I need to close a circuit (connect common to open) in order to trigger a gate to open. I'd like to do this using a Spark Core. Do I just use a simple relay to close the circuit....triggering the relay with a pin off the spark?
Look on the Arduino websites. This is well documented. Search "arduino driving a MOSFET". Yes, you will need a Mosfet transistor as your switch that is turned on/off by your Spark Core/arduino/raspberry pi/micro-of-the-day-on-a-board.