Circuitron 800-5520 SD-2 3-Position Semaphore Driver for Tortoise Switch Machine

Use with the Tortoise Switch Machine and an upper or lower quadrant semaphore-style signal. Includes all 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 SD02 to indicate all three positions. All scales
Requires 10-18V DC power