Minimalist Arduino GPS Parser

The Sparkfun Redboard and other toys can be a lot of fun indeed.  What I like about the Arduinos, is that the board support packages are very good and it is very easy to intersperse regular C with the simple Sketch code.

Here is a minimalist on the fly parser for NMEA GPS data positioning that I've been playing with.  It receives and analyzes one byte at a time, so there is no delay.  You have the data the very moment it is available:

// Minimal GPS Parser
// Herman Oosthuysen, 2016

#include <string.h>
#include <SoftwareSerial.h>

// GPS serial: 9600N81
// Example GPS data capture
//$GPGSA,A,3,11,31,27,14,,,,,,,,,2.09,1.85,0.96*08
//$GPRMC,155741.000,A,2413.4311,N,05541.2983,E,1.19,45.34,240816,,,A*5D
//$GPVTG,45.34,T,,M,1.19,N,2.21,K,A*03
//$GPGGA,155742.000,2413.4313,N,05541.2985,E,1,4,1.85,263.9,M,-29.9,M,,*77

//Time, Lat, North, Long, East, Fix:
//$GPGGA,155743.000,2413.4317,N,05541.2986,E,1,

//Heading true, heading magnetic, speed knots, speed kph
//$GPVTG,45.34,T,,M,1.19,N,2.21,K

const int rxpin=8;
//const int txpin=9;
const int txpin=255; // Rx only, frees up a pin
SoftwareSerial serial_gps(rxpin, txpin);

char ch = 0;
int cnt = 0;
int csv = 0;
int fix = 0;
int res = 1;
char dat[16];
char tim[16];
char lat[16];
char lng[16];

void setup()
{
  Serial.begin(9600);
  serial_gps.begin(9600);
}

void loop()
{
  if(serial_gps.available())
  {
    ch=serial_gps.read();
    //Serial.print(ch);

    // simple parser, start with $
    if(ch == '$')
    {
      cnt = 0;
      csv = 0;
      fix = 0;
    }
    else
    {
      dat[cnt++] = ch;
     
      if(ch == ',')
      {
        dat[--cnt] = 0;
        cnt = 0;
        csv++;

        if(csv == 1)
        {
          res = strcmp(dat,"GPGGA");
          if(res == 0)
            fix = 1;
        }

        // Assume N, E
        if(fix == 1)
        {
          if(csv == 2)
            strcpy(tim, dat);
          else if(csv == 3)
            strcpy(lat, dat);
          else if(csv == 5)
            strcpy(lng, dat);
          else if(csv == 6)
          {
            Serial.print("Tim: ");
            Serial.println(tim);
            Serial.print("Lat: ");
            Serial.println(lat);
            Serial.print("Lon: ");
            Serial.println(lng);
            fix = 0;
          }
        }
      }
    }
  }
}

The result is:
Tim: 154417.000
Lat: 2413.4364
Lon: 05541.2907

Cool, now you all know exactly where I live.

In days gone by, there were phone directories, now, there is GPS.

There are Arduino GPS libraries available, but they are too complex for my liking.  For a toy, one can make some assumptions to simplify things, which saves processing cycles and memory.  I don't see the need to verify the checksum, or check whether the position is north and east - I'm not going to drive my toy car to the other side of the globe.

The Arduino software and Redboard works pretty good on my Mac, but if I unplug it from the USB port, then I have to reboot the Mac to get the USB serial port to work again when I plug it back in.  There should be a way to force the Mac to reload the driver, but I haven't gotten round to diving into the OSX weeds to figure it out yet.

Have fun!

Herman