August 14, 2017

Why did the train cross the road?

Prototype scene of traffic sharing road with train on Fries Ave in April 2000. Photo by Dave at EJ&E Archive.
After our unsuccessful attempt to get the "simple" grade  crossing warning lights wired up using the materials I had on hand I decided to tackle the project anew. First step was to read the directions, again.

I am using a Logic Rail Grade Crossing Pro. It is a full function grade crossing circuit that can handle flashing crossing lights, motor control for gates, and a bell circuit. The user has to provide the lights, gates, motors and bells. In addition, if using LEDs, the user has to provide the appropriate resistors.

The wood screw in the center secures the
circuit to the benchwork
The instructions include a chart to tell you what resistance to use for the LEDs for several power supply voltages. I used a 12V power supply, so I needed 470 ohm resistors. Of course I didn't have any on hand.  Luckily, we have a store in the area that sells some electronic components and is open on weekends. My go-to stores for that kind of stuff used to be Radio Shack as it was close to my house, but they went bankrupt. There is a good electronic supply shop in Alexandria, but they have regular business hours during the week and are closed on weekends, which makes it hard for me to get there during a normal work week.

Even though I was only using the crossing lights, there were still 14 different wires that had to be attached to the circuit and run to different spots on the layout. I made a wooden chassis with a terminal strip to try to help keep all the wires organized. I engraved letters on the wooden chassis for each connection. The large letters are easier to read when the circuit is mounted on the layout upside down.  I also built harnesses for the wires that I ran to each signal and photocell. I used heat shrink tubing to make the harnesses. Unfortunately the magnet wires that came with the signals were fragile -  two broke in the harnesses and two others shorted inside the tube. So I replaced all the magnet wires in the model signals with 32 gauge stranded wire.

The Grade Crossing Pro uses a series of 4 photocells to determine train occupancy and direction.  You put the two photo cells on each side of the crossing and if you wire them correctly they will control the crossing in a realistic manner. The circuit includes potentiometers to adjust the photocell sensivity.  I found that the adjustment would only work well when all four photocells were hooked up. Then it was simple to adjust for room light.

If I turn off the room lights the grade crossings will trigger if their power is on. So I have to make sure that switch is also off when quitting for the night.

Here is a video showing its operation.

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