This post contains supplemental information for my YouTube video titled “Model Railroad Speedometer Arduino Circuit – Part 1”

My project is based off initial work by Steve Spence on his YouTube channel:
https://www.youtube.com/user/sspence65

Here is a diagram of the circuit:

I have done a full re-write of the Arduino code to include the following features:

• scale speed is calculated in O-scale
• speed can be detected in either direction
• circuit will not “reset” based solely on time while a train is still triggering one or both sensors

Here is my Arduino code:

/*
Model Railroad Speedometer

-------------------------------------------
Bobot's Trains and Maker Zone
https://www.youtube.com/user/BobotsTrains

03/11/2017
Complete code re-write adding detection
in both directions and continuous train
length detection of before reset
-------------------------------------------

-------------------------------------------
Original concept by:
Steve Spence
https://www.youtube.com/user/sspence65
-------------------------------------------
*/


#include "Wire.h"
#include "Adafruit_LEDBackpack.h"
#include "Adafruit_GFX.h"

Adafruit_7segment matrix = Adafruit_7segment();

//user variables
float distance = 18;   //distance between sensors (inches)
int scale = 48;   //scale of model to report scale speed  (O-Scale = 48)

int sensor1 = 4;   //sensor1 digital pin
int sensor2 = 5;   //sensor2 digital pin
int s1Open = 1;   //is START sensor open/uncovered? (goes to 0 if covered/triggered)
int s2Open = 1;   //is END sensor open/uncovered? (goes to 0 if covered/triggered)

float startmillis, finishmillis, elapsed, miles, hours, mph, scaleMPH;
bool started1 = false;    // set to TRUE if START sensor has been triggered 
bool started2 = false;    // set to TRUE if END sensor has been triggered 

bool initialized = true;   //set to TRUE once all sensors are cleared for a period of time and ready to read
float previousmillis;

void setup() {
  //Serial.begin(9600);
  pinMode(sensor1, INPUT);
  pinMode(sensor2, INPUT);
  matrix.begin(0x70);
  matrix.setBrightness(12);
  matrix.print(0.0);   //clear display to show 0
  matrix.writeDisplay();
}

void loop() {

  //read respective sensor if not already triggered
  if (!started1) {s1Open=digitalRead(sensor1);}
  if (!started2) {s2Open=digitalRead(sensor2);}

  // if neither sensor previously triggered and both sensors currently uncovered and several seconds have passed
  // determine if we can "reset" all variables and set the display to "8888"
  if ((!started1 && !started2) && (s1Open && s2Open) && ((millis() - previousmillis > 5000)))  {
    bool goodtogo = true;
    float starttesttime = millis();

    // assure no sensor triggers for several seconds before even attempting "reset"
    while ((millis() - starttesttime) < 5000) {
      if (!digitalRead(sensor1) || !digitalRead(sensor2)) {
        goodtogo = false;
        break;
      }
    }

    // neither sensor was previously triggered, nor triggered in last several seconds, so "reset"/initialize vars and display
    if (goodtogo) {
      initialized = true;
      started1 = false;
      started2 = false;
      previousmillis = millis();
      matrix.print(8888);   //clear display to show 8888
      matrix.writeDisplay();
    }
  }

  // Sensor 1 is triggered, neither sensor was previously triggered, and we were in initialize mode
  if ((!s1Open) && (!started1 && !started2) && (initialized)) {
    started1 = true;
    initialized = false;
    startmillis = millis();
    }

  // Sensor 2 is triggered, neither sensor was previously triggered, and we were in initialize mode
  if ((!s2Open) && (!started1 && !started2) && (initialized)) {
    started2 = true;
    initialized = false;
    startmillis = millis();
    }

  

  //a first sensor (START) was previously triggered and now a second sensor (END) is triggered, calculate and display scale MPH 
  if (((started1) && (!s2Open)) || ((started2) && (!s1Open))) {
    finishmillis=millis();
    //Serial.println("Finished");
    
    elapsed = finishmillis-startmillis;
    
    elapsed = elapsed / 1000;    //seconds
    //Serial.print("Seconds: ");
    //Serial.println(elapsed);
    miles = distance / 63360;   //miles
    hours = elapsed / 3600;   //hours
    mph = miles / hours;
    scaleMPH = mph * scale;
    //Serial.print("Scale MPH: ");
    //Serial.println(scaleMPH);
      
    //slow blink if between 50 and 69 scale MPH
    //fast blink if over 70 scale MPH
    if ((scaleMPH >= 50) && (scaleMPH < 70)) {
      matrix.blinkRate(3);   
    } else if (scaleMPH >= 70) {
      matrix.blinkRate(1);   
    }

    // print scale MPH on display
    matrix.print(scaleMPH);
    matrix.writeDisplay();

    // reset
    delay(5000);   //wait
    matrix.blinkRate(0); 
    matrix.print(0.0);   //clear display to show 0
    matrix.writeDisplay();
    started1 = false;
    started2 = false;
  }
}