// This example shows how to work with external interrupts.
// Wiring supports external interrupts 0-7, which are
// triggered by digital i/o pins 0-3 and 36-39. Arduino
// supports external interrupts on pins 2 and 3.

int n = 0;                     // number of interrupts counted


void setup() { 
  Serial.begin(9600);          // start serial communication
  pinMode(39, INPUT);          // make pin 39 an input pin
  
  // attach routine myRoutine() to ext interrupt 7, and
  // generate it when the associated pin (39) falls from
  // HIGH to LOW. Alternatives are LOW, CHANGE, RISING.
  attachInterrupt(7, myRoutine, FALLING);
}


void loop() {
  Serial.println(n);           // print current value of n
  delay(200);
}


void myRoutine() {
  n++;                         // count this interrupt
}