Here’s a relatively easy project that can save you some money, energy, and in this builder’s case, unnecessary trips to the basement. It’s a power outlet controlled by the serial port of a PC. The builder made it so that, whenever he printed anything out, the printer would turn on and stay on for 30 minutes, shutting down if no new jobs came through. This serial-controlled switch was especially useful in that the printer in question is in his basement not near his desk and prior to the switch, he’d have to go down there and turn the printer on before printing a job. This fix nicely automates the process.
He created a Perl background daemon to run on his Linux server which houses the serial port he used. He used a solid state and a mechanical relay to do the power switching.