The circuits on this page can be used with the 2011, 2008 and 2004 versions of the Automatic Grade Crossing Circuit that are shown on other pages at this site.
Most of the diagrams on this page show the 2004 - Grade Crossing circuit board but these circuits will also work with the 2008 and 2011 circuit boards.
The flasher circuits depend on whether the circuit board uses a LM555 or a LM556 oscillator as the flasher.
Before installing this circuit on a layout this simple 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 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.
CdS photocells can be used with the Grade Crossing Circuit with out changing the circuit board.
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.
The grade crossing circuit can be used where there is a crossing with a passing siding.
If a second train is occupying the crossing for either track, the flashers will stay on after the first train has departed.
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 in the full two track crossing but if only one train uses the crossing at a time, the system will give prototypical operation.
Extra phototransistors can be purchased for multiple track crossings using only 1 circuit board.
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.
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.
If the trains travel in one direction only through the crossing, only three phototransistors are needed.
Unconfirmed - The Walters #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.
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.
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.
The signals in the next circuit turn from GREEN to RED when a train is in the protected section of track.
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.
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.
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.
The sensitivity of the phototransistors can be increased by adding resistors at the input terminals of the circuit board.
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.
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.
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.
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 http://www.ironpeng.com/ipe/ and http://ittproducts.com
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.
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.
08 December, 2012