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How do I use a push to break switch to turn something on?

Discussion in 'General Electronics Discussion' started by tickers, Jul 5, 2011.

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  1. tickers


    Jul 5, 2011
    I have a component with about 10mm of travel, and I need to activate a lamp as soon as the component travels at all.

    The only suitable switch I could find was a push to break plunger switch, how can I use the PTB switch to get a voltage across the lamp?
  2. daddles


    Jun 10, 2011
    Such tasks can sometimes be done with a roller microswitch. Here's an example. The switch/roller assembly is positioned mechanically so that the switch activates where you want. Such switches are also available without the roller and that form may be usable for your application instead. These switches are typically SPDT, meaning they have both NO (normally-open) and NC (normally-closed) contacts.

    (FYI, the term "Microswitch" is a tradename, but it has entered the general lexicon like Kleenex or Variac.)
  3. tickers


    Jul 5, 2011
    Would the microswitch not be damaged by overtravel though? I want the switch to activate after even a small amount of motion, but be able to handle 10mm of further travel.

    I already have a push to break plunger switch, which brakes with the smallest amount of motion.
  4. duke37


    Jan 9, 2011
    If the lamp is low voltage, you can drive this with a transistor. The base of the transistor should be connected to the positive supply through a resistor and your switch should be connected between base and ground, thus, when the switch is opened, base current flows and the transitor turns on.
  5. TBennettcc


    Dec 4, 2010
    Genius! Brilliant! I love it!
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