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Train RR Crossing LEDs Scheme 1

 

In order to implement a railroad crossing scheme, it is necessary to detect the position of the model train relative to the railroad crossing.  A pair of Reed Switches will do the trick in a relatively cost effective manner.

What is a Reed Switch? A Reed Switch is comprised of a set of swich contacts hermetically sealed in glass. For this application which is appriximately one inch and about one eighth inch in diameter. It has a sausage-like shape.   The switch contacts are normally open and will be energized when it is placed in close proximity with a magnet.

The following figure depicts a pair of Reed Switches, associated magnets, and a Twin Coil Latching Relay used to turn power on and off to the LED Flashing circuit previously described.

Let’s walk through the figure in detail.

1) Assume that the train will be going in the direction from Reed Switch A toward Reed Switch B, passing accross the railroad crossing.

2)  As it passes over Reed Switch A, which is located between the train rails, Magnet A attached below one of the train cars causes Reed Switch A to momemtarily causing Coil A of the latching Relay to to enegize. This in turn causes the +12 vdc return (Power Supply negative) to turn on the Flashing LED circuit, which are wired to the Cross Bucks.

3) P.S.  The latching Relay is needed because the Reed Switch (not a latch) will only close when it is close to the magnet.

4) As the train passes over Reed Switch B, it will momentarily close causing Coil B to reset the Latching Relay back to its normally open position, thereby disconnecting the +12 Vdc Power Source from the Flashing LED circuit.

5) Reed Switch A can be located a suitable distance from the crossing (appoiximately 5 feet).

6) Reed Switch B can be located pass the crossing by about 1 foot.

Important Concern:  This scheme will only work for a train traveling from Reed Switch A towards Reed Switch B. This is because Coil B would have to now become the “set coil” and Coil A would have to become the “reset coil”. If you link to the Model Railroad Train RR Crossing Scheme 2, you can see how to resolve this problem.

If you wish to acquire a better understanding of Electronics Theory, I suggest you go to  the following  link: Electronics

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