The firmware is configured so that the six Arduino pins 8-13 are active-high relay coil driver outputs and pins 2-7 are active-low indicator inputs (reporting the physical state of the relay). (Note ...

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 ...