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rc timer circuit help

Discussion in 'Electronic Basics' started by [email protected], Jul 10, 2013.

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  1. Guest

    I have a GSM controller that can switch a relay for a minimum time of 1 sec, however I need a 300ms pulse. I am looking for a circuit that can take the 1 sec relay output (as an input) and give me a 300ms output for a second relay.
    Thanks for any help.
  2. Jon Kirwan

    Jon Kirwan Guest

    Does the 300ms start at the beginning of the 1s output
    duration or at the end of it? In any case, have you looked at
    the 74121 (various families), 74HC221, or 74HC123 to use
    together with an external BJT or MOSFET switch?

  3. Jasen Betts

    Jasen Betts Guest

    how precise do you need to be?
  4. Guest


    Does not need to be that precise but should be below 500ms.
  5. Guest

    The out put is a dry contact relay.
  6. whit3rd

    whit3rd Guest

    If this were a system with DC power supply, and logic-level output, it's easy. If it's
    an AC-power (mains) system, things get trickier: the best might be an AC timed relay
    connected in series, that turns OFF after 300 msec, and resets when power is

    It matters a lot what kind of power is available (and what the nature of the intended
    load is).
  7. Guest

    Thanks all, going with the capacitor, resistor suggested by John, simple and effective.
  8. Fred Abse

    Fred Abse Guest

    Named for a Kansas City undertaker.
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