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Identify required component!

Discussion in 'General Electronics Discussion' started by omarsmith, Jun 8, 2012.

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  1. omarsmith


    Jun 8, 2012
    Hey there, I've popped in here to ask a very brief (and hopefully simple) question about a component I need for a simple circuit I'm building.

    I'm in need of some type of switch, but I'm having a bit of a hard time explaining what it is I want! Let me attempt to explain its desired operation:
    • Momentary switch
    • Does not become 'electrically closed' as it is depressed as a usual momentary switch would, but once it is released (or "opened")
    • Only remains electrically closed briefly once it is released.

    I need it to trigger an IC by shorting two contacts (across which this 'switch' will be placed, of course), perhaps a little similar to the rig you could see in this video (watch 8:10 to8:32). I realise that in the demo video the switch is a simple momentary microswitch where the electronics handle when they operate - but perhaps the desired effect could be produced using one or more relays, but I'm lost as to what configuration I'd need! Many thanks to anyone who responds.
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    one option is to have a SPDT switch that, when pressed, shorts a small capacitor. When released the capacitor is connected across the pins of the IC.
  3. GreenGiant


    Feb 9, 2012
    sounds like you are describing an NC SPDT relay, triggered by as little as 3V (IC's usually output 5V) and will be normally closed until triggered which causes it to open when there is voltage across the coil
  4. omarsmith


    Jun 8, 2012
    Still looking...

    Hey GreenGiant, unfortunately that's confused me a little, can you explain it again?

    I've also heard a hint that I could use something called a falling-edge D-type flip flop, effectively an IC which acts as a switch, changing state when a signal current changes from high to low level. Sadly they are most commonly found designed the other way round (for example IC number 4013)

    If possible I would prefer to build this circuit with the aid of relays, unless it proves reasonably simple to do it with an electronic solution like this - all those pins confuse me, too! :D
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