const byte myLED_pin = 2;

unsigned long myBlinkTimer;
byte myCounter = 0;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  Serial.println("Hello, I am the ESP32!");
  pinMode(myLED_pin, OUTPUT);
  digitalWrite(myLED_pin, LOW);
  myBlinkTimer = millis();
}


// ! ist der Not-Operator
// ! LOW = HIGH
// ! HIGH = LOW   => dreht den Schaltzustand um
// ! digitalRead(myLED_pin)    = NOT Schaltzustand von myLED_pin
// aus myLED_pin = LOW wird HIGH
// aus myLED_pin = HIGH wird LOW ==> blinken


void loop() {
  if ( TimePeriodIsOver(myBlinkTimer,250) ) {
    digitalWrite( myLED_pin,  ! digitalRead(myLED_pin) );

    Serial.print(digitalRead(myLED_pin));
    myCounter++;

    if(myCounter > 10) {
      myCounter = 0;
      Serial.println();
    }
  }
}

// nicht blockierendes Timing ist 1000 mal besser als delay()
boolean TimePeriodIsOver (unsigned long &startOfPeriod, unsigned long TimePeriod) {
  unsigned long currentMillis  = millis();
  if ( currentMillis - startOfPeriod >= TimePeriod ) {
    // more time than TimePeriod has elapsed since last time if-condition was true
    startOfPeriod = currentMillis; // a new period starts right here so set new starttime
    return true;
  }
  else return false;            // actual TimePeriod is NOT yet over
}