void setup() {
  Serial.begin(9600); // Initialize serial communication at 9600 baud
  pinMode(LED_BUILTIN, OUTPUT); // Example: set an LED pin as output
  Serial.println("Hello!");
}
void loop() {
  // Serial.println("Hello!");
  if (Serial.available() > 0) {
    char command = Serial.read(); // Read a single character command
    if (command == 'H') {
      digitalWrite(LED_BUILTIN, HIGH); // Turn LED on
      Serial.println("LED ON");
    } else if (command == 'L') {
      digitalWrite(LED_BUILTIN, LOW); // Turn LED off
      Serial.println("LED OFF");
    }
  }
}