Photo Interrupter with external interrupt to count RPM

Other Hardware Sensors
1

So I am trying to get a Photo Interrupter (http://nz.element14.com/kingbright/ktir0611s/photo-interrupter/dp/2079964?Ntt=207-9964) to work on one of my Mega 2560 external interrupts so I can count revolutions of a DC motor.

I have tested it with using analog reads and serial prints to test that it is working but I wanted to know if I can use it with one of my external interrupt pins (assuming I will need to send a digital signal not an analog to do that)

My testing code to get it to simply light up the pin 13 led when it is blocked is

int sensor =20;
int LED = 13;
 
void setup()
{
  pinMode(LED, OUTPUT);
  pinMode(sensor, INPUT);
  
  attachInterrupt(3, counter, RISING);
  
}

void loop()
{

   digitalWrite(LED, LOW);
   
}

void counter()
{
  digitalWrite(LED, HIGH);
}
2

You should be able to use it as an i/p on a interrupt pin.
I do not have a Mega, only a uno.
There are two interrupts on a uno 0 and 1 which are pins 2 ans 3.
Make sure the pins on your mega are interrupt pins and it is wired properly.

3

So i have changed it up to

int ledPin = 13;                // LED connected to digital pin 13
int photoPin = 3;               // 
int val = 0;
int count=0;

void setup()                    // run once, when the sketch starts
{
 pinMode(ledPin, OUTPUT);      // sets the digital pin as output
 pinMode(photoPin, INPUT);  
 
 attachInterrupt(1, counting, RISING);
}

void loop()                     // run over and over again
{
 val = digitalRead(photoPin);
 if (val==LOW)
 {
   digitalWrite(ledPin, LOW);
 }
 else
 {
   digitalWrite(ledPin, HIGH);
 }
}

void counting()
{
  count=count+1;
  Serial.print(count);
}

It can digitally read the sensor but I can't get anything inside the interrupt loop to work. Any ideas?

4

You cannot do Serial.print inside a interrupt routine.
Set a flag, then in loop if the flag is set do your printing then reset the flag.