Connecting a 12V Relay to Arduino

To connect a 12V relay to the Arduino you need the following things:- 1 Arduino- 1 diode for example 1N4007- 1 NPN transistor for example 2N2222 (in the US) or BC548 (in Europe)- 1 relay for example one with coil voltage 12V and switching voltage 125VAC/10 A- 1 multimeter Step 1: Measure the Coil Resistance We are going to measure the coil resistance to calculate the current.First we must find the coil:On some relays the pins are labeled so you can just measure at pin 2 & 5.Otherwise you have to measure at every pin:Between two pins you should have...