Reed Switch ???

Discussion in 'General Electronics Chat' started by adam_fozz, Mar 26, 2012.

  1. adam_fozz

    Thread Starter New Member

    Jan 19, 2012
    7
    0
    Hi all,

    Can somebody please take a look at this circuit (in the link below) and tell me why they dont just use a normally closed reed switch attached directly to a buzzer.

    http://freecircuitdiagrams4u.blogspot.com.es/2010/01/simple-door-alarm-circuit.html

    I notice that it is common to use normally open switches in door alarms but I dont understand as surely having a circuit break rathern than make when the door is opened is the opposite of what you need!

    Thanks in advance
    Adam
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    The current requirements for the buzzer "could" exceed a reed relays rating.

    As far as why not use normally open.. Having the relay "de-energize" upon a door open signal requires more components/complexity.

    For "more critical" circuits I "de-energize" the relay upon door open signal (or whatever) so that if your relay ever decides to go out on you it will act like a door open signal and makes it easier to troubleshoot. Its more of a "fail safe" solution but does require more components.
     
  3. adam_fozz

    Thread Starter New Member

    Jan 19, 2012
    7
    0
    Ok thanks. What I'm trying to do now then is use a simple battery door alarm as a switch to stop a motor when the magnet comes to the Rees switch. Is there a way to do this.

    The device has a reed switch a capacitor and a sound chip. The speaker is attached to the capacitor. Any idea where I can plug in my motor circuit to make this work???

    Thanks
    Adam
     
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