switch help

Discussion in 'The Projects Forum' started by benha, Jan 4, 2011.

  1. benha

    Thread Starter Active Member

    Jan 4, 2011
    35
    1
    Hi,

    I've been poking around looking for a switch that meets my needs and I can't find anything. I'm hoping that's just for lack of the right terminology and that y'all can point me in the right direction.

    I have an alarm circuit on my boat with a klaxon above my bunk to warn me if <insert bad thing detected by radar/gps here> happens.

    I'd like to insert a switch into that circuit so I can push a button to kill the klaxon so I don't go deaf while I'm getting my pants on and running to the bridge.

    Ideally, this is a simple pushbutton that breaks the circuit to the alarm and stays depressed until the power to the klaxon is disconnected, at which point the button returns to its normal (closed) position.

    I'm envisioning a pushbutton held depressed by an electromagnet that de-energizes and releases the button once the alarm is remedied.

    Does such a thing exist? If it matters, this is a 12V system and the alarm draws about 50mA.

    -Ben
     
  2. k7elp60

    Senior Member

    Nov 4, 2008
    478
    69
    You could use a push off, push on switch. That is you push the switch to turn the klaxton off, and when the alarm problem has been resolved then you push the botton again and the power to the klaxton is restored.
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    This would leave the possibility of leaving the Klaxon in the "Off" mode inadvertently.

    If you cannot get to the internals of the alarm, something like an SCR driving a relay inline with the wire to the klaxon would work, if the power to the siren was +12V. The momentary Normally open button would pull the gate high, opening the relay, when the +12V goes away, the SCR resets and the relay closes again.

    Just an idea until more info on what is available for inputs and outputs.
     
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,576
    231
    An auto-reset, SCR, alarm bypass without a relay. The "+12V" is the alarm-switched feed to the Klaxon. Not knowing what the Klaxon draws for current, the spec'd SCR may or may nor be appropriate.
    Nit-picky stuff: The alarm silences "after" the button is pressed and released. If you want it to silence "when" the button is pressed, put a N/C pushbutton between the SCR's anode and the Klaxon.

    Ken
     
  5. benha

    Thread Starter Active Member

    Jan 4, 2011
    35
    1
    This is great. Thanks!
    Specs on the Klaxon (actually a piezo warbler) are 12v with a max current of 50mA. Will that work with the spec'd components?

    And another "dumb" question. Looking around online for MCR100-6 SCRs, there appear to be lots of options: MCR100-6RL, MCR100-6RLRA, MCR100-6RLRM, MCR100-6ZL1, MCR100-6G, MCR100-6RLG, MCR100-6RLRAG, MCR100-6RLRMG, etc...

    Uh... I can't make sense of these things, and I haven't found a cheat sheet to help. What's the difference?


    -Ben
     
    Last edited: Jan 5, 2011
  6. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,576
    231
Loading...