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question about previous circuit design by john fields

Discussion in 'Electronic Basics' started by Wayne, Apr 20, 2006.

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  1. Wayne

    Wayne Guest

    In a previous thread (which google groups will not let me post to),
    John Fields designed a circuit for me that is working great:
    http://groups.google.com/group/sci.electronics.basics/browse_frm/thread/bbb66379544dfcd2/#

    I want to add a fourth output to this circuit that will be always on,
    unless the the timer pause button is pressed, at which time that fourth
    circuit would shutoff for the same amount of time as the other 3, then
    restart like the others. What do I need to add to the circuit to
    accomplish this?
     
  2. John Fields

    John Fields Guest

     
  3. Wayne

    Wayne Guest

    Thanks, as always! I'll try this later today.
     
  4. Wayne

    Wayne Guest

    I tried this, but it's kinda working backwards to what I want. U2-13
    isn't going hight until I press S1, when I release S1, it goes low.
     
  5. Wayne

    Wayne Guest

    I meant to say, it's low until I press S1, then it goes high until the
    delay finishes, then it goes low again; it's opposite of what I want.
     
  6. John Fields

    John Fields Guest

    ---
    Yeah, I got it backwards. The switch switches Vcc, not ground,
    duh... Sorry about that.

    Connect U2-11 and U2-12 to either U2-4 or U2-8, take your output
    from U2-13, and that oughta do it. :)
     
  7. Wayne

    Wayne Guest

    That did it, but brings up another question. Prior to this change, the
    circuit almost always started in the correct state and would start
    cycling the pumps immediately. Now that I've made this change, so far,
    it always comes up as if S1 has been pressed and I have to wait for the
    ~30 minutes to lapse and then it starts up as normal. Is there a
    modification that will make it always come up correctly?

    Thanks again, this is a great little circuit
     
  8. John Fields

    John Fields Guest

    ---
    I'm surprised. It should _always_ have come up in the paused
    condition...
    ---
    ---
    Yes. I've emailed it to you and posted the circuit to abse in case
    anyone else is interested.

    Just as an aside, in order to make sure the circuit works properly
    it would be a good idea to put a 0.1µF cap across Vcc and ground at
    each of the chips, and a larger cap (say 100µF or so) across the
    supply where it connects to the board.
    ---
     
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