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Random ON/OFF Timer Circuit

Discussion in 'Electronic Basics' started by tom, Jun 1, 2005.

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  1. tom

    tom Guest

    Hello All

    I was wondering if anyone can help with or knows where I can find a
    random ON/OFF timer circuit that will switch a 6-12v DC relay ON
    between a random period of say 5 to 20secs and then turn OFF for
    another random period of say 5 to 15secs.

    I'm building an outdoor device and I'm trying to simulate random

    Any help will be greatly appreciated.

    Regards Tom McMurtrie
  2. John Fields

    John Fields Guest

    So, you want it to turn ON for a random interval of not shorter than 5
    and not longer than 20 seconds, and then at the end of the ON period
    you want it to turn OFF for a random interval of not shorter than 5
    and not longer than 15 seconds, and then you want the cycle to repeat
  3. tom

    tom Guest

  4. tom

    tom Guest

    That is correct, the cycle would continue to repeat.

    Regards Tom
  5. Pending a more elegant solution, you could adapt this circuit I
    designed for my 'Surf Synthesiser' many years ago:

    That delivers an output duration (simulating gaps between successive
    breakers) chosen randomly from 10 preset values from roughly 9s to 20s
    (determined by the resistor choices). It sounds like you need TWO such
    4017 sections, one for ON and one for OFF.

    But if I was tackling your task from cold, I'd probably start by
    playing with a couple of pseudo-random generators made from shift
  6. John Fields

    John Fields Guest

    Seems like you only need one. I'm working up a solution with an 8 bit
    PRSG feeding the broadside load of an 8 bit down-counter. When the
    counter times out it toggles a dflop wired as a divide-by-two (which
    turns the relay on and off), advances the PRSG by one state, and
    drives a 5 second one-shot which loads the counter with the new value
    from the PRSG and holds the counter off for 5 seconds.

    In order to get the two timeouts, I'm using a 555 as an astable with
    the frequency switched from about 17Hz for the 20s timeout to about
    26Hz for the 15s timeout. The dflop will switch the frequency by
    changing timing caps, since that's easier because they're ground

    Those numbers come from 256 counts in 15 seconds when the PRSG loads
    all ones into the counter for the 20 second timeout and 256 counts in
    10 seconds when the PRSG loads all ones into the couner for the 15
    second timeout.

    I'll post the schematic to abse when I'm done. Hopefully, later on
  7. Neat! Look forward to seeing it.
  8. John Fields

    John Fields Guest

  9. Nice stuff! I'm hoping the OP will ask you for some narrative, as it
    would save me a lot of time <g>.

    But, hey, that's arguably even more complex than my 4017 suggestion!
  10. tom

    tom Guest

    Hi John,

    Thanks for your help along with the other guy's replies too.

    I have had a browse through alt.binaries.schematics.electronic under
    "Random ON/OFF....." but I haven't managed to see a link to the

    Would it be appropriate to forward it to me direct at
    [email protected] (remove the 2nd @)

    Thanks Tom
  11. John Fields

    John Fields Guest

  12. Thanks. Looks good. Only wish I had time to either simulate or
    breadboard it <g>.
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