GPS Sirfstar III garbage data

Forum 2005-2010 (read only) Hardware Troubleshooting
1

I would like some help figuring out why the arduino is not displaying the correct GPS data. The GPS has a fix and seems to be sending some data. Please look at the screenshot below.

The GPS is connected to the arduino like this...

GPS to Arduino
GND ---- GND
5V ------ 5V
RX ------ Pin 3
TX ------- Pin 2
GND ----- GND (digital side)

This source code mentions a powerpin. Does anyone know how this powerpin is set up?

// A simple sketch to read GPS data and parse the $GPRMC string
// see http://www.ladyada.net/make/gpsshield for more info

#include <AFSoftSerial.h>

AFSoftSerial mySerial =  AFSoftSerial(2, 3);
#define powerpin 4

#define GPSRATE 4800
//#define GPSRATE 38400


// GPS parser for 406a
#define BUFFSIZ 90 // plenty big
char buffer[BUFFSIZ];
char *parseptr;
char buffidx;
uint8_t hour, minute, second, year, month, date;
uint32_t latitude, longitude;
uint8_t groundspeed, trackangle;
char latdir, longdir;
char status;

void setup()
{
  if (powerpin) {
    pinMode(powerpin, OUTPUT);
  }
  pinMode(13, OUTPUT);
  Serial.begin(GPSRATE);
  mySerial.begin(GPSRATE);
   
  // prints title with ending line break
  Serial.println("GPS parser");

   digitalWrite(powerpin, LOW);         // pull low to turn on!
}


void loop()
{
  uint32_t tmp;
 
  //Serial.print("\n\rread: ");
  readline();
  // check if $GPRMC (global positioning fixed data)
  if (strncmp(buffer, "$GPRMC",6) == 0) {
   
    // hhmmss time data
    parseptr = buffer+7;
    tmp = parsedecimal(parseptr);
    hour = tmp / 10000;
    minute = (tmp / 100) % 100;
    second = tmp % 100;
   
    parseptr = strchr(parseptr, ',') + 1;
    status = parseptr[0];
    parseptr += 2;
   
    // grab latitude & long data
    // latitude
    latitude = parsedecimal(parseptr);
    if (latitude != 0) {
      latitude *= 10000;
      parseptr = strchr(parseptr, '.')+1;
      latitude += parsedecimal(parseptr);
    }
    parseptr = strchr(parseptr, ',') + 1;
    // read latitude N/S data
    if (parseptr[0] != ',') {
      latdir = parseptr[0];
    }
   
    //Serial.println(latdir);
   
    // longitude
    parseptr = strchr(parseptr, ',')+1;
    longitude = parsedecimal(parseptr);
    if (longitude != 0) {
      longitude *= 10000;
      parseptr = strchr(parseptr, '.')+1;
      longitude += parsedecimal(parseptr);
    }
    parseptr = strchr(parseptr, ',')+1;
    // read longitude E/W data
    if (parseptr[0] != ',') {
      longdir = parseptr[0];
    }
   

    // groundspeed
    parseptr = strchr(parseptr, ',')+1;
    groundspeed = parsedecimal(parseptr);

    // track angle
    parseptr = strchr(parseptr, ',')+1;
    trackangle = parsedecimal(parseptr);


    // date
    parseptr = strchr(parseptr, ',')+1;
    tmp = parsedecimal(parseptr);
    date = tmp / 10000;
    month = (tmp / 100) % 100;
    year = tmp % 100;
   
    Serial.print("\nTime: ");
    Serial.print(hour, DEC); Serial.print(':');
    Serial.print(minute, DEC); Serial.print(':');
    Serial.println(second, DEC);
    Serial.print("Date: ");
    Serial.print(month, DEC); Serial.println(char(34));
    Serial.print(date, DEC); Serial.println(char(34));
    Serial.println(year, DEC);
   
    Serial.print("Lat: ");
    if (latdir == 'N')
       Serial.print('+');
    else if (latdir == 'S')
       Serial.print('-');
    Serial.print(latitude/1000000, DEC); Serial.print('°', BYTE); Serial.print(' ');
    Serial.print((latitude/10000)%100, DEC); Serial.println(char(34)); Serial.print(' ');
    Serial.print((latitude%10000)*6/1000, DEC); Serial.print('.');
    Serial.print(((latitude%10000)*6/10)%100, DEC); Serial.println(char(34));
   
    Serial.print("Long: ");
    if (longdir == 'E')
       Serial.print('+');
    else if (longdir == 'W')
       Serial.print('-');
    Serial.print(longitude/1000000, DEC); Serial.print('°', BYTE); Serial.print(' ');
    Serial.print((longitude/10000)%100, DEC); Serial.println(char(34)); Serial.print(' ');
    Serial.print((longitude%10000)*6/1000, DEC); Serial.print('.');
    Serial.print(((longitude%10000)*6/10)%100, DEC); Serial.println(char(34));
   
   
  }
  //Serial.println(buffer);
}

uint32_t parsedecimal(char *str) {
  uint32_t d = 0;
 
  while (str[0] != 0) {
   if ((str[0] > '9') || (str[0] < '0'))
     return d;
   d *= 10;
   d += str[0] - '0';
   str++;
  }
  return d;
}

void readline(void) {
  char c;
 
  buffidx = 0; // start at begninning
  while (1) {
      c=mySerial.read();
      if (c == -1)
        continue;
      Serial.print(c);
      if (c == '\n')
        continue;
      if ((buffidx == BUFFSIZ-1) || (c == '\r')) {
        buffer[buffidx] = 0;
        return;
      }
      buffer[buffidx++]= c;
  }
}
2

the powerpin its to turn on the module when it goes LOW...

I see the code and I think you have the pin inverted...pin 2 TX and pin 3 is RX....

It should be:

AFSoftSerial mySerial = AFSoftSerial(3, 2);

I think...check that...

3

I tried switching the pins in the sketch and this is what is displayed in the serial window.

the powerpin its to turn on the module when it goes LOW...

Should I make pin 4 control whether the 5 volts reaches the GPS? I'm kind of new to the arduino, do you mean a pull down resistor configuration? Arduino Tutorial - Lesson 5

4

But what GPS module you are using? What its the default speed rate for that module?

5

The module is some type of Sirf star III. It does not look the modules on sparkfun.com or ladyada's store. I removed it from a Haicom HI-701.

The specs are at the bottom of the page:
http://www.easydevices.co.uk/pp/Car_Kits/GPS_Mounts/ASUS_A600_CAR_HOLDER_WITH_BUILT_IN_GPS.html

6

That's the sort of garbled output I receive when I am using the wrong baud rate. Try the others and see what happens. Maybe the GPS module is running at 9600bps rather than 4800?

7

I'd start by writing a very simple sketch to write the incomming data to the debug terminal and get rid of everything else till you get that working.