Exclusive optical sensors in the base of each signal detect an adjacent train.
Just set them down and connect 2 wires to power for a working signal.
When the train passes the signal, the indication will change to RED or stop and hold until the train has passed. 4 seconds after the train passes, the signal will change to YELLOW or caution.
After 4 more seconds, it will change back to GREEN or clear.
The signal only needs (9-18V AC or DC) power to operate, but it does have an input (YELLOW) and an output (WHITE) for additional possibilities.
The new "V" version signals have variable delay (1-60 sec.) which can be set by the user.
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