/* Program 6-3: Counting Pulses
* External pulses from pin 13 are fed to pin 3 (interrupt 2) of Arduino
* the ISR counts up pulses and displays them on the Serial Monitor
*/
volatile int count = LOW;		

void setup() {
  pinMode(13, OUTPUT);    /* set pin 13 as output, for generating pulses */
  pinMode(3, INPUT);  //make pin3 interrupt as input, pin 13 pulses are fed to pin3
  Serial.begin(9600); 
  attachInterrupt(digitalPinToInterrupt(3), PulseCounterISR, RISING);
}

void loop() {
    digitalWrite(13,HIGH);  /* turn on the LED */
    delay(750);             /* delay 750 ms */
    digitalWrite(13,LOW);   /* turn off the LED */
    delay(750);             /* delay 750 ms */

   
}

//Interrupt Service Routine
void PulseCounterISR() {
  count++;              //count up pulses
  Serial.println(count);     // Display pulse counts on Serial Monitor      
}