String readString; int baz = 5 ; void setup() { Serial.begin(9600); pinMode ( baz , OUTPUT ); } void loop() { while (Serial.available()) { delay(50); char c = Serial.read(); readString += c; } if (readString.length() > 0) { Serial.println(readString); if (readString == "R") { digitalWrite ( baz , HIGH ) ; } readString = ""; } }