GPS NEO-6M

#include <SoftwareSerial.h>

// GPS NEO-6M canonical example for Arduino Uno
// Wiring:
// GPS VCC -> 5V
// GPS GND -> GND
// GPS TX  -> D4 (Arduino receives on this pin)
// GPS RX  -> D3 (Arduino transmits on this pin)

SoftwareSerial gpsSerial(4, 3); // RX, TX

char lineBuffer[120];
uint8_t lineIndex = 0;

void setup() {
  Serial.begin(9600);
  gpsSerial.begin(9600);

  Serial.println(F("GPS NEO-6M example started."));
  Serial.println(F("Waiting for NMEA sentences..."));
}

void printField(const char *label, const char *value) {
  Serial.print(label);
  Serial.print(value);
}

void handleRMC(char *sentence) {
  // Example: $GPRMC,hhmmss.sss,A,llll.ll,a,yyyyy.yy,a,x.x,x.x,ddmmyy,,,A*hh
  char *fields[12] = {0};
  uint8_t count = 0;
  char *token = strtok(sentence, ",");
  while (token && count < 12) {
    fields[count++] = token;
    token = strtok(NULL, ",");
  }

  if (count < 10) return;
  if (fields[2] == NULL || fields[2][0] != 'A') {
    Serial.println(F("No GPS fix yet."));
    return;
  }

  Serial.println(F("--- Valid Fix (RMC) ---"));
  if (fields[1]) printField("Time (UTC): ", fields[1]), Serial.println();
  if (fields[3] && fields[4]) {
    Serial.print(F("Latitude: "));
    Serial.print(fields[3]);
    Serial.println(fields[4]);
  }
  if (fields[5] && fields[6]) {
    Serial.print(F("Longitude: "));
    Serial.print(fields[5]);
    Serial.println(fields[6]);
  }
  if (fields[7]) {
    Serial.print(F("Speed (knots): "));
    Serial.println(fields[7]);
  }
  if (fields[8]) {
    Serial.print(F("Course (deg): "));
    Serial.println(fields[8]);
  }
  if (fields[9]) {
    Serial.print(F("Date (ddmmyy): "));
    Serial.println(fields[9]);
  }
}

void handleGGA(char *sentence) {
  // Example: $GPGGA,time,lat,N,lon,E,fixquality,numsat,hdop,alt,M,...
  char *fields[15] = {0};
  uint8_t count = 0;
  char *token = strtok(sentence, ",");
  while (token && count < 15) {
    fields[count++] = token;
    token = strtok(NULL, ",");
  }

  if (count < 8) return;
  int fixQuality = fields[6] ? atoi(fields[6]) : 0;
  int satellites = fields[7] ? atoi(fields[7]) : 0;

  Serial.println(F("--- GGA Status ---"));
  Serial.print(F("Fix quality: "));
  Serial.println(fixQuality);
  Serial.print(F("Satellites: "));
  Serial.println(satellites);
  if (fields[8]) {
    Serial.print(F("HDOP: "));
    Serial.println(fields[8]);
  }
  if (fields[9] && fields[10]) {
    Serial.print(F("Altitude: "));
    Serial.print(fields[9]);
    Serial.print(' ');
    Serial.println(fields[10]);
  }
}

void loop() {
  while (gpsSerial.available()) {
    char c = (char)gpsSerial.read();

    if (c == '\n') {
      lineBuffer[lineIndex] = '\0';
      lineIndex = 0;

      // Trim trailing carriage return if present
      char *sentence = lineBuffer;
      size_t len = strlen(sentence);
      if (len > 0 && sentence[len - 1] == '\r') {
        sentence[len - 1] = '\0';
      }

      if (strncmp(sentence, "$GPRMC", 6) == 0 || strncmp(sentence, "$GNRMC", 6) == 0) {
        char temp[120];
        strncpy(temp, sentence, sizeof(temp));
        temp[sizeof(temp) - 1] = '\0';
        handleRMC(temp);
      } else if (strncmp(sentence, "$GPGGA", 6) == 0 || strncmp(sentence, "$GNGGA", 6) == 0) {
        char temp[120];
        strncpy(temp, sentence, sizeof(temp));
        temp[sizeof(temp) - 1] = '\0';
        handleGGA(temp);
      }
    } else {
      if (lineIndex < sizeof(lineBuffer) - 1) {
        lineBuffer[lineIndex++] = c;
      } else {
        lineIndex = 0; // overflow protection
      }
    }
  }
}