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Open door buzzer circuit help

Discussion in 'General Electronics Discussion' started by FredElias, Oct 21, 2016.

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  1. FredElias


    Oct 21, 2016
    I want to build a ringing small "door open" notification device.

    - battery powered (9V ideally)
    - magnetic door sensor such as this:
    ----> this is a not a security application so normally open works for me.

    - a FAT bright red LED, L

    - a buzzer B

    - a 2 position switch:
    position 1: buzzer screams if door open, LED off
    position 2: LED on, no buzzing

    - volume adjustment through R2
    - a main on/off switch turning device completely off

    Can somebody help be build the circuit for this? I drew what I think the circuit should look like but can somebody help with component selection: L, R1 and R2 and B

    I'm going source parts from electronics supply store 5 mins away from my home.


    Attached Files:

  2. HellasTechn


    Apr 14, 2013
  3. Kiwi


    Jan 28, 2013
    My understanding of magnetic reed switches is that the Normally Open(NO) and Normally Closed(NC) refers to the contacts when a magnet is NOT present.
    I assume that the magnet and switch will be together when the door is closed and will separate as the door is opened?
    I believe that you need a NC switch that will be closed with the door open, sounding the buzzer, and will open as the door closes, turning the buzzer off.

    Instead of using two switches I would use a single on-off-on switch to give LED-off-Buzzer.
  4. FredElias


    Oct 21, 2016
    Hey guys!

    Thanks for the replies. I actually finished the project today using the LED-off-buzzer switch and a NO switch - circuit closes when the contacts are not facing each other.

    I'm using this to remind myself to close the garage door (my workshop!) as it is full of dust and quite cooler than the rest of the house.... not closing the door properly drives my wife mad!!! :)

    The device works great.... however having the buzzer go off AUTOMATICALLY when I open the door is really annoying!!

    I would like to add a time delay on the switch. Timer would close the circuit maybe 5 seconds after contact is closed.

    Any idea as to how to achieve this? Ideally I would only have to add a component somewhere on the line (I wish!) - else I am open to redoing it.

  5. KTW


    Feb 22, 2015
    Have you considered a door closer?
  6. FredElias


    Oct 21, 2016
    Yes! And even tried one. But it being the garage door there is a windbreaker seal around the door frame thus a "lot" of force is required to close the door.... too much force for spring-loaded door closer.
  7. FredElias


    Oct 21, 2016
    Allright friends, I read a lot on timer circuits and I need help selecting values again. It seems obvious I need to use a 555 chip.

    Circuit specs:
    - Power is 9V battery
    - When the door switch is CLOSED, LED turns on and timer starts counting.
    - Once time delay is expired, LED turns off and buzzer starts screaming!
    - Timer can be adjusted using variable resistor from instant or few seconds, to 1-few minutes (upper limit less important than lower limit)

    Any advice as to how to build this? Which IC555 model should I use? Resistor / capacitor values and configuration?

    Any help greatly appreciated, thanks!
  8. eetech00


    Nov 17, 2014
    I think this will do what you want.

    Attached Files:

  9. KTW


    Feb 22, 2015
    You can buy a cheap delay timer off ebay ready to go.
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