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input - 0 to 5V transition, output - 0 to 2 seconds controlable duration pulse (0 to 5V)

David Herzog
Prodigy 30 points
Other Parts Discussed in Thread: LM555

need to find an IC (or made up from several ICs) that will generate a single pulse as follows:

Input signal: 0V to 5V transition only.

Output signal: Single pulse. The time duration of the pulse (width) can be changed

                       (with resistor potentiometer) from approx 0.5 sec to approx 2 sec. (hight = 5V )

  • 0
    Guru 22270 points

    Hello Dave,

    It sounds like you are looking for a one-shot timer.  This can be done with transistors, resistors and a capacitor.  Or you can configure a 555 time to do the same.  There is also a variation of the monstable multivibrator that can be used.  There are plenty of examples on the Internet for them.  There is probably a TI design note as well.  You can search the TI site to see.

    Thanks,

  • 0 in reply to Greenja
    Prodigy 30 points

    LM555 in Monostable Operation mode, can the Input Trigger pulse be as wide as you want, since only the initial negative transition trigers

    the generation of the output pulse. What happens if the Input Trigger pulse is few seconds wide ?

  • 0 in reply to David Herzog
    Guru 22270 points

    For the 555 timer, the are about 20 tutorials on the web that can better explain and describe how to set it up to do what you are asking than I can.

    The whole idea behind a one shot that the input produces a specific length output pulse regardless of the input duration.  The video tutorials are well worth watching.

    Thanks,

  • 0 in reply to Greenja
    Prodigy 30 points

    As a matter of fact 555 in its "monostable timer" configuration offers a single pulse output provided that the input "trigger" pulse has shorter time duration

    than the output pulse (all the tutorials are based on short pulse input).  see http://www.ti.com/lit/ds/symlink/lm555.pdf  , page 7. In comments segment of the data sheets of 555 this fact is specifically indicated.

    And I am looking for an IC that generates a single puse triggered by High-to-Low or (Low-to-High) transition, regardless how long the "Low" state, following the transition, lasts .

    looking forward to hear from you.

    Thanks.

      

  • 0 in reply to David Herzog
    Guru 22270 points

    Well, I'm glad you did some research.  There was a tutorial of a transistor version of the mono stable multivibrator that  I thought did this.  I had used one a long time ago for an AC unit that that didn't have an automatic restart when there was a power failure.

    You can always put a JK FlipFlop before the 555 timer.  That IC will only transition on a low to high.  Or you could implement it with transistors.  Once again, you would have to search the net for the circuit.

    Thanks,