int ledPin = 11 ; // a LED int interruptPin=2; // a presence sensor #define interruptOffset 2 void setup() { Serial.begin(9600); Serial.print("setting up"); pinMode(ledPin, OUTPUT); pinMode(interruptPin, INPUT); attachInterrupt(interruptPin-interruptOffset, presence, CHANGE); // can be LOW, RISING, FALLING, CHANGE // if it is LOW, the interrupt will keep coming as long as the pin is on LOW } void loop() { } void presence(){ Serial.println(digitalRead(interruptPin)); digitalWrite(ledPin, !digitalRead(interruptPin)); }