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USB-Sensing Mains Power Switch

Do you have to manually switch your PC's peripherals on (and later off again) each time you boot your PC? If so, this project will make life a lot easier. It monitors your PC's USB port and automatically turns all that other gear on and off as required.

By JIM ROWE & MAURO GRASSI

Many early PCs had an IEC-type 240V outlet socket on the back of the box that was switched by the PC’s own on/off switch. This allowed you to automatically switch power to the computer’s monitor, printer and other peripherals when the PC itself was switched on or off.

Click for larger image
Fig.1: how the unit is used. All peripherals plus the monitor are plugged into the power distribution board. Note that a USB keyboard or mouse must be connected to the USB Switch if you are using a desktop PC.

All you had to do was plug a power distribution board into this outlet and then plug the peripherals into this board. The power switch on the front of the PC then controlled everything – all very neat and convenient.

Unfortunately, this handy switched power outlet disappeared when the PC manufacturers changed over to software-controlled power supplies. So with most newer PCs, you’re now forced to use a power distribution board with its own master power switch, if you want to control all your peripherals with a single switch.

Of course, that means you have to remember to manually switch on the peripherals when you switch on your PC and vice versa. And that can be a real nuisance. If you forget to turn the peripherals on, the computer won’t recognise the monitor or any USB peripherals when it boots and may have to be restarted.

Apart from that, having to manually switch everything on and off at the wall socket can be a real nuisance. Not only that, it can also be impractical if the wall socket is inaccessible because it’s hidden behind a desk or some other piece of furniture.

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