void setup() {
  Serial.begin(115200);
  pinMode(12, OUTPUT); 
  Serial.println("Ca commenence!");
}

void loop() {
  if (Serial.available()) {
    String message = Serial.readStringUntil('\n');
    if (message == "LED_ON") {
      digitalWrite(12, HIGH);
    } else if (message == "LED_OFF") {
      digitalWrite(12, LOW);
    } else {
      Serial.print("Message:");Serial.println(message);
    }
  }
}