Silicon ChipSeptember 1998 - Silicon Chip Online SILICON CHIP
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SEPTEMBER 1998  1 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.dse.com.au Contents Vol.11, No.9; September 1998 FEATURES Blocked Air Filter Alarm For Cars – Page 32 . . .   4  Troubleshooting Your PC; Pt.5 Software problems and DOS games – by Bob Dyball 14  Electromagnetic Compatibility Testing; Pt.2 Emissions and interference – by Marque Crozman 28  Time Alignment Testing of Loudspeakers The importance of correct driver time alignment – by Terry Paget 92  Special Subscriptions Offer Plus Gear Change Indicator – Page 66 Buy a subscription to “Silicon Chip” before end of September 1998 and get a bonus wallchart Waa-Waa Pedal For Guitars – Page 36 PROJECTS TO BUILD 32  A Blocked Air Filter Alarm Simple device tells you when it’s time to change the air filter element – by Adrian Cuesta 36  A Waa-Waa Pedal For Your Guitar All the circuit details plus how to build a foot pedal – by John Clarke 58  Build A Plasma Display Or A Jacob’s Ladder Two fun projects for the price of one – by Branco Justic 66  A Gear Change Indicator For Cars It tells you when to change gear – by John Clarke 80  A Capacity Indicator For Rechargeable Batteries A 3-digit display shows the remaining battery capacity in ampere-hours – by Rick Walters SPECIAL COLUMNS 20  Serviceman’s Log The old radio from the Cadillac – by the TV Serviceman 76  Vintage Radio A short history of spy radios in WW2; Pt.1 – by Rodney Champness DEPARTMENTS   2  Publisher’s Letter 26  Circuit Notebook 44  Order Form 53  Product Showcase Plasma Display/Jacob’s Ladder – Page 58 Capacity Indicator For Rechargeable Batteries – Page 80 89  Ask Silicon Chip 94  Market Centre 96  Advertising Index SEPTEMBER 1998  1 PUBLISHER'S LETTER Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Production Manager Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Rick Walters Reader Services Ann Jenkinson Advertising Manager Brendon Sheridan Phone (03) 9720 9198 Mobile 0416 009 217 Regular Contributors Brendan Akhurst Rodney Champness Garry Cratt, VK2YBX Julian Edgar, Dip.T.(Sec.), B.Ed Mike Sheriff, B.Sc, VK2YFK Ross Tester Philip Watson, MIREE, VK2ZPW Bob Young SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $59 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 8, 101 Darley St, Mona Vale, NSW 2103. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9979 5644. Fax (02) 9979 6503. ISSN 1030-2662 * Recommended and maximum price only. 2  Silicon Chip What to do with all those old computers Just recently, a colleague of ours was faced with an ulti­matum from his wife. The whole lower storey of his house was chock full of olden-day electronics and he was faced with having to get rid of most of it. Sadly, most of it went to the tip because there was no-one or no organisation that we knew of who had a use for it. Simply, it was worthless; ie, having zero worth. Of course, this cleanout was partly prompted by the edito­rial featured in the December 1996 issue, entitled “Going for the big clean-out”. This colleague had so much “good stuff” lying about that he did not know where to start. And even though a lot of stuff has gone to the tip, he is still sorting it out, trying to decide what to keep and what to toss. Even more sadly, a good deal of the stuff that went to the tip was old computers and some weren’t really all that old. Apart from old IBM PCs and clones, there were quite a few 386 and 286 machines as well. Most of these had no monitors but they all had keyboards, hard and floppy disc drives and so on. And a good few of them would have been working or it was possible to make them work with say, a repair to the switchmode power supply. Clearly, it was just not economic to fix and put them in working order, especially as there was no immediate use for them. Actually, I do have a confession to make. The sight of all these computers going to the tip was too much to bear and I gave in to the temptation. I grabbed a couple of 386 machines with the intention of using them for word-processing at home. My rationale (which my wife will probably see right through) is that many times I can’t use the “good” Pentium machines at home because they are being monopolised by my daughters. With a little work, I’ll be able to set these additional machines up so that, while we won’t have one machine per person, there will almost always be a machine available for word-processing, editing and similar lowly tasks. Apart from my valiant efforts to rescue some unloved ma­chines, this situation must be repeated many times throughout Aus­tralia. How many of us have an old 286, 386 or 486 machine that is still quite usable but we have no use for it as a computer? Clearly, there must be some use for these old machines or parts of these old machines. Perhaps the power supplies can be put to other uses or the cases can be used for other electronic equip­ ment, for example. Do any of our readers have any ideas on this topic? Perhaps you’ve come up with a new and unusual way of using a computer that was otherwise useless. If so, we would like to know about it. Why not send those ideas in and if there are any really worthwhile ones we might publish them in an article. In fact, let’s make it interesting: for the best idea for using an old computer, we will give a prize of $400. So send those ideas in and we’ll announce the winner (hopefully there will be a winner) in the coming December issue. Leo Simpson M croGram Computers PCMCIA Video Capture Card Web-Based Training from $9.95 per month* A number of courses are “Microsoft Learn about Microsoft Office, Word, Access, PCMCIA Video Capture card complete Certified Professional - Approved Study Excel, Windows 95, FrontPage, C++, HTML, with software. Designed to provide Guides” Internet Explorer, Windows NT and more! smooth, full-motion video for appliOver 160 courses on offer cations such as Video Mail, Video Conferencing or *Full details at www.tol.com.au Full-Motion Video Capture to AVI file format. The card is $39 100 Mbps Network Starter Kit WIN 95/98 compatible for easy installation & setup and Cat. 11272 Ethernet Card ISA BNC/UTP PnP Jmp provides 640 x 480 resolution with 30fps capture rate. Serial to Fibre Optic Converter This SOHO Network Star ter Kit contains two The fibre optic converter allows serial 10/100Mbps PCI Ethernet cards, one 4 Port 100BaCat. 3375 PCMCIA Video Capture Card $739 input signals to be converted to fibre seTx hub, two 5 metre cables & detailed installation VGA Monitor Splitters optic signals for long distance, high manual. These splitter modules enable up to 16 speed & high quality communication. Cat. 11900 Network Starter Kit $349 monitors to share the same informaThere are 3 LED indicators which cortion of a host PC simultaneously. The respond to RxD, CTS & power signals. Year 2000 BIOS Card ideal way of providing multiple displays in training rooms, Cat. 15074 RS422/485 to Fibre Optic Converter $499 Even Pentium motherboards are not airport terminals, clubs, etc. The splitter can be up to 15m $499 immune to the Year 2000 bug! 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Cat. 11282 Ethernet Card PCI UTP/STP 10/100Mbps Cat. 11271 Ethernet Card PCI BNC UTP/STP $59 $39 Year 2000 BIOS Card Add a second user to your PC. Two users can now concurrently access one PC. Even share one modem & one ISP account! Total Cost of Ownership is much lower & more cost-effective. Cat. 11295 Ethernet Hub & LAN Card 5 Port UTP 10Mb $109 Internal PCI Plug & Play 5 Port hub and LAN card does not require external power supply and is a cost effective solution for SOHO users. One port can be used as an uplink port for easy expansion, or used for hub connectivity at the server. Cat. 11639 Active Noise Cancellation VGA PC Share Simultaneously Buddy Dealer Enquiries Welcome FreeFax 1 800 625 777 $599 Bar Code Slot Reader An alternative to magnetic card readers (no expensive card writer is required). Ideal for club membership cards etc. A bar code is affixed to the membership card & the card swiped through the reader. It is a keyboard wedge model & the decoder is built-in. Cat. 8562 Cat. 8563 Bar Code Slot Reader KB Wedge Bar Code Slot Reader Serial $459 $459 Converter SVGA to RGB Allows the use of an RGB monitor with either VGA or SVGA output. It is designed for high resolution graphics monitors & has H and PCMCIA BAR CODE WAND V synch signals added to the Turn your handheld PC into a powerful data collection terminal. Plug the card into your handheld PC (H/PC), Green video channel. RGB to SVGA converters are launch keyboard emulation software and you can use also available. SVGA to RGB Converter $189 the pen-like contact scanner wand to copy bar code Cat. 15063 Cat. 15064 RGB to SVGA Converter $194 data directly into any Windows CE program. Cat. 8672 PCMCIA Bar Code Wand $1015 E & OE All prices include sales tax Come and visit our online catalogue & shop at www.mgram.com.au Phone: (02) 4389 8444 $129 10Mbps Ethernet 5 Port Hub & LAN Card “Buddy”- Two Users - One PC Active Noise Cancelling Technology cancels background noise before it’s recorded. A must for Speech Recognition. In fact, most speech recognition software programs 4 Port USB Hub A self powered USB hub that has one up- bundle a passive noise cancellation stream port & four down-stream ports. microphone. Active is even more effective. It’s also It supports both full speed (12M bps) better for Internet Telephony & Interactive Gaming. and low speed (1.5M bps) devices & is Cat. 3377 Headset / Desktop - Ear & Mic ANC100 $72 compatible with the USB 1.0 Specification. It also supports Cat. 3379 Headset - Ear (Either) & Mic ANC500 $78 both self-powered & bus-powered modes. It has overcurrent Cat. 3380 Headset - Ear & Mic (Stereo) ANC550 $110 detection & power ready LEDs for each port. Cat. 3381 Headset - Ear & Mic (Disconnect) ANC600 $125 Cat. 2628 Cat. 3359 sales<at>mgram.com.au info<at>mgram.com.au Australia-Wide Express Courier (To 3kg) $10 We welcome Bankcard Mastercard VISA Amex Unit 1, 14 Bon Mace Close, Berkeley Vale NSW 2261 Vamtest Pty Ltd trading as MicroGram Computers ACN 003 062 100 MICROGRAM 0998 Fax: (02) 4389 8388 Web site: www.mgram.com.au FreeFax 1 800 625 777 SEPTEMBER 1998  3 COMPUTERS: Software problems & DOS games Troubleshooting Your PC; Pt.5 This month, we’ll take a break from hard­ware problems and cover some of the more common software problems. We’ll de­scribe the cures for these ailments and give you some tips on preventing problems from occurring in the first place. By BOB DYBALL Here are some really good ways to make your PC crash, or at the very least make it slow, unstable and more likely to lose the data you hadn’t quite got around to backing up yet: •  Let your children leave school or university homework diskettes in the floppy disc drive. This will make it easy for you to get a virus, particularly if you leave the boot order set to A:,C: in the CMOS setup. •  Always try to use the oldest utili4  Silicon Chip ties you can find and never ever look for patches or upgrades. •  Use old video or sound drivers, or even drivers intended for a different card (and then blame either Bill Gates or some other software company when your system doesn’t work properly). •  Buy yourself a $20 recycled DOS game and install the old DOS sound­ card, mouse and CD drivers while in Windows 95 (this is guaranteed to make Windows 95 run ever so slowly and make the game virtually unplay­able). •  Never defragment your hard disc drive. •  Never run Scandisk and always press Escape to quit Scandisk if it runs at boot-up (what’s life without some risks, eh?). •  Always have lots and lots of utilities running in the back­ground so that your system resources run low. •  Always press the Reset button to reboot (clicking Start, Shut­ d own, Restart or using Ctrl-Alt-Delete is for sissies). •  Always turn off your PC while Windows is still running (why waste time waiting to shutdown?). •  Run maximum disc compression, even if you only have a 486 or P-100 with 8Mb of RAM. •  Try to get by with as little RAM as possible and try to run Windows with Fig.1(a): the web is the place to go for the latest Windows drivers and www. winfiles.com is an excellent starting point. It also offers a host of useful tips bug fixes, utilities and how to articles, plus a wealth of other information. zero bytes free on the hard disc. OK, so that’s a list of exactly what not to do to your PC but its surprising how often problems occur because users do these very things. So seriously, what can you do to not make your PC crash? Well, you can start by not doing any of the things listed above. Instead, here are some preventative measures you can take: Preventing viruses I still find that many people are fearful about downloading files from bulletin boards or from the Internet when in reality, your PC is more likely to catch a virus because a diskette was left in the floppy drive. In my opinion, constantly running a background anti-virus program is usually an unnecessary waste of computer resourc­es. Instead, it’s much better to manually scan floppy discs and any new software or downloads. In addition, you should periodically check your whole system. In the prevention department, ensure that you set the “boot order” in CMOS to C:,A: rather than A:,C: – just in case you or someone else leaves a floppy disc in the A: drive. Even if the disc is not infected, it can still waste time while booting up. Upgrades, patches & FAQs Most programs will need a patch or upgrade at some time or another, sometimes to correct minor cosmetic problems and sometimes to correct more serious bugs that were not picked up during development. These upgrades (or patches) are usually “posted” on the software developer’s website or FTP server. If you are getting errors in a program, the first thing to do is to check out the FAQs (Frequently Asked Questions) for that program on the company’s website. Most of the bigger companies maintain a collection of FAQs and you will often find the answer to your problem here. In addition, you get 24-hour 7-day support off the net without having to make time-wasting (and sometimes expensive) calls. Sometimes, when support for older software has dried up, you may need to try using a “search engine”; eg, www.yahoo.com.au (see Fig.7) or www.anzwers.com.au, etc. Try searching for the word FAQ and the names of both the program and the Fig.1(b): Frank Condron’s World O’Windows is another excellent source of Windows drivers, with links to a comprehensive list of companies. This has to be one the best free sources of Windows information and updates on the web (www.conitech.com/ windows/). Fig.1(c): most hardware manufacturers post up-to-date drivers for their products directly on a web site. This Diamond Multimedia site lets you download the latest drivers for the company’s range of video cards and for other products in the company’s range. company. Often, fans of a particular game will maintain support websites with patch­es, tips and hints long after the company that developed the soft- ware has forgotten about it. Never underestimate the importance of using up-to-date drivers. All too often, a program won’t work simSEPTEMBER 1998  5 colours are set for the VGA display. Many programs require “High Colour” or 16-bit colour (65,536 colours) to work correctly and may not work properly with say 256 colours. Sometimes this will appear in an obvious way but that’s not always the case. For example, who would have expected that “Failed to create 3DRM device from clipper” really means click “Start, Settings, Control Panel, System, Performance, Graphics; decrease hardware acceleration to one notch back from full”; “change to 16-bit high color”; and “turn off 3D hardware acceler­ation in DirectX”! Fig.2: begin setting up your DOS games shortcut by clicking the Program tab in the MS-DOS Prompt Properties dialog box. Running older DOS software in Win95 or Win98 ply because an old video driver, sound driver or other driver is being used within Windows, while everything else works perfectly. You might even need to update Direct X for the latest Windows 95/98 games and this may, in turn, require updated video drivers to support all the new features. Although you can use the older 16-bit software and drivers with Windows 95 or Windows 98, it’s best not to as they will slow your system down dramatically. For this reason, it’s wise to use only 32-bit drivers and 32-bit software, if you have a choice. Sometimes the video mode you run a driver in is critical. I’ve lost count of how many people run into problems with Micro­ soft Encarta (and other programs) simply because too few Some companies specialise in “recycled” games, buying the rights a year or two after the program was first released, then redistributing the program for $20 or so. If you must run DOS games on a Win95 (or Win98) machine and the game won’t run within Windows itself (either in a DOS box or full-screen), then there are a few tricks you should know. First, a word of advice – don’t be provoked into setting up a “dual-boot” system until you have tried “DOS Single Mode” (or Single DOS Mode). A dual-boot system gives you the choice of booting to either old DOS or to Windows 95. This might seem simple enough and is occasionally necessary, but it does have its dangers. For example, it is quite possible to corrupt your file system, lose files or directories, and lose long file names – all because an older program doesn’t write correctly to the hard disc. Old Fig.3: clicking Advanced at Fig.2 brings up this dialog box. Select “MSDOS Mode” to bring up Fig.4. Fig.4: selecting “Specify a new MSDOS configuration” lets you edit the default configuration files. 6  Silicon Chip DOS doesn’t “know” how to write correctly to newer operating systems like Windows 95 or Windows 98 in all situa­tions, either. In some cases, older DOS programs can run under Windows 95 or Windows 98, though some settings need to be made to the prop­erties of the DOS “window” running the program. Let’s see how you go about this. Although many DOS games will run under Windows 95 or Wind­ows 98, some do not perform as well as they do under DOS (or they might not work at all). Normally, DOS will single-mindedly run just one program while Windows can multi-task; ie, it can run a number of programs, including more than one DOS application, at the same time. If you find your DOS program performs poorly or not at all, you don’t need to install DOS and try to set up a dual-boot system. Nor do you have to set up separate boot discs with all the necessary drivers to boot from your floppy drive. Instead, just follow the steps listed below and you will be able to run just about any old DOS program. Basically, what we are going to do is set up a desktop shortcut that exits from the GUI (graphical user interface) and reboots the machine into Single Mode MS-DOS. In addition, we are going to create special auto­ exec.bat and config.sys files for that shortcut, to enable your soundcard, CD-ROM and DOS games to work. Note, however, that these files are different from the autoexec.bat and config.sys files that are normally used when you boot your computer, so don’t try to edit these. Step 1: Try to identify the program’s memory requirements. A quick glance at the user manual, a readme file or the carton the program was packed in will tell you how much and what sort of RAM (EMS or XMS) is required. Step 2: copy the “MS-DOS Prompt” icon from the Start menu to the Windows 95/98 desktop. To do this, right click the “Start” but­ton, click “Open”, double click “Programs”, right click “MS-DOS Prompt” and click “Copy”. Now close the “Start Menu” window, right click a blank area on the desktop, and click “Paste”. Step 3: Right click this new icon and click “Properties”. Step 4: Click the tab at the top marked “Program” (Fig.2). Fig.5: click the Configuration button at Fig.4, then select all of the options shown here except “Direct Disk Access” (ie, leave this one unchecked). Click the OK button to return to the “Ad­vanced Program Settings” dialog box. Fig.6: this warning message appears each time you are about to go to DOS mode but can be disabled if you wish by deselecting “Warn before entering MS-DOS mode” at Fig.4. Step 5: You now have to change this shortcut so that it runs MS-Dos Single Mode. To do this, first click the “Advanced” Button to bring up the “Advanced Program Settings” dialog box (Fig.3). Step 6: select the “MS-DOS mode” checkbox (Fig.3), then select “Specify a new MS-DOS configuration” (Fig.4). Step 7: Click the “Configuration” button. A warning message will now appear. Click the “Yes” button. Step 8: In the “Select MS-DOS Configuration” dialog box (Fig.5) select all of the options except “Direct Disk Access” (ie,, leave this one uncheck­ ed). Click the OK button to return to the “Ad­ vanced Program Settings” dialog box. Step 9: Click the “OK” button to return to the “MS-DOS Prompt Properties” dialog box. Click the “OK” button here. Step 10: Copy the old MS-DOS files normally left on the Wind­ows95/98 CD-ROM to the \Windows\Command directory of your hard disc. Windows 95 users will find these files in the \OTHER\OLDMSDOS directory, while Windows 98 users will find them in the \TOOLS\OLDMSDOS directory. Step 11: Double-click the new icon you’ve just edited. You will see a warning message (Fig.6) telling you that you’re about to go to DOS mode. Note: if you prefer to disable this warning, remove the tick from the checkbox labelled “Warn before entering MS-DOS mode” in the “Advanced Program Settings” dialog box. Step 12: Click “Yes” and your system will now exit from the familiar Windows 95 interface and restart in “Single MS-DOS mode” (normally dropping you at the C:\WINDOWS prompt). Step 13: Once you are in DOS Single mode, install DOS drivers for your mouse, CD-ROM and soundcard. Quite often, install programs will add device driver entries to the top or bottom of config.sys and/or auto­ exec.bat. You may need to edit config. sys in order to place the line DOS=SINGLE back at the top. You may also have to edit your autoexec.bat file if the REM section, which is normally at the very end, has anything added after it by the driver installation program. Check your config.sys and autoexec.bat files after you install the DOS drivers and before you reboot. You can either use TYPE (to view the file) or EDIT (to view and/or edit the file), followed by the file name. A few rules The rules for DOS Single mode are: Rule 1: never move the line DOS=SINGLE from the top of config.sys (this line is added automatically during reboot but will not appear in the properties dialog box under Windows). Rule 2: never move the last few lines in autoexec.bat fol­lowing the REM statements (these are also added in by Windows during reboot). Rule 3: when installing DOS modem drivers in DOS single mode, be careful not to install Windows 3.x drivers as well (many driver install discs will do both). If you are running Windows 95 or Windows 98, you definitely don’t want old 16-bit drivers, if you have a choice. Rule 4: don’t install DOS drivers while in Windows 95 or Windows 98 GUI mode. Although this might allow you to boot back to DOS and run an old game, it will adversely affect performance when you are back at the graphical interface. Restarting the PC To restart or reboot your system but stay in DOS Single mode, simply press Ctrl-Alt-Del. Alternatively, to return to Wind­ows 95 (or Windows 98), type EXIT at the DOS prompt and press the “Enter” key. Once back in Windows you might like to rename the shortcut icon Fig.7: if support for older software has dried up, try using a search engine (such as www.yahoo.com.au or www.anzwers.com.au to find what you want. SEPTEMBER 1998  7 Fig.8: Typical Config.Sys File For Single Mode Dos DOS=SINGLE DOS=HIGH,UMB Device=C:\WINDOWS\Himem.Sys DEVICE=C:\WINDOWS\COMMAND\EMM386.EXE RAM 8192 FRAME=E000 FILES=30 BUFFERS=20 DEVICEHIGH=VIDE-CDD.SYS /d:mscd001 COUNTRY=061,,C:\WINDOWS\COMMAND\COUNTRY.SYS SHELL=C:\COMMAND.COM C:\ /e:384 /p Fig.9: Config.sys With No Expanded Memory DOS=SINGLE DOS=HIGH Device=C:\WINDOWS\Himem.Sys FILES=30 BUFFERS=20 DEVICE=VIDE-CDD.SYS /d:mscd001 COUNTRY=061,,C:\WINDOWS\COMMAND\COUNTRY.SYS SHELL=C:\COMMAND.COM C:\ /e:384 /p you’ve been working on (right click it, click “Rename” and enter the new name). You can also make a couple of copies which you can modify to suit other games. Three such shortcuts are all that’s normally required: one for games requiring EMS (extended memory), one for those requir­ing XMS (expanded memory), and one for games that run without EMM386.EXE (the expanded memory manager). Once you’ve renamed them accordingly, right click them in turn and edit their properties as required. I’d suggest a config.sys file similar to that shown in Fig.8 but please note that these are specific to my sound card, mouse and CD-ROM. Your config.sys file will differ somewhat, unless you have exactly the same hardware. The config.sys file shown in Fig.8 is from my machine when running DOS Single Mode. This particular one is for 8Mb of EMS RAM and can be used for games like the earlier Wing Commander series that required EMS RAM to run. The first line only appears in “DOS Single Mode” and, as stated above, is added by Windows during the reboot into DOS. Note: if you install new DOS software or drivers while in “DOS Single Mode”, be sure to check that this line stays at the top of 8  Silicon Chip config.sys, as mentioned before. Some install programs will simply tack new lines to the top of config.sys, which may confuse matters when it’s time to return to Windows. The fourth line is used to create 8Mb of EMS RAM (ideal for games that need EMS). The word AUTO could have been used in place of the 8192 and this will automatically allocate as much free EMS RAM as there is to spare from the pool of XMS RAM. Be careful here, as sometimes AUTO will not work with some games, while a fixed value will. Note that the FRAME statement might not work on all PCs but is useful to try, as it can give an extra chunk of UMB RAM in many cases. Having this extra UMB and using it will mean more conventional RAM is available to your games. The seventh line is my CD-ROM device driver for DOS. If you can’t find the driver disc for your CD-ROM, try looking on your Windows boot/ install disk. There will usually be a suitable DOS CD-ROM driver there as well. Adding DEVICEHIGH= rather than simply DEVICE= will save conventional RAM by loading the driver into a special area of RAM known as the Upper Memory Blocks, or UMB for short. This area, which is squeezed in between your VGA card’s BIOS ROM and the System/Boot BIOS ROM, can be used to save conventional RAM (often, there’s as much as 192Kb of extra space there). The parameters required for your CD-ROM drive may well vary, so check the manual or the driver disc for a “readme” file which describes the requirements. Often, the DOS install routine on the CD-ROM driver disc will set the correct parameters up for you, so you don’t have to enter them manually. Line 8 is an optional extra. It tells DOS Single Mode to display dates in the dd/mm/yy format, instead of in the default mm/dd/yy format which is for the US. The 061 refers to the country code and usually follows the ISD phone prefix. Line 9, another optional one, sets up the environment space. The figure after the /e: set the number of bytes. Too much and you waste conventional RAM, too little and you might find you haven’t enough room for “tricks” like SET PATH=%PATH% (as below). A different config.sys is required for games that don’t run with EMM386 loaded – see Fig.9. These programs include the origi­nal DOS versions of “Need for Speed” and the earlier EA Sports range such as “FIFA 96”. Note that you don’t get UMB RAM without EMM386.EXE which means that you need to change DOS= HIGH,UMB to read DOS=HIGH. Since this configuration limits how much conventional RAM there is, you might find you cannot add DOSKEY, SMARTDRV or some other driver that you might otherwise have included. Fig.10 shows a config.sys that’s best suited for games that don’t need EMS but need XMS and lots of conventional RAM. Exam­ples of programs like this include Duke Nukem 3D, DOOM 1, DOOM 2, and Rise of the Triad (Rott). Here the only thing of note that’s different from before is the addition of NOEMS instead of RAM 8192 in line 4. This will save some conventional RAM and of course leave all the free extended RAM as XMS for your programs. Configuring autoexec.bat Fig.11 shows a typical autoexec. bat, as seen from “DOS Single Mode”. In this file, the first line and the last seven lines (shown in bold type) are added by Windows during the reboot from GUI mode into DOS Single Mode. They will appear in DOS Single Mode but not in the properties dialog box under Windows. Again, as with config.sys, check the locations of these lines (using EDIT from the DOS prompt) before you return to Wind­ows GUI mode. As before, many games or device driver install pro­grams will simply add new lines to the top or bottom of your autoexec.bat and this can again create problems when you try to return to GUI mode. The lines in italics are ones I have added and need only be inserted once. The %path% trick is used to add some of your own subdi­rectories to the normal path statement. I keep most of my DOS utilities on a third hard disc in a \BIN directory. Placing my path before the other paths, referred to as %path%, means I can use a batch file or other editor with the name EDIT in preference to the one included in the \WINDOWS\ COM­MAND directory. The next two lines were inserted by the soundcard’s DOS install program. If you have a jumpered sound card, you might see only the BLASTER environment variable. Jumperless (soft­ware configured) or Plug ‘n Play (PnP) cards will need a utility such as DIAGNOSE to set the card to the desired IRQ, DMA channels and so on. If you don’t use a DOS PnP setup utility or some other configuration program, the sound card might initialise to a default setting which may not work. I have an internal modem on COM3 IRQ5 and so my sound card is set to IRQ10 (by using I10 in the SET BLASTER line). Normally, the card would go to IRQ5, which would conflict with the modem and possibly cause the PC to lock up. Mouse & CD-ROM drivers The next line sets up the DOS mouse driver. Sometimes if you have a mouse on COM2, or use a 2 or 3-button switchable mouse, you might need to add parameters to tell the mouse what to do. Usually, typing MOUSE /? Or MOUSE /help will bring up a list of options (assuming your mouse driver is mouse.com). Next, we load another driver for the CD-ROM drive. MSCDEX has a number of parameters, as follows: /L:x sets the drive letter to the x: drive; Fig.10: Config.Sys With XMS But No EMS DOS=SINGLE DOS=HIGH,UMB Device=C:\WINDOWS\Himem.Sys DEVICE=C:\WINDOWS\COMMAND\EMM386.EXE NOEMS FRAME=E000 FILES=30 BUFFERS=20 DEVICEHIGH=VIDE-CDD.SYS /d:mscd001 COUNTRY=061,,C:\WINDOWS\COMMAND\COUNTRY.SYS SHELL=C:\COMMAND.COM C:\ /e:384 /p Fig.11: Autoexec.bat For Single Mode DOS <at>ECHO OFF SET TMP=C:\WINDOWS\TEMP SET TEMP=C:\WINDOWS\TEMP SET PROMPT=$p$g SET winbootdir=C:\WINDOWS SET PATH=C:\WINDOWS;C:\WINDOWS\COMMAND set path=e:\bin;%path% SET BLASTER=A220 I10 D1 H5 P330 T6 C:\SB16\DIAGNOSE /S LH E:\BIN\MOUSE LH MSCDEX /d:mscd001 /l:g /m:20 /e LH SMARTDRV 8192 REM REM The following lines have been created by Windows. Do not modify them. REM C: CD C:\WINDOWS CALL C:\WINDOWS\COMMAND.COM C:\WINDOWS\WIN.COM /WX /M:n sets the number of buffers to n (generally, more is faster but it also uses more memory in the process); and /E tells MSCDEX to use expanded memory for its buffers instead of conventional memory. Many people simply leave the /E there and ignore the error message if there is no EMS, as MSCDEX uses conventional RAM if there is no EMS RAM anyway. Adding Smartdrive, a caching program, is optional. If you have spare XMS RAM, adding this will generally speed up hard disc access. And, provided its loaded after MSCDEX, Smartdrive will cache the access to the CD-ROM, speeding this up as well. Some programs, however, do not benefit from Smartdrive. In other cases the conventional or UMB RAM used by Smartdrive could even reduce the free memory to less than that required for the program to run. If you want to cache your hard disc but not your CD-ROM drive, place Smartdrive before the MSCDEX line. Rebooting into Win95 Usually, all you need to do is type EXIT and press Enter to return to the normal GUI mode in Windows. However, if you have forgotten to clean up your config.sys and autoexec.bat files as outlined above, you might get some quirky results. If you do strike problems, don’t panic and reach for the reset button. If you can’t Ctrl-Break, hit Ctrl-Alt-Del a couple of times to reboot, then hit shift-F5 when you see the “Starting Windows 95” message. This will bypass all the startup files and take you straight to the C: prompt. From there, you can then use EDIT to tidy up (or rename) your config.sys and auto­ exec.bat files before restarting SC the computer. SEPTEMBER 1998  9 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 EMC Explained Pt.2: The Question of Emissions In the first article in this series we talked about the various EMC standards which are applicable to electronic equipment and discussed the CE and C-tick symbols. In this article, we discuss emissions – all the signals which can be radiated by electronic equipment. By MARQUE CROZMAN Any electric or magnetic field with a frequency above 9kHz is classed as an electromagnetic emission if it is radiated by the equipment in which it was generated (50Hz mains harmonics or subharmonics are also classed as emissions). Many pieces of equipment are designed to produce emissions – radio transmitters, for example. Others are not supposed to, but do, such as the old hair dryer that causes lines across the TV. In some situations this can just be plain annoying, others are serious and yet others potentially life-threatening. There are countless examples but we’ll mention just a few. •  Certain office telephone systems near the ABC television station in Sydney rectify ABC audio into the handset when facing a particular direction - an unintentional form of music-on-hold. •  An instrument panel of a wellknown airliner carried the warning “Ignore all instruments while transmitting HF”. A police department in the USA complained that coin-operated electronic games were causing interference to their highway communications system. 14  Silicon Chip •  Most ordinary domestic telephones suffer from buzzing caused by light dimmers and most are also strongly affected if someone uses a digital mobile phone close by – the symptom is strong and rapid clicking. •  A particular make of car would stall Fig.1: schematic diagram of a 50Ω/50uH CISPR artificial mains network or LISN circuit. This is used to isolate the equipment under test from the mains supply. The impedance graph below shows that the circuit presents a flat 50Ω from about 300kHz up. on a section of freeway opposite a high power transmitter. The cars would have to be pushed or moved until far enough away to restart. Eventually the section of freeway had to be screened with wire mesh. •  Amateur radio repeater communications have been adversely affected on the 6-metre band by set top pay-TV decoders. Free-to-air TV reception is also affected by set-top units and can even be degraded by radiations from VCRs. •  Probably the most tragic example of an electromagnetic interference (EMI) disaster was the sinking of the HMS Sheffield in the Falklands war. The missile warning radar that could have detected the fatal incoming Exocet missile was turned off because it interfered with the ship’s satellite communications system. Electromagnetic interference events are unfortunately becoming common and now cause the banning of use of certain devices in sensitive areas such as hospitals, aircraft and other places where critical systems are in use. As semiconductor technology continues to shrink and the number of million transistors per device increases, power dissipation becomes a problem. As a result, supply voltages have dropped. Initially the common supply voltage for logic was 12V, then 5V and is now 3.3V. With this lowering of supply voltage and the families of logic commonly used today, immunity to noise is also decreasing, making equipment more susceptible to emissions from other devices. Also, the demands of the computing industry for more speed and grunt are causing logic to get faster and faster with switching speeds now equivalent to frequencies in the UHF region. This translates to a greater potential for emissions, if not corrected. Standards covering emissions When CE was put together, the greatest urgency was placed on generating generic and Information Technology Equipment (ITE) standards. ITE equipment commonly had microprocessors in it with clock frequencies in the MHz range - with the largest possibility of causing interference within the VHF and UHF radio bands. Therefore, this type of equipment was one of the first Fig.2: different kinds of interference produce widely differing responses from average, peak and quasi-peak detectors. to be tackled. One of first generic standards to emerge was EN50081 and this called up the product standards of EN550022, EN550011 and EN550014 (See inset box). These standards had significant consequences, since as well as being product standards, they set up limits and testing procedures that are now being applied in other standards - with wording such as “Limits and testing methods as per Class B EN550022”. In theory, the frequencies covered in the EMC Directive range from DC to daylight but in practice, what has Fully Accredited Testing for determined the frequency bands and methods for testing relates closely to the physics of the particular phenomena. Thinking back to basic radio theory, consider what is involved to effectively transmit a signal on frequency X. On the AM radio band (520kHz to 1630kHz), antennas are extremely large and require long lengths of wire for effective radiation of the signal. A quarter wavelength antenna suitable for the AM band is of the order of 62 metres. To transmit a signal in this band requires a source on that fre- Global Markets EMC Technologies' Internationally recognised Electromagnetic Compatibility (EMC) test facilities are fully accredited for emissions, immunity and safety standards. >> NATA endorsed reports for ALL electrical products covered by the and regulations >> Accredited Competent Body for TCF approval >> Anechoic chamber for accredited immunity testing. Field uniformity ensures that your products are not "over tested". DC – 1000MHz <at> 100-200V/m, 1-18GHz & >50-100V/m >> Open Area Test Site (OATS) available for hire for DIY testing >> Low ambient OATS in Melbourne, Sydney and Auckland (NZ) >> RF testing DC – 40GHz >> CE (Europe), FCC (USE), VCCI (Japan) EMC Technologies Melbourne T: +61 3 9335 3333 F: +61 3 9338 9260 E: melb<at>emctech.com.au Sydney T: +61 2 9899 4599 F: +61 2 9899 4019 E: syd<at>emctech.com.au Auckland T: +64 9 360 0862 F: +64 9 360 0861 E: auklab<at>emctech.com.au Visit our website: www.emctech.com.au SEPTEMBER 1998  15 EMC GENERIC & PRODUCT STANDARDS MOTOR-OPERATED AND ELECTRIC TOOLS EN50081 part 1:1992 Also known as AS/NZS 4251.1:1994 Generic emission standard, part 1: Residential, commercial and light industry environment Scope: All apparatus intended for use in residential, commercial and light industrial environments - both indoor and outdoor, for which no dedicated product or product-family emission standard exists. Equipment in this environment is considered to be directly connected to the public mains supply or to a dedicated DC source. For the purposes of testing, the equipment is considered to be operating normally, ie, fault conditions are not taken into account. TESTS Enclosure: * Radiated emissions 30MHz to 1000MHz as per EN55022 Class B (applicable only to apparatus containing processing devices operating above 9kHz). AC mains: * Mains harmonics up to 2kHz (applicable only to apparatus covered within the scope of EN60555-2 and EN60555-3) * Conducted emissions 150kHz to 30MHz as per EN55022 Class B * Discontinuous interference measured at spot frequencies as per EN55014 if relevant. An appendix outlines proposed additional tests on signal, control and DC power ports: conducted current 150kHz to 30MHz as per draft amendment to EN55022. EN50081 part 2:1993 Also known as AS/NZS 4251.2:1994 Generic emission standard, part 2: Industrial environment Scope: All apparatus intended for use in the industrial environment - both indoor and outdoor, for which no dedicated product or product-family emission standard exists. Equipment in this environment is not connected to the public mains network but is considered to be connected to an industrial power distribution network with a dedicated distribution transformer. For the purposes of testing, the equipment is considered to be operating normally, ie, fault conditions are not taken into account. TESTS Enclosure: * Radiated emissions 30MHz to 1000MHz as per EN55011. AC mains: * Conducted emissions 150kHz to 30MHz as per EN55011; impulse noise appearing more often than 5 times per minute is also covered. Applicable only for apparatus at less than 1000V RMS AC. An appendix outlines proposed additional tests on signal, control and DC power ports: conducted current 150kHz to 30MHz as per draft amendment to EN55022 plus limits on mains harmonic emissions EN55014: 1993 Also known as AS/NZS 1044:1995 AMDT1:1997 Limits and methods of measurement of radio disturbance characteristics of electrical motor-operated and thermal appliances for household and similar purposes, electric tools and electric apparatus. Scope: All appliances whose main functions are performed by motors and switching or regulating devices, unless the RF energy is intentionally generated or intended for illumination. Excluded are apparatus covered by other CISPR standards as well as regulating controls incorporating semiconductor devices with a rated input current of more than 25A per phase and stand-alone power supplies. For the purposes of testing, the equipment is considered to be operating normally; fault conditions are not taken into account. TESTS AC mains: * Conducted emissions from 148.5kHz to 30MHz measured on a test site using 50Ω/50µH CISPR artificial mains network. * Conducted emissions from 30MHz to 300MHz by means of the absorbing clamp; battery-operated appliances which cannot be mains connected, regulating controls incorporating semiconductor devices, rectifiers, battery chargers and converters excluded. * Discontinuous interference (clicks) measured on spot frequencies for appliances which generate such interference through switching operations. 16  Silicon Chip INFORMATION TECHNOLOGY EQUIPMENT EN55022: 1994 Also known as AS/NZS 3548:1995 now AMDT 2 Limits and methods of measurement of radio disturbance characteristics of information technology equipment. Scope: All appliances whose primary function is either (or a combination of) data entry, storage, display, retrieval, transmission, processing, switching or control and which may be equipped with one of more terminal ports for information transfer and with a rated supply voltage not exceeding 600V. Class A equipment is for use in other than class B environments; class B equipment is suitable for use in domestic establishments. For the purposes of testing, the equipment is considered to be operating normally; fault conditions are not taken into account. TESTS Enclosure: * Radiated emissions from 30MHz to 1000MHz measured at 10 metres on a test site. AC mains: * Conducted emissions from 150kHz to 30MHz measured on a test site using 50Ω/50µH CISPR artificial mains network. INDUSTRIAL, SCIENTIFIC AND MEDICAL (ISM) RF EQUIPMENT EN55011: 1991 Also known as AS/NZS 4251.1:1994 (AS/NZS2064.1997) Limits and methods of measurement of radio disturbance characteristics of industrial, scientific and medical (ISM) radio frequency equipment. Scope: Apparatus designed to generate and/or use locally radio frequency energy for industrial, scientific, medical, domestic or similar purposes, excluding telecommunications equipment, information technology and applications covered by other CISPR standards. ISM equipment is divided into classes: Class A equipment is for use in all establishments other than domestic. Class B equipment is suitable for use in domestic establishments. Group I equipment is that in which the RF energy generated is necessary for its internal functioning. Group 2 equipment is that in which RF energy is generated for material treatment and spark erosion. For the purposes of testing, the equipment is considered to be operating normally; fault conditions are not taken into account. TESTS Enclosure: * Radiated emissions 30MHz to 1000MHz measured on a test site (Class A or B) or in situ (Class A only). Group II Class A equipment to be measured from 150kHz to 1000MHz but with relaxed limits, below 30MHz measurement is performed with a loop antenna. AC mains: * Conducted emissions 150kHz to 30MHz measured on a test site using 50Ω/50µH CISPR artificial mains network. Group II Class A equipment subject to less stringent limits. IMPORTANT ITE STANDARDS Some of the first Information Technology Equipment (ITE) standards were those developed for equipment with the greatest possibility of causing interference on the VHF and UHF radio bands. The ITE standards above were significant in not only setting up the standards for the type of equipment itself but also set the testing procedures for later standards for other types of equipment. quency and a radiator – to get the signal to propagate into the atmosphere. In other words, the signal source has to be connected up to a long length of wire for propagation to take place. Moving up to the shortwave band, say at about 15MHz, requires a 5-metre cable to make a radiating quarter wavelength. For our piece of equipment to effectively radiate at these frequencies, we require these lengths of wire for it to propagate. Most pieces of equipment do not have cables this long, or do they? If the equipment is connected to the 240VAC 50Hz mains in some way, we find that we now have lengths of wiring that easily approach quarter wavelengths at these frequencies. Experience has shown that most interference in these bands has been due to emissions getting into the mains wiring and propagating in this way. Consequently, frequencies between 150kHz (some standards such as EN55015–lighting, test from 9kHz up) and 30MHz are measured by testing the RF voltage levels that are injected into the 240VAC 50Hz mains supply. These are known as “conducted emissions”. Above 30MHz, the lengths of wiring required to make an effective antenna become much shorter (2.5 metres or less). This comes within the realm of cables commonly found in or connected to electronic equipment. Testing is therefore carried out with the equipment’s signal and interconnecting cables attached. In the VHF bands and above, the lengths of cable required to provide an effective antenna come down to very short pieces of wire – equivalent to the tracks on PC boards. Measuring these kinds of emissions can be done with AT LAST EMC PRECOMPLIANCE FOR THE NON-EXPERT! PMM7000 Precompliance System The One Simple Low Cost Solution For All Your Emission Problems •    Very easy to use Windows Software included •    A High Quality and Performance EMI Receiver •    Internal 16 Amp LISN for Conducted Emission •    Antenna Included for Radiated Emissions •    Bandwidth from 150kHz - 1GHz •    Ideal for Product Development and Precompliance •    Average, Peak and Quasi-Peak Detectors •    In-built Pulse Limiter Protection CONSULTANT TECHNOLOGY AUSTRALIA PTY LIMITED Telephone (02) 9452 3831   Facsimilie (02) 9451 7421 adms-cta<at>zip.com.au SEPTEMBER 1998  17 Fig.3: the response of a quasipeak detector varies depending on the repetition rates of pulse interference. Thus, to make an accurate measurement using a quasipeak detector, the receiver must listen to the signal for a period longer than the timeconstants of the detector itself. dipole antennas but broadband antennas, typically bi-conicals and log-periodics, are more practical. Measurements of directly radiated signals extends from where the conducted emissions leave off at 30MHz and continues up to 1GHz. Above 1GHz, special techniques are required to generate and propagate signals. Experience has shown that without the use of these techniques, emissions in these bands are unlikely. Technically, there is no magical transition at 30MHz but measuring conducted emissions above this frequency leads to problems of cables resonating (at multiples of half wavelengths). On the other side, using antennas to measure signals below 30MHz (commonly with loop antennas) generally means that you are within the near-field of the source, which can lead to either false high or low readings. Sometimes these methods have to be used. For example, in places where very large pieces of equipment cannot be moved to a laboratory for testing, they are tested on-site instead. Testing emissions Measuring conducted emissions is done via an artificial mains network device known as a Line Impedance Stabilising Network (LISN) as shown in Fig.1. It provides well-defined impedance at RF across the measuring point, with a coupling point for a measuring device, and it isolates the “equipment under test” (EUT) from unwanted interference signals on the 50Hz mains supply. Typically, a high-pass filter with a cut-off frequency of 9kHz is also inserted in the line of the measuring device . This is to prevent the measuring device from being affected by high level harmonics from the mains itself. The circuit shown is for a single line only. Testing is carried out on all mains connections: Active and Neutral 18  Silicon Chip on single phase systems or otherwise on all three Actives and Neutral on 3-phase systems. Testing is carried out inside a screened room with adequate filtering on the 50Hz mains supply side of the LISN device. This is to ensure that the hash is at least 10dB below any signals like to be measured (-20dB is a better figure). Test receivers Conformance measurements are normally made using what is known as a test receiver. It is similar to a spectrum analyser, but has a distinct difference in that it has a tunable preselector. Spectrum analysers suffer from the problems of having a wideband front end. A wideband front end lets in all signals so that if there is a strong signal close to the one you are trying to measure, it may swamp the signal of interest. Test receivers, on the other hand, use a tracking filter that only lets through the frequency bandwidth you want to look at, thereby eliminating the problems found in normal spectrum analysers. Test receivers therefore can only look at a single frequency at a time. Most are now software-controlled; scanning bands of frequencies is done by automatically stopping the receiver momentarily at each frequency and recording the level, to build up the same type of display shown on a spectrum analyser. In fact, many test receivers are special digital spectrum analysers with a box sitting next to them holding a digitally controlled tracking filter. Signal detection Test receivers have three types of detection: peak, quasi-peak and average. The differences between the levels measured by these three detectors when responding to various types of emissions are shown in Fig.2. All detectors respond to the RMS value of the unmodulated RF voltage. Some test receivers also include various types of demodulators, so that ambient signals can be distinguished from equipment emissions. The peak detector follows the top of the envelope of the signal and measures the highest level present. EMC tests do not use the peak detector but it is good for quick measurements and gives an indication where possible problems may be, providing a "worst case" picture of emissions. The average detector will provide the same reading as the peak detector where a signal is continuous (ie, unmodulated) but otherwise the reading will be lower. The drawback of this kind of detector is that it is completely insensitive to pulsed interference. The standards allow for this and require that limit levels of 10dB to 13dB lower be used with average detection compared with the quasi-peak detection method. Quasi-peak detection has come into vogue with the advent of EMC testing. It is basically a peak detector with a weighted response, tailored to represent the subjective human response to pulse-type interference. Interference that is intermittent and occurs infrequently is far less annoying than that occurring frequently. Fig.3 shows the response of the quasi-peak detector to increasing repetition rates of constant amplitude pulse interference. Thus, to make an accurate measurement using a quasi-peak detector, the receiver must listen to the signal for a period longer than the time-constants of the detector itself. A peak detector would typically take less than 5 seconds to make a sweep of the conducted band from 150kHz to 30MHz, whereas doing the same sweep with a quasi-peak detector could take about 2-1/2 hours. A software-controlled test receiver will normally make an initial measurement using the peak detector and tag all frequencies where the peak measurement was less than 10dB below the limit line. The quasi-peak detector would then look at these tagged frequencies to gain a true reading of the level being emitted. This data would then be combined to form the total emissions graph for the equipment under test (EUT). Fig.4 shows the quasi-peak limit lines for EN55011 and EN55022 Class A and B equipment conducted emissions. Fig.5 shows the radiated emission limits for the same standards. Testing equipment for conducted emissions The equipment is set up inside the screened room either sitting on a non-conductive table or on the floor, depending on its size. 3-metre lengths of cable are then connected to any ports that have cables connected to them in its normal operation. For instance, a modem will have cables connected for connection to the phone line, RS232 lines and a power supply. These cables do not have to be connected to anything – with the stipulation that we need to operate the equipment in a manner that simulates normal operation. The cables are there so that if any port is leaking emissions, they will provide a path of propagation. Assuming the equipment is table-mounted, the cables are hung off the table and bundled up so that they do not come in contact with or near the floor. The device’s power connection is then hooked up to the LISN device and made to operate in its normal mode. Assuming also that the device just plugs into the wall, the test receiver then makes swept measurements of both the Active and Neutral lines using its peak detector. Any measurements then found to be less than 10dB from the limit line are then looked at again but this time using the quasi-peak detector. These results, together with the rest of the peak results, are combined to give the conducted emissions result. As long as the equipment does not exceed the limit line for the standard being tested, it has passed and it’s on to radiated emissions testing. Radiated emissions Radiated testing is generally carried out on an Open Area Test Site (OATS) that is low in ambient emissions. Such an installation is located at Mount Colo, north west of Sydney. An OATS consists of a meshed ground plane around the immediate area of testing. A mechanically operated turntable on which the EUT is placed sits at one end of the meshed area and a movable mechanically operated antenna sits at the other. It is normally situated 10 metres away from the EUT, although this is determined by the standard Fig.4: this shows the quasi-peak limit lines for EN55011 and EN55022 Class A and B equipment conducted emissions. Fig.5 the radiated emission limits for the same standards. being applied. Some standards require 3m or 30 metres. Tuned dipole antennas are more accurate but take a long time to perform tests. Broadband antennas are more convenient and allow faster testing, so they are what is normally used. Two kinds of broadband antenna are used, the bi-conical and the log-periodic. The bi-conical antenna is used for the band spanning 30MHz to 300MHz, while log-periodics continue from 300MHz to 1000MHz. Horn antennas are used above 1GHz. Again, the equipment is set up on a non-conducting table which is is mounted on the turntable, if it is deemed a table-mounted piece of equipment; otherwise, it sits directly on the turntable. 3-metre cables are connected to all the ports. An access point in the centre of the turntable provides power. Testing is carried out with antennas in both the horizontal and vertical axes. As with the conducted measurements, a pre-scan is initially carried out using the peak detector. Peaks less than 10dB below the limit line are then looked at more closely. This involves using the quasi-peak detector as previously used, but with a difference in that the maximum level of the peak is then determined. As the antennas are directional and the equipment may be emitting in a particular direction (which may be away from the antenna), both the EUT and the antenna are moved to look for the peak of the emission. This involves initially altering the height of the antenna while looking for a maximum and once found, the turntable is rotated until the absolute maximum is reached. This reading then becomes the emitted level that is used as the final measurement. This continues for each peak which less than 10dB below the limit. One can easily see how time-consuming this can be if the emissions from the device are close to the limit. This whole process is done in the horizontal axis and then repeated in the vertical axis. Many hours can be taken up just looking at peaks. On the other hand, if the designers have done the utmost to minimise emissions and all emissions are 10dB below the limit, the test can be carried out in less than an hour – allowing for set-up and antenna changing. SC SEPTEMBER 1998  19 SERVICEMAN'S LOG The old radio from the Cadillac Your serviceman is not a vintage radio buff. Even so, one can find oneself propelled into the vintage scene without looking for it. And if the customer wants a special job done and is happy to pay for it, who am I to quibble? I never cease to be surprised at the types of jobs service­men are asked to take on. I suppose because the larger, more impersonal businesses specialise more, there are gaps in the market for small operators to fill. As a result, some rather unusual jobs often wind up on my counter. Recently, three ancient AM car radios were brought in by a garage owner who specialises in modifying and restoring old 1950s Cadillacs – in particular, left to righthand drive conversions. The items in question were all dead and before anyone pooh-poohs a simple device such as an AM car radio, these were anything but (simple, that is). 20  Silicon Chip The first set belonged to a 1955 Cadillac Eldorado convert­ ible, one of 4500 sold worldwide for that year. This once top-of-the-line limousine had electric everything (almost), such as windows, seats, soft top and even a photocell to automatically dip the headlights for oncoming traffic. Ironically though, it didn’t have an electric-powered antenna. Instead, this was operated by a vacuum line from the inlet manifold but controlled by the radio. The radio was, sur­ prisingly, 12V negative chassis; this at a time when many Ameri­can vehicles still used a 6V battery (some with a positive chas­sis). The set was manufactured by Delco in Indiana, USA (model No. 7265845). In the car, the radio appears to be the same size as a modern unit, with the usual pushbuttons and rotary controls. However, the front facia is just the tip of the iceberg because once it’s out on the bench, the complete unit is actually quite large and heavy (see photo). The tuning uses an automatic self-seeking motorised search system which is really quite ingenious. A concealed front flap hides a number of red plastic markers and these move switch contacts that function as preset memory marker stops. When a switch closes, the tuning pointer stops. There is a large bar at the top. When this is pressed, the radio will stop at every station it can receive. One rotary The front facia of this old AM car radio (from a 1955 Cadillac Eldorado convert­ible) is just the tip if the iceberg, as the complete unit is really quite large and heavy. The defunct 3-pin vibrator is shown in front of the loudspeaker. control varies the sensitivity for town or country use. If you press one of the pushbuttons, the tuning will travel from left to right and back again until it stops at the corresponding marker for that pushbutton. The circuit for the set uses eight valves (some of them dual types) and one vibrator, plus assorted transformers, relays and vacuum switches. The incoming 12V rail is applied via the usual capacitor/inductor interference suppressor and power switch and is then fed to the vibrator power supply. With power applied, the lamps and filaments all glowed but the 12V could be measured only up to the vibrator (a 3-pin Delco 507; part no. 1220155). Vibrator power supplies Many of our readers will be too young to be familiar with vibrator power supplies but most old hands will remember them. They appeared a few years before the war and lasted until the solid state era took over. They became the heart of most mobile radio equipment. The basic requirement was to take DC from the vehicle bat­tery and transform it to an HT rail voltage, typically 250V. And, since DC cannot be transformed directly, the battery voltage had to be first converted to AC, applied to a suitable step-up trans­former, and the stepped-up AC then converted back to DC. It was a rather clumsy, roundabout process but it was the best that was available at the time. Converting the 12V DC to AC was the fundamental requirement and this was the function of the vibrator. In its simplest form, it consisted of a vibrating reed which was driven at about 100Hz by a coil with its own set of interrupter contacts. The reed itself was fitted with two contacts (one on each side) and these alternately mated with two fixed contacts (this was called a non-synchronous type). The vibrator output is fed to the primary winding of the step-up transformer, which is centre-tapped. The centre-tap is connected to the negative rail, while the reed is connected to the +12V rail. Each side of the primary is connected to one of the fixed contacts and so +12V is applied alternately to each half of the primary winding. The overall effect is to apply a 100Hz square wave to the primary. And the end result is a high voltage 100Hz square wave across the transformer secondary. From here on, there are several options: (1) the AC may be rectified by a bridge rectifier; (2) the secondary may be centre-tapped and rectified by a second set of contacts on the reed (a synchronous vibrator); or (3) the AC may be rectified by a conventional rectifier valve or, as in this case, by a cold cathode gas-filled OZ4 rectifier valve (the OZ4 is an unusual approach in this country). The vibrator was an expendable device. The contacts eventu­ally eroded to the point where they no longer functioned effectively and the unit had to be discarded. Because of this, it was fitted with a valve type base – typically 4-pin or 6-pin – and mounted in a conventional valve socket. So much for basic background. The vibrator in this set was fairly conventional but was fitted with a 3-pin base. More impor­tantly, it wasn’t functioning, probably because its contacts had eroded. It was vibrating in the physical sense but was not gener­ating any worthwhile voltage. So where to from here? The chance of finding a replacement vibrator, particularly a “foreign” one, was virtually nil. The best one could hope for would be to find a local one in an old set that was gathering dust in somebody’s shed. However, this would involve rewiring the set to suit and, in any case, I didn’t yet know whether the rest of the set was functional. To test this, I removed the vibrator and connected 12V AC (from a spare mains transformer) across half the primary of the vibrator transformer. And I was rewarded with signs of life. The OZ4 was glowing a magenta colour (which is not unusual in a gas-filled device) and there was a HT voltage of about 150V. This was too low and it was varying but at least it was a start. SEPTEMBER 1998  21 They sure don’t make ’em like this any more. The ancient AM radio came from this 1955 Cadillac Eldorado convertible which, at the time, was undergoing restoration and conversion from lefthand to righthand drive. Despite its size, there’s plenty of room behind the dashboard for the old radio. Removal of the dashboard was necessary so that it could be restored and to improve access to the floorpan so that a new hole could be cut on the righthand side for the steering column. There was a 15kΩ resistor and a 0.007µF 1.6kV capacitor across the secondary winding. The wax had melted off the paper capacitor and the resistor was discoloured. Both measured within 20% of their rated values but I replaced them anyway. I also replaced a 0.47µF 100V paper capacitor across the primary of the vibrator transformer but it was all to no avail. By now, it looked as though the OZ4 rectifier was also faulty. I removed it 22  Silicon Chip and fitted two 1N4007 diodes in its place and suddenly we were in business. The EHT shot up to nearly 300V at switch-on and then, as the valves began drawing current, dropped to a respectable 240V. Furthermore, sound was now emerg­ ing from the loudspeaker and the radio was working! Replacement vibrator Having established that this 43-year old radio still worked, there remained the problem of finding a suitable replace­ment vibrator. But even if one was found it would almost certain­ly be secondhand. Could I justify using it? What if it failed in a few months? Could a solid state multivibrator circuit be sub­stituted? Perhaps – but this would amount to a major design exercise and would be prohibitively expensive. It looked as if this was the end of this historic radio when I happened to mention the problem to Phil Watson, an edito­ rial contributor to SILICON CHIP. He promptly informed me that he had already written an article nearly 25 years ago for another magazine on how to make a solid-state “vibrator” circuit. When we finally unearthed the actual article, I discovered that it had all the information that was necessary. All I would have to do was build the circuit and make a few modifications to suit. I went back to the garage proprietor and told him to advise his client that I believed the radio could be repaired but that it would be fairly costly because of the modifications involved. He telephoned back the next day and said to go ahead. The original magazine article described a plug-in replace­ ment unit. Unfortunately, I didn’t have room inside the radio to mount this so I decided to build it using discrete components mounted directly on the chassis. Instead of using 2N3055 transis­tors with TO-3 cases, I used MJE3055s with TO-220 cases instead. These were screwed to the main chassis with insulating washers and bushes. The other components were simply wired in point-to-point fashion, in a similar manner to the other parts in the set (see photo). This was made easier by the fact that modern electrolytic capacitors are now one third the size of their counterparts from 1975. By playing around with the series resistors and capacitors in the base circuits of the transistors, I was able to adjust the unit to oscillate comfortably at 100Hz and deliver 260V. The completed multivibrator circuit drew 2A at 13.6V and the radio now worked perfectly. And with the metal screen refitted over the vibrator circuitry, it was hard to guess that any modifications had been made – except that there was no mechanical vibrator or rectifier valve fitted. I called around a month later to see the radio installed in the car, which tell you about them in next month’s column. The Masuda TV set Fig.1: this solid state multivibrator circuit was used to replace the defunct mechanical vibrator in the old Delco car radio. The various components for the solid state multivibrator were wired into the old radio in point-to-point fashion, to match the style of the other parts. was now perfectly converted to right­ hand drive (in fact, you would never guess that the steering wheel had once been on the left). The radio was working in-situ and it sounded very good indeed. However, there was still a minor problem. Because of the larger current drain (6A), the battery now has a tougher job. If its voltage drops, the reduced valve gain due to lowered filament voltages causes the radio’s self-seeking tuning system to become erratic. It may be necessary to have the car’s electrical system modified to cope but that’s up to the mechanics. The other sets The other two Delco radios were slightly later models (7272505) with five valves and one transistor. I haven’t tackled these yet but hope to solve all the problems in these two sets in the next week or so. All going well, I’ll The next customer’s problem involved a Masuda TV set with one of the most puzzling series of faults I have encountered for a long time. Mr Cleary’s set was a late-model S21TXS Chinese-built 51cm Multi System Stereo set with Teletext. His main com­plaint was that he couldn’t tune the set because it kept drift­ing. However, he did list five other faults: (1) no colour, even when the set was correctly tuned; (2) no Teletext; (3) no stereo; (4) no remote control; and (5) the set would cut off after a few minutes. I tackled problem 4 first and on disassembling the remote control, found it to be full of some unspecified liquid. The only thing for it was a complete wash and clean in sugar soap. Fortu­nately, the liquid had not been there long enough to corrode the PC board tracks and after drying it thoroughly and applying a little CRC 2-26, it worked perfectly. But I despaired over the five remaining faults, although I suspected that there was a common denominator – if only I could find it. The thought of fixing five separate faults, all diffi­cult, did not bear contemplating. The first thing was to check the main voltage rails. I was lucky enough to have a circuit diagram and even though this didn’t give voltages, I could guess at what they should be. The main HT rail was 105V and there was also a secondary rail of 14V, the latter feeding a subsidiary 5V rail. I also established that there were 18V and 12V rails de­rived from the secondary of the horizontal output transformer (T302). There was no significant ripple on these rails when checked with the CRO and I concluded that they were correct and that the other rails also looked reasonable. When the set was switched on, it initially gave a very good monochrome picture on all channels, which gradually slipped off tune. What’s more, the self-seeking tuning system never stopped on the stations and couldn’t be persuaded to lock in. I checked the 33V tuning voltage source which supplies the tuning voltage (VT) via IC004 and transistor Q001 (2SC1815Y), the latter con­trolled by pin 1 of the microprocessor (IC001). SEPTEMBER 1998  23 Serviceman’s Log – continued which seemed OK. However, when I removed the coil from within the ferrite pot, there was a tiny green spot of corrosion on the winding itself. After an hour of microsurgery, I managed to connect another fine wire to the break and reassemble the coil. To my delight, reinstalling the coil fixed all the problems at once – even the Teletext now worked. The circuit has pin 17 marked as “Demo” or presumably demodulator but I suspect that this is in fact the AFC coil. Subsequently, I found that Canberra TV in Melbourne has all the spare parts for the Masuda and I ordered a new (secondhand) coil from them. The customer is nearly as happy as I am. The Philips VCR The whole chain was spot on and was rock steady. Despite heating and freezing the entire set and bashing the daylights out of it, I found there no were no dry joints and the fault was not influenced by temperature. This was getting to be too difficult. Why not concentrate on one of the easier faults? I thought of having a go at fixing the no colour but before that, I would isolate the Teletext functions by unplugging the sub-modu­le. This uncovered a whole new can of worms when I discovered that the Teletext circuit did not really match the set I was working on. The Teletext module has four plugs into the main motherboard but only three were shown on the circuit: CN701, CN703 and CN704 (CN702 was not shown). And CN703 was incorrectly drawn. Eventually, I worked out that CN702 was connected to an unmarked S201 connector (which went to the AV sockets) and to pins 53, 51, 50, 49 and 47 of IC201, which is a TA8659AN 64-pin jungle IC. Unplugging the Teletext module killed the vertical and horizontal sync and I worked out that the video went through CN704 and into pin 27 of IC701 on the Teletext module. From there it came out on pin 1 of IC701 and back through CN704 to pin 33 of IC201. I installed a temporary fix 24  Silicon Chip by shorting the two pins of CN704 to restore the sync. All the faults were still there. Next, I connected the colour bar generator to the AV sock­et. The set gave perfect colour bars and the picture was steady for well over an hour. This told me that most of the colour decoder circuitry was working and confirmed the power rails must be OK as well. This meant that the fault had to be either in the IF modu­le, the tuner or the microprocessor-controlled tuning circuit. Because this set boasted a video output socket, I connected this to a monitor. The picture on the monitor was still drifting off tune and there was no colour, so the colour decoder and jungle circuits had to be OK. The fact that there was no colour or sometimes only a flash of colour on one side indicated that a tuned circuit or IF amplifier was faulty. As I had a TDA2459 IF amplifier IC in stock, I decided to replace it. But first I checked the surrounding coils with an ohmmeter, and – surprise, surprise – when I measured L107 (213908) it was open circuit. Well, I was happy at finding this but, at the same time, I worried about where I was going to get another one. The coil was encased in a ferrite pot and fitted with an adjustable slug. I pulled it out and examined the leads, My last story for this month involves a Philips VR3442/75 video recorder, which uses a JVC mid-drive “mecha” deck. It be­longed to Mr Arnott who complained that the picture and sound were slow and that there were noise bars. The problem had ini­ tially been intermittent but had now become permanent, much to the customer’s frustration. After he had gone, I plugged it in and put in an SP (stan­dard play) pre-recorded tape and it worked perfectly. I made a recording and played it back too, and was beginning to think he had done something silly. I left it on soak test with an E240 tape in it and went on with other work, checking it every so often in passing. About two hours later, I finally saw the problem and it was exactly as had been described. And the reason was obvious – the display showed it was now in LP (long play) mode and not in standard play as I had left it. I put it back on the workbench, removed the covers, lifted the motherboard and examined the tape alignment. Usually if a machine switches itself from SP to LP it is due to a problem with the ACE (Audio, Control, Erase) head and the fault is accompanied by no real-time clock display, However, in this case, the clock was still working and the tape alignment was correct. It is not normally possible to measure the control pulse output from the head as it is so low and tends to be noisy but there was no signal at TP401, the official test point after the amplifiers inside IC401. I spent some time testing and checking all the circuits around IC401 but to no avail. The problem was intermittent but getting more and more permanent with time. Heating, freezing and vibrating it made no difference. Another symptom was that it played fast in the LP mode. I decided to mull it over with some of my colleagues in the trade. One mentioned that quite often the ACE head may be worn and still give enough output to operate the real-time clock. However, the output may be insufficient for it to decide which speed it was on. Fired with fresh confidence, I delved inside the video’s entrails and examined the ACE head under a strong light. Eureka! – it was indeed pitted and worn. I ordered a replacement and fitted it a few days later. My joy was immediately crushed – it had made no difference at all. Fortunately, one of my mates had recently scrapped the very same model because the deck was beyond economic repair. He had robbed it for parts but I was welcome to the carcass for test purposes. I immediately seized the offer because I felt that I should be able to get to the bottom of this – especially as I also had a copy of the service manu- al. My first course was to swap over IC401, BU2827AS, the servo control IC, which had just about all the circuits pertaining to the missing control pulses but it still made no difference. I also fruitlessly replaced C421, C420, C418 and then tried measuring the voltages on all the pins but they were all pretty close. However, when I checked the nominal 5V rail at test point TP903, I found that it measured 5.6V despite being marked on the circuit as 5.3V. Initially, I didn’t think that this was all that signifi­cant, until I found a reference in the manual indicating that it should be 5V exactly. And as I was becoming more and more desper­ate, I grasped at the straw and set preset pot R805 to exactly 5.00V, at test point TP903. Although I was making only a 0.6V adjustment, the pot’s wiper had to be moved nearly 45°. But suddenly the speed switched back to SP mode and the picture and sound were perfect. I altered the position of pot R805 several times to confirm this and then examined the circuit, expecting some component to have failed that required this change in the preset. However, even swapping the transistors with those from the other chassis made no difference – although I did notice that there was an extra driver transistor (Q804) on my chassis, which wasn’t fitted on the scrapped chassis. To cut a long story short, I couldn’t fault the power supply and can only assume that the pot had been set carelessly during manufacture at one extreme of the operating voltage range. Subsequently, this preset voltage changed slightly due to compon­ent aging and this was enough to upset the apple cart. I now appreciate the service manual statement that “if the working voltage becomes higher or lower the VCR will malfunction”. But I really can’t see why they didn’t fit a 3-pin IC regulator such as an LM7805 instead. Anyway, I soak tested the video for a further week before allowing it to go home and thanked all my colleagues for their help, although I did get a few “I knew that” comments when quizzed as to what fixed the problem. But then, there is always some smart Alec who knows the answer SC afterwards. SEPTEMBER 1998  25 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. 0V output for adjustable 3-terminal regulators Three-terminal adjustable regulators are widely used but they have one major shortcoming. This is the inability to adjust right down to 0V, due to the 1.25V reference voltage between the “adj” and “out” pins. This circuit overcomes the problem by applying -1.25V to the “adj” pin, allowing the output to stabilise at 0V. In effect, the 0V line is raised by the voltage drops across diodes D1-D3 and then a regulated negative supply is provided by diodes D4 & D5. The zero adjustment is then provided by trimpot VR1. VR2 then adjusts the output voltage in the normal way. S. Carroll, Timmsvale, NSW. ($25) Simple relay voltage booster Have you ever needed to power a 12V relay from 6V or 9V? If so, this simple circuit might be what you need. A typical relay needs close to its full rated supply voltage at the moment of power-up to ensure that the contacts pull in reliably but then only about half of that voltage is necessary to hold them in. This circuit takes advantage of that fact by initially providing double the supply voltage to the relay, allowing reliable operation of 12V relays from a 6V or 9V supply, or 24V relays from a 12V supply. 26  Silicon Chip When power is first applied, C1 is charged rapidly to +6V while the relay is not energised. A positive voltage greater than about 3V applied to the control input switches on Q1, which also turns on Q2. Q2 connects one side of the relay’s coil to the +6V rail while Q1 effectively shorts the positive terminal of C1 to 0V. The negative terminal of C1 is now at a potential of -6V, which is applied to the other side of the relay, raising the potential across the relay to 12V and energising it. The relay voltage then fairly rapidly falls back to the supply voltage, the period being determined by the RC time constant of the relay coil resistance and the value of C1. S. Carroll, Timmsvale, NSW. ($25) Automatic reversing for model trains Many enthusiasts do not have room for a large model railway layout but they do have space for a long shelf layout with perhaps a single or a pair of tracks. The trains must then be reversed each time they come to the end of the track. This circuit accomplishes that automatically. In operation, the train travels along the length of track, slows and then stops. It then sets off smoothly in the other direction, where the process is repeated. The delay at each end is adjustable from a few seconds to over a minute. It is designed to operate in conjunction with a speed controller incorporating inertia and braking. This prototype circuit was used with the speed controller which appeared in the February 1993 issue of SILICON CHIP. The circuit uses three relays, one with its contacts in parallel with the speed controller’s brake switch, one to provide forward/reverse track switching and the third to switch between a pair of reed switches. The train has a small magnet fixed underneath and when it comes to the end of the track it passes over reed switch 1 (RS1). This causes C2 to be discharged via diode D2 and RS1. This pulls pin 3 of IC1 low which causes pin 2 of IC1 to also go low and rapidly discharge C3 via diode D3. This causes pin 12 to go high, turning on Q1 and relay RLA which then operates the brake on the speed controller. This causes the train to slow and stop. C3 recharges slowly until Q1 turns off, releasing the brake and also feeding a positive pulse to the clock input of JK flipflop IC2a which then changes state. This causes Q2 to turn on (or off), reversing the train which now starts in the opposite direction. Relay RLC also selects reed switch RS2 so that when the train arrives at the other end of the track, RS2 will operate to discharge C2 and so the cycle repeats. Adjusting trimpot VR1 or changing the capacitance of C3 can vary the stop time at the end of each trip. Reed switches were used instead of phototransistors so that this automatic reversing facility would only be triggered by a loco fitted with a magnet underneath. Steve Opperman, Mowbray, Tas. ($45) DVM adaptor for high frequency AC Most inexpensive DVMs will not accurately measure AC vol­tages above the audio range. This circuit doesn’t have the low frequency accuracy of the precision rectifiers inside most DVMs but it is not limited by the op amp. Instead, diodes D1 & D2 establish the upper frequency limit, allowing meaningful peak-to-peak RF voltage measure-ments to be made to around 100MHz. Maximum input voltage with a 12V supply is 10V peak-to-peak. Diodes D3 & D4 establish a DC bias voltage for the non-inverting input of the op amp and this is matched, at the invert­ing input, by diodes D1 & D2. Signals rectified by D1 & D2 are filtered by the 0.1µF capacitor associated with D1 and then IC1 amplifies the voltage difference at its inputs and is set for a gain of -1. Because the input diodes are forward-biased, the circuit responds to very small signals instead of being limited to the diode forward conduction voltage. G. LaRooy, Christchurch, NZ. ($35) SEPTEMBER 1998  27 Time-alignment te of loudspeakers While there are a whole host of factors to be considered in the design of a loudspeaker system, such as drivers, enclo­sure, crossover network and so on, one factor which is often neglected is time-alignment. This article demonstrates how criti­cal time alignment can be. By TERRY PAGET* Australian Audio Consultants has recently commissioned new testing equipment designed to test a pair of loudspeakers, such as tweeter and woofer, for accurate time alignment. Time align­ ment ensures that when the same signal is fed to a tweeter and woofer, the acoustic wavefronts combine for the most linear frequency response. We believe that accurate time alignment is critical for loudspeaker development. A widely held belief is that time align­ment is only necessary for 1st order (6dB/octave) crossover networks and that it is unnecessary for 2nd order or steeper crossover slopes. While this may hold true for the crossover’s effect on frequency response, it does not take into account time alignment’s effect on clarity. If a complex music signal from two different drivers arrives at your ears with a slight time dif­ference, the resultant signal will be degraded and not as clean as it should be. This is often referred to as “timesmear” in some industry circles. Now a 1st order crossover network centred at, say 3kHz, may combine the outputs from woofer and tweeter over the range 1kHz to 10kHz. A time alignment error would have an effect over this very wide frequency band. With a second order crossover network, the frequency overlap would be restricted to 2kHz to 6kHz. Thus, the “time smear” effect would be less noticeable but would still be important since the 2kHz to 6kHz frequency band is most important for music reproduction. Some pundits hold that a driver’s acoustic centre is in line with the voice coil for both woofers and tweeters. Others hold that it is in line with the voice coil for woofers and that it is just in front of the dome for tweeters. The truth is that a driver’s acoustic centre varies with frequency and with driver mechanical design. Equipment is available to test individual drivers to deter­mine their acoustical centres but that information is not what a loudspeaker designer really needs. What is needed is the rela­tionship between the acoustical centres of the drivers being considered in a design. Test method Fig.1: the top two traces here show the on-axis response of two identical Morel MW-144 142mm bass-mid drivers. The bottom trace is the zero offset position (where the drivers are in perfect time alignment), while the middle two traces are for the ±5mm offset positions. 28  Silicon Chip Our new test method measures the summed output of two driv­ers, both in-phase and out-of-phase. A single microphone is used to record the results and the high frequency driver is physically moved away from or towards the low frequency driver. Gated sinewaves provide the measurement signals and are used to remove boundary reflections that would otherwise make the results unus­able. In the first example of Fig.1, two identical Morel MW-144 142mm bass-mid drivers are used. The top * Terry Paget is the principal of Australian Audio Consultants. sting two traces are the on-axis response of the two drivers. As you can see they are nearly identical. The bottom trace is the zero offset position, where the drivers are in perfect time alignment. You can see that cancellation causes an almost identical trace some 20dB down in amplitude, which is what is expected to happen. The middle two traces are for the ±5mm offset positions. Cancellation is not perfect and the -5mm position does not follow the original driver response curve. Remember that these offset errors are a mere 5mm! With these drivers placed on a flat baffle with an ordinary dome tweeter, the typical offset error would be 20mm or so. Fig.2 shows the zero offset position with the traces for 10mm and 20mm added. As you can see, cancellation does not take place evenly and in fact some reinforcement occurs as frequency increases. Real world example While the above graphs prove the system’s capabilities, they do not show a real world example, so let’s Fig.2: this graph shows the zero offset position with the traces for 10mm and 20mm added. As you can see, cancellation does not take place evenly and in fact some reinforcement occurs as frequency increases. Fig.3: the responses of the woofer and tweeter between 1kHz and 10kHz. These limits are sufficient to show all likely frequencies that will overlap when these two drivers are used in a speaker system. look at one. For this example, the drivers under test are the Morel MW 168 160mm woofer and the DMS 37 soft-dome horn-loaded tweeter. Fig.3 shows the response of the woofer and tweeter between 1kHz and 10kHz. These limits are sufficient to show all likely frequencies that will overlap This is the Morel MW-144 142mm bass-mid driver, as used in the first test. Figs.1 & 2 show its on-axis response for different time alignments. SEPTEMBER 1998  29 Fig.4: the woofer and tweeter responses, with their outputs summed for tweeter offsets of 0mm, 5mm, 10mm, 15mm and 20mm. The Morel DMS 37 soft dome tweeter. Fig.5: the combined response with one driver driven out of phase. The results are now dramatically dif­ferent, compared to Fig.4. Fig.6: this was the optimum response found by trial and error for the tweeter and woofer pair. when these two drivers are used in a speaker system. Fig.4 shows both woofer and tweeter responses, with their outputs summed for tweeter offsets of 0mm, 30  Silicon Chip 5mm, 10mm, 15mm and 20mm. There do not seem to be any major differences in the graphs. Now let’s look at the combined response with one driver driven out The MW-168 160mm mid-bass driver features very high peak power handling. of phase. The results in Fig.5 are dramatically dif­ferent. The offsets are for 0mm, 5mm and 15mm and none of these are what we would expect for a correct level of cancellation with these drivers. These graphs require a considerable interpretation but consider the quite dramatic differences in the traces for differences as small as 5mm. Further testing provided the best tweeter offset for this pair of drivers and this is shown in Fig.6. The two drivers were placed on a baffle, properly time aligned and a crossover de­ signed. The resulting frequency response is depicted in Fig.7. The two lines are for the normal response with 552 data points and with 1/3rd octave smoothing of the response. The 1/3rd octave smoothed response has been shifted down 5dB for clarity. The response is better than 2.0dB for the normal response and better than 1.5dB for the smoothed response. Fig.8 shows the impedance curve for the system shown in Fig.6. The crossover network used only six components. Fig.7: the frequency response for the system depicted in Fig.6. The two lines are for the normal response with 552 data points and with 1/3rd octave smoothing of the response. The 1/3rd octave smoothed response has been shifted down 5dB for clarity. Conclusion In conclusion, the single most critical area of loudspeaker development is driver selection. Get this correct and all your efforts can be directed into being creative and designing a great loudspeaker. Get driver selection wrong and most of the develop­ment time goes into fixing problems. We believe that accurate time alignment data is a critical parameter for driver Fig.8 shows the impedance curve for the system shown in Fig.6. selection and thus loudspeaker development. For further information on this service, contact Australian Audio Consultants, PO Box 11, Stockport, SA 5410. Phone/fax (08) 8528 2201. SC Australian Audio Consultants - Sole Australian Distributors P.O. Box 11, Stockport S.A. 5410 Phone or fax 08 85 282 201 CLIO Test System Professional Electrical and Acoustical testing • Dual Channel, Measures Phase • Sinewave testing, Gating • MLS Analysis • FFT Analysis • Digital Signal Generator • Dual Channel Audio Oscilloscope • 1/3 Octave Analysis • Reverb & Decay • Measures THD, 2nd &3rd HD, IM dist. • Provides Waterfall plots, ETC curves, Polar Plots etc. • Measures T&S parameters, Capacitors & Inductors Fully featured professional system System including Microphone Only $1551.00 tax ex Automated Quality Control system also available Morel Loudspeaker Drivers Highest Quality Loudspeaker Drivers • Hexatech Voice coils for prodigious power handling • 118mm (4.5” ) bass drivers 150Watts • Drivers shielded for A/V use. • Transient power to 1 kW • Morel use Neodymium and double or triple ferrite magnets • Available in matched pairs • Miniature tweeters available • MW 168 162mm bass driver 150W 88dB $159.00 • DMS 37 horn loaded Tweeter 200W 93dB $111.00 • MDM 55 Dome Midrange 200W 90.5 dB $129.00 • MW 265 222mm Bass Driver 150W 90dB $172.00 Call or write for full specifications - Wholesale enquiries welcome SEPTEMBER 1998  31 Save dollars and time with this easy-to-build indicator that tells you when you need to change your car’s airfilter element. Modern EFI cars house the airfilter inside an airbox (above). But what is the condition of the filter inside? This Blocked Filter Alarm will tell you when a filter change is needed. Blocked Filter Alarm Modern cars with electronic fuel injection use a flat panel airfilter contained within an airbox. The filter catches dust, rocks, birds and small children, preventing these potentially damaging entities from entering the engine. Over a period of time the filter gradually gets blocked as the holes in the “sieve” get filled. This restricts the air flow entering the engine which adversely affects power and economy. As a result regular changing of the air filter is required. The owner’s manual will generally state a time period or a distance travelled between filter changes. But is your car’s filter being changed when it actually needs to be changed? If you live in a dusty area, the filter may need replacing well before 32  Silicon Chip the manufacturer’s specified time or distance requirements are exceeded. In fact, most owners’ manuals state something along the lines of “Filters will need to be changed more frequently if the vehicle is operated in dusty areas for extended periods”. That means that your vehicle may be By ADRIAN CUESTA suffering in performance and economy, even if you (or your car service company) are strictly following the nominated service intervals. Conversely, if you drive only on sealed roads, the filter may be being changed when it’s unnecessary. And some air filters are not cheap – you can pay up to $80 for a filter element for some imported cars! So what do you do? We have the answer – build this Blocked Filter Alarm and change the filter only when it’s necessary to do so! How it works The Blocked Filter Alarm uses a pressure switch to detect when there is a lower pressure on the downstream side of the element than on the upstream. When the switch closes, a piezo buzzer inside the cabin sounds, indicating the filter is restricting airflow. But how does it work? Any restriction of the intake to the engine will cause the pressure to drop to below atmospheric. In fact, the throttle butterfly can be regarded This VT Commodore filter is so dirty that the alarm sounded whenever full throttle was applied over 3000 rpm. as a huge restriction when it is in any position other than fully open, explaining why there is normally a partial vacuum present in the inlet manifold. If the air filter is flowing freely, there will be very little pressure drop across it. As the filter becomes more and more blocked, the pressure drop will increase. If a pressure switch of the right sensitivity is fitted, it will close when the filter blockage becomes excessive. Two different switches There are two different pressure switches that can be used. Both are available from RS Components (stores in each Australian capital city) and both are compact and light. Which one you decide to use will depend on how sensitive you want the alarm to be. The first goes by the official name of Cat No 317-948. It costs about $18 and is designed to close when it is subjected to a differential pressure of 0.9 psi (6.2kPa). Now that pressure might not mean much to you – is a 0.9 psi pressure drop across a filter high or low? Pressure drops across air filters are usually measured in inches of water and 0.9 psi represents about 25 inches of water – a heck of a lot! This means that Switch #1 is only suitable for vehicles for which you are prepared to tolerate a high amount of filter blockage. An earthmoving machine or stationary engine working well below its rated output could use this switch to trigger the alarm. However, in your family car, a pressure drop of this magnitude would be excessive – unless you are a real skinflint when it comes to changing air filters! The second switch has the Cat No 317-443. It is a much more sensitive switch and is also much more expensive - about $67. This switch closes when the pressure differential reaches 0.072 psi (0.5kPa) – about 2 inches of water. During the development of this project, we experimented with a Holden VT Commodore V6 with a heavily soiled filter. Switch #1 would not trigger, however Switch #2 sounded the alarm whenever full throttle and more than 3000 rpm was used. Changing to a clean filter silenced the alarm. Installation Installing the alarm shouldn’t take you longer than an hour or so. Step number one is to examine the airbox closely. Take particular note of where the induction tube leaves the airbox and heads to the airflow meter or directly to the engine. The box half that contains this exit tube is the one on which you need to install the switch. The next step is the same whichever switch you chose to use. Drill a small hole through the plastic of the box to allow the installation of the pressure sensing port. Before drilling the hole, look inside the box to make sure that there is room for the port to extend a few millimetres into the box. Also consider where the switch will be when the box is re-installed – you don’t want the switch body fouling anything. Switch #1 can be mounted directly Switch #1 (left) costs about $18 and operates at a pressure differential of 25 inches of water. This makes it suitable for use where a high degree of filter restriction is acceptable. Switch #2 (right) is very sensitive, operating at two inches of water. At $67 it is also much more expensive than Switch #1. SEPTEMBER 1998  33 The piezo buzzer is mounted within the cabin. We used a pulsing Matsushita buzzer but any low current buzzer can be used. on the airbox. The switch has two ports; you need to use the one that is sticking out of the side of the switch, rather than the one surrounded by the threaded collar. If you drill a hole of the correct diameter, you will be able to push-fit the projecting switch tube through the hole, causing the switch to be a snug fit up against the airbox wall. Some silicone rubber sealant will hold the switch in place, or alternatively you can make a small bracket and screw it to the airbox. If you do this, use self If you decide to use Switch #2 you will need to buy a few miniature plastic irrigation fittings (bottom). These are available from hardware stores at a cost of about 10 cents each, and are used to plumb the switch to the airbox. The PVC hose is supplied with the switch. 34  Silicon Chip tapping screws inserted from the outside of the box - you don’t want nuts inside the box that could fall off... Switch #2 is more easily mounted adjacent to the airbox – on the inner guard, for example. The switch is supplied with a length of PVC tube which is easily connected to the airbox. A miniature plastic irrigation “connector” fitting (available for about 10 cents from hardware stores) can be screwed into the drilled hole and the connecting tube pushed over the top. There is no need to use clamps to hold the hose on but make sure that you connect the hose to the pressure port on the switch that is closest to the two spade terminals. If the vehicle is being used in very harsh conditions, it would be wise to house the switch in a small box. This prevents any chance of the switch being adversely affected by heat or dust. Note that both switches are rated for a maximum temperature of 50°C. Wiring As the above circuit shows, the wiring is very simple – just make sure that you get the polarity of the buzzer correct. We used a pulsing Matsushita piezo buzzer but any other low current 12V buzzer is fine. Mount the buzzer within the cabin and power the circuit from an ignition-switched fused supply. The power supply to the radio is often easy to access, as is the cigarette lighter circuit. If using the cigarette lighter as the power source, fit a low current fuse to the buzzer circuit – the cigarette lighter probably uses a 20A fuse! Testing With the ignition switched on, test that the buzzer sounds when you apply suction to the pressure switch port. The easiest way to do this is to suck on the port (or on a new tube going to the port!). Switch #1 requires a good suck while Switch #2 triggers very easily indeed. Once you have ascertained that the buzzer sounds when tested in this way go for a drive. The buzzer should remain quiet – unless the filter is very dirty, of course! Remove the filter element from the box and block off a good portion with a piece of cardboard. Hold this Drill a single small hole in the airbox to provide a pressure tapping point for the switch. On this VT Commodore airbox the air temperature sensor is adjacent. Switch #1 in place. The pressure sensing nipple pushes through the drilled hole, bringing a flat on the switch body snugly up against the side of the airbox. The switch can be glued into place or a small bracket made to hold it. temporarily in place with some electrical tape, and place the cardboard on the side of the filter which faces the atmosphere (ie, not the engine side!). When you drive the car hard in this form the alarm should sound, indicating that the filter is posing a restriction. NORBITON SYSTEMS NS_PC101 card for XT/AT/PCs allows access to 48 I/O lines. There are 5 groups (0 to 4) available on a de-facto industrial standard 50-way ribbon cable used in STEbus and VMEbus 19" rack mount control systems. The board uses 2 x 8255 ICs. Multiple boards can be used if more I/O lines are required. NS_LED PCB gives visual access to five groups (0 to 4) of the NS_PC1OX. There is a total of 40 status LEDs. The board offers a 25-way “D” type female socket. The lines are driven by 74244 ICs & configured as a parallel printer port. This socket gives access to printer port kits, eg, stepper motors, LCDs, direct digital synthesis. NS_16_8 PCB is a system conditioning card with 16 optically isolated inputs set-up for either 12V or 24V operation. The board provides 8 single pole, double throw relays with 10 Amp contact rating. The second type of switch can be mounted on the inner guard or strut tower and connected to the airbox by the provided PVC hose. In very harsh conditions mount the switch in a small box. With system installed as described, the switch detects the total pressure drop of the filter, the filter box and the inlet duct to the box. We have taken this approach because any pressure drop (wherever it occurs) will have a negative impact on engine performance. KITS & CARDS NS_DC_DC is a step down converter with an input range 11 to 35V DC and an output of 5 volts DC at 5 Amps, with an output ripple of approx 150mV. There is an IN/OUT 50-way connector isolating the 5V and 12V+ &12V- rails of the PC power supply. This segregates PC’s power when working on prototypes. NSDC_DC1 module used with NS_DC_DC & NSDC_DC4 converters is a 5V to 12V(+/-) step- up converter. The board utilises 743 switch mode IC with 2 x 12V regulators, with output ripple of approx 200mV. NS_UTIL1 prototyping board has 1580 bread board holes access to any 3 groups (0 to 4) on the 50-way cable pinout. Power is available from the 50-way cable format 5 volts at 2 Amps & 12V+ 12V- at 1 Amp. There is provision for array resistors with either a ground or positive common connection. For brochure write to: Reply Paid 68, NORBITON SYSTEMS, PO Box 687, Rockingham WA 6968 http://www.users.bigpond.com/norbiton However, if your alarm is over-sensitive because the intake in front of the airbox is too restrictive, you may need to plumb the switch so that its second port is connected to the other side of the filter. That way, just the pressure drop of the filter element is SC being monitored. Protect Your Valuable Issues Silicon Chip Binders REAL VALUE AT ★  Heavy board covers with 2-tone green vinyl covering $12.95 PLUS P & P ★  Each binder holds up to 14 issues ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A12.95 plus $A5 p&p each (Aust. only). Just fill in & mail the handy order form in this issue; or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. SEPTEMBER 1998  35 A WAA-WAA PEDAL One of the most popular sound effects with guitarists is waa-waa. There are two components to waa-waa – the electronics which shape the guitar’s output waveform and the foot pedal which the guitarist uses to control the amount of waa-waa introduced. This project not only gives you the electronics but the all-important construction details for the waa-waa pedal too! by JOHN CLARKE What is waa-waa? It’s one of the classic guitar sounds, still very popular today even though it’s been around since the late 1950s. The name is very close to the sound – instead of the pure guitar note, it goes waa-waa. How does waa-waa work? The sound of the guitar is altered by passing it through a narrow tunable bandpass filter and the tuning is done by varying the position of the foot pedal. Well, what does that mean? Say we had a narrow filter centred on 2kHz. The sound of the guitar would be quite 36  Silicon Chip shrill and quite different to the sound that would be obtained if the filter was centred on say 500Hz or 1kHz. If you have a graphic equaliser, you can get the same effect by just pushing the slider for 1kHz all the way up and all the others, all the way down; then trying do the same thing with other bands. If we now vary that tunable filter by moving the foot pedal up and down we can change the guitar sound at will. We can make it go “Wee waa waa we ooo ..” Well, hopefully you now get the general idea. There are a couple of other subtle changes to the tone. One is in fact that at centre frequency a purer tone is produced because the bandpass filter attenuates the harmonics produced by the guitar strings. Another is that the harmonics are even more pronounced as the bandpass filter centre frequency is adjusted away from the fundamental. One big advantage the SILICON CHIP circuit has over many commercial waa-waa units is that its sharpness of response (or “Q”) is fairly constant over its range. This contrasts with FOR YOUR GUITAR many units where the sharpness falls away at higher notes, resulting in a much inferior sound. Another advantage: because the pedal adjusts a DC level, there won’t be the hum often experienced with many waa-waa units. And finally, the SILICON CHIP waa-waa unit has excellent linearity over its range, making it not only easier to control but also producing a better sound. The Design The SILICON CHIP Waa-Waa Effects Unit is described in two parts – the electronics and a separate foot pedal which controls the amount of “waa”. With the obvious exception of the foot-pedal control potentiometer, all the waa-waa effects unit electronics  Performance Bandpass frequency :............................................. 50Hz to 2.8kHz Bandpass Q: ......................................................... 4.35 to 4.76 from 100Hz to 2kHz Bandpass adjustment with VC................................ 16% Bandpass frequency linearity with control pot ....... <5% Maximum input signal ........................................... 220mV rms Frequency response .............................................. -3dB <at>47Hz and 2.8kHz Signal to Noise Ratio ............................................. 78dB with 20Hz to 20kHz filter                     (with respect to 220mV input) Total Harmonic Distortion ...................................... 0.3% <at> 1kHz and 200mV input mount on a small PC board. This can be housed inside the guitar itself or in a small plastic case. Connection is simple: a pair of 6.35mm jack sockets mounted on the PC board accept standard phono plugs – one for input from the guitar and the other the output to the amplifier. Also on the PC board is a small slider switch which selects effects “in” or “out” – effectively an on/off switch for the waa-waa unit. Power for the The complete waa-waa setup: the electronics housed on a small PC board, along with the matching foot pedal which controls the level. SEPTEMBER 1998  37 Fig.1: in conjunction with the text below the block diagram details the operation of the waa-waa unit. unit is taken from a 12V DC plugpack. Block diagram The waa-waa unit connects between the guitar and the amplifier. To understand the operation of the waa-waa unit, refer to the block diagram (Fig. 1). The nominal 50mV output from the guitar is increased to a little over 500mV by amplifier IC1a (gain of 11). Maximum input before clipping is 220mV so there is plenty of headroom – 12dB in fact. This amplified signal is then fed into the “heart” of the circuit, the adjustable bandpass filter (IC2), whose centre frequency is controlled by the voltage controlled oscillator, IC3, in turn adjusted by the foot controller VR1. What happens is this: as the foot pedal potentiometer is varied from minimum to maximum resistance, the output of IC3 varies from 5kHz up to 280kHz. IC2, a National Semiconductor MF5CN, first divides this by 100, giving a bandpass centre frequency range of 50Hz to 2.8kHz. But the MF5CN does very much more than that. While it is called an adjustable bandpass filter, it can be considered as a number of cascaded filters in which the capacitors are varied by switching them rapidly in and out of circuit. This has the effect of varying the amount of capacitance in each of the filter stages and thereby causes the filter’s cutoff frequency to track the clock frequency – just as we want. There is a negative, though: this rapid switching generates a fair amount of hash on the signal. So the signal then passes through a low pass analog filter (also part of IC2) which reduces these switching artefacts to a minimum. Fig.2, the oscilloscope waveforms, shows the difference between the unfiltered and filtered signals. The processed signal is then adjusted in level by preset pot VR2. The purpose of this is to give the same level whether the waa-waa unit is switched in or out of circuit. This switching is accomplished by S1. The circuit While the circuit achieves a great deal, the SILICON CHIP Waa-Waa Unit is remarkably simple and easy to build. It comprises just three low cost ICs and a few other components. Signal at the guitar input jack is AC-coupled to the non-inverting input of op amp IC1a via a 0.22µF capacitor. Fig.2: the top trace shows the switched output from the bandpass filter; the lower trace after smoothing by the 2.8kHz pass filter. 38  Silicon Chip A 10Ω resistor and 10pF capacitor at this input prevents any radio frequency pickup which could easily be brought in from the guitar leads. The op amp is biased via the 22kΩ resistor tied to the 5V rail. The gain of IC1a is set by the 220kΩ and 22kΩ feedback Parts List - Waa Waa Unit Electronics 1   PC board ,code 01307981, 105 x 60mm 1   miniature DPDT slider switch (S1) 2   PC board mounting 6.35mm mono jack sockets 11 PC stakes 1   slider pot (10kΩ to 50kΩ) (VR1) 1   10kΩ horizontal trimpot (VR2) Semiconductors 1 TL072 dual op amp (IC1) 1 MF5CN switched capacitor filter (IC2) 1 4046 phase lock loop (IC3) 1 1N4004 1A 400V diode (D1) 1 10V 1W zener diode (ZD1) 1 5mm red LED (LED1) Capacitors 1 470µF 25VW PC electrolytic 1 100µF 16VW PC electrolytic 1 1µF 16VW PC electrolytic 1 0.22µF MKT polyester 4 0.1µF MKT polyester 1 .039µF MKT polyester 1 .0047µF MKT polyester 1 470pF MKT polyester or polystyrene 1 47pF ceramic 1 10pF ceramic 1 1.8-22pF trimmer (VC1) Resistors (0.25W 1%) 1 1.5MΩ 2 7.5kΩ 1 100Ω 1 220kΩ 1 3.6kΩ 1 33Ω 2 22kΩ 2 2.2kΩ 1 10Ω 6 10kΩ 1 220Ω resistors at the pin 2 inverting input. High frequency rolloff is about 15kHz and is set by the 47pF capacitor across the 220kΩ resistor. The low frequency rolloff is 7Hz, as set by the 1µF capacitor connecting the 22kΩ resistor to ground. This rolloff is also augmented with the 0.22µF coupling capacitor and 22kΩ resistor combination at the guitar input which causes rolloff below about 33Hz. As already mentioned, IC2 is the MF5CN, a universal monolithic switched capacitor filter. It comprises a general purpose active filter block and an op amp all in the one package. The Q and gain of the filter is set by the resistors at pin 3. We selected a Q of about 4.5 as set by the ratio of the 10kΩ resistor at pin 1 and 2.2kΩ resistor at pin 2. Gain is set at -1 by the 10kΩ resistance at pin 1 and 10kΩ input resistor to pin 3. The bandpass output is at pin 1 and this signal is filtered with a 2-pole low pass active filter comprising the 7.5kΩ resistors, 3.6kΩ resistor, the .039µF capacitor and the .0047µFcapacitor connecting to pins 12 and 13 of IC2. These pins are the inverting input and output of the op amp which is internal to IC2. The filter rolls off at 2.8kHz to suppress the switching noise from the pin 1 output. This filter is a Chebychev type which rolls off at a steeper rate beyond the -3dB point than the standard Butterworth filter. Since the minimum switching frequency is 5kHz when the bandpass filter is centred on 50Hz, the filtering will provide a significant attenuation of the resulting 5kHz noise. At higher bandpass frequencies, the attenuation will be greater. Output from the filter is AC-coupled via a 1µF capacitor to the VR2 attenuator and thence to the effects in/out switch, S1. The out position of S1 effectively bypasses the whole waa-waa circuit. The 100Ω resistor in the output prevents oscillation of the op amp in IC2 when connected to a capacitive load such as a screened cable. The 10kΩ resistor to ground provides a charging path for any coupling capacitor con- Fig. 3: The circuit diagram reveals that most of the hard work is done by IC2 and IC3. All components fit onto a small PC board which could be mounted inside the guitar if you wish. SEPTEMBER 1998  39 nected to the output. The voltage controlled oscillator comprises just the oscillator portion of a 4046 phase-locked-loop, IC3. Minimum oscillator frequency is set by the 1.5MΩ resistor at pin 12 and the 470pF capacitor between pins 6 and 7. Maximum frequency is set by the 10kΩ resistor at pin 11 and the 470pF capacitor. Trimmer capacitor VC1 provides a small amount of frequency adjustment. Oscillator range can be varied between these two extremes by adjusting the voltage at pin 9. When VR1 takes pin 9 to the +10V supply, the oscillator produces its maximum frequency. Conversely, the lowest oscillator frequency is produced when VR1's wiper is at ground. Fig.4: use the component overlay in conjunction with the PC board photograph below and the PC board pattern (facing page) when placing components and you shouldn't go wrong. Just remember to take care with polarised components. Supply Two supply rails are required, 10V and 5V. The regulated 10V rail is obtained in the conventional way but the way the 5V rail is obtained is a little unusual. Power for the circuit is from a 12V DC source such as a plugpack. Diode D1 prevents damage to the circuit if the power supply is connected backto-front while the supply is filtered with a 470µF capacitor. Zener diode ZD1 and the series 33Ω resistor regulate the supply to 10V. A regulated CAPACITOR CODES     Value     IEC Code EIA Code   ❑  0.22µF   220n  224   ❑  0.1µF   100n  104   ❑ 470pF   470p  471   ❑ 47pF   47p  47   ❑ 10pF   10p  10 RESISTOR COLOUR CODES            ❑       ❑        ❑       ❑        ❑       ❑       ❑    ❑        ❑       ❑    ❑    No. 1 1 2 6 2 1 2 1 1 1 1 40  Silicon Chip    Value       4-Band Code (1%) 1.5MΩ brown green green brown 220kΩ red red yellow brown 22kΩ red red orange brown 10kΩ brown black orange brown 7.5kΩ violet green red brown 3.6kΩ orange blue red brown 2.2kΩ red red red brown 220Ω red red brown brown 100Ω brown black brown brown 33Ω orange orange black brown 1Ω brown black gold brown 5-Band Code (1%) brown green black yellow brown red red black orange brown red red black red brown brown black black red brown violet green black brown brown orange blue black brown brown red red black brown brown red red black black brown brown black black black brown orange orange black gold brown brown black black gold brown ELECTRONIC COMPONENTS & ACCESSORIES •  LARGE RANGE OF ICs, RESISTORS, CAPACITORS & OTHER COMPONENTS •  MAIL ORDERS WELCOME! CROYDON STORE ONLY ELECTRONIC DISPOSALS CLEARANCE! •  OPEN FRAME 240V INDUCTION MOTORS 600 WATT AND 900 WATT. Construction All components for the waa-waa effects unit mount onto a PC board coded 01307981 and measuring 105 x 60mm. It can be fitted into a plastic utility box measuring 130 x 68 x 43mm or, as previously mentioned, mounted inside the guitar if space permits. The foot pedal can be made up from some Medium Density Fibreboard (MDF) and a slider pot – see details overleaf – or a commercial unit can be used. Begin construction by checking the PC board for shorts between tracks or open circuits. Follow the overlay diagram of Fig. 4 and start by soldering in the two links and all the resistors, using the accompanying colour code table as an aid in checking the values. Next insert and solder the 11 PC stakes – note that 6 are located in the S1 position. When inserting the ICs, make sure they are oriented with pin 1 in the position shown. Similarly, diode D1 and the zener diode ZD1 mount with their stripes towards the edge of the board. Ensure that all polarised capacitors are correctly inserted. S1 is installed by soldering the switch pins on top of the PC stakes. If you elect to mount S1 off the board (for example, on the guitar itself), these PC stakes can be used to connect flying leads. LED1 mounts on the PC board or it too can be externally mounted – just make sure you keep the orientation the same. The last components to install and solder are the trimpot (VR2) and the two 6.35mm phono sockets. If building the waa-waa unit from a kit, you should be supplied with PC board mounting sockets. •  LARGE VARIETY OF DISPOSALS TRANSFORMERS AT GIVEAWAY PRICES! Croydon Ph (03) 9723 3860 Fax (03) 9725 9443 MilduraPh (03) 5023 8138 Fax (03) 5023 8511 M W OR A EL D IL C ER O M E supply is necessary to ensure that the VCO operates over the same frequency range regardless of variations in the input supply. The 5V rail is derived from the 10V rail using a 10kΩ resistive divider and a 100µF capacitor. While this gives 5V, it is at too high an impedance to be usable. The Op amp IC1b (actually a “spare” op amp in IC1) converts this to a low impedance source. The 0.1µF capacitor decouples the output, while the 220Ω resistor in IC1b’s output prevents oscillation due to the capacitive loading. 600 WATT - $15 EACH OR 10 FOR $100 900 WATT - $18 EACH OR 10 FOR $120 Truscott’s ELECTRONIC WORLD Pty Ltd ACN 069 935 397 30 Lacey St Croydon Vic 3136 24 Langtree Ave Mildura Vic 3500 Testing Connect a 12V source to the appropriate PC stakes and check that the LED is lit. If not, you probably have the supply wrongly connected. If the LED is lit, check that there is about 10V between pin 4 and pin 8 of IC1 and 5V between pin 10 of IC2 and pins 4, 7, 9 and 11. There should also be 10V between pin 10 of IC2 and pins 5 and 6 and between pins 8 and 16 of IC3. Temporarily connect a linear poten-tiometer (any value from 10kΩ to 50kΩ will do) to the VR1 PC stakes. You are now ready to test the waa-waa unit with your guitar. Plug in and switch on power and with S1 set for “in” play a few notes. Adjust VR1 to get the waa-waa effect. You may need to adjust VC1 for best frequency range coverage. VR2 is adjusted to give the same volume is between effects in and out. Overleaf: How to construct a foot pedal SEPTEMBER 1998  41 How to construct a foot pedal Here's how we built our foot pedal using MDF, aluminium pieces and a slider pot. Because the slider pot is horizontally mounted the overall height of the foot pedal is kept low compared to a vertically mounted pot. This increases player comfort. Build the foot pedal as shown with 12mm MDF and 12mm square timber – a softwood such as pine is ideal. The lid is fitted with a standard cupboard door hinge secured with countersunk wood screws. We painted the foot pedal black inside and out. The top of the pedal, both hinged and fixed sections, were covered in speaker carpet. The slider pot actuator is made up using 12mm x 3mm 42  Silicon Chip The choice is yours: you can buy a commercial pedal suitable for a waa-waa or a swell unit, or build your own. Here's how we built a robust foot pedal using MDF, scrap timber and aluminium pieces and a slider pot. Parts List - Foot pedal 1 300 x 300mm piece of 12mm MDF 1 1m length of 12 x 12mm timber (pine is ideal) 1 160mm length of 12 x 3mm aluminium 1 20mm length of 12 x 12mm aluminium angle 1 6.35mm stereo jack socket 1 cupboard door hinge (50 to 60mm long) 1 slider pot with 45mm travel 10kΩ to 50kΩ 1 tension spring 22mm when closed 1 10mm OD rubber grommet 1 cable tie 1 rubber foot for lid stopper 4 rubber feet for underside of pedal These photographs of various internal views of the pedal, in conjunction with the dimensioned drawings at left, should enable even a novice constructor to build a robust, reliable foot pedal for the waa-waa unit. Miscellaneous Wood screws, 3mm screws, PVA glue, speaker carpet. aluminium, 110mm long. It is bent in a vyce to curve around a 9mm mandrel (eg, a drill) as shown. The other end is bent at about 45 degrees and a 4mm spigot formed on the end using a file. This spigot is designed to insert into a 5mm hole in the actuator pivot plate (also made from aluminium) which mounts on the foot pedal lid. A tension spring is secured to the slider pot actuator as shown with a cable tie. The other end is screwed to the spring tie point on the base of the foot pedal. The slider pot is secured to the base of the foot pedal with 12 x 12mm angle brackets 10mm long. M3 screws secure the pot to the angle bracket while the bracket is secured to the foot pedal with countersunk wood screws. The 6.35mm jack socket mounts on the side of the foot pedal and part of the wooden side will need to be recessed with a chisel so that the threaded portion can protrude and be secured with its nut. The actuator pivot plate is attached to the underside of the foot pedal lid with short wood screws. The slider pot actuator is attached to the slider pot by inserting the small rubber grommet into the 9mm bend and then placing this over the slider pot actuator. The slider pot is wired as shown, with the wiper going to the tip connection on the socket. The earth end of the socket connects to the earth end of the slider pot. The pot should be wired to the waa-waa unit so that the bandpass filter operates on higher frequencies as the pedal is depressed. When the slider actuator is attached into the pivot plate the pot should slide back and forth as the pedal is pressed. A small amount of grease or graphite will lubricate the slider pot actuator where it contacts the base of the foot pedal. Transporting the foot pedal is as simple as lifting the lid slightly and disconnecting the actuator from the pivot plate. The lid can then SC be closed onto the stop. SEPTEMBER 1998  43 ORDER FORM BACK ISSUES MONTH YEAR MONTH YEAR PR ICE EACH (includes p&p) 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. TOTAL $A B INDERS Pl ease send me _______ SILICON CHIP bi nder(s) at $A12.95 + $5.00 p&p each (Australi a only). N ot avail abl e elsewhere. Buy five and get them postage free. cial See Spe – er Subs Off Page 88 $A SUBSCRIPTIONS  New subscription – month to start­­____________________________  Renewal – Sub. No.________________    Gift subscription  GIFT SUBSCRIPTION DETAILS RATES (please tick one) 2 years (24 issues) 1 year (12 issues) Australia (incl. GST)  $A135  $A69.50 Australia with binder(s) (incl. 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Please have your credit card details ready 44  Silicon Chip 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 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au PRODUCT SHOWCASE Tektronix recalls LCD scopes Tektronix has announced that it is voluntarily recalling its TDS210 and TDS220 oscilloscopes after determining that certain incorrect uses of the product could cause the ground connection to fail. Although Tektronix has received reports of situations in which the ground lead on the oscilloscope has opened when the products were incorrectly used, the company is not aware of any injuries to users. However, a failure of the ground connection does have the potential of exposing the user to the risk of serious personal injury or death. If a user incorrectly connects a probe ground lead to a voltage source or incorrectly touches the ground ring near the probe tip to a voltage source, a circuit board track in the oscilloscope’s electrical ground path may open. Once this occurs, the product may appear to function normally; however, the unit is no longer properly grounded. Subsequent use of the product could then result in a serious electrical shock to the user. Tektronix is conducting the voluntary recall to prevent this possibility of injury to its customers and is part of the company’s overall commitment to providing reliable, safe and high-quality products. This recall applies to approximately 60,000 TDS210 and TDS220 units, as follows: TDS210 - serial numbers below            BO49400 or CO10880 TDS220 - serial numbers below       BO41060 or CO11175 Customers should stop using the recalled oscilloscopes immediately and contact Tektronix to receive instructions on how to return the product for modification. Customers should not assume the product is properly grounded even if it appears to be functioning properly. Customers can receive instructions for returning the product by contacting Tektronix Australia at 1800 023 342 ext. 193, or by visiting the com-pany’s web site at www.tek.com/ measurement. NiCd & NiMH fast charger uses microcontrollers This super fast charger employs a microcontroller and uses the patented Reflex charging method. This avoids the well-known memory effect in NiCd cells and completely does away with the need to discharge a battery before re-charging. Charging times are very short and can be as little 3 minutes, ranging up to one hour, depending on the depth of discharge and the cell capacity, which can range from 110mAh to 7Ah. The charger also handles the new “fast-charge” NiCd batteries, ranging from 1.4A.h to 10.9A.h, including the new 2000 SCR. Minimum time for fast charge batteries is 3 minutes, maximum only 15 minutes, depending on the depth of discharge. Batteries can be left indefinitely on the charger without any detrimental effect whatsoever. There is no time limit. The patented Reflex charging method involves a high positive current charge pulse once every second, followed by a high current short duration discharge pulse. The discharge pulse removes gas bubbles which accumulate on the cell plates during fast charging. This not only increases the available plate surface, but it also keeps the cell impedance low and reduces operating temperature. This allows higher charge currents and therefore faster charging times. The Smart Fastcharger can be used in the workshop or out in the field, powered either from an optional power supply or from 12v or 24V car batteries, depending on your needs. For complete, technical detail, supplied free. contact Smart Fastcharg- ers, 2567 Wilmot Road, Devonport, Tas 7310. Phone (03) 6492 1368; fax (03) 6492 1329. Laser power meter for CD players Leader Instruments have released the handheld LE 8010 Laser Power Meter for measuring optical power output from a laser diode. Since the meter is calibrated at a wavelength of 780nm, this instrument is suitable for CD player and Mini Disc recorder maintenance applications. It features a wide measuring range of up to 10mW. For further information, contact Stantron Australia Pty Ltd, PO Box 4760 North Rocks, NSW 2151. Phone (02) 9894 2377; fax (02) 9894 2386. SEPTEMBER 1998  53 IQFive battery charger analyser Premier Batteries has released the IQFive battery charger analyser. This is an enhanced version of the IQ Plus Six Station unit adding an RS232PC interface. The interface permits users to print out test results of each station for easy reference and improved monitoring of battery performance. The IQFive also offers the ability to conduct long term cycle tests for life testing or forming of new batteries. A range of additions have been added to enhance the performance, reliability and ease of use of the unit. A 6-module unit is currently available and a 3-module unit will be released in early 1999. For further information, contact Premier Batteries Pty Ltd, 9/15 Childs Road, Chipping Norton, NSW 2170. Phone (02) 9755 1845; fax (02) 9755 1354. Variable motor speed control ICs Two ICs from GEC Plessey Semiconductors (GPS) have been released for variable speed motor control applications in white goods such as washing machines, fan drives in air-conditioning systems, water pumps and general purpose industrial inverters. The SA828 3-phase PWM generator IC is designed for use in high efficiency AC induction motor drive systems. Switching carrier frequencies up to 24kHz allow ultrasonic operation of inverter power switches. The power waveform is stored in an onchip ROM. Two standard waveform options are available: sine plus third harmonic (a popular means of increasing motor power output for a given line supply voltage to the inverter) or pure sinewave. Other waveforms can be provided to customer order. The SA828 operates as a stand-alone microprocessor peripheral, imposing just a small processing overhead on the microprocessor as it requires attention only if the frequency of am54  Silicon Chip plitude of the output waveform needs to be changed. Any of the popular 4 or 8-bit microprocessors and microcontrollers can be interfaced with the SA828. The SA838 is a single-phase variant and is available for applications such as uninterruptible power supplies or single-phase induction motor drives. SA828/838s are available in both plastic DIL and SOP packages, for the temperature range -40 degrees C to +85 degrees C. There is an evaluation board (PWMDEMO) to provide engineers with a quick low-cost method of assessing the SA828/838 ICs. It has everything needed to develop a low-cost controller for variable speed 3-phase induction motor drives and the other applications. PWDEMO can also be connected to a PC for programming via Windows. For further information, contact GEC Electronics Division, Unit 1, 38 South Street, Rydalmere NSW 2116, Phone (02) 9638 1888; fax (02) 9638 1798. EMC modular test system for conducted interference The new Schaffner model 2050 modular EMC immunity test system is suited for applications such as design and manufacture of industrial electronics, office automation, telephone and data communication equipment, medical appliances, as well as domestic appliances and components. The Schaffner model 2050 modular EMC immunity test system can be configured for conducted immunity testing on single and 3-phase power lines, data and telephone lines. Its capabilities cover immunity compliance testing to EN50082-1/2 (and related product standards), as well as IEC1000-4-x and ANSI-IEEE standards. Telco options available allow for testing to CCITT, FCC, ETSI and Bellcore specifications, with special modules available for component testing. The range of plug-in modules and extension units includes surge and burst pulse generators, simulation sources and a range of line couplers for power, data communication and telephone lines. Plug-ins and extensions are automatically recognised by the mainframe control unit and appropriate menu options provide integrated control of the entire test system from the 2050 panel or from an optional remote PC. For further information contact Westek Industrial Products Pty Ltd, Unit 2, 6-10 Maria Street, Laverton North, Vic 3026. Phone (03) 9369 8802; fax (03) 9369 8006. Keyboard and mouse adapter for Notebooks P I E n g i n e e r i n g ’s Keyboard and Mouse Adapter is an active device that allows the simultaneous use of both a full-size keyboard and normal mouse on a notebook computer. The adapter works with all notebooks that feature a PS/2 keyboard/mouse port. It requires no external power supply, drawing its power directly from the notebook port. Driver software is included for Windows 95 and Windows 98. No additional IRQ’s or Com ports are required. Recommended retail price is $129.00, including sales tax and it comes with a 12-month warranty. For further information, contact the Australian distributor, BJE Enterprises Pty Ltd, 124 Rowe Street, Eastwood, NSW 2122. Phone (02) 9858 5611; fax (02) 9858 5610. Floating voltage measurements with Fluke Scope Meter Phillips Test & Measurement and Fluke Corporation has introduced the new Fluke DP 120 Differential Voltage Probe for oscilloscopes. This allows users to safely make floating voltage measurements on electrical and industrial power systems. Each instrument channel used with a DP 120 probe can be connected to a different ground potential. When used with a battery-operated instrument like the ScopeMeter, for example, a single DP 120 provides a dual-channel measurement capability on systems with two different ground potentials. The DP 120 has a 20MHz bandwidth and selectable 20x or 200x attenuation. It is designed for use with the handheld, battery-powered Fluke 123 Industrial ScopeMeter test tool and ScopeMeter B series, as well as (bench type) Fluke oscilloscopes. Typical applications for the DP 120 include measurements on variable-speed motor controls, UPSs, process controllers and other systems with multiple ground levels. The DP 120 is designed and built to meet industrial safety standards. Double insulation and an insulated BNC connector allow use for measurements in 600V RMS IEC1010-1 CAT III and 1000V RMS CAT II overvoltage conditions. UL listing and CSA approval are pending. For more information on the DP 120 probe contact Philips Test & Measurement, 34 Waterloo Road, North Ryde, NSW 2113. Phone (02) 9888 0416; fax (02) 9888 0440. Measuring adjustable speed drives Phillips Test & Measurement and Fluke Corporation have extensively updated the application note entitled, “Measurement of Adjustable Speed Drives with Fluke Meters.” Available free of charge, the new 28-page application note comes in response to the high demand from maintenance technicians who service adjustable speed drive (ASD) motors. ASDs control the speed and torque of a motor electronically. Industry experts estimate that within the next three to five years, adjustable speed drives will control 50 percent of motors. While these devices are making facilities and mechanical equipment more efficient than ever before, they are also presenting new challenges for maintenance and troubleshooting. The pamphlet focuses on electrical measurements that can be used to diagnose bad components and other conditions that may lead to premature motor failure in adjustable speed drives. It covers the topics of safety, traditional and unique motor measurements, as well as how power quality problems affect ASD operation. The application note also addresses possible causes and solutions, in addition to how to make the measurements. For a free copy of the application note, “Measurement of Adjustable Speed Drives with Fluke Meters,” contact Phillips Test and Measurement, 34 Waterloo Road, North Ryde, NSW 2113. Phone (02) 9888 0416; fax (02) 9888 0440. SMART® FASTCHARGERS One charger for all your Nicad & NiMH batteries As featured in ‘Silicon Chip’ Jan. ’96 Designed for maximum battery capacity and longest battery life Charge: Power tools  Torches  Radio equipment  Mobile phones  Video cameras  Radio controlled models  Field test instruments  Lap-top computers  Toys  Dust busters  Others  The REFLEX® charger is powered from a Power Supply (optional) or from 12 or 24V batteries. AVOIDS THE WELL KNOWN MEMORY EFFECT. SAVES MONEY and TIME. Restore Nicads with memory effect to remaining capacity and rejuvenate many 0V worn-out Nicads. CHARGES VERY FAST plus ELIMINATES THE NEED TO DISCHARGE: charge standard batteries in max. 1 hour and the ‘fastcharge’ batteries in max. 15 min. Partially emptied batteries are just topped up. Batteries always remain cool, increasing both the total battery life and the useful discharge time. DESIGNED AND MADE IN AUSTRALIA For a FREE detailed technical description please Ph: (03) 6492 1368 or Fax: (03) 6492 1329 2567 Wilmot Rd, Devonport, TAS 7310 SEPTEMBER 1998  55 Low-cost calibrators with measure & source functions TOROIDAL POWER Two new hand-held calibrators for use in the maintenance of industrial process instrumentation have been released by Yokogawa. Called the “Handy Cal”, both units feature simple operation with a basic accuracy of 0.05%, a large 5-digit liquid crystal display and auto power-off. With weight and size about the same as a digital multimeter, they operate from either AA batteries (50 hours life) or optional AC plug-pack adaptor. Both come with carrying cases and extra long leads. The CA11 is a voltage/current calibrator capable of sourcing and measuring up to 30V or 24mA DC. Output can be changed from 4 to 20mA in 4mA steps or 1 to 15V in 1V steps. Alternatively, output can be increased or decreased at a constant rate for either 16 or 32 seconds sweep time. It can also sink up to 24mA from an external supply, making loop checks simple. The CA12 is a temperature calibrator which can deliver signals equivalent to thermocouple types K, E, J, T, N and R as well as PT100 resistance thermometer sensors. When generating thermocouple signals, a sensor for reference junction compensation provides high accuracy. An optional external RJC sensor is also available. For further information contact Yokogawa Australia Pty Ltd, Centrecourt D1-D2, 25-27 Paul St, North Ryde, NSW 2113. Phone (02) 9805 0699; Fax (02) 9888 1844. 240V inverter with high start-up capacity While many inverters can deliver 150W, there are some which do not have enough power to drive electronic items which require a higher starting current. The Portawatz 150i from Bainbridge Technologies (Statpower) has a continuous rating of 150W but has a surge capacity of 400W and a peak power rating of 300W, making it suitable for use with many domestic products such as computers, TVs and stereos. The inverter meets the European CE Standard and also has Australian C(tick) approval. It weighs only 500 grams and measures 158 x 68 x 48mm. It plugs into a standard 12V cigarette lighter socket as found in cars, boats, buses, etc. The inverter is claimed to run 3 to 5 hours without draining the battery and automatically shuts down before the battery is discharged, leaving enough power to start the engine. For further information contact Bainbridge Technologies Pty Ltd, 77 Shore St Cleveland, Qld 4163. Phone (07) 3821 3333; Fax (07) 3821 1333 56  Silicon Chip TRANSFORMERS Manufactured in Australia Comprehensive data available Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 9476-5854 Fx (02) 9476-3231 Oscilloscope adapter for fine pitch probing This new oscilloscope probing kit from Emulation Technology enables designers and technicians to perform fine-pitch probing from 0.8mm to 0.3mm on IC packages. Three separate probing kits are available, depending upon the lead pitch being probed. Each kit contains parts for use with two probes, including four MicroGrippers and two Dual-lead adapters. For further information, contact the Australian distributor, BJE Enterprises Pty Ltd, 124 Rowe St, Eastwood, NSW 2122. Phone (02) 9858 5611; fax (02) 9858 5610. 4½” METAL CUTTING LATHE (6" with riser blocks) Precision and ruggedness to suit industry, school or hobby use. Over 25,000 sold worldwide. Made in USA 2 year warranty buys a lathe with $429 drilling tailstock, pulleys and belt, 3 jaw chuck, Jacobs chuck etc. You supply the motor – an old appliance motor will do! Accessories available: Compound slide, 4 jaw chuck, faceplate, collets, milling attachment, and many more. Write or phone for photo brochure and price lists. TAIG MACHINERY 59 Gilmore Crescent. Garran. ACT. 2605. Ph: 015 26 9742 (Business); (02) 6281 5660 (AH); Fax: (02) 6285 2763 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. The advertiser, BBS Electronics, is no longer in business. Two fun projects for the price of one! Build a PLASMA DISPLAY . . . or a JACOB’S LADDER These two projects have absolutely no practical use at all; they are just gimmicks but they are a lot of fun. The one PC board can be used to build a Plasma Globe Display or a Jacob’s Ladder. 58  Silicon Chip Design by BRANCO JUSTIC* This photo shows the "works" of the Plasma Display version, with the inset showing the insulating shield in place. Be careful if you need to apply power when the case is open: some parts of the circuit can bite! About ten years ago, Plasma Balls an award-winning school or science lation circuit to control the output. were all the rage and lots of people project. Let’s have a look at the Jacob’s Ladder had them. Now, they are nowhere to circuit first, as shown in Fig.1. But be warned – this project can be seen. But while those Plasma Balls “bite” the hand that feeds it (more on IC3, a 555 timer, is connected as a looked quite fancy they were relatively this subject anon). standard astable oscillator with its freexpensive. The Plasma Ball to be dequency of around 25kHz determined For those who want to know more scribed is really cheap and is based on, by the components connected to pins about the Jacob’s Ladder, you can wait for it, a standard 240VAC electric refer to the September 1995 issue of 2, 6 & 7. The approximate square wave light bulb. Virtually any size, rating or SILICON CHIP. output from pin 3 is connected to IC1, style of light bulb may be used, provida hex inverter package. IC1a inverts High voltage power supply ed it has a clear glass bulb. After all, the signal from pin 3 of IC3 before it there wouldn’t be much point in using drives three paralleled inverters IC1b, Both the Plasma Ball display and one with a frosted bulb, would there? 1c & 1d which provide base current the Jacob’s Ladder depend on a high And just to show how cheap to two transistors connected it is, you could even use an as complementary emitter folelectric light bulb with a blown lowers, Q1 & Q2. filament! Bet that’s the first time Pin 3 of IC3 also drives paryou’ve ever seen a possible use alleled inverters IC1e & IC1f for a blown light bulb, except which provide base current The inverter in this project produces a perhaps, as a meal for a perto another two transistors high AC voltage of around 25kV or more former in sideshow alley! connected as complementary at around 25kHz. The second use for the PC emitter followers, Q3 & Q4. board is to drive a Jacob’s LadIn turn, the complementary Do not be tempted to touch the Jacob’s der. This consists of two vertical emitter follower pairs drive Ladder display or the Plasma display as wires which are close-spaced at the gates of two Mosfets, Q5 & it will give a strong burning sensation the bottom and splayed apart to Q6, and these drive the stepup rather than an electric shock. increase the gap. A high voltage transformer, T1. This is a teleapplied to the wires causes a vision flyback transformer and spark discharge which rises it gives the maximum high magically to the top and then restarts voltage supply. This is generated by an voltage output at its resonant frequenat the bottom. inverter which steps up 12V DC from cy. Trimpot VR1 varies the operating frequency of IC3 and this is adjusted This is accompanied by fizzing a plugpack supply to an AC voltage of and crackling noises which add to around 20kV. This inverter is basically to give the maximum output voltage, the effect. It’s spectacular and a real all there is to the Jacob’s Ladder circuit as we will discuss later. attention getter – just the thing for while the Plasma Ball adds a moduThat’s really all there is to it as far as WARNING SEPTEMBER 1998  59 (Right): The internal view of the complete Jacob's Ladder version, albeit with all the components on the board to also suit the Plasma Display version. The PC board pattern suits both the Jacob's Ladder and Plasma Displays – building the “universal” version (with all components) means you can swap between versions merely by inserting (Jacob's Ladder) or removing (Plasma Display) one link. Note the generous dollops of silicone sealant over the ladder wire connection points to help prevent flashover inside the case. the inverter is concerned because the high voltage secondary drives the Jacob’s Ladder wires directly. Since the inverter runs at about 25kHz, a power supply filter consisting of inductor L1 and the 1000µF capacitor, decouples the supply for the transformer from the rest of the circuit. Plasma display circuit The Plasma display circuit uses the inverter circuit just described together with a pulse width modulator (PWM) circuit which varies the supply voltage. The full circuit is shown in Fig.3 and as you can see, it is virtually identical with Fig.1 apart from the addition of the PWM circuit involving IC2, a 4093 quad NAND Schmitt trigger and Mosfet Q7. IC2a is connected as a standard Schmitt trigger oscillator with its on/off times variable by trimpots VR2 & VR3. Its output at pin 3 drives three paralleled gates (IC2b, 2c & 2d) acting as inverters to drive the gate of Q7. This rapidly switches on and off the supply to the main inverter and thereby varies the high voltage drive to the light bulb. PC board assembly A close-up of the“universal” PC board, made to suit either the Plasma Display version or the Jacob's Ladder version. In this case it is for the Plasma Display as the shorting link (circled centre top of PC board) is missing. The inset shows this link in place for the Jacob's Ladder version. 60  Silicon Chip All of the circuit components, with the exception of the flyback transformer (T1), are mounted on a PC board measuring 81 x 71mm. Fig.2 shows the component layout for the Jacob's Ladder version while Fig.4 shows the "universal" version. Insert the wire links, resistors and capacitors first, followed by the transistors and trimpots. Then insert and solder the ICs followed by the Mosfets. Each Mosfet is fitted with a flag heatsink. Note that in both prototypes depicted in the Fig.1 (above): The simpler circuit of the two – this one is for the Jacob's Ladder version. In some ways it is the more spectacular display. An added bonus is that you don't need to replace light globes! Fig.2 (below): There are several differences between this Jacob's Ladder PC board layout and the universal board layout overleaf. If you don't want to build the Plasma Display, you can save on quite a few components. SEPTEMBER 1998  61 photos, trimpot VR1 is mounted on the copper side of the PC board. A hole is then drilled in the case lid to allow VR1 to be adjusted for maximum EHT output. Both the PC board and the flyback transformer are mounted on the lid of a standard plastic utility box measuring 158 x 95 x 53mm. Before doing that though, you need to connect four primary wires from the flyback transformer to the PC board. As supplied, the primary leads are enamelled copper wire, with two wires having red enamel and the others having clear enamel. The idea is to join a red and clear wire together and connect the pair to the centre-tap (CT) connection on the PC board. The remaining red and clear enamelled wires are connected to the other primary terminations on the PC board. Before soldering the wires, the ends should be stripped of enamel and then sleeving should be slipped over their full length to prevent any possibility of shorts. With the wires connected, the transformer is then secured to the lid of the case using contact adhesive. Do not use hot-melt glue for this task as it will not work. The PC board is mounted on the lid using screws and nuts in the corners but not before drilling an access hole for screw- Parts List - (Plasma Display) 1  PC board, 81 x 71mm 1  plastic utility box, 158 x 95 x 53mm 1  TV flyback transformer (see text) 1   ferrite cored inductor (L1) 1   5kΩ trimpot (VR1) 2   50kΩ trimpots (VR2,VR3) * 3  flag heatsinks 1   12-15V DC plugpack transformer 1   240VAC light bulb (see text) Semiconductors 1   4049 hex inverter (IC1) 1   4093 quad NAND Schmitt trigger (IC2) * 1   555 timer (IC3) 2   C8050 NPN transistors (Q1,Q3) 2   C8550 PNP transistors (Q2,Q4) 2   BUK453-100A Mosfets (Q5,Q6) 1   IRF9530 Mosfet (Q7) * 2  1N4148 or 1N914 diodes (D1, D2)* Capacitors 2   1000µF 25VW electrolytic 1   220µF 25VW electrolytic 1   2.2µF 16VW electrolytic * 2   0.47µF monolithic 1   .012µF metallised polyester (greencap) 1   .01µF metallised polyester (greencap) 1   .0022µF ceramic 2   220pF ceramic Resistors (0.25W, 5% tolerance) 4   10kΩ 1   3.9kΩ 2   33Ω 2   22Ω 1W Fig.3: the circuit for the Plasma Display contains the components necessary to modulate the supply. 62  Silicon Chip 1   470Ω 2   1Ω 1W * Miscellaneous Hookup wire, screws, nuts, washers, hot melt glue, silicone sealant, spaghetti sleeving, insulator, solder. * Not required for Jacob's Ladder version - see text driver adjustment of trimpot VR1. To make the Jacob’s Ladder, use a coat hanger or similar heavy gauge wire, with two lengths cut to around 150mm long. Solder a couple of loops to the wires at one end so that they can be secured with screws and nuts to the base of the plastic box. You will want to attach solder lugs to the screws so that you can terminate the EHT wires. You need to space and bend the Jacob’s Ladder wires so that they have about a 5mm gap at the bottom, widening gradually to around 30mm at the top. This is to ensure that the spark travels upwards. Once the EHT connections are made, give them a liberal coating of silicone sealant or hot melt glue to prevent the possibility of flashover inside the box. For the Plasma display, any size 240VAC light bulb will work but you get Fig.4: The "universal" PC board component layout with wiring diagram for the Plasma Display. The dotted link (arrowed) must be removed for Plasma Display operation. Here the wire halo can clearly be seen. It is made from some stiff wire, bent into a circle so it sits just clear of the glass surface. That gap between wire and glass is important, because... ...This is what happens if you let the halo touch the globe: the display is briefly more spectacular but very quickly burns a hole through the glass. Here endeth the lesson (and the globe)! The connection to the globe (bottom) and halo (top) from the underside. The globe mounting is a push fit in an appropriate-sized hole with little notches for the bayonets to fit through. SEPTEMBER 1998  63 Silicon Chip Binders REAL VALUE AT $12.95 PLUS P&P Where To Buy The Kit All parts for this project are available from Oatley Electronics who own the design copyright. Their address is PO Box 89, Oatley, NSW 2223. Phone (02) 9584 3563; Fax (02) 9584 3561. Pricing is as follows:    PC board plus all on board components:.................................... $29.00    13.8V 1A plug-pack.................................................................... $12.00    Suitable plastic box...................................................................... $5.00 Note: the basic kit may be supplied with a few unused but surplus-recovered parts (eg, Mosfets) to keep the price low. These binders will protect your copies of S ILICON 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.   Hold up to 14 issues   80mm internal width  SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A12.95 plus $A5 p&p. Available only in Australia. 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 Enclosed is my cheque/money order for $________ or please debit my ❏ Bankcard  ❏  Visa   ❏ Mastercard Card No: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Card Expiry Date ____/____ Signature ________________________ Name ___________________________ Address__________________________ __________________ P/code_______ 64  Silicon Chip a much better display with as large a bulb as possible. Cut a hole in base of the case to take the bulb’s metal base (either bayonet fitting or Edison screw bases may be used). Solder one of the EHT wires from the transformer to either or both of the filament connections of the lamp (it doesn’t matter that you “short” them). The other EHT lead goes to a “halo” wire which is mounted close to and around the bulb, as shown in the photos. This halo wire is essential to obtain a good discharge pattern in the bulb. Note that the halo wire must not touch the bulb otherwise the electric discharge will concentrate at that point and will melt a hole through the bulb within a few seconds. Again, give the EHT lead connections inside the case a liberal coating of silicone sealant or hot-melt glue to prevent the possibility of flashover. It’s also a good idea to glue a piece of good insulation material (thick plastic, perspex, elephantide, etc) right over the electronics. One of the photos shows what we mean: a piece of stiff PTFE cut to the size of the PC board and glued to the top of the EHT transformer using holt melt glue or silicone sealant. This is especially important for the plasma display version (where the bulb connections could be close to the PC board) but won’t be out of place in the Jacob’s ladder version either. Adjusting the voltage Once you have the Jacob’s Ladder unit complete, it is time to connect a 12V to 14V DC plugpack and apply power. The Jacob’s Ladder wires must be vertical otherwise the spark will not climb. However, to make your initial adjustment, turn the unit on its side, apply power and adjust trimpot VR1 for the most intense electric discharge across the wires. Turn off the power and sit the case normally, so the ladder wires are vertical. Apply power again and the discharge should climb up the wires and then restart at the bottom. Don’t even think of touching the electrodes as they will give you a nasty sting or burning sensation. Always be wary of young children as it is a fascinating device and little fingers love to touch . . . Plasma display The procedure for setting up the Plasma display is similar but you have three trimpots to adjust. Again, VR1 is adjusted for the strongest discharge. VR2 and VR3 are then adjusted to rapidly switch the display on and off, if that’s what you want, or merely to adjust the brightness of the discharge. A word of warning here: we’ve already mentioned how it is possible to melt a hole in the glass bulb if the halo wire touches the glass. The same thing can happen if you turn up the discharge intensity too high; all of sudden the discharge will concentrate at one point and a pin hole appears in the glass. That then spells the end of the display as far as that particular bulb is concerned. Still, as we said earlier, you can use blown bulbs so it is still a cheap SC exercise. * Branco Justic is the Managing Director of Oatley Electronics Pty Ltd. Silicon Chip Bookshop SUBSCRIBE   AND GET   10% OFF SEE PAGE 92 Guide to Satellite TV Installation, Recept­ion & Repair. By Derek J. Stephen­son. First published 1991, reprinted 1997 (4th edition). This is a practical guide on the installation and servicing of satellite television equipment. The coverage of the subject is extensive, without excessive theory or mathematics. 383 pages, in hard cover at $55.00. Servicing Personal Computers By Michael Tooley. First published 1985. 4th edition 1994. Computers are prone to failure from a number of common causes & some that are not so common. This book sets out the principles & practice of computer servicing (including disc drives, printers & monitors), describes some of the latest software diagnostic routines & includes program listings. 387 pages in hard cover at $90.00. Video Scrambling & Descrambling For Satellite & Cable TV By Rudolf F. Graf & William Sheets. First pub­lished 1987. This is an easy-to-understand book for those who want to scramble and unscramble video signals for their own use or just want to learn about the techniques involved. It begins with the basic techniques, then details the theory of video encryption and decryption. It also provides schematics and details for several encoder and decoder projects, has a chapter of relevant semiconductor data sheets, covers three relevant US patents on the subject of scrambling and concludes with a chapter of technical data. 246 pages, in soft cover at $50.00. The Art of Linear Electronics By John Linsley Hood. Pub­lished 1993. This is a practical handbook from one of the world’s most prolific audio designers, with many of his designs having been published in English technical magazines over the years. A great many practical circuits are featured – a must for anyone inter­ ested in audio design. 336 pages, in paperback at $70.00. Digital Audio & Compact Disc Technology Produced by the Sony Service Centre (Europe). 3rd edition, published 1995. Prepared by Sony’s technical staff, this is the best book on compact disc technology that we have ever come across. It covers digital audio in depth, including PCM adapters, the Video8 PCM format and R-DAT. If you want to understand digital audio, you need this reference book. 305 pages, in paperback at $90.00. Surface Mount Technology By Rudolph Strauss. First pub­lished 1994. This book will provide informative reading for anyone considering the assembly of PC boards with surface mounted devices. Includes chapters on wave soldering, reflow­soldering, component placement, cleaning & quality control. 361 pages, in hard cover at $99.00. Radio Frequency Transistors Principles & Practical Applications. By Norm Dye & Helge Granberg. Published 1993. This book strips away the mysteries of RF circuit design. Written by two Motorola engineers, it looks at RF transistor fundamentals before moving on to specific design examples; eg, amplifiers, oscillators and pulsed power systems. Also included are chapters on filtering, impedance matching & CAD. 235 pages, in hard cover at $95.00. Guide to TV & Video Technology By Eugene Trundle. First pub­lished 1988. Second edition 1996. Eugene Trundle has written for many years in Television magazine and his latest book is right up date on TV and video technology. 382 pages, in paperback, at $55.00. Electronics Engineer’s Reference Book Edited by F. F. Mazda. First published 1989. 6th edition. This just has to be the best refer­ ence book available for electronics engineers. Provides expert coverage of Your Name__________________________________________________ PLEASE PRINT Address____________________________________________________ _____________________________________Postcode_____________ Daytime Phone No.______________________Total Price $A _________ ❏ Cheque/Money Order  ❏ Bankcard  ❏ Visa Card  ❏ MasterCard Card No. Signature_________________________ Card expiry date_____/______ Return to: Silicon Chip Publications, PO Box 139, Collaroy NSW, Australia 2097. Or call (02) 9979 5644 & quote your credit card details; or fax to (02) 9979 6503. Prices valid until 30th September, 1998 all aspects of electronics in five parts: techniques, physical phenomena, material & components, electronic design, and applications. The sixth edition has been expanded to include chapters on surface mount technology, hardware & software design, semi­-custom electronics & data communications. 63 chapters, soft cover at $160.00. Audio Electronics By John Linsley Hood. Pub­lished 1995. This book is for anyone involved in designing, adapting and using analog and digital audio equipment. Covers tape recording, tuners & radio receivers, preamplifiers, voltage amplifiers, power amplifiers, the compact disc & digital audio, test & measurement, loudspeaker crossover systems and power supplies. 351 pages, in soft cover at $75.00. Understanding Telephone Electronics By Stephen J. Bigelow. Third edition published 1997 by Butterworth-Heinemann. This is a very useful text for anyone wanting to become familiar with the basics of telephone technology. The 10 chapters explore telephone fundamentals, speech signal processing, telephone line interfacing, tone and pulse generation, ringers, digital transmission techniques (modems & fax machines) and much more. Ideal for students. 367 pages, in soft cover at $55.00. ✓ Title Price ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ Guide to Satellite TV $55.00 Servicing Personal Computers $90.00 Video Scrambling & Descrambling $50.00 The Ar t Of Linear Electronics $70.00 Digital Audio & Compact Disc Technology $90.00 Surface Mount Technology $99.00 Radio Frequency Transistors $95.00 Guide to TV & Video Technology $55.00 Electronic Engineer's Reference Book $160.00 Audio Electronics $75.00 Understanding Telephone Electronics $55.00 Postage: add $5.00 per book. Orders over $100 are post free within Australia. NZ add $10.00 per book; elsewhere add $15 per book. TOTAL $A SEPTEMBER 1998  65 Get maximum acceleration with this: GEAR CHANGE   INDICATOR Changing gear in your car at the optimum speed can im­prove your acceleration times drastically. This Gear Change Indicator tells you when to change gear to obtain the best possible acceleration. By JOHN CLARKE Many car enthusiasts are prepared to invest large sums of money improving engine performance, traction and suspension. They do this to improve their driving pleasure but also to obtain the best possible acceleration from their car. That is all well and good, especially as money spent in improving the 66  Silicon Chip performance generally leads to a safer and more enjoyable vehicle. But those same enthusiasts often overlook the fact that a better driving technique can produce an improve­ment that far outweighs the cost. In other words, while one person may invest several thou­sand dollars in a turbocharger system and engine management modifications, zero-cost improvements in acceleration times can be had simply by driving the car more intelligently. While this may seem unlikely, let’s look at the facts. First, the person with the turbocharged car may lose valuable acceleration time in excessive wheel spin and sideways movement at the start and second, he may “red­ line” the engine rpm before changing gears. But another driver with a similar car may have accelerated down the track not having spun the wheels once or having lost traction. The benefit can be greatly improved accel­ eration, without all the sound and fury. How do you know when to change gears for optimum accelera­tion? The gear change points for best acceleration are usually not at the tacho­ meter’s redline limit in each gear. In general, while you might drive to the redline in first and second gear, you would not attempt to wind it out in 3rd and 4th. We’ll see why, later. Conversely, changing gear too early may result in less than the maximum possible acceleration. This is where the SILICON CHIP Gear Change Indicator comes into the picture. First of all, you need to know what engine speed gives maximum acceleration in any gear. Later in this article, we’ll tell you how to make a precise measurement of acceleration at all engine speeds in all gears. Surprising though it may seem, the best acceleration is obtained at a dif­ferent engine speed in each gear, regardless of what car you have. The trick is to change gear just as the acceleration in a particular gear falls below the maximum available in the next gear. Fig.1 shows acceleration versus road speed for a particular car through the gears. Regardless of how good your mem­ ory is, you won’t have time to think about these different gear change points while you are driving, so the idea is to program them into the Gear Change Indicator. It then sounds a buzzer and flashes a lamp to indicate when a gear change is due. The S ILICON C HIP Gear Change Indicator is a small box with four adjustment control knobs, one for each gear change. The Indicator is suitable for cars with 3, 4 or 5-speed gearboxes. 1st Gear 2nd Gear 3rd Gear 4th Gear Fig.1: this graph shows maximum acceleration versus speed through the gears for a 4-cylinder car. Maximum accelera­tion in 1st gear is obtained by taking it to the redline limit on the tacho but in second gear you would change up earlier. Third gear gives better acceleration than fourth at speeds above 100km/h. You can adjust the controls to indicate gear change points at any speed. Any control can be disabled by setting its knob fully clockwise. The lamp lights and the buzzer sounds whenever one of the preset speeds is reached. By making a simple change to the cir­cuitry, you can arrange to have the gear change indication pro­vided on Up changes, or both Up and Down changes. When you set the indicator to provide both Up and Down changes, there is a 6km/h difference in the speed indicat­ ed for changing up compared to the change down point. This hysteresis is necessary for correct circuit operation. The vehicle speed is detected by a magnet and Hall Effect sensor, with the magnet installed on the tailshaft or on the drive shaft of a front wheel drive car. The magnet spins past the Hall Effect sensor, producing a signal which is proportional to the shaft speed. Note that there is no need to measure the engine speed and nor is there any need, strictly speaking, to have a tachometer. Block diagram Fig.2 shows the block diagram of the Gear Change Indicator. As mentioned, the magnet spins past the Hall Effect sensor and this sends a signal to the frequency-to-voltage converter, IC1. This produces a DC voltage proportional to speed. The higher the speed, the higher the voltage output from IC1. Four comparators, IC2aIC2d, monitor this converter voltage Fig.2: the block diagram of the Gear Change Indicator. The magnet spins past the Hall Effect sensor and this sends a signal to the frequencyto-voltage converter, IC1. This produces a DC voltage proportional to speed. SEPTEMBER 1998  67 68  Silicon Chip Fig.3: the circuit of the Gear Change Indicator uses an LM2917 frequency- to-voltage converter to generate a voltage which is proportional to the vehicle and this is fed to four comparators to drive the lamp and buzzer. and each compare it against their own reference. The reference is the speed setting for each gear change. VR1 sets the reference voltage level for IC2a which in turn switches its output when the speed voltage just goes above this reference. Similarly, VR2, VR3 and VR4 set the reference voltages for comparators IC2b, IC2c and IC2d, respectively. VR1 adjusts the speed setting for the 1-2 gear change. VR2 is for the 2-3 change, VR3 is for the 3-4 change and VR4 is for the 4-5 change. Each comparator output includes a delay which triggers the buffer, Q1 & Q2, for a short time, whenever a comparator detects a voltage rising (or falling) from its reference level. The buffer drives the buzzer and lamp to indicate that the speed for a gear change has been reached. Circuit description The full circuit for the Gear Change Indicator is shown in Fig.3. The speed sensor to detect shaft movement is a UGN3503 Hall effect sensor. Its output at pin 3 is filtered with a series 100Ω and a .001µF capacitor to remove high frequency hash and the signal is then applied directly to pin 1 of IC1 and to pin 11 via a voltage divider. These two pins are part of a comparator which switches its (internal) output each time the magnet passes the sensor. Following the comparator within IC1 is a charge pump. This basically shuffles charge from the 0.1µF capacitor at pin 2 to the 10µF capacitor connected to pins 3 & 4, at each comparator switching. The 10kΩ resistor and trimpot VR5 at pins 3 & 4 dis­charge the 10µF capacitor. The output at pin 5 of IC1 is a buffered version of the pin 3/4 capacitor voltage. As noted previously, this voltage is directly proportional to the drive shaft speed; the higher the speed, the higher the voltage. Pin 5 of IC1 drives the inverting comparator inputs of IC2a, IC2b, IC2c & IC2d, all of which are part of an LM324 quad op amp package. Potent­ iometers VR1-VR4 are the reference voltage potentiometers for the four comparators. One side of each pot is connected to ground while the top side is connected to a +3.8V supply derived via diodes D9 & D10 from the +5V rail. Thus, the potentiometer wipers can be adjusted to produce any voltage between 0V and +3.8V. The wiper outputs of the potent­ iometers are applied to the comparator non-inverting inputs (pins 3, 5, 10 & 12) via 22kΩ resistors. The 1MΩ resistors between the comparator outputs and the non-inverting inputs provide the “hysteresis” we referred to earlier. This hysteresis causes the output of the comparator to quickly go low when the speed voltage at the inverting input goes above the reference input. The comparator will not go high again until the speed voltage drops by more than about 80mV. This hys­teresis prevents the comparators oscillating above and below the threshold voltage, due to ripple or hash on the speed voltage at the output of IC1. Each comparator’s output connects to a delay unit consist­ing of an exclusive-OR (XOR) gate and a 100kΩ resistor, a 10µF capacitor and a diode. The four XOR gates are in IC3, a quad XOR gate package. The output of an XOR gate goes high whenever its inputs are different. In other words, if one input is high and the other input low, then the XOR gate output will be high. If both inputs are either high or low, then the output will be low. We use this property of the XOR gate to provide a high output for a short time on every change in the comparator output. When comparator IC2a’s output goes from a high to a low, which happens when the speed voltage is increasing, pin 8 of IC3a also immediately goes low. But pin 9 remains high, since the 10µF capacitor at this pin was previously charged via diode D1. Consequently, the output of IC3a goes high for one second and it drives the base of transistor Q1 via its respective output diode (D5) and the 47kΩ resistor. When Q1 is on, it also switches on transistor Q2 to drive the 12V lamp indicator and buzzer. Diode D11 and the 10µF capacitor Parts List 1 PC board, code 05308981, 117 x 102mm 1 PC board, code 05308982, 31 x 25mm 1 plastic case, 140 x 111 x 35mm 1 front panel label, 133 x 27mm 4 10kΩ linear 16mm PC mounting pots (VR1-VR4) 1 200kΩ horizontal trimpot (VR5) 4 19mm diameter knobs 1 12V indicator lamp and bezel 1 12V buzzer 1 or 2 button magnets 1 M3 screw and nut 4 self-tapping screws 1 rubber grommet 1 100mm length of 0.8mm tinned copper wire 10 PC stakes Semiconductors 1 LM2917 frequency-to-voltage converter (IC1) 1 LM324 quad op amp (IC2) 1 4030 quad XOR gate (IC3) 1 UGN3503 Hall sensor (Sensor 1) 1 7805 5V 3-terminal regulator (REG1) 1 BC547 NPN transistor (Q1) 1 BC327 PNP transistor (Q2) 1 16V 1W zener diode (ZD1) 10 1N914, 1N4148 signal diodes (D1-D10) 1 1N4004 1A diode (D11) Capacitors 1 100µF 16VW PC electrolytic 8 10µF 16VW PC electrolytic 4 0.1µF MKT polyester 1 .001µF MKT polyester Resistors (0.25W, 1%) 4 1MΩ 1 2.2kΩ 4 100kΩ 1 470Ω 1 47kΩ 1 100Ω 4 22kΩ 1 10Ω 5 10kΩ Miscellaneous Hookup wire, aluminium bracket, solder, etc. reduce the voltage spikes when the buzzer switches off. UP/DOWN change indication So far we’ve seen what happens when a change UP is indicat­ed but SEPTEMBER 1998  69 Capacitor Codes  Value  0.1µF  .001µF IEC 100n 1n EIA 104 102 what happens when the output of IC1 flicks below the reference voltages of each of the comparators IC3a-IC3d? Looking at IC3a, when the comparator output goes high, which occurs with a falling speed voltage, the 10µF capacitor at pin 9 is quickly charged via diode D1. Thus the output of IC3a at pin 10 goes high only very briefly and so there is no lamp or buzzer indication. So what if you require the circuit to indicate a gear change point when changing up or down a gear? You only need to remove the diode at the input to each XOR gate (D1-D4). This will give a delayed output from the XOR gate on both rising and fall­ing speeds. Power for the circuit comes from the vehicle’s 12V battery via the ignition switch. The 10Ω resistor and 16V zener (ZD1) suppress any voltage transients on the supply before it is ap­plied to the regulator (REG1). The 100µF capacitor at the input to REG1 decouples the supply, while the 10µF and 0.1µF capacitors at the output improve transient response of the regulator and also decouple the supply rail. REG1 provides the +5V supply for sensor 1, IC1, IC2 & IC3. Note that the 12V lamp and buzzer are powered via Q2 directly from the +12V supply. Fig.4: the component layout for the main PC board and sensor PC board. Note that the sensor board should be given an overall coating of silicone sealant to make it weatherproof. Construction The Gear Change Indicator is wired Resistor Colour Codes  No.   4   4   1   4   4   1   1   1   1 70  Silicon Chip Value 1MΩ 100kΩ 47kΩ 22kΩ 10kΩ 2.2kΩ 470Ω 100Ω 10Ω 4-Band Code (1%) brown black green brown brown black yellow brown yellow violet orange brown red red orange brown brown black orange brown red red red brown yellow violet brown brown brown black brown brown brown black black brown 5-Band Code (1%) brown black black yellow brown brown black black orange brown yellow violet red black brown red red black red brown brown black black red brown red red black brown brown yellow violet black black brown brown black black black brown brown black black gold brown The indicator buzzer mounts directly on the PC board but could also be mount­ed remotely and connected back to the board via flying leads if you wish. Make sure that all parts are correctly oriented. up on two PC boards. The main PC board (code 05308981) measures 117 x 102mm, while the smaller sensor PC board (code 05308982) measures 31 x 25mm. The main PC board mounts into a plastic case measuring 140 x 111 x 35mm. You can begin construction of the Gear Change Indicator by checking the PC boards for shorts between tracks, possible breaks and undrilled holes. Fix any defects before proceeding further. Then you can insert and solder in all the wire links, as shown on the overlay diagram of Fig.4. Next, insert and solder the resistors and then the ICs can be installed, taking care with their orientation. Be sure to place the correct IC in each place. Solder in the diodes, including the zener (ZD1), and take care with their orientation. The transistors can be installed next and be sure to place the correct type in each position. Insert the capacitors and note that the electrolytic capacitors need to be inserted with the correct polarity. The 3-terminal regulator (REG1) is mounted horizontally, with its metal tab towards the PC board. Bend the leads to insert them into the holes allocated, before securing the regulator with a screw and nut. Next, insert the PC stakes and trimpot (VR5). The poten­tiometers mount directly on the PC board. The sensor board is assembled with the Hall Effect sensor and capacitor mounted flat on the board, with the labelled side of the sensor facing up. Later on, this board will be installed underneath the vehicle but we’ll talk about that later. Drilling the case The front panel of the case requires four holes for the potentiometers and one for the indicator lamp. Use the front panel label as a guide to the positioning of the holes. Drill the hole in the rear panel for the rubber grommet. Affix the front panel label in position and trim around the holes with a sharp hobby knife. The main PC board and front panel can then be se­cured with four self-tapping screws into the integral standoffs in the base of the case. Connect hookup wire from the +12V and GND terminals on the main PC board and pass these through the SEPTEMBER 1998  71 Measuring Acceleration Using A Low-Cost Clinometer Above: the LEV-O-GAGE sailing clinometer is available from ships’ chandlers such as Whit­worth’s Nautical World. It should be mounted horizontally inside the car on a window or door using double-sided adhesive tape. Fig.5: a clinometer can indicate the direction of the vector sum of the car’s acceleration and the force of gravity which is 1G. At 1G acceleration, the clinometer will indicate an angle of 45 degrees. grommet. Similarly, connect up wires to the +, Sig and GND terminals which are re­quired to connect to the sensor PC board. The lamp bezel is secured to the front panel and wired to the PC board as shown. We secured the buzzer to the PC board using self-tapping screws. Alternatively, you could mount the buzzer outside the case so that it can be heard more easily. Make sure that the red (+) wire on the buzzer is connected to the positive terminal on the PC board, as shown. Testing Apply 12V between the +12V and 72  Silicon Chip GND terminals on the main PC board. Check that the output of regulator REG1 is +5V and that the voltage at the cathode (K) of diode D9 is about +3.8V. If you want to check operation of the buzzer, you will need to apply some voltage to pins 5 & 10 of IC1 using a 10kΩ resistor between these pins and the +3.8V supply at the cathode of D9. Now adjust VR1 and check that the buzzer and light come on for a short time for each downward rotation of the pot past the threshold point. Note that if you want to check the circuit operation using a signal gener- Measuring acceleration in terms of G is easier than you think and can be done using an inexpensive boating clinometer. This measures the angle of slope from the horizontal axis. It comprises a semi-circular sealed tube which is filled with a clear fluid and a small metal ball. The fluid damps the movement of the ball but does not affect the accuracy of the reading. As the instrument is tipped off axis, the ball moves along the tube and indicates the angle of inclination. To make measurements, the clin­ ometer is mounted in the car so that forward acceleration causes the ball ator, pin 1 of IC1 needs to be biased to about +2.5V. This can be done using a 10kΩ resistor from pin 1 to pins 9 & 8 (ie, +5V). We recommend that you use a 10µF coupling capacitor from the output of the signal generator to the input of the Gear Change Indicator. Installation The Gear Change Indicator can be installed using automotive connectors to make the connection to the +12V ignition supply, via the fused accessories line. Use automotive wire for this connection. The ground connection can be made to the chassis Fig.6: you can use this graph to convert the clinometer angle readings to acceleration. to move backwards. When the car is stationary or not accelerating (or braking) the clinometer will measure zero degrees. If your car was able to accelerate at 1G, the clinometer would indicate 45°. What the clinometer is doing is indicating the direction of the vector sum of the 1G acceleration and the force of gravi­ty which is also 1G. Without going into the physics involved, the tangent of the angle indicated by the clinometer is equal to the G force due to acceleration. Fig.5 illustrates the concept. So, for example, if the angle is 45°, its tan- gent is 1, for 1G. If the angle is 10°, the acceleration is 0.18G and so on. The clinometer we used was called a LEV-O-GAGE sailing clinometer. It is available from ships’ chandlers such as Whit­worth’s Nautical World who have stores in Brisbane and Sydney. Whitworth’s catalog number is 52381 and it can be purchased via mail order by phoning (02) 9939 1055. The clinometer needs to be mount­ ed horizontally (using double-sided adhesive tape) to a passenger side window or door. This will allow a passenger to take the readings of with an eyelet and self-tapping screw. You will probably want to suspend the case underneath the edge of the dashboard, in a position convenient to the driver. By the way, while our prototype does not show it, you will need an on/ off switch for this indicator, otherwise it will drive you to distraction when you are travelling in normal traffic. It is possible to install a miniature toggle switch next to the lamp on the front panel. The sensor board is mounted near the drive shaft as shown in Fig.7. Temporarily mount the button magnet in place with a cable tie and secure the board so that the magnet will directly pass the sensor with about 2-3mm clearance. Wire the sensor board to the main PC board using hookup wire. Test that the Gear Change Indicator works at low speed by rotating pot VR1 as you travel along. If nothing happens, try adjusting trimpot VR5. If this does not help, remove the magnet and turn it around so that the op­posite pole is facing out and test again. If the Gear Change Indicator cannot be made to work at any speed, the magnet may not be powerful enough or the gap between angle as measured on the clino­meter as the driver calls out the speed. This procedure should be done at maximum throttle in each gear on a straight and level stretch of road, traffic and speed limits permitting. The measurements can be later plotted on a graph displaying acceleration in G against speed in km/h, as in Fig.1. You can use the graph of Fig.6 to convert the angle readings to acceleration. You can also use this clinometer to check the rate of deceleration during braking. In this case, the ball will move in the opposite direction. sensor and magnet is too big. When you have the unit operating, use epoxy resin to perma­nently secure the magnet to the drive shaft. The sensor PC board should be protected from moisture with a generous coating of non-corrosive silicone sealant (roof and gutter sealant). Now adjust VR5 so that you can get a good useful range of rotation on the gear change controls. If VR5 is too far anticlockwise, then the controls will only operate down at very small angles of rotation. This is because the voltage change against speed will be small. If VR5 is wound fully clockwise, then you may not SEPTEMBER 1998  73 The sensor PC board should be protected from moisture by applying a generous coating of non-corrosive silicone sealant (roof and gutter sealant) to both sides. be able to adjust a gear change pot to work at high speed. This is because at high speed, the output from IC1 may be higher than the 3.8V adjustment avail­able on each gear change pot. Some compromise therefore must be found with the adjustment of VR5. Fig.7: the button magnet is secured to the driveshaft using epoxy resin and a cable tie, as shown here. Fig.8: here are the actual size artworks for the two PC boards. Gear-change points It is now time to find out at what speed you should be changing each gear. To do this, you need to measure and plot full-throttle acceleration in each gear, using a boating clinome­ter, as discussed in a panel in this article. When you have done this, you need to adjust the potentiome­ters, so that the lamp lights and the buzzer sounds when the requisite speeds are reached. The adjustment is best done by initially setting all pots fully clockwise. Then by driving at the gear change speed (in any gear), adjust the relevant pot slowly anticlockwise until the alarm goes off. This is the setting for that pot. If you only have a 4-speed gear box car or if fifth gear provides less accel­eration than fourth at any speed, then the 4-5 control can be disabled by winding VR4 fully SC clockwise. Gear + + + + 1-2 2-3 3-4 4-5 74  Silicon Chip + Change Indicator Fig.9: at left is the fullsize artwork for the front panel. You can use it as a template for drilling the holes. 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Kit includes CONDITIONS APPLY. DON’T MISS THE PCB, all on-board BARGAINS NOT SHOWN IN THIS AD components, electret ON OUR BARGAIN CORNER PAGES microphone, switches & (UPDATED REGULARLY) OVER 25,000 small surplus speaker.$19 HITS PER WEEK.!!! PC Data Acquisition Unit **********CLEARANCE SPECIAL******** www.ozemail.com.au/~oatley Use the parallel port of your PC as a real UHF AUDIO-VIDEO TRANSMITTER. SOON TO BE (oatleyelectronics.com) world interface. It enables your PC to both Your own mini Tv broadcast station. MODEL TRAIN CONTROLLER KIT: monitor & control external events and Send video from VCR's or $15 Ref: SC Jul 95. Allows two trains to run on devices. The world is a mixed analog & cameras to TVs in your one track, without hitting each other due to digital world. With the appropriate sensors home. Inc. Metal case speed difference. When a train breaks an the PC can monitor physical variables telescopic antenna & leads: IR beam it switches off power to a portion such as pressure, temperature, light 12V operation, tunable (G01) of track, until the other train catches up & intensity, weight, switch state, movement, $20 or $15 with camera purchase breaks another beam at another location. relays, etc, process the information and NEW POCKET SAMPLER DATA It uses a relay to switch sections of track. then use the result to control physical devices such as motors, sirens, other LOGGER KIT FOR PC'S, Fits into a Main PCB: 96 x 66mm, IR Sensing PCB's: db25 housing. Plugs into your printer 59 x 14mm: (K58) $28 relays, servo motors (up to 11) & two port, samples over a 0-2V or 0-20V range, stepper motors :$200 over intervals of 1 hr.-100uS. Useful, to SOLID STATE 4-6A PELTIER EFFECT LASER DIODE POINTER ( Key-chain ) monitor battery charging. Can also be COOLER / HEATER 3 . 3 A <at> 1 4 V P E LT I E R : $ 2 7 , 6 A Very bright small ( 650 nM ) pointer. used as a basic low 5KHz CRO! <at>15VPeltier: $35, both are approx. supplied with 5 extra lens caps that Inc. all on-board 40X40X4mm, temperature controllable produce various patterns, components, by reducing supply voltage /current, will shapes and symbols PCB, Db25 even work from a 1.5V battery!! With data like animals etc. housing & sheet, diagram & circuit for a fridge / $29 software heater. Peltier (K90) $25 effect Device: LASER DIODE MODULE AUTOMATIC LASER LIGHT SHOW KIT: (G02) 12V Same quality module that MKIII. Automatically changes every 5 60 is used in the above secs, & is adjustable. Each motor has 8 laser pointer: $24 *** FANTASTIC BARGAIN *** speeds, one motor is reversible, & one can COMPUTER POWER SUPPLY PCB: stop. Countless great displays from single New assembly. 45 x 108 x 200mm. 120 / HIGH RESOLUTION MONITOR to multiple flowers, collapsing circles, 230V AC input. DC outputs are +5V<at> Brand new 240V rotating single and multiple ellipses, stars, 6A,+ 12V <at> 1A,-12V<at>1A,-5V<at>1A. Data 30cm enclosed etc. No more mirror & motor alignment Inc.RU approval. Mains computer monitor hassles with motor mounting on the PCB input . Be Quick: + video conversion and align with “Allen Key”. Kit includes (Ps6) $12 ea. kit. Gives better PCB, all on board components, three or 4 for $36 resolution than TV! small DC motors, mirrors, precision Limited good qty. IR RECEIVER FRONT END MODULE adjustable mirror mounts : (K83) BARGAIN PRICE. This device contains an IR receiver diode, an amplifier TELLEFUNKEN DUAL GaAs-MES-FET tuned to 38KHz, a bandpass Cf300, LOW NOISE (NF=1.1<at>800Mhz) filter, an AGC section & deWould make extremely low tector circuit. $2 Ea or 10 for $15 noise RF amp (Gps 23db). With brief info. $3 Ea or 5 for $13 PLASMA DISPLAY BALL KIT: High Power High Frequency TRANSISTOR SPECIALS EHT generator that will give an PRO. STUDIO QUALITY REVERB BU-205 exciting plasma discharge with Three spring units. Dim.: 425 x 110 x HIGH VOLTAGE 33mm. Input Z=190 ohms, output Z=2.6 a std light bulb or make Jacobs $2.50 Ladder or Laden Jar & other EHT k ohms, recommended AC drive = 2SD-1554 applications. Can be converted to 6.5 mA. A circuit diagram HIGH VOLTAGE a DC. Supply with a HV diode. of a stereo pre$5.00 Inc. EHT transformer + PCB amp tested **SPECIAL**SPECIAL**SPECIAL** + all on-board parts & 1KV. fast using this FOR $1 EXTRA WITH EACH ORDER Diode + application notes. Req unit:$40(A10) WE WILL SEND A WIRING KIT !!! Great for cars, radios mobile phones, fog **CCD CAMERA SPECIAL 32 & 40mm** 12V <at> 0.5-2A. Special price $29. $29 16KV. Diode $1.50 lights etc. 4 colours, 2 guages of wire, The best "value for money" CCD camera Spade connectors, fuse holders, fuses. on the market! 0.1 lux, High IR response & BRAND NEW STD LCD DISPLAYS 17+ mtrs. of wire. Limited offer!!! just $1 hi-res. Performs better than most cheaper 1 line x 16 char. : $16 models. 42mm With: Pinhole (60deg.), 78 2 line x 16 char. with *** SPECIAL BARGAIN *** LED back-light:$24 12V/7Ah GEL BATTERY BARGAIN deg.; 92 deg.; 120 deg.;$89 Fresh stock of NEW standard battery $25 or 150 deg: $104 NEW HITACHI LASER DIODES 32mmWith: Pinhole (60 40mW / 785 nM For scientific, NEW ! 4Ch. UHF deg.), 78 deg.; 92 deg.;120 medical & industrial applications : LEARNING REMOTE deg.;$110, 150 deg: $125 $65 35 mW / 650 nM : $90 Can be programmed as HIGH QUALITY DC MOTORS a spare for your current *** SPECIAL *** 3V - 8v DC motors with feedback winding BRAKE LIGHT INDICATOR-60 LED KIT remote or to replace up for speed sensing ect. 40mm diameter This kit has two PCB's + current limit to 4 other units and X35mm long $3 combine into 1:(TX1) $39 resistors + 60 LED's to make a very bright UHF DATA TRANSMISSION *** HALF PRICE SUPER SPECIAL*** brake light etc. 600mm long: $15 Stamp sized Xtal locked 433.9MHz Lm338 adjustable ( TO3 package ) 5A superhetrodyne receiver module $25 voltage regulator with internal overload Small matching transmitter kit: $12 protection, + application *********CLEARANCE SPECIAL********* notes for a variable FLUORESCENT LIGHT HIGH 1.2V- 33V 5-20A FREQUENCY BALLASTS New,"slim power supply. line" high frequency electronic ballasts. Half price at Flickerless starting, long tube life, high just $6 Ea efficiency, Dimable. limited stock 1 x 36W or 4 for $16 tube, 28 x 4 x 3 cm: (G09F) just $18 $35 $19 $40 $60 $69 $40 VINTAGE RADIO By RODNEY CHAMPNESS, VK3UG Behind the Lines: A Short History of Spy Radios in WW II; Pt.1 Operating a spy radio within occupied Europe during World War 2 was a risky business. In this, the first of three articles, we take a look at the equipment used and the techniques employed to avoid getting caught. Since World War II, we have seen many films which have shown snippets of the French Resistance and the spy radios that were used for their clandestine activities. These films, although based on fact, were dramatised and were certainly not always as accurate as they could have been. After all, why should the facts spoil a good story! Gathering information about a country that you are at war with and arranging for people behind the lines to create sabotage was considered a legitimate activity by all sides. In Britain, the organisations that were very involved in this activity during World War II were the Special Operations Executive (S.O.E.) and Military Intelligence (MI6). How did these radio transmitter units get into the hands of the Resistance? They were largely flown in by the various air­craft such as the Westland Lysander and the Lockheed Hudson. These aircraft were able to land on makeshift airfields, to drop off materiel and to transport agents in and out of the country. Two and four-engine bombers were used for larger airdrops. The radio operators who used the small radio transceivers were always in considerable danger of discovery. German radio direction finding groups 76  Silicon Chip from the Gestapo had large numbers of receivers with panoramic displays attached to them and could monitor virtually all high frequencies (HF) at the one time. Once a suspect signal was detected, it was then observed on a normal communications receiver and a recording made on a wire recorder. Radio direction finders were also immediately put into operation and a direction obtained from each station listening to the signal. It was normal to use three of these stations to get the direction to a clandestine station. The three directions were plotted onto a map and a small area, called a “cocked hat”, was obtained where the three lines nearly intersected (the direction finding equipment wasn’t accurate enough to have all three lines intersect at the one point). The clandestine radio transmitting station would be within the cocked hat, which was a triangle of about 16km per side. A triangle of this size occurred because the direction finding sta­tions were usually several hundred kilometres away from the transmitter being traced. The main fixed direction finding sta­tions were at Brest, Nuremberg and Augsbourg. Because the radio operator usually only had about three different crystals to control the transmitter frequen- cy, the German monitoring service could easily keep an eye on these fre­ q uencies. When transmissions were again heard they started from the extremities of the cocked hat triangle and took more bear­ings. By this means, often over a period of several days or even weeks, the size of the area that the transmitter was located in would be reduced to something like a triangle of about 200 metres a side. If the clandestine/spy radio operator kept on operating from this location he or she was very likely to be caught. Countermeasures To minimise the chances of being caught, the operator was told to only transmit for very short periods - about 3 minutes maximum - and to shift location regularly. One feature of the early spy radios was the use of a simple two or three-valve regenerative receiver. However, when being used for Morse code (CW) reception, the regenerative detector would radiate enough signal for it to be picked up by any German radio detection groups in the near vicinity. As a result, superhet receivers quickly superseded TRF receivers. Another favourite technique of the Gestapo radio detection groups when closing in on a spy radio installation was to remove the mains power from a building block. If the transmission imme­diately ceased, then it was highly likely that the clandestine radio was located in that block. After that, it was only a matter of time before the operator was found and “suitably dealt with”. To overcome this tactic, many of the later sets were fitted with both battery Fig.1: the 3-valve Paraset featured a regenerative receiver based on detector stage V1 and audio output stage V2, plus a crystal-controlled transmitter stage (V3). The RF power output was 4-5W, while the operating frequency range was from 3-7.6MHz. and mains power supplies and could be switched from mains to battery operation within a second or so. The break in the transmission was so short as to be unnoticeable and this could be a real life saver. The operators also often had what we would call “cockatoos” or lookouts to warn of suspicious activities, so that they could close down quickly. Although the Germans had a very extensive network of listening sets and radio direction finding equipment, not many of the spy radio operators were caught. However, the activities of the radio direction finding troops meant that the agents couldn’t go about their clandestine work in a careless way. If they did, they soon ended up in a German prison, which usually had fatal results. Technical history Obviously, the radio transmitting and receiving equipment used by the resistance radio operators was purpose-built to suit the job in hand. The equipment needed to be: (1). Small enough and light enough to be carried in an incon­ spicuous suitcase. Small enough to fit in a coat pocket was even better and such equipment was available late in the war. (2). Usable with both mains (110V and 230V) and battery supply (usually 6V). (3). Able to change over from mains to battery operation quickly to avoid detection as detailed earlier in the article. (4). Able to transmit on a variety of radio frequency bands between about 3MHz and 8MHz and preferably up to around 16MHz. This meant that communications could be maintained at almost any time of the day or night from anywhere in occupied Europe. (5). Sufficiently powerful to achieve the previous requirement. This usually required 3-30 watts of radio frequency (RF) output. The receiving stations in Britain and elsewhere had sensitive receivers and large antennas. (6). Able to transmit CW (Morse code). Transmitters for Morse code are simpler to make and have a much greater range for the same power than an AM (amplitude modulated) transmitter. Addi­tionally, the voice of the operator would not be recognised by those hunting him/her and Morse code is much more accurately copied than voice transmissions under diffi- cult reception condi­tions. (7). Simple in design and easy to use. (8). Fitted with a non-radiating receiver, which ultimately ruled out regenerative receivers. The receiver did not have to be tremendously sensitive as the transmitters in Britain were rea­sonably powerful at 250 watts. And there was access to a 15 kilowatt transmitter if needed. (9). Maintained accurately on frequency so that the operator at the listening station knew where to look for the signal. This was achieved by using a small selection of quartz frequency crystals. (10). Headphone operation only. Radios were banned in occupied countries, so no “radio” noise could be tolerated. In any case, it was easier to produce sets for headphone operation. The Third Reich did have a number of approved broadcast band only sets which had limited reception range so that stations outside their borders could not easily be tuned. (11). A quiet Morse key. Some were quieter than others and many were enclosed to keep noise down and to make sure the operator didn’t receive an electric shock. SEPTEMBER 1998  77 Fig.2: the 51/1 transmitter used three 6AM5 valves, two to rectify the high voltage from the transformer and the third as the oscillator. The whole circuit operated at half mains supply and this, together with the dangerously high DC voltages that were present at many points, meant that it had to be well insulated from the operator. Did the spy radios achieve all of these ideals? No, but there were a number of really good tries and most of the later sets did incorporate most of the criteria listed above. The sets of the Resistance A number of radios had been developed prior to World War II and the Mark XV transceiver is probably the oldest and best known of its kind. Built around 1938, it weighed in at more than 20kg and certainly wasn’t a lightweight suitcase set. The Mk.XV operated from 3.516MHz and the transmitter had two valves - a 6F6 crystal oscillator and a 6L6 RF power amplifi­ er - which produced an output power of 15-20W. The receiver was a 3-valve regenerative set and had the disadvantage of radiating a signal which proved useful for the German radio location groups. Following on from the Mk.XV was the Paraset transceiver. This set, complete with its power supply, weighed in at around 4.5kg and featured an operating frequency range was from 3-7.6MHz. It was a very simple unit with a 2-valve regenerative receiver based on 6SK7 valves – one used as a regenerative detec­tor and the other as the audio output. Like the Mk.XV, this receiver also radiated a handy signal for the 78  Silicon Chip Gestapo radio detection groups. Because of this, the Paraset was mainly used in country areas where the receiver’s signal would not be detected. The transmitter section was based on a single 6V6 valve, used as a crystal controlled oscillator cum power output stage. The RF power output was of the order of 4-5W and the communica­ tions range was around 800km. Following on from the Paraset were the “Polish Sets”, de­signed and built by a group of Polish civilian refugees. These sets were a considerable improvement over the previous sets and were only surpassed by the British-designed Type 3 Mk.II and the Type A Mk.III later in the war. The BP3 was a relatively large and heavy set that could be operated from either the AC mains or from 12V DC. It covered the frequency range from 2-8MHz and was suitable for both AM and CW operation. It used a 2-valve 30W transmitter stage and a 4-valve superhet receiver. Correct tuning of the transmitter was achieved by observing the meter on the front panel and three neon or incandescent lamps. The AP3 was manufactured in 1943 and weighed about 18kg without the ancillary pieces of equipment that went with it. By contrast, the AP4 was a smaller transceiver which weighed in at about 4kg (including the 120/220V AC power supply). It operated from 2-8MHz using a single valve in the transmitter (with 8W output) and a 3-valve super­het receiver. The correct tuning of the transmitter was accomplished by observing the brightness of a neon and an incandescent lamp. In 1942, SOE (Special Operations Executive) was authorised to build its own sets. The Type A Mk.II was the first transceiver produced and started the trend towards using the more rugged American Loctal valves. This set would appear to be the predeces­ sor of the Type A Mk.III, as many of the features are similar although not as well thought out as in the Mk.III. The Mk.II came as three separate units: transmitter, re­ceiver and power supply. Its operating frequency range was from 3-9MHz and it used a single valve for the transmitter stage and another three valves for the superhet receiver (with a regenera­tive detector). Receivers like this were commonly called “super-gainers” within the amateur radio fraternity. Packed in its suitcase, this set weighed about 8kg. The Mk.II was superseded by the much improved Mk.III which will be described in the third article in this series. The Type 3 Mk.II (B2) and the Type A Mk.III, ar- 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. Call in or send SSAE for our current catalogue The Type 3 Mk.II (B2) was arguably one of the best of the World War 2 spy radios. It was supplied in either a suitcase or in two waterproof steel boxes and consisted of three separate assemblies (more on this set next month). guably the best of the spy radios, will also be described in future articles. Miniature valves From 1944 onwards, sets using miniature valves became available and these sets were much smaller than earlier types. They did not replace the earlier sets like the Type 3 and the Type A however, as each had its own niche in the clandestine radio communications networks. One example was the 53 Mk.I receiver which used some of the first miniature valves and measured just 100 x 89 x 32mm. Its accompanying 110/220V AC power supply was the same size and the combined weight of the two units was just over a 1kg. This was a 3-valve TRF unit with regenerative detector and a tuning range from 3-12MHz. It was quite an achievement to fit the parts into such a small space at that time. Another interesting set is the MCR1 “Biscuit” receiver. It was given the name “Biscuit” because it was delivered in a bis­cuit tin! About 10,000 of these sets were produced and a number made their appearance on the Australian surplus market somewhere around 1947. The MCR1 measured 240 x 89 x 64mm and weighed about 1kg. It cov- ered the frequency range from 150kHz to 15MHz using four plug-in coil boxes, with a gap above the broadcast band. The set is somewhat unusual in that the lowest band tunes from 1501600kHz in one go. I suspect that it used low pass filters in lieu of tuned circuits in the aerial and RF stages to get this tuning range. The MCR1 was a 5-valve superhet and was based on miniature 1.4V battery valves. I understand that it used 1T4s, a 1R5 and a 1S5 and fed headphones. It could be used on batteries or with a separate AC/DC power supply that could operate from 97-250V. Smallest transmitter The smallest transmitter commonly used was the coat pocket-sized 51/1. It measured 146 x 114 x 38mm and weighed 0.6kg com­ p lete with its inbuilt 200/260V AC power supply. It operated from 3-10.5MHz, the output power from the transmitter stage was 3-4W and the transmitter tuning controls were adjusted for maximum brilliance from an inbuilt neon tube. This set was intended as an emergency transmitter, to be used where there was considerable risk attached to using the superior but much more obvious Type A Mk.III or Type 3 Mk.II. RESURRECTION RADIO 242 Chapel Street (PO Box 2029) PRAHRAN, VIC 3181 Tel (03) 9510 4486 Fax (03) 9529 5639 A person carrying a suitcase could easily create some suspicion whereas a transmitter carried in a coat pocket was much less obvious. The set used three 6AM5/CV136 valves, two as mains rectifiers and one as the transmitter oscillator/output valve (Fig.2). Summary In the period from 1941-1945, the equipment used was progressively miniaturised and reduced in weight. Some types like the 51/1 transmitter weighed in at only 600 grams, had a power output of 3W and could be carried in a coat pocket. In general, the transmitters were improved while the receivers evolved from simple TRF regenerative units to high-performance multi-band superhets. The early regenerative receivers were a liability when used for Morse code reception as the oscillating detector could easily be picked up by any radio direction finding equipment in the near neighbourhood. This made capturing a spy radio operator and the equipment a relatively easy task. Next month, we’ll take a close look SC at the Type 3 Mk.II set. SEPTEMBER 1998  79 Are you one of those modern day adventurers who has a van or a “boat” which uses solar panels to keep the batteries charged? The question always is “how full is the battery? Do we watch TV tonight or will it flatten the battery?” This capacity indicator will answer those questions. The 3-digit display shows the available battery capacity in ampere-hours. By RICK WALTERS A capacity indicator for rechargeable batteries What is a battery capacity indicator? It is a monitor which computes the charge, in ampere-hours (A.h), fed into and out of a battery and then shows the result on a 3-digit display. If the battery is fully charged and then put into service, the monitor will thereafter give an indication of the remaining charge avail­able at any time. As presented, the Battery Capacity Indicator is housed in a standard plastic instrument case with a 3-digit display set into the top cover. In this 80  Silicon Chip form it could be wall-mounted to give a permanent display of available battery charge. Yes, that means that it is designed to monitor the charge into just one battery or bank of batteries and once calibrated, it cannot be connected to another battery without the setting up procedure being repeated for this new battery. To do the setup, the top cover of the case is removed to reveal the PC board. First, there is a 2-position slide switch (S1) which has settings labelled “USE” and “CAL”. There is also a red LED and up near the 3-digit display, three tiny pushbutton switches. These are labelled “SET H”, “SET T” and “SET U”. There are just two steps involved in the calibration procedure. In use, the battery to be monitored must first be fully charged and connected to the Battery Capacity Indicator. The 3-digit display must then be set to indicate its ampere-hour capacity. This is done by moving the slide switch (S1) to the CAL setting. The red 3mm LED will light, indicating that you are in setup mode. The SET H, SET T and SET U buttons are now pressed and released in turn until the digits, which continuously cycle through 0-9, display the correct battery capacity. This done, the slide switch is set to USE. From then on the display will count down as the battery is discharged and will count up as it is charged. Brief circuit description Have a look now at the circuit of Fig.1. Essentially, it moni­tors the current into and out of the battery through a shunt resistor of 100mΩ; that’s 100 milliohms or 0.1Ω. IC1 monitors the shunt resistor and its output voltage swing of 0-3V DC represents a current of 0-3A. (If your battery needs to work at higher currents, you will need to use a proportionately lower value of shunt. For example, if you wanted to work over a range of 0-12A, the shunt resistor would need to be 25mΩ to keep the same input voltage range; ie, a maximum of 300mV DC. Q1, IC2 and IC3 form a voltage-tofrequency converter which produces a frequency output of 100Hz/amp. This frequency is fed to pin 8 of the microcontroller (IC4) via transistor Q2. Pin 9 senses whether the battery is charging or discharging. As just explained above, the maximum battery capacity is set by switches S2, S3 and S4. IC4 checks the status of jumpers J1, J2 and J3 and performs the appropriate division to match the input shunt. IC4’s output is on pins 15-18 and is BCD (binary coded decimal). This is fed to IC5, a BCD to 7-segment decoder which decodes and drives the multiplexed 3-digit display. REG1 provides a stable 5V supply for the digital ICs. IC6, Q3 and Q4 provide a -18V supply which is stabilised by REG2 to -12V and REG3 to -5V. As the battery is charged and discharged, the display will change to represent the available ampere-hours in the battery. When the battery discharges below 10% of its capacity, the dis­play will begin to blink, which should catch your eye, warning you that the battery is nearly discharged. Once the hundreds digit reaches zero, it is blanked and the tens digit is Parts List 1 PC board, code 11106961, 155 x 84mm 1 plastic case, 190 x 100 x 40mm (Jaycar HB6036 or equivalent) 1 8MHz crystal 1 slide switch (S1; DSE P7602 or equivalent) 3 miniature pushbutton switches (S2-S4; Jaycar SP0730 or equival­ent) 1 47kΩ 5-pin 4-resistor network (RN1) 1 20kΩ 25-turn trimpot (Altronics R-2384 or equivalent) Semiconductors 1 MAX472CSA current monitor (IC1; available from Veltek) 2 TL071 operational amplifier (IC2,IC3) 1 BCIu programmed micro­ controller (IC4; available from SILICON CHIP for $25 including postage & packing) 1 4543 decoder driver (IC5) 1 4093 quad NAND Schmitt trigger (IC6) 3 HDSPH101 7-segment common anode LED displays (DS1DS3) 1 78L05 voltage regulator (REG1) 1 79L12 voltage regulator (REG2) 1 79L05 voltage regulator (REG3) 1 2N7000 N-channel Mosfet (Q1) 2 BC548 NPN transistor (Q2,Q4) 1 BC558 PNP transistor (Q3) 7 1N914 diodes (D1-D7) 1 10V 500mW zener diode (ZD1) 1 3mm red LED (LED1) Capacitors 2 100µF 25VW PC electrolytic 5 100µF 16VW PC electrolytic 1 0.1µF MKT polyester 3 0.1µF monolithic ceramic 1 .018µF MKT polyester 1 .01µF MKT polyester 1 .0022µF MKT polyester 2 22pF NPO ceramic Resistors (0.25W, 1%) 1 1MΩ 4 10kΩ 2 120kΩ 1 2.2kΩ 2 100kΩ 1 1kΩ 3 47kΩ 3 470Ω 1 33kΩ 2 220Ω 2 22kΩ 1 100Ω Miscellaneous 1 18-pin IC socket (IC4) 1 14-pin wire wrap IC socket (DS1-DS3) 1 16-pin wire wrap IC socket (DS1-DS3) 3 PC stakes 2 mini shunt 4 3mm x 6mm screws 4 3mm x 10mm countersunk screws 4 3mm flat washers 4 3mm toothed washers 4 3mm x 12mm threaded spacers also blanked once the display counts below ten. This information is fed to pins 9 & 10 of IC4. Detailed circuit description Voltage-to-frequency converter The heart of the monitor is a new IC from Maxim (a MAX472) which amplifies and converts the current flowing through a shunt resistor at its input to an output voltage across a load resis­tor. The voltage across this resistor is directly proportional to the current through the shunt. What’s more, the output voltage is always positive, although the shunt current obviously reverses direction depending upon whether the battery is being charged or discharged. The direction of the current is indicated by the voltage at pin 5 of this IC, being zero when the battery is charging and +5V when it is discharging. IC2, IC3, Q1 and their associated components form a vol­ t age-tofrequency converter. The output voltage from pin 8 of IC1 is applied to the inverting input (pin 2) of IC2. This IC has a .018µF capacitor connected from its output to this input, while its other input is at ground potential. The positive voltage at the output of IC1 will tend to pull pin 2 of IC2 high through the 120kΩ resistor, but its output (pin 6) will swing negative to hold the potential at pin 2 the same as pin 3 (ground) via the .018µF capacitor. The outcome of this is that the output of IC2 ramps down at a linear rate towards the -12V supply. SEPTEMBER 1998  81 82  Silicon Chip IC2’s output is fed through a 47kΩ resistor to the invert­ing input of IC3 which is used as a comparator. The non-inverting input is fed from the CAL control VR1 which can set the potential at pin 3 between -3V and -5V. When the voltage at pin 2 reaches this preset level, the output of IC3 (which was low because the inverting input was higher than the non inverting input) will swing high (+12V). The 1MΩ resistor from the output to the non-inverting input applies positive feedback which makes this output transition more rapid. This high output at pin 6 is fed via D1 and the 10kΩ resis­tor to turn on Mosfet Q1. The .018µF capacitor is discharged through the 100Ω resistor and the 120kΩ resistor from IC1 which was connected to the input, is now effectively connected to IC2’s output where the voltage from IC1 can have no effect. Thus IC2 becomes a unity gain buffer and its output will sit at the potential of the non-inverting input (ground). Once this happens, the comparator output will swing low (-12V) again and D1 will cease conducting. The .0022µF capacitor which would have charged to +10V now discharges through the 100kΩ resistor and when it reaches Q1’s gate threshold voltage the Mosfet will turn off and the cycle will begin all over once more. The 10V zener diode (ZD1) protects the gate of Q1 from excessive voltage. It also acts as a voltage clamp for the .0022µF capacitor. The net result is that IC2 & IC3 oscillate at up to 300Hz, depending on the current through the input shunt resistor. Each time the output of IC3 swings high, it turns on Q2 and its collector is pulled down to ground. This negative edge of this 5V transition is recognised by IC4, as will be explained later. Power supply The battery and the external charger are used as the posi­tive supply for the operational amplifiers and the 3-terminal regulator REG1 provides Fig.1 (left): the circuit monitors the current into or out of the battery and displays the battery charge in ampere-hours on the 3-digit display. a stable +5V supply for the digital circuitry. We use IC6, a 4093 quad Schmitt trigger, to generate the required negative supply rails. IC6a is connected as a Schmitt trigger oscillator, with its operating frequency determined by the 22kΩ resistor and .01µF capacitor. Its square wave output is buffered by IC6d before driving transistors Q3 & Q4 and is also buffered by the paralleled gates, IC6b & IC6c. This is done to provide plenty of current drive for the following rectifier stage. This works as follows. When the output of IC6d (pin 11) is high Q4 will turn on, pulling the 100µF capacitor at its collector to ground. When pin 11 is low, Q3 will be turned on and the 100µF capacitor will be pulled up to the battery voltage (+12V). The paralleled outputs of IC6b & IC6c feed the square wave to D2 and D3 through another 100µF capacitor. D2 conducts each time the negative side of its capacitor tries to swing positive and clamps the potential at the anode of D2 and the cathode of D3 to +0.6V. When the square wave swings negative, D3 will conduct and pull the negative end of the capacitor at the junction of D3 and D4 low and at the same time Q3 will be turned, on pulling the positive end towards the battery potential. Thus, this capacitor should be charged to roughly twice the battery voltage. The next time pin 11 swings high Q4 will turn on, holding the positive side of the electro at ground and causing D4 to conduct and charge the 100µF capacitor at the input of REG2. Unfortunately, we don’t get twice the battery voltage, due to diode voltage drops, transistor voltage drops and so on but you can expect around -18V at the input of REG2 with a 12V bat­tery. SILICON CHIP This advertisment is out of date and has been removed to prevent confusion. Silicon Chip Binders REAL VALUE AT $12.95 PLUS P&P Microcontroller Some readers may be disappointed that we have used a micro­controller for IC4 but be assured that it would have been almost impossible to include all the functions that we have, using discrete integrated circuits. We certainly would not have been able to fit it all in the plastic case that we have used. The main details of the micro­ controller program are out­lined in a separate panel in this article entitled “Main Program Subroutines” (if you want the full listing, it will be ★  Heavy board covers with 2-tone green vinyl covering ★  Each binder holds up to 14 issues ★ SILICON CHIP logo printed on spine & cover Price: $A12.95 plus $A5 p&p each (Australia only) Just fill in & mail the handy order form in this issue; or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. SEPTEMBER 1998  83 available on floppy disc from the Silicon Chip offices at $10 including p&p). The software consists of four main routines, CAL (calibrate), JSET (jumper settings), COUNT and BLINK. After carrying out each of these routines it jumps back to CAL which starts the whole sequence all over again. This microcontroller has three sets of input/outputs known as ports. Port 0 has three pins, P00, P01 and P02, which can be programmed all as inputs or all as outputs. We have assigned these as outputs to turn on the display digits. Port 2 is able to have each pin set individually as an input or an output. It has been set up with P20-P23 as outputs which supply BCD informa­tion to the decoder, IC5. P24-P27 have been programmed as inputs. The Port 3 lines can only be used as inputs but here we have the choice of digital inputs or analog inputs if we switch them to the non-inverting inputs of two comparators. In analog mode, the P33 input is switched to the inverting input of both comparators. This allows us to carry out A-D (analog to digital) conversions and so on. Calibration (call CAL) IC4’s pin 4 (P27) is normally pulled high by the 47kΩ resistor. When slide switch S1 is set to CAL, the port is pulled low and LED1 is lit. The LED is a reminder to make sure you don’t leave the switch in the CAL position as the unit will not count in this mode. P24, P25 or P26 which may have been held at ground by having jumpers J1-J3 fitted will now be pulled high by the 47kΩ resistors as the 22kΩ pullup resistor reverse-biases diodes D5, D6 & D7. When P27 is low, the micro scans P24, P25 and P26 in turn, checking whether they are high or low. A port can only be low if the SET switch for that port is pressed. Once it finds a low port it begins to increment the digit for that display. Each display digit is individually set until the fully charged battery capaci­ty is shown. Switch S1 should now be moved to USE. This allows P27 to be pulled high again and any ports with jumpers fitted to be pulled low. Divider (call JSET) Fig.2: the component layout for the PC board. IC1 is a surface-mount type on the copper side of the board. The second subroutine checks to see which jumpers (if any) are fitted. This goes back to the input requirements of IC1. It’s not much use fitting a 600A shunt if you only intend to draw 8-10A from the battery as the output from Resistor Colour Codes  No.   1   2   2   3   1   2   4   1   1   3   2   1 84  Silicon Chip Value 1MΩ 120kΩ 100kΩ 47kΩ 33kΩ 22kΩ 10kΩ 2.2kΩ 1kΩ 470Ω 220Ω 100Ω 4-Band Code (1%) brown black green brown brown red yellow brown brown black yellow brown yellow violet orange brown orange orange orange brown red red orange brown brown black orange brown red red red brown brown black red brown yellow violet brown brown red red brown brown brown black brown brown 5-Band Code (1%) brown black black yellow brown brown red black orange brown brown black black orange brown yellow violet black red brown orange orange black red brown red red black red brown brown black black red brown red red black brown brown brown black black brown brown yellow violet black black brown red red black black brown brown black black black brown Table 1: Current Division Ratios Shunt Imax Pre Main Jumpers Required 100mΩ 3A /18 /200 J2 + J3 25mΩ 12A /18   /50 J1 + J3 10mΩ 30A /18   /20    J3 2.5mΩ 120A /18    /5    J2 1mΩ 300A /18    /2    J1 0.5mΩ 600A /18    /1   none IC1 will be only 10% of 3V and temperature and component tolerances may affect the accu­ racy. Once the input current range is selected and a suitable shunt connected, the matching jumpers must be fitted. The micro scans P24, P25 and P26 and calculates the division ratio JDIV (1 - 200) listed in Table 1. Counter (call COUNT) The counter is a register in IC4 which is pre-loaded with a value of 1800. Each time a negative transition occurs at P31, an interrupt is generated (see panel entitled “Interrupts – Programmable Dividers”). The micro then looks at the voltage at P32 to see whether the count represents a unit of charge (low) or a unit of discharge (high). A count is then added to or subtracted from the total. When the register reaches 3960, a count is added to COUNTC (the charge counter). If it reaches zero, a count is added to COUNTD (the discharge counter) and then it is reset to 1800. But why 3960 and not 3600? When a lead acid battery (and probably all others) is charged you can never get as many A.h out of it as you put into it. We have been given figures from 10-20% less. To make the reading conservative (we’re sure you would rather have more A.h than indicated rather than less), we elected to allow 1800 + 20% x 1800 + 1800; thus 3960. COUNTC and COUNTD are continually compared with JDIV and once either reaches the value of JDIV, a count is added to or subtracted from the display. P33 is not used and is tied to P32 as this was a lot easier than taking it to ground when laying out the PC board. Blink (call BLINK) As mentioned earlier, once the display shows the battery has less than 10% of its maximum capacity, This is the view inside the completed prototype. The three small pushbuttons at top right are used to set the full battery capacity, after which the unit will indicate the available charge. it will begin to blink. This is done in this subroutine where the displayed values are compared with the blink values and if the displayed digits indicate less, then the display is made to blink by loading the decoder with a value of 10, which causes the display to be blanked. Multiplexer The display digits are multiplexed (sequentially switched) to eliminate the need for three BCD (binary coded decimal) to 7-segment decoders and 12 BCD output lines on the micro­ controller. The BCD value to be dis- played is loaded into P20-P23 and this is decoded by IC5 and applied to the appropriate segments of the display. The relevant P0 output is then taken high to display the value. One millisecond later, the next P0 value is loaded and the next BCD value is output. The 4543 was chosen as it displays a horizontal bar at the top of the six and the bottom of the nine which our old favourite, the 4511, doesn’t. The multi­plex­ing is done at a 1ms rate and due to the persistence of vision of the eye, the digits all appear to be lit at once. The Hewlett Packard displays that are used give high brightSEPTEMBER 1998  85 Check the continuity from each track to the IC pin with a multimeter, as it can look like the joint is soldered when it is really open circuit. The wire-wrap sockets for the displays should now be fitted. Cut each socket in half and use one 14-pin and one 16-pin section for each row. The tops of the LED displays, when they are seated in the sockets, should be adjusted so that they are 19mm above the PC board. This done, solder the four corner pins and check that everything is square before soldering the other 26 pins. The displays should be recessed about 1mm from the front of the case when the board is mounted on the 12mm spacers specified. We fitted a piece of neutral density Polaroid, which is 0.5mm thick, in front of the displays. If you plan to use any­thing else, you may have to vary the distance from the PC board to the front of the displays. Finally, recheck the polarity of all diodes and capacitors, and the orientation of the ICs against the overlay diagram. DO NOT fit IC4 at this stage. Testing Fig.3: check your PC board against this full-size etching pattern before installing any of the parts. ness at very low currents and should not substituted with any other type. Assembling the PC board The first step is to inspect the copper pattern against the artwork pattern of Fig.3. Fix any faults before proceeding. Next fit and solder the 17 links, followed by the resistors, diodes, the socket for IC4 and the integrated circuits. Keep adding parts in ascending height order. There are two components to be mounted on the copper side of the board. The first is a 0.1µF monolithic ceramic capacitor between pins 5 and 86  Silicon Chip 14 on IC4. There are round pads to solder the leads to and also to help you identify the correct pins. The second is IC1, the surface-mount MAX472. First, you must fit the finest tip you own to your soldering iron and pre-tin the pads on the board. This done, position the device on the pads, with the dot which indicates pin 1 adjacent to the 1 numeral etched in the copper. Hold the IC with tweezers or place a finger on it, then solder pin 8. Next, get it centred on the pads and solder pin 4. Once you are satis­fied that it is located properly, solder the other pins. To test the unit you will need a power supply or a 12V battery. Connect a link between the LOAD and the BATT+ pins on the lower edge of the PC board. Then connect the 12V supply to the BATT+ and BATT- pins and measure the current. It should be about 20-25mA. Measure the following voltages (all with respect to BATT-): +5V on pin 16 of IC5 and pin 5 of IC4, +12V on pin 7 of IC2 and IC3 and pin 14 of IC6, -12V on pin 4 of IC2 and IC3 and -5V at the output of REG3. If all voltages are within 10% they are acceptable. Disconnect the power supply. Fit IC4 into its socket, making sure that pin 1 is towards the centre of the PC board. Reconnect the power supply and set S1 to CAL (if it is not already) and the LED should light. The displays should show 315. Holding down the SET H button should cycle the hundreds digit, the other buttons should do the same for their respective digits. Set the display to show 025 and switch S1 to USE. The hundreds digit should blank. If 005 is set both digits should blank. Disconnect the power supply again. Remove the link and wire a 4.7Ω resistor across the LOAD and BATT+ pins. Do not fit any jumpers to J1, J2 or Main Program Subroutines The main program consists of four subroutines: MAIN: call CAL call JSET call COUNT call BLINK jr MAIN ;See if calibrate switch is set ;Look at jumper settings ;See if count needs updating ;Blink the display if under-range ;Do it all again The following is extracted from the assembler listing. It can be written with any word processor that can save as an ASCII text file. The semicolons at the beginning or anywhere in a line indicate to the assembler that the rest of the line is a comment and should be ignored. ;Calibrate updates the display to show the maximum battery ;capacity. This can only occur when S1 is set to CAL ; CAL: ld TEMP,P2 ;If bit 7 is low S1 has been set to and TEMP,#10000000b ;calibrate jr NZ,CALEND ;If calibrate not required - exit clr BLKFLG ;If the display is U/R stop the blink cp REGH,REGD ;If the hundreds digit is blanked jr NZ,CALOOP ;then unblank it and display zero ld REGH,#00 ;If the hundreds are not blanked CAL10: cp REGT,REGD ;then the tens cannot be blanked jr NZ,CALOOP ;If the hundreds are blanked ld REGT,#00 ;then check the tens display CALOOP: ld TEMP,P2 ;while in CAL mode keep and TEMP,#01110000B ;looking at the pushbuttons cp TEMP,#96 ;If button SETH is pressed jp Z,SETC ;set the value of hundreds cp TEMP,#80 ;If SETT is pressed jp Z,SETD ;set the value of tens cp TEMP,#48 ;If SETU is pressed set value jp Z,SETU ;for units CALCON: ld TEMP,P2 ;If bit 7 is still low S1 is and TEMP,#10000000b ;still set to calibrate jr Z,CALOOP ;look at pushbuttons again ld BLINKT,REGH ;Then load one tenth of hundreds max ld BLINKU,REGT ;& 1/10 of tens max in blink registers cp REGH,#00 ;If the hundreds digit displays zero jr NZ,CALCLR ;then blank it, and if it is blanked ld REGH,REGD ;check to see if the tens digit is cp REGT,#00 ;displaying zero. If so then also jr NZ,CALCLR ;blank the tens digit ld REGT,REGD ; CALCLR: ld COUNTPH,#%07 ;Set the prescaler to its median ld COUNTPL,#%08 ;count of 1800 clr COUNTC ;and get rid of any counts which may clr COUNTD ;have accumulated in these registers ld REGCH,REGH ;Then load the maximum capacity ld REGCT,REGT ;registers with the count values ld REGCU,REGU ;for the fully charged display CALEND: ret ;and return J3. Reconnect the power supply. The display should show 315 and after about 18 seconds should indicate 314 and continue to count down. What we are doing is monitoring the current drawn by the unit itself, using a very high (by comparison) value of shunt resistor. The fact that the display is counting down indicates that the unit is discharging the battery or power supply you are using. If you now carefully ground pin 9 of IC4, the unit will count up until it reaches 325 and then stop. This only occurs if you don’t set the display to a different value. Once you set it, to say 275, the reading will never go above this value and the display will begin to blink at 10% of the value you set (in this example 27). Calibrating The final step is to calibrate the voltage to frequency converter. For this you will need a 5.6kΩ resistor, a 2kΩ vari­able resistor, an accurate multimeter and a frequency counter. Connect the resistors in series, with the 5.6kΩ resistor connect­ed to the +12V supply and the 2kΩ variable to the 2.2kΩ resistor at the output of IC1. Adjust the variable resistor until the voltage across the 2.2kΩ resistor is exactly 3V. Now adjust VR1 until the frequency at pin 6 of IC3 is 300Hz. VR1 is a calibration control. If you SEPTEMBER 1998  87 Interrupts – Programmable Dividers The frequency of the crystal at pins 6 and 7 of IC4 is divided by 2 for the internal clock and by 8 for the internal timers. In this device there are two pre-scalers which can divide by any ratio from 1 to 64, and two programmable dividers with ratios from 1 to 256. Each pre-scaler is connected to a divider so we can get division ratios from 1 to 16,384. This means that with our 8MHz crystal we can program internal frequencies from 1MHz to 61Hz. If we program a pre-scaler to divide by 50 and a divider to divide by 20 we end up with a frequency of 1kHz (1ms) which is used to step the multiplexer. What’s more we can cause the micro to execute a certain subroutine (interrupt) each time the divider counts down to zero. Put very simply the processor stops whatever it is doing and begins executing the interrupt program. The code for the multiplex display interrupt is shown below. On the final line, iret (Interrupt RETurn), means go back to what you were doing before the interrupt occurred. ;MPX is T0, the multiplex timer, set to switch the digits ;sequentially once per millisecond ; MPX: push RP inc BLINKC ld P2,REGD rl REGC cp REGC,#08 jr NZ,MSTEP ld REGC,#01 ld POINTER,ΩREGD MSTEP: ld P0,REGC inc POINTER ld P2,<at>POINTER cp BLKFLG,#00 jr Z,MEND cp BLINKC,#30 jr LT,MEND ld P2,REGD MEND: pop RP iret find that your battery still has a reasonable capacity when the display reading is low, turn it clockwise one turn and see what improvement this makes in due course. This makes the V-F converter run slightly slower, which will indicate a lesser discharge SIL CH IC O IP N ; ;Add one millisecond to the blink counter ;Blank display before stepping to next digit ;Step to the next digit ;If it points past the units digit ;set it to point to the hundreds ;Then get the data back in synch ;with the digits ;Display the desired digit ;and the corresponding data ;If the blink flag is reset ;do the normal display ;but if it is set and the ;blink counter has accumulated ;30ms or more then blank ;the display for the remaining ;200 odd milliseconds ; and thus indicate a larger reserve. Once all the checks are satisfactory, remove the 4.7Ω resistor and mount the spacers in the case using the countersunk screws, then mount the case on the wall or wherever and retain the unit in the case using 3mm screws. Am per eH ou rs B CAATTE IND PA RY ICACITY TO R Fig.4: here is the full-size front panel artwork. 88  Silicon Chip Normally you will set the maximum battery capacity and put the top on the case but you could drill three small holes in it above the setting switches and a small slot above the slide switch, maybe even mounting the LED on the full length of its leads so that it just protrudes through the cover. The battery capacity could then be set without removing the top. Three leads must be run from the indicator: two to the battery and one to the load end of the shunt. For obvious reasons, the shunt must be very close to the battery. The big decision is what value of shunt to use. If you were using the indicator to monitor a car battery, then even if your starter motor draws 600A for 5 seconds, this is less than 1 A.h, and if you choose a 30A shunt the loss of an ampere-hour is insignificant. Obviously the shunt must be able to carry this high current without damage. Of course, if you started the motor 10-15 times a day then the error becomes significant. Only you can make the decision. Once you decide on the shunt, you must fit the appropriate SC jump­ers on J1-J3 to match it. 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. Changes to multipurpose battery charger I have assembled a Multi-Purpose Battery Charger (as de­scribed in the February & March 1998 issues) from a Dick Smith Electronics kit. While most of the late changes found their way into this kit, the instructions specified 20 turns on L1, although this has been amended to 10 turns in the Errata in the May 1998 edition of the magazine. Modifying the coil at this stage is likely to be messy. What is the effect if the coil is left at 20 turns? The four times increase in inductance should not be critical but does the ferrite core saturate? I have some other comments on the project: (1) The ver­satility could have been improved if one or two other battery voltages had been included. You and your advertisers promote the charger for “radio control” purposes but it is suitable neither for 4.8V NiCd receiver batteries nor 8.4V (7-cell) NiCd batter­ ies, the most common configuration for electric model aircraft. Using the sixth position on the multi-position voltage selector switch could have accommodated one or other of these voltages. Jump starting modern cars I understand that when jump-starting modern cars (with sensitive electronic equipment), it is desirable to place a filter across the battery terminals of the car being started. As I understand it, the filter is to protect the car’s electronic equipment. I would be grateful if you could let me know if you have further information on this. In particular I would like to see the filter circuit that has been used. (B. T., , Shelley, WA). •  We do not know of any filter (2) Describing the charger as delivering almost 6A is misleading. What is the relevance of RMS current to battery charging? Charge is the integral of current with respect to time, so average (arithmetic mean) current is the only relevant measure. Referring to the formulas in the Philips data sheet, the fast charge cur­rent with the circuit values shown is about 3.1A (average). So the claims of charging a 1.2Ah battery in under 15 minutes are fanciful. (3) The series pass transistor (Q1) is operated in switching mode. It is surprising to find no resistor between base and emitter. This is usually included to provide a discharge path for base charge and speed up the turn-off characteristics, thereby reducing power dissipation in the device. Is there a reason why it has been omitted in the present case? (K. H., Glen Iris, Vic). •  The 20 turns on inductor L1 can be left as is unless you are having problems with the charger operating correctly. The core will not saturate with 20 turns in place. Although we attempted to produce a truly multi-purpose charger (hence the name) it is not possible to cater for every­thing. You can of course readjust the divider resistors on the which could be effective when connected across a car battery. Nor do we know of any special requirement for jump starting modern cars, apart from the typical procedure set out in the instruction manual regarding the final connection via the vehicles’ chassis. Jump starting should not damage a car’s electronics but it may be necessary to reload the identification number (PIN) for the radio to work again. Also in some cars where the engine management or transmission has a “learning” capability, it may be necessary to drive a reasonable distance for the car to relearn your driving habits. voltage selector switch to suit your application. For a 4-cell battery (4.8V), use a 33kΩ resistor between the junction of the 100kΩ resistor and the 10kΩ resistor at pin 19 of IC1 and the new 4.8V selection on switch 5a. For an 8.4V battery (7 cells) use two 33kΩ resistors in parallel. RMS current is crucial to battery charging since it is this value which provides the charging energy. In virtually every battery charger except one charging at pure DC, the RMS current will be much higher than the average current. To calculate the charging energy you need to take the integral of the RMS current over time. The formulas given in the Philips data do not strictly apply for our circuit design since the charging current results from a full-wave rectified AC source rather than DC. We have verified that a 1.2Ah battery can be charged in about 15 minutes and this was also verified by the Dick Smith Electronics kit department staff who built their own prototypes. There is no need for an external resistor between base and emitter of the series pass transistor. This is because the TIP147 already has a nominal 4.7kΩ resistor incorporated between base and emitter. AC camera supply wanted A couple of months ago my AC power adapter for my camcorder packed up. I have built a NiCd battery charger since then and it works quite well but I don’t have an AC supply to run my camera. I have built up a couple of power supplies but they both have the same problems of overheating. I have tried several output tran­sistors like MJ10012 & TIP2955 but they all suffer from the same problem. I was browsing through some back issues and came across the 2A SLA battery charger of July 96. This looked very interesting to me, as it was a switchmode design which SEPTEMBER 1998  89 Command decoder won’t fit I have followed your articles on Command Control with great enthusiasm and have purchased kits for the encoder and decoders. The only trouble is, now that I have the encoder PC boards in my hot little hands, I realise that I can’t fit them into my locomo­tives. They are 48-class diesels (NSW outline, HO scale). I noticed that the lead photo for this project, showing an array of NSW locomotives, included a couple of 48 class locomotives so I had automatically assumed that the decoder would fit into them. It’s just not possible. I think I will have to return the kits. What do I do now? (E. D., Dooralong, NSW). •  By any standards, the 48-class is quite a small diesel loco and its plastic body is largely filled by the heavy diecast chassis, so you really are up against it. We’re afraid that when the lead photos were taken for that story, the requirement was for any array of locos that “looked good”. No-one had a second thought about whether the decoders would fit into all those locos. We apologise for that. looks capable of providing 7.2V at the necessary current. Can you tell me if this idea will work and what alterations will be necessary? If not, have you designed or printed anything along these lines? I don’t want anything elaborate, just a straightforward power supply of 7.2V and enough current to run my camera. (K. L., Tweed Heads South, NSW). •  As we understand it, you actually need a 7.2V DC supply for your camcorder and this could be provided by a circuit we pub­lished in the May 1992 issue, called “The Eliminator”. This was used in conjunction with a 12V DC plugpack and employed an LM317 adjustable regulator to provide a number of selectable output voltages. This circuit could be easily modified to provide close to 7.2V. It should be capable of delivering 500mA or so which should be adequate for your camcorder. 90  Silicon Chip Even if you were using a commercial DCC encoder with a surface mount PC board, you would be up against it in trying to fit it into a 48-class. However, all is not lost. Most modellers tend to run their locos with at least a small “consist” of roll­ing stock and typically, the 48 would pull at least five or six wagons. The solution is to permanently couple a wagon to the loco and it can contain the encoder board with space to spare. Some modellers have taken the same approach when adding our “Diesel Sound Simulator” to their locos. It makes it much easier to fit the sound board and the small loudspeaker. Yes, it does mean that you won’t be able to operate your 48-class locos as “light engine” (ie, running by themselves) but in most layout operations that should not present a problem. A similar problem occurs with British outline HO model steam locos. Since the loco itself has very little space inside, the motor is mounted in the tender (ie, tender drive). Again, in this situation, the only practical way to add Command Control or DCC encoders is to install them in a permanently coupled wagon or carriage. Speed control for fast fridge Could you advise if the 12/24V speed control circuit de­scribed in the June 1997 issue would be suitable to run a large 12V camping fridge from a 24V supply in a 4WD vehicle that will be travelling in Northern Australia for two months. Once they have gone there is not much I can do, so I have to make something that is as close as possible to “bullet proof”. The fridge draws 7A and will be running 12-14 hours per day. My friend will also want to run three or four 12V fluoro units. There may be short periods of time that 15-18A will be drawn by other stuff, like tyre pumps, etc. If you feel this design is not suited, can you suggest an alternative that may do the job? (T. C., Grovedale, Vic). •  The speed control is certainly up to the task of running the fridge from 24V but we’re not keen on using the same speed con­trol for all the other tasks. A better approach would be to dedicate one speed control for the fridge and another for the lights, etc. That way, there is less risk of being without the fridge if the speed control circuit is blown. Multiple windings for 600W inverter I have an enquiry regarding the 600W DC-DC converter de­scribed in the November 1996 issue of SILICON CHIP: can the transformer have multiple windings? I would like to use an ampli­fier module that has the output and driver stages powered sepa­rately. I am assuming that the primary winding is for 12-14V. Is this the case? (L. W., Prospect, Tas). •  The transformer could have multiple centre-tapped secondary windings but only one secondary winding would have the feedback connected and would be the only one to be precisely regulated. The primary winding is for 12-14V, as you suggest. NiCd discharge indicator Would you please illustrate for me and other readers who may be interested, a circuit for a warning light to illuminate when an individual NiCd cell in a bank of cells is approaching full discharge. I use five NiCds in series to externally power some 6V electronic devices (radio, CD player and tape player) and as always, one cell discharges first and if I am not careful, it gets driven beyond full discharge. I would favour a circuit that powers an OK green light which would go out and be replaced by a red light which would come on when total battery voltage falls below say 5.5V, or whatever you recommend, when under load. (J. A., Casuarina, NT). •  Your requirement to individually monitor all the NiCd cells in a pack of five is a fairly tall order. It means that you need separate window comparators for each cell and with two op amps per window comparator, that means a total of 10 op amps and then you would need LEDs to provide the warning indication. There may be simpler ways of doing this but they Explaining logic conventions I am writing with regard to your article on Command Control in the May 1998 issue, of which I have enclosed copies of pages 62, 68 and 69. Please could you explain what Table 1 and Table 2 mean? And what does “pins tied high or tied low” mean? Also how are they “hard wired?” Could you supply a diagram or a couple of examples of how to wire the receiver/decoder channels? (C. B., Ferntree Gully, Vic). •  In general, whenever a pin is said to be tied “high” it is connected to the positive supply rail for that are not immediately obvious. Since you say that one cell is always in danger of being driven beyond full discharge, we wonder if your problem is really one of cell mismatch. When you discharge a pack of cells, they should all come down more or less evenly to around 1V/cell or 5V for a 5-cell pack. If, when you do this, one cell is a good deal less than 1V or worse, is reverse-charged, then clearly that cell is faulty and should be replaced. We have published a number of NiCd cell dischargers which will discharge a pack to 1V per cell and then stop. The relevant projects in question were: Automatic NiCd Discharger, November 1992; and Automatic NiCd Discharger, September 1994. In addition, we published a Single Cell Discharger in May 1993. We can supply the above back issues for $7.00 including postage, except the November 1992 issue, in particular chip. So in the decoder, tying a pin high means that it is connected to the +5V rail. In this case, the relevant pins are “hardwired” by soldering a small link of tinned copper wire (or a resistor pigtail) from the relevant pin to pins 5 or 16 (ie, +5V; high) or pins 8 or 14 (ie, 0V, low). For example, if you wish to wire your locomotive decoder for channel 3 operation, tie pins 9 & 10 to pins 8 or 16 and tie pins 1 & 15 to pins 5 or 16. In this case, it would be easy to bridge across between pins 15 & 16 and then just have one link to connect pin 1 across to pin 16. We hope this makes the concept a little clearer for you. which case we can photocopy the article for $7.00. Using the HEI in twin-coil systems As the building and successful installation of the original SILICON CHIP High Energy Ignition into my Nissan Patrol marked my entry into the world of electronic kits, I read with interest about the new improved universal system in the June 1998 issue. It looked ideal for improving the spark on my modified motorbike. Unfortunately, despite having the feature of “twin points input for twin coil engines”, further reading revealed that this was for use on 2-stroke twin-cylinder engines. Foiled again! But there neatly boxed in was the answer in the Multi-Spark CDI, designed for 2-stroke and 4-stroke engines in motorbikes” as published in the September 1997 issue. A back issue was obtained and I sat down, ready to make out the shopping list, but despite reading the article many times, I cannot see how the unit can be used on 4-stroke motorbikes. Is this false advertising by SILICON CHIP or a lack of understanding on my part? My problem is that, like most Japanese bikes, mine has twin coils with each one triggered by a separate reluctor pickup and firing two plugs simultaneously, one on the compression stroke and the other on the exhaust. Even if a dual reluctor pickup assembly was constructed, there is still the problem of only a single coil output. As the system is in two sections, would it be possible to duplicate the capacitor switcher circuit for each reluctor/coil and run them off a single high voltage inverter? Or is there an easier answer? With cost and space consideration, building two complete units is not really feasible. (M. H., Wembley Downs, WA). •  As far as we can tell from your accompanying diagram, your existing bike ignition system effectively comprises two ignition systems, one for each coil and separately fired by reluctor. If this is correct, the only way to build an equivalent system would be to build two high energy systems or two multi-spark CDI sys­tems. We would not recommend the building of the high energy system, as described in June 1998, as it is unlikely to give any more output than the original equipment on your bike. You could build two multi-spark systems but there is little point unless your bike’s modifications are likely to require an increased spark. Such modifications could include porting and polishing, higher compression ratio or supercharging. 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. SEPTEMBER 1998  91 3 1 2 GREAT REASO SUBSCRIBE NO Every new or renewing subscriber* between now and June 30 gets a FREE copy of the superb SILICON CHIP/JAYCAR Wall Data Chart. THAT’S WORTH $10.95 ALONE! Every new or renewing subscriber* between now and June 30 qualifies for an EXCLUSIVE 10% discount on ANY SILICON CHIP merchandise: books, software, EPROMS & microprocessors, binders, back issues, etc 92  Silicon Chip * This offer applies to Australian subscribers only ONS TO OW TO 3 The best reason of all: you’ll actually save money! Not only will you get your copy of SILICON CHIP BEFORE it’s on the news-stands – it’s cheaper getting your copy mailed direct to you – and you’ll never miss an issue! HURRY! TAKE ADVANTAGE OF THIS STRICTLY LIMITED OFFER TODAY! Yes Please! I want SILICON CHIP delivered every month to my letterbox and I want to take advantage of the exclusive subscribers’ offers. Name............................................................................................. PLEASE PRINT Address.......................................................................................... ....................................................................Postcode..................... ❑ New Subscription (month to start....................................) ❑ Renewal (Sub No from wrapper.......................................) I want ❑ One Year <at> $59 ❑ Two Years <at> $112 or ❑ 1Yr with binder <at> $72 ❑ 2 Yr with binders <at> $138 This is a YES! This offer also applies to GIFT SUBSCRIPTIONS: Call SILICON CHIP to place your order for a gift subscription. Here’s how to order: or or Fax this coupon (or a copy) to SILICON CHIP on (02) 9979 6503 – 24 hours a day Post this coupon (or a copy) to SILICON CHIP, PO Box 139, Collaroy, NSW 2097 You can even order by phone with your Bankcard, Mastercard or Visa Card: Call SILICON CHIP on (02) 9979 5644 9am-5pm, Monday to Friday FAX or POST ORDERS: Card No: Expiry Date:_______/_______ Signature:__________________________ (Yes, we do accept cheques or money orders by post!) March 1998  93 MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. FOR SALE SPEAKERWORKS: specialist in speaker repairs and par ts. DIY refoam kits: 3 1/2 ", 4", 5", 6", 7", 8", 9", 10", 11", 12" and 15" $39.95. Includes shims, dustcaps and adhesive. Largest inventory of cones, surrounds, gaskets, spiders, dustcaps, grilles, foam and cloth and 4,700 custom voice coils. Phone 02 9420 8121, Fax 9420 8131. ELECTRONIC ENGINEERING SERVICES: digital & analog, embedded & Windows/PC based designs, complete solutions or design advice/assistance. Phone 03 9807 9886. Email caddy<at>netspace.net.au PIC84/12 PROGRAMMERS: Many models available. Also other PIC-driven devices. EST (02) 9789 3616 or www. internetezy.com/au/~sesame PCBS MADE, ONE OR MANY. Low prices, hobbyists welcome. Sesame Electronics (02) 9554 9760 sesame<at>internetezy.com.au http:// www.internetezy.com.au/~sesame C COMPILERS: everything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC12, 68HC16, 8051/52, 8080/85, 8086 or 8096: $145.00 each. Macro Cross Assemblers and Disassemblers for above CPUs + 6800/01/03/05, 6502 and 68HC12 now combined at the new low price of $75. Debug monitors: $75 for 6 CPUs. All compilers, XASMs and monitors: $480. 8051/52 Simulator (fast, now incl. 80C320): $75. Try the C-FLEA Virtual Machine for small CPUs, build a “C-Stamp”. Demo desk: FREE. All prices + $5 p&p. Atmel Flash CPU Programmer: Handles the 89Cx051, the 89C5x and 89Sxx series, and the new AVRs in both DIP and PLCC44. Also does most 8-pin EEPROMs. Includes socket for serial CLASSIFIED ADVERTISING RATES Advertising rates for this page: Classified ads: $10.00 for up to 12 words plus 50 cents for each additional word. Display ads (casual rate): $25 per column centimetre (Max. 10cm). Closing date: five weeks prior to month of sale. To run your classified ad, print it clearly on a separate sheet of paper, fill out the form below & send it with your cheque or credit card details to: Silicon Chip Classifieds, PO Box 139, Collaroy, NSW 2097. Or fax the details to (02) 9979 6503. Enclosed is my cheque/money order for $­__________ or please debit my ❏ Bankcard   ❏ Visa Card   ❏ Master Card Card No. Signature­­­­­­­­­­­­__________________________  Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ 94  Silicon Chip ISP cable. $189, $35 tax, $10 p&p. 20-pin SOIC adaptor only $70. Credit cards accepted. GRAN­TRONICS PTY LTD, PO Box 275, Wentworthville 2145. Ph (02) 9896 7150 or Internet: http://www.grantronics.com.au VIDEO CAMERAS - SURVEILLANCE - CCTV SPECIALS: 380 x 0.2 SILICON PCB MODULE $69! 450 TVL DIGITAL COLOUR PCB $320! DOME HOUSINGS $10! 50 LED DIY Infra Red Illuminators $19! MODULES: AWFUL-CMOS only $49! PREMIUM 400 x 0.05 SONY CCD & CHIPSET from $91. CAM­ERAS: 36 x 36 from $88. Dome from $91. DIGITAL COLOUR MODULES: 330 TVL from $220. DIGITAL CAMERAS: 330 TVL from $180. 450 TVL from $370. DIGITAL COLOUR DOME from $189. ACCESSORIES: 30 + Lenses, Infra-Red Illuminator Kits, IR LEDs, Polarising, Colour, Infra-Red Cut & Pass Filters for Image Enhancement, Exposure, Focus & Glare Control. ANCILLARY EQUIPMENT: Quads 4 pix 1 screen from $280. SWITCHERS 4 & 8 Ch from $126. MULTIPLEXERS FULLSCREEN FULL-RESOLUTION VCR Recording/Playback from $826. ALSO: Monitors, Outdoor Housings, Brackets, Dummy Cams, CCTV-TV/VCR I/F Modules, Motorised Pan Units etc. TV Modulator/Mixer/Amplifier Modules from $14. PACKAGED SETS! QUAD + 4 CAMERAS + Power Supplies from $689. 400 + Page CCTV Technical Reference Manual $95 or FREE! 2 Year WARRANTY available for most items! DISCOUNTS: based on ORDER VALUE, BUYING HISTORY, for CASH/CHEQUE & NEW ZEALAND BUYERS! BEFORE you BUY Ask for our Illustrated Catalogue/Price List with Application Notes. Allthings Sales & Services 08 9349 9413 Fax 08 9344 5905 HOMEBUILT DYNAMO, engineering dreams into reality. “An absolutely marvellous book for the true ex­ perimentalist!” Elektor Electronics. (www.onekw.co.nz) SWITCH MODE PS Single thru quad outputs Huge range in stock. 5V - 48V models available. * * THE ELECTRONIC KIT SPECIALISTS KIT ASSEMBLY SERVICE Also: KIT SALES, REPAIRS, MODIFICATIONS and Custom Circuit Design and Component Sales CONTROL ELECTRONICS NSW AUST Phone: (02) 6654 5458 TELEPHONE EXCHANGE SIMULATOR, SC February 1998. Test all sorts of equipment without the cost of extra telephone lines. Melbourne 9806 0110. LOGIC ANALYSER 100Ms/s 32-Channel Kit $1275. Stand alone, not a plug in PC Card. Requires a VGA or EGA monitor - user supplied. Edge and Level Triggering. Multiple Triggering Modes such as, Trigger on pulse width too long or too short, Clock Stop, User Defined Storing, 2 Level Sequencer. Request brochure from: Peter Baxter, Tantau Australia, PO Box 1232, Lane Cove 1595, Sydney. Ph: 02 9878 4715 Fax: 02 9888 7679 Email: peter.baxter<at>tantau.com.au. All manuals on the website: www.tantau.com.au. Revised, no prototype area, “8051 Proto-Board” EA Feb 93. $30. WEATHER STATIONS: Windspeed & direction, inside temperature, outside temperature & windchill. Records highs & lows with time and date as they occur. $399.00 complete plus sales tax if appli­cable. Optional rainfall and PC interface. Used by Government Departments, farmers, pilots, and We have the solutions – we print electronics! Four-day turnaround, less if urgent; Artwork from your own positive or file; Through hole plating; Prompt postal service; 29 years technical experience; Inexpensive; Superb quality. Printed Electronics, 12A Aristoc Rd, Glen Waverley, Vic 3150. Phone: (03) 9545 3722; Fax: (03) 9545 3561 Call Mike Lynch and check us out! We are the best for low cost, small runs. Computronics Corporation Ltd 6 Sarich Way, Technology Park, Bentley, WA, 6102 Ph. 08 9470 1177 Fax 08 9470 2844 Specifications at www.computronics.com.au 651 Forest Rd, Bexley 2207 makes all the project PCBs published in SILICON CHIP and other Australian magazines Tel +61 2 9587 3491 Fax 9587 5385 http://www.cia.com.au/rcsradio/ Need prototype PC boards? KITS-R-US PO Box 314 Blackwood S.A. Ph/fax 08 8270 3175 FMTX2A Universal Stereo Coder $49 FMTX2B 30mW Xtal Locked 100MHz Transmitter $49 FMTX1 1-3 Watt Free Running Transmitter $49 FMX1 200mW Full Broadcast Transmitter, built & tested $499 FM220 10-18 Watt FM BGY133 Philips Linear $499 FM1525 25 Watt Discrete Linear FM Band $499 FM2100 110 Watt Discrete Linear FM Band $699 FM3000 300 Watt Discrete Linear FM Band $1499 Philips 828E/A VHF Receiver Boards (6 metres) $9 AWA 721 VHF Receiver Boards (2 metres) $9 AWA 721 VHF transmitter boards 1 watt (2 metres) $19 Philips 323 UHF transmitter boards 500mW (70cm) $19 AEM 35 Watt Little Brick Audio Power Amp $15 Digi-125 200W RMS Audio Power Amp $39 CA Clipper Compiler, new in box $49 6dBd Gain Colinear FM Band Antenna $999 Roll Smart-1 FM Station Audio Processor $999 Free catalog on disk of discounted surplus components Same day shipping, credit cards OK, circuits supplied. SPECIAL STEAM BOAT KITS $14 SERVICE AGENTS WANTED Applications are invited Australia wide for service agents, especially in remote areas. We require specialists in the repair and maintenance of professional audio, RF and electronic lighting equipment. Written applications can be forwarded to the following address or faxed to 02 9582 0999. Applications close Friday 30th October 1998. JANDS ELECTRONICS The Service Manager Locked Bag 15 MASCOT NSW 1460 Positions At Jaycar We are often looking for enthusiastic staff for positions in our retail stores and head office at Rhodes in Sydney. A genuine interest in electronics is a necessity. Phone 02 9743 5222 for current vacancies. weather enthusiasts. Other models with barometric pressure, humidity, dew point, solar radiation, UV, leaf wetness, etc., etc. Just phone, fax or write for our FREE catalogue and price list. Solar Flair/Ecowatch ph: (03) 5968 4863 fax: (03) 5968 5810, PO Box 18, Emerald, Vic., 3782. RAIN BRAIN AND DIGI-TEMP KITS. Also 60 channel Moni-temp with alarms and PC Data logging. Mantis Micro Products, 38 Garnet Street, Niddrie, 3042. (03) 9331 4786. Fax (03) 9331 4782 http://www.home.aone.net.au/ mantismp ELECTRONIC ENGINEERING SOLUTIONS: No matter what problem what industry we will find you a solution that meets your needs. Specialising in schematic & PCB design, custom Windows based software, embedded control, Windows/PC based test equipment, turnkey solutions. Fast turn around with competitive rates. DAMUE PTY LTD, 46 Whitby Road, Kings Langley NSW 2147. Phone (02) 9624 2802. Fax (02) 9624 2651 or E-mail alovell<at>ibm.net A NEW address for Acetronics http://www.acetronics.com.au On-line PCB quotes, free software, DIY PCB supplies plus many other items & services. 02 9743 9235. KIT ASSEMBLY ANY KITS ASSEMBLED: professional, speedy service. Phone Neville Walker (07) 3857 2752. WAREHOUSE SALE SILICON CHIP is having a once-only warehouse sale on Saturday, September 12th between 9.00 AM and 5.00 PM. ON-SALE: SILICON CHIP back issues, binders and data wallcharts, old and newish semiconductor data books which are excess to our requirements, electronics reference books, surplus electronic components, some working project prototypes. Come and pick up some data books at bargain prices – once they’re gone, they’re gone forever. The address: SILICON CHIP, Unit 8/101 Darley St, Mona Vale, 2103. SEPTEMBER 1998  95 14 Model Railway Projects Advertising Index Australian Audio Consultants.......31 Computronics..............................95 Shop soiled but HA LF PRICE! Our stocks of this book are now limited. All we have left are newsagents’ returns which means that they may be slightly shop soiled or have minor cover blemishes. Otherwise, they're undamaged and in good condition. SPECIAL CLEARANCE PRICE: $3.95 + $3 P&P (Aust. & NZ) This book will not be reprinted Yes! Please send me _____ copies of 14 Model Railway Projects at the special price of $A3.95 + $A3 p&p (p&p outside Aust. & NZ $A6). Enclosed is my cheque/money order for $­A__________ or please debit my Consultant Technology Aust. ......17 Dick Smith Electronics..................... ................................ IFC,OBC,10-13 EMC Technologies.......................15 Harbuch Electronics....................56 Instant PCBs................................95 Jands Electronics........................95 Jaycar .............................. 45-52,95 Kits-R-Us.....................................95 Microgram Computers...................3 Norbiton Systems........................35 Oatley Electronics........................75 Printed Electronics.......................95 Procon Technology......................95 Quest Electronics........................41  Bankcard     Visa Card    MasterCard RCS Radio...................................95 Card No. Resurrection Radio......................79 Signature­­­­­­­­­­­­___________________________  Card expiry date______/______ Scan Audio..................................83 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). Silicon Chip Bookshop.................65 Silicon Chip Wallchart..................25 Silicon Chip Subscriptions..... 92-93 Smart Fastchargers.....................55 Solis.............................................96 Taig Machinery............................56 Training OnLine Pty Ltd...............26 Truscott’s Electronic World...........41 HELP SAVE THE NIGHT SKY! We are losing our heritage of starry night skies. Poor, inefficient outdoor lighting is causing glare and “light pollution”. This wastes energy and increases greenhouse gas emissions. You can help by joining SYDNEY OUTDOOR LIGHTING IMPROVEMENT SOCIETY (SOLIS). SOLIS aims to educate and inform about quality outdoor lighting and its benefits. We also lobby councils, government and other bodies to promote good lighting practice. SOLIS meetings are held third Monday night of each month at Sydney Observatory. Individual membership is $20 pa. Donations are also welcome. Cheques payable to “SOLIS c/- NSAS”, PO Box 214, West Ryde 2114. Email: tpeters<at>pip.elm.mq.edu.au 96  Silicon Chip Zoom EFI Special......................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. MORE FROM YOUR EFI CAR! Own an EFI car? Want to get the best from it? You’ll find all you need to know in this publication EFI TECH SPECIAL Here it is: a valuable collection of the best EFI features from ZOOM magazine, with all the tricks of the trade – and tricks the trade doesn’t know! Plus loads of do-it-yourself information to save you real $$$$ as well . . . HERE ARE JUST SOME OF THE CONTENTS . . . n Making Your EFI Car Go Harder n Building A Mixture Meter n D-I-Y Head Jobs n Fault Finding EFI Systems n $70 Boost Control For 23% More Grunt n All About Engine Management n Modifying Engine Management Systems n Water/Air Intercooling n How To Use A Multimeter n Wiring An Engine Transplant n And Much More including some Awesome Engines! AVAILABLE DIRECT FROM SILICON CHIP PUBLICATIONS PO BOX 139, COLLAROY NSW 2097 - $8.95 Inc GST & P&P To order your copy, call (02) 9979 5644 9-5 Mon-Fri with your credit card details! FROM THE PUBLISHERS OF “SILICON CHIP”