Diamond crossing with gate controller & relay lockout

Pat Logan’s layout. The first train to reach the crossing holds it. The other track’s crossing section stays dead until the first train clears both of its sensors.

Sensors

A B C D
A/B are on Track 1 and C/D are on Track 2. A sensor lights while a train is over it. Grey means its signal is locked out while the other track holds the crossing.

Gate controller

Gates UP
Both tracks clear

Relay 1 → Track 1 section

POWER ON
Released. Track 1 crossing section is live.

Relay 2 → Track 2 section

POWER ON
Released. Track 2 crossing section is live.

How it works

  1. Detection. When a train reaches the first sensor on its track (A or C), the Gate Controller lowers Gate 1 and Gate 2. The gates stay down until that train has cleared the far sensor (B or D). They only go back up once both sensors on every track are clear.
  2. Power cut. The occupancy signal that drives the gates also drives one of our single relays. It kills track power on the other track’s crossing section (the shaded block at the diamond).
  3. Lockout. When the second train reaches its own sensor, it cannot take the crossing or cut power to the first train. Its signal is locked out while the first train holds the crossing.
  4. Hand-off. When the first train clears its far sensor, its relay drops out and the waiting train’s section comes back on. If the second train is still sitting on its sensor, the crossing passes to it, so the gates stay down for it.

Relay 1 cuts Track 1’s crossing section and picks up when Track 2 holds the crossing. Relay 2 cuts Track 2’s section and picks up when Track 1 holds it. The two relays are cross-locked, so only one can be energized at a time.

Event log

    TRACK POWER BUS (DCC or DC) — one rail Track 1 crossing section (gapped rail) Track 2 crossing section (gapped rail) Precision Detector Sensor A red · black · yellow +12V GND Precision Detector Sensor B red · black · yellow +12V GND Precision Detector Sensor C red · black · yellow +12V GND Precision Detector Sensor D red · black · yellow +12V GND TRACK 1 DETECTORS TRACK 2 DETECTORS +12VDC GND DETECT OMRON DPDT RELAY 1 cuts Track 1 when Track 2 holds NC COM NO NC COM NO POLE 1 POLE 2 +12VDC GND DETECT OMRON DPDT RELAY 2 cuts Track 2 when Track 1 holds NC COM NO NC COM NO POLE 1 POLE 2 +12V GND +12V GND TRACK 1 DETECT (A or B) TRACK 2 DETECT (C or D) NO: not used NO: not used SIGNAL CONTROLLER Behavior 8 or 9 (alternate flash) +12V GND DETECT +12V GND D1 D2 OUT 1 OUT 2 COM Crossing flashers Gate 1 & Gate 2 flash while either track detects a train
    Track 1 detector signal (yellow wires from A and B) Track 2 detector signal (yellow wires from C and D) Signal after passing through the other relay’s lockout contact Track power ● = joined. A wire that hops over another is not connected.

    Wire list: every screw terminal

    #FromTo
    Track 1 detection
    1Sensor A yellow + Sensor B yellow (joined)Relay 1, Pole 2 COM
    2Relay 1, Pole 2 NCRelay 2, DETECT
    Track 2 detection
    3Sensor C yellow + Sensor D yellow (joined)Relay 2, Pole 2 COM
    4Relay 2, Pole 2 NCRelay 1, DETECT
    Track power
    5Track power busRelay 1, Pole 1 COM
    6Relay 1, Pole 1 NCTrack 1 crossing section (gapped rail)
    7Track power busRelay 2, Pole 1 COM
    8Relay 2, Pole 1 NCTrack 2 crossing section (gapped rail)
    Gates / flashers
    9D1 banded end → Track 1 detect lineD1 other end → Signal Controller DETECT
    10D2 banded end → Track 2 detect lineD2 other end → Signal Controller DETECT
    11Signal Controller outputsCrossing flashers (alternate flash)
    Power
    1212 VDC supply +Every red wire / +12VDC terminal
    1312 VDC supply −Every black wire / GND terminal

    NO terminals are not used. Run every board from the same 12 VDC supply so all the detector signals share one ground.

    Parts

    QtyProductJob
    4MTT Precision DetectorSensors A and B (Track 1), C and D (Track 2)
    2MTT DPDT Relay for Precision Detector, 5APole 1 switches track power. Pole 2 is the lockout.
    1MTT Signal ControllerCrossing flashers, set to behavior 8 or 9
    2Small Schottky diode (e.g. 1N5817)Lets either track trip the flashers without tying the two tracks’ detector signals together
    112 VDC supplyPowers everything

    What happens

    1. Train 1 reaches Sensor A. The Track 1 signal goes through Relay 1’s closed Pole 2 contact (wire 1 → 2) into Relay 2’s DETECT. Relay 2 pulls in. Its Pole 1 opens and Track 2’s crossing section goes dead. The flashers start through D1.
    2. Train 2 reaches Sensor C. Its signal arrives at Relay 2 Pole 2 COM (wire 3). Relay 2 is pulled in, so its NC contact is open and the signal never reaches Relay 1. Track 1 keeps power, and Train 2 stops at its dead section.
    3. Train 1 clears Sensor B. Relay 2 drops out. Track 2’s section comes back on, and Pole 2 closes again. If Sensor C still sees Train 2, its signal now reaches Relay 1 (wire 4). Relay 1 pulls in and locks out Track 1. The crossing passes to Train 2.

    Placement and settings

    Sensors A and C: aim each one at the spot where a stopped train waits, just before its dead section. That way the waiting train still holds its detector signal when the crossing clears.

    Detector timeout: the line is only “occupied” while a detector sees the train or is timing out. Set the timeout long enough to cover the gap between the two sensors on each track.

    Dead sections: gap one rail at both ends of each section. Make the section longer than your longest locomotive.

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