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OCTOBER 2021 ISSN 1030-2662 10 The VERY BEST DIY Projects! 9 771030 266001 $1150* NZ $1290 INC GST INC GST Two- or Three-Way Active Crossover SMD Test Tweezers The Tele-Com Phone Intercom Gravitational Waves how they are detected Build your own Arduino® Compatible Oscilloscope This little test tool is designed to be easily put together if you need a very basic scope in a hurry. The maximum sample rate is about 700 samples per second, and it's limited to the 0-5V that the Arduino® analogue pins can handle. Still, it's sensitive enough to pick up the 50Hz noise from mains wiring without making contact. Also includes a tone generator, so you can compare signal frequencies too. SKILL LEVEL: BEGINNER USB Lead not included. For step-by-step instructions scan the QR code. CLUB OFFER BUNDLE DEAL 3995 $ www.jaycar.com.au/oscilloscope See other projects at SAVE 25% www.jaycar.com.au/arduino KIT VALUED AT $55.85 240V Soldering Irons Stainless steel barrel. Impact resistant handle. Electrically safety approved. 40W TS1475 $19.95 80W TS1485 $24.95 JUST FROM 5 $ 6 95 Hook-Up Wire Pack $ 2 metres of 8 different colours of 13 x 0.12mm hook- up wire. 16 metres total. WH3025 100 $ gift card Awesome projects by On Sale 24 September to 23 October, 2021 95 IP65 Sealed ABS Enclosures ABS plastic. IP65 rated. Wide range, sizes from 64Wx58Dx35Hmm to 240Wx160Dx90Hmm. HB6120-HB6134 FROM 1995 $ DON'T FORGET YOUR SOLDER! 15g, 200g, & 1kg available. FROM $2.75 Got a great project or kit idea? 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 ONLY 2495 $ Assorted LED Pack Contains 3mm and 5mm LEDs of mixed colours. 100 pieces. ZD1694 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.10 October 2021 SILICON CHIP www.siliconchip.com.au Features & Reviews 14 Detecting Gravitational Waves Despite being theorised to exist in 1905, it wasn’t until 2015 that gravitational waves were actually detected. The article details the properties of gravitational waves and the efforts to detect these ripples in space – by Dr David Maddison 61 El Cheapo Modules: 3.8GHz Digital Attenuator This self-contained 1MHz to 3.8GHz digitally programmable attenuator, with an OLED screen, can reduce a signal level by 0-31dB in 1dB steps – by Jim Rowe 70 Review: PicoScope 6426E USB Oscilloscope The PC-based PicoScope 6426E has four analog channels, 12 bits of resolution, 5GS/s sampling rate, a waveform generator and more! – by Tim Blythman Gravitational waves are ‘ripples’ in spacetime that are produced by accelerating masses. Detecting them is tricky, as it requires incredibly sensitive equipment as detailed in the article – Page 14 82 Review: Solder Master ESM-50WL Cordless Iron The Solder Master ESM-50WL from Master Instruments is the newest contender in the sphere of battery-powered soldering irons – by Tim Blythman 90 UT-P 2016 MEMS Woofer Reproducing audio signals down to 20Hz, the UT-P 2016 midrange driver is only tiny in size, not power – by Allan Linton-Smith Constructional Projects 30 Tele-com – an intercom using analog phones The “OzPlar” Tele-com is a private line automatic ringdown unit, also known as a PLAR or intercom. It lets you connect two analog telephones to communicate over short or long distances – by Greig Sheridan & Ross Herbert The Tele-com intercom provides you with an easy way to connect two analog telephones. It provides all you need to make these phones functional – Page 30 42 Two- or Three-Way Stereo Active Crossover – Part 1 Our Active Crossover can be used for two- or three-way speakers, includes muting to eliminate switching transients, a subsonic filter to protect subwoofers, and can work with the Tapped Horn Subwoofer from last month – by Phil prosser 64 SMD Test Tweezers Made with just 11 components, our Test Tweezers measure the value of SMD resistors and capacitors, plus it shows diode orientations and calculates their forward voltages; all this is displayed on an OLED screen – by Tim Blythman 76 Touchscreen Digital Preamp with Tone Control – Part 2 Introduced last month, we finish off our new Digital Preamp by describing how to build it, test it and wire it up – by Nicholas Vinen & Tim Blythman Your Favourite Columns 84 Serviceman’s Log Life on the ‘bleeding edge’ – by Dave Thompson This Two- or Three-Way Active Crossover can be powered by 2430V DC, split rail DC or low-voltage AC. It has level control for all three bands, typically draws around 150mA, and has a mono or stereo output for subwoofers – Page 42 94 Vintage Radio Reinartz 4-valve reaction radio – by Fred Lever 103 Circuit Notebook (1) Colour recognition using LEDs and an LDR (2) Battery charger with WiFi interface Everything Else 2 Editorial Viewpoint 4 Mailbag – Your Feedback siliconchip.com.au 29 Product Showcase 106 Silicon Chip Online Shop 108 Ask Silicon Chip 111 Market Centre Australia’s magazine 112 Noteselectronics and Errata 112 Advertising Index Our SMD Test Tweezers identifies resistors (10W (10W to 1MW 1MW), capacitors (1nF to 10μF), diodes & LEDs. It runs from a single lithium coin cell with around five years of standby life2021  1 – Page 64 October Cover image source: www.ligo. caltech.edu/image/ligo20160615f 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 Reader Services Rhonda Blythman, BSc, LLB, GDLP 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 Staff (retired) Ross Tester Ann Morris Greg Swain, B. Sc. (Hons.) 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 (Australia only): 12 issues (1 year): $105 24 issues (2 years): $202 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. ISSN 1030-2662 Printing and Distribution: Editorial Viewpoint The chip shortage is now a component shortage I mentioned the severe semiconductor shortages in my June 2021 editorial. By that time, we had been having problems getting some parts for a few months, but it was clearly getting worse. Many common parts were unavailable, with long lead times. Things have only gone downhill since then. It isn’t just products like ICs and semiconductors that are becoming hard to get, but even basic components like ceramic capacitors and inductors are running out. And the situation with semiconductors like microcontrollers and Mosfets is becoming ridiculous, with whole ranges completely out of stock and astronomical lead times. I’m not joking about that. We were trying to buy some NXP Mosfets (PSMN1R030YL) for one of the kits that we sell, and not only were they out of stock everywhere, but one major supplier quoted us an estimated backorder delivery date of April 25th, 2024 – over two and a half years from now! This is a major headache for us. How can we publish constructional projects if we don’t know whether readers will be able to buy the parts to build them? Even if we check and stock levels look healthy now, by the time we publish the article (which can range from a few weeks to a few months), they could all be gone and not available for a long time. We used to keep around one month worth of parts for the kits and programmed microcontrollers we sell, perhaps 10-20 of each. Now we have to keep 6-12 months worth, often well over 100 of each, because of how quickly the suppliers run out of stock and how long it takes to replenish them. So we’re paying a lot more up-front and we have to find space to store them all. I can only imagine it’s an even bigger headache for manufacturers, service centres and others who have to order in reel-size quantities and require a much more comprehensive range of parts for assembly or repair. And the fact that everyone is scrambling to get the parts they’re going to need for the foreseeable future can’t be helping with the shortages. Given that the lead times for many out-of-stock components are already midto-late 2022, it’s clear that these shortages are not going away any time soon. By the time that stock arrives next year, much of it might already have been sold, and what’s left will likely be quickly snapped up. Fundamentally, the only ways to solve a situation where demand is grossly outstripping supply is to either significantly increase supply or reduce demand. Increasing supply is not easy or quick, and I don’t see the demand dropping just yet (but it will have to eventually). So we’d all better prepare for this situation to continue for some time. ElectroneX postponed again Given the current Australian COVID-19 situation, it comes as no surprise that ElectroneX had to be postponed again, this time until April next year. Please see the full announcement on page 29 for more details. Exciting competition funded by Dick Smith Also, don’t miss the competition announcement on page 13 of this issue. It’s an excellent opportunity for budding electronics enthusiasts to have the chance to win a substantial cash prize, and it sounds like a fun challenge. We’ve timed it so that entrants will have the Christmas/New Year break to work on their designs. Depending on how many entries we get and their quality, we might also end up featuring some of them in the magazine; we’ll definitely be featuring the best entry, as described in the announcement. by 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 October 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 had the right to edit, reproduce in electronic form, and communicate these letters. This also applies to submis­ sions to “Ask Silicon Chip”, “Circuit Notebook” and “Serviceman’s Log”. My experience with cardiac MRI The feature on Advanced Medical & Biometric Imaging in the August issue (siliconchip.com.au/Article/14983) prompted me to write about my experience with advanced medical imaging. I had an electronic device implanted in my chest, an Implantable Cardioverter Defibrillator (ICD). I have had a long history of heart palpitations. After seeing multiple doctors and trips to hospital emergency departments, I was on a first-name basis with some Ambos. I was finally referred to a cardiac electrophysiologist (and a cardiologist too). They sent me for a cardiac MRI, which showed I had scarring from a viral heart infection that disrupts the electrical pathways. The ICD implanted in my chest controls the palpitations (actually premature ventricular contractions). The ICD records cardiac events and transmits data to the specialist over the mobile telephone network via a home monitoring system beside my bed. Now I can hear ICD alarm tones coming from inside my chest. A short beep means I’m near a strong magnet. A long beep means the internal battery is running out. If I hear ‘wee-waa’, it’s time for another ambulance ride. It’s a bit unnerving hearing alarm tones come from inside my chest! The ICD is affected by magnetic and electromagnetic fields. I’m definitely not allowed to operate an arc welder or powerful radio transmitter! The wonders of advanced medical imaging did it for me! Peter Johnston, Merimbula, NSW. home from the hospital. I was aware of such technology from past readings and hospital visits, but now I am living proof of the results of all this mind-blowing technology and how lucky we are in this country to have access to it all. Hans M., Southern Highlands, NSW. First-hand experience with medical imaging Predecessors of Nano TV Pong Thank you for the very interesting article on Advanced Medical Imaging (August-September 2021; siliconchip. com.au/Series/369). I was at Westmead Hospital (Sydney) for over six weeks. I received a stent to repair my aorta. While still in the emergency department, I developed pains they could not explain. I can’t go into details as there would be not enough space to print it all. Anyway, several CT scans taken over a number of days finally revealed that a blood vessel to my liver needed repairing. Another stent later, my life was saved. Thanks to the unbelievable skills of the surgeons, the specialists operating this machinery and analysing the findings, my life and that of countless other patients are being saved every day! I read the article after returning I refer to your recent project published in the August 2021 issue, “Nano Pong on Your TV” (siliconchip.com. au/Article/14988). Back in my school days, when I became interested in electronics, I acquired a “Top Projects” magazine from Electronics Today. I built a few of the projects including the Stereo Amplifier 482, which used two of the popular ETI 480 amplifier modules and the ETI 131 General Purpose Power Supply (modified for higher current). But your article reminded me of the first project I built from this magazine called “Selecta-Game”, project number 804. It offered a choice of six games with on-screen scoring and sound: tennis, soccer, squash, practice and two rifle games. It was based on a single-chip device, the AY-3-8500 from General Instrument Corporation. ALSO AVAILABLE 10% OFF YOUR NEXT SEPTEMBER ORDER WITH DISCOUNT CODE SCOCT10 FREE SHIPPING AUSTRALIA WIDE 4 Silicon Chip THE TOOLS TO BUILD THE FUTURE w w w. p h i p p s e l e c t r o n i c s . co m Australia’s electronics magazine siliconchip.com.au “Setting the standard for Quality & Value” Established 1930 ’ CHOICE! 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All prices include GST and valid until 25-11-21 07_SC_270921 CNC Machinery 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 6 Silicon Chip It offered other features such as high/low speed, large/ small bats, manual/auto serve and two bat strike angles. I noticed it is listed in your Electronics Today International index on your website and thought that some of your readers might be interested. Tony Cassaniti, Kotara (Newcastle), NSW. Our Serviceman isn’t suicidal I was just reading the Serviceman’s Log article on the Roland DX2 repair (August 2021). Does he say he connected the output from a variac directly to the DX2 on page 62? This is very dangerous – every variac I’ve ever seen is an auto-transformer and, as such, is not isolated from the mains. Sorry, I don’t mean to be a downer, but kids read these magazines – I know I did. D. T., Sylvania, NSW. Comment: rereading that section, you’re right that it does sound like he connected the variac directly to the low-voltage AC input of the device being tested. Of course; that is a terrible idea. We checked with Dave Thompson, and he confirmed that he had a plugpack connected to the variac output, feeding the low-voltage AC from that to the keyboard. He’ll have to be more careful how he words it next time! Happy with local PCB service After a career in electronics, I retired to a farm that grows barley, beef and wine grapes – all of which have suffered from trade disputes with one of our large overseas customers. As a consequence, I am trying to avoid dealing with companies located in that particular country. To this end, I found an advertisement in Silicon Chip for an Australian-based PCB manufacturer. They were a little more expensive than the overseas suppliers I had used in the past, but significantly faster turn-around (seven days from order to delivery) and with excellent quality. Importantly, they are local and have responsive support. I am not associated with the company but am more than happy to endorse an Australian company that provides an equivalent service. Paying a little more to support Australian jobs and to a supporter of Silicon Chip is a no-brainer. Tom Pankhurst, Mt Barker, WA. The CablePI does work In the October 2019 issue of Silicon Chip, you responded to a correspondent on the perceived limitations of the “CablePI” device as issued to Tasmanian energy consumers by Aurora Energy, Tasmania’s electricity retailer. Your response has the following quote, “It appears that the Cable PI has only two connections to Active and Neutral and is only capable of detecting High or low voltage. Without an Earth connection, it has no chance of detecting many of the possible faults that may occur.” I wish to respond to this claim. Having spoken with one of the original design engineers, the CablePI device was designed to detect broken or sub-standard Neutral connections, arguably one of the most dangerous situations that can cause electric shocks. It does this by monitoring the loop impedance between Active and Neutral. Australia’s electronics magazine siliconchip.com.au 1 MONTH Up to daily use on a single charge [2] 3 HEAT MODES Under plus BOOST Function 10 Model No: ESM-50WL 50Wh seconds Lithium Ion Powered CORDLESS SOLDERING IRON Superior runtime 10 second heat up Boost function Lasts up to 270 mins on low setting[1], 160 mins on high setting, or up to 1 month[2] of daily usage out of every charge. 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SKU: CMS-007 Price: $142.95 ea For Wholesale prices Contact Ocean Controls Ph: (03) 9708 2390 oceancontrols.com.au Prices are subjected to change without notice. 8 Silicon Chip The CablePI demonstrated its value when a broken Neutral on a pole-top transformer was detected simultaneously by devices plugged into powerpoints in neighbouring homes. I recall as an electrical apprentice years ago, we were called to a vacant block in a local town where plumbers had just excavated, then cut through a buried copper pipe. We tested across the cut and measured quite a healthy mains voltage with a full 10A of alternating current flowing. This situation could easily have been fatal. The problem was that the primary Neutral wire in the MEN connection of the adjoining property’s switchboard had pulled out of the Neutral link, causing return current to flow in the system Earth and plumbing. The CablePI would have alerted the resident of this issue so that repairs could have been carried out. My son has also been in the electrical contracting game for years and has had many calls to CablePI alerts where faulty circuit Neutrals have needed repairs. T. Ives, Penguin, Tas. Many electronic enthusiasts use ultrasonic cleaning machines as they produce excellent results for most cleaning applications. I recently decided to clean my spectacles in my ultrasonic cleaning machine, using just warm water and dishwashing detergent. This removed the coating on the lenses and left the lenses so badly obscured by blotches that the spectacles were unusable. I took the spectacles to my optical maker and was told never to clean spectacles in an ultrasonic cleaner as damage will occur to the coatings on the lenses. I asked if the lenses could be recoated and was told no, we have to make new lenses. My spectacles are multifocal and cost over $600, so I had to get another pair of spectacles made up in a hurry as I was in trouble, and it cost me big time. Please be aware that advertisements online, in magazines etc promote cleaning spectacles in ultrasonic cleaning machines. I say: do not do it; it is not worth the risk. Other equipment I would never clean in ultrasonic cleaners are watches which may have jewelled bearings cemented in place. The cement can give way, resulting in the jewel breaking off. Ultrasonic cleaning machines are great, but please be aware that spectacles and sensitive instruments/watches should never be cleaned in them. Anthony Rudd, Newport, Vic. Model railway is not a dying hobby I am afraid I must disagree totally with John Crowhurst in his letter (“You’re 20 years too late”, Mailbag, September 2021) when he says that model railways are dying out. Nothing could be further from the truth! It’s gratifying to hear that Mr Crowhurst is interested in model railways, but it seems that he’s been out of the game for a while. The hobby is actually thriving. I could name ten monthly publications worldwide devoted to the hobby just off the top of my head. I have been a moderator on the UK-based N Gauge Forum for nearly 10 years, and we have almost 9000 Australia’s electronics magazine siliconchip.com.au members worldwide in this scale alone. There is also the long-standing Australian Model Railway magazine, regularly in newsagents. Tokyo-based company Kato continues to turn out high-quality model railway locomotives for the Japanese and American markets, and has recently entered the UK arena. The Australian market, while small compared to these, is on a healthy footing. Silicon Chip has long been a supporter and publisher of model railway projects (indeed, Founding Editor Leo Simpson is a self-confessed model railway buff), and long may it continue. Of course, microcontroller platforms such as Arduino have many applications to the hobby, and this in itself has resulted in continued interest in model railways. DCC is also a control system that is really taking off. Sound is also becoming very popular. This magazine has already published projects on these topics, and I look forward to future projects in these fields. Model railways dying out? I don’t think so. They are more popular than ever! George Green, Figtree, NSW. Amateur radio isn’t dead yet either I would like to suggest that VHF/UHF transmissions are not dead, as shown by the ACMA’s list of Registered transmitters in the ACMA Register of Radiocommunications Licences (RRL). The problem is that most communications in the VHF and UHF bands have gone digital. The advantages are that the coverage area increases compared to analog at the same frequency and power. In addition, the base station can select which handsets are switched on by a particular transmission. This keeps the radio quiet unless the user requires the message. It also provides privacy. For those in the outback, two Australian manufacturers make high-frequency transceivers that also use digital transmission and ‘selcall’. Selcall enables connection to the telephone network and slow data transmission. As far as broadcast is concerned, I suggest you look at Public Schedule Data (hfcc.org) for a list of high-frequency broadcasters. Search SWL on the internet, and you will find active high-frequency listening groups. Broadcast is converting to digital as well. Digital Audio Broadcasting has been operating in Adelaide and other capital cities since 2009 and is common in Europe. The website www.drm.org shows the digital broadcast system for all broadcast frequency bands, including high-frequency. For example, Radio New Zealand Pacific has been broadcasting digitally since 2005. You mention increasing noise levels as a problem. I notice that DRM can decode high-quality sound with an RF signal-to-noise ratio of just 10dB. Analog transmissions with that signal to noise ratio are unintelligible. So yes, the days of the analog scanner are numbered because digital transmission has taken over. If all of these older hobbies have gone, what has been the replacement? Learning to program small microprocessors, which have been the subject of projects in this magazine for quite a few years, is one. Alan Hughes, Hamersley, WA. 10 Silicon Chip Australia’s electronics magazine siliconchip.com.au Our capabilities CNC Machining UV Colour Printing Enclosure Customisation Cable Assembly *** Box Build *** System Assembly Ampec Technologies Pty Ltd Australia’s electronics magazine siliconchip.com.au Tel: (02) 8741 5000 Email: sales<at>ampec.com.au Web: www.ampec.com.au FEBRUARY 2021 37 Errors in Bush VTR103 – Vintage Radio, August 2021 Having read the August 2021 Vintage Radio column by Ian Batty on the Bush VTR103 radio (siliconchip.com. au/Article/14999), I was pretty surprised to read the technical description of the VHF mixer circuit. Glancing at the circuit as drawn by Mr Batty, I noticed an error. To check this, I went online but could only find a circuit of the mixer in question, not the entire radio. However, this mixer circuit confirmed my doubts about the drawing in your magazine and the technical explanation. The redrawn circuit on pages 102 & 103 shows the collector of mixer transistor Q2 connected to the local oscillator tuned circuit, thus grounding the 10.7MHz IF signal at 10.7MHz via L5 (70nH). L5’s reactance at this frequency is only 4.6W, much too low to match the output impedance of the mixer. Also, as drawn with the first IF transformer primary L6 and capacitor C11 configured as a series tuned circuit, its low impedance at resonance does not help to match the mixer output. If C11 were moved to the left, to be in series with L5 instead of L6, L5 would be coupled to Q2’s collector via C11, and L6 would be connected directly to the collector of Q2. C11 is then effectively connected across L6 via L5, and L5’s low reactance can be ignored at the intermediate frequency. This forms a parallel-tuned circuit, transferring the entire mixer output to the first IF transformer, where it is needed. The relatively high inductance of L6 (3.15μH) does not affect the functioning of the VHF oscillator, with C11 simply coupling the collector of Q2 to L5 to provide feedback, to ensure oscillation at 105MHz or so. Finally, the purpose of inductor L4 is not to raise the input impedance of Q2 but to lower the emitter impedance at the IF, thus reducing its degenerative effect and increasing the conversion gain. The value of inductor L4 is chosen to be sufficient to allow operation at VHF while effectively decoupling via C6 at 10.7MHz. L4 may increase the input signal slightly, but without C6, it is of no real benefit. Many receivers of this vintage did not employ C6 or L4, Ferguson being a typical example. By the way, the photo of the VHF front end on page 100 also labels the 12 Silicon Chip RF amplifier coil as the antenna coil, a minor error. I always go straight to Ian Batty’s Vintage Radio articles. His writing, draftsmanship and photography are of great credit to him and this magazine. If nothing else, this just goes to show how the inadvertent misplacement of one component can alter the apparent operation of a complex circuit and lead one’s understanding of it to be erroneous. Victor G. Barker, Gorokan, NSW. Ian Batty responds: Thank you, Victor Barker, for your attention to the Bush VTR103 article. I’m pleased that you find my articles to be of a high standard. You are correct about C11 – it should be in series with the CT2/C10/L5 oscillator tuned circuit. I transcribed it incorrectly from the original drawing. The corrected version returns Q2’s collector to ground via the first FM IF transformer primary, L6, making the C11/L6 combination a conventional parallel-tuned circuit, not a seriestuned circuit as I wrongly stated in that article. A corrected version of the drawing and the relevant text has been substituted in the online issue on the Silicon Chip website. You are also correct about the labelling of the photo on p100. The righthand coil is the RF amplifier (load) coil. As to the purpose of L4, as Q2 operates as a common-base amplifier for both local oscillation and conversion, its emitter must be above RF ground. L4’s inductive reactance serves this purpose, while allowing Q2 emitter to connect to supply via the combination-bias emitter resistor R4 with associated bypass capacitor C6. The Philips Data Handbook “Semiconductors and Integrated Circuits, Part 2” from September 1967 has data and an application circuit for the AF124. The Bush FM tuner is very similar to the one shown in the Philips Handbook, with an inductance of Australia’s electronics magazine 0.86μH for L4. This gives a reactance of some 470W at 88MHz, rising to 540W at 100MHz. Considering that the input admittance of the AF114 at 100MHz is some 15mS (equivalent to about 60W), L4’s reactance is high enough for it to have a negligible shunting effect on signals over the tuning range of 88~100MHz. RF amplifier Q1’s load is therefore mainly the input impedance of Q2. At some 60W, the low voltage gain of Q1 (less than three times) makes sense. If, as you say, the purpose of L4 is to lower the emitter impedance at the IF, the circuit would be best without L4, as its omission would reduce Q2’s emitter impedance to the lowest possible value. That would give a gain at 10.7MHz that is essentially Q2’s current gain multiplied by the resonant-circuit impedance of L6/C11, divided by Q2’s input impedance (the classic Av formula). Since Q2 operates as a common-base amplifier for signals both at FM and intermediate frequencies, the effect of emitter degeneration/series current feedback on common-emitter amplifier circuits does not apply. In summary, omitting L4 would allow neither signal injection (via C5), nor positive feedback for oscillation (via C7), as Q2’s emitter would be connected directly to RF ground. So I still believe that my statement that “L4’s high reactance improves the converter stage’s input impedance…” is correct. DIY Electronics Australia lab supply still going after 30+ years My 1987-vintage Electronics Australia power supply, designed by John Clarke, is still my primary workbench supply to this day (pictured below). I built it from an Altronics kit, although I replaced the Earth post with a yellow post and added a 7812 to give a fixed +12V output. Greig Sheridan, SC Sydney, NSW. siliconchip.com.au Design Contest Win $500+ Dick Smith challenges you Win $500 by designing a noughts-and-crosses machine that can beat 14-year old me! Dick Smith has described in his new autobiography how one of the turning points in his life, at age 14, was succesfully building a ‘noughts-and-crosses machine’ (also known as tic-tac-toe) that could play the game as well as anyone. Keep in mind that this was in 1958, when nobody had computers; it was a purely electromechanical device. Email Design to Enter Design your own noughtsand-crosses circuit and send your submission to compo<at> siliconchip.com.au including: a) Your name and address b) Phone number or email address (ideally both) c) A circuit or wiring diagram which clearly shows how the device works d) Evidence that your device can always play a perfect game (it never loses) e) A video and/or supply images and text describing it f) Entries requiring software must include source code The deadline for submissions is the 31st of January 2022. ➠ ➠ Win $500 + Signed Copy of Dick Smith's Autobiography ➠ Four winners to be decided, one each for the following categories: ➊ The simplest noughts-andcrosses playing machine most ingenious noughts➋ The and-crosses playing machine youngest constructor to ➌ The build a working noughts-and- DICK SMITH crosses playing machine most clever noughts-and➍ The crosses playing machine not using any kind of integrated processor The entry we judge overall to be the best will also be featured in our Circuit Notebook column and receive an additional $200. ‘Businessman, adventurer, philanthropist…Di ck Smith is a true Australian legend.’ JOE CITIZEN Conditions of entry Dick Smith writes 1) You must be a resident of Australia or New Zealand 2) One entry per family (Silicon Chip staff and their families are not eligible) 3) Submissions will be confirmed within 7 days. If you do not receive a confirmation of your submission, contact us to verify that we have received it 4) Chance plays no part in determining the winner 5) The judges’ decision is final 6) The winners will be decided by the 3rd of February 2022 and will be notified immediately By 1958 I’d advanced from building crystal radio sets to designing and building what I called a noughts and crosses machine. It really was an early computer. I used second-hand parts from a telephone exchange to build it. It would play noughts and crosses against anyone and no one could beat it. This was a great boost to me, because while I was no good at rote learning and theory, I was fine at practical things. The fact that my mind was capable of working out how to build this complex machine gave me confidence as I left school. Now I just had to find a job. Because this was such a turning point in his life and he’s so enthusiastic about youngsters learning electronics, he’s putting up $2000 of his own money to award to people who can come up with a modern version of his noughts-and-crosses machine. Silicon Chip will judge the entries. Winners will be announced in the March 2022 issue of Silicon Chip magazine and will also be contacted directly for payment information. siliconchip.com.au Australia’s electronics magazine October 2021  13 Detecting Gravitational Waves By Dr David Maddison The confirmation of the existence of gravity waves involved the most sensitive measurements ever made. This article describes the past, present, and future efforts to detect these unimaginably hard-tomeasure (and quite fascinating) phenomena. Illustration Credit: LIGO, NSF, Aurore Simonnet (Sonoma State U.) Source: https://apod.nasa.gov/apod/ap160211.html O ne of Einstein’s many predictions that has been proven correct was the existence of gravitational waves, predicted by Einstein in 1916 and first directly observed on the 14th of September 2015. The idea of gravity as mass distorting space-time was described in Einstein’s General Theory of Relativity, first presented to the Prussian Academy of Sciences in 1915. This theory includes refinements to Newton’s Law of Universal Gravitation. General Relativity is the currently accepted explanation of gravitation, describing gravity as a geometric property of space and time (space-time) in four dimensions – three of space and one of time. There had previously been other attempts to describe gravitational waves, but Einstein was the first to get the concept right. Einstein thought his prediction of the existence of gravity waves was of academic interest only, as he did not believe they could ever be detected 14 Silicon Chip due to being so slight. In 1935, he had second thoughts about the existence of gravitational waves. But the journal he presented his paper to, Physical Review, refused to publish it due to an error. Then in 1957, Richard Feynman said they must be real based on the theory and used his “sticky bead” argument to convince others that they were real. For details on this, see the website at siliconchip.com.au/link/ab9f Explanation of gravity waves Unlike Newton, Einstein did not describe gravity as a force. In General Relativity, space-time is ‘flat’ without matter, but the presence of matter causes space-time to curve, and this distortion is manifest as gravity. It is relatively easy to visualise this by considering a heavy ball placed on a taut rubber sheet or trampoline (see Fig.1). Suppose another ball is in the vicinity of the distortion caused by this object. In that case, it will either rotate Fig.1: a massive object distorts the surrounding space-time, represented by the grid, creating a ‘gravity well’ to which other objects are attracted. They may orbit, bypass or fall into the other object depending on their velocity. Australia’s electronics magazine siliconchip.com.au around (orbit), bypass or fall into the “gravity well” created by the first ball (plus make one of its own), depending upon its velocity. This means that any mass accelerating through space-time also generates gravitational waves analogous to waves on a pond (see Fig.2), with the waves being distortions in space-time. An orbiting object is under constant acceleration in the physics sense, although that does not necessarily mean a change in its speed. Technically, the velocity of an object in a stable orbit is constantly changing while its speed is constant, because the direction of the vector is continually varying, even though its magnitude remains essentially constant. Examples of two bodies under acceleration that generate gravity waves include two massive objects, such as black holes orbiting each other, or massive objects merging such as a black hole or neutron star (see Fig.3, the panel below and siliconchip.com. au/link/ab9t). A stationary (non-accelerating) object does not emit gravitational waves. All accelerating objects with mass, no matter how tiny the mass, emit gravitational waves, but the effect is so small as to not be measurable in any realistic sense. Thus, the observation of gravitational waves is only possible when supermassive objects like black holes and neutron stars orbit or merge. Even the orbit of Jupiter about the Sun does not emit realistically measurable gravitational waves, even though Jupiter is 318 times as massive as Earth. A gravitational wave causes physical dimensions to change as it passes through space, by either stretching or compressing the distance between objects, but the effect is unimaginably tiny. Relevant video and audio links In 2016, University of Western Australia Emeritus Professor David Blair spoke to the ABC about the first discovery of gravitational waves in 2015. You can listen to that program at siliconchip.com.au/link/ab9h Also see the video titled “OzGrav: A new wave of discovery” at https://youtu. be/jMwHppyQiZw Read articles about gravitational waves written by Professor David Blair at https://theconversation.com/profiles/david-blair-4285/articles There is an Australian initiative to explain Einsteinian physics to children, The Einstein-First Project: www.einsteinianphysics.com Fig.2: waves on a pond are a familiar analogy for gravitational waves, although they are (essentially) two-dimensional while gravity waves are threedimensional. Source: www.pexels.com/photo/water-drop-photo-220213/ Even the gravitational waves formed by the collision of two black holes might alter the distance between Earth and the nearest star system Alpha Centauri, 41,343,000,000,000km (4.37 light years) away, by about one part in 1020 or 0.041mm, depending upon how far away the black hole is. That is less than the thickness of human hair. Another way to look at it is that in the LIGO detector we will discuss, the length change is one-thousandth of the width of a proton (subatomic particle). No matter how near or far a black hole might be, the effect is incredibly small. The creation of gravitational waves involves the loss of energy from the originating system, such as by orbital decay (‘inspiral’), merger and ‘ringdown’ (as the union is consolidated) of massive objects like white dwarfs, neutron stars or black holes. Like electromagnetic radiation, such as light or radio waves, the energy carried by gravitational waves follows the inverse square law with distance. That is, if you double the distance, the signal strength is 1 ÷ 4 (1 ÷ 22); if you triple the distance, the strength is 1 ÷ 9 (1 ÷ 32) etc. However, also like electromagnetic radiation, the amplitude of the waves Fig.3: the orbit of two massive objects (in this case, white dwarf stars), leading to the emission of gravitational waves as their orbits decay toward a final merger. This might end in a supernova explosion, as shown in the third panel. These types of gravitational waves would be detectable with a space-borne instrument such as LISA. Source: NASA. siliconchip.com.au Australia’s electronics magazine October 2021  15 Multiple gravity waves detected in January 2021 Two important, independent gravitational wave events were recently published. Both involved the merger of a neutron star and a black hole, and were recorded ten days apart. One event was caught on both LIGOs and Virgo. The other was only picked up by one LIGO detector, as the other was down for maintenance and the signal-to-noise ratio on Virgo was inadequate. The original paper “Observation of Gravitational Waves from Two Neutron Star–Black Hole Coalescences” can be viewed at siliconchip.com.au/link/ab9u diminishes according to an inverse law. So if the distance between the source of a gravitational wave and the detector is doubled, the amplitude is 1/2; if the length is tripled, the amplitude is reduced to 1/3 etc. The original ‘inflation’ of the universe when it rapidly expanded from an infinitesimally small ‘singularity’ is also thought to have generated gravity waves. Still, these would be so small now that it is believed that it will be many decades before the technology exists for these to be detected. They would be similar to the cosmic microwave background radiation (see below) but represent an earlier period, and are referred to as the gravitational wave background. Gravitational wave astronomy Fig.4: this diagram shows the characteristic frequencies and ‘strain’ (dilation of space) caused by the gravity waves of various cosmic events. The coloured bars and black lines show the capabilities of various types of detector. Events below the black lines cannot be detected. Original Source: C. Moore, R. Cole and C. Berry (CC-BY-SA 1.0). Fig.5: the gravity waves originating at the time of the Big Bang should still exist today. The cosmic microwave background is only visible to 379,000 years after the Big Bang. The relic gravitational waves from the Big Bang can penetrate through the dense matter from before then, right up to the instant the universe came into being. Source: NASA. 16 Silicon Chip Australia’s electronics magazine The ability to observe gravitational waves opens up a whole new field of astronomy and physics in general. It could answer questions about the nature and extent of so-called dark matter and dark energy (if they really exist), the gravitational wave “footprint” of the universe at the time of its creation and give a better understanding of the formation of neutron stars, black holes and their mergers. First indirect observation of gravity waves The first indirect evidence for gravitational waves was found in 1974 by R. A. Hulse and J. H. Taylor Jr. They received a Nobel Prize in 1993 for their discovery. Looking at a binary system consisting of a neutron star and a pulsar (see the panel on page 21) called PSR B1913+16, they noticed a decay in the orbital period of 76.5 microseconds per year, and a reduction of orbital radius of 3.5m per year, leading to what will be the final ‘inspiral’ event (coalescence of the two bodies) in 300 million years. The decay of the orbit is due to energy released as gravitational waves, and the amount was in precise agreement with Einstein’s General Theory of Relativity. The amount of power radiated in the form of gravitational waves here is 7.35 x 1024 watts, which is 1.9% of the energy emitted by our Sun in the form of light. Incidentally, the gravitational power radiated from our solar system due to the orbit of the planets about the Sun is about 5kW. siliconchip.com.au Gravitational wave frequencies An important aspect of the observation of gravitational waves is the frequency and ‘strain’ (dilation of space-time) of such waves. Different cosmic events cause gravitational waves of different frequencies and strains, and this determines the type of detector that is appropriate to use. Unfortunately, any one type of detector is not suitable for all events. Some characteristics of various cosmic events and their associated strains, along with specific detector capabilities, are shown in Fig.4. In that figure, any event with properties below the black line is beneath the noise floor of the detector and cannot be detected. Events above the black lines and represented by coloured areas can be detected. Fig.6: an example of what low-frequency ‘stochastic’ gravitational waves might look like, as produced 10-36 to 10-32 seconds after the Big Bang. These cannot be sensed with present detectors. They would sound much like radio static if played as audio. It is hoped that other types of low-frequency signals can be detected with projects such as the IPTA. Source: LIGO. Lowest frequencies There is believed to be evidence of the relic gravitational waves formed at the instance of the Big Bang, when the universe was thought to have sprung into being from an infinitesimally small singularity (see Figs.5 & 6). These are at the lowest frequencies, in the microhertz or nanohertz range or even lower. The microwaves that permeate the cosmos, the ‘cosmic microwave background’ radiation (Fig.7), can be viewed to a point about 379,000 years after the Big Bang. But the matter from before that time is too dense to allow observations of light or microwaves before that, as the microwaves or light energy would have been absorbed. The cosmic microwave background is the farthest we can look back to the beginning of the universe. However, nothing can shield gravitational waves, so these should be visible as the “gravitational wave background” starting at a time close to the universe’s beginning. Still, the effect is so tiny that detection (of the gravitational wave background) is thought to be decades away, At a slightly higher frequency are waves from supermassive black-hole binaries with masses billions of times that of our Sun, presumed to exist at the centres of galaxies, resulting from previous galactic mergers. This is what the International Pulsar Timing Array (IPTA) aims to detect – see Fig.8. siliconchip.com.au Fig.7: a map of the cosmic microwave background radiation, a relic of the time 379,000 years after the creation of the universe. Primordial gravitational waves predate this and may have influenced its structure. As measured in the microwave spectrum, the difference in temperature from the hottest to the coldest points is a mere 200 millionth of a degree. Source: NASA/WMAP Science Team. Fig.8: the gravitational wave spectrum, showing signal sources and relevant detectors (NS in the diagram stands for neutron star). Source: NASA Goddard Space Flight Center. Australia’s electronics magazine October 2021  17 Fig.9: Australia’s Parkes Observatory, a 64m radio telescope participating in the International Pulsar Timing Array (IPTA) to look for gravitational waves. Source: Wikimedia user Diceman Stephen West. The IPTA is a cooperative effort of the European Pulsar Timing Array (EPTA), North American Nanohertz Observatory for Gravitational Waves (NANOGrav), Indian Pulsar Timing Array (InPTA) and Australia’s Parkes Pulsar Timing Array (PPTA) – see Fig.9. As you can imagine, detecting a nanohertz gravitational wave signal can take many years, as 1nHz is only one cycle every 32 years or, for microhertz, one cycle every 11 or so days. However, one would not have to observe a complete cycle. Medium frequencies Medium-frequency gravitational waves of about 0.1mHz (millihertz) to 1Hz are created by inspiral events, where objects with extreme mass ratios (one much more massive than the others) spiral into each other and merge (see Fig.10). This includes massive binary star systems circling each other (see Fig.11); ‘resolvable galactic binaries’, that is, binary star systems within our own galaxy which are not too obscured by noisy signals from other sources, perhaps with Sun-sized stars; massive binary star systems within or outside the galaxy; and Type 1A supernovae (exploding stars). It has been proposed to pick up medium frequency gravitational waves with space-based detectors such as the joint NASA and European Space Agency evolved Laser Interferometer Space Antenna (LISA) scheduled 18 Silicon Chip Fig.10: the expected gravitational wave signal from an ‘inspiral’, resulting in the merger of two black holes. The frequency increases as the two objects get closer and closer, as a spinning ice skater goes faster when they move their arms closer to their body. The gravitational wave amplitude also increases as they move closer to merging. This was the type of event that LIGO first detected. Source: LIGO. for launch in 2034, and the Japanese DECi-hertz Interferometer Gravitational-wave Observatory (or DECIGO). High frequencies High-frequency gravitational waves are much easier to detect than the others, although it is still extremely difficult. They have a frequency of approximately 10Hz to 1kHz, or more. Phenomena that cause these waves include inspiral and merger of binary objects such as neutron stars and black holes and core collapse of supernovae. The first gravitational wave directly observed was in this frequency range. Gravitational wave observatories for this frequency range include LIGO (USA), Virgo (Italy), GEO600 (Germany) and KAGRA (Japan). Attempts to directly observe gravitational waves The main problem with detecting gravitational waves is their tiny magnitude, making their measurement the most challenging of all, as incredibly sensitive instruments are required. The primary detection methods have been resonant mass antennas, laser interferometers and pulsar timing arrays. There are some other methods under development. Resonant mass antennas Resonant mass gravitational wave antennas were the first type of detectors developed. They consist of a large metal mass isolated from vibrations and possibly cooled to a low temperature. They are designed to have a particular resonant frequency, much like a bell or a tuning fork. If a gravitational wave passes through them, they Australia’s electronics magazine should resonate, and that resonance could be amplified and detected. A resonant mass antenna at the University of Western Australia (UWA) called NIOBE consisted of a 1.5-tonne cylindrical niobium bar with a resonant frequency of 710Hz, cooled to 5K (-268°C) with superconducting electromechanical sensors – see Fig.12. This was one of five similar detectors which operated in the 1990s. NIOBE achieved world-record sensitivity. It was used in joint observations with other similar detectors from 1993-1998. This experiment was performed under the leadership of Professor David Blair. Today, it is believed that resonant mass antennas are not sufficiently sensitive to detect anything other than the most powerful gravitational waves. However, there are still two spherical resonant mass antennas in operation, MiniGRAIL (the Netherlands – see Fig.13) and Mario Schenberg (Brazil). The MiniGRAIL consists of a precisely machined 1400kg, 68cm sphere of aluminium-copper alloy cooled to 20mK (thousandths of a degree) above absolute zero, -273°C. It has a resonant frequency of 2.9kHz and a bandwidth of about 230Hz. Its sensitivity is relevant to detecting events such as instabilities in rotating single and binary neutron stars, small black-hole or neutron-star mergers etc. The Brazilian device is similar. Laser interferometers An interferometer is a device that uses the interference pattern of two light beams (or other types of electromagnetic beams) from a common source to measure distances, by siliconchip.com.au Fig.11: a continuous gravitational wave might be generated from two black holes or neutron stars in a stable orbit around each other, or a massive irregular object rotating on its axis (for a neutron star, the irregularity need only be centimetres high). A detector like LIGO could sense such events, but it would need to have its sensitivity increased. Image courtesy: LIGO. examining the interference pattern caused by selective reinforcement or cancellation of the beams when they are combined. When using light waves such as lasers, the distances measured can be extremely small, down to 1/1000th of a subatomic particle’s width! For gravitational wave detection, low-noise, high-sensitivity detectors are required, but these did not become available until the late 1990s. There have been attempts to build suitable interferometers since the 1960s. The operation of a laser interferometer is shown in Fig.14. In regular operation (1), a laser light source in the black box strikes a beam splitter (half-silvered mirror) at an angle, and it is split into the beams shown in blue and red. These beams reflect off the cyan mirrors at the end of the two arms. The beams recombine via the beam splitter. The recombined beams are in phase and create a certain interference pattern, indicated by the purple circle. In (2), a gravitational wave (yellow) passes through the detector, and this changes the length of one or both arms, and thus the interference pattern of the recombined beam (white circle), indicating the presence of a gravitational wave. In reality, the beam travels down each arm 280 times. The overall design of the LIGO Fig.13: the internal mechanism of the MiniGRAIL resonant mass gravitational wave detector, designed and built in the Netherlands. 1 2 Fig.12: a cross-section of the Australian NIOBE detector. It was built around a niobium metal bar weighing 1.5 tonnes. The bar had a resonant frequency of 710Hz, was cooled to 5K (-268°C) and fitted with superconducting electromechanical sensors. siliconchip.com.au Australia’s electronics magazine Fig.14: a simplified diagram showing how interferometric gravitational wave observation works. Any change in the relative lengths of the two arms causes a change in the interference pattern on the detector at the right; constructive interference in case (1) and destructive in case (2). Source: Wikimedia user Cmglee (CC-BY-SA 3.0). October 2021  19 Fig.15: the basic configuration of the LIGO laser interferometer. Original Source: Wikimedia user MOBle. Fig.16: one of the LIGO mirrors. These mirrors are suspended on fine glass fibres and are among the most perfect mirrors ever made. Their stability is the key to the operation of the instrument. There is a video on the mirrors titled “EPISODE 1 LIGO: A DISCOVERY THAT SHOOK THE WORLD” at https:// vimeo.com/203776385 Fig.17: the two 4km-long arms (in a V shape) of the LIGO Hanford Observatory at Richland, Washington, USA. Source: LIGO/Caltech. 20 Silicon Chip Australia’s electronics magazine interferometer is shown in Fig.15. Its design is based on the Michelson interferometer, which has been in use since 1887. LIGO also has light storage arms in the form of a so-called Fabry-Pérot optical resonance cavity, which stores light for about a millisecond before leaving the storage arm to recombine with the other arm at the beam splitter. Laser amplification is achieved in the light storage arm when it is “on resonance” and said to be “locked”, and constructive interference of the laser light occurs. When the laser is locked in this mode, it is extremely sensitive to length changes due to gravitational waves. The “test masses” in the diagram are mirrors that allow a small amount of light transmission. LIGO LIGO (The Laser Interferometer Gravitational-Wave Observatory; www.ligo.org) has a long history of development, funding and politics beyond the scope of this article. It consists of two separate observatories, one in Washington state, USA and the other in Louisiana, about 3000km away or 10ms at the speed of light – see Figs.16 & 17. Two observatories are needed to confirm that any observations are real and enable an estimate of the source of any event detected. Additional instruments elsewhere in the world would make the localisation of an event more accurate. The observatory is operated by Caltech and MIT. When it was first built, it made observations from 2002 until 2010, during which time no gravitational waves were detected. The instrument was then upgraded to the Advanced LIGO, and observations formally began again on the 18th of September, 2015. The first observation of a gravitational wave was confirmed to have been made on the 14th of September 2015, several days before formal observations had begun, although the instrument was still operational for testing before that – see Fig.18 and the video titled “The Sound of Two Black Holes Colliding” at https://youtu.be/ QyDcTbR-kEA Further events were detected on the 26th of December 2015, the 4th of January 2017, the 14th of August 2017 and more since then (Fig.19). Apart from US organisations and funding agencies, some foreign siliconchip.com.au Other Earth-based interferometric detectors Apart from LIGO, other operational interferometric gravitational wave observatories are Virgo (Italy, two 3km arms), GEO600 (Germany, two 600m arms) and KAGRA (Japan, two 3km arms). siliconchip.com.au Hanford, Washington (H1) Livingston, Louisiana (L1) 1.0 0.5 0.0 Strain (10­21) ­0.5 ­1.0 H1 observed L1 observed H1 observed (shifted, inverted) Numerical relativity Reconstructed (wavelet) Reconstructed (template) Numerical relativity Reconstructed (wavelet) Reconstructed (template) Residual Residual 1.0 0.5 0.0 ­0.5 ­1.0 0.5 0.0 ­0.5 512 Normalized amplitude Frequency (Hz) agencies from the UK, Germany and Australia’s Australian Research Council and universities make essential contributions to LIGO. Each LIGO observatory has two 4km-long interferometer arms at right-angles to each other. A laser beam passes up and down each 4km tube, which is under a very high vacuum. This vacuum is one-trillionth that of Earth’s atmosphere, eight times less dense than space, and this is the largest-volume sustained high vacuum on Earth. The beams travel up and down each tube 280 times to increase the effective arm length to 1120km, increasing sensitivity. If a gravitational wave passes through the arms, the local space-time is altered and the length of one or both arms changes depending on the direction and polarisation of the wave. This results in a slight change in the phase of the laser beam arriving at the detector, which shows up as a difference in the interference pattern. The change in length is much less than the wavelength of light, but the interferometer will respond to this fractional change. The observatory has multiple extremely advanced measures to reduce noise and vibration from sources such as earthquakes, vehicles and people walking and even the thermal noise from atoms vibrating in various components. There are ongoing plans to improve the sensitivity of LIGO even further. The more gravitational-wave observatories exist, the more accurately the source can be determined. LIGO had plans to build an observatory in Australia on the site of AIGO (see below), where there is a provision for land for the two required 4km-long arms. Western Australia was a preferred location for the third LIGO observatory for many reasons; however, the Australian Government of 2011 did not commit to funding it, so this observatory will now be built in India instead (see www.ligo.caltech.edu/ page/ligo-india). 256 128 64 32 0.30 0.35 Time (s) 0.40 0.45 0.30 0.35 Time (s) 0.40 0,45 Fig.18: the first observation of gravity waves, signal GW150914 on the 14th of September, 2015, showing the signals received at the two Advanced LIGO detectors in the USA. The difference of 7ms in the arrival of the signal between the two sites reflects the delay taken for the gravitational wave travelling at the speed of light. It is less than the 10ms taken for a straight line because the signal arrived at a 45° angle between the two sites (cosine(45°) ≈ 0.7). Source: B. P. Abbott et al. (LIGO Scientific Collaboration and Virgo Collaboration). Fig.19: a selection of gravitational waves with time-frequency spectrograms above; brighter colours represent a stronger signal. If played back as audio, the signal typically sounds like a chirp. Source: LIGO Scientific Collaboration and Virgo Collaboration/Georgia Tech/S. Ghonge & K. Jani. Cosmic Explorer (cosmicexplorer. org) is a proposed ground-based interferometer with 40km-long arms. The Einstein Telescope is a European observatory proposal under study, to be built underground with 10km long arms, achieving higher sensitivity than LIGO. The optics will also be cooled to -263°C (about 10K). Australia’s electronics magazine There are some other proposals, but they don’t seem to have widespread support at this stage. Space-based interferometric detectors Detectors like LIGO can sense higher frequency gravitational waves, but much longer arms are required to October 2021  21 Fig.20: an artist’s concept of one of the LISA satellites with the laser beam from the distant LISA satellite visible, and small thrusters being fired for station keeping. Source: AEI/MM/ exozet. Fig.21: the proposed arrangement of the three LISA satellites, with arm lengths of 2.5 million kilometres. Source: Max Planck Institute for Gravitational Physics (Albert Einstein Institute) / Milde Marketing Science Communication / Exozet Effects. detect those of medium frequency than can be achieved on Earth. LISA (Laser Interferometer Space Antenna) is intended to be put into space in 2034. It is a joint NASA and ESA (European Space Agency) project, but it is led primarily by the ESA. It will be used to observe such phenomena as mergers of massive black holes at the centres of galaxies, small objects orbiting massive black holes (with an extreme mass ratio) and binary star systems in our galaxy; possibly also gravitational waves from the Big Bang. The detector will be in the form of a Michelson interferometer, just like LIGO, but without the light storage capability. It will have a total of three satellites with two ‘arms’ of 2,500,000km extending from a master satellite, with light travelling to the other satellites through the vacuum of space (see Figs.20 & 21). There will be a free-floating mirror within each satellite so that the mirror is free of forces that the satellite is subject to. The satellite constellation will be in the same orbit as the Earth but trailing it by 50 million kilometres. DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) is a proposed Japanese space-based detector designed to be sensitive to the frequency band 0.1Hz to 10Hz, thus filling the gap of the sensitive bands of LISA and LIGO. It is hoped to launch in 2027. The overall layout will be similar to LIGO, with 1000km-long arms, and it will be placed in Earth orbit, at an altitude of 2000km. Big Bang Observer (BBO) is a proposal from the ESA for four LISAlike triangles (a total of 12 spacecraft) in solar orbit with arms of about 50,000km. Its purpose will be to observe gravitational waves from the Big Bang. Pulsar Timing Arrays Fig.22: how IPTA works. This notto-scale image shows the fabric of space-time represented by the green grid distorted by gravity waves (grey and cloudy), millisecond pulsars (dark spheres) and the Earth. The millisecond pulsars emit spinning radio beams which are monitored. Source: David Champion, Max Planck Institute for Radio Astronomy. 22 Silicon Chip As mentioned above, the International Pulsar Timing Array (IPTA; www.ipta4gw.org) is an international cooperation that involves Australia’s Parkes Observatory. Instead of using 4km-long baselines like Earth-based projects such as LIGO (see below), it uses an array of millisecond pulsars throughout the universe, monitored by a system of radio telescopes – see Fig.22. Millisecond pulsars are extremely fast-spinning neutron stars (see panel) Australia’s electronics magazine that emit highly predictable and stable pulses. These can be used as the basis of a clock. If a gravity wave alters the distance between the pulsar and a radio telescope on Earth, the timing of that pulse will be altered. By monitoring variations in the arrival time of these pulses due to the stretching and compression of spacetime, gravity waves may be detected, and their origin determined. The pulsar frequencies selected are around 100ms (ie, ~10Hz), while the gravity wave frequencies that can be detected are of the order of microhertz and nanohertz. Australia’s contribution Fifty-six Australian scientists were involved in the first observation of gravitational waves, and Australia now has 45 years of experience in the field. Contributions to gravitational wave research continue to come via the Australian Consortium for Interferometric Gravitational Astronomy (www.aciga. org.au) and The Arc Centre Of Excellence For Gravitational Wave Discovery (www.ozgrav.org). Universities involved in these organisations include the ANU, Charles Sturt University, Monash University, Swinburne University, University of Adelaide, University of Melbourne and the UWA. The CSIRO is also involved. As related by Emeritus Professor David Blair (siliconchip.com.au/link/ ab9h), among the contributions made were: • Technology to measure distortions in the laser light waves passing through the mirrors • Technology for aligning the output beams • Technology for preventing the detectors from becoming unstable • Supercomputer-based data analysis to extract signals from the noise Professor Blair also indicated that part of the Australian experience were contributions in: • Learning to make quantum measurements on masses ranging from micrograms to tonnes • Making mirrors precise to atomic dimensions, to reflect light with unsurpassed perfection • Learning how to suppress natural vibrations of atoms due to heat, and larger vibrations from Earthquakes, vehicles and people siliconchip.com.au Neutron stars, pulsars and black holes Fig.23: a simulated image of a neutron star with accretion disk and gravitational lensing. Gravitational lensing occurs when the mass of the body distorts light coming from behind. Source: Wikimedia user Raphael.concorde. A neutron star starts as a star about 10-25 times more massive than our Sun. At the end of its life, it explodes in a supernova and most of its mass is blown away or converted into electromagnetic energy. What remains is the gravitationallycollapsed core of the star, which is incredibly dense and composed only of the subatomic particles known as neutrons; no atoms are present – see Fig.23. A matchbox-sized piece of a neutron star would weigh three billion tonnes, the same amount as a cube • Detection of signals that were one billion times (or more) lower than the ambient vibrations • The programming of supercomputers to mimic the human ability to pick complex sounds from background noise • Learning how to prevent spurious noise from powerful laser lights from affecting detectors He mentioned the following contributions to Advanced LIGO: • Gingin team: vibration-isolation systems, giving the world’s best performance • ANU: length-stabilisation system and technology that uses quantum entanglement to reduce noise in the detector’s laser • University of Adelaide: sensors siliconchip.com.au Fig.24: the features of a pulsar, including its spin axis, magnetic field axis (which does not necessarily correspond to the spin axis) and magnetic field lines. Pulsars are neutron stars with strong magnetic fields. Beams of light are emitted along the magnetic axis, and if it is aligned with Earth, a “lighthouse” effect is seen. There could also be an accretion disc from other matter falling into the pulsar. from the Earth measuring 800 x 800 x 800m. A neutron star has a radius of about 10km, and a mass of about 1.4 times that of our Sun. Some spin several hundred times per second, have magnetic fields and emit beams detectable on Earth, and are known as pulsars (Fig.24 & 25). They are much like a “cosmic lighthouse”. The fastest known pulsar spins 716 times per second. For stars that are sufficiently massive, or neutron stars that accumulate sufficient additional matter to enable errors in the laser to be corrected at the level of 1/20,000 of the wavelength • UWA: the team predicted (and was proven correct) that the laser light in Advanced LIGO would create sounds in the mirrors, which would cause the detectors to become unstable, and went on to develop methods to control these instabilities • Charles Sturt University: detector calibration and characterisation of detection methods • The CSIRO: provision of some of the optical coatings on the Advanced LIGO mirrors There is also a special need for a southern-hemisphere gravitational wave detector. This would allow very Australia’s electronics magazine Fig.25: an image of a pulsar from NASA’s Chandra X-ray Observatory satellite, showing its jet, an outflow of ionised matter along its axis of rotation. such as when the core remnant is 3-4 solar masses or more, it will undergo complete gravitational collapse. Rather than stopping at the stage of neutron star, a black hole will be formed. A black hole has such powerful gravity that not even light can escape, and it will swallow any object, including stars, that come too close. Most galaxies are thought to have a supermassive black hole at their centre, with a mass ranging from 100,000 to one million times that of the Sun (or more). Neutron stars and black holes are the smallest and densest known objects in the universe. Neutron stars, pulsars and black holes can form binary pairs, orbiting each other, in any combination. accurate mapping of the source and greater sensitivity. If the source location were accurately known, radio, X-ray and optical telescopes could also observe the source. Other present contributions include Swinburne’s supercomputer via OzGrav. Australian International Gravitational Observatory AIGO is an Australian gravitational wave facility near Gingin, Western Australia, about one hour from Perth. It is primarily used for developing instrumentation for gravitational wave detection. It has an interferometer with 80m-long arms, and should funding ever become available, sufficient land October 2021  23 Fig.26: the present and future AIGO facilities and other facilities on-site near Gingin, Western Australia. Fig.27: a simplified diagram of the proposed Australian NEMO gravitational wave observatory. PRM is power recycling mirror; BS is beam splitter; ITM is input test mass (mirror); ETM is end test mass (mirror); SRC is signal recycling cavity; and SRM is signal recycling mirror. to build two 4km-long interferometer arms as used by Advanced LIGO (see Fig.26). The site houses the Australian International Gravitational Research Centre and also the Gravity Discovery Centre, which you can visit at gravitycentre. com.au See the video from 2012 titled “AIGO Australian Interferometric Gravitational wave Observatory” at https://youtu.be/BLO1fgkqa6g NEMO The Neutron Star Extreme Matter Observatory (NEMO) is an exciting Australian proposal to build a gravitational wave observatory explicitly designed to observe the merging of neutron stars that form a black hole – see Fig.27. Such mergers are estimated to occur about once every five minutes somewhere in the universe. They involve transforming the nuclear matter of neutron stars into a black hole or singularity, which is essentially the opposite process of the Big Bang, when a singularity transformed into nuclear matter. Such observations would give great insight into what happened in the Big Bang plus other related phenomena. The proposed technology uses a powerful laser and ‘quantum squeezing’ of light to achieve a very high sensitivity at a fraction of the cost of other gravitational wave detectors. The detector is optimised to be most sensitive in the 1-4kHz band of interest for the mergers being studied. For a paper about NEMO – “A kHzband gravitational-wave detector in the global network” – see siliconchip. SC com.au/link/ab9g Things you can do at home You can volunteer to participate in the search for gravity waves and gamma ray and radio pulsars using idle time on your computer with Einstein<at>Home (see Fig.28). This is a global-distributed computing project, and the free software automatically downloads and analyses data from LIGO, GEO600, VIRGO and the Arecibo radio telescope and the Fermi Gamma-Ray Telescope satellite. You might be aware that the Arecibo radio telescope collapsed, but old data sets from it are still being analysed. As of September 2020, 55 radio pulsars and 25 gamma-ray pulsars have been discovered by Einstein<at>Home (see https://einsteinathome.org). You can also participate in Gravity Spy, which helps scientists sort data ‘glitches’ from real gravitational wave signals. This is done by looking at signals and deciding what category they fit into. See www.zooniverse.org/projects/ zooniverse/gravity-spy There is no chance of a hobbyist doing their own gravitational wave observations, but they can observe the cosmic microwave background (CMB) radiaFig.28: the Einstein<at>Home tion. This can be done using old analog TVs, or even modern TVs with an anascreensaver, showing its log reception option. computation status. A small proportion of the noise that can be seen when tuned to an unused channel is attributable to the CMB; similarly, with an FM radio tuned between channels, a small amount of the hiss is from the CMB. You can make measurements of the CMB using a satellite TV and dish according to the description at the following link, but you will probably need access to liquid nitrogen. This is used by some restaurants and bars as well as laboratories – but follow all safety precautions if you obtain some. See https://portia.astrophysik.uni-kiel.de/~koeppen/CMB.pdf 24 Silicon Chip Australia’s electronics magazine siliconchip.com.au Maker Build It Yourself Electronics Centres® Creality® LD-002R Resin 3D Printer SAVERS! Affordable entry level resin printer for fast, strong & smooth prints. . Get creating this October prints! 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NEW! 14.95 23.95 $ ESP32 Wi-Fi & Bluetooth Dev Board Arduino Starter Platform Kit Includes hard to find HDD screws Sale Ends October 31st 2021 T 3062 Fader F5 SAVE 10% 29 $ T 3063 Deoxit D5 High Temperature Polyimide Tape T 2982A 50mm H 8954 Passive $ The ultimate magic ‘fix-it’ sprays n K 8394A Purple n K 8395A Blue n K 8396A Red n K 8397A Black n K 8398A Grey n K 8399A White » Perth: 174 Roe St » Joondalup: 2/182 Winton Rd » Balcatta: 7/58 Erindale Rd » Cannington: 5/1326 Albany Hwy » Midland: 1/212 Gt Eastern Hwy » Myaree: 5A/116 N Lake Rd K 9643 19.95 $ Plug & Header Connection Kit Straight boxed 2.54mm PCB connectors and plugs in 2, 3, 4 and 5 way. Plus crimp pins to suit plug housings. 150pcs total. Victoria 08 9428 2188 08 9428 2166 08 9428 2167 08 9428 2168 08 9428 2169 08 9428 2170 » Springvale: 891 Princes Hwy » Airport West: 5 Dromana Ave 03 9549 2188 03 9549 2121 New South Wales » Auburn: 15 Short St 02 8748 5388 Queensland » Virginia: 1870 Sandgate Rd 07 3441 2810 South Australia » Prospect: 316 Main Nth Rd 08 8164 3466 Please Note: Resellers have to pay the cost of freight & insurance. Therefore the range of stocked products & prices charged by individual resellers may vary from our catalogue. © Altronics 2021. E&OE. Prices stated herein are only valid until date shown or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. *All smartphone devices pictured in this catalogue are for illustration purposes only. Not included with product. B 0091 Find a local reseller at: altronics.com.au/storelocations/dealers/ PRODUCT SHOWCASE ElectroneX rescheduled to April 2022 Following the ongoing situation with COVID-19 in NSW and other states, a decision has been made to reschedule ElectroneX – the Electronics Design & Assembly Expo at Rosehill Gardens from 5-6 April 2022. Noel Gray, Managing Director of show organiser AEE said: We were hopeful that we would be able to stage the show in November but it has become apparent that until the vaccination rates reach a high level and states and business can open up again, we had no choice but to move the event to 2022. Whilst there may be a relaxing of restrictions and travel by November, for the safety and wellbeing of our exhibitors, visitors and staff we consider it was better to take a cautious approach and move the Expo and SMCBA conference to next year. The majority of other Expos in NSW have also had to reschedule to 2022 and it has been a challenging time for the exhibition and event Industry. Last held in Sydney in 2018, the Expo was almost sold out and exhibitors have been very supportive of the move to April next year. ElectroneX is Australia’s major dedicated high-tech event that showcases new technologies, components, contract manufacturing services, manufacturing equipment and supplies and solutions for the electronics and manufacturing industries. Alternating between Melbourne and Sydney, over 1000 senior decision makers attend including design engineers, electronic and general engineers, technical engineers and management that are involved in design, service or utilise electronics in manufacturing. Visitors can register for free to attend the Expo in April next year at www. electronex.com.au Australasian Exhibitions and Events Pty Ltd Suite 11, Pier 35-263 Lorimer St Port Melbourne VIC 3207 Tel: (03) 9676 2133 mail: ngray<at>auexhibitions.com.au Web: www.auexhibitions.com.au Easy-PC PCB design suite version 25 released Number One Systems has announced the release of Easy-PC version 25, with over 25 new technology features based on user requests from professional PCB designers. Easy-PC is packed with time saving features providing everything required to easily create schematics, PCB layout, and manufacturing outputs, making the task of PCB design much quicker. A set of libraries is also included, as is a component search engine with over 15 million parts available to download and use for free. A few of the new enhancements found in version 25 of Easy-PC include: • Differential Pairs with length matching are now supported in Easy-PC. • Vias can be specified as ‘tented’. A tented via is one that is covered with solder resist during the manufacturing stage. • New Design Rule Checks have been added to enhance the checking of the design so that errors can be rectified at an earlier stage. • Resize Shape enables shapes to be replicated and resized. The resizing can be both larger and smaller than the original shape selected. For the additional 25+ Easy-PC enhancements found in version 25, go to https://www.numberone.com/ latest-version Easy-PC with integrated schematic capture and PCB Layout starts at $457. Number One Systems https://numberone.com/ sales<at>numberone.com Rugged silicon carbide power solutions now available at 1700V Microchip has expanded its silicon carbide portfolio with a family of high-efficiency, high-reliability 1700V silicon carbide Mosfets and power modules. Microchip’s 1700V silicon carbide technology is an alternative to silicon IGBTs. This new silicon carbide product family allows engineers to move beyond IGBTs. It uses twolevel topologies with reduced part counts, greater efficiency and simpler control schemes. Without switching limitations, power converters can be significantly reduced in size and siliconchip.com.au weight, freeing up space, or extending the range and operating time of battery-powered commercial vehicles – all at reduced overall system cost. Features include gate oxide stability, excellent avalanche ruggedness and parametric stability. A degradationfree body diode eliminates the need for an external diode with the silicon carbide Mosfet. A short-circuit withstand capability comparable to IGBTs allows them to survive harmful electrical transients. A flatter RDSon curve over junction temperature from 0 to 175°C enables the power system to operate Australia’s electronics magazine at greater stability than other silicon carbide Mosfets that exhibit more sensitivity to temperature. Other Microchip silicon carbide products include schottky barrier diodes at 700V and 1200V, available in bare die and a variety of discrete and power module packages. Microchip Technology Inc. Unit 32, 41 Rawson Street Epping 2121 NSW www.microchip.com October 2021  29 The Tele-com an intercom using analog phones by Greig Sheridan & Ross Herbert Put your old analog telephones to use and build an intercom! Perhaps you have a classic or retro telephone like this red "batphone", or one of the other Bakelite phones with a real bell that generates a fantastic ring sound. Now you can not only hear it again but actually speak to someone at the other end! T echnically, the Tele-com is a ‘private line automatic ringdown unit’, known in the industry as a PLAR. That means that it allows two PSTN telephones to be automatically connected by simply lifting one handset. Colloquially, though, most people would just call it an intercom. Because of this, the device which allows the Tele-com to operate is referred to as the OzPLAR. If you need two-way communication between two nearby locations such as a house and a shed, or a granny flat, or just two rooms in a home, it doesn’t get much more convenient than this. Pick up the phone and the other end rings, then when the other person picks up, you can have a conversation. While the NBN supports analog telephones, we suspect that many people (like us) simply haven’t bothered plugging them in, and now have a box of spare phones. Rather than throw them away, now you can put them to good use. The central OzPLAR unit to which 30 Silicon Chip both telephones are connected (described in this article) performs the following functions; • Provides power to the phones (‘transmission battery feed’). • Detects when a phone is picked up (‘off-hook detection’). • Automatic ringing of an electromagnetic or electronic AC bell. • Ringing uses standard PSTN cadence – Australia/NZ/UK/EU/ USA (long & short) selectable. • The caller hears a ringtone while the called telephone is ringing. • Upon answer, ringing ceases and a speech path is established between the two telephones. • Both telephones must be replaced on-hook after a call before a new connection can be established. • Ring-trip (stopping the ring signal) occurs during either the silent or ringing period, when the called telephone is taken offhook. The design is based entirely on discrete components and logic ICs and has been designed with flexibility in Australia’s electronics magazine mind. The PCB accommodates various alternative parts for the battery feed and the ringing generator. See the features panel for more information. Circuit details The complete circuit of the Telecom is shown in Figs.1 & 2, with Fig.2 having the ring related circuitry (including cadence generation), and Fig.1 the rest. The overall circuit has a few basic jobs: 1. Power the telephones 2. Detect when one is picked up 3. When a call is initiated, cause the called phone to ring and send a ringtone to the calling phone 4. When the other phone is picked up, stop the ringtone and establish voice communications 5. Reset the system when both phones are restored on-hook To achieve this, it consists of multiple interconnected circuit blocks. The left-hand section in Fig.1 is the ‘battery feed’ and loop detect/ring trip circuit, whilst the middle section is the logic engine which detects line status siliconchip.com.au Features of the Tele-com Can be run from 2 x 12V batteries for an off-grid, portable or temporary setup Powered from a 24V DC inline power supply; no mains wiring is involved Support for 48V DC power input (optional) Ring tone is provided to the calling party 20Hz ringing supply for improved ringing of mechanical bells Support for optional bespoke cadence Superior audio performance over longer/ mismatched lines (using an IC-based battery feed) Onboard jumpers (or an external switch) to select AU/NZ/UK, EU or two variations of the USA cadence Choice of inductor-based or solid-state battery feed Crystal-locked source for the cadence generator and ringing inverter requires no adjustments Easy to build using locally-available parts (also readily available overseas) (off-hook/on-hook) and ensures that ringing output occurs only when the first telephone goes off-hook. The far-right section in Fig.1 includes the components required to add an optional polarity reversal on answer (“ROA”) to the calling telephone. Public telephones (PT) connected to Step-by-Step and ARF crossbar switching systems in the now discontinued PSTN used the reversal of the line polarity as the signal to deposit the caller’s money in the coin tin. This option requires 48V operation to work. Off-hook detection & ring trip When a telephone is taken off-hook, current passes through the optocoupler LED associated with the calling telephone (OPTO1 for the one plugged into CON3/4 or OPTO2 for CON5/6). Its output transistor therefore conducts and initiates a series of events to ring the other telephone. The voltage across each optocoupler LED is limited by zener diodes ZD1 & ZD2. At the same time, a low-pass filter siliconchip.com.au This “batphone” is an example of an old analog telephone that could be used with the Tele-com. It’s important to note that not all analog telephones have rotary dials, some have push-button keypads instead; both types will work. Australia’s electronics magazine October 2021  31 Fig.1: the Tele-com circuit, minus the ring and cadence generating circuitry, shown separately in Fig.2. The telephones plug into the sockets at the top and bottom of the left-hand side. The circuitry between them mainly involves supplying current to the phones and ensuring that voice signals pass between them. To the right, we have logic to detect when a phone is picked up and either ring the other phone or ‘answer the call’ if the other has already been picked up. 32 Silicon Chip Australia’s electronics magazine siliconchip.com.au (470W/220μF) bypasses 20Hz ringing signals around the optocoupler LED in the called telephone circuit, to prevent it from conducting during ringing. When the called telephone is taken off-hook to answer, current will flow through the LED in the optocoupler associated with the called telephone, thereby initiating ring trip. Ring trip can take place during the ringing period or the silent period. Initiating a call The following description refers to siliconchip.com.au a call initiated by a telephone connected to CON4 (or CON3) when the board is constructed with the inductorbased battery feed (see below). Note that in this case, the 1μF capacitors in the feed bridge are replaced by links (LK3 & LK4). When the telephone is taken offhook, 24V DC flows through transformer L1 (wired as an inductor) and the 68W resistor, the normally-closed contact of relay RLY1b, the LED in OPTO1, the telephone and back to ground via the normally-closed Australia’s electronics magazine contact of relay RLY1a, the 68W resistor, LK3, and transformer L2 (also wired as an inductor). The off-hook condition detected by OPTO1 results in a high level at the input of schmitt-trigger inverter IC1a. The resulting low output on pin 2 starts the calling process through the combined action of AND gate IC2c and NOR gate IC3a. The Q1 output on pin 1 of J-K master/slave flip-flop IC4a is preset high in the idle state. With both inputs of IC2d now high, its output at pin 11 also goes October 2021  33 high. This feeds into both IC2a and IC2b; however, the low level on IC2b pin 5 prevents RLY1 from operating. Since both inputs of IC2a are high, the output will also be high, which results in RLY2 operating. The RLY2 contacts disconnect the battery feed from the telephone at CON6 (CON5), and instead apply +24V to one leg of the line and the ringing (Vring) signal to the other, causing this telephone to ring. At the same time, the high level at the output of IC2d (pin 11) is inverted by IC1e, sending the Cadence Start line low to enable the crystal oscillator 34 Silicon Chip and the logic controlling the ringing inverter, shown in Fig.2. ‘Cadence’ refers to the timing of the ring bursts and silent periods. 4060 counter IC5 is held in reset at idle, but now commences oscillating. The reset signal is also removed from decade counter IC6, flip-flop IC4b and the cadence generator decade counters IC7 and IC8. Cadence Start is also presented to pin 8 of NOR gate IC10c, which in conjunction with IC7 and IC8, controls the cadence of the AC ringing signal (when set for Australia, producing the traditional ring ring...ring ring... sound). Australia’s electronics magazine The 3.2768MHz crystal oscillator based on X1 has its frequency divided by IC5 to produce 200Hz at its O13 output. This is divided by IC6 to produce the 20Hz alternating signal required for the efficient operation of electromagnetic telephone bells. This signal is also fed to the input of IC1b and IC10a, and in conjunction with the cadence signal at the output of IC1f, enables the ringing inverter. The 20Hz signal at IC6 pin 12 is halved by IC4b to produce the 10Hz clock signal for IC7. The outputs of IC7 go high sequentially, producing a one-second clock signal to feed IC8. siliconchip.com.au Fig.2: the rest of the circuitry which wouldn’t fit on Fig.1. At left is the cadencegenerating circuitry; the outputs of IC7 go high in sequence at 100ms intervals, while those of IC8 go high at one-second intervals. These signals are fed into a series of logic gates depending on the position of jumpers on JP1-JP3 and possibly LK5, resulting in a signal at output pin 10 of IC10c that indicates whether the phone should be ringing or not at any given moment. This is then converted into an AC voltage sufficient to ring a telephone by Mosfets Q6 & Q7 and transformer T1. The outputs of the 4017 decade counters, IC7 and IC8, are encoded in a manner that determines the on-off cadence pattern sent to the ringing inverter – see Fig.3 for details. Regardless of the cadence selection, the instant Cadence Start goes low, the ringing inverter is enabled, and the called telephone commences ringing. When the inputs to NOR gate IC10c are both low, its output is high. This is inverted by IC1f and fed to one input of gates IC10a and IC10b. The second input of these two gates alternates high or low following the 20Hz drive signal, while IC1b ensures that both Mosfet drive signals are complementary (ie, alternately phased). Mosfets Q6 and Q7 alternately switch the 12V DC supply through each primary winding of transformer T1. Due to the step-up ratio, an alternating voltage in the order of 120V peakto-peak is produced in the secondary. PTC thermistor PTC1 provides overcurrent protection, while the 2.2kW resistor provides a degree of clamping of the output voltage, should there be no load connected. While the ringing inverter is operating, the 6.8nF capacitor, normally bypassed by RLY2a, feeds a minute amount of the ringing voltage back to the calling telephone, serving as the ringtone. ► Cadence generation & selection Fig.3: this logic analyser screengrab demonstrates how the cadence generation circuitry works. Ch0 is the Cadence Start line (active-low), Ch1 is the 200Hz square wave at the O13 output of IC5, Ch2 is the 20Hz signal from pin 12 of IC6, Ch3 is the 10Hz signal at TP5 feeding into pin 14 of IC7, and Ch4 is the resulting cadence signal at pin 10 of IC10c (inverted so it is active-high). This shows the AU cadence. siliconchip.com.au Australia’s electronics magazine Jumpers JP1, JP2 and JP3 allow easy selection of the ‘ring-ring-pause’ (400ms on, 200ms off, 400ms on, two seconds off) cadence familiar to Aussies, our Kiwi neighbours and the UK. Other options are for the European cadence (one second on, four seconds off) and the two common versions of the US cadence (two seconds on, four seconds off and one second on, two seconds off), commonly referred to as “US Long” and “US Short” respectively. There are many cadences globally, and they’re documented in the ITU PDF at www.itu.int/ITU-T/inr/forms/ files/tones-0203.pdf Let’s assume the board is set up for AU cadence. When Cadence Start goes low (t=0.0s), the counter in IC6 is released from its reset state and commences counting. At that same instant, the reset signal is removed from IC4b, IC7 & IC8 in readiness for clock ticks to arrive. October 2021  35 ► Having just been released from reset, output O0 of IC7 is high. Pin 12 of NOR gate IC9 is thus high, so its output is low. O0 of IC8 is also high. This feeds to pins 12 and 13 of IC10d via JP2 pins 2 & 3, and thus pin 11 of IC10d is low. For a brief period, the inputs of NOR gate IC3d are both low, so its output is high. IC1d again inverts this to a low signal and this is fed via JP1 pins 1 & 2 to pin 9 of IC10c. The ringing inverter is enabled and it generates the 20Hz alternating voltage to ring the telephone. 100ms later, counter IC7 increments, sending O1 high, then on to O2 & O3. The ringing generation is maintained by linking these outputs to IC9’s inputs, resulting in a continuous on-period of 400ms. Outputs O4 & O5 of IC7 are not connected, so for those two 100ms ticks, IC9 has all low levels on its inputs, its NOR output goes high, so the ringing inverter is disabled for 200ms. For the final 400ms of the first one second of cadence, IC7 outputs O6-O9 are clocked sequentially high, and the ringing inverter is enabled again. At t=1.0s, IC7 resets and IC8 increments, sending its O0 output low. IC10d now prevents further signals from IC7 and IC9 from enabling the ringing inverter for the remaining period of the selected cadence pattern up until the instant output O3 of IC8 goes high, at t=3.0s. This signal, via JP3 pins 2 & 3 and diode D5, resets IC7 & IC8 and the cadence pattern repeats. The US and EU cadences are simpler, as IC9 and its related logic are no longer in play. JP2 instead directs either O0 or O1 of IC8 via IC10d and JP1 to the ringing inverter’s drive logic, thereby enabling the inverter which produces ringing for either one second (EU, US-S), or two seconds (US-L). The silent period for both AU and US-S cadence is terminated after three seconds, when output O3 of IC8 goes high, as explained earlier. The silent period for the EU cadence is terminated after five seconds, via JP3 pins 1 & 2 and diode D5. The silent period for US-L cadence is terminated after six seconds, when output O6 of IC8 goes high, via diode D4. Bespoke cadence creation is beyond the scope of this article, but any combination of 100ms on/off times can be created by mating the required O outputs of IC7 with up to eight inputs of IC9. This is via the pins of JP1-JP3, CON7, CON8 & LK5 as described at https://greiginsydney. com/ozplar-customisation/#bespoke Called party answers (ring trip) The 20Hz ringing voltage is superimposed upon the 24V DC supply. This ever-present DC allows the LED in the optocoupler associated with CON6 (or CON5) to conduct when the handset is lifted to answer a call. That’s regardless of whether it happens during a ringing or silent period. When ringing is present, the LED is prevented from conducting by the low-frequency filter formed by the two 470W resistors and the 220μF NP capacitor. The 10MW resistor provides a slight ‘off’ bias to the base of the optocoupler transistor, while the 56pF capacitor minimises noise pickup in the base connection. The 330kW resistor acts as the emitter load for the optocoupler output transistor. When answered, the optocoupler transistor turns on, and the resulting low at the output of inverter IC1c pin 6 causes NOR gate IC3a pin 3 to go high, thereby resetting flip-flop IC4a, causing its Q1 output to go low and RLY2 to release. The low on IC4a Q1 also causes the Cadence Start line to This is the finished Tele-com PCB without the optional IC-based battery feed, 48V power input components or “polarity reversal on answer” feature. 36 Silicon Chip Australia’s electronics magazine siliconchip.com.au go high, holding all the counters reset and disabling the ringing inverter. The release of RLY2 restores the change-over contacts to normal, thus connecting the called telephone to the battery feed and establishing a speech path between the two telephones. One party clears If we assume the telephone at CON4 (or CON3) hangs up first, the output of OPTO1 goes low and pin 2 of IC1a goes high. IC3a’s output goes low, removing the reset on IC4a, but the flip-flop’s outputs remain unchanged in the absence of any other stimulus. If this telephone again goes off-hook before the other telephone hangs up, the reset on IC4a is once more asserted, but again there is no change of state in its outputs, so the speech path remains connected. Fig.4: this shows the simplest way to power two telephones. Two high impedance inductors allow DC current to supply the transmitter while blocking AC signals through the low resistance of the battery. However, the proportion of the available current to each telephone is dependent upon the length of both lines and a very long line may reduce the current to an unworkable level. Both parties clear If the telephone at CON6 (or CON5) hangs up after the other telephone goes on-hook, both of the inputs to IC2c become high, causing its output to go high, setting the flip-flop in IC4a and restoring all circuitry to the idle state in readiness for the next call. Indicator LED The bi-colour LED (LED1) displays the various phases of a call. At idle, driver transistors Q3 (red) and Q4 (green) are both off, preventing both LEDs from illuminating, despite Q5 being on at this time. When a telephone is being called, both Q3 & Q4 are fully on while Q5 switches alternately on and off in response to the 20Hz LED drive signal, resulting in both red and green LEDs following the ring cadence. When a call is in progress, both telephones are off-hook. The green LED is illuminated due to the high on the output of IC3c forcing Q4 to conduct, while the low on the output of IC3b holds the red LED off. These two gates toggle when only one party has hung up, resulting in a steady red LED to indicate a possible fault condition – see the troubleshooting section below. Feeding power to the phones The Tele-com can be configured to use an inductor-based battery feed, as shown in Fig.4, where a 24V DC supply is fed to both legs of the line siliconchip.com.au Fig.5: this is a more complicated battery feed scheme known as a Stone Bridge which uses virtual inductors to feed DC current to each telephone independently, with capacitors coupling speech signals between them. It can handle very long lines over 1km in length. The virtual inductors are contained in a special IC available via eBay or suppliers of obsolete components via inductors L1 and L2. Since the total available current must be shared between both telephones, the current to each telephone is dependent mainly upon line length, ie, the shortest line gets the most current. The two 1μF capacitors shown on the circuit diagram are omitted and replaced by links in this case. Tests show that good speech is possible with line lengths up to 500m or more in this configuration – quite adequate for most situations. Provision has also been made to replace the inductor-based battery feed with an electronic battery feed using special 8-pin ICs – see Fig.5. The use of two such devices allows the implementation of what’s known as a Stone Bridge, such that the transmitter current supply to the two telephones is separate and determined only by individual line lengths. In Fig.5, the electronic battery feed ICs are depicted as individual inductors designated IC13 and IC14. The electronic battery feed device was designed by AT&T with the part Australia’s electronics magazine number LB1011. It is now obsolete and available only from electronics surplus component suppliers (eg, via eBay). It simulates two separate inductors having very high impedances at voice frequencies. When IC13 and IC14 are installed in place of inductors L1 and L2, the two 1μF capacitors need to be fitted to the board. These capacitors provide speech coupling between the two telephones connected to CON4 (or CON3) and CON6 (or CON5). In this configuration, the maximum current in each telephone circuit is approximately 36mA, so line lengths of several kilometres are possible. Optional reversal on answer To allow this Tele-com to work with with public (coin) telephones that require a line reversal on answer, the polarity of the line to CON6 (or CON5) can be made to reverse when the telephone at CON4 (or CON3) answers a call. This means that the public telephone must be connected to CON6 (or CON5). October 2021  37 Parts List – Tele-com 1 double-sided PCB coded 12110211, 200.5 x 143mm 1 PacTec LH96-200 ABS instrument case or equivalent, 260x180x65mm [Altronics H0476, RS 291-4169, Mouser 616-74213-510-039] 1 set of front & rear 3D-printed panels (size to suit case, see www.thingiverse.com/thing:4922521) 1 24V DC 2A power supply [Altronics M8970D, WES SMP2500-24RLP + ACL104-075] 1 3VA 12+12V PCB-mount mains transformer (T1) [Altronics M7024A ➊] 2 600W:600W isolation transformers ➋ (L1, L2) [Altronics M1000 or Triad TY-305P/306P/400P] 2 Omron G5V-2-H1DC12 12V DC coil relays or equivalent (RLY1, RLY2) [Altronics S4150] 1 3.2768MHz crystal resonator (X1) 1 RXEF030 300mA hold current PTC thermistor (PTC1) [element14 1175861, Mouser 650-RXEF030, Digi-Key RXEF030-ND] 1 10kW 9-pin, 8-element SIL resistor network (RN1; only needed for bespoke cadence) [element14 9356819, Digi-Key 4609X-101-103LF-ND] 1 PCB-mount barrel socket, 2.1/2.5mm inner diameter (CON1) [element14 1854512, RS 805-1699] 3 right-angle two-way pluggable headers (CON2, CON3, CON5) [Jaycar HM3102 + HM3122, Altronics P2592 + P2512, element14 2527811 + 2527762] 2 PCB-mounting 6P6C “RJ12” sockets (CON4, CON6) [Altronics P1425, Jaycar PS1474, Wurth 615006138421] 2 1-pin headers (can be snapped from a longer strip) (CON7, CON8; only needed for bespoke cadence) 3 3-pin headers with shorting blocks (JP1-JP3) 1 2x10-pin header or header socket (LK5; only needed for bespoke cadence) 5 PCB pins (optional; for test points TP1-TP5) 12 M3 x 6mm panhead machine screws 6 6mm-long M3-tapped spacers 6 6mm-long 6G self-tapping screws (PacTec case only) 3 300mm-long 4mm-wide cable ties 5 14-pin DIL IC sockets (optional) 5 16-pin DIL IC sockets (optional) 1 12-pin snappable IC socket strip (optional, for OPTO1-2) ➊ alternatives include RS 504-464, element14 1712727 (Vigortronix VTX-120-003-612), Mouser 553-FS24-100 (Triad FS24-100) & 838-3FD-324 (Tamura 3FD-324), RapidOnline 88-3883 (Vigortronix VTX-120-3803-412) Semiconductors 1 40106B or 74C14 hex inverter IC, DIP-14 (IC1) 1 4081B quad 2-input AND gate IC, DIP-14 (IC2) 2 4001B quad 2-input NOR gate ICs, DIP-14 (IC3, IC10) 1 4027B dual J-K flip-flop IC, DIP-16 (IC4) 1 4060B 14-stage ripple-carry binary counter IC, DIP-16 (IC5) 3 4017B decade counter/divider ICs, DIP-16 (IC6-IC8) 1 4078B 8-input OR/NOR gate IC, DIP-14 (IC9) 2 4N35 optocouplers, DIP-6 (OPTO1, OPTO2) 1 Switchmode 12V 1A regulator ➌ (Pololu D24V10F12 or Aug20; siliconchip.com.au/Article/14533) (REG3) 3 BC547 100mA NPN transistors (Q1-Q3) 2 BC557 100mA PNP transistors (Q4, Q5) 2 IRFZ44N 55V, 49A N-channel Mosfets (Q6, Q7) 1 3-pin bicolour/tricolour (red/green) common cathode 5mm LED (LED1) [Jaycar ZD0252] 38 Silicon Chip 2 3.3V ±5% 1W zener diodes (eg, 1N4728A) (ZD1, ZD2) 1 MBR10100 100V 10A schottky diode, TO-220 (note: not dual [CT] version) (D1) 2 1N4004 400V 1A diodes (D2, D3) 3 1N4148 or equivalent small signal diodes (D4-D6) Capacitors 2 220μF 10V non-polarised (NP/BP) electrolytic [Altronics R6600A or Mouser 667-ECE-A1AN221U] 2 100μF 63V electrolytic 1 1μF 100V MKT 3 100nF X7R ceramic 2 6.8nF 63V MKT 2 56pF 50V NP0/C0G ceramic disc 2 18pF 50V NP0/C0G ceramic disc Resistors (all ¼W 5% metal film unless otherwise stated) 3 10MW 1 2.2kW 3W 5% 2 330W 2 330kW 2 1.5kW 4 68W ➌ 6 10kW 4 470W 2 15W Additional parts for IC-based battery feed (exclude parts marked ➋ above) 2 AT&T/Lucent LB1011 battery feed ICs, DIP-8 (IC13, IC14) [eBay or one of the suppliers listed at www. digipart.com/part/LB1011AB] 2 8-pin DIL IC sockets (optional) 2 1μF 250V MKT capacitors 2 470nF 63V MKT capacitors 2 1kW ¼W 5% resistors 4 180W ¼W 5% resistors ➌ Additional parts for reversal on answer 1 Omron G5V-2-H1 12V DC coil telecom relay or equivalent (RLY3) [Altronics S4150] 1 16-pin DIL IC socket 1 4027B dual J-K flip-flop IC, DIP-16 (IC12) 1 BC547 100mA NPN transistor (Q8) 1 1N4004 400V 1A diode (D7) 1 10kW ¼W 5% resistor Additional parts for 48V DC supply (exclude parts marked ➌ above) 1 Traco TMR 6-4812 48V DC to 12V DC converter (REG1) [Mouser 495-TMR-6-4812] OR 1 Mean Well SKMW06G-12 48V DC to 12V DC converter (REG2) [Mouser 709-SKMW06G-12] 4 390W ½W 5% metal film resistors 4 150W ¼W 5% resistors Resistor Colour Codes Australia’s electronics magazine siliconchip.com.au The Tele-com is recommended to be built into the PacTec LH96-200 enclosure as shown (which can be purchased from RS Components or Mouser). However, mounting holes for the larger Altronics H0476 case are also provided on the PCB. Two flip-flops (IC12a and IC12b) are interconnected to provide this function. With both telephones onhook, both flip-flops are held reset. When either phone goes off-hook, the reset signal is removed. If the telephone connected to CON6 (CON5) is the caller, the output of IC2b presents a high to pin 7 of IC12a, setting this flip-flop. The high on the Q1 output is tied to the J2 input of IC12b, and with J2 high and K2 low, an answer signal from IC4a pin2 will toggle IC12b and set output Q2 high. NPN transistor Q8 then switches on and RLY3 operates, reversing the line polarity of CON6 (CON5). Should the telephone connected to CON4 (CON3) initiate a call, pin 7 of IC12a will not be set, and the J2 input to IC12b will remain low; therefore, the outputs of this flip-flop will not change state when the answer signal from IC4a pin 2 is applied to pin 13 of IC12b. RLY3 will remain in the unoperated condition and the line polarity will not be reversed. Flip-flops IC12a and IC12b will reset siliconchip.com.au only when both telephones are restored on-hook, causing RLY3 to release. Power supply The power supply takes an incoming +24V DC through reverse-polarity protection diode D1, and REG3 supplies +12VDC to power the logic, relays and the ringing inverter. A linear 7812 regulator was tried during the design phase, and replaced with a switchmode equivalent due to excessive heat dissipation, particularly when ringing. For an application where a higher ringing duty cycle is anticipated, or the Tele-com is to be powered from batteries, a switch-mode equivalent should be used instead (eg, our August 2020 design; see siliconchip.com.au/ Article/14533). If a 48V DC supply is to be used, REG3 is omitted and instead, a MeanWell (REG2) or Traco (REG1) DC-DC converter is fitted to accept the higher input voltage and step it down to +12V. Construction The Tele-com project is built on a Australia’s electronics magazine double-sided PCB coded 12110121 that measures 200.5 x 143mm. Start by giving the PCB a quick visual inspection for any obvious damage (although that is quite unusual). Use the PCB overlay diagram, Fig.6, as a reference during construction but note that there are a few different options that affect which components are fitted. If you are planning to build the Telecom with a custom cadence, you will need to cut some tracks on the underside of the board below LK5, separating the rows of pads on either side. Take care when cutting these tracks, as there is very little separation between the two rows of pads. If you plan to add the Reversal on Answer relay RLY3, there are two tracks noted with the word “cut” on the underside of the board – they are also indicated on the component overlay as two short lines joining two of the centre pads below RLY3. In both cases, if cutting, check with a continuity tester to ensure that the tracks have been completely separated before continuing. October 2021  39 The six mounting holes in the board fit mounting posts in the PacTec LH96200 enclosure. If you’re using that case, you can jump to the board assembly. If you’re building into the Altronics H0476 instead, there are two holes near the rear (connector) edge that align with two mounting posts under the board. They’re marked on the component overlay (Fig.6) with “#” marks. Temporarily screw the board to these, as this will align the board correctly within the box, then use the mounting holes in the four corners as a template to drill holes that will support the board. Remove the temporary screws and continue with the assembly. Breaking with tradition, mount the connectors first and ensure these all align and project through the rear panel. The pads for the power and screw connectors have been drilled oversize to provide a little extra wriggle room. Continue with the resistors and other low-profile components like the axial diodes and the crystal. If you’re building it with the inductor-based battery feed, don’t forget to replace the 1μF capacitors to the right-hand side of the transformers with links. Also, if you’re building for a 48V supply, note that the resistors marked on the overlay with an asterisk have different values for 48V. See the parts list for details. You can then install the SIL resistor array if you will be using the custom cadence feature, with its dot at the end shown in Fig.6 and on the PCB silkscreen. Now add the capacitors, starting with the smallest ceramic types and working your way up to the bigger ones. Confirm the polarity of the two electrolytics at the top right of the board and double-check that you have non-polarised electros adjacent to the telephone connectors. Now is also a good time to fit the PTC thermistor. The LED should be soldered at full extension onto the board if it’s to go into the PacTec case; however, you’ll need to add some short flying leads for it to reach the panel in the Altronics case. Add the remaining active components (ICs, regulators, optos and transistors), plus the TO-220 package diode, ensuring all the ICs have pin 1 on the right-hand side, and the TO-220 40 Silicon Chip devices all face left (with their metal tabs to the right). The use of IC sockets is recommended (including the optos), but check that +12V and GND (0V) are present on the correct pins before inserting ICs in their sockets. The optional test point PCB stakes and jumpers can be fitted next, then the relays, which must be orientated as shown in Fig.6. If you need LK5 and haven’t already fitted it, do so now, along with the headers for jumpers JP1-JP3. Follow with the switchmode DC-DC converter (REG1 or REG2) if you will be using a 48V supply. Finally, fit the transformers one by one. Place them, then wrap a cable tie around them firmly before soldering their pins. Take extra care if you’re using Tamura or Triad transformers for T1, as these can go into the board either way, but only one way is correct. Their ‘mains’ winding faces the rear panel connectors. The formers of both have pin numbers moulded into them, with the “1-2-3-4” side being the mains side. Troubleshooting There isn’t much to testing it. Plug in a couple of known-good telephones, apply the appropriate DC voltage and check that it works as expected. If you encounter problems, the nature of the fault should tell you which part of the circuit requires attention, but always start by confirming that the “Vin” voltage (24/48V) and 12V rails are present. You can sometimes isolate faults by touching the top of each IC, where any heat detected indicates a faulty device (CMOS ICs generally don’t produce significant heat unless they are faulty). If you’ve done this before, you probably know to apply a little saliva to your fingertip first to prevent burning yourself. No sidetone You should only connect knowngood telephones to the Tele-com. You should hear ‘sidetone’ if they are working correctly – some amount of your own voice is audible in the receiver. The easiest way to check for sidetone is to gently blow into the transmitter – you should hear the resulting hiss in the receiver. If sidetone is absent in either telephone, start by checking that power is switched on and 24V (48V) is present Australia’s electronics magazine on the board test pins. If the fault is not in the telephones, then check the wiring. If one is working and the other not, follow the circuit with your multimeter and compare between the two channels until the fault reveals itself. Don’t forget to swap the phones as a first check! No ringing First, check that jumpers JP1-JP3 are correctly set for one of the ring cadence patterns – follow the silkscreen legend on the board adjacent to these jumpers to select the desired cadence. If there’s no ringing when the first telephone goes off-hook, check the LED. If the LED is not lit at all, first make sure that it is a common-cathode device and driver transistors Q3, Q4 & Q5 are fitted in their correct positions. Briefly short pins 4 & 5 of OPTO1 or OPTO2. If that brings it to life, there’s most likely a problem with the optocoupler or the components on the LED side of this device. Check that the 3.3V zener cathodes are both facing ‘up’, towards the rear panel. If one of the relays operates when a telephone goes off-hook, that confirms that the main logic engine is functioning correctly. If neither relay operates, this narrows your focus to IC2-IC4 or the 12V rail. If the LED is flashing, this confirms the oscillator and cadence components are working OK, suggesting you should check the Mosfets and transformer. TP4 should have a pulsing 120V (approximately) alternating voltage on it, according to the selected cadence. Check also that the centre tap on the secondary of the transformer has +12V applied. If the LED is lit but not flashing, check with an oscilloscope, logic probe, or the frequency range on your multimeter that TP5 (near the LED) is fluctuating at 10Hz. If 10Hz is present, focus on IC7, IC8, the jumpers LK5, JP1 & JP2, diodes D4, D5 & D6, and the 10kW resistor immediately adjacent to these diodes. If TP5 is not fluctuating at 10Hz, focus on the 3.2768MHz crystal, its loading caps, IC5, IC6 & IC4b. Cadence problems An unexpected cadence indicates an incorrect placement or missing jumper on LK5 or JP1-JP3. Try changing siliconchip.com.au Fig.6: assembly of the Tele-com is straightforward, but there are quite a few different options, some of which involve fitting different parts. So you won’t necessarily install everything shown here. It’s best to work out what you will or won’t be mounting, and the components that might change in value, before you start. As you build the board, be careful to ensure that all the ICs, diodes, LED, optocouplers, transformers, transistors and polarised electrolytic capacitors are orientated correctly, as shown here. If using a 48V DC supply the four 180W resistors in the centre red box, and marked with an asterisk, are replaced with 390W resistors, while the 68W resistors marked with an asterisk become 150W. the jumpers to select an alternative cadence. If correct operation can be achieved when set to the EU or US cadences but not AU/NZ/UK, check that IC7 and IC9 are correctly seated. Check also that RN1 is not reversed and has the correct internal configuration, and one end pin is common. If you’ve cut the tracks under LK5 siliconchip.com.au in anticipation of using a custom cadence, make sure you have inserted links to replace the track segments which have been cut. If problems remain, confirm that TP5 is pulsing at exactly 10Hz, re-check the board for any solder shorting adjacent IC pins and repeat the ‘touch test’ on the tops of the ICs. Australia’s electronics magazine Red LED on idle If both telephones are on-hook and the LED is solid red, there’s most probably a fault on the line or with one of the telephones, causing one not to be correctly seen as on-hook. Unplug each phone in turn to see if the LED extinguishes. If it does, the fault is in the wiring or telephone itself. SC October 2021  41 PART 1: BY PHIL PROSSER Low-cost Two- or Three-Way Active Crossover We are frequently asked for active crossover designs because they can provide significant benefits for driving loudspeakers compared to passive crossovers. They allow you to use a separate amplifier for each driver, avoid the need for large power-carrying inductors and capacitors and provide much closer to ideal performance. This Crossover also suits the Tapped Horn Subwoofer we presented last month. W hen building a really serious speaker system, an active crossover and independent amplifiers for bass, mid and high frequencies should be front and centre in your consideration. The general configuration of a three-way loudspeaker system with an active crossover is shown in Fig.1. While excellent results can be achieved with a conventional passively crossed-over system, passive crossovers significantly limit your driver choices and cabinet design. A versatile, active solution is the best way to get the most out of those expensive drivers. One major advantage of active crossovers is that even when the subwoofer or woofer is driven into clipping, which they often are, the mid and high channels remain unclipped and clean. Another benefit is the ability to use a 24dB per octave crossover on the mid-range driver, reducing the amount of low-frequency signal it must handle below the crossover 42 Silicon Chip point, consequently minimising midrange cone excursion. This is often observable by the mid-range sounding ‘cleaner’. We have published several active crossovers in the past, both simple and complicated. There is often a trade-off between cost and versatility, which this project seeks to address. This project makes no compromise with sound quality and includes new features such as turn-on muting to de-thump the output and a subsonic filter to protect your expensive subwoofer. Our last two published designs are a 3-Way Active Crossover in the September & October 2017 issues (siliconchip. com.au/Series/318) and a DSP Active Crossover and Parametric Equaliser in the May-July 2019 issues (siliconchip. com.au/Series/335). Both are excellent designs but cost significantly more to build than this one, and the DSP version is also quite a bit trickier to build. This version eschews the adjustability of those two designs to keep the Australia’s electronics magazine cost and complexity down. You can still set the crossover points where you need them, but that’s done by selecting resistor and capacitor values, so you can’t change them on the fly. In a domestic setting, a typical subwoofer, mid-range driver and tweeter configuration might use crossover frequencies at say 90Hz and 3kHz. This system might use a subwoofer amplifier of 100W plus mid-range and high-frequency amplifiers of 50W each (per channel). Many readers would have these amplifiers already. Of course, using higher power amplifiers is fine. The mid-range and tweeter channels will be delivering only a few watts of continuous power, but having the headroom of a 50W or 100W amplifier means that massive dynamics can be delivered. We plan to follow this article up with a compact, low-cost amplifier of which you can build five or six into a single housing along with a shared siliconchip.com.au heatsink and power supply. So if you don’t already have the amplifiers but want to build a system with an active crossover, keep an eye out over the next couple of issues! Features The outstanding features of this design are: A multi-way active crossover Because every project is different, you can use the same board to make a two-way or three-way crossover by fitting the parts required and setting a few jumpers. Versatile power supply Excellent results can be achieved using low-cost class-D amplifiers available on the internet, but these mostly require a single DC supply rail. A higher-power Class-AB amplifier can be used for the best results, such as our Ultra-LD series, which provides split rails (±15V DC) for the preamplifier. This Active Crossover can run from either supply type, again by varying a few components and two jumper selections. Crossover frequencies set by passive parts To make the crossover frequency adjustable using a potentiometer would require four-ganged potentiometers, which are expensive and results in a much larger PCB. Using fixed resistors and capacitors reduces cost significantly and avoids the potential of someone turning a dial that they really should not touch! Mono/stereo subwoofer output This gives you a fair bit of flexibility. Even if you have two subwoofer channels, if your crossover frequency is set below 100Hz, you might want to use the mono option (ie, drive both with the same signal). Subsonic Filtering Many subwoofer/bass enclosures use vented, bandpass and sometimes hornloaded arrangements. These systems require frequencies below their range of operation to be filtered out. Failure to do this can lead to over-excursion and/or overheating and failure of the driver. All professional sound systems include this. Turn-on/off delay An active crossover is connected directly to a power amplifier and your expensive speaker drivers. Especially when operating from a single-rail, the crossover must not generate a ‘thump’ siliconchip.com.au Features & Specifications ● Two-way or three-way stereo active crossover ● Can be powered from 24-30V DC, split rail DC (±12-15V) or low-voltage AC (9-12V or 18-24V CT) ● Muting to eliminate switch-on and switch-off transients ● Subsonic filter to protect vented subwoofers and remove unneeded subsonic signals ● Low noise and low distortion; <0.0022% THD+N, 20Hz-20kHz ● Low-cost design using available parts; cheaper than building pairs of passive crossovers. ● Mono or stereo subwoofer output. ● Level controls for all three bands. ● Modest power demands; typically draws around 150mA. AUDIO SIGNAL SOURCES Tuner, Phono, CD, DVD etc. Fig.1: the basic configuration of a hifi system using a three-way active crossover (only one channel shown). Each individual driver in the cabinet has its own amplifier, with the signal being split into three to feed these, each containing signal components over a different range of frequencies to suit the drivers. HIGH FREQUENCY POWER AMPLIFIERS PREAMP WITH SOURCE SELECT & VOLUME CONTROL ACTIVE CROSSOVER MIDRANGE POWER AMPLIFIERS HIGH MIDRANGE LOW FREQUENCY POWER AMPLIFIERS LOW/SUBWOOFER Fig.2: plots of total harmonic distortion plus noise against frequency for each output, with the test frequencies chosen to be well within the bandpass of each. The actual harmonic distortion is extremely low, virtually unmeasurable with our equipment. These readings are basically noise; the subsonic filter adds more noise, hence higher readings with it enabled (note that LF noise is not very audible). Australia’s electronics magazine October 2021  43 Fig.3: the solid coloured lines show the left-to-right channel coupling within each band, while the dashed coloured lines show the right-to-left coupling (it’s basically the same, so the solid lines tend to hide the dashed ones). The thin black lines show the worst-case inter-band coupling. A single-rail DC supply gives slightly worse results for the LF outputs. at power on and off. We have included relays to disconnect the outputs both at switch-on (until it stabilises) and switch-off. Performance We measured the performance of the Active Crossover to characterise distortion, crosstalk (channel separation) and the operation of the output muting. One trick when measuring the performance of a crossover is that the test signals need to be within the passband of each filter, unlike a preamp, where we can do most of our tests at 1kHz. The measurements were made with crossover points at 90Hz and 2.7kHz, so our test frequencies are within each band (ie, not too close to 90Hz Fig.4: the same plot as Fig.3 but with a split rail DC supply (using an AC supply gives the same result). As you can see, this improves the LF results greatly, and the MF results somewhat. However, even with the single DC supply rail, crosstalk is hardly a concern given that it is less than -55dB in the worst case. or 2.7kHz). The results are shown in Figs.2-4. The distortion/noise performance does not vary depending on the supply configuration, but the crosstalk does, so that is plotted in two separate graphs, Figs.3 & 4. The solid coloured lines show the left-to-right channel crosstalk, the dashed lines the right-to-left channel crosstalk (which is generally the same, so mostly hidden under the solid lines). The thin black lines show the worst-case inter-band crosstalk for signals fed into that band (ie, how much of it bleeds into the other band outputs). When powered with a single supply rail, the low frequency-cross talk is not as good as the dual-rail configuration. This is because some of the signal leaks into the virtual ground (described below), which has a higher impedance at low frequencies in the single-supply configuration. That said, the worst-case crosstalk of -60dB at low frequencies, improving to -80dB to -90dB at higher frequencies, is as good as many amplifiers. So it probably doesn’t matter that much, but a dual-rail or AC supply configuration is preferred for optimal performance. Figs.5 & 6 show the Active Crossover in action. In Fig.5, the frequency response of the LF output is shown in green with the subsonic filter bypassed and in blue with it active. The red curve is the MF output and the mauve curve is the HF output. Similarly, Fig.6 shows the LF and Fig.5: frequency response plots for the LF (blue & green), MF Fig.6: similar plots to Fig.5 but with the Crossover (red) and HF (mauve) outputs showing how they cross over. configured for two-way use without the subsonic filter. The green curve is with the subsonic filter bypassed, while the blue curve shows the effect when it is active, rolling off the output steeply below 20Hz. 44 Silicon Chip Australia’s electronics magazine siliconchip.com.au What is a Linkwitz-Riley filter and why use it? A Linkwitz-Riley filter is a fourth-order low-pass or high-pass filter (-24dB/ octave), comprising two second-order (-12dB/octave) Butterworth filters connected in series (hence the alternative name ‘Butterworth-squared’). This is different from a fourth-order Butterworth filter. The corner frequency of a filter is generally defined as the -3dB point. Cascading two filters down by 3dB at the corner frequency gives -6dB at this frequency, rather than the -3dB you would get with a fourth-order filter. The Butterworth configuration gives a perfectly flat passband (assuming ideal components). Consider that the sound from a pair of in-phase speaker drivers (eg, tweeter and mid or mid and woofer) combines via constructive interference. This follows different rules from power summing, with two -6dB signals constructively interfering to give a 0dB result. The roll-off characteristics of the Butterworth filter, combined with the -6dB figure at the crossover frequency, gives a flat summed response across the entire frequency range covered by both drivers (assuming ideal drivers, ideal sound radiation patterns etc). Of course, various factors combine to cause the response to be less than perfectly flat in the real world. But using a Linkwitz-Riley crossover filter arrangement is usually a great starting point and gives excellent results, assuming the drivers are well-matched. MF output frequency responses in blue and red respectively, with the unit configured as a two-way crossover with the subsonic filter bypassed. Operational overview Fig.7 is the block diagram of the Active Crossover. We’ll start by describing how it works as a 3-way crossover, then discuss the 2-way option. The stereo input signals are fed into a pair of filter blocks (blue) which separate out the high frequencies. The treble signals from these blocks go to the level control & buffering section at upper right (blue), then via the de-thump relay to the treble (HF) output connectors at upper right. The mid/low signals from the LOW OUTs of those two blocks are fed to another pair of virtually identical IN Mid/Low range Linkwitz Riley Filter LOW OUT IN HIGH OUT Turn your attention now to the whole circuit, which is spread across Figs.8-10, as it is quite large. Note that there are two ground symbols used LIN HIGH OUT High Frequency Level Controls & Buffers RIN De-thump Relay L LOUT G ROUT G R LOW OUT MF OUTPUTS (LEFT CHANNEL) (LEFT CHANNEL) INPUTS Circuit details HF OUTPUTS 3 or 2 way SELECT High/Mid range Linkwitz Riley Filter filter blocks (green) via two 3-way links. The high-frequency outputs of these blocks are the mid-frequency signals (as the treble has already been removed), and these go to another level control & buffer block and then, via a second relay, to the mid-frequency (MF) outputs. The low-frequency outputs of these green filter blocks contain only the bass signal. This goes through the final level control/buffer section, then optionally to the subsonic high-pass filter to remove any signals below 20Hz (which can be bypassed via the two three-way links at the bottom). Either way, it goes to the LF outputs via the third de-thumping relay. The power supply circuitry provides appropriate regulated DC supply rails to run the rest of the circuitry, plus some discrete logic to control the three de-thumping relays. This is so they disconnect the outputs for the first few seconds of operation and also switch off immediately when power is removed, before the supply rails can decay enough to affect the output signals. L LIN G RIN Mid Frequency Level Controls & Buffers De-thump Relay L LOUT G ROUT G R G R High/Mid range Linkwitz Riley Filter IN Mid/Low range Linkwitz Riley Filter HIGH OUT IN LOW OUT M O NO SUBW HIGH OUT +IN/AC G ND GND –/AC –IN/AC Low Frequency Level Controls & Buffers LOUT ROUT (RIGHT CHANNEL) 3 or 2 way SELECT +/AC RIN LOW OUT (RIGHT CHANNEL) POWER IN (DC or AC) LIN Power Supply & Switch-On/ Off Detection SINGLE/DUAL RAIL JUMPERS +9V or +18V V+ LEFT SUB FILTER OUT/IN Subsonic High Pass Filters 0V or +9V Signal ground –9V or 0V V– Relay drive RIN LIN (CF = 20Hz) LF OUTPUTS De-thump Relay L LOUT G ROUT G RIGHT SUB FILTER IN / O U T R Fig.7: a block diagram showing how the Active Crossover works. The blue-shaded boxes are bypassed for two-way operation, and the two lower links can bypass the red-shaded subsonic filter. The Crossover is based on several fourth-order state variable filters plus a fourth-order Sallen-Key filter. We split off the high-frequency signals first, so they have minimum processing and additional noise, as your ears are very sensitive to this. All outputs include level control and buffering. siliconchip.com.au Australia’s electronics magazine October 2021  45 Fig.8: the main part of the Active Crossover circuit. It looks pretty complicated, but if you refer back to the block diagram (Fig.7), you will see that it consists of repeating patterns (filter blocks etc). Each state variable filter consists of four cascaded op amp stages with feedback from the last to the first. This has the somewhat unusual characteristic that it acts as a low-pass and high-pass filter simultaneously. 46 Silicon Chip Australia’s electronics magazine siliconchip.com.au Changing the subsonic filter frequency The project as presented gives a 20Hz subsonic cutoff, and we recommend that you stick with it. This means 220nF capacitors in Fig.9 (eight arranged in pairs across the centre top of the PCB) and 36kW resistors (eight again, surrounding those capacitors). To change the subsonic filter cutoff frequency to 30Hz, for high-power and PA work, stick with the 220nF capacitors but change those eight 36kW resistors to 24kW. For a 15Hz subsonic cutoff (for the young and brave only!), leave the 220nF capacitors alone but change the eight 36kW resistors to 47kW. siliconchip.com.au Australia’s electronics magazine October 2021  47 throughout. The symbol with three horizontal lines is the power supply ground and is tied to the 0V supply input. The triangular symbol is the signal ground, and it’s tied to power ground for AC or split DC supplies. However, when a single-ended DC supply is used, this triangular symbol connects to a generated half-supply rail (ie, 12V for a 24V DC supply). The input and output signals are AC-coupled to allow for this signal voltage offset throughout the filter chains, regardless of the supply configuration; all that changes is the signal ground voltage. The PCB has stereo inputs, each of which has a 47kW pull down, feeding through a DC blocking capacitor (if you are using a single-rail power supply, you can use polarised electrolytics with “+” toward the level controls for all capacitors). This feeds through a ferrite bead and is bypassed to ground with a 100pF capacitor to reduce susceptibility to RF interference. All operational amplifiers (op amps) are NE5532 dual low-noise types. These have been selected as they deliver excellent performance at a modest cost and are available from many sources. The selection of resistances in the circuit has been made to minimise noise. This has influenced the R and C selections for the filters, with higher resistances only being used for very low frequencies. The crossovers are based on a fourth-order state variable filter configured with a Q of 0.5, forming a Linkwitz-Riley (Butterworth-squared) alignment. The state variable filter is slightly more complicated than the more common Sallen-Key filter. Still, it has the benefit that the crossover frequency is easily calculated and set by four equal resistor and capacitor values. The filter also separates both the high and low-frequency components of the input. Hence, an error in resistor or capacitor values simply results in a shift of the crossover point without otherwise affecting how they combine later. The component values shown are for a low-frequency crossover at about 88Hz and a high-frequency crossover at about 2.7kHz. For the low-frequency point, we have used 12kW and 150nF for R and C. This choice was made as 150nF is a practical maximum size for an MKT film capacitor, and a 12kW is 48 Silicon Chip Table 1 – R & C values for a range of crossover frequencies Desired frequency R Ideal C value Actual C value Actual frequency (nominal) 80Hz 13kW 153nF 150nF 82Hz 88Hz 12kW 151nF 150nF 88Hz 100Hz 11kW 145nF 150nF 96Hz 110Hz 12kW 121nF 120nF 111Hz 120Hz 9.1kW 146nF 150nF 117Hz 150Hz 10kW 106nF 100nF 159Hz 360Hz 4.3kW 103nF 100nF 370Hz 400Hz 4.7kW 85nF 82nF 413Hz 440Hz 4.3kW 84nF 82nF 450Hz 500Hz 4.7kW 68nF 68nF 498Hz 1kHz 4.7kW 34nF 33nF 1026Hz 1.5kHz 4.7kW 23nF 22nF 1539Hz 2kHz 4.3kW 19nF 18nF 2056Hz 2.5kHz 4.3kW 15nF 15nF 2468Hz 2.7kHz 2.7kW 22nF 22nF 2679Hz 3kHz 2.4kW 22nF 22nF 3014Hz 3.3kHz 2.7kW 18nF 18nF 3275Hz How does a state variable filter work? A state variable filter essentially consists of a series of cascaded integrators (similar to high-pass filters) with the output of each feeding back to one of the inputs of the first. In this case, each filter uses four cascaded integrators. A state variable filter has three useful outputs that can be picked off at various points: a low-pass output, high-pass output and bandpass output. The main advantage of a state variable filter (besides providing those various output signals) is that its Q can be precisely controlled via resistance values. As described in Wikipedia, “Its derivation comes from rearranging a high-pass filter’s transfer function, which is the ratio of two quadratic functions. The rearrangement reveals that one signal is the sum of integrated copies of another... By using different states as outputs, different kinds of filters can be produced.” For more details, including the mathematical derivation, see https://w. wiki/3e6K not such a high resistance value that it will compromise noise performance. For the high-frequency section, we have used 2.7kW and 22nF as R and C. The reasoning here is that 2.7kW is low enough to minimise noise, but not so low as to adversely load the op amps, and 22nF is a standard capacitor value. Of course, you will have specific frequencies at which you want to cross your speakers over. Table 1 provides component values for a range of useful frequencies, or you can use the following formula: f = 1 ÷ (2 × π × R × C). We’ll have some tips on how best to assemble the board if you envisage Australia’s electronics magazine fine-tuning your crossover frequency after construction. The final part of the circuit is the subsonic filter. This pair of conventional Sallen-Key filters in series provides a 24dB per octave high-pass filter. We have used these rather than state variable filters as there is no need for both high and low pass outputs, so this approach is simpler and cheaper. We have kept all resistors and capacitors the same value to simplify the parts list and construction procedure. This requires the filter to have a gain of 3.8dB per stage, or a total of 7.7dB. We have reduced this with an input siliconchip.com.au Fig.9: the LF output buffering and level control circuitry (at centre) is the same as for the other two outputs, but the LF output also has the optional subsonic high-pass filter circuitry. JP6 & JP7 select whether the LF output connector gets its signal from before or after the subsonic filters, which also provide some gain. LK1, if jumpered, mixes the L & R signals and sends the resulting mono signal to both LF output channels. attenuator to 6dB, as our experience is that having a bit of extra output available for the sub is handy. If the subsonic filter is bypassed, this gain is not available. We have set a cutoff frequency of 20Hz for this, which is low enough for any sensible purpose. If you really want, you can set this to a lower frequency or bypass it entirely, but if you have anything other than a sealed sub, we strongly advise against this. siliconchip.com.au Suppose you plan to use this crossover in a high-powered system or for PA applications. In that case, we recommend increasing the subsonic filter cutoff frequency to 30Hz, as PA subs almost always roll off at 30Hz or higher. See the panel titled “Changing the subsonic filter frequency” which explains how to do this. The mono function introduces two 1kW resistors in the audio path before the subwoofer level control. Australia’s electronics magazine This allows a jumper to be inserted to convert the LF output to mono. This means that the maximum level on the subwoofer output drops by slightly less than 1dB. This has been taken into account in the subsonic filter and associated attenuator. Power supply The power supply is pretty well standard, although a little complicated as you can configure it in a few October 2021  49 Price Changes For Silicon Chip Magazine From October 31st 2021, the price of Silicon Chip Subscriptions will change as follows: Online (Worldwide) Current Price New Price 6 Months $45 $50 12 Months $85 $95 24 Months $164 $185 Print Only (AUS) Current Price New Price 6 Months $57 $65 12 Months $105 $120 24 Months $202 $230 Print + Online (AUS) Current Price New Price 6 Months $69 $75 12 Months $125 $140 24 Months $240 $265 Print Only (NZ) Current Price New Price 6 Months $61 $80 12 Months $109 $145 24 Months $215 $275 Print + Online (NZ) Current Price New Price 6 Months $73 $90 12 Months $129 $165 24 Months $253 $310 Print Only (RoW) Current Price New Price 6 Months $90 $100 12 Months $160 $195 24 Months $300 $380 Print + Online (RoW) Current Price New Price 6 Months $100 $110 12 Months $180 $215 24 Months $330 $415 All prices are in Australian Dollars The cover price of the October issue onwards will be $11.50 in Australia. The New Zealand cover price will remain the same at $12.90. SILICON CHIP 50 Silicon Chip Parts List – 2/3-Way Active Crossover 1 double-sided PCB coded 01109211, 176 x 117.5mm 1 case (ideally metal; plastic OK if plugpack is used) 1 transformer or plugpack (see text) 3 10kW dual gang 9mm log potentiometers (VR1-VR3) 3 2A 12V DC coil telecom relays (RLY1-RLY3) [eg, Altronics S4130B or S4130C] 4 4-way polarised headers (CON1, CON2, CON4, CON5) 1 3-way mini horizontal terminal block (CON3) 6 3-pin headers with shorting blocks (JP1-JP3, JP5-JP7) 1 2-pin header with shorting block (LK1) 4 4-way polarised header plugs with pins (for CON1, CON2, CON4 & CON5) [Altronics P5474+P5470A, Jaycar HM3404] 2 4mm ferrite beads (L1, L2) 2 16 x 22mm TO-220 PCB-mount heatsinks [eg, Altronics H0650] 2 TO-220 insulation kits (insulating pads & bushes) 15 8-pin DIL sockets (optional, for the op amps) 4 M3-tapped spacers, length to suit # 8 6mm panhead machine screws & shakeproof washers # 1 1m length of twin-core shielded cable # 8 chassis-mount RCA connectors # (eg, four red, four white) 1 AC/DC power connector # (depends on supply used) # parts to suit a typical standalone application; different parts may be required depending on your case, power supply and whether you plan to integrate the Active Crossover with other modules. Semiconductors 15 NE5532 dual low-noise op amps, DIP-8 (IC1-IC6, IC8, IC10-IC17) 1 LM317T adjustable positive linear regulator, TO-220 (REG1) 1 LM337T adjustable negative linear regulator, TO-220 (REG2) 2 BC557 100mA PNP transistors, TO-92 (Q1, Q2) 3 BC547 100mA NPN transistors, TO-92 (Q3-Q5) 1 5.1V 400mW zener diode (ZD1) 8 1N4004 400V 1A diodes (D1, D2, D5, D7-D11) 2 1N4148 signal diodes (D3, D4) Capacitors 2 1000μF 50V electrolytic (16mm diameter) 1 470μF 25V low-ESR electrolytic (10mm diameter) 1 220μF 25V electrolytic (8mm diameter) 12 47μF 50V low-ESR electrolytic (8mm diameter) 2 47μF 50V non-polarised electrolytic (8mm diameter) [eg, Jaycar RY6820] 5 47μF 35V electrolytic (5mm diameter) 4 10μF 35V electrolytic (5mm diameter) 8 220nF 63V MKT 8 150nF 63V MKT ★ 25 100nF 63V MKT 8 22nF 63V MKT ★ 2 100pF 50V C0G/NP0 ceramic disc Resistors (all 1/4W 1% metal film) 3 100kW 10 4.7kW 3 47kW 1 3.6kW (R1 for single-rail operation) 8 36kW ★ 10 2.7kW ★ (only 8 of the 2.7kW change) 4 33kW 2 1.6kW (R1, R2) 12 22kW 8 1kW 8 12kW ★ 2 330W 6 10kW 2 270W 8 7.5kW 6 100W 8 5.6kW ★ change these values to alter the crossover frequencies (90Hz & 2.7kHz with the values given) Australia’s electronics magazine siliconchip.com.au Fig.10: the power supply section at top is the usual rectifier/filter/regulator arrangement to produce split rails from an AC (or dual rail DC) supply. JP1 & JP2 control how the outputs of this section are fed to the rest of the circuitry. This allows a single-rail DC supply of approximately 24V to be fed into CON3 and the circuit will still operate normally (with slightly reduced channel separation). The transistors at bottom switch on the de-thumping output isolation relays a few seconds after power-on, when everything has settled, and switch them off immediately when the supply rails start to collapse. different ways. Diodes D5, D8, D10 & D11 act as a bridge rectifier for an AC input at CON3 or reverse polarity protection for DC. If using AC, preferably a centre-tapped transformer (or two windings in series) should be used, although using a transformer with a single secondary is possible. Two 1000μF capacitors are used for storage/smoothing, and these feed positive and negative adjustable regulators, REG1 and REG2, set up to deliver ±9V. With an AC or split DC supply where both these rails are present, the two grounds mentioned earlier are jumpered together via a shorting block across pins 1 & 2 of JP2. In this case, the -9V rail is the negative rail, with pins 1 & 2 of JP1 shorted. If DC is applied, only the positive siliconchip.com.au regulator section is powered, and resistor R1 is changed to 3.6kW to double the output voltage to 18V. This gives the op amps the same effective supply voltage as with AC or split DC supplies. A virtual ground half-supply rail (ie, about 9V) is generated by a pair of 4.7kW resistors and bypassed with 470μF and 100nF capacitors, and this is connected to all the signal ground points (it’s shorted to power ground by the jumper for AC operation). There are capacitors between the input ground and virtual ground spread through the PCB to ensure it has a low AC impedance to ground at all points. De-thumping The switch-on/off detect circuit Australia’s electronics magazine does two things. First, it provides a startup delay of about five seconds to allow the virtual ground to settle before connecting the outputs. Until this time, the relays short the outputs to ground. This circuit also monitors the virtual ground, and if it deviates more than 0.6V from half of the positive and negative rail, it switches the output off. Note that this requires your supply rails to be within a couple of hundred millivolts of each other in a dual-rail setup. As long as you use 1% resistors to set up adjustable regulators, that should be the case. Otherwise, you will need to shunt one or the other to get a good match. PNP transistors Q1 and Q2 compare the voltage between two equal October 2021  51 Fig.11: without the de-thumping relays, the unit’s outputs produce a large excursion at switch-on. Fig.12: here is the switch-off pulse without the de-thumping relays; pretty bad at 5V swing! This is what the finished Active Crossover PCB looks like if you are building the dual-rail version with the optional subsonic filter. Fig.13: with the de-thumping relays in place, there is no longer a noticeable excursion at switch-on. Fig.14: it is now also similarly wellbehaved at switch-off with the relays added. 52 Silicon Chip voltage dividers, but one has a long time constant created by the 220μF bypass capacitor. These transistors have their collectors joined, creating a single logic output that drives NPN transistor Q4 to discharge a 47μF delay capacitor, thus disabling the output relays at switch-on and switch-off. The specified relays have 12V DC coils. 5.1V zener diode ZD1 performs two functions. Firstly, it sets a reference voltage for Q3/Q5 so the 47μF delay capacitor must charge to about 6V before the relays switch on. Its second function is to drop the 18V total supply voltage to 12V for driving the relays (with a modest drop across NPN driver transistor Q3). To illustrate the need for muting, Australia’s electronics magazine Figs.11 & 12 show the subwoofer output for the single-rail version at switch-on and switch-off (lower trace) without the muting relays. Those excursions would cause massive thumps, possibly damaging the driver! Figs.13 & 14 shows the same measurements with the relays operating. There is still an excursion of a few millivolts, but nothing significant and certainly no hazard to your speaker drivers. That’s all we have space for this month. The following article in our next issue will have all the PCB construction details along with instructions to set up and test the unit, some tips on how to use it and a troubleshooting section. SC siliconchip.com.au 40th ay d h t r i n B o i t a r b e l e C 21 ale r, 20 On S tobe 3 Oc 2 o t r mbe epte 24 S CAN PRINT LARGER MODELS 3 X FASTER PRINTING SPEEDS THAN EARLIER MODELS NEW Anycubic Wash & Cure Plus Machine 4K HIGH RESOLUTION FOR HIGHLY DETAILED PRINTS Rotating curing platform with full 360° curing operation. 405nm UV light. TL4423 JUST 1149 $ Anycubic 500ml Resin NOW 5995 $ Anycubic Resin 3D Printer Arduino® Compatible 4K Larger build volume of 192Lx120Wx245Hmm. 8.9" 4K LCD. Fast printing speed (3 x faster than Learning Kit previous models). More detailed prints compared SAVE $20 Includes UNO board, breadboard, plenty of prototying hardware, modules, components and instruction booklet to get you started. XC3900 NEW 2.4" LCD 2.5" LCD JUST 59 $ ODB-II Engine Code Reader SAVE $99 TL4425 TL4426 TL4427 TL4428 TL4429 JUST 3995 EA VALUED AT $1648 4X CLEARER THAN 1080P! NEW JUST 749 $ JUST 1080p HD DVR Event Camera Accurately identify car problems. 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Ideal for home automation, IoT, lighting control projects, & much more. 10A <at> 250VAC contact rating. XC3804 59 95 SAVE $10 YUN Wi-Fi Shield Allows you to easily program & operate your Arduino project over Wi-Fi & allow it to access the Internet. Contains a tiny Linux computer with Wi-Fi, ethernet & USB. XC4388 ® 40 YEARS HERE'S A SELECTION OF THE MANY ELECTRONICS PRODUCTS WE'VE BEEN SELLING FOR DECADES! JUST 17 $ 95 EA Panel Meters MU45 Moving coil type. 44mm hole. 0-1mA to 0-30V available. QP5010-QP5022 NOW 7 $ NOW $ Smart Wi-Fi Relay Kit NOW Development Board 2495 95 SAVE 15% $ NOW 5295 95 Bluetooth® V4.0 BLE Module Brings Bluetooth 4.0 standards to your Arduino® project. Configurable as master or slave. Provides a serial communication channel. 5V IO & power. XC4382 NOW 995 95 $ SAVE 20% EA SAVE 25% DHT11 Shield for Wi-Fi Mini 433MHz Wireless Modules Create a tiny environmental sensor node. Uses pin D4 for DHT11 interface. Suitable to plug into breadboard for prototyping. 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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. No rainchecks. Savings off Original RRP. Prices and special offers are valid from 24.09.2021 - 23.10.2021. Using Cheap Asian Electronic Modules By Jim Rowe Self-Contained 3.8GHz Digital Attenuator This digitally programmable RF attenuator module can attenuate RF signals from 1MHz to 3.8GHz by 0-31dB in 1dB steps. It doesn’t need to be controlled by an external microcontroller; it has one built in. You control it using four small pushbutton switches, while a tiny OLED screen shows the current setting. I reviewed one of the simpler digitally programmable RF attenuator modules back in the June 2018 issue (siliconchip.com.au/Article/11090). It could be configured either by a separate microcontroller unit (MCU) like a Micromite or Arduino, or a six-way DIP switch. It was based on the Peregrine Semiconductor PE4302 attenuator IC, mounted in the centre of a 33 x 24.5mm PCB without any shielding. Despite that, it turned out to have quite respectable performance up to about 1.5GHz. Above that, attenuation errors tended to grow, but the module was still quite practical for many applications. I recently noticed this new digitally programmed step attenuator for sale. It is only a little larger, but has a built-in MCU with a tiny OLED and some small pushbutton switches for easy attenuation adjustment. I ordered one from Banggood (ID number 1769385; siliconchip.com.au/link/ab8p). At the time of writing, it is priced at about $30.00 plus $6.70 for shipping siliconchip.com.au to Australia. I haven’t been able to find any information regarding its manufacturer, but like most of these modules, it is almost certainly made in China. This module measures 42 x 32 x 22mm overall, not counting the SMA connectors at each end for RF input and output. The digital attenuator section is on a 33 x 22.5mm PCB inside a 42 x 32 x 10mm CNC machined aluminium block which forms the ‘case’. Most of the control section is mounted on a second PCB measuring 42 x 32mm, which forms the top of the case. The 26mm diagonal (38 x 12.5mm) OLED is mounted on top of the second PCB. The PE4302 digital attenuator chip used in the earlier attenuator module was made obsolete in 2018 and is no longer available. This new module uses the HMC472 from Hittite Microwave Corporation, a company acquired by Analog Devices in 2014. The HMC472 is similar to the PE4302 in many ways. It is described as a 6-bit digital step attenuator using Australia’s electronics magazine GaAs MMIC technology, and can provide attenuation from 0dB to 31.5dB in 0.5dB steps for DC to 3.8GHz signals. It comes in a 24-lead Lead Frame SMD package measuring 4 x 4mm. Unlike the PE4302, it runs from 5V DC rather than 3.3V. The insertion loss at the 0dB setting is rated at 1.1-1.2dB below 350MHz, 1.5dB at 2GHz and 1.9dB at 4GHz. I wasn’t able to find a complete circuit for the new module, but I worked out a basic block diagram for it, shown in Fig.1. The HMC472’s RF1 input pin is coupled to the SMA connector via a 1nF capacitor, with its RF2 output pin configured similarly. Apart from various bypass capacitors, that is the whole attenuator section. The control section is based on an STM32F103C8T6 microcontroller. You may have noticed that it controls only five of the six programming lines of the HMC472: V1 to V5. The unused V6 line is the one that controls the 0.5dB attenuator stage inside the HMC472, which explains why this module only provides 1dB steps. October 2021  61 Fig.1: block diagram for the programmable RF attenuator. This module, like many of the others we’ve discussed recently, is controlled by a popular STM32 ARM microcontroller. Presumably, the module designers decided that given the attenuation error rating of the HMC472, ±(0.35dB + 5%), and the difficulty in avoiding further frequency-related errors due to PCB layout etc, there wasn’t much point in providing 0.5dB steps. The user determines the attenuation setting using the three small pushbutton switches (S1-S3), and the current attenuation setting is shown on the OLED module. The MCU drives this via a standard I2C serial interface. When power is first applied, the MCU sets the attenuation to 0dB. To increase the attenuation, you first press S2 (the OK button) and then press S1 (+) until the display shows the attenuation setting you want. Then if you press S2 again, this will be the new setting. To reduce the attenuation, you press S2 once more, then press S3 (-) until the OLED shows the new setting you want, and then press S2 again. It’s pretty straightforward, although the tiny pushbuttons used for S1-S3 do have a small amount of contact bounce. This can sometimes force you to press the + or - button again to correct any accidental ‘overshoot’ before pressing S2 to finalise the change. The CH340E USB-serial interface chip shown in Fig.1 has been provided to allow the attenuation setting to be programmed from a computer. So the mini USB socket is not just for feeding power to the module (controlled by power switch S4), but also to allow external control. Fig.2: a graph of the module’s performance at an attenuation setting of 0dB. This was measured between 100kHz and 4.4GHz, using Signal Hound’s Spike software with a USB-SA44B spectrum analyser and a matching USB-TG44A tracking generator. 62 Silicon Chip Australia’s electronics magazine There’s not a great deal of information provided on external control, but I found a very brief explanation in the “Customer Q&As” section of the Banggood info on the module: The protocol is simple 9600 Baud serial: “wvXXYYn” sets the attenuator to XX.YYdB. “rn” returns the model number. Search GitHub using ATT6000 or emptemp for python code (https://github.com/emptemp/ att6000_control). I tried this, but I didn’t get very far. Using the serial terminal app Tera Term (V4.105) with the virtual com port driver set for 9600 baud, I tried all of the possibilities I could think of to try and get the attenuator module to ‘listen’ to a command like “wv1300n”. I tried sending the command in uppercase instead of lowercase, with and without the “n” at the end, followed by an LF or a CR or a CR-LF, using 8-bit coding or 7-bit coding and so on. But there was no response or reaction from the module, whatever I tried. It stayed stubbornly set for 0dB of attenuation. So I’m not sure about how to control the module from a PC or MCU. Checking it out I measured the performance of the new attenuator module using my Signal Hound USB-SA44B HF-UHF spectrum analyser and its matching USB-TG44A tracking generator, both controlled by the latest version of Signal Hound’s Spike software (V3.5.15) in its SNA (scalar network analysis) mode. I checked the performance of the module at a number of different attenuation settings: 0dB (to see its insertion loss), -5dB, -10dB, -15dB, -20dB, -25dB and -30dB, to get an idea of the module’s overall performance. After examining the results I then checked the response at three further settings: -1dB, -18dB and -31dB. During each of these tests, I saved an image of Spike’s plot of the test results. The first of these (the one for a setting of 0dB) is shown in Fig.2. Spike cannot combine multiple results into a single composite plot, so I assembled one by importing them into CorelDraw and tracing each plot. The result is shown in Fig.3. The uppermost 0dB plot shows the insertion loss of the module over the entire frequency range. It is less than 2dB (as claimed) up to about 1.5GHz, but then wobbles around a bit until it siliconchip.com.au reaches about -2.5dB at 2.64GHz and then -3.5dB at around 2.95GHz. Essentially, the insertion loss remains under 2.0dB over much of the frequency range, apart from some deviations between 1.5GHz and 3.8GHz. Most of the lower plots in Fig.3 have a shape almost identical to that of the top 0dB plot, just separated by the chosen attenuation setting. This is also true for the uppermost blue line, with the attenuator set at -1dB. But notice that above about 2.2GHz, the higher attenuation plots (-20dB and greater) develop a small number of minor bumps and dips. These are very apparent in the -30dB plot, for example, and also in the blue -31dB plot just below it. I suspect that many of these minor variations are due to small resonances inside the HMC472 chip and its surrounding tracks on the attenuator PCB. There might also be standing waves inside the attenuator box at specific frequencies. These plots reveal that the attenuator’s performance relative to its insertion loss is quite respectable, at least for frequencies up to about 1.5GHz and settings up to around -20dB. But the errors increase above 1.5GHz and with levels above -20dB. This attenuator would still have many practical uses above 1.5GHz and settings over -20dB, either if the exact amount of attenuation at a given frequency is not critical, or if you use the plots of Fig.3 to correct for the errors. The middle blue plot in Fig.3, for a setting of -18dB, was to see if setting the attenuator to -18dB would give an actual attenuation of -20dB over as much of the frequency range as possible. This worked for frequencies around 880MHz and 3.8GHz, but the overall shape of the plot was unchanged and still gave significant deviations both less than and greater than the desired -20dB figure. The side view of the attenuator module shows the control switches, and the very tight spacing between the RF and USB power connectors on the right. This photo is shown at approximately 150% scale for clarity. Another is that the RF output SMA connector and the mini USB power connector are too close together, so you have to unplug the USB cable to connect or disconnect an SMA cable to the RF output just below it. You also have to adjust the SMA connector’s outer hex sleeve so that a flat is uppermost; otherwise, you won’t be able to reconnect the USB cable. Before I finished writing this review, I went onto the Banggood website to check on the price of this module. I was surprised to see that a larger and apparently better module had become available (ID 1648810; siliconchip. com.au/link/ab8r). This newer attenuator module is advertised as having a frequency range of LF to 6GHz, an attenuation range of 0-31.75dB in steps of 0.25dB and an insertion loss of less than 1.5dB (but with the qualification that “it will be a little larger” at the high-frequency end). Currently, they are advertising it for $51.80, plus $6.70 for postage to Australia. So it costs nearly double that of the module I’ve reviewed here, but it might turn out to be worth it. I suspect it is based on the Analog Devices HMC1119, which has a range of 100MHz to 6.0GHz, seven control bits to give a setting range from 0 to 31.75dB in 0.25dB steps and a specified insertion loss of 1.3dB at 2.0GHz. I am planning to order one of these and SC write it up when it arrives. Conclusions Overall, this new attenuator module is reasonably good value for money. It is suitable for a fairly wide range of applications, especially if you use the curves of Fig.3 to correct for the inevitable attenuation errors. But it does have a few shortcomings. For example, the module might not be controllable from a PC, Arduino or Micromite. siliconchip.com.au Fig.3: following on from Fig.2, this is the combined plot of testing the module at various attenuation settings from 0dB to -30dB in 5dB steps, and then three extra tests at -1dB, -18dB and -31dB. Australia’s electronics magazine October 2021  63 SMD Test Tweezers By Tim Blythman This clever little device is made from just 11 components. Yet it can measure the values of many SMD resistors and capacitors, plus show diode and LED orientations and measure their forward voltages. It’s quick and easy to use, and is powered by an onboard button cell, with a high-contrast OLED screen to show the readings. W orking with SMD parts can be tricky. Reading component markings can be a strain on the eyes, if the component is even marked! Devices like SMD capacitors are totally anonymous and, once removed from their packaging, almost impossible to tell apart. These SMD Test Tweezers make it easier by telling you all about a component by simply picking it up. In some cases, these Tweezers can also measure the properties of a component once it has been soldered to a board (although, depending on the circuit configuration, sometimes the readings will not be accurate). As time passes, fewer electronic parts are available in through-hole variants and increasingly manufacturers are building products mostly or entirely from SMDs. They are smaller and cheaper than through-hole parts, can be mounted on both sides of a board (often with internal traces running underneath) and are also less sensitive to shock and vibration. Of course, while parts being smaller can be advantageous, it also presents problems when working with them. Certain tools, such as tweezers and a magnifier, are indispensable. Once you’ve had a chance to try out our SMD Test Tweezers, we think you will be adding them to your bag of SMD tricks! The tweezers SMD parts are very awkward to read with a multimeter. On many occasions, we’ve been pressing multimeter Features & Specifications ● ● ● ● ● ● ● ● ● ● 64 Identifies and measures resistors, capacitors, diodes & LEDs Compact OLED display readout Runs from a single lithium coin cell, around five years of standby life Auto power on and off Displays own cell voltage when no component is connected Can measure components in-circuit under some circumstances Can perform thousands of measurements before the cell is exhausted Resistance measurements: 10W to 1MW Diode measurements: polarity and forward voltage, up to about 3V Capacitance measurements: 1nF to 10μF Silicon Chip Australia’s electronics magazine probes into the ends of an SMD part, trying to get a reading, only for it to fly off and never be found again. Tweezers provide a much more natural way to do this, and as you don’t need to apply much pressure, there is less chance of the part taking flight. Even better, since tweezers are a convenient way to pick up and handle such parts, if we incorporate the measuring tool into the tweezers, it can tell you what part you are handling while you are in the process of placing it on the board. The SMD Test Tweezers measure whatever component is present between its tips, so there are no extra fiddly movements to make. You pick up the part, and the screen displays its assessment. The Tweezers automatically detect the difference between resistors, capacitors and diodes, including many LEDs. With a maximum applied current of 0.3mA at 3V, there’s virtually no chance of causing damage. The Tweezers can measure resistances from around 10W to 1MW and capacitances from 1nF to 10μF. These ranges are slightly limited, but increasing them would significantly complicate the design, and a large percentage of SMD components fall within those ranges. siliconchip.com.au The Tweezers also check diode polarity and forward voltage. If an LED is picked up, it will also be illuminated dimly so that you can check the colour. The forward voltage measurement is limited by the 3V available from the small coin cell that powers it. We’ve got no doubt that this tool will find much use in the hands of even our most SMD-savvy readers. Design We set out to make this tool compact, so it uses a tiny 0.49in (12.5mm) diagonal OLED screen. This is the same module we used in the Shirt Pocket Audio DDS Oscillator in the September 2020 issue (siliconchip. com.au/Article/14563) We’re also using a small 8-pin microcontroller, a PIC12F1572 in the SOIC package. We explained why we chose this out of all the 8-pin PICs in the November 2020 issue (on page 83; siliconchip.com.au/Article/14648). Suffice to say that it is a compact and capable part that puts some older 8-pin PICs to shame. And it’s cheap too. The design uses one small PCB to house the main operating parts, including the microcontroller, while another pair of PCBs form the arms. We added some custom brass tips to our prototype, but this is not absolutely necessary. Another option is to purchase premade tweezer test leads that can be combined with the main PCB to give a similar result. Fig.1: the Tweezers circuit is remarkably simple; it uses just one resistor and three microcontroller pins to perform all its tests. An I2C OLED display keeps the pin count within the limits of the tiny 8-pin microcontroller. Once the OLED screen is fitted, it will be tricky to access these parts, so check that everything is as it should be before proceeding further. With the four components fitted to the PCB, it should look something like this. Circuit details The complete circuit for the Tweezers is shown in Fig.1, and it is extraordinarily simple. The test functions are provided by a 10kW resistor connected between pins 2 and 5 of IC1. Pin 5 also connects to one of the Tweezer arms and thus to the device under test (DUT). The other Tweezer arm connects to IC1’s pin 3. All the tests are done by placing different voltages on pins 2 and 3, then using the micro’s internal ADC (analog-to-digital) converter to measure the voltage on pin 5 relative to the cell voltage. The cell voltage is also measured by using it as a reference to measure the micro’s internal 1.024V reference. CON2 is a 4-pin header that connects to the OLED module. This uses an I2C serial interface which is provided by pins 6 and 7 of IC1. The I2C siliconchip.com.au pull-up resistors are fitted to the OLED module, so they are not needed in our circuit. The PIC12F1572 does not have a hardware I2C peripheral, so these pins are driven ‘manually’ by the software. We’ve chosen pins 6 and 7 so that if IC1 needs to be programmed, it can be done before the OLED module is fitted, which would otherwise interfere with the programming signals. Microcontroller IC1 is powered by coin cell BAT1, which is bypassed by a 100nF capacitor. IC1’s MCLR pin is pulled up to its supply voltage by a 10kW resistor so that it operates normally as long as power is applied. CON1 is an in-circuit serial programming (ICSP) header, with its pins connecting to IC1’s pins 4, 1, 8, Australia’s electronics magazine 7 and 6 respectively. You can use it to program IC1 in-circuit if needed. That is not necessary if you purchase a pre-programmed PIC chip. Component sensing The IOTOP and IOBOT designations on the schematic denote the normal IO states of these pins. When idle, pin 2 is pulled high and pin 3 is pulled low. This matches the designations of CON+ and CON-. On each measurement cycle, IC1 measures its internal 1.024V reference relative to its supply rails, and calculates the cell voltage based on this. This might be used later to calculate diode forward voltages; if no component is detected, the cell voltage is displayed. October 2021  65 The next test is to see if a capacitor is present. Pin 2 is taken low, and a series of samples are taken of the voltage at pin 5, until pin 5 is below half the cell voltage, or 255 samples have been taken. If IC1 doesn’t see the voltage fall like a capacitor discharging, it reports that it does not identify a capacitor. This can also happen if the capacitance is too low (which causes the voltage to drop faster than IC1 can make its measurements) or too high (which causes the voltage to not change enough over the sample period). The capacitance is calculated based on the voltage drop and the time taken, although an approximation is used to avoid the computationally-expensive log function; our code comes within a handful of bytes of filling the available program space. The accuracy of the approximation is only significant at values near the upper measurement limit. Given that many capacitors are only specified to within 20%, this is sufficient for most purposes and will be adequate to tell components apart unless they are very close in value. The capacitance test is done first as it means that the time since the last sample can be used to ensure that the capacitor is as close to fully charged as possible. Note that you should not connect a charged capacitor to the Tweezers (or any similar meter). If it is charged to more than a few volts when it is connected, or the polarity is reversed, it could easily damage microcontroller IC1. Even if it doesn’t, it will probably not be measured correctly. If a capacitor is not detected, then the idle state is restored for 200μs (to allow the voltage to settle). The micro then takes a measurement of its pin 5 voltage, flips the polarity for another 200μs, takes another measurement and then flips the polarity back. The algorithm averages 16 samples at each polarity to improve accuracy. Fig.2: this shows the various ways that the Tweezers measure component values. Resistance is measured using the well-known resistance divider formula, while the diode test measures the voltage across the device in both directions. Capacitance measurement is based on the change in voltage over a time interval when discharged via the known resistance. There’s not much to see on the back of the Tweezers, but note that one arm, the OLED header (CON2) and the cell holder (BAT1) are all quite close together. Double-check for short circuits before fitting the coin cell. 66 Silicon Chip Australia’s electronics magazine Every second raw ADC measurement is adjusted to account for the fact that it was taken with reversed polarity. If the two voltage measurements are close, then the part is assumed to be a resistor and the value is reported according to the voltage divider formula (see Fig.2). If one value is close to full rail and one value is not, then the part is probably a diode of some sort, and the forward voltage and direction are reported. This can include LEDs, silicon and schottky diodes. The LED portion of phototransistors and opto-isolators should also show a diode reading. Bi-colour LEDs and other diode networks may not be detected, as they will conduct and not appear open-circuit in the reverse direction. If you’re clever, you can probably identify bipolar transistors by connecting the tweezers across their suspected base & emitter pins and identifying the junction polarity; it should be detected like a diode. LEDs connected with their anodes to CON+ and cathodes to CON- will be forward-biased by the idle current and supplied with a few hundred microamps of current, which should be enough to light them dimly and indicate that they are working. The Test current is quite low due to the 10kW resistor, no more than around 300μA. Thus the forward voltage indicated may be a bit lower than what you might expect (eg, by reading the data sheet). For example, silicon diodes measure about 0.5-0.6V. Once determined, the part type and value (or cell voltage) is displayed simply as a number with the appropriate units and multiplier; to differentiate the cell voltage from the diode voltage, a diode symbol is shown with polarity matching the part in relation to the Tweezer probes. After five seconds of no part being detected, the OLED is put into a lowpower mode, pin 5 is enabled as an interrupt source, and the microcontroller goes into sleep mode. You can wake up the micro by simply touching the tweezer probes together, which changes the pin state. So you can see how such a simple circuit can perform various tests to detect and measure a range of components. Fig.2 shows how these algorithms work in a bit more detail. When the OLED is active, current siliconchip.com.au consumption is around 4mA. This drops to 5μA when the microcontroller is sleeping, and the OLED is shut down. Thus, the cell life will depend mainly on the time the Tweezers are actually used. A typical CR2032 coin cell has a capacity of 220mAh, giving a standby life of around five years, which is good considering a coin cell has a typical ‘shelf life’ of 10 years. We will be selling a kit for this project for $35 (SC5934). It includes all components, except the cell & brass tips. See page 106 for details. Construction If you haven’t already jumped into working with SMD parts, you’re going to start now because we’ve designed the SMD Test Tweezers with SMD components. Use the top and bottom PCB overlay diagrams shown in Fig.3 as a guide during construction. The main part of the SMD Tweezers is built on a PCB coded 04106211 that measures 28 x 26mm. We recommend using solder flux (ideally paste, although a liquid flux pen is better than nothing), a finetipped adjustable iron, solder wicking braid and a magnifier. We also suggest using a pair of tweezers. Since flux can generate smoke when heated, you should work somewhere with good ventilation. Also, check if your flux has a recommended cleaning solution; in a pinch, isopropyl alcohol is a good all-round substitute, with methylated spirits usually doing an acceptable job. Start by securing the PCB to your work surface with the component side facing up. If you don’t have a PCB vice or holder, use some Blu-Tack to stick it to your desk. Apply flux to the pads for the SMD components, then hold IC1 in place. If all the leads are inside their pads, then We’ve left our Tweezers bare to show the construction details, but you might like to cover the main PCB with a short piece of wide heatshrink. This will also serve to hold the coin cell in place. that is fine. IC1 should have a small dot marking pin 1; ensure that this is at the end closest to the 100nF capacitor as marked on the PCB. Clean the tip of your iron and apply a small amount of fresh solder. Then touch the iron to one corner pin of IC1. This should cause the solder to flow onto the lead. If the part looks to be flat against the PCB and still within all the pads, then solder the remaining leads by touching the iron to them. You can add more solder to the iron if needed, and more flux can help too. The only problems with using too much flux are that it will generate more smoke and take a bit longer to clean up. Otherwise, more is generally better. If you find that you have bridged any pins, then it’s easiest to solder the remaining pins before fixing this, as it will help keep the IC in the correct place. Then apply more flux, press the braid against the bridged pins with your soldering iron, and gently slide the braid away once it draws up the excess solder. Inspect the pins with a magnifier before proceeding, and repeat any of the above steps if necessary. You might need to clean up any residual flux if it impedes your view between the pins. The remaining parts can be soldered similarly, with the difference being that none are polarised, and they all have much larger leads and pads. Place the sole capacitor next; it will probably be the only part without markings. Solder one lead, check for correct positioning within the pads and against the PCB, then solder the other lead. Retouch the first lead if necessary. Then fit the resistors; they are both the same value. They aren’t polarised, but it’s good practice to orientate the markings to match the text on the PCB to help with troubleshooting. Flip the PCB over to mount the cell holder. A similar soldering technique will work for the cell holder, with the Fig.3: despite only a handful of components being present, we have used both sides of the PCB. One advantage of SMD components over through-hole parts is that it’s much easier to have parts on both sides without concern over where the leads go. Keep an eye on IC1’s orientation; once it’s fitted, the rest of the assembly is quite straightforward. siliconchip.com.au Australia’s electronics magazine October 2021  67 Fig.4: there are no components mounted on the arm PCBs; they are basically just flexible conductors that are soldered to the main PCB and clamp the DUT at the other ends. difference being that it is a bit larger, so it will need more heat. Turn your iron up if it is adjustable. Place the cell holder, ensuring that the opening faces towards the curved end of the PCB. If it looks like you might not be able to get the cell in or out, then it is probably the wrong way around. Apply some flux and tack one lead. Check that all is aligned correctly, then solder the other. You can then retouch the first pin if needed. That completes the surface-mounted parts, and this is a good point at which to clean off the residual flux. Because many flux cleaners are flammable solvents, you should allow the PCB to dry thoroughly after this step. If you have a blank microcontroller, now is a good time to program it. Do it before installing the OLED module, as this can interfere with programming when plugged in. Programming IC1 You can skip over this section if you have a pre-programmed microcontroller, which will be the case if you have purchased it from the Silicon Chip Online Shop. Otherwise, you’ll need a PICkit 3 or PICkit 4 programmer to program this chip, plus the MPLAB X IPE (integrated programming environment) software, a free download from the Microchip website (usually bundled with the MPLAB X IDE). You can also use a Snap programmer if you modify it according to the instructions on p69 of our June 2021 issue (see siliconchip.com.au/Article/ 14889). This is necessary as the Snap programmer cannot supply power otherwise (or you could figure out another way to temporarily apply power to the micro during programming). While it is possible to solder a programming header to the Tweezers PCB, since it will only be used once and would get in the way after that, we prefer to use gentle force to hold the header in place against the pads during programming. Select the PIC12F1572 as the target part in the IPE, then open the 0410621A.HEX file. After that, simply press the Program button to start the process (start to apply pressure to hold the header pins to the PCB just before you do that). If you get the ‘Programming/Verify complete’ message, then programming has completed successfully. Otherwise, try again. Detach the programmer before moving on to the next step. Completion If you want to add metal tips to your Tweezer arms (made from PCBs coded 04106212 measuring 100 x 8mm), it is easier to do so before fitting them to the Tweezers. Cut pieces of brass strip roughly to size. The pieces can be fine trimmed to matching lengths once the Tweezers have been assembled. Parts List – SMD Test Tweezers 1 double-sided PCB coded 04106211, 28 x 26mm (main PCB) 2 double-sided PCBs coded 04106212, 100 x 8mm (Tweezer arms) 1 PIC12F1572-I/SN or PIC12F1572-E/SN 8-bit microcontroller programmed with 0410621A.HEX, SOIC-8 (IC1) 1 0.49in 64x32 OLED module (Silicon Chip Online Shop Cat SC5602) 1 surface-mount coin cell holder (BAT1) [Digi-key BAT-HLD-001-ND, Mouser 712-BAT-HLD-001 or similar] 1 CR2032 or CR2025 lithium button cell 1 5-pin right-angle male pin header (CON1; optional, needed for programming IC1 only) 1 100nF SMD 50V X7R ceramic capacitor, 3216/M1206 size [Altronics R9935] 2 10kW 1% SMD resistor, 3216/M1206 size [Altronics R8188] 2 15 x 2mm short pieces of thin (eg, 1mm) brass sheet for Tweezer tips (optional) 1 40mm length of 30mm diameter clear heatshrink tubing (optional; see text) 2 100mm lengths of 10mm diameter heatshrink tubing (optional; see text) 68 Silicon Chip Australia’s electronics magazine Solder one strip to the end of each arm, letting each overhang by around 5-10mm. Keep in mind that the bars should be on the inside of the arms when assembly is complete (see our photos for details). Try to get some solder into the holes in the PCB, as this will add mechanical strength. The surface-mounting copper pads are essentially glued to the PCB, so it doesn’t take much to tear them off. If you don’t have brass strip, it will pay to add some small blobs of solder to the Tweezer tips. This will provide a larger contact area and also some resistance against the tips wearing down. Place the arms onto the Tweezers PCB at the CON+ and CON- pads and roughly align their positions. Their ends should be separated about 10mm-15mm with no pressure applied; this gives a reasonable working force and range. This gap also means that the Tweezers can be used to test through-hole parts like axial-leaded resistors, diodes and capacitors. We found that fitting the arms flush with the edge of the PCB made the soldering easier and kept the CON+ arm clear of the CON2 OLED connection. It also looks tidier; see our photos. Once you’re happy with their positions, apply a generous amount of solder to both sides of the joins to secure them in place. Try out the action, tension and alignment of the arms and adjust if necessary. You can also trim and dress the tips if fitted. Squeezing the arms together and drawing a fine file over the tips will align them if they are slightly different lengths. To make the tips of the arms parallel, place fine sandpaper or a flat file between the tips and work them until the tips are satisfactory. This will also help add some texture to the tips to help them grip components and avoid the possibility of them flying into the yonder! The OLED screen The OLED module is the last piece to fit. The header supplied with the module has a spacer of just about the siliconchip.com.au You can get pre-made tweezers with leads designed to be connected to other pieces of equipment like a multimeter. If you prefer these, you can cut off the banana plugs and solder them to our main board instead of our PCB-based arms. If doing this, ensure that the positive lead goes to the CON+ pad on the PCB and CON- to the black lead. That time of year is nearly here... CHRISTMAS Spice up your festive season with eight LED decorations! Tiny LED Xmas Tree 54 x 41mm PCB SC5181 – $2.50 Tiny LED Cap 55 x 57mm PCB SC5687 – $3.00 Tiny LED Stocking 41 x 83mm PCB SC5688 – $3.00 right depth to mount the OLED parallel to the main PCB, although the pins probably need trimming. Start by soldering the pin header to the PCB at CON2, preferably with the longer pins facing up. This will make them easier to trim later. Check that there are no bridges between the pins of CON2, the CON- arm and the cell holder. Tack one lead of the OLED to the top of the header and check that it looks right and is not touching anything underneath; adjust it if necessary. Solder the remaining pins and then trim the excess pin length from the top, taking care not to damage the OLED screen. Then remove the protective film on the display. Using it Insert the lithium cell with the negative terminal against the PCB. The OLED should spring to life and show a reading just over 3V for a fresh cell. Squeezing the arms together should show a resistance of a few ohms. If you have no display at all, check the OLED connections. If there is no resistance measurement, you might have a problem with your test circuitry; check the resistors, IC1 and the Tweezer arms. After the Tweezers go into sleep mode, they use low-power digital sensing to wake up. Thus, they might siliconchip.com.au wake up if connected to some but not all parts. Reverse-connected diodes and high-value resistors may not wake the Tweezers, but nearly all capacitors (when discharged) appear to do so. In that case, simply short the Tweezer tips together, then probe the component. Once a part has been detected, the Tweezers will stay awake until no part has been detected for five seconds. Caution Like any project that uses coin cells, the Tweezers should be kept well away from children who may ingest them. The Tweezers also have quite pointy tips, another reason to keep them out of reach of curious fingers. You can apply a piece of wide, clear heatshrink tubing to the main PCB body to insulate and protect it. This can also be used to secure the coin cell in place; it should not be due for replacement too often, and the heatshrink can be replaced at such times. You might also like to fit some thinner heatshrink to the arms. This will provide more insulation and also add a softer gripping surface to the Tweezers. SC Australia’s electronics magazine Tiny LED Reindeer 91 x 98mm PCB SC5689 – $3.00 Tiny LED Bauble 52.5 x 45.5mm SC5690 – $3.00 Tiny LED Sleigh 80 x 92mm PCB SC5691 – $3.00 Tiny LED Star 57 x 54mm PCB SC5692 – $3.00 Tiny LED Cane 84 x 60mm PCB SC5693 – $3.00 We also sell a kit containing all required components for just $14 per board ➟ SC5579 October 2021  69 Review by Tim Blythman PicoScope 6426E USB Oscilloscope The PicoScope 6426E USB Oscilloscope is a high-performance software-driven oscilloscope. As most of our experience is with standalone/benchtop type ‘scopes, we were interested in trying it out when Emona Instruments offered to loan us an evaluation unit. I n February this year, we purchased a BitScope Micro PC-based oscilloscope to build a low-cost Virtual Electronics Workbench (siliconchip.com. au/Article/14751). While the concept is similar – both scopes lack screens and buttons, connecting to a computer instead for display and control – Pico Technology’s 6000E series of PC-based oscilloscopes is in an entirely different league. The unit we received for testing is the 6426E four-channel, 1GHz bandwidth scope with a maximum 5GS/s (gigasamples per second) sampling rate. But there is much more to the scope than these basic specs imply. The 6426E has the so-called FlexRes feature, which means that it can sample voltages with a resolution of eight bits (256 steps), 10 bits (1024 steps) or 12 bits (4096 steps). This is 12 bits of true hardware resolution, not achieved by averaging multiple samples of lower resolution. If the full 1GHz sampling rate is not needed, then the 6426E can also perform oversampling and software enhancement to provide an effective resolution of up to 16 bits. This extra resolution can be handy in audio work or anywhere that a high dynamic range is needed. It can only sustain the 5GS/s sampling rate with the vertical sampling resolution set to 70 Silicon Chip eight bits, reducing to 1.25GS/s when using two channels at 12 bits due to hardware bandwidth limitations. Given that you’d typically need the higher vertical resolution when looking at lower-frequency signals like audio, that doesn’t seem like a significant problem. The scope feature that we found most interesting is the sheer volume of sample data that the unit can capture, up to four gigasamples. That means that the 6426E can sustain its maximum 5GS/s sampling rate (on one channel) for up to 800ms. There are great benefits to having long capture times. Once you have sampled an event, it will be a great boon to be able to look over the surrounding times to see the complete circumstances. For example, there is nothing more frustrating than debugging digital communication and only capturing a fraction of the transaction, especially if it’s a rare event. This long sample size potentially allows many seconds or even minutes of data (at lower sampling rates) to be captured and analysed after the fact. These high sampling depth and rate capabilities also mean that FFT (spectral) analysis can be more detailed; the spectrum view can be accessed by a single click in the user interface. Range of scopes The 6426E that Emona supplied us for review is just one of Pico Technology’s 6000E series of scopes, and it is pretty well top-of-the-range. There are nine units with different feature combinations listed at the time of writing. The range starts with a 300MHz bandwidth unit that lacks the FlexRes feature, limited to eight PicoScope 6426E Features & Specifications • • • • • • • • Voltage resolution: eight bits (256 steps) to 12 bits (4096 steps) Channels: 4 x 1GHz analog, plus 16 x digital with optional MSO pods fitted Sampling rate: 5GS/s maximum Capture memory: 4GS Waveform generator: 50MHz, 200MS/s, 14-bit Update rate: 300,000 waveforms per second Software: PicoScope 6 and PicoSDK (free) Other features include: serial decoding, mask limit testing, high-resolution waveform timestamping Australia’s electronics magazine siliconchip.com.au Software The PicoScope 6426E accepts Pico Technology’s intelligent probes as well as standard passive probes on the front panel. Optional mixed-signal oscilloscope (MSO) pods for digital signals can be plugged in at lower right. Up to two MSO (mixed signal oscilloscope) pods can be plugged into the front of the 6000 series ‘scopes. These are optional extras and were not included with the unit we tested. ► Even before we received the unit to test, we made sure to download the necessary software. In a very refreshing change from much software these days, the PicoScope 6 software does not need a login or e-mail address to use or download. PicoScope Version 6.14.44 is the latest release and the first version to support the 6000E series scopes. On Windows, the software is around 210MB to download and around 230MB installed. The installation process was straightforward and included the necessary drivers. It’s a good sign when things like this just work. There are also beta (pre-release) versions of PicoScope 6 for macOS and Linux. Early versions of PicoScope 7 are also available. The notes indicate that this version will eventually support all current and many discontinued PicoScope models, so ongoing support looks good. ► bits (256 steps) of vertical resolution. Also, this basic unit (the 6403E) only has 1GS of storage. There are also eight-channel units, although these are only available with 500MHz bandwidth: the 6804E (eightbit resolution only) and 6824E (with FlexRes). These scopes can also be fitted with one or two optional mixed-signal oscilloscope (MSO) pods. These provide eight digital signal inputs each; our review unit was not supplied with these. But this doesn’t stop the scope from being useful for digital work. There is an online tool for configuring and viewing the scope options at: www.picotech.com/oscilloscope/ 6000/picoscope-6000-overview The scope comes in a padded clamshell case and with all the basics needed to use it, including four 500MHz 10:1 passive probes. Active probes are also available as an option at the time of purchase. The front panel features the four BNC socket inputs plus a pair of test points for Earth and a square-wave output. The rear is dominated by a fan grille with USB and power connections on one side and three BNC sockets on the other. These sockets are for the auxiliary trigger input, 10MHz timebase siliconchip.com.au ► Hands-on testing Standard inclusions are four passive 10:1 500MHz probes. The probes also come with a variety of useful accessories, including spring tip, ground spring and colour coding rings. Active probes are also available. Australia’s electronics magazine October 2021  71 ► Screen 1: when the PicoScope application is started, connected probes are automatically detected and the trace is displayed. Common settings are above and below the main trace window. Screen 2: a comprehensive set of probe settings are available via a drop-down for each connected probe. It’s handy to have all these settings in one place. Screen 3: when the trigger is activated, it ► appears as a yellow diamond that can be moved around to set both the trigger threshold and delay. A separate window is used to modify more advanced trigger settings. 72 Silicon Chip Australia’s electronics magazine input and AWG (arbitrary waveform generator) output. The body is extruded aluminium with rubber bumpered corners. It feels solid and comes with a 12V power brick of the type that would typically accompany a laptop computer, and a sturdy USB 3.0 (A-B) cable, as well as the necessary manuals. While we scanned the Quick Start Guide, getting started was as simple as connecting the power brick, connecting the unit to the computer with the USB cable and starting the PicoScope software. Connected probes are automatically detected and displayed. Screen 1 shows the initial display on launching the software with the scope connected. User interface While PC-based scopes are necessarily different to the alternative, they also tend to offer more options. The trick is learning where all the settings and selections are hidden. We found the PicoScope software to be laid out in a fairly intuitive manner. An A3 poster guide is available, briefly explaining the main features and where their controls are located. Within the main window, there are three main rows of controls (plus the standard window menus). The first row has the timebase and sample settings, the second the channel ranges. Interestingly, the vertical channel ranges aren’t set per division but for the entire vertical scan. It’s not what we’re used to, but it makes sense to do it this way, as you typically know the range of signals to expect and can simply set the vertical range to match. Screen 2 shows the settings that are available for each probe (channel). A third row below the trace window has the trigger settings, so the most commonly used features are suitably grouped and easy to find. The PicoScope software makes excellent use of the PC interface — the method of setting Triggers is both remarkable and straightforward. Once the trigger is enabled, a yellow diamond appears on the screen and can simply be dragged around to set the trigger point. The vertical position of the trigger determines the threshold, while the horizontal position determines the delay (or amount of pre-sample and post-sample). This is shown in Screen 3. siliconchip.com.au As well as the basic trigger options, there are advanced options such as window, interval, level, runt pulse and digital boolean logic trigger conditions, including those dependent on multiple signals. With the zoom tool selected, a region of the trace can be selected for closer inspection. As well as the zoomed window, an overview panel is shown, allowing the zoomed section to be panned around and inspected. This is seen in Screen 4. Features In the course of working on some of our current projects, we tried out some of the different features of the 6426E. Of particular interest to us is the serial decoding feature. Several protocols can be decoded, and these are accessed from the Tools → Serial Decoding menu item. The dialog box with its options is seen in Screen 5. We used an I2C decoder to monitor signals being sent to an I2C OLED display. Screen 6 shows the data being correctly detected, packetised and decoded. While this looks like quite a bit of data, what is being displayed is only a fraction of what the PicoScope has stored. Up to 32 separate captures are also kept and can be examined using the ‘buffer overview’ feature. This makes it easier to examine longer sequences, and different captures can be compared and viewed, including any decoded serial data associated with the raw scope waveforms. Screen 7 shows the small window that provides the waveform overview and allows easy selection of captures to view. Screen 4: the zoom tools are simple and intuitive. The Zoom Overview allows the zoomed region to be panned around. Menus We cannot cover all the features of the 6426E, but we will highlight some that we thought were of particular interest. Taking a screenshot is as simple as using the Edit → Copy as Image menu item. There is also a “Copy as Text” option to allow easy pasting of data into a spreadsheet application. Various measurements can be applied to a trace, allowing easy assessment of things like frequency, duty cycle, RMS value and even digital aspects such as the number of edges. These can be applied to the entire screen display or between manually set rulers on the screen; the rulers can siliconchip.com.au Screen 5: a comprehensive range of serial protocol decoders are available. We were impressed to see that the DCC digital command protocol for model railways is present. Australia’s electronics magazine October 2021  73 Screen 6: we tested the I2C decoder and found that the PicoScope had no trouble detecting data packets that matched what we expected. Within the Preferences settings are a comprehensive range of functions to which keyboard shortcuts can be allocated. While it is easy enough to use the mouse for most features, we think that being able to set up shortcut keys for frequently used actions will be very handy for people who use the scope a lot. Waveform generator The waveform generator output is available from one of the BNC sockets at the rear of the scope. It can produce square waves and sinewaves up to 50MHz, and other waveforms at lower frequencies. Arbitrary waveforms can be taken from either a CSV file or an existing scope trace. Digital bitstreams can be entered as binary or hexadecimal data. Conclusion Screen 7: the Buffer Overview allows up to 32 screens of data captures to be viewed and compared. Any applicable decoding is also made available below the window shown. simply be dragged and dropped like the trigger marker. Screen 8 shows the available measurements. As well as serial decoding, the Tools menu allows ‘Math Channels’ to be added. There are simple (sum, difference, product) channels available 74 Silicon Chip directly from the menu, but you can also enter custom equations. The interface for entering equations looks a lot like a scientific calculator. There are also Tools menu options for masks, alarms and reference waveforms. Australia’s electronics magazine The 6426E is an impressive machine with a comprehensive set of features. We did not find it wanting in any of the tests we threw at it. In fact, we struggled to get it anywhere near its limits. It is a handy tool for working with digital electronics through the numerous decoders, even though it has impressive specifications in the analog domain. The 6000E range of ultra-deepmemory oscilloscopes is available from Emona Instruments. Ring them on 1800 632 953 or e-mail testinst<at> emona.com.au Visit siliconchip.com.au/link/ab9j for a list of all the PicoScope products they sell or refer to their advertisement on the inner back cover. SC siliconchip.com.au ► ► Each optional MSO pod provides eight digital channels and includes a number of adapters, ground clips and test hooks to connect to the circuit under test. Screen 8: the measurements listed here can be applied over the entire span of a buffer, or limited to specific ranges using adjustable rulers. ► siliconchip.com.au Australia’s electronics magazine The A3136 1.3GHz Active probes are an optional extra, but are necessary for working at frequencies higher than passive probes can support. The Intelligent Probe Interface powers the probe from the scope and facilitates automatic probe detection and unit scaling. October 2021  75 Part 2: by Nicholas Vinen & Tim Blythman Touchscreen & Remote Digital Preamp with Tone Controls Our new Digital Preamplifier, introduced last month, combines high audio fidelity with convenience. It provides input switching, volume adjustment, bass/mid/ treble controls via remote control and a colour touchscreen. It can be built as a standalone unit or integrated into a power amplifier. Having explained how it works, now we’ll go through the construction and testing procedures. T his Preamp brings analog & digital circuitry together, giving the best aspects of both. It’s a relatively simple design with excellent audio quality thanks to its analog roots, but it avoids the complexity of the multiple, expensive ICs that would be needed for a purely digital design. It also avoids using mechanical parts that can wear out, like a mostly analog design using a motorised potentiometer. It has a good range of features including a colour touchscreen interface, infrared remote support, a threeband tone control, a wide gain range and four stereo inputs. Last month’s article explained how all of this is achieved using a Micromite LCD BackPack, two quad low-distortion digital potentiometers and a handful of op amps. That article also had all the relevant performance data. Now that we’ve explained how it all works, let’s start on the assembly procedure. Construction The main PCB overlay for the Digital Preamp is shown in Fig.7. This board is coded 01103191 and measures 206 x 53mm (shown rotated). As mentioned last month, we don’t think the bypass relay (RLY4) and its associated components are necessary, so we have shown them greyed out. Instead, we recommend that you fit 76 Silicon Chip two wire links, shown in red. These let the signal pass to the output without RLY4 being fitted. Assembly is pretty straightforward, with just two SMDs on the board (IC6 & IC7). Those parts are quite large, similar in size to a 14-pin DIP IC, and with widely spaced pins are not hard to solder. Start with those two parts. Find their pin 1 markings and make sure they are orientated correctly, then apply flux paste to all the pads, rest the IC on top and tack one pin down. Check that all the pins are correctly aligned over their pads, then solder them. With enough good-quality flux paste on the pads, you can just load your iron with solder and drag it across the pins, and good joints will form. Clean off the flux residue and carefully inspect the joins to ensure they have all formed properly (with the fillet touching both the pins and the pads) and that there are no bridges between adjacent pins. If you find bridges, apply more flux paste and use some solder wick and a fair bit of heat to remove the excess solder. Repeat the cleaning and inspection process to verify all is OK. Now move on to the resistors, but leave off the larger 1W resistors for now. Note that two of the 100W resistors need ferrite beads slipped onto their leads before soldering – see Fig.7. Australia’s electronics magazine Check each batch with a DMM set to resistance mode before fitting them to the board, and you can then fit those two wire links shown in red using resistor lead off-cuts. Next, mount the diodes. All diodes are polarised, so check their cathode stripes against Fig.7 and the PCB silkscreen before soldering them in place. D1-D12 are all BAT42 schottky types, while D13-D15 are standard 1N4148 signal diodes. Follow with zener diode ZD1. Bend REG4’s leads down by 90° about 6mm from its body, insert them into the PCB and then attach its tab to the mounting hole securely using a short machine screw, washer and nut. Once it’s solidly attached and square, solder and trim its leads. Now you can solder op amps IC1-IC5 to the board, ensuring they are orientated correctly. You can instead solder sockets if you prefer; they make swapping op amps easier but can lead to reliability problems long-term. Follow with bridge rectifier BR1, ensuring its + lead (usually longer) goes into the marked hole. Install the two trimpots (both 500W) and then the three relays in a row, RLY1-RLY3. Ensure the stripes on the relays are positioned as shown, as it is possible to install them backwards. Next, mount all the TO-92 package devices. These are transistors Q1-Q3 siliconchip.com.au and Q5-Q7 plus regulators REG1REG3. As there are five different device types in similar packages, be careful to check the markings so that you don’t get them mixed up. Now is a good time to fit all the ceramic capacitors (two different values) and MKT capacitors (five different values). Refer to Fig.7 and the PCB to ensure the right ones go in the correct locations. Then fit the headers for links LK1-LK3 but do not insert the shorting blocks yet. Follow with the DC socket (if you plan to use it) and the 18-pin header, plus the 3-way terminal block, with its wire entry holes facing the outside of the board. If you are going to fit LED1 onboard, do it now, with its longer anode lead soldered to the pad marked “A”. Otherwise, you could mount a header in its place, or solder a twin lead later. Also install the two 10W 1W resistors now. Bend their leads so that they are suspended a few millimetres above the PCB surface to allow air to circulate, as they get pretty hot. As mentioned last month, you could opt to use 2W resistors, or perhaps four 4.7W 1W resistors arranged in pairs and mounted vertically to spread out the heat load. Then fit all the electrolytic capacitors, with their longer positive leads to the pads marked with a + symbol. Note that the two 47μF caps need to have their leads splayed out to fit the pads provided. That just leaves the RCA sockets. The right-angle sockets will have plastic tabs that clip into the holes drilled into the PCB. Once you have pushed siliconchip.com.au them down fully so they are flat on the PCB, solder their leads. You should also push the vertical connectors down fully before soldering the two tabs and central pin on each. Building the BackPack You have the option of using the Micromite BackPack V2 with a 2.8inch colour touchscreen (May 2017; siliconchip.com.au/Article/10652) or the Micromite BackPack V3 with a higher-resolution 3.5-inch touchscreen (August 2019; siliconchip.com. au/Article/11764). The main advantages of the 2.8-inch version are lower power consumption and the fact that it will more easily fit into a slimmer case. The 2.8-inch screen module is 38.5mm tall, while the 3.5-inch screen is 56.5mm tall. A 1RU case is 44.5mm tall, so it would be difficult to fit the 2.8-inch version into one, while fitting the 3.5-inch version would be impossible. A 2RU case would fit either. Regardless, it’s up to you; build the one you prefer based on the instructions published in those previous issues. Assembly is pretty straightforward, especially if you’re making it from a kit, so if you’re an experienced constructor, you probably don’t need instructions. We can supply a kit for either version with the microcontroller pre-programmed with the appropriate software. The 2.8-inch version is available at siliconchip.com.au/ Shop/20/4237 while the 3.5-inch version is at siliconchip.com.au/ Shop/20/5082 Whichever version you purchase, Australia’s electronics magazine Fig.7: rather than fitting RLY4, we suggest you solder short wire links (shown in red) and then omit the other components (in green) including Q4, Q8 and six resistors. This is the tone control bypass circuitry which we found didn’t improve the performance. Also, watch the orientation of the ICs, relays and diodes, especially IC6 and IC7, as they are hard to reverse if you get it wrong. They should have a dot or divot in the corner to indicate pin 1. October 2021  77 make sure to select the right software. If you’re programming the chip yourself (eg, you already have a BackPack), note that there are two versions of the software to suit the two different BackPacks and screens. See the panel on loading the software below for details. Wiring it up Next, we need to make up the cable and adaptors that will connect the BackPack to the Preamp board. The one which attaches to the BackPack also hosts the infrared receiver (see Fig.8). The two adaptors use identical PCBs (coded 01103192 and measuring 12.5 x 45.5mm). Both are fitted with a SIL header socket strip and a box header, but only one has the resistor, capacitor and infrared receiver onboard. This is the one that plugs into the BackPack. Assemble them as shown in the photos and the overlay diagram, Fig.9. Next, you will need to crimp the IDC sockets onto the ribbon cable, as shown in Fig.10. Adjust the length of this cable to suit your installation. Ideally, you should use an IDC crimping tool to do this, such as the Altronics Cat T1540. However, in a pinch, you can do it in a vice (pun intended) with pieces of timber on either side to protect the plastic. Note that some IDC connectors come in three pieces, as shown in our diagram, with a bar on top to clamp the strain relief loop and another part below to press the cable down onto the blades in the socket. But we’ve also seen two-piece connectors with no strain-relief bar, and if you have that type, omit the loops. There are two things to be careful of. Firstly, don’t compress the plastic so much that you break the top-most part of the connector, as that is not hard to do. Secondly, make sure that the pressure is applied evenly, and all the parts of the socket have been fully pressed together (listen for clicks). This is so that the blades all cut through the insulation and make contact with the copper inside. The main cause of failures in these ribbon cables is due to one or more of the blades failing to cut through the insulation fully, leading to open-circuit connections. For some installations, it might be better to crimp the IDC connectors onto opposite sides of the ribbon cable, rather than the same side as shown in Fig.10. You can do it either way, as long as you make sure that the triangle moulded into the IDC socket indicating pin 1 points to the red striped wire in the ribbon cable at either end. Testing You can perform some basic tests on the main board before connecting the ribbon cable to it. Even if you plan to power the final device from a mains transformer, you can use a 12V AC plugpack or dual-tracking bench supply for testing. With links LK1-LK3 open and nothing connected to the board, apply power. Use a voltmeter to probe the pins on the headers for LK1-LK3 closest to the edge of the board, taking care not to accidentally short across the pairs of pins. A convenient ground point for the black probe of the DVM is the mounting screw for REG4. You should get a measurement close to +5.5V for LK1, +12V for LK2 and -12V for LK3. Adjust VR1 until the reading for LK1 is between 5.49V and 5.50V (or as close as you can get). If you can’t achieve that, or either of the other two readings is way off, remove the power and check for faults in the power supply area. Also check the +5V rail, which will Fig.8: this small adaptor circuit makes it easy to wire up the Preamp board to the Micromite LCD BackPack using a ribbon cable with standard IDC connectors crimped at each end. The IR receiver and its supply filter are only fitted to the board at the BackPack end. ► Fig.9: build one Adaptor board with all the components, as shown here (refer to our photos to see how we bent the IR receiver lead to reach the front panel), while the second Adaptor board should only have CON1 & CON2 fitted. One of these Adaptor boards need to be connected to the Micromite BackPack as shown in the lead photo. 78 Silicon Chip Australia’s electronics magazine siliconchip.com.au power the backpack by probing the right-most lead of REG4. It should be between 4.8V and 5.2V. We’ll assume that you have already loaded the software onto the BackPack; if not, unplug it and do so now, using the usual procedure. The panel titled “How to Load the Preamp Software” has some helpful hints. If you can apply 5V power to the BackPack (eg, using a USB cable with JP1 fitted for the V2 or V3 BackPacks), then you can check that the software loads up normally. Press the buttons and step through the screens. Everything should ‘work’; it just won’t do anything without the Preamp board connected. Assuming it all looks good, remove power, wait a minute or so for the capacitors to discharge and place shorting blocks on LK1-LK3. Plug the ribbon cable firmly into the adaptor board without the IR receiver, then plug its SIL socket into CON8, orientated as shown in our photos. Similarly, plug the ribbon cable into the other adaptor board and the BackPack’s I/O header, as shown in our photos. Now is a good time to verify continuity between pin 1, where the header mounts on the BackPack PCB, and on the preamp PCB, right in the corner. This will verify that you haven’t reversed the connections anywhere. It’s a good idea to check all the pins for continuity between the two boards, as this can show up ribbon cable crimping problems or soldering problems. Once you’re satisfied, reapply power to the preamp board and verify that the LCD screen comes alive, and you can switch between Presets 1-4 by pressing the buttons. By default, these select between inputs 1-4, and you should hear soft clicks coming from the relay(s) each time you switch inputs. Next, adjust VR2 to get exactly half the 5.5V rail voltage at pin 5 of IC4 (ie, very close to 2.75V if your 5.5V supply is spot on). Now it’s time to connect the Preamp’s outputs to an amplifier with its volume wound down, and one of the stereo inputs to a signal source such as a Blu-ray player or MP3 player. Select that input by pressing the associated preset button on the screen. This should pass the signal through moreor-less unaltered, although it might be somewhat attenuated. Start the signal source and slowly wind the amplifier volume up to confirm that you can hear the audio passing through the Preamp. Ensure it is not overly distorted and that both channels are present; otherwise, you probably have a circuit fault. If it seems OK, try adjusting the volume using the on-screen controls, and check that switching to another input effectively mutes the signal. You can also now go into the EQ settings screen and try adding some bass/ mid/treble boost or cut, to verify that those sections of both channels are operating correctly. Remote control Now is also a good time to test out the remote control, if you plan to use one. The Jaycar XC3718 should ‘just work’ while the Altronics A1012A needs to be set to Aux preset 0776 (see its manual for details on how to do that). Point the remote at the IR receiver and check the following functions: • Volume up/down should change the audio level, and you should get a large on-screen display to show you the new volume level (see Screen 9); the popup only shows on the MAIN screen • The mute button should toggle the mute function; since the Jaycar remote lacks a mute button, the play/pause button operates this function • The CH UP and CH DN keys can be used to tweak the band settings after first selecting a band using buttons 7 (bass), 8 (mid-range) or 9 (treble) ► siliconchip.com.au Australia’s electronics magazine Fig.10: here is one way to assemble the ribbon cable. You can also put the IDC connectors on opposite sides of the cable if it suits your installation better; just make sure that the pin 1 triangle marking on each socket points to the red striped wire in the cable. Also be careful to crimp the connectors properly (firmly) without doing it so hard that you shatter the plastic. October 2021  79 How to Load the Preamp Software Loading the software As you might expect with the option to run the software on either a 2.8in or 3.5in display, there are two different HEX files. The MMBasic software is written to work with both but requires different display drivers. If you have a blank chip, use a PIC programmer or the onboard Microbridge to load the appropriate HEX file, as this is less effort than loading MMBasic and then loading the program separately. None of these choices exclude you from accessing and tweaking the MMBasic program to customise it. The HEX file is named “0110319A Preamp 2.8in.hex” for the 2.8in display or “0110319B Preamp 3.5in.hex” for the 3.5in display. If you have a pre-programmed PIC from the Silicon Chip Shop, you will not need to load any software, and the program will start on power-up. You will have specified whether you need the 2.8in or 3.5in display variant at the time of ordering. Loading the software from scratch If you are building the Preamp with the 2.8in display, you simply need to configure the Micromite to work with that screen. From the console, enter the following commands: OPTION LCDPANEL ILI9341, LANDSCAPE, 2, 23, 6 and for the touch panel: OPTION TOUCH 7, 15 Then calibrate the touch panel using the same parameters as we have in our HEX file: GUI CALIBRATE 0, 143, 293, 893, 685 If the above calibration is not accurate, you can simply run: GUI CALIBRATE ... to perform a full manual touch calibration. • Number keys 1-6 should select one of the six presets Final wiring After mounting the unit in the case, all that’s left is to wire up the power supply – assuming you aren’t using the onboard barrel socket. If you have a transformer with a single secondary, wire it between either pins 1 & 2 or 2 & 3 of CON6. If it has twin secondaries, connect them in series in-phase and then wire the junction to pin 2 of CON6 and the other ends to pins 1 & 3, either way around. Similarly, if it’s a centre-tapped secondary, connect the tap to pin 2 and the other wires to pins 1 & 3. If you have a source of ±15V DC, wire the rails to pins 1 & 3 of CON6 either way around, with GND to pin 2. If you are building the Preamp into a full amplifier, connect RCA plug leads to the amp module inputs and plug them into the vertical outputs (CON4 & CON5) on the board. You should be ready to rock’n’roll – or whatever takes SC your fancy! And for the 3.5in display Since the Micromite firmware does not include a driver for the ILI9488 touch controller in the 3.5in panel, a separate library file needs to be loaded to provide that feature and activate it when the Micromite starts up. Load the “ILI9488 Library.bas” file onto the Micromite using MMEdit or your preferred serial terminal program. Enter the following commands at the Micromite prompt: LIBRARY SAVE CPU RESTART OPTION TOUCH 7, 15 GUI CALIBRATE 0, 3891, 3851, -1277, -860 Again, you can simply use the GUI CALIBRATE command without parameters if you find our calibration doesn’t match your hardware. At this stage, you will have a Micromite loaded with an appropriate display driver, which you can test with the GUI TEST LCDPANEL and GUI TEST TOUCH commands. Screen 9: we showed photos of most of the screen displays last month, but here’s one we didn’t show: the large volume number shown when you adjust the volume via the remote control. It’s large enough to see across a room. Each step equates to about one-third of a decibel. The MMBasic file The MMBasic file is designed to work with either display driver; indeed, any display with a similar or higher resolution to the 2.8in display should work, although we can’t vouch for the scaling on other screens that we haven’t tested. This file also contains an abridged version of the above notes in comments near the start of the file. Simply load the “Digital Preamp.bas” file using MMEdit or your serial terminal program and run it from the MMBasic prompt. You should be greeted by the MAIN screen and the sound of relays clicking as the Digital Preamp initialises. The initial condition has input one connected with nominal midpoint (all zeroes) volume, preamplifier and tone control settings. This corresponds to modest gain across all bands. At this stage, the Micromite is in the same state as if it were loaded with the HEX file as described earlier. 80 Silicon Chip Australia’s electronics magazine In this screen, you can adjust the tone control and preamplification settings and see how the Preamp's frequency response will be affected. siliconchip.com.au The updated Altronics A1012A Univeral Remote Altronics has recently updated their A1012 Universal remote control to a newer model, the A1012A (siliconchip.com.au/link/ab9m). We have used the A1012 to control our projects for many years now (along with some contemporary Jaycar remotes). This new model has some minor changes compared to the earlier version, which affect how it works with the Digital Preamp. While the design, styling, and button layout have changed, many button functions are the same. The six device buttons near the top have changed too, with the CD and VCR buttons being replaced by DVD and HD buttons. The setup process for the A1012A is similar to the older A1012. You select one of the devices using its button near the top, press the SET button, then enter a code. The A1012A uses four-digit codes, while the A1012 used threedigit codes. A glance through the codes list for both devices shows at least a partial correspondence between the two units. For example, we often use AUX code 171 for Micromite projects. The testing we did a few years ago showed that this setting produces distinct codes that are consistently detected by MMBasic’s inbuilt IR decoder. In the A1012 code list, this code is shown as third in the list for several manufacturers. When we referred to the A1012A’s code list and tried the third code for the same manufacturers, we found that it gave the same codes and thus worked with our Digital Preamp. So AUX code 0776 on the A1012A is a good substitute for AUX code 171 on the A1012. We haven’t exhaustively tested all the buttons, but it certainly worked for all the functions we tried. Over the last few years, we’ve created a few projects that use A1012 TV codes 089 and 170. It appears that TV codes for the A1012A don’t correspond one-to-one to those of the A1012, presumably due to newer TVs evolving and having more features. Still, we found that the codes 0088, 0149 and 0169 were suggested for TVs on the A1012A’s code list that would have required TV codes 089 and 170 on the A1012. So we tested these codes with an Arduino board that we had equipped with an infrared receiver (see siliconchip.com.au/Article/11196 for the hardware we used). The codes that we received were all identical to those used for the A1012, so it appears that these remotes are mostly interchangeable, and probably only differ in the more obscure codes. So, if you are updating any Micromite projects from the A1012 to the A1012A, we suggest using AUX code 0776. Other projects we have published that make use of the A1012 include: • Currawong Valve Amplifier, November 2014 to January 2015 (siliconchip.com.au/Series/277) • High Visibility GPS Clock, December 2015 & January 2016 (siliconchip.com.au/Series/294). • Preamp and Input Selector, March, April & September 2019 (siliconchip.com.au/Series/333 & siliconchip.com. au/Article/11917). • Altronics MegaBoxes, December 2017 & December 2019 (siliconchip.com.au/Series/322). All of these use the TV codes mentioned above, so they should work fine with the A1012A programmed with TV codes 0088, 0149 or 0169. Note that the Jaycar Cat AR1975 “Total Contol 4 Device TV Remote Control” is similar to the Altronics A1012A in many ways, and we will likely use that in future projects where their small XC3718 remote cannot be used (eg, due to having just 21 buttons, which was enough for this Preamp). Remote control code map: A1012 AUX 171 TV 089 or TV170 siliconchip.com.au A1012A AUX 0776 TV 0088, TV 0149 or TV 0169 Australia’s electronics magazine Silicon Chip Binders REAL VALU E AT $19.50 * PLUS P&P Are your copies of SILICON CHIP getting damaged or dog-eared just lying around in a cupboard or on a shelf? Can you quickly find a particular issue that you need to refer to? 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. H 80mm internal width H SILICON CHIP logo printed in gold-coloured lettering on spine & cover Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Order online from www. siliconchip.com.au/Shop/4 or call (02) 9939 3295 and quote your credit card number. *See website for delivery prices. October 2021  81 Review by Tim Blythman Solder Master ESM-50WL Cordless Soldering Iron Battery-powered soldering irons are becoming the preferred choice when soldering needs to be done away from mains power or in tight spaces. The Solder Master ESM-50WL from Master Instruments is the latest contender. L ike the Wagner SI50HSK cordless soldering iron we reviewed in the April 2021 issue (siliconchip.com. au/Article/14828), the ESM-50WL is being marketed as a replacement for butane (gas) powered soldering irons. However, there are some significant differences between them. We received a test unit from Master Instruments, a company prominent in the battery engineering space. They have had substantial input into this Australian-designed product. The ESM-50WL Cordless Iron comes as a complete kit in a padded clamshell case. It includes the Iron, two tips, a protective heat-resistant silicone tip cover, both 12V (vehicle accessory socket) and universal (100V-240V) mains chargers, and a small tube of lead-free solder. The kit is ideal for keeping in the toolbox for those who know they might need to use a soldering iron anytime. The two chargers mean it can be kept charged no matter where you are. As you might expect from Master Instruments, the Iron does not skimp on batteries. The battery is rated at 14.4V 3.45Ah (50Wh) and comprises four Panasonic cells. The chargers are rated at 1A, so the battery will charge from flat in a few hours, although generally you’ll only need to top it off, taking less than an hour. The nominal continuous running time is up to 270 minutes on ‘low mode’. We found that we never came Boost mode gives more power (27W) when needed for 25s close to running it down in our tests. Master Instruments reckon it’s the longest-lasting battery on the market. In use The ESM-50WL Cordless Iron is a powerful unit. We used it to assemble a project PCB, however, we found that it was overpowered for such a small task, as even on the lowest setting (480°C), it put out quite a bit of heat. We then tried using it to solder heavy-duty wires onto some 70W LED panels on a thick aluminium-core PCB. For this job, it excelled. There is no doubt that this is a serious tool for heavy-duty work. It also handled splicing together some thick copper wires with ease. Battery and temperature LED indicators Temperature settings: low (480°C), medium (520°C) and high (570°C) LED for work illumination Heating time: under 10 seconds! Dimensions: 235mm x 52mm x 37.8mm Comes as a kit in a clamshell carry case including two interchangeable tips Battery: 14.4V 3.45Ah (50Wh) Li-ion The power button for the Solder Master ESM-50WL is located on the left-hand side. The yellow indicators on the top of the device show how hot the tip will become, while the blue lights indicate the battery charge left in 25% steps. 82 Silicon Chip Australia’s electronics magazine siliconchip.com.au For those that want even more heat, its boost mode can provide 27W for up to 25 seconds. The controls and LEDs are clear and visible on the top of the Iron, and it is well-balanced. The shape lends itself well to being placed flat on a work surface between uses, without fear of melting anything. An included silicone tip cover can be fitted while the Iron is hot and allows it to be packed away safely. The Iron also has a white LED which is aimed towards the tip for illumination of the work. This lights up the work area nicely, but as it’s only lit while holding down the heat button, it isn’t that useful for positioning the tip before soldering. Some of the suggested users include automotive and marine engineers, telecommunication techs and HVAC (heat, ventilation & air conditioning) installers. Those sound like the sort of jobs that will make good use of the portability, power and long running time that this Iron provides. Construction & servicability The shell is fire retardant polycarbonate and ABS, and the Iron also appears made to be serviced, with a full range of spare parts available. The DC jack, for example, seems to be a standard barrel type and the tip holder is a silicone-lined gland, both of which are well-suited to straightforward user servicing and repair. Conclusion The Solder Master ESM-50WL Cordless Iron is a powerful unit and would be well-suited as a gas iron replacement for those involved in heavy-duty work, in difficult situations. The kit provides a small but complete and versatile set of accessories to accompany the Iron. While more expensive than a comparable gas iron, we think it has significant advantages, including having several charging options and being usable in places where an open flame is not safe. The Solder Master ESM-50WL Cordless Iron retails for $369.95 and is available from resellers like Wagner Electronics Super Store (siliconchip. com.au/link/abau). For more information on this and related products, see www.soldermaster.com.au/ and www. master-instruments.com.au/category/ Solder_Master/2263 SC siliconchip.com.au The soldering iron comes in a padded clamshell case. The case contains the iron with protective cover, two tips, a universal mains charger, a car charger and a tube of lead-free solder. This 3D internal view of the soldering iron showing the battery pack is from the YouTube video: https://youtu.be/iwcwJBnLshA This same YouTube video also has a 3D external view of the soldering iron. Australia’s electronics magazine October 2021  83 SERVICEMAN'S LOG Life on the ‘bleeding edge’ Dave Thompson When new technology comes along, I prefer to sit back and watch what happens before I take the plunge down that particular rabbit hole. This is a different philosophy than many people I know, including family members, who simply must have the very latest widget, gadget and toy available. Some people seem to need the latest gadgets. Control your home lights, entertainment system and air conditioner with your phone or home PC? Check. Have the latest electric car? Check. Own the latest drone with an 8K stabilised camera? Check. Ask Siri, Cortana or Alexa to order washing-up powder for you? Check. Don’t get me wrong; I’m not averse to these things and usually embrace technology, especially if it makes life easier. The problem with early adoption is that many manufacturers these days forgo 84 Silicon Chip stringent product testing and simply let their customers do it all for them, attempting to resolve any problems that crop up on the fly, in the hope that product sales will cover the costs of finishing the development (or recalling it in worst-case scenarios). Gone are the days of focus groups, mass testing and in-depth trials. The problem is that consumer security and privacy often suffer from this damn-the-torpedoes, seat-of-the-pants approach. Australia’s electronics magazine This is a tried-and-true business strategy, though. Japanese companies have done this for years. As a nontechnical example, say a manufacturer wants to try a different flavour of ice cream. In Japan, they simply make it and release it into the market. If it takes off, they reap the rewards. If no one buys it, they quietly withdraw it and move on to another flavour. siliconchip.com.au Items Covered This Month • Life on the ‘bleeding edge’ • A failed computer that needed • • new capacitors Cheating the (arcade) system An Astor Mickey OZ repair *Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz In other markets, manufacturers would trial the flavour, get feedback from different groups and then decide whether to produce and market it. The latter process takes much longer, involves a lot more people and costs a lot more money. This is partly how the Japanese took over the automobile and electronics industries, and it appears that many western businesses have finally figured out how this approach could work for them. The biggest problem, of course, is that we consumers then become the testers for all new products, and as we all know from history, that doesn’t always work out so well. We’ve heard about mobile phones and laptops that catch fire (and now electric cars are doing this as well due to battery manufacturing faults; the Chevrolet Bolt was recently recalled in the USA due to multiple fires). We have clothes dryers that melt and burn the house down (multiple recalls by several manufacturers) and even aircraft that crash because of some unforeseen software glitch. So there’s a lot to be said then about not being an early adopter; many of us tend only to buy products that have been well and truly wrung out, though, in this era, that is becoming increasingly difficult. Early adoption experiences There are exceptions to my selfimposed rule, though; I recall buying my first digital camera, way back in the 90s; a Casio QV-100 [my first digital camera was the very similar Epson PhotoPC – Editor]. It was a marvel of engineering at the time, and as I was soon to be travelling overseas, I was looking forward to taking lots of snaps with it. At the shop, I asked many questions siliconchip.com.au about it, and the older gentleman salesman openly admitted that I probably knew more about it than he did; he couldn’t keep up with all this ‘new’ technology. I purchased the camera anyway, for a staggering amount of money by today’s standards, simply because I needed one and it was available. It was new tech and expensive, but I considered it worthwhile. This camera boasted a resolution (switchable!) of either 320 x 240 or 640 x 480 pixels. This meant that at maximum resolution, it had a megapixel count of, um, zero point three. That was cutting edge at the time, but sadly we don’t see many Casio digital cameras these days. It took good photos as long as I was in full, glaring sunlight and didn’t move a muscle while taking the shot. I still have most of those shots, and while they look a bit washed out, like looking at a 1970s-taken instant polaroid snap, they are all still perfectly viewable and remarkable for the time. The big problem with this camera, aside from the situation-limited snapping opportunities and need for a huge amount of light, was that it ate AA batteries for breakfast. I just couldn’t keep it supplied with power, and with no option for an external supply, my use of it became very limited. Of course, everyone now has a camera on their phone; some models have over-100-megapixel cameras and batteries that last for days even with heavy use; something early adopters of this tech could only dream about. For better or worse, technology marches on. I still have that camera somewhere, but it is obviously of no use to me other than some sentimental value. So, while being an early adopter has some perks, it isn’t always the best way to go. I recently broke my rule about being cautious in this regard when I had the opportunity to upgrade my home computer. What’s that old saying? A plumber’s pipes are always clogged, a cobbler’s children run around barefoot and a mechanic’s car is always on the verge of breaking down. I’m sure there’s one of these idioms for every profession. The fact is, I last purchased parts for my home computer in 2010, just before the quakes hit and ruined everything. Since then, I’ve installed an SSD or two, but the main components (motherboard, CPU, and RAM) Australia’s electronics magazine were all from that era. It was a monster machine at the time and far more powerful than I needed it to be, but I used well-worn, triedand-true technology when building it. There were faster CPUs and newer tech components, but I chose bits I knew worked with each other, and history has proven that I made the right call. I didn’t even really need to upgrade; the machine was working fine and even played the latest games quite well, so there was no mad panic. I’d been planning on buying something new for a while, though, and when some money became available from my mum’s estate, I took the plunge. This time, against all my instincts, I looked at the latest new tech and assembled a machine based on what was available. This was made a bit more difficult as many of my suppliers have been hit by COVID-19 and the resulting chip shortage that has crippled the likes of Toyota, Tesla and other high-tech manufacturers (and is still in full effect, if not actually getting worse!). Obviously, this is eventually going to roll downhill all the way to me, a tiny micro-business trying to supply computer hardware to my clients, and that is precisely what has happened. These days I’m fortunate if I can get a new Intel or AMD CPU, RAM, or a decent motherboard with which to build machines. And as for graphics cards – fuhgeddaboudit! In many ways, I was painted into a corner as to buying what was available for myself, and this is even more onerous when I try to buy parts for my clients. The cautious among us might ask why I just didn’t wait, but with no end to the shortages in sight and an increasingly turbulent market, I decided to just go for it. I ended up with the very latest Intel ‘prosumer’ (HEDT) CPU (with 16 cores!) and a motherboard to match it. I decided on 32 gigabytes of RAM, just because I could, and one terabyte of the latest M.2 solid-state drive that mounts directly to the motherboard. My excitement knew no bounds as I waited for the parts to arrive; this machine would be bigger and better than anything I’d ever owned before, and I couldn’t get it soon enough! Eventually, the parts arrived – some had to come from out of town, which made the waiting even more fraught. When all the bits were here, I set about October 2021  85 assembling it all. There was nothing that I hadn’t done before a thousand times, so I expected it to go together and just work. How wrong I was! The fact is, my mum probably could have worked out how to put it all together. Computer people seem to like making a big mystery out of the whole thing, likely so they can charge more money, but there is really no big secret to assembling a computer. In the old days, when one had to manually set IRQs and other weird parameters, perhaps it was somewhat more difficult, but today it is a bit like building a Lego set. Everything from putting the bits into a case and installing Windows is so turn-key that anyone who gives it a go would likely succeed. Like with many disciplines, though, the real skill comes when something goes wrong. For example, anyone can plumb in a gas line, but what if it isn’t done correctly? Anyone can wire a three-pin plug, but what if they make an error and swap Active and Neutral? Or leave some strands of wire sitting outside the plug? One of my first electric shocks when I was a kid was because of a single copper strand left caught in the plug body... So, I assembled all the bits and, with the wiring and cabling sitting temporarily away from everything, hit the ‘go’ button. All the fans and the built-in LED lighting fired up. I’m not a fan of all this lighting stuff in computers, but as it was built-in and a controller was supplied with the motherboard, I wired it in anyway. But there was nothing on the monitor, and after about 30 seconds, there were five short, sharp beeps alerting me that something was wrong. Interestingly, most motherboards and computer cases don’t come with a speaker anymore. Older cases had threeinch (75mm) permanent-magnet speakers mounted somewhere, and motherboards usually have speaker output connectors. These days, tiny piezo speakers are more popular, so I added one to this build as I’ve collected several. Most motherboards have what they call POST (power-on self-test) codes programmed into the BIOS. These beep codes tell us what is going on, be it a memory, video, or CPU fault. Without adding a speaker, I’d have no idea what was going on, or why I was getting no video output. So, five beeps. Another problem with this new technology is that when you buy a motherboard, there is very little documentation with it. I recall buying Windows 95 back in the day, and it came with a paperback book on how to use it. Tech manufacturers soon realised that printing hard-copy books was both a money-pit and a profit-losing strategy, and soon stopped doing it. Instead, these days a ‘QR’ code is included so you can go online and download the user manual for any given piece of hardware. I hit the web to find out what a fivebeep code means on my Gigabyte motherboard and soon discovered it means a CPU problem. I re-seated the CPU, ensuring once again I didn’t have any wayward pins or obstructions in the socket, but no matter what I tried, I could not get past the five beeps problem. Great! This is just what I needed. I counted myself fortunate this wasn’t a client’s machine; at least I could sort it out at my leisure because it was for myself. In the end, I had to call the tech support guys at my suppliers. They often hear of common problems or glitches and can advise workarounds or solutions. In this case, they 86 Silicon Chip knew nothing because the motherboard and CPU were so new that no information had filtered down the line. All they could do was offer to take it back and get it working. When paying in the region of two grand for just these parts, having these safety nets in place is often a lifesaver. While I was pretty sure (especially after assembling in the order of thousands of machines over the years) that I hadn’t messed anything up, anything is possible. As I couldn’t get it going, I ended up sending the entire box back to the supplier. They contacted me a few days later and confirmed that the problem remained even though they had tried other CPUs of the same type and other supposedly supported motherboards. There were no advisories and no updated BIOS for the motherboard, even though it was nearly six months old by this time. So all they could do was offer me a different CPU that they eventually confirmed did play nicely with my motherboard. They told me that occasionally the system would give five beeps and not boot in about one out of every twenty attempts, but it always powered up normally on the subsequent try. I was OK with that; all I wanted was something that worked, at least most of the time, for now. They shipped it back to me with the offer that if it was still playing up after six months and any interim BIOS updates, they would replace the board and/or CPU to get it working properly. Again, I was OK with this solution; I empathised with these guys as they try to keep abreast of all the new tech streaming out from manufacturers. I also know all too well that most of this hardware these days is thrown out into the marketplace with the bare minimum of testing. Manufacturers will simply placate consumers from suppliers on down through the chain to me with the next model if it proves to be too flawed to fix. This is the way of the world now, and while I broke my own early-adopter rule and paid the price for it, at least now I have a machine that works. In fact, that is what I am typing this column on. I haven’t had any instances of it not booting yet, but if I do, I will take those suppliers up on their offer to provide a new, more stable platform. At the end of the day, this is all they can do, and indeed is all I can do now as well. In the future, I will be a bit more cautious about buying the very latest thing, especially with a customer’s machine. While they might want it, I will be relating my experiences as a warning that it might not be the best way forward. If this had happened with a customer’s machine, it would have been an embarrassing situation. I’d have had to explain why their brand-new whiz-bang machine doesn’t work correctly and that it would take a few weeks before we could get it resolved. That just makes me look like a cowboy, and I don’t like that one bit. A failed computer that just needed new capacitors A. M., of Blackburn, Vic, was faced with an old, broken computer that nobody wanted to fix. But the problem seemed obvious, and the replacement parts were inexpensive, so why not give it a go... The unit in question is a TECS computer of about 2002 vintage running Windows XP. It started playing up in early 2020, being hesitant to get to the desktop promptly, sometimes going through various problems, screens and repeated restarts before finally getting to the desktop. Australia’s electronics magazine siliconchip.com.au Once there, the machine worked with no faults – it was only the startup that was the problem. Finally, it got to the stage where it would not get to the desktop no matter what. I took it to a computer repair outfit in Melbourne. They found a large number of capacitors on the motherboard that were bulging, and suggested that this was the cause of the problem. But they were not willing to fix it. As I had nothing to lose, I opened the computer and found seven bulging capacitors scattered over the motherboard. Carefully taking photos and notes of which cables went where, I took the motherboard out and examined both sides. It seemed to be only a double-sided PCB, which gave me a chance. I carefully noted the polarity of the faulty capacitors, even though the printed overlay on the board indicated this. It was tricky getting the old caps out of the plated through-holes, but with care and a hot iron and some solder wick, I got them all out. Suitable direct replacements are difficult to obtain at a reasonable cost. All were 6.3V devices, mainly 1000µF, but one 3300µF. I got replacements with higher voltage ratings that were physically larger than the originals, but there was enough room to fit them. After two evenings’ work, I had replaced the defective capacitors and reassembled the computer. Upon powering it up, I had to answer a few silly configuration questions; then it went to the desktop right away. All the programs seemed to work, but the big test was a restart. I shut it down, restarted, and it went straight to the desktop. I consider that a victory. Three months later, it is still going well. After this, I made sure to save all my critical files to an external hard drive. Cheating the (arcade) system M. F., of Wyongah, NSW was reading the Arcade Pong article (June 2021; siliconchip.com.au/Article/14884) and was reminded of a repair he was involved in some time ago... After arriving in Australia in 1988, my family and I initially settled in Newcastle, NSW – a beautiful place. My first job was as a service technician for A. Hankin & Co, a Newcastle/Sydney company that had quite a few Arcade Game centres. They also had a manufacturing facility based in Darby St, where they made their own arcade machine cabinets from timber. One of my main tasks was troubleshooting problems that the field techs couldn’t fix, and one such situation arose on a Monday morning. I was called into the boss’ office as soon as I arrived, and was told to get to Pelican airport ASAP as I was on the early morning flight to Sydney. Upon my arrival, I was picked up by one of the Sydney techs and taken to their main arcade showroom in George Street. When we got there, the lady in charge showed me a gadget and said that she had confiscated it from some kids over the weekend. It was a gas igniter and gave one heck of a spark. I tried it on a couple of machines, and each gave 99 credits (the maximum amount). If the kids had used it sensibly, they would never have been caught! I found that it didn’t work on every machine, but mainly on ones with a credit board manufactured in-house. The board just accepted pulses from a coin mechanism siliconchip.com.au Australia’s electronics magazine October 2021  87 This Astor Mickey OZ was inherited in a state of large dust accumulation. However, on the bright side the underside of the chassis was fairly clean. The underside of the chassis had some of its electrolytic capacitors replaced, and a new power cord had to be installed. The restored radio can be seen in the adjacent photo. 88 Silicon Chip Australia’s electronics magazine and issued a credit. It could be used with mechanical and electronic coin counters. I went back to my trusty workshop and grabbed such a board. Sure enough, every time I hit it with a zap from the igniter, 99 credits would come up. Like the Pong machines described by Dr Hugo Holden, I used an antenna to ‘catch’ the zap. I managed to fix it by running some wire around the PCB, close to the edge. I left one end open, and connected the other to the Reset input. The wire was simply glued to the original boards until subsequent batches had it embedded as a track. Now if the board was zapped, it simply reset and sat waiting for a real credit pulse. Game over! A tale of an Astor Mickey radio When C. K., of Mooroolbark, Vic saw a vintage radio sitting unused, he couldn’t help himself. He offered to get it working again, and succeeded in that endeavour... We have a favourite restaurant in the Dandenong Ranges, east of Melbourne. It was there that I saw an old radio used as a decoration. Looking into the back, I saw that it was in a bad way, absolutely choked with decades of accumulated dust. I asked the owner what she knew about it. Apparently, it had been in the family for a considerable time. I suggested that I might be able to restore it for her. She agreed to this and said next time we are in, she will give us a free meal! As you can see from the photos, the dust accumulation was unlike anything I had ever seen. It took quite a lot of work with the vacuum cleaner before it could be handled. Surprisingly, under the chassis was quite clean. I discovered that this was a 1934 Astor Mickey which had been featured in a Silicon Chip article written by Rodney Champness (March 2004; siliconchip.com.au/Article/3438); that article included the full schematic. Editor’s note: we will publish an updated article to the Astor Mickey OZ very soon, so we’re refraining from publishing another circuit until then. This design shows how far back the standard superheterodyne design goes. The first valve, a 6A7, is a pentagrid converter that multiplies the signal from the antenna with the local oscillator. The resulting 455kHz siliconchip.com.au difference signal is amplified by variable mu pentode 6D6. There are two intermediate frequency (IF) transformers, L7/L8 and L9/L10. These are tuned by trimmer capacitors in the sides of the IF transformer cans, accessible from the back. A 6B7 dual-diode-pentode valve provides envelope detection and audio amplification. The filtered negative DC voltage from the diodes also provides automatic gain control to V1 and V2. Finally, the type 43 pentode drives the speaker through a transformer. In 1934, there were no permanent magnet speakers. Instead, it uses electromagnet L14 which drops almost half of the voltage from the 25Z5 rectifier. The centre tap of the transformer is connected to the electromagnet coil, which has a resistance of 1.875kW. This puts the centre tap at about -122V, from which the grid bias is obtained for V4 via the resistive divider of R17 and R18. Provision is made for an external electromagnetic speaker via a four-pin socket on the back. There is a rather heavy-duty switch accessible from the side to switch between the internal and external speakers. There was no power cord with the radio, but two pins were sticking out of the middle of the chassis in the back designed for some kind of plug. I replaced this with a small plate made out of 1.6mm aluminium and fitted it with a cable clamp to hold a three-core mains cable. The radio had two large 8μF electrolytic capacitors that I would not trust, so I immediately replaced these with the only large, high voltage electros siliconchip.com.au that I had, which were 100μF/350VW! Checking for any obvious shorts, I carefully applied power. There were no signs of distress; all the valve filaments lit up, and on turning up the volume, I heard some noises coming from the speaker. Attaching an outside antenna to the red wire out the back, I could actually pick up some stations. I was amazed that after all this time, all the 86-year-old valves were still working. So what else needed doing? There were a couple of capacitors with high voltages across them, so I replaced them with modern ones. It was also a time before ferrites and iron dust cores, so all the coils are air wound. This meant that the only adjustments for the aerial and oscillator coils were with capacitor trimmers. As it turned out, they were not far off, but the IF trimmers needed considerable tweaking to get them to 455kHz. Rodney Champness mentioned that this set suffered from overheating. With the rectifier and output valve side by side, the heat discolours the top of the cabinet. The 25Z5 filament is 25V at 300mA. This is a 7.5W heat source, to which would be added the inefficiency of the rectifier and transformer losses. I cut off the filament wire and soldered in two 1N4004 diodes. This gives a slightly higher DC voltage, but is justified in this case. As for the filter capacitors, the 100μF units were a bit over-the-top, so I replaced them with smaller ones, rated at 47μF/350V. One problem with electromagnet speakers was residual Australia’s electronics magazine hum, but with these capacitors, there is none. There is no power switch. I thought of replacing the volume control with one that included a switch, but there is no room. Likewise, there is no dial lamp, as there is no dial as such. There was probably more work in restoring the cabinet than the electronics. It had a few cracks and the walnut veneer had a few missing bits. I filled these with an appropriate wood filler that turned out to be too light, so I had to darken it. The inside of the cabinet was raw timber, so I sprayed it flat black. A couple of coats of satin varnish improved the appearance. Finally, there were some holes in the speaker cloth, so I replaced this with “vintage” speaker cloth I got on eBay, which was a reasonable match to the original. Once everything was tuned up, I measured the performance, and it is certainly not brilliant. The Melbourne stations come through fairly well with an outside antenna, but using a signal generator, it needs about 50μV for an acceptable signal-to-noise ratio. Does that matter? Not really; the radio is unlikely to be used as such, but will continue to be a decoration at the restaurant. That’s assuming the owner will keep it – this model can fetch up to $1000 on eBay! I went for lunch to the restaurant with the restored radio, and the owner was really pleased with it. She followed it up by saying she has several other old radios that I might like to look at. Who says there is no such thing as a free lunch? SC October 2021  89 And now . . . by Allan Linton-Smith THE UT-P 2016 MEMs WOOFER! Back in May 2020 we told you about the amazing, minuscule UT-P 2017 MEMS Tweeter from USound. We mentioned that it had a “big” brother (if big is the right word!) – the UT-P 2016 “woofer” or midrange driver. This tiny device can provide full range reproduction down to 20Hz and all our tests proved that it also has a great deal of potential. A ustrian developer USound launched the UT-P 2016 at the same time as the UT-P 2017. Both are MEMS or Micro Electrical-Mechanical Systems. Identical in size, the main difference between the two is that the UT-P 2016 is intended for wide-range speaker roles while the UT-P 2017 is designed as a tweeter. These devices have the potential to be very cheap because they can be manufactured using integrated circuit (IC) fabrication and device packaging processes. And from a manufacturing viewpoint, they are also easy to mount because they can be soldered in place by reflow soldering techniques, which is how most SMD components are incorporated into commercial applications. These MEMs speakers are in fact SMD speakers! 90 Silicon Chip These little speakers can be made far more easily than conventional moving-coil miniature speakers. It has been estimated that MEMS speakers will require around one thousand times less manufacturing time to produce! USound woofer performance Listening tests with the woofer were encouraging. A variety of music was auditioned including jazz, piano, classical and hard rock and the tiny MEMS speakers performed admirably with all genres. Our Test Bed: the MEMS speaker was mounted on a small PCB with the recommended 3mm gap. This feeds directly into our Bruel & Kjaer microphone but it is slightly different from the manufacturer’s setup, accounting for slight differences in the specifications. The back pressure from the small port in the rear of the speaker allows it to “breathe”, especially at low frequencies. Australia’s electronics magazine siliconchip.com.au Particularly impressive was the very lifelike reproductions of drums, possibly because of the excellent transient response. The big advantage of a tiny item like this is that it allows a frequency response to low frequencies for in-ear or near-earware which add to the realism of rumbles, quakes and explosions. Also because it is effectively a capacitor, its impedance has no significant peaks or troughs especially at lower frequencies. These often dog conventional dynamic drivers. It is easy to drive and does not require much current. Virtually any amplifier, even a preamplifier will be OK as long as it can deliver up to 5.3V RMS (15V peak-to-peak) although, as we said in the May 2020 issue (siliconchip.com.au/Article/14441), we would be reluctant to use a Class-D amplifier. Frequency response The USound MEMS UT-P 2016 woofer is quite smooth below 2kHz at its near maximum input of 15V pk-to-pk and this is close to the manufacturer’s test data. At low frequencies (below 1kHz) there is almost no variation in the measurements which were made in a closed test setup. A “normal” dynamic speaker would fall off dramatically below 100Hz and would also have significant peaks and troughs. Most headsets using dynamic drivers would also have these peaks and troughs, so this speaks highly of the excellent engineering of these MEMS speakers. We noted that in their “Danube” +2.5V to +5.5V C3 10uF 10V B2 GAIN C6 A3 AUDIO_IN 1uF 6.3V B3 C9 1uF 6.3V GND VDD SHDN_N GAIN SW VBST VAMP IN+ OUT+ IN- OUTSGND PGND D2 GND D1 C1 A1 C7 B1 C8 A2 D3 1uF 35V +15V R3 10K MEMs_BE MEMs_TE 1uF 35V R4 10K LM48580 GND GND Fig.1: the manufacturer’s suggested circuit for driving the MEMS UT-P 2016. It uses an LM48580 IC which comes in a tiny SMD DSBGA package measuring approx 2mm x 1.5mm (intended for hearing aids). Although small size is important, unfortunately this particular chip has 10% distortion at 10kHz and we feel that there are better alternatives. siliconchip.com.au plus for movies with a lot of dinosaurs or explosions etc. The graph was produced with the recommended maximum DC bias of 15.0V and a peak-to-peak input of 15V from an Audio Precision System Two generator. This generator has an output impedance of 30Ω and is not used to drive bigger speakers without using a power amplifier. What this means is that amplifiers for the MEMS speakers can be preamplifiers because the current demands are low. Distortion measurements C5 1uF 25V U2 C2 AMP_ENABLE D1 4.7uH C4 1uF 10V GND spectacle kits, USound have used a tweeter and woofer along with a DAC which doubles as an electronic crossover set at approximately 3.5kHz. We believe this is a reasonable setup for the MEMS speakers but because the woofer peaks at 3.3kHz with an SPL of 104dB we think that a crossover point of 1-2kHz might be better if the UT-P 2017 tweeter was incorporated. The speaker had no problem with an SPL of 83dB at 20Hz, which is very good indeed and would definitely be a L2 C3 GND The specifications for the UT-P 2016 show that the parameters are really tiny compared to bigger woofers . . . and any other speaker is bigger than this one! Remarkably the tiny size is really not a disadvantage because the membrane can easily respond below 20Hz for earware. Australia’s electronics magazine Although the distortion figures look high, it is not unusual to see THD+N figures of 20% or higher even in dedicated subwoofers. This is partly because the levels of sound at 20Hz, for example, are very low and the higher harmonics and noises which are generated at the higher frequencies (like “whooshing” or “huffing” noises) are reproduced more efficiently and increase the amount of THD+N at low frequencies. This little microspeaker having a very flat response means it is relatively low in distortion at 20Hz and this is a definite advantage. October 2021  91 FREQ RESPONSE UT-P-2016 MINI SPEAKER P-P INPUT FREQ RESPONSE UT-P 2016 MINI SPEAKER 15V P-P15V INPUT +50 THD+N VS FREQUENCY USOUND U-TP 2016 17V P-P INPUT 100 +40 50 +30 +20 d B r 20 + 10 0 % 10 A -10 5 -20 -30 2 -40 -50 20 30 40 50 70 100 200 300 400 500 600 Hz 800 1k 2k 3k 4k 5k 6k 8k 10k 20k Hz USound woofer practical applications All sorts of innovations come to mind when you can have a thin woofer and mount it on a flat surface. The obvious one is for earphones, earbuds and headphones but there are many other novel uses and this particular unit can be used virtually NΩ /2$' NΩ Ω +] 92 Silicon Chip )5(48(1&< 20 30 40 50 70 100 200 300 400 500 600 800 1k 2k 3k 4k 5k 6k 8k 10k 20k Hz Fig.2: frequency response of the USound MEMS woofer is quite smooth below 2kHz at its near maximum of 15V p-p and is close to the manufacturer’s test data. Zero dBr was set at 1 Pascal which represents a sound pressure level of 94dB so the peak is an SPL of 104dB. The speaker had no problem in reproducing 83dB at 20Hz! The graph was produced with the recommended maximum DC bias of 15.0V. Naturally, the distortion level is higher at low input levels because when the voltage drops below about 1V, the SPL is almost inaudible and the resultant signal-to-noise ratio is also low. As the input approaches the maximum of 15V peak-to-peak the distortion level drops to around 2-3% which is not bad for any speaker. There are no microphones which do not have their own distortion. Ours contributes about 0.3-0.4% so the best measurement using this system is about 1-1.5% because the microphone actually multiplies the distortion – it doesn’t simply add to it. 0.9 Fig.3: this plot of THD+N vs frequency shows that our prototype is as the manufacturer designed and has a fairly low distortion in the 2-3kHz range. Naturally this speaker would use a low pass filter at 3kHz or higher to be in its “happy” range and would mate well with the UT-P 2017 tweeter. anywhere you have restricted space and power, and require close proximity stereo or surround. An example is audio visual and virtual reality glasses. For this, USound market a two-piece unit (left & right) to act as “near ear” speakers, complete with a tiny MEMS woofer and tweeter. These have a crossover point of 3.54kHz and promise excellent performance down to 20Hz. These can also be obtained from Digi-Key for around A$700 per pair. This device is called the “Danube” with respect to its German origin. It is designed to fit in a spectacle frame. The sound travels directly into the ear and the speaker “cabinet” is a dipole design. They do have inbuilt DAC and audio amplifiers but require a power supply and a 16-pin connector as well as a Bluetooth receiver. USound also market ready-to-go spectacles in their “Fauna” range and these come in a variety of styles and include a microphone for connecting to a phone. We were not able to get hold of a pair for testing but were able to obtain a similar Asian product on ebay for $75 including GST. These are remarkable products and the stereo effect is quite stunning. The sound seems to be coming from a distance – your brain tells you that N+] it must be out there Australia’s electronics magazine because you can hear background sounds as well. When you turn your head, the distant sounds seem to follow – it’s quite an experience! You don’t need to constantly pull out those annoying earbuds or remove a headset to hear someone talking to you either. Overall it’s a very pleasant and comfortable arrangement. I didn’t try it for VR but I am sure the experience would be enhanced with the type of freedom the spectacles add. Of course, if you don’t normally wear glasses, you can always get them as sunnies or simply tinted. Your local optometrist can easily arrange to have your personal prescription lenses fitted. In fact, our local guy is fitting up our $75 unit as this article is being written. Conclusion No doubt tremendous advances have been made to create such a tiny speaker with excellent performance characteristics. The current and potential applications will no doubt increase over time. The capability of manufacturing billions of these little devices using integrated circuit technology and the ability to install them on electronic devices using flow soldering techniques will inevitably reduce prices in the usual fashion. These devices are currently very expensive but so far, it has been a monopoly for USound. We just have to wait for more players to enter the market! Editor’s note: the UT-P 2016 has been recently obsoleted and replaced with the similar UT-P 2018, which we have not yet tested. siliconchip.com.au ; UPDATE: CUI DEVICES MODEL CDS-13138-SMT IMPEDANCE VS FREQUENCY 8 OHM MEMS 9.8 9.6 Speaker Impedance (ohms) While strictly speaking this tiny speaker from CUI Devices isn’t a true MEMS device, we include it as a possible alternative. It is about the same price as the USound MEMS speakers and is available from Digi-key China (Cat 102-3536-2-ND). This particular speaker measures 13 x 13 x 4mm; about five times larger than the tiny USound 2016 but has a much poorer performance. However, the larger size does make it much easier to handle and solder. That makes it more useful for DIY projects. It is a purely dynamic speaker and requires no power supply which would make it useful for miniature devices. From the frequency response curve and the distortion data of the CUI MEMS speaker, we would conclude that it would be adequate for voice reproduction and frequencies above 1kHz. It would be useful where a range of high frequency tones are required such as instrument SC keyboards, small computers etc. (Actual size) 9.4 9.2 9.0 8.8 8.6 8.4Ω 8.2 20 50 100 200 500 1k 2k 5k 10k 20k Frequency (Hz) Graph 1: the CUI has a resonance of 800-900Hz because it is a dynamic speaker, as opposed to the USound 2016 MEMS which is an electrostatic speaker. The resonance shows that this speaker will not reproduce much below 1kHz. THD+N VS FREQUENCY 8 OHM MEMS FREQUENCY RESPONSE 8 OHM MEMS Additional Resources: Product Page | 3D Model | PCB Footprint date 01/20/2020 page 1 of 5 d B MODEL: CDS-13138-SMT │ DESCRIPTION: SPEAKER r A FEATURES • • • • SMT (surface mount) speaker reflow solder capable wide operating temp range compact size Graph 2: it is pretty obvious that this speaker is very poor compared to the USound devices. It has a huge peak around the 7kHz point and has virtually nothing below 1kHz, as you might expect from the impedance data. Graph 3: the distortion is acceptable from 2kHz to 20kHz but there is high distortion in the low frequency range due to the poor frequency response. This creates a high signal-to-noise ratio below 1kHz. SPECIFICATIONS The CUI Devices CDS-13138SMT mounted on a small piece of perfboard to allow easier connection (shown life size). siliconchip.com.au parameter conditions/description input power maximum power: IEC-60268-5, filter 60s on/120s off, 10 cycles at room temp impedance at 1.5 kHz, 1.0 V resonant frequency (Fo) at 1.0 V frequency response output SPL ±10 dB Fo sound pressure level at 0.7 W, 0.1 m ave, at 1.0, 1.6, 2.0, 3.2 kHz at 1.0 W, 1.0 m ave, at 1.0, 1.6, 2.0, 3.2 kHz 84 67 distortion at 2.0 kHz, 0.7 W buzz, rattle, etc. must be normal at sine wave between Fo ~ 20 kHz dimensions 13 x 13 x 4.0 magnet Sm2Co17, Ø6.0 x 1.0 mm material LCP cone material mylar terminal surface mount, Au plating min typ max units 0.7 1.0 W 6.8 8 9.2 Ω 840 1,050 1,260 Hz storage temperature -40 yes dB dB 5 % V 1.1 -40 RoHS Hz 90 73 mm Australia’s electronics magazine operating temperature yes 20,000 2.37 weight washable 87 70 g October 2021  93 85 °C 85 °C Vintage Radio Reinartz Reinartz “4-valve” “4-valve” reaction reaction radio radio By Fred Lever I built this simple battery-powered AM radio set using the “Reinartz” tuning principal and early 1930s to 1940s components (well, mostly; I cheated in a couple of places). I did this for a few reasons. One is that it was a learning exercise; I knew that it was possible to build a radio set like this, but I didn’t fully understand all the details. Now I do. I also succeeded in turning a load of old junk into a working radio! R einartz tuning is also known as reaction tuning, and I was keen to build a radio using this principle. I wanted to build it such that it would appear to be a radio designed and built in the 30s. So I drew up the circuit shown in Fig.1. I initially toyed with the idea of using battery triodes such as the type 30 or mains-powered tetrodes such as type 24A. But I ended up using two type 57 amplifier pentodes and a type 47 pentode output valve driving the loudspeaker. I could have used a type 80 rectifier but instead, I used a silicon bridge rectifier hidden in a defunct 5V4. This allowed me to wind the HT secondary on the transformer as a single winding. I also wound on 2.5V heater windings, with centre taps for bias and grounding. To get to this arrangement, I had to do lots of prototyping different circuits, fabricating of parts and re-thinking and re-designing when my tests failed. This article presents the receiver in its finished state, with a lot of the development detail left out. Circuit details Valve V1 is a type 57 pentode which works as a three-grid stage, with tuning, feedback, gain control and AM detection. Each grid of the type 57 has some level of DC bias or signal applied. The combination of the tapped antenna coil and tuning capacitor selects the desired AM signal frequency and this signal is applied, via a grid-leak resistor and capacitor, to the control grid (top cap). 94 Silicon Chip Australia’s electronics magazine siliconchip.com.au The amplified plate energy is fed back through to the suppressor grid (pin 4) in phase, via the coil connections and varied by the feedback varicap. This sharpens up the selectivity of the tuned circuit with the best operating position just before oscillation. The screen grid of the valve (pin 3) has a variable DC bias applied, which varies the valve amplification slope, and this is the gain control. All three controls interact to some degree, so they must be adjusted to get the best reception of the tuned station. The valve also acts as a biased detector with a resultant RF signal at the plate (pin 2) including the audio modulation component. The coil labelled “RFC” and the following R/C network attenuates the RF component of the signal, leaving only the audio component. How is that for all-in-one circuit operation? And this principle was understood in 1930! Fig.1: this circuit was built around the principle of reaction (“Reinartz”) tuning and designed to imitate a radio from the 1930s, as shown by the use of type 47 & 57 valves from that decade. However, there is an exception in the use of a silicon bridge rectifier for V4 instead of an equivalent valve. Valve V2 V2 acts as an audio voltage amplifier, as the signal level from V1 is siliconchip.com.au The chassis in its initial, very dirty state. Australia’s electronics magazine October 2021  95 fractions of a volt; not enough to drive the output valve directly. The control grid (top cap) of V2 is fed from the volume control potentiometer. The valve is self-biased at the cathode (pin 5). The suppressor grid (pin 4) is connected to the cathode, and the screen grid (pin 3) is biased at a steady DC level. Valve V2 thus raises the signal level to a few volts at high impedance, suitable for valve V3’s control grid. Valve V3 V3 acts in combination with the output transformer to supply a low impedance drive signal to the loudspeaker, as V2 cannot drive a low-impedance load. Its output impedance is around 50kW, so even with an impedance-matching transformer, it just isn’t capable. The signal from V2 is coupled to the control grid of V3 (pin 3) via a 20nF capacitor. V3 acts as a voltage amplifier, but as it operates at a much higher current and from a higher voltage supply, it can drive the speaker transformer primary, which has an impedance of a few thousand ohms. The transformer steps down the voltage and also the impedance from V3’s anode, transferring power to the 8W speaker coil. V3 is centre-biased by a resistor in the filament ground lead. This raises its cathode voltage to about +17V, placing it on a linear portion of its operating curve. The filaments of V1-V3 are powered from separate centre-tapped windings on the mains transformer. For V1 and V2, the tap is Earthed. “Valve” V4 V4 is the silicon diode bridge rectifier which converts the 230V AC from Two 1930s-vintage power transformers were cleaned and reassembled to act as the power and output transformers. the HT winding of the power transformer into about 325V DC to power the anodes of V1-V3 via an RLC lowpass filter. Valve V4 is a cheat, as the diodes are soldered into the base, and the bottle part is disconnected completely. Thus the set looks like it has a rectifier valve, but it has actually gone solid state! The ~325V DC drops to around 290V after the π filter. You will note a sacrificial 100W resistor in one of the AC secondary leads. If the rectifier or one of the filters shorts, this resistor will smoke and be the (cheap) part that burns, if the fuse does not blow first. The power transformer I had two circa-1930 transformers in my junk box that looked like they would work as the mains power and audio output transformers. Both had turns ratios of 50:1. I stripped one and found the core size was 25 x 25mm of some poor rusty grade of iron lamination. I have previously used a value of five turns per volt on one-inch silicon core, so I started with that level of flux excitation. The power required is about 30W (for 4W audio output!), half of which is for the filaments and half for HT. The primary current would therefore be about 0.125A (30W ÷ 230V). The wire selected has to carry that current; I had some 0.32mm diameter (120mA-rated) wire handy, so I decided to use that for both new primary and secondary HT. Naturally, I added several layers of insulation between the primary and secondary, for safety’s sake, and also between each winding. If I had used a valve rectifier, I would have had to add a 5V winding and double the number of HT turns, with a centre tap, because the valve would only give me a half-bridge. The transformer would then work the iron harder and run hotter with the extra 10W load. So it was nice to leave the rectifier heater winding out and simplify the HT secondary. The 2.5V secondaries provide the valve filament current. Two are required, and both were made using one layer of 1.2mm diameter (2.3A-rated) wire. Output transformer Before stripping the second unit, I felt it might do the audio job as it stood A 5V4 valve envelope was used as a dummy with 1N4004 diodes installed in its base. This acted as V4 while retaining a ‘vintage’ appearance. 96 Silicon Chip Australia’s electronics magazine siliconchip.com.au with the 50:1 ratio and the wire sizes used. For a 4W loudspeaker, this makes the reflected load approximately 10kW (4W x 502); a bit higher than V3’s rating of 7kW. This was borne out by my testing. I wired the transformer across a type 47 valve and loaded its secondary in steps from 2W to 16W. The transformer has an output response rising from 2W, flattening off at 8W and remaining constant to 16W. There was no real peak, indicating that the valve is very ‘soft’ in its plate resistance, and the surrounding losses control the power delivered more than the active device. I found the frequency response to be poor below 100Hz but reasonable between 200Hz to 3kHz, then falling off above 5kHz. I thought this was satisfactory, especially for the 1930s level of performance I was after. So I left the transformer as it was and just dipped it in varnish to seal it up, making it look like its power transformer mate. The cabinet was based on a two-door utility cabinet that had been left out in a council clean-up. The top shelf would house the RF, tuning and detector sections while the bottom would be for the power supply and audio valves. While not winning any points for tidiness, this is the testing bench for the early stages of the radio. Given the high voltages involved, we strongly advise our readers not to prototype valve radios like this. siliconchip.com.au Australia’s electronics magazine October 2021  97 The cabinet The chassis was made from an old computer case and holes were marked and drilled for the various component locations. Having settled on the major components and after proving that each circuit section would work using breadboard lash-ups, I turned my thoughts to the cabinet. I looked around the workshop for some timber or a box of some sort, and spied the perfect thing. It was a twodoor utility cabinet left over from a council clean-up; just the ant’s pants to house my radio, I thought, although I realise that others may not share my enthusiasm. After measuring it, I concluded that the top section had enough room to fit the RF valve, tuning and detector circuits, with the power supply and audio valves at the bottom. That way, on the front panel, the three tuning controls (tuning, reaction and gain) would be up top with the volume knob, power switch and pilot lamp below. Making the chassis I cut some metal from old computer cases and mocked up the front panels for both sections. That looked promising, so I made the front-end chassis by riveting the flat steel sheets together in an “L” shape. The valve socket is spaced off the bottom with a square Perspex insulating sheet. The tuning controls bolt onto the metal front panel. I used as many very old components as I could, favouring parts that had ceramic or Bakelite in them. I used a six-wire connecting cord to join the front-end and power supply sections. This carries the filament and HT supplies, plus the audio feed. The power supply has a deep chassis section, allowing most of the modern parts to be hidden out of view underneath. The resistors and capacitors were fitted onto tag strips with only the valves and transformers showing on top. The volume control, power switch and a big lamp bolt onto the front panel. The metal panels I took from the computer case have stiffeners and some important-looking vent holes, so I arranged the parts around to make it look like they were meant to be there. Painting the chassis & cabinet When the metal cutting was finished, I grabbed some spray cans and experimented with getting some different textures on the metal. First I degreased the metalwork, washed it 98 Silicon Chip Australia’s electronics magazine siliconchip.com.au and dried it. I then sanded back the front panels with 80 grit emery paper so they were matte grey, with straight scratches in a horizontal flow line, like brushed aluminium. I then sprayed on a thick coat of black, and watched as it soaked into the scratches and then dimpled up with a mottled look. Next, I sprayed a thick coat of gloss over the top to fix the dimpling in position. I also sprayed the back and top of the chassis with a light coat of black, followed with a misted spray of aluminium silver that “pooled” slightly upon landing on the wet black, mimicking the old baked enamel “stove” finish. I let that harden and sprayed a couple of layers of clear coat over to fix it. I left the underside of the supply chassis in the basic light-grey PC colour. Next, I power sanded all the timber cabinet surfaces to get rid of the shine and grease, then transitioned it from white to brown. As the first step, I gave it a coat of black as a base, and when that was tacky, added a coat of mission brown all over. When that had hardened, I filled in some of the inset panels and beading with gold paint as a contrast, then sealed the lot with coats of clear gloss. The top section of the radio encompasses the tuner arrangement. Front panel appearance I thought the front panels might look good with screw-on nameplates over the controls. In the old days, we used to make labels from “Traffolyte” black-on-white sheet and mark them with an engraving machine. I don’t have access to an engraving machine or a Traffolyte supply, so I The bottom section of the radio handles the power supply and audio. Both chassis are shown here connected together for further testing. The chassis were de-greased, sanded and cleaned before being painted with a finish similar to an old stove. siliconchip.com.au Australia’s electronics magazine October 2021  99 The completed tuner arrangement section of the radio mounted in the cabinet. The tuning coil is a twoinch air-core solenoid winding without ferrite. Originally this was mounted vertically, but mounting it parallel to the chassis helped reduce interference. Many of the leads were also replaced with stiff copper wire to prevent de-tuning and varying feedback levels. ► The finished audio and power supply ► section of the radio. The type 57 valve (V2) also needed shielding to prevent it coupling to the output valve and transformer. The front view of the finished radio chassis and cabinet. The front panel uses screw-on nameplates, which were made using thick cardboard pieces sprayed with lacquer. A low-powered laser engraver along with some nice timber would also work well if you have one. 100 Silicon Chip Australia’s electronics magazine siliconchip.com.au uncontrolled instability. On close inspection, I found that I had reversed the ground and grid wire ends of the main tuning coil – a simple goof. Thus, the plate feedback winding was always adjacent and uncontrollably coupled to the control grid by leakage capacitance. Reversing the tuning winding wires swapped the feedback coil back to the Earthy end of the tuning coil, and allowed me to connect the feedback wires minus the screaming. The coil then worked, but with it standing vertical on the steel chassis, it performed poorly compared to the prototype on timber breadboard. Flux fields fudged it by printing up thick cardboard pieces, spraying them with lacquer and mounting them with 5/32in screws. Making the RF stages work Once I’d finished assembling the RF and audio stages, I powered them up using bench supplies. Despite having proven that individual circuit sections worked earlier, I struck some interesting problems. This is where I learnt more about 1930s radio design and reaction circuits. After a safety check for shorts, I powered the tuner section up, temporarily hooked to an external audio amplifier. The tuner screamed and made blurting motorboat noises, and only faintly allowed radio 2RPH through. The feedback gang did nothing, and the screen gain control only worked like a switch, all or nothing! The tuning control only vaguely worked, and the whole thing was worse than a dud crystal set. Oh dear. I disconnected the coil feedback paths and ran it as a straight TRF detector, and found the coil then tuned in stations over the broadcast band normally, but with low gain and poor selectivity. Whenever I tried to put a feedback wire back on the coil, I got The tuning coil is just a plain 2-inch air-core solenoid winding with no ferrite to concentrate the flux field. The flux field is therefore a toroid coming out of the winding ends and linking end-to-end down the length of the solenoid. Nearby metal will interfere with this flux field. The solution was to mount the coil with its axis parallel to the chassis, high enough off the metal surface to avoid any damping, as you can see in my photo at upper left. Also, I found that moving some of the leads de-tuned the station or changed the feedback level. I replaced those sensitive wire runs with stiff tinned copper wire. The whole thing then settled down and became reliable, stable and worked as in my prototype tests. Stations could be tuned in and lifted clear of adjacent stations with appropriate settings of the gain and feedback controls. Finishing the power supply The underside view of the chassis that houses the power supply section. siliconchip.com.au Australia’s electronics magazine In building this section, I wanted to put all the parts onto tag strips, but I did not fuss too much about using all 1930s components. Some of the capacitors are brand new but being out of sight, don’t detract from the look of the chassis. I fitted the clunky-looking old school parts on the top where they could be seen. I wound the smoothing choke on a 15mm core with about 600 turns of the same gauge wire as used on the power transformer. The resulting choke measured about 2H and with the 40μF filter caps, it’s good enough to remove most of the hum. See the photo adjacent for an underside view. October 2021  101 Fig.2: the detector plate (V1) was fed with a 915kHz sinewave, showing just the carrier signal. True to form, once I’d finished everything, plugged in the speaker and powered it up, there was more screaming instability and wall-to-wall 50/100Hz hum that was not there before! The 50Hz and 100Hz components were mainly due to the negative HT and signal rails not being bonded to chassis ground. Another minor source of hum and instability was not having the speaker secondary grounded. With those problems cleared up, I was left with oscillation when the volume control was turned up. The reason was simple. There is no way you can have an unshielded valve like a type 57 adjacent to the output valve and transformer and not get coupling through the air. Just placing a hand between the two valves removed the instability. I fitted a shield over the type 57 valve, and that was all that was needed. The tabletop speaker Fig.3: this carrier signal was then modulated at 450Hz, but note this isn’t a ‘typical’ modulated waveform, as the valve is already affecting it. I wanted something that looked the part and once more, dipped into the junk box looking for inspiration. This speaker was made from a kitchen colander, a monitor stand and a discarded car speaker driver (as shown in the photo at upper right). I sprayed it the same mission brown as the set, and it plugs into the audio chassis via a jack plug. The result may make the purists wince a bit, but I was quite pleased with the finished product. It works! Fig.4: at the tuner’s output the choke and stray capacitances have rolled off the RF carrier to nearly zero. To my joy, the whole radio then worked as expected. With a 10m external aerial, at Springwood in the NSW Blue Mountains, I could tune in all the Sydney stations plus a hint of others down in the hiss and crackle. The feedback and gain controls worked as before, varying the gain and selectivity. With an output of only a couple of watts, the speaker delivers a comfortable listening level. Detector wave shapes Fig.5: the audio at the amplifier valve’s plate (V2) before being sent to the grid of V3. 102 Silicon Chip I took some scope screen grabs of the wave shapes around the detector. They are a bit different from those of a receiver with clear-cut RF stages with separate diode detectors. Feeding the detector with a 915kHz sinewave gave the waveform shown in Fig.2 at the detector plate. This shows a carrier with some small, Australia’s electronics magazine The completed tabletop speaker. It consists of a computer monitor stand, colander, and an old car speaker. Like the rest of the design, it’s a hodgepodge of parts. unknown modulation at about 9kHz. Perhaps this is a beat frequency from an adjacent carrier, or some form of low-frequency self-oscillation. I then modulated the carrier at 450Hz and the plate signal, shown in Fig.3, illustrates the valve ‘detecting’ the signal in its own way. At the output point of the tuner, the audio signal has most of the carrier (and the odd 9kHz signal) removed by the radio-frequency choke (RFC), acting as a low-pass filter (Fig.4). Valve V2 then amplifies the audio, providing plenty of voltage for the grid of V3 (Fig.5). The whole story For those interested, I’ve written a series of articles with much more detail on the design and construction of this set. The complete saga has all the gritty of design failures and goofups. I’ve posted it on the “Vintage Radio” website hosted by Brad Leet. You can read all these details at the following links: https://vintage-radio.com.au/ default.asp?f=12&th=30 https://vintage-radio.com.au/ default.asp?f=12&th=44 SC 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. Colour recognition using LEDs and an LDR I decided to make a box that determines the colour of objects placed upon it. Rather than using a prebuilt module or phone app, I’m doing it from first principles, using three LEDs (red, green & blue) and a light-dependent resistor (LDR). I have found that both adults and children are very impressed and spend quite a bit of time playing with it. On the top, it has an LCD screen that shows the result, an on/off switch, a pushbutton for initiating a test and a cylinder that has the LDR and LEDs mounted in the bottom. The object to be measured is placed over the cylinder. When you press the pushbutton, the microcontroller inside switches each coloured LED on sequentially and measures the intensity of the reflected light using an LDR, a constant current source and the analog-todigital converter in the microcontroller. Circuit Ideas Wanted siliconchip.com.au It converts the LDR resistance to a voltage that it can measure using a constant current source. The percentage of each colour is calculated, along with the overall colour of the object. The result is displayed on the LCD screen. The results are quite reproducible, and it works for different shade intensities of each colour. Consider a purple object. It would reflect most of the blue or red light incident on it, but not green. So when the blue or red LED is lit, the LDR resistance is low, and when the green LED is lit, the LDR resistance is high. This is how the unit can determine the colour of the object. All the components are available offthe-shelf and are mounted on a simple PCB that plugs into the display. To cater for the considerable variation in parameters of the coloured LEDs and LDR, four potentiometers are used for the initial calibration, which only requires a DVM. Place a white object over the sensor and remove IC1 from its socket. Short socket pin 2 to ground, set VR2 mid-way and measure the voltage at socket pin 15. Then short socket pin 13 to ground instead of 2, and adjust VR3 to get the same voltage at pin 15. Repeat for socket pin 12 and VR4. If you can’t get the voltages equal, adjust VR2 one way or the other then repeat the above steps. Finally, replace the micro, press the test button and check the readings. Adjust VR1 to get them all above 200, and re-adjust VR2-VR4 (if necessary) to make the readings equal. The Gerber files for the PCB and CAD drawings for the box and LED/ LDR holder, along with the HEX file and BASIC source code for the PIC are available from siliconchip.com. au/Shop/6/5931 Les Kerr, Ashby, NSW. ($120) 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 October 2021  103 Battery charger with WiFi interface This battery charger can charge one to four AA, AAA, 14500 or 18650 size NiCad, NiMh or Li-ion cells at up to 500mA. The charge voltage, current, cell temperature rise and time limits are set and controlled via a web page that can be accessed using the browser on your smartphone, tablet or PC. This is accessed via your usual home WiFi network, using a fixed IP address set in the code. One handy feature of this design is that the mAh charge capacity of each cell is shown. This allows the rapid identification of good or faulty cells. The system operates with a closed-loop proportional controller that adjusts the current and voltage to user-defined limits, regulating within about ±5mA and ±10mV. End of charge occurs when: 1) The cell has switched from constant current to constant voltage control, and its current has reduced to 50% of the setting, or; 2) The cell reaches its temperature rise limit, or; 3) The time limit is reached. The charger is built using an old ‘dumb’ charger case, six separate modules, a 7805 linear regulator and a handful of discrete components. A pre-built LM2596-based stepdown converter module (MOD1; siliconchip. com.au/Shop/7/4916) is used to reduce the 12V DC input supply to a voltage suitable for charging the cells. This is then connected to one or more cells via a four-channel relay module (MOD5) and schottky diodes D1, D4, D7 & D10. This arrangement allows the micro to determine which cells are being charged and at what voltage. The charge voltage is controlled by varying the duty cycle of a PWM signal produced at digital output D8 by the D1 Mini (MOD2). This connects to the bottom of the LM2596’s feedback voltage divider, so the lower the average voltage from D8, the higher the cell charge voltage. Added trimpot VR1 and the module’s onboard trimpot set the maximum and minimum voltages respectively. The LM2596 can also be switched off via digital output D7, which is wired to the LM2596’s enable pin as shown. This pin of the regulator is not brought out to a header on the module, so it must be lifted off the board and wired with a flying lead. The charge current and voltage of each cell is monitored separately using two ADS1115-based analogto-digital converter (ADC) modules (MOD4 & MOD6; siliconchip.com.au/ Shop/7/4633). These have four channels each, so there are eight channels in total. Four channels are used to sense the voltage across each cell, via a 1kW protection resistor. The other four channels are used to determine the voltage across the 1W 5W current-sense resistors. These ADC modules interface to the micro via a shared I2C serial bus. As the ADC modules run off 5V and the D1 Mini runs off 3.3V, a four-channel bi-directional logic level converter (MOD3) is used, similar to the Sparkfun BOB-12009. All five DS18B20 digital temperature sensors are connected in parallel to digital input D3 of MOD2, with a 4.7kW pull-up resistor. As each sensor has a unique ID, the micro can query them individually even though they use the same pin for communication. A 12V 2A regulated plugpack A screenshot of the battery charger’s web interface. supplies power and can charge four Li-ion cells at up to 500mA each. I have prepared a comprehensive user manual for the charger in PDF format, can be downloaded from siliconchip. com.au/Shop/6/5933 along with the firmware for the D1 Mini module. Note that in addition to lifting and soldering to pin 5 of the regulator on the LM2596 buck module, you also need to change the 330W resistor connecting the feedback pin to ground to a 2.7kW resistor, plus you need to wire Left: the exterior of the charger case shown with two 18650 cells being charged. Right: the underside of the charging board. 104 Silicon Chip Australia’s electronics magazine siliconchip.com.au the wiper of VR1 to pin 4 of the regulator IC, or one of the components that connect to it. Finally, a small finned heatsink must be glued to the LM2596 chip siliconchip.com.au using thermal heatsink glue to reduce temperature rise when charging at the higher currents. The 7805 regulator must also be fitted with a small finned heatsink. Australia’s electronics magazine The accompanying screenshot shows what the web interface looks like when it’s all up and running. Phillip Webb, Hope Valley, SA. ($150) October 2021  105 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. 10/21 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 24LC32A-I/SN 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 PIC16F1705-I/P PIC16F88-E/P PIC16F88-I/P $15 MICROS Digital FX Unit (Apr21) RF Signal Generator (Jun19), Si473x FM/AM/SW Digital Radio (Jul21) RGB Stackable LED Christmas Star (Nov20) Shirt Pocket Audio Oscillator (Sep20) ATtiny816 Development/Breakout Board (Jan19) Ultrabrite LED Driver (with free TC6502P095VCT IC, Sep19) LED Christmas Ornaments (Nov20; specify variant) Nano TV Pong (Aug21), SMD Test Tweezers (Oct21) Car Radio Dimmer (Aug19), MiniHeart Heartbeat Simulator (Jan21) Refined Full-Wave Universal Motor Speed Controller (Apr21) Model Railway Level Crossing (two required – $15/pair) (Jul21) Motor Speed Controller (Mar18), Heater Controller (Apr18) Useless Box IC3 (Dec18) Tiny LED Xmas Tree (Nov19) Microbridge (May17), USB Flexitimer (June18) Digital Interface Module (Nov18), GPS Finesaver (Jun19) Digital Lighting Controller LED Slave (Dec20) Ol’ Timer II (Jul20), Battery Multi Logger (Feb21) 5-Way LCD Panel Meter (Nov19), IR Remote Control Assistant (Jul20) Ultrasonic Cleaner (Sep20), Electronic Wind Chime (Feb21) 20A DC Motor Speed Controller (Jul21) Flexible Digital Lighting Controller Slave (Oct20) Automotive Sensor Modifier (Dec16) Remote-controlled Preamp with Tone Control (Mar19) UHF Repeater (May19), Six Input Audio Selector (Sep19) Universal Battery Charge Controller (Dec19) ATSAML10E16A-AUT High-Current Battery Balancer (Mar21) PIC16F1459-I/SO Four-Channel DC Fan & Pump Controller (Dec18) PIC32MM0256GPM028-I/SS Super Digital Sound Effects (Aug18) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sep19) PIC32MX170F256B-50I/SP Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) Micromite DDS for IF Alignment (Sep17), Tariff Clock (Jul18) GPS-Synched Frequency Reference (Nov18), Air Quality Monitor (Feb20) RCL Box (Jun20), Digital Lighting Controller Micromite Master (Nov20) Advanced GPS Computer (Jun21) Touchscreen Digital Preamp [2.8in/3.5in version] (Sep21) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) PIC32MX795F512H-80I/PT Maximite (Mar11), miniMaximite (Nov11), Colour Maximite (Sep12), Touchscreen Audio Recorder (Jun14) $20 MICROS dsPIC33FJ64MC802-E/SP dsPIC33FJ128GP306-I/PT dsPIC33FJ128GP802-I/SP PIC32MX470F512H-I/PT PIC32MX470F512H-120/PT PIC32MX470F512L-120/PT 1.5kW Induction Motor Speed Controller (Aug13) CLASSiC DAC (Feb13) Ultra-LD Preamp (Nov11), LED Musicolour (Oct12) Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) Micromite Explore 100 (Sep16) PIC32MX695F512L-80I/PF PIC32MZ2048EFH064-I/PT Colour MaxiMite (Sep12) DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) DIY Reflow Oven Controller (Apr20) $30 MICROS KITS, SPECIALISED COMPONENTS ETC SMD TEST TWEEZERS KIT (CAT SC5934) (OCT 21) $35.00 PCBs, micro, other onboard parts and heatshrink (no cell or brass tips) NANO TV PONG SHORT FORM KIT (CAT SC5885) (AUG 21) $17.50 PCB and all onboard parts only (does not include controllers) MODEL RAILWAY LEVEL CROSSING (JUL 21) $15.00 $5.00 - 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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 DCC PROGRAMMER (INC. HEADERS) ↳ WITHOUT HEADERS 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 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) DATE 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 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 PCB CODE SC4716 09107181 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 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 Price $7.50 $5.00 $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 $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 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT 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 BK1198 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 HIGH-CURRENT BATTERY BALANCER (4-LAYERS) MINI ISOLATED SERIAL LINK REFINED FULL-WAVE MOTOR SPEED CONTROLLER DIGITAL FX UNIT PCB (POTENTIOMETER-BASED) ↳ SWITCH-BASED ARDUINO MIDI SHIELD ↳ 8X8 TACTILE PUSHBUTTON SWITCH MATRIX HYBRID LAB POWER SUPPLY CONTROL PCB ↳ REGULATOR PCB VARIAC MAINS VOLTAGE REGULATION ADVANCED GPS COMPUTER PIC PROGRAMMING HELPER 8-PIN PCB ↳ 8/14/20-PIN PCB ARCADE MINI PONG Si473x FM/AM/SW DIGITAL RADIO 20A DC MOTOR SPEED CONTROLLER MODEL RAILWAY LEVEL CROSSING COLOUR MAXIMITE 2 GEN2 (4 LAYERS) BATTERY MANAGER SWITCH MODULE ↳ I/O EXPANDER NANO TV PONG LINEAR MIDI KEYBOARD (8 KEYS) TOUCHSCREEN DIGITAL PREAMP ↳ RIBBON CABLE / IR ADAPTOR DATE 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 MAR21 MAR21 APR21 APR21 APR21 APR21 APR21 MAY21 MAY21 MAY21 JUN21 JUN21 JUN21 JUN21 JUL21 JUL21 JUL21 AUG21 AUG21 AUG21 AUG21 AUG21 SEP21 SEP21 PCB CODE 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 14102211 24102211 10102211 01102211 01102212 23101211 23101212 18104211 18104212 10103211 05102211 24106211 24106212 08105211 CSE210301C 11006211 09108211 07108211 11104211 11104212 08105212 23101213 01103191 01103192 Price $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 $12.50 $2.50 $7.50 $7.50 $7.50 $5.00 $10.00 $10.00 $7.50 $7.50 $7.50 $5.00 $7.50 $35.00 $7.50 $7.50 $5.00 $15.00 $5.00 $2.50 $2.50 $5.00 $12.50 $2.50 OCT21 OCT21 OCT21 01109211 12110121 04106211/2 $15.00 $30.00 $10.00 NEW PCBs 2-/3-WAY ACTIVE CROSSOVER TELE-COM INTERCOM SMD TEST TWEEZERS (3 PCB SET) We also sell an A2 Reactance Wallchart, RTV&H DVD, Vintage Radio DVD plus various books at siliconchip.com.au/Shop/3 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 Using Battery Lifesafer with heavier load We have an Engel camping fridge in the car which runs off a 100Ah auxiliary battery. It all works tolerably well unless we spend too long in camp without running the car, or I forget to switch it off at the end of a trip. Over the decades, we have ruined several thousand dollars worth of batteries by running them flat. It didn’t much matter as the auxiliary batteries only lasted 6-12 months anyway. Now we have moved the battery out of the engine bay and have a DC-DC charger to control the charge rate. The latest investment is a LiFePO4 battery. If I can cure the over-discharge problem the new battery should outlast the car (unless the vibration kills it). As a first try, I bought a 10A low voltage cut-out for $15 at the corner store. I didn’t really expect it to work and it didn’t survive the first switch-on. The same store has a 20A version for $47. The catalog suggests it can switch off fridges but the pamphlet in the box doesn’t suggest it can turn them on. I took it back while it still had all its smoke left inside. Looking at your Dual Battery Lifesaver (December 2020; siliconchip. com.au/Article/14673) it is only rated at 5A per channel, but the fridge only draws about 3.5A after the switch-on surge. The switching Mosfets Q1 and Q2, in themselves, seem to be fairly robust devices with a continuous current rating of 80A each. Furthermore, it appears that the two channels can be run in parallel by bridging the inputs and outputs and using appropriate divider resistors. I don’t imagine you have tested the unit for switching on motors but, as an informed guess, would you expect it to work? Thank you for a great magazine that has kept me entertained and somewhat up-to-date over the years. I probably still have a copy of the first issue somewhere at the back of the shed. (M. F., Samford, Qld) 108 Silicon Chip • We agree that those Mosfets are likely rugged enough to withstand switching the fridge load. However, the Dual Battery Lifesaver PCB is not designed to handle the likely peak current. Also, without a heatsink, the Mosfets risk overheating when the fridge starts. If you want to try it, instead of mounting the Mosfets on the PCB, bolt them to a piece of metal to act as a heatsink and solder the power wires directly to the drain and source pins instead of connecting them via the PCB (in the same manner as they would be connected via the PCB). You will also need to connect the Mosfet gate and source pins to the PCB; the drains do not need to be connected. Transformer output voltage is a bit high I have just finished building the 45V 8A Power Supply (October-December 2019; siliconchip.com.au/Series/339). My mains voltage sometimes rises to 245V AC, giving me 60V out of the rectifier bridge. As mentioned in the article, this is the limit of REG3. Will that be a problem? Could I use the Mains Moderator project (March 2011; siliconchip.com. au/Article/937) to solve this, or is there another way around it? Also, the 4700µF capacitors in the parts list (Altronics R5228) have a 12.5mm pin spacing whereas the PCB holes are 10mm apart; they fit but won’t sit flat on the board. They are also physically larger than those shown in your photos. (A. V., Ferntree Gully, Vic) • The LM317HV will be running very close to its limit. The 60V rating applies between the input and output, so you might be able to run it with a higher input if you are not running the output down to 0V, or allowing the current limiting to pull the output down, but we would not recommend it. The Mains Moderator would be well suited to bringing the mains voltage down, although you might have to Australia’s electronics magazine fine-tune it to avoid getting an output voltage that’s too low. Its 450W rating should be fine for the 45V 8A PSU. Suppliers change the physical dimensions of their components from time to time. As long as they have the appropriate voltage and capacitance ratings, they should be fine. Alternative to KSA1220 transistor It looks like the KSA1220AYS transistor used in the SC200 audio amplifier (January-March 2017; siliconchip. com.au/Series/308) as the VAS current source and one of the output drivers has been obsoleted by most suppliers (and is out of stock everywhere). The entire KSA1220 series looks to be on its way out. Its complementary KSC2690 transistor seems to still have plenty of stock available, but it’s kind of pointless if we’re specifically going for complementary pairs. Is there an alternative transistor pair I could use? (T. S., Balcatta, WA) • We can’t find any official replacement for the KSA1220 series, but the TTA004B seems like a reasonable substitute and is still available. It is a good idea to change both driver transistors (Q11 & Q12) and the Vbe multiplier (Q10) at the same time, and the complementary TTC004B should be suitable for Q10 & Q11. You might as well change Q8 to a TTC004B at the same time. We also sell a kit of parts for the SC200, which includes two KSA1220s: siliconchip.com.au/Shop/20/4140 Problem with SC200 amplifier module I’ve build two of your SC200 amplifier modules. When monitoring the voltage across the 6.8W safety resistors, the positive rail reading is always 0.3V higher than that of the negative rail. In my case, the readings are 1.177V and 0.851V. The power supply appears to be OK and with a sinewave input, the siliconchip.com.au output appears clean and smooth with no clipping. I have replaced transistors Q1-Q4 but it made no difference. I have also discovered that Earthing the heatsink is very important as not doing this will result in instability problems. I hope that you can help in resolving my problem. (R. S., Nowra, NSW) • We did not experience any instability with a non-Earthed heatsink while testing our prototype. However, it is a good idea to Earth the heatsink anyway. We suspect you must have a fault somewhere on your board if the positive rail current is higher than negative. There should not be much current flowing through ground and that is the only other power supply connection. First, check that the output voltage sits close to 0V with the input shorted out. Then check the voltage across the 10W resistor which is above CON3. It should be low – just a few millivolts at most. Also check the voltage across the 100W 1W resistor near the top righthand corner of the board. It should be about 1V. Check that the voltages across the two 6.8kW resistors are about 28V each. You might also want to try swapping the two safety resistors around just to make sure the imbalance is not due to them being different values. But a 38% difference should not be possible given that they should have, at worst, 10% tolerances. If that all checks out but the imbalance remains, you could have a leaky capacitor somewhere on the board, given that the remaining ground connections not checked via the above methods are to bypass capacitors. Clip detector circuit wanted I was wondering if the clipping circuit from your SC200 amplifier could be used for other amplifier modules, or have you published a universal clipping detector? Also, have you ever published a distortion detector like this one (https://damore-engineering. myshopify.com/products/dd-1)? • Yes, the clipping circuit can be used on many amplifiers. If the supply rails are substantially different from the ±56V used for the SC200, the values of the resistors connected from zener diodes ZD1 and ZD2 to ground might need to be changed. siliconchip.com.au For example, if the supply rails are ±20V, the resistors would need to be approximately half their original values. That would mean changing the 33kW resistor for ZD1 to about 15kW, and the 68kW resistor for ZD2 to about 33kW. We also published a clipping indicator in Circuit Notebook (January 1990; siliconchip.com.au/Article/7328). That one is a bit more complicated as it involves two ICs, although its operation is easier to understand. The only distortion analyser we have published is the Low-Frequency Distortion Analyser from April 2015 (siliconchip.com.au/Article/8441). While it was designed primarily to monitor distortion of the 50Hz mains waveform, it should work with a 1kHz audio tone, although its supported signal range of 3-20V is a bit limiting. You could use a switched attenuator to measure the distortion of higher amplitude signals (such as from a highpower amplifier) and an op-amp based gain stage to measure lower amplitude signals. As it can measure distortion down to about 0.1%, it is more sensitive than the product you linked, and it gives a proportional reading rather than just a go/no-go indication. We might see if we can come up with a revised version of that project that can handle a broader range of signal amplitudes and possibly a digital readout as well as better performance (ie, the ability to measure distortion below 0.1%). It is also possible to measure distortion levels with extreme accuracy using the USB SuperCodec (August-October 2020; siliconchip. com.au/Series/349) with the Balanced Input Attenuator add-on (November & December 2020; siliconchip.com.au/ Series/349). It requires a PC, but it can handle signals from below 1V RMS to 50V RMS in four ranges. How to limit eBike motor power Is there any way to limit the current going to the motor with the High Power DC Motor Speed Controller (January & February 2017; siliconchip.com.au/ Series/309)? I need to achieve 200W output from the controller to an eBike motor using a 52V DC supply. Can the current limiting be made switchable so that the 200W limit can be enabled and disabled? Australia’s electronics magazine Also, can a larger eBike motor sold as being, say, 1500W be limited by a controller to either 200W or 250W and then be considered a 200W or 250W motor to meet the legal limits for public use? (P. B., Cooloongup, WA) • There isn’t any easy way to limit the power with that controller design. A simple current limit does not necessarily restrict the power to the motor, as the voltage also needs to be considered for power measurement. One way to limit the power is to adjust the maximum throttle limit trimpot (VR2) to reduce the motor drive at full throttle, under maximum load. However, this adjustment could limit the top speed when running at lighter loads. The motor power could also go above the set limit at lower speeds when the engine is heavily loaded. It would be possible to switch between two maximum throttle limit adjustments by adding a second trimpot and arranging the switch to connect one into the circuit at a time. To implement a power limit correctly, you would need a supervisory circuit that can measure the voltage and current applied to the motor and multiply them to determine the instantaneous power. It would then need to be able to reduce the throttle setting if the limit has been reached. Such a device could certainly have a switchable power limit that it enforces. We have not yet designed such a circuit. We have seen motorbikes with a power limit so that inexperienced riders can use the bike. The power restriction can be removed once the rider has gained a licence allowing them to ride a more powerful bike. The power limit is set by the manufacturer. Whether you can use a 1500W bike limited to 200W or 250W in public is a legal/regulatory question, not an engineering question. The bike in question might need to be tested and verified by the WA motor registry (or similar registration authority) before the bike can be used. Controlling a 2.5kW oven electronically Have you published a thermostat to control a 2.5kW mains-powered heating element? I’m hoping to improve the accuracy of the temperature in my oven. (E. M., Capel, WA) • We haven’t published a design specifically suited for that purpose. October 2021  109 However, we have published thermostats that could be adapted to control a mains-powered heating element drawing around 10A. For example, our High-Temperature Thermometer/ Thermostat (May 2012; siliconchip. com.au/Article/674) could be adapted by omitting its onboard relay and using it to drive an external mains-relay. The Jaycar SY4040 heavy-duty chassis-mount relay is suitable; it has contacts rated at 250V AC, 30A. The mains wiring must be kept isolated from the 12V DC coil wiring and enclosed and insulated according to our usual standards. The only modification required to the controller PCB is that the 10kW resistors at the collector of Q1 and base of Q2 should be reduced to 1kW so that Q2 can drive the lower-impedance SY4040 relay coil. Using a 3-phase VFD to drive a 1-phase motor A Vevor inverter variable frequency drive (VFD) rated at 2.2kW can be purchased for under $100 delivered. They are advertised as requiring a 220V AC single-phase or three-phase input and having a three-phase output. Enquiries to suppliers haven’t clarified whether these units can drive single-phase motors as well as three-phase. I built the Silicon Chip VFD (Inductor Motor Speed Controller, April & May 2012; siliconchip.com.au/ Series/25), but unfortunately, it failed. It did provide either single-phase or three-phase output, which is what I need. Could the Vevor unit be used to drive a single-phase motor? (I. P., Fullarton, SA) • We don’t know the details of that device, so we can only guess. There is no fundamental reason why a threephase VFD can’t drive a single-phase induction motor. But if it monitors the per-phase current, it might refuse to drive a single-phase motor. Note that this means the maximum motor power the unit can drive will likely be reduced (possibly by up to 67%). Be careful using equipment advertised to run from 220V AC on a 230240V AC mains supply. We’ve heard of 220V AC equipment having components with insufficient ratings for our mains voltage, leading to rapid failures. Components used for 230-240V AC mains are generally rated for at least 250V AC and typically 275V AC. 110 Silicon Chip Remember that the same caveats apply for starting single-phase motors at lower speeds, as described in the first IMSC article (April 2012). In short, shaded pole and permanent split capacitor (PSC) motors are usually OK. Capacitor start/run or centrifugal switch equipped motors must be either started at close to maximum speed or modified to start at lower speeds. They can be damaged by continued operation at lower speeds unless modified to ensure the start switch does not re-engage. Given that the unit you describe is a three-phase controller (like our design), you have the option of modifying the motor to use one of the other phases for starting. If doing this, the start winding will need to be disconnected by a relay after a few seconds to prevent it from burning out. Regarding your comment that the IMSC you built failed, we wonder if you are aware of the design changes published in the December 2012 and August 2013 issues (see siliconchip. com.au/Article/469 and siliconchip. com.au/Article/4219). These involved PCB and component changes to overcome some problems that constructors experienced which didn’t show up in any of our prototypes. Perhaps the most significant upgrade that you can perform while repairing your IMSC is to replace the 20A-rated IGBT bridge originally specified (STGIPS20K60) with an upgraded 30A version that became available (STGIPS30C60). That part has now been discontinued, but we have secured a small stock for those still wishing to build or repair this device, available from siliconchip. com.au/Shop/7/2814 From leaking pipes to errant sheep I have a minor underground leak somewhere in the water pipe running from the water meter to my house. Have you ever published a “super microphone” that I could position on the ground surface (along the run of the pipe) to listen for water escaping under pressure from the leak? Secondly, I want to protect some trees from sheep that I occasionally get in and am thinking that a DIY electric fence (with a maximum length of about 50m) could be made using a car ignition coil. Have you published Australia’s electronics magazine anything suitable to do that? (T. S. R., Patearoa, NZ) • Finding a slowly leaking pipe by listening would be difficult as the leak would be unlikely to be making much noise. Our most suitable project would be the Electronic Stethoscope (August 2011; siliconchip.com. au/Article/1119). The listening probe would need to make good contact with the ground for you to have any chance of it working. Alternatively, you could use a soil moisture probe to find the wettest area, which might indicate where the leak is. They are available from hardware shops or nurseries. We published a DIY electric fence controller that used a car ignition coil in July 1995. See siliconchip.com.au/ Article/5131 Voltage Interceptor has been superseded In December 2009, you published John Clarke’s project, the “Voltage Interceptor For Cars With ECUs”. He wrote about a voltage interceptor that could effectively change the output signal of any given sensor for improved performance or reliability. I saw that Jaycar used to sell this kit and the hand controller, but they discontinued both several years ago. Is there anywhere I can get this or a close alternative? (B. I., MacArthur, Vic) • The Voltage Interceptor has been upgraded in the December 2016 issue as the Automotive Sensor Modifier (siliconchip.com.au/Article/10451). While there is no kit for this, the main parts, such as the programmed microcontroller and PCB, are available from our Online Ship (see siliconchip.com. au/Shop/?article=10451). Multi Voltage Monitor has been superseded I want to build your Vehicle Multi Voltage Monitor design (May 2006; siliconchip.com.au/Article/2666). I have looked at the Jaycar and Altronics websites but I can’t find any signs of a kit for this project. Is that correct? I presume I can get the PCB from you, then get all the components myself, which I’m keen to do. I have just built the Battery Monitor from Electronics Australia, May 1987! continued on page 112 siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip FOR SALE FOR SALE KIT ASSEMBLY & REPAIR LEDsales 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 LEDs and accessories for the DIY enthusiast PMD WAY offers (almost) everything for the electronics enthusiast – with full warranty, technical support and free delivery worldwide. Visit pmdway.com to get started. LEDs, BRAND NAME AND GENERIC LEDs. Heatsinks, LED drivers, power supplies, LED ribbon, kits, components, hardware – www.ledsales.com.au Lazer Security For Quality That Counts... QUALITY LED PRODUCTS + MORE Massive parts clearance sale, limited stock. Go to lazer.com.au ASSORTED BOOKS FOR $5 EACH Electronics and other related subjects – condition varies. Some books may have already been sold. Bulk discount available. 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 TRONIXLABS PTY LTD would like to thank all of our customers for their support and feedback. For any enquiries or customer technical support, please email support<at>tronixlabs.com PCB PRODUCTION 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 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 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 October 2021  111 Notes & Errata Tapped Horn Subwoofer, September 2021: the Altronics C3088 driver specified for this design has been discontinued. Wagner Electronics (www.wagneronline.com.au) sell suitable alternatives: the SB Acoustics SB20PFC30-8 ($55) and SB20PFCR30-8 ($56.50). These cost less than the originally specified driver and give very similar performance. The only design change required is to increase the diameter of the driver hole from 180mm to 187mm. Advertising Index Altronics...............................25-28 Ampec Technologies................. 11 Analog Devices..................... OBC Dave Thompson...................... 111 Touchscreen Digital Preamplifier, September 2021: in the circuit diagram (Fig.6) on pages 42 & 43, the Vdd pins of IC6 and IC7 are incorrectly shown connected to +12V. They actually connect to +5.5V. Dick Smith Contest.................... 13 Battery Manager, August 2021: in Fig.3 on page 72, Q2 has been incorrectly drawn with a P-channel Mosfet symbol. It is an N-channel Mosfet, like Q1 and Q3. The gate, drain and source pins are marked correctly. Emona Instruments................. IBC Bush VTR103 AM/FM radio, Vintage Radio, August 2021: in the circuit diagram (Fig.2) on pages 102 & 103, capacitor C11 should have been shown in series with L5, not L6. This means that C11 and L6 form a parallel resonant network, not series resonant as stated in the text. Also, the right-most label in the photo at the bottom of p100 is wrong. It is the VHF RF amplifier load coil, not the VHF antenna coil. Jaycar............................ IFC,53-60 Single-Chip Silicon Labs FM/AM/SW Digital Radio Receiver, July 2021: the specified 3.3V regulator for REG2 (LM2936-3.3) has swapped input & output pins compared to the footprint on the PCB. So if you use this regulator, install it facing the opposite direction to that shown in Fig.5 on page 68, or mount it on the opposite side of the PCB but with the flat side facing as shown. Also note that its part code is incorrectly written as LP2936-3.3 in the circuit diagram, Fig.3, on page 67. 7-Band Stereo Equaliser, April 2020: an error has been found in the 7-Band Stereo Equaliser PCB (01104202 RevB). There is a missing track between the 10nF and 2.2nF capacitors above IC7 – they should be in parallel, but only one side of the pair is connected. This causes the second-highest band to operate at the wrong frequency. If you have a PCB with this error, solder a short length of wire (eg, a component lead off-cut) between those two pads. This error will be fixed with the RevC PCB. CLASSiC DAC, February-May 2013: revised firmware for the DAC (0110213B.HEX) is available for download from our website. This fixes pushbutton debouncing problems and includes changes to the IR reception code to better reject noise. Also, some people have complained that one or more TOSLINK input LEDs light up when there is no signal present. This is usually fixed by adding 30pF ceramic capacitors across the empty pairs of pads near the TOSLINK receivers. The November 2021 issue is due on sale in newsagents by Monday, October 25th. Expect postal delivery of subscription copies in Australia between October 25th and November 12th. It is a great kit that Jaycar are still selling here in NZ. (B. N., Dunedin, NZ) • You can look up kit information via our Article Search feature (siliconchip. com.au/Articles/ContentsSearch). Enter the project name (or part of it) in the “Name” field but watch out for differences in punctuation etc. Searching for “Voltage Monitor” shows that there were two kits, DSE K4608 and Jaycar KC5424, both of which have been discontinued. We generally don’t sell PCBs for projects published before 2010 because many of them have been superseded now (there are exceptions). In this 112 Silicon Chip case, it has been functionally replaced by the 10-LED Bargraph from February 2018. This later version doesn’t require any special-purpose ICs and it is also very flexible in its configuration. We sell the PCB for it at siliconchip.com. au/Shop/8/3272 It should be possible to use that to do virtually everything the Vehicle Multi Voltage Monitor can do. You might want to read the article first to determine what parts you need. For example, the 10-LED Bargraph calls for 10 3mm through-hole or M3216/1206 SMD LEDs of unspecified colour, while the Vehicle Multi-Voltage Australia’s electronics magazine Digi-Key Electronics.................... 3 Hare & Forbes............................. 5 Keith Rippon Kit Assembly...... 111 Lazer Security......................... 111 LD Electronics......................... 111 LEDsales................................. 111 Microchip Technology.................. 9 Ocean Controls........................... 8 PHIPPS....................................... 4 PMD Way................................ 111 SC Christmas Decorations........ 69 Silicon Chip Binders................. 81 Silicon Chip Shop...........106-107 Silicon Chip Subscriptions....... 50 Solder Master.............................. 7 Switchmode Power Supplies....... 6 The Loudspeaker Kit.com......... 10 Tronixlabs................................ 111 Vintage Radio Repairs............ 111 Wagner Electronics................... 87 Monitor uses two yellow, six green and two red rectangular LEDs. As far as we can tell, you should be able to fit those same rectangular LEDs to the 10-LED Bargraph PCB (or use 3mm round LEDs with the same colour scheme). You will want to set up the 10-LED Bargraph in linear mode, using the 10 1kW resistors specified in the parts list, just like the Multi-Voltage Monitor. The only trick is that if you want to achieve the 9-16V range option offered by the Multi-Voltage Monitor, you will need to replace R1 with a 5.6V zener diode, with its anode connected to ground. SC siliconchip.com.au “Rigol Offer Australia’s Best Value Test Instruments” Oscilloscopes NEW 200MHz $649! New Product! 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