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GCA186-2 Railroad Crossing


By Peter Giling


Making barriers moving is easy now adays with servo motors.
But if we like to have this controlled the way it should, there is more needed than just the servo itself.
In the real world, for example, there is a system that senses when the tail of a train just has passed the crossing area, or counting all the whees/axes before and after the crossing.
That can be done in many ways, but it always come to the fact , that it does not matter if a train is 50 wagons long,
or just a locomotive.
One way to achieve that on our miniature world, is doing it completely manual.
But that is not the way I would prefer, so I started making a solution for a friend in a different way.
It starts with the idea that whether he is driving a train manually or automatic (with Rocrail of course !),
this system should always work.
GCA186-2 is meant to work totally independant from any other system.
All we need is a 9-16V transformer or Adapter.

Now the basic is to fix at least two magnets under the train, one in front, and one under the last waggon.
More than two is no problem, the limit = 255.
Next we need four hall sensors to be mounted between the sleepers, so that they will sense the magnets under the train. see GCA173
NOTE: For a one way traffic, only sensor A and C are needed!
Be sure that the train should fit completely between sensor A and sensor C, and/or between point D and B.

Many different options should be possible, depending on the software in this unit.
That is made easy by using a medium scale micro processor.
The example here is a 2 direction single track crossing.

Assume that a train approaches from the left hand side.
The train first activates sensor A.
The GCA186-2 will start flashing the lights, switch on the relay which could possibly be used to activate any sound,
and shortly after that the barriers descend.
Board contains two outputs for servo's.
In the mean time the train continues, and the magnet under the last wagon also passes sensor A.
Now, GCA186 has counted two magnets.
Passing sensor B has no effect here.
But as soon as the train passes point C, the count down starts.
When the last wagon passes sensor C, two magnets have been counted, meaning that the rails are clear and
the barriers should rise again etc.
But that is not the complete end of it.
To avoid that the systems starts again on passing point D,
the train also has to count the magnets passing point D in the same amount as sensor A, before the whole system is reset.
So far the flashing lights are still on, you should be familiar with the next expression:
Flashes and sound will stop after the last sensor also has counted the correct amount of magnets.
If you swap A with D and B with C in this text, you have the explanation for the opposite way.
For a one way traffic, different firmware will be available, also for double track .
This board cannot service more than doubletrack, nor can it service double track with each two direction driving.
That would need many more sensors , which there is no input for.
Contact Peter if you need that.


  • control for two flashing leds, also possible on the barriers itself, because only 2 wires are needed
  • free relay contact available for sound options
  • two barriers each with its own motor, thus easy to install
  • high and low position of barriers are adjustable
  • Adjustable between starting flashing (and sound) and barriers to go down
  • Barriers will go up directly but ONLY after the last magnet has passed.

This means that the length of the train is sensed.!

The prototype board

The usual item, to proove that it works, is not yet available

Hardware files


All firmware is developed with Picsimulator from Oshonsoft.

gca186_2-en.txt · Last modified: 2018/11/26 02:49 by rainerk