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Railway Grade Crossing Circuit

Prototypical Signal And Gate Operation

This circuit automaticly controls railway grade crossing signals and gates in a prototypical manner.

The circuit uses a bidirectional time delay that staggers the gates and lights so that they operate as would be seen at a typical grade crossing.

Railway Grade Crossing Circuit board can be built in three configurations:

1 – Controls + Crossing Signals And Gates.

In the Signals and Gates version of the circuit: When a train enters the protected section of track the flashers operate for a set time before the crossing gates start to lower. After the train clears the grade crossing, the signals will stay flashing until after the gates are up fully. Both time delays can be adjusted to suit actual conditions.

2 – Controls + Crossing Signals Only. (For a crossing without gates.)

In the Signals only version of the circuit: The flashers are activated when a train enters the protected section of track and will shut off approximately two seconds after the train clears the crossing. The components that control the delays for the flashers and gates are left off of the circuit board.

3 – Controls Only. (For a second, or more, track at a crossing.)

In the Controls Only version of the circuit: The circuit is used to control a second and other tracks at a crossing via the multitrack terminal on the first track’s circuit boards. The components that control the delays for the flashers and gates and the components that operate the flashers are left off of the circuit board.

This circuit is designed to directly control crossing gates that are powered by stall-motor type switch machine drivers.

Components omitted from the Gates Only and Controls Only circuit boards can be installed later to restore the functionality of the circuits.

The Grade Crossing circuit uses six visible and infrared light sensitive phototransistors to detect a train and control the circuit.

The Grade Crossing circuit has a dual output signal driver allowing it to directly drive most signal wiring configurations without added circuitry.

One Grade Crossing circuit board can also be used to protect multiple tracks by using additional phototransistors.

The Grade Crossing circuit can supply up to 100 milliamps for LEDs, small incandescent lights or other circuits such as sound units or can drive larger loads through transistors or relays.

Circuit Diagram


Component List

Qty Circuit Part Number – Gates Part Type Digi-Key Number
2 IC 1, 2 LM339 LM339NFS-ND
2 IC 3, 4 LM556 LM556CNFS-ND
6 D1, 2, 3, 4, 5, 6 1N4148 1N4148DICT-ND
6 Q1, 2, 3, 4, 5, 6 PHOTOTRANSISTORS 160-1030-ND
1 Q7 2N3904 2N3904FS-ND
1 Q8 2N3906 2N3906FS-ND
1 C1 100uF P5152-ND
1 C2 2.2uF P5175-ND
1 C3 4.7uF P5177-ND
1 C4 0.22uF 495-1106-ND
1 C5 10uF P5178-ND
2 C6, 9 1.0uF P5174-ND
1 C7, 8 22uF P5179-ND
6 R1, 2, 3, 4, 5, 8 1M 1.0MQBK-ND
5 R6, 7, 9, 15, 17 33K 33KQBK-ND
2 R10,  24 100K 100KQBK-ND
7 R11, 12, 13, 19, 20, 22, 25 10K 10KQBK-ND
2 R14, 21 2.2K 2.2KQBK-ND
3 R16, 18, 23 1 MEG POT 3306F-105-ND
4 Terminal Block 2 Position, 5mm. ED1601-ND
2 Terminal Block 3 Position, 5mm. ED1602-ND


Once You have the Module built, you can refer to the following practical connection diagrams:-

One Track Crossing

One Track Crossing

Multiple Track Crossing

Output Options 


Grade Crossing Circuit Operation Notes

  • The signal flashers will turn OFF if a train enters and then backs out of the crossing.
  • The crossing circuit is ready for the next train in either direction approximately five seconds after both “DISABLE” sensors are uncovered. If a departing train is still covering a “START” sensor after this time the flashers will be reactivated.
  • MANUAL controls can also be used to start and stop the flashers if desired. The START push button could be replaced by or paralleled by a SPST toggle switch to keep the flashers activated during switching operations.
  • When the MANUAL controls are used, the same gate and flasher delays are present as with the phototransistor sensors.
  • The ‘MULTITRACK’ terminal (8) is used to connect circuit boards together for multiple track crossings. When the MULTITRACK terminal is used to control the crossing circuit, the same gate and flasher delays are used as when the phototransistor sensors control the circuit.The ‘MULTITRACK’ terminal is an input only and cannot be used to control other circuits. Terminal 11 can provide a positive output signal to control other circuits if needed.
  • Normal room lighting is used to detect the trains. If night operation is needed the circuit can be controlled by other circuits or by providing infrared light for the phototransistor sensors.
  • The circuit is designed to use phototransistors but can also be controlled by CdS photocells by using external resistors in parallel with the R1, R2 and R3.
  • Low coil current relays can also be controlled by terminals 9 and 10.
  • Bell circuits and small relays can be controlled via terminal 11.
  • Requires a regulated 12 volt power supply.
  •   WARNING – If the polarity of the power supply for this circuit is reversed or the circuit is connected to an to an AC or DCC source, the circuit will be damaged. The maximum supply voltage is 15 Volts DC.


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