#8000 ServoMaster provides detection and activation for Crossing Gate Signals & 3 position Semaphore Signals. For Crossing Gate Signals 4 optical sensors will allow single track bi-directional operation or dual track uni-directional operation. Expansion kits will allow up to 3 additional bi-directional tracks. The unit also controls the crossing lights for common anode LED's. An output is provided to add a bell sound module(not provided). The ServoMaster requires 9-16 volts, AC or DC rated at least 500ma.