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    Here are 2 simple, low cost circuits which can be used to shut off the mains switch to any audio or video equipment (such as Computer,  CD-DVD player, and amplifier). These Computer,  CD-DVD player, and amplifiepowerare very helpful to those in the habit of falling asleep with their computer , TV or music system on.
    The circuits will also protect the equipment from getting damaged due to high voltage spikes whenever there is a re-sumption of power after a break. This is possible because the equipment will getswitched off automatically under such conditions but will not get switched on automatically on resumption of mains supply.

Full Circuit [Download]

Source: http://www.electronicsforu.com