Arduino Model Railroad Scale Speedometer – Finished

We finally finished the Scale Speedometer Project, and are heading off to the Charleston Area Model Railroad Club to install it. We used the Adafruit I2C 7 Segment backpack, a Arduino Nano clone, and two IR transceivers, for  total project cost of around $20. The code below is fully functional, all you need to do is adjust your scale, and distance between the sensors. Make sure your sensors do not extend above the height of the rails, or couplers could catch on them. I used a dremel to route out the holes, and superglue to fix them in place, but superglue leaves a white residue, so you may want to try a different adhesive. Watch the video!

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Get the IR Sensor Board at http://arduinotronics.blogspot.com/2017/06/6-channel-infra-red-transceiver-sensor.html

Arduino Nano Clone
7 Segment BackPack
IR sensors

Use the Adafruit Tutorial to assemble and connect your 7 segment backpack. Use the IR Sensor Tutorial to connect the IR sensors.

Update: Decreasing the resistance of the IR LED resistor (we finally used 100 Ohm) or increasing the resistance of the pullup resistor on the photo-transistor (we finally used 100k) can make the circuit more sensitive (up to 15mm depending on reflectance of car bottom), especially for larger scales with larger gaps. Do not burn out the IR LED with too low of a resistance (no less than 68 Ohm, 1/2w at 5v input).

#include  “Wire.h”
#include “Adafruit_LEDBackpack.h”
#include “Adafruit_GFX.h”

Adafruit_7segment matrix = Adafruit_7segment();

//user variables
float distance = 24; //inches between sensors
int scale=87;

int sensor1 = 4;
int sensor2 = 5;
bool s1Covered;
bool s2Covered;
float start, finish, elapsed, miles, hours, mph, scaleMPH;

int started=0, finished=0;
int scale=87;

void setup() {
// put your setup code here, to run once:
Serial.begin(9600);
pinMode(sensor1, INPUT);
pinMode(sensor2, INPUT);
matrix.begin(0x70);

}

void loop() {
// put your main code here, to run repeatedly:
//Serial.println(“Ready ….”);
matrix.print(0.0);
matrix.writeDisplay();
//finished=0;
s1Covered=digitalRead(sensor1);
if (s1Covered==0 && started==0){
start=millis();
started=1;
Serial.println(“Started”);

}
s2Covered=digitalRead(sensor2);

if (s2Covered==0 && started==1){
finish=millis();
finished=1;
Serial.println(“Finished”);

elapsed = finish-start; // millis

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);

// print a floating point
matrix.print(scaleMPH);
matrix.writeDisplay();
delay(25000);

started=0;
finished=0;
}
}