if the clock rate is really fast compared to the Spacewriter swing time, all that will be seen is a single column of flashing LEDs. VR1 sets the clock rate and is adjusted to prevent any significant smearing of the display as it travels in space. Another parameter which requires adjustment is the delay before the message starts after the mercury tilt switch closes. If it starts immediately, the first characters will appear to be squashed or will not be discernible at all. And if the message begins too late, the display will start too far to You just wave the Spacewriter back and forth to display a message that appears suspended in thin air (computer processed photograph). the right and may not be completed before the swing is finished. VR2 sets this delay parameter and is also adjusted to suit the user. As well as driving the LEDs (via Q1-Q7), the data lines for the memory are also connected to a computer printer port for programming. During this process, counters IC3 & IC4 are clocked under software control, with S1 selecting the strobe signal from the printer port. The printer port also provide the read /write selection for IC1 and provides the necessary reset signals for the counters. Circuit details Refer now to Fig.3 for the circuit details of the Spacewriter. It consists of just five ICs, several transistors, diodes and LEDs, a 3-terminal regulator and a handful of other passive parts. IC1 is the memory which stores the character information. This is a TMS6264L 8Kb x 8-bit memory which May 1997  55 means that it has eight data lines and 8192 spaces. Since we are using only 64 locations for each of the four possible stored messages, the memory size far exceeds our requirements. However, the device was chosen because of its low cost compared to smaller static RAM devices. As shown, data lines D1-D7 from IC1 drive transistors Q1-Q7 via 2.2kΩ resistors. Q1-Q7 in turn drive the Spacewriter LEDs (LEDs1-7) via 15Ω current limiting resistors. The data lines also connect to the PORT.A printer port of a PC for programming. IC3 & IC4 are the counters and these drive address lines A3, A1, A5, A4, A2 & A0 of IC1. The A12, A6 and A7 inputs are normally tied low via 10kΩ resistors but can be pulled high via switches S3 and S4 to access data in another memory block. Note that the address lines are not in any particular se­quence and the labelling shown is the convention of the 6264 device. The address lines can be in any order since we are pro­ gramming and replaying data in the same sequence. IC2 is a 7555 timer configured to operate in astable mode. This clocks counters IC3 & IC4 when switch S1 is in the Space­write position. The clock frequency is set by the RC components connected to pins 6 & 7 and is adjusted using VR1. IC2’s pin 3 output also drives the E1-bar input (pin 20) of IC1 via a 56  Silicon Chip .056µF capacitor. This is a select pin which sets the data lines in a high impedance state and shuts down the memory when it is high. We have used this feature to produce a short on-time for the LEDs when pin 3 of IC2 is low (this prevents the display from smearing). When pin 3 of IC2 goes high, IC3 and IC4 are clocked to the next address and the E1-bar input of IC1 goes high to disable the memory. IC3 and IC4 are presettable up/ down counters which have been set to count in binary. In addition, the two counters have been cascaded by connecting the carry out (pin 7) of IC3 to the carry in (pin 5) of IC4. The presettable jam inputs at pins 4, 12, 13 and 3 (corre­sponding to J1, J2, J3 and J4) are all tied low so that when the Preset Enable (PE) input at pin 1 is pulled high, the Q outputs all go low. This resets the counter to zero. Initially, IC2 is reset when the output of NAND gate IC5c pulls pin 4 low. In greater detail, IC5c and IC5b together form an RS flipflop. When IC5b’s output (pin 11) is low, IC5c’s output (pin 3) is high and vice versa. These outputs are set and reset by low-going pulses to pins 12 & 2, respectively. When mercury switch S2 closes, the 1µF capacitor at the input of Schmitt NAND gate IC5d charges via VR2. The output of IC5d then goes low and briefly pulls pin 2 of IC5c low via a Programming When the circuit is connected to a PC printer port, the D1-D7 lines of PORT.A are used to apply the character codes to memory IC1. Control over this operation is enabled using the W-bar input at pin 27 of IC1, the PE inputs of IC3 & IC4, and the clock input to IC3 via switch S1b. These signals use the D0 output of PORT.A and the -D0 and -D1 outputs of PORT.C, respec­tively. Initially, counters IC3 & IC4 are reset using -D0. The requisite codes are then applied to the data inputs of IC1 with the W-bar input low to write the data to the memory. The clock signal from -D1 increments the memory locations. This entire programming process is controlled by software (either SPCWRI.EXE or SPCWRI.BAS). The user Fig.3 (right): the final circuit consists of just five ICs, several transistors, diodes and LEDs, a 3-terminal regulator and a handful of other passive parts. IC1 is the memory chip which stores the character information  Fig.2: the block diagram of the Spacewriter. The memory block stores the LED codes to make up the messages and each memory location is sequentially accessed using coun­ters IC3 and IC4. The memory data lines from IC1 switch the LEDs on and off via driver transistors Q1-Q7. .001µF capacitor. This capacitor then quickly charges again via its associated 220kΩ resistor and pin 2 of IC5c goes high again. As a result, pin 3 of IC5c briefly goes low and then high again to reset IC2. It also resets IC3 and IC4 by applying a pulse to their reset enable (PE) inputs via a .001µF capacitor. IC2 now applies clock signals to the pin 15 inputs of IC3 and IC4 via S1b. At the 64th clock pulse, the Q3 output of IC4 (pin 14) goes high. This high is inverted by IC5a and a low-going pulse is applied to pin 12 of IC5b (part of the RS flipflop) via a .001µF capacitor. The flipflop now toggles, with pin 11 of IC5b going high and pin 3 of IC5c going low. IC2 is thus held in the reset condition and clocking ceases. D4 is included to prevent the pin 1 inputs of IC3 & IC4 from going below ground potential when pin 3 of IC5c switches low. Similarly, D1 & D2 protect the inputs of IC5b & IC5c when the outputs of IC5a & IC5d go high. D3 quickly discharges the 1µF time delay capacitor when the mercury switch opens, to reset the delay circuit. May 1997  57 This view shows the completed PC board prior to final installation in the tube. Note how the mercury switch has been oriented at a 45° angle to IC1. This is necessary to ensure that it only closes when the Spacewriter stops at the end of the lefthand arc. simply boots the program and types in the messages on the keyboard. Power is derived from a 9V battery via switch S1a and this is fed to 3-terminal regulator REG1 to derive a regulated 5V supply for the circuit. Note that REG1 is a low-power device to minimise the drain from the battery. The quiescent current is nominally about 4.5mA with the mercury switch open and about 6.7mA when it is closed. The 10µF capacitors at the input and output of REG1 prevent instability and improve transient response of the regulator. In addition, a 10Ω resistor is included between the +5V rail and the LEDs to decouple them from the rest of the circuit. Construction The SILICON CHIP Spacewriter is built on a PC board coded 08305971 and measuring 292 x 18mm. This is housed in a 400mm length of 32mm conduit with end caps. An adhesive label is at­tached to the lower end cap to indicate the switching positions, while a second dress label is attached to the side of the con­duit. The software is available in Quick Basic and also as an execut­able (.exe) file which does not require Basic. The executable version only operates with a printer port located at hexadecimal 0378-037A. Begin construction by checking the PC board for breaks and shorts between tracks. Check also that the PC board will slide inside the conduit and file it down to size if necessary. Fig.4 shows the parts layout on the PC board. It is neces­sary to install the links first, as some of these are located under the ICs. The ICs can then be installed, taking care to orient them correctly as shown on the diagram. The diodes can go in next but note that D4 and D5 are mounted end on. The resistors are all mounted end on as well (see Table 1 for the resistor colour codes). The transistors and REG1 should be pushed down onto the board so that their lead lengths are only about 3mm long. When these parts are in, install Table 2: Capacitor Codes ❏ ❏ ❏ ❏ ❏ Value IEC Code 0.1µF 100n .068µF   68n .056µF   56n .001µF    1n the seven LEDs. These must all be mounted so that the top of each LED is 15mm above the PC board. This is best done by cutting a strip of cardboard 15mm wide and then using this as a gauge to adjust the LEDs. Note that you may need to adjust the LEDs later on, so leave a couple of millimetres spare when you trim their leads. The mercury switch is mounted flat against the PC board but must be oriented at a 45° slant to IC1 as shown. This en­sures that it only closes when the Spacewriter stops at the extremity of the lefthand arc. The capacitors can now be mounted, using Table 2 to deci­ pher the Table 1: Resistor Colour Codes ❏ No. ❏  3 ❏  7 ❏  8 ❏  7 ❏  1 58  Silicon Chip Value 220kΩ 10kΩ 2.2kΩ 15Ω 10Ω 4-Band Code (1%) red red yellow brown brown black orange brown red red red brown brown green black brown brown black black brown EIA Code 104 683 563 102 5-Band Code (1%) red red black orange brown brown black black red brown red red black brown brown brown green black gold brown brown black black gold brown Fig.5: the PC pattern is shown here at 71% of actual size. It can be enlarged to full size on a photocopier set to a 1.41 enlargement ratio. values of the MKT types. The electrolytics (ie, those labelled 1µF and 10µF) must be oriented as shown. They must also be pushed all the way down onto the PC board to allow clearance inside the conduit tube. Next, install trimpots VR1 & VR2 and the two pushbutton switches (S3 & S4). Note that the latter must be oriented so that their flat sides face towards REG1. Finally, go back over the assembled PC board and check that all parts have been installed correctly and that all the solder joints have been made. Drilling the conduit The next step in the assembly is to drill the conduit to accept the LEDs and the switches. Begin by drilling seven 5mm holes for the LEDs. These holes must be in a straight line 6.3mm apart and beginning 30mm from the top end of the conduit. The two switch holes go on the same line but are drilled to 10mm diameter and are located 280mm and 295mm from the top edge of the conduit. Next, make a slot in the conduit to accept the 25-pin D socket (to connect the printer cable). This slot is positioned directly opposite the LED holes and must be positioned low enough to avoid fouling the end cap. The D socket is secured using two self-tapping screws and you will need to drill holes for these as well. The other end cap must be drilled to accept the slider switch knob and Fig.4: install the parts on the PC board and complete the wiring as shown here. Note that the wiring for the DP3W slider switch varies according to the type of switch you have, so be sure to check this carefully. May 1997  59 The Spacewriter is programmed from a PC printer port via this D25 socket which is located immediately behind the LEDs. the associated securing holes. Use the label as a guide to drill and file the necessary holes. Now check that the PC board fits into the conduit neatly and that the LEDs and pushbutton switches mate correctly with their respective holes. The PC board is secured in position by the end caps. In addition, a nylon screw is threaded into a hole in the conduit directly opposite the push­ button switches. This screw presses against the back of the PC board and ensures that the board cannot move when the switches are pressed. Don’t make the hole for this nylon screw too big – it must be a tight fit. We also drilled holes to allow screwdriver The slider switch is mounted on the bottom end cap. access to trimpots VR1 and VR2. Once everything fits correctly, remove all the parts and paint the conduit black. This increases the contrast between the LEDs and the background and makes the message easier to read. Wiring The wiring to the D25 socket and the slider switch is all run using rainbow cable – see Fig.4. Note that Fig.4 shows the wiring details for two different slider switches. That’s because the DSE P7614 has its wiper contacts at one end of the switch while the Altronics S2030 has its wiper contacts towards the centre. The table in Fig.4 lists the various wire lengths. Cut the leads to length and solder them to the PC board first. The wires to the D25 socket are then passed through the socket cutout in the conduit and soldered to the relevant pins. Similarly, the wires for the switch and battery clip exit from the bottom end of the conduit. Connect the switch leads and don’t forget the wire that runs from pin 14 of the D25 socket to the corresponding switch terminal. The battery clip leads will have to be extended so that they have an overall length of 150mm. This will allow the battery to be slid into the tube with the clip towards the end. Be sure to cover the joins in the wires with insulation tape. Finally, we soldered a 20mm dia­ meter loop of tinned copper wire to the strip of copper labelled “pull out here” at the end of the PC board. This makes it easy to remove the board from the tube, should the need arise. Testing Programming the Spacewriter is easy. You just boot the software and follow the on-screen instructions to enter four different messages, each up to 10 characters long. Note that the letters always appear in upper case format. 60  Silicon Chip It’s best to run a few preliminary checks on the unit before final assembly. Connect the battery, switch on and check that there is 5V between pins 14 & 28 of IC1, pins 1 & 8 of IC2, and pins 8 & 16 of both IC3 & IC4. There should also be 5V bet­ween pins 7 & 14 of IC5. If you don’t get the correct voltages, switch off imme­diately and locate the fault before proceeding. If everything checks out correctly, shake the board so that the mercury switch briefly closes. Check that the LEDs flash on when you do this (the pattern will be quite random at this stage). If all is well, disconnect the battery and adjust both VR1 and VR2 to their midpoint settings. This done, the board assembly can pushed into the conduit and the D25 socket and slider switch installed. The battery is installed through the bottom end of the conduit (near the slider switch), with its clip nearest the end cap. Don’t forget the nylon screw that presses against the back of the PC board immediately behind the pushbutton switches. Using the software To check the address of the printer port in Windows 95, double-click the System icon in Control Panel, click the Device Manager tab, select the printer port from the list of devices, click Properties and select the Resources tab. PARTS LIST 1 PC board, code 08305971, 292 x 18mm 1 self-adhesive label (for bottom end cap) 1 Spacewriter software (Spcwri.bas, Spcwri.exe) 1 400mm length of 32mm diameter conduit 2 32mm conduit end caps (Clipsal No. 262/32) 1 DP3W slider switch plus screws, Altronics S2030 or DSE P7614 (S1) 1 mercury switch (S2) 2 momentary pushbutton PC mount switches (S3,S4) 1 25-pin “D” panel socket 1 100kΩ (104) horizontal trimpot (VR1) 1 500kΩ (504) horizontal trimpot (VR2) 1 3mm x 18mm Nylon screw 2 self-tapping screws to secure D socket 1 600mm length of 5-way rainbow cable 1 300mm length of 10-way rainbow cable 1 300mm length of 0.8mm tinned copper wire 1 9V battery 1 9V battery clip Semiconductors 1 TMS6264L low power 8K x 8-bit static RAM (IC1) 1 7555, LMC555CN or TLC555 timer IC (IC2) 2 4029 CMOS 4-bit up/down counters (IC3,IC4) 1 4093 quad Schmitt NAND gate (IC5) 1 78L05 low-power 5V regulator (REG1) 7 BC338 NPN transistors (Q1-Q7) 5 1N914 switching diodes (D1-D5) 7 5mm high intensity red LEDs (LED1-LED7) Capacitors 4 10µF 16VW PC electrolytic 1 1µF 16VW PC electrolytic 1 0.1µF MKT polyester 1 .068µF MKT polyester 1 .056µF MKT polyester 3 .001µF MKT polyester Resistors (0.25W, 1%) 3 220kΩ 7 15Ω 7 10kΩ 1 10Ω 8 2.2kΩ Miscellaneous Black paint, solder, D25 plug-toplug lead As mentioned above, the software is supplied as both an executable (.exe) file and as a Quick Basic file (.bas). The .exe file can be copied to your hard disk and you simply type SPCWRI at the DOS prompt to load the program. Alternatively, you can double-click the SPCWRI.EXE file in the Windows File Manager or Explor­er. After that, it’s simply a matter of following the on-screen instructions to program the unit. Note that this program uses a printer port address at 0378. If you need to check what printer ports you have, type MSD at the DOS prompt. Alternatively, for Windows 95, double-click the System icon in Control Panel, click the Device Manager tab, select the printer port from the list of devices, click Properties and select the Resources tab. If you don’t have a printer port on 0378, the Basic program can be used instead. This is run in Quick­ Basic using the “File Run” command. The advantage of the Basic program is that the printer port address can be chang­ed if required. To program the unit, first connect the Spacewriter to the printer port of the PC using a D25 plug-to-plug lead. This done, switch the Spacewriter to the RECORD position, type in a message of up to 10 characters and press ENTER. The LEDs on the Spacewriter will flash and you then switch to the SPACEWRITE position before disconnecting the D25 lead. Warning: switching the unit OFF erases all recorded messages. Now wave the Spacewriter in front of you to see if the message appears. You will probably need to adjust the clock rate and delay using VR1 and VR2 – just adjust them until the mesSC sage appears correct. Where To Get the Software The software for this design is available from Silicon Chip Publications for $7.00 (includes disc) plus $3.00 p&p – see order form page 33. May 1997  61 SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. MAILBAG Easy method of making PC boards I have been experimenting with several methods of producing circuit boards using the ironed-on laser print method and have had great success with the following approach which I thought I would share. I produce the track layout (in reverse) on a CAD package and print it out on a HP Laserjet 4 on plain copy paper. I then cut both the circuit board material and the laser print to the final size, clean the copper side of the board with fine steel wool, dry it and attach the laser print (toner side to the cop­per, of course) at the corners with masking tape. The board is then placed on the back of a large upside-down heavy-duty heatsink, with the paper facing upwards. This provides a stable flat base for the circuit board and also helps to conduct the excess heat away. A single sheet of linen is placed over the board and the board is ironed with a clothes iron on its highest setting for four minutes. The whole setup is allowed to cool slowly, then the board is soaked in water until the paper starts to separate from the toner, which should remain attached to the copper of the board. The rest of the paper is then gently rubbed away until almost no paper fibre is left and the board is left to dry. It is then just a matter of touching up any holes in the toner with a waterproof pen and etching the board in the normal manner. In most cases, the board requires little or no touching up before etching and gives more than adequate results for most projects. I have done boards with tracks less than 1mm wide, with similar widths of separation, all with good to excellent results using this method. It should also be noted that re- sults are better with cheap­er grades of paper, as they disintegrate and release the toner more readily than more expensive coated stocks. L. Turner, Glen Iris, Vic. Pay TV programs not worth the money In the March 1997 issue, the Publisher struck a good point about pay TV and I just had to comment. We used to subscribe to the Galaxy satellite service. The sound was excellent as it was in digital but the picture, although reasonable, was subject to weather conditions. If there was heavy cloud or rain, the signal would drop out all together and you received nothing but a blank screen. Too bad if it rained for a week! Also, on extremely hot days, the decoder overheated and required fan-forced air to keep it cool. The only way then to get the thing going again was to switch off and on again and wait for it to go through its start-up sequence. Obviously the decoders were not designed for Australian conditions. We were unfortunate to have gone through three decoders before we found one that worked properly. As for programs, Leo Simpson hit it right on the mark – we got nothing but endless reruns of the bionic bumbles and Battle­ star Galactica, repeated movies month after month (yes, it even happens on pay TV) as well as poor programming. Also, apart from the standard channels, if you wanted extra ones, you had to pay for them, at $10 a channel. That is wrong, especially when you pay so much in the first place. We also complained continuously about repeated programs to the point that we decided that $50 per month for the same stuff month in, month out, was not on. It was better value for money to go to the local video shop and hire the latest releases. Since going back to free to air programs, we can honestly say that TV has been so enjoyable and as for the “ugly TV antenna”, that’s something we just have to live with. R. Birt, Morphett Vale, SA. Safer test for computer mains wiring I want to comment on J. Richard­ son’s letter concerning dangerous computer wiring in the “Mailbag” page of the March 1997 issue. As I understand the letter, the lead which should have extended the Earth from the power point to the chassis was in contact with the Active wire. In the last paragraph he says the “earth leakage breaker did not trip . . .”. Assuming he was referring to a modern current-operated device known as a safety switch or residual current device (RCD), then the device acted correctly and did not trip. The reason is RCDs are current operated and the domestic types are designed to trip at a nominal current of 30mA. With a little arithmetic, you need about 8kΩ impedance between Active and Earth with a nominal 240VAC line to trip the device. His DMM would typically have an input impedance of 10MΩ and so would not have tripped the RCD and as far as his “hand brush­ing” technique is concerned, this is admirable but for most people, not a repeatable reliable test as far as impedance goes. Might I suggest a far safer test would be to check for continuity between the Earth pin of the plug and all exposed metalwork, before it is plugged in. I have a real thing about safety and the attitude from the supplier is unforgivable. Why not publish their name? D. Hire, Annandale, NSW. May 1997  67 PRODUCT SHOWCASE Clever learning remote has LCD panel The control screen changes according to the device selected. These photos shows the displays for a TV (left) and a CD Player (right). These days, virtually every TV, video and audio appliance comes with an infrared remote control. Everyone would agree that these remotes are wonderful, even if they do possibly contribute to expanding waist lines. On the other hand, if you have more than two in use, it can be frustrating if you grab the wrong one to change a channel or some other function. If you have a Dolby surround sound setup in your home you could easily end up with four or five remotes in the living room alone. Some people we have seen keep their remotes in a little rack on a coffee table in front of their listening/viewing posi­tion but most people are just not that organised. If you are one of the latter, this learning remote could be Video capture IC from Philips Philips has announced the industry’s first single-chip video capture front end to connect directly to a VGA graphics controller. The SAA7112 is the first in a new generation of ICs from Philips designed to make possible a new range of multimedia-enabled VGA cards. With its multistandard decoding of NTSC, PAL and SECAM, high-performance 3D scaling, versatile image port interface and digital video expansion port, the SAA7112 eliminates the need for 68  Silicon Chip glue logic in the design of VGA/ video systems. The video image port interfaces directly to the majority for you. It will learn and reproduce all the functions of up to eight infrared remote controls and it does so without the need for any buttons on its control panel. By contrast, most learning remote controls seem to have a huge array of buttons and while they might “learn” all the wanted functions with ease, the human user generally has a harder time trying to figure out which button to press. The other big problem with IR remote controls, learning types or otherwise, is that you can’t use them in subdued light or in the dark. In fact, most remotes are pretty hard to use at the best of times if you are calling for some of the lesser used functions. This is where the Touchlight SUR9000 comes into the pic­ture. Instead of making do with a large array of tiny pushbuttons with legends that only people with microscope-vision can read, it has a large backlit LCD screen with 40 function “keys”. Each “key” is activated merely by pressing the relevant portion of the screen. If you want, it will emit a soft beep each time you press a key and if you are using it in subdued light or in the dark, it will light up the keyboard of VGA controllers and is configurable to support a variety of setups. In addition, a bidirectional video expansion port with half-duplex capability allows either real-time decoded YUV data to be output from the decoder or a second video stream to be input directly to the scaler (eg, from an MPEG decoder or video phone CODEC). More information on Philips semiconductors can be obtained by accessing the Philips Internet Home Page located at http://www. semiconductors.philips.com; or contact Philips Compon­ents, 34 Waterloo Rd, North Ryde, NSW 2113. BassBox® Smoke alarm panel from DSE Those who want to build the Smoke Alarm Control Panel pub­ lished in the January & February 1997 issues of SILICON CHIP will be interested in this full kit from Dick Smith Electronics. It features a drilled and screen-printed plastic case with square buttons instead of the round buttons featured in the prototype. The top has a thick steel panel which covers the entire case and it is nicely finished in grey enamel and is punched for the buttons and LEDs. In fact, the sample assembled kit looks more attractive than our prototype. Inside, the two fibreglass PC boards have rolled solder tracks for ease of soldering. The backup each time a key is pressed. The backlighting is only activated if the SUR-9000 senses low light conditions and then it automatically turns off about five seconds after a key is pressed. Once all the remote control functions have been learnt for each of your appliances, it can then provide a particular control screen for that device. For example, if your press CD, it will bring up a screen with CD play functions such as Play, Pause, Fast Forward, etc. The unit is powered by four AAA cells and these have an estimated life of 2-3 months, depending on how much it is used. It also has a further 3V cell buried inside it to back up all the programming so that you don’t lose anything when the main batteries go flat or are being replaced. This 3V battery will maintain the programming for up to three years. For anyone who wants the ultimate remote control, this has to be the one. It is available at $199 from Altronics, 174 Roe St, Perth, WA 6000. Phone 1 800 999 007. Fluke automotive multimeter GEC Electronics has announced the introduction of the new Fluke 18 automotive meter, a rugged, easy to use multimeter for most common measurements. As well as measuring DC and Design low frequency loudspeaker enclos­ures fast and accurately with BassBox® software. Uses both Thiele-Small and Electro-Mechanical parameters with equal ease. Includes X. Over 2.03 passive cross­over design program. battery and five smoke detector boards are included in the price. It sells for $159 (Cat. K-8001). Extra smoke detector PC boards are available at $5.50. The Smoke Alarm Control Panel kit is available from all Dick Smith Electronics stores and resellers. $299.00 Plus $6.00 postage. Pay by cheque, Bankcard, Mastercard Visacard. EARTHQUAKE AUDIO PH: (02) 9949 8071 FAX: (02) 9949 8073 PO BOX 226 BALGOWLAH NSW 2093 STEPDOWN TRANSFORMERS 60VA to 3KVA encased toroids Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 9476-5854 Fx (02) 9476-3231 AC volts, resistance and continuity, it measures capacitance and min/max in all modes. It is auto-ranging although a particular range can be selected and locked in by pressing the range button a number of times. No current ranges are provided, in keeping with the in­tended automotive application of the meter. The Fluke 18 is supplied with a holster, leads and alliga­ tor clips. It comes with a 3-year warranty. For further information, contact GEC Electronics Division, Unit 1, 38 South St, Rydalmere 2116. Phone (02) 9638 1888; fax (02) 9638 1798. Labelling machine for PC boards Brady Australia has announced the release of their new Printer Applicator Machine (PAM). It prints via a thermal trans­fer process and is designed to apply labels to PC boards and components. Features of the machine include programmable label positioning, barcode scanner, label repeat and recovery and on or off-line configuration. For more information, contact Brady Australia by telephon­ing 1 800 620 816. May 1997  69 Monolithic accelerometer Analog Devices’ new ADXL250 is the first dual-axis ±50g accelerometer available commercially with signal conditioning, on a single monolithic IC. A radical redesign of acceler­ -ometer circuit architecture has enabled greater integration for higher performance and 1/5th the power consumption of the first-generation devices. The ADXL150, a single-axis version, also includes on-board signal conditioning. Both devices provide reduced drift, lower noise, and smaller packaging, compared to existing solutions. KITS-R-US RF Products FMTX1 Kit $49 Single transistor 2.5 Watt Tx free running 12v-24V DC. FM band 88-108MHz. 500mV RMS audio sensitivity. FMTX2A Kit $49 A digital stereo coder using discrete components. XTAL locked subcarrier. Compatible with all our transmitters. FMTX2B Kit $49 3 stage XTAL locked 100MHz FM band 30mW output. Aust pre-emphasis. Quality specs. Optional 50mW upgrade $5. FMTX5 Kit $98 Both a FMTX2A & FMTX2B on 1 PCB. Pwt & audio routed. FME500 Kit $499 Broadcast specs. PLL 0.5 to 1 watt output narrowcast TX kit. Frequency set with Dip Switch. 220 Linear Amp Kit $499 2-15 watt output linear amp for FM band 50mW input. Simple design uses hybrid. SG1 Kit $399 Broadcast quality FM stereo coder. Uses op amps with selectable pre-emphasis. Other linear amps and kits available for broadcasters. 70  Silicon Chip The ADXL150/250 devices are available in a hermetic, 14-pin, surface-mount CERPAK package. For further information, contact Hartec, 205A Middleborough Road, Box Hill, Vic 3128. Phone 1 800 335 623. They are available from Oatley Electronics at the following prices: blue $1.50 each or 10 for $10; red $1.10 each or 10 for $7.00. Oatley Electronics are at 66 Lorraine St, Peakhurst, NSW 2210. Phone (02) 9584 3563; fax (02) 9584 3561. Super bright blue & red LEDs 0-30V 2.5A power supply LEDs just keep getting brighter and brighter as these clear-lensed 5mm devices demonstrate. The red version puts out three candelas while the blue version puts out 400 millicandelas, both at the maximum current of 20mA. As is usual with high-brightness LEDs, these have a narrow beam by virtue of the integral lens. Readers wanting to build a power supply for their workbench will think twice when they see this fully built supply rated at 0-30V at up to 2.5A. It is quite a large unit considering its fairly modest power output although that may reflect the manufac­turer’s use of a standard case for a range of supplies. It measures 149mm wide, 142mm high and 237mm deep, including the knobs and output terminals. It weighs 2.8kg. Two LCD panels provide readouts for the current and voltage settings which are adjustable via the adjacent knobs. The main output is available from the large binding post terminals on the lefthand side of the panel. As well, there are two pairs of spring-loaded terminals for fixed 5V and 12V PO Box 314 Blackwood SA 5051 Ph 0414 323099 Fax 088 270 3175 AWA FM721 FM-Tx board $19 Modify them as a 1 watt op Narrowcast Tx. Lots of good RF bits on PCB. AWA FM721 FM-Rx board $10 The complementary receiver for the above Tx. Full circuits provided for Rx or Tx. Xtals have been disabled. MAX Kit for PCs $169 Talk to the real world from a PC. 7 relays, ADC, DAC 8 TTL inputs & stepper driver with sample basic programs. ETI 1623 kit for PCs $69 24 lines as inputs or outputs DS-PTH-PCB and all parts. Easy to build, low cost. ETI DIGI-200 Watt Amp Kit $39 200W/2 125W/4 70W/8 from ±33 volt supply. 27,000 built since 1987. Easy to build. ROLA Digital Audio Software Call for full information about our range of digital cart players & multitrack recorders. ALL POSTAGE $6.80 Per Order FREE Steam Boat For every order over $100 re­ceive FREE a PUTT-PUTT steam boat kit. Available separately for $19.95, this is one of the greatest educational toys ever sold. Free instrumentation reference & catalog National Instruments has announced its full-colour 1997 Instrumentation Reference and Catalog. This free 696-page catalog describes the company’s software and hardware products that engineers and scientists can use to develop integrated, PC-based instrumentation systems for test and measurement and industrial automation. The catalog includes tutorials on data acquisition, GPIB, VXI, industrial automation, product line overviews and selection guides. New product highlights include object-oriented Lookout MMI/SCADA software, Bridge VIEW industrial automation software, a new line of VXI-DAQ instrument modules, IMAQ Vision (machine vision) software and the company’s first image acquisition board. The catalog also describes new versions of LabVIEW, LabWindows/CVI, HiQ, Measure, Virtual­ Bench and Component Works application software products, as well as numerous new data acquisition products. For more information, contact National Instruments Austra­lia, PO Box 466, Ringwood, Vic 3134. Phone (03) 9879 5166; fax (03) 9879 6277. Readers can also access information by email at info.aust­ ralia<at>natinst.com or through the Instrumentation Web at www.natinst.com/ outputs which can both deliver up to 500mA. The supply is priced at $199 and is available from Altron­ics, 174 Roe St, Perth, WA 6000. Phone 1 800 999 007. Low loss IGBTs BBS Electronics, Australian distributor for Harris Semicon­ ductor, has released the Harris HGTP7N60C3. This IGBT boasts the industry’s lowest overall losses at its 7A (110°C) 600V rating and can switch higher currents than more expensive Mosfets at 50-100kHz switching rates in some supply configurations. Applications for the ultrafast switching IGBT consist of line-voltage switching power supplies and fractional-horsepower motor control. The switching supply uses include PCs, home entertainment systems and small un­interrupt­ible power supplies. Motor-control uses include power tools and small appliances. The new 600V 7A IGBT is available in TO-200, TO25x and TO-26x package variations, including through-hole and surface mount. There are versions with and without internal “hyperfast” anti-parallel diodes. Depending on the package and for quantities of 1000, IGBTs without a diode range in price from $1.43 to $1.51. With a diode, prices range from $2.04 to $2.46. The new IGBT is rated at 14A and 600V breakdown at a 25°C case temperature (7A at 110°C). At 150°C, the maximum saturation voltage at 7A is 2.4V. For further information, contact BBS Electronics Australia Pty Ltd, Unit 24, 5-7 Anella Ave, Castle Hill SC 2154. Phone (02) 9894 5244. FM radio receiver for PCs Dubbed the Wizard Radio, this nifty little stereo FM broadcast band receiver plugs into a spare RS232C serial (COM) port on your PC. It has an audio output which connects via a short cable to the line input of your PC’s sound card, plus an input for a dipole antenna (supplied). The unit is driven using software which works with both Windows 3.1x and Windows 95. This features electronic tuning, 10 pre­ settable memories for favourite stations, auto-seek tuning, and a digital frequency readout. It can even be set to switch on and off at preset times and you can record and replay selections using the Sound Recorder & Player. The unit is priced at $49 from Altron­ics, 174 Roe St, Perth, WA 6000. Phone 1 800 999 007. The Wizard radio plugs into a spare COM port on the computer & connects to your sound card & to a dipole antenna. The on-screen display for the Wizard Radio lets you tune and scan channels. You can also store and edit up to 10 preset channels and record and replay selections using the Sound Recorder & Player. May 1997  71 RADIO CONTROL BY BOB YOUNG Transmitter interference on the 36MHz band In previous months we have discussed the possibility of transmitter interference on the 36MHz band. This month, we pres­ent a series of measurements which finally demonstrates an area where FM is actually superior to AM. What’s this? Is Bob Young about to recant and admit that FM has been superior to AM all along? Well, not quite. But I have been able to demonstrate and measure practical cases of interfer­ence between transmitters on the 36MHz band for both AM and FM transmitters and the results are very interesting. In the February 1997 column we warned of the possibility of transmitter intermodulation causing interference when two trans­mitters separated by 455kHz were operated simultaneously on the 36MHz band. Then in March 1997 we presented solutions aimed at preventing this problem. This month we look at practical situations wherein this form of interference may arise if the correct operational pro­cedures are not adhered to. How serious is the problem? For those who have missed previous Fig.1: the spectrum plot of the mixer output, before the filter­ing, of an AM receiver operating on 36MHz from a transmitter on the correct frequency (channel 631, 36.310MHz). The fundamental output is at 455kHz. Note that there is some jitter in the spec­trum plot due to the frequency shift keying of the transmitter. 72  Silicon Chip articles, the problem we are discussing is the transmitter inter­ mod­ ulation component that will arise in the mixer of any single conversion receiver regard­ less of frequency, when two transmitters separated by 455kHz are operated simultaneously. As the 36MHz band is the only Australian R/C band wide enough to accommodate transmitters 455kHz apart, this problem is exclusive to that band. Having discovered this potentially serious problem, it was up to me to make more measurements to define whether it was going to be a real problem on the operating field. With that in mind I gathered a representative batch of modern R/C equipment of various brands with the help of several trade houses, together with receivers of various brands from Fig.2: the intermodulation product of two FM transmitters sepa­rated by 460kHz operating at the same distance from the receiver. In this instance the correct transmitter has been turned off for the sake of clarity. Note that the amplitude of the two signals is actually slightly higher than the original shown in Fig.1. Fig.3: this scope plot shows the normal output of a typical Japanese FM receiver at a test point after the detector, squelch and noise filtering, with the primary and one of the intermodu­lating pair of transmitters operating simultan­ eously. The receiv­er is on 36.370MHz and the other trans­ mitter is on 36.070MHz. Note that there is no sign of any interference. my own stock. Then it was into serious measurements in order to get a better grasp of the situation. No mixer output Modern FM receivers present us with a problem here as the output of the mixer is not easily accessible. This is because almost all models use an IC receiver chip. Therefore we had to cheat in this respect. Fig.1 shows a spectrum plot of the mixer output, before the filtering, of an AM receiver operating on 36MHz from an FM transmitter on the correct frequency (Channel 631, 36.310MHz). While this method might seem invalid, the method of modula­tion does not matter at this point, as we are only looking at the raw, undifferentiated 455kHz mixer component. Note the amplitude of the 455kHz component. By the way, there is only one spike at 455kHz; the double spike in the photo is due to jitter in the spectrum plot due to the frequency shift keying of the transmitter. Fig.2 shows the intermodulation product of two FM transmit­ters separated by 460kHz operating at the same distance from the receiver. In this instance the correct transmitter has been turned off for the sake of clarity. Note that the amplitude of the two signals is actually slightly higher than Fig.4: this scope plot shows the output of the same receiver (as Fig.3) at the same test point but with the primary (wanted) transmitter switched off and an unmodulated signal generator on x36.075MHz and a transmitter on 36.530MHz. Here we are generating an exact 455kHz intermodulation (difference) product from two interfering transmitters. the original shown in Fig.1. Now the really important point to note is that this receiv­er is tuned to 36.310MHz, which is nowhere near the frequencies of the two offending transmitters. So here we have proof of the central point of this series of articles: two transmitters operating simultaneously and sepa­rated by 450kHz or 460kHz will generate a strong 450kHz or 460kHz component in the mixers of every single conversion receiver operating on the 36MHz band. This is regardless of the frequency of the receivers and the frequencies of the intermodulating pair of transmitters! Yes, you understood perfectly. All 59 receivers will be affected simultaneously by just one pair of inter­ This photo shows some of the equipment used to make the measurements discussed in this month’s article. Not shown are the spectrum analyser and some of the receivers. May 1997  73 Fig.5: this shows the same setup as before but with the signal generator at 36.071MHz, just 4kHz away from the 455kHz ideal. Note how distorted the signal has become, indicating severe attenuation in the receiver bandwidth filter. modulating transmitters. As a matter of interest, I checked to see if a pair of 36MHz transmitters would interfere with 29MHz receivers and fortunately they did not. So this potential transmitter interference problem is not just a theory. It does exist and is easily measurable. Two trans­ mitters separated by 450- 460kHz will generate a powerful inter­ modulation component in the mixers of single conversion receiv­ers. The level of this component can equal or exceed the primary transmitter signal, depending upon a whole range of factors. The most obvious factor is the relative signal strength ratios between the primary transmitter and the inter­modulating pair. This is a most important factor in R/C operations and we will examine this later. More subtle factors include mixer compres­sion and bandwidth of the mixer output. Mixer compression arises due to the fact that the mixer can only handle a finite signal level. As more signals arrive at the mixer the amplitude of each component is reduced accordingly. Theoretically, if the intermodulation product is 455kHz, the mixer bandwidth should not play any part in this discussion. However, in the real world the intermodulation product is not 455kHz but 450kHz or 460kHz, 74  Silicon Chip Fig.6: this shows the same receiver with the same two transmit­ters operating but with the third transmitter also switched on. This transmitter is on 36.530MHz, so the intermodulation compon­ent is 460kHz. Note how disturbed the output has become. While capture has not been achieved, the wanted transmitter has lost control. because of the 10kHz spacing between adjacent channels (see March 1997 issue). So the mixer bandwidth becomes an important factor. 5kHz protection Fig.3 shows the normal output of a typical Japanese FM receiver at a test point after the detector, squelch and noise filtering, with the primary and one of the intermodulating pair of transmitters operating simultaneously. The receiver is on 36.370MHz and the other transmitter is on 36.070MHz. Note that there is no sign of any interference. Fig.4 shows the output of the same receiver at the same test point but with the primary (wanted) transmitter switched off and an unmodulated signal generator on 36.075MHz and a transmit­ter on 36.530MHz. Here we are generating an exact 455kHz inter­ modulation (difference) product. Note that we are getting the perfectly normal output wave­form even though we are generating the control signal from the intermodulation product on a receiver nowhere near the two RF signal sources (36.370MHz). The unmodulated signal generator is necessary to generate a normal waveform. If two modulated trans­mitters were used the resultant composite modulation would drive the servos wild. Now we arrive at the interesting bit. Fig.5 shows the same setup as before but with the signal generator at 36.071MHz, just 4kHz away from the 455kHz ideal. Note how distorted the signal has become, indicating severe attenuation in the receiver band­width filter. This is the saving grace in this whole affair. Three distinct and separate factors have come together in the real world to make practical operation a reasonably safe proposition. First, due the fact that the channels are spaced every 10kHz and that the IF is 455kHz, the intermodula­tion product falls midway between two channels; ie, 5kHz away from the channels on either side. Second, modern receivers have a typical bandwidth of around +5kHz and -7kHz (<at> 40dB) and the attenuation of any signal 5kHz away from 455kHz is such that the genuine 455kHz signal will become dominant. This then leads to the importance of the third factor, “capture effect”, which ensures that only the dominant signal has control. So does transmitter intermodulation present a serious prob­lem in the real world on the 36MHz band? The answer is a reserved no. Why are there reservations? Answer: because of the variations in receiver performance. Can you guarantee that your receiver’s bandwidth is as good as typical Fig.7: capture can occur if the conditions are correct. Here the signal generator is set at 36.075MHz to simulate a transmitter off-frequency or a receiver with a wider than usual bandwidth and the third transmitter is on 36.530MHz. To achieve capture, the primary transmitter has been moved away, thus simulating condi­tions which can be encountered on flying fields. modern receivers (+7kHz, -5kHz)? Can you guarantee that the relative transmitter signal ratios will always favour the wanted transmitter? Let’s look at some of these factors in more detail. Fig.6 shows the same receiver with the same two transmit­ters operating but with the third transmitter also switched on. This transmitter is on 36.530MHz, so the intermodulation compon­ent is 460kHz. Note how disturbed the output has become. While capture has not been achieved, the wanted transmitter has lost control. To achieve this result, the inter­ modulating pair of trans­mitters had to be much closer to the receiver than the primary transmitter. With all three transmitters at equal distances from the receiver, there was no sign of any interference. Capture In the testing done so far on a small batch of imported receivers, results varied from excellent to good. Even different models from the same manufacturer gave different results in regards to capture, as would be expected from normal production tolerances. In most instances, capture was difficult to obtain, requir­ing unrealistic signal ratios – signal ratios that could never be achieved on any R/C field. Fig.8: this shows the result of an AM receiver subjected to an identical level of intermodulation interference as the FM receiv­er in Fig.4. Whilst AM receivers have capture ratios of 100:1 or more, long before capture the signal becomes very disturbed as shown here. In one instance, capture could not be achieved but that receiver just simply stopped working. Again, this was at unrealistic signal levels. Remember here that the receiver has already captured its primary transmitter and in order to take control away from that primary, the interference must exceed the level of the primary signal. The ratio between the interfering signal and the primary signal is known as the capture ratio and is usually in the order of 1-3dB. In simple ratio terms, these correspond to trans­mitter signal ratios of 1.12:1 up to 1.41:1. Now we can see why the 5kHz difference between the inter­modulation product and the primary product is so important. If the signal level of the intermodulation product can be reduced to just below the primary, capture is virtually impossible. Fig.7 shows that capture can occur if the conditions are correct. Here the signal generator is set at 36.075MHz to simu­late a transmitter off-frequency or a receiver with a wider than usual bandwidth. The third transmitter is on 36.530MHz. To achieve capture, the primary transmitter has been moved away, thus simulating conditions which can be encountered on flying fields. Note the ripple on the baseline of the scope trace, indi­cating a strong transmitter still present on the correct frequen­cy. And finally what of the situation that started all of this – two models operating on frequencies 450kHz or 460kHz apart? A quick test indicated that with just two transmitters operating (607, 653), the servos started to jump as the second transmitter (607) came close to the receiver. (653). The same test repeated with a receiver on 637 showed no sign of interference, even with the transmitter antenna touching the receiver antenna. Thus there is still a case for not operating two overlapping frequencies simultaneously, regardless of the foregoing arguments. What does it mean in the field? What it means is that under normal conditions, using FM receivers, there is little likelihood of any interference being experienced as long as safe operating practices are followed. Here I should refer to the discussions and illustrations of the flying field layout published in the July 1995 issue of SILICON CHIP. Fig.9 is reproduced from that article. This depicts the real danger of transmitter inter­modulation in a practical sense. If the intermodulating pair of transmitters are located at the end of the May 1997  75 Fig.9: this diagram is reproduced from the July 1995 issue of SILICON CHIP. It depicts the real danger of transmitter intermod­ulation in a practical sense. Interference is more likely when the controlling transmitter is further away from the receiver. flightline closest to the model and the primary transmitter is situated at the far end of the flightline, then we have the conditions for interference, if not capture. Even mild interference on final approach is enough to result in a damaged model. A similar set of conditions can prevail on glider fields where a pilot may leave the flightline to go down the field to the bungie site during launch. After launch and before the pilot can return to the flightline, the model may pass close to the group of transmitters and thus the intermodulating pair, thereby setting up conditions for interference. Time and time again we return to the absolute necessity for adherence to the correct operational procedures on all R/C fields. Ignore this warning at your peril! What about AM? This leaves us with the final point to discuss in this issue. There have 76  Silicon Chip been rumblings for some time about AM receivers being plagued with interference on 36MHz. The MAAA is considering banning AM on 36MHz as a result. The ubiquitous grapevine attrib­ utes this interference to harmonics from the broadcast FM trans­ missions. I wonder if this problem is due to transmitter inter­ modulation? Fig.8 shows the results of an AM receiver subjected to an identical level of intermodulation interference as the FM receiver in Fig.4. Whilst AM receivers have capture ratios of 100:1 or more, long before capture the signal becomes very dis­turbed as in Fig.8. Thus without capture effect to protect them, AM receivers could suffer badly on 36MHz as long as overlapping pairs of transmitters are allowed to operate. There is no doubt that capture effect, whilst a two-edged sword, does give the FM re­ceiver the edge over AM in this situation. On 29MHz, this situation does not apply and my original remarks regarding AM versus FM still apply. And if overlapping transmissions are stopped, AM should be perfectly safe on 36MHz. Actually this entire series of articles was sparked off some months ago as a result of “experts” in a club telling a beginner who was constantly crashing to get rid of his “inferior” 36MHz AM equipment or he would not be allowed to fly in that club. It would be the ultimate irony if it turned out that it was the “superior” FM transmitters causing this poor fellow’s miser­ies! In conclusion, as a result of the uncertainties surrounding the problem of transmitter intermodulation I would recommend that transmitters 450kHz or 460kHz apart not be operated simultaneously on model flying fields. The Silvertone Keyboard provides a simple method of controlling this situation. Acknowledgement I would like to extend my appreciation to Hobby Headquar­ters (NSW) and L. O’Reilly Pty Ltd (SA) for the loan of the equipment used in this SC article. Bob Young is the principal of Silvertone Electronics. Phone/fax (02) 9533 3517. BOOKSHELF Understanding Telephone Electronics Understanding Telephone Electronics, by Stephen J. Bigelow. Third edition published 1997 by Butterworth-Heineman. Soft covers, 232 x 187mm, 367 pages. ISBN 0 7506 9994 2. Price $34.95. Among the many different fields of electronics, telephone electronics has to be one of the most inscrutable to anyone who has a conventional electronics background. Partly this is because telephone systems were developed long before electronics technol­ogy appeared on the scene but there also appears to be a particu­lar mindset or philosophy amongst tele­ phone engineers which makes it difficult for ordinary mortals to penetrate. Which is all the more reason why this book entitled “Under­ standing Telephone Electronics” is so welcome. Originally produced by the staff of the Texas Instruments Information Publishing Centre in 1983 & 1984, it has since been revised and updated in 1991 and is now in its third edition. Most text books produced by Texas Instruments are well-written and it was the same with this book. There are 10 chapters in all and the first one goes right back to basics, talking about the telephone system as it is in the USA, local loops, the public switched telephone network (PSTN), channel bandwidths and levels and so on. It then becomes more technical, and mentions multiplexing, DC signalling, tone sig­nalling, digital codes and PCM. It also covers older technology such as Strowger switching and uniselect­ ors, crossbar switching, reed relays and then brief­ly goes on with radio relay links, wave guides and optical fi­bres. Chapter 2 covers the conventional telephone set and gives simplified circuits of a rotary dial set and anti-tinkle and speech muting. Anti-tinkle prevents the bells in phone handsets on a line from tinkling when one of the phones is being used to dial out. Now that phones use tone dialling it is not much of a problem any more. Carbon microphones are covered, as well as dynamic and electret types. Ringer circuits and ring cadence are described and, most importantly, there is a good description of the “induction coil” and the “hybrid circuit” carryovers from ancient times. Briefly, the hybrid circuit is a multiple winding transformer which converts the incoming two-wire circuit to a four-wire circuit with separate transmit and receive signals. As part of this description, there is a discussion of line balancing and sidetone. Sidetone is often misunderstood but it refers to the amount of sound from the microphone which appears in the earpiece. Sidetone is necessary so that the caller can hear his/her voice in the earpiece, so that he/she knows how loudly to speak. With insufficient sidetone, the caller will tend to shout. Conversely, too much sidetone leads to acoustic feed­ back whistles and so the caller tends to speak too softly. Chapter Three is devoted to electronic speech circuits and it is preceded with a good rundown on conventional speech cir­ cuits. The electronic speech circuit discussed is the Motorola MC34014 and it is covered in considerable detail. Once you under­­stand this device, you will have a good knowledge of virtually any small single IC phone although this chip does not incorporate tone dialling. This function is covered in Chapter Four. Again, as part of the coverage, the text gives good back­ground on rotary pulse dialling. Electronic dialling chips are briefly covered and DTMF (dual tone multi-frequency) is dis­ cussed, along with well-known decoders such as the Texas Instru­ments TCM5087. Electronic ringers are also featured, both single tone and multi-tone types, with the latter type used almost universally today. The chapter wraps up with a complete electron­ic phone using Motorola chips: an MC­ 34014 for the speech side, an MC34017 as the ringer and an MC145412 as the dialler. Most of this technology is now old-hat and most phones are now completely integrated with one chip providing all the func­tions discussed above. Hence, Chapter Five covers the continued on page 92 May 1997  77 Pt.9: Sampling Scopes For Ultra High Frequencies Typical digital scopes have a bandwidth which is limited to less than half their sampling rate. But a different design, known as sampling or digitising oscilloscope, is not limited by the sam­pler speed and can achieve a bandwidth as wide as 50GHz. By BRYAN MAHER So far in this series we have described many digital real time oscilloscopes and we have talked about the limitation of bandwidth which is related to the sampling rate. The reason such scopes are referred to as “real time” is that they can acquire sufficient samples in one pass of the input signal, from a single trigger, to show the waveform accurately. With this ability they faithfully display one-shot wave­ f orms and changing signals. By one pass of the input signal we mean the waveform accepted by the scope following one trigger event. The bandwidth of any oscilloscope is limited by two circuit sections. Firstly, there is the bandwidth lim78  Silicon Chip itation of the input analog circuits. Secondly, there is the Nyquist limit of the sampling circuitry and as discussed in previous chapters of this series, the Nyquist limit determines that this bandwidth limita­tion is always half the sampling rate. Hence, when operating in real time, a scope must sample more than twice as fast as the signal frequency and preferably, five or 10 times faster. That Nyquist factor means no scope can operate in real time with a bandwidth above about 2GHz, because present technology can’t sample faster than 8 billion samples per second (8GS/s). But a 2GHz bandwidth is not good enough for today’s mi­crowave and sat- ellite communications systems. Nor is it good enough for measurements on radar or fibre optic systems. That demands scopes with bandwidths between 3GHz and 50GHz. Such scopes can measure pulse risetimes and propagation delays in picoseconds! One picosecond (ps) is equal to one millionth of a microsecond (10-12). Oscilloscope risetime It’s a fact of life that every oscilloscope has a risetime of its own. That figure is intimately related to the scope’s bandwidth by the equation: Risetime = 0.35/Bandwidth. Naturally we use consistent frequency and time units, such as: seconds/Hertz or nanoseconds/GHz, etc. For example, a scope of 1GHz bandwidth has a risetime equal to (0.35/1GHz) = 0.35ns = 350ps. What does this mean in practice? Imagine we had some hy­pothetical pulse in which the voltage rises to full value in­stantly; ie, in no time at all (zero risetime). Suppose we dis­played that pulse on an oscilloscope which has 350ps risetime (1GHz bandwidth). In this case, the trace on the screen would take 350 picoseconds to rise from 10% to 90% of full height. We would therefore think that our pulse had a 350ps risetime, when in fact it hasn’t. We would be seeing the rise delays of the oscilloscope circuits, not the pulse. In many digital circuits, things happen so quickly that the system won’t work if the risetime of some pulses exceeds the design margin. Fig.1 shows the situation in typical tele­communi­cations equipment. They use ultra-fast synchronous digital ICs, where the bit rate is so high that pulses are somewhat rounded. The system clock tells each circuit when to interrogate a pulse line, to decide if that pulse is at logic 0 or logic 1 level. The aim is to examine the pulse close to its middle. In Fig.1(a) the pulse risetime is so fast that the voltage has risen above the logic 1 level before the clock circuits take a look, at time t1, t2, etc. So those pulses are correctly read as logic 1 every time. But Fig.1(b) shows a different case. Here, because of some fault condition, the pulse risetime is too slow. You’ll notice that when the system interrogates the pulse line at time t1, the pulse is still rising. It does not reach the logic 1 voltage level until a later time, w1. So that pulse is incorrectly read as a logic 0. And the next pulse in Fig.1(b) is also slow in rising but just reaches the logic 1 level at clock time t2. So any slight jitter in the pulse or clock timing could read that pulse cor­rectly as a logic 1 sometimes but erroneously as a logic 0 at other times. Also, the throughput or pulse propagation delay (time bet­ ween pulse into and out of an integrated circuit) must remain within prescribed limits. When things go wrong the technician or engineer must have an ultra-high bandwidth oscilloscope to measure these rises and delays in pico­seconds. Displayed risetime Every oscilloscope has its own risetime, so how are we to know the true value for an input pulse? The answer comes from the equation: Risetime displayed = √{(scope risetime)2 + (pulse risetime)2} You might say the presentation on the screen is always a stretched picture of the actual data pulse. In the particular case when the ri- Fig.1: fast rising pulses (a) reach logic 1 level before interrogation at clock times t1 and t2, so are read correctly. But slow rising pulse (b) reaches logic 1 level at later time w1, so is incorrectly read as a logic 0. setimes of pulse and scope are equal, then the screen displays a pulse rising nearly one and a half times slower than reality. Say the risetimes of both are equal to T picoseconds. Then: Displayed risetime = √(T2 + T2) = √(2T2) = 1.41T. No technician or engineer has time to sit and calculate the true risetime of every measurement, especially in a system break­down situation. The only practical solution is to use an ultra-wide bandwidth oscilloscope. This will have extremely fast inter­ nal risetime, miles faster than the get-up-and-go-time of the pulses to be measured. Pulse bandwidth Similarly every pulse has a bandwidth, related to its rise­time (or fall time, whichever is the faster) by an inversion of the previous equation: Bandwidth = 0.35/risetime. The practical meaning is that the bandwidth of any pulse tells us what bandwidth oscilloscope we need to display it, with errors of no more than 3dB and risetime stretch no more than 1.4 times. The bandwidth of a pulse bears no relation to its repeti­tion rate. For example, a slowly repeating pulse which rises extremely fast each time it does occur still requires a wideband scope to display it accurately. Ultra-wide bandwidth digital oscilloscopes are on the mar­ket, like the Hewlett Packard model HP54750A. With two HP54752A plug-ins, all four channels have a 50GHz bandwidth and a minus­cule 7ps internal risetime. The horizontal timebase speeds can be selected from 10ps/div to 1s/div. To achieve its enormous bandwidth, this scope uses a system called sequential equivalent time sampling, suitable for repeti­ tive signals only. This we’ll describe in a moment. The Autoscale control automatically sets vertical sensitiv­ity, offset scaling and timebase speed to display two cycles of the signal. It can capture 34 waveforms/second, each with 500 sample points. The maximum data record length is 4096 sample points per channel and the highest sampling rate is 40kS/s. The 12-bit A/D converter gives a vertical resolution of 4096 decision levels and averaging provides 15-bit words (32,768 decision levels). The display can resolve 256 points vertically and 451 points horizontally, in eight colour gradations. The intriguing question is how can any manufacturer make such ultra-wide bandwidth oscilloscopes when it’s impossible to sample anywhere near 50GS/s? We will now try May 1997  79 Fig.2: protection diodes D1 and D2 and the attenuator allow a scope to display large voltages or the amplifier A1 can raise small signals to viewable size. However, these components limit the scope’s analog bandwidth. to answer that question, albeit briefly. In the foregoing applications, usually the signals are waveforms repeating for many periods. This fact gives a luxury not enjoyed by real time digital scopes and opens up a whole new ball game. Provided we never want to display one-shots or fast chang­ing waveforms, continuously repeating signals allow a completely different design approach. For bandwidths from 2GHz up to 50GHz, manufacturers make two major changes. Design trade-offs In real time scopes, the stray shunt capacitances of the input protection diodes, attenuator and amplifier, shown in Fig.2, act to limit the analog bandwidth. To avoid this restric­ tion, the first change in designing ultra-wide bandwidth scopes is to just don’t use those components in the front end. That leaves the sampler right at the oscilloscope input terminal, as you can see in the simple block diagram of Fig.3. Next, a low bandwidth amplifier A2 is placed after the sam­pling bridge. This does not restrict the overall sys- tem band­width, because the sampler has converted the input signals to lower frequencies. With these changes we have an ultra-wide bandwidth front end but two trade-offs are inevitable. With no attenuator, we can only apply small signals to this type of scope. Typical sensitiv­ities range from 1mV/div to 250mV/div, with a maximum signal voltage of ±2V. Without any protection diodes, high voltages at the input can cause damage. Although an internal trigger takeoff is generally provided, the loading of this circuit does reduce the bandwidth. So usually the scope is triggered externally by the communications system clock. In describing real time digital scopes in this series, we have become familiar with samplers running much faster than the signal frequency; sampling speeds are typically between 200MS/s and 8GS/s. But in the quest for 50GHz bandwidth, aiming for even faster sampling speeds can’t work, because no sampler can be made to run twice as fast as 50GHz. But the sampling rate and band­width are intimately related only in real time oscilloscopes. In aiming for ultra-wide bandwidth, manufacturers replaced real time mode and high speed samplers with a completely differ­ent system. It is called “equivalent time sampling” and in this scheme there is no direct relation between sample rate and band­width. It comes in two types, known respectively as sequential and random. And always the signal must be repetitive. Sequential equivalent time In sequential equivalent time scopes, the sampling bridge in Fig.3 operates at relatively slow rates, typically 40kS/s to 200kS/s. And this speed bears no relation to the input signal frequency. To take each sample, the actual time the sampler switch remains momentarily closed is called the sampling interval. This can be as short as 10 femtoseconds (femto = 10-15). And that’s an incredibly short time for a switch to stay closed before it opens again. Often only one sample is taken following each trigger event. The scope Fig.3: to avoid loss of analog bandwidth, ultra-high frequency sampling scopes place the sampler right at the input terminal. But this restricts the range of input voltages to about ±2V. 80  Silicon Chip might be triggered 4000 or 40,000 times each second, running until it accumulates hundreds or thousands of samples into the memory (RAM). This process is illustrated in the example shown in Fig.4. Nothing happens until the scope is triggered. Then 0.1ps after the first trigger event the first very short sample is taken. It is amplified and immediately digitised in the A/D converter and the resultant digital data is stored in RAM. While all that converting and data storing was being done, the scope was not ready to be triggered again, so many thousands of cycles of the analog signal will pass in the circuit unseen. But this is not a problem because we are assuming that the signal is repetitive. When the trigger circuit eventually rearms, the next trig­ger is accepted and 0.2ps later sample number 2 is acquired, amplified, digitised and stored in the RAM, as illustrated in Fig.4. Next, 0.3ps after the third accepted trigger event, sample number 3 is taken and similarly converted to a digital word which is placed in the RAM. And so on. Each time the oscilloscope triggers, it takes one more sample, always at a longer time after the trigger. We illustrate this process in Fig.4 but show only 10 points for simplicity (in reality between 500 and 5000 are taken). When the RAM contains enough samples or if the trigger ceases, or if the operator tells it to halt, the scope stops sampling. Now the display microprocessor sorts out all those digitised samples held in the memory. It reassembles them all onto the screen as a lot of bright points, as in Fig.5, in the same order as they were taken. That’s why this is called sequen­tial equivalent time sampling. The horizontal coordinate of each is proportional to the time increment after the respective trigger event for that sample was taken. The vertical coordinate is proportional to the value of the digital word, which reflects the analog voltage of each sample. Fig.4: in sequential equivalent time sampling, ultra-high frequen­cy oscilloscopes take just one sample each time the scope is triggered. At each signal pass, the timing between trigger and sample is progressively incremented. Equivalent sampling rate If 500 trigger events occur and after each one sample is taken, we will have 500 samples of the signal all digitised and stored in memory. Each sample was taken 0.1ps later after the respective trigger than the previous sample. Fig.5: after accumulating hundreds or thousands of samples, the scope reassembles them all in one display to represent the re­petitive signal waveform. May 1997  81 The ultra-high frequency Hewlett Packard HP54750A scope with plug-ins provides up to four 50GHz channels. Feedback A/D converters yield 12-bit digital words or 15 bits with averaging. Horizontal resolution is 62.5fs, with 8ps time interval accuracy. The maximum sampling rate is 40kS/s. The horizontal timebase ranges from 10ps/div to 1s/div. So the 500th sample was taken 50ps after the 500th trigger. That means the whole screen display represents 50 picosec­onds of the live input signal. As there are 10 major horizontal divisions across the screen, we call the display timebase 5ps/div, the equivalent horizontal resolution of this sampling oscilloscope. When displayed on the screen we’ll have 50 sample points per horizontal division, each represented as a bright point of light. They’ll be close enough together to look like a continuous trace. Of course nothing in the display is actually moving any­where near 5ps/ div speed. We know from previous chapters that the trace on the screen is redrawn at the slow rate of 60 times per second. The display only represents 50 sample points per 5ps. But what you see on the screen is equivalent to a scope running at the impossible speed of 500 samples every 50 picosec­onds, or 10,000GS/s. This is the equivalent sampling rate. No real time scope can take samples at anything like that speed but an equivalent time oscilloscope doesn’t 82  Silicon Chip have to. It just reassembles all those samples into a display which appears to have that stupendous sampling rate. If the screen in Fig.5 displays two cycles of the input signal, it must be that the analog input has a real period of 50ps/2, meaning a frequency of 40GHz. But we assumed before that the scope was being triggered 40,000 times per second. That means the sampler is running at only 40kS/s. So after each sample is taken, about a million cycles of the signal flow through the circuit before the scope is again triggered and the next sample taken. So the two cycles displayed on the screen are representative of 500 million signal cycles. Now we see why the analog input must be repetitive for equivalent time scopes. To emphasize this aspect, these ultra-high bandwidth in­struments are known as a sampling (or digitizing) equivalent time scopes. No aliasing Provided a suitably fast sweep speed is chosen, there are so many sample points per cycle of the in- put signal that no alias ghosts will appear on the screen. By this means the Nyquist frequency limit can be exceeded and aliasing avoided. But too slow a sweep speed could restrict the number of samples taken so that aliasing could invade the display. By using this equivalent time sampling system, a scope which samples at only 40kS/s can quite successfully display 50GHz signals! As a bonus, this slower sampling rate allows designers to use high accuracy 12-bit or 14-bit feedback A/D converters, which provide 16,384 decision levels in the digitisation. This allows mathematical operations of great accuracy and eliminates steps in the screen display. There’s more to this story but we must leave it until the next (and final) chapter of this series. References (1). HP54750 reference book: HP publications 5091-3756E and 5952-0163. (2). Tektronix publications 47W-7520, 85W-8306, 85W-8308, 47W-7209. SC Acknowledgement Thanks to Tektronix Australia and Hewlett Packard Austra­lia and their staff for data and illustrations. ORDER FORM BACK ISSUES MONTH YEAR MONTH YEAR PR ICE EACH (includes p&p) TOTAL Australi a $A7.00; NZ $A8.00 (airmail ); Elsewhere $A10 (airmail ). Buy 10 or more and get a 10% discount. Note: Nov 87-Aug 88; Oct 88-Mar 89; June 89; Aug 89; Dec 89; May 90; Aug 91; Feb 92; July 92; Sept 92; NovDec 92; & March 98 are sol d out. All other issues are currently i n stock. $A B INDERS Pl ease send me _______ SILICON CHIP bi nder(s) at $A12.95 + $5.00 p&p each (Australi a only). N ot avail abl e elsewhere. Buy five and get them postage free. $A SUBSCRIPTIONS  New subscription – month to start­­____________________________  Renewal – Sub. No.________________    Gift subscription  RATES (please tick one) 2 years (24 issues) 1 year (12 issues) Australia (incl. 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Please have your credit card details ready OR Fax (02) 9979 6503 Fax the coupon with your credit card details 24 hours 7 days a week Mail order form to: OR Reply Paid 25 Silicon Chip Publications PO Box 139, Collaroy 2097 No postage stamp required in Australia May 1997  83 VINTAGE RADIO By JOHN HILL A look at signal tracing, Pt.2 Last month’s Vintage Radio described the restoration of an old Healing Dynamic Signalizer (signal tracer). This month, we will put it through its paces and use it to check a typical superhet receiver. In the early years of radio, technicians managed with a minimum of test equipment. A torch cell and small globe for a continuity checker, plus a pair of headphones and a voltmeter would just about make up a complete test kit for the mid-1920s serviceman. In those days, receiver ailments were mainly exhaust­ ed batteries, faulty valves and open circuit audio transformers. As receiver complexity increased so did the need for more elaborate test instruments. It wasn’t long before valve testers, multimeters and other instruments were in regular use. When fault finding, a multimeter can contribute much to the task in hand. It can be used to measure voltages, check resistor values, and to check for shorts or open circuits. It is particu­larly useful for tracking down open-circuits in coils and trans­ formers. In fact, most faults can eventually be found by using a multimeter. But it can take some time and that is something the serviceman cannot afford. Something that would find faults quick­ly was one of the main requirements which lead to the devel­ opment of the signal tracer. This de- A service kit for a mid-1920s radio serviceman would consist of a torch cell and globe, a voltmeter, and a pair of headphones. As receivers became more complex, the need for better test equipment increased. 84  Silicon Chip vice removes a lot of the guesswork from radio servicing. The big advantage of the signal tracer is that it can tap into the various stages of a receiver. It can check both radio and audio frequencies, amplify the signal and then play it through a speaker. Signal tracers vary in complexity. Some are quite elaborate with multiple tuned circuits, a built-in VTVM (vacuum tube volt­meter) and a modulated oscillator to supply a steady signal source. Unfortunately, such up­market tracers are now few and far between, and types such as the Healing are about as upmarket as vintage radio repairers are likely to find. If anyone locates one of those really good ones, then they are lucky indeed. Typical test procedure Enough of this wishful thinking. Let’s hook up the old Healing and proceed with the proposed test. We will run through a typical late 1930s 5-valve superhet with a 460kHz inter­ me­diate frequency (IF) – see Fig.1. But first, a check for obvious faults, such as valves not lighting or a non-operative high tension (HT) supply, should be made. An open field winding or shorted filter electrolytic would be good reason for no HT voltage. A signal tracer is best used for finding obscure faults, rather than easily recognised ones. For the test proper, a steady signal source is required. There are two choices: a modulated radio frequency (RF) signal generator or a radio station. In this example, an RF signal gen­erator will be used, as it supplies a uniform signal which can be varied by the generator’s attenuator. The RF generator is con­nected to the receiv- 1 2 3 4 5 6 8 7 er’s aerial and earth terminals, while the tracer’s earth clip is attached to the receiver’s chassis. The next step is to set the RF generator to around 600kHz and turn the attenuator full on (ie, maximum signal output). I use 580kHz as it saves having to change frequency bands on the tracer later on in. A low frequency rather than a high frequency test signal is chosen, as it is less affected by the loading affect of the RF probe. The tracer’s RF probe is then placed on the receiver aerial terminal (point 1 on Fig.1) and, with its RF and AF gain controls set to maximum, the tracer is tuned to the 580kHz signal. The output from the tracer’s speaker is fairly low during this test but can be heard to peak as the tracer’s tuning dial is correctly positioned. Failure to find a signal at this first test point would suggest a short cir- cuit between the aerial terminal and chassis. Next, the RF probe is placed on the converter valve control grid. A more convenient connection may be to the fixed plates of the tuning capacitor (2). The receiver should then be tuned to 580kHz, as indicated by the tracer’s speaker. Although the test signal has not yet encountered a valve, the signal at this second test point should be considerably louder than the first. The reason is that the signal is now tuned to resonance. This may vary a little from set to set, as the gain is dependent on the efficiency, or “Q”, of the aerial coil. Failure to pick up a signal at this test point would indicate a faulty aerial coil, shorted tuning capacitor, or a shorted trimmer capacitor. We now shift the RF probe to the As one of the tracer’s frequency ranges is 220-590kHz, 580kHz is a convenient frequency for broadcast band signal tracing. 9 Fig.1: a typical 1930s 5-valve superhet radio circuit. The numbers marked in red correspond to the test points listed in the text. next test point, at the plate of the converter valve (3). If all is well the signal will be much stronger now (due to stage gain) and the RF gain control may require backing off a little. Retuning the receiver Note that when probing the first few RF test points, the receiver should be retuned each time the probe is moved. That’s because the RF probe has a tendency to load the circuit and detune it slightly. However, once past the first intermediate frequency (IF) transformer, this retuning procedure is no longer necessary. Faults frequently occur in a frequency changer stage and, when checking the plate of the converter valve, several frequen­cies should be present. Let’s take a closer look at these fre­quencies. With the tracer still set at 580kHz, The receiver’s intermediate frequency can be easily checked by first tuning to it on the tracer dial. Failure to pick up the IF at the converter valve plate indicates trouble in the oscillator cir­cuit. The tracer dial is shown here tuned to 460kHz. May 1997  85 Once again, due to stage gain, the signal level rises dramatically at the plate of the IF amplifier valve (5). If the signal is not present at the plate, either the valve is defective or a component associated with it has broken down; eg, screen resistor, bypass capacitor, etc. Second IF stage Tracing signals through a radio is easier if a modulated RF signal gen­erator is used. This close-up view shows a Heathkit generator set to 580kHz (middle scale on dial). the signal should be loud and clear at the plate, indicating that the stage is ampli­fying the signal. The set’s IF signal should also be there and tuning the tracer to 460kHz will confirm its presence if the oscillator circuit is working OK. The oscillator frequency should also be present at the converter plate and, with the receiver tuned to 580kHz, the oscillator frequency should be 1040kHz (ie, 580kHz + 460kHz). Although the oscillator is not modulated, it picks up some of the RF generator’s modulation in the converter valve and can be heard softly at 1040kHz. If there is no IF signal at the converter plate, it’s a fair indication of either a faulty valve or a defective oscilla­tor circuit. In that case, a thorough check out of this stage will be required. Testing beyond the first IF transformer (4) with the tracer set to 580kHz will reveal no signal at all and it is necessary to retune the tracer to the receiver’s IF, in this case 460kHz. The reason for this is straightforward. Although the original fre­quency of 580kHz and the IF of 460kHz are both present at the converter plate, only the 460kHz signal passes through the first IF transformer. If this signal is absent at the grid of the IF amplifier valve, we look for a fault in either the first IF transformer or its associated circuitry. Three working receivers were used to check the old Healing signal tracer and, in each instance, it was found that the signal strength decreased considerably as it passed through the first IF transformer. This decrease, however, is a false condition, caused by the RF probe loading the transformer secondary and detuning it. Retuning the secondary winding while the probe was in place proved this point. As the transformer was retuned, the test signal increased accordingly. If the signal tracer fails to locate an intermediate frequency (IF) signal at the converter plate, it could well be caused by an open circuit oscillator coil. 86  Silicon Chip Following the 460kHz signal further, it must pass through the second IF transformer and onto the detector diode. The signal loss through the second IF transformer is not as noticeable as the first, possibly due to the loading effect of the diode. If the signal is not present at the diode (6), check the second IF transformer windings and accompanying circuitry. At this stage, it is time to use the audio probe. The first component the audio signal encounters after the detector is the receiver’s volume control. If that control is backed off, no audio signals would be found in any of the audio stages. Place the audio probe on the moveable arm connection of the volume potentiometer (7) and rotate the control until the signal is heard. If nothing happens then an open or shorted volume control is the likely cause. Continuing on from the volume control, the audio signal should be present on each side of the coupling capacitor (if one is used) which feeds the signal to the control grid of the first audio amplifi­er. There should be similar volume levels on each side of this cou­pling capacitor. A noticeable increase in gain will be evident when the probe is moved to the first audio valve plate (8) and the AF gain control or the receiver’s volume control may need to be backed off. If there is no signal at the plate, Frequency converter valves such as the 6J8G are often the cause of non-functioning radio receivers. A lot of problems can be found in and around converter stages. Vintage Radio Repairs Sales Valves Books Spare Parts See the specialists * Stock constantly changing. * Top prices paid for good quality vintage wireless and audio amps. * Friendly, reliable expert service. When probing the secondary of the first IF transformer, there is an apparent loss of signal strength due to the detuning effect of the RF probe. Call in or send SSAE for our current catalogue RESURRECTION RADIO 242 Chapel Street (PO Box 2029) PRAHRAN, VIC 3181 Tel (03) 9510 4486 Fax (03) 9529 5639 Above: this dual purpose probe and earth clip can be used for tracing both RF and audio signals. either the valve or its associated parts are faulty. Again, there should be little or no volume drop when check­ ing both sides of the coupling capacitor between the first audio valve and the output valve. But a fairly solid increase in volume should be noticed at the plate of the output valve (9). If there is a signal at the grid of the output valve and none at the plate, then the fault could be in the valve itself or the output transformer that couples the valve to the speaker. So that takes us through the basic process of signal trac­ing. Although we went through our test step by step, the job can be speeded up a little if so desired. By probing only the control grids of each valve a lot of steps can be eliminated. Probe the grids until the signal stops, then backtrack to where it is found again. Somewhere in between is where the trouble spot must be found. When using a signal tracer it should Silicon Chip Binders only take a few minutes to set up the equipment and track down the approximate location of a fault. That’s the big advantage offered by a tracer – speed and accuracy! While the instrument takes a while to get accustomed to, its value as a troubleshooter soon becomes evident. Intermittent faults Having gone through the routine described above and grasped the broad concept of signal tracing, the experimenter is in an excellent position to embrace what is probably the most valuable feature of all. We refer to the problem of the intermit­ tent fault and the role a signal tracer can play in tack­ling this type of problem. Next month’s Vintage Radio will look at this problem in greater detail and describe how to make and use a simple untuned tracer. While the un­tuned tracer lacks the versatility of the tuned type, it is nevertheless a handy test instrument – particu­larly SC if you have no other type. These beautifully-made binders will protect your copies of SILICON CHIP. They are made from a dis­tinctive 2-tone green vinyl & will look great on your bookshelf. Price: $A11.95 plus $3 p&p each (NZ $8 p&p). Send your order to: Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. May 1997  87 Silicon Chip Back Issues January 1991: Fast Charger For Nicad Batteries, Pt.1; Have Fun With The Fruit Machine; Two-Tone Alarm Module; LCD Readout For The Capacitance Meter; How Quartz Crystals Work; The Dangers of Servicing Microwave Ovens. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Low-Cost Inverters For Fluorescent Lights; Low-Cost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages. September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice. 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 1989: Auxiliary Brake Light Flasher; What You Need to Know About Capacitors; 32-Band Graphic Equaliser, Pt.2; The Story Of Amtrak Passenger Services. 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 1989: Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; The Burlington Northern Railroad. June 1990: Multi-Sector Home Burglar Alarm; Low-Noise Universal Stereo Preamplifier; Load Protector For Power Supplies; Speed Alarm For Your Car; Fitting A Fax Card To A Computer. July 1989: Exhaust Gas Monitor; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm; The NSW 86 Class Electrics. July 1990: Digital Sine/Square Generator, Pt.1 (Covers 0-500kHz); Burglar Alarm Keypad & Combination Lock; Simple Electronic Die; Low-Cost Dual Power Supply; Inside A Coal Burning Power Station. 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. January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Phone Patch For Radio Amateurs; Active Antenna Kit; Designing UHF Transmitter Stages; A Look At Very Fast Trains. 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. August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/Square Generator, Pt.2. September 1990: 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. 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. March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; A Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal Wideband RF Preamplifier For Amateur Radio & TV. April 1991: Steam Sound Simulator For Model Railroads; Remote Controller For Garage Doors, Pt.2; Simple 12/24V Light Chaser; Synthesised AM Stereo Tuner, Pt.3; A Practical Approach To Amplifier Design, Pt.2. May 1991: 13.5V 25A Power Supply For Transceivers; Stereo Audio Expander; Fluorescent Light Simulator For Model Railways; How To Install Multiple TV Outlets, Pt.1. June 1991: A Corner Reflector Antenna For UHF TV; 4-Channel Lighting Desk, Pt.1; 13.5V 25A Power Supply For Transceivers, Pt.2; Active Filter For CW Reception; Tuning In To Satellite TV. 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; The Snowy Mountains Hydro Scheme. August 1991: Build A Digital Tachometer; Masthead Amplifier For TV & FM; PC Voice Recorder; Tuning In To Satellite TV, Pt.3; Step-By-Step Vintage Radio Repairs. 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. 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; Turn-stile 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. ORDER FORM Please send me a back issue for:  July 1989  September 1989  January 1990  February 1990  July 1990  August 1990  December 1990  January 1991  May 1991  June 1991  October 1991  November 1991  April 1992  May 1992  September 1992  October 1992  April 1993  May 1993  September 1993  October 1993  February 1994  March 1994  July 1994  August 1994  December 1994  January 1995  May 1995  June 1995  October 1995  November 1995  March 1996  April 1996  August 1996  September 1996  January 1997  February 1997                    September 1988 October 1989 March 1990 September 1990 February 1991 July 1991 December 1991 June 1992 January 1993 June 1993 November 1993 April 1994 September 1994 February 1995 July 1995 December 1995 May 1996 October 1996 March 1997                    April 1989 November 1989 April 1990 October 1990 March 1991 August 1991 January 1992 July 1992 February 1993 July 1993 December 1993 May 1994 October 1994 March 1995 August 1995 January 1996 June 1996 November 1996 April 1997                   May 1989 December 1989 June 1990 November 1990 April 1991 September 1991 March 1992 August 1992 March 1993 August 1993 January 1994 June 1994 November 1994 April 1995 September 1995 February 1996 July 1996 December 1996 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 ___________ 88  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. January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Experiments For Your Games Card. 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. March 1992: TV Transmitter For VHF VCRs; Thermostatic Switch For Car Radiator Fans; Telephone Call Timer; Coping With Damaged Computer Directories; A Guide To Valve Substitution In Vintage Radios. 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. April 1992: IR Remote Control For Model Railroads; Differential Input Buffer For CROs; Understanding Computer Memory; Aligning Vintage Radio Receivers, Pt.1. 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. 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. July 1992: Build A Nicad Battery Discharger; 8-Station Automatic Sprinkler Timer; Portable 12V SLA Battery Charger; Multi-Station Headset Intercom, Pt.2. August 1992: 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 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. April 1993: Solar-Powered Electric Fence; Audio Power Meter; Three-Function Home Weather Station; 12VDC To 70VDC Converter; Digital Clock With Battery Back-Up. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Alphanumeric LCD Demonstration Board; The Microsoft Windows Sound System; The Story of Aluminium. June 1993: AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; Digital Voltmeter For Cars; 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 Z80Based 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. 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; Build a 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: Dolby Surround Sound - How It Works; Dual Rail Variable Power Supply; Talking Headlight Reminder; Electronic Ballast For Fluorescent Lights; Temperature Controlled Soldering Station; 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; Cruise Control - How It Works; Remote Control System for Models, Pt.1; Index to Vol.7. January 1995: Sun Tracker For Solar Panels; Battery Saver For Torches; Dolby Pro-Logic Surround Sound Decoder, Pt.2; Dual Channel UHF Remote Control; Stereo Microphone Preamplifier;The Latest Trends In Car Sound; Pt.1. February 1995: 50-Watt/Channel Stereo Amplifier Module; Digital Effects Unit For Musicians; 6-Channel Thermometer With LCD Readout; Wide Range Electrostatic Loudspeakers, Pt.1; Oil Change Timer For Cars; The Latest Trends In Car Sound; Pt.2; Remote Control System For Models, Pt.2. December 1995: Engine Immobiliser; 5-Band Equaliser; CB Transverter For The 80M Amateur Band, Pt.2; Subwoofer Controller; Dolby Pro Logic Surround Sound Decoder Mk.2, Pt.2; Knock Sensing In Cars; Index To Volume 8. January 1996: Surround Sound Mixer & Decoder, Pt.1; Magnetic Card Reader; Build An Automatic Sprinkler Controller; IR Remote Control For The Railpower Mk.2; Recharging Nicad Batteries For Long Life. February 1996: Three Remote Controls To Build; Woofer Stopper Mk.2; 10-Minute Kill Switch For Smoke Detectors; Basic Logic Trainer; Surround Sound Mixer & Decoder, Pt.2; Use your PC As A Reaction Timer. March 1996: Programmable Electronic Ignition System; Zener 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. 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. 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. April 1995: Build An FM Radio Trainer, Pt.1; A Photographic Timer For Darkrooms; Balanced Microphone Preamplifier & Line Filter; 50-Watt Per Channel Stereo Amplifier, Pt.2; Wide Range Electrostatic Loudspeakers, Pt.3; An 8-Channel Decoder For Radio Remote Control. 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. 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. January 1997: How To Network Your PC; Using An Autotransformer To Save Light Bulbs; 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. 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; Door Minder; 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. 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. 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. 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. November 1995: Mixture Display For Fuel Injected Cars; CB Transverter For The 80M Amateur Band, Pt.1; PIR Movement Detector; Dolby Pro Logic Surround Sound Decoder Mk.2, Pt.1; Digital Speedometer & Fuel Gauge For Cars, Pt.2. 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-APhone Loud Sounding Alarm; Control Panel For Multiple Smoke Alarms, Pt.2. March 1997: Driving A Computer By Remote Control; Plastic Power PA Amplifier (175W); Signalling & Lighting For Madel Railways; Build A Jumbo LED Clock; Audible Continuity Tester; Cathode Ray Oscilloscopes, Pt.7. April 1997: Avoiding Win95 Hassles With Motherboard Upgrades; TV Picture-In-Picture Unit; A Low-Tech Timer With No ICs; Digital Voltmeter For Cars; Loudspeaker Protector For Stereo Amplifiers; Train Controller For Model Railways; Installing A PC-Compatible Floppy Drive In An Amiga 500; Cathode Ray Oscilloscopes, Pt.8. PLEASE NOTE: November 1987 to August 1988, October 1988 to March 1989, June 1989, August 1989, May 1990, February 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 at $10 including packing & postage. May 1997  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. Is gas cheaper than electricity? We have gas and electricity at our home and I have been told that gas is much cheaper as an energy source than electrici­ty. How do I compare the two? My gas bill rate is 1.3155 cents/ megajoule. How does this compare with electricity. (B. J., Chatswood, NSW). • These days, gas is generally sold by the megajoule and this can be easily converted to kilowatt-hours, the unit for electric­ity consumption. One joule is equivalent to one watt being used for one second; ie, a joule is a watt-second. Therefore, to con­vert mega­joules to kilowatt hours we first divide the figure by 3600 to convert it to watthours and then divide again by 1000 to obtain kilowatt-hours. Therefore, 10 megajoules divided by 3,600,000 becomes 2.778 kilowatt-hours. By the reverse process, we can convert one kilo­watt-hour to 3.6 mega­joules. To convert the rate charge of 1.3155 cents per megajoule to a kilowatt-hour charge, multiply by 3.6 to get 4.7358 cents/kWh. This is less than half the normal Sydney (Energy Australia) rate of 10.15 cents/kWh but that is not the whole story. AGL, for example, also adds in what they call a supply fee of $18 a quar­ter (three months) and this can greatly increase the effective rate if you only have a small gas bill. For domestic off-peak hot water, the equivalent electricity charge in Sydney is only 3.72 cents/kWh and this is quite a bit cheaper than the gas rate. It may also be the case that gas burners are not as efficient as electric elements for heating and cooking and so there may be an effective increase in the rate for gas. The short answer to your question is that gas is probably cheaper if you use it for heating in your home. In environmental terms though, it is much more efficient to burn gas in the home for heating and cooking than to use electricity produced in coal-burning power stations. Using a scope as a heart monitor I am looking to connect up a scope as a heartbeat monitor for a school project. I have access to a 15MHz analog scope but I need to know what sort of probes to use. Could you please help me? (B. H., Tamworth, NSW). • We do not think an ordinary oscilloscope is of much use in monitoring or displaying heart beats. For a start, Master/slave for fast clocks With reference to your recent article entitled “Fast Clock For Model Railways” in the December 1996 issue of SILICON CHIP, is it possible to arrange for a master/ slave situation? (R. P., Zill­ mere, Qld). • It would be possible to have the Fast Clock Driver control additional clock movements. You would need to add an additional two NAND gates to drive each move90  Silicon Chip ment. The accompanying diagram shows the concept. However, since the Fast Clock Driver uses only three cheap ICs, you may find it easier just to build a separate clock driver for each movement. the slowest timebase speed of a typical oscilloscope is around 0.2 seconds per division, meaning that it takes two seconds for the beam to trace across all 10 divisions on the screen. By contrast, a typical heart rate might be 80 beats/ minute or 1.3 per second. That means that you could only display one beat on the screen. To be really practical, at least five beats should be dis­played. To do that would require a timebase setting of one sec­ond/division. Such a speed setting is only available on a digital storage oscilloscope. Apart from that, it is doubtful wheth­ e r a standard oscillo­ s cope would be sensitive enough to display the very small voltag­es involved in the measurement of heartbeats. High power audio amplifier I have just read about a high power audio amplifier in the April issue of an electronics magazine. It is claimed to deliver up to 4000 watts into a 4Ω load and 8000 watts into 2Ω; all this in a 3-unit high rack case. It is also claimed to have special power supply circuitry and a “four-tiered” DC supply to give efficiency close to a class-D design. Is this really a fair dinkum design or have I been lured into an “April Fool” spoof. (T. H., Leichhardt, NSW). • Well, for an April issue, you can never be sure but we think the amplifier is a genuine product. What we can be certain about is that no amplifier running from 240VAC mains could ever deliv­er 8000 watts continuously, for two reasons. First, normal 240VAC mains GPOs or power points, as most people call them, are limited to 10 amps. That limits the power input to 2400 watts continuous. Even allowing for higher than normal efficiency of, say, 80%, that would limit the amplifier to about 1900 watts total or 950 watts per channel. It is also true that an amplifier which was able to deliver 8000 watts continuously in bridge mode would have a “worst case” power dissipation of about 9900 watts. This occurs when the amplifier is delivering about 40% of its rated power into a real (loudspeaker) load. Now whatever new principles may have been brought to bear in this design, we are certain that it is not possible to dis­sipate 9900 watts in a 3-unit high rack case without achieving complete meltdown. Just for comparison, 9900 watts is almost 10 times the rating of a standard 1kW bar radiator and you know how hot they run! The clue to the amplifier’s likely mode of operation is the phrase “4-tiered DC supply”. We think it is a variation of the class-G mode developed by Hitachi years ago. Thus, the supply rails of the amplifier are modulated in line with the input signal, to minimise dissipation in the output transistors. Thus, if the amplifier can deliver 4000 watts into 2Ω in stereo mode, we would guess than it can supply about 2000 watts peak into 4Ω and possibly 500 or 600 watts RMS per channel on a continuous basis. Maybe our estimates are a little conservative but we stick to the general principle that the ratings of 4000W and 8000W can only be short duration figures. Kit assembly service needed I have subscribed to SILICON CHIP for some years and have made up many of the kits. However, a few years ago I had a stroke which left my right arm paralysed. I have recently been given a smoke alarm kit as published in the January 1997 issue and though I appreciate it, I am unable to assemble it myself. I would be very grateful if you could put me in touch with somebody who could assemble the kit for payment. I would pay all transport costs, etc. (Name & address supplied but withheld). • Yours is a fairly common request and one which we used to refer to one of a number of people who provided a kit repair and assembly service. At the moment we are unable to nominate anyone who could do the job. There is apparently still a need for this type of service and it could be an opportunity for readers wanting a part-time business. In the meantime, if Tweaking the SLA battery charger My friend and I have constructed three SLA battery chargers from the circuit in the March 1990 issue of SILICON CHIP. We are currently using an SLA battery manufactured by GND Technologies (Exide, Bosch, Marshall, etc.). The technical division of GND has advised me that they require +14.8V charging to satisfactorily bring the electrolyte to 1275 spg which is not currently occurring. I find it difficult to work out the equations to adjust key voltages and current but by leaving Rs, Rt, Ra, Rd & Rc the same and changing Rb to 30kΩ, it may do what is required. The result paper-wise is Voc +15.53V (appears to be too high), Vf +14.68B & Vt +9.99V. The there is a reader who lives in Canberra or the surrounding area who could help this reader, please contact SILICON CHIP by phoning (02) 9979 5644. Questions on locomotive lighting I have some questions about the “Constant Brilliance Light­ing Circuit” featured in the March 1997 issue of SILICON CHIP. Most of the light globes in model locomotives and carriages are 14V-16V globes. Can the output voltage of the project be increased to run these existing globes so that they do not have to be replaced with 3V globes? It is often very hard to replace the globes in a locomotive with a different style. If the constant brilliance lighting circuit was only in­creased to 6V output so that the existing loco lights were only partly illuminated and no capacitor was connected in series, what would be the maximum safe DC train controller voltage that could be used so that the 14V-16V globes could operate safely? (S. H., Woonona, NSW). • It should be possible to use the unit without any modifica­tions to the basic circuit to drive 14-16V lamps, although the brilliance will be reduced. However, you may need to experiment with the value of the capacitor in se- present voltage output is 13.5VDC. Any comment you may be able to give would be of assistance. (G. R., Tura Beach, NSW). • We assume you are using the data supplied in an article from the March 1990 issue on the UC3906. The equations to adjust Voc, Vf & Vt are interactive and so changing one value will alter the others as well. Adjusting Rb to 30kΩ will give close enough Vf and Vt values but with a high Voc. Try increasing the value of Rd at pin 10 to reduce the Voc value. Your charger is at present producing a slightly low value for Vf. This probably means that the reference in the UC3906 is slightly low. You may need to alter the calculated values of resistance in order to obtain 14.8V. ries with each lamp and it may not be possible to use a mixture of 3V and 14V lamps. Try a 0.47µF capacitor in series with each 14V lamp and adjust the brilliance to suit. You may then need to use smaller value capacitors in series with 3V grain-of-wheat bulbs to avoid over-driving them. Upgrading the drill speed control I am interested in building the Heavy Duty Speed Control as featured in the September & October 1992 issues of SILICON CHIP but I have a problem. I want to use it on a high-speed industrial router with a nameplate rating of 10 amps. I need to do this because some router bits need a lower speed to make a cleaner cut; the full router speed causes burning of the cut and overheating of the bit itself. What modifications are required to make it suitable? Do I need to use a bigger Triac? (P. V., Subiaco, WA). • As published, the design is only suitable for appliances rated up to 5A and we are a little wary of using a speed con­troller at higher currents? Having said that, the basic design is suitable for higher currents but needs physical modifications. First, the wiring and PC board is not adequate May 1997  91 Electromagnetic wave meter I am writing to you to suggest a design for an electromag­ netic wave meter in a future issue. With the recent interest in the effect that transmissions from mobile tele­phones and towers might have on the human brain-box, I thought it would be useful if these radio transmissions could somehow be measured. I had in mind that the device would be very simple and one that could be connected to a multimeter to show the amount of electromagnetic radiation in the surrounding atmosphere. These measurements could then be done and seen by anyone who might be concerned about the transmissions. (B. F., Morphett Vale, SA). • As you suggest, such a device is fairly simple in concept but not easy to produce in practice. They are normally referred to as signal strength meters and are widely used in RF communica­ t ions, particularly by installers of TV antennas and microwave dishes. The catch is that they are not simple devices in practice because you need a tunable antenna, usually a dipole with adjust­able tele­ scopic elements, and the circuit itself needs to be tunable to the frequency of interest. Most critical of all, it needs to be calibrated and have a flat response over a very wide range of frequencies, if it is to be of use in measuring most communications services. In fact, if it was to measure mobile phone and microwave services, it would need a calibrated response up to 2GHz or more. Commercial units just covering TV services can easily cost $1000 or more. With these aspects in mind, we do not envisage publishing a suitable circuit. Second, when operated with a speed control, you can expect that the brushes may wear more than usual and one brush may wear more than the other, by dint of being operated with DC rather than AC. The specified Triac has a rating of 40A and so there should be no need to substitute a higher-rated unit. Fan timer wanted for 10A currents. Second, we would strongly suggest the substitution of a cartridge fuse instead of the glass-link 2AG fuse. You would need to wire the unit so that heavy currents were not carried by the PC board conductors. In other words, the Active wire would go direct to a chassis-mounted cartridge fuse­holder and then to the A2 terminal of the Triac. The Triac itself would not be wired into the PC board but would need to be mounted on a fairly substantial heatsink. The whole circuit would there­fore need to be mounted in a larger case. Finally, we have two warnings about using a speed control with a heavy duty router. These appliances generate large amounts of heat in their windings and they depend on the internal fan running at full speed to keep the whole motor cool. This means that you must not operate the unit at low speeds, otherwise you run a high risk of burning it out. I have a need for a circuit to automatically switch off a mains powered appliance after a preset time; specifically, bath­room exhaust fans which are left on by my family and sometimes run all day. I envisage a simple timer circuit using a Triac for switching and, if possible, being directly mains operated; ie, no need for a separate power supply. The circuitry could be housed in wall cavity behind the switchplate or alternatively, in a small jiffy box, plugging directly into the fan outlet. (N. W., Berowra Waters, NSW). • Such a timer is certainly feasible but it is unlikely to be much cheaper as a do-it-yourself project than a commercial timer from HPM or Clipsal. They are available in a mechanical form with a big button which you press in and then it takes 20 minutes (adjustable) or more to pop out and switch off. These pushbutton timers are widely used in home units for stairwell lighting. Alternatively, you can obtain them in electronic form and they can be part of a multiple switchplate. They are available from electrical wholesalers. Bookshelf – from p.77 Chapter Seven covers the circuit at the telephone exchange end of the loop and again the old methods are detailed before the SLIC is discussed. This is another of those inscrutable telephone terms. It stands for Subscriber Line Interface Circuit. By the way, ever wanted to know what PBX stands for? The answer is “private branch exchange”. PABX? Try “Private Automatic Branch Exchange”. Also covered are voice frequency filters, codecs, DTMF receivers and cross-point switching. Chapter Eight covers network transmission including channel banks, multiplexers and repeaters. Chapter Nine is on more famil­iar ground and discusses modems, fax machines and fax modems. Finally, Chapter 10 focuses on wireless telephones and these include cordless phones in homes and cellular phones. This last chapter is a little out of date, since this area of technology has been moving so fast. Overall, this is a very useful text for anyone wanting to familiarise themselves with telephone technology. It won’t make you an expert but will give you a good introduction to tele­phone electronics. The book is well-priced at $34.95 and is available from the SILICON CHIP SC office. (L.D.S). MC34010 and the use of microprocessors. Also covered are speaker phones (for hands-free use) and the featured chip is the Motorola MC34118. This is similar to the MC­34018 used in the Hands-Free Speaker­phone published in the September 1998 issue. Chapter Six explains digital transmission techniques and much of this will be familiar to anyone who knows about A/D and D/A converters although there are special twists such as u-law and A-law compand­ers, delta modulation and time-division multi­ plexing. 92  Silicon Chip electronic design, and applications. The sixth edition has been expanded to include chapters on surface mount technology, hardware & software design, semicustom electronics & data communications. 63 chapters, in hard cover at $120.00. Silicon Chip Bookshop Radio Frequency Transistors Newnes Guide to Satellite TV Installation, Recept­ion & Repair. By Derek J. Stephen­son. First published 1991, reprinted 1994 (3rd edition). This is a practical guide on the installation and servicing of satellite television equipment. The coverage of the subject is extensive, without excessive theory or mathematics. 371 pages, in hard cover at $55.95. Guide to TV & Video Technology By Eugene Trundle. First pub­lish-­ ed 1988. Second edition 1996. Eugene Trundle has written for many years in Television magazine and his latest book is right up date on TV and video technology. 382 pages, in paperback, at $39.95. Servicing Personal Computers By Michael Tooley. First published 1985. 4th edition 1994. Computers are prone to failure from a number of common causes & some that are not so common. This book sets out the principles & practice of computer servicing (including disc drives, printers & monitors), describes some of the latest software diagnostic routines & includes program listings. 387 pages in hard cover at $59.95. format and R-DAT. If you want to understand digital audio, you need this reference book. 305 pages, in paperback at $55.95. The Art of Linear Electronics By John Linsley Hood. Pub­lished 1993. This is a practical handbook from one of the world’s most prolific audio designers, with many of his designs having been published in English technical magazines over the years. A great many practical circuits are featured – a must for anyone inter­ested in audio design. 336 pages, in paperback at $49.95. Components, Circuits & Applica­ tions, by F. F. Mazda. Published 1990. Previously a neglected field, power electronics has come into its own, particularly in the areas of traction and electric vehicles. F. F. Mazda is an acknowledged authority on the subject and he writes mainly on the many uses of thyristors & Triacs in single and three phase circuits. 417 pages, in soft cover at $59.95. Digital Audio & Compact Disc Technology Electronics Engineer’s Reference Book Hard cove Produced by the Sony Service Centre (Europe). 3rd edition, published 1995. Prepared by Sony’s technical staff, this is the best book on compact disc technology that we have ever come across. It covers digital audio in depth, including PCM adapters, the Video8 PCM Power Electronics Handbook Your Name__________________________________________________ PLEASE PRINT Address____________________________________________________ _____________________________________Postcode_____________ Daytime Phone No.______________________Total Price $A _________ ❏ Cheque/Money Order r Edited by F. F. Mazda. version now available First published 1989. 6th edition. This just has to be the best refer­ ence book available for electronics engineers. Provides expert coverage of all aspects of electronics in five parts: techniques, physical phenomena, material & components, ❏ Bankcard ❏ Visa Card ❏ MasterCard Card No. Signature_________________________ Card expiry date_____/______ 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. Principles & Practical Applications. By Norm Dye & Helge Granberg. Published 1993. This book strips away the mysteries of RF circuit design. Written by two Motorola engineers, it looks at RF transistor fundamentals before moving on to specific design examples; eg, amplifiers, oscillators and pulsed power systems. Also included are chapters on filtering, impedance matching & CAD. 235 pages, in hard cover at $85.00. Surface Mount Technology By Rudolph Strauss. First pub­ lished 1994. This book will provide informative reading for anyone considering the assembly of PC boards with surface mounted devices. Includes chapters on wave soldering, reflow­ soldering, component placement, cleaning & quality control. 361 pages, in hard cover at $99.00. Audio Electronics By John Linsley Hood. Pub­lished 1995. This book is for anyone involved in designing, adapting and using analog and digital audio equipment. Covers tape recording, tuners & radio receivers, preamplifiers, voltage amplifiers, power amplifiers, the compact disc & digital audio, test & measurement, loudspeaker crossover systems and power supplies. 351 pages, in soft cover at $52.95.  Title ☐ ☐ Newnes Guide to Satellite TV ☐ Guide to TV & Video Technology ☐ Servicing Personal Computers ☐ The Art Of Linear Electronics ☐ Digital Audio & Compact Disc Technology ☐ Power Electronics Handbook ☐ Electronic Engineer's Reference Book ☐ Radio Frequency Transistors ☐ Surface Mount Technology ☐ Audio Electronics Postage: add $5.00 per book. Orders over $100 are post free within Australia. NZ & PNG add $10.00 per book, elsewhere add $15 per book. TOTAL $A Price $55.95 $39.95 $59.95 $49.95 $55.95 $59.95 $120.00 $85.00 $99.00 $52.95 MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. CLASSIFIED ADVERTISING RATES FOR SALE 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. C COMPILERS: Ever ything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC12, 68HC16, 8051/52, 8080/85, 8086 or 8096: $140.00 each. Macro Cross Assemblers for these CPUs + 6800/01/03/05 and 6502: $140.00 for the set. Debug monitors: $70 for 6 CPUs. All compilers inc ‘HC12, XASMs and monitors: $480. 8051/52 or 80C320 Simulator (fast): $70. Disassemblers for 12 CPUs only $75. Try the new C-FLEA Virtual Machine for small CPUs, build a “C-Stamp”. Demo disk: FREE. All prices + $5 p&p. GRAN­ T RONICS PTY LTD, PO Box 275, Wentworthville 2145. Ph/Fax (02) 9631 1236 or Internet: http://www.mpx.com.au/~lgrant. 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 HOMEMADE GENERATORS: how to instructions. Eight pages free text and colour photos on the Internet at: http://www.onekw.co.nz/ MICROCRAFT PRESENTS: Dunfield (DDS) products are now available ex-stock at a new low price; please ask for our catalogue. Micro C, the affordable “C” compiler for embedded applications. Versions for 8051/52, 8086, 8096, 68HC08, 6809, 68HC11 or 68HC16 $139.95 each + $3 p&h • Now on special is the SDK, a package of ALL the DDS “C” compilers for $399 + $6 p&h • EMILY52 is a PC based 8051/52 high speed simulator $69.95 + $3 p&h • DDS demo disks $7 + $3 p&h • VHS VIDEO from the USA (PAL) “CNC X-Y-Z using car alter­nators” (uses car alternators as cheap power stepper motors!) $49.95 + $6 p&h (includes diagrams) • Device programming EPROMs/PALs etc from $1.50 • Fixed price electronic design and PCB layout • Credit cards accepted • All goods sent certified mail • Call Bob for more de­tails. MICRO­ CRAFT, PO Box 514, Concord NSW 2137. Phone (02) 9744 5440 or fax (02) 9744 9280. JAPANESE QUALITY & TECHNOLOGY At Very Competitive Import­ er-Direct Prices. AUTOMATIC IRIS, MANUAL IRIS & VariFocal CS LENSES. Manual Iris from $49. Auto Iris from $93. VariFocal from $75. Allthings Sales & Services 09 349 9413 fax 09 344 5905. !!!!!!! THE TINIEST !!!!!!! VIDEO CAMERA MODULE PCB 28 x 28 mm, IR & Low light sensitive, with Pinhole Lens. 09 349 9413. WARNING ! WARNING ! WARNING ! WARNING !!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!! VIDEO CAMERA MODULES Beware of higher or lower prices for a similar Camera! BUY A BETTER CAMERA AT A SIMILAR PRICE! With a CHOICE OF ..... 380, 460 & 600 TVL Resolution. Low Light & IR Sensitive 0.05 lux. TEENY WEENY 28 mm x 28 mm PCBs. ELEVEN Board Lenses. FOUR Pinhole Lenses. IR Cut/ Pass & Polarising Filters. 800 + nm 52 mW/Sr IR LEDs. Ancil­lary Equipment. BEFORE & AFTER-SALES SERVICE, HELP & ADVISE! Before you Buy! Ask for our Detailed, Illustrated Price List with Application Notes. Also available CCTV Technical, Design & Refer­ence Manuals & Inter-Active CD ROM. Allthings Sales & Services 09 349 9413 fax 09 344 5905. CCTV - TV VCR INTERFACE TV RF MODULATOR - MIXER - ANTENNA AMPLI­F IER. $30. Use with Video Cameras & Microphones. VCR Like In­stallation. 09 349 9413. !!!!!!!!! MAY SALE !!!!!!!!! !! STOCK REDUCTION!!!! LIMITED QUAN­ TITIES! MONITORS 5.5-inch Video/ Audio 12-14 VDC I/P, 10.5 VDC Reg O/P $110. VIDEO CAMERA MODULES 600 TVL 0.05 lux with Lens $99. VIDEO CAMERAS 600 TVL $119. VIDEO CAMERAS with Two-Way Audio, & 8mm Lens $135. COLOUR VIDEO CAMERAS 420 TVL with Lens $339. QUAD SCREEN DIGITAL PROCESSORS display four images on one screen, with Alarm I/O $419. WIRELESS TX & RX Modules $35. WIRELESS VIDEO/AUDIO RECEIVERS with AFC & Plug Pak $79. DIY CCTV 5.5 inch Plug-In Sets, IR LED-Audio-Camera, 20M Cable, & Plug Pak $299. ALLTHINGS SALES & SERVICES, phone 09 349 9413, fax 09 344 5905. MicroZed Computers PO Box 634, ARMIDALE 2350 (296 Cook’s Rd) Ph (067) 722777 – may time out to Mobile 014 036775 Fax (067) 728987    (Credit Cards OK) http://www.microzed.com.au/~microzed BASIC STAMPS & PIC Tools With third party supporting products, all in stock Easy to learn, easy to use sophisticated CPU based controllers Credit cards OK   Send two 45c stamps for info MEMORY * MEMORY * MEMORY SPECIAL! Ex Tax! 4Mbx9 – (3 Chip) 60ns $50 30-PIN SIMM For Quality Assembly On Time Every Time 356 Gilbert Rd. West Preston Victoria 3072 PCB Assembly PCB Design Prototyping Wiring Looms OEM Manufacture Mobile 018 378750 CAR/RALLY COMPUTER KIT: including fuel sensor & speed sensor. 68HC05 & HC11 DEVELOPMENT SYSTEMS: Oztechnics, PO Box 38, Illawong NSW 2234. Phone (02) 9541 0310. Fax (02) 9541 0734. http://www.oz­technics.com.au/ SIMPLE PIC84 PROGRAMMER: SIMMS (Parity/No Parity) 4Mb 30 PIN-70 $50 $44 4Mb 72 PIN-70 $53 $36 8Mb 72 PIN-70 $104 $72 16Mb 72 PIN-70 $168 $146 32Mb 72 PIN-70 $324 $285 EDO SIMMS (60ns) 4Mb/8Mb $39/72 16Mb/32Mb $146/290 64Mb/128Mb $1075/2112 LASER PRINTER MEMORY 4Mb HP 4&5 $42 8Mb HP 4 & 5 $83 All other models available $Call LIFETIME WARRANTY!! COMPAQ 16Mb ARMADA 1100 $234 All other models available $Call TOSHIBA 8Mb Portege/ Sat EDO $131 16Mb Portege/ Sat EDO $262 16Mb Tecra 500/610 Sat $245 All other models available $Call IBM 16Mb T.Pad 755, 360 EDO $263 All other models available $Call DIMMS 4Mb - SO - 72 PIN $36 8Mb - SO - 72 PIN $72 16Mb - SO - 72 PIN $159 8Mb/16Mb - 168 PIN $70/144 32Mb/64Mb - 168 PIN $306/600 SYNCHRONOUS (SDRAM) 168 PIN - 16Mb $150 168 PIN - 32Mb $327 168 PIN - 64Mb $696 Ex Tax Pricing – Delivery $8. Pricing as at 07/04/97. Phone for latest. Sales Tax 22%. Credit Cards Welcome. We Also Buy And Trade-In Memory. PELHAM PTY LTD Suite 6, 2 Hillcrest Rd, Ph: (02) 9980 6988 Pennant Hills, 2120. Fax: (02) 9980 6991 Email: pelham1<at>ozemail.com.au LED model 6 lights $65, LCD 16x2 char. $75, P+H $3. Also low-cost design, prototyping and microcontroller programming service. Eastern Electronics (02) 9789-3616, Fax (02) 9718-4762. SILICON CHIP FLOPPY INDEX WITH FILE VIEWER Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands are listed on the screen, so you’ll always know what to do next. Notes & Errata also now available: this file lets you quickly check out the Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate the item of interest. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. Price $7.00 each + $3 p&p. Send your order to: Silicon Chip Publications, PO Box 139, Collaroy 2097; or phone (02) 979 5644 & quote your credit card number; or fax the details to (02) 979 6503. Please specify 3.5-inch or 5.25-inch disc. May 1997  95 RAIN BRAIN AND DIGI-TEMP KITS: 8-station controller and 8-chan­ n el, RS232 digital thermometer uses the incredible DS1820 sensor. Call Mantis Micro Products, 38 Garnet St, Niddrie, 3042. P/F/A (03) 9337 1917. http://www.home.aone.net.au/mantismp SEND A BLANK MESSAGE to help<at> dontronics.com for details on how to join our SiClub and List Server Support group. We have a free Basic Interpreter for the PIC16C84. Largest range of PIC related products South of the Equator. PCBs MADE, ONE OR MANY. Low prices, hobbyists welcome. Sesame Electronics (02) 9554 9760. Fax: 9718 4762. Email: skybus<at>zip.com.au SATELLITE DISHES: international reception of Intelsat, Panamsat, Gori­ zont,Rimsat. Warehouse Sale – 4.6m dish & pole $1499; LNB $50; Feed $75. All accessories available. Videosat, 2/28 Salisbury Rd, Hornsby. Phone (02) 9482 3100 8.30-5.00 M-F. DIY SECURITY ALARM SUPPLIES Professional grade equipment PIRs, autodialler alarm panels, CCTV, cable etc. Send for price list. All prices wholesale. AFFORDABLE ALARMS, 7 Firefly Crescent, Lawnton, Qld. 4501. MAY SALE: For three days only we will be offering many items, some of which were never previously advertised. Some clearance and never to be repeated prices will apply. A complete list will be available at our WEB SITE for three days in May: 9th, 10th, and Microprocessor For Digital Effects Unit This is the 68HC705-C8P pro­gramm­ ed micro­pro­cessor IC for the Digital Effects Unit (see Feb­. 1995). Price: $45 + $6 p+p Payment by cheque, money order or credit card to: Silicon Chip Pub­lica­ tions. Phone (02) 9979 5644; Fax (02) 9979 6503. Advertising Index Altronics.........................................3 Av-Comm.....................................43 Dick Smith Electronics.14,15,34-37 Earthquake Audio........................69 Harbuch Electronics....................69 Instant PCBs................................95 11th. Orders will only be accepted up to the 12th May. Orders may be picked up at our premises but only by prior arrangement. KIT OF THE MONTH: We are producing many more exciting kits than the magazines can publish! We will endeavour to release at least one new kit every month and give you a detailed description on our WEB SITE. Just “click” on to the KIT OF THE MONTH icon on our WEB SITE. Coming: Laser beam communicator, low cost car alarm, laser fence, new time lapse interface for CCD camera - VCR secur­ity, low cost 2 channel UHF remote control with a ready made transmitter, extremely effective 10 led IR illuminator etc. VISIT OUR WEB SITE: Visit our very active (continuously updated) WEB SITE. You will find: OUR COMPLETE CATALOGUE - KIT OF THE MONTH - NEW RELEASES AND PRODUCT HIGHLIGHTS - STOP PRESS - ORDERING INFORMATION. VISIT: http://www.ozemail.com.au/~oatley OATLEY ELECTRONICS Phone (02) 9584 3563. Fax (02) 9584 3561. Jaycar ............................IFC, 45-52 Kits-R-US.....................................71 Macservice..................................27 MicroZed Computers...................95 NSW Police Service......................5 Nucleus Computer Services........17 Pelham.........................................95 Resurrection Radio......................87 Rod Irving Electronics .......... 62-66 Silicon Chip Back Issues....... 88-89 Silicon Chip Bookshop.................93 Silicon Chip Binders.................5,96 Silicon Chip Model Wallchart...OBC Silicon Chip Software..................33 Smart Fastchargers.....................17 Telstra..........................................13 Tortech.........................................79 SILICON CHIP BINDERS These binders will protect your copies of SILICON CHIP. ★ Heavy board covers with 2-tone green vinyl covering ★ Each binder holds up to 14 issues ★ SILICON CHIP logo printed in goldcoloured lettering on spine & cover Price: $A14.95 each (incl. postage in Aust). NZ & PNG orders please add $A5 each for p&p. To order, just fill in & mail the order form in this issue to: Silicon Chip Publications, PO Box 139, Collaroy 2097; Or phone (02) 9979 5644 & quote your credit card details or fax (02) 9979 6503. 96  Silicon Chip WAR Audio..................................87 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.