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How to add a two way switch to this circuit?

Discussion in 'Electronic Design' started by saurabh9, Jul 10, 2008.

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  1. saurabh9

    saurabh9 Guest

    Please have a look at the circuit at:
    It is from the article at

    The circuit it to turn on or off a AC bulb by a microcontroller. My
    question is, can we somehow safely add a manual override switch near
    the bulb, so that even if the microprocessor is not working, we can
    turn the switch on/off manually? If yes, how will the circuit then
    look like?
    Sorry if this is a simple question as I am just starting in
    electronics and electrical circuits.
  2. Adrian C

    Adrian C Guest

    You put a switch in parallel to the relay contacts.
    Sure. This is a simple question that involves basic technology of a
    bulb, a switch and a power source. Given that this has risen for you as
    a problem, I'd complete the rest of the exercise NOT using mains line
    voltage until you are certain that it does indeed work. Get someone
    qualified to check your electrical work.
  3. Adrian C

    Adrian C Guest

    Adrian C wrote:
    we can
    Ah sorry, didn't see that bit. What I suggested would only allow manual
    switching to the on state IF the microcontroller had it switched off.

    You need a three position switch

    Position 1 - off
    Position 2 - uProcessor Controlled
    Position 3 - on
  4. ehsjr

    ehsjr Guest

    You can use a single pole, double throw, center off
    switch, like this:

    AC ----o |

    In the off position, the AC is not connected to
    either pole of the switch.

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