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Switching AC w/ Logic Level

Discussion in 'Electronic Basics' started by [email protected], Jun 1, 2007.

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  1. Guest

    I've found a few threads but nothing with exactly looking for what I'm
    looking for.

    I need to switch 24VAC (HVAC control) and 120VAC (2A and 10A) with a
    PIC. What is the best way to do this? Opto-Isolated TRIAC, SSR?

    Your suggestions on your favorite parts for the job would be greatly


  2. Jamie

    Jamie Guest

    just drive a low voltage coil relay via a NPN transistor in open
    collector state through the coil. Emitter to common and base to
    an output via a resistor to force the tranny into saturation.
    put a FlyBack diode on the coil other wise, you'll take out
    your tranny and maybe the pic in a short time.
    also., make sure you mount the relays away from the pic. We had
    cases where the EMF of the coil actually caused problems with the
    program in the PIC which forced a reload of the code.
  3. I like opto isolated solid state relays for my home
    projects, for their ruggedness and simplicity of a direct
    logic drive. But for production designs, they are high cost.
  4. I agree. When your are coming to do your own circuit, then you cannot
    beat an isolating transformer and a SCR/Triac for cost saving. You
    would have to cide into your pic to drive them with a few kilhertz
    square wave though.

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