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MARCH 2021 ISSN 1030-2662 03 The VERY BEST DIY Projects! 9 771030 266001 $995* NZ $1290 INC GST INC GST High-Current Battery Balancer Isolated Serial Link use it with our Battery Balancer FREE with this issue* The History of Videotape quadruplex ❚ helical scan ❚ cassettes ❚ digital *Australia only All About Capacitors how how they they work work and and where where to to use use them them Want to build your very own Smart plug? $6995 CLUB OFFER BUNDLE DEAL Here’s a great project that lets you use your Smartphone (using Bluetooth®) to turn on/ off any appliance such as a TV, computer, table lamp, etc. directly from the power point without getting up off the couch or out of bed. SAVE 20% KIT VALUED AT $89.75 SKILL LEVEL: Beginner For step-by-step instructions scan the QR code. www.jaycar.com.au/bluetooth-powerpoint See other projects at www.jaycar.com.au/arduino What You Need: 1 x Arduino® Compatible UNO Board 1 x Arduino® Compatible Bluetooth®V4.0 BLE Module 1 x Wireless Transmitter Module 433MHz 1 x Mains Outlet 1 x 40 Piece 150mm Plug to Socket Jumper Leads JUST 14 $ 95 A mixed pack of jumper leads for your Arduino®, breadboarding and prototyping projects. 150mm long. WC6027 100 gift card Awesome projects by On Sale 24 February to 23 March, 2021 JUST 39 $ Jumper Leads Mixed Pack 100 Pieces $ XC4410 $29.95 XC4382 $29.95 ZW3100 $13.95 MS6149 $9.95 WC6028 $5.95 Light Duty Hook-up Wire Pack 8 Rolls Quality 13 x 0.12mm tinned hook-up wire on plastic spools. 8 rolls of different colour included. 25m on each roll. WH3009 Got a great project or kit idea? JUST 4495 95 $ Heatshrink Pack with Gas Powered Heat Blower An assortment of 160 heatshrink tubes in 7 different colours and sizes, plus 1 gas powered heat gun with Piezo ignition. TH1620 If we produce or publish your electronics, Arduino or Pi project, we’ll give you a complimentary $100 gift card. Upload your idea at projects.jaycar.com Looking for your next build? Silicon Chip projects: jaycar.com.au/c/silicon-chip-kits Kit back catalogue: jaycar.com.au/kitbackcatalogue 1800 022 888 www.jaycar.com.au Shop online and enjoy 1 hour click & collect or free delivery on orders over $99* Exclusions apply - see website for full T&Cs. * Contents Vol.34, No.3 March 2021 SILICON CHIP www.siliconchip.com.au Features & Reviews 10 Hoarding: Urban Electronic Archaeology Sorting through an extensive collection of electronic items is a task not too dissimilar to working on an archaeological dig site. It’s why it’s important to have items properly recorded to help sort the ‘rubbish’ from the ‘gems’ – by Dr David Maddison 30 Fetrons, and the All-Fetron Radio Fetrons are a solid-state replacement (typically drop-in) for pentode (sometimes triode) valves. I was so fascinated by them I decided to design a radio using only Fetrons – by Dr Hugo Holden 44 The History of Videotape – Quadruplex Our Battery Balancer can handle up to four series-connected batteries per unit, and suits most common battery types. It can handle batteries or cells from 2.5-15V, with a charging current up to 50A – Page 21 The first article in a series of four detailing the history of tape-based recording, starting with Ampex’s quadruplex recorder and ending with the move to digital video – by Ian Batty, Andrew Switzer & Rod Humphris 72 All About Capacitors There’s a lot to consider when choosing what capacitors to use for a design, due to the huge variety of them. This article explains how most capacitors are made, how each type differs and what performance you can expect – by Nicholas Vinen Constructional Projects 21 High-Current Four Battery/Cell Balancer – Part 1 Many battery balancers are inefficient due to dumping excess charge for a given cell. But our new Battery Balancer redirects that extra charge into other cells, charging faster with little heat or waste – by Duraid Madina 68 Mini Isolated Serial Link A look at the beginnings of videotape recording, starting with systems like the BBC’s Vera and Ampex’s quadruplex VR-1000A – Page 44 This postage-stamp sized module provides isolated, bi-directional, full-duplex serial communications. It can easily be used with our new Battery Balancer to charge even more batteries or cells – by Tim Blythman 84 Battery Multi Logger – Part 2 Following on from last month, we will go over the construction, setup, testing and calibration required to finish your Battery Multi Logger – by Tim Blythman 92 Electronic Wind Chimes – Part 2 In the final part of this series, we cover how to modify the wind chime itself so that it can be driven by a series of solenoids. You can then play your own tunes without relying on the wind – by John Clarke Your Favourite Columns This Mini Isolated Serial Link can be used with our Battery Balancer to manage even more batteries or cells. But it’s also useful any time you need to send isolated signals between two boards – Page 68 39 Circuit Notebook (1) Low-noise mic preamp (2) Two quartz crystal oscillators using a flip-flop (3) Displaying digits using single RGB LEDs (4) The Omnidetector 61 Serviceman’s Log If it isn’t one thing, it’s another – by Dave Thompson 100 Vintage Radio Kriesler Triplex 41-21 portable transistor radio – by Ian Batty Everything Else 2 Editorial Viewpoint 4 Mailbag – Your Feedback siliconchip.com.au 98 Silicon Chip Online Shop 106 Product Showcase 107 Ask Silicon Chip 111 Market Centre Australia’s magazine 112 Noteselectronics and Errata 112 Advertising Index Capacitors come in all shapes and sizes, and because of this it is confusing trying to pick one. So we’ve detailed some of the important aspects of capacitors, such as dielectrics etc – Page 72 March 2021  1 www.facebook.com/siliconchipmagazine SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke, B.E.(Elec.) Technical Staff Jim Rowe, B.A., B.Sc. Bao Smith, B.Sc. Tim Blythman, B.E., B.Sc. Nicolas Hannekum, Dip. Elec. Tech. Technical Contributor Duraid Madina, B.Sc, M.Sc, PhD Art Director & Production Manager Ross Tester Reader Services Ann Morris Advertising Enquiries Glyn Smith Phone (02) 9939 3295 Mobile 0431 792 293 glyn<at>siliconchip.com.au Regular Contributors Dave Thompson David Maddison B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Ian Batty Cartoonist Brendan Akhurst Founding Editor (retired) Leo Simpson, B.Bus., FAICD Silicon Chip is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 626 922 870. ABN 20 880 526 923. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Subscription rates (12 issues): $105.00 per year, post paid, in Australia. For overseas rates, see our website or email silicon<at>siliconchip.com.au Recommended & maximum price only. Editorial office: Unit 1 (up ramp), 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9939 3295. E-mail: silicon<at>siliconchip.com.au ISSN 1030-2662 Editorial Viewpoint Older devices involved creative engineering While I am not particularly into ‘retro’ electronics like vintage radios, vintage computers etc, I find some of the articles on these topics quite interesting. You can tell that the designers of these devices had to be very clever to use the meagre resources available to them to solve some quite tricky problems. Take the four-part series of articles on Videotape Recording starting in this issue (on page 44). Younger readers (say, those under 30) probably don’t remember much about videotape. I was young when the VHS/Beta ‘war’ was raging, and by the time I was old enough to use a VCR, VHS had taken over. I remember the machines being quite finicky, and they would sometimes go wrong (in the worst case, ‘eating’ a tape) for no apparent reason. But for the most part, they worked quite well, albeit with video quality that I now consider awful. Having read the articles mentioned above, I realise now how complicated the loading systems were. With so many parts having to move in concert, in a device produced at a relatively low cost, it’s no wonder they went wrong sometimes! So my hat’s off to the engineers that designed those mechanisms; it must have been a lot of effort to get them to work reliably. Another thing that’s apparent in reading these articles is how much ‘outsidethe-box’ thinking went into developing the core technologies enabling video recording, especially helical scan. It seems kind of obvious in retrospect, but it took lots of smart people many years to develop a device which could record an hour or two of video on a reasonably compact, easy-to-use and low-cost cassette. It was an incremental, evolutionary process too, as is so common with technological advancements. There were several generations of video recording between the first useful machines (Ampex quadruplex) and the final ‘sorted’ generation of consumer machines, which I guess you could say was hifi VHS. Each generation made certain improvements, but often retaining shortcomings that would be addressed in future. It helped that the later semiconductor technology allowed more signal processing to be crammed into smaller machines. I guess my point is that you might enjoy those articles even if you’re too young to remember the technology being described, and aren’t terribly interested in the topics themselves. You might still learn something and enjoy the journey of discovery. I can make a similar comment about the article on Fetrons; they are interesting because they give you a glimpse of the transitional period when valves were being phased out in favour of transistors. Again, it took innovative engineering to make transistors operate like valves. Also, consider some of the techniques described in our Vintage Radio columns like reflexing, combined mixers/oscillators and some of the design choices in early transistor sets. Even if you aren’t really into radio, you can appreciate the amount of work that went into getting the most performance out of a few (then costly) active devices. That’s the sort of engineering that I really appreciate, and I think the people who came up with those ideas must have done a lot of brainstorming to reach those ‘Eureka!’ moments. Printing and Distribution: Nicholas Vinen 24-26 Lilian Fowler Pl, Marrickville 2204 2 Silicon Chip Australia’s electronics magazine siliconchip.com.au siliconchip.com.au Australia’s electronics magazine March 2021  3 MAILBAG your feedback Letters and emails should contain complete name, address and daytime phone number. Letters to the Editor are submitted on the condition that Silicon Chip Publications Pty Ltd may edit and has the right to reproduce in electronic form and communicate these letters. This also applies to submissions to “Ask Silicon Chip”, “Circuit Notebook” and “Serviceman”. BWD602 successfully repaired Thanks for publishing my letter asking for help in the February issue (page six). I have managed to get the BWD602 working again. It uses 18 transistors, one dual valve and several diodes. Seven transistors were faulty; two were overheated to the point of charring the fibreglass board. Two resistors were open-circuit, and one polyester cap was shorted. I also replaced most of the electrolytic capacitors. It was built around 1970 and incorporates a signal generator (0.5Hz to 500kHz), a 7W amplifier, a variablegain preamp, 6.3V AC supply, 0-24V DC supply, 0-300V DC supply and a 0 to -50V DC supply. Happy days, and thank you for your help. Trevor Collins, Bellevue, WA. 60.0kHz (JJY). The distance is 7320km (Sydney minus 453km). Amazing for the tiny ferrite rod inside the watch. What I really like is the “synchronisation successful” display on the bottom right. If it is visible, the signal was received OK! Hans J. Schaefer, Armidale, NSW. More information on the microtester Radio Time Signals article feedback Dr David Maddison’s article on Radio Time Signals in the February issue was an excellent read (siliconchip. com.au/Article/14736). Now I know how my Casio 3043 watch really works! I bought it in 2011 in Germany and used it a lot, until fate (my wish) brought me to Australia eventually. Sadly, I got no signal in Sydney (had to do with Llandilo on SW then). I was surprised... But I have lived in Armidale, NSW for a couple of years now – Australia’s highest township (almost 1000m high). I live in the highest part, North Hill. I tried my watch again, with the help of the very good manual, which suggested linking to Japan. Setting the world time to Tokyo, and putting the watch overnight on a window ledge pointing North, synchronisation happened quite reliably, every midnight (in Tokyo)! According to the manual, I must be connected to Fukuoka/Saga on 4 Silicon Chip 11V, thus defeating the point of using a power meter to check that it’s getting the correct voltage. Peter Gutmann, Auckland, New Zealand. Comment: you have a good point; it’s always a good idea to check the shunt value in any current meter before using it, to ensure that it is well matched to the expected maximum current. This device appears to have an excessively high-value shunt resistor. The voltage drop should ideally be under 100mV for low-voltage appliances. Panel meter burden voltages The December 2020 article “Mini Digital Volt/Amp Panel Meters” (siliconchip.com.au/Article/14678) mentions the PZEM-031 which has a built-in shunt and is less complex to set up than the PZEM-051. Readers should be aware that this model, or at least one of the many ones available from AliExpress, seems to have a considerable load-dependent voltage drop, around 100mV at 150mA load and 0.9V at 2A load. So if you’re using it to measure the voltage fed to a device, the device is getting somewhat less voltage than the meter is displaying, depending on the load current. If you have several of them, you can chain them and see the voltage drop lower and lower in each subsequent meter. For example, feeding 12V to a device could result in it getting, say, Australia’s electronics magazine I have read Silicon Chip since the start, and Electronics Australia before that. You are turning into a bit of “Popular Mechanics”, which is not a problem for me, as I have a broad range of interests. The article on the History of the Aussie GPO in the September 2020 issue was good (siliconchip.com. au/Article/14573). I am not interested in Vintage Radio, but I know some people like it. I got the February 2021 issue last night and read it today. The article on the Transistor Microtester was very interesting. I found the following comment online, which was apparently written by the inventor of the device. Thanks for another good edition. Laurence Stonard, Leichhardt, NSW. Karl-Heinz Kübbeler writes: I’m the creator of the original version of this tester; it uses an ATmega8 and a 16x2 character LCD as mentioned in the video. I started this project in early 2009. After seeing a similar commercial tester (Atlas DCA 55), I thought it would be an interesting project to try building a similar device myself. As far as I remember (it’s so long ago...), my first version could only detect bipolar transistors, diodes, Mosfets and resistors. For this reason, I called it a “Transistor tester”. siliconchip.com.au But the component detection – by only applying different currents by two different resistors on each pin and checking how the voltages change – worked far better than I had imagined. So I thought the project may be useful to others and decided to release it. I released the code completely free to everyone in a German microcontroller forum. At this time I was 16, had been programming C for only about two years, and didn’t even know about open source licenses! So it’s completely OK for me that others make money off the project. I’m really pleased and impressed that this project got that popular and developed further by the community. Many features shown in the video were added by the community and not by me: inductor detection, Vloss and ESR measurement for capacitors, the battery voltage display, and several more. Since the community versions completely surpassed it, I stopped active maintenance of the original version at some point in 2012. Just one more thing about the capacitor measurement. In the original version, it just shorts the capacitor to discharge it, then charges it via a resistor, and measures the time until an I/O pin connected to the capacitor changes from low to high. This threshold voltage isn’t too accurate; therefore, the capacitance reading also isn’t very precise. There is no fancy measurement at 1kHz; in 2009, I didn’t know that capacitances are typically measured at 1kHz. Editor’s comment: I understand what you mean by the reference to Popular Mechanics, but as I said in my February editorial, I do not intend to ‘dumb down’ the magazine. Silicon Chip is first and foremost about electronics, but we have always tried to balance the highly technical articles with somewhat less technical articles that we hope have broad appeal. This goes back to the first issue in November 1987, which included an article on the transition from steam to electric locomotives, and other general interest columns. We certainly won’t stop publishing projects or technical features. I think most readers will agree that there are plenty of interesting articles in this issue, and we have plenty more coming up in the next few magazines. 6 Silicon Chip Magazine enjoyed I have been reading Australian electronics journals since Radio and Hobbies in the late 1950s (I was born in 1946). I am very happy to see the successful passing of Silicon Chip into new hands. The quality of the magazine is excellent, and I think there are few journals of this type and quality anywhere in the world. Silicon Chip has just the right mix of different types of articles. I’m amazed that you can continue to come up with complex original projects at such a pace. Keep up the good work! Jim Goding VK3DM, Princes Hill, Vic. It’s a small world I have just begun to read the February edition of Silicon Chip and find I am in much agreement of what you have stated in your Editorial Viewpoint. It is good to have a reasonable mix of projects and not overload a copy with too many projects. It keeps the interest much longer. I found the letter in your Mailbag section by Rob Fincher very interesting (January 2021, pages 4-5). His experience is so similar to mine, first attending RMIT and then working within my first employer’s workplace, namely ICIANZ (which was later changed to Orica). I was at the ICI research facility in Ascot Vale, and he was at No.1 Nicholson Street, Melbourne (also known as ICI House). We might have even met. It was very common for the instrument apprentices where I worked to build stereo amplifiers. My first one was the Playmaster 10-10, which I modified later because I found that the sinewave turned into a triangle wave at about 10kHz! The tuners never really turned out as expected, although they sort of worked. The stability and sensitivity could not match that of commercial units. I replaced it with the 20W amplifier out of the Philips Applications Book 2nd Edition, 1971. With that modification, I tossed out the regulated portion of the power supply, removing most of the heatsinking and improving the power output and frequency response. It was matched with the Playmaster 127 control unit all within the same cabinet as an integrated amplifier. Although rarely used, the unit is still working. Australia’s electronics magazine My experience, which will be different from Rob, is in the design and repair of scientific laboratory instrumentation. For example, rewinding the condenser lens coil of an electron microscope (very old Hitachi one from the 1970s). I had to use Lotus 123 with Lotus measure on an old PC XT to auto-range an HP oscilloscope via the HPIB bus (similar to GPIB) for analog signal measurements, and designed specialised instrumentation which could not be purchased. Those sort of things were difficult to do in the 70s and 80s, but are now commonly embedded in the instruments bought off-the-shelf. Finally, I thought I’d mention that I just fixed a fault in a vintage Denon precision audio equipment system comprising of a tuner, a graphic equaliser and an amplifier type PMA 55. A power transistor in the amplifier somehow got all three legs dislodged from the PCB. The tuner also was faulty in that one of the primary 120V windings was open-circuit. As there are no more parts available for this unit, I could not repair the tuner, but the amplifier was an easy fix. There are no circuit diagrams nor manuals that I could find. The unit is not even listed on the Denon website. But it all ended well, and the amplifier and graphic equaliser are now working well. I do not know whether it was a manufacturing fault or someone else changed TR902 because only the power transistor leads’ tips were soldered. I improved it slightly by dropping the leads so that the thick part of the leads gave mechanical strength to the solder joints. Wolf-Dieter Kuenne, Bayswater, Vic. ` j v `j jv `v `jv Suggestions for future articles Having more articles than space is truly a good problem to have, on which I have a few thoughts. I have been delighted with Silicon Chip, for many years now, and would be happy if you didn’t change anything, however... Considering your staff wages, rising material costs and the need to make a profit for sustainability, I believe you must, at least, keep up with CPI. I would be happy to pay a little more each year for your quality magazine as my pension goes up most years. To me, Silicon Chip represents great value. siliconchip.com.au h Delivering more The widest selection of semiconductors and electronic components in stock and ready to ship au.mouser.com australia<at>mouser.com I don’t use binders as the issues tend to sag and become misshapen due to gravity and also they are not protected from vermin. I keep yearly groups in large zip-lock bags fully sealed, marked by date, and my oldest editions are still in pristine condition. Therefore, a few extra pages will make no difference for storage. Constructional project articles could be reduced in size by removing the actual ‘construction’ or ‘assembly’ sections and making them available for download from your website for those readers who will actually make the project. You could then include much more detailed descriptions and pictures to assist with the actual assembly. I would like more articles on modern radio-controlled equipment. Your series on El Cheapo Modules could include some from Pololu. I, only accidentally, came across a very clever Pololu Simple Motor Controller G2, for which I am very grateful. Their range of innovative boards is extensive, and their local service is exceptional via Core Electronics. Maybe you could counter much of the rubbish on YouTube. I hope this makes your decision making on content a little easier! Stephen Somogyi, Barrington, NSW. Comment: thanks for the feedback. We try to avoid putting too much article content online because some readers either can’t access online content or don’t want to. Also, it means that articles are no longer self-contained. Obviously, it would help with space constraints, but there are quite a few downsides, so we prefer not to do that. As for the problem fitting magazines in binders; while you might not use them, many people do, so we still have to consider whether the maga- 8 Silicon Chip zines will fit. It would be awkward to only fit 11 issues in a binder, and while we could have larger binders made, they would be considerably larger and more expensive. USB SuperCodec built using custom panels I wanted to share some photos of my completed USB SuperCodec (AugustOctober 2020; siliconchip.com.au/ Series/349). Initially, I wanted to apply a sticker on each panel, but then opted to make a stencil. However, after contacting different sources to build it, it turned out that no-one could make a stencil with small characters. So I contacted several local workshops and looked for laser engraving, settling on this one: www.masutai.com I initially provided a modified .psd file (from the original PDF), but they could not work with it on their machines, so I had to redo the design from scratch with Adobe Illustrator to provide 2D-compatible files. I sent them my artwork together with the two original panels, and they engraved them. I have to say the result is very convincing (as shown below), especially on the red anodised aluminium! The unit works very well; I will now experiment with measurements of my amplifier. I’m supplying the artwork for you to put on your website, in case other readers want to do the same (in .ai and .eps formats) – siliconchip. com.au/Shop/11/5623 Olivier Aubertin, Singapore. The power section tests were successful. The article then said to connect the MCHStreamer to the computer and confirm the NPN transistor’s collector goes high, but it never did. With USB disconnected, the baseemitter voltage on the transistor was 0.67V. With USB connected, it was 0.145V, so the transistor should have turned off. But the reset line (collector of the transistor) never went high. It was like there was no pull-up resistor, even though the DS1233 datasheet mentions one. Phil suggested that I use a multimeter set on a low ohms range to probe between the various pins and try to find a short circuit on the board. I got a measurement of 750W between Vcc and RST, indicating there was a short circuit somewhere. I only have a 4-digit meter, but it was still able to point me toward the IC that had the short. Once I knew where to look, I managed to find it – it was hiding right down in the gap between the pin 5 and 6 leads of IC6. I used a magnifier with a built-in light – without that, I’m doubtful that I’d have found it, as my phone doesn’t have a macro mode, so it’s hard to get focus. Anyway, a little flux and a brief touch with the soldering iron was all that it needed. Stephen Gordon, Thurgoona, NSW. Another request for a digital preamp Tricky fault-finding was successful I have just read the February issue and note that on p112, in Ask Silicon Chip, there is a letter from O. A. in Singapore. Your reply indicated that you are working on a new digital preamp design. Years ago, I built the “Precision Preamplifier ’96” designed by Douglas Self and featured in Wireless World. Australia’s electronics magazine siliconchip.com.au I would like to thank Phil Prosser for helping me to find the fault in my USB SuperCodec (August-October 2020; siliconchip.com.au/Series/349). This preamp is still running well after nearly 25 years – but it does not have remote control! What is does have, however, is an analog active gain stage with its many advantages, one of which is excellent channel balance solely dependent on a pot’s mechanical alignment. A digital design may no longer require a ganged pot, but if the active gain feature could be incorporated along with tone controls, plus remote control – I can’t wait to build it. Regards, and thanks-in-hope! Norman Hughes, Sanctuary Point, NSW. I support the suggestion by J. C. of Point Cook, Vic in the August 2020 issue regarding an acoustic guitar preamp project. I would certainly build one, and I imagine there are a lot of musicians out there who have added pickups to a variety of instruments who would also be interested. I’m assuming it will have a high impedance input option to suit the various piezo pickups available. Regarding tone control options, Maton guitars have AP5 preamps installed, which have an excellent reputation. They have treble and bass controls, plus a sweepable mid, which is a good combination. I have a Fishman piezo pickup on a violin which I have been putting through one of your 12V DC amplifiers. My preamp is guitar-based, with treble and bass controls only, so it is a bit limited. Barry Larkin, Cranbourne South, Vic. ably doesn’t help if the line is disconnected at times, but it might make reconnection faster. It would be good if you could consider making a tester that would allow you to listen/view the VDSL in a way that would give a good indication of whether it’s OK or faulty. I vaguely remember seeing that line current did something to keep your line clean, and ring current could also help. But I am fairly sure they run the FTTN lines dry. Roger Plant, Belgrave Heights, Vic. Nicholas comments: most FTTN modems/routers should have diagnostics interfaces accessible from the web interface (usually in the “Advanced” tab or similar). It would be challenging to come up with a standalone device with the same analysis capabilities. You make an interesting point regarding the DC line voltage improving DSL signals, and the lack of a polarising voltage on NBN connections. At my previous two residences, the only way to get the DSL to remain semistable (after the NBN was announced and telcos stopped maintaining the lines) was to leave a phone off-hook. There are several theories about why this works, but quite clearly it did. The good news with FTTN is that the line back to the node should be a lot shorter than it was for DSL, which had to go back to the exchange. But if you have bad joints in your home, in the pit(s) out on the street, etc, I could imagine that DC bias would help. As you say, with FTTN that has likely been eliminated, so you’re out of luck. You’ll just have to keep complaining until they fix your line! NBN pitfalls Another option for subwoofer port Support for acoustic guitar preamp project Not so long ago, if my telephone was working poorly, I could ring the ISP using the landline, and often they would get the idea while trying to communicate through the clicks and other line noise. With FTTN, it’s a lot more opaque. You can’t listen to the line noise. I complained about dropouts on our FTTN connection. Its a bit tedious, as when it drops out, it will often take at least five minutes to come back (sometimes hours). I am on a low-speed plan (with expensive 4G for backup); they seem to have simply dropped the possible line speed to increase the SNR. That probsiliconchip.com.au In the Bass Block Subwoofer article (January 2021; siliconchip.com.au/ Article/14710), the Author suggests using PVC pipe or conduit to make the port, with limitations because only specific diameters are available. For the 32mm x 40mm port, I have an alternative to offer. My wife has some fabric tubes (probably from Spotlight), and one is 40mm external diameter, 34mm internal, and 143cm long. It cost nothing (except for having to buy the fabric, I suppose). If I make one, I will coat the tube with paint or varnish to seal the cardboard. Paul Gill, Manly, Qld. SC Australia’s electronics magazine March 2021  9 HoARDING: urban Electronic Archaeology Don’t let this happen to you! If you have a large collection of anything (including electronics), you must have a succession plan. It would also be a good idea for you to periodically ‘clean house’ and allow collectors – young and old – to pick up items you don’t absolutely need. I recently had the task of sorting through an extensive might be). He had told me that he usually paid $2-5 each collection of electronic items which were part of a defor these at the weekend markets. ceased estate. As I had been a long-time friend of the 2) Huge numbers of CDs and floppy disks, mostly for comdeceased, I was permitted to ‘rescue’ any interesting items puter games, likely never used. I found, as they would otherwise end up in a landfill. 3) Many car parts, mostly incomplete or used, mostly There were a vast number of items in the hoard, but Holden-related and including at least two ‘grey motors’ before I had a chance to go through it, drug addicts and and one ‘red motor’. other thieves were reported to have broken in and taken 4) Lots of scrap metal. anything that could be sold on the street. 5) Numerous pieces of electronic or mechanical equipWhat remained (see opposite for an example) was of ment, usually incomplete or broken, in various states of little-to-no monetary value, but still of interest to elecdisassembly with components missing or, in the case of tronic enthusiasts. In fact, by taking items away, I was many electrical or electronic items, with the power cords probably saving the estate the cost of disposing of them. cut off. This is likely because it is illegal in Victoria to The collection was accumulated over a lifetime, mostly sell electrical items without an electrical safety test, and being purchased from second-hand markets, one being the for the low value of many items, that is not worthwhile. well-known Laverton Market in Leakes Rd, Laverton, Vic. 6) Many broken items, as items covered the floor nearly Many of the other items seem to have been discarded everywhere. Apart from a few ‘goat tracks’ with limited by industrial or government laboratories. visibility of the floor, mostly one had to walk on these Most of the items were filthy, with 50 or so years of items to move around the house. If they weren’t broken accumulated dust and grime, plus damage from being when acquired, they soon would be. (Some rooms were thrown into a heap rather than stacked correctly. To get unreachable due to items stacked floor to ceiling). the items shown here into presentable condition required The full extent and composition of the hoard is not known extensive cleaning at the time of writing, because what was recovered and preUnlike some hoards, I did not find much actual rubsented here is only what was obvious and at the surface bish, just a lot of ‘stuff’ in several general categories: level. In many areas, the hoard was a metre or more thick. 1) A staggering number of generic desktop PCs. These A variety of older electronic items I found were handwere mostly from the 1990s and 2000s, made for various scientific or technical and not collectible computers (such as purposes. Back in the day, it was common original IBM, Apple or Commodore PCs By Dr David Maddison for large government, university and com10 Silicon Chip Australia’s electronics magazine siliconchip.com.au mercial laboratories to make their own equipment as it wasn’t always commercially available, or it would take too long to order it from overseas. The items I recovered represent an interesting cross-section of electronics for virtually the whole of the twentieth century. The collection of articles presented here also includes items he gave me while he was alive. Where I found multiple similar items, I will show the Australian-made item if there is one. Postscript Although my friend was known by work colleagues to be brilliant, when he passed away, there were no funeral arrangements. So besides showing some interesting items, this article also serves as something of a memorial or tribute to his life. Appropriately for a collector of elec- Just a small part of what I was faced with . . . after drug addicts and thieves had tronics, his initials were A. C. already gone through it. Vintage Gallenkamp switchboard ammeter (1910s) I found this Gallenkamp ammeter, estimated to be made around 1910, based on a very similar one I found in a catalog (see below). It was found halfimmersed in water. Philips valve radio ‘battery eliminator’ (1920s) Valve radio batteries were expensive. These devices replaced two of the three battery types (the “B” and “C” batteries) with a mains supply. The technology at that time made it difficult to eliminate the “A” battery. The one I found is a Philips 3003, made in Holland and very popular in Australia. It appears that somebody tried to repair it as many wires were disconnected. For more information on this device, including a circuit diagram, see www.tuberadio. com/robinson/museum/ Philips_3003/ siliconchip.com.au Ormond variable condenser (capacitor) (1920s) This was in a pile of rubbish, but it caught my attention because it had screw terminals. I measured its maximum capacitance as 450pF and determined it to be from the UK brand Ormond, and almost certainly the No. 3 model. It featured “S.L.F.” or “straight-line frequency”. This meant that through the rotation of the dial, the corresponding frequencies would be linearly proportional to the dial position. According to Radio Retailing magazine of December 1925, this “improves the tuning of a set and has been developed to meet conditions which were becoming almost intolerable, namely, the crowding of the stations in the lower part of the present broadcast range”. Headphone and headphone parts (1920s to 1940s) The oldest such item I found was made by Brandes Ltd, London, and marked “superior matched tone”. It is one driver from a pair of headphones. According to radiomuseum.org, this item dates from approximately 1924-1932. It is marked “BBC” (probably not the broadcaster) and “Made in England”. Its nominal impedance is 1000. I also found a Brunet & Cie driver from their Casques et Écouteurs Type F model, dated around 1924 (according to radiomuseum. org). It was available with an impedance of either 500 or 2000. Another was a complete set of Australianmade Q-Plus brand headphones. I could not find any information online about them, but Q-Plus was an Australian manufacturer operating from 1947 to at least 1965. Australia’s electronics magazine March 2021  11 Astor radio dial (1930s?) This dial is from an Astor Super Six. I found one such radio for sale which described it as being from the 1930s. It incorporated an English-made turntable into a (presumably) Australian-made AM radio. Smashed or incomplete valve radio chassis (1940s and 1950s) There were several valve radio chassis without enclosures, all incomplete and/or damaged, as was typical of most items in the hoard. I passed these on to collectors for spare parts, as they were beyond any hope of restoration. Many of the chassis were corroded, meaning that their transformers were probably also internally corroded and thus unusable. Vintage panel meters (1940s to 1970s) I found a variety of vintage panel meters. Here are a few that were Australianmade (top row) as well as some from the UK, USA and Japan. Except for the one by Ernest Turner Electrical Instruments Ltd, I could find no information to date these accurately, so I had to make educated guesses based on their styles. Philips model 164 radio (1955) This radio is Australian-made. It was a rare example of a radio from the hoard in a semicomplete condition – except that Vintage fluorescent light starter (1950s) This unusual fluorescent starter is a General Electric (USA) FS-850 “Watch Dog” model. According to the GE “Catalog of Large Lamps” from 1956, “Watch Dog starters provide automatic cut-off at the end of lamp life. This eliminates blinking and protects the ballast. When a new lamp is installed, a touch of the manual reset button makes the starter operative again.” Flashing fluorescent lights used to be a common and annoying problem, and failing tubes could lead to ballast damage. It’s a pity this design wasn’t more widely adopted.     Australian-made toggle switch   (1950s?) This Australian-made threeposition toggle switch of open construction is marked “0.5A 250 V.A.C. Only” and “G.W. Engineering P/L Sydney Australia”, and was probably made for a radio. This shows the diversity of Australian electronic manufacture before 1972. Admiral 5AW valve radio (1950s) This was one of the first, if not the first, valve radio made in Australia (and worldwide!) with a printed circuit board (PCB). This model was released in 1956, and we published an article on it in May 2019 (siliconchip.com.au/Article/11633). It came with an optional clock; in this case, the clock was not fitted. I gave this to a collector for parts. Mains timer (1950s?) The electromechanical device shown at left counts to 55 minutes and 59 seconds before switching off a mains-powered device. It is unbranded, but powered by a Warren Telechron someone has put the dial on upside down! For more on this radio, go to www.radiomuseum.org/r/ philipsaus_164.html GEC KT88 audio amplifier valve (1950s) The KT88 was introduced by GEC in 1956 for audio amplification, although the manufacturing date of the one I found is unknown. It is an example of “new old stock”, but although this valve was apparently not used, I was advised by a valve expert that about 10% of “new old” valves are gassy and unusable. The type of valve is a “kinkless tetrode”, hence the KT designation. It can utilise plate voltages as high as 800V, and in ClassAB1 configuration, can produce 100W of audio power at 2.5% total harmonic distortion, or 50W at much lower distortion. This valve is still produced today in China, Russia and Slovakia. A modern-day Russian version of this tube is reviewed in the video titled “Genalex Gold Lion KT-88 Tube Review With Audiophile Music” at https://youtu.be/q0QuC2hsWcU 12 Silicon Chip Type B3 synchronous motor. They were well known for the fine and very accurate clocks they made. Since a synchronous motor runs at the mains frequency, over the long term, such clocks are incredibly accurate because of the long-term stability of the mains frequency. Judging from the advertisement for the type B3 motor used in this device, I estimate that it is from the 1950s. Telechron motors, and the clocks they were used in, have a fascinating history. Australia’s electronics magazine siliconchip.com.au Power resistor (1950s) Here’s a power resistor from the Resistance Product Company (RPC) of Harrisburg, Pennsylvania (USA). It is a type BBM of 1.25M ±15% and has screw connections at either end. I measured it at 1.018M, which is a bit low, but consider that it is likely 60-70 years old and appears to have some burn marks. I found an advertisement for this series from 1951, stating that it is a high voltage resistor. Home or laboratory-made power board (1950-1960s?) Powerboards were not always commercially available, and in the early days, had to be custom made. Early examples were patented in the United States in 1929, 1950 and 1970. Still, the first successful commercial application seems to be an invention by Australian engineer Peter Talbot in 1972 (working at Kambrook), which was not patented. The one shown here has a master switch and five individually switched outlets. The master switch was combined with a Westinghouse brand circuit breaker of unknown rating (since the label has worn off), which was made in Sydney. Antique toggle switches (1950s to 1960s?) I found a variety of toggle switches, including one made in Australia, probably from before 1972 (and maybe long before that), when most Australian electronic manufacturing ceased. The Australian brand was Arrow Alpha, and the switch is rated at 240VAC, 10A (part number was 93A 402A). Resistance box (1950s-1960s?) The box shown below was probably laboratory-made; upon disassembly, I was surprised to see that the resistors were 5% tolerance types. But they may have been individually selected for having the desired resistances, because they are generally stable in their resistance value, no matter what it may be. It contained resistors of IRC brand (USA), ERG, Painton (UK) and others. siliconchip.com.au Decade capacitance box (1950s to 1960s?) This is a Danbridge DK4AV capacitance box, made in Denmark. It has a variable capacitance of nominally 50-1050pF plus x0.001, x0.01 and x0.1 dials marked 0 to 10, representing incremental values of 0.01µF, 0.1µF and 1µF respectively. That gives it a total possible range from 50pF (0.00005µF) to 1.11105µF. Its circuit is shown at right. In testing this item, I noticed that the values provided by the far-left dial weren’t correct, indicating that one or more of the associated capacitors might be faulty. Danbridge still exists, but didn’t respond to my inquiries. The item bears a sticker saying it was supplied by Geo. H. Sample and Son Pty Ltd. That company was established in 1921 and still exists today (www.johnsamplegroup.com). They became distributors for Hewlett Packard products in 1946, and in 1967, HP purchased the electronics division of Sample to establish their own Australian operation. Selection of Australian radio vibrators (1950s and 1960s) Vibrators were used in early valve car radios to produce the high voltages required for the valve anodes from the 6V or 12V car battery. They work by mechanically opening and closing contacts at around 100-150Hz and feeding an approximate square wave into a transformer, which steps the pulsed DC voltage up, after which it is rectified and filtered. We have published several articles on vibrators over the years (eg, in October 1995, September 2003, October 2003, December 2015). For the latest information, see siliconchip.com.au/Article/9647 and www.cool386.com/msp/msp.html Precision resistance blocks (1950s and 1960s) This unbranded set of resistance “blocks”, possibly laboratory-made, is labelled 10.000, 50.000, 100, 500, 1000, 5000, 0.1M, 0.5M and 1M, all ±0.1%. Measurements indicate that they are all out of tolerance. The resistors within these blocks are branded IRC (International Resistor Corporation), and were high-precision wirewound types of model WW4J. These were typically used in precision instruments. I found advertising for that series of resistors in US industrial electronics magazines from 1955 to 1964. Australia’s electronics magazine March 2021  13 Current source? (1950s to 1960s?) This appears to be custom made. We believe it is a low current source, and the current was set according to the meter. Examination revealed that it had two switches and a range of probably 1-100mA. They are Muirhead rotary stud switches, with a series of very low resistance shunts made from resistance wire. Patent for the Muirhead switches was first filed for in 1952 added features, or Wendell-West might have made it. But no documentation exists online to confirm that. Even though this example had melted at some point in its history, and probably hadn’t been turned on in 40 or 50 years, it functioned well. It had an outer case, but that was in very poor condition.    VARIAC (1960s) VARIAC is a trade name for a continuously variable autotransformer made by General Radio. But in Australia, Warburton Franki was licensed to use that name (it has now become generic). (UK patent GB743709A) and the USA in 1953 (US Patent US2786104A) – see the PDF at siliconchip.com.au/link/ab5u According to the US patent, the purpose of these switches was to offer low contact resistance, maintain the low resistance over a long period and provide a switch that would operate indefinitely without lubrication. Universal bridge (1960s) The Marconi Instruments TF2700 of 1962 vintage measures resistance, capacitance and inductance. This instrument is obsolete, as modern instruments provide far simpler and faster means of measuring those parameters. Transistor radio (1960s) This is a bit of a mystery. It is an “eight transistor” radio with medium wave (broadcast band) AM (MW), a shortwave (SW) band. But it has nine transistors, not eight as indicated on the front. No identifying marks as to the brand are apparent; it might have fallen or worn off, but it was made in Hong Kong. It looks remarkably similar to a Wendell-West CR-7A, which was made both in Japan and Hong Kong in 1968. However, looking at online references, we could find no information that the CR7A was ever built with SW reception. Given its remarkable similarity to the CR-7A, we suspect that it was an unauthorised copy of that model with 14 Silicon Chip The one shown here looks to be the V5 Series model rated at 600VA, with an input voltage of 240V AC and output between 0 and 280V AC, as shown in the advertisement at right (from 1963). For some interesting commentary on variable autotransformers, see https://soundau.com/articles/variac.htm Mystery Australian power supply (1960s) I found this unbranded but seemingly professionally-made (in Australia) 30V, 1A adjustable power supply in the backyard, with grass growing through it. Its main power transistor was an RCA 2N1490, introduced in 1957 and replaced by the 2N3055 in 1969. There was also a 2N657 transistor with what looked like a 1965 date stamp. It also had Australian-made capacitors in it, meaning that it was almost certainly made before 1972 when much of our industry ceased producing. It had a double-sided PCB as a subassembly. As there is no branding on the supply, it might have been made in an industry or government laboratory. Australia’s electronics magazine Precision potentiometer (1960s) This precision multi-turn wirewound potentiometer is a Beckman Helipot 7286. According to the Science History Institute (https://digital.sciencehistory.org/works/ q811kk07w), it was made between 1950 and 1969. siliconchip.com.au Helipot stands for helical potentiometer. These devices were invented in 1940 by Arnold O. Beckman for his pH meter, but were later used in radar equipment during WW2 due to their high precision. Electromechanical timing device (1960s) This item starts and stops an electromechanical timer when the start/stop button is pressed, like a stopwatch. It is reset using the rotary wheel. It runs up to 99999.9 seconds or about 27 hours. Markings on internal components suggest dates of 1964 and 1965. This item is unbranded and appears to be laboratory-made. High-power 5 resistive load (1960s?) This unbranded item looks to be professionally made, possibly in a laboratory. It contains a very large custom-manufactured, handwound power resistor on a ceramic former. The windings are coated in ceramic cement. It measured precisely 5, indicating that it is a precision component. Collection of resistors (1960s) I found many vitreous enamelled wirewound resistors. They are high-quality British-made Welwyn W24 types of 22K ±5%. These were mostly used in commercial and military equipment, but were also used in some consumer products such as early TVs. They probably date to the 1960s. This type of resistor is still produced today, with a power rating of 14W and voltage limit of 750V. TT Electronics now own Welwyn. Electronic project box made from an oil can (1960s?) Before you could visit Jaycar, Altronics or other retailers to buy an electronic project box, it was necessary to fabricate your own. The one shown here was made from some scrap galvanised steel sheet and part of an oil can. According to the Castrol website (see siliconchip. com.au/link/ab5v), Castrolite with “Liquid Tungsten” as written on the repurposed can siliconchip.com.au was introduced in the 1960s. Selenium rectifier (1960s?) Before semiconductor rectifiers such as germanium or silicon p-n junction diodes, solid-state rectifiers were made from selenium (also a semiconductor) in contact with cadmium selenide on a metal substrate, with steel or aluminium as the carrier plate for the selenium. They were sometimes known as “metal rectifiers”. Many such plates could be stacked to provide a greater voltage capability. They are not easy to test with modern ohmmeters because they have a forward voltage of around 2-5V per plate, so the ohmmeter would have to provide a high bias voltage; otherwise, they would read open-circuit. They were invented in 1933 and used until the 1960s, when replaced with silicon diode rectifiers. Grundig GDM308 microphone (1960s) According to the radiomuseum.org website, the microphone shown here was made around 1965. AWA Teleradio 60B (1960s) This Australian-made AWA Teleradio 60B transceiver used hybrid technology, with transistors throughout, except for the transmitter oscillator and final amplifier, which used valves. Its frequency range was 2-10MHz. Also, refer to the advertisement below. We don’t know exactly when the 60B model was released, but according to radiomuseum .org, the 60A was released in 1965. The only difference between the two was the value of a single resistor, reducing the output power from 35W to 25W for the 60B for regulatory reasons. One of the predecessors of the 60A/B was the AWA Teleradio 3BZ coast watcher’s radio, which was used during WW2 in Australia by coast watchers. It was an important radio for the war effort. See the video titled “3BZ coast watchers radio found in jungle” at https://youtu.be/ dT2elMKmwzM For further details and circuit diagrams for this radio, see the following links: siliconchip.com.au/link/ab5w siliconchip.com.au/link/ab5x siliconchip.com.au/link/ab5y Australia’s electronics magazine March 2021  15 Telephone bell (1960s) This telephone extension bell was manufactured in 1965 by Amalgamated Wireless (Australasia) Ltd (AWA) in Australia. It is 12/3B and is rated to ring at 70V AC. Each coil has a resistance of 500. Department of Supply capacitors (1960s or 1970s?) Here’s a package of ten capacitors from the Australian Government Department of Supply, which ceased to operate in 1974. The brand was possibly Apcos. Presumably, these capacitors were for military use. Telephone magneto and bell (1960s?) This old telephone magneto and bell might be considered a piece of kinetic folk art. The wires had become disconnected, but the idea was that the bell would ring when the magneto is turned. BWD Oscilloscope (1960s) The BWD 502 oscilloscope is from 1966. It has a 5-inch CRT (cathode ray tube) for display, as was typical at the time, and used five valves (two 6DJ8s, one 6BL8 and two 6AU6s) and 11 transistors (four 2N3694s, six BC107s and one 2N3565). I’m not sure if it works as the power cord had been cut off. BWD Electronics Pty Ltd was a Melbourne-based company which made electronic test equipment, from 1955 until the company was deregistered in 1993. It was founded by John Beesley, Peter Wingate and Bob Dewey, hence the name. The company was purchased by McVan Instruments, which is now the Dutch company Observator Instruments (siliconchip.com. au/link/ab5z). Many documents such as manuals and advertising related to BWD can be found at www.kevinchant.com Voltage reference (1960s or 1970s?) This voltage reference is home-built or, more likely, laboratory-built. It uses a 1N429 zener diode as a voltage reference. 16 Silicon Chip Hi-Need electronic sample book (1960s?) This electronic component sample book contains samples and technical information of every component the Japanese company sells or sold. We could find no reference to this company online. The components appear to be of mid1960s vintage (many different types of components are stamped with either “64” or “66”). See the video I made titled “Hi-Need electronic component sample book” at https://youtu.be/ C0tqY89MiTk Dual power supply (1970s) Modern power supplies have become quite small, especially compared to this one, given the modest output it produces. It provides a relatively modest 2 x 0-20V at 1A, yet occupies a 19-inch rack enclosure. The semiconductor date stamps show 1978. Timer/counter/frequency meter (1970s) This piece is presented as it was found. Examination revealed a semiconductor with a date stamp of 1974, so this would be its approximate manufacturing date. The device was unbranded, but it had a circuit board inside labelled “RMIT Department of Applied Physics”. It could have been a teaching aid. CB radio power supplies (1970s and 1980s) Many readers will remember these; Australian-made 12V, 2A power supplies for CB radios used in base-station configurations, created for the 27MHz CB craze of the late 1970s and 1980s. Later, UHF CB on 477MHz took over. Unlike modern power supplies, these were not switchmode but used a transformer and rectifier. I found many of these in the hoard, mostly with their cords cut and evidence of having been exposed to the elements. The example shown is the Panther brand, which was either made or distributed by G.A.F. Control Pty Ltd in Melbourne. It had approval number V77486/ PS132. Australia’s electronics magazine siliconchip.com.au e u g o l a t a C 2021-22 ! W O N T U O 00 new lines! 2 1 r e v O . s ic n st in electro te la e th h it w d 424 pages fille Yours FREE with this issue of Silicon Chip. If you didn’t receive your copy, contact your newsagent or register at www.altronics.com.au/catalogue to receive one by post for FREE! 1300 797 007 ® Shop online 24/7 <at> altronics.com.au Build It Yourself Electronics Australia’s electronics magazine MarchCentres 2021  17 siliconchip.com.au Akigawa L-120B multimeter (1970s or 1980s) This photo shows a late 1970s or 1980s miniature analog moving-coil multimeter, with a mirrored scale and 2mm jack sockets. It has a typical-for-the-era 20k per volt DC meter impedance. It is a neat piece, but I couldn’t find any reference to it online. Analog meters aren’t obsolete, and still have niche uses today, such as watching values change that would be too fast to see on a digital meter. However, due to their lower impedance than digital meters, they do load circuits more. Electronics Australia Low Distortion Audio Oscillator (1980s) This was built from a kit, described in the December 1986 and January 1987 issues of Electronics Australia. It featured an ultra-low-distortion audio oscillator in the range 10Hz to 100kHz with a very stable output level. The low-distortion feature is vital for the accurate setting of steep-cut notch filters and measuring the low distortion of modern amplifiers. It was built with the optional meter which would have cost an extra $25. Apart from some dirty switch and potentiometer contacts, it still works well. The table below shows a comparison of the distortion specifications of this oscillator with those of a commercial HP 209A (first made in 1968, but still in use today). Clearly, the EA project was an outstanding performer! Frequency 20Hz 100Hz 1kHz 10kHz 20kHz 100kHz EA design < 0.0075% < 0.0015% < 0.001% < 0.002% < 0.005% < 0.02% HP 209A in low-distortion mode 0.085% 0.077% 0.038% 0.047% 0.055% 0.051% Table 1 – sinewave THD performance comparing the EA signal generator with the HP209A Realistic SA-10 (1980s) This low-cost Realistic SA-10 audio amplifier was a surprisingly popular amplifier, produced from 1975 to 1994. It was sold in Australia by Tandy (owned by Radio Shack in the USA). They started production with a silver face, which was changed to black in 1979. Even today, they are popular as a bench test amplifier (despite mediocre performance at best!). This one has a QC mark date code of 1985. There were three versions produced, including a discrete version and an IC-based version. All had an output of 1W/channel with 10% THD. See the video titled “Realistic SA-10 stereo amplifier” at https:// youtu.be/K8DvfmOkDDc This one is the 31-1982B, with a ceramic cartridge input (popular at the time) rather than a more modern magnetic one. 18 Silicon Chip Homemade breadboard rig (1980s) This looks like a home- or laboratory-made breadboard rig which includes a signal generator, frequency meter and multimeter. It is made to a very high standard. Inside are Intersil 7107 LED DPM and Intersil ICM 7226A evaluation kits, as well as some custom boards. The Intersil boards provide the 3.5-digit LED display, A/D converter, voltage reference and clock; and 8-digit multifunction frequency counter and timer respectively. For further information on the ICL71XX series see siliconchip. com.au/link/ab60 and for information on the 7226A, see siliconchip. com.au/link/ab61 We estimate this piece is from the early 1980s, as the 7226A IC had a 1981 date code on it and the unit employed Australian-made Ferguson transformers. Speedie Walkvision TV (1990s) A near-totally useless item (today!) is this battery- or DC-operated monochrome TV. According to radiomuseum.org, it would have been made around 1990. “Test Master” (1990s) This looks like it might have been made from a kit but we could not identify it as being from SILICON CHIP, EA or any other Australian electronics magazine. It is a beautifullymade test apparatus that provides power, audio amplification, square and sinewave generation and transistor test functions. Unusually for a homemade device, it includes cable-lacing and edge connectors. We found a receipt inside for a component used to build it from Dick Smith Electronics, dated 1991. Electric fence energiser (1990s) Here’s a weatherbeaten, Thunderbird M200 electric fence energiser, probably from the 1990s or 2000s. These units were made in Mudgee, NSW by Country Electronics Pty Ltd. As with many devices in the hoard, the power cord had been cut off, so its working condition is unknown. We couldn’t easily open the unit to inspect it because, even though it had a screwon back, it had also been sealed with adhesive. It is mains-powered and can energise up to 20km of electric fence with 6.8-7.2kV “zaps” to encourage livestock not to try to cross it. It consumes about 7-11W. Australia’s electronics magazine siliconchip.com.au Electret microphone (1990s) The Realistic/Radio Shack 33-1065 stereo electret microphone shown here was discontinued around 1992. The individual microphones are hinged for storage or greater spatial separation. It is battery-powered and was made in Japan. As a matter of trivia, this model was used as the basis of a movie prop in Ghostbusters 2 (the “Giga Meter” – see below). Helping to put you in Control Universal Input to 4-20mA Transmitter Universal Thermocouple, RTD and voltage Input to 4-20mA Transmitter mounted in an IP65 weatherproof box. SKU: KTA-367 Price: $132.28 ea ESP32 Controller Arduino-compatible ESP32 controller with 2 relay outputs, 2 transistor outputs, 2 optoisolated inputs, 2 0/4-20 mA analog I/Os, 2 0-10 VDC analog I/Os and 4 GPIOs. Interfaces using USB, RS-485 serial, I2C, Wi-Fi or Bluetooth. DIN rail mountable. SKU: KTA-332 Price: $251.90 ea Sinclair multimeter (1970s) Sinclair made a variety of innovative products such as calculators (from 1973), electronic watches (1975), handheld TVs (1983) and the ZX80 (1980) and ZX81 (1981) computers. This PDM35 multimeter was released in 1979. Sinclair was a company known not to waste anything, hence their low prices. Inspection of the multimeter reveals that the case has been repurposed from Sinclair’s line of calculators. Descendants of the Sinclair companies still exist. After the company broke up around 1978, there was a series of spin-off companies and mergers and acquisitions. Since 2013, what remained of Sinclair is now known as Aim-TTI or Aim and Thurlby Thandar Instruments (www.aimtti.com). Digirail OEE WiFi The DigiRail OEE is the ideal tool to monitor and examine the performance of your production lines. It reads the sensors that monitor the operation of machines, devices or processes and determine operation time. SKU: SIG-111 Price: $241.95 ea N1030-RR PID Temperature Controller N1030-RR Compact sized PID Temperature Controller with auto tuning PID 230VAC powered. Input accepts thermocouples J, K, T, E and Pt100 sensors. Two Relay outputs. SKU: NOC-322 Price: $105.55 ea 750W ELDM Brushless AC Servo Motor Leadshine ELDM8075V48HM-A4 750 W brushless AC servo motor with 1000 line encoder. SKU: MOT-457 Price: $306.85 ea Other reports on electronic hoards David Jones from EEVBlog investigated another Australian hoard. However, that one was extremely neat and well-organised, with a staggering number of salvaged electronic components as well as a collection of SILICON CHIP magazines. See the video titled “EEVblog #737 - World’s Biggest Collection Of Electronics Components” at https://youtu.be/x8nbHYOc8ns Helping people like me in future When you make an electronic device, it would be a good idea to place a label inside describing what it is, the source, when it was built and who built it. That will make the job of future electronics archeologists much easier! SC Brushless Servo Motor Drive The ELD2-RS7030 brushless servo drive, power range from 25W to 1200W, are special DC input, motion control product designed for machines and applications that request a best balance between reasonable cost and outstanding performance with MFC/vibration suppression. SKU: SMC-411 Price: $380.83 ea RTD Temperature probe with magnet fixing RTD probe with magnet fixing for surface temperature measurement. -50 to 200 ºC. Silicon Cable 3 meters. SKU: CMS-007 Price: $142.95 ea Help for hoarders If you Google “help for hoarders”, you will find a large number of resources to help such people. The Victorian Government, for example, has a web page on the problem at https://www2.health.vic.gov.au/ageing-andaged-care/wellbeing-and-participation/hoarding-and-squalor I’m sure other states would have similar. siliconchip.com.au For Wholesale prices Contact Ocean Controls Ph: (03) 9708 2390 oceancontrols.com.au Prices are subjected to change without notice. Australia’s electronics magazine March 2021  19 Our capabilities CNC Machining UV Colour Printing Enclosure Customisation Cable Assembly *** Box Build *** System Assembly Ampec Technologies Pty Ltd Australia’s electronics magazine Australia’s electronics magazine 20 Silicon5000 Chip siliconchip.com.au Tel: (02) 8741 Email: sales<at>ampec.com.au Web: www.ampec.com.au siliconchip.com.au FEBRUARY 2021 37 Care for your rechargeable batteries. . . High-current Battery Balancer Part 1 - by Duraid Madina Properly balancing batteries is critical for a long life, especially if they are lithium-based rechargeable types. But many balancers are inefficient, as they dump excess charge for a given cell, restricting how fast you can charge the batteries and wasting power. Not this one – it redirects that extra charge into other cells, so you can charge fast with little heat or waste! M ost rechargeable batteries consist of an array of nominally identical cells, connected in series, parallel or series/parallel to meet particular voltage, current, and capacity requirements. Batteries with many series-connected cells often only expose the connections at the extreme ends. For example, a typical lead-acid car battery has six cells (2V x 6 = 12V) but only two terminals. To charge such a battery, we apply a higher voltage than the total of all the cells across those two terminals, and current flows through all six cells, increasing their state of charge. But there is no guarantee that each cell starts with an identical voltage, and despite their identical construction, cell capacity can vary, especially as the battery ages. This is not a big problem with car batteries because lead-acid cells tolersiliconchip.com.au ate slight overcharging well. By overcharging the battery a little, cells with a lower charge get a chance to ‘catch up’ to the others, while the most highly charged cells dissipate the charging current as heat. Despite this, large lead-acid battery banks (as might be used in a renewable energy installation) will last longer if they are kept balanced. In this case, you might have several batteries in series, so not only do you need to be concerned about inter-cell balancing within a given battery, you also need to consider balancing the charge between batteries. The fact that you might be using batteries with different ages and possibly even from different manufacturers makes this even more critical. Then there is the case of lithium-ion and similar rechargeable cells. There is a great variety of lithium chemistries around, but many of them do not tolAustralia’s electronics magazine erate overcharging. They also can be easily damaged by over-discharging. So keeping lithium rechargeable batteries balanced is even more crucial. Since this Balancer can handle cell voltages as low as 3V and as high as 15V, it is suitable for a wide range of balancing tasks, including balancing the cells within a lithium-ion battery, or balancing individual lithium-ion or lead-acid batteries. Each Balancer can handle up to four cells (or groups of cells) or batteries, and you can combine multiple balancers for larger installations. Avoiding cell damage One conservative option would be to immediately stop charging as soon as any cell reached its maximum permissible voltage, but that would leave the remainder of the cells not quite fully charged. Left unchecked, what might start March 2021  21 The Battery Balancer is constructed on a single 4-layer PCB just over 100mm wide, so it’s small enough to slot in anywhere. Got more than four batteries? Build as many Balancers as you need! as a minimal imbalance between the cells, could over repeated charge/discharge cycles develop into a much larger imbalance, with the result that as a whole, the battery has significantly less usable capacity. Worse, when the battery is fully discharged, those cells which were not fully charged could become over-discharged and damaged. So we need a way to ensure that as a battery is charged and/or discharged, the cells are kept in balance. Each is then charged to approximately the same voltage, so that the battery capacity remains good and the cells degrade equally. This way, a battery need not be discarded just because one cell has degraded more rapidly than the others (a common problem!). The simplest way to do this is to shunt current around any cell that has a higher voltage than the others during charging. We have used that approach in the past, for example, in our March 2016 Battery-Pack Cell Balancer (siliconchip.com.au/Article/9852). That design could handle packs with up to six cells, but only provided about 200mA of balance current. That limited it to applications with chargers up to 10A, and it got quite warm during operation, as all that power was being turned into heat. Our new Balancer, being much more efficient, produces much less heat for a given balance current and thus can handle much higher battery charge currents – to 50A or more, assuming the cells are matched to within 5% (a fairly conservative figure for a healthy battery). 22 Silicon Chip Operational overview This Battery Balancer helps to ensure that cells in a battery are kept in balance by periodically checking the cell voltages and moving charge from cells at a higher voltage to cells at a lower voltage. To do this, it has three main sections, as shown in Fig.1. These are: 1) A voltage sensing front-end which draws very little current from the cells. 2) A control section consisting of little more than a Microchip SAM-L10 32-bit microcontroller, which also draws hardly any current when idle (according to Atmel, the “industry’s lowest power in its class”). 3) A power section for moving charge between cells. The Balancer has been designed to achieve a high level of practical efficiency in three ways. Firstly, the amount of power consumed when not actively balancing cells is kept low, by allowing virtually everything to be switched off, and ensuring that most of what remains draws very little power. Secondly, the amount of power required to see if balancing required is kept low, through the use of simple but energy-efficient voltage dividers. Thirdly, instead of using inefficient schemes for balancing such as simply dumping charge from cells that have too much charge into resistive loads, the Balancer recycles charge by taking it from cells that have too much, and adding it to those that have too little. We have also tried to make the balancer flexible; not only can it balance batteries of up to four cells, or sets of up to four batteries, but with a small amount of external help, it can serve as a battery charger and even a battery discharger! Transferring charge SC Ó Fig.1: while highly simplified, this shows the basic configuration of the High-current Battery Balancer. Microcontroller IC2 measures the voltage across each battery/cell via resistive dividers. If one has a voltage that is significantly higher or lower than the others, it transfers power into or out of the imbalanced cells via the four power transfer blocks. These can efficiently transfer energy to or from one battery/cell to the entire ‘stack’, and by extension, between multiple batteries/cells via the stack. Australia’s electronics magazine Perhaps the most critical part of the Battery Balancer is the section which transfers charge between batteries/cells (and maybe also a charger or a load). This section is replicated four times on the board, once for each battery/ cell that can be connected. A simplified version of this circuit is shown in Fig.2. This section can transfer energy to or from the battery/cell shown at the left and the complete battery/“stack”. Energy can be transferred from one battery/cell to another via the “stack”. Let’s suppose we notice that one cell has a voltage that is lower than the other three. We can use that cell’s power section to transfer charge from the whole battery to that cell, to bring it into balance. This happens cyclically. First, the “stack-side” transistor (QX) siliconchip.com.au is switched on and current begins to flow from the battery, through the stackside transformer winding, energising the transformer’s core. Because the cell-side power transistor (QY) is off, the voltage across the cell-side transformer winding quickly rises. A moment later, the stack-side power transistor is switched off, and the cellside power transistor (QY) is switched on. This transfers the energy from the transformer’s core into the cell. When this is estimated to have completed, the cell-side power switch is turned off and the cycle repeats, with a duty cycle proportional to the desired rate of charge transfer. The inductance of the transformer can be chosen relatively freely. Transformers with higher inductance allow operation at lower frequencies, but have higher resistive losses. Transformers with lower inductance require operation at higher frequencies, but have lower resistive losses. Note, however, that transformers with particularly low winding inductances tend to have slightly reduced coupling between the windings, though only a few such transformers have coupling so poor as to be a significant factor for this Battery Balancer. The voltages at the drains of QX and QY can exhibit significant inductive ringing. If it is too severe, it might exceed the transistor ratings. We have attempted to keep the in- Features & specifications • • • • • • • • • • • • • • • Balances two, three or four series-connected cells or batteries Suits li-ion, LiPo, LiFePO4, lead-acid, AGM and other chemistries Each cell or battery can range from 2.5V (fully discharged) up to 15V maximum Balancing current: up to 2.5A Charging current: up to 50A Efficiency: typically around 80% Quiescent current: around 100µA per battery/cell 5mm spade lug connections for high-current batteries 2.54mm-pitch pin header for connecting smaller batteries Switching frequency: typically 100kHz Multiple Balancers can be combined for balancing more cells or batteries It can also act as an efficient battery charger or discharger Four onboard status LEDs plus one adjustment potentiometer Serial status/debugging interface Compact size (108 x 80mm PCB) ductance of these paths low by placing these devices very close to their respective transformers. But for higher-voltage applications, it is still prudent to place series RC snubbers (ie, Csnub and Rsnub) across the transformer windings. For lower-voltage applications (eg, balancing lithium-ion cells), these snubbers can be safely omitted, and that might even result in a small efficiency gain. The micro controls Mosfets QY and QA via an ISO7041 isolator because the negative end of the battery/cell is not connected to ground (unless it is the bottom-most in the stack). The driving scheme is a bit more complicated SC Ó Fig.2: a stripped-down version of the circuitry in each power transfer block. Power goes between the battery/cell and the stack via Mosfets QX and QY and the transformer. QX is ground-referenced, so it is controlled from a microcontroller output pin, while QY is referenced to the negative cell/battery terminal. Therefore, the signal from the microcontroller to control QY goes through an ISO7041 isolator, which is powered from a 3.3V rail derived from the cell/battery voltage. siliconchip.com.au Australia’s electronics magazine than shown here, as will soon become apparent. The ISO7041 is powered by its own ‘floating’ 3.3V regulator from the battery/cell, to allow for the battery/cell voltage to vary over a wide range. Note how the negative terminals of the bypass capacitors both for the individual battery/cell and for the stack are connected via N-channel Mosfets, rather than directly to the negative terminal of the battery/cell and GND respectively. This is to provide a ‘softstart’ function which greatly reduces the sparks generated when connecting up batteries or cells. Full circuit details The full Battery Balancer circuit is shown in Fig.3, although two of the four charge balancing circuits have been partly omitted to save space. All four are configured identically. Now you can see the full detail of this part of the circuit, which reveals a few extra subtleties. Firstly, the isolator outputs cannot drive the Mosfet gates and microcontroller directly as they are too weak to achieve the required switching speeds. We spent a lot of time investigating the use of integrated gate driver ICs in that role, but most of them have a significant quiescent current draw and stop functioning at low supply voltages. While this could be resolved for the lower cell power sections by deriving their supply rails from ‘one cell up’, this would leave the topmost power section needing an alternative source of power, eg, from a boost converter. Instead of using integrated gate drivers, we decided instead to use simple NMOS/PMOS transistor pairs March 2021  23 24 Silicon Chip Australia’s electronics magazine siliconchip.com.au Fig.3: the full Battery Balancer circuit consists of four identical sections at left, which efficiently transfer power between the batteries/cells and the ‘stack’ connected between CON2 and CON7. The control and sensing section is at right, and is based around 32-bit microcontroller IC2. The voltage sense resistive dividers are disconnected using Mosfets when they are not in use to keep the quiescent current draw low. LEDs7-9 and LED11 flash to indicate when charge is being transferred to or from specific cells. siliconchip.com.au Australia’s electronics magazine March 2021  25 Scope1: this shows how the power switching Mosfets are driven. For clarity, two isolated pulses are shown. The red and blue traces show stack side and cell side PWM signals for balancer channel 2 (gate driving inverter inputs) as driven by the microcontroller and digital isolator, respectively. The yellow and green show the stack side and cell side power Mosfet gate voltages (gate driving inverter outputs). The majority of the ringing on these traces is due to measurement error. configured as inverters. Happily, there are many dual SMD Mosfets available which include one N-channel device and one P-channel device, so each inverter is contained within a single package. In the case of the uppermost section of the circuit, these are Q11 and Q12. In each case, the Mosfet driving the stack side of the transformer (eg, Q9) is connected source-to-ground, and is a logic-level FET. It is driven by the 0-3.3V output of the inverter pair which are themselves driven from a microcontroller digital output pin (in this case, pin 22, labelled SSPWM3). A 10kΩ pull-up resistor is provided at the input of each of these Mosfetdriving inverters so they have a low output when the micro is not in control of that pin (eg, it is in reset or being programmed). The other transformer-connected Mosfet (eg, Q10) has its source connected to the junction of this battery/ cell and the one below. So as described above, it is driven by an isolator that runs off a 3.3V floating supply referenced to that same voltage. Therefore, the Mosfet-driving inverter is also connected across this 3.3V floating supply, to provide an appropriate swing for that Mosfet. It too has a 10kΩ pull-up resistor to hold the Mosfet off by default. But note that the Texas Instruments ISO7041 low-power digital isolator has variants with different default pin states. The 26 Silicon Chip Scope2: here, the red and blue traces are as in Scope 1, but the yellow and green traces show the drain voltages of the main switching Mosfets (ie. the bottom ends of the power transformer) – the stack side node is in yellow, while the cell side node is in green. Here, less of the ringing on the switching nodes is due to measurement error, particularly in the phase where both power Mosfets are off, allowing their drains to float. one we have chosen provides high outputs if its inputs are not driven, or the input side of the device is not powered (as opposed to the ISO7041F, which offers low outputs). This provides us with a safe ‘resting’ state. 1Ω resistors limit the power through the gate drive inverters, adding to the inverters’ intrinsic ~0.2Ω output resistance. This keeps the peak gate drive currents below 3A. It is not critical that the low-dropout (LDO) floating regulator (REG3 here) falls out of regulation if the cell voltage drops below 3.3V, as both the isolator and gate driver are capable of operating below this voltage. Note though that if a cell voltage is ever at less than 2.5V (a dangerously low voltage for a lithium-polymer cell, and a very low voltage for a lithium-ion cell), no attempt will be made to transfer charge to or from this cell. Instead, it is assumed that a battery with cell voltages this low is likely to have minimal charge, and so even if imbalanced, merely charging the entire battery will quickly bring the cell voltages above 2.5V. Balancing can then resume long before any of the cells approach full charge. For more details on how charge transferral works, refer to scope grabs Scope1 & Scope2 and their captions. Voltage sensing To know which batteries or cells should be charged or discharged, the Australia’s electronics magazine Battery Balancer needs to be able to take accurate voltage measurements across each battery/cell. Sensing low voltages accurately is becoming easier; high-performance analog-to-digital converters (ADCs) are readily available, and modern microcontrollers often include ADCs that would have been considered high-performance not that long ago. In our case, the SAM-L10 micro has a 12-bit ADC capable of taking one million samples per second. As we need to sense voltages up to around 60V (say, four 12V lead-acid batteries in series under charge), a kind of front-end is required to bring these voltages down into typical ADC ranges. One option would be to use operational amplifiers (op amps) that can tolerate these higher voltages, to divide (and possibly shift) the voltages as required. Suitable parts are not hard to find, but they are not cheap. Moreover, because the voltages the Battery Balancer needs to sense do not vary quickly, very little in the way of high-frequency performance is required, so offset-correcting chopperstyle op amps are applicable. However, the performance of the required op amp circuits would be dominated by the accuracy of the connected resistors. The power consumption of these op amps, while impressively low in many devices, is high enough that we couldn’t leave them powered all the time. siliconchip.com.au So instead, we use a simple switchedcapacitor, switched-ground resistive voltage divider, as shown in Fig.3. To avoid the constant power consumption of an always-on voltage divider, we add low-side NMOS FETs (Q8a, Q13a, Q19a & Q24a). Even very small signal FETs introduce only a couple of ohms of error while on. When off, however, the voltage can drift above the tolerance of the microcontroller input pins. So a second set of NMOS pass transistors (Q8b, Q13b, Q19b & Q24b) ensures the microcontroller never sees such voltages. Once again, we can take advantage of dual Mosfet packages so that each pair of transistors is just one part to be soldered to the board. To save microcontroller pins, all of the voltage dividers share a common pair of control lines. To take a set of voltage readings, first, the low-side NMOS switches are turned on, enabling the divider. Next, the pass gate NMOS switches are turned on, allowing the filter capacitors to start settling towards their respective values. Finally, the microcontroller’s onboard ADC takes its samples, allowing the software to know the voltage across each battery or cell. With the 100kΩ/2.2kΩ dividers used, and the 12-bit ADC having a 1.65V reference, the nominal sensed voltage range is 0-76.65V, and the resolution is 18.7mV. That’s precise enough to detect small differences between 12V battery voltages. Refer to Scope3 for more information on how this process works. For lower voltage batteries such as li-ion, LiPo or LiFePO4 packs with cells typically ranging from 2.7-4.2V, the resistive dividers are changed to 100kΩ/6.8kΩ which gives a range of 0-25.9V and a resolution of 6.3mV, which means we can balance out inter-cell voltage differences starting at about 10mV. A virtually identical arrangement is used to sense the voltage across the whole stack using Mosfets Q18a & Q18b (which will probably be the same as one of the cells, but not necessarily the same one, hence the separate divider) and also the rotation of potentiometer VR1 via Mosfets Q7a and Q7b. This is used to set various parameters, which will be described later. While an independent stack voltage monitor might seem redundant, it comes in handy when using the Battery siliconchip.com.au Parts list – High Current Battery Balancer (suitable for 12V battery balancing; see below for other options) 1 four-layer plated through PCB coded 14102211, 108 x 80mm 4 4.7µH 1:1 transformers (T1-T4) [eg, Coilcraft MSD1278**] 5 3A fast-acting SMD fuses, M6125/2410-size (F1-F5) [eg, Bourns SF-2410FP300W-2] 1 0.75A fast-acting SMD fuse, M6125/2410-size (F7) [eg, Bourns SF2410FP075W-2] 2 SMD ferrite beads, 470W <at> 100MHz, M2012/0805-size (FB1,FB2) [eg, Taiyo Yuden BK2125HM471, Murata BLM21AG471SZ1D or Kemet Z0805C471BSMST] 1 100kW vertical multi-turn trimpot (VR1) 1 momentary SPST tactile pushbutton switch (S1) 11 5.08mm pitch PCB-mount vertical spade lugs (CON2-CON12) [eg, Altronics H2094/H2095] 1 5-pin straight or right-angle header (CON13; optional – for smaller battery packs) 1 4-pin header (CON14) 1 8-pin header (CON15; optional, for ICSP) 1 2x4-pin header (JP1) 1 jumper/shorting block (JP1) Semiconductors 1 ATSAML10E16A-AUT 32-bit microcontroller programmed with 1410221A.hex, TQFP-32 (IC2) 4 ISO7041 4-channel digital isolators, QSOP-16 (IC4,IC6,IC8,IC10) [Note: not ISO7041F] 5 NJW4184U3-33B# 3.3V LDO regulators (REG1,REG3,REG5,REG7,REG9) 4 BUK9Y4R8-60E* NMOS FETs, LFPAK-56 (Q1-Q4) 1 BUK9Y8R5-80E* NMOS FET, LFPAK-56 (Q5) 1 UM6K34N dual NMOS FET, SOT-363 (Q7) 5 UM6K31N dual NMOS FETs, SOT-363 (Q8,Q13,Q18,Q19,Q24) 8 BUK9Y14-80E* NMOS FET, LFPAK-56 (Q9,Q10,Q14,Q15,Q20,Q21,Q25,Q26) 8 QS6M4 dual NMOS+PMOS FETs, SOT-457T (Q11,Q12,Q16,Q17,Q22,Q23,Q27,Q28) 4 3mm or 5mm through-hole LEDs (LED7-LED9,LED11) 4 SMD 24V* TVS diodes, SMB size (M3226/1210) size (ZD1-ZD4) [eg, SMBJ24A] 1 SMD 64V* TVS diode, SMB size (M3226/1210) size (ZD5) [eg, SMBJ64A] 2 5V ESD clamp diode arrays (D6,D10) [Littlefuse SP0503BAHTG] Capacitors (all SMD M2012/0805 size X7R ceramic unless otherwise stated) 4 100µF* 35V radial organic polymer electrolytic (eg, Kemet A759KS107M1VAAE031) 2 47µF* 80V radial organic polymer electrolytic (eg, Kemet A759KS476M1KAAE045) 4 4.7µF 100V or 10µF 75V M3226/1210 11 10µF 50V ** for lower-current applications, Coilcraft 8 4.7µF 6V MSD1278-562 is a suitable alternative 6 1µF 50V # AP7370-33Y-13 is a suitable alternative 8 470nF 6V 3 100nF 50V Note: Csnub and Rsnub components 5 1nF 50V C0G     are not fitted for 4V/cell version 8 470pF* 250V C0G (Csnub) Resistors (all SMD M2012/0805 size 1% metal film unless otherwise stated) 5 100kW 0.1% 8 10kW 5 2.2kW* 0.1% 4 680W 5 330W 5 100W 5 20W 8 30W* (Rsnub) 8 1W M1608/0603-size Parts for ~4V cell balancing (eg, li-ion) – substitute for asterisked (*) items above 5 BUK9Y1R3-40H NMOS FETs, LFPAK-56 (Q1-Q5) 8 BUK9Y12-40E NMOS FET, LFPAK-56 (Q9,Q10,Q14,Q15,Q20,Q21,Q25,Q26) 4 SMD 10V TVS diodes, SMB size (M3226/1210) size (ZD1-ZD4) [eg, SMBJ10A] 1 SMD 24V TVS diode, SMB size (M3226/1210) size (ZD5) [eg, SMBJ24A] 4 100µF 16V radial electrolytic polymer capacitors 2 33µF 35V radial electrolytic capacitors 5 6.8k 0.1% M2012/0805 size metal film resistors Australia’s electronics magazine March 2021  27 Scope3: this shows the voltage sensing circuit in operation. The yellow trace shows the voltage to be measured (~12V) and the green trace shows the divided voltage present on the micro input pin (~240mV). The red trace is the voltage divider enable line, which has a duty cycle of less than 1%, minimising power consumption of the voltage dividers. The blue trace is the divided voltage pass control line, which ensures that only stable divided voltages reach the micro input pin. connections are via fuses, which is always a good idea given how much current a large battery (or in some cases, even a small one) can deliver if there is a fault. Each input also has a zener diode across it (after the fuse) which provides two functions. One, if a cell or battery is connected backwards, the zener will immediately conduct and blow the fuse. Two, if the cell or battery voltage is too high for some reason (eg, you’ve connected to the wrong battery terminal), the zener will go into avalanche breakdown, and in most cases, the fuse will again blow. By the way, in the parts list we’ve specified unidirectional transient voltage suppressors (TVSs) instead of zener diodes for these parts. They are effectively zener diodes, just with very high pulse current handling capability. Also note that the actual clamping voltage will be somewhat higher than the specified voltage, depending on the current being delivered from the source. We have taken that into account when selecting the parts, so that the protected parts of the circuit will not be exposed to damaging voltages at any reasonable current level. As the micro monitors all the various voltages, it will shut down if any of them are out of range. For example, if a cell voltage is too low for the circuit to function. Control section Balancer in other applications. For example, it can be used to allow charging batteries from other power sources such as solar panels, or also as a battery charger. It can even be used in conjunction with another Battery Balancer, to transfer energy between two different batteries, in either direction, while keeping both in balance. Note that to avoid error, we don’t take voltage readings while the power section is active. Soft starting/spark mitigation We found that the first prototype produced some nasty sparks when connecting batteries (as is not uncommon). This was mainly due to the inrush current to charge the capacitor banks. These sparks could possibly damage the connectors, or even weld them! We therefore decided that, since it was not difficult to mitigate this, we would do so. When power is first applied, the Mosfets in series with the negative terminals of each set of bypass capacitors are off. Those capacitors therefore slowly charge via the parallel 20Ω resistors. After the initial battery connection is made but before any balancing takes place, the microcontroller switches these Mosfets on, presenting the full decoupling capacitance only after the connection is made. The Mosfets effectively increase the ESR of the capacitor banks a little. However, with on-resistances that are a fraction of an ohm, the capacitors are still able to do their job of stabilising the cell and battery voltages nicely. The Mosfet turn-on time is quite slow as there are no inverters to drive them, but as they only switch on after the capacitors have charged, this doesn’t matter. While we still recommend taking care to positively connect batteries to the Balancer and being prepared for some amount of sparking to take place, this approach does greatly reduce the sparking that typically occurs. Circuit protection You will have no doubt noticed that all cell and battery 28 Silicon Chip The microcontroller section is quite straightforward due to the high level of integration on the SAM-L10 micro (IC2). Its internal oscillator is more than adequate as an instruction clock source in this application. Current-limiting resistors on digital outputs 15, 16, 23 & 24 are provided for it to drive four status LEDs directly (more on these later). ESD clamps are connected across the programming and UART interfaces to protect them from static discharge as these pins could be externally accessible. The microcontroller derives its power from linear regulator REG1, another NJW4184U3-33B. This was chosen to minimise quiescent current and operate over a relatively wide input voltage range (up to 35V). Its output passes through ferrite beads before reaching the microcontroller supply pins. It also provides power to the ‘near side’ of the various low-power digital isolators and the stack-side gate drivers. As these consume only a few milliamps while active, the power dissipated in the linear regulator is only a few tens of milliwatts in the worst case, when it is powered by a fullycharged 12V battery. While the gate drivers consume small amounts of current on average, they do so in an extremely bursty fashion, so they each have a local bypass capacitor. Software The Battery Balancer software is fairly simple, but it took some development to get it right, and there were a few choices to be made along the way. Perhaps the most critical task the CPU has to perform is producing the eight PWM signals required for balancing. There are many larger microcontrollers, frequently aimed at motor control applications, that feature large numbers of advanced PWM generators. The SAM L10 is small, inexpensive, and sips power, but has a more limited set of peripherals. The Balancer needs to produce short pulses of variable length at variable frequencies; if a pulse is too long, substantial currents can flow through the Balancer, leading to a blown fuse and possibly damage to other components, particularly the power Mosfets. Moreover, the Balancer needs Australia’s electronics magazine siliconchip.com.au to produce two PWM signals per cell. To achieve this, we use a software-driven approach. When a cell is to be charged or discharged, we define a “blip” routine as a series of instructions that are either NOP (no-operation), or single-I/O set/clear instructions. With a 16MHz CPU frequency, this allows us to control pulse trains with roughly 60ns precision. We then compute the desired number of ‘blips’ up to a safe maximum (currently set to 10,000), disable interrupts, and call the blip routine in a loop. Once the blip routine has run the desired number of times, the software stops all power train activity and determines the next course of action. Voltage sensing When not in the middle of charging or discharging cells to bring a battery into balance, the Balancer periodically checks the cell/battery voltages to determine which should provide charge, and which need to be given charge. We set the ADC voltage reference to Vdd/2 (ie, around 1.65V), noting that as the power train is inactive, the power consumption and consequently noise on the Vdd LDO output will be relatively small. Therefore, this voltage should be nice and steady. To measure a set of cell voltages, we first enable the resistor dividers by connecting their bottom ends to ground via the small-signal NFETs, and then enable the pass-transistor NFETs. We then pause for about 1ms while the capacitors on each of the sense lines settles towards their final value. Finally, we use the ADC to sample each of the settled lines before disabling the pass transistors and voltage dividers. The rotation of potentiometer VR1 is sensed at the same time that the other voltages are measured. It can be used to configure both the peak balancing current and the cell mismatch threshold above which balancing takes place. Serial/USB interface The microcontroller features a UART, which is connected (via slew-limiting resistors and ESD clamping diodes) to pin header CON14. This can be easily converted to USB through the use of third-party ICs or cables such as FTDI’s “TTL-234X-3V3”, though note that these cables cannot be plugged directly into this header; some jumper leads will be required. If electrical isolation is required (or at least desired), our Mini Isolated Serial Link project, starting on page 68 of this issue, could be connected between the Balancer board and the USB/serial adaptor. This board can be programmed by plugging a PICkit 4 into the ICSP header (CON15). For safety, this should only be done with no batteries or cells connected to the Balancer. The board features four LEDs, one for each battery/cell. These are off by default but blink slowly if a battery/cell is being charged, or rapidly if a battery/cell is being discharged. The power consumed by the Balancer’s control logic is small compared to that consumed by the LEDs while switched on! For this reason, the LED duty cycles have been kept low. Next month In part two of this feature next month, we will cover building the Battery Balancer, testing it, configuring it and using it, as well as some safety tips. SC siliconchip.com.au POWER SUPPLIES PTY LTD ELECTRONICS SPECIALISTS TO DEFENCE AVIATION MINING MEDICAL RAIL INDUSTRIAL Our Core Ser vices: Electronic DLM Workshop Repair NATA ISO17025 Calibration 37 Years Repair Specialisation Power Supply Repair to 50KVA Convenient Local Support SWITCHMODE POWER SUPPLIES Pty Ltd ABN 54 003 958 030 Unit 1 /37 Leighton Place Hornsby NSW 2077 (PO Box 606 Hornsby NSW 1630) Tel: 02 9476 0300 Email: service<at>switchmode.com.au Website: www.switchmode.com.au Australia’s electronics magazine March 2021  29 Not quite vintage radio . . . or is it? by Dr Hugo Holden The Fetron . . . and the one and only all-Fetron radio You would probably be aware that there are some similarities between valves (aka vacuum tubes) and field-effect transistors, or FETs. You may also know that some people have created valveequivalent devices based on FETs. But did you know that there were commercially-made semiconductorbased triode and pentode equivalents known as “Fetrons”? I am fascinated by these, so I built a superhet using little else. 30 Silicon Chip Australia’s electronics magazine siliconchip.com.au T he Fetron, a unique combination of N-channel Junction Field Effect Transistors (JFETs), using the Cascode configuration, was a product of research and development in the Aerospace and Avionics industry (by the Teledyne Company in the USA) in the early 1970s. They were built primarily as a plugin valve or solid-state pentode replacement, although triode equivalents were also made. The basic idea behind the Fetron was to have the electrical properties of a pentode, but no microphony and no heater power consumption, along with the other advantages of semiconductors: greater efficiency and reliability, with lower noise and higher gain. Fetrons usually had a much higher amplification factor than the valve they replaced. Teledyne also produced a range of semiconductor devices such as high-voltage Junction FETs and they still produce beyond excellent-quality miniature RF relays. Every Teledyne product I have inspected and used has always impressed me with its innovative nature, outstanding manufacturing quality, excellent physical appearance and electrical performance. Because of this, I decided to engineer a multi-band radio composed of entirely Fetrons, powered by a single 90V battery or DC supply, and incorporating some of my other favouriteTeledyne devices. Replacing valves with semiconductors The idea of replacing a valve with a plug-in transistor substitute has occurred to many people since the invention of the transistor. Although there are mathematical models for transistors as voltage-to- Reproduced rather significantly larger than life size, this is the TS6AK5 used in the Fetron Receiver. The type number is designed to show its equivalence to the 6AK5 valve. current control devices, fundamentally, they are current-to-current control devices. I know that some people disagree with this (for example, audio guru Douglas Self), but it is generally accepted to be true. In most instances, the input (baseemitter) current controls the output (collector-emitter) current. Valves, on the other hand, are voltage-to-current control devices or transconductance amplifiers, where usually the grid-to-cathode voltage controls the anode-to-cathode current. Transistors in the grounded-emitter configuration have a much lower input resistance than valves in the groundedcathode configuration. When high-voltage JFETs arrived on the scene, they were possible substitutes for the triode valve. They had a similar transfer function of gate voltage versus drain current, compared to grid voltage versus anode current for the triode. Also, JFETs have a similarly high input impedance to a valve. In the grounded-source or grounded-cathode circuit, both the JFET and the triode are influenced by the effective amplification of the drain-togate (or anode-to-grid) capacitance – known as the Miller effect. This capacitance, which is intrinsic to the device, is multiplied by its amplification factor. This limits the high-frequency response and results in significant input to output feedback as the operating frequency increases. In triode circuits, if a tuned circuit with a similar resonant frequency is placed in both the grid and the anode circuit, oscillations occur due to the feedback capacitance and the two resonant circuits exchanging energy with each other. Historically, the Miller capacitance problem was solved with an added neutralisation capacitor feeding back an out-of-phase signal from a coil extension on the anode resonant circuit to the grid (or to the base in a transistor circuit) via a small adjustable capacitor. In early transistor radios, intermediate frequency (IF) amplifiers using devices such as the OC45, which had a sizeable internal feedback capacitance, required neutralisation. Later, better transistors such as the OC169, AF117 or AF127 had a much lower feedback capacitance and didn’t require neutralising in 455kHz IF stages. In vintage TRF radios based on triode valves, the added neutralising capacitor was called a Neutrodon Fig.1: four more-or-less equivalent inverting amplifier circuits. At left is the pentode valve, followed by a pair of triodes in a cascode configuration, two JFETs in the same configuration and the simplified scheme used in the Fetron (which requires specific JFET characteristics). siliconchip.com.au Australia’s electronics magazine March 2021  31 and the radios sometimes called Neutrodynes. Neutralisation is not necessary for grounded drain (collector or anode) or ‘follower’ circuits because the drain (collector or anode) voltage is pinned to a fixed potential, preventing signal feedback via the Miller capacitance to the input gate (base or grid). The pentode, however, has the unique property of high isolation between its input(grid) and its output (anode) due to the screen grid. Pentode valves, for example, are excellent in radio frequency (RF) stages or intermediate frequency (IF) amplifiers as they are stable with a tuned circuit in both the grid and the anode circuit. Fig.1 shows several similar amplifying stages with ‘black box’ input and output circuits. No resistors or bias components are shown, to keep it simple. For the pentode, the screen grid voltage is held at a constant voltage K. This is usually done by connecting it to a resistive divider with a bypass capacitor, or connecting it to the HT supply. Two triodes arranged in Cascode work similarly, by clamping the upper triode’s grid to a fixed voltage K, which sets the upper triode’s cathode to another fixed potential (k). This stabilises the anode potential of the lower triode, and as a result, the Miller effect is eliminated. The JFET equivalent of the Cascode is also shown; to package this circuit in a single device would require four leads. Also, the ‘screen’ connection would require a different bias voltage compared to a valve circuit, so it could not be a direct replacement. The Fetron solves this problem by connecting the gate of the upper JFET to another voltage source; ingeniously, the source voltage of the lower JFET. This voltage is usually constant from an AC perspective in most valve circuits, as the cathode is typically bypassed. If it is not, it still does not matter, as any AC component coupled via the gate of the upper JFET via its source and the drain to the lower JFET is in phase with the input voltage on the gate of the lower JFET. Hence, there is no potential difference across the Miller capacitance (from gate to drain) of the lower JFET. Thus, the Miller effect is still eliminated. 32 Silicon Chip These pages, reproduced from the May 1973 issue of “Practical Wireless” magazine, show that Fetrons were more than a twinkle in an engineer’s eye The drain current properties of the two JFETs within the Fetron have to be carefully chosen for this configuration to work. Equivalent devices Reproduced above is a historical article (1953) on the TS6AK5 Fetron, which was designed to be equivalent to a 6AK5 pentode. There was also the TS12AT7, equivalent to the 12AT7 triode. Note the very high amplification factor of the TS6AK5 Fetron of 22,500, compared to the 2,500 for the 6AK5 valve, even though most of the other parameters are nearly identical. The drain resistance is very high at 5MΩ, as the JFET is an excellent constant-current source. The transconAustralia’s electronics magazine ductance (gm) or ratio of change in plate (drain) current to grid (gate) voltage is also the ratio of the amplification factor to the plate (drain) resistance. In this case, it is 4500μmhos (22,500 ÷ 5,000,000Ω); about the same as the 6AK5 valve. There are three “features” of the Fetron not alluded to in the data. The first is that the metal can must be Earthed if it is being used in a radiofrequency application. The second is that if the input terminal (gate of the lower JFET) is taken positive with respect to the source (cathode connection), the gate suddenly draws current. In the 6AK5 valve, this is a very gentle process, but the TS6AK5 suddenly conducts as the gate siliconchip.com.au runs from a single 90V battery, although later I built a 90V DC mains supply. It is a dual-band single conversion superhet with a tuned RF stage. The frequency coverage is 550kHz to 1650kHz (MW) and 5.7MHz to 18.2MHz (SW). The antenna is a 6-inch (150mm) long, 12.7mm diameter ferrite rod which also works well for shortwave up to about 10MHz. The MW coils are wound with 60-strand Litz wire. Above 10MHz, an external antenna is useful for the shortwave band. The 11 Fetrons are all TS6AK5s, used as follows: • one for the RF amplifier, • one for the local oscillator (LO), • one for the LO buffer, • one for the mixer, • two as IF amplifiers, • one for the audio preamplifier and • four for the audio output stage, wired in parallel for 1W undistorted Class-A output into a 3.2Ω, 4-inch (100mm) speaker. The LO buffer is needed to provide an output to drive a frequency counter. Two Teledyne 2N4886 high-voltage Nchannel JFETs are also used in a bridge circuit for a signal strength meter (Smeter). The detector, AGC and oscillator self-bias diodes are 1N663A silicon diodes (which were one of AMD’s first products). Band changing almost fifty years ago! In the early 1970s, many electronics hobbyists were still coming to grips with the relatively new transistors and other semiconductors. PN junction becomes forward-biased. In most circuits such as amplifiers, the grid (gate) always has a negative bias, so this is not a problem. However, in oscillator circuits that use grid current self-bias, if a Fetron is plugged in place of the 6AK5, the gate draws significant current and the oscillator malfunctions, producing a distorted output with multiple harmonics. This can be solved with a diode in the gate circuit to provide the self-bias function. The third is that practical experiments with the Fetron indicate that the input-to-output isolation is not quite as good as the 6AK5, in that when used in IF stages with identical tuned siliconchip.com.au circuits in the input and output, they are a little more prone to instability. The higher amplification factor might be the reason, as this tendency can be eliminated with a small amount of degeneration to lower the stage gain. So despite the Fetrons being marketed as plug-in valve substitutes, they were not always a suitable direct replacement, depending on the specific circuit. Designing & building an all-Fetron radio I built the radio shown in the photos, which has some unusual features. Its complete circuit is shown in Fig.2. As the Fetrons have no heaters, it Australia’s electronics magazine Band changing is via three miniature Teledyne latching RF relays. These are controlled by a band change switch on the front panel, which is an industrialgrade motor switch from Telemecanique, so it will not wear out in a hurry, and it has a good feel to it. The main three-gang tuning capacitor is driven by an Eddystone ball-epicyclic reduction drive knob and dial assembly. Incandescent lamps are used to illuminate the dial. I also placed lamps inside the battery voltmeter and the Smeter. These meters are moving-coil types which were intended for use in helicopter avionics. I repainted and labelled the faces for voltage and Sunits, respectively. These days, LEDs might be used with a consequent reduction in current. The radio-frequency trimming capacitors are metal vane ceramic variable types, and chassis-mounted. March 2021  33 SC Ó FETRON DUAL BAND RADIO RECEIVER Fig.2: the full circuit of my Fetron-based radio, a superhet with an RF stage, two IF stages and a Class-A audio output. It uses 11 Fetrons (four in parallel in the audio output stage), two JFETs and three silicon diodes. The MW/ SW band switching is achieved using three latching RF relays in metal cans, also manufactured by Teledyne. The RF coils were wound on formers and then placed inside military spec shielding cans with high permeability adjustable powdered iron cores. The IF transformers are 465KHz American-made Miller units. The audio output transformer is made by Hammond in the USA and supplied by AES. Two of the 12V lamps are in the meters, with the remaining six on a stripline PCB added into the base of the Eddystone dial. 34 Silicon Chip Note the 1N663A diode in the gate circuit of the local oscillator for self-bias, to prevent the Fetron gate conduction problem described above. The input is fuse- and diode-protected. Unlike a valve, a Fetron could be damaged by the application of reverse polarity DC. Earthing the Fetrons To Earth the Fetron bodies, I modified the ceramic valve sockets. I did this by removing the phosphor bronze Australia’s electronics magazine and spring assembly from some standard miniature test laboratory clips and fitting them into the centre metal ring of the valve socket using a small machined bush. The phosphor bronze wire is slipped through the spring and then through the centre of the socket from the top. The bush is soldered into the valve section on the socket base, and the bronze wire is folded over and cut off after it passes through the clearance hole in the bush. This results in the siliconchip.com.au flat-top section of the phosphor bronze wire projecting a little above the top of the socket. When the Fetron is plugged into the socket, the bronze wire springs against the Fetron’s base, securing the Earth connection to the Fetron body without having to make a soldered connection. Mechanical construction The chassis is grey painted steel. It was supplied by AES (Antique Electronic Supply, USA). After making all siliconchip.com.au the holes, I painted the bare edges. To prevent any surface damage, I heavily coated the chassis and panel in plastic tape while cutting the holes, so that they remained scratch-free. The front panel was crafted from 3mm thick stainless steel and treated to create an engine turning finish (also known as jeweling or guilloché). All the hardware used in the radio, mostly 6-32 and 4-40 UNC machine screws, is stainless steel. These were supplied by PSME (PreAustralia’s electronics magazine cision Scale Model Engineering) in the USA. The Fetron sockets are ceramic with gold-plated pins. The wiring in the unit is with highquality Teflon multi-coloured hookup wire from a submarine parts supplier. The front panel handles are chromeplated brass. The switch labels, for the most part, are pre-made items which came from the electronic markets in Akihabara, Japan. The tag boards used on the radio underside also came from there. March 2021  35 No-one is expecting you to be able to build your own Fetron Radio from these photos . . . but just in case (!) you can get a very good idea of both the above-chassis layout and the under-chassis wiring. The Speaker mesh is perforated aluminium with a clear lacquer applied. Captive pressed stainless steel 4-40 nuts were fitted to the chassis base to allow repeated removal of the base plate. The three Teledyne RF relays (in TO-5 cases) have spring clips to Earth their metal bodies. 36 Silicon Chip Australia’s electronics magazine siliconchip.com.au SC Ó DC-DC CONVERTER FOR FETRON RADIO The latching relays save battery power and are driven by a simple RC network, which provides a current pulse to execute band changing. The two TO-5 cased JFETs for the S-meter can be seen in the chassis underside view with the red, green and black sleeving on their leads. The three-gang variable capacitor is mounted with posts within rubber grommets to prevent acoustic feedback to the capacitor’s plates. As all of the trimmer capacitors and adjustment potentiometers for the S-meter are chassis-mounted (just above the 2N4886 JFETs), all adjustments can be made from above the chassis top. I created the dial artwork in a photo editor and made it as a transpar- Fig.3: the circuit of my 12V-to-90V step-up supply which I use to power my Fetron radio when I don’t want to use the 90V Nicad battery! It’s designed to bring NPN transistors Q1 and Q2 (which drive transformer T1) into and out of conduction slowly, at 40Hz, eliminating EMI which would otherwise affect radio reception. ent sticker, which I then applied to the metal Eddystone dial plate. I very carefully cut the kidney-shaped meter holes in the dial plate and front panel by hand. Power supply The radio itself draws about 47mA <at> 90V, making its power consumption around 4W. That is significantly less than a valve radio employing 6AK5s because there is no heater demand. The current consumption with the dial lamp string running is 75mA. About 2.5W is consumed by the Class-A audio output stage, which has a current drain of 28mA. A Class-AB output stage would draw significantly less, but calculations showed that it would have been My home-made power supply PCB is pleasingly simple. It is dominated by the PCB-mounting transformer, two TO-66 package driving transistors and high-voltage output filter capacitors. siliconchip.com.au Australia’s electronics magazine March 2021  37 These scope grabs just how gentle the switching waveforms of transistors Q1 and Q2 are. Even at the longer timebase used in the left-hand scope grab, you can see that they are not vertical lines but rather smooth ramps, reducing the higher-order harmonics that are typical of square waves and this minimising high-frequency EMI. more difficult to attain the 1W output with two paralleled Fetrons per side. Also, a phase inverter circuit or transformer would have been needed to drive them. The Class-A output stage, although a little more powerhungry than Class-AB, does give very good results with pleasant-sounding audio reminiscent of a typical valve radio. I made the 90V battery from many 2000mAh AA-sized NiCad cells and stuck Eveready logo on it for a bit of fun. Step-up supply Ideally, the radio would be powered by a rechargeable 12V battery or 12V DC plugpack. This would require a 12V-to-90V switch-mode converter. Many enthusiasts of valve radios have attempted this sort of converter, but RFI or radio frequency interference (affectionately referred to as “hash”) is a significant problem. This can result in buzzing signals being detected by the radio. A medium-wave or shortwave radio makes a very sensitive detector of radiated electromagnetic fields! Most people would be surprised by the high levels of RFI I modified the sockets by soldering in a brass bush and using it to hold a spring-loaded bronze wire which contacts the Fetron case when it is inserted. This means that I can Earth the Fetron case to provide adequate shielding, without affecting their pluggability or having an ugly solder joint on the case. 38 Silicon Chip emitted by appliances like computers and flat-panel TV sets. These signals can not only cause interference on shortwave reception, but they can also desensitise RF receivers in home automation systems. Some folks have had solar systems with switchmode inverters installed, only to find that their garage door controllers stop working! So I set about creating an RFI-free step-up circuit to power my radio. The result, shown in Fig.3, is somewhat similar to Ken Kranz’s Battery Vintage Radio Power Supply from the December 2020 issue (siliconchip.com.au/ Article/14670), although there are some important differences. It delivers 90V <at> 50mA with an input of 12.6V <at> 550mA, giving an overall efficiency of 65%. There is no detectable RFI above 150kHz; I didn’t even bother shielding it. It uses a Jaycar PCB-mounting toroidal transformer, driven in push-pull mode at around 40Hz. Its low operating frequency, combined with the ironcored transformer reduces the switching events per unit time, and this helps compensate for the deliberately slow switching transitions. The slower transition time contains lower HF spectrum components. The switching time and transition shape were controlled by tuning the primary of the transformer with a large capacitor and RC snubber networks on the transistor’s collectors. Also, the drive to the switching transistors is adjusted to be enough to gain saturation of the collector-emitter voltage to 380-400mV and no lower. Experimentation shows that all other things being equal, the RFI increases significantly the more heavily the transistor is saturated. RFI is produced when the transistor suddenly comes out of heavy saturation The two scope grabs above show the collector waveform from one of the 2N3054A transistors at two different timebases. You can see that the transistor switches slowly between being in and out of conduction, over about 0.8ms each time. While this reduces the efficiency, this is offset by the slow switching speed, so the number of switching events per unit time is relatively low compared to most switch-mode PSUs. SC Australia’s electronics magazine siliconchip.com.au CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions will be paid for at standard rates. All submissions should include full name, address & phone number. Low-noise microphone preamp Wired microphones often need phantom power, and the preamp needs to have significant and adjustable gain to give a reasonable output signal level. The mic preamp must be able to drive a long cable with significant capacitance, have low noise and be robust. This circuit shows a flexible preamp that can be used with many wired microphones, based on a TDA7052A BTL (bridge-tied load) power amplifier chip, with an extra gain stage on its input based on an NPN transistor. The signal from the microphone at CON1 passes through a 200W/680pF low-pass filter to remove RF, and is then AC-coupled to the base of lownoise NPN transistor Q1. It is configured as a common-emitter amplifier with emitter degeneration and a 47pF Miller capacitor to reduce its gain at Circuit Ideas Wanted siliconchip.com.au high frequencies. This stage has a gain of about 50 times (34dB). The inverted output signal at the collector of Q1 is then fed to the pin 2 input of IC1 via two optional RC filters, a low-pass filter selected by switch S1 and a high-pass filter selected by S2, which operates in conjunction with IC1’s input resistance of 15-25kW. IC1 provides a further adjustable gain of about 1-60 times (0-35.5dB) for a total maximum gain of around 3000 times (70dB). The gain is adjusted using VR1, which controls the voltage at pin 4 of IC1 in conjunction with IC1’s internal constant current source. The in-phase and out-of-phase output signals from pins 8 & 5 are then AC-coupled to two separate outputs, at CON4 and CON5. These could also be connected to the pins of a single balanced output socket. IC1 can deliver over 1W, so it has plenty of power to drive long cable runs. It can also easily drive headphones or even a loudspeaker to modest volume levels (depending on its sensitivity). About 1mA of phantom power for the microphone can be selected using switch S3. This is regulated by zener diode ZD1 and the 4.7kW bias resistor, and filtered by a 1kW/100µF RC lowpass filter to remove supply ripple. The unit is powered by a DC supply of around 12-15V connected to CON2, or a 19V laptop/notebook power supply brick can be connected to CON3. The extra three series diodes drop its output voltage to a safer level of around 17V. Petre Petrov, Sofia, Bulgaria ($80). Got an interesting original circuit that you have cleverly devised? We will pay good money to feature it in Circuit Notebook. We can pay you by electronic funds transfer, cheque or direct to your PayPal account. Or you can use the funds to purchase anything from the SILICON CHIP Online Store, including PCBs and components, back issues, subscriptions or whatever. Email your circuit and descriptive text to editor<at>siliconchip.com.au Australia’s electronics magazine March 2021  39 Two quartz crystal oscillators using a flip-flop I needed a 10MHz signal to clock my system, but there was no room left on my board for a crystal oscillator implementing any of the circuits commonly employed. I did have an unused flipflop, though, but with only enough room for a few external components. The unused flip-flop was one of the two in a 74HC74, so I designed two oscillator circuits that use the flip-flop as the active element. In these flip-flops, the set and reset inputs are active low, whereas the clock input is triggered by rising edges. In both my circuits, the clock and data inputs are unused and so they are tied to ground. In flip-flops with direct set and reset inputs, if both of these inputs are active simultaneously, both outputs will be in an ‘invalid’ state. In the case of the 74HC74, this is a defined state, with both outputs (Q and Q) high. Therefore, if the set input is held low, the reset input state will appear inverted at the Q output, while the Q output will stay high. This inversion is used in my circuit on the left. This inverter is used to make a Pierce crystal oscillator, where the quartz crystal, resistors and capacitors form a feedback network from the Q output to the Reset input. Thus, the flip-flop oscillates between the ‘invalid’ condition and a ‘valid’ one, inverting the state of the reset input and producing the 180° phase shift necessary for the Pierce oscillator to function. The quartz crystal works in parallel resonance (actually, between series resonance and anti-resonance) and presents an inductive reactance. The 1MW resistor makes the flip-flop oscillate even if the crystal is not connected, and is necessary for the crystal-controlled oscillations to start. The 560W resistor reduces the drive level on the crystal and discourages overtone modes of oscillation. C2 and C3 are the load capacitors. The required values depend on the crystal’s specified load capacitance, the IC's input and output capacitances, and the stray capacitances of the circuit. For a 10MHz, 20pF crystal, with C2 and C3 at 27pF, I obtained 10.000MHz. For a 15pF crystal, you would need values around 22pF. I tested this circuit with 10 crystals from 2MHz to 20MHz in increments of 40 Silicon Chip around 2MHz, and it worked properly in all cases. Scope1 shows the voltages at either end of a 10MHz crystal in this circuit. The phase difference is near 180°, which indicates that most of the phase shift of the feedback network occurs in the crystal in this parallelresonant oscillator. In the right-hand circuit, the same flip-flop is employed to make a crystal resonate at, or close to, series resonance. The negative feedback given by the two resistors makes the flipflop oscillate, and the quartz crystal establishes the oscillation frequency, where the phase shift across the crystal is 0°. Capacitors C2 and C3 proved necessary to stabilize the oscillator with some crystals, and their value depends on the particular crystal. I tested this circuit with several crystals, and it worked properly between 2MHz and 16MHz. C2 required values between 0pF and 100pF while C3 needed to be between 0pF and 22pF. Scope2 shows the voltage across the crystal in this circuit. The signal with the highest amplitude is the one at the Scope 1 Australia’s electronics magazine pin 6 end. The phase difference is close to 0°, indicating resistive behaviour, which happens at series resonance. This 12MHz crystal oscillated in series resonance at 11.995MHz with C2 = 100pF and C3 = 22pF. One way to determine if a quartz crystal is overdriven is to increase the supply voltage slightly; if the oscillator frequency decreases, the current through the crystal is too high. I tested this by increasing the supply from 5V to 5.2V for several crystals; in both circuits, the frequency increased slightly, which indicates that the power on the crystals is reasonable. Since the outputs of these circuits are taken directly from the crystal circuits without buffering, they should be connected to high-impedance, CMOSlike inputs. These circuits may be used, for example, together with the remaining flip-flop on the same chip, connected as a dividing-by-two toggle flip-flop. That could be useful since dividers like the CD4060B/74HC4060 lack a divide-by-two output. Ariel G. Benvenuto, Parana, Argentina. ($100) Scope 2 siliconchip.com.au Displaying digits using single RGB LEDs With embedded systems these days, engineers must often deal with very small PCB footprints, so suitable displays (especially for debugging) can be difficult. My idea is to display multidigit numbers using just a few RGB LEDs, where the digital value of 0-9 is shown using standard resistor colour codes (black, brown, red, …, white). The circuit shown in Fig.1 is minimalistic, using just one high-brightness RGB LED controlled by a tiny PIC10F200 (the world’s smallest 6-pin microcontroller). It uses three simultaneous PWM pulse trains, each with an independently controllable duty cycle. By varying the duty cycles, the intensity of the red, green and blue elements within the RGB LED create different colour mixes. While seven of the required colours are easy to obtain: red, green, blue, yellow (red+green), purple (red+blue), white (red+green+blue) and black (led off), achieving the three remaining colours required some experimentation and fine-tuning of a look-up table (see the table at right). The current-limiting resistors have also been individually adjusted to obtain the same brightness precisely, using a lux meter. The RGB led should be used with a white diffuser to mask the individual red, green, blue elements (even with SMD RGB LEDs, these elements are distinctly visible). Pin 6 in the circuit shown monitors the status of pushbutton S1, which allows you to cycle through the available digits values/colours (Fig.1). This pin has an internal pull-up enabled for that micro pin so that it can detect button presses. As shown in Fig.3, this circuit can be used in cascade, with discrete logic OR gates, creating a multi-digit display. Alternatively, a single 8-pin microcontroller can drive a four-digit LED display, as shown in Fig.2. The source code (1dgtRGB.ASM and PWMLEDS.INC) is available for download from siliconchip.com. au/Shop/6/5781 This suits the 6-pin PIC10F200 and would need to be modified for the PIC12F617 or other micros. Its size is optimised, and it uses macros to ease understanding. It occupies just 116 program words and nine data bytes. The code is fully commented, to make it easy to adapt to other microcontrollers. Benabadji Mohammed Salim, Oran, Algeria. ($100) Fig.1 Fig.2 Fig.3 siliconchip.com.au Australia’s electronics magazine March 2021  41 The Omnidetector This circuit can detect many different things: heat, light, liquid, metal, touch and much more, using little other than a common hex Schmitt-trigger inverter IC. Using two oscillators, it can detect changes in inductance (L), capacitance (C), and resistance (R). So it can use many different kinds of sensors to detect changes in various physical phenomena. I tested the following cases, and noted the performance they yielded. In all but the last two cases, these require no modification to the circuit – only switching sensors and readjustment: • shadows, ie, interrupted light • sunrise, without fail, even on a cloudy day • heat – it will pick up a change of less than 1°C • fire – of course, fire generates plenty of heat • metal – it detects small lumps of metal (but see the text for more details) • magnetism – it detects magnets in close proximity (but see the text) • pressure – one kg or more, using suitable conductive foam • touch – it detects the lightest touch, including animal paws • body capacitance – with a 400mm range, or 250mm for a hand • electrical switching – it will detect switching in wires at 300mm range • rain – light or heavy, with a stripboard sensor • liquid – it can distinguish different liquids, eg, milk and water Of course, it does some things better than others. It works particularly well with shadows, heat, fire, pressure, rain, liquid, touch and body capacitance. Apart from the versatility and sensitivity listed here, the circuit has two distinct advantages. Firstly, it is extremely stable, even without a regulator. This is achieved by using two identical oscillators. Any environmental changes, or changes in the supply voltage, affect both oscillators equally. Secondly, the circuit is exceptionally efficient, drawing just over 1mA current on standby. With quality AA batteries, this will provide three months of uninterrupted service. On the surface of it, the idea behind the Omnidetector is a simple one. Take any two sensors that are equal somehow – both measuring (say) tempera42 Silicon Chip ture via a changing resistance. If the value of one of these changes, one merely needs to notice that change to trigger an alarm. The unchanged value serves as the reference or benchmark. However, if both sensors’ value changes equally (say, due to ambient temperature), this is not detected. Two stages of the 40106 CMOS hex Schmitt inverter IC, IC1a and IC1f, act as side-by-side oscillators. The pairs of sensors are connected identically in these oscillators’ feedback networks (between points C & D and E & F). If these oscillators are in perfect sync, there is no significant activity at mixer input pin 5 of IC1c. This mixer feeds a charge pump connected to the gate of Mosfet Q1. This then switches LED1 or a small alarm. Q1 typically switches at 3V, while the charge pump provides up to 7V. In theory, one would never be able to tune these two oscillators to be in such perfect sync as to cancel each other out. A mere 1Hz difference between IC1a and IC1c would be enough to trigger the alarm. That is solved using frequency lock, which is ordinarily something one seeks to avoid. A 470W resistor limits the current drawn by IC1; the 47pF capacitor provides minimal smoothing. This makes the oscillators prone to frequency lock. They cannot draw current at once, so they operate alternately. If they come anywhere near each other (within about 2% frequency-wise), they lock on to each other, and the mixer output remains quiescent. The problem is that the frequency lock is a little too strong. At higher frequencies especially, the circuit is reluctant to break lock, and this affects sensitivity. Therefore, IC1d is used to introduce a little flutter, which is something one ordinarily avoids at all costs. It is called a wobbulator. It may seem odd as it isn’t connected to anything – except the power supply. It draws as much power as the 470kW feedback resistor will allow, and it does so out of sync, at about 25kHz. This unsettles the other oscillators just enough to make the lock more fluid. Diodes are not used to mix the two signals at the input of IC1c, as their capacitance (a few pF) would interfere with operation beyond about 50kHz. Resistors are used instead. The resistor from pin 5 of IC1c to ground is 1MW while the mixer resistors are 470kW, to ensure that the voltages at the inAustralia’s electronics magazine put of IC1c do not get ‘stuck’ inside the Schmitt trigger hysteresis window. Points “A” and “B” are provided for connecting identical sensor plates, but a single plate can be attached to one of the points, with 10kW series resistors to prevent static electricity from damaging IC1. Note that the gate capacitor for Mosfet Q1 has no bleeder resistor. Instead, charge leaks away through surrounding components (mainly reverse current through D1 & D2), which takes about three seconds. The additional (optional) circuitry in the blue box is for switching a small relay. It is taken from my Magnetometer article (December 2018; siliconchip.com.au/Article/11331). This is designed to avoid any instability in the circuit when a relay is used, and adds a timer. Without such a circuit, the Omnidetector could become unstable when switching significant loads, and sensitivity could be greatly reduced. The circuit – including its sensors – needs to be soldered, not tested on a breadboard because of the high frequencies involved. A DIL socket is recommended for the CMOS IC, in case anything goes wrong. Use a 9V or 12V battery as a power supply, or a well-regulated 9-12V DC mains supply. The sensors Some of the sensors which were successfully tested are: 1. Proximity sensor. Attach two tin plates around 200mm per side (or aluminium foil, or copper-clad fibreglass) to terminals A and B, separately. Solder link wires across terminals C and D, and E and F. Tune oscillator IC1a to 100kHz to begin with (or adjust VR1 to 100kW, and VR2 to its mid-point). Then adjust VR3 and VR4 until the best result is obtained when moving a hand near a plate. There is more than one setting which will work here, but some are better than others. Note that the plates can detect hands through objects, such as books or tabletops. 2. For light detection, adjust multiturn variable resistors VR1-VR4 far back and connect two LDRs (light-dependent resistors) between terminals C-D and E-F. Their value will be quite high, say about 100kW. If these are pointed at a light source, the Omnidetector will pick up interrupted light with ease. If siliconchip.com.au the light source is more than a few metres away, lenses may be required to focus the light on the LDRs. Some street lights are trickier to use than others – sodium lamps, for instance, where the light is harshly pulsed. If the LDRs are suitably adjusted, the circuit will not be triggered by the sunrise. But it could be set up to detect a morning shadow, so that one has a sunrise alarm. 3. For heat detection, use identical NTC or PTC thermistors. A nominal value of about 100kW is good. VR1VR4 are again turned far back, and the two thermistors wired to terminals C-D and E-F. In use, the output will be triggered if one thermistor is warmed or cooled relative to the other. 4. It can detect a weight of about 1kg (10N force) or more using electrically conductive foam. Use foam sheets which offer a resistance of about 50kW when uncompressed, sandwiched between pieces of copper clad board. Wire the foam pads to terminals C-D and E-F; it might be possible to hook up only one pad, replacing the other with a wire link, and still obtain good results. siliconchip.com.au The pressure pad may be placed under a mat or a carpet, or conversely, under an item which should not be picked up. 5. A rain alarm using stripboard sensors. A single sensor is sufficient. Join together alternate tracks to give two connection points. You will get a resistance of about 100kW-500kW in drizzle, or 20kW-100kW in mediumto-heavy rain. Stripboard sensors are open-circuit until they detect something, so they need to be wired in parallel with VR1 or VR3. Such a sensor can also be used as a touchpad, although it will not be as effective as the plate type. 6. Metal detector coils. We borrowed the design of two coils from Andy Flind’s classic Buccaneer detector, which is in the public domain. These are IB (Induction Balance) coils. Note, however, that the Omnidetector does not function as an IB detector. Since both coils are active, it is a BB (Beat Balance) detector. The coils are attached to terminals C-F, with a Faraday shield going to 0V. These coils are arranged with some Australia’s electronics magazine overlap, as with IB. One can now detect small lumps of metal at close proximity, although extreme patience resulted in a crimp bottle-top being detected at 100mm. Try a higher frequency first, say 250kHz (adjust VR3 to 25kW and VR4 to its mid-point). In this case, a resistor in parallel with Q1’s gate capacitor will improve responsiveness. The coils will also pick up moving magnetic fields at close proximity, such as a ball magnet. 7. The Omnidetector can detect flowing liquid and even the difference between various liquids. Take two tin plates about 40mm square and solder leads to them. Cover both sides with paper, then soak them in epoxy resin and allow them to dry. Use spacers to mount them about 5mm apart. Liquid can now flow between the (insulated) plates. These sensors replace the 47pF capacitors at pins 1 & 13 of IC1a/IC1f, although one could also wire them in parallel, with lesser sensitivity. Don’t forget the link wires. Rev. Thomas Scarborough, Capetown, South Africa. ($150) March 2021  43 The History of Videotape – part 1 Quadruplex By Ian Batty, Andre Switzer & Rod Humphris Analog videotape is now obsolete. But it was state-of-the-art for many decades, and during that time, a video recorder was arguably the most advanced piece of electronic equipment in many homes. The history of video recording is quite fascinating, and this series of articles provides an in-depth explanation of how it came about and changed over the years. www.historyofrecording.com/ampexvrx1000aniv.html A udiotape recording and playback predate videotape, with early magnetic recording of audio demonstrated in 1898. Oxide tape was invented in Germany in 1928. By the time serious work on videotape recording started in the 1950s, audiotape was already widely used. Audiotape use amplitude-based recording; a stronger signal creates proportionally stronger magnetic patterns on the tape. Audio signals are in the frequency range of 20Hz to 20kHz, a range of ten octaves or three decades. This is not especially difficult to achieve with magnetic tape. Videotape, however, needs to cover 44 Silicon Chip the range of 60Hz to at least 4.2MHz for the US NTSC standard, or 50Hz to 5MHz for CCIR/PAL (see Fig.1). This is a range approaching 17 octaves. That’s a much bigger challenge. On playback, tape head output doubles for every doubling in frequency (ie, output increases at 6dB/octave). Let’s say that we can get away with a video signal that has a signal-to-noise ratio (SNR) of 40dB. From 50Hz to 5MHz, the signal ratio due to the 6dB/ octave effect is 100dB! That means that our tape system SNR needs to be at least 140dB (Fig.2). That is simply not possible. So video signals cannot be recorded and played back using Australia’s electronics magazine conventional amplitude recording. Another reason why amplitude recording cannot be used for video is that any tiny variations in tape-to-head contact (dropouts) would severely affect the replayed picture (Fig.3). Variations in the tape’s oxide layer would also cause major visual disruptions, especially if the signal level falls and the synchronising signals cannot be detected. Tape-to-head speeds Tape systems work well up to a frequency where the wavelength of the recorded magnetic pattern approaches the width of the tape head’s magnetic siliconchip.com.au Fig.1: the recording bandwidth needed for a direct (linear) analog transcription of standard audio and video (PAL) signals. The horizontal axis is logarithmic; video covers 16.5 octaves (five decades) while audio covers 10 octaves (three decades). The BBC’s Video Electronic Recording Apparatus (VERA) was an attempt to record video onto tape in a similar manner to audio. It used stationary heads and a very high tape speed, necessitating huge tape reels. Despite their size, each reel only lasted 15 minutes! Source: www.vtoldboys.com Ampex’s Harold Lindsay (left) and Alexander M. Poniatoff (right) with the well-regarded Ampex 200 audiotape recorder. Source: www. historyofrecording.com Fig.2: the signal from the tape head increases by 6dB for every doubling in frequency. This shows the impossibility of recording a video signal directly to tape, since to avoid saturation at 5MHz and signals below 50Hz being lost in the noise, the system would need an impossibly high dynamic range of 140dB. gap. At precisely one wavelength, the signal on one side of the head has the same amplitude and polarity as that on the other side. With no difference in the magnetic field, there is no output from the head. So the combination of head gap width and tape speed determines the frequency at which head output falls to zero, and thus the maximum recordable frequency. For the NTSC limit of 4.2MHz and a practical head gap of only 2.5µm, the required tape speed is 21 metres/sec (2 × 2.5 × 10-6 × 4.2 × 106 × 103). That’s the entire length of an old-fashioned 2400 foot/731m reel in about 35 seconds! It’s siliconchip.com.au worse for the CCIR/PAL bandwidth of 5MHz, needing a tape speed of 25m/s, giving a reel playtime under 30 seconds. So it is not practical to use linear tape recording for video recording. VERA Despite all these apparent problems, some hardy folks did give amplitude recording a try. The BBC’s Video Electronic Recording Apparatus (VERA) from 1952 took on the challenge, using stationary heads and a very high tape speed. Unable to accommodate the required 405-line standard’s bandwidth of 3MHz with amplitude recording, Dr Australia’s electronics magazine Peter Axon’s team ingeniously split the entire signal into three bands. Band A contained signals 50Hz~100 kHz (including synchronising signals), frequency modulated onto a 1MHz carrier. Band B contained signals 100kHz~3MHz using amplitude modulation. Band C frequency-modulated the audio signal onto a 250kHz carrier. Splitting the video bandwidth did allow the 405-line bandwidth of 3MHz to be accommodated, and demonstrated the principle of recording video on tape. VERA’s development lasted until 1956, by which time US company ...continued on page 48 March 2021  45 A A Timeline Timeline of of Videotape Videotape Recording Recording 1956: Ampex VR-1000A The VR-1000A was the first of Ampex’s 2-inch quadruplex recorders (www.flickr.com/photos/82365211<at> N00/2215654688/). Prior to this Ampex had worked magnetic tape systems that were based off the Germans’ work on the Magnetophon. 1965: Ampex VR-5000 One of the first Type-A format VTRs, 1-inch tape, one head and helical scan (www.ebay.com/itm/273727570578). 1969: Philips LDL-1002 Has a recording time of 45 minutes and runs from a 50Hz AC synchronous motor (https://commons. wikimedia.org/wiki/File:Philips_ ldl_1002.jpg). 46 Silicon Chip 1956: RCA TRT-1B RCA’s first workable video tape recorder. Recordings made on the TRT-1B were also compatible with the earlier Ampex VR-1000A (www. lionlamb.us/quad/rca.html). 1965: Sony CV-2000 The world’s first consumer videotape recorder (https://youtu.be/ wHiBxlhzgyY). 1969: Akai VT-100S Records up to 20 minutes onto 1/4inch tape and has a separate camera unit with a built-in mic (https://youtu. be/iaPAyVcXz_0). The difference between the VT-100 and 100S was the inclusion of a stop-motion feature. Commercial Equipment Australia’s electronics magazine 1958: BBC VERA Here is the first live demonstration of VERA in 1958 by Richard Dimbleby: https://youtu.be/YCyxPLXLaKA Source image: http://archive. totterslane.co.uk/tech/vera.htm 1967: Sony DV-2400 The “Portapak” was the first consumer-oriented portable videotape recorder and could record up to 20 minutes (https://en.wikipedia.org/ wiki/File:Sony_AV-3400_Porta_Pak_ Camera.jpg). 1969: IVC 800 A 1-inch videotape colour recording/ playback machine (https://youtu.be/ EIhI85cHIfg). It also has slow motion playback and two audio tracks. Consumer Equipment siliconchip.com.au 1971: Sony VO-1600 The first video cassette recorder; it used Sony’s U-matic system and had a TV tuner (www.labguysworld.com/ Sony_VO-1600.htm). 1975: Sony SL-7300 The first standalone Betamax player, it was called the SL-7200 in America (http://takizawa.gr.jp/uk9o-tkzw/tv/SL6300.pdf). 1976: JVC HR-3300 The first VHS recorder, it could hold two hours of footage per cassette (https://en.wikipedia.org/wiki/ File:JVC-HR-3300U.jpg). 1983: Sony BMC-100P The “Betamovie” is an early camcorder for the Betamax format (https://en.wikipedia.org/wiki/ File:Sony_Betamovie_BMC-100P.jpg). siliconchip.com.au 1972: Philips N1500 This was the first device to use the commonly known VCR format (https:// en.wikipedia.org/wiki/File:N1500_ v2.jpg). 1976: Ampex VPR-2 1974: Sony VO-3800 The first portable U-matic recorder. While it records in colour, it can only play back in black & white, and needs a separate power supply to display colour (www.labguysworld.com/ Sony_VO-3800.htm). 1976~85: Bosch BCN 52 Two Ampex VPR-2s that used 1-inch Type-C videotapes which replaced quadruplex (www.vtoldboys.com/ hw1980.htm). 1976: Sony BVU200 The Sony BVU200 was one of the first “broadcast video” U-matic players before being replaced by Betamax. 1985: Sony Handycam The first Video8 camcorder which succeeded the Betamax-based models (https://en.wikipedia.org/wiki/ File:Handycam-dvd.JPG). Australia’s electronics magazine A 1-inch Type-B recorder with digital timebase corrector (TBC) playback, slow motion and visible shuttle. https://commons.wikimedia.org/wiki/ File:BCN_52_type_B_VTR.jpg 1999: Sony DCR-TRV103 The first Digital8 camcorder. Outside of Sony the only other manufacturer of Digital8 devices was Hitachi. March 2021  47 While there will be some difference in playback signal level between sync tip and peak white frequencies (due to the 6dB/octave effect), these will be removed by the limiting amplifiers used in FM receiver/playback systems. Ideally, the playback response will be flat from 50Hz to 5MHz, the required range of 100,000:1 or five decades. FM signals are recorded at tape saturation level. This ensures a high playback signal, but also removes the need for the tape biasing critical to amplitude systems. Rotating heads Fig.3: a simulation of what you could expect to see upon playback of a linearly recorded video signal due to small variations in the head-to-tape distance and variations in the properties of the tape’s oxide layer. In this example, you can see a large-scale dropout at the top and a few one-line dropouts near the centre. This image was taken from the 1923 episode “Felix the Ghost Breaker” of Felix the Cat (https://archive.org/details/FelixTheCat-FelixTheGhostBreaker1923). Ampex had successfully demonstrated its superior and revolutionary quadruplex system. Already obsolete, VERA first went to air in 1958. VERA’s high tape speed of 5m/s meant that a 520mm diameter reel of tape (over 4.2km!) only ran for some 15 minutes. The American experience was similar to the BBC’s. Bing Crosby Enterprises, owned by popular entertainer Bing Crosby, was already using Ampex 200 audio recorders in their studios. One was modified for a tape speed of 360 inches/s (over 30km/h!), and did play back a grainy image. The Radio Corporation of America (RCA) also demonstrated a linear system. Like VERA, these systems used stationary heads, high tape speeds, and gigantic reels of tape. These linear, amplitude-based systems could not be made practical. The solution: frequency modulation Conventional amplitude modulation must always occupy a bandwidth of twice the highest modulating frequency. Also, it’s impractical to use a modulating frequency more than a fraction of the carrier frequency for AM. Frequency modulation (FM) can occupy any required bandwidth (Fig.4). 48 Silicon Chip Narrow-band FM (NBFM) occupies a bandwidth that’s a fraction of its highest modulating frequency, while broadcast FM uses a bandwidth that’s five times its highest modulating frequency. It’s also possible to frequencymodulate close to the carrier frequency. Video frequency modulators commonly use a carrier frequency of a few MHz for the synchronising signal frequency (synch tip) level (zero signal volts), and a carrier frequency some two to three times that for peak white level (one signal volt). The actual rate of modulation (corresponding to the frequency of the modulating video signal) is accommodated by circuit design. Additionally, frequency-modulated systems are highly immune to variations in signal amplitude. This means that tape dropouts and other imperfections will have much less effect in frequency-modulated recording systems. Could we have linear AM systems for total frequency modulation and overcome the signal quality and bandwidth problems? Maybe. But that would leave the 20km/h-plus tape speeds that made these systems impractical. The solution is rotating head mechanisms. A rotating head moves relative to the tape, as well as spooling from the supply to takeup reel. This was Ampex’s stroke of genius. The magnetic track could lie at a slant angle across the tape, with multiple tracks in parallel (see Fig.5). This means narrow tracks, and narrowing the magnetic track makes the SNR worse. But frequency-modulated systems do not respond to noise for signals of moderate strength, so the designers can define a track width that gives an acceptable SNR for the frequency modulated record/playback system. The tape heads were mounted on a spinning disc, running almost at right angles to the tape’s direction of travel (Fig.6). Known as the headwheel, its rotational speed easily allowed writing/reading speeds across the tape in the metres/second range. This allowed the tape transport’s longitudinal speed to be greatly reduced, giving the practical, standard speed of 15ips or 381mm/s. Readers may anticipate the need for high-precision control of tape speed Fig.4: the basic principle of encoding an analog video signal using frequency modulation (FM) which makes recording it onto tape a much simpler affair. This is essentially the same approach used in analog TV broadcasting. Australia’s electronics magazine siliconchip.com.au Fig.5: the Ampex quadruplex videotape layout. The tape is moving horizontally while the head is moving vertically, so the video tracks are laid down at an angle. The audio, cue and control tracks are laid down in the traditional method, along the length of the tape. and head positioning. These are done by servomechanisms. Servos will be described fully in the following article. Ampex quadruplex Alexander M. Poniatoff founded Ampex in 1944, using his initials, and ex(cellence) for the name. Releasing the high-performing Ampex 200 audio recorder in 1948, Poniatoff and his company anticipated the use of tape recording for television, beginning experiments in 1952. Ampex’s 1956 demonstration of their VR-1000 rendered other designs obsolete, and “quad” would become the industry standard. There were two complications, however. First, although the tape could be wrapped to conform to the circumference created by the spinning heads, any wrap over 90° was impractical. Fig.6: the Ampex quadruplex head mechanism. The head is in the centre while the vacuum shoe, which keeps the tape in contact with the head, is at left. Source: https://youtu.be/ fpBRuheelu4 siliconchip.com.au But, since the video signal is continuous, there must be continuous head-totape contact. So the head wheel was designed to carry four heads, with the tape wrap a little over 90°. This guaranteed continual headto-tape contact, and head switching could be done electronically. The tape was made to conform to the arc of the heads by a curved “shoe”, aided by a vacuum system. The shoe is visible to the left in Fig.6. The head rotational speed was dictated by the minimum acceptable headto-tape speed to give sufficient record/ replay bandwidth, and this meant that only some 16 picture lines could be written or read in one head scan. This meant that any mistiming between heads would distort the picture – an effect known as head banding. To prevent track-to-track interference, unrecorded guard bands were left between each recorded track on the tape (see Fig.7). Also, during playback, it was vital that the heads aligned accurately to the centres of the transverse tracks. The audio was recorded on a linear track, just as with a conventional audio recorder. A control track with alignment pulses was added, and on replay, these were detected and fed to the head servomotor to ensure accurate head tracking and correct picture re-assembly. The high tape-to-head speed, combined with frequency modulation, gave the full video bandwidth without any band-splitting (as in VERA), and high immunity to tape defects. The transverse recording brought two further benefits. Firstly, tape stretch, a serious problem with linear recording, was minimised by the nearvertical track angle. Since the heads were servoed to the index pulses, these would separate or close up as the tape Fig.7: when the “Magna-see” slurry was applied to a quad tape, the video track strips became visible. Each strip encodes 16 lines of video. As there is a gap between the strips, it is possible to cut and splice quad tape by hand. You just need to know exactly where to cut! Australia’s electronics magazine March 2021  49 stretched, keeping the head scanner aligned to the centre of each track. Secondly, each track contained a complete number of picture lines, and it was possible to ‘expose’ these with a fine magnetic slurry called Magnasee, as shown in Fig.7. So editors could visually locate end-of-frame edit pulses and successfully cut-and-splice an original tape with no visual disturbance to the replayed picture. (16 x 64). But that isn’t good enough. Videotape itself is not rigid – it will suffer stretch errors that even the most aggressive servos cannot correct. No mechanical servo can respond with microsecond accuracy, at microsecond intervals. Even errors in the tens of nanoseconds (10-8 seconds) will be evident if the VTR’s output is put to air. Timebase correction VTRs are mechanical gadgets with two critical electromechanical servo systems. The tape transport servo controls the tape speed, and this determines whether the off-tape video will exactly match the vertical rate of station syncs. If this isn’t done, the VTR video will roll vertically and cannot be put to air. The headwheel servo controls the headwheel’s rotational speed, and this determines whether the off-tape video will exactly match the horizontal rate of station sync. If this is not done, the VTR video will slide horizontally, or be offset left or right compared to station sync and cannot be put to air. Remember that in the late 1950s, digital technology was restricted to massive computers the size of a small bus. So the solution was to use an array of switchable delay lines to ‘juggle’ the replay video’s timing, and force it into exact synchronism with the station references. These analog timebase correctors (TBCs) used selectable delay lines with periods from 125 nanoseconds, augmented by a continuously-variable secondary system. Yes, analog TBCs were large, expensive and complex, but videotape could only replace film if the VTR’s playback images could be made to follow station sync. Timebase errors So, Ampex’s VT-100 could record and play back high-quality video. And the playback picture looked fine on a monitor connected directly to the VTR. But it proved impossible to feed that replay video into a studio system for broadcast for reasons relating to station synchronisation. Every TV station has a master reference that generates sync pulses (station sync) for the cameras, the vision mixers and other program sources, ensuring that every image is framed exactly. Every image is absolutely ‘in-sync’ with every other, so that any superimposing (such as a crossfading from one camera to another) shows the two images blending without one ‘drifting’ over the other. This was never a problem with putting film to air; “telecine” used a TV camera that viewed the image from an ordinary movie projector that ran the film, and that TV camera was locked to station sync. But the VTR’s playback signal was not in sync with the station. We can design a servo system that forces the VTR’s tape transport to run at precisely the station’s 50Hz frame sync rate. We can also add a headwheel servo to make sure the headwheel scans exactly 16 lines in 1024 microseconds The analog TBC circuit (see Fig.8) comprises, first, a stepped, digitallycontrolled delay line from 0.125µs to 63.875µs. The coincidence detector senses the time error between the station sync and the off-tape video. The coincidence detector’s control output sets the switchable delay line to a delay which is some multiple of 0.125µs. The output is now stable in time, but it may not be exactly in-phase with the station sync, and this would give an image slightly displaced to the left or right relative to an image from a studio camera. The second stage in the process uses analog processing: the analog coincidence detector sends a control signal to a continuously-variable (analog) delay line. This allows the TBC to ‘trim’ the video output so that it is precisely in phase with station sync. The VTR’s output could then be mixed with any other station source (such as a camera), and show no displacement error across the screen. If this sounds complicated, you’re right. And recall that this was implemented in valve technology. RCA’s TRT-1, competitor to the Ampex machines, is the size of six refrigerators! Over time, design advances reduced quadruplex technology in size and improved video quality. NTSC and PAL colour systems were designed for monochrome compatibility. As quad machines had always had the capability of recording the entire video bandwidth, this meant that they could record and play back colour video too. Timebase correction was vital for successful colour operation. While monochrome systems could tolerate timing and phase errors, the NTSC colour system transmitted colour infor- The TRT-1, RCA’s first 2-inch VTR, took up six full racks (the three racks shown here are half the machine). Each was about the size of a domestic refrigerator. TBCs were required to interface VTRs to broadcast studio feeds. As technology progressed and transistors took over from valves, TBCs shrank, and their capabilities improved. Source: www.lionlamb.us/quad/ ► An Ampex VR-3000 “portable” ► VTR. These were popular with reporters as the tape could be re-used many times, as opposed to film, which could be used only once and then discarded. Source: wikimedia user Gunnar Maas 50 Silicon Chip Australia’s electronics magazine siliconchip.com.au mation as a phase-modulated signal. Any phase errors during replay would create visible shifts in hue; reds might become greenish, giving a deathly cast to the faces of actors and newsreaders. By the time colour television was introduced, advances in timebase correction were able to cope with VTR phase errors, giving faithful reproduction within the fundamental limitations of NTSC. The most advanced quad machine was Ampex’s VR-3000 (shown at lower left). Its ability to record and play back video, and a wide range of other signals, saw it used by the US military as an aid to vehicle- and aircraft-mounted surveillance systems, as well as its peaceful use in replacing movie film as the reporter’s medium of record. Its portability demanded the usual circuit rethinking and redesign. By then, solid-state electronics was well-established as the technology of choice, allowing compact electronics such that it was mainly the mechanical transport which dictated the equipment’s final size. But there was one last challenge. Large quad machines used vacuum or air-pressure systems to bring the tape into proper contact with the headwheel. This was impractical with the VR-3000, so an elaborate and highlyprecise tape guide/shoe mechanism was required. Most quad machines have gone to scrap. Some remain in the hands of dedicated collectors and museums. The few in working order are used to recover archival tapes for digitisation and preservation, or in live demonstrations of this ingenious technology. The operator recalls Randall Hodges was one of the earliest operators of VTR technology. He recalled his experiences for this article. Before videotape, news gathering and other outside-the-studio material was shot on film, or came in by a remote relay. Film had been around since 1923. It had matured by the 1950s – everyone knew how to use it and equipment was plentiful. Film worked fine, but it needed expensive developing equipment and chemicals, and it could only be used once. Processing easily took 45 minutes to an hour. Film copying used specialist equipment and was costly and time-consuming. And if the camera operator missed a shot, if it was siliconchip.com.au Fig.8: the basic principle of analog timebase correction. The correction needs to be continuously variable over a range of 0-64µs. Since it was too difficult to do this in a single stage at the time, a 0-300ns continuously variable delay was combined with a series of switchable 125ns delay lines. out of focus or poorly framed, no-one could tell for sure until the film had been developed and run. So videotape recorders (VTRs) were genuinely revolutionary. You could record and play back instantly, and the audio track could be recorded simultaneously, or separately in post-production to match the vision. You could also copy videotape easily, cheaply and almost instantly. Although a reel of tape was expensive, good-quality tape was OK for perhaps a hundred re-uses, thus making it economical compared to single-use movie film. The VTR made it practical to record shows for repeat transmission, or to pick out segments for inclusion in other shows. Yes, it was possible to film a television monitor (called a “kine” or “kinny”), but the quality was never very good, and duplication of film stock is expensive. ing back a tape recorded on a different VTR: RCA to Ampex, or vice-versa. High-frequency playback equalisation varied between machines, so we would record colour bars at the start of every tape. For an interchanged tape, we would play back the colour bar section and adjust equalisation for each of the four heads. Head wear could also lead to one (or more) tracks being recorded at lower amplitude compared to the others. This would demand adjustment regardless of where the tape had originated. Tape problems Early formulations used “brown tape” (ferric oxide), which was quite noisy and shed oxide like dandruff. This grade of tape would cause head clogs that could wipe out the signal from one head (or all four) completely. Common quad problems Head-banding could be a problem with the early machines playing back their own tapes. Since each video track was only 16 lines, it was vital that each head played back with exactly the same signal strength. It became more common when playAn Ampex quadruplex VTR (video tape recorder) in use. There were various different configurations over the history of the machines; in this case, the controls are next to the tape reels with monitoring equipment overhead, but other machines were narrower with a smaller side control panel and more rack-mounted equipment above and below the tape deck. Australia’s electronics magazine March 2021  51 The improved “black tape” (chromium dioxide) was much better. Its signal-to-noise ratio was superior, and it shed much less oxide. With brown tape, we’d be on standby with a lint-free cloth and a spray can of Freon (later phased out in favour of isopropyl alcohol). The headwheel spins at over 10,000 RPM, and the video head tips are less than a millimetre wide. If you think this sounds like a highly precise circular saw, you’re right! The combination of the shoe curvature and the vacuum guiding system theoretically ensures that each head makes first contact with the tape a little way in from the extreme edge. This prevents the head from catching on the tape edge, and ensures that the tape runs smoothly. Tape damage can take many forms, but edge damage (scalloping) creates a “wavy” edge, and this can allow the video head to impact the extreme edge of the tape. And cut it in half! In the worst case of putting a program to air, we would have to rapidly pause the VTR, open the shoe, draw maybe half a metre of tape through the head stations and wrap it onto the takeup reel, then punch it into play and hope that the tape would make it to the end of the program. Those were fun days! Going to air Servos take some time to run up to speed and lock, with the first generation of quad machines needing eight seconds from pushing play to delivering guaranteed stable off-tape video in sync with the station. We called this the pre-roll or rollback time. But quad VTRs do not give an image in pause, and cannot be played in slow motion, so we couldn’t use any visual cues to set the pre-roll timing. What we would do is find the start of the required program material by rocking the tape backwards and forwards and listening for the start of the audio. We would then manually roll the tape back, counting the one-second cue pulses as we did. We’d hear a “whoop” each time we rolled past a cue pulse, so eight whoops back would give us the pre-roll timing. Because we were rocking the tape manually, it was pretty slow compared to its normal 15ips speed, so the cue pulses’ usual clean ‘pips’ came out spread over time, and at a much lower audible frequency. We’d leave the VTR in pause and wait for the producer’s cue. Let’s say the show’s presenter was going to do a cross to VTR. The producer would know pretty well when the presenter was eight seconds from the cross, and would call up the VTR. We’d hit play, and the VTR would start and lock within the eight-second window. As the announcer threw to the VTR, the producer (or the panel operator) would punch to tape, and the VTR program would go to air. We eventually moved to Ampex AVR-2000s. These had much better servos, reducing our pre-roll times to four seconds. Good as those were, quad technology still could not produce a still picture or slow motion. If you ever used the next generation of helical scan VTRs (“C” format, Umatic, Beta, VHS or Video8), you will probably know that the tape could run at any speed from still frame to picture search, and give a picture of some kind. But quad offered none of these conveniences. It was ‘play or nothing’. Cooked by the valves When I started, we didn’t offer today’s 24/7 service, so the VTRs were turned off after the last show finished. Later on, we just left everything running 24/7. The first generation of valve-equipped VTRs put out a lot of heat. Our first operating rooms had no air conditioning, so it was uncomfortable for us and less than appropriate for the VTRs. Videotape likes the same range of temperature and humidity that people do, and this may have contributed to the poor reputation of the oldfashioned “brown tape”. It was a great relief when we finally got proper air conditioning. Over time, valve technology was superseded by solid state, greatly reducing the amount of waste heat generated by the VTRs and making our lives more comfortable and the machines more reliable. Quad cartridges We would air many shorts; mostly station promos and advertisements. These were recorded on two-minute lengths of two-inch quad tape, held in cartridges loaded into a conveyor system. The idea was that you’d cue up the cart, then hit play and put it to air. But they could be unreliable; so much so that we’d occasionally just record the whole ad break to open-reel quad tape and run it from the VTR rather than the cart machine. Conclusion The authors would like to thank Randall Hodges for assistance in writing this article. Next month, in the second part of four in this series, we describe the helical scan VTR technology and the first round of videotape format wars. References & videos While it looks awkward and bulky by today’s standards, this sort of portable video recording system revolutionised how TV was recorded and broadcast; especially the news. Source: www.labguysworld.com 52 Silicon Chip Australia’s electronics magazine VERA: youtu.be/rWCstPCcuKk An excellent presentation on quad technology: youtu.be/fpBRuheelu4 Editing two-inch videotape: youtu.be/7YtmwB9Ds5Y Cartridge machines: youtu.be/wM_2upiGUO0 Footage of Alexander M. Poniatoff: archive.org/details/cst_00007 A thorough written history: www. labguysworld.com/VTR_TimeLine. htm SC siliconchip.com.au by b o e r DIY H a w d r a H Hardcore electronics by On Sale 24 February to 23 March, 2021 Digital Microscopes Excellent for educational purposes and suitable for many applications. 600x magnification. USB QC3191 NOW $79.95 SAVE $20 Rechargeable with 4.3" Screen QC3193 NOW $99 SAVE $30 Bonus Gift FREE 1kg Filament Buy 1 x TL4256 Get 1 x 1kg Flashforge Filament of your choice free TL4269-TL4276. Flashforge Adventurer 3 3D Printer Compact structure with no angular design. Ready to use and no levelling printing. Removable, heatable and bendable plate. Automatic filament feeding. Print up to 150Lx150Wx150Hmm. TL4256 899 $ JUST Quad 14 Segment Alphanumeric Display Module This official kit from Arduino®. Kit includes UNO board, breadboard and plenty of prototyping accessories. Perfect gift for a young electronics enthusiast or maker in the making. 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Winners notified via email by 14/5/21 and published at jaycar.com.au/dmax-jaycar by 17/5/21. Promoter is Jaycar Pty Ltd. ABN 65 000 087 936. 320 Victoria Rd Rydalmere NSW 2116. Authorised under NSW Authority No. TP/00716, and ACT Permit No. TP 21/00078 and SA Permit No. T21/71. Actual prize vehicle not shown, specifications may vary. For full terms and conditions refer to jaycar.com.au/dmax-terms Your Club, Your Perks. KEEP UP TO DATE WITH THE LATEST OFFERS & WHAT’S ON! JOIN NOW! 1800 022 888 www.jaycar.com.au Over 100 stores & 130 resellers nationwide HEAD OFFICE 320 Victoria Road, Rydalmere NSW 2116 Ph: (02) 8832 3100 Fax: (02) 8832 3169 ONLINE ORDERS www.jaycar.com.au techstore<at>jaycar.com.au Arrival dates of new products in this flyer confirmed at the time of print. Call your local store to check stock. Occasionally discontinued items advertised on a special / lower price in this flyer have limited to nil stock in certain stores, including Jaycar Authorised Resellers, and cannot be ordered or transferred. Savings off Original RRP. Prices and special offers are valid from 24.02.2021 - 23.03.2021. SERVICEMAN'S LOG If it isn’t one thing, it’s another Dave Thompson Sometimes, even when there are no customers lining up, work comes along anyway. It isn’t always welcome, but when your tools go down, you have to fix them. It doesn’t help that I’m afflicted with the Serviceman’s Curse, so I’m allergic to paying for replacement tools when it’s possible to (uneconomically) fix them! Over the past year, plenty of local businesses have folded; there simply isn’t the customer traffic to keep the doors open any more due to lockdowns and general economic malaise. While our overall revenue has dropped, as you would expect with a lot less work coming in, the silver lining is that I finally have some free time to get onto those little jobs that I’d been putting off. Those of you who live the rock and roll life of a serviceman know that sometimes things don’t go according to plan. An anticipated five-minute job can easily turn into a two-day mission in the flash of a shorted battery connector or a clumsily-placed screwdriver. That sort of thing doesn’t happen to me, of course! But I do hear rumours that it happens to other, less-careful people. The first small job created itself when I went to use my soldering station, and the pencil was still cold 10 minutes after I switched it on. The astute among you will know soldering irons are meant to be hot, so the fact that I could hold on to the wrong end need, of it without being burntyou told me that something was up! The pencil connects to the soldering station using one of those multi-pin screw-on plugs, sometimes called a GX-16 series connector. I removed and re-connected it, and it seemed sound, so I guessed that the pencil’s element had gone open-circuit. Confirming this theory proved to be more difficult than I imagined, mainly because the pencil itself appears to be a moulded unit. Everything is set into it at manufacture, and it cannot be disassembled to reveal the innards. The cable stress reliever at the bottom can be prised out, but the element appears to have no means of being removed, other than by cutting into the pencil’s plastic body. This makes them inexpensive to manufacture, but not great for repairs. I think they expect people to throw away the dead pencil and buy a new one. The problem is that I’ve used this pencil for a while now and having just ‘broken in’ a new tip, it is perfect for the work I do. To bin it without at least trying to repair it you want. would be, well, frankly against my serviceman’s code! So electrical checks would have to be made via the GX connector. I For full details on how to enter, drawing & rules head to: jaycar.com.au/dmax-jaycar Items Covered This Month searched for circuit diagrams online for my model. Once located, my mul• It’s always the other thing timeter confirmed there was no resist• Coin counter repair ance or continuity through the element from any of the pins, let alone the • Alternative security systems designated ones, which told me all I • LED rose garden repair needed to know. It was dead! • Electric fence energiser repair get that thing win that thing SPEND $50 OR MORE FOR A CHANCE TO WIN AN ISUZU D-MAX *Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz siliconchip.com.au Borrowing a spare Fortunately, I have a spare pencil. But when I say spare pencil, I mean spare soldering station. While it is very much like my usual one, I originally Australia’s electronics magazine March 2021  61 * purchased it as a desoldering station. My faulty unit has a temperatureadjustable soldering iron on one side and a hot air wand on the other. In contrast, the ‘spare’ station has the same soldering iron setup, with a temperature-adjustable desoldering gun and suction pump arrangement on the other. The desoldering ‘gun’ on this station looked great on paper, but doesn’t work well in practice. The ‘real’ version this unit was copied from might work very well, but this one doesn’t, at least for me. It has one of those pistol-grip style handles, with a hollow, heated tip. Pressing the ‘trigger’ on the handle activates the suction pump, so I can theoretically hoover up the molten solder. Sadly, it is useless; it wouldn’t suck the froth off a lager. Also, the element won’t ‘take’ solder, similar to the metal on some cells; the solder simply doesn’t stick to it. I’ve tried ‘seasoning’ it with various solder pastes to no avail. So trying to heat a solder joint is a lesson in frustration. The bottom line is that I’ve never gotten it to work, which is why it sits in the corner of the workshop. I expected it to work as well as the other station, but it just doesn’t. I’ve long accepted this and have moved on. On the plus side, the integrated soldering iron has almost never been used. I simply unscrewed/unplugged that pencil and installed it on my other station, which immediately resolved my cold-tip issue. However satisfying this quick-fix may have been, I still had a dead pencil, and by extension an incomplete soldering station (useful or not). And as a serviceman, that bothered me. A quick search on AliExpress revealed that a replacement element was available for just a few dollars. Or, I could get a whole new pencil and cable/connector for only a few bucks more than that. Even better (for a tool junkie), a new pencil plus two spare elements could be had for around the same money! You already know which option I went for. Of course I am going to try to fix the broken one. Now I know what you are thinking; did I fire six shots or only five? Oh no, sorry, wrong script. You are thinking that if the pencil is moulded and cannot be disassembled, how will I replace the element? 62 Silicon Chip Well, I’m glad you asked as it’s a good question! Anything can be disassembled with the right tools and the right attitude. A hammer tap here, or a Stanley-knife blade applied there, or even a junior hacksaw placed just so can achieve amazing results. These apparently-sealed devices can be opened, repaired and glued almost seamlessly back together without anyone (but us!) knowing about it. I used to watch Dad opening moulded-plastic power supplies using a carefully calibrated hammer tap, and when the thing was repaired, he simply glued it back together. That was in the days when such power supplies cost a small fortune and were worth repairing. That obviously isn’t the case today; I literally have cartons full of these supplies that will likely never be used, but the philosophy of the repair still stands, and I thank my Dad for passing that on to me. I wouldn’t usually do this for a paying customer, but to repair my own tools or appliances, I’ll give anything a go. If I ruin the pencil, I’m out a few bucks, but it’s the serviceman’s creed and the principles of repair that compels me to at least try. I’ll let you know how it goes! Some more light work To be realistic; many repairs are simply not worth the cost. Recently, I had an LED ceiling light stop working. It had only been installed (by me) a few years ago and hadn’t had a lot of use. Maybe a few minutes a week of ‘on’ time, if that. These lights are commonly called “UFO” lights because they look like a flying saucer. But they are different than downlights which require cutting large circular holes in the ceiling. These ones come with a fitting that simply replaces the existing battenmounted socket we are all familiar Australia’s electronics magazine with, and the new UFO light slots into place, hiding the socket. That makes retrofitting ceiling lights a breeze. We did our entire house with these, and it was an effortless job to convert all our incandescent lights to LED versions, without a bunch of tools, mess and headaches. And they’ve been great; the light is better, brighter and more economical than our original lamps and fitting them was super-easy. I’d installed a dozen others in the house, and they’ve all done a whole lot more work. Why this one died is likely down to the fact that 10% of these lights will fail in the first few years, and that’s an acceptable failure rate for modern manufacturers. Retailers simply replace the unit and chuck the dead one in a skip. Now, if you are afflicted with the Serviceman’s Curse, you know you can’t just throw something out without at least pulling it apart and looking at it. So I had to take it down and open it up. At the same time, I ordered another one, because even though it is seldom used, we need a light in that spot and at only $11, replacing it is the obvious solution. It also means that I could work on it at my leisure without hearing “get that bloody light working!” The housing popped open without much hassle. Inside is a 200mm diameter PCB with a bunch of surfacemounted LEDs soldered to it. Another small PCB is mounted in a central cutout, containing the LED driver. A sniff with my serviceman’s nose told me something had electrically given up the ghost. The usual suspects My first step was to remove and check the two electrolytic caps that dominate the driver board. I fired up my soldering station and went to try to desolder those two caps, but the pencil was stone cold. I think you already know how that went! After resolving that, I removed the caps and checked them with my trusty Peak Electronics ESR meter. One measured 15W, which is on the high side. The other one was also high, but not as out-of-spec as the first one. I replaced both and reassembled the board into the light. I powered it up with my non-Variacbranded Variac, and the LEDs sprang into life. Success! It is now reinstalled siliconchip.com.au and happily illuminating our spare room. So it was well worth having a go, and when the replacement I ordered finally arrives, I’ll have a spare. I must be cursed It’s never fun when the tools we rely on to do our job don’t work. Last week I fired up my computer to write this article, and my machine wouldn’t boot. The old saying is that a plumber’s pipes are always clogged, and while I’m not sure what that means, I’m pretty sure it applies to me! My main computer is a monster that I built 11 years ago, so I’ve been reluctant to upgrade it. That’s because it was still going very well, played all the high-performance games I ever wanted to play, and it has always been there for me. For it to fail to boot up one morning was quite devastating. While I’ve always tried to make these servicing stories non-computer-centric (as it is a dull trade), some readers might find it interesting. If a machine doesn’t boot, I usually start by removing everything but the absolute basics to get the motherboard up and running. In this case, that still resulted in no boot. I then started removing and replacing RAM, and suddenly, I had a POST (power-on selftest) screen. I replaced the single stick I’d left installed one-by-one with the three others, and with the third, the machine didn’t boot. Leaving that out, but with the other three sticks installed, the machine booted happily. After 11 years, one stick of RAM had failed, and that broke everything. You just cannot take things for granted in servicing. printer had broken. The bureaucracy she works for had said this 12V device was “too dangerous to use” in this state! That sounds to me that this is a statement from someone with more ego than knowledge. In any case, the solution was simple. It took me an hour or two to design a new cover in OpenSCAD. I was then able to 3D print the cover, and the deadly 12V inside was safely locked away. The next coin counter fault was a problem common to many cheap devices: the front panel membrane switch developed a fault, so the PRINT button no longer worked. Pulling it apart was easy enough, with just three countersunk self-tapping screws holding the upper case in place. I did have to cut one wire tie; this prevented the rotating coin counter mechanism inside catching on the multi-core wire connecting the front panel. If I had designed it, I would have used a reusable clip/U-channel to position the wire safely. But this worked, even if it did make disassembly (and reassembly) a bit more of a hassle. Next, I unscrewed the front panel PCB, unplugged the front panel membrane switch connector and very carefully removed the complete front panel membrane switch assembly. Then, using a thin blade (the knife from a Swiss Army Card works really well), I separated the two halves of the membrane near the PRINT button. Unsurprisingly, one of the conductive tracks was open circuit. To determine if this was the only fault, I ran some leads to the correct pins on the PCB and found that the coin counter beeped when I shorted these two wires together, simulating a press of the PRINT button. Well, I had found the fault, but now I had to figure out how to fix it. The likelihood of getting a replacement front panel was low-to-zero. This was a major problem for the canteen, as the coin counter is used every (work) day and having to count coins manually meant a lot of extra work. Then I had a thought: as only one button was faulty, why couldn’t I just add another switch? Initially, I was just going to drill an extra hole somewhere and use a standard 6mm pushbutton switch; that would work but look a bit ugly. But then I remembered I had some tiny switches that measured 3mm x 6mm and were only 1mm high. I purchased these as spares for repairing car remote controls. After a bit of measuring, it looked like I could shoehorn one of these switches to fit into a hole cut in the plastic case underneath the existing PRINT button, so that’s what I did. For speed and simplicity, I drilled two 3mm holes next to each other and Coin Counter repair G. C., of Salamander Bay, NSW has found (like many others) that it can be easier to replace a cheap failed part with a higher quality alternative than it is to fix the original part. In this case, it was one of those horrible membrane buttons. His solution means that it’s unlikely to fail again… My daughter runs a canteen for a large organisation and even with email ordering, it’s still necessary to count all the cash each day. They use an unbranded coin counter that’s simply labelled “Coin Counter”. I have fixed it previously; it was a totally unnecessary repair, in my opinion. The small cover for the docket siliconchip.com.au The coin counter and small docket printer. Australia’s electronics magazine March 2021  63 filed until the switch fitted inside, then used double-sided tape to re-glue the membrane switch to the case. I pressed the tiny switch into its new home and tweaked its vertical position. When the switch activated reliably when the PRINT button area was pressed, I added a couple of drops of super glue to make it permanent. I then soldered thin (wire-wrap) wires to it, then soldered the other ends to the PCB tracks. Happily, the coin counter is back in service and working perfectly and, even better, it’s externally unmodified – the only difference is that now you can feel a click when the PRINT button is pressed. I would go so far as to say that after this repair, it’s better than new! Alternative security systems R. M. of Scotsdale, WA, found out that there are really cheap security systems, and really expensive security systems, and neither is all that appealing. Luckily, he found a middle ground... Our community shed needed better security as several of the keys had disappeared over the years. As the only member with any electronic knowhow, I was volunteered to search out a suitable replacement. I went to the biggest security shop in the local town and made enquiries. They suggested an RFID system priced at around $3500. As the shed is a small non-profit organisation, I knew that we couldn’t afford that. After some discussion, the committee authorised a budget of $200 and let me loose. 64 Silicon Chip Australia’s electronics magazine I tried sourcing a cheap (~$50) RFID unit from overseas via eBay, but shortly after I hooked it up and got it working, it failed. So I had to send it back and get a refund. During wanderings through Google, I had come across a more elaborate (and more expensive) four-door controller from Jaycar. After the “fleabay” controller failed, Jaycar (bless ’em) put it on special and dropped the price by a good $50. The committee agreed, and we were soon in possession of a nice sturdy box of tricks that actually worked. That left the actual door strike. Electro-mechanical striker latches require the door to be sturdy and close-fitting. But our big metal shed ain’t all that flash. The door (square steel frame, steel sheet) swings on one of the portal trusses. And when the wind blows or the sun shines, there is a perceptible movement of a few millimetres between door and frame – enough to make the standard latch system unreliable. However, at the back of my farm there’s an old ute with two solid door locks. I nabbed one which is now doing excellent service on our shed. With a 12V actuator to pull the release lever, it has enough slop to handle the geometry changes, and plenty of strength to hold the door shut. For our little installation, the supplied software is overkill. It’s designed to control many doors of many departments and keep records of all the workers’ movements. It is mind-boggling in complexity, and the instruction man- siliconchip.com.au ual is a masterpiece of confusion and poor translation. For example, on the circuit layout, it shows two pins labelled “J9: Joint of closing door by force”. I contacted Jaycar to ask what this meant, and eventually, the answer filtered back: it is a disable input. Close the circuit (joint of), and all doors would stay locked (closing door by force). It makes me wonder if they created the manual using machine translation! I spent many hours decoding the manual and experimenting with the software. The process of registering each user is vital, and there are two ways one can do it. One is a bulk entry method, and the other, more detailed, allows individual entry. I chose this way as we wanted to enter our members’ details one at a time, but I could not get it to work. I thought it must be my fault, so I summoned the local PC expert. He went straight to the “bulk entry” system, and it worked! Don’t bother with that other way, he said, it’s no good. So, finally, we have a working secure entry setup. The total cost was around $370 with the backup battery and trickle charger. Now if a member leaves, or doesn’t cough up the yearly subscription, we can simply click a button and forbid entry. He’d have to resort to removing a sheet of corrugated iron with a screwdriver to get in! LED rose garden light repair B. P., of Dundathu, Qld has some unusually ornate solar garden lights, so siliconchip.com.au when they started to fail, it was worthwhile taking the time to fix them... Some time ago, my wife was given a white LED rose garden light. We noticed on the packet that there were also yellow and pink LED roses, so after finding out that a nearby discount shop sold these, we got a yellow one and a pink one too. Later, my wife received another two LED roses, pink and yellow. However, this new yellow rose only had a single flower, whereas the others had two or three flowers each. We noticed that in the mornings, it was only the single yellow rose that was still lit; the other four roses were no longer lit due to having more LEDs (and presumably exhausting the battery charge faster). After a while, we noticed that both the white rose and the original yellow rose no longer lit at night. I had a look at the yellow rose to see what the problem was. After removing the four screws from the bottom of the small box containing the solar panel and battery, I could see that water had leaked into the box, causing the positive battery connection to become rusty. The wire had also broken off it and the battery terminal was rusty as well. I re-sealed the wires coming from the solar panel properly with hot melt glue, then cleaned up the battery terminal. It was so badly rusted that I decided to clean it and coat it with solder while I was soldering the wire back on. I also tested the battery and found that it was still OK. Australia’s electronics magazine With the battery refitted, the rose still didn’t work. I measured the voltage on the battery terminals with the solar panel lit and got a reading of 2.18V, so the solar panel was charging the battery, but some other fault was preventing the LED from turning on at night. I removed the circuit board and checked the switch, which was still functioning correctly. The circuit board looked clean, with no corrosion. I then realised that I had a spare circuit board from one of our garden lights that had been run over and smashed by a courier, so I decided to use that to get the LED rose working again. This board did not have a switch, but I didn’t think that really mattered. I disconnected the original circuit board and wired up the replacement circuit board, which was quite easy, as all the connection points on both PCBs were marked S+, S-, B+ and B-. The wires from the LEDs were too short, so I just used some scrap wire to extend them. When I tested the rose, it still didn’t work, but I noticed that the YX8018 IC was bent over, so I straightened it and checked the bottom of the circuit board. I found that the solder joints were cracked, so I re-soldered them, but the rest of the PCB was OK. Now the rose worked, so I sealed up the hole where the switch used to be mounted with hot melt glue. With the yellow rose now reassembled and working, I took a look at the white one. I found that the same water ingress problem had affected this light. After re-sealing the wires from the solar panel, I found that I could use the battery connector from the smashed garden light to replace the rusted one as it was the same size. Once cleaned and reassembled, the white rose now also worked again. The next morning, I was outside before dawn, and I was amazed to see that the yellow rose that I had just repaired was still lit brightly. I put this down to the more complex circuit in the garden light PCB that I had transplanted, which is apparently more efficient than the simple circuit in the original LED rose. As can be seen in the photos, the ‘basic’ rose PCB consists of just one YX8018 IC and an inductor, whereas the better garden light PCB has both of these plus a diode and capacitor. March 2021  65 At left is one of the ‘basic’ LED rose PCBs which had started to rust, while to its right is a superior garden light PCB. This makes quite a difference to the efficiency of the circuit. I have also repaired several other garden lights. Two had bad solder joints on the LEDs, and I also had to replace the RGB sequencing LEDs in several lights when they malfunctioned (the blue elements failed). I found some seven colour LEDs on eBay, which sequence red-green-bluewhite-green-pink-warm white-repeat, as the three-colour RGB LEDs were harder to find and more expensive. I’ve also replaced the 150mA Liion cells in all our garden lights with new “1000mAh” (probably actually 400mAh) cells, so they now last all night, as long as they have sufficient sun exposure during the day. Even though these lights are not expensive, it was still worth repairing them, as it saved some money and saved them from landfill. Electric fence energiser repair K. G. of One Tree Hill, SA, has repaired quite a few electric fence energisers over the years, but this one posed some unique challenges... I’ve written about the repair of electric fence energisers before (July 2015; siliconchip.com.au/Article/8707); every now and again, I get one from the local fodder store owner to see if I can fix it. These devices apply a short, high voltage pulse to a bare galvanised iron wire running along the fence, supported on insulators. They are used to control the movement of stock. Most operate from the mains, but some models are powered from 12V DC, generally with a solar panel to keep the battery charged. The Earth side of the energiser output is connected to three or more Earth stakes spaced out by a few metres, as recommended by the manufacturer. The pulses have a typical duration of about 30µs and the region of 5-8kV. The pulse repetition rate is about 1.3 seconds. The main difference between units is the energy in each pulse (measured in Joules). This Gallagher model MBX1500 was made in New Zealand and is the largest I have come across yet. Its pulse energy is 3J, and it is suitable for fence runs as long as 94km! A touch on the fence wire would be excruciating, but not particularly dangerous. Testing the unit on the bench brought some low-level intermittent clicking instead of the regular pronounced clicks every 1.3 seconds. This model is capable of being run from the mains as well as 12V DC; there is Servicing Stories Wanted Do you have any good servicing stories that you would like to share in The Serviceman column in SILICON CHIP? If so, why not send those stories in to us? It doesn’t matter what the story is about as long as it’s in some way related to the electronics or electrical industries, to computers or even to car electronics. We pay for all contributions published but please note that your material must be original. Send your contribution by email to: editor<at>siliconchip.com.au Please be sure to include your full name and address details. 66 Silicon Chip Australia’s electronics magazine a compartment in the rear to hold a 12V, 7Ah SLA battery in addition to the mains cable and plug. The two halves of the case come apart after removing six deeply recessed selftapping screws. Fortunately, they are normal Philips head types rather than one of the many ‘security’ screws used these days. Inside was an offline switchmode power supply (SMPS). This, or the 12V battery, fed into a DC-DC converter stepping the low voltage DC up to several hundred volts to charge the main capacitor. Then there was the circuitry associated with the pulse transformer. There was also a second PCB containing four LCDs plus a 40pin PIC microcontroller. In its working condition, the unit displayed the output pulse voltage and energy, plus two other parameters which didn’t seem to apply to this unit. So it was quite a complex unit with many SMD components down to M2012 (0805) size. When fault-finding electric fence energisers, I first test the large pulse capacitor(s). There are two in this unit, one 30µF and the other 6µF, both rated at 1200V. After ensuring they were discharged, I measured their capacitance with my Peak Component Analyser. The larger one was 13µF and the other 3µF, both well down on their original values. This is quite common with these components, but such a drop should only reduce the energy of the pulses, not stop the unit working altogether. Despite this, I ordered some replacements from a local Adelaide firm and carried on with my testing. The other component to test early siliconchip.com.au is the main SCR which discharges the capacitor into the primary of the pulse transformer. This appeared to be OK as the voltage across the larger pulse capacitor was a couple of hundred volts and fluctuating with the intermittent clicking. I then measured the voltage out of the offline SMPS which I found to be only 4-10V with fluctuations, instead of a steady 12-15V. I fed 12V DC from my bench supply to the SMPS output with the mains input disconnected. The energiser started working normally, with believable values on the LCD screens. Looking at the SMPS more closely, I noticed a large electrolytic capacitor with a small bulge in the top. It was the 100µF 40V filter capacitor on the output of the mains bridge rectifier. I removed the capacitor and tested it on my Electronics Australia ESR Meter. The reading was about double the typical value shown on the front panel of the meter; not a show-stopper but it needed to be replaced. As I didn’t think this was the main cause of the problem, I refitted the old one to continue my search for the real culprit while I ordered a new capacitor. It wasn’t available from the local outlets as it was a low-profile device 30mm in diameter and only 20mm high, so it took a few days to arrive from Perth. siliconchip.com.au The primary active device in the SMPS was a power Mosfet with an integrated control circuit in a TO-220 package, riveted to a small heatsink. It’s coded TOP227Y (TOPSwitch-II) and is made by Power Integrations Inc. This makes for a much-reduced component count as it contains the oscillator, PWM modulator, voltage reference plus all the protection circuits and the power switching Mosfet. The circuit used in the energiser turned out to be very similar to an application circuit shown in the data sheet (shown below). As the TOPSwitch device had so much of the circuitry in it, I decided replacing it would be a worthwhile punt. The only stock I could find was from Digi-key. I ordered two of the devices as the postage cost from the USA was more than the device itself. I can’t fault the delivery time; I placed the order online on a Tuesday, and it arrived at my local PO on the following Monday. Unfortunately, replacing the TOPSwitch device didn’t help my problem except to eliminate it as the source of the fault. Referring to the figure, I measured R3 and C5 on the control input of the TOPSwitch. R3 was fine, but C5 was rather low in capacitance, about 30µF rather than 47µF. I didn’t pay much attention to that at the time. Australia’s electronics magazine One point of difference between the MBX1500 circuit and that from the data sheet is the use of a TL431 voltage reference rather than the zener diode shown. I replaced the TL431 and also the optocoupler connected to it, but neither changed the result. I also tested the low-voltage DC rectifier (D2) and filter capacitor (C2), the latter for both capacitance and ESR. Both were OK. I was by then wondering where to turn next. I read the data sheet more carefully and realised the part played by the cap on the control input was quite important. So I removed the 47µF capacitor and measured its ESR. The typical value is 1-2W, but this one was so high that it was above the maximum reading of the ESR meter, which is 100W. In other words, it was virtually open-circuit. I lost no time in replacing C5 with a new one, which had a 1W ESR reading. The power supply came good immediately, and the energiser started its regular clicking with 7.6kV pulse voltage showing on the LCD. The capacitor was a through-hole type mounted between the PCB and the heatsink. The elevated temperature of this position probably hastened its demise. I put the three PCBs back in the housing and screwed the cover on, then left the unit to run overnight as a soak test which it passed with no SC problem. March 2021  67 Mini Isolated Serial Link This tiny module (about the size of a postage stamp) provides bidirectional, isolated, full-duplex serial communication. That makes it ideal for when two (or more) boards running from separate supplies need to pass information to each other. It can also carry isolated logic signals. Among its many other uses, it can be used to join two of the Battery Balancers (described in this issue). By Tim Blythman T he High-current Four Battery Balancer project starting on page 21 can handle more than four batteries (or cells) by stacking multiple units. But for that to work, they need to communicate with each other, even though their ground potentials will be quite different; possibly as much as 60V DC apart. To connect their onboard serial links so they can work as a single unit, a serial isolator is needed. This little device uses optoisolators to provide thousands of volts of effective isolation while allowing the serial data to pass through unchanged. Another important use for a device like this is connecting a computer to a device that you’re testing, to prevent any possibility of damage should the device malfunction and feed a high voltage to its serial pins. If you have a single Battery Balancer and wish to monitor or control its operation on a computer, it would be a good idea to use this isolator between the two, for safety. We already published the Zero Risk Serial Link in January 2019 (siliconchip.com.au/Article/11360) for this purpose, but that board includes a power supply for the isolated 68 Silicon Chip device, which often isn’t necessary. That makes the board much larger and more complicated than necessary. In cases where both communicating devices have individual power supplies, this design is a better choice. New design By dispensing with the power circuitry and using six passive SMDs, we’ve managed to squeeze the required circuitry into a PCB that measures just 26.5 x 23.5mm. That’s small enough to be connected inline with your serial link and encased in a short length of large di- These same-size renders of the front (left) and rear (right) of the Isolated Serial Link PCB show just how tiny it is. Whether you use vertical header pins, as shown here, or horizontal, as shown in our photos, is up to you. Incidentally, the renders were taken directly from the new Altium Designer 21, which we reviewed in January (siliconchip.com.au/article/14705). Australia’s electronics magazine ameter heatshrink tubing. Despite this small size, it isn’t hard to build. Fig.1 is the complete circuit diagram. The operation is simple. On the transmitting side, a current loop is formed between the TX pin and the selected supply rail (3.3V or 5V) via one optoisolator LED (OPTO2 for CON1 and OPTO1 for CON2). This is via a 220Ω current-limiting series resistor. So when the TX pin is high, no current flows through the LED, and when it is low, about 10mA (for a 3.3V supply) or 18mA flows. This pulls the RX pin at the opposite end low by activating the Darlington transistor in the other half of the optoisolator. When no current is flowing through the LED, the Darlington is off, so that pin is held high by a 1kΩ pull-up resistor. The configuration is identical for data flowing from CON2’s TX pin to CON1’s RX pin as it is in the other direction. A 100nF bypass capacitor stabilises the voltage across the Darlington on either side. Pin headers CON1 and CON2 are identical, and could be soldered directly to one of the communicating boards (eg, a Battery Balancer) using four of the six pins. siliconchip.com.au Alternatively, all six pins of CON1 can be soldered to a CP2102-based USB-serial module, allowing the combination to plug straight into a computer. Note that only four pins are connected in either case. For the CP2102 module, the 3.3V, RX, TX and GND pins are used. JP1 gives us the flexibility to choose which pin is used for power. If JP1 is set to the 5V position, power is taken from the pin next to GND on CON1. For a CP2102 module, this is the 5V USB supply. However, it corresponds to the 3.3V supply pin on the Battery Balancer; the Battery Balancer’s serial port operates at 3.3V, so that is where we want to connect. For CP2102 modules, you would generally place the jumper in the 3.3V position, which connects to the supply pin marked 3.3V on those modules. Indeed, regardless of whether the GND on either side is at the same potential, the Mini Isolated Serial Link can also be used to provide translation between different signalling levels. To keep the PCB small, we have not added a slot in the PCB to increase the creepage distances, as this would require a larger PCB area to prevent the PCB from breaking when flexed. Thus, the Mini Isolated Serial Link is not suitable for mains voltage isolation. Communication details Practically all TTL serial communications we have seen have the signals idling at a high level. Because we have arranged the optos Fig.1: the circuit is practically the minimum necessary for a pair of 6N138 optoisolators. The 220Ω Ω resistors in series with the opto LEDs limit the LED current while the 1kΩ Ω pull-up resistor holds the output high when the opto is off. The 100nF bypass capacitors are the minimum specified in the 6N138 data sheet. SC Ó siliconchip.com.au Features & specifications • Provides optically isolated bidirectional serial communications • Baud rates up to 57,600 (using 6N138) or 1,000,000 (using 6N137) • Each device can have 3.3V or 5V signal levels (ie, it can act as a level shifter) • Supply current (3.3V): between 0mA (TX & RX high) and 13mA (TX & RX low), average ~6mA • Supply current (5V): between 0mA (TX & RX high) and 23mA (TX & RX low), average ~10mA • Offset voltage: up to 100V DC or 60V AC between GND on either side to only switch on when the input voltage is low, and because the Darlington outputs pull low when active, the signal is not inverted across the device. If we had terminated the TX current loops to GND instead of the supply rail, it would instead act as an inverter. You might have noticed that we’re using a different optoisolator in this project compared to the Zero Risk Serial Link. This option is slightly more spaceefficient for similar speeds. Dual versions of the PC817 devices used for the Zero Risk Serial Link exist, but they are now obsolete, so we had to find an alternative. The footprint used by the 6N138 is also very similar to that used by the 6N137 optoisolator that we used previously in the Flexible Digital Lighting Controller (October-December 2020; siliconchip.com.au/Series/351). The 6N137 is a very fast device (up to 10Mbaud), but requires a 5V supply to meet specifications. In other words, if both sides of your Mini Isolated Serial Link will operate at 5V, you could replace OPTO1 and OPTO2 with 6N137s and work at a much higher speed, up to 1Mbaud or possibly even more. But because we wanted this design to have the flexibility to work with devices using 3.3V signalling levels, as it is very common (and a requirement for use with the Battery Balancer), we are using 6N138 parts instead. The 220Ω resistor value is chosen to work with both the 6N137 (at 5V) and the 6N138 between 3.3V and 5V. The 6N138 has much lower current requirements than the 6N137, so you could increase those values up to around 1kΩ if your transmitter has limited current capacity, or you l l MINI ISOLATED SERIAL LINK Australia’s electronics magazine March 2021  69 Fig.2: as suggested by the circuit diagram’s symmetry, the component layout and PCB traces are also symmetrical if rotated 180° about the centre. Ensure that each opto’s pin 1 faces towards the edge of the PCB. To keep the PCB small, we have put the pin markings on its back. Both the overlay and photo are full size. want to reduce the supply current somewhat. Similarly, the 1kΩ pull-up resistors could be increased in value if the current consumption on the output side is a problem. This will limit the maximum baud rate, though, as the circuit depends on this resistor to pull the output high promptly. Our testing shows that this device will work reliably up to 9600 baud with 3.3kΩ LED series resistors (instead of 220Ω) and 10kΩ pull-up resistors replacing the 1kΩ types. The 3.3kΩ value is the largest possible due to the nominal 0.5mA threshold current needed by the opto LEDs for correct operation; the 10kΩ value could go higher, but at risk of worse interference rejection. Maximum baud rate and could simply be used to pass any low-speed logic signals between two systems, such as an error flag, reset signal or on/off signal. Option The few options for this project revolve around the connections to CON1 (and identical CON2) and the corresponding configuration of JP1 and JP2. For connecting to a CP2102 module, use a 6-way header (pins or socket) to suit the module. In this case, the associated jumper is set in the 3.3V position. While we have shown a pin header and jumper shunt, you could use a short wire link to bridge two pads if you will not change this configuration. For our testing, we fitted the unit with a 6-way female header socket to allow a CP2102 module with a pin header attached to plug in, as that is how a CP2102 module typically comes. But you could reverse that, or just solder the two together using a single pin header. For connection to 4-way header on the Battery Balancer, it’s a case of bridging the 5V pad on JP1 or JP2. This means that the four central pads on that side of the Mini Isolated Serial Link (in the order 5V, GND, TX, RX) are available for connection. These four pins would also be the preferred way of using the Mini Isolated Serial Link with jumper wires or similar, if for no other reason but neatness. You could use a 4-way socket header plugged into a 4-way pin header on the Battery Balancer or even solder it directly to the PCB. We’ve built a few variants to show in the photos, so you can see how some of these options work. Since it is a small and simple project, you can make these selections once the other parts have been fitted. Construction The Mini Isolated Serial Link is built on a 27 x 24mm double-sided PCB coded 24102211. Refer to the PCB overlay diagram, Fig.2, to see where the parts go. If you are using SMD (gullwing) optoisolators, fit these first; otherwise, leave the through-hole variants until last. Like any project using surfacemounted parts, solder flux, tweezers, magnifiers and a fine-tipped iron are handy to have, while solder braid (wick) will help with solder bridges. But this project is simple enough that you might get away without them, as long as your eyesight is good! To fit the SMD optoisolators, align the parts with their pads, noting that pin 1 of each part is at the edge of the PCB; the two parts are rotated 180° relative to each other. Tack one lead to its pad and check that it is correct, especially that you can access the pads on both sides of the optoisolator and that all pins are flat against their pads. If not, melt the solder with the iron and tweak the part until it is aligned and symmetrical. Solder the remaining pins. You can flip the board over and apply more solder through the holes in the pads The 6N138 datasheet indicates rise and fall propagation delays of around 10µs and 1.6µs under typical conditions, setting a hard limit of about 100,000 baud as the bits will start to run into each other. A graph also indicates that the rise delay increases with temperature, which will further skew and distort the data. We did some tests with a CP2102 module plugged into each side of the Mini Isolated Serial Link to see what sort of speeds we could achieve with the specified components. This testing occurred at room temperature, so we would expect the results could be worse at higher temperatures. Testing at 115,200 baud led to data being corrupted about once every 20 bytes. This is not surprising given that propagation delays noted above. At 57,600 baud we didn’t see any This oversize photo show how you errors at all, nor at 38,400 baud. could connect two computers over Note that the Mini Isolated Serial Link can also be used in situations a serial link while providing opto-isolation. Two CP2102s are connected to the where it does not carry serial data. It Mini Isolated Serial Link using female header strips at CON1 and CON2. The jumpers JP1 and JP2 are set to the 3.3V position using blobs of solder. will work at any speed down to DC, 70 Silicon Chip Australia’s electronics magazine siliconchip.com.au Build the world’s most popular D-I-Y computer! ALL-NEW COLOUR 2 Again reproduced oversize for clarity, this shows the Mini Isolated Serial Link with a CP2102 on one side (with blue jumper shunt setting this side to 3.3V) and a four-way header on the other side. The second side has a red jumper shunt fitted to source power from the topmost pin on the four-way header. if you want to be sure they are connected properly. Fit the resistors and capacitors similarly. Check each part against the photos and overlay. Secure each part in the correct place with one pin before soldering the remaining pin. Our photos show large but shiny balls of solder. In this case, as long as there are no bridges, more solder is better than not enough. If you are using through-hole optoisolators, fit them now. Gently bend the leads to allow them to slide into the holes. You may be able to feed the leads into one side, then use the PCB to bend the leads so that the other side can be rotated into place, allowing the leads to spring back and hold the part in Parts list – Isolated Serial Link 1 double-sided PCB coded 24102211, 26.5 x 23.5mm 2 6N138 optoisolators (DIP or gullwing SMD; see text for alternatives) 2 1kW SMD resistors, M3216/1206 imperial size (see text for alternatives) 2 220W SMD resistors, M3216/1206 imperial size (see text for alternatives) 2 100nF 50V X7R SMD ceramic capacitors, M3216/1206 imperial size 2 6-pin headers (CON1,CON2) (see text for other options) 2 3-pin headers with jumper shunts (JP1,JP2) (see text for other options) Jumper wires etc to suit your application siliconchip.com.au Plastic Case Optional See SILICON CHIP July & August 2020 place (or use flat pliers or an IC lead straightening tool before insertion). Check that the pin 1 markers are towards the edge of the PCB then solder one pin. Check that the parts are flat, then solder the remaining pins. If you are using pin headers and jumpers, fit these next. If setting the supply options (JP1, JP2) permanently, use short lengths of tinned copper wire (or component lead off-cuts you might have from another build) and trim the excess after soldering them in place. Finally, fit the headers you need and/or solder the board to another device like a CP2102 module or Battery Balancer as needed. 480MHz, 32-bit processor; 9MB of RAM; 2MB flash memory; 800 x 600 pixel colour display Don’t miss your opportunity to experience Australia’s own worldclass, world-famous single board computer that you build and program yourself, using the world’s easiest programming language – MMBASIC. Learn as you build! Testing and usage The Mini Isolated Serial Link is simple enough that it should just work as long as you exercised care during construction. If you must test it first, use the arrangement shown with two CP2102 modules and open two serial terminal programs on your computer. We find that TeraTerm is a simple but versatile terminal program (and it’s free to boot). There will be more information for use with the Battery Balancer next month on how to connect two Balancers using the Mini Isolated Serial Link. Essentially, once they are connected, they should automatically detect each other and begin communicating so that they act as a single five-to-eightbattery (or cell) balancing unit. Our photos show various other ways of connecting the Mini Isolated Serial Link. Because of the inherent symmetry, you can treat each side of the PCB independently to mix and match what you are connecting to it. SC Australia’s electronics magazine And it’s so easy to build because all the hard work is done for you: the heart of the Colour Maximite II, the Waveshare CPU Module (arrowed) is completely pre-assembled and soldered. YOU SIMPLY CAN’T GO WRONG! Short Form Kit includes: Waveshare CPU module pre-loaded with MMBasic the PCB – with solder mask and screen overlay front & rear panels to suit plastic case shown above and all other components required to build the Does not include plastic instrument case, Colour Maximite 2 CR12xx cell or USB power supply/cable 14000 $ All this for only Plus $10.00 p&p in Aust SILICON CHIP SUBSCRIBERS: $AVE 10%! Subscriber’s price just $126 plus p&p Order now (or more information) at www.siliconchip.com.au/shop/20/5508 March 2021  71 All About Capacitors Capacitors are probably the most misunderstood of the passive components, due to the many different types available, their many parameters and greatly varying performance. This article should give you an understanding of the most common types, how they differ, and how to choose the right ones for your design. By Nicholas Vinen C apacitors come in all shapes and sizes. Some are much smaller than a grain of rice, while others are huge and used in banks to launch aircraft weighing many tonnes into the air! Because there are so many different types, it can be very confusing trying to choose one. Even if you know what capacitance and voltage rating you need, there could be hundreds or even thousands of matching parts. Some of those might not work at all in your circuit, while others might work but not very well, and some will be very expensive. You need to narrow the choice down to just a handful and then pick one. We have tried to break the following descriptions into digestible sections, despite their complexity. If you find yourself overwhelmed, give yourself time to digest what you have read so far, then read the rest later. Capacitor dielectrics Fundamentally, a capacitor is just two conductors (originally flat plates) separated by an insulator (the “dielectric”). But because the area of the plates required for any significant capaci72 Silicon Chip tance is quite large, modern capacitors are typically arranged as many layers of smaller conductors and insulators connected in parallel, allowing for a more compact package. In some cases, the ‘plates’ are not even flat but instead are spiral coils, or 3D structures such as the etched surface of a metal foil or granular materials. Etched or granular materials have a much higher capacitance per volume, as capacitance is proportional to surface area and inversely proportional to the distance between the plates. This creates a tradeoff; thinner dielectrics give more capacitance, but have a lower breakdown voltage, so the maximum voltage applied to the capacitor must be kept lower. This is the main reason that a capacitor with a higher voltage rating, but the same capacitance, tends to be physically larger; its dielectric layer(s) need to be thicker. The type of insulating (dielectric) material used has a strong effect on capacitor behaviour, and for this reason, capacitors are mostly categorised by the dielectric type. Different dielecAustralia’s electronics magazine tric types have their own trade-offs in terms of capacitance, voltage ratings, linearity, current handling and more. Some widely used dielectric materials for capacitors are: • Ceramics (typically metal oxides) • Metal oxide layers (in electrolytic capacitors) • Plastic films • Mica • Paper • A Helmholtz plane of solvent molecules (as in ‘double layer’ super/ultracapacitors) The most common types of capacitors in use today are ceramic and electrolytic, followed by plastic film types. These three types of capacitors have important sub-categories which strongly affect their behaviour. One property of all dielectric materials is the dielectric constant (“K”). The larger this number, the higher the capacitance for a similarly constructed device. K can vary with temperature, voltage, age and other properties. While high K values make for greater capacitances in a small volume, there are significant penalties in other areas, as we describe below. siliconchip.com.au Ceramic capacitors Fig.1: the range of capacitances and voltages available in 3.2 x 2.5mm SMD ceramic capacitors today. Both larger and smaller sizes are available, extending the range of values down to 0.1pF (1.6 x 0.8mm) and up to 470µF (4.5 x 3.2mm). Note how some types of ceramic dielectric are available to higher working voltages, and others to a higher maximum capacitance. (original source: Wikipedia) If you look at the PCB of just about any modern electronic device, you will find it covered in ceramic capacitors. They are cheap, reliable, perform very well and are available in a wide range of capacitances and voltage ratings. Because modern ceramic capacitors are fabricated in bulk, they can have anywhere from one to many thousands of layers. This gives them a wide capacitance range, from fractions of a picofarad up to hundreds of microfarads, in a small package – see Figs.1-3. Ceramic capacitors are typically robust and long-lasting, and are not polarised (they can handle negative or positive voltages). Ceramic capacitors are available with voltage ratings from just a few volts up to several kilovolts. Ceramic capacitors with voltage ratings above 500V tend to use different types of ceramic to those below 500V, and have slightly different properties. The most common ceramics used are based on titanium dioxide (TiO2) or barium titanate (BaTiO3) with additives to tweak their properties. As there are so many different possible combinations, they are arranged in various categories based on their performance. The categories are based on the initial tolerance of the capacitor (ie, the variation of real samples from the rated value), how the capacitance changes with temperature (the temperature coefficient) and how it changes with applied voltage (the voltage coefficient). The most common type codes are NP0 or C0G (different names for the same category), JB, SL0, X5R, X5S, X6S, X7R, X7S, X8L, Y5V and Z5U. To take three examples, NP0/C0G types have very close tolerances and no or minimal capacitance variation with temperature or voltage. They also have a low dielectric constant, so they are relatively large for a given capacitance value and voltage rating. As a result, they are also quite expensive. Fig.2: the structure of typical SMD and through-hole ceramic capacitors. SMD ’chip’ ceramics are made of many layers; throughhole disc capacitors may have a single layer construction, as shown here, or increasingly these days, a similar internal structure to a multilayer SMD capacitor. Multi-layer through-hole capacitors are usually encapsulated in epoxy, while the single-layer disc types can be encapsulated in ceramic. (original source: Johanson Dielectrics) Fig.3: the manufacturing process for multi-layer SMD ceramic capacitors. To keep the cost low, they are made in large sheets and after lamination is complete, the sheets are sliced up into individual capacitors. Those are then fired (similarly to ceramic pottery) and the end terminals are added, which provide a way to solder to the capacitor while also electrically joining every second layer. (original source: Johanson Dielectrics) siliconchip.com.au Australia’s electronics magazine March 2021  73 A set of ceramic capacitors ranging from 47pF to 2.2µF. Table 1: Class 2 capacitor codes First letter Middle number Last letter lower temperature upper temperature change in capacitance over given temperature range X = -55°C 4 = +65°C P = ±10% Y = -30°C 5 = +85°C R = ±15% Z = +10°C 6 = +105°C L = ±15%, +15 / -40% above 125°C 7 = +125°C S = ±22% 8 = +150°C T = +22 / -33% 9 = +200°C U = +22 / -56% V = +22 / -82% Fig.4: a cross-section of one layer of a standard aluminium electrolytic capacitor. The anode and cathode are both made from etched aluminium foil, for a large surface area. A thin layer of aluminium oxide is formed on the anode, which acts as the dielectric layer. The conductive electrolyte allows electrons to flow between the cathode right up against that oxide layer, so only the oxide layer separates the two halves of the capacitor, maximising capacitance per area. (original source: Wikipedia) Fig.5: like ceramic capacitors, electrolytics are made up of many layers to give higher capacitance, but they are typically wound in a coil rather than made from flat layers (with some exceptions). Once the leads are attached, the coil is inserted into a can with a rubber bung almost sealing it. We say almost because a small amount of airflow is needed to prevent the electrolyte from drying out. (original source: Wikipedia) 74 Silicon Chip Australia’s electronics magazine On the other hand, Y5V ceramics are very compact for a given capacitance value and voltage rating, but they have a very poor initial tolerance, and their capacitance is reduced dramatically at elevated temperatures and higher applied voltages. The benefit is that they are quite cheap to produce. Dielectrics like X5R and X7R are in between those two; they are larger than Y5V types for a given capacitance and voltage, but smaller than NP0/C0G. Similarly, their tolerances are intermediate, as are their production costs. Therefore, these capacitors are very popular as a reasonable ‘middle ground’. Note that NP0/C0G ceramics are almost ideal capacitors. They have very stable capacitance values over temperature and voltage, low ESL (equivalent series inductance) and ESR (equivalent series resistance), a low dissipation factor and excellent linearity. Their only real disadvantages are a low maximum capacitance value (due to their relatively high volume) and high cost. We’ll describe the meanings of those performance parameters in some detail later in this article. If the two/three-letter schemes given above look like gobbledygook to you, that might be because there are multiple different naming/categorisation schemes. The most common schemes are from the EIA, which consist of a letter, a number and a letter. But they don’t always mean the same things. For the most common type of ceramic capacitors (Class 2), the first letter and following number refer to the minimum and maximum temperature range, while the third letter gives the tolerance of the capacitance over this range – see Table 1. Better-performing capacitors are the ones with a smaller capacitance change over a broader range, like X7R. Electrolytic capacitors In an electrolytic capacitor, one plate is a metal foil while the other ‘plate’ is a conductive liquid or gel solution, known as the electrolyte. The metal foil is etched to increase its surface area greatly, and the liquid or gel is in intimate contact with this foil, separated only by a very thin oxide layer. Therefore, electrolytic capacitors have very high casiliconchip.com.au pacitance values for their volume (see Figs.4 & 5). For this reason, “electros” are typically used for ‘bulk’ bypassing or filtering applications. Their asymmetry, and the fact that the oxide layer is formed by electrons flowing from one ‘plate’ to the other, means that they are generally polarised. So one of their leads must always be at a higher voltage than the other (although there are ways around this – described later). Electrolytic capacitors typically range from a bit under 1µF up to 100,000µF or more, with voltage ratings from a few volts to several hundred volts. Traditionally, the metal foil used was aluminium. However, other metals can be used, giving certain performance advantages. For example, tantalum, while more expensive, generally results in a capacitor which can handle more current and with a lower ESR (see Figs.6 & 7). Further refinements to the electrolytic capacitor came with the discovery that an organic polymer gel could be used as the electrolyte, giving a roughly ten-fold decrease in overall ESR (Figs.8 & 9). As such, organic polymer (‘solid’) aluminium electrolytic capacitors outperform standard tantalum capacitors, and solid tantalum capacitors perform even better again, approaching that of some ceramics but with a better capacitance-to-volume ratio (see Fig.10). Other, more exotic types of electros are hybrid polymer electros (which combine liquid and polymer electrolytics) and niobium polymer electros; niobium is cheaper than tantalum but performs similarly. Tantalum and solid electrolytics tend to occupy the space between traditional electros, which are still A set of electrolytic capacitors ranging from 10µF to 68mF (68,000µF). Note how the can-type electros have a stripe to indicate the negative lead, while the rectangular SMD types have a stripe showing the positive lead. siliconchip.com.au Fig.6: while tantalum electrolytics work on the same principle as aluminium types, the construction method is necessarily quite different due to the properties of tantalum. Tantalum particles are sintered to form a porous slug, which is then immersed in a manganese dioxide electrolyte. Graphite and silver in contact with the electrolyte form the cathode connection, while tantalum wire acts as the anode. (original source: Wikipedia) Fig.7: this gives you an idea of how the tantalum particles are sintered and attached to a tantalum wire lead to form the body of the capacitor. (original source: Wikipedia) Fig.8: polymer or ‘solid’ aluminium electrolytic capacitors use an organic polymer (plastic-like) electrolyte which has roughly ten times the conductivity of a wet electrolyte. This allows for more compact electrolytic capacitors with much higher ripple current ratings and lower ESR values. Other techniques like comprehensive lead stitching are often combined with the polymer electrolyte to maximise performance. (original source: Wikipedia) Figs.9(a) & (b): an alternative construction for polymer electrolytic capacitors which uses the same cathode construction as a sintered tantalum capacitor. This halves the number of dielectric layers, significantly increasing capacitance at the cost of a more complicated manufacturing process and more expensive inputs. Polymer tantalum capacitors are made much the same as regular tantalums, just with a different type of electrolyte. (original source: Wikipedia) Australia’s electronics magazine March 2021  75 Fig.10: an impedance vs frequency graph comparing four different types of electrolytic capacitor and a multilayer ceramic capacitor (MLCC) with the same self-resonant frequency. The tantalum-polymer capacitor comes closest to the MLCC in terms of performance at the resonant frequency, while being superior at lower frequencies, likely due to a higher capacitance value. (original source: Wikipedia) Fig.11: traditional electrolytic capacitors are wound with four layers: two metal foils and two paper separators which are soaked in electrolyte. Note the multiple tabs which ensure that current doesn’t have to flow too far to reach any point on the foils. Anode and cathode tabs are lined up together so they can be welded to the appropriate leads. (original source: TDK) Fig.12: for highperformance (eg, lowESR) capacitors, the lead tabs are stitched into the aluminium foils, with the metal of the lead tab and foil being joined at multiple points throughout the foil to provide a low-resistance, low-inductance path for current to flow. Electrolytic construction Fig.13: SMD electrolytic capacitors come in different forms, but the can style uses very similar construction to a through-hole radial capacitor. The main differences are that the can sits on a plastic platform with the leads bent horizontally under it, so that the capacitor sits on the PCB and the leads rest on their respective pads. (original source: Panasonic) 76 Silicon Chip widely used for bulk filtering, and ceramics, which are used more for local or high-performance supply bypassing. For example, tantalum or polymer electros might be used in switch-mode power supply circuitry, where very high pulse current handling and good filtering (low ESR) is critical. Non-polarised (NP) or bipolar (BP) electrolytic capacitors are effectively two polarised electrolytic capacitors connected back-to-back. You can create an NP electro from two polarised electros by joining either the negative or positive leads together, although the internal construction of an NP/BP may be somewhat different in practice. But the result is the same. This works because when one of the two capacitors is reverse-biased, it acts a bit like a diode, and the other capacitor does all the work. When the voltage reverses, the capacitors swap roles. Strangely, you can often get better performance by connecting two polarised electros back-to-back, at a lower cost than a dedicated NP capacitor! This is probably due to economies of scale; polarised electros are made by the squillions while NP capacitors are used in fairly specialised roles. Another thing to note about electros regarding polarity is that it is safe to apply a reverse polarity voltage longterm as long as it is low (ie, below the threshold where it starts to conduct). This means that polarised electros are quite suitable for use as AC-coupling capacitors even if the polarity of the voltage across them is not known, as long as that voltage never exceeds about ±1.5V DC. Australia’s electronics magazine Traditionally, electrolytic capacitors are ‘wound’. Two long strips of aluminium foil are chemically etched to increase their surface area, then a strip of paper (or some other porous insulator) soaked in electrolyte is sandwiched between them. Each conductive strip has one or more tags, for ultimately attaching leads, projecting from one side (see Figs.11-13). This sandwich is then wound into a roll, with a second paper layer to separate the anode and cathode. With the leads in place, the roll assembly is inserted into a can. More electrolyte is added, and a rubber bung to seal it. Current is passed through the casiliconchip.com.au Fig.14: SMD polymer electrolytic capacitors are available in various packages including cans like regular electros. The main difference is the use of a separator sheet impregnated with a conductive polymer instead of paper soaked in an electrolyte solution. (original source: Panasonic) pacitor to form the required insulating layer, up to a voltage somewhat above the desired rating (which determines the oxide layer thickness). The process is slightly different for tantalum and polymer capacitors; SMD tantalum and polymer capacitors in rectangular prism packages may be made in layers rather than wound. But the result is much the same: a metal conductor with a large surface area separated from a conductive electrolyte only by a very thin oxide layer (see Figs.14-16). If the leads were only connected to the conductive foils at one point each, the ESR and ESL of the capacitor would be poor, as current must flow along a spiral path to reach the inner and outer layers of the capacitor. For this reason, all but the most basic electros usually have extra conductive paths giving current a ‘short cut’ to move between the layers of the capacitor. Higher performance electros also have the tabs ‘stitched’ into the foil at multiple points to reduce resistance and improve conductivity between them, in addition to having numerous tabs spread throughout the roll, that all join to one of the two leads. Plastic film capacitors Fig.15: SMD tantalum electros are made similarly to through-hole types, but the sintered tantalum grains are formed in a rectangular prism shape to create a more compact and convenient package. (original source: Wikipedia) Fig.16: the same type of semirectangular SMD package can also be used to house polymer aluminium electrolytic capacitors. (original source: Wikipedia) Some through-hole tantalum capacitors ranging from 3.3µF to 47µF. For these capacitors, polarity is indicated by a plus sign (+) on one side of the body. siliconchip.com.au Australia's Australia’s electronics magazine Plastic film capacitors are not used as much commercially these days since ceramic capacitors are much cheaper and are available with very low ESR and ESL figures. However, in cases where linearity or safety are essential, plastic films are still widely used. Most plastic film capacitors have better linearity than all but the best (NP0/C0G) ceramics or mica capacitors, and they can be designed to fail gracefully (going open-circuit). Plastic film capacitors are available from a few dozen picofarads up to a few tens of microfarads, and have voltage ratings ranging from around 16V up to several thousand volts. The failure mode is vital in mains applications, where capacitors are connected between Active and Neutral or Active and Earth. If they were to fail short circuit, a fire could result, or it could be a shock hazard. While ceramic X/Y-class capacitors exist, generally, higher-value mains-rated (X/Y) capacitors use either polyester (PET), polypropylene (PP) or polycarbonate (PC) films. March 2021  77 Fig.17: plastic capacitor construction is similar to ceramic, with alternating layers of plastic (the dielectric) and conductive metal film or foil in between, staggered to create many capacitors in parallel (original source: Wikipedia). Like ceramic capacitors, the plastic dielectric used has a significant effect on capacitor properties. And similarly, the plastics with the lowest dielectric constants that result in the bulkiest capacitors (like polypropylene and polystyrene [PS]), tend to have the best performance figures, Fig.18: plastic capacitors can be made from stacks of sheets, similarly to ceramics, or from rolled-up strips, similarly to electrolytics. The stacking process tends to be more timeconsuming and expensive, but it can give better density, so it is used for some SMD plastic capacitors. such as good linearity factors and low dissipation factors. Other plastics used for capacitors include polyphenylene sulfide (PPS), polyethylene naphthalate (PEN) and polytetrafluoroethylene (PTFE). One interesting property of metallised plastic film capacitors is ‘self- healing’. This is where a physical defect or the application of excessive voltage might damage the capacitor, but it will not fail entirely; instead, a small area of the metallisation burns away, reducing the capacitance by (hopefully) a tiny amount – usually not enough to affect its function. Fig.19: the roll manufacturing process for metallised plastic capacitors. While metal foil can be used instead of metallisation, it tends to result in a bulkier capacitor with inferior properties. (Source: Wikimedia user Elcap) 78 Silicon Chip Australia’s electronics magazine siliconchip.com.au A set of film capacitors from 50pF to 1µF. This effect is taken advantage of to provide the higher safety margin required for mains-rated capacitors. Plastic capacitor construction Like ceramic capacitors, plastic film capacitors usually need many layers to give a usable capacitance value. However, they are not normally formed by deposition methods. Therefore, they must be either stacked or wound (see Figs.17-19). Stacked capacitors are made in the way you might guess: with alternating layers of conducting foils and dielectric films. The conducting foils are staggered so that when they are joined along each edge, they form interlocking ‘combs’ and thus effectively, many single-layer capacitors in parallel. Making capacitors that way is timeconsuming and expensive, though. Rather than using metal foils, the dielectric can also be coated with a film of conductive material which provides a thinner and more uniform layer, improving performance and allowing more layers to be packed into the same space for higher density. Wound plastic film capacitors are made similarly to electrolytics as described above. A sandwich is created with the dielectric film between two strips of metal foil, with the strips slightly offset. This assembly is wound up into a roll, and in most cases, the roll is squashed flat to better fit into a rectangular prism shape. A metallisation layer is sprayed onto the ends of the roll to connect the layers, and leads are attached. This is why the conductors are offset; each layer is only exposed at one end of the roll, or else the sprayed metal layer will short out the capacitor. After this, the capacitor is typically impregnated with silicone oil or another insulating fluid to prevent moisture ingress. The terminals are then attached and the capacitor is encapsulated, sometimes by being dipped, other times by being sealed into a pre-formed plastic case. To make plastic film capacitors with a voltage rating above 630V DC, partial metallisation can be used to effectively form multiple capacitors in series using the same basic techniques. This can extend voltage ratings up past 3000V DC (see Fig.20). As well as small-signal capacitors and those for mains filtering, plastic dielectric capacitors are also used in motor run applications. Many motor start capacitors are electrolytic types, but electros are not suitable for handling the continuous current and high voltages that motor run capacitors are subjected to. So they are typically made with polypropylene or similar plastic dielectrics and thick metal films to handle high currents continuously. Electrical double-layer capacitors (EDLs) Fig.20: the basic method of plastic film capacitor manufacturing doesn’t work very well for applied voltages above about 630V. Higher voltage ratings are possible, but the capacitor needs to be internally separated into several elements connected in series, so that the dielectric material only has a fraction of the applied voltage across it. (original source: Wikipedia) siliconchip.com.au Australia’s electronics magazine These are often known as supercapacitors or ultracapacitors. They are a variation on electrolytic capacitors, with extremely high capacitances but usually low voltage ratings, and often very high internal resistances (and thus low operating currents). We published an article on ultracapacitors in April 2008 (siliconchip.com.au/ Article/1793). EDLs use similar conductive polymers with a very high surface area for both the positive and negative electrodes, with a common electrolyte in contact with both. Anions and cations in the electrolyte form insulating Helmholtz layers in direct contact with the surfaces of both electrodes. These layers are only one atom thick, and as mentioned at the start of the article, capacitance is proportional March 2021  79 Fig.21: as the name suggests, a double-layer (EDL) capacitor effectively has two dielectric layers, one at the surface of the anode and one at the cathode, with a conductive electrolyte between the two. The advantage is that these layers are super-thin, just one molecule wide, giving extremely high capacitances in a small package. However, this thin dielectric layer results in a very low voltage rating, typically either 2.7V or 5.5V (source: Wikimedia user Elcap). to surface area and inversely proportional to dielectric layer thickness. You can’t get a much thinner layer than one atom (see Fig.21). Given the large surface area of the electrodes, EDL capacitors can have values exceeding one Farad in a package not much bigger than a can 19mm in diameter and about 16mm tall. The fact that the current must pass through two polymer layers plus an electrolyte, neither of which is especially conductive, is why the current delivery of EDLs is generally limited. The extremely thin dielectric layer is the reason why voltage ratings of only 2.7V or 5.5V are common. Both of these problems can be mitigated by connecting many EDL capacitors in parallel (to improve current handling) or series (to increase the voltage rating, at the expense of capacitance). Higher voltage EDLs usually have multiple internal EDLs in series. You might be using an ultracapacitor without realising it; Mazda introduced its i-ELOOP system in vehicles from 2011, and it is now in many vehicles. This system recovers kinetic energy during braking to rapidly charge an ultracapacitor, then uses that energy to charge the vehicle battery over a longer period. Other types of capacitor Silvered mica capacitors unsurprisingly use mica, a type of mineral, as the dielectric. Mica was chosen both for its good dielectric properties and because its crystalline structure makes it very easy to cleave into super-thin sheets; just what you need to achieve a decent capacitance. A thin layer of silver is applied to each side, and voila, you have a capacitor with excellent linearity and low leakage. An example of an 806pF 300V mica capacitor. The 1% rating means its actual value will be in the range of ~798-814pF. Mica capacitors have mostly been replaced by ceramic or plastic film types, as both are significantly cheaper to manufacture and achieve similar performance. Some still value mica caps for audio circuits. Besides good linearity, another property of mica capacitors is that they usually have tight toler- ances due to their predictable thickness, measurable surface area and low temperature coefficient. Another type of non-polarised capacitor that was widely used but is now far less common (although still available) is the paper capacitor (sometimes known as an MP [metallised paper] capacitor). These have also mostly been supplanted by ceramic or plastic film capacitors. The main disadvantage of paper capacitors is that they can absorb moisture from the air and fail; older types have also been known to catch fire! Modern capacitors usually combine paper and plastic (usually PET or polypropylene) to overcome these disadvantages. Their main advantage is low cost. One benefit that paper capacitors retain is that they usually have zinc metallisation compared to the aluminium metallisation of plastic capacitors. This provides better ‘self-healing’ capabilities due to its lower-energy evaporation process. Variable capacitors Variable capacitors work either by varying the amount of overlap between two sets of metal plates, or by chang- Fig.22: the simplest type of variable capacitor, used in many vintage radios, is just two sets of interleaved metal plates where the amount of overlap can be adjusted. Air is the dielectric. Miniature trimmer caps tend to use a plastic or mica dielectric and bring the two plates closer together or further away to vary the capacitance. 80 Silicon Chip Australia’s electronics magazine siliconchip.com.au Some varcaps (variable capacitors) from various older radios. ing the spacing between two plates (possibly separated by a plastic or mica dielectric). In many cases, the dielectric is air. As such, the range of capacitance for a typical tuning capacitor is generally from a few picofarads up to a few hundred picofarads (see Fig.22). They are typically used as part of an RF oscillator or filter circuit, so low picofarad values give the required time constants with reasonable values for other components (usually inductors). Oddball types The capacitors described above probably cover 99% of the capacitors you might come across, but other types exist. That includes those with a glass or silicon dielectric, or even a vacuum! Capacitor parameters In addition to its construction/dielectric (ceramic, aluminium electrolytic, tantalum electrolytic, plastic film, plastic foil etc), a capacitor is described by its capacitance, tolerance, voltage rating(s), ripple current rating(s), leakage current rating(s), operating temperature and expected lifespan. Furthermore, each capacitor type has several associated performance metrics, which may be fixed or vary with parameters like temperature, applied voltage, signal frequency, age etc. These include the ESR (equivalent series resistance), ESL (equivalent series inductance), dissipation factor (DF or delta [Δ]), temperature coefficient (tempco), voltage coefficient, linearity and more. We’ll describe all of these, starting with the parameters which typically form part of a model or part code. siliconchip.com.au Capacitance: the nominal capacity of the device, measured with no or little charge (typically around 0.51.0V across the capacitor) and at room temperature. For very low-value capacitors (fraction of a picofarad to a few picofarads), the measured capacitance can be affected by the connected PCB tracks/ pad or wires, or even the device’s lead length. Tolerance: how close you can expect the capacitance to be compared to the nominal value. If you have a 10µF ±10% capacitor, if its value is less than 9µF or more than 11µF, then it would be considered faulty. However, during actual use, its capacitance could vary outside this range, as explained below. Voltage rating(s): the applied DC voltage across the capacitor terminals can safely vary from 0V up to this figure. For non-polarised types like ceramic or plastic film, it can also be negative, meaning the full range of operating voltages is effectively doubled (ie, -50V to +50V for a 50V capacitor). Some capacitors have a higher ‘surge’ voltage rating which will not damage them if applied for a limited period, but that is less common these days. Note that you sometimes need to keep the voltage below the rating for good performance; more on that shortly. Ripple current rating(s): all capacitors have some intrinsic resistance and therefore heat up as current passes through them; current flows through a capacitor during both charging and discharging. For example, if a capacitor is used to filter the output from a bridge rectifier turning AC to DC, it supplies the full load current most of the time Australia’s electronics magazine (when the bridge is not conducting). But it also must absorb large pulses of current to recharge when the bridge comes into conduction, 50 or 100 times per second. Such circuits must be designed to avoid exceeding the RMS ripple current rating of the filter capacitor(s) or else they can rapidly overheat and fail. There are generally different figures given at low (50/100Hz) and high (100kHz) frequencies, due to the changing impedance of the capacitor, from both its capacitance and its ESL (see below). The ripple current rating is usually higher at higher frequencies. Leakage current rating(s): some capacitors (eg, electros) can have a fairly significant leakage current through the capacitor even when the voltage is steady. This is usually proportional to the applied voltage. Ceramic, plastic film and mica capacitors also have leakage currents, although they are generally very low and are often (but not always) of no concern. This is important in some applications, like sample-and-hold buffers, where the voltage across a capacitor must remain stable for relatively long periods. Operating temperature: critically for electrolytic capacitors, this is the maximum temperature at which the capacitor is guaranteed to meet the stated performance figures. It is also the temperature at which the expected lifespan (if given) is calculated. Capacitor lifespan roughly doubles for each 10°C below the rated temperature, and halves for each 10°C above it. Typical ratings are 85°C, 105°C and 125°C. We recommend using 105°Crated capacitors with an expected lifespan of at least a few thousand hours to avoid early failures. Lifespan: usually stated in thousands of hours MTBF (mean time between failures), with 1000 hours at the lower end and about 10,000 hours at the upper end. If you can find a capacitor rated to last for 10,000 hours at 125°C, it’ll probably outlast the rest of the circuit! Performance metrics Equivalent series resistance (ESR): this is a crucial metric for most capacitors as it has a strong effect on how well the capacitor can smooth DC voltages, and how much heat is generated at higher currents. March 2021  81 You can think of a real capacitor like an ideal capacitor with a resistor in series; the lower the value of that resistor, the less it is ‘isolated’ from the circuit it is connected to. Typical ESR values are a few ohms for a low-value electrolytic capacitor, down to a few milliohms for a large, low-ESR electrolytic, tantalum, polymer or ceramic capacitor. Equivalent series inductance (ESL): just like ESR, you can imagine that all capacitors have a low-value inductor internally connected in series with the capacitance. This has little effect at low frequencies, but can make the effective impedance of the capacitor so high that it is useless at higher frequencies. ESL is critical for applications like bypassing multi-GHz ICs such as CPUs and RF devices. Smaller capacitors generally have a lower ESL, and certain construction methods can dra- Fig.23: by definition, the temperature coefficient of an NP0 ceramic capacitor is zero (or very close to it). On the other hand, Y5V ceramic capacitors vary in value wildly with temperature. Z5U is a little better at lower temperatures, but still poor at high temperatures. X5R and X7R are the ‘go to’ ceramic dielectrics because they are cheaper and more compact than NP0 capacitors, but have a much more modest temperate coefficient than Y5V or Z5U. (source: Wikipedia & Johanson Dielectrics) Fig.24: the variation with temperature of the dielectric constant, K, for several ceramic materials. You can see that X5R and X7R have a much higher K than C0G/NP0, making for higher capacitances in a smaller volume, with only a slight variation over the temperature range. The vast variation for Y5V and Z5U makes them unattractive. While they give a high capacitance at room temperature, at very high or low temperatures, the K value drops below that of both X5R and X7R. (original source: Digi-Key) 82 Silicon Chip Australia’s electronics magazine matically reduce the ESL of larger capacitors. The combination of capacitive reactance, ESR and ESL produces a characteristic valley-like impedance curve for most capacitors, as shown previously in Fig.10. Dissipation factor (DF): also known as tan(δ), is the reciprocal of the ratio of the ESR and capacitive reactance, and as such, is typically a number close to but slightly less than one. It can be easier to tell how close to ideal a given capacitor is by looking at the DF rather than ESR, and it can also make it easier to compare the performance of capacitors with different values of capacitance. Temperature coefficient (tempco): how much the capacitance changes with temperature. In an application where the capacitance is used to define a frequency (eg, in an oscillator or filter), this must be minimised to prevent frequency drift with temperature. Hence, NP0/C0G ceramics or plastic film capacitors are generally preferred in those roles (see Figs.23 & 24). This is very important to keep in mind with high-K dielectrics like Y5V ceramics; they can lose 80% or more of their capacitance at elevated temperatures! That’s made even worse by… Voltage coefficient: how much the capacitance changes as the capacitor is charged. This causes two main problems. One is a loss of effective capacitance; combined with the poor tempco of Y5V ceramics, a 10µF 6.3V Y5V capacitor at 80°C, charged to 5V, might have less effective capacitance than a 1µF 50V X5R capacitor under the same conditions! (See Figs.25 & 26). This is why we steer well clear of cheaper Y5V ceramics. The other problem with a high voltage coefficient is that it dramatically impacts linearity. So, perhaps unintuitively, standard aluminium electrolytic capacitors are better for audio coupling than most high-quality multi-layer ceramic capacitors. NP0/C0G ceramics are the exception, but they are huge and horrendously expensive at the sort of values required for most audio coupling applications. Linearity: this is not something you will find on most data sheets, and there is no standard way of representing it. But it is a real effect that varies sigsiliconchip.com.au nificantly between different capacitor types. The easiest way to measure it is to form a simple RC filter (low-pass or high-pass) with a relatively low-value, linear (thin film) resistor and a capacitor. You then feed a very pure sinewave into the filter, at a frequency near the -3dB point, and measure the distortion figure of the voltage across the capacitor. The resulting % THD is inversely proportional to the capacitor’s linearity. A very linear capacitor like a polypropylene or NP0/C0G ceramic capacitor will introduce an unmeasurable level of distortion (below 0.0001%). Other plastic film types like polyester are slightly worse, resulting in a measurable but not worrying level of distortion (say 0.0005%). Other capacitors like high-K ceramics, electrolytics and so on could give distortion measurements of 1% or more, reflecting the fact that their I/V curves are not straight. In some cases (eg, electros), the curves can even have hysteresis, meaning they are a different shape for charging and discharging. This is most important in audio circuits, although other circuits (eg, RF) might be sensitive to linearity too. Note that electros are fine for audio coupling, even though they are not terribly linear, as the applied AC voltage in that role is so small that it isn’t a significant effect (unlike the voltage coefficient of many ceramics, which makes them unsuitable for that role, despite probably being more linear than electros). Ageing: capacitors can change value over time, usually decreasing due to degradation of the dielectric. Typically, those with a tighter initial tolerance will tend to maintain their capacitance better over time (see Fig.27). This is apart from an actual failure of the component, which might manifest as a much lower capacitance, higher ESR, higher leakage (especially at voltages approaching the rating) or some combination of the three. Further reading • • • • • • • Types: Ceramic: Electrolytic: Tantalum: Polymer: Film: Supercaps: https://w.wiki/q86 https://w.wiki/q87 https://w.wiki/q88 https://w.wiki/q89 https://w.wiki/q8A https://w.wiki/q8B https://w.wiki/q8C SC siliconchip.com.au SMD Capacitor Actual Size: 0603 0805 1206 1210 1812 Fig.25: the measured value of a range of 4.7µF X5R and X7R capacitors with the application of a range of DC voltages. Note how the physically larger capacitors tend to retain their capacitance better as they are charged to a similar voltage. (original source: Maxim) Fig.26: the change in capacitance over voltage for several different ceramic dielectrics. While the 100V and 400V capacitors seem to perform poorly, consider that the X-axis is a percentage of the voltage rating. Due to this effect and the temperature coefficient, Y5V or Z5U capacitors can easily fall below 10% of their rated values, and below even 5% at temperature extremes! (Original source: Wikipedia) Fig.27: if you need another reason to avoid Y5V ceramics, here is a comparison of the loss in capacitance due to aging with the more robust X7R types. According to the originators of this graph, Johanson Dielectrics, the value of Y5V capacitors drops at roughly three times the rate of a comparable X7R capacitor (original source: Johanson Dielectrics). Australia’s electronics magazine March 2021  83 • Monitor up to 3 batteries from 6 to 100V • Currents to 10A (or 100A+ with shunt) Versatile Battery Multi-LOGGER Part 2 – By TIM BLYTHMAN WITH TOUCHSCREEN LCD In Part 1 of our new Battery Multi-Logger last month, we described how it combines the functions of a Micromite LCD BackPack along with voltage and current sensing hardware, and power-saving techniques, all on a single PCB. Now we’ll go over the construction, testing, setup and calibration procedures so you can build and use it. B • • • • efore getting to the assembly instructions, let’s quickly review the Logger’s capabilities. It can handle batteries from 6-100V and monitor up to three bidirectional currents of up to 10A using its onboard shunts, or much more (to 100A or beyond) using external shunts. Its own power consumption is less than 1mA while actively logging with the screen off. It can display the current and historical data on a 2.8-inch backlit LCD touchscreen, and the data can also be downloaded to a computer over USB for further analysis. It tracks the current battery stateof-charge in both amp-hours (Ah) 84 Silicon Chip and watt-hours (Wh), and it has a current measurement resolution of around 0.1% of full-scale, which equates to 10mA steps when using the internal shunts. All of these functions are built onto a small PCB. As all the user interface features are accessed via the touchscreen, it can easily be integrated into other devices through a rectangular cutout in the case. Construction The Battery Logger is built on an 86mm x 50mm double-sided PCB coded 11106201. Fig.5 shows where the components go, on both sides of the board. As usual for assembling a board Australia’s electronics magazine with many SMDs, it is useful to have the following on hand: flux paste, solder braid (wick), a magnifier, tweezers and an adjustable temperature iron. The smallest parts have pad spacing under 1mm, so solder bridges are almost inevitable, hence the need for flux paste and solder wick. Since flux tends to generate smoke, use a fume extraction hood or work in an outdoor area, where the smoke can more easily dissipate. One of the most fiddly parts is the USB socket, CON5, so start by fitting that. Dispense flux onto the pads and then sit the USB socket in place; it should lock into the holes in the PCB. Add some more flux to the tops of the pins. siliconchip.com.au The Multi-Logger can be mounted in a UB5 Jiffy Box like many Micromitebased projects and as seen here. But you might like to use the bezel to mount the Multi-Logger in the front panel of your equipment enclosure; you could then use the Jiffy Box to protect the rear of the unit. With a clean tip, add solder to your iron, then press it against the small pins and pads together. The socket’s metal shroud tends to get in the way a bit. Once you are sure that you have soldered all the pins, check for bridges and remove them if necessary, then solder the larger tabs on the shroud in place. ICs Solder the ICs (IC1-IC6 and REF1, on the back of the PCB) next. We suggest fitting IC5 first, as it has the finest pin pitch. For each of the ICs, check the orientation of pin 1 against the PCB silkscreen by matching the dot before soldering any pins. IC6 is asymmetric, so although this part is small, it is easy to orientate correctly. Note that some of the ICs might not have a dot to indicate pin 1. Instead, they will have a bevel along one edge or a line at one end; in each case, this feature is nearest to pin 1. For REF1, the pin 1 indicator might even be a tiny laser-etched cross. When soldering the ICs, apply flux to the pads, then rest the IC in place and tack one lead. Check the positioning, ensuring that the part is flat and aligned within its pads. If not, remelt the solder and adjust the part with the tweezers. After the part is located correctly, solder the remaining pins. Don’t worry about solder bridges as they happen, as it is easier to remove multiple bridges later, all at the same time. Apply exsiliconchip.com.au tra flux if necessary during soldering. To remove bridges, apply fresh flux and press the solder braid against the excess solder with the iron. When it melts, allow it to draw up the solder and then gently pull it away from the component. The surface tension between the component and the pad should hold enough solder to maintain a good connection, even if the solder braid removes most of it. Now is a good time to inspect your work closely with a magnifier, as making changes will be harder as more parts are added. It’s a good idea to clean away excess flux first; isopropyl alcohol is a good all-round choice, but specialised flux cleaning products often do a better job. Transistor and regulators The next trickiest parts are the transistors and regulators in SOT-23 packages. There are six such parts in three types: Q1 & Q3 (P-channel Mosfets), Q2 & Q4 (N-channel Mosfets), and REG1 & REG2 (LDO regulators). Fortunately, they will only fit one way, so use a similar technique to the ICs. Solder one lead and check the position before soldering the remaining leads. The remaining SMDs all have much larger pads, so are much easier to deal with. Resistors and capacitors Many of the remaining parts are 3216-sized (3.2 x 1.6mm; or 1206 imperial) resistors and capacitors. The resistors should be marked with their Australia’s electronics magazine values, while the capacitors are typically not, so take extra care with the capacitors and don’t mix them up. We recommend working with one value at a time. Where possible, we’ve marked the resistors and capacitor values below the part itself; the exception is the parts around IC4. Remember that if you are using external shunts for current sensing, you omit the three 15mΩ shunt resistors. Leave the larger shunt resistors aside for now, even if you intend to fit them. For the remaining parts, check the value printed on the silkscreen against the value on the part, which will be a numerical code that you can match in our parts list. For each part, apply flux to the pad, solder one lead, check and adjust if necessary and then solder the other lead. Refresh the first lead if necessary. Most of the capacitors are 100µF, 10µF or 100nF types, so we recommend placing these first. The 100µF and 10µF capacitors will most likely be larger, so they won’t be too hard to differentiate. All four 100µF types are fitted to the back of the PCB. Use the same method as for the resistors. Follow up with the remaining capacitors, taking note of their value before removing from the packaging and working one at a time. There are two small inductors (L2 and L3) which also have 3216 dimensions; they are soldered in much the same way. The larger 120µH inductor (L1) might require a hotter iron to solder. March 2021  85 Fig.5: the PCB photos shown above are of an early prototype, so they differ slightly from the overlays which are our final design, including up-to-date component values. There are components on both sides, although the back of the board is much more sparsely populated. Take extra care with the orientation of all ICs, the two diodes and the LED. Most of the other components are unpolarised. Use the same technique of working on one lead at a time. Sometimes you get better heat transferral by pressing the long edge of your soldering iron tip onto the pad. Then solder the other lead. Next, solder the button cell holder. Again, you might need to turn up your iron to supply more heat. Add flux to the pads and locate the holder such that a cell can be inserted from the edge of the PCB. Tack one pad down and when you are happy with it, solder the other pad. Refresh the first pad to relieve any stress on the PCB pads. Check our photos to see how it should look. And the rest There are two surface-mounted diodes; they are both fitted with their cathodes facing towards REG2 (as that is what they supply!). You may well be using surfacemounting or through-hole parts for LED1 and S1. Fit these two next. LED1’s cathode faces to the right, towards CON1. Most surface-mount LEDs have their cathode marked with a green dot, but double-check this, as some do not. 86 Silicon Chip At this stage, practically all the SMDs have been fitted, so it is a good opportunity to clean off any excess flux left on the PCB. JP1 is not usually needed, so can be left off (we used it in our testing), but JP2 is required. Fit the jumper shunt to make it easier to manipulate and solder one lead. Check it is square and flat, then solder the other leads. If you have pre-programmed microcontrollers (IC1 and IC2), then fit the shunt to JP2 on the bottom two pads (as seen in our photo). This is the ‘RUN’ position. If you need to program IC1, then fit the shunt to the top two pads (near the PCB mounting hole). For programming, you will only need to fit CON1, as IC2 can program IC1. But if you have a programmer, you might find it quicker and easier to fit both for programming anyway. We used right-angled headers for CON1 and CON2 to make it easier to debug, but straight headers will also work, and fit under the LCD. The connections for the 2.8in LCD are made up of a 4-way and a 14-way female header. Only the 14-way header is needed for the current version of the Australia’s electronics magazine software, although having both headers will make the assembly more robust. Use the 2.8in LCD as a jig to fit the headers. You might need to solder pin headers to the LCD if they are not preinstalled; most do not come with the 4-way header fitted. In that case, plug the headers into the sockets and insert them into their respective PCBs. The headers sockets go on our PCB, with the pin headers on the LCD side. Solder the headers in place, keeping the PCBs parallel. Then gently separate the LCD from the PCB, wiggling it if necessary. The final step in assembling the PCB is to fit CON3 and CON3A, the battery and load connections. Mount them on the back of the PCB to allow access even after the stack is assembled. Verify that you have fitted the three larger 15mΩ shunts if you will not be using external shunts. Programming If you have pre-programmed ICs, you don’t need to worry about this step and should proceed to the setup section. Both IC1 and IC2 need firmware to siliconchip.com.au work. The only way to program IC2 in-circuit is to use ICSP header CON1 and a programmer such as a PICkit 3 or PICkit 4. You can use the MPLAB X IPE (integrated programming environment), which is available as a free download as part of the MPLAB X package from www.microchip.com/mplab/mplabx-ide Choose PIC16F1455 as the device and your programmer from the Tool drop-down. Connect the programmer to CON1 according to its instructions and browse for the Microbridge HEX file (2410417A.HEX). Then press the Program button to upload it. With the IPE open, you can also use this to upload the firmware for IC1. Connect the programmer to CON2, select PIC32MX170F256B as the Device and browse for 1110620A.HEX. Upload this file with the program button. After programming is done, don’t forget to move JP2 to the RUN (lower) position. Microbridge and MMBasic If you’re inclined to tinker with the BASIC code, you can program IC1 with the MMBasic files too, although that is a bit more involved. We’ll outline the steps, with the assumption that you have a bit of experience with the Micromite environment, know your way around MMBasic quite well and are comfortable uploading files to the Micromite. If you don’t want to do this, skip to the next section. You will need the Microbridge firmware on IC2 and start with JP2 in the PROGRAM position, as it needs (at the very least) the HEX file for the BASIC environment to be uploaded to IC1 first. This can be done with a PICkit and the IPE (as outlined above), but instead of the Battery Logger firmware, you should choose the latest Micromite MMBasic firmware file. Alternatively, the MMBasic firmware can be uploaded by the Microbridge by pressing S1 (to enter programming mode). Then use a program like pic32prog or P32P GUI to upload the Micromite MMBasic HEX file. We used version 5.5.2. JP2 can now be moved to the RUN position. From the BASIC environment (a serial port running at 38,400 baud), you should run the commands to set up the 2.8in LCD and touch siliconchip.com.au Fig.6: we ran this diagram last month to show what the Logger can do. We’re repeating it now as you might want to use it as a guide when wiring it up. When using the internal shunts, the battery connects across CON3, and the positive ends of your loads or chargers go to the terminals of CON3a. All load and charger negatives go straight to the battery. When using the external shunts, follow diagram (C) and make sure the wiring from the battery to the shunts is short and thick for maximum precision. panel as per usual for a V2 Micromite BackPack. OPTION LCDPANEL ILI9341,    LANDSCAPE, 2, 23, 6 OPTION TOUCH 7, 15 GUI CALIBRATE The BASIC files are arranged as a library file supplementing the main source code. This allows the Micromite to compress some of the data it uses. Load the library.bas file, then run the command: Australia’s electronics magazine LIBRARY SAVE This saves and compresses the library file. Next, load the main Battery Logger.bas file and run it. These instructions are in the library.bas file. Setup and operation If you haven’t already done so, fit a CR2032 cell to the BAT1 holder, fit the LCD panel and connect the Logger up to a computer or USB power supply via CON5. If you programmed IC1 with the hex file specific to this project, March 2021  87 Screen1: the main screen provides all the critical statistics for your battery, as well as three simple menu options for accessing other features. The greyed values seen are capacity calculations which are not yet valid, as the Logger has not detected a complete charge and discharge cycle; they will light up brighter when that happens. then the Logger software should start straight away. If you loaded the BASIC files yourself, you might need to run the program manually for the first time. You should see Screen1 appear at startup. An error message might appear for the first few seconds while the program waits for a valid battery reading to occur; if it does not disappear after about ten seconds, there could be a problem with IC5. The voltage shown after “V=” should be zero, as you don’t have a battery connected yet. You might see some readings for the current values, though, as we have not completed the calibration yet. I1 corresponds to the Logger’s own current use, while I2-I4 are the currents measured through the terminals of CON3A, as shown in Fig.5. These values might jump around a bit, but the long-term averages are the most important figures. At right are the capacity and state of charge measurements. CHGv% is a simple linear calculation between nominal full and empty voltages, while CHGm% is based on measured current since the last full and empty states. The CHGm% reading won’t be entirely accurate until the battery has experienced a complete charge and discharge cycle. Similarly, the capacity readings will not be meaningful right away. At upper right is a countdown timer; when this reaches zero, the display will blank. This is the normal mode, where the Logger is logging, but does 88 Silicon Chip Screen2: the Data screen provides a graphical view of the logged data. Different timespans can be shown, and the display will automatically scroll once a minute to show current data. The Weeks option provides around a fortnight of data. Data can also be dumped as CSV rows over the console serial port with the Export button. not need to display anything, thus saving power. The counter can be reset by touching anywhere on the Main screen. This timeout only happens from the Main screen shown in Screen1, so make sure to return to it each time you finish accessing the Logger’s graphical interface. To reactivate the screen, press and hold the touch panel until the backlight illuminates. For maximum power efficiency, the Micromite only checks the panel at one-second intervals, so it might take a second or so of touch to wake it up. The Logger waits for the touch to be released before displaying the main screen, so you can’t accidentally press a button when waking it up. The interface is fairly intuitive, but we’ll walk through the various screens anyway. Screen2 is reached by pressing the Data button and displays a graph of the voltage and currents. The current scale (left-hand side) can be manually set, while the voltage scale uses the nominal full and empty values. By default these are set to 14.4V and 11.0V, to suit a 12V lead-acid battery. The buttons along the bottom set this page to display the various scales, with the time frames shown at the bottom of the screen. In each scale, the Export button does a dump of data to the serial port. This data is produced so that it can be saved as a CSV (comma separated value) file and then can Australia’s electronics magazine be opened with most spreadsheet programs. Pressing Exit returns to the Main display. Screen3 is accessed using the Settings button. Each value shown can be changed by pressing the respective button. Screen4 shows a number being entered, in this example to update the current year. If the number entered is invalid, a message is displayed. Pressing OK prompts for the new value to be confirmed (see Screen5). The time and date settings are immediately saved to the real-time clock and are displayed on this and the main screen. The two B/L values are for the backlight brightness as a percentage, from 1-100. The first value (B/L) is used most of the time. The second value (B/L dim) is used for the last five seconds before the screen shuts down, to indicate that this is about to happen. A minimum value of 1% is allowed for either setting to ensure that the display is always visible. The V(full) and V(empty) values should be set to suit your particular battery. You can’t set the V(empty) value to be higher than the V(full) value. The Timeout value sets how long the display stays on before blanking at the Main screen. This has a minimum of five seconds, as this is the period of dimming that occurs before blanking. A large value can be used to stop the display blanking; eg, a period of 99999999 seconds is around three siliconchip.com.au Screen3: the Settings screen provides the most common options for configuring the Logger, including battery voltages, time and date and backlight controls. Each entry is validated to ensure it does not conflict with other values (such as the ‘Empty’ voltage being higher than the ‘Full’ voltage) and then immediately saved to flash memory. years. The “I scale” value sets the limits of the graph on the Data page only. Setting a value of 20 will cause the graph to span from -20A to 20A. The “V(sdown)” value sets a critical battery limit. Below this level, the Logger sleeps for much longer periods between activity. The MMBasic code sets this to 15 seconds. Since the ADC (IC5) goes to sleep after each conversion, the result is that current consumption drops even lower than the normal ‘screen off’ mode. This setting is intended to preserve a battery that already is heavily discharged. You can still use the Logger, although you will have to touch the screen for up to 15 seconds to wake it up, and the data will be much more sparse, as it won’t be logging as frequently. Still, you should be able to quickly identify that there is a problem with the battery and rectify it. To disable this feature (eg, for testing without a battery connected), set this value to 0V. In this case, the buck regulator will shut down below around 5.5V, causing the Logger to power off completely unless it is powered from USB. Calibration The remaining button on the Main page goes to the Calibrate page (Screen6). You should always calibrate the V factor first, as the measured current depends on the voltages measured being accurate. siliconchip.com.au Screen4: the Entry screen is displayed whenever a number needs to be entered. The symbol at lower left allows the last typed character to be deleted. Since negative numbers are not used, there is no minus symbol. Internally, there is a V factor (the ratio between the actual voltage and the raw 24-bit ADC reading) for each of the four dividers, but only one is displayed, as they should all be similar to within component tolerance. The nominal value is 100V/16,777,216; ie, a full-scale reading at 100V. The four V factors allow compensation for variations in the dividers, mostly due to component tolerances. They allow the three current sense dividers to be zeroed against the primary voltage divider. Thus, this step should be done first before attempting to calibrate the individual currents; otherwise, there will be an offset from zero. You’ll need to hook up your battery, or, at the very least, a stable voltage source above 6V. Higher voltages will mean that the quantisation error (due to steps between consecutive ADC values) will be proportionally less, potentially giving slightly better calibration. Don’t hook up anything to CON3A though, as we don’t want any current flow to skew the results. If possible, leave the USB supply connected too, as this will minimise the load on the battery, with the display running from USB power. In this case, the only battery drain will be the no-load quiescent current of IC4, at around 10µA. Hook up a voltmeter to the battery terminals and allow the unit to settle for a minute. This reading must be stable for optimum results. Press the “Volts” button and acknowledge that Australia’s electronics magazine there is no load on the terminals. Enter the battery voltage as displayed on the voltmeter. A page will show the various V factors and an estimate of how much they vary. If there is a variation of more than a few percent (due to component tolerances), you might have a problem with the dividers, such as a wrong component value or a spurious load on the battery. You can confirm the new values by pressing OK, or use Cancel to investigate further. The calibration is stored to flash and used immediately. Go back to check that the displayed currents (I2I4) have settled near zero. This means that the calibration is correct. The remaining calibrations are not so critical as they won’t produce an offset in the results, but will simply give incorrect current scaling. The default values are calculated from nominal component values; you will have to change these if you are using external shunts. Current calibration The current calibration method is straightforward. A known load is applied to each terminal, the current is measured and entered into the Logger, and it then calculates the conversion ratio. For I2-I4, these are the external loads at CON3A, while I1 is the Logger’s own current. Thus for I2-I4, the load should be applied between CON3A and the battery negative. March 2021  89 Screen5: each Entry value is validated before being processed and saved to provide a way of safely making changes. In this case, the actual current being displayed on the main screen will be negative (the battery is discharging). Still, you can only enter a positive value, so you should just enter the magnitude of the current. The initial values are set in the MMBasic program but can also be altered here, which you need to do if you are using shunts with values other than 15mΩ. The current calibration values are simply the inverse of the shunt resistance in ohms, so the default 15mΩ shunts have a calibration factor of 66.67. For I1, you will probably need to disconnect the battery to allow an ammeter to be connected in the Logger’s supply. When doing this, disconnect the USB cable and ensure there is no load on any of the CON3A terminals. The nominal value of the factor used for I1 is the inverse of the shunt resistor resistance (in ohms) divided by the op-amp circuit’s gain. Consider that the measured shunt voltage would be the same as if the shunt resistance was multiplied by the gain. So the default value is the inverse of 0.1Ω, (ie 1/0.1) = 10, divided by 100, or 0.1 Screen6: the Calibration screen provides a mostly automated way of adjusting the Logger to account for component tolerances. The operator simply needs to enter a meter reading (volts or amps), and the Logger calculates the calibration factors to produce the desired value. In this form, it can be mounted in a box. Still, we expect most people will use the acrylic panel as a bezel to mount the Logger in an equipment enclosure, with wires connecting internally and the touch panel being accessible from outside. To do this, separate the LCD and Logger PCB by wiggling gently. Decide which side of the bezel you would like visible; we prefer the matte face, but it is reversible, so you can put the gloss side to the outside if you want. Thread four of the M3 screws through the front of the bezel, place the washers over the threads, then follow with the LCD. The spacers provide clearance for the leads that protrude from the back of the headers. Secure the M3 screws with the tapped spacers. Reconnect the Logger PCB and secure it to the stack with the remaining M3 screws. This complete assembly can now be attached, for example, to the front door of an equipment cupboard, using an M3 screw and nut in each corner to secure it. When the cabinet is opened, the battery connections can be accessed from the rear. Protecting the back of the Logger is easily done with the UB3 Jiffy box. The included screws might be too short if they need to screw through a panel, but the pillars will line up with the holes in the bezel. Mounting and completion With everything calibrated and set up, you can mount and connect up the Battery Logger. Being a similar size and shape to the V2 Micromite BackPack, the Battery Logger can be fitted with the laser-cut acrylic front panel designed for UB3 Jiffy boxes. 90 Silicon Chip When fitted to the inside of an equipment enclosure, the important features are available for maintenance access, including cable terminations and the RTC backup battery. Australia’s electronics magazine siliconchip.com.au Screen7: any conditions that need to be satisfied for accurate calibration are prompted before the calibration begins. While this adds an extra step, it means there is little chance for the calibration to fail. In this case, all you need is a few holes in the side or back of the box to run the wires. To complete the wiring, you can follow the three examples shown in Fig.6 (reproduced from last month). This shows options for use with internal and external shunts, including one possibility of sharing terminals on CON3A if you have more than three total loads plus charging sources. There should ideally be a fuse on each wire out of CON3A (or in the high-current wiring leading to the shunts). There should also be a fuse in the wire leading from the battery posi- Screen8: as noted, all values are checked for validity before being saved and used by the Multi-Logger. In this case, a brief but helpful message is provided to allow the user to work out what went wrong. tive to CON3’s positive terminal. This way, a fault in the Logger or any of the connected loads cannot short out the battery. The wiring will be specific to individual arrangements, so we can only offer general advice. in the future. You will see that we haven’t left many microcontroller pins unused, but we have broken out two pins to a header at the top right of the PCB. These are connected to the Micromite’s I2C pins, as we figured that would be a good way of expanding the device (they are already used for the real-time clock, but I2C is a shared bus). 3.3V power and ground connections are also available at nearby CON2, while CON6 connects to the Micromite’s second COM port (COM1), at pins 21 and 22. That provides a dedicated communications channel that could be used SC to add more features. Conclusion Like many of our projects, especially those written in MMBasic, we expect people will want to customise, tinker and perhaps improve the software. We look forward to hearing what features readers would like to add, as we are already planning to supplement the Logger with extra hardware OR T HI S : T HI S . . . Every article in every issue of SILICON CHIP Can now be yours forever in digital (PDF) format! Nov 1987 Dec 2019 n High-res printable PDFs* n Fully searchable files - with index n Viewable on 99.9% of personal computers & tablets * Some early articles may be scans Software capable of reading PDFs required (freely available) Digital edition PDFs are supplied as five-year+ blocks, covering a minimum of 60 issues. They’re copied onto quality metal USB flash drives (at least 32GB). Just order which block(s) you want! n Nov 1987 - Dec 1994 n Jan 1995 - Dec 1999 n Jan 2000 - Dec 2004 n Jan 2005 - Dec 2009 n Jan 2010 - Dec 2014 n Jan 2015 - Dec 2019 Each five-year block is priced at just $100, and yes, current subscribers receive the normal 10% discount. If you order the entire collection, the 6th block is FREE (ie, pay for five, the sixth is a bonus!). All PDFs are high resolution (some early editions excepted) and the USB Flash Drives are high quality metal USB3.0, so if you save the files to your PC hard disk, the USB Flash Drives can be used over and over! Want to know more? Full details at siliconchip.com.au/shop/digital_ pdfs siliconchip.com.au Australia’s electronics magazine March 2021  91 ELECTRONIC Wind Chimes Part 2: finishing it off – by John Clarke Last month, we described how our new Electronic Wind Chime worked, and how to build the electronics. Now we get to the tricky bit – modifying the wind chime itself so it can be driven by a series of solenoids. Fear not, because we have detailed instructions on how to accomplish this, and finish the build by putting it all together and setting up the electronics. W Our finished Electronic Wind Chime. It’s based on a commercial wind chime but ours works when there’s no wind. 92 Silicon Chip e modified a Carson Home Accents “Amazing Grace” 640mm Sonnet Wind Chime to incorporate the solenoid drivers. It is a 5-chime type with 31.5mm outside diameter tubes. The longest tube is 590mm and shortest at 450mm. The solenoids are supported on a circular ring made from 9mm MDF (medium-density fibreboard). This ring is held in place with an inverted U-shaped piece made from MDF and a couple of right-angle brackets. The whole frame is attached to the wind chime’s attachment hook with an M5 screw and nut. For our prototype, the clapper plate was made using an 80mm diameter piece of 1mm aluminium sheet. The plate (shown in Fig.7) is designed to cater for the 5-chimes arranged 72° apart around the diameter. The plate includes holes for the strings and a slot to allow the clapper plate to be placed over the clapper while its central support string is still attached. The frame needs to be sized so the base plate can be positioned at a height where the solenoids and levers are inAustralia’s electronics magazine line with the top of the clapper plate. There are two holes for the string attaching each solenoid to its chime. These need to be far enough apart so that the string does not touch the chime tube when pulled taut. This clapper plate can be glued in place, or held with a small self-tapping screw into the clapper after the string has been threaded. The 100mm x 10mm rectangular solenoid levers are made from 1mm aluminium sheet; the two end holes are 3mm in diameter. Note that two holes are not centred, but placed close to one side, to give the best rotational movement when attached to the solenoid plunger. The pivot point is a wood screw into the base plate. This should be long enough and screwed in sufficiently for the lever to sit horizontally, without being too tight to move. The hole in the solenoid plunger was drilled to 2.5mm and then tapped for an M3 thread. That allows the lever to be secured at the fulcrum with just a 10mm-long M3 screw and no nut, with the screw acting as a bearing. Alternatively, you could drill 3mm diameter holes and secure them with machine screws and nuts. siliconchip.com.au A close-up of the “business” end of the electronic wind chimes, showing how the solenoids are placed around the ring. The solenoids do not strike the chime tubes; rather, they pull the clapper towards the tube which makes the sound. In this photo, some of the catch strings and pull strings were removed from the closest chime tubes for clarity. The pivot hole is slightly elongated by about 1mm, to allow for the lever to move freely, allowing for length changes between the screws as it rotates with solenoid movement. A 6.3mm-long untapped spacer keeps the pivot raised and is secured with a 15mm-long No.9 countersunk wood screw into the base plate. The solenoids are attached using screws into the solenoid housing. Our solenoids have M2.5-tapped mounting holes, so they are secured using M2.5 x 12mm screws. If no holes are provided, they can be glued in place instead. Other options The clapper plate and levers could be made from a material other than aluminium. The levers need to be thin siliconchip.com.au enough to freely rotate within the solenoid plunger slot. An easier material to work with is the Presspahn or similar electrical insulation material, such as the Jaycar HG9985. This can be cut with scissors and a sharp craft knife. The sizes given for the wooden frame and base plate are notional; these really depend on the wind chime you are using. The circular ring base plate needs to have an inside hole large enough so the chime tubes can freely swing without hitting it. The outer diameter needs to be sufficient for attaching the solenoids, with room for the pivot screws. While we used MDF for the frame and base plate, you could make the Australia’s electronics magazine frame from solid timber instead. The base plate does not need to be circular – it could be made in a polygonal shape instead. The number of straight sides could equal the number of chimes; for our 5-tube chime, that would be a pentagon. Note that once the solenoids and levers are in place, there is not necessarily a convenient point to attach the frame to the chime where it will not interfere with at least one lever. This is especially true with an odd number of solenoids. However, there should be one side of the frame that can be directly attached to the base plate. The other leg can be supported with a bracket that is raised above the base plate using a screw and March 2021  93 nuts to clear lever movement (see our photos for details). Alignment Reproduced from last month, this shows our recommended arrangement for the solenoids to drive the wind chimes. The solenoids press on levers that pull the clapper via a string to strike the associated tube. A second set of strings prevents the clapper from swinging around and hitting other tubes unless the associated solenoid is energised. 94 Silicon Chip Australia’s electronics magazine The frame needs to be aligned correctly to the base plate. This is so that when the frame is held by the wind chime attachment hook, the solenoid levers and strings are positioned correctly, so that the clapper is pulled along the radial line from the centre of the clapper to the centre of the chime tube for each solenoid. If it is not possible to get this alignment without the frame interfering with the solenoid drivers, the positioner at the top of the wind chime may need to be rotated. Rotating the chime positioner will effectively twist up the strings at the attachment hook, so it will not stay in this rotated position. The solution is to tie the chime positioner against the side of the frame. A small hole in the side of the chime positioner and another in the frame will allow for a short length of string or stiff wire to hold the chime positioner in its rotated position. Stringing the chime The pull strings must normally be loose. These pull the clapper toward the chime near the end of the lever travel. The loose stringing is for two reasons: firstly, the solenoid pulling force is not particularly strong at the beginning of its movement from its resting position, and it is greatest when it fully pulls in the plunger. The looseness allows the solenoid to ‘build up strength’ before it starts moving the clapper. The second reason is so that when one solenoid pulls the clapper in its direction, it is not affected by the strings becoming taut on the opposite side. The looseness needs to be a compromise between being tight enough to be able to pull the clapper against the chime, and loose enough not to affect the opposing solenoid pulls. The strings pass through the clapper holes and back to the lever, and are secured by passing the string through the lever hole. An M3 x 6mm screw and M3 nut can be used to secure the string in the hole. This more easily allows fine adjustments compared to tying a knot. A refinement to the design is to include catch strings. These catch and siliconchip.com.au hold the chime tube, preventing it from swinging back to re-strike the clapper after striking the chime tube. Their lengths are such that they are loose when the tube sits in its usual position, but is tight enough to prevent it swinging back and hitting the clapper. The string ends are held to the base plate by clamps. We used polyester string, which becomes unravelled if cut with scissors or a knife. Instead, the string was cut to lengths with a hot soldering iron tip that both cut and welded the string ends to prevent fraying. We don’t recommend you use your primary, highquality iron to do this, though! You can also cut the string and then use a lighter to weld the ends before they unravel. Wiring Use sufficient gauge wire (eg. 19 x 0.1mm strands) or similar for the larger solenoids, so that voltage drops will not affect solenoid operation. If the wire cross-sectional area is too small, then the solenoids may not work with longer wire runs back to the main PCB. We used a 7mm tube loom to hold the wires in place and keep the appearance neat. The +12V wires to each solenoid are connected together and brought back to terminate into the positive terminal of CON1 or CON6. The second wire of each solenoid connects between the solenoid outputs at CON1-CON6 and the negative terminal of the solenoid. After soldering the solenoid wires to the extension wires, insulate the joints using electrical tape or heatshrink tubing. When finished, we attached the wire loom to the top of each solenoid using cable ties so that it won’t move around. The main enclosure housing the PCB can be located on a timber beam above the wind chime attachment, or further away out of sight. S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 Randomness off Randomness on Delay varies in 128 steps between 10s and 1280s (21:20) Delay varies in 64 steps between 10s and 640s (10:40) Delay varies in 32 steps between 10s and 320s (5:20) Delay varies in 16 steps between 10s and 160s (2:40) Delay varies in eight steps between 10s and 80s (1:20) Delay varies in four steps between 10s and 40s (0:40) Delay multiplier varies randomly between one and five times actual Delay multiplier varies randomly between one and three times actual Delay multiplier varies randomly between one and two times actual Delay multiplier varies randomly between one and 1.5 times actual Table 1 – switch actions at power-up remove the shorting block from JP2 and switch on the power. LED2 should light, indicating that there is power. VR2 can then be adjusted to set the light threshold that switches the Electronic Wind Chime on or off. With the LDR in normal shaded daylight, place your finger over the LDR and adjust VR2 so that LED1 (the status LED) starts flashing at 2Hz. This indicates that playback is paused. Lifting your finger from the LDR should result in that LED switching off. The more clockwise VR2 is adjusted, the darker the light needs to be to pause playback. Calibration The LDR is ignored during calibration and recording. It is only used during playback, and only if JP2 is open. This is so that calibration and recording are not interrupted by a change in light level. Each solenoid can be independently calibrated for the drive voltage (using PWM) and for the on-period. These two parameters are adjusted using VR1 and JP1, as described below. The 500Hz PWM duty cycle can be adjusted between about 5% to 100% in approximately 0.75% steps. This varies the average voltage between Fig.6: we cut a sheet of aluminium to this shape and screwed it to the top of our timber clapper, to allow the five strings to be easily attached. Setting up There are several options that need to be set in the Electronic Wind Chime controller before you can use it. LDR adjustments If you prefer not to have the Wind Chime paused during darkness, place a shunt on JP2. In this case, the LDR does not need to be installed. But if you do want it to stop at night, siliconchip.com.au Australia’s electronics magazine March 2021  95 600mV and 12V in about 90mV steps. The on-period can be set to between 2ms and 254ms in approximately 2ms steps. Initially, all solenoids receive the full 12V drive voltage (100% duty cycle) for a duration of 254ms. To initiate calibration, press and hold the control switch (S13) at power-up. The status LED (LED1) lights for 200ms then flashes off for 200ms and then on again. This indicates that calibration has been activated. Press a solenoid switch (S1-S12) to select which solenoid is to be calibrated. The status LED extinguishes, and the solenoid drive parameters are now ready to be adjusted for the chosen solenoid. When JP1 is shorted, the PWM duty cycle can be adjusted with VR1, and when JP1 is open, the drive duration (on-period) is adjusted with VR1. Once you have set JP1 and adjusted VR1 for the setting you want to make, press the control switch (S13) to temporarily store that particular parameter. This will also drive the relevant solenoid, so you can check whether the setting is correct. If not, readjust VR1 and press S13 again. If you want another solenoid to have the same parameter, the switch (S1S12) for that solenoid can be pressed, and the control switch (S13) pressed again to store the current parameter value for that solenoid. We have also provided a means of monitoring the current VR1 setting using a multimeter measuring the voltage between TP1 and TP GND. That makes it easier to replicate suitable values for other solenoids. The status LED (LED1) lights each time you press the control switch for the duration of the solenoid drive. Lower PWM duty cycles will cause the solenoid to move more slowly. Adjust the solenoid on-period to allow sufficient time for the solenoid to pull the clapper against the chime tube, but short enough for it to pull away before the chime tube returns after being struck. As mentioned, the solenoid parameters are initially only temporarily stored. The values will be lost when the power goes off unless they are stored in flash memory. This is also done with the control switch. While pressing the control switch for a short period tests the solenoid drive, a longer press (one second or more) will store all solenoid parameter values into the permanent flash memory. LED1 will light again if the switch is held for one second or more, to indicate that the values have been written to flash. To exit the calibration mode, switch off power. When power is switched on again, without S13 being pressed, the Wind Chime Player starts up in playback mode. You can return to the calibration mode again by repeating the above procedure, to re-adjust those parameters. Only the parameters for the selected solenoid or solenoids will be changed. Previously stored parameters will remain unchanged unless new parameters are stored for that solenoid. trol switch, S13, after power-up. The status LED, LED1, lights and stays lit, indicating that recording has begun. You can then press the individual solenoid switches to activate the solenoids, and it records the sequence you provide and the pauses in between. You can close one solenoid at a time. The PCB includes white screenprinted squares above each switch so you can write the perceived note using a fine marker pen. We say the perceived note because the sound from the chime comprises many overtones, which may affect the apparent frequency. It may also appear to shift in frequency after initially struck. The perceived note cannot be easily measured with a spectrum analyser. Probably the easiest method is to use a guitar tuner or similar device and adjust it until its apparent frequency matches the chime, then look at what note you have selected. For more information on the perception of sounds from wind chimes, see www.leehite.org/Chimes. htm#The%20strike%20note and www. sarahtulga.com/Glock.htm During recording, you can play out a tune if you are musically inclined, or just some nice sounds that appeal to you. Short gaps between chime strikes, these can be waited out in real time before driving a solenoid for another chime. Longer intervals may become tedious to wait out in real time, but we have a solution to that... Recording a sequence Time warp To make a recording, press the con- By pressing the control switch for Here’s the Electronic Wind Chime PCB placed inside the case, albeit without any cables connected, while at right the front panel and label are placed. 96 Silicon Chip Australia’s electronics magazine siliconchip.com.au longer than one second, that period stored for the current pause is multiplied by ten. The status LED flashes at 1Hz to meter out the time (one flash is one second of real time, but ten seconds of delay). Be careful when pressing S13, since if you press it for less than one second, instead of activating the time warp, it will end the recording. After a short press of the control switch, the entered sequence will be written to flash memory, and it will return to playback mode. If no solenoid switches were pressed while in record mode, the previous recording will remain in memory. Playback SILICON CHIP www.siliconchip.com.au + Power + Wind Chime ePlayer + . - . - 12VDC Input SILICON CHIP www.siliconchip.com.au Wind Chime ePlayer + 12VDC Input At power-up, the Electronic Wind Chime starts in playback mode. This plays back the recorded sequence, repeating it in a continuous loop. The initial setting is for no randomness in the delay periods between chime strikes – in other words, it faithfully reproduces your recorded sequence. Adding randomness Two front panels designs are provided – one has provision for through-panel switch and LED As mentioned earlier, whereas the other panel doesn’t. These can also be downloaded from siliconchip.com.au you can add randomness to the delay between If you haven’t already pressed any chime strikes. This is selected by press- the maximum value selected. The opat power-up, then ing switch S2 while powering up. Wait tions are 1280s (21:20), 640s (10:40), of these switches + Power for the status LED (LED1) to flash after 320s (5:20), 160s (2:40), 80s (1:20) and the initial setting is with randomness CHIP SILICON off. If randomness is switched on (us40s (0:40). about one second before releasing S2,www.siliconchip.com.au These options are selected by hold- ing S2), then the 10s to 1280s (21:20) indicating that the randomness feature ing one of switches S3, S4, S5, S6, S7 randomness change rate is selected, has been enabled. + along with the 1-5 times delay 12VDC range. The setting is stored in permanent and S8 at power-up – see Table 1. Note that you can press andInput hold You can also change how much varimemory. If you want to switch the randomness off, hold switch S1 at power ation you want in the delays. There are more than one switch at power up up and wait for the status LED to light four options, selected by holding one to select more than one option at the of switches S9, S10, S11 or S12 down one time. before releasing it. For example, you could switch ranThere are two randomness param- at power-up. The delay multiplier varies random- domness on (with S2), set the randometers that can be adjusted. One is the ly between one and the maximum value ness change rate at up to 320s with S5, rate; how often the random value changes. This can be set to six differ- selected. S9 selects a range of 1-5 times, and the randomness variation to beent values. The randomness changes S10 1-3 times, S11 1-2 times and S12 tween one and three times with S10, at an interval between ten seconds and 1-1.5 times variation (also see Table 1). all at the same time. + Wind Chime ePlayer . SC siliconchip.com.au Australia’s electronics magazine March 2021  97 SILICON CHIP .com.au/shop ONLINESHOP HOW TO ORDER INTERNET (24/7) PAYPAL (24/7) eMAIL (24/7) MAIL (24/7) PHONE – (9-5:00 AET, Mon-Fri) siliconchip.com.au/Shop silicon<at>siliconchip.com.au silicon<at>siliconchip.com.au PO Box 139, COLLAROY, NSW 2097 (02) 9939 3295, +612 for international You can also pay by cheque/money order (Orders by mail only) or bank transfer. Make cheques payable to Silicon Chip. 03/21 YES! You can also order or renew your Silicon Chip subscription via any of these methods as well! The best benefit, apart from the magazine? Subscribers get a 10% discount on all orders for parts. PRE-PROGRAMMED MICROS For a complete list, go to siliconchip.com.au/Shop/9 $10 MICROS ATmega328P ATmega328P-AUR ATtiny85V-10PU ATtiny816 PIC10F202-E/OT PIC12F1572-I/SN PIC12F617-I/P PIC12F675-I/P PIC12F675-I/SN PIC16F1455-I/P PIC16F1455-I/SL PIC16F1459-I/P PIC16F1507-I/P PIC16F1705-I/P PIC16F88-E/P PIC16F88-I/P $15 MICROS RF Signal Generator (Jun19) PIC16F1459-I/SO Four-Channel DC Fan & Pump Controller (Dec18) RGB Stackable LED Christmas Star (Nov20) PIC16F877A-I/P 6-Digit GPS Clock (May09), 16-bit Digital Pot (Jul10), Semtest (Feb12) Shirt Pocket Audio Oscillator (Sep20) PIC32MM0256GPM028-I/SS Super Digital Sound Effects (Aug18) ATtiny816 Development/Breakout Board (Jan19) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sep19) Ultrabrite LED Driver (with free TC6502P095VCT IC, Sep19) PIC32MX170F256B-50I/SP Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) Touchscreen Voltage / Current Ref. (Oct16), Deluxe eFuse (Aug17) LED Christmas Ornaments (Nov20; specify variant) Micromite DDS for IF Alignment (Sep17), Tariff Clock (Jul18) Temperature Switch Mk2 (Jun18), Recurring Event Reminder (Jul18) GPS-Synched Frequency Reference (Nov18), Air Quality Monitor (Feb20) Door Alarm (Aug18), Steam Whistle (Sep18), White Noise (Sep18) RCL Box (Jun20), Digital Lighting Controller Micromite Master (Nov20) Trailing Edge Dimmer (Feb19), Steering Wheel to IR Adaptor (Jun19) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21) Car Radio Dimmer (Aug19), MiniHeart Heartbeat Simulator (Jan21) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) Motor Speed Controller (Mar18), Heater Controller (Apr18) Useless Box IC3 (Dec18) PIC32MX795F512H-80I/PT Maximite (Mar11), miniMaximite (Nov11), Colour Maximite (Sep12), Touchscreen Audio Recorder (Jun14) Tiny LED Xmas Tree (Nov19) $20 MICROS Microbridge (May17), USB Flexitimer (June18) Digital Interface Module (Nov18), GPS Finesaver (Jun19) dsPIC33FJ64MC802-E/SP 1.5kW Induction Motor Speed Controller (Aug13) Digital Lighting Controller LED Slave (Dec20) dsPIC33FJ128GP306-I/PT CLASSiC DAC (Feb13) Ol’ Timer II (Jul20), Battery Multi Logger (Feb21) dsPIC33FJ128GP802-I/SP Digital Audio Delay (Dec11), Quizzical (Oct11) 5-Way LCD Panel Meter (Nov19), IR Remote Control Assistant (Jul20) Ultra-LD Preamp (Nov11), LED Musicolour (Oct12) Ultrasonic Cleaner (Sep20), Electronic Wind Chime (Feb21) PIC32MX470F512H-I/PT Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) Wideband Oxygen Sensor (Jun-Jul12) PIC32MX470F512H-120/PT Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) Flexible Digital Lighting Controller Slave (Oct20) PIC32MX470F512L-120/PT Micromite Explore 100 (Sep16) Auto Headlight Controller (Oct13), Motor Speed Controller (Feb14) $30 MICROS Automotive Sensor Modifier (Dec16) PIC32MX695F512L-80I/PF Colour MaxiMite (Sep12) Remote-controlled Preamp with Tone Control (Mar19) PIC32MZ2048EFH064-I/PT DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) UHF Repeater (May19), Six Input Audio Selector (Sep19) DIY Reflow Oven Controller (Apr20) Universal Battery Charge Controller (Dec19) KITS, SPECIALISED COMPONENTS ETC MINI ISOLATED SERIAL LINK COMPLETE KIT (CAT SC5750) (MAR 21) $10.00 All parts required to build the project including the PCB MINIHEART HEARTBEAT SIMULATOR (CAT SC5732) (JAN 21) All SMD parts, including IC2 – does not include PCB AM/FM/SW RADIO $5.00 (JAN 21) $2.50 $3.00 $7.50 - PCB-mount right-angle SMA socket (SC4918) - Pulse-type rotary encoder with integral pushbutton (SC5601) - 16x2 LCD module (does not use I2C module) (SC4198) LED CHRISTMAS ORNAMENTS (CAT SC5579) (NOV 20) Complete kit including micro but no coin cell (specify PCB shape & colour) RGB STACKABLE LED CHRISTMAS STAR (CAT SC5525) $38.50 Complete kit including PCB, micro, diffused RGB LEDs and other parts FLEXIBLE DIGITAL LIGHTING CONTROLLER PARTS $14.00 (NOV 20) (OCT 20) 4 x Si8751AB ICs, 8 x S1HB15N60E-GE3 Mosfets, switchmode converter module, 6N137 opto, high-voltage resistors and capacitors plus SMD LEDs. $100.00 D1 MINI LCD WIFI BACKPACK KIT (OCT 20) Complete kit including 3.5-inch touchscreen, PCB and ESP8266-based module SHIRT POCKET AUDIO OSCILLATOR $70.00 (SEP 20) Kit: including 3D-printed case, and everything else except the battery and wiring $40.00 - 64x32 pixel white OLED (0.49-inch/12.5mm diagonal) $10.00 - Pulse-type rotary encoder with integral pushbutton $3.00 COLOUR MAXIMITE 2 (JUL 20) Short form kit: includes everything except the case, CPU module, power supply, optional parts and cables (Cat SC5478) $80.00 Short Form kit (with CPU module): includes the programmed Waveshare CPU modue and everything included in the short form kit above (Cat SC5508) $140.00 MICROMITE LCD BACKPACK V3 KIT (CAT SC5082) (AUG 19) Includes PCB, programmed micros, 3.5in touchscreen LCD, UB3 lid, mounting hardware, Mosfets for PWM backlight control and all other mandatory on-board parts $75.00 Separate/Optional Components: - 3.5-inch TFT LCD touchscreen (Cat SC5062) $30.00 siliconchip.com.au/Shop/ - DHT22 temp/humidity sensor (Cat SC4150) - BMP180 (Cat SC4343) OR BMP280 (Cat SC4595) temp/pressure sensor - BME280 temperature/pressure/humidity sensor (Cat SC4608) - DS3231 real-time clock SOIC-16 IC (Cat SC5103) - 23LC1024 1MB RAM (SOIC-8) (Cat SC5104) - AT25SF041 512KB flash (SOIC-8) (Cat SC5105) - 10µF 16V X7R through-hole capacitor (Cat SC5106) $7.50 $5.00 $10.00 $3.00 $5.00 $1.50 $2.00 VARIOUS MODULES & PARTS - CP2102 USB-UART bridge $5.00 - 15mW 3W SMD resistor (Battery Multi Logger / Arduino PSU, Feb21) $2.50 - DS3231(M) real-time clock SMD IC (Battery Multi Logger, Feb21) $3.00 - MCP4251-502E/P (Arduino Power Supply, Feb21) $3.00 - Pair of CSD18534 (Electronic Wind Chimes, Feb21) $6.00 - IPP80P03P4L04 (Dual Battery Lifesaver / Vintage Radio Supply, Dec20) $5.00 - 16x2 LCD module (Digital RF Power Meter, Aug20) $7.50 - WS2812 8x8 RGB LED matrix module (Ol’ Timer II, Jul20) $15.00 - MAX038 function generator IC (H-Field Transanalyser, May20) $25.00 - MC1496P double-balanced mixer (H-Field Transanalyser, May20) $2.50 - AD8495 thermocouple interface (DIY Reflow Oven Controller, Apr20) $10.00 - Si8751AB 2.5kV isolated Mosfet driver IC (Charge Controller, Dec19) $5.00 - I/O expander modules (Nov19): PCA9685 – $6.00 ¦ PCF8574 – $3.00 ¦ MCP23017 – $3.00 - SMD 1206 LEDs, packets of 10 unless stated otherwise (Xmas Ornaments, Nov20): yellow – $0.70 ¦ amber – $0.70 ¦ blue – $0.70 ¦ cyan – $1.00 ¦ pink (1 only) – $0.20 - ISD1820-based voice recorder / playback module (Junk Mail, Aug19) $4.00 - 23LCV1024-I/P SRAM & MCP73831T (UHF Repeater, May19) $11.50 - MCP1700 3.3V LDO regulator (suitable for USB M&K Adapator, Feb19) $1.50 - LM4865MX amplifier & LF50CV regulator (Tinnitus/Insomnia Killer, Nov18) $10.00 - 2.8-inch touchscreen LCD module with SD card socket (Tide Clock, Jul18) $22.50 - ESP-01 WiFi Module (El Cheapo Modules, Apr18) $5.00 - WiFi Antennas with U.FL/IPX connectors (Water Tank Level Meter with WiFi, Feb18): 5dBi – $12.50 ¦ 2dBi (omnidirectional) – $10.00 - NRF24L01+PA+NA transceiver, SNA connector & antenna (El Cheapo, Jan18) $5.00 - WeMos D1 Arduino-compatible boards with WiFi (Sep17, Feb18): ThingSpeak data logger – $10.00 | D1 R2 with external antenna socket – $15.00 - ERA-2SM+ MMIC & ADCH-80A+ choke (6GHz+ Frequency Counter, Oct17) $15.00 - DS3231 real-time clock module with mounting hardware (El Cheapo, Oct16) $5.00 *Prices valid for month of magazine issue only. All prices in Australian dollars and include GST where applicable. # P&P prices are within Australia. Overseas? Place an order on our website for a quote. PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT THEREMIN PROPORTIONAL FAN SPEED CONTROLLER WATER TANK LEVEL METER (INC. HEADERS) 10-LED BARAGRAPH ↳ SIGNAL PROCESSING FULL-WAVE MOTOR SPEED CONTROLLER VINTAGE TV A/V MODULATOR AM RADIO TRANSMITTER HEATER CONTROLLER DELUXE FREQUENCY SWITCH USB PORT PROTECTOR 2 x 12V BATTERY BALANCER USB FLEXITIMER WIDE-RANGE LC METER (INC. HEADERS) ↳ WITHOUT HEADERS ↳ CASE PIECES (CLEAR) TEMPERATURE SWITCH MK2 LiFePO4 UPS CONTROL SHIELD RASPBERRY PI TOUCHSCREEN ADAPTOR RECURRING EVENT REMINDER BRAINWAVE MONITOR (EEG) SUPER DIGITAL SOUND EFFECTS DOOR ALARM STEAM WHISTLE / DIESEL HORN DCC PROGRAMMER (INC. HEADERS) ↳ WITHOUT HEADERS OPTO-ISOLATED RELAY (INC. EXT. BOARDS) GPS-SYNCHED FREQUENCY REFERENCE LED CHRISTMAS TREE DIGITAL INTERFACE MODULE TINNITUS/INSOMNIA KILLER (JAYCAR VERSION) ↳ ALTRONICS VERSION HIGH-SENSITIVITY MAGNETOMETER USELESS BOX FOUR-CHANNEL DC FAN & PUMP CONTROLLER ATtiny816 DEVELOPMENT/BREAKOUT PCB ISOLATED SERIAL LINK DAB+/FM/AM RADIO ↳ CASE PIECES (CLEAR) REMOTE CONTROL DIMMER MAIN PCB ↳ MOUNTING PLATE ↳ EXTENSION PCB MOTION SENSING SWITCH (SMD) PCB USB MOUSE AND KEYBOARD ADAPTOR PCB LOW-NOISE STEREO PREAMP MAIN PCB ↳ INPUT SELECTOR PCB ↳ PUSHBUTTON PCB DIODE CURVE PLOTTER ↳ UB3 LID (MATTE BLACK) FLIP-DOT (SET OF ALL FOUR PCBs) ↳ COIL PCB ↳ PIXEL PCB (16 PIXELS) ↳ FRAME PCB (8 FRAMES) ↳ DRIVER PCB iCESTICK VGA ADAPTOR UHF DATA REPEATER AMPLIFIER BRIDGE ADAPTOR 3.5-INCH LCD ADAPTOR FOR ARDUINO DSP CROSSOVER (ALL PCBs – TWO DACs) ↳ ADC PCB ↳ DAC PCB ↳ CPU PCB ↳ PSU PCB ↳ CONTROL PCB ↳ LCD ADAPTOR STEERING WHEEL CONTROL IR ADAPTOR GPS SPEEDO/CLOCK/VOLUME CONTROL ↳ CASE PIECES (MATTE BLACK) RF SIGNAL GENERATOR RASPBERRY PI SPEECH SYNTHESIS/AUDIO BATTERY ISOLATOR CONTROL PCB ↳ MOSFET PCB (2oz) MICROMITE LCD BACKPACK V3 DATE JAN18 JAN18 FEB18 FEB18 FEB18 MAR18 MAR18 MAR18 APR18 MAY18 MAY18 MAY18 JUN18 JUN18 JUN18 JUN18 JUN18 JUN18 JUL18 JUL18 AUG18 AUG18 AUG18 SEP18 OCT18 OCT18 OCT18 NOV18 NOV18 NOV18 NOV18 NOV18 DEC18 DEC18 DEC18 JAN19 JAN19 JAN19 JAN19 FEB19 FEB19 FEB19 FEB19 FEB19 MAR19 MAR19 MAR19 MAR19 MAR19 APR19 APR19 APR19 APR19 APR19 APR19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 JUN19 JUN19 JUN19 JUN19 JUL19 JUL19 JUL19 AUG19 PCB CODE 23112171 05111171 21110171 04101181 04101182 10102181 02104181 06101181 10104181 05104181 07105181 14106181 19106181 SC4618 04106181 SC4609 05105181 11106181 24108181 19107181 25107181 01107181 03107181 09106181 SC4716 09107181 10107181/2 04107181 16107181 16107182 01110181 01110182 04101011 08111181 05108181 24110181 24107181 06112181 SC4849 10111191 10111192 10111193 05102191 24311181 01111119 01111112 01111113 04112181 SC4927 SC4950 19111181 19111182 19111183 19111184 02103191 15004191 01105191 24111181 SC5023 01106191 01106192 01106193 01106194 01106195 01106196 05105191 01104191 SC4987 04106191 01106191 05106191 05106192 07106191 Price $12.50 $2.50 $7.50 $7.50 $5.00 $10.00 $7.50 $7.50 $10.00 $7.50 $2.50 $2.50 $7.50 $7.50 $7.50 $7.50 $7.50 $5.00 $5.00 $5.00 $10.00 $2.50 $5.00 $5.00 $7.50 $5.00 $7.50 $7.50 $5.00 $2.50 $5.00 $5.00 $12.50 $7.50 $5.00 $5.00 $5.00 $15.00 $.00 $10.00 $10.00 $10.00 $2.50 $5.00 $25.00 $15.00 $5.00 $7.50 $5.00 $17.50 $5.00 $5.00 $5.00 $5.00 $2.50 $10.00 $5.00 $5.00 $40.00 $7.50 $7.50 $5.00 $7.50 $5.00 $2.50 $5.00 $7.50 $10.00 $15.00 $5.00 $7.50 $10.00 $7.50 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT CAR RADIO DIMMER ADAPTOR PSEUDO-RANDOM NUMBER GENERATOR 4DoF SIMULATION SEAT CONTROLLER PCB ↳ HIGH-CURRENT H-BRIDGE MOTOR DRIVER MICROMITE EXPLORE-28 (4-LAYERS) SIX INPUT AUDIO SELECTOR MAIN PCB ↳ PUSHBUTTON PCB ULTRABRITE LED DRIVER HIGH RESOLUTION AUDIO MILLIVOLTMETER PRECISION AUDIO SIGNAL AMPLIFIER SUPER-9 FM RADIO PCB SET ↳ CASE PIECES & DIAL TINY LED XMAS TREE (GREEN/RED/WHITE) HIGH POWER LINEAR BENCH SUPPLY ↳ HEATSINK SPACER (BLACK) DIGITAL PANEL METER / USB DISPLAY ↳ ACRYLIC BEZEL (BLACK) UNIVERSAL BATTERY CHARGE CONTROLLER BOOKSHELF SPEAKER PASSIVE CROSSOVER ↳ SUBWOOFER ACTIVE CROSSOVER ARDUINO DCC BASE STATION NUTUBE VALVE PREAMPLIFIER TUNEABLE HF PREAMPLIFIER 4G REMOTE MONITORING STATION LOW-DISTORTION DDS (SET OF 5 BOARDS) NUTUBE GUITAR DISTORTION / OVERDRIVE PEDAL THERMAL REGULATOR INTERFACE SHIELD ↳ PELTIER DRIVER SHIELD DIY REFLOW OVEN CONTROLLER (SET OF 3 PCBS) 7-BAND MONO EQUALISER ↳ STEREO EQUALISER REFERENCE SIGNAL DISTRIBUTOR H-FIELD TRANSANALYSER CAR ALTIMETER RCL BOX RESISTOR BOARD ↳ CAPACITOR / INDUCTOR BOARD ROADIES’ TEST GENERATOR SMD VERSION ↳ THROUGH-HOLE VERSION COLOUR MAXIMITE 2 PCB (BLUE) ↳ FRONT & REAR PANELS (BLACK) OL’ TIMER II PCB (RED, BLUE OR BLACK) ↳ ACRYLIC CASE PIECES / SPACER (BLACK) IR REMOTE CONTROL ASSISTANT PCB (JAYCAR) ↳ ALTRONICS VERSION USB SUPERCODEC ↳ BALANCED ATTENUATOR SWITCHMODE 78XX REPLACEMENT WIDEBAND DIGITAL RF POWER METER ULTRASONIC CLEANER MAIN PCB ↳ FRONT PANEL NIGHT KEEPER LIGHTHOUSE SHIRT POCKET AUDIO OSCILLATOR ↳ 8-PIN ATtiny PROGRAMMING ADAPTOR D1 MINI LCD WIFI BACKPACK FLEXIBLE DIGITAL LIGHTING CONTROLLER SLAVE ↳ FRONT PANEL (BLACK) LED XMAS ORNAMENTS 30 LED STACKABLE STAR ↳ RGB VERSION (BLACK) DIGITAL LIGHTING MICROMITE MASTER ↳ CP2102 ADAPTOR BATTERY VINTAGE RADIO POWER SUPPLY DUAL BATTERY LIFESAVER DIGITAL LIGHTING CONTROLLER LED SLAVE AM/FM/SW RADIO MINIHEART HEARTBEAT SIMULATOR I’M BUSY GO AWAY (DOOR WARNING) BATTERY MULTI LOGGER ELECTRONIC WIND CHIMES ARDUINO 0-14V POWER SUPPLY SHIELD DATE AUG19 AUG19 SEP19 SEP19 SEP19 SEP19 SEP19 SEP19 OCT19 OCT19 NOV19 NOV19 NOV19 NOV19 NOV19 NOV19 NOV19 DEC19 JAN20 JAN20 JAN20 JAN20 JAN20 FEB20 FEB20 MAR20 MAR20 MAR20 APR20 APR20 APR20 APR20 MAY20 MAY20 JUN20 JUN20 JUN20 JUN20 JUL20 JUL20 JUL20 JUL20 JUL20 JUL20 AUG20 NOV20 AUG20 AUG20 SEP20 SEP20 SEP20 SEP20 SEP20 OCT20 OCT20 OCT20 NOV20 NOV20 NOV20 NOV20 NOV20 DEC20 DEC20 DEC20 JAN21 JAN21 JAN21 FEB21 FEB21 FEB21 PCB CODE 05107191 16106191 11109191 11109192 07108191 01110191 01110192 16109191 04108191 04107191 06109181-5 SC5166 16111191 18111181 SC5168 18111182 SC5167 14107191 01101201 01101202 09207181 01112191 06110191 27111191 01106192-6 01102201 21109181 21109182 01106193/5/6 01104201 01104202 CSE200103 06102201 05105201 04104201 04104202 01005201 01005202 07107201 SC5500 19104201 SC5448 15005201 15005202 01106201 01106202 18105201 04106201 04105201 04105202 08110201 01110201 01110202 24106121 16110202 16110203 16111191-9 16109201 16109202 16110201 16110204 11111201 11111202 16110205 CSE200902A 01109201 16112201 11106201 23011201 18106201 Price $5.00 $5.00 $7.50 $2.50 $5.00 $7.50 $5.00 $2.50 $10.00 $5.00 $25.00 $25.00 $2.50 $10.00 $5.00 $2.50 $2.50 $10.00 $10.00 $7.50 $5.00 $10.00 $2.50 $5.00 $20.00 $7.50 $5.00 $5.00 $12.50 $7.50 $7.50 $7.50 $10.00 $5.00 $7.50 $7.50 $2.50 $5.00 $10.00 $10.00 $5.00 $7.50 $5.00 $5.00 $12.50 $7.50 $2.50 $5.00 $7.50 $5.00 $5.00 $2.50 $1.50 $5.00 $20.00 $20.00 $3.00 $12.50 $12.50 $5.00 $2.50 $7.50 $2.50 $5.00 $10.00 $5.00 $2.50 $5.00 $10.00 $5.00 MAR21 MAR21 14102211 24102211 $12.50 $2.50 NEW PCBs HIGH-CURRENT BATTERY BALANCER (4-LAYERS) MINI ISOLATED SERIAL LINK We also sell an A2 Reactance Wallchart, RTV&H DVD, Vintage Radio DVD plus various books at siliconchip.com.au/Shop/3 Vintage Radio Kriesler’s Kriesler’s 41-21 41-21 mantel/portable mantel/portable set set By Ian Batty Electrically, the set is also somewhat interesting. It uses a reflexed second intermediate frequency (IF) amplifier, with that transistor also acting as an audio preamp. The design is similar to the Philips MT4 that I described in September 2017 (siliconchip.com.au/ Article/10806). Like that set, the reflexed stage needs carefully-managed signal levels, so the 41-21 has a two-gang volume control potentiometer. More on that later. So despite its dial drive, it’s an Australian set worth an article. First appearances The Kriesler "Triplex" 41-21 is an all-transistor, battery-powered radio which uses reflexing. It was produced in the late 50s/early 60s and was sold with a plastic case that came in one of three colours (pink, brown or red). Engineers are a chummy lot. During my Air Force days, I encountered a variety of engineering types needed to keep an aircraft flying: mechanical engineers for the engines, airframes and controls, electrical engineers for the electrical systems and controls, electronics engineers for the radio, radar navigation and instrument systems, and commerce types for supplying all the parts needed. But when I took a look at the Kriesler 41-21 (manufactured from 1959 to 1961), I started wondering whether the 100 Silicon Chip mechanical engineering folks at Kreisler were ‘in dispute’ with the electronics engineer cohort. Surely no-one could have come up with the labyrinthine dial drive in this otherwise fine set unless they had some axe to grind. Yes, I get that it’s a way of accommodating a 130mm long dial with a 41mm diameter drum on the tuning gang, when an 82mm diameter drum would otherwise be needed. But I would have put in a 2:1 gear set to the drum and simplified the rest of the arrangement. Australia’s electronics magazine The curved, rippled front with its coloured inset and black case rear is a pleasing alternative to the “square black box” so often resorted to in the late 50s/early 60s. The “slide rule” dial is some 130mm long; plenty of space to list all the stations of the day. The side-mounted volume control is placed for easy adjustment. The separate on/off switch eases the load on the volume control; ie, it doesn’t need to be rotated every time you turn the set on or off, giving a longer trouble-free life. Circuit details The set’s circuit is shown in Fig.1. The main difference between the 4121 and the identically-cased 41-21A is the 21A’s use of a single-tuned third IF transformer. All transistors are Philips/Mullard “OC” series germanium PNPs, with a negative power supply (ie, positive ground). Ferrite rod L2 is tuned by the antenna section of the tuning gang, C3A. A low-impedance secondary matches to the base of the converter via capacitor C2, in parallel with 2.2kW resistor R1 (the bottom half of the converter’s bias divider). C2 is there to overcome the resistance of R1 at radio frequencies siliconchip.com.au and deliver full signal to the converter. The ferrite rod also provides a primary for connection to an external antenna and Earth. L1 (100µH) helps to match the capacitance of an electrically-short wire antenna to L2’s tuned secondary. Kriesler’s original circuit correctly describes L1 as a compensating coil. It isn’t there for interference suppression. L1 is wound using its parallel 3.9kW resistor as a former. This resistor dampens the L1/antenna resonance. Converter TR1, an OC44, uses selfexcitation and emitter injection with feedback from collector to emitter via oscillator coil L3 and 10nF capacitor C4. This allows signal injection directly to the base for testing. As usual, the base-emitter bias voltage is lower than you’d expect, as the converter needs to operate closer to Class-B than the normal Class-A used in the IF and first audio stages. Class-B operation allows the converter to go into cutoff over part of the local oscillator’s (LO) waveform, ensuring the non-linearity vital to converter action. You may wonder at TR1’s emitter and base voltages of 1.15V and 0.75V, with the emitter higher than the base. This makes it seem as though TR1’s base-emitter is reverse-biased and would never conduct. This would be the case for a Class-A amplifier, but TR1 works as an oscillator, and I measured a signal of around 6V peakto-peak at the emitter. TR1 repeatedly swings in and out of conduction due to the oscillator’s excursions, creating the non-linearity needed for conversion. I measured values of 0.75V and 0.94V respectively when the LO was stopped. For this set, LO operation can be confirmed by circuit measurement. It’s not a wholly reliable test though, and my preference is always to use the radiation test first. Tuning The 41-21’s tuning gang uses identical sections, so 480pF padder capacitor C6 restricts the LO’s frequency swing and ensures that it’s kept 455kHz above the incoming signal. The converter’s 455kHz signal is developed across the tuned, tapped primary of first IF transformer IFT1. Its tapped, tuned secondary feeds first IF amplifier TR2, an OC45. TR2’s significant collector-base capacitance demands neutralisation, siliconchip.com.au The Kriesler 41-21 with the case open shows the double-sided PCB and 5-inch Magnavox speaker. The in-built ferrite rod is hidden behind a cover at the top of the case. and this is done on the circuit board, with traces from the collector and base passing by each other. There’s no actual connection, but their proximity is engineered to provide 4pF of capacitance (C12). Neat. (See photo Fig.2). As usual with first IF amplifiers, TR2’s upper bias resistor, R5, is high in value at 150kW. This allows the AGC voltage developed by demodulator diode D2 to be fed back via 10kW resistor R7 to reduce TR2’s collector current with increasing signal strength, thus reducing its gain. Stage bypassing (C11, C14) is di- rectly back to the emitter rather than to ground, saving on emitter resistor R8’s customary bypass capacitor and giving improved bypassing. Extended AGC action 2.7kW dropping resistor R9 works in combination with R6 and D1 to provide extended AGC action. With no AGC applied, TR2’s collector voltage is around 6.1V. Although OA70 diode D1 and its series 3.9kW resistor R6 connect to the input of the first IF transformer, they have no effect with weak signals as D1 is reverse-biased. A close-up of the dial and the latch for the case. Australia’s electronics magazine March 2021  101 As signal strength increases and TR2’s DC collector voltage rises towards 6.8V, D1’s cathode becomes more negative, and it eventually comes into conduction. At this point, the signal at the first IF transformer’s input is partly shunted to AC ground, reducing the converter stage gain. This extends the AGC’s control range from the approximate 30dB increase in signal input achieved with AGC on the first IF amplifier alone, to as much as 60dB. TR2 feeds the tuned, tapped primary of second IF transformer IFT2. Its untuned, untapped secondary feeds the base of the second IF amplifier, TR3 (OC44). Why use the premium OC44 where you’d expect to find the lower-spec OC45? The answer is gain. The OC45’s hFE is 50~125, while the OC44 offers an improved range of 100~225. This should be advantageous to the audio function of this reflexed stage. Reflexing As mentioned earlier, the stage around TR3 is reflexed, amplifying both the 455kHz IF signal and the demodulated audio signals. The IF section follows common design practice. Like the first IF amplifier, this stage employs printed circuit tracks to provide neutralising capacitance (C16, 3pF). TR3 feeds the tuned, tapped primary of third IF transformer IFT3 and its tuned, tapped secondary feeds OA79 demodulator diode D2. The 41-21A set uses a single-tuned transformer (tuned, tapped primary, untuned, untapped secondary) for IFT3. D2’s output is applied, via R19, to the top of volume control R16’s first section. Confusingly, it’s labelled R16B. The DC component is fed, as the AGC voltage, via R7 to AGC filter capacitor C9 and then to first IF amplifier TR2’s base. R16B’s wiper feeds audio, via C20 and R13, to the base of the reflexed IF amplifier, TR3. Now, as an audio amplifier, TR3’s emitter needs to be bypassed for audio by 33µF capacitor C17 (in the original schematic this was 32µF). So why use a dual-gang volume pot? TR3 has a difficult job: it must amplify millivolt-level IF signals and much higher level audio signals without interaction. Recalling that valve reflexes were bedevilled by cross-modulation and 102 Silicon Chip Fig.1: The original Kriesler 41-21 schematic shows capacitors C21/23 in reverse polarity, and neutralising capacitor C16 should connect directly to the base of TR3, both have been fixed here. On some sets R12 is not fitted; if IF regeneration occurs, it's best to fit this R12 as shown. Similarly, an extra OA79 diode was fitted across the oscillator coil (L3), with its cathode to the collector. minimum volume problems, Kriesler’s designers have restricted the maximum possible IF signal (via the AGC system) and audio signal (by R16B) to ensure TR3’s correct operation at audio and IF signal frequencies. Audio stages Amplified audio is developed across 1.5kW collector load R15, and fed via C21 to the second section of the volume control, R16A. Audio stage gain is around 5.5 times, which might seem poor. But it’s in line with other similar circuits: the Bush TR82C’s first audio stage (TR4 on that circuit) delivers a gain of just 5.0 times. R16A’s moving contact feeds audio, via C23, to the base of audio driver TR4. This is an OC75, a higher-performing version of the OC70/71 types with a higher hFE (current gain) of 90~130 compared to 20~40 and 30~75 respectively. The manufacturer’s diagram for this set has the symbols for C21 and C23 mistakenly reversed. My redrawn diagram fixes this. TR4 drives the primary of phasesplitter transformer T1, with its secondary matching anti-phase signals into the low base impedances of the two output transistors, TR5 and TR6. TR4 gets audio feedback from the speaker via R32 (47kW), while R24 (560W) and C29 (22nF) apply top-cut. In common with transformer-coupled Australia’s electronics magazine stages, TR4 delivers a volt of signal into T1’s high-impedance primary for a stage gain of around 50. As T1 is a step-down transformer, the signal applied to the bases of TR5 and TR6 is considerably lower. TR5/6, both OC74s, operate in ClassB, with bias provided by the divider R25-27. R27, a CZ9A thermistor, acts to reduce the applied bias at higher temperatures, compensating for the natural fall in base-emitter voltage needed for a particular collector current as transistor junction temperature rises. 10W emitter resistors R29/R30 help equalise gains between TR5 and TR6, as well as providing some local negative feedback. The output transistor collectors drive output transformer T2, which matches them to the speaker. There’s another top-cut network across its primary, comprising 100nF capacitor C31 and 330W resistor R31. Disaster awaits The manufacturer’s diagram shows the output stage’s bias divider with a single adjustable resistor between the decoupled battery supply (at C28) and the output bases. What if you accidentally set this resistor to its minimum value? You’ll be attempting to apply many volts to the output bases. Expect them to draw massive collector current and possibly to suffer overheating and destruction. siliconchip.com.au I have a suggested modification below to solve this. Maybe the bloke who designed the dial drive also did this part of the circuit. Clean-up My sample was in good physical condition, with no cracks in the case. It just needed a bit of polish to bring it back to a reasonable condition. Mechanically, though, it had a broken/missing dial cord. Cue Lalo Shifrin music: “Your mission, should you choose to accept it...” In addition to the dial problem, I found it extremely noisy with the volume control wound up; less so at low/ zero volume. Contact cleaner on the volume control helped a bit, but I eventually traced the fault to capacitor C8. This 50nF green ceramic capacitor was acting like an erratic partial short circuit. Converter TR1’s collector voltage would crash down by as much as a volt, then recover, then drop by maybe half a volt, and so on. Leaky caps usually soak up a fairly constant amount of current; this was the first that I’ve seen like this. I thought of replacing it and all the others with greencaps to eliminate possible future recurrences. But that dial drive was lurking in the background, and I was wondering how I could make up those drive pulleys. About this time, I attended the HRSA RadioFest in Canberra. I was griping about this set when another member said he might have one among siliconchip.com.au the boxes of transistor sets he was getting rid of (he was ‘downsizing’). Bingo! It was the 41-21 version (double-tuned third IF), but otherwise identical, and with a functional dial drive. A simple cabinet swap gave me the set in this article: a good cabinet with a working dial mechanism. It was the classic case of “collect two, get one good”. The only bother was the original wire trimmer, which insisted on tuning to above 1700kHz. It’s easy to remove the tinned wire from the ceramic former but harder to add to it. I popped a Philips “beehive” into its place. That dial drive mechanism Kevin Chant’s website has the dial cord diagrams (www.kevinchant.com/ kriesler2.html). It has three assemblies: the securing loop (top), the pulley cord driving the gang’s drum, and the station scale cord (bottom). I’ll leave you to download it and try to work out how to fix it if your set has a broken dial cord. The one I started on had nothing but the dial drum, pointer and driveshaft remaining. You also need two floating pulleys to complete the job. How good is it? It’s good without being great. The reflexed audio stage helps it produce 50mW output for 150µV/m at 600kHz or 120µV/m at 1400kHz, with noise figures of 11dB and 12dB respectively. Fig.2: TR2 needs neutralisation, which is done on the circuit board via parallel traces from the collector and base of TR2. This provides approximately 4pF of capacitance. Australia’s electronics magazine March 2021  103 For the standard signal-to-noise ratio of 20dB, the required signal figures are 370µV/m at 600kHz and 225µV/m at 1400kHz. RF bandwidth is ±0.95kHz (-3dB) or ±23.7kHz (-60dB). AGC works reasonably well, with a 35dB signal increase giving a +6dB rise in output. Its audio response is 95~1200Hz from the antenna to speaker and 170~7000Hz from volume control to speaker, with a 2dB rise around 1kHz. Maximum output is around 130mW for 10% total harmonic distortion (THD). At 50mW, THD is 4.2%; at 10mW it’s 2.5%. At half battery, the maximum audio output is 25mW at clipping, and 20mW output gives 6% THD. 41-21 versions As noted above, the significant change from the 41-21 to the 41-21A was the substitution of single-tuned third IF transformer IFT3. There was one minor change: IFT3 retained a tuned, taped primary, but was fitted with an untuned, untapped secondary, simplifying the circuit and making alignment easier. The service manual also hinted at a 41-21B version which used a new dial drive mechanism, although no other information could be found on whether this set ended up being manufactured. Special handling Be very careful when adjusting the output stage bias. As noted above, the design contains a potentially catastrophic mistake: with only R25 in the “hot” end of the output stage’s bias divider, it’s possible to apply almost the full 9V to the bases of TR5/TR6. I have modified the review set with a 3.3kW series resistor. This allows plenty of adjustment without the danger of frying the output transistors. Conclusion I like the way this set looks, and it has good performance with just enough circuit quirks to make it interesting, without baffling us poor electronics engineers. While I would not buy one with the dial cord apparatus missing, “your mileage may vary”. Hopefully, the de104 Silicon Chip Even though they've used a double-sided PCB, the radio still has an ample amount of wiring, along with a number of unused holes. scription above will be of use if you do take the plunge. Thanks to Jim Greig of the HRSA for the loan of his set, and Charles McLurcan (also of the HRSA) for a set with the dial cord assembly intact. Not a member of the HRSA? Go to: http://hrsa1. com to see how we can help you with our exciting radio hobby. Australia’s electronics magazine Further Reading For the circuit and service notes, see Kevin Chant’s fine website: www. kevinchant.com The service notes contain the cording diagram with dimensions. This model in particular can be found at: www.kevinchant. com/uploads/7/1/0/8/7108231/41-21. pdf SC siliconchip.com.au WHAT DO YOU WANT? PRINT? OR DIGITAL? RY 2021 FEBRUA 1030-2662 ISSN ts! Y Projec BEST DI The VERY 02 1 9 771030 26600$ 1290 $ 995* NZ INC GST INC GST s na l e Sig ernet im Ttim S or the int aingdtraio without GP e R of cking keep Apps droid to MakingApAn r using p Inven mputer ade your Co How to Upgr Batter y Multi-Log ger en 100A!) 10A (or ev 6-100V <at> th this Micro ly Workbench wi Supp Clean up your USB-controlled Power & Oscilloscope EITHER . . . OR BOTH The choice is YOURS! Regardless of what you might hear, most people still prefer a magazine which they can hold in their hands. That’s why SILICON CHIP still prints thousands of copies each month – and will continue to do so. But there are times when you want to read SILICON CHIP online . . . and that’s why the online version www.siliconchip.com.au is maintained at the same time. WANT TO SUBSCRIBE TO THE PRINT EDITION? (as you’ve always done!) No worries! WANT TO SUBSCRIBE TO THE DIGITAL (ONLINE) EDITION? No worries! WANT TO SUBSCRIBE TO BOTH THE PRINT AND THE DIGITAL EDITION? No worries! SILICON CHIP, Australia’s most read, most respected and most valued electronics reference magazine, makes it so easy for you. And even better, we offer short-term subscriptions (as short as six months) so you can effectively “try before you commit”. And, of course, as a subscriber, you’ll know you’ll never miss an issue AND $ave money! Here’s the deal: If you’re in Australia, you can subscribe to the print edition (only) of SILICON CHIP for $105 for a full 12 months (12 issues) – that’s almost $15 less than the over-the-counter price AND we pick up the postage. If you’re overseas, you can subscribe to the print edition – email us for the rates for your particular country. If you’re anywhere in the world, you can subscribe to the online edition of SILICON CHIP for $AU85. And, of course, from anywhere in the world, you can subscribe to both print and online editions – in Australia, the price is just $125 (only $20 more than the print edition price). Overseas – again email us for the rates in your country. While your subscription is current, you can download software, PCB patterns, panel artwork etc FREE OF CHARGE! Want more information? Log onto our website and click on “subscriptions” www.siliconchip.com.au PRODUCT SHOWCASE Raspberry Pi Pico – available from element14 element14 has announced the availability of the first product built on Raspberry Pi-designed silicon: Raspberry Pi Pico. This new product brings high performance, low cost, and ease of use to the microcontroller market, in a $5 development kit. The Raspberry Pi Pico is available to purchase from https://au.element14. com/3643332 At the heart of the Raspberry Pi Pico is the RP2040, a Raspberry Pi-designed micro. It features two 133MHz ARM Cortex-M0+ cores; 264KB of on-chip SRAM; 26 GPIO pins; dedicated hardware for commonly used peripherals and a programmable I/O subsystem for extended peripheral support; a 4-channel ADC with internal temperature sensor; and built-in USB 1.1 with host and device support. The RP2040 microcontroller offers high performance for integer workloads, a large on-chip memory, and a wide range of I/O options, making it a flexible solution for a wide range of microcontroller applications. Key features include: Memory: 264KB of on-chip SRAM; 2MB of on-board QSPI Flash. Interfacing and mechanicals: 26 GPIO pins, of which three can be used as analog inputs. 0.1-inch through- hole pads with castellated edges for SMT assembly. Power: on-board power supply to generate 3.3V for the RP2040 and external circuitry. Wide input voltage range, from 1.8V to 5.5V, giving designers the flexibility to select their preferred power source. Developer tools: simple drag and drop programming via micro-USB. 3-pin Serial Wire Debug (SWD) for interactive debugging. C-based SDK, MicroPython port, and extensive examples and documentation. To find out more about the Raspberry Pi Pico, visit www.element14.com/ community/docs/DOC-96021/ element14 72 Ferndell Street Chester Hill, NSW 2162 Phone: 1300 361 005 Web: https://au.element14.com/ Crocus CT220 – the industry’s first TMR contactless current sensors Mouser is now stocking the CT220 XtremeSense contactless current sensors from Crocus Technology. The CT220 sensors are powered by Crocus' XtremeSense tunnel magnetoresistance (TMR) 1D technology, which enables them to detect slight changes in AC or DC. The sensors offer a 2.7V to 5.5V supply voltage range and 1.2mA supply current rating in a 5-lead SOT23 package. It measures the magnetic field of the current flowing through a busbar or PCB trace and converts it to an analog output voltage that represents the field and current. These sensors achieve a typical total output error of ±0.5% while sensing fields as low as 5mA. CT220 current sensors feature an inherently high isolation, making them the ideal solution for applications where product safety compliance is a requirement. These applications include motor controls, solar inverters, power distribution units and power supplies, and Internet of Things (IoT) devices. To learn more, visit www.mouser. com/new/crocus-technology/crocusct220-xtremesense-sensors/ Mouser Electronics Inc. Phone: (852) 3756 4700 Web: www.mouser.com/ Postponement of ElectroneX to September 2021 AEE, organisers of ElectroneX, have been closely monitoring the COVID-19 situation and following recent outbreaks and border closures over the Christmas period, and have made the decision to postpone ElectroneX (Electronics Design and Assembly Expo) at Rosehill Gardens in Sydney until 1516 September 2021 which also brings the Expo back into the normal September timeframe. This cautious approach will provide sufficient time for the vaccine roll-out to be implemented and for state governments to provide more certainty in relation to their border closure policies 106 Silicon Chip which is currently having a major impact on interstate business. Due to the lead time that is required for the promotion of the show and the need for companies and visitors to be able to freely travel to NSW, we believe this is the best decision to help ensure the overall success of the Expo. In accordance with the terms and conditions, all contracts and payments that have been made will be transferred to the rescheduled dates. If you have any questions in relation to the rescheduling please contact Noel Gray on 0407 943 817 or Vee Johnson on 0422 399 818. Australia’s electronics magazine AEE ElectroneX Noel Gray – Managing Director AEE PO Box 5269 South Melbourne, VIC 3205 Phone: (03) 9676 2133 Mobile: 0407 943 817 Web: www.electronex.com.au/ Mail: ngray<at>auexhibitions.com.au siliconchip.com.au 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. Send your email to silicon<at>siliconchip.com.au How to measure harmonic distortion I recently found out about your magazine, and I bought several of your older issues that were very helpful. Do you have a magazine where you described how to measure THD (total harmonic distortion) on audio amplifiers? (B. G., Neu-Isenburg, Germany) • We have not published a dedicated article on the topic, although we have touched on it several times over the years. To measure THD of an amplifier, you need to use a distortion analyser and a low-distortion signal (sinewave) generator. We have published several articles on these in the past. The most recent article is the USB SuperCodec (August-October 2020; siliconchip.com.au/Series/349) and the matching Balanced Input Attenuator (November-December 2020; siliconchip.com.au/Series/349). Those articles also included details on analysis software that can be used in combination with the SuperCodec for measuring THD+N, signal-to-noise ratio, channel separation etc. In terms of a build-it-yourself instrument for distortion measurements, the USB SuperCodec will be hard to beat. We use an Audio Precision System Two, which cost quite a bit new (and they still go for a fair bit of money used). What is a PC stake? I am building the High Power Ultrasonic Cleaner (September & October 2020; siliconchip.com.au/Series/350), and I have a question about the parts list. What is a PC stake? What does it look like, what is it made of and what is its purpose? Can I make one myself (out of thick copper wire)? I can find no mention of them on Jaycar’s website, for instance. (D. P., Noumea) • A PC stake is a small hardened pin (typically 0.9mm to 1mm in diameter) that fits into a hole in a printed circuit board (PCB). It is used to allow wires to be easily soldered, or as a point siliconchip.com.au for connecting multimeter or oscilloscope probes. They are generally optional, and in this case, can be left off if you are happy to directly solder wire or hold a probe to the PCB pad. Jaycar sell PC stakes, Cat HP1250 (they call them “PCB pins”, which is the same thing). Identifying charred component for repair I have an Ozito SNG-956 Staple/Nail Gun that has a burnt-out resistor R1. The circuit appears to use the typical capacitor/resistor in series from the mains to a bridge rectifier to provide DC to the rest of the circuit. I wonder if anyone knows where I can find a circuit diagram for it, or the value of R1. This is quite an old tool, and unfortunately, Ozito can’t get the circuit diagram from the manufacturer. so at the moment, I’m stuck with not being able to repair it. (B. P., Dundathu, Qld) • If the resistor is in series with the capacitor feeding the bridge rectifier, it’s likely to be a relatively low value like 1-10W. Its primary purpose would be to limit the inrush current when power is first applied, and perhaps act as a ‘fuse’ of sorts (it sounds like it did...). It might also exist to drop some of the voltage (although we don’t think that is a very wise design decision), in which case using a low value could cause other components to overheat. Increasing feedback for Motor Speed Controller I purchased an old gem facet machine with a ¼hp induction drive. It shook, rattled and totally stuffed up soft gem faceting. I have modified it to work with a small universal motor and your Full Wave 230V Universal Motor Speed Controller (March 2018; siliconchip.com.au/Article/10998). Actually, I’m using two universal motors, both running via the same type of speed controller. One starts and runs perfectly; I just needed to Australia’s electronics magazine adjust the feedback pot (VR2). The feedback works well, maintaining a fixed speed. This is important for a faceting machine when cutting soft gemstones; unlike diamonds that can handle speed variations, the speed is more critical for soft gems. But the other universal motor will not start, no matter the setting on VR2. I connected a desk lamp in parallel with the motor, and off it went. The speed control was great; remove the lamp load, and the motor continues to run. However, there is a slow-speed point where this motor stops rotating. The only way to get it going again is to have the lamp connected in parallel with the motor. I note that the slow speed point on the other motor is much slower. It appears to be a back-EMF sensitivity constraint; this motor requires a lower feedback threshold to start and rotate as slowly as the other motor. Can I change the CT feedback loop components to improve the sensitivity for motors such as this? Also, can some of the feedback bridge’s values and its associated RC network be adjusted to increase the voltage feedback to the PIC? (J. T., Teneriffe, Qld) • You would need to add more turns of the mains wire through the transformer. That might be difficult as the hole is a small diameter. Select 10A mains wire that will allow more turns through. You could also increase the 510W loading resistor that is across the AX1000 transformer coil. A larger value will increase the output voltage. We used 510W but, for example, a 2.2kW resistor would give a higher feedback voltage. There is a limit to the output versus current response, and it becomes non-linear with greater resistance values. Note: J. T. got back to us and said: “I increased the 510W loading resistor that is across the AX1000 transformer coil to 1kW, and doubled the number of winding through the CT. It works perfectly now.” March 2021  107 Larger display for RPi Tide Clock I want to build the Raspberry Pi Tide Chart from July 2018 (siliconchip.com. au/Article/11142), but I want a larger display than the 2.8in TJCTM24028 screen you used. Do you know if there is a larger screen that is compatible, which could be plugged or wired in to replace the existing small LCD? I would like to put it in a frame that can be placed on the wall for everyone to see. (R.W., Mt Eliza, Vic) • 3.2in and 3.5in variants of the ILI9341-based 2.8in display we used in that project are available, with the same pinout as the TJCTM24028. We suspect that the mounting holes and SD card reader would not match, but the 14-way header for the LCD and touch appears to be the same in each case (which is all that is needed for the Tide Clock). For example, see siliconchip.com. au/link/ab6y and siliconchip.com. au/link/ab6z We haven’t tested any of these, so we can’t comment with any certainty that they would work. Using any other display controller (instead of an ILI9341) would require a major rewrite of the code. Note, though, that you would have many more options for larger (and cheaper) screens if you used one with an HDMI input (ie, a small computer monitor), which is natively supported by the Raspberry Pi. Effect of changing crossover inductor The recommended inductor for the Majestic loudspeaker crossover (June & September 2014; siliconchip.com. au/Series/275), in series with the woofer, is a 2.7mH inductor. The Jaycar Cat LF1330 inductor that was recommended is no longer available. With COVID restrictions, most European suppliers aren’t exporting down under. I can get a 2.5mH air-cored inductor locally. Would this be suitable, or would I need to make other changes? (P. S., Hamilton, NZ) • We doubt you would notice the difference. That is only a 7.4% difference in value, and the tolerance of these inductors is probably ±20% anyway. There might be slightly more midrange getting to the woofer (it has the bandwidth to reproduce up to a few 108 Silicon Chip kHz). In the unlikely event that you can hear the difference, and it is bothersome, you could add 180µH or 220µH air-cored inductors in series with the 2.5mH types. Just make sure they are mounted at right-angles, so their magnetic fields don’t interact. Increasing DC-DC Converter soft-start time I am building the DC-DC Converter to power the CLASSiC-D Class-D amplifier (May 2013; siliconchip.com.au/ Article/3774). Would increasing the value of the 47kW resistor connected to IC1’s pin 4 and the 10µF capacitor be a suitable way to increase the circuit’s soft-start time? I have found that connecting the Mk.3 power supply board with six 4700µF capacitors is too much all at once, resulting in blown STP60NF06 Mosfets, and I am hoping that a softstart modification would make the two projects compatible. Also, the TL494CDR switchmode controller is out of stock at element14 and Mouser at the moment. Are the TL494IDR or TL494CD (both from Texas Instruments) suitable alternatives? (E. B., Viewbank, Vic) • You can slow down the soft-start by increasing the value of the capacitor (originally 10µF) at pin 4 of IC1. 22µF or 47µF capacitors would be suitable. The 47kW resistor value should not be changed. As for the TL494CDR IC specified, the following types are also suitable: TL494CN, TL494CNE4, TL494IN or TL494INE4. In fact, any 16-pin DIP version of the TL494 should work. CLASSiC-D overheating and motorboating I built two of your CLASSiC-D ClassD amp modules (November-December 2012; siliconchip.com.au/Series/17) from Jaycar kits, Cat KC5514. My construction experience is extensive, having been employed by a competitor for six years as the national production manager for local manufacture and kit assembly and tech support. After many years of continual use, my Series 5000 150W modules have died with the 2SK49 and 2SK134 transistors failing, so I decided to upgrade the modules to the cooler/more efficient Class-D type and get more power, 240W into 4W. Australia’s electronics magazine I used a multimeter to check all resistor values and used my phone camera to zoom in on the diode and capacitor markings to make sure I had the correct values in the correct locations on the board. The larger components are easily read, so I completed the PCB assembly and also drilled the heatsinks at the full 75mm height. The steps to confirm the board setup is correct worked as per the instructions, and I can get a clear sound from the amp modules. I’m using a ±50V supply rails from a 35-0-35V toroidal transformer. The amplifiers have tested with the correct voltages, and when I plug in an RCA male to 3.5mm jack cable into my mobile phone, I get clear sound. However, the heatsink is very hot with no signal applied and no speaker connected. When I connect a signal and 8W speaker, the sound remains clear for about one minute, but then I can no longer touch the heatsink, and the amp has distortion until it is turned down and cools a bit. Also, when I plug in a DJ mixer or other preamp device, the amp gets a low-frequency oscillation at full power and the speaker is thumping at full volume. Unfortunately, I lost a lot of gear in a bushfire, so I currently do not have an oscilloscope or signal generator. I’m hoping you can provide some insight into what steps I can take to resolve these problems. (D. F., Perth, WA) • The heatsinks are probably running hot due to the dead time not being sufficient for the Mosfets being used. You can initially lift the 5.6kW resistors between pin 9 and pin 12 of IC1 on each amp board to get the maximum dead time setting (DT4). If the heatsinks run much cooler, that tells you that it was definitely the dead time setting at fault. Our original design uses the DT2 setting. If DT4 works OK, you might like to try DT3, which will give lower distortion. To test this, change the 5.6kW resistor to 8.2kW and the 4.7kW resistor, from pin 9 to ground, to 3.3kW. You will need to verify that the heatsink temperature is still OK with this setting, but if so, it will give you better performance. As for the low-frequency oscillation, that’s possibly due to the power supply cycling up and down in voltage when delivering a high power output. This is explained on pages 21 and 22 of the IRAUDAMP5 Refersiliconchip.com.au ence Design document (siliconchip. com.au/link/ab2a). The recommendation to solve this is to reverse the input and output phases of one of the amplifier modules. This is catered for on our modules by op amp IC2 and link LK2. Simply move the LK2 shunt on one of the modules to the alternative position, then swap the speaker wires to CON3 on that same module. Using Bridge Adaptor with Class-D amplifiers I built a couple of your Bridge Adaptor For Stereo Power Amps (July 2008; siliconchip.com.au/Article/1887) from Altronics K5566 kits, and they work perfectly. Can this adaptor be used with a Class-D amplifier? (P. N., via email) • It depends on the amplifier but probably not, because most Class-D amplifiers already run in bridge mode. If you can’t tell from the amplifier specs/data, check to see if there is continuity between either of the output terminals and ground (generally if there is continuity, it will be with the black/negative output). Continuity to ground suggests that the output is not bridged and you could use a bridge adaptor. Lack of continuity suggests that it is already bridged. You can also tell looking inside the amplifier as a bridged ClassD amplifier usually has two filter inductors per output (ie, four for a stereo amplifier). 12V to 15-35V Inverter output dropping I have just built the 12V 100W Converter With Adjustable 15-35V DC Output (May 2011; siliconchip.com. au/Article/1009). At the top of page 79, there is a graph which shows at 25V you should get 3A. I have hooked up a 12W LED floodlight (Jaycar SL3931), tested on my bench supply at 25V DC as drawing 600mA. But the inverter output drops from 25V to 9V and the current increases to 1.5A, which is not good. I can adjust the output voltage from 12V to 30V. The pin 5 voltage is 1.25V but does change on varying the output. The voltage at the gate of Q1 is very low, less than 1V. I cannot get a steady 10V reading. Reading the project notes, it says I should get 10V at siliconchip.com.au the gate of Q1. I do not understand whether this is with the circuit under load or not under load. At pin 2, I measure a 32kHz signal. Do you know why it can’t drive the floodlight with 24V DC at 600mA? (M. T., Upper Swan, WA) • The lack of output power can be due either to the input supply not being able to deliver the required current and so dropping the voltage, or the current detection resistance is high (R1 on the circuit). Check the input supply and note that it will need to provide over twice the output current when delivering a 25V output with a 12V input. If the input supply is holding up, possibly R1 (the 0.025W resistor) is the wrong value or the connections to the PCB are high resistance. Check the value and also the soldering of this component to the PCB. You might have a dry joint. Power factor correction and mains-borne noise Leo Simpson’s March 2011 editorial (siliconchip.com.au/Article/921) claimed that power factor correction circuitry won’t reduce your energy usage or save money. Yet in this IEEE article, they point out that smart meters can misread when dirty power is fed into them: siliconchip.com.au/link/ab70 As power factor correction reduces noise (aka dirty power), why wouldn’t it reduce your power bill? (M. C., via email) • Power factor correction (PFC) doesn’t usually reduce mains-borne noise. In fact, it can increase noise on the mains supply. Capacitive PFC shifts the current phase to be closer to the voltage waveform, to compensate for inductive loads. It might provide some noise filtering, but that is mostly incidental to how it works. On the other hand, active PFC, which improves the power factor of switching supplies using switching techniques, can inject more noise due to its switching action. Also, power factor correction would typically be applied on the load side of the meter. It’s unlikely to do anything to affect incoming noise from external sources, which must be significant if it is passing through the low-impedance mains distribution network. Australia’s electronics magazine The primary way to reduce noise is filtering. Mains filters are simple and readily available. If smart meters are misreading, that suggests they do not have adequate filtering on the input side and their metering circuitry. Freq/voltage converter for RPM counter Have you published a project or projects that shows how to create a DC voltage directly proportional to frequency, for example, using the LM2917 IC? I want to make an RPM counter for the tail shaft of an irrigation engine. (P. H., Gunnedah, NSW) • Try the Twin-Engine Speed Match Indicator for Boats from the November 2009 issue (siliconchip.com.au/ Article/1622). It could be used for a single engine by tying the pin 10 non-inverting input of IC3c to ground and deleting IC2 (LM2917) and its associated components. There are kits available for this project from Jaycar (Cat KC5488) and Altronics (Cat K6220). Amplifier and power supply kits wanted Do you happen to sell a kit for the 20W Stereo Class-A Power Amplifier (September 2007; siliconchip.com. au/Article/2341), including the chassis? If not, do you have the PCBs and the chassis? Also, do you have a linear DC power supply kit that is not a bench type? I want a supply with 5V, 9V, 12V and 15V outputs, either variable/switchable or a single output with 2A capability. Preferably with chassis. (D. S., via email) • The only kit available for the 20W Class-A amplifier with a chassis was Altronics Cat K5125, but unfortunately, it has been discontinued. We believe that the case is no longer available. You would need to make your own chassis from a standard vented rack case or similar. We do have the PCBs for that project, which you can purchase via this link: siliconchip. com.au/Shop/?article=2283 As for the power supply, we don’t have a non-bench supply that meets your requirements. However, you might want to take a look at the 4-Output Universal Voltage Regulator (May 2015; siliconchip.com.au/ Article/8562). March 2021  109 This has 5V and 3.3V fixed outputs and adjustable positive and negative outputs up to 22V. It does not have 2A capability, however, replacing the LM317 with an LD1085 would likely mean that you can draw over 2A (and possibly as much as 3A) from the positive adjustable output, given a sufficiently beefy DC input supply and enough heatsinking. Failed LC Meter from 2008 I built the LC Meter described in your May 2008 issue (siliconchip.com. au/Article/1822) from an Altronics kit that same year. I was so happy with the result that I have not bothered to build the updated versions described since. However, when I went to use the unit the other day, I noticed the capacitance reading was high. I checked the readings against several capacitors of known value and found that all readings were out by the same amount. I could get useful results from the readings by measuring a known capacitor first, calculating a fudge factor to correct the error in the readings and then applying that factor to the unknown capacitor’s reading. While this allowed me to get on with the work I was doing, I feared it might be the start of bigger problems. I went back to the instructions and re-ran the calibration procedure and found that it gave 0.00pF when started and 49435 with the jumper shunt in LK2, but the display vanished with the jumper in LK1. I checked all solder joints and reflowed a couple of suspect ones without any change in the performance. I cannot see any solder bridges. Any suggestions of what I should check next? (C. K., Parkhurst, Qld) • There isn’t a whole lot to go wrong in that circuit. The lack of display suggests that the microcontroller isn’t running. First, check that the output of REG1 is a steady 5V (4.75-5.25V). The fact that your readings shifted by a consistent amount before it failed completely suggests that there may be a problem with crystal X1. If its frequency changed then that could throw the calibration out, and if it failed entirely then the micro would not run. Check for a 4MHz signal at pin 15 of IC1 (eg, using a scope or frequency meter). 110 Silicon Chip If there is no oscillation then there is something wrong with either crystal X1 or microcontroller IC1. If you have a PIC programmer, it would be a good idea to attempt to reprogram IC1. While we find PICs very reliable, there is a slight possibility that your IC1 chip has failed. In that case, you can order a replacement programmed PIC from us; see siliconchip.com.au/ Shop/9/1277 If the voltage across the electro is low, as is in many coupling circuits where both ends of the capacitor are nominally at ground potential, the orientation doesn’t matter. Typical electrolytic capacitors can tolerate a small DC voltage of either polarity (up to say ±500mV) indefinitely. Modifying the Four Input Mixer I have a question about the FM Wireless Microphone project from your October 1993 issue (siliconchip.com. au/Article/5343). I have been trying to work out how the RF oscillator based around NPN transistor Q3 works, but I have not been able to. There needs to be capacitance across inductor L1 to form a resonant circuit. Is this the Miller capacitance between the transistor base and emitter? I cannot see where the feedback path is for the oscillator, either. Sadly, the article does not specify a value for L1. If you could help me understand how the oscillator works, I would be most grateful. (A. C., Gembrook, Vic) • The 1pF capacitor across inductor L1 forms part of the capacitance necessary for oscillation to occur, but is only a small contributor. Q3’s Miller capacitance would also make a small contribution. The rest is via the 15pF coupling capacitor, which is in series with 33pF and 15pF capacitors to ground. That combination has a total capacitance of around 6pF, and is effectively in parallel with the 1pF directly across L1. You also have to consider trace inductance etc which will significantly reduce the effectiveness of that extra capacitance at 95MHz. As for feedback to make Q3 oscillate, that would be the 33pF capacitor between its base and emitter. The base and emitter are effectively 180° out of phase, so that plus the phase shift introduced by that capacitor should be enough to sustain oscillation. Making RF oscillators work reliably and at a particular frequency is a bit of a black art. It must have taken quite a bit of tweaking for Oatley to come up with the circuit as presented. We could be accused of going into too much detail in our circuit descriptions these days, but your question makes it clear that there was far too little detail in these early articles. There’s continued on page 112 I want to build a variant of the Versatile Four Input Mixer from the June 2007 issue of Silicon Chip (siliconchip.com.au/Article/2256). I only want two inputs, one for a guitar and the other for a CD player. Can I delete the master volume control (VR8) and only use the headphone volume control (VR9)? I want this project to be heard on headphones only. Could you please tell me what other components need to be deleted or added, especially around the master volume control. Also, in this design, you have some coupling electrolytic capacitors that the input goes into the positive side, yet there are some where the negative side is fed a signal. How do you determine which way the cap is supposed to go in these cases? (J. R., Hoppers Crossing, Vic) • You could take the connection that goes to the top of the master volume pot (VR8) and connect this to the top of the headphones volume control VR9 instead. Remove the original connection from the main output. Then the output socket and master volume control can be removed. Electrolytic capacitors are orientated based on the expected DC voltage at either end, ie, with the positive lead to the more positive side. You need to do some circuit analysis to determine the DC operating conditions at either end, or run a simulation, or just build the device with a non-polarised capacitor and measure the voltage before substituting an electrolytic capacitor. One of the trickier aspects of this sort of calculation is taking into account op amp or amplifier input bias currents; analog IC inputs can source or sink current, or do neither, and sometimes that changes depending on certain factors. Australia’s electronics magazine Help to figure out how an oscillator works siliconchip.com.au MARKET CENTRE Cash in your surplus gear. Advertise it here in SILICON CHIP PCB PRODUCTION KIT ASSEMBLY & REPAIR PCB MANUFACTURE: single to multi­ layer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au VINTAGE RADIO REPAIRS: electrical mechanical fitter with 36 years ex­ perience and extensive knowledge of valve and transistor radios. Professional and reliable repairs. All workmanship guaranteed. $17 inspection fee plus charges for parts and labour as required. Labour fees $38 p/h. Pensioner discounts available on application. Contact Alan, VK2FALW on 0425 122 415 or email bigalradioshack<at>gmail. com FOR SALE GREAT VALUE PARTS and more are found in the Tronixlabs eBay store via tronixlabs.com.au – for enquiries or support please email support<at> tronixlabs.com LEDs, BRAND NAME and generic LEDs. Heatsinks, fans, LED drivers, power supplies, LED ribbon, kits, components, hardware, EL wire. www.ledsales.com.au ASSORTED BOOKS FOR $5 EACH Selling assorted books on electronics and other related subjects – condition varies. All books can be viewed at: siliconchip.com.au/link/aawx Email for a postage quote, quote photo numbers when referring to a book: silicon<at>siliconchip.com.au DAVE THOMPSON (the Serviceman from S ILICON C HIP) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, NZ but service available Australia/NZ wide. Email dave<at>davethompson.co.nz KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com Silicon Chip Binders REAL VALUE AT $19.50 * PLUS P &P Keep your copies safe, secure and always available with these handy binders These binders will protect your copies of SILICON CHIP. They feature heavy-board covers, hold 12 issues & will look great on your bookshelf. Silicon Chip Publications Order online from www. siliconchip.com.au/Shop/4 ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone Glyn (02) 9939 3295 or 0431 792 293. 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 Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. siliconchip.com.au Australia’s electronics magazine March 2021  111 Notes & Errata USB SuperCodec, August-October 2020: in the Fig.13 circuit diagram on page 88 of the September 2020 issue, pin 12 of IC7 (SDOUT) should not be shown connected to pin 9 of IC6. Instead, it goes to the I2S_ADC1 connection at the right edge of Fig.12 on p86. Car Altimeter, May 2020: the design is missing one schottky diode (D8) which connects from the cathode of ZD1 (schottky anode) to the positive terminal of the battery (schottky cathode). This is needed to charge the battery. It can be added to the underside of the PCB, as shown in the accompanying photograph. Advertising Index Altronics..................17, CATALOG Ampec Technologies................. 20 Analog Devices..................... OBC Dave Thompson...................... 111 Digi-Key Electronics.................... 3 Emona Instruments................. IBC Jaycar............................ IFC,53-60 Keith Rippon Kit Assembly...... 111 LD Electronics......................... 111 LEDsales................................. 111 Microchip Technology.................. 5 Mouser Electronics...................... 7 Ocean Controls......................... 19 SC Colour Maximite 2............... 71 Silicon Chip Binders............... 111 Silicon Chip Shop...............98-99 6GHz Touchscreen Frequency Counter, October-December 2017: in the circuit diagram on pages 30 & 31 of the October 2017 issue, a 1µF bypass capacitor is missing between the anode and cathode of REF1. Also, in the overlay diagram (Fig.3) on p86 of the November 2017 issue, the board shown is RevA; the final (RevB) board adds a 100µF capacitor just to the left of REG2, with its positive lead towards the regulator. The April 2021 issue is due on sale in newsagents by Thursday, March 25th. Expect postal delivery of subscription copies in Australia between March 23rd and April 9th. hardly any mention in that article of how the circuit works! Disconnecting the charger on full battery Some time ago, you advised me how to modify the “Add-On Regulator for 12 Volt Battery Chargers” published in Electronics Australia, June 1997, to charge a 24V SLA battery. I have used it for several years, but I am now planning to upgrade to a 24V Lithiumion battery. If I set the charge voltage to 28.5V, will I need to add extra circuitry to disconnect the battery at this point? Will one of the cut-out modules, as available from eBay, be suitable for this? (B. C., Dungog, NSW) • Yes, you would need to switch off the charger when the Lithium-ion 112 Silicon Chip battery is charged. You could use our Threshold Voltage Switch (July 2014; siliconchip.com.au/Article/7924), sold as a kit by Altronics (Cat K4005) and Jaycar (Cat KC5528). Any other similar device should also work. Graphic Equaliser level matching problem I have been using an Electronics Australia Graphic Analyser for many years, even though it spends most of its life in the cupboard. I drive it with an electret mic which is switchable between 600W and 50kW. The problem is that to get a decent level on the LED display, I must have the sound level in the room extremely high, to the point that I must wear ear protection and only do it when nobody else is at home. Australia’s electronics magazine Silicon Chip PDFs on USB....... 91 Switchmode Power Supplies..... 29 The Loudspeaker Kit.com........... 9 Tronixlabs................................ 111 Vintage Radio Repairs............ 111 Wagner Electronics................... 64 It has always been that way, but it seems that it would be best to do the process at a normal listening level. Is there something I can do to increase the mic preamp gain, or might there be some other problem? The original build did have problems with many dead or partially-dead quad op amps. Might there be more remaining undetected? (R. A., Hunter’s Hill, NSW) • We suggest that you use a preamplifier to boost the microphone signal. Then you won’t need to have the volume so loud. You could use our Multi-Role Champion Preamplifier published in the June 2015 issue (siliconchip.com.au/ Article/8609). It is inexpensive and easy to build, and its gain can be adjusted to suit your needs. We can supply the PCB for that project. SC siliconchip.com.au “Rigol Offer Australia’s Best Value Test Instruments” Oscilloscopes NEW 200MHz $649! New Product! 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