Relay for switching on a PC

We used a PC without advanced power management. With the means of a modem, which was on power all time, and the following circuit, a calling telefax was able to switch on our PC, but not the monitor and printer. To do so I had connected the ring indicator RI between modem and PC to this circuit.

Also I had connected the handshake wire DTR of the available COM3 port to this circuit. The program WinTimer, which notices that there are no inputs from the user, shut down Windows 3.1 after a quarter of an hour without user. Then autoexec.bat carried out the commands SMARTDRV /C and COPY COM3 and thus switched off the PC automatically.

Three push buttons allowed me to switch on and off the whole PC system or switch off only monitor and printer while doing a backup. The modem switch was designed for temporarily swichting off modem and telefax switch.

Only a skilled electrician is allowed to build this circuit, because it carries voltage with danger to life. Beyond this scheme he must care for shielding against touch and connect the protection ground, otherwise he will expirience ... (180,314 Byte)

relay circuit

Last update on this page: October 18th 2003