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  1. KrisBlueNZ

    Telephone Ringing Circuit

    All good advice on this thread, and you're doing everything right. The conventional way to interface an optocoupler to a micro is to ground the emitter, connect the collector through a resistor (e.g. 10k) to the positive supply rail, and connect the microcontroller input to the collector. You...
  2. KrisBlueNZ

    An OPAMP with input offset voltage

    OK I'll have a go. I have to assume that the op-amp has infinite input resistance. The formulas for the voltages at the two op-amp inputs are: 1. . V_inverting_input = (Vin + Vout) / 2 2. . V_non_inverting_input = Vout / 6 This circuit has one stable condition because there is more negative...
  3. KrisBlueNZ

    Battery Powered Power Supply

    Here's another design you can try. It's based on an SCR made from two discrete transistors. It's pretty simple so it's probably worth prototyping. Obviously there's no need to include QK at the moment; you only want to check the on/off button functionality.
  4. KrisBlueNZ

    Battery Powered Power Supply

    I'm not sure what to suggest. Ideally I think the 4013-based design is simplest but that didn't seem to work. Here's something you can try. Increase the 100 nF capacitor to 10 uF and add a 180k resistor in parallel with it. With the circuit ON, measure the voltage on that capacitor and post it...
  5. KrisBlueNZ

    XTR 117 help!!!

    Thanks for the response. I'm reposting your schematic (from your previous post) here for easy reference. So you are actually using a real XTR117? You are not trying to simulate it with discrete components and op-amps? It's very important that all the circuitry on the left side of the...
  6. KrisBlueNZ

    newbie looking for advice

    That's not an experience I would recommend to a beginner. Reputable sites and DIY magazines take care to make sure the projects they offer are clearly explained, properly documented, and workable, so that beginners who try them will be encouraged, rather than discouraged, by their first...
  7. KrisBlueNZ

    Battery Powered Power Supply

    Those substitutions should be fine. My best guess is some kind of problem with C3. A 100 nF capacitor (also known as 0.1 uF) should be marked "104". Check that, and upload a photo of the breadboard layout.
  8. KrisBlueNZ

    Tic-Tac-Toe

    His posts seem to be just promoting the blog, yes.
  9. KrisBlueNZ

    LM217's in parallel is OK?

    Interesting. Thanks for the info.
  10. KrisBlueNZ

    newbie looking for advice

    I second Steve's opinion. Every electronic project I've seen so far on instructables.com is poorly designed and borderline unworkable. Many web sites have build-it-yourself projects and these range from poor to good, with the occasional excellent site. I emailed someone at instructables.com and...
  11. KrisBlueNZ

    Weird behavior of audio interface at 20KHZ

    20 kHz is normally beyond the frequency limit of human hearing except for young children. It's also at or beyond the frequency limit of the audio compression typically used with videos. Why would you want to do anything with a 20 kHz tone? Try a 10 kHz tone. You should get more sensible...
  12. KrisBlueNZ

    Tic-Tac-Toe

    Cute :-)
  13. KrisBlueNZ

    Zany Clock

    It looks rather hard to read. A display with higher resolution and/or greyscale and/or colour would be a lot better.
  14. KrisBlueNZ

    Need help with car headlight alarm

    The circuit you posted is workable, but the transistor needs a protection diode between base and emitter to protect it against reverse base-emitter current, which can damage it. Something like a 1N914 connected with its anode to the base and cathode to the emitter will do this. Also, I don't...
  15. KrisBlueNZ

    TDA1554

    Start by measuring the voltages at all pins of the TDA1554 relative to GND. Post the list here. It's probably something simple and obvious. Edit: When you measure the pins, be very careful not to put pressure on the probe in such a way that it could slip off the pin and jam itself between two...
  16. KrisBlueNZ

    LM217's in parallel is OK?

    Good advice from Steve. Why are you using NiCd cells? I thought they were banned under RoHS (Cadmium in the waste stream is a no-no). What country are you in?
  17. KrisBlueNZ

    XTR 117 help!!!

    1. The power supply that you're using to provide the input voltage must be FULLY ISOLATED from the other components. I recommend using a potentiometer or trimpot (5k resistance) between VREG and IRET to generate the test voltage. 2. You said "BC547 transistor is used". In which circuit...
  18. KrisBlueNZ

    Battery Powered Power Supply

    So the two-MOSFET circuit wouldn't stay switched ON? That's odd. Perhaps the startup pulse from the pushbutton wasn't long enough to charge the smoothing cap fully. I don't know. You can't use the J174/177, it's a depletion-mode JFET device. You need an enhancement-mode MOSFET. You can use a...
  19. KrisBlueNZ

    Battery Powered Power Supply

    If you add smoothing capacitance across the switched voltage rail, it will drop slowly when the circuit turns off. This is because there is very little load current being drawn from that rail. This slow voltage decay will happen with my switching circuit (using the two-MOSFET latch and...
  20. KrisBlueNZ

    N channel high side switch

    OK, if you want immediate control of the MOSFET, my suggestion of starting and stopping the drive to a transformer that generates the gate bias will not work. The last schematic on the page you linked to is a good idea, but it requires an isolated power supply that can be referenced to the...
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