USB External Component Shutoff Circuit


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This may not work on modern computers because they have USB power always on
This very simple circuit that will turn off anything when you shutdown your computer. It works by used the power of the usb port to turn on a relay. when you computer is off the usb port has no power and the relay open circuits the devices that are pluged in.

Get this relay if you are going to use less than one amp.
1-Amp SPDT Micro Relay-5VDC Model: 275-240 at Radio Shack
others wise get 255-1103-ND from digikey.com
It can handle 10 amps but requires shipping

Get a usb cord and cut it keeping the computer side long. Strip the +5 and ground wires i.e. 1 and 4,probable black and red. Click here for USB pinout
Attach them to the coil of the relay.
Then cut one of the power wire and solder one end to normally open (NO) and the other end to common.

see the pic

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