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No look window circuit

  1. Apr 10, 2007 #1
    I have a signal and it oscillate bewteen 0 and 10V for 400ms when triggered. What is the easiest way to design a circuit that look for the first low of the pulse and output a high for 100ms while ignoring the pulses in the last 300ms?

    I prefer not to use uC.


  2. jcsd
  3. Apr 10, 2007 #2


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    Staff: Mentor

    Have your signal trigger a counter that counts for 100ms with logic that puts out a high for that 100ms, and more logic that watches the counter for another 300ms+, and then halts/resets the counter and re-enables the counter's trigger. Would something like that work? You can use something like the HC4060 oscillator+timer IC, and use a 32kHz watch crystal at the oscillator stage.
  4. Apr 10, 2007 #3
    I'm gonna try using two 555 timers and both will be in one shot mode. The timer "A" will be set to output a 100ms when triggered and timer "B" to 400ms when triggered. The output of "A" will be inputted into "B" trigger pin. Finally output of "B" will be NAND with the 400ms pulse signal.

    I think this will work but is there a simpler way? I'm using two ICs bu prefer to just use one.
    Last edited: Apr 10, 2007
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