SIM800L GSM Module with Arduino | AT Commands | Library

Sharath · September 4, 2018

SIM800L GSM Module with Arduino | AT Commands | Library

By Sharath Arduino AT Commands, GSM Module, SIM800L, Sim800l library 35 Comments Like: 0

SIM800L Module is a small GSM/GPRS Module and ideal for small ideal projects. The module supports quad-band GSM/GPRS network, available for SMS and GPRS message data remote transmission. SIM800L is advanced than its previous SIM900 modules.

There are other multiple versions of SIM800 is available. The choices of models depend upon the application needs. But SIM800L is used widely for common applications. The features of different models are given below.

SIM800L has FM functionality.
SIM800C has Bluetooth functionality.
SIM800F is pin compatible to the SIM900 module.
SIM868 is dual sim version with GNSS and small form factor.

The AT Commands are mostly the same for all GSM Modules based on SIMCOM AT Commands except its additional features like Bluetooth, FM will vary. Refer the datasheet for more details.

The SIM800L can work up to 2 Amps current at peak. It also has a low power consumption feature that consumes 1mA Current in sleep mode. You need to power the module from 3.7V to 4.4V as per the datasheet. More than that will damage the module. You can use a buck converter like LM2596 to achieve this voltage and current range.

Features:

2G Quad-band 850/900/1800/1900MHz
Receive and make calls using the speaker and microphone outputs
Receive and send SMS
Listen to FM radio broadcasts
GPRS multi-slot class12 connectivity: max. 85.6kbps(download/upload)
GPRS mobile station class B
Controlled by AT Command (3GPP TS 27.007, 27.005 and SIMCOM enhanced AT Commands)
Supports Real Time Clock
Operating Voltage range 3.4V ~ 4.4V
Supports A-GPS
Low power consumption, 1mA in sleep mode
Micro SIM Card Support

LED Blinking status:

If the power to the SIM800L is enough, the onboard LED starts blinking according to its operation. If the power is not enough it will receive poor signal and search for network all the time (if still searching adjust the trimpot slightly but do not exceed much than 4.7v). The frequency of the blinking denotes the following:

Every second: searching for a network.
Every three seconds: connected to a network.
Twice per second: connected through GPRS.

Note: The SIM800L accepts only 2G (No 4G)

In this tutorial, we will see how to use SIM800L GSM module with an Arduino.

Pin Details:

At the backside of the module, you can find the pin details printed on it. We will be using 5 Pins to connect with Arduino for basic operation. They are

NET – Antenna pin for the module (Spring Type included). You can use an external antenna via an uFL Connector available on the module for a better signal reception.

VCC – Power supply 3.4V to 4.4V with min 2 Amp. (LM2596 with a 9/12V 1Amp adapter input and it should be adjusted to 4.2V recommended).

RST – Reset

RXD – Receiver to the module – 3.3V Logic (To be connected to Arduino TX Pin. Voltage divider recommended).

TXD – Transmitter from the module (To be connected to Arduino RX Pin).

GND – Ground.

Circuit Diagram:

Before making connections, make sure the LM2596 output is set to 4.4V by adjusting the potentiometer on the LM2596 module. You can use a Multi-meter to check the voltage (or) you can use the LM2596 Module with Display. As we know the SIM800L accepts 3.6V – 4.4V and 2Amps, the SIM800L module can draw much current as needed from the LM2596 with a fixed voltage.

The RX Pin of SIM800L Module Should connects to TX Pin of the Arduino. Similarly, the TX Pin of SIM800L should connect to RX Pin of Arduino. In simple logic, a receiver can receive some data only if it is transmitted from somewhere. Similarly for the transmitter side, when some data is sent, the other should receive it to make use of it.

Note: For long time use a voltage divider is recommended as the TX & RX Pins of SIM800L is 3.3V Logic level. We only need a voltage divider at the RX Pin of SIM800L. Because a 3.3v from SIM800L can be able to handle by a 5V Arduino Pin (TX) (probably a lesser voltage, but it takes even a 2.7v as a high signal).

Voltage Divider for 5V to 3.3V is

Vin = Arduino’s TX = 5V

Vout = SIM800L’s RX = 3.3V

R1 = 1.7K Ohm

R2 = 3.3K Ohm

Alternatively, you can use this Bi-Directional Level Shifter.

Simple Code to send AT Commands and display data from GSM Module on Serial Monitor:

The following code will read the GSM data via Software Serial and print it on Serial Monitor. Similarly, it sends the user entered string from Serial Monitor to the GSM Module.

#include <SoftwareSerial.h>

String tempSerial, tempGSM;

SoftwareSerial gsm(10, 11); // RX, TX of Arduino



void setup() {



  Serial.begin(9600); //Set Serial Monitor Baudrate

  Serial.println("SIM800L Test");

  gsm.begin(4800); // Set GSM Baudrate



}



void loop() {



//Read from GSM and Print on Serial Monitor

  if(gsm.available())

  {

    tempGSM = gsm.readString(); // Read from GSM and Store it in this variable.

    Serial.println(tempGSM);    //Print the string from GSM to Serial Monitor.

  }



//Write to GSM from user given Serial Monitor Inputs(AT Commands)

  if(Serial.available())

  {

    tempSerial = Serial.readString(); //Read from Serial Monitor and store it in this variable.

    gsm.println(tempSerial);   //Send the Serial Monitor Strings(AT Commands) to GSM.

  }

}

By using the serial monitor, we send AT Commands to the GSM Module to perform various functions. But we will see few AT commands in this tutorial. You can refer the AT Commands datasheet for various AT Commands.

AT

If you send this, the GSM Module will reply ‘OK’. This means the GSM Module is communicating with Arduino.

ATD 98XXXXXXXX;

This command is used to dial a number. You need to add a semicolon (;) after this command. The syntax is ATD<space><mobilenumber>;

SMS Function:

To send or read SMS from the module we need to set the module to SMS mode and then use the AT Commands for SMS.

To set the GSM Module in SMS mode, use the following code.

AT+CMGF=1

Once it returns OK, then use the second command to read the SMS.

AT+CMGR=1

To Send an SMS, set the GSM Modem to SMS mode using ‘AT+CMGF=1’ and then use the following command.

AT+CMGS="98XXXXXXXX"

The modem will return an arrow to enter the message (>). Type the message and hit enter.

Note: To exit from SMS Mode we need to send ‘Ctrl+Z’ in ASCII Form. So after the SMS functions finished we need to send ’26’ to get back to normal mode. The ’26’ is the ASCII Character for ‘Ctrl+Z’.

Syntax to send the ASCII Character to GSM:

gsm.println((char)26);// 26 is ASCII code of CTRL+Z

How to use SIM800L Library?

To simplify the operation, there is a library available on GitHub to use SIM800L GSM module. You can download the SIM800L Library zip file and install it on your Arduino IDE. Once downloaded you can open File>Examples>SIM800L and upload the code. In this library, the Software Serial pins are assigned to 10(RX), 11(TX) and 2 (RST) of Arduino by default. You can modify it on the library if you want.

Sample Code to send SMS using SIM800L Library:

/*   

 *    PINOUT:

 *        _____________________________

 *       |  ARDUINO UNO >>>   SIM800L  |

 *        -----------------------------

 *            GND      >>>   GND

 *        RX  10       >>>   TX   

 *        TX  11       >>>   RX

 *       RESET 2       >>>   RST

 *                

 *   POWER SOURCE 4.2V >>> VCC

*/



#include <Sim800l.h>

#include <SoftwareSerial.h> //is necesary for the library!!

Sim800l gsmModule;  //to declare the library



void setup(){

                gsmModule.begin(); // initializate the library.

                gsmModule.sendSms("+91XXXXXXXXXX","the text go here"); // (Mobile Number, Text to be sent).



}



void loop(){

                //do nothing

}

We write the code only at the setup loop because it needs to be sent only once. Upload the code and you can receive the SMS on the number you entered on the code.

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SIM800L GSM Module with Arduino | AT Commands | Library