gistfile1.ino

// This sketch demonstrates INPUT_ PULLUP and Interrupts
int ledPin = 7;
volatile boolean flashy = false;   //necessary declaration for passing adjusting global variables with interrupts

void setup()
{
  pinMode(ledPin, OUTPUT);
  pinMode(2, INPUT_PULLUP);
  attachInterrupt(0, interruption, FALLING);    //attaches interrupt to Digital 2 with internal pull-up resistor
}

void loop()
{
  int period = 5000;
  if (flashy) period = 50;
  digitalWrite(ledPin, HIGH);
  delay(period);
  digitalWrite(ledPin, LOW);
  delay(period);
}

void interruption()      //interrupt function
{
  flashy = ! flashy;
}