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Automatic Railway Grade Crossing Flashers

Automatic Railway Grade Crossing Flashers

This circuit provides realistic operation of the flashing signals at level railway crossings. The circuit uses six visible/infrared light phototransistors to control the operation of the flashers and can supply up to 100 milliamps for LED flashers or small incandescent lights.

When a train travelling in either direction covers one of the “START” sensors the signal will turn ON and the signal LEDs will flash. 
The flashers will remain ON until approximately two seconds after the last car has passed completely through the crossing and both of the “STOP” sensors are uncovered.
As the train leaves the protected section of track, the “DISABLE” sensors prevent the flashers from being turned ON again by deactivating the “START” sensors.
The “START” sensors are reactivated approximately 5 seconds after the “DISABLE” sensors have been uncovered.

Operation Notes
The flashers will turn OFF if a train enters and then backs out of the crossing.
The circuit is ready for the next train in either direction approximately five seconds after the “DISABLE” sensors are uncovered. If the departing train is still covering a “START” sensor after this time the flashers will turn on again.
Manual controls can start or stop the flashers as desired. The START push button could be replaced by a toggle switch in order to keep the flashers activated during switching operations.
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 sensors.
The circuit is designed to use phototransistors but can also be controlled by CdS photocells by changing the values of resistors R1, R2 and R3.
If protection is needed in one direction only as with double main lines then only four sensors would be needed for each track.
The Crossing Circuit requires a regulated 12 volt power supply. The current draw is about 3 milliamps when the flashers are OFF and about 35 milliamps when they are ON.
Crossing gates and bells can be controlled buy using the Multi Track terminal as an output to control these devices. The Multi Track terminal is also used to connect the circuitboards together for multiple track crossings.
The diagrams show one circuit board for each protected track at a crossing. It is possible to use one circuit board to protect multiple tracks but fully automatic control is not possible when this is done.

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