Many enthusiasts will be using their PCs as data loggers, controllers or as web servers. ln these cases it is important that the machine is kept powered up for as great a fraction of the time as possible, even if there has been a power cut or if the power button is inadvertently pressed by another member of the household. Today's operating systems offer a range of automation options and it is perfectly possible to arrange things so that the computer starts itself up automatically. Circuit diagram : Always on for PCs Circuit Diagram The 'always on'circuit shown here automatically restarts an ATX PC in the above situations. There are just two components: a Schottky diode connecting the power but-ton pin on the motherboard to the +5 V line on the power supply, and a capacitor from the power button pin to ground. The capacitor is a 68 pF tantalum type rated at 6.3 V, and the diode is a type SB 120, rated at 20 V and 1 A. The total component cost is in the sub-one-bee...