Timer delay with relay on for 4 seconds

Discussion in 'General Electronics Chat' started by Aggie, Mar 5, 2013.

  1. Aggie

    Aggie Thread Starter New Member

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    Need help with a circuit design which can fulfill the below mentioned criteria:

    Circuit status is normal when power on, when triggered (through a magnetic contact switch by opening a door) should start a timer delay for 15 seconds, on expiry of the delay the relay should come on for 4 seconds, and then circuit should back in normal status. during the course of the 15 seconds timing delay a reset should also be available to bypass the relay on for 4 seconds.

    thanks
  2. thatoneguy

    thatoneguy AAC Fanatic!

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    Need translation to exact terms.


    • On trigger, delay of 15 seconds is started.
    • At end of 15 seconds, a high level is output for 4 seconds.
    • If trigger occurs during the 4 second high level output, the output is delayed an additional 4 seconds.

    The high output can activate a relay, turn on a light or buzzer, etc.

    Is this correct?
  3. Aggie

    Aggie Thread Starter New Member

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    Ok I need a simplest circuit to do the following, I need to monitor a vault door with the following logic.
    Step 1. Door opened (entry) - start of timer delay for 15 seconds,
    Door closed (Still inside vault) - timer still running.
    Step 2. Reset Timer with reset switch.

    Step 3. Door Open (Exit) - Start of timer delay for 15 seconds,
    Door closed - timer auto reset.
    The above step are executed under normal circumstances.

    If under duress, the reset switch is not pressed and the relay should activate on the expiry of the 15 seconds delay just for 4 seconds to trigger an alarm and reset itself to normal state. so the cycle can be repeated on.

    Hope this helps
  4. tracecom

    tracecom Well-Known Member

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    The simplest circuit would involve a microcontroller. Is that an acceptable option?
  5. ScottWang

    ScottWang Well-Known Member

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    If your description more clearly as set to hi or low when door open or close, maybe it can using CD4017 and NE555, it just maybe.
  6. Aggie

    Aggie Thread Starter New Member

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    A microcontroller or CD4017 and NE555, options are acceptable, please guide me if any circuit is available which fulfills the criteria.

    Thanks
  7. Aggie

    Aggie Thread Starter New Member

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    Normal operation condition
    Door open (Entry Trigger) starts a timer delay low state for 15 seconds, Door close (once inside), Timer is Reset with a reset switch before expiry of 15 seconds, Awaiting trigger, Door open (Exit Trigger) starts a timer delay of Low state for 15 seconds, Door closed before the 15 seconds delay expires (exit complete) Auto reset, Awaiting next Door open (Entry trigger).
    Under Duress conditions
    Door open (Entry Trigger) starts a timer delay low state for 15 seconds, Door open / close (once inside), Timer expires after 15 seconds timer delay(Timer not reset), Output goes High State (triggers Relay) Relay remains on for 4 seconds, then auto resets timer, Awaiting trigger, (Door open)

    Please help!!!
  8. ScottWang

    ScottWang Well-Known Member

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    Door open (Entry Trigger) -- Hi or Low?
    Door open (Exit Trigger -- Hi or Low?
    Door close (once inside) -- Hi or Low?

    Timer is Reset -- Hi or Low?
    (exit complete) Auto reset -- Hi or Low?
    auto resets timer -- Hi or Low?

    If you describe as below and also labeled the Hi or Low, it will more easier to understand.
    1. ....
    2. ....
    3. ....
    4. ....
    ......
    ......
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