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How to control 12vdc relay with microcontroller!

Discussion in 'Microcontrollers, Programming and IoT' started by lockoutseniorproject, Mar 19, 2012.

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  1. lockoutseniorproject


    Mar 19, 2012
    Microcontroller - arduino uno

    Relay - simple 12vdc spdt relay

    I was wondering if the microcontroller outputs enough voltage to control this relay, and how i would go about making these components work together - thank you!
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    No, you will need to use the arduino's output to drive a transistor and use that to switch the relay current. You will also need a diode across the relay contacts to protect the transistor.

    This lays it out really well.
  3. lockoutseniorproject


    Mar 19, 2012
    where would we attach the external power supply in your diagram? also would a 3906 transistor suffice.
  4. GreenGiant


    Feb 9, 2012
    The external power would connect to Relay Power V+

    That transistor would work, but be cautious it is only rated for up to 300mA so without a current limiting resistor you run the risk of burning it out
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