need a circuit that'd be basic to many but magic to me

Discussion in 'The Projects Forum' started by dogfuel, Dec 21, 2009.

  1. dogfuel

    Thread Starter Member

    Apr 13, 2009
    10
    0
    Hi -

    I have an instantaneous switch that completes a circuit ... for the solution (gps-based) to work, the circuit needs to be closed for 2 seconds or as long as the switch is closed.

    My problem is obviously when the operator closes the switch for less than two seconds ... would someone describe how to delay the opening of the circuitfor 2-3 seconds (exact time is not critcal)? It is ok if the same delay comes after the switch is opened, regardless of how long the switch is closed.

    Thanks!
     
  2. Art

    Distinguished Member

    Sep 10, 2007
    785
    61
    a transistor and capacitor to hold the transistor closed.
     
  3. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    In the following circuit, the relay will activate immediately upon closing of switch and only release about 2 seconds after switch is opened. Relay will be keep energised as long as switch is closed.

    [​IMG]
     
  4. dogfuel

    Thread Starter Member

    Apr 13, 2009
    10
    0
    Thank you!
     
  5. Dan-O

    Active Member

    Jul 26, 2009
    38
    0
    Which components could be changed to alter the time delay?
    I have a similar need.
     
  6. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    The circuit timing is determined by the resistor from pin7 to +V (47K shown above) and the 47uF capacitor.

    Increase the value of either or both will increase the delay timing. Avoid resistor value higher than 1MΩ and capacitor value larger than 470uF.
     
  7. Dan-O

    Active Member

    Jul 26, 2009
    38
    0
    Is there a way to calculate the delay?
    Edit: I think I found the calculator----> Here?
     
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