Additional Circuits For The 2004, 2008 and 2011

Automatic Grade Crossing Circuits

Some of the diagrams on this page show the 2004 Grade Crossing circuit board. The inputs to the 2004 board are identical to those of the 2011 board and work exactly the same.

The 2004 and 2008 Grade Crossing circuit boards are no longer available.

2011 Automatic Railway Grade Crossing Circuit

All of the phototransistor circuits on this page can be used with the 2011 circuit boards.

Circuit board Connections For Multiple Track Crossings

Fully Protected 2 And 3 Track Crossings

  The following diagrams shows how two and three circuit boards are connected for multiple track crossing with full automatic protection for each track. Any number of tracks can be protected using circuit boards for each track at the crossing.

2 Tracks - 2 Circuit Boards With A Crossover

  The switch machine contacts short circuit the Q4 START DISABLE sensors so that trains waiting for the crossover to be set to normal will restart the signals as the crossing train is departing.

  For this to happen the waiting train must be over the START sensor and/or be blocking the crossing while it waits for the crossover to be set to normal.

  If a train is blocking the crossing of the impassible track when the crossover is returned to Normal the signals will remain on until the waiting train has cleared the crossing.

  This is not a perfect solution as a train arriving from the West on the North track must block the crossing to keep the signals on after the train making the crossover departs.

3 Tracks - 3 Circuit Boards

  The diagrams above show one circuit board for each protected track at a crossing. One circuit board can protect multiple tracks but fully automatic control is not possible when this is done.

Main Track With A Passing Track Using 1 Circuit Board

2 Tracks At Crossing

  The grade crossing circuit can be used where there is a crossing with a passing siding.

  If a train is occupying the crossing on either track, the flashers will stay on until both trains have departed.

1 Track With A Siding #1 Using 1 Circuit Board

  The grade crossing circuit can also be used where there is a crossing with a siding.

  Because only one circuit is used, fully automatic operation is not possible as with the full, two track crossing but if only one train uses the crossing at a time, the system will give prototypical operation.

1 Track With A Siding #2 Using 1 Circuit board

  Extra phototransistors can be purchased for multiple track crossings using only 1 circuit board.

One Track With Two Close Crossings Circuit

  The next circuit is similar to one in use at the London Model Railroad Group's layout where there is two grade crossings that are quite close together.

  The circuit is set up so that as the train approaches, both sets of crossing signals start at the same time but they turn off separately as the train leaves each crossing.

Sensor Arrangement For A Complex 3 Track Crossing

Using 2 Circuit Boards

Crossings With Short Approaches

  This arrangement of the phototransistor sensors can be used at crossings that have a very short approach distances or are occupied by trains for long periods such as in an industrial switching area or near a passenger platform.

  Multiple tracks can be protected by modifying the basic Grade Crossing circuit and adding diodes to isolate the sensors for the separate tracks.

Asymmetric Approaches To Crossing Using 1 Circuit Board

  Long approach on one side of the crossing and a short approach on the other side.

Double Diverging, One Track Crossing Using 1 Circuit Board


Other Multiple Track Crossings

2 Main Lines And 2 Passing Tracks Using 2 Circuit Boards

4 Tracks At Crossing


Unprotected Siding Or Yard Lead - 1


Unprotected Siding Or Yard Lead - 2


Four-Quadrant Type Crossing Gate Control

  This section shows how the Grade Crossing Circuit can be added to so that it can control Four-Quadrant type crossing gates. Operation of this type of gate system is shown in the video at this link.

Operation Lifesaver, Four-Quadrant Type Gates Video

  The first schematic shows a 1 track crossing. The gate motors are driven by two 556 timer ICs that are controlled by the main circuit board. The timing diagram on the schematic shows the order in which the gates open and close.

  The values of the timing components in the circuit can be adjusted if longer of shorter delays are needed.

  The Grade Crossing circuit triggers the Quadrant Gate timers when terminal 9 goes HIGH and allows these timers to reset when terminal 9 goes LOW.

  The gates and signal lights will have the same delay times as they would in the basic crossing circuit.

  The circuit used to drive the Four-Quadrant gate motors can also be built using two of the switch machine drivers from a 556 Timer Stall-Motor Switch Machine Drivers PCB as shown in the following diagram.

  The next schematic shows a 2 track crossing protected by two circuit boards. The gate control portion of the second board is used to control the gates for the traffic lanes that exit the crossing.

  This method is more complicated to set up than the single track crossing as it requires the timing of the sets of gates to be set individually.

  A two track crossing can also be protected as shown in the one track crossing diagram by using two external 556 timers. A Controls Only configured circuit board would then be used for the second track.

Signals Adapters

Common Anode and Cathode Connected LED Adapters

  Unconfirmed - The Walthers #933-2914 crossing signals are wired in a common anode circuit but the Black wire is the positive and the Red wires are the negative.

  The NJ International, Inc. Crossbuck Signal Model 1095 are wired in a common anode circuit configuration.

  The Oregon Rail crossbucks specify common anode wiring.

TOMAR - Common Anode LED - Adapter

  This circuit can be used to connect common anode wired LEDs such as TOMAR Industries, crossing signals to the Automatic Grade Crossing circuit.

  The 22 ohm resistors distribute the current evenly though the LEDs. The 1K ohm resistors limit the current flow through the LEDs and can be changed if the brightness of the LEDs needs to be adjusted.

'Two Wire' LED Connection (Bipolar)

  The circuit in the following link will allow the crossing flasher LEDs to be connected using only two wires instead of three as in the circuits above. This could make wiring of small scale signals easier.

Green And Red Signals

  The signals in the next circuit turn from GREEN to RED when a train is in the protected section of track.

Incandescent LED Circuit

  This circuit when used with a 555 timer will cause light emitting diodes to turn on and off more slowly. This will make the LEDs appear similar to incandescent lamps.

Driving High Current Lamps

  This circuit can be used to drive higher current light bulbs that are found in older or large scale signals. The adapter can be connected directly to the Automatic Grade Crossing circuit or through optoisolators if a separate power supply is to be used for the bulbs.

Controlling External Circuits

Adding Capacitors To The Circuit's Inputs

  If there is electrical noise that causes the crossing circuit to trigger falsely a small capacitor can be added to the START terminal. This will make the crossing circuit slightly slower to activate but will not affect the operation of the circuit.

  The diagram shows capacitors at the DISABLE and STOP terminals but these would only be needed. if the flashers shut off unexpectedly.

  If the trains are very fast, the DISABLE sensor may have to be moved farther from the START sensors when using added input capacitors.

Adding Resistors To The Circuit's Inputs

  The sensitivity of the phototransistors can be increased by adding resistors at the input terminals of the circuit board.

Using Normally Open Reed Switches As Inputs

  Normally Open microswitches could also be used to control the grade crossing circuits. This might be more suitable for outdoor layouts or G Scale and larger trains.

Using CdS Photocells With The Grade Crossing Circuit

  CdS photocells can be used with the Grade Crossing Circuit without modifying the circuit board and adding external resistors at the input terminals.

  The variable resistors shown on the diagram above can be replaced by fixed resistors by measuring the resistance of the photocells under actual conditions and selecting the proper replacement.

  There is more information on this in Section 1 of the Basic Visible and Infrared Light Detectors page at this site.

Using Block Occupancy Detectors To Activate the Flashers

  Block Occupancy Detectors (BODs) can be used to activate the crossing signals as long as they have a steady output state while any detectable cars are in the protected section of track.

  The signal to stop the flashers should still be phototransistors as a BOD would be too slow and not suited to sensing a section of track that is shorter than many cars. Also, every car in the train would have to be detectable not just the first and last cars.

  Most BODs have a LOW output when a train is detected and would use Circuit 1 in the following diagram.

  The input to stop the flashers should be phototransistors as a BOD would not be suited to sensing a section of track that is shorter than many cars.

  The section of track that is sensed by the BOD can be any length on either side of the crossing.

Other Motor Types

  The voltage from terminals 9 and 10 does not turn OFF. If motors other that the stall type are used to drive 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 the motor's power requirements, a separate power supply will likely be needed for the gate drive motor.

Servo Motor - Crossing Gate Drive Control Circuit

  The Grade Crossing Circuit can also control servo motors through a circuit board available from Sparkfun Electronics WIG-13118 Servo Trigger. (The circuit board is available from other sources as well.)

  The longest, as programmed, travel time for the WIG-13118 is about 3.4 seconds. This could be increased by reprogramming the controller chip on the circuit board. A more suitable travel range might be 2 to 10 seconds.

Stall Motor Crossing Gate Driver Circuit

  The next two circuits can be used to drive stall-motor switch machines to lower and lift crossing gates.

  The printed circuit board for the 556 Timer Stall-Motor Switch Machine Drivers circuit could be used to make Crossing Gate motor drivers. See the "Additional Circuits" section of the page.

Crossing Gate Driver Circuit

Grade Crossing Bell Ringer Circuit

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

  Electronic grade crossing bells at and

  These devices have not been tested with the Automatic Grade Crossing circuit on this page but should work.

  A DCC To DC - Accessory Power Supplies that could be used to supply the crossing circuit.

Grade Crossing Circuit Testing

Circuit Board Testing

  Before installing the Grade Crossing circuit on a layout, this circuit can be used to test the circuit board and demonstrate its operation.

  SPST switches are used in place of the phototransistors to simulate their function. An open or closed switch is the same as a covered or dark phototransistor.

  This circuit can be also used for the 2004 and 2008 circuit boards as the input terminals are the same for both.

  If switches are not available, disconnecting of connecting the wires where the switches are will also work.

Phototransistor Inputs Testing

  The diagrams shows the expected voltages at the input terminals when the phototransistor input sensors are lit or dark.

Testing Phototransistor Installations

2004 Grade Crossing Circuit Schematic

2008 Grade Crossing Circuit Schematic

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Please Read Before Using These Circuit Ideas

  The explanations for the circuits on these pages cannot hope to cover every situation on every layout. For this reason be prepared to do some experimenting to get the results you want. This is especially true of circuits such as the "Across Track Infrared Detection" circuits and any other circuit that relies on other than direct electronic inputs, such as switches.

  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.

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28 February, 2017