Fullscreen HTML5Med Res (??MB)HTML4

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 has the right to edit, reproduce in electronic form, and communicate these letters. This also applies to submissions to “Ask Silicon Chip”, “Circuit Notebook” and “Serviceman’s Log”. Grid interconnects are DC‽ I loved the story on the Australian electrical grid in the August 2023 edition (siliconchip.au/Article/15900) and was stunned to learn there’s so much high-voltage DC in the system. Please tell me there will be a follow-up article that will go into more detail on how rectification, AC ‘restoration’ and synchronisation take place at that scale. Greig Sheridan, Hamilton, NSW. Comment: We published an article in the September 2008 issue on Basslink that you might like to read (siliconchip.au/ Article/1943). It explained how the AC-to-DC and DC-to-AC conversion worked. It is very common for long-distance links to be DC because there are significant advantages in both efficiency and cost at higher power levels. It also means that different AC sections of the grid don’t have to be synchronised. Notes on building the LC/ESR Meter I noticed in the LC & ESR Meter project article (August 2023; siliconchip.au/Article/15901) that you suggested the Altronics H0401 case for this instrument. Since I had purchased the two separate boards and a H0400 case (the larger one), I thought that would be a suitable option. The photos shown below are of the completed instrument, which works very well. I mounted the connectors and switch on an internal panel so that the case can be opened without disturbing the wiring. The ‘zero’ switch for ESR has been mounted at right angles to the board and is accessible at the back of the case. The Arduino Uno board I used has a second set of solder pads just inside the header strips, so I ran all the wires from them except two wires to the LC board. Once I decided this would work, I fitted header pins to the LC board but only in the positions used, which allowed the two boards to be stacked again as per the original version (June 2018). In hindsight, I should have put the Uno stack on the right-hand side of the case, as the I2C adaptor for the LCD screen is almost pressed against the relays when the case is closed. I also modified the print statements for line 3 of the display so it shows which range is in use. I noticed a schematic error: the wiring for switch pole S1a is shown reversed in relation to what the software requires, ie, +5V should go to the ESR side of the switch. The same error is repeated in Fig.3 on page 60. Ian Malcolm, Scoresby, Vic. Comment: thanks for reporting that error, which we have put into an erratum in the October 2023 issue. If wired as per the original diagram, the software can be easily changed to reverse the sense of the switch. The combined PCB was verified to work with the original software, so the switch on it is wired correctly, as expected by the published software. Transformers have a hard life A few years ago, I modelled the behaviour of the common ‘linear’ power supply circuit with a transformer, bridge rectifier and filter capacitor(s) to determine the currents involved. I write ‘linear’ because the circuit is not truly linear; it is called that to distinguish it from switchmode supplies. One alarming outcome was that the RMS transformer current was over twice the DC load current. More recently, the publication of your bench supply (30V/2A; siliconchip.au/Series/403) re-awakened my interest, so I decided to make some measurements with a real supply. I used an old 1980s piece of equipment fitted with A finished LC/ESR Meter fitted into a larger Altronics H0400 case. siliconchip.com.au Australia's electronics magazine November 2023  5 an AR 5502 transformer (two 22V 1.5A secondaries wired in parallel). The results were less extreme but were still somewhat concerning. The circuit used a 4700μF filter cap and produced 33.6V DC unloaded and 28.4V when loaded with a 33W resistor. The measured load current was 0.85A DC, and the transformer secondary current was 1.503A RMS. The ratio of secondary RMS current to DC load current is therefore 1.77. All measurements were taken with a single Keysight U1242C DMM. The DMM burden voltage for current measurements could be up to about 0.5V, which would have a noticeable but ultimately inconsequential effect in my view. I was able to download a data sheet for AR transformers (from 1966!), which describes the 5502 as having two 22V 1.25A secondaries, rated to supply 25V DC at 1.5A when connected in parallel. This implies 55VA to supply 37.5W, and the ratio of secondary RMS current to DC load current is about 1.67. Also notable is that the DC voltage is much lower than the 31V DC that might be expected at first sight. No information was furnished about the required rectifier and filter circuit. The peak voltage of a nominally 22V sinewave that we might expect the filter capacitor to charge to is over 31V, although the rectifier would take off a volt or two. I measured the secondary resistance and leakage inductance of the 5502 transformer at 100Hz with primary shorted and secondaries in parallel, and they came out to 2.5W and 1.7mH, respectively, so that would account for some of the voltage loss. So, a transformer with secondaries rated at 2.5A is underrated for a 2A DC supply. These results suggest that a secondary rating of about 3.5A is recommended to keep the transformer within specifications at the full current of the supply. This is not to say that the supply is in imminent danger of fire or explosion; transformers are pretty robust, in my experience. However, other components inside the case could be affected by the heat produced, and ultimately, if the supply is run at full current for extended periods, the transformer insulation is likely to degrade over time and could eventually fail. I appreciate that it is not always convenient to specify parts of bespoke design for projects such as this. Still, perhaps a warning about continuous operation at full current might be prudent. Phil Denniss, Darlington, NSW. Comments: You are right, and we are aware of this when we design circuits powered by transformers. It’s unavoidable that a transformer feeding a bridge rectifier and capacitor filter bank will draw high peak currents as most of the current is drawn near the mains sinewave’s peak. Also, the rectified DC voltage is higher than the RMS AC voltage. Thus, the VA drawn from the transformer will be substantially higher than might be expected from a basic analysis. Pretty much all power supplies we have published in Silicon Chip and that have been in EA, as well as similar commercial power supplies, suffer from this in that their transformers are technically required to produce more VA than their specification at full load. Typically, transformer ratings are conservative as the transformer designers/manufacturers know they will likely be used with a rectifier and capacitor filtering. The transformers will have a rough time but, in our experience, you 6 Silicon Chip Australia's electronics magazine siliconchip.com.au can draw the specified DC VA from the transformer without any problems. Partly, this is because the transformer output will begin to reduce as it is loaded beyond its ratings. Some transformers with less generous margins could run hot under these conditions, but in our experience, that is relatively unusual. Running a power supply at its maximum rating (where the transformer is effectively overloaded) will cause heat buildup and sometimes shut down from the output regulator. It is very rare to find a transformer that has failed, even with supplies that have been used for decades and used near their maximum ratings. It is usually a semiconductor or capacitor that goes faulty first. Feedback on magazine price changes Thank you for your efforts in keeping the online subscription price increase very reasonable. Considering the change in your electricity tariff, a $5 increase for a 12-month online subscription is justified. I have been a Silicon Chip reader from the very beginning. I visited Leo Simpson’s house when he and Greg Swain were assembling the second issue on Leo’s table tennis table under his home. Due to my previous military service, my body is not that of a young person anymore, and I don’t get the time in my workshop that I would like. I look forward to receiving my copy of Silicon Chip each month. The enjoyment I receive from my online subscription is well worth the 5% increase. Well done, guys and gals. Keep up the magazine’s high standards. Jeff Monegal, North Maclean, Qld. How vibrators were adjusted pre-CRO Further to R. H.’s query in Ask Silicon Chip, October 2023, concerning vibrator calibration in the pre-CRO era, adjustments were first made statically. Contacts were set to a specific gap using feeler gauges. The RCA 7604 vibrator from 1933 (which I described in the HRSA’s “Radio Waves” magazine, January 2020) also had a tension adjustment, set by hanging calibrated weights from the contacts. Adjustment instructions can be seen at www.cool386.com/files/rca_vib_adjust.jpg These static adjustments were then fine-tuned with a crude dynamic adjustment, which essentially was to set the contacts for minimum sparking. In the early days of vibrator power supplies (1931-1934), their operation was not yet fully understood, so determining suitable adjustment specifications to start with involved a degree of trial and error. Hence, the seemingly vague and non-scientific approach. A later improvement was to set the contact gap using a microscope with a calibrated graticule. By the mid-1930s, oscillographic displays were being used for the dynamic adjustments. Dwell meters have also been used, but they only suit separate drive type vibrators (such as the Oak). This method was described in the “Radio & Hobbies” Serviceman article for November 1947. However, by this time, tolerances in the parts were so small that little or no adjustment was required in the final assembly. Contact adjustment entails obtaining a specific duty cycle, typically 70-90%, depending on manufacturer and type. For Oak, it is 80% for the primary contacts. The secondary contacts for synchronous types are set to a few percent less since these contacts must open before and close after the primary contacts. The choice of duty cycle is a compromise between efficiency and mechanical considerations. Contacts must also be adjusted for an equal duty cycle. Otherwise, a DC component is created, reducing efficiency due to transformer core magnetisation and rapidly eroding one set of contacts. The components making up a vibrator power supply are all interdependent, and their specifications are critical. In simple terms, a particular transformer and timing (buffer) capacitance must be selected to suit a specific vibrator type, as well as each other. Any deviation could lead to transformer saturation and/or contact erosion due to the timing capacitance being too little or too great. The important point is that there is reason behind the adjustment settings. Unfortunately, the apparent simplicity of a vibrator power supply is a trap for the unwary. Merely getting a vibrator to function with random adjustments will likely lead to poor reliability. Up until around 1934, vibrator manufacturers provided repair and adjustment instructions for service technicians, along with replacement parts. However, one technician’s Dual-Channel Breadboard Power Supply Our Dual-Channel Breadboard PSU features two independent channels each delivering 0-14V <at> 0-1A. It runs from 7-15V DC or USB 5V DC, and plugs straight into the power rails of a breadboard, making it ideal for prototyping. Photo shows both the Breadboard PSU and optional Display Adaptor (with 20x4 LCD) assembled. Both articles in the December 2022 issue – siliconchip.au/Series/401 SC6571 ($40 + post): Breadboard PSU Complete Kit SC6572 ($50 + post): Breadboard PSU Display Adaptor Kit 8 Silicon Chip Australia's electronics magazine siliconchip.com.au A must have reference for your projects in the year ahead. 2024-25 Catalogue OUT NOW! Register for your complimentary printed copy at www.altronics.com.au/catalogue/ Your electronics supplier since 1976. Shop in-store at one of our 11 locations around Australia: WA » PERTH » JOONDALUP » CANNINGTON » MIDLAND » MYAREE » BALCATTA VIC » SPRINGVALE » AIRPORT WEST QLD » VIRGINIA NSW » AUBURN SA » PROSPECT Or shop online 24/7 <at> altronics.com.au © Altronics 2023. E&OE. Build It Yourself Electronics Centre® ability to adjust a vibrator correctly might not be as good as another, so reliability, along with the manufacturers’ reputations, began to suffer. Furthermore, once the science of vibrator power supplies was better understood, it was realised that few service personnel would have the necessary skills or instruments to provide the precision adjustments required outside of the factory. For this reason, from the mid-1930s, most vibrator manufacturers sealed the mechanism inside the can, with the whole unit to be replaced if it failed. If someone “had a go” at repairing it, the obviously deformed can seal would absolve the manufacturer of any ensuing reliability problems. John Hunter, Hazelbrook, NSW. Trick for troubleshooting HDMI to VGA converters I recently bought a HDMI to VGA converter from OfficeWorks but it didn’t work correctly. The display flickered about once a second. I then tried a different brand from Jaycar and the same thing happened. After buying a few on eBay, I finally found one that worked. The one that works communicates with the VGA monitor to get its list of supported resolutions, while the faulty ones don’t. I discovered a simple way of finding out if the design of a HDMI to VGA converter was faulty. Just measure the voltage between VGA pins 9 and 10, which should be 5 volts. Converters should provide 5V to a display monitor to power up its 24LCS22A or similar EEPROM and then use the I2C protocol to read Extended Display Identification Data (EDID). Faulty ones don’t. I had assumed that a reputable brand $40 converter would work better than a no-brand $10 converter, but I was wrong. John Rajca, Mount Kuring-gai, NSW. Possible cause of mains switch arcing I am responding to the query on “causes of mains switch arcing” on page 106 of the October issue. As I test many different products for immunity at high levels of surge and fast transients, I often see the failure of bypass capacitors usually used across motors or in the AC filter circuit. The worst of the older type is the RIFA brand in a clear case, particularly if they are a few years old. Most will temporarily short out, then the offending capacitor’s internal wrap will burn through and usually, but not always, spill out or crack the case. If such a capacitor is fitted across the motor, its failure would pop the circuit breaker due to the high instantaneous current. If the capacitor was in the AC filter, it could have tripped due to Earth leakage for a three-pin plug product. If there is no capacitor anywhere, your editorial suggestion may have been the cause. Often, the use of a calibrated hammer around the motor housing will show up the intermittent motor. Still, after applying the hammer, I suggest that an ohmmeter check to Earth would be sensible before plugging it in and testing further. Braham Bloom, EmiSolutions, Russell Lea, NSW. We should have long-range digital radio broadcasts The Cambridge Consultants/CML module is the most significant consumer development in radio since the invention 10 Silicon Chip of the superheterodyne receiver in 1918. This device uses the inverse Fourier calculation in a chip invented by the ‘black hole’ hunting astronomers at the CSIRO in Australia in 1997 (see siliconchip.au/link/abpt). The use of Fourier Analysis enables the increase in data transmission speed to allow the insertion of gaps in the transmissions, which allows reflections to dissipate. That means crystal-clear high-frequency (shortwave) broadcasting over thousands of kilometres. The above technology is also used in DAB+, which has been broadcasting at high power in major Australian cities since 2009. DRM is much better for regional and remote areas because its lower-frequency transmissions cover much larger areas. There are currently three digital radio standards: Digital Radio Mondiale (DRM), HD Radio (HDR) and Digital Audio Broadcasting+ (DAB+). Analog TV was shut down in 2013, freeing up the 45-68MHz range, which is now unused except for the 6m amateur radio band. These frequencies are lower than the FM band (87.5-108MHz). Simulcasting is possible without coverage area restrictions from interference with other broadcasters. It is also possible to install a high-powered HF DRM transmitter in the centre of Australia and cover the whole continent. Radio New Zealand Pacific is now building a new HF DRM transmitter to be a companion to the existing DRM transmitter, which started transmitting in 2007. While Gospell is using the module mentioned earlier in pocket radios, I hope you will now extend its design for use in vehicle infotainment systems so that TPEG data can be used during emergencies for causing the navigation system to re-route vehicles around police roadblocks. Journaline includes slideshow images in all their receivers with larger touchscreens, so multiple emergencies can be indexed with separate maps, and instructions can be selected and displayed. This would be very useful with high-frequency broadcasting in Australia and the Pacific, for example, where cyclones and tsunamis travel across large areas. India already covers 1.4 billion people with DRM broadcasts. Now Pakistan, with 248 million people, has started rolling a high-power medium-frequency DRM transmitter that can also cover adjacent countries. China (1.4 billion) and Indonesia (279 million) have also adopted DRM, so over 3.3 billion people will be able to receive DRM broadcasts soon. The USA (340 million), Canada (39 million) and Mexico (130 million) can access HDR radio. The European Union (451 million) and the UK (68 million) have access to DAB+ radio. A low-cost DRM/DAB+ receiver could be built. With both technologies, no wasteful carrier signal is radiated, reducing transmission costs and pollution even compared to the digital transmissions used for wireless internet. In the 2021 census, Australia has 26 million people, including around 16 million covered by DAB+, leaving 9 million needing DRM for digital radio in rural and remote regions. The biggest advantage of broadcast radio in emergencies is that it will continue operating when the mobile phone network fails when needed most! The CML module can receive all broadcast bands used in Australia, including HF (shortwave), which the ABC Australia's electronics magazine siliconchip.com.au closed down in 2017 despite having crystal clear broadcasting over huge areas. A high-power DRM HF transmitter in the centre of Australia could give millions of people access to two broadcasts. They currently have no access to live radio while mobile. Those programs could continue at lower quality while emergency information is transmitted simultaneously. With the closure of regional newspapers, DRM can also transmit an electronic newspaper, including a touch index to stories that can include coloured images. This would be considerably cheaper than trying to cover the 80% of Australia’s land area not covered by streaming using the mobile phone network. Finally, I am pleased that high-definition TV channels will soon be the default selection for terrestrial TV, instead of the blurry standard-definition version. This will commence in Tasmania on Thursday, 5th of October. Alan Hughes, Hamersley, WA. More on LED light bulb interference with AM radio Readers who are shortwave radio listeners or amateur radio operators may be interested in a short video from Peter Parker, VK3YE, prominent Melbourne amateur radio operator and “ham” radio author. He just published a short video demonstrating problems with RFI (radio frequency interference), or as hams call it, QRM, from LED light bulbs. This is a significant contributor to electrical noise in the environment. See https://youtu. be/H8twPwskQNI Dr David Maddison, Toorak, Vic. An idea for dealing with junk email I have just read your editorial covering spam emails (“Junk email is getting out of control”, June 2023). A solution for those with a website could be as simple as blocking all emails by default unless they are solicited. Let’s say that I would like to email you. I would go to your web page and register my email with your site. You then send me an email that contains my email passkey. That passkey is unique to my email address and is registered with your site. Every email I send to your domain must contain the passkey in the subject heading. At your end, you set your spam filter to scan the subject heading, any email without a valid passkey is filtered out, and your server sends back a single email that advises of the process required to email Silicon Chip. No passkey, no email to your desk. Of course, you could program your server to accept some businesses that will not follow this rule; let’s call them exceptions. And, of course, if any user abuses their passkey, even selling it on or by becoming a spambot, you withdraw their access. You could even send an email advising of their breach and the process for reinstatement. Until a better solution is found, involving some real effort to catch those paying for the spambots, we will continue to be plagued by unsolicited advertising and scams. In the interim, best of luck with your spam filters and if you happen to adopt the process listed above, please send me your bank account details so that the Nigerian prince and I can reward you for your actions. Ian Ashford, Taminick, Vic. Comment: that is an interesting idea; it has been raised ...continued on page 14 siliconchip.com.au Australia's electronics magazine November 2023  11 before, although this is the first time a Nigerian prince has suggested it. Still, we think that it’s infeasible in our situation. We run a business that needs to be contactable by our customers and the general public; we can’t expect all our customers to go out of their way to adhere to such a solution. This problem needs to be solved at a high level by governments and internet infrastructure providers. There needs to be a way to report spam to a central authority that permanently blocks all internet traffic from the originating addresses until they can prove they have stopped sending the junk. That would force virus-infected computers acting as botnets and open relays to be fixed. Renewables do not provide base load generation I have been a hobbyist in electronics since the days of building crystal sets and have enjoyed Silicon Chip magazine since its first publication (also previously Radio & Hobbies, EA etc). I would like to comment on your editorial on ‘renewables’ (April 2023). I have retired after sixty years in the commercial refrigeration service, installation and maintenance industry. Most switchboards I worked on required three-phase power, ie, 440V AC at 400-600A per phase 24/7. As far as I can see, my work area was a fraction of the power grid state-wide, much of which requires baseload power generation. I applaud the domestic solar panel scheme as worthwhile; however, it is not a practical means of providing base load power, nor are those expensive, disastrous wind farms. Should we have to look at alternatives to coal, the obvious choice is nuclear. Everyone, including me, would love to have solar-powered semi-trailers, trains etc, but it ain’t gonna happen. Could I ask you to explain the term ‘renewables’? As far as I can see, the energy is not ‘renewable’ but generated alternatively. Rex Mower, Empire Bay, NSW. Comment: “renewable” refers to the fact that power derived directly or almost directly from the sun (solar photovoltaic, wind, hydroelectric etc), as well as geothermal, can be expected to operate almost indefinitely. It should be five billion years or so before the sun becomes a red giant; until then, PV panels, wind generators etc should continue to operate. While much of the energy in coal, oil, natural gas and so on would have also been derived from the sun (eg, causing ancient trees to grow that eventually became buried and turned into coal), that is over a much longer timescale (hundreds of millions of years) so those resources will be used up much faster than they could ever be replenished. So, while it is a matter of timescales, we think “renewables” is a fair enough term. While hydro and geothermal energy can provide baseload generation, the amount of energy that can be generated that way is limited mainly by geology. Hence, as per the April editorial you referred to, energy storage is the problem that needs to be solved to allow renewables to provide large-scale baseload power. The debate about whether and SC how they can do that is ongoing. Silicon Chip as PDFs on USB ¯ A treasure trove of Silicon Chip magazines on a 32GB custom-made USB. ¯ Each USB is filled with a set of issues as PDFs – fully searchable and with a separate index – you just need a PDF viewer. ¯ 10% off your order (not including postage cost) if you are currently subscribed to the magazine. ¯ Receive an extra discount If you already own digital copies of the magazine (in the block you are ordering). The USB also comes with its own case EACH BLOCK OF ISSUES COSTS $100 OR PAY $500 FOR ALL SIX (+POSTAGE) NOVEMBER 1987 – DECEMBER 1994 JANUARY 1995 – DECEMBER 1999 JANUARY 2000 – DECEMBER 2004 JANUARY 2005 – DECEMBER 2009 JANUARY 2010 – DECEMBER 2014 JANUARY 2015 – DECEMBER 2019 WWW.SILICONCHIP.COM.AU/SHOP/DIGITAL_PDFS Ordering the USB also provides you with download access for the relevant PDFs, once your order has been processed 14 Silicon Chip Australia's electronics magazine siliconchip.com.au