String comdata = ""; void setup() { Serial.begin(9600); while(Serial.read()>= 0){} //clear serialbuffer pinMode(13, OUTPUT); } // the loop function runs over and over again forever void loop() { if(Serial.available()>0){ delay(1); comdata = Serial.readString(); // Serial.print("Serial.readString:"); // Serial.println(comdata); if(comdata=="1") { Serial.println("ok"); digitalWrite(13, LOW); delay(1); digitalWrite(13, HIGH); delay(1);digitalWrite(13, LOW); } } comdata = ""; }