Nuts and Volts - August 2015

reset, so we can use a start and finish value later to get very accurate real time. When the back of the train finally clears the outer most sensor (E1), it records a “finish” time and computes the speed.

Speed is dependent on your scale, and by changing the scale factor (87 for HO scale, 48 for O, etc.), this scheme will work for any model railroad big or small. The computation of scale speed takes the milliseconds of elapsed time, the distance traveled in inches, and the scale of the model, and turns it into a scale MPH. The same sequence occurs for a train going eastbound with only a difference in the displayed train direction.

The LCD uses the built-in library of the Arduino to produce the display shown for a westbound train. After a delay, the display goes back to a clear block.

Making All Model Railroad Animation More Realistic

If you enjoy realistic animation as one more facet of model trains, you can give it a big lift by using a microprocessor and servos. In the larger scales, the commercial crossing gates and moving accessories are usually driven by a solenoid. It’s way too “jerky” to be realistic, and begs for the installation of a servo to slow it down. It would be fairly simple to rebuild the device with a servo attached, then slow down the motion and change the timing to come on and off like we did with the flashers in this project. Look around your layout. There are

■ FIGURE 4. Overall program logic for the flasher/ speedometer.

Microprocessors and Model Trains Meet Head On!

In order to bring the hardware and software together, a mockup was needed on the bench. Track sensors (LDRs) were mounted in a strip of plywood. A piece of prepainted track roadbed from another project was on hand and worked out just fine. The LCD — which would eventually be mounted in the track framework fascia near the flashers — was also tied to the Arduino Uno with plug ended jumpers.

After software debugging and speedometer time checks, the entire unit is ready for mounting and permanent wiring. It works for any scale model railroad and fits in a very small amount of space.