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Persistant circuit with a tactile switch

  1. Dec 12, 2012 #1

    I have a set of switches that would look good on my project however they are all tactile SPST. Is there anyway (without the use of an IC) to turn these momentary switches into a SPDT and/or a latching SPST.

    I want to switch the circuit on and off with a green and red led changing colour depending on the state and also switch a set of lights on and off.

    It would also be good if they remembered their state when the entire circuit is switched off.

    Thanks for any advice.
  2. jcsd
  3. Dec 12, 2012 #2


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    Staff: Mentor

    It doesn't sound like you can do what you want. What's wrong with using some simple flip-flops (FFs)? Or else look at switch manufacturer websites until you find a style of latching switch that you like...
  4. Dec 12, 2012 #3
    I wouldn't say you can't do it, but the circuit is going to get very complicated very fast, compared with just slapping some ICs down. A slow clock and a T-flipflop will do what you want to a degree: The output will change states as long as the button is held down, and hold whatever state it has when released, so you'd want the clock no faster than 1-2Hz or it'll toggle too fast for you to accurately let go in time.

    If you use the switch to trigger a oneshot, the oneshot can then act as the trigger to the flipflop.

    Without using ICs you're talking about at least a dozen different parts required to build this circuit, and you need to build it for each button.
  5. Dec 12, 2012 #4


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    Science Advisor
    Gold Member

    Use a mechanical latching relay. The kind with 2 coils. Arrange the contacts so that each time the switch is pushed it activates the coil that will change the contact position. Use a cap in series so it doesn't chase its tail.
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