unsigned char c;

void setup(){
  Serial.begin(9600);
}

void loop(){
  if(Serial.available() >0){
    c=Serial.read();
    Serial.write(c);
  }
}

unsigned char c;

void setup(){
  Serial.begin(9600);
  pinMode(13, OUTPUT);
}

void loop(){
  if(Serial.available() >0){
    c=Serial.read();

    if(c == '1') {
      digitalWrite(13, HIGH); 
      Serial.println("LED ON");
    }
    else if(c == '0') {
      digitalWrite(13, LOW);
      Serial.println("LED OFF");
    }
  }
}