void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
  Serial.begin(9600);
}
void loop() {
  String readString;
  String Q;

  
  if (Serial.available() > 0) {
//    int state = Serial.read();
    char c = Serial.read();
    if (c == '0') {
      digitalWrite(LED_BUILTIN, HIGH);
      Serial.println("LED OFF");
    }
    
    if (c == '1' ) {
      digitalWrite(LED_BUILTIN, LOW);
      Serial.println("LED ON");
    }
  }
  delay(50);
}