Issue with SIM800l


I'm trying to make a communication between Arduino Uno and a SIM800l.
My shield can be connected to 5V so I've connected it to a PC power supply, assuring the 2A current.

The problem is when I receive the information from SIM800l before sending a command like "AT", the only responses I have are strange characters like "á" or "ÿ". I've tried it with software serial ports and hardware ports on an Arduino Mega too. The baud rate is configured at 9600.

Any idea?


Hello @hambert
Look for the baudrate set in the Serial Monitor, it should matches with the baudrate in the code.

Thank you for the response.

The Serial Monitor baud rate matches with both Software Serial and hardware Serial in the code.
Here is the code I´m using

#include <SoftwareSerial.h>
//Creo un puerto de serie Software ya que el hardware lo tengo ocupado
SoftwareSerial sim800l(3,4);
void setup() {
  //Se inicializa la comunicacion del puerto de serie de Arduino para mostrar los mensajes
  sim800l.begin(9600);//El modulo sim800l tiene una velocidad de 9600bps
void loop() {
  if(sim800l.available()){    //Si el sim800l en el puerto de serie software esta disponible, mostrar en el puerto de serie de arduino lo que envíe el sim800l
  if(Serial.available()){    //Enviar al sim800l lo que se lea del puerto serie hardware


Finally it´s solved.

I thinks that there was a problem with the shield syncronization, I tried all possible baud rates, and finally I tried to put a different baud rate value, and after some attemps, it worked at 113000