The SIGM20 is able to detect that a train has passed a signal set at red. It does this because a track sensor belonging to the track just beyond the signal mast can be programmed. The SIGM20 can't intervene on LocoNet to have the throttle speed demand reduced to zero: but it can controla relay to remove the power to the track immediately beyond.
(That isn't as blunt an instrument as it sounds. If the relay is activiated, it can switch +12v DC to the track after the signal. If the train decoders are programmed for "brake on DC" then the train will come to a smooth stop.)
To use this function, a DTX8B add-on board will be needed. The outputs of that board, instead of driving additional signal masts, will control one relay for each of the 8 signals driven by the board. The board can't directly drive the relay coil: an additional driver will be needed. We supply the RLY2: a dual pole relay with transistor driver assembled onto a circuit board.
We provide the circuit diagram for the DTX8B and RLY2 in the "documentation" section: competent electronics hobbyists may want to assemble their own drivers for this.
