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Recent content by throbscottle

  1. throbscottle

    Karcher window vac WV2 not charging

    This is more for the benefit of others who may have similar problems, since I've "fixed" mine (read - modified slightly so it works) even though I still don't understand what's actually wrong. I have a Karcher WV2 window vac. It came to me without it's original charger. Got a USB substitute...
  2. throbscottle

    Replacement polyfuse

    This is per port, btw. Did you specify total?
  3. throbscottle

    Replacement polyfuse

    Gosh, that's higher than I thought! Thanks Tony
  4. throbscottle

    Replacement polyfuse

    I am repairing a 5 port USB-2 charger - about 10 years old. It has what I assume is a resettable fuse on each of it's ports, and 3 of these have failed permanently at various amounts of Kohms. I suppose they could be normal fuses but it just seems improbable. They are white, 0805 size, flat like...
  5. throbscottle

    Filtering for a signal level detector

    Last post on this topic. I eventually obtained nice pulses from the motor's commutator, with the high pass filter first to get rid of the once-per-revolution "rumble" and the worst variation in pulse size. After that the noise from PWM was easily removed with just the 330uH + 1.8uF combo. At...
  6. throbscottle

    Filtering for a signal level detector

    In case anyone is still interested... I made it work in LTSpice - 3 signals do a rough approximation of what I'm getting from the motor. Diff amp, low pass then high pass filters, boost to a somewhat untidy pulse train, 555 to convert the signal to PWM, filter, level shift and amplify. Not sure...
  7. throbscottle

    Filtering for a signal level detector

    Well, things are looking a lot better! I set up a diff amp as the input, unity gain, and the worst of the high frequencies disappeared! So thanks for that diver, sound advice. Next, single stage gain just over 2, feeding a 2 stage RC filter (3k+10n then 1k+100n). Resulting signal is discernible...
  8. throbscottle

    Filtering for a signal level detector

    Hi schmitt trigger. It's a permanent magnet motor fitted with anti-spark ring I believe. I get discernible pulses from the commutator switching but there is a lot of noise as well, including I have realised, PSU noise as well as the PWM noise. It's pretty horrible. I did try diver's suggestion...
  9. throbscottle

    Filtering for a signal level detector

    Ok, so it's a permanent magnet motor, lightly loaded. Pretty sure it has an anti-spark ring. Periodic interrupts are possible but mean adding at least 1 extra connection to the main board, and providing some means of remembering the values. Also I'm not sure if the IRF21531 half-bridge driver...
  10. throbscottle

    Filtering for a signal level detector

    500 revs per second, not 500 Hz. 5 pole commutator gives 10x value (apparently). Makes it tricky. I was quite surprised that my simple filter worked at all, it was only a crude test - I'd got a 3 stage active filter design lined up fresh from TI's web-bench - but then didn't build it! Anyway...
  11. throbscottle

    Filtering for a signal level detector

    I'm making an analogue tachometer for my PCB drilling machine, but the level detector at the end isn't very good - help please! Here's the setup: The 5 pole motor is driven by a 10KHz PWM signal and does up to 30K RPM. The actual adjustment range starts at about 10K I think. A 0.1 ohm sense...
  12. throbscottle

    Digital chip input handling

    If you can live with the active low inputs, the 74HC74 does the same thing and is specified as able to work with slow rising signals. I have one quite happy working away with a 4.7uF/47K combo tied to it's clock input (gives around a 1s delay). OTOH it's a POR you have so you are using a pretty...
  13. throbscottle

    Strange 555 failure

    Okaaaayyy... I don't have that equipment or training unfortunately. It would be very interesting though. For me it's more a case of "is it something I did?" - If I can work out what failed it gives more of an answer to that question. But it's looking like, no, I was just unlucky. I have managed...
  14. throbscottle

    Strange 555 failure

    Mentioned in post #8
  15. throbscottle

    Strange 555 failure

    Hmm, I was thinking a failure connecting the threshold and trigger reference inputs together. But your idea seems more likely. The chip does partially work, the astable was running, just with the wrong frequency/duty, and limited range in the control. I suppose if I see what voltage the trigger...
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