SIM800L - AT Commands not doing anything on Arduino Serial Monitor

Question

I am trying to send AT commands to SIM800L through Arduino's Serial Monitor. However when I type any command in the serial monitor nothing happens. I'm using an Arduino MEGA 2560 and the TX/RX of the SIM800L is connected to 9 and 10 respectively. Here is the code:

#include <SoftwareSerial.h>
SoftwareSerial GPRS(9, 10);
boolean state, lastState;
void setup()
{
 pinMode(2, INPUT_PULLUP);
 state = digitalRead(2);
 lastState = state;
 GPRS.begin(9600);
 Serial.begin(9600);
 GPRS.println("AT+CMGF=1");
 delay(1000);
}
void loop()
{
 while(GPRS.available()) {
 Serial.write(GPRS.read());
 }
 lastState = state;
 state = digitalRead(2);
 if ( state != lastState ) {
 sendSMS();
 }
 delay(500);
}
void sendSMS() {
 Serial.print("Switch was turned ");
 Serial.println(state ? "on" : "off");
 GPRS.println("AT+CMGS=\"+64XXXXXXXXX\"");
 delay(500);
 GPRS.print("Switch was turned ");
 GPRS.println(state ? "on" : "off");
 GPRS.write( 0x1a ); // ctrl+Z character
 delay(500);
}

Any help would be much appreciated!

EDIT2: I forgot to mention but I am able to send, receive, and call from the GSM Module (with a different code). However I am not able to read the the received messages, since I only get a +CMT "SM", message and I can't exactly use AT+CMGR or CMGL commands because the serial monitor does nothing with them. here's the code for that:

#include <SoftwareSerial.h>
SoftwareSerial sim(9,10);
int _timeout;
String _buffer;
String number = "+639XXXXXXXXX"; //-> change with your number
void setup() {
 delay(1000); //delay for 7 seconds to make sure the modules get the signal
 Serial.begin(9600);
 _buffer.reserve(50);
 Serial.println("Lets go!");
 sim.begin(9600);
 delay(1000);
 Serial.println("Type s to send an SMS, r to receive an SMS, and c to make a call");
}
void loop() {
 if (Serial.available() > 0)
 switch (Serial.read())
 {
 case 's':
 SendMessage();
 break;
 case 'r':
 RecieveMessage();
 break;
 case 'c':
 callNumber();
 break;
 }
 if (sim.available() > 0)
 Serial.write(sim.read());
}
void SendMessage()
{
 Serial.println ("Sending Message");
 sim.println("AT+CMGF=1"); //Sets the GSM Module in Text Mode
 delay(1000);
 Serial.println ("Set SMS Number");
 sim.println("AT+CMGS=\"" + number + "\"\r"); //Mobile phone number to send message
 delay(1000);
 String SMS = "Wala kang jowa!";
 sim.println(SMS);
 delay(100);
 sim.println((char)26);// ASCII code of CTRL+Z
 delay(1000);
 _buffer = _readSerial();
}
void RecieveMessage()
{
 Serial.println ("SIM800L Read an SMS");
 delay (1000);
 sim.println("AT+CNMI=2,2,0,0,0"); // AT Command to receive a live SMS
 delay(1000);
 Serial.write ("Unread Message done");
}
String _readSerial() {
 _timeout = 0;
 while (!sim.available() && _timeout < 12000 )
 {
 delay(13);
 _timeout++;
 }
 if (sim.available()) {
 return sim.readString();
 }
}
void callNumber() {
 sim.print (F("ATD"));
 sim.print (number);
 sim.print (F(";\r\n"));
 _buffer = _readSerial();
 Serial.println(_buffer);
}

• jsotola: when I type any command in the serial monitor nothing happens ... you don't have any code for that
• YMSmash: @jsotola i thought it would take any AT commands automatically in the serial monitor? anyway i'll add my code that i used where i could send/receive/call the phone but not read any messages i receive
• jsotola: the arduino will not do something on its own ... try this code ... arduino.cc/en/Tutorial/SoftwareSerialExample
• Majenko: Why are you using SoftwareSerial on a Mega?!?!

Answer 1

Do not use SoftwareSerial on a Mega2560 unless you absolutely know what you are doing.

SoftwareSerial does not work on many of the pins of the Mega2560, and since there are other hardware serial ports available there is seldom any reason to resort to using SoftwareSerial anyway.

Connect your SIM800L to the TX1/RX1 pins of the Mega2560 then communicate using the pre-defined Serial1 object.

• YMSmash: I see. I looked up some stuff regarding my question on other posts and almost everyone says to not use SoftwareSerial with Mega2560. Althought tbh I still don't completely understand what to do. Do I simply remove everything related to SoftwareSerial? How do I use the hardware serial ports; do I still need to code them in like in software serial or can i just connect the SIM800L to the TX1/RX1 without worrying about anything else? Dumb questions I know, but I've been out of touch with Arduino for over a year no so please bear with me...
• Majenko: Of course you have to code them in. You read with Serial1.read() and write with Serial1.print(...) in the exact same way as any other form of serial communication. You can't just plug random things in and expect the Arduino to magically know what they are and how to work with them.
• YMSmash: i guess what i really wanted to ask there was whether i needed to include another library like software serial. so basically i dont have to use any libraries now, right? What I still don't understand is that everyone seems to be using SoftwareSerial <GSM name>(<TX>,<RX>) to connect their GSM modules to their Arduino, regardless of whether it's an UNO or a Mega. If I'm not supposed to use SoftwareSerial, what should I be replacing that with? Or am I missing something completely here?
• Majenko: No libraries needed. Nothing to define. Serial1 is already defined for you. Just use Serial1.print() and Serial1.read() where you use sim.print() and sim.read() and so forth.
• YMSmash: oh so i can just do something like sim(<TX>,<RX>) without anything before it and then it's already defined as Serial1?

Answer 2

1. Make sure the RX of your arduino board is connected to TX of GSM and the TX should be connected in RX of GSM module.
2. Next try to do this

 GPRS.begin(9600); 
 Serial.begin(115200);

3. Also double check your wirings, if you have a tester you might wanna check if both end are connected with each other. And in the loop try to print this Serial.println(GPRS.available()) if it is not greater than 0 then you have a problem with your connection.

 #include <SoftwareSerial.h>
 SoftwareSerial sim(2,3); 
 
 void setup() {
 // put your setup code here, to run once:
 Serial.begin(115200);
 sim.begin(9600);
 }
 
 void loop() {
 // put your main code here, to run repeatedly:
 while(Serial.available() > 0){
 sim.write(Serial.read());
 }
 
 while(sim.available() > 0){
 Serial.write(sim.read());
 }
 }

diagram reference. enter image description here

Hope this help.

• Juraj: why would you wire it to RX/TX of the Mega and what is the GPRS object in your answer?
• homerio: Where did I get the GPRS? from his code. well actually just follow my supper simple diagram from the link bellow for you to understand imageup.me/images/a49982fe-c592-44d7-b696-ed80e725fec5.png and follow my supper simple code for you again to understand. :-) #include <SoftwareSerial.h> SoftwareSerial sim(2,3); void setup() { Serial.begin(115200); sim.begin(9600); } void loop() { while(Serial.available() > 0){ sim.write(Serial.read()); } while(sim.available() > 0){ Serial.write(sim.read()); } }
• Nick Gammon: @homerio Your link gives "Oops! An unhandled exception occurred while processing the request.".
• Nick Gammon: @homerio Comments are not for posting images and code. Please amend your answer to make it clearer.
• Nick Gammon: Follow this link also for the diagram reference - you can embed images into answers. That is better because external links can become link-dead.