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  1. KrisBlueNZ

    Voltage limiting without altering waveform

    This version adds a bipolar voltage detector and indicator LED. The NPN transistors are all BC547B or 2N3904. PNPs are all BC557B or 2N3906. You can adjust the LED series resistor value to give the desired current with the voltage rails you are using. You apply an adjustable signal to the...
  2. KrisBlueNZ

    Voltage limiting without altering waveform

    BobK, yes it will. Do you think that will damage it? I doubt it would. duke37, are you sure he wants to measure 400VAC? If so, yes an external divide-by-10 or divide-by-100 probe would be a very good idea. There's no point clipping after the op-amp; the op-amp will clip the signal itself! The...
  3. KrisBlueNZ

    Voltage limiting without altering waveform

    This thread is going round in circles. This is my suggestion. It consists of a range switch, an overvoltage protection circuit, and an op-amp buffer. There's a negative rail generator as well. You can delete that part if you already have a negative supply rail available. It needs a DC power...
  4. KrisBlueNZ

    Mysterious diode identification help!

    Updated schematic.
  5. KrisBlueNZ

    Voltage limiting without altering waveform

    You don't need to cut off the signal to the sound card. As long as it is voltage-limited (clipped), it won't damage the card. You just need an indicator to tell you that the signal is being clipped (if it's not already obvious from looking at the shape of the waveform that you capture with the...
  6. KrisBlueNZ

    Mysterious diode identification help!

    Yes, you're right, it's T2. Thanks for that information; I will correct and update the schematic. Re parts to order along with the transistors. I suspected those big carbon resistors because they can be a common fault, but they're OK at the moment, so it's up to you whether you replace them or...
  7. KrisBlueNZ

    Led sequencer/scanner

    R1 and C1 determine the frequency of the 555 oscillator, which is for you to choose. The formula is roughly f = 0.7 / (R C) where f is the frequency in Hertz, i.e. number of pulses per second; R is R1 in ohms; C is C1 in farads (not microfarads!) Generally, you choose C1 (a typical value in...
  8. KrisBlueNZ

    Voltage limiting without altering waveform

    Yes, you're right, it will clip the waveform. Automatically increasing the attenuation when clipping occurs is a bit tricky. It's called AGC (automatic gain control), or if you want discrete attenuation steps, so you can calculate the correct amplitude of the signal you're measuring based...
  9. KrisBlueNZ

    Genius! Please tell me the theory which apply on this

    Many people here will not help less-experienced users with circuits that have outputs that are not isolated from the mains. This is because we don't want you to electrocute yourself. We can't stop you, but we don't want to have been involved in any way.
  10. KrisBlueNZ

    12v LED Strobe Controller

    Yeah LOL. But the miscommunication isn't over yet :-) That's still FAR too vague for me. You need to define what you want in terms of the steps of a sequence, as I showed you. I'm sorry if you find it difficult, but you really WILL have to read my responses carefully, step-by-step, and try to...
  11. KrisBlueNZ

    12v LED Strobe Controller

    OK. I'd say you should probably replace the existing controller with a single one that can generate the patterns you want. So the LEDs are already mounted and wired into these pods, and each pod just needs 12VDC across it to light the LEDs, right? In that case, we can treat these pods as "black...
  12. KrisBlueNZ

    Voltage limiting without altering waveform

    duke37's advice is good. A diode limits the voltage across it in the forward direction. When the voltage across a diode in the forward direction is less than the diode's forward voltage (around 0.6V for a general-purpose silicon diode), the diode conducts little current and appears as an open...
  13. KrisBlueNZ

    12v LED Strobe Controller

    Welcome to the electronics point forums! You need to provide more information. Can you draw a picture of how your LEDs will be arranged, and scan it and post it here. And write a description of how you want them to flash in each display mode. Look at it from the point of view of time periods...
  14. KrisBlueNZ

    MOSFETs IN SERIES

    Good.
  15. KrisBlueNZ

    MOSFETs IN SERIES

    Good. Yes, that's probably a good idea. Your circuit is right apart from the gate drive. For cleanest switching and best safety, you should have a 10k current-limiting resistor in series with EACH diode, instead of a single resistor in series with the 12V source. If possible, use FUSIBLE...
  16. KrisBlueNZ

    PCB not functioning

    Hi partyanimallighting, OK, I've looked at the schematics and the design is pretty straightforward (although the schematics are not very clearly drawn). I will describe the general design, starting with the universal power supply schematic. AC mains voltage enters at the top left, on "HOT" and...
  17. KrisBlueNZ

    PCB not functioning

    I'm working on a reply.
  18. KrisBlueNZ

    Problem with old ceiling fan

    Yes, you definitely need to re-grease the bearing(s) after you clean them out. It's just like flushing your car's oil system using petrol or some other solvent. The solvent makes the grease much more liquid, so it will come out and bring the dirt with it. Then the bearing is unlubricated, so you...
  19. KrisBlueNZ

    Audio problem 900W active speaker

    I agree with CC, please post some clear photos including closeups of ALL the boards. Is it possible that the white stuff is just thermal paste? It looks like toothpaste and is put between the power transistors/MOSFETs and the heatsink to improve heat transfer. Photos are the next step. Without...
  20. KrisBlueNZ

    instead of optocoupler?

    Do you know how/why the optocoupler "exploded"? Was it because of excessive voltage across the isolation barrier, or excessive current into the LEDs, or something else? If it was caused by overvoltage across the barrier, I'd suggest (as GreenGiant did) that you use a device with a higher...
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