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  1. AnalogKid

    circuit breaker alarm

    Correct me if I'm wrong - the goal is to inhibit the sensor output at power-up, and prevent the beeper from beeping for a few seconds while you leave the room. After that, the sensor controls the beeper without delays - when the sensor "sees" something, the beeper goes off immediately. Yes /...
  2. AnalogKid

    circuit breaker alarm

    Again, need a lot more information. PIR device part number / model number / vendor / website - anything? Voltage and current ratings for the buzzer? What is the voltage for the circuit? What is the PIR device output signal when it senses someone - a high voltage level, a low voltage level...
  3. AnalogKid

    Power failure alarm

    Here is a first pass at a dual-555 solution. Of note is the very large timing capacitor for the 2-hour delay. Cleaned-up version to come. ak
  4. AnalogKid

    Power failure alarm

    That is a significant change from So now the beeper beeps for only one minute, but after a 2 hour delay? That would be a 2 x 555 circuit, one for the 2-hour delay and one for the 1-minute beeper time. But there is another approach. 2 hours is a loooooong time for a simple R-C timer circuit...
  5. AnalogKid

    Power failure alarm

    Nope. With the components shown, the 555 is pulsing power to a self-contained piezo beeper, the kind with a 1-transistor oscillator built-in. In very round numbers, the 555 oscillator is driving it at 1 second on and 1 second off, not at the 2 kHz to 4 kHz needed for direct drive to a bare...
  6. AnalogKid

    Power failure alarm

    That circuit has several problems. Why is there a 10 K resistor in series with the beeper. That will make for a very quiet "alarm", if the beeper sounds at all. Without connections dots, it is impossible to say if the circuit will even work. It shows the 555 powered by only the battery. The...
  7. AnalogKid

    Power failure alarm

    Your question is missing a *lot* of detail. What is the relationship between the timer and the alarm? Do you expect the battery to power the alarm for 2 hours? 2 hours is a loooong time for a 555 timer circuit; even the CMOS version would be iffy.. Rather than have us waste time trying to...
  8. AnalogKid

    want to tinker with my UPS.....

    I do. Can you post a sketch of the various components and how you have them connected now, and another with your proposed changes? Paraphrasing Rear Admiral Joshua Painter, "Engineers don't take a dump, son, without a schematic." ak
  9. AnalogKid

    want to tinker with my UPS.....

    Why? If the battery voltage and the battery chemistry are identical, the charger doesn't know or care about the capacity; all discharged batteries (of the *same chemistry*) look alike. The charger circuit will run longer before shifting down to trickle mode, but it already has a fan so that...
  10. AnalogKid

    want to tinker with my UPS.....

    OR, in American: Tang Yew Berry Mulch. ak
  11. AnalogKid

    I need a 350V, 1A PSU

    The LR8 has a max output current of 30 mA, and there is no application circuit in the datasheet to boost this. Also, its minimum input-to-output differential voltage is 12 V, while the LM317's is around 2 V at a 1 A output current.. ak
  12. AnalogKid

    I need a 350V, 1A PSU

    Based on that post, here's a plan. 1:1 or 1:2 isolation transformer plus a low voltage transformer gets you a peak voltage after rectification of 370 V. With lotsa filter capacitance, the ripple voltage minimums are around 355 V to 360 V. An LM317 regulates this to a flat 350 V. ak
  13. AnalogKid

    I need a 350V, 1A PSU

    Harris used to make something similar, in a TO-220 package for higher output current. I think they are all obsolete now. Note that the grand old LM317 will work in this application. It's 43 V rating is for the voltage from its input to its output, not from its input to GND.
  14. AnalogKid

    I need a 350V, 1A PSU

    A power Factor correcting (PFC) front end is a regulated boost converter. Usually these are non-isolated. One of these plus a 1:1 isolation transformer could do what you want. You might have to post-regulate it to reduce the high-frequency ripple. Is a 350 V output switcher a possibility, of...
  15. AnalogKid

    I need a 350V, 1A PSU

    Fixed 350 Vdc or adjustable over a range? What is the minimum output current expected? Some supplies have a minimum output current requirement; below that amount, the output regulation becomes unstable, the output impedance increases, etc. What does "smooth" mean? Filtered but with some...
  16. AnalogKid

    Mosfets as voltage dividers.

    That is an all linear supply, with the output current limited to around 2 to 2.5 A (not the 7 A stated on the drawing.) Also, D1 - D4 are rated for only 3 A. The circuit output voltage is adjustable from 10 V to 19 V -ish, it the power transformer can support it. You can replace the...
  17. AnalogKid

    Mosfets as voltage dividers.

    That is not much information to work with. Make and model of the bench power supply? Reason it needs to be rebuilt? In what way is it not working normally? Link to one of the videos you describe? Supply, its front panel, the board - anything? ak
  18. AnalogKid

    Mosfets as voltage dividers.

    What this?
  19. AnalogKid

    Help Repurposing an LED Sign Panel

    P.h.o.t.o.s.
  20. AnalogKid

    Simple Hall sensor alarm circuit?

    That is the safe way to start if you have no clues to the approximate current levels you are measuring. But in this case there are lotsa clues. Except for accidentally dead-shorting the batter, you are probably safe starting with the low range. But . . . At its heart, what you have is a volt...
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