At points I might do something that might be dangerous because I'm comfortable with some tools or techniques but please always use your common sense and don't try everything you see here.

In this quick Arduino tutorial I will explain how you can control a relay using the Arduino Board, one 1K and one 10K resistors, 1 BC547 transistor, one 6V or 12V relay, one 1N4007 diode and a 12V fan ...

An Arduino Pro mini handles the selection between outputs by driving a selection of relays with appropriate timing. An interesting detail here is what [Lajt] calls a ‘sacrificial relay’ in the ...