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Odd circuit question

Discussion in 'Electronic Basics' started by Richie, Jul 16, 2003.

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  1. Richie

    Richie Guest

    I need a switching circuit that requires me to hold down a momentary
    switch for a few seconds before it turns on and turns off when i let
    go of the switch. I've been playing with a npn transistor, a
    capacitor and some resistors but haven't had any luck. Does anyone
    know what this type of circuit is called so a can research it or give
    me some pointers to build something like this. Any help would be
    appreciated.
    Thanks
    Rich
     
  2. How much power can the circuit consume when it isn't in use?
    What voltage supplies do you have available? How many
    transistors is okay to use? What voltage for the output when
    the switch is not pressed and what voltage when it is pressed?
    Can you use normally closed momentaries or only the normally
    open variety? Is it okay to use a ramped voltage at the output
    during the "few seconds" delay? Or must it be held fairly solid
    until the delay is over?

    I doubt this is what you are looking for, from the above, but
    you might play with this so that you can say what it doesn't do
    that you want:

    +V
    |
    +V |
    | \ R1
    | / 82k
    R2 \ \
    330k / |
    \ ,--------+
    | c +-------> OUT
    | |/ Q1 |
    +---| NPN | +
    | |\ ----- C1
    | e -----
    o | | 10uF
    \ | |
    S1 \ gnd gnd
    o
    |
    |
    gnd

    The output voltage will rise along an exponential ramp when the
    switch is closed. Otherwise, the output will be grounded.

    Anyway, best of luck.

    Jon
     
  3. Dave

    Dave Guest

    I think you are looking for a delay circuit. You can buy solid state time
    delay circuits at a good supply house. Some have a fixed delay, others
    are variable by adding a few components.

     
  4. ~^Johnny^~

    ~^Johnny^~ Guest

    Use this one:
    One chip (555), one transistor, two resistors, two caps, a diode
    and a N.O.mom pb. :)

    http://gyrogearloose.com/images/delay-on.png

    It's basically a modified missing pulse detector.
    Just adjust R1 - C1 for the desired turn-on delay.


    -keep it simple; use junkbox parts
    --
    -john


    ~~~~~~~~
    "The first step in intelligent tinkering is to
    save all the parts." - Aldo Leopold
    ~~~~~~~~
     
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