Controlling simple relay switch via USB

Question

I\'m looking to control a mains powered light from a simple relay switch connected via USB to the computer.

The relay switch isn\'t even a USB device, it\'s just a s

Answer 1

Most of the USB to Serial or USB to RS232 $10 converters support hardware handshaking. Use one of those as a single channel digital io.

Connect your transistor that will drive the relay to DTR on the converter board and command DTR ON/OFF with the converters driver.

A 2N7002 is a good transistor to use (FET actually) since it will work from 3V and doesnt need any resistors anywhere.