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  1. KrisBlueNZ

    How to make a fan unit RF dmx controllable

    You've posted in the right part of the forum. Dave was just saying that HE couldn't help you. Since no one else has responded, you can probably assume that no one here can help you. You should have used a more descriptive title for your thread - mention DMX, fan, varying speed, and wireless...
  2. KrisBlueNZ

    2M+ ohm resistors not resisting

    The voltage adjustment trimpot in that module isn't 2M; it's 10k. This is indicated by the marking "103" on it, which means "1, 0, then three zeros", i.e. 10000 ohms or 10 kilohms. The module may not do what you want. Certain components, mainly the large inductor, are chosen to work over...
  3. KrisBlueNZ

    School Project Help.

    Well, you can use a depletion-mode JFET as a variable resistance to provide adjustable attenuation, or you can use an LDR with an LED. And you can make an op-amp or a comparator from a long-tailed pair.
  4. KrisBlueNZ

    Help needed; analyze omron output plc circuit

    This is a very straightforward digital output circuit. Starting from the left of the top diagram, the "internal circuits" represents the inside of the PLC. When the PLC wants to activate an output, it applies a voltage between the middle and bottom wires coming out of that "internal circuits"...
  5. KrisBlueNZ

    School Project Help.

    Hi again, Have a look at the LM13700. Data sheet is here: http://www.ti.com/lit/ds/symlink/lm13700.pdf It's a dual operational transconductance amplifier that can be used as a variable-gain amplifier. It can operate from +/- 5V. You need to monitor the peak-to-peak amplitude at the output...
  6. KrisBlueNZ

    Help for School Project

    Actually, I doubt I'll be able to help you much. I have no experience with robotics. I really just replied to try to point out how vague that specification was, because if there IS anyone here with robotics experience, I assume they would expect a much better specification than that. Now that...
  7. KrisBlueNZ

    Help for School Project

    I probably shouldn't have said anything. I can't help with any component recommendations. Sorry for wasting your time.
  8. KrisBlueNZ

    Help for School Project

    So do you think you'll be able to get the robot through the gate in less than half a second?
  9. KrisBlueNZ

    audio amplifier with unstable output offset voltage

    OK. Well, it's difficult to be sure what to do if the schematic doesn't match the unit. Rapid freeze could tell you which component(s) are failing. My guess is that a transistor may be becoming leaky as it warms up. If VT2, 4, 5 and 7 match the unit, they seem to me to be the most likely...
  10. KrisBlueNZ

    Computer Power Unit Failure

    Good point rleo6965. Even if the PWM chip didn't cause the MOSFET to fail, it could have been damaged when the MOSFET died. It would be hard to test; perhaps the best option would be to replace it just in case.
  11. KrisBlueNZ

    required delay before function execution!!

    In a general sense, you need some kind of multi-tasking, or an approximation of it. You need to have some code running "in the foreground", but all the time, you also need to have your alarm handling code doing its thing as well. There are a number of ways to handle this. The best way depends...
  12. KrisBlueNZ

    Help for School Project

    That's a very vague specification. Does the robot have to be able to steer? The specification doesn't say whether the gates can all be in a line or not. You mentioned a "track" but this isn't part of the specification. Do the gates open like hinged doors or like sliding doors? Do you have a...
  13. KrisBlueNZ

    audio amplifier with unstable output offset voltage

    A quick Google search doesn't show any specifications or equivalents for KA103A, only a Russian supplier who will sell them to you. In this case any small silicon diode will work; I'd use a 1N914 or 1N4148. But I doubt that the diodes on VT6's base are at fault. I was just making a point. Why...
  14. KrisBlueNZ

    Beginner question: diodes?

    Cool! Nice work.
  15. KrisBlueNZ

    audio amplifier with unstable output offset voltage

    Thanks for that. It's an improvement... I think! OK. There can be subtle clues. Also this is an unusual amplifier. I think it could be quite helpful to see some photos of the amplifier. Both sides of the PCB could be relevant. When semiconductors get old, the faults they exhibit can be quite...
  16. KrisBlueNZ

    Voltage limiting without altering waveform

    Right.
  17. KrisBlueNZ

    audio amplifier with unstable output offset voltage

    That schematic is hard to read. Line drawings are best in GIF or PNG format, not JPG (JPG is designed for continuous-tone images like photographs). I assume you scanned it at a higher resolution than the image you uploaded? I would convert it to greyscale, increase the contrast so ALL the...
  18. KrisBlueNZ

    Computer Power Unit Failure

    There could also be other components that either failed first, and caused the main switching MOSFET to fail, or failed as a result of the heavy current that flowed when the MOSFET went short. I would check the rectifier diode(s) on the secondary side, and check all diodes on the primary side...
  19. KrisBlueNZ

    Bulldog Security Remote Start RS82i

    Why do you think that diode is faulty? It doesn't look damaged. Even if the diode measures short-circuit it's possible something else has failed. The only way to know for sure would be to remove the diode from the circuit and test it separately. What happened to cause the unit to fail? Did it...
  20. KrisBlueNZ

    audio amplifier with unstable output offset voltage

    As Harald suggested, the problem is probably thermal and you can use rapid freeze (in an aerosol can) to find which component is causing it.
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