interrupts_basic.ino

const int buttonPin = 2;
const int ledPin = 9;

volatile int countdown = 0;

void setup() {
  // put your setup code here, to run once:

  pinMode(buttonPin, INPUT_PULLUP);
  pinMode(ledPin, OUTPUT);
  
  attachInterrupt(digitalPinToInterrupt(2), setState, FALLING); 
}

void loop() {
  analogWrite(ledPin, countdown);
  countdown = max(countdown-10, 0);
  delay(100);
}

void setState(){
  countdown = 255;
}