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 ...

Of course he could modify a refrigerator and humidifier to be controlled separately, but [Mike] decided the best course of action would be to control line voltage with an Arduino. [Mike] started ...