How To Interface GPS With Arduino- (Part 27/49)

The GPS module used in this project is SR-91 based GPS module which can communicate the data regarding the current location to a PC or microcontroller through the serial port. The image of the GPS module used for this project is shown below;

Fig. 2: SR-91 based GPS Module for serial communication

The arduino board used in this project is the arduino pro-mini board and the IDE version of the arduino is 1.0.3 for windows. The image of the arduino pro-mini board and the arduino IDE are shown below;

Fig. 3: Typical Arduino Pro-Mini Board

Fig. 4: Arduino IDE Software Window

Since the arduino pro-mini board has no circuitary for interfacing it with the serial port or the USB port of the PC, an external USB to TTL converter board is required to connect it with the PC. This hardware helps in programming the arduino board and also helps in the serial communication with the USB port of the PC.

Fig. 5: External USB to TTL converter board for programming Arduino and serial communication

It is assumed that the reader has gone through the project getting started with arduino and tried out all the things discussed there.

The Arduino read the serial data from the GPS module using the serial communication functions provided by the Arduino library. The functions like Serial.begin() which helps to initialize the serial port with a given baud rate, Serial.write() to send a data to the serial port, Serial.available() and Serial.read() functions to read data from the serial port are used in this project and they are already discussed in previous projects on on how to do serial communication with the Arduino, how to send and receive serial data using arduino  and how to do serial debugging with the Arduino. 

Using the function Serial.read() the Arduino continuously reads the data from the GPS module, looking for Latitude-Longitude details. The GPS send the data in standard NMEA format which consist of the real time data regarding the current position. The format includes so many sentences and among them one particular sentence referred to as “Global Positioning System Fix Data” is extracted to read the Latitude Longitude.

The screenshot of the “Global Positioning System Fix Data” among the NMEA format data output from the GPS module is shown in the following image;

Each sentence has a sentence identifier, actual data separated by commas and a check sum which has to be extracted to make it in readable format. The details of the sentence “Global Positioning System Fix Data” is given in the following table;

Fig. 6: Details of sentence “Global Positioning System Fix Data”

To simply output the Latitude-Longitude coordinate using the Arduino, the code written for the project continuously reads the characters from the GPS module and check them for two consecutive ‘G’ s, so as to get the sentence starting with $GPGGA. Once the message is found the code seeks through the message, skipping the letters till the first two commas and printing the rest as the Latitude, till the following comma. The code again skips the characters till it found another comma and the following letters till the next comma are printed as Longitude.

The code uses do-while loop to look for particular characters or set of characters, as an example to ignore all the letters till two consecutive ‘G’s the code uses the following statements;

//==================== searching for “GG” ===================//

    do

    {

        do

        {

            while ( !Serial.available() );   

        } while ( ‘G’ != Serial.read() );

        while(!Serial.available());

    } while ( ‘G’ != Serial.read() );

//==================== searching for “GG” ===================//

Similarly to ignore all the letters till a comma is received the code uses the following statements;

//=======================================//

    do

    {

        while ( !Serial.available() );   

    } while ( ‘,’ != Serial.read() );

//=======================================//

When the coding is finished one can verify and upload the code to the Arduino board as explained in the project how to get started with the Arduino . The Arduino board can then be connected to the PC using USB to TTL converter board and geographical coordinates can be read using any serial monitoring software or using the Arduino IDE’s serial monitoring software itself as explained in the project how to do serial debugging with the Arduino.

Project Source Code

###




/*============================ EG LABS ===================================//


 Demonstration on how to use PS2 MOUSE with an arduino board

 

 The circuit:

 LCD:

 * LCD RS pin to digital pin 12

 * LCD Enable pin to digital pin 11

 * LCD D4 pin to digital pin 7

 * LCD D5 pin to digital pin 6

 * LCD D6 pin to digital pin 5

 * LCD D7 pin to digital pin 4

 * LCD R/W pin to ground

 * 10K resistor:

 * ends to +5V and ground

 * wiper to LCD pin 3


LED:

 * LED anode attached to digital output 9

 * LED cathode attached to ground through a 1K resistor

 

 GPS:

 TX PIN OF GPS TO RX1 PIN OF ARDUINO

 SHORT THE GROUND PINS OF ARDUINO AND GPS


============================== EG LABS ===================================*/


#include <LiquidCrystal.h>


// initialize the library with the numbers of the interface pins

LiquidCrystal lcd(12, 11, 7, 6, 5, 4);


// give the pin a name:

int led = 9;

// incoming serial byte

int inByte = 0;         


void setup()

{

  // set up the lcd's number of columns and rows: 

  lcd.begin(16, 2);

  lcd.print("ENGINEERS GARAGE");

  lcd.setCursor(0, 1);

  lcd.print(" GPS  INTERFACE ");

  

  // initialize the led pin as an output.

  pinMode(led, OUTPUT);  

  // start serial port at 9600 bps

  Serial.begin(4800);

  // wait for a while till the serial port is ready

  delay(100);


  // send the initial data once //    

  Serial.print('n');

  Serial.print("       EG LABS    ");

  Serial.print('n');

  Serial.print('r');

  Serial.print(" GEOGRAPHICAL CORDINATES");

  Serial.print('n');

  Serial.print('r');

  Serial.print('n');

  

  digitalWrite(led, HIGH);       

}


void loop ()

{ 

//==================== searching for "GG" ===================//

    do

    {

        do

        {

            while ( !Serial.available() );    

        } while ( 'G' != Serial.read() );                    // reading a character from the GPS

      

        while(!Serial.available());

    } while ( 'G' != Serial.read() );

//==================== searching for "GG" ===================//


//============== seeking for north cordinate ==============//

    do

    {

        while ( !Serial.available() );                       // reading a character from the GPS    

    } while ( ',' != Serial.read() );


    do

    {

        while ( !Serial.available() );                       // reading a character from the GPS

    } while ( ',' != Serial.read() );

//============== seeking for north cordinate ==============//


//============== printing the north cordinate ===============//

    Serial.print(" N: ");

    do

    {

        while ( !Serial.available() ); 

        inByte = Serial.read();                              // reading a character from the GPS

        Serial.write ( inByte );                             // printing the Latitude

    } while ( ',' != inByte );

//============== printing the north cordinate ===============//


//============== seeking for east cordinate ==============//

    do

    {

        while ( !Serial.available() );                       // reading a character from the GPS

    } while ( ',' != Serial.read() );

//============== seeking for east cordinate ==============//


//============== printing the east cordinate ===============//

    Serial.print(" E: ");

    do

    {

        while ( !Serial.available() ); 

        inByte = Serial.read();                              // reading a character from the GPS

        Serial.write ( inByte );                             // printing the Longitude

    } while ( ',' != inByte );

//============== printing the east cordinate ===============//

    Serial.println();

    

    delay ( 1000 );

}

###
 

Circuit Diagrams

Circuit-Diagram-Interfacing-GPS-Arduino

Project Components

Project Video

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Filed Under: Arduino
Tagged With: Arduino, gps
 

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