UNO

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

void loop() {
  if(Serial.available()){
    char c = Serial.read();
    if (c == 1) {
      digitalWrite(led,HIGH);
    } else if (c == 2){
      digitalWrite(led, LOW);
    }
  }
}