I got my GPS module working with some filtering for the right lines. I program mainly by trial and error so the code might not be elegant or by the book. But it works. I started with the softserial example from Heather: http://www.arduino.cc/en/Tutorial/SoftwareSerial. I changed it here and there and made it to filter out a specific NMEA rule.
I was quite suprised when I discovered how easy it is to use avr-libc library.
Any comments are welcome.
//Created August 15 2006
//Heather Dewey-Hagborg
//http://www.arduino.cc
//reworked to GPS reader
//Dirk, december 2006
#include <ctype.h>
#include <string.h>
#define bit9600Delay 84
#define halfBit9600Delay 42
#define bit4800Delay 188
#define halfBit4800Delay 94
byte rx = 6;
byte tx = 7;
byte SWval;
char dataformat[7] = "$GPRMC";
char messageline[80] = "";
int i= 0;
void setup() {
pinMode(rx,INPUT);
pinMode(tx,OUTPUT);
digitalWrite(tx,HIGH);
digitalWrite(13,HIGH); //turn on debugging LED
SWprint('h'); //debugging hello
SWprint('i');
SWprint(10); //carriage return
Serial.begin(9600);
}
void SWprint(int data)
{
byte mask;
//startbit
digitalWrite(tx,LOW);
delayMicroseconds(bit4800Delay);
for (mask = 0x01; mask>0; mask <<= 1) {
if (data & mask){ // choose bit
digitalWrite(tx,HIGH); // send 1
}
else{
digitalWrite(tx,LOW); // send 0
}
delayMicroseconds(bit4800Delay);
}
//stop bit
digitalWrite(tx, HIGH);
delayMicroseconds(bit4800Delay);
}
char SWread()
{
byte val = 0;
while (digitalRead(rx));
//wait for start bit
if (digitalRead(rx) == LOW) {
delayMicroseconds(halfBit4800Delay);
for (int offset = 0; offset < 8; offset++) {
delayMicroseconds(bit4800Delay);
val |= digitalRead(rx) << offset;
}
//wait for stop bit + extra
delayMicroseconds(bit4800Delay);
delayMicroseconds(bit4800Delay);
return val;
}
}
void char2string()
{
i = 0;
messageline[0] = SWread();
if (messageline[0] == 36) //string starts with $
{
i++;
messageline[i] = SWread();
while(messageline[i] != 13 & i<80) //carriage return or max size
{
i++;
messageline[i] = SWread();
}
messageline[i+1] = 0; //make end to string
}
}
void loop()
{
digitalWrite(13,HIGH);
//only print string with the right dataformat
char2string();
if (strncmp(messageline, dataformat, 6) == 0 & i>4)
{
for (int i=0;i<strlen(messageline);i++)
{
Serial.print(messageline[i], BYTE);
}
}
//Serial.print(SWread(),BYTE); //use this to get all GPS output, comment out from char2string till here
}