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How to build a simple device that turns off external appliances when your computer shuts down

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This very simple circuit will turn off anything when you shutdown your computer. It works by using the power of the usb port to turn on a relay. When your computer is off the usb port has no power and the relay opens the circuits to the devices that are plugged in.


Cost Time Difficulty Age Group
20$US 30m easy 12+


  1. Cut the usb cord, keeping the computer side long.
    • i.e. cut the B-plug off
  2. Strip the +5 and ground wires
    • the 1 and 4 wire, probable black and red. See USB pinout below
  3. Solder wires to the coil of the relay.
  4. Cut one of the power cords wires and solder one end to normally open (NO) and the other end to common.

Pictorial DiagramEdit



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