const int ledPin = 13;  // LED connected to digital pin 13

void setup() {
  pinMode(ledPin, OUTPUT);   
  Serial.begin(9600);        
  Serial.println("Enter 'ON' to turn the LED on, or 'OFF' to turn it off.");
}

void loop() {
  if (Serial.available() > 0) {
    String command = Serial.readStringUntil('\n');  
    command.trim();  

    if (command.equalsIgnoreCase("ON")) {
      digitalWrite(ledPin, HIGH);  
      Serial.println("LED is now ON.");
    } 
    else if (command.equalsIgnoreCase("OFF")) {
      digitalWrite(ledPin, LOW);  
      Serial.println("LED is now OFF.");
    } 
    else {
      Serial.println("Invalid command. Please type 'ON' or 'OFF'.");
    }
  }
}