Looking for a circuit that

Discussion in 'General Electronics Chat' started by doug08, May 20, 2013.

  1. doug08

    Thread Starter Member

    Jan 30, 2011
    153
    2
    can be triggered on and off ONLY after receiving 2 negative pulses within roughly 3 seconds time. If only one pulse is received, I want nothing to happen. Any ideas or links?


    Thanks.
     
  2. Sensacell

    Well-Known Member

    Jun 19, 2012
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    266
    How about a charge pump and a comparator?

    What do these pulses look like? voltage amplitude? rise /fall time?
     
  3. doug08

    Thread Starter Member

    Jan 30, 2011
    153
    2
    maybe 1/4 to 1/2 sec each in duration. A stable positive voltage that experiences a voltage drop, but not to zero.
     
  4. WBahn

    Moderator

    Mar 31, 2012
    17,715
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    You could use a 555 timer that is triggered by the first pulse and that enables the circuit for three seconds with a subsequent pulse required within that window to activate the circuit. Now, what do you mean "triggered on and off"? Do you mean that once the second pulse is recognized that the circuit is turned on and then turns off automatically? Or do you mean that it is toggled upon recognizing the second pulse and stays in the new state until a subsequent pair of pulses is received?

    It would be most helpful if you would provide a sketch of what you are looking for.
     
  5. Sensacell

    Well-Known Member

    Jun 19, 2012
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    Can you be more specific? What voltage? What would the 'LOW' state voltage be?

    How about a drawing showing the input waveform and the desired output?
     
  6. MrChips

    Moderator

    Oct 2, 2009
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    Get each pulse to trigger a monostable multivibrator with a pulse duration of about 1-2 seconds.
    Feed the AND condition of the two monostable outputs into a third monostable set for any desired duration.
     
  7. doug08

    Thread Starter Member

    Jan 30, 2011
    153
    2
    I figured the 555 would work, but can someone post a link to the circuit that "WBahn" is talking about? Either type he mentioned will work.

    Thanks!
     
  8. MrChips

    Moderator

    Oct 2, 2009
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    I suspect such a link does not exist. You are creating a unique scenario. I suggest you provide the information requested: a timing diagram of what you expect to happen and a clearer description of what you mean by "triggered on and off".

    There are many experts here on circuit design and we haven't got a clear picture of what you are trying to accomplish.
     
  9. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    You could have a 555 triggered by the first pulse,that enables a cd4017 for 3 seconds, and the clock pin pulses on the next trigger signals ,set the 4017 to count to 2 or 3.
     
  10. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
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    What is supposed to happen if a third pulse happens during the interval?
     
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