How to interface GSM/GPRS Shield (SIM900A/SIM900/SIM800) To an Arduino

Introducing rhydoLABZ GSM/GPRS Shield, an all-in-one cellular shield that lets you add voice, text/SMS, data and bluetooth^* connectivity to your arduino project in an easy to use pluggable shield. This cellular shield from rhydoLABZ is available as three different variants, built with different cellular engines (SIM900, SIM900A and SIM800). All of these are identical in features except that the SIM900 and the SIM800 are quadband versions (operates in 850/900/1800/1900 MHz), while SIM900A is the dualband version (operates in 900/1800 MHz) . And additionally SIM800 has an added features, bluetooth connectivity. All the three variants are pretty much identical in its formfactor and design. These fits on top of any classic Arduino or compatible, and packs a surprising amount of technology into it’s little frame.

The GSM/GPRS Modem is having internal TCP/IP stack to enable you to connect with internet via GPRS. The shield is manufactured with Automatic Pick and place machine to meet the high quality standards. On its own, this shield can’t do anything. It requires a microcontroller like an Arduino to drive it! Additionally a SIM Card with cellular connectivity! The shield can be powered either via Arduino or directly over RMC connector. It comes presoldered with 3.5mm jack for audio out as well as mic in. You can grab some stacking headers from our store, if you would like to stack a shield on top.

Features

AT command interface
Quad-band and Dual-band variants*
Make and receive voice calls
Send and receive SMS messages
Send and receive GPRS data (TCP/IP, HTTP, etc.)
Bluetooth: compliant with 3.0+EDR*
USB Connector for Firmware Updation*
Configurable Baud rate (9600-115200, factory default value: 9600)
Standard Audio Jack Connectors for external speaker and mic
Selectable interface between hardware serial port and software serial port
Inbuilt Powerful TCP/IP protocol stack for Internet data transfer over GPRS.
Level shifting circuitry to make it Arduino-safe
SMA Connector with external antenna
Indicator LEDs for Power and connectivity
Standard Flap type SMA Socket
ESD Protection over TVS Zener array
Separate Reset switches for both Arduino and the shield
Slide switch to swap the shield between Arduino and PC
Provision to select between hardware and software serial ports

NOTE: Shield has inbuilt voltage regulation circuitry and reverse polarity protection, allows you to connect wide range unregulated power supply (7V – 12V)

SIM900A, SIM900 & SIM800

SIM800 modules are upgraded version of its previous successful GSM/GPRS/GPRS module series SIM900. There are multiple sub versions of each series, each of which cater to a different set of users and applications. SIM900 comes in the form of full version Quad band SIM900 & dual band version SIM900A. SIM800 itself is the full version Quad band SIM800. There are other SIM800 & SIM900 versions but very less information available about them, so they have not been discussed.

What extra does SIM800 modules give me compared to SIM900 series modules? SIM800 GSM modules have a inbuilt Bluetooth stack, accessible using AT commands.

SIM900 and SIM900A modules operate from 3.2V to 4.8V supply range while SIM800 modem operates from 3.4V to 4.4V supply range (Reduced operating range!). Same AT commands used for simple call/sms functionality in SIM900, SIM900A can be used with the SIM800, but SIM800 series have added AT command set for supporting extra features like bluetooth.

SIM800 module is needed only if you need those additional features that are not present in SIM900 series modules, like the Bluetooth functionality which was missing in SIM900 series. SIM800 and SIM900 can be operated worldwide because they can operate in all four GSM bands used across the world.

Layout

LED Indications

The Network LED indicates the various status of GSM module eg. Power on, Network registration & GPRS connectivity. When the modem is powered up, this NETWORK LED will blink every second. After the Modem registers in the network (takes between 10-60 seconds), this LED will blink in step of 3 seconds. At this stage you can start using Modem for your application,showing that modem is registered with the network.

Connection Interfaces

Jumper Connections

Selecting Hardware Serial / Software Serial for communication

The shield is designed such that the GSM module communicates with Arduino either via Hardware serial / Software pins as selected by J3, J4. By default, the shield comes with Hardware serial communication i.e, the GSM module communicates with Arduino via Hardware serial pins [D0 – RX, D1 – TX]. On the other hand, if J3, J4 are shifted to Software serial side, then the GSM module communicates with Arduino via software serial pins [with D8 configured as software RX and D7 as software TX , Refer the code snippet given below]

PKEY using Arduino

PWRKEY pin of GSM modem is to turn modem On/Off externally using open collector transistor or switch. You can turn on/off the modem alternately by driving the PWRKEY to a low level voltage for a short time (2-3 sec) and then release. This pin is pulled up to 2.9V in the GSM Modem.

In the shield, it is connected to digital pin 9 of Arduino via jumper J10. Shorting the jumper and removing R16 from board enables you to power on /off the modem by Arduino.

RST using Arduino

RST pin of GSM modem is active low. In the shield, it is connected to digital pin 10 of Arduino via jumper J11. Short J11 and make the pin 10 HIGH to reset the modem.

Audio Jacks

The Shield contains two audio stereo jacks on board. The first is the audio input jack (labeled “MIC”). This allows you to input audio from any device such as an MP3 player, or cellular phone using a basic audio cable. The second audio jack is the audio output, labeled “SPEAKER”. This jack allows you to route the audio out to a speaker.

Getting Started

Lets check out on getting started with this shield on Arduino.

Insert an activated SIM Card to the SIM Socket (K5), provided on the bottom side of the shield.
Make sure if the antenna is installed properly
Confirm the Jumper connection for the communication port (Software or Hardware -J3,J4)
Adjust the slide switch as desired (USB – to communicate with the PC directly without an ATmega328 on your Uno, Arduino – to communicate with the ATmega328 on your Uno)
Stack the shield and power up the Arduino

Test your shield

Having familiarized with the shield, now its time to use it for practical applications. What would be the first thing you want to do with it? Send out a text (SMS)? All of these can be done using the AT Commands – mother tongue for cellular modules. These are simple textual commands sent to the modem over its serial interface, which makes it easy to communicate with the modem over any serial terminal software.

Copy the given code and paste it in a new sketch on your Arduino IDE. To run the code, the slide switch should be on the USB side and J3, J4 should be shifted to S-RX & S-TX respectively. Compile and burn it to your Arduino

//Arduino will patch a serial link between the computer and Shield at 9600 bps 8-N-1
//Computer is connected to Hardware UART and the Shield is connected to the Software UART 

#include <SoftwareSerial.h>

SoftwareSerial SimShield(8, 7);           // Shield is connected to Arduino via softwareserial port
unsigned char buffer[64];                 // Buffer array for data recieve over serial port
int count = 0;                            // Counter for buffer array 

void setup()
{
  SimShield.begin(9600);                  // The SimShield baud rate   
  Serial.begin(9600);                     // The Serial port of Arduino baud rate.
}

void loop()
{
  if (SimShield.available())              // If data is coming from softwareserial port ==> data is comming from gprs shield
  {
    while(SimShield.available())          
    {
      buffer[count++] = SimShield.read(); // Writing data into array
      if(count == 64)break;
    }
    Serial.write(buffer,count);           // If no data transmission ends, write buffer to hardware serial port
    clearBufferArray();                   // Call clearBufferArray function to clear the stored data from the array
    count = 0;                            // Set counter of while loop to zero
  }
  if (Serial.available())                 // If data is available on hardwareserial port ==> data is comming from PC or notebook
  SimShield.write(Serial.read());         // Write it to the SimShield shield
}

void clearBufferArray()                   // Function to clear buffer array
{
  for (int i=0; i<count; i++)
  buffer[i] = NULL;                       // Clear all index of array with command NULL
}

//Arduino will patch a serial link between the computer and Shield at 9600 bps 8-N-1

//Computer is connected to Hardware UART and the Shield is connected to the Software UART

#include <SoftwareSerial.h>

SoftwareSerial SimShield(8, 7); // Shield is connected to Arduino via softwareserial port

unsigned char buffer[64]; // Buffer array for data recieve over serial port

int count = 0; // Counter for buffer array

void setup()

{

SimShield.begin(9600); // The SimShield baud rate

Serial.begin(9600); // The Serial port of Arduino baud rate.

}

void loop()

{

if (SimShield.available()) // If data is coming from softwareserial port ==> data is comming from gprs shield

{

while(SimShield.available())

{

buffer[count++] = SimShield.read(); // Writing data into array

if(count == 64)break;

}

Serial.write(buffer,count); // If no data transmission ends, write buffer to hardware serial port

clearBufferArray(); // Call clearBufferArray function to clear the stored data from the array

count = 0; // Set counter of while loop to zero

}

if (Serial.available()) // If data is available on hardwareserial port ==> data is comming from PC or notebook

SimShield.write(Serial.read()); // Write it to the SimShield shield

}

void clearBufferArray() // Function to clear buffer array

{

for (int i=0; i<count; i++)

buffer[i] = NULL; // Clear all index of array with command NULL

}

Now open up the Arduino serial monitor with the com port connected to Arduino and baud rate set as 9600. Start sending AT commands over the serial monitor to communicate with the shield, and you will get back the response from the shield. Make sure to add up carriage return while sending commands.

If you are using the shield over the hardware uart pins, then you could use the below given code on your Uno to send out a test message.

void setup()
{
  Serial.begin(9600);   
  delay(500);
}

void loop()
{
  Serial.print("AT\r");
  delay(500);
  Serial.print("AT+CMGF=1\r"); // Set the shield to SMS mode
  delay(500);
  // send sms message, the phone number needs to include the country code e.g. For an Indian contact such as 9876543210 then the string     must be:
  // +919876543210
  Serial.println("AT+CMGS = \"+xxxxxxxxxx\"");
  delay(500);
  Serial.println("Test Message"); //the content of the message
  delay(500);
  Serial.print((char)26);//the ASCII code of the ctrl+z is 26 (required according to the datasheet)
  delay(500);
  while(1);
}

void setup()

{

Serial.begin(9600);

delay(500);

}

void loop()

{

Serial.print("AT\r");

delay(500);

Serial.print("AT+CMGF=1\r"); // Set the shield to SMS mode

delay(500);

// send sms message, the phone number needs to include the country code e.g. For an Indian contact such as 9876543210 then the string must be:

// +919876543210

Serial.println("AT+CMGS = \"+xxxxxxxxxx\"");

delay(500);

Serial.println("Test Message"); //the content of the message

delay(500);

Serial.print((char)26);//the ASCII code of the ctrl+z is 26 (required according to the datasheet)

delay(500);

while(1);

}

Resources

AT Commands (SIM900A/SIM900)
AT Commands (SIM800)
Datasheet (SIM900)
Datasheet (SIM800)

Shop with us

*NOTE: Kindly note that the quad band variants of the shield comes with SIM900 and SIM800, whereas SIM900A is the dualband version. The Bluetooth functionality and USB debug features are available on the SIM800 variant only. Certain features such as display interface, PWM output etc requires customization of the firmware.

Serial.print("AT\r");
  delay(100);

1 2	Serial.print("AT\r"); delay(100);

30 Responses to "How to interface GSM/GPRS Shield (SIM900A/SIM900/SIM800) To an Arduino"

SHAHID says:

February 9, 2016 at 12:09 pm

i didn’t get idea about jumper j3 and j4. what should i do exactly? even the test code provided is not working for me

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1. Hari Krishnan says:
  
  February 13, 2016 at 11:16 am
  
  The purpose of these jumpers are to switch between the hardware uart & software uart(7-tx & 8-rx).
  If the sample code is not working with your board, we strongly recommend checking those jumpers.
  The sample code is developed for boards configured for software uart.
  
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  1. ajin george reji says:
    
    July 19, 2018 at 9:06 pm
    
    jumpers?? is it a toggle switch??
    
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    1. Hari Krishnan says:
      
      August 1, 2018 at 2:05 pm
      
      The DPDT switch is used for selecting shield in USB or Arduino(RX,TX) mode.
      There are two jumpers J3 and J4, by shorting the jumpers to S-Tx and S-Rx the shield work in soft uart and if we short to H-Tx and H-Rx it work in hardware uart.
      
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Sashi Joseph says:

May 6, 2016 at 7:37 pm

Can we upload firmware to the arduino with the shield inserted?
If yes then which position of the dpdt slide switch would be better,Arduino or USB?

Also,would it make sense to keep the GSM reset switch pressed when uploading code to the arduino?

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1. Hari Krishnan says:
  
  May 23, 2016 at 10:16 am
  
  In the GSM shield, four debug pins will be listed out in the board, feel free to use those pins for the firmware modification.
  Please refer the below link for details regarding the firmware updation.
  http://www.rhydolabz.com/wiki/?p=14083
  
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  1. Shashank Varshney says:
    
    March 11, 2017 at 8:37 pm
    
    I think he is asking whether he can upload code to Arduino with GSM Shield inserted on arduino.
    
    I want to know the function of DPDT switch available on the GSM shield.
    
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    1. Hari Krishnan says:
      
      March 22, 2017 at 4:35 pm
      
      Adjust the DPDT slide switch as desired (USB – to communicate with the PC directly without an ATmega328 on your Uno, Arduino – to communicate with the ATmega328 on your Uno). So you can upload code to Arduino with GSM Shield inserted on arduino board just by sliding DPDT switch to USB position.
      
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GANESH says:

October 7, 2016 at 8:11 pm

i buy a gsm 800 shield , i am not able to see j3 and j4 jumper. kindly guide how to use.

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1. Hari Krishnan says:
  
  November 8, 2016 at 12:42 pm
  
  Dear Ganesh,
  Jumper J3 and J4 are used for switching the serial communication between the Hardware serial and Software serial. Hardware serial is default serial communication in arduino,ie Digital pin 0 and 1 are used for communication(D0 as Rx pin and D1 as Tx). For software serial digital pin 7 and 8 are used for communication(D8 as Rx pin and D7 as Tx pin). J3 is used for switching between S-RX(software Rx) and H-RX(Hardware Rx). J4 is used for switching between S-TX(software Tx) and H-TX(Hardware Tx).
  
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Kiran says:

May 15, 2017 at 1:11 pm

Instead of stacking it on Arduino, how to power up this module using RMC Connector?? What are the necessary equipments we need to buy?? I am new to this field, so your assistance could be valuable.

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1. Hari Krishnan says:
  
  June 7, 2017 at 11:37 am
  
  K1 is the RMC connector for giving power supply to the module instead of stacking it on arduino. A 2 pin RMC male connector is provided in the shield and package includes a 2 wire female RMC cable. 7-12V from a 0-30V/2A DC power supply can be used to power up module.
  
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Ajit says:

June 15, 2017 at 5:45 pm

Hey I am working with GSM shield since last month, but i’m not able to interface with Arduino. Help me out

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1. Hari Krishnan says:
  
  June 23, 2017 at 11:51 am
  
  To interface Arduino with GSM shield kindly do the following steps.
  
  Insert an activated SIM Card to the SIM Socket (K5), provided on the bottom side of the shield.
  Make sure if the antenna is installed properly
  Confirm the Jumper connection for the communication port (Software or Hardware -J3,J4)
  Adjust the slide switch as desired (USB – to communicate with the PC directly without an ATmega328 on your Uno, Arduino – to communicate with the ATmega328 on your Uno)
  Stack the shield and power up the Arduino
  NB: It is strongly recommended to use a stand-alone 2A power adapter, because the PC’s USB port might have not enough power to support the Arduino and GSM modem.
  
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Pro says:

August 12, 2017 at 6:08 pm

Thanks

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Mohamed says:

August 24, 2017 at 3:59 pm

Hello Harry,

Will the SIM900A module work in the North African countries without issues?

Thanks in advance!

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1. Hari Krishnan says:
  
  October 5, 2017 at 4:00 pm
  
  SIM900A is a dual band GSM modem being able to operate only in 900,1800 MHz bands & SIM900A can only be used in Asia, as it is region locked to Asian markets.
  
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Umer says:

September 3, 2017 at 1:12 pm

How can I Connect 2.8inch touch tft screen shield from wave share and this gsm module shield toghther with Arduino uno..I bought all three from Rhydolabz only.

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1. Hari Krishnan says:
  
  October 9, 2017 at 3:29 pm
  
  Place the GSM shield on the arduino UNO and place the Touch screen over the shield.The GSM nor the touch screen share any pins. The pins used for GSM are D0 and D1 and the pin used for interfacing arduino and touch screen are
  Arduino PIN |Symbol | Description
  D3 |TP_IRQ | Touch panel interrupt
  D4 |TP_CS | Touch panel chip select
  D5 | SD_CS | Micro SD card chip select
  D7 | LCD_DC | LCD data/command selection
  D9 | LCD_BL | LCD backlight control
  D10 | LCD_CS | LCD chip select
  D11 | MOSI | SPI data input
  D12 | MISO | SPI data output
  D13 | SCLK | SPI clock
  
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saurabh says:

October 16, 2017 at 9:06 pm

Hi all,

I was wondering what is the difference between the gsm/gprs module and the gprs shield module.

And as stated on the site the sim900a module works only in asia. What about the 900 module? I live in us , does the sim900 module works in us?

Any information on this or any help is greatly appreciated.

Thanks,
Saurabh

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1. Hari Krishnan says:
  
  October 17, 2017 at 2:47 pm
  
  SIM900 is a Quad band device which operates in 850/900/1800/1900 MHz that works everywhere, while SIM900A is the Dual band version which operates in 900/1800 MHz and is regionally restricted & SIM900A can only be used in Asia, as it is region locked to Asian markets.
  GSM/GPRS module is something that you can connect( interface) data, add voice, txt msg with the arduino using standard jumper cables. GPRS Shield, an all-in-one cellular shield that sits on the arduino and quite literally shield it.
  
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Deepak Awasthi says:

November 12, 2017 at 7:22 pm

Sir,
I purchased sim 800 shield and Uno board from rhydolabz.
I want to to connect sim 800 shield and uno board without stacking it on uno board.
The connections are
Ardunio GSM
Tx Rx
Rx Tx
Gnd Gnd

But i don’t know where Tx and Rx are present in Sim 800 shield.
Please help me.
Thanks in advance.

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1. Hari Krishnan says:
  
  November 15, 2017 at 12:23 pm
  
  The TX and RX pin of sim800 shield is in the 1st and 2nd pin (digital side) of the shield respectively.
  
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ashokkumar says:

February 7, 2018 at 11:56 am

sir can u send me gps gsm program for aurdino

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1. Hari Krishnan says:
  
  February 10, 2018 at 4:45 pm
  
  Please go through this wiki page
  
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Hari Krishnan says:

May 14, 2018 at 2:08 pm

Please go through this link
Familiarize with rhydolabz Tracking Shield

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Ashams says:

July 22, 2018 at 11:27 pm

Will the module I.e GSM stacked on arduino send values when powered independently with no connection with pc through serial port.

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1. Hari Krishnan says:
  
  August 1, 2018 at 12:56 pm
  
  Yes,We can establish communication without connecting to PC by powering through adaptor or power supply(Communication as per the program uploaded).
  
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sudarshan says:

December 8, 2018 at 9:25 pm

Hi, I set up GSM SIM900A on top of the Arduino board, but i failed to invoke the SIM900A shield through the Arduino IDE or AT Command tester. My shield is not responding, I tried different programs not no use. The following result got from AT Command tester. Please help me out.
…
…
Sending AT query..
Disconnecting port COM4.

Retry connecting COM4 at 230400

Sending AT query..
Disconnecting port COM4.

Retry connecting COM4 at 230400 with flow control enabled

Sending AT query..

Invalid or no response from the device. Please check the modem port and the baud rate.Disconnecting port COM4.

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1. Hari Krishnan says:
  
  January 8, 2019 at 2:54 pm
  
  Use 9600 as baud rate.If you are using any terminal software put the DPDT switch in USB.
  
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