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Single pulse output

Discussion in 'PCB Layout, Design and Manufacture' started by Simon_m74, Jun 7, 2018.

  1. Simon_m74

    Simon_m74

    28
    1
    Jul 25, 2016
    Hi
    I`m trying to make a system that :
    When a button is pressed, a single short pulse is output - once, no matter how long the button is held for. although the button can be pressed repeatedly, for a single pulse each press.

    I`m thinking about using a 555 timer to time the short pulse, and a SR latch to set the timer?

    So the button press sets the latch, with outputs a pulse for say 1ms - upon which the timer resets the latch, and disables the button input, until the button is released.

    Either can you help with that, as I cant get my head round it, or am I barking up the wrong tree?
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    9,043
    1,811
    Nov 17, 2011
    The term to look for is "monostable multivibrator" or "one shot". A 555 is a suitable chip to do this. No SR latch is required.
     
    Simon_m74 likes this.
  3. Alec_t

    Alec_t

    2,607
    686
    Jul 7, 2015
    Here you go :
    555-monostable.PNG
     
    Simon_m74 likes this.
  4. Simon_m74

    Simon_m74

    28
    1
    Jul 25, 2016
    Thanks guys!!!
    I`ll be building and testing soon!
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,158
    2,676
    Jan 21, 2010
    Be aware that your switch may bounce. If the duration of the required pulse is short, the switch bounce may cause multiple pulses to be generated. For longer pulse duration, the bouncing may elongate the pulse by the duration of the bouncing.

    One fix is to have a second monostable (with a duration longer than any expected bouncing) trigger the monostable that produces the desired length pulses. The first (longer period) monostable is triggered by the switch (and limits the rate at which you can press the button) while the second produces an accurate and repeatable short duration pulse.
     
  6. Simon_m74

    Simon_m74

    28
    1
    Jul 25, 2016
    Thanks for that.
    I tested the VR machine (that I need the `credit button for`.
    The output will connect to the left joystick port of an Amiga computer, on the `joystick-back` pin.

    I tested simply, by plugging in a joystick, and pulling back : A credit accepted!

    So I`ll now build at least for of these, to go onto my 4 VR machines.
     
    (*steve*) likes this.
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