3keer kloppen = bellen

int pin = A0;
int x = 0;
int klop = 1;
unsigned long duration;
unsigned long previousMillis ;
unsigned long currentMillis ;
unsigned long kloptijd1 ;
//unsigned long kloptijd3 ;
void setup()
{
  Serial.begin(115200);
  pinMode(pin, INPUT);
  pinMode(11, OUTPUT); //buzzer
  pinMode(2, OUTPUT);
  pinMode(3, OUTPUT);
  pinMode(4, OUTPUT);

  kloptijd1  = millis();
}
void loop()
{
  duration = pulseIn(pin, HIGH);

  if (((unsigned long)(millis() - kloptijd1) >= 1000)  )
  {
    unsigned long verschil = millis() - kloptijd1;
    digitalWrite(2, LOW);
    digitalWrite(3, LOW);
    digitalWrite(4, LOW);
    Serial.println("timeout " +  String(verschil));
    klop = 1; //reset teller
    Serial.println (kloptijd1);
  }




  if (duration > 0)
  {
    currentMillis = millis();
  }
  // Serial.println (x++);
  // How much time has passed, accounting for rollover with subtraction!
  if ((unsigned long)(currentMillis - previousMillis) >= 300) {
    // antidender , we komen hier niet rap direkt terug
    digitalWrite(2, HIGH);
    Serial.print  ("              klop :  ");
    Serial.println (klop++);
    //laatste geziene klop , om :
    kloptijd1 = millis();
    Serial.print  ("laatste klop om  :  ");
    Serial.println (kloptijd1);


    if (klop == 2) {
      digitalWrite(2, HIGH);
      // digitalWrite(3, HIGH);
      // digitalWrite(4, HIGH);
      // Serial.print  ("    DING DONG :  ");
      // klop = 1; //reset teller
    }


    if (klop == 3) {
      digitalWrite(2, HIGH);
      digitalWrite(3, HIGH);
      // digitalWrite(4, HIGH);
      // Serial.print  ("    DING DONG :  ");
      // klop = 1; //reset teller
    }




    if (klop == 4) {
      digitalWrite(2, HIGH);
      digitalWrite(3, HIGH);
      digitalWrite(4, HIGH);
      Serial.println  ("    DING DONG :  ");
      klop = 1; //reset teller



      for (int x = 1; x <= 3; x++)
      {
        analogWrite(11, 255);
        delay(600);

        analogWrite(11, 0);
        delay(50);
      }




    }




    // Use the snapshot to set track time until next event
    previousMillis = currentMillis;
  }









}