2011 - Automatic Railway Grade Crossing Circuit.

  The information on this page will be maintained for the users of the existing 2008 Grade Crossing circuit boards.

  This circuit automatically controls 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 crossing.

  The 2011 Grade Crossing Circuit is fully compatable with the earlier amd later crossing circuits and can be used with these circuits at multiple track crossings.

The 2008 Automatic - Railway Grade Crossing Circuit board can be built in three ways:

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. (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 and subsequent tracks 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.

  In the 2008 Grade Crossing circuit, the flashers are on for a set period before the gates start to close and the signals will keep flashing until the gates are up fully. Both of these time delays can be adjusted to suit actual conditions.

  The Grade Crossing circuit has a two output signal driver with two outputs allowing it to directly drive almost any signal wiring configuration.

  The Grade Crossing circuit is designed to directly control crossing gates that are operated by stall-motor type switch machines.

  The protected section of track can be any length on either side of the crossing. The Grade Crossing circuit works in both directions and can be connected to other grade crossing circuits to provide fully automatic protection for multiple track crossings. One board can also be use to protect more than one track if needed.

Gates and Flashers Circuit Board Photo

  The 2008 Grade Crossing circuit is an upgraded version of the 2004 - Automatic Railway Grade Crossing Circuit that is available through this site.

  The 2008 circuit uses the same phototransistor control scheme as the 2004 Railway Grade Crossing Circuit and is fully compatible with the earlier circuit for combined use at multiple track crossings.

  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.

  The circuitboard has been designed to be easy to build and install. Widely available and inexpensive components are used in its construction. None of the parts are static sensitive.

  The following diagram shows how the 2008 Automatic Grade Crossing circuitboard is connected for a typical 1 track crossing.

  Typical flasher, bell and gate drive motor connections are shown on other diagrams on this page and others.

  The next diagram shows the relative positions of the six phototransistors along a protected section of track.

  The lower portion of the diagram shows the timing of the signals and gates a train passes through the protected section from left to right. (The delays work in both directions of travel.)

1.   When a train traveling in either direction covers one of the "START" sensors, the crossing signals will start to flash.

2.   After a short delay the crossing gates start to lower. (The delay is adjustable.)

3.   When the train has cleared the crossing the gates will start to lift after about 2 seconds.

     (The grade crossing will be protected until both of the "STOP" sensors are uncovered.)

4.   The signals will remain on for a short time after the gates are fully up. (The delay is adjustable.)

5.   As the train leaves the protected section of track, the "DISABLE" sensors prevent the flashers from starting again by deactivating the "START" sensors.

6.   The "START" sensors are reactivated approximately 5 seconds after the "DISABLE" sensors have been uncovered.

  Sensors 1 or 6 must be covered before sensors 2 or 5, depending on the direction of travel, or the signals will not start. Sensors 2 and 5 disable sensors 1 and 6.

  The next diagram shows the changes in the output terminals of the grade crossing circuit as a train travels through the protected section of track.

  The 2008 Grade Crossing Flasher circuit uses LM556 dual timer IC to provide two outputs of opposite phase that can drive LEDs in common cathode, common anode or back-to-back configurations.

  Only one set of signal LEDs is shown in three of the diagrams, more sets of signals can be connected as needed.

  The circuit's output can also drive small incandescent lamps connected in the same general arrangements as shown for the LEDs. Small relays and sound circuits can also be controlled by the output of the circuit.

  The 2008 Grade Crossing Flasher circuit can drive signals with 'common anode' connected LEDs such as TOMAR Industries crossing signals without the adapter circuitry needed by the 2004 Grade Crossing Circuit.

  Operation of the stall-motor can be slowed by adding a resistors or potentiometer to the circuit. The potentiometer will allow better control of the speed of the gates.

  NOTE: In some installations, while the gate drive motor is running, the crossing signals may flash very quickly. A particular cause has not been found for this but with the potentiometer conneced as shown in the circuit above the problem can be eliminated.

  Several motors can be operated at the same time if needed but each should have its own speed reducing resistor.

  The power from terminals 9 and 10 does not turn OFF. If motors other that the stall type are used to drive the gates, a method of stopping them at the ends of their travel will have to be built into the motor's power circuit. An example circuit is shown below.

  Depending on its power and speed requirments, a separate power supply will likely be needed for the gate drive motor.

•   The 2008 circuit uses the same operating system as, and is fully compatible with the 2004 - Railway Grade Crossing Circuit. The basic control and operating information for the 2004 circuit applies to the 2008 circuit.

•   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 the "DISABLE" sensors are uncovered. If a departing train is still covering a "START" sensor after this time the flashers will be restarted.

•   MANUAL controls can also start and stop the flashers if desired. The START push button could be replaced by a toggle switch in order 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 is used to connect circuitboards 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.

    In the 2008 Grade Crossing circuit the 'MULTITRACK' terminal is an input only and cannot be used to control other circuits. Terminal number 11 can provide signals 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 changing the values of resistors R1, R2 and R3 or by using external resistors in series with the photocells.

•   Small relays could also be controlled by terminals 9 and 10.

•   Bell circuits and small relays can be controlled via terminal 11.

•   The 2008 - Automatic Crossing Circuit requires a regulated 12 volt power supply.

  The following schematic is for the 2008 Grade Crossing Flasher circuit for a single track crossing. Connections for the signal lights, sound circuits and gate drive motors are shown on other diagrams.

  The diagrams show the three versions of the circuit.

Gates and Flashers Circuit Schemtic

Flashers Circuit Schemtic

Controls Only Circuit Schemtic

  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.

Click On The Picture For A Much Larger View

  The circuitboard measures 2 inches by 5.9 inches and has been commercially and has not been tinned. The copper side of the board has a protective clear coat to prevent oxidation.

  The circuitboard has been designed to be easy to build and install. Widely available and inexpensive components are used in its construction. None of the parts are static sensitive.

  When installing the components on the circuit board start with parts with the lowest height and work up to the tallest parts. For example starting with the jumper wires then diodes then resistors, IC's, transistors, capacitors and terminal blocks.

  For full protection of a 2 or more track crossing, the second and subsequent tracks can be protected by the 2004 - Automatic Railway Grade Crossing Circuit.

  The extra tracks at the crossing will have the same flasher and gate delay times as the first.

  One circuitboard and extra phototransistors are used at a multiple track crossing if only one train at a tie uses the crossing.

  The circuits on this page can be used with either the 2004 or 2008 versions of the Automatic Grade Crossing Circuits shown at this site.

  These circuits include:

• Fully Automatic - 2 And 3 Track Crossings
• One Direction Only Crossing - 1 Circuitboard
• 1 Track With A Siding - 1 Circuitboard
• One Track With Two Crossings Circuit
• Crossings With Short Approaches
• Railway Grade Crossing Test Circuit
• 'Two Wire' LED Connection (Bipolar)
• Common Anode and Cathode Connected LED Adapters
• TOMAR - Common Anode LED - Adapter
• Incandescent LED Circuit
• Controlling External Circuits
• Adding Capacitors To The Circuit's Inputs
• Using Normally Open Reed Switches As Inputs
• Using Block Occupancy Detectors To Activate the Flashers
• Stall Motor Crossing Gate Driver Circuit

  The circuits on this page show connections for the 2004 version of the Grade Crossing circuit but they will also work for the 2008 version of the Grade Crossing circuit.

  This circuit is a driver for a mechanical - Grade Crossing Bell Ringer - that was originally built for the London Model Railroad Group.

  If you use any of these circuit ideas, ask your parts supplier for a copy of the manufacturers data sheets for any components that you have not used before. These sheets contain a wealth of data and circuit design information that no electronic or print article could approach and will save time and perhaps damage to the components themselves. These data sheets can often be found on the web site of the device manufacturers.

  Although the circuits are functional the pages are not meant to be full descriptions of each circuit but rather as guides for adapting them for use by others. If you have any questions or comments please send them to the email address on the Circuit Index page.

03 October, 2011