"andrew" wrote in message
...
PCPaul wrote:

Sounds like a 5V/12V relay plugged into a parallel port line (or even a
serial port handshake line) which then switches a 24V supply to drive the
main relay would be simpler - that way you don't need to drive USB
directly.

I was hoping to use a low power PC which has no serial output but I could
use a usb to serial converter.

You could use X10.