#include <SoftwareSerial.h>
    SoftwareSerial monserial(0, 1);//rx and tx

const int ledPin = 7;
char command; 

void setup() {
  pinMode(ledPin, OUTPUT);
  monserial.begin(9600);
}

void loop() {
  if (monserial.available() > 0) {
    command = monserial.read();
    if (command == 'H') {
      digitalWrite(ledPin, HIGH);
      monserial.write("LED encendido\r\n");
    }
    else if (command == 'L') {
      digitalWrite(ledPin, LOW);
      monserial.write("LED apagado\r\n");
    }
  }
}