int led = 13;

void setup() {
  // put your setup code here, to run once:
  pinMode(led, OUTPUT);
    Serial.begin(9600);

  
}

void loop() {
  if (Serial.read() == 'N') {
     digitalWrite(led, HIGH);
  }else if(Serial.read() == 'F') {
     digitalWrite(led, LOW);
  }

  
 }