Best Answer hanzibal, 09 May 2013 - 10:14 AM
Hi! For this, you need an npn transistor like a bc547 and an external 12V power supply. No soldering required if you got a breadboard and you don't need a noisy relay since there's no current to speak of. Assuming there's a current limiting resistor inside the LED holder (which there ought to be), connect as follows: Positive pole of your dome to +12V from the power supply 0V (ground) of the power supply to common ground Negative pole of the dome to the collector of the transistor Transistor emitter to common ground Base of the transistor to a digital output of your Netduino via a 2-10k resistor As for the switch, connect com to ground and the normally open pole to a digital input of your Netduino with pullup enabled. Go to the full post