interrupts_serial_debounce.ino

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

volatile int count = 0;

volatile long lastIncrement = 1;
const long minButtonPressTime = 100;

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

  pinMode(buttonPin, INPUT_PULLUP);
  Serial.begin(38400);
  
  attachInterrupt(digitalPinToInterrupt(2), setState, FALLING); 
}

void loop() {
  Serial.println(count);
  delay(1000);
}

void setState(){
  if (millis() > lastIncrement + minButtonPressTime){
    lastIncrement = millis();
    count++;
  }
}