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 ...

The project illustrates the control of a PC fan speed and using an Arduino microcontroller to read a LM35 temperature sensor. The use of an optocoupler is covered along with Pulse Width Modulation ...