Fullscreen HTML5Med Res (??MB)HTML4

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 Motor speed controller recommendation I am hoping you can point me in the right direction. I am looking for a variable speed controller, which is harder to find than hen’s teeth in New Zealand. I came across an article on your website about building one (230V/10A Speed Controller For Universal Motors, February & March 2014), then discovered that you sell some of the parts for it. If this is the correct product? Does it come with a list of instructions on how to build it and what else would be required to make it complete? I am looking to control the speed of a 230-240V 7.2A 1650W brush router (S. W., Christchurch, NZ). • While you could build that and it should work for your application, we recommend you instead build our April 2021 controller design (Refined Full-Wave Motor Speed Controller; siliconchip.com.au/Article/14814). It is cheaper and smaller than the 10A 230VAC Universal Motor Speed Controller you mentioned. The instructions for building it are all in the April 2021 issue, which you can purchase at the following links: siliconchip.com.au/Shop/2/5795 (printed) or siliconchip.com.au/ Shop/12/5797 (online/PDF). We also sell the PCB and programmed PIC for that project at siliconchip.com.au/ Shop/?article=14814 With those, you would just need to source the remaining components from a convenient electronic store, as per the parts list in the magazine. Building Reflow Oven firmware in MPLAB Can you help me import the C source files for the Reflow Oven project (April-May 2020; siliconchip.com. au/Series/343) into MPLAB IDE? I have Harmony v2.06 installed, but MPLAB doesn’t seem to import the project correctly (via the open project option). It brings in the original programmer’s file 108 Silicon Chip locations, and the project fails to build. Is there an easier way than having to alter the source file locations manually in the configuration files? (T. B., Footscray, Vic) • We have run into this problem before. You might need to create a new project and add each source file in over the template. Be aware that there are several versions of Harmony. This project uses the old “vanilla” one. We tried getting it to compile against a newer version without much luck. There are some instructions on migrating projects available via web searches, which you should hunt down. Adding tone controls to Nutube preamp I am building the Nutube Preamp project (March 2020; siliconchip.com. au/Article/12576) to combine with the 20W Class A amplifier (May-August 2007; siliconchip.com.au/Series/58) as a small guitar amp. I figure the “cleanness” of the Class A power amplifier would allow the qualities of the Nutube to be appreciated without colouration from power amplifier distortion. I wish to use the left and right channels as two mono inputs switched by one pole of a foot-switch controlled DPDT relay, the other pole switching the selected output to the main power amplifier, with LED channel indication. This doesn’t seem to pose too much of a problem for me. But I also wish to incorporate a three-stage Baxandall tone circuit in each channel. I have found several of these circuits in Silicon Chip projects, and I think the one in the 2-Channel Guitar Preamp from November 2000 to January 2001 seems like a good choice (siliconchip.com.au/Series/134). Other possibilities are Baxandall circuits from the 4-Channel Mixers from June 2007 & 2012 (Mix-It!; siliconchip. com.au/Article/644) or one gleaned from the Digital Preamp from September 2021, without the digital control. Australia’s electronics magazine Please advise how I could insert one of these into the Nutube circuit, either by using it in the feedback loop of one of the existing op amps or adding another op amp or two for the feedback loop and as a buffer. I have a couple of spare OPA1662AIDs, or I could use an LM833 or TL072 if need be. Also, effects send and receive would be a fine addition! Finally, on the Nutube PCB screen printing, parts list, component layout diagram and circuit diagram are specified three 100μF/25V electrolytic capacitors, one of which for the Supply/2 filter is shown as much smaller than the other two.Is this correct? And please explain what the dot means following the μF on some of the electrolytic capacitors in Fig.10 on page 28. (I. H., Essendon, Vic) • The Baxandall tone control circuitry could be placed as a separate circuit between the preamplifier output and the power amplifier input. We recommended that you use OPA1662 op amps for the tone control circuitry rather than LM833s. While TL072s have a low input current, they do not have the low distortion figures of the previously mentioned op amps. Your enquiry concerning the 100μF capacitors and the size differences is related to the asterisks following the capacitor values. Those capacitors with the * (asterisk) are to be 25V rated and so are larger than their 16V counterparts. Questions about the Super-9 FM Radio I have almost completed building the Super-9 (November & December 2019; siliconchip.com.au/Series/340) but have a few questions. The 33kW resistor shown above IC3 is labelled 10kW on the PCB I received. Which is the correct value? When winding T1 and L6, the parts listing states that I should use 0.25mm diameter enamelled copper wire, but in the winding instructions on p63, it says 0.125mm. Which is correct, and siliconchip.com.au should it be 11.5 turns on two layers, or do all 23 turns for T1 need to be all one layer? (R. S., Epping, Vic) • Use the 33kW resistor as shown in the articles and ignore the screen printing on the PCB. As for the T1 windings, we think it’s better to use 0.25mm diameter wire as this makes the winding easier, and it is less likely to break when winding. You can make the 23 turns in two layers (it would fit in just one layer if using the finer wire). Questions on Water Tank Meter project I have three questions about the February 2018 Water Tank Level Meter/ Weather Station project (siliconchip. com.au/Article/10963). If I cut holes in the box for relative humidity (RH) measurements, will that expose the boards and pins to corrosion from high moisture air? As I am primarily after the water tank measurement feature, can I leave out those holes without ill effect? Can I use the same kit for a second tank without the weather station components, or do I need the whole circuit to be complete? If I get this going, I would like to somehow control the pump for that tank, which is 300m away from the tank. (A. R., Darkan, WA) • If you do not have holes in the case, the RH reading will remain constant as it will measure the RH inside the sealed box and not external air. Suppose you want the RH sensing feature to work but avoid the possibility of corrosion due to moisture in the air. In that case, you’d either have to conformally coat the board (but not the sensor!) or place the sensor in a separate, ventilated compartment somehow. The RH/temperature sensor and barometer can be left out, and the water tank level sensing will still work. The circuit does not provide for controlling a water pump based on water level, but it could be modified to do so. That would require extra lines in the software, adding logic to decide when to switch the pump on and off and drive a digital output pin appropriately. As your pump from the tank, you could have another ESP8266/ESP32 query the water level over WiFi, but that would require considerable design work. siliconchip.com.au Monitoring solar power generation I have some questions regarding using solar power at home rather than selling it for the feed-in tariff. As the buy-back rates (feed-in tariff) for electricity generated with solar panels becomes lower (we have had two price reductions in the past year), it is becoming more prudent to use as much generated power at home as possible. Heating water is a good one, as I have a 1000L spa and a storage hot water system. Do you have a way to sense when generated power is going back to the grid and how much? Could this power be diverted to heat the spa or hot water system? Time clocks don’t do the job. In winter, there are times we must purchase power as the panels do not generate enough for the house usage and the spa on dull days. Should there be insufficient power available, is it possible to switch off some loads that are not needed, like pool pumps or washing machines? I have 6kW of north-facing panels on the roof. (M. S., Umina Beach, NSW) • You need an energy meter that can show power flow to and from the solar system and the power grid. We have published power meters in the past but they are not suitable for your application. However, commercial units are available. For example, see www. energymatters.com.au/flex/solarenergy-monitor/ Choosing the right ferrite bead for an amp First off, thanks for all of your team’s hard work in keeping electronics accessible to the non-engineer. I plan to build some SC200 amplifier modules (January-March 2017; siliconchip. com.au/Series/308) and am sourcing the parts. Do you have a value for the small ferrite bead, FB1? Looking at different suppliers, I see that most are from Fair-Rite Products Corp. Their Beads-on-Leads are listed by impedances at various frequencies. They are arranged as Higher Frequencies, Broadband Frequencies and Lower Frequencies. I’m assuming it is in the Broadband category, but other than that, I’m stumped. (J. R., Norco, CA, USA) • You could make an argument for looking at beads that suppress either Australia’s electronics magazine Broadband Frequencies (25-300MHz) as that covers the FM broadcast band, or Lower Frequencies as that covers AM and the sort of frequencies that virtually all switchmode converters operate at. We think the latter (Lower Frequencies) would be the most useful as switch-mode EMI breakthrough will be more of a problem than FM pickup in an amplifier in most cases. As this is a signal path, choose one with a higher impedance value. The other thing you need to check for is that it will fit in the available space. This design uses a loose bead that’s slipped over a resistor lead, so you will need a bead without a lead about 5mm long. It would be possible to solder a resistor and ferrite bead in series, in an inverted-V shape off the board, if you particularly wanted to use a beadon-lead style product (in which case their product number 2773005111 would be good). While both are likely tight fits, you could try their product number 2673028602 at 5.6mm long or, for better performance, 2673000301 at 6mm long. You should be able to squeeze those into the available space. Adding input switching to Currawong amplifier I am currently building a Currawong valve amplifier (November 2014-January 2015; siliconchip.com. au/Series/277) with the added remote board, and I propose to add the 3-input Selector board from the Ultra-LD preamp of January 2012 (siliconchip.com. au/Article/821). I note that you still sell the PCBs for both projects. Can I select the input channel with the version of the PIC chip software supplied for the Currawong remote? Thanks in advance for your help. (G. D., Melba, ACT) • Yes, this should work as the 3-input selection is already integrated into the Currawong remote control software. Instead of soldering the three 10kW resistors to CON13, fit the box header and run a ribbon cable to the 3-input Selector board. Make sure that pin 1 on the cable is in the correct position at both ends. Senator speakers built using thicker MDF I have been looking through back December 2021  109 issues at your different speakers and would love to build your Majestic speakers (June-September 2014; siliconchip.com.au/Series/275), but that was vetoed. So on to the Senators (September-October 2015; siliconchip. com.au/Series/291). How critical is the internal volume? The plans call for 18mm MDF but I have two sheets of 20mm MDF that have been lying around for years. Therefore, the internal dimension will be reduced in one direction by 4mm, the volume reduction being 0.865L (4mm × 726mm × 298mm). Will this make a noticeable difference, or should I add 4mm to the relevant panels? Hopefully I will still be able to use just one sheet! (M. D., Paynesville, Vic) • Using 20mm MDF will probably make almost no difference. The original box was actually a Bunnings kitchen cabinet kit, to make it easier for amateurs who might not have the skills or tools to cut and join MDF accurately. The material was melamine-coated, pre-cut and drilled. It’s hardly a precision design, and should forgive you for that difference of less than one litre. Soft-starting a large induction motor I have a single-phase 1500W induction motor powering a dust extractor which has been causing overload problems at startup. I recently discovered your Soft Starter article (April 2012; siliconchip. com.au/Article/705), and it appears to be rated for steady-state loads up to 10A (2300W), which suggests it could be a possible solution. However, I note that most of the ‘inrush’ currents described in the design article are very large currents (200A) but very short periods (milliseconds). On the other hand, this motor seems to induce a startup current of around 25A that lasts for about 1-2 seconds. The thermistor specified in the article, the SL32 10015, is rated for a steady-state current of 15A, but I can’t find any clarification on whether this 1-2 second startup period should be considered a ‘steady state’ load. Should it be able to cope with the longer startup draw of such a motor? (Rowan, via email) • The motor startup current is not a 110 Silicon Chip steady-state load by definition. 25A for 1-2 seconds is quite a significant energy pulse, though. Unfortunately, the thermistor data sheet doesn’t provide a curve showing its current handling vs pulse length to allow us to determine if that is safe. Note that the MS32 10015 is a larger version of the SL32 10015 and is more likely to survive that sort of punishment. We do not recommend using this simple type of Soft Starter for a large induction motor because they draw a high current at startup to get up to speed. Their rotational speed is related to the mains frequency, but the Soft Starter will not affect the applied frequency. Also, in your case, the motor starts up under load. You really need a variable frequency drive (VFD) to smoothly ramp up a large induction motor like that. Our 1.5kW Induction Motor Speed Controller design from April & May 2012 (updated in December 2012 & August 2013) can do that – see siliconchip. com.au/Series/25 If you decide to build it, consider using the upgraded 30A bridge, available from our website at siliconchip. com.au/Shop/7/2814 Note that the IGBT bridge used in that design is no longer being manufactured, so you could have difficulty sourcing it anywhere else. Our VFD (IMSC) supports automatic ramping up and down, so you do not have to adjust the speed manually each time. It is an expensive solution, but there isn’t any other practical way of controlling a large induction motor. Small induction motors like shaded pole motors used on fans can be softstarted with a thermistor. As the motor gets larger, you run into the fact that it needs a large amount of energy to spin up and that isn’t easily spread out over a longer period without changing the supply frequency. In theory, if you had enough thermistors in series/parallel it could work, but the startup time could be quite long. You could use our Soft Starter circuit, but it would need to be housed in a larger box with a bank of off-board thermistors connected to the board using mains-rated wiring. A set of four such thermistors in series/parallel would handle four times the total energy, but we aren’t sure if that would be enough for your Australia’s electronics magazine application. Multiple rapid starts might lead to failure. Absent is a proper curve in the data sheet, the only way to find out for sure is to try it. Circuit to detect white ants One of Australia’s biggest but smallest pests is the white ant. Rarely seen, but highly destructive. A proud and meticulous homeowner may not even notice the first hint of their activity. What they need is a monitoring system or even a small handheld device that could be used like a stethoscope. Touch the target area with a microphone probe attached to a finely tuned and filtered amplifier, and listen for the sound of your house being devoured by thousands of tiny teeth. (P. S., Whitsunday, Qld) • Have a look at the Electronic Stethoscope we published in August 2011 (siliconchip.com.au/Article/1119). It should be suitable to listen for white ants, especially in the quiet of the night. The PCB is available from our Online Shop (siliconchip.com.au/ Shop/8/721). Boosting the current from tracking regulators Can you help me? I need a dual power supply of 1.25-25V using LM317T/337T giving at least 2A from both rails. I have looked on the web but could not find anything specific. (R. M., Melville, WA) • The LM317 and 337 are rated at 1.5A maximum. However, higher-current equivalents are available. For example, the LT1085 (positive) and LT1033 (negative) are pin-compatible and rated at 3A. So the simplest solution is to use those devices instead. Another way to do it is to use the LM317 and LM337 with added current-boosting transistors. We showed how to do this in the HighCurrent Adjustable Voltage Regulator article (May 2008; siliconchip.com.au/ Article/1830). That design was only a positive regulator using an LM317, but the same principle could be applied to the LM337 using an NPN transistor (or Darlington) instead. If you use a BD650 Darlington to boost the positive rail, the complementary BC649 could be used for the negative rail. continued on page 112 siliconchip.com.au