Finally got the photo interrupter working!

A photo of my working photo interrupter. Here is the trick to getting a new photo interrupter working (tipped off by this thread). There are 2 sides to the gate; the transistor and the emitter.

Phototransistor:

• look at the datasheet and see which side is the emitter and which is the collector.
• start by setting up the phototransistor as an analog input analogread() will output values from 0-1023

IR emitter:

• look at the datasheet to see how much voltage and current the LED can handle. Mine was 50mA
• Hook up the LED to that output. In my case digital I/O gives 5V and 40mA.

Test:

• watch the serial monitor I started off getting values that ranged from 0 to 3, then after fiddling with resistors (taking away the resistor to the emitter and adding a 10K to the transistor).
• Got to the point where I read 10-20 when the gate was blocked and 1010-1020 when the gate is open. (my Photo interrupter took a 10K resistor, my Photo Reflective Sensor will take a 100k or 1m resistor all I have is 10K resistors and 5 of them in series brought the reading up to 400)
• Now change the code from analogRead() to digitalRead() (and switch the input wire) see if you get 111100001110001111 when you move something between the gate.

Resources:

1. Helpful forum post on troubleshooting a photogate
2. Code and schematic on testing a photogate
3. basic setup and pictures of a photogate, and code using attachinterrupt()

Here is the test code that I used:

int val;

void setup()

{

pinMode(13, OUTPUT);
pinMode(2, INPUT);

Serial.begin(9600); // sets the serial port to 9600

digitalWrite(13, HIGH);
}

void loop()

{

val = digitalRead(2); // read digital input pin 2
//val = analogRead(0); // read analog input pin 0

Serial.print(val); // prints the value read
Serial.print(" "); // prints a space between the numbers

delay(100); // wait 10ms for next reading

}