#6.3.3. LED

const int ledPin = 13;

char receivedChar;

void setup() {

  pinMode(ledPin, OUTPUT);

  Serial.begin(9600);

}

void loop() {

  if (Serial.available()) {

    receivedChar = Serial.read();

    if (receivedChar == 'o') {

      digitalWrite(ledPin, HIGH);

      Serial.println("LED ON");

    } 

    else if (receivedChar == 'f') {

      digitalWrite(ledPin, LOW);

      Serial.println("LED OFF");

    }

  }

}