Circuitron 5520 – SD-2 3-Position Semaphore Driver

Use with the Tortoise Switch Machine and an upper or lower quadrant semaphore-style signal. 

Includes al the logic circuitry to drive the signal to all three positions. Works with BD-1 or BD-2 Block Occupancy Detectors. A minimum of two blocks must have detectors installed for the SD-2 to indicate all three positions. 

Requires 10-18V DC power. Semaphore signal not included, circuit only.