void setup() {
  Serial.begin(9600);
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
    if (Serial.available ()> 0) { 
    char ch = Serial.read ();
    if (ch == '0') {
      digitalWrite(LED_BUILTIN, LOW); 
    }
    else if (ch == '1') {
      digitalWrite(LED_BUILTIN, HIGH);
    }
  }
}