Tuesday, January 3, 2017

Model Railroad Crossing Lights

For the Charleston Area Model Railroad Club, We have combined our train detector circuit from the scale speedometer project with a LED Crossing Light to make it simple to indicate a train is coming to a crossing. The next step is to add a servo operated crossing bar, and bell sounds, but I'm getting ahead of myself.

The Circuit:
The detection circuit is the same as the scale speedometer. A TCRT5000 IR LED / Phototransistor pair, with two resistors, connected to an Arduino input (D8). You can lower the value of the Phototransistor pullup resistor to 10k-50k ohm (instead of 80k-100k ohm) to reduce it's sensitivity to ambient light. Increase the value of the IR LED resistor (68 Ohm) to reduce range. Never drop IR resistor below 68 Ohms.

The output is a off the shelf LED crossbuck with 2 red LED's and a common anode. I put a 300 ohm resistor on the common and connected to 5v, and connected the two cathodes directly to arduino outputs D11 and D12. Add a second LED Crossbuck (with resistor) to the same outputs for the other side of the crossing. See the video below the code.

The code checks to see if the phototransistor is lit (a 0 or LOW), and activates the lights (LOW is lit, HIGH is off)) as long as it is.

//int sensor1 = 1;

void setup() {
  pinMode(8, INPUT);
  pinMode(12, OUTPUT);
  pinMode(11, OUTPUT);

// the loop function runs over and over again forever
void loop() {
  digitalWrite(11, HIGH);
  digitalWrite(12, HIGH);

  int sensor1 = digitalRead(8);
  if (sensor1 == LOW){
    digitalWrite(12, HIGH);
    digitalWrite(11, LOW);
    digitalWrite(12, LOW);
    digitalWrite(11, HIGH);

Finished board for two track sensors and 2 crossing lights.

Monday, January 2, 2017

Model Railroad Turnout Control - Arduino MOSFET

One of the projects we are working on is Turnout Control. Most home layouts are using Atlas or Bachmann track with solenoid type turnouts like the one shown here. More professional layouts use slow moving motors like the Tortoise. Our goal is to make these turnouts controllable with an arduino, so that future projects using train detectors and DCC can allow more automation. So here is the beginning of our project. This one uses the above Bachmann turnout (arduino servo control article coming soon), a arduino nano, two IRL520 MOSFETS, two resistors, and two diodes. The schematic is as follows:

The diodes protect the MOSFET from inductive spikes when the solenoid coils fire. The two MOSFETS engage the solenoid coils to move the turnout. the two resistors keep the MOSFET from randomly conducting when there's no input signal, by pulling the gate to ground (off). This uses two digital outputs on the arduino called straight and turn. The next article will show the board layout and wiring of the arduino, turnout and power supply. For more projects based on MOSFETS, see http://arduinotronics.blogspot.com/search?q=mosfet