int buttonPin =  7;
int buttonState = HIGH; 
int lastButtonState = HIGH ;

int ledState = LOW ;
int ledPin = 3;

void setup() {
  Serial.begin(115200);

  pinMode(buttonPin, INPUT_PULLUP);
  pinMode(ledPin, OUTPUT);

  // controle of LED goed is aangesloten
  digitalWrite(ledPin, HIGH);
  delay(1000);
  digitalWrite(ledPin, LOW);

}

void loop() {

  buttonState = digitalRead(buttonPin);
  //Serial.println(buttonState);

  if (buttonState != lastButtonState) 
  {
    // ontdender vertraging
    delay(20);
    // knop is veranderd
    Serial.println(F("knop veranderd"));
    // onthoud laatste state
    lastButtonState = buttonState;

    // als de knop is ingedrukt
    if(buttonState == LOW)
    {
      Serial.println(F("knop nu ingedrukt"));
      if(ledState == HIGH)
      {
        ledState = LOW; 
      }
      else
      {
        ledState = HIGH;
      }
      digitalWrite(ledPin, ledState); // schakel LED om
    }
    else
    {
      Serial.println(F("knop losgelaten"));
    }
  }
}