Need help with a circuit to close two electronic switches.

Discussion in 'The Projects Forum' started by phr0ze, Jan 23, 2009.

  1. phr0ze

    Thread Starter New Member

    Jan 23, 2009
    2
    0
    Ok. I am going to have lots of terms wrong. So bear with me.

    I have a momentary switch (S1). I want this momentary switch to control two other momentary switches (S2, S3) in a seperate device. Basically, I want to replace S2 and S3 with something controlled by this circuit.

    I prefer to keep S2 and S3 isolated from this circuit, so I'm thinking relays.

    Here is the description of how it needs to work.

    When S1 is pushed S2 needs to close for a preset amount of time (say 30 seconds).
    When S1 is pushed and S2 is closed, S2 timer needs to restart and S3 needs to close for a short duration (fraction of a second).

    S2 and S3 share the same common so they do not need to be isolated from each other.

    I have been searching for hours and I'm getting lost with all the Latching, debouncing, one-shot stuff. I'm at this point not even sure what to search for.

    Any help at all, even if you could just tell me what to look for.


    Thanks,
    John
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    How much current is flowing through the switches ?
    Perhaps you can use some optocouplers to replace the switches.

    Greetings,
    Bertus
     
  3. phr0ze

    Thread Starter New Member

    Jan 23, 2009
    2
    0
    I'll have to test the current but that looks like a great way to isolate the circuits.

    Thanks!
     
  4. GirishC

    Active Member

    Jan 23, 2009
    58
    0
    One way is you can use 555 in astable mode for the delay. You need to place a transistor across timing capacitor. The momentarily trigger pulse (active low) will turn off the transistor. Thus disabling the capacitor being charged. When transistor turns off capacitor charges through resistor giving required timing.

    Let me know whether this suits your need.

    GirishC
     
  5. GeneratorPanels.com

    New Member

    Dec 5, 2008
    6
    0
    A SCR (Thyristor) can be used as an on/off latching circuit. It is only when current is applied to the gate that the SCR switches ON and anode current flows. Once this anode current flows then the gate current can be removed and the anode current will continue to flow. To switch the SCR off the anode current must be reduced to zero.

    I think your project can be built with the SCR, 556 timer, cap and resistor (or potentiometer if you want to set a variable range to the 30 seconds... 0-60 seconds, etc).

    www.generatorpanels.com
     
  6. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    A SCR will work with AC only.
    When used with DC it will stay latched.

    Greetings,
    Bertus
     
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