In my previous post, I explained some basic concepts about GPS, how it works, how information is encrypted into it and how to understand the code that we receive through it etc. But always to receive these codes, sit down and decrypt it ourselves will be a tedious task. If we have a GPS module in our hand and spend a lot of time in trying to understand it then what is the point in having GPS at all. I know we have devices that decodes the GPS short descriptions and displays the relevant info on a screen but when we want to extract only some particular info that we require for a project that we are doing, we need something to do this for us.
We can use microcontrollers or other circuits to do this for us. I used my Arduino to do this for me with a little bit of coding. First I displayed the extracted info on my monitor through the serial port, then I again made some changes to display it on an LCD as we would be talking portable. 😀
Here is the code that I used to extract the GPRMC datas.
There are codes (sketches in Arduino) for most of the sensors at Arduino Website.
#include <string.h>
#include <ctype.h>
int ledPin = 13; // LED test pin
int rxPin = 0; // RX PIN
int txPin = 1; // TX TX
int byteGPS=-1;
char linea[300] = "";
char comandoGPR[7] = "$GPRMC"; // string to filter out GPRMC
int cont=0;
int bien=0;
int conta=0;
int indices[13];
void setup() {
pinMode(ledPin, OUTPUT); // Initialize LED pin
pinMode(rxPin, INPUT);
pinMode(txPin, OUTPUT);
Serial.begin(4800);
for (int i=0;i<300;i++){ // Initialize a buffer for received data
linea[i]=' ';
}
}
void loop() {
digitalWrite(ledPin, HIGH);
byteGPS=Serial.read(); // Read a byte of the serial port
if (byteGPS == -1) { // See if the port is empty yet
delay(100);
} else {
linea[conta]=byteGPS; // If there is serial port data, it is put in the buffer
conta++;
Serial.print(byteGPS, BYTE);
if (byteGPS==13){ // If the received byte is = to 13, end of transmission
digitalWrite(ledPin, LOW);
cont=0;
bien=0;
for (int i=1;i<7;i++){ // Verifies if the received command starts with $GPR
if (linea[i]==comandoGPR[i-1]){
bien++;
}
}
if(bien==6){ // If yes, continue and process the data
for (int i=0;i<300;i++){
if (linea[i]==','){ // check for the position of the "," separator
indices[cont]=i;
cont++;
}
if (linea[i]=='*'){ // ... and the "*"
indices[12]=i;
cont++;
}
}
Serial.println(""); // ... and write to the serial port
Serial.println("");
Serial.println("---------------");
for (int i=0;i<12;i++){
switch(i){
case 0 :Serial.print("Time in UTC (HhMmSs): ");break;
case 1 :Serial.print("Status (A=OK,V=KO): ");break;
case 2 :Serial.print("Latitude: ");break;
case 3 :Serial.print("Direction (N/S): ");break;
case 4 :Serial.print("Longitude: ");break;
case 5 :Serial.print("Direction (E/W): ");break;
case 6 :Serial.print("Velocity in knots: ");break;
case 7 :Serial.print("Heading in degrees: ");break;
case 8 :Serial.print("Date UTC (DdMmAa): ");break;
case 9 :Serial.print("Magnetic degrees: ");break;
case 10 :Serial.print("(E/W): ");break;
case 11 :Serial.print("Mode: ");break;
case 12 :Serial.print("Checksum: ");break;
}
for (int j=indices[i];j<(indices[i+1]-1);j++){
Serial.print(linea[j+1]); //prints the corresponding data
}
Serial.println("");
}
Serial.println("---------------");
}
conta=0; // Reset the buffer
for (int i=0;i<300;i++){ //
linea[i]=' ';
}
}
}
}
Everyday Mischief 
