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Activate a relay using laptop's parallel port

Discussion in 'General Electronics Discussion' started by hrgwea, Apr 13, 2011.

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  1. hrgwea


    Apr 13, 2011
    Hi, guys. I'm new here. Forgiveme if this is too newbie.

    I have a relay that I want to switch on using one of the output pins on the parallel port.

    This is what I've got:

    The relay is powered by a 5V DC adapter and the transistor should act as a switch.
    But i dont know where to connect the parallel port's ground pin.

    If I just connect the 5V pin to the transistor's base (like the diagram shows), it doesn't work.
  2. Resqueline


    Jul 31, 2009
    Ground to emitter/-5V. Add base resistor (value depends on port, transistor, & relay data).

    Attached Files:

  3. hrgwea


    Apr 13, 2011
    It works. Thanks.
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