I've set up an Arduino to read a GPS and output part of the NMEA stream to its serial port. I'm trying to read that serial stream on my laptop using processing and although I can now read an NMEA sentence, every time I loop to read the next one its the same sentence (based on the time code). When I restart the program it reads a new sentence but it doesn't update. Should I be flushing the buffer contents before I try to read from the port again?

Appreciate your advice.
Jim Salacain

import processing.serial.*;

Serial myPort;  // Create object from Serial class
 int val;             // Data received from the serial port
 PFont font;
 int y = 0;
 int i=0;
 int j = 0;
 String valstring;
 String timecode;
 String lattcode;
 String longcode;
 String hemiNScode;
 String hemiEWcode;
 String altcode;
 String[] NMEA;

void setup()
{
  size(400, 400);
  font = loadFont("Helvetica-48.vlw");
  textFont(font, 18);
  myPort = new Serial(this, "/dev/tty.usbmodemfa131", 38400);
}

void draw()
{
  do {                                             // Look for start of NMEA sentence
    if ( myPort.available() > 0) {      // If port is available,
      val = myPort.read();                // read a byte and store it in val
    }
  } while (val != 36);                       // While val <> "$"

// Start reading the NMEA sentence

    do {
        if ( myPort.available() > 0) {  // If data is available,
          val = myPort.read();            // read it and store it in val
        }
        valstring = valstring + str(char(val));
    } while (val != 13);                     // Loop until EOL
   
    NMEA = split(valstring, ",");

    print("time: ");
    println(NMEA[1]);
    print("Lat: ");
    println(NMEA[2]);
    print("Hemi N/S: ");
    println(NMEA[3]);
    print("Long: ");
    println(NMEA[4]);
    print("Hemi E/W: ");
    println(NMEA[5]);
    print("Alt: ");
    println(NMEA[9]);
    println(" ");