I am having a problem connect 12V SPDT relay ( http://www.maplin.co.uk/p/12v-dc-10a-spdt-interface-relay-n29aw )with Arduino. I am using N4001 diode to connect both coils than I am connecting one side of the diode with 5V and the other side with the collector of P2N2222A transistor, emitter of this transistor is connected GND and base with 5V through 1K resistor. Common of relay is connected to 12 V and I am just trying to light up an simple LED (later i will use for something else). My 12V supplier is an sealed lead acid battery with 12 Volt and 1.3Ah. Only problem that I can think is that I am not using the right diode or I am not supplying 12 in breadboard. Any help would be appreciated.