12 vdc timer circuit

Discussion in 'Homework Help' started by aurorathor, Feb 18, 2010.

  1. aurorathor

    Thread Starter New Member

    Feb 18, 2010
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    I need a simple 12VDC circuit to extend the time of a normaly open circuit by about 2 sec. My wife's office has an electronic door strike to open the employee door tied to a keypad. The keypad is basicaly a normaly open relay. My problem is that the keypad doesn't give enough time to open the door. 2 seconds or so should be plenty of time.
     
  2. retched

    AAC Fanatic!

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    There should be a potentiometer to adjust the length of time for the door open cycle.

    Is it a magnetic type or a "buzzer" type?
     
  3. aurorathor

    Thread Starter New Member

    Feb 18, 2010
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    i guess you would call it a "buzzer", the door strike opens to let the latch pass by. there is no timer on the latch or keypad.

    the first pic is the strike open (with power applied)

    the second is closed (no power)
     
    Last edited: Feb 20, 2010
  4. retched

    AAC Fanatic!

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    The thing is, you will need to use the existing wiring to trip a circuit that will allow the solenoid to stay energized longer. You should look on the circuit board to see if there are any POTs that adjust how long the solenoid is energized. It wouldn't be on the catch.

    This is the type?:
    [​IMG]
     
    Last edited: Feb 20, 2010
  5. aurorathor

    Thread Starter New Member

    Feb 18, 2010
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    that is the type, i didn't see any pot on the latch it is simply a solenoid. using the existing wiring is no prob, i am the one who put it in in the first place
     
  6. retched

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    On the keypad.. The keypad usually has a few dip switches or jumpers to select between times.

    Some newer keypads allow programming. You press a few buttons or hold two at the same time then you can choose (usually between 4 times) the length.
     
  7. aurorathor

    Thread Starter New Member

    Feb 18, 2010
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    the problem is that this keypad is designed for an auto gate opener that only needs a pulse, I made it work with the strike. the only dips i see are for wireless transmitter fq
     
  8. retched

    AAC Fanatic!

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    ahh. you can pulse a 555 to start a timer that will allow the relay to stay closed for x seconds
     
  9. aurorathor

    Thread Starter New Member

    Feb 18, 2010
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    i just need a scat to build - i haven't tried to design a circuit in many years and am VERY rusty
     
  10. retched

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  11. aurorathor

    Thread Starter New Member

    Feb 18, 2010
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    i'll try that tyvm
     
  12. retched

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    Cmos 555 will give you 200ma to use on the relay coil.

    Your very welcome. If you want to change the timing, you can change the cap and resistors. But if six sec is good, then your set.
     
  13. aurorathor

    Thread Starter New Member

    Feb 18, 2010
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    that should be plenty, again thanks alot
     
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