Timed repeating switch help

Discussion in 'General Electronics Chat' started by pandafman, Dec 26, 2011.

  1. pandafman

    Thread Starter New Member

    Dec 26, 2011
    I am a chemistry and math major so my knowledge of circuits terminology is limited, and it is making it hard to find information on how to go about making a switch I need. What I want to do is have a switch setup where I would depress a momentary and then the signal would turn on and off at a set time interval until I release the momentary switch. I have read some about capacitor resistor oscillators, but I am not sure if they would have a zero charge during the off period of the cycle. If anyone can give me a general idea of where to begin looking or what the term is for such a switch I would appreciate it.
    The project is intended to turn on a solenoid for a moment and then have a timed delay before the solenoid turns on again.
    An help is greatly appreciated!
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
    What you want is an astable multivibrator activated by a switch from what I understand.

    You can use this with some modifications:
    It's from Wikipedia, section "Astable". The formulas to calculate the time delays you will also find there. Pin 4 would not be connected to Vcc in your case but to a NO switch which goes to Vcc and a pull-down resistor which goes to GND. The output can drive a MOSFET or other transistor which drives the solenoid.
    Sorry about the incomplete description. Maybe I find some time to draw this later. Unless someone else does it.

    The circuit will then turn the output on and off in regular intervals as long as the switch is pressed (closed).
    There are also other members here that may have the circuit already drawn and ready to post. (like Bill Marsden) I just can't find it right now.
  3. praondevou

    AAC Fanatic!

    Jul 9, 2011
    More or less like this:

    You need to tell us the time intervals you want and solenoid specs to configure this circuit. It also needs bypass caps which I forgot to draw.
    • sol.png
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    Last edited: Dec 27, 2011