This circuit is designed to help minimise the quiescent power consumption of PCs and notebooks, using just our old friend the 555 timer and a relay as the main components. The circuit itself dissipates around 0.5 W in operation (that is, when the connected PC is on); when switched off (with the relay not energised) the total power draw is precisely zero. A prerequisite for the circuit is a PC or notebook with a USB or PS/2 keyboard socket that is powered only when the PC is on.
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