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 Decoding USB Cable Tester messages I have just completed the USB Cable Tester (November & December 2021; siliconchip.com.au/Series/374). What a great little gadget. I found a few high-resistance cables, which I disposed of. The ability to distinguish between power-only vs data cables allowed me to exercise my label maker. However, even after re-reading both articles again, as well as the June 2021 USB expose, I remain confused about the meaning of several displayed messages. I wonder whether you can explain what these messages mean. For example, when I plug both ends of a particular cable in, it is reported as “POWER ONLY”. On the next line, the message “CHECK UFP” is present. But the meaning of that is unclear, and I am not sure what to do about it. When the DFP (USB-A) is unplugged, it now reports what appears to be a single-ended UFP analysis: “UFP: DP ,DM ,” What do “DP” and “DM” mean, and what can be inferred from the blank field following each? (R. M., Ivanhoe, Vic) ● You are correct that the display size sometimes limits the amount of information that can be displayed, but we thought we struck a reasonable balance. The DM and DP designation refer to specific conductors in the USB cable (also known as D- and D+). These can be seen in the Fig.1 schematic in the first article, where they connect to the various USB sockets. As noted on page 93 of the second article, “Check DFP” (or UFP) is a prompt that you can get more detailed results by testing one end only. You appear to have realised this. The resulting “UFP: DP ,DM ,” message indicates that the DM and DP wires of the upstream-facing port (UFP) are connected together. That they are not shown elsewhere means they are not detected at the other end of the cable. We didn’t see this type of cable in 108 Silicon Chip our testing, but it is consistent with some non-standard cables made for charging only. The shorted pins are detected by some chargers or power supplies to produce a specific charging current, usually more than 500mA. So that cable is only suitable for power. The blank fields simply make the display more legible by aligning the listed items. In general, any DFP or UFP indication apart from GND and SHLD being connected (in anything but a power-­ only cable) is not a good sign. The specifics of that message will only be helpful if you intend to repair the cable. USB Cable Tester is only for passive cables I have built the USB Cable Tester and have a question about USB-C cables containing an E-Marker chip. Does the Tester work with these cables? I have a USB-C to USB-C cable with a chip in it, and the Tester tells me it is Power Only and 0+ 0-. Both ends of the cable are right-angle connectors, making it difficult to try all the combinations as the USB-C sockets are close together. Thank you for another excellent project. The SMD Test Tweezers are useful for SMDs and also through-hole resistors, with their tiny colour code bands. (J. B., Blackwood, SA) ● We don’t have many cables with chips, so we weren’t confident in advising what the USB Cable Tester would do when connected to one, especially as different brands would probably implement different features. The Tester only applies a minuscule current, probably not enough to activate any electronics in the cable. If power is needed to allow the data lines to work, they may not be detected at all, as appears to be the case with your cable. Testing USB 2.0 Micro-B cables Regarding the Micro-B connector on the USB Cable Tester, I have some Australia's electronics magazine equipment that uses the USB 1.1-2.0 Micro-B plug. Will that fit into part of the USB 3.x Micro-B socket? (A. F., Salamander Bay, NSW) ● As far as we know, all USB plugs/ sockets are backwards compatible. The USB 3.x Micro-B socket is basically a USB 2.0 Micro-B socket with an extra socket (with more pins) alongside it. So you would just plug the USB 1.12.0 Micro-B plug into that portion of the socket and ignore the rest. The USB Cable Tester can check just about any passive cable. The only thing it can’t do is verify signal integrity for high-speed transfers – that would be hard to do without making it much more expensive and complicated. Finding an amplifier kit for a beginner I’ve read your magazine for a long time, but I’m only at a beginner level with electronics. I want to build an amplifier project from your magazine that I can buy in kit form from Jaycar or Altronics. Ideally, I would like to build a stereo amplifier with a bit of power, but one that is not overly complex to build. I was thinking of building the Compact 12V 20W Stereo Amplifier (May 2010; siliconchip.com.au/Article/152) using the Altronics kit, Cat K5136. I don’t particularly need the 12V option, but I thought this might be easy enough to build. Do you have any other recommendations for amplifier kits that I can buy off the shelf? (E. M., Hawthorn, Vic) ● We agree that this kit is an excellent amplifier for beginners to build. Most other kits would involve mains wiring, whereas this one runs from a safe, low voltage, but is still very useful. 20W per channel can be plenty depending on the speakers and the room. If you ‘graduate’ to a more experienced level and want to build a mains-powered amplifier, the recent Hummingbird miniature power amplifier is easy to assemble and can siliconchip.com.au deliver up to 100W. See the December 2021 issue (siliconchip.com.au/ Article/15126). SMD Tweezers drawing too much current I ordered one of your Christmas Ornament kits & the SMD Tester Tweezers kit (Cat SC5934, October 2021; siliconchip.com.au/Article/15057). I built the Test Tweezers kit first to check I had the LEDs around the correct way on the Ornament. I have noticed that SMD Test Tweezers have a thirst for batteries. When the display is on, the current draw is about 6mA, but when it is idle, it only drops to 3mA! That drains button cells in just a few hours. I can run it off an external 3V battery pack with no problems. I built it partly for the novelty, and to test SMD parts before trying to solder them in future kits. Still, it’s a fun testing toy to have. Thanks for all the hard work selling these kits. (M. A., Artarmon, NSW) ● That definitely doesn’t sound right. The expected sleep current is a few microamps. We’ve built a few prototypes, and they all sit happily idle for weeks at a time and wake up when needed, which they wouldn’t do if they were drawing that much current all the time. We suspect that either the OLED is misbehaving or the micro is not going to sleep. Check that the display is completely blank after the five second timeout. The 6mA drain during use sounds quite high, so we think something is continuously drawing an extra 3mA. That would also explain the high sleep current. While faulty PICs are rare, we have come across them occasionally, so that is possible. But we think more likely it is the screen, and you should be able to confirm that by unplugging/ desoldering it. Spot welder for making Li-ion batteries Have you published any articles/ projects on spot welders for making Li-ion battery packs? (Tom, via email) ● We haven’t, although we will be publishing one in the near future. While you can find many designs for spot welders online. Do not make one that uses direct mains power – they are not safe. siliconchip.com.au Errors programming newer PICs I am trying to convert from the older PIC series that I am used to, such as the PIC16F88, to the more modern (and lower-cost) devices such as the PIC16F1455, but I have run into a problem trying to program them. In July 2010, you published an article on using the PICkit 3 to program micros which I have followed since. In my setup, I use the PICkit 3 to power the PIC. When I went to program the PIC16F1455, the programming software said that I would have to download new firmware for the programmer, which it did automatically. I then followed the standard procedure for programming in the past, and received a message saying: PK3Err0045: You must connect to a target device to use PICkit 3. PK3Err0035: Failed to get Device ID I had definitely ticked the box saying power device from PICkit 3. I repeated the process and received the same result, this time using a DVM to confirm that I had 5V on the device. I changed back to a PIC12F617 that I programmed before, and received the same error message. So now I can’t program at all. I am using MPLAB IDE V8.91. Have you come across similar problems and can you help me solve my problem? (L. K., Ashby, NSW) ● We have run into problems like this, especially programming newer PICs with older programmers like the PICkit 3. The PICkit 4 seems to handle this a bit better (although the PIC16F1455 is supported by the PICkit 3). We usually use MPLAB X these days since we need the latest version to work with the latest parts. We tested programming a PIC16F1455 using MPLAB v8.91 (one of the versions just before they switched to the X series), and we also couldn’t get it to connect to or read from the part (although it updated the programmer firmware as expected). Retrying with MPLABX v5.05, it worked straight away. MPLAB v8.91 is from 2013, and the PIC16F1455 is about the same age, so it’s a bit of a ‘bleeding edge’ combination (that’s now about eight years old). The Microchip Archive has at least one newer MPLAB version pre-X Australia's electronics magazine (v8.92) and all the older MPLABX versions, which you can download from siliconchip.com.au/link/abcc We recommend that you try using a newer version of the IDE. Even if you insist on using the pre-X IDE for development, you could still install MPLAB X and use the programming software (IPE) that comes with it to flash the chips. Universal Dimmer has limited IR angle I have been using John Clarke’s Universal Dimmer with Remote Control since it was published in February & March 2019 (siliconchip.com.au/ Series/332). I recently converted a large room into a home cinema and installed the dimmer in place of an existing wall switch beside the screen. The switch controls four LED lamps and works fine if not using the remote. But I find that unless the remote faces the switch directly (ie, perpendicular to the touchplate at 5m), it is not recognised, implying a very narrow angle of sensitivity. The problem is that it does not respond at my preferred seating position approximately 6m away from and 30° to the face of the touchplate. What, if anything, can be done to enable me to allow the remote/touchplate combination to work from my preferred seating? (N. H., Sanctuary Point, NSW) ● You could use an infrared remote control extender. This receives and retransmits the infrared signal from an infrared LED closer to the receiver and from a different direction. Alternatively, use an infraredto-433MHz transceiver. This eliminates the need for a wire between the receiver and the IR retransmitting LED. We described such a device in the January 2022 issue (siliconchip.com. au/Article/15182). Sourcing 9mm pots from overseas I bought all your parts to make the 3-Way Active Crossover (September & October 2017; siliconchip.com. au/Series/318), including the SMD pack and potentiometers VR3-6. Now I am having difficulty sourcing 10kW potentiometers VR1, VR2 and VR7-VR10. February 2022  109 I am based in Canada, and I don’t want to order from Jaycar; I would prefer to find a local distributor. I am guessing that these are Alpha units. Do you have the part numbers? (N. M., North Saanich, BC, Canada) ● Digi-Key or Mouser should be able to help you. They are both based in the USA and have Bourns potentiometers that are equivalent to the Alpha pots that we used. Search for the following Bourns part numbers on either website: PTD902-2015F-A103 10kW dual logarithmic, one required PTD901-1015K-B103 10kW single linear, one required PTD902-2015K-B103 10kW dual linear, four required Inconsistency in SC200 current measurements I just read the letter from R. S. in the Ask Silicon Chip section of the October 2021 issue regarding an imbalance in the quiescent current of the SC200 audio amplifier (January-March 2017; siliconchip.com.au/Series/308). I was wondering if this was sorted out because I built four modules and all had exactly the same difference in the positive and negative rail. I presumed it was OK as the modules seem to work fine. I’ve just purchased the parts to build two Hummingbird amplifier modules for my tweeters, and I’ll be following that with the Three-way active crossovers. Thanks for the great work. (T. B., Bumberrah, Vic) ● While looking into this enquiry, we re-read the original letter and discovered a discrepancy. The SC200 articles state that the safety resistors should be 68W 5W types, but R. S. noted that they were 6.8W, and we took his word for it. Now that we think about it, they probably were 68W, meaning the imbalance was only 5mA, not 50mA. There is a slight imbalance in the current drawn by the SC200 amplifier, on the order a couple of milliamps, which is swamped by the module’s quiescent current once the bias has been set. But before the bias is set, the difference would be apparent. The difference has to do with 4mA flowing from the positive rail to ground, though the two 6.8kW series resistors at the collector of Q6, and the 2mA or so through the 22kW resistor at the collector of Q7 between the 110 Silicon Chip negative rail and ground. The result is an imbalance of about 2mA, so the positive rail safety resistor can be expected to have a voltage drop about 140mV higher than the other. We aren’t sure why R. S. noted a drop of roughly double that, but it might come down to resistor tolerances, capacitor leakage or something else we hadn’t considered. As long as the imbalance equates to just a few milliamps, the output sits near 0V and the bias control responds as expected, we think the amplifier modules should work fine. Trouble getting LCD BackPack to work I have built your Advanced GPS Computer kit, but the LCD screen does not light up. It has 3.3V power to it. I note in the August 2019 article on the Micromite LCD BackPack V3 that there is a section on driving the 3.5-inch touchscreen; is this software incorporated in the pre-programmed software for the processor? The LCD Touchscreen still doesn’t work if I remove the GPS board. I assume that the V3 Backpack should work without the GPS board. Without the GPS board plugged in, I am using the USB to power the Backpack. The LCD still does not illuminate. The only change I made on the GPS board was because I could not source the IRLML2244 P-Channel Mosfet. I have an IRLML2244 on order from RS Components with delivery due on the 23rd of December, but the date keeps slipping; I ordered it in August. So I used an IRF9540N P-channel Mosfet instead. (J. L., Tauranga, NZ) ● You cannot replace the IRLML2244 with an IRF9540N as it is not a logic-­ level Mosfet (it’s also in a totally different package). The -3.3V gate drive voltage will not be sufficient to switch it on to any significant extent. The parts situation is extremely frustrating, but element14 and RS both have suitable parts in stock, such as the BSS308PEH6327XTSA1 (element14 Cat 2432719, RS Cat 823-5500). You mention that the screen has 3.3V power. Where are you measuring this? The LCD panel is only fed 5V (from the USB socket) and has its own 3.3V regulator. The separate backlight supply is also 5V. If you have some photos of your assembled PCBs, that may help us diagnose further. Australia's electronics magazine With the BackPack powered via the USB socket, a quick way to test the backlight is to short the two leftmost pins of VR1 (MANUAL BACKLIGHT) on the V3 BackPack PCB. You could solder a jumper header for testing. This should power the backlight directly, even if the LCD is not initialised. The pre-programmed PIC is set up to initialise the LCD, however. The fact that it is not lighting up points to a problem somewhere on the BackPack PCB. Check around Mosfets Q1 and Q2. Q1’s gate should be at +3.3V due to the pull-up resistor, while Q2’s gate should be at 0V, being pulled down by Q1. Sourcing parts for CDI project from overseas Greetings from France. Some time ago, I purchased components from you for the Multi-Spark Capacitor Discharge Ignition (CDI) project (December 2014 & January 2015; siliconchip. com.au/Series/279), including the PCB, transformer components, ICs, Mosfets etc. It’s now wintertime in France, so I wanted to assemble the kit and purchase the rest of the needed parts locally. I’m looking for the S14K275 VAC metal oxide varistor (Jaycar RN3400, Altronics R4408), but I can’t find that exact part here. Same for the Vishay BCC23922105 100nF class X2 275V AC capacitor. Are there any alternatives to these, or can you suggest where I can purchase them? (P. H., Saint-Pierre-surOrthe, France) ● The S14K275VAC is a metal oxide varistor (MOV) with the following specifications: • Disc diameter: 14mm • Lead pitch: 7.50mm • Operating voltage: 275V AC • Clamping voltage: 710V AC • Peak current: 4500A • Maximum energy: 115J Farnell in France (fr.farnell.com) sell the EPCOS B72220S0271K101 (catalog code 1004363), which should be a suitable replacement. The 100nF 275V AC capacitor is an X2-rated metallised polypropylene (MKP) capacitor with a 15mm lead pitch. Farnell also has an equivalent to this, the EPCOS B32922C3104M000 (catalog code 1112840). continued on page 112 siliconchip.com.au Obsolete parts in older projects Could you please tell me whether any hard-to-get parts are required to build the Constant High-Current Source from June 2002 (siliconchip. com.au/Article/4065) or the 50W DC Electronic Load from September 2002 (siliconchip.com.au/Article/4029)? I realise that you probably don’t have PCBs for these projects. (R. M., Melville, WA) ● For the Constant High-Current Source from June 2002, the heatsinking arrangements might need to be changed to suit available heatsinks. The remaining parts are commonly available. For the 50W DC Electronic Load Advertising Index Altronics.................................37-40 Dave Thompson........................ 111 Digi-Key Electronics...................... 3 Emona Instruments.................. IBC Jaycar.............................. IFC,53-60 Keith Rippon Kit Assembly....... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology.................. 5 Mouser Electronics..................OBC Ocean Controls............................. 7 PMD Way................................... 111 SC RTV&H on USB...................... 75 SC USB Cable Tester.................. 91 SC Vintage Radio Collection...... 10 Silicon Chip Subscriptions.......... 6 Silicon Chip Shop.................... 101 The Loudspeaker Kit.com............ 9 Tronixlabs.................................. 111 Vintage Radio Repairs.............. 111 Wagner Electronics..................... 87 112 Silicon Chip from September 2002, the STW34NB20 200V, 34A N-channel Mosfet is obsolete, so an alternative will be required. Suitable parts that are currently available include the IRFP240PBF, IRFP250(N)PBF, IRFP260(N/M)PBF and IXTH26P20P. Searching for another discontinued part I am trying to build the Sound Level Meter from your Electronics Test Bench book but I am having difficulty finding a three-position, two-pole switch with the correct pin placement. This project is probably over 20 years old. Is there some way I can mimic what the switch does with jumper pins, perhaps? Failing that, where would I get such a switch? (S. N., Clayton North, Vic) ● You are right that switches with the contact arrangement used in that project are no longer available. Switches are available with a similar layout, but you will have to wire it to the board using flying leads. You could use a DP4T slide switch from Altronics (Cat S2040) and wire the switch terminals to the PCB, with the third and fourth positions wired in parallel. You could also use the Altronics S2033 (4P3T) slide switch and ignore the third pole. It would also be possible to wire up a rotary switch like Altronics S3008 or S3022, or Jaycar SR1212. The PreChamp is an old design I am building several PreChamp pre-amplifiers (July 1994; siliconchip. com.au/Article/5252) to increase the signal output from the line output jack (not the headphone jack) on a TV, and plugging the resulting increased signal into a Bluetooth transmitter then to Bluetooth headphones. It works OK, but I’m not happy with the resulting audio quality when compared to another pair of wireless headphones that I have. Using a signal generator and a Hantek USB scope, I have discovered that the frequency response of the PreChamp is not flat. With a constant input level at all frequencies, I found that at 100Hz the output level was 85mV but at 10kHz, the output level climbed to 200mV, and at 15kHz, the level was 225mV. Australia's electronics magazine I have altered the Preamp’s gain by changing the two resistors to 1500W and 150W using the formula printed in the magazine, giving a gain of approximately 11 times, which is around 21dB. Would this have altered the frequency response of the PreChamp? I suspect not. Can you suggest any components that I can change the value of to get the frequency response flatter? (N. L., Christchurch, NZ) ● The PreChamp is quite an old design and we would not design something like that today. As a result, it has relatively poor frequency response flatness. Still, it should not be behaving in the manner you have described. Our circuit analysis of the original design shows that it has a plateau-type response with -3dB points at around 60Hz and 100kHz, and -1dB points at around 115Hz and 37kHz. So it suffers a fair bit at the lower frequency end, but should be pretty flat at the high end, up to about 20kHz. Changing the gain-setting resistors doesn’t have much effect on the calculated response. Note that we published a new design in January 2013 – the Champion (and Pre-Champion). That circuit has a much flatter frequency response. We even published frequency response and distortion graphs in that article, unlike the original Champ/PreChamp. Still, we aren’t sure why you are getting an increased response at higher frequencies. That points to an increase in feedback impedance with frequency, but the only non-resistive element in the feedback network is the 1.5nF capacitor, which should have the opposite effect. The only explanations we can come up with are that your input coupling capacitor is too low in value or faulty, which would cause lower frequencies to have more attenuation and thus give you a rising response with frequency. It could also be a similar problem with the output coupling capacitor. SC The March 2022 issue is due on sale in newsagents by Monday, February 28th. Expect postal delivery of subscription copies in Australia between February 28th and March 11th. siliconchip.com.au