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 a transformerless resistive PSU, 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 by a moderator: May 15, 2013
  2. bertus


    Apr 5, 2008

    I am closing this thread as it violates AAC policy and/or safety issues.

    6. Restricted topics.

    The following topics are regularly raised however are considered “off-topic” at all times and will results in Your thread being closed without question:

    • Any kind of over-unity devices and systems
    • Automotive modifications
    • Devices designed to electrocute or shock another person
    • LEDs to mains
    • Phone jammers
    • Rail guns and high-energy projectile devices
    • Transformer-less power supplies
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