auto reset timer

Discussion in 'The Projects Forum' started by JeffS, May 15, 2013.

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  1. JeffS

    Thread Starter New Member

    Jan 9, 2013
    Hi All

    I need some help with certain aspects of my simple project, I have successfully achieved my goal using a micro however, this particular circuit needs to work on minimal component count and more importantly cost. So has to be done with ideally 1 7555/555 timer and as few as possible supporting components.

    Project Description: Door Sensor/Timer/Alarm
    The aim is to monitor status of a door [open | closed]

    On door open:

    - switches 220vac to strip lighting
    - starts adjustable timer 1 - 20 minutes

    IF on timer expiry
    - - door open - 12 vdc piezo sounds till door closed
    - - door closed - reset timer, await door open

    On door close:
    - 220vac to strip lighting off
    - turn off piezo [if active]

    Door sensor | circuit Input
    NO reed switch

    I have used both 555 | 7555 to create adjustable timer circuit no problem, however I have a few problems I cant work out how to accomplish.

    1. The output goes high on timer start and low on timer end, cant work out how to apply this to a relay | transistor to only switch piezo on AFTER timer end.?
    2. How to trigger the timer to start, and then reset timer if door closes before timer end, using only one input (door reed)?
    3. How to trigger timer as well as switch vac to lights using only one input (door reed)?


    The schematic is VERY incomplete please read it as so.
    Any pointers or ideas, schematics etc would very much be appreciated.

    Last edited: May 15, 2013
  2. edwardholmes91

    Active Member

    Feb 25, 2013
    Why re-post something that was posted on a thread that has already been locked? Is there something that you didn't understand about Bertus' reply?
    Last edited: May 15, 2013
  3. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
  4. Georacer


    Nov 25, 2009
    Do not re-post closed threads. Third time is not the charm.
  5. Wendy


    Mar 24, 2008
    For me it is, I don't like to ban people, but I will do it.
  6. bertus


    Apr 5, 2008

    I closed the other thread as there was a mains powered powersupply in the schematic.
    I removed the drawing that contained the circuit, to avoid other people to get hurt or even killed.

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