My purpose was to send SMS using GSM SIM800L coreboard and Arduino UNO. Here is the code

    #include <SoftwareSerial.h>

//Create a software serial object to communicate with SIM800L
SoftwareSerial mySerial(3, 2); //SIM800L Tx & Rx is connected to Arduino #3 & #2

void setup()
  //Begin serial communication with Arduino and Arduino IDE (Serial Monitor)

  //Begin serial communication with Arduino and SIM800L


  mySerial.println("AT"); //Once the handshake test is successful, it will back to OK

  mySerial.println("AT+CMGF=1"); // Configuring TEXT mode
  mySerial.println("AT+CMGS=\"+ZZxxxxxxxxx\"");//change ZZ with country code and xxxxxxxxxxx with phone number to sms
  mySerial.print("TEST"); //text content

void loop()

void updateSerial()
  while (Serial.available()) 
    mySerial.write(Serial.read());//Forward what Serial received to Software Serial Port
    Serial.write(mySerial.read());//Forward what Software Serial received to Serial Port

And here is the serial monitor output

 22:31:19.430 -> Initializing...

However, when I run the code, I get the text message to my mobile phone, but I can't see any AT commands in the serial monitor. It only outputs "Initializing..." . All the connections and baud rates are okay, checked a thousand times. Has connected 2A, 4.4v power supply to the GSM coreboard and shorten the wires, and sho No bad soldering joints. GSM module red led flash per 3 seconds. And again, I'm getting the text message to my phone. So that means the problem is with the Arduino serial monitor or code, not in the hardware. I need to see AT commands because I need to put more commands through the serial monitor, I tried typing and click send, But it's not showing anything. Any assistance you can provide would be greatly appreciated.

  • 1
    have tried a lower baud rate? ... that is one of the first things to try when debugging serial comm – jsotola May 14 at 20:32
  • Yes, I have tried many baud rates, 4800, 9600, also higher baud rates – Udara Sampath May 15 at 4:41

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