Как отправить сообщение из openHab на Arduino serial COM port?

String readString;
  
  void setup() {
    Serial.begin(9600);
    Serial.println("serial test 0021"); // so I can keep track of what is loaded
  }
       

  void loop() {
    while(Serial.available()) {
      delay(10);  
      char c = (char)Serial.read();
      readString += c;
    }
       
     if (readString.length() > 0) {
       Serial.println(readString);
       readString="";
     }
  }