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555 Timer Push-On, Push-Off but with timer as well

Discussion in 'General Electronics Discussion' started by Ben Parker, Oct 22, 2015.

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  1. Ben Parker

    Ben Parker

    Sep 21, 2015

    I have a monostable 555 timer circuit that activates a relay. This is used to turn a pump on for 60 seconds, it also turns turns on the 555 astable circuit to flash the LED on the momentary switch.

    At present the momentary switch triggers the timer, however what i would like is to use the same switch to reset the timer if required. Ie if 30 secs through the cycle you want to stop the timer. I cant find the circuit i need, can anyone help?

  2. Bluejets


    Oct 5, 2014
    Reset pin is terminal 4 on your 555 but would require an additional switch.
  3. Colin Mitchell

    Colin Mitchell

    Aug 31, 2014
    Here is the push-ON push-OFF circuit you need:
  4. AnalogKid


    Jun 10, 2015
    The circuit in post #3 is a bistable, or toggle flipflop that latches alternatively in the high and low output states. It does not have the one minute timer in post #1.

    To modify your original circuit, change the pushbutton switch to a SPDT toggle switch that is center-off and momentary in both directions (or non-momentary if you return it to the off position manually). Toggle one way to start the timer, toggle the other way (connected to the reset input) to reset the timer. The 555 reset input will need a pullup resistor to Vcc.

    Last edited: Oct 23, 2015
    Martaine2005 and Bluejets like this.
  5. GPG


    Sep 18, 2015
    I think this will work It represents the first 555. Time between pushes is ~ 4 secs.Not tested or simmed.
    Edit All small signal diodes 1N4148. One of them may not be necessary

    Attached Files:

    Last edited: Oct 25, 2015
  6. GPG


    Sep 18, 2015
    Make R2 R3 1MΩ. As they affect the timing R1 may need adjusting.
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