ARDUINO + GPS = INDICATOR LIMIT AREA

 /*
 Example code for connecting a Parallax GPS module to the Arduino
 Igor Gonzalez Martin. 05-04-2007
 [email protected]
 English translation by djmatic 19-05-2007
 Listen for the $GPRMC string and extract the GPS location data from this.
 Display the result in the Arduino's serial monitor.
 */
 #include <string.h>
 #include <ctype.h>
 int ledPin1= 10; // LED test pin
 int ledPin2= 9; //LED warning limit
 int ledPin3= 8; //LED warning over limit
 int byteGPS=-1;
 char linea[300] = "";
 char comandoGPR[7] = "$GPRMC";
 int cont=0;
 int bien=0;
 int conta=0;
 int indices[13];

 int lat = 0;
 void setup()
 {
   pinMode(ledPin1,OUTPUT);       // Initialize LED pin
   pinMode(ledPin2, OUTPUT);
   pinMode(ledPin3, OUTPUT);
   Serial.begin(4800);
   for (int i=0;i<300;i++){       // Initialize a buffer for received data
     linea[i]=' ';
   }


 }
 void loop()
 {
   digitalWrite(ledPin1, HIGH);
   byteGPS=Serial.read();         // Read a byte of the serial port
   if (byteGPS == -1) {           // See if the port is empty yet
     delay(100);
   } else {
     // note: there is a potential buffer overflow here!
     linea[conta]=byteGPS;        // If there is serial port data, it is put in the buffer
     conta++;
     Serial.write(byteGPS);
     if (byteGPS==13){            // If the received byte is = to 13, end of transmission
       // note: the actual end of transmission is <CR><LF> (i.e. 0x13 0x10)
       digitalWrite(ledPin1, LOW);
       cont=0;
       bien=0;
       // The following for loop starts at 1, because this code is clowny and the first byte is the <LF> (0x10) from the previous transmission.
       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
             // note: again, there is a potential buffer overflow here!
             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]);
               }

               Serial.println("");

               //********** Checking Latitude limit ******************
               if(i==2)//i=2 indicate latitude
               {
                      //convert latitude data to int
                      int k = indices[i];
                      lat = (linea[k+1]-48)*1000 + (linea[k+2]-48)*100 + (linea[k+3]-48)*10 +(linea[k+4]-48);
                      if(lat > 55)
                      {
                              //Led on when latitude value larger than 0055
                              digitalWrite(ledPin2, HIGH);
                      }
                      else
                      {
                              digitalWrite(ledPin2, LOW);
                      }
                 }
                 //***************************************************
         }

         Serial.print("Latitude: ");
         Serial.println(lat);
         Serial.println("---------------");
       }
       conta=0;                    // Reset the buffer
       for (int i=0;i<300;i++){    //
         linea[i]=' ';
       }
     }
   }
 }