Interrupt example - The AVR way

gistfile1.c

/**
Interrupt example - The AVR way
For use with Arduino UNO and other 328 Arduino's
- Connect a button to pin 2 (with 10k pulldown)
- Connect a LED to pin 9 (with 220/330 Ohm resistor)

Nov 2013, Jens Brynildsen http://flashgamer.com/arduino/
**/

#include <avr/io.h>
#include <avr/interrupt.h>

byte ledPin = 9;

void setup(void)
{
  Serial.begin( 9600 );
  pinMode(2, INPUT);
  digitalWrite(2, HIGH);    // Enable pullup resistor
  pinMode(13, OUTPUT);
  digitalWrite(13, LOW);
  
  EICRA |= (1 << ISC01);    // Trigger on falling edge
  EIMSK |= (1 << INT0);     // Enable external interrupt INT0
  sei();                    // Enable global interrupts
}

// Interrupt Service Routine attached to INT0 vector
ISR(INT0_vect)
{
  digitalWrite(13, !digitalRead(13));    // Toggle LED on pin 13
  Serial.println("Interrupted!");
}

void loop(void)
{
  // fade in from min to max in increments of 5 points:
  for(int fadeValue = 0 ; fadeValue <= 255; fadeValue +=5) {
    // sets the value (range from 0 to 255):
    analogWrite(ledPin, fadeValue);
    // wait for 30 milliseconds to see the dimming effect
    delay(30);
  }

  // fade out from max to min in increments of 5 points:
  for(int fadeValue = 255 ; fadeValue >= 0; fadeValue -=5){
    // sets the value (range from 0 to 255):
    analogWrite(ledPin, fadeValue);
    // wait for 30 milliseconds to see the dimming effect
    delay(30);
  }
}