#include <SoftwareSerial.h>

#define RX    0   // 
#define TX    1   // 
SoftwareSerial Serial(RX, TX);
int led = 7;
int val = 0;

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

}

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