Model Train Technology

Merging Tracks Signaling B

Version B adds a third detector on the shared track past the merge. It feeds both detector lines through diodes, so a track keeps its claim on the shared track until its train is well past the merge.

Merging tracks relay interlock with a detector past the merge Detectors 1 and 2 feed their controllers through normally closed relays K1 and K2, which are cross-wired so only one track can get a green. Detector 3, on the shared track past the merge, feeds both detector lines through a diode at each connection. Track 2 Track 1 Shared track Detector 2 Detector 1 Detector 3 Diode Diode B A Relay K2 (normally closed) Relay K1 (normally closed) coil coil Controller 2 Controller 1 Signal 2 Signal 1

Active detector signal Inactive wire Train

How detector 3 shares both lines

Detector 3 connects to the detector 1 and detector 2 lines through a diode at each connection, ahead of the relays. The diodes let detector 3 drive either line while stopping line 1 and line 2 from feeding into each other. Because detector 3 joins ahead of the relays, it’s locked out by the same relays as detectors 1 and 2.

A train must reach detector 3 before it leaves detector 1 or 2, or the lock drops for a moment. Diode direction depends on the detector’s output: they’re drawn for outputs that pull the line low, with the band toward detector 3. Reverse them for outputs that drive the line high.