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push and hold switch

Discussion in 'General Electronics Discussion' started by Jimbob96, Jan 19, 2015.

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  1. Jimbob96

    Jimbob96

    13
    3
    Nov 27, 2014
    hi I am working on a project at the minute that is for my A level electronics coursework. I am building a traffic light system and I have started by building a binary counter that counts down from 30 seconds to 0. I have built an astable using a 555 timer IC. The problem that I have is that I want the countdown to only start when the button has been pressed for a short time and then reset when the count down finishes. I have tried just adding a push button between the astable and the binary countdown but of course the button has to be continually pressed in order for the counter to count down.
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    10,579
    2,359
    Nov 17, 2011
    Look into RS-flipflops. The pushbutton can e.g. set the flipflop, enabling count down. The counter can reset the flipflop when it reaches 0 count, thus disabling further counts. The output of the flipflop will control a gate that in turn enables or disables the clock to the counter. Or use a counter with an enable input.
     
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