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Help with relays

  1. Jun 6, 2010 #1
    Hi everyone! So I'm working on a little home project and could use some advice. I'm making a little thing where I have a microcontroller that sets a pin high at certain intervals. When that pin goes hi, I would like it to turn on the plugged-in lighting unit, and when the pin goes low, I would like it to turn off the plugged-in lighting unit. The plugged-in lighting unit will just be a regular desk lamp made to connect to a 120V regular AC outlet.

    So my question I guess is: how do I do the switching for the lamp? A relay? Are there relays that can use like a 3.3V hi pin from a microcontroller to turn on and off, and are still robust enough to pass 120VAC from a wall outlet? If not, is 12V more reasonable/are there relays that can handle that (I'm thinking maybe outdoor 12V lighting instead)?

    In case your wondering, I'm making stage lighting stuff for my band. Thanks!
  2. jcsd
  3. Jun 6, 2010 #2
    You could use a solid state relay which typically have on of like 5 volts which are capable to output a voltage as high as like 400V
  4. Jun 6, 2010 #3
    You could make a relay driver like this:

    [PLAIN]http://interactive.usc.edu/members/phoberman/relayCircuit.gif [Broken]
    Last edited by a moderator: May 4, 2017
  5. Jun 6, 2010 #4
    Thanks so much for your responses.

    Last edited by a moderator: May 4, 2017
  6. Jun 7, 2010 #5


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    Unless you need a full disconnect, it's usually sufficient to break the hot line. Breaking neutral means that a nicked power cord might expose someone to 120V relative to ground, whereas breaking the ground conductor may not turn off the unit, but will break the case ground (if present) and remove the protection that affords (in case a wire or something breaks loose inside the case and electrifies the whole case!)

    EDIT: To add to waht's point, you can usually find relays with 12V coils (make sure that they're capable of switching the types of current you expect, and that they're rated for 120V AC!) The ratings will usually be printed right on the relay. The coil will switch on at some voltage less than 12V--if you only have 9V as your main power source, that may or may not be enough, and you'll have to do some experimentation.
  7. Jun 7, 2010 #6
    Thanks for your input -- So would something like this work: http://www.sparkfun.com/datasheets/Components/T9A_DS.pdf

    Just to switch the hot (black) wire on and off, and I'll keep neutral and ground connected? It seems like it has a 5v - 110v coil, too, so I should be able to switch it with my main 9v source, correct?
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