Category: GSM,GPS

SIM808 is all in one module with GSM , GPRS,GPS & BLUETOOTH.SIM808 is advanced compared to SIM908.

SIM808 has GNSS receiver which enables easy GPS FIX.

In this post we explore how to parse GPS data ( without using TNYGPS library) & send it through inbuilt GSM

SIM 808 has 2 antenna sockets one  for GSM  & other for GPS. A stub antenna is used for GSM & a magnetic external patch antenna is used for GPS.

Do not interchange these 2 antennae. The antenna socket nearest to SIM808 chip is for GPS.



Connection between Arduino UNO & SIM808 is simple.

Gnd to Gnd

Tx of SIM808 to Rx of Arduino (soft serial digital pin 7)

Rx of SIM808 toTx of Arduino (soft serial digital pin 8)

A separate power adapter of 12v 2amp is required for SIM808 board.

Insert valid SIM on to the slot at the  back of SIM808 board

Power on & notice the NETWORK LED .It blinks fast initially & when it gets network it blinks slowly ,once per second.




We’ll use a serial to usb cable to monitor SIM808 serial port. We can also test AT commands through this port ,before uploading Arduino code.

Connect the cable to PC & note the COM port allotted under Device Manager .

Another COM port is allotted to Arduino board.Note this also.


Before uploading code on to Arduino , let us check the AT commands.

For this open a PUTTY Terminal & select SERIAL.

Feed in the COM port of the USB-RS232 cable &baud rate as 9600. & click open.

Image 1


Type in AT ,the SIM808 module responds with OK.

ATD is the command to dial a number

AT+CMGF=1 , AT+CMGS=”phone no.” are for sending SMS.

All GSM related commands are similar to that of SIM800 or SIM900.

Some cases of empty SMS delivery is reported .i.e you receive SMS on mobile but has got no message.

To solve this problem set the following parameter.


This has to be done before you set the module to Text mode using AT_CMGF=1

Image 2

GPS related AT Commands are similar to that of SIM 908.



AT+CGPSPWR=1 sets the GPS engine ON


AT+CGSINF=0 returns a single NMEA sentence of GPS.

AT+CGPSSTATUS?   returns the Status of GPS whether it has got FIX or not.

If GPS has not received FIX , the NMEA sentence will read all  0 s

Relocate the GPS antenna & wait for some time to get a FIX. If the GPS antenna faces open SKY you get a FIX within seconds.

Image 3

Once GPS gets a FIX , AT+CGPSINF=0 returns a valid NMEA sentence.

AT+CGPSINF=32  returns a single GPRMC sentence


Image 4


Now let us see the SIM808 specific GPS commands

SIM808 has inbuilt GNSS receiver

AT+CGNSPWR=1  turns on the GNSS power

AT+CGNSSEQ=”RMC”  parses the NMEA sentence related to GPRMC

Now issuing the command AT_CGNSINF returns a valid NMEA  GPRMC sentence



Image 5


Now let us upload the code that parses RMC data &sends SMS with google maps link


Arduino code Download :



#include <SoftwareSerial.h>
SoftwareSerial sim808(7,8);

char phone_no[] = “xxxxxxx”; // replace with your phone no.
String data[5];
#define DEBUG true
String state,timegps,latitude,longitude;

void setup() {

sim808.print(“AT+CSMP=17,167,0,0”);  // set this parameter if empty SMS received



void loop() {
if (state !=0) {
Serial.println(“State  :”+state);
Serial.println(“Time  :”+timegps);
Serial.println(“Latitude  :”+latitude);
Serial.println(“Longitude  :”+longitude);



sim808.print (longitude);
sim808.println((char)26); // End AT command with a ^Z, ASCII code 26

} else {
Serial.println(“GPS Initializing…”);

void sendTabData(String command , const int timeout , boolean debug){

long int time = millis();
int i = 0;

while((time+timeout) > millis()){
char c =;
if (c != ‘,’) {
data[i] +=c;
} else {
if (i == 5) {
goto exitL;
if (debug) {
state = data[1];
timegps = data[2];
latitude = data[3];
longitude =data[4];
String sendData (String command , const int timeout ,boolean debug){
String response = “”;
long int time = millis();
int i = 0;

while ( (time+timeout ) > millis()){
while (sim808.available()){
char c =;
response +=c;
if (debug) {
return response;


Following is the serial port monitor screenshot.

Once the command AT+CGNSINF is issued ,it returns a valid RMC sentence.

The latitude,longitude is then parsed

SMS is then sent with parsed data appended to google maps link.

Image 7


Pleae note Code is written to send SMS every 20 secs.







In this post let us explore the GPS Module built on UBLOX Neo series & then parse the data to send SMS with google maps link.

Arduino UNO is used to control the GPS module.

The GPS module used here has provision for connecting an external magnetic patch antenna.This enable the GPS to get FIX  within seconds even while testing indoor.

To test the GPS we need an USB to TTL  module.Or we can use our Arduino itself with a small hack.

Connect the RST pin of Arduino to GND.This will bypass the bootloader of Arduino & we can use the serial IC of Arduino to communicate with GPS.

Connect Tx of GPS to TX of Arduino & Gnd toGnd.

Note that the connection is STRAIGHT here & not reverse .Remember this connection will be reverse while we actually upload code to Arduino & use it in regular mode.

We can power the GPS module from Arduino itself. Connect 5v of Arduino to 5v of GPS.

Wait for some time for the GPS to get FIX. Once a FIX is received a green LED flashes on the GPS board indicating that GPS is ready with data flow.


Connect the USB of Arduinot o PC & open the DEVICE MANAGER to note the COM port allotted.

Open the Arduino IDE & select the PORT allotted.

Image 8


Image 9

Open the SERIALMONITOR to see the FLOW of NMEA sentences

We’re interested  in GPRMC which is the recommended minimum data for gps

There is an interesting link where we can decode the GPRMC sentence & understand the contents

Copy & paste a GPRMC sentence in this site to decode the contents.



If you notice a V  in GPRMC sentence ,it means GPS has not yet got a FIX. Relocate the antenna & wait for some time to receive a FIX & V changes to A .

Now the RMC sentence has all  the  data latitude,longitude,time,speed,altitude,etc..

Image 4



Image 10


Copy a portion of the data flow & paste it on to a Notepad.

Save it as text file with a name.


Image 11


To visualize the data , go to this link

Click on Choose file & select the notepad file saved.

Select the Output Format as GOOGLE MAPS  & click MAPIT.

Image 12

You can see the location on Map.

Image 13


Now your GPS is working.Let us go for a practical demo with Arduino.

To parse the data there are libraries that make life easier.

One such library is TINYGPS++ from Arduiniana

Download the library ,unzip it.

Image 14

Rename it to TinyGPSPlus & copy paste to Arduino –> Libraries.

Image 15

Open the Arduino IDE to see a list of examples against TinyGPS++

Select the FULLEXAMPLE  code.

Image 16

Here Softwareserial is used & digital pins 4 is defined as RX , 3 as Tx

Connect the Tx of GPS to  Rx of Arduino (digital pin 4)

Gnd toGnd.

As we only receive data from GPS , a single connection is enough. Tx of GPS toRx of Arduino

Image 17


Now upload the code & open the Serial monitor on baud 115200.

No data is received

Image 19

This is because of BAUD RATE mismatch.

Change the GPS Baud (not the serial baud)  to 9600 & then upload.


Image 20


Now you get data which is displayed neatly on serial monitor.

Image 21

In the next example we shall parse the GPS data & send SMS as google maps link using a GSM.

For this we use the previous version of library TINYGPS .


Image 22

Download the library & install it.

Here we use SIM900 GSM .A separate power source of 12v 1amp is required for GSM.

Connection between Arduino & GPS :


Tx of GPS connected to Rx of Arduino


Gnd to Gnd

5v of Arduino to 5v of GPS.


Connection between Arduino & GSM


Gnd to Gnd

Tx of GSM to Rx (soft serial pin 7) of Arduino

Rx of GSM to Tx (soft serial pin 8) of Arduino




Download the code from here


In this code we make use of older version of TINYGPS library to parse the latitude,longitude data,


Image 23

The data parsed is then appended to google maps link&sent as SMS .

Every 20 seconds an SMS is sent.You can modify the code so that you get SMS only when you call to the GSM.


Image 24


Upload the code & get the SMS on themobile no. you provided in the code.

Touch on the SMS link to see the location of GPS.


IMG_20180421_170826         IMG_20180421_170829






GSM controlled RELAY with Arduino

In this post we ‘ll control a relay through GSM by sending message.

Parts required  :

GSM SIM900 or SIM800

Relay board  (12v board with active HIGH , i.e if you send HIGH from Arduino then Rlay will be ON)

Arduino UNO

DC connector cable & 12v adapter

We’ll make it simple   By sending SMS $a1 Relay is made ON

BY sending SMS $a0 the Relay is switched OFF

GSM SIM900 board is used in this demo , but you can use SIM800 also. A valid SIM to be inserted in to the slot on GSM board. Do not use 4G SIM like JIO , as the SIM 800 / 900 is 2G /3G enabled.



A 1 channel relay board is used which is a 12v relay & needs a HIGH to enable the relay. Note that if you use a relay board with opto coupler , it needs a LOW to switch ON the relay .In this demo we use a 12v , HIGH enable relay which uses a simple NPN transistor to switch ON the relay.



i.e from Arduino Digital pin you send a HIGH to switch ON the relay.



Digital pin 8 of Arduino is connected to Relay board INPUT

Rx of Arduino to Tx of GSM , Tx of Arduino to Rx of GSM

GND of Arduino to GND of GSM

12V Adapter is used as power source. Power socket is provided on GSM & Arduino boards . DC connectors are used to power up GSM & Arduino .As Arduino has 5v regulator on board you can safely use 12v at power socket.

The +ve pin of Relay board is looped with +12v of adapter & -ve to GND of Relay board.

Ensure that all GND pins are made common , that of GSM , Arduino & Relay boards.




Following is the Arduino code to be uploaded. Remember to disconnect wires at Rx/Tx while uploading code to Arduino.

You can Download the Code HERE



char inchar; // variable to store the incoming character

int Relay = 8;


void setup()


pinMode(Relay, OUTPUT);

digitalWrite(Relay, LOW);



Serial.println(“AT+CMGF=1”); // set mode to text



// just to get a notification when SMS arrives &direct out SMS upon receipt to the GSM serial out




void loop()


//If a character comes in from the GSM…

if(Serial.available() >0)


if (inchar==’$’)



if (inchar==’a’)



if (inchar==’0′)


digitalWrite(Relay, LOW);

Serial.println(“Relay OFF”);


else if (inchar==’1′)


Serial.println(“Relay ON”);

digitalWrite(Relay, HIGH);



Serial.println(“AT+CMGD=1,4”); // delete all SMS







A char variable inchar is used to store the incoming SMS

The relay pin is defined as DIGITAL pin 8

Inside setup function , the Relay pin is declared as OUTPUT using pinMode & then initially it is made LOW

Serial.begin(9600) ; starts Serial communication at baud 9600.

AT+CMGF=1 confirms TEXT mode operation of GSM .Notice the use of SerialPrintln which provides a Carriage Return


// just to get a notification when SMS arrives &direct out SMS upon receipt to the GSM serial out

The AT command +CNMI is used to specify how newly arrived SMS messages should be handled. You can tell the GSM/GPRS modem or mobile phone either to forward newly arrived SMS messages directly to the PC, or to save them in message storage and then notify the PC about their locations in message storage.

Syntax: AT+CNMI=<mode>,<mt>,<bm>,<ds>,<bfr>


This command selects the procedure for message reception from the network.


<mode>: controls the processing of unsolicited result codes

Note: Only <mode>=2 is supported.

<mt>: sets the result code indication routing for SMS-DELIVERs. Default is 0.

0: No SMS-DELIVER indications are routed.

1: SMS-DELIVERs are routed using unsolicited code: +CMTI: “SM”,<index>

2: SMS-DELIVERs (except class 2 messages) are routed using unsolicited code: +CMT:…….

AT+CNMI is used anyway just to get a notification when a SMS arrives, in order to read the content of the stored SMS you have to use AT+CMGL= or AT+CMGR=…


Inside Loop

If any serial data is available it is assigned to inchar variable

If the first character is $ , the inchar variable is replaced with next Serial character

If the next character is a , again the inchar is replaced with next serial character

Finally , if the character is 1 , the pin 8 is made HIGH & relay is made ON

If the final character is 0 , pin 8 is made LOW , thus making the relay OFF.

SMS $a1 makes the Relay ON

SMS $a0 makes the Relay OFF

Only basic code is explained in this post to just ON or OFF the relay. Further improvements can be done like :

1. Relay status sent back as SMS to the caller

2. Programming can be done so that SMS from particular Master number only is considered

& SMS from other number will not control the relay

3. Pump starter can be made ON / OFF by using 2 relays .One relay contact used to START the motor & other to STOP .While connected with STARTER we need to momentarily switch ON / OFF the relays. This is similar to manually pressing the START or STOP button of the motor starter.

Support video :



In the previous post part-1 I explained the initial setup of starting a Server on PC on a port , setting the Windows firewall to allow the port for external communication , PORT FORWARDING set up in the Router config, etc..

In this part 2 I’ll show a practical demo of sending Temperature data to the Server.

As given in part 1 , start a server on distant PC on port 350 & do the port forwarding settings in Router config as explained.

A LM35 sensor is connected to pin A0 of Arduino & a GSM SIM900A is connected to pins 7 , 8 , Gnd of Arduino. As Soft Serial library is used in the code , pins 7 & 8 are declared as soft Rx & Tx.

The Rx pin goes to Tx of GSM , Tx connected to Rx of GSM , GND is made common.An external power source of 12v 1A is used for the GSM.

Download the Arduino code HERE


#include <SoftwareSerial.h>
SoftwareSerial myGsm(7,8);
float temp;
int tempPin = 0;
void setup()




myGsm.println(“AT+CSTT=\”bsnlnet\”,\”\”,\”\””);//setting the APN,username & password


myGsm.println(“AT+CIFSR”); //get IP address





void loop()

void printSerialData()


void sendtemp()
temp = analogRead(tempPin);
temp = temp * 0.48828125;
Serial.print(“TEMPERATURE = “);



The Analog pin A0 is assigned as tempPin to read the LM 35 sensor data.

Initially any previous IP connection is SHUT  using the command


This is essential to start a fresh TCP/IP comnnection.

Single IP connection mode is set by


GPRS is attached using


Task is started with the command


The Access Point Name of the mobile service provider can be known  by placing the SIM on your Android mobile. It’s shown under

Settings  –> More..  –>  Cellular Networks –> Access Point Names

In my case the APN is bsnlnet , user name & password are empty



Then we bring up the Wireless connection with GPRS using


This takes a little moment , so a delay of 6 secs is a must in the code.

The IP address assigned by GPRS is obtained by


Now we start up TCP connection with Server IP address & Port number of distant server


Once the connection is established , we send data using


A CTRL+Z is required to send data which is executed using hex 1A


Upload the code to Arduino & open the Serial monitor to watch the AT commands executed



Following is the screen shot at the Server side.


Image 3




This tutorial is of 2 parts.

First part explains the following :

–Starting a Server on your PC  & start listening on a port (say 350) . For this we use SOCKET TEST or HERCULES software

— Once the port is listening , we test communication locally using PuTty

— Windows Firewall setting has to be done for a NEW INBOUND RULE allowing port 350 for communication.

— For connecting to this port from external world , PORT FORWARDING to be done in Router’s Virtual Server setting so that any contact to the public IP is routed to the PORT 350 .


Second part is practical demo using GSM SIM900 or ESP8266 with Arduino.


The following picture shows my simple home network connections.A BINATONE make Router is used to connect to the Internet provider Airtel Broadband.The IP address of the Router is

which is the Gateway IP address used to access the settings on Router.My Laptop is connected over WIFI to this Router.The Router assigns a local IP address to my PC which is

Apart from these, the Internet Provider assigns a Public IP to my Network which is

This is the IP by which external world can contact my network.

Note that all these IP addresses are DYNAMIC & changes every time I power up the Router.

In another post I’ll explain how to make these IP addresses STATIC , so that the IP remain the same always.



All the Network Tools I’ve used for this demo can be downloaded HERE.

Let us start  a server on port 350 using the SOCKET TEST tool.

This tool allows us to start a server easily.Click on the SERVER Tab & then feed in the port number where you want to listen.



Now the server is up & running.It starts listening on port 350.

Remember to avoid the standard ports like 80 ( http) , 21 (FTP), 23 (TELNET), 22 (SSH) ,etc which are well known ports ,pre assigned for the particular protocol.

The dynamic range of port number you can assign goes up to 65535 or 2^16-1 (16 bits).

The IP address of the router can be known from the command window

RUN –> CMD –> ipconfig

The Default Gateway IP is the address of the Router.





Once the port is assigned for the server , you can use the ADVANCED PORT SCANNER tool to verify the port on the particular IP.

In the screen shot below you can see that the port number 350 is discovered as a TCP Server port on my PC whose local IP is



While the port scanner is scanning , you get messages on your SOCKET TEST window.

Here you can see the Port scanner software connecting to the port & then disconnecting after scanning.



Alternatively you can use a PUTTY serial port tool to test local communication.

Select the connection type as RAW & provide the host IP which is & thtn the port number 350


Click on open , to see the New client connection on the Socket test window.



Now you can test two way communication between  socket test (server) & putty ( client).





The Windows Firewall settings has to be done to allow the port 350 to listen from outside.

Open the Windows Firewall & Advanced Security window.

Click on Inbound Rules & then New Rule.



Select the Rule Type as PORT & in the next screen select protocol as TCP.

Under Specified local ports feed the port number as 350



Under Action window select Allow the Connection

Next window is Profile window , here tick mark all – Domain,Public & Private.

Provide a name to the Rule & save it.

Now your PORT 350 is allowed to listen by the Windows Firewall.




This step is final where you redirect the incoming request to the port number of local IP where the server is started.

Here my local PC’s IP is   &  server is started on port 350.

Anyone from external world connecting to my public IP has to be directed to the port 350 on local IP

This is called PORT FORWARDING , which is very widely used in CCTV Remote viewing & in Gaming.

The setting has to be done in your Router.

Type in the Gateway IP of your Router , here it is , on your browser & provide the user name & password.

Here is an excellent website showing all screen shots of almost all Routers in the world


Mine is BINATONE Router.

You’ve to search for something called VIRTUAL SERVER on the router setting.




For my Router it’s hidden under ADVANCED SETUP –> NAT –> VIRTUAL SERVER

For more details you can visit the above portforward link

Create a new Virtual server listing by entering the

— Port number , which is 350 .Enter same number at all fields like start & stop.

— Local IP address , here you provide the IP where server is started ,

— save the listing



Once saved , the port number 350 is open to outside world.

Online port open test tools are available


Once you open the link , your public IP will be automatically shown.

Fill in the PORT number to be checked & click on CHECK button.

If you see SUCCESS , then you’re done with PORT FORWARDING






Following is the list of AT commands used by the GSM SIM900A to contact the server.

This is for part 2 of the post.PART 2 LINK HERE



cooltext753793315   cooltext753790696



This post is on retrieving particular Data from a web page using SIM900A & Arduino.

For e.g we shall retrieve the Blog Status hits of my blog in which you’re reading this.

We’ve to create an API link for this data so that data can be retrieved using SIM900A.

To create API link we use the website.

First let us read the XPATH details of the data wanted as below :

The procedure is related to Google Chrome WebBrowser


Image 1


Right click on the data to be retrieved & click on INSPECT .




A highlighted code will be displayed on which Right click & then select COPY  –> COPY XPATH



The copied XPATH detail has to be used in THINSPEAK account to create the API link.

Open your thingspeak account & click on APPS –> THINGHTTP



Click on NEW THINGSPEAK to create a new “thing”.



You can provide a suitable Name for the App & under URL provide the website link from where you want the data from.

Method is GET & version is 1.1



Scroll down to bottom & under the PARSE STRING field paste the XPATH copied from the website.


Click on SAVE & you see the API LINK generated.



You can use this API link in your browser to confirm the data retrieved.

Image 15

Now let us see the practical application using SIN900A GSM & ARDUINO.

The connections between Arduino & GSM are :

Rx of GSM —> pin 8 (Tx) of Arduino   (since we use the SoftSerial in Arduino code , we declare pins 7 & 8 for Serial communication)

Tx of GSM –> pin 7 (Rx) of Arduino


A separate power source is required for the GSM.

Following are the AT commands used


DOWNLOAD Arduino code HERE


#include <SoftwareSerial.h>
SoftwareSerial myGsm(7,8);

void setup()


myGsm.println(“AT+SAPBR=3,1,\”CONTYPE\”,\”GPRS\””);//setting the SAPBR,connection type is GPRS

myGsm.println(“AT+SAPBR=3,1,\”APN\”,\”\””);//setting the APN,2nd parameter empty works for all networks


myGsm.println(“AT+HTTPINIT”); //init the HTTP request

myGsm.println(“AT+HTTPPARA=\”URL\”,\”\””);// setting the httppara,
//the second parameter is the website from where you want to access data

myGsm.println(“AT+HTTPACTION=0”);//submit the GET request
delay(8000);//the delay is important if the return datas are very large, the time required longer.
myGsm.println(“AT+HTTPREAD=0,20”);// read the data from the website you access

myGsm.println(“AT+HTTPTERM”);// terminate HTTP service


void loop()

void printSerialData()



AT+SAPBR is used to declare the Connection Type as GPRS

& Then the APN –Access Point Name of the mobile service provider is given.

An empty string also will work.Or you can slide the SIM into your Android mobile

under Settings –. More –> Cellular Networks  –> Access Point Names

you get the APN details

AT+SAPBR=1,1  enables the GPRS & APN settings & then HTTP is initialized with AT+HTTPINIT

HTTP parameters are then provided as “URL” & the API link we created earlier.

Note to use HTTP ( not HTTPS) in the link, as we use AT commands for HTTP only here.

AT+HTTPACTION=0 enables GET action

The GSM respons with


Here 0 means GET action & 200 means OK , 12 bytes are retrieved.

If you get 600 instaed of 200 ,then it means a Network Error.

AT+HTTPREAD command is used to read the Data.


Image 11

cooltext753793315   cooltext753790696


A6 GSM  is introduced by the makers of ESP8266 , AI-THINKER.

The module is much cheaper than SIM900 & connections are quite simple.In this post we shall see how to connect with Arduino to make a call & send SMS.

A mobile adapter is enough to power up the A6 GSM module.The Vcc pin of GSM must be looped with PWR_KEY pin.This acts as a chip enable.You can leave this connected or remove after a moment.The module just requires a HIGH trigger at PWR_KEY pin while started.

A valid SIM is used at the back side of the module.The SIM slot provided is for a Micro SIM.If you ‘ve a Nano SIM you need to use a converter to fit the slot.

The RxD pin of A6 GSM is connected to Tx of Arduino

The TxD pin of A6 goes to Rx of Arduino.

GND pin of A6 to GND of Arduino.







Power up the module & then after a moment make a call to the SIM number used in the GSM module from another phone.If you get the RING Back tone , it means the module is ready.As there is no LED indication provided , this initial step is required to confirm working.


Making a CALL


Connect the USB cable of PC to Arduino & upload this code for making a call.Remember to disconnect connections at Rx/Tx before uploading the code.

Image 1


The mobile number to be called is stored in an Array of char variable.

In the void setup() code we begin Serial communication at 9600 baud.Though the default baud rate of A6 GSM is 115200 , it is effective to use 9600 baud .

ATD command followed by the number to be called is used to make a call.

A semicolon at the end is not a must as in SIM900.The call will be made even if you do not use a semicolon.

After a delay of 8 secs ATH command is sent to terminate the call.

You can open the Serial monitor of Arduino & watch the AT commands landing.You should set the baud rate as 9600 in the Serial monitor as well.

The void loop() function is left empty.In case you try the code inside loop , the call will be repeatedly

made for ever.


Sending SMS

Now let us see the method to send SMS.

Following screenshot shows the code for sending SMS.

Image 2


DOWNLOAD Arduino code HERE


which will allow you to read and write SMS messages as strings instead of hexadecimal characters.

Serial.println is used to send the AT command with a New line (Enter).

After a delay of 2 seconds next command


is sent.The target phone number is to be given within double quotes. Note the usage of

Serial.write(0x22)  which is the ASCII equivalent for double quotes.

0D followed by 0A are the ASCII equivalents for  CARRIAGE RETURN & LINE FEED.

The delay of 2 seconds is a must after setting the GSM to text mode AT+CMGF=1

Try this code without the delay , you won’t get response.

After the 0D , 0A a delay of 2 seconds is provided & then the message to be sent is given.

CTRL+Z is finally given to send the message.

This is provided by the ASCII equivalent 1A or char(26)

Watch this video :



cooltext753793315    cooltext753790696


After the huge success of the ESP8266 IOT modules , the AI-THINKER company now introduces the new GSM Module A6.In near future this module will be available at half the price of SIM900.




This is mini GSM / GPRS core development board based on GPRS A6 module. It supports dual-band GSM/GPRS network, available for GPRS and SMS message data remote transmission.
The board features compact size and low current consumption. With power saving technique, the current consumption is as low as 3mA in sleep mode.

– Working frequency: quad-band network, 850 / 900 / 1800 / 1900MHz
– Working voltage: 4.5~5.5V DC (On-board voltage regulator circuit supply power for A6 module)
– Working current: maximum of 2A
– Sleep current: 5mA
– Onboard Micro SIM card holder, you can install Micro SIM card
– Onboard Micro USB interface for external power supply
– Communication Interface: TTL serial port
– Baud rate: 115200bps and it can also be set by AT command.
– Interface logic voltage: 3.3V
– Make and answer phone calls using a headset and electret microphone.
– Send and receive SMS messages.
– Send and receive GPRS data (TCP/IP, HTTP, etc.) .




To test the module we make use of an USB-TTL module built on CP2102 .



The connections between A6 GSM & CP2102 module are :

A6 GSM             USB-TTL Board

———-       ————

UART_TXD    —>  Rx

UART_RXD    —>  Tx

GND            –>    GND

The A6 GSM can be powered up with a cell phone charger for which a mini usb socket is provided at the back side.Its advisable to use 5v 2Amp adapter.

Insert a valid SIM to the SIM holder seen at the bottom side of the module.




Connect the USB-TTL board to the PC & open the Device Manager to note the COM port alloted.

Open the TERMINAL Software & select this port .Select baud rate as 115200 & click connect.





The GSM module takes around 10 secs to boot up & finally you get CREG 1.

Now you can type in AT commands.The GSM A6 module requires a Carriage Return after every AT command .You can tick mark the CR found at the bottom right of Terminal before sending any command.Or you can make use of the SET MACROS function .Here you store the AT commands followed by $ sign & then 0D .

The $ sign is to Append & the 0D is the ASCII for Carriage Return.


AT commands are stored in M1,M2,M3,… as shown in screen shot above.

Now if you click on M1 , AT command is sent with CR & you get OK response.

Clicking M2 will send ATDxxxx to dial a number . The semicolon after the number is not a must as in SIM900.

ATH disconnects the call.

To send SMS

AT+CMGF=1  to set the TEXT Mode


Now you get a  >   symbol & the module waits for you to type in the message.

After typing the test message a CTRL+Z is to be sent .This is done by appending 1A which is the ASCII for the CTRL+Z

Watch this demo video :



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GSM–Handling Received SMS

This post is intended to illustrate the received SMS by a GSM module like SIM900.AT commands to handle the received SMS are explained in detail.

We shall use a SIM900 module on RS232 breakout board & an USB-UART converter board to connect it to the PC.

Following is the setup to test received SMS using SIM900.

Image 9

A terminal software like PUTTY is used to read out the COM port where GSM is connected to PC through USB-UART board.

As you connect the USB-UART board to PC ,the PC allots a COM port which can be seen under Device manager.Open the PUTTY terminal & set this to read the serial port.


Image 10

Open the Putty terminal & type in AT .If your modem settings & connections are fine you get an OK response from the modem.

Preferred Storage Area


To select the Storage area for SMS type in

AT+CPMS  command .This sets the Preferred Message Storage area.

To know the Message areas supported by our GSM ,enter the AT command


Image 1

As seen above ,our modem returns all 3 message storage areas as SM , which refers to the Message storage area on the SIM card.

The first SM specifies the message storage area that will be used while Reading or Deleting SMS.

The second SM specifies the area that will be used when sending SMS from message storage or writing SMS  to storage.

The third SM specifies the preferred message storage area for storing newly received SMS.

In our case ,SM is the preferredstorage area for all SMS functions , Read , Send & Receive.

The other storage areas are ME (storage area on GSM Modem/Mobile phone) ,   MT (read from all storage area associated with GSM),   BM (incoming Broadcast message storage area) ,   SR  (status report)   &  TA (Terminal adapter )


To know the SMS Service center address (SMSC)


The mobile network operator’s service center number will be displayed.


Image 2

The number 145 in +CSCA is the address type .145 refers to International number starting with +.

SMS Modes


The next AT command


reports the SMS modes supported by the GSM. 0 is for Text mode & 1 is for Protocol Data Unit (PDU) mode.Our modem reports (0,1)  supporting both SMS modes.

To check if your modem supports the text mode, you can try the following command:


If the modem responds with “OK” this text mode is supported. It is  possible to send only simple text messages in this mode.

To know the current message format use the command



Reading Messages from Storage Area


To read messages from SIM storage type in


Image 3


The Modem responds with + CPMS: followed by Used space & Maximum space.

In our modem there are currently 2 messages in memory (used space ) & maximum storage capacity is for 30 messages.

To list out all messages in the SM storage  type in


The modem responds with a list of all messages in the storage area.

Image 4


+CMGL: 1  is the Memory Index number used to read or delete message

“REC READ”  is the status message.If the message is not Read it shows REC UNREAD

“+91xxx “    is the phone number from where the message originated.

“,”    Next column is the reference number of the message.Generally this field is empty.

“13/09/19…”  is the Date & time of received SMS in yy/mm/dd,hh:mm : ss format

Finally the actual message in text format is displayed.


To list out a particular  message , use the CMGR command with the index number of the message to be read.

AT+CMGR=2   to list the message at index 2

AT+CMGR=4   to list the message at index 4

Image 5


Deleting Messages


To delete a message use CMGD command with the index number of message to be deleted.

AT+CMGD=1    to delete the message at index 1.

Image 6

You can issue the command AT+CMGL=”ALL” to see that the message at index 1 is deleted.

To delete all the messages in the storage area there is no such command like AT+CMGD=”ALL”.

Use the following notation to delete all messages.


1 is the Index value & 4 is the flag value

To know the index & flag values allowed


Image 7

1 to 30 can be assigned to index parameter & all five flag values from 0 to 4 are supported.

By default flag value is 0 which means “Delete message at location <index>”

Flag value 1 – Delete all READ messages ,ignoring value of index.

Flag value 2 – Delete all READ & SEND messages.

Flag value 3 – Delete all Read,Sent & Unsent messages.

Flag value 4 –Delete all messages.


Image 8

You can see from above screen shot that all messages are deleted after issuing AT+CMGD=1,4.


AT+CNMI – New message indication to Terminal Equipment TE.

Selects procedure how receiving of new messages from the network is indicated to the TE.

The following command sets the indicators for receiving an SMS message.


AT+CNMI=1,1,0,0,0 Set the new message indicators.



<mode>=1 discard unsolicited result codes indication when TA – TE link is reserved.

=2 controls processing of unsolicited result codes & forward them directly to Terminal Equipment TE


<mt>=1 SMS-DELIVERs are delivered to the SIM and routed using unsolicited code.

<bm>=0 no cell broadcast message indications are routed to the TE.


<ds>=0 no SMS-STATUS-REPORTs are routed.


<bfr>=0 Terminal Adapter ( TA) buffer of unsolicited result codes defined within this command is flushed to the TE (Terminal equipment).


The following command saves the SMS settings. Once the SMS commands have been saved, the initialization commands do not need to be sent again until they are changed.



toSave SMS settings. This may take up to 10 seconds.


Watch this support video :

Handling Received SMS with SIM900 GSM

GPS Receiver Module–Part 2


Part 1 – GPS theory  here


SKYTRAQ GPS-634 Module


There are numerous GPS modules available in the market.

In this post, I am going to use GPS-634R module manufactured by SKYTRAQ , a Taiwan based leading GPS Chipset manufacturer.

GPS-634R is a highly integrated smart GPS module with a ceramic GPS patch antenna. The antenna is connected to the module via an LNA – Low Noise Amplifier.

The module is with 51 channel acquisition engine and 14 channel track engine, which be capable of receiving signals from up to 65 GPS satellites and transferring them into the precise position and timing information that can be read over either UART port or RS232 serial port.

Both of the LVTTL-level and RS232 signal interface are provided on the interface connector, supply volt is 3.6 to 6v DC.The module can be used with your Desktop PC, Laptop, or a microcontroller. It supports the NMEA 0183 protocol, as do many GPS modules.


gps-634r            Image 1

We are going to start by connecting the module to our PC using an Evaluation Board shown below:

This board will allow you to use a standard 12v AC adapter and a 9 pin Serial cable to connect the GPS module to your PC or Laptop.In Laptops you don’t have a Serial port.Make use of an USB to UART board to connect to USB port.

We shall use a board made by NSK Electronics ,which uses a CP2102 Siicon Labs USB –UART IC, a reliable one.

Connect the GPS module to the breakout board.Only we need 3 wires Vcc (pin 1),GND (pin 2) & the TX (Serial Data out). The TX wire should be connected to Rx pin on the board.

The 9 pin D connector of the breakout board is connected to the USB-UART converter using a Serial cable (straight one not cross).The USB connector of USB-UART board is then connected to the Laptop using a A-B USB cable.

Provide a 12v DC adapter to the break out board.The power LED will glow.

At the bottom of the GPS Module a status LED glows.This LED glows still (always On) in Non-Fix mode & starts blinking once the GPS module is outdoor and has started tracking.

We shall make use of a Terminal Software COOLTERM to read out the COM port where GPS is connected.



Image 2


Open up the Device Manager & note down the port number allotted to the USB-UART board.




Now open the Terminal software COOTERM . You can download it here

Click on Options & then under Serial port select the port allotted to your USB-UART board as seen in the Device Manager.The other settings are Baud Rate –9600, Data Bits – 8 , Parity –None  &  Stop Bits – 1  (9600 8 N 1) .




If you click CONNECT button you can see your GPS in action & NMEA Sentences flying out.


Image 45






The $GPRMC Sentence  is the most useful one and contains the position fix.



GP is the Prefix for GPS followed by RMC which is Recommended Minimum Sentence.

All data are separated by Commas.

054006.999 is the current time in Greenwich Mean Time (not your local time). In this example it is 05 Hours 40 Minutes 06 Seconds & .999 MilliSeconds.

Next is the STATUS CODE : “ A “ means Active & GPS HAS GOT A fix.” V” means Void or Data Invalid

Next 4 pieces of Data are Geo Location Data.

1059.8519,N -> Latitude 10 Degrees , 59.8519 decimal minutes NORTH

07657.4794,E -> Longitude 76 Degrees ,57.4794 decimal minutes EAST.


Next Data is Ground Speed in Knots.In this example I’m indoor & not moving.So it is 000.0

Next Data is Tracking Angle 166.0

Next Data is the DATE of FIX 120313 means 12th of March ,2013

Next 2 commas indicate Empty field.One is for Time in secs since last DGPS updated & the other is DGPS station ID number.In this example both fields are empty.

Finally a checksum data is presented which starts with an “*” symbol followed by 2 Hex digits.


Now we shall use a GPS STUDIO Software called TRIMBLE to view the MAP.

Download TRIMBLE GPS STUDIO from  here


Click Disconnect in  the COOLTERM window to close the port.


If Windows Firewall blocks Trimble , click Allow Access to start TRIMBLE.

Under New Connection Select the port COM6 (allotted to USB-UART).



In the next window select the Baud Rate as 9600 ,Parity – None , Data Bits – 8 ,& Stop Bits –1



Click OK.

Now you can see the individual data like Latitude,Longitude,Date ,Time , etc.. are extracted from the NMEA sentences & displayed in their respective boxes.

To see the NMEA sentences click  Monitor – > View RAW Data.

To view the MAP click on Map button at the right top of the Monitor screen.

The position of the GPS is seen as a Red Dot .To see Satellite or Terrain Views you can click on the respective buttons.

If the GPS is fixed in a Car , the Red dot will move on the map following the movement of the Car.




Now let us take the GPS setup into a Car.

DSC00528      DSC00521

This is the  whole setup we are taking into a car.

A 9V battery is enough to power up the GPS module.The GPS module is connected to Laptop using an USB-UART board.Trimble Studio is started and the COM port of USB-UART board is entered into the port settings of Trimble Studio.



DSC00534      DSC00524


The GPS Module is placed at the front of Dash Board to get a clear sky view. A Reliance Data card is used for providing Internet connectivity.

Below is the screen shot of the Map plotted according to the movement of the Car.



Watch this video  :


GPS MODULE – SKYTRAQ 634–Testing & plotting MAP



For availability of this GPS module & break out board contact :


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