GPS clock...

Forum 2005-2010 (read only) General Exhibition
#1

Using the TinyGPS library and a serial 20x4 display, I created this simple clock…

http://www.flickr.com/photos/mowcius/3694162390/

here is the very basic messy code…

#include <NewSoftSerial.h>
#include <TinyGPS.h>

TinyGPS gps;
NewSoftSerial nss(9, 8);

void gpsdump(TinyGPS &gps);
bool feedgps();
void printFloat(double f, int digits = 2);

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

void loop()
{
  bool newdata = false;
  unsigned long start = millis();

  // Every 50 milliseconds we print an update
  while (millis() - start < 50)
  {
    if (feedgps())
      newdata = true;
  }
  
  if (newdata)
  {
    gpsdump(gps);

  }
}

void printFloat(double number, int digits)
{
  // Handle negative numbers
  if (number < 0.0)
  {
     Serial.print('-');
     number = -number;
  }

  // Round correctly so that print(1.999, 2) prints as "2.00"
  double rounding = 0.5;
  for (uint8_t i=0; i<digits; ++i)
    rounding /= 10.0;
  
  number += rounding;

  // Extract the integer part of the number and print it
  unsigned long int_part = (unsigned long)number;
  double remainder = number - (double)int_part;
  Serial.print(int_part);

  // Print the decimal point, but only if there are digits beyond
  if (digits > 0)
    Serial.print("."); 

  // Extract digits from the remainder one at a time
  while (digits-- > 0)
  {
    remainder *= 10.0;
    int toPrint = int(remainder);
    Serial.print(toPrint);
    remainder -= toPrint; 
  } 
}

void gpsdump(TinyGPS &gps)
{
  unsigned long age;
  int year;
  byte month, day, hour, minute, second, hundredths;

  feedgps();
  
  gps.crack_datetime(&year, &month, &day, &hour, &minute, &second, &hundredths, &age);
  Serial.print("Time: "); 
  
    if (hour < 10){
    Serial.print("0");
    Serial.print(static_cast<int>(hour +1));
}
  else
  Serial.print(static_cast<int>(hour +1)); 
 
  Serial.print(":"); 
  
    if (minute < 10){
    Serial.print("0");
    Serial.print(static_cast<int>(minute));
}
  else
  Serial.print(static_cast<int>(minute)); 
  
  ; Serial.print(":"); 
  
  if (second < 10){
    Serial.print("0");
    Serial.print(static_cast<int>(second));
}
  else
  Serial.print(static_cast<int>(second)); 
  
  Serial.print("                                                                  ");


}
  
bool feedgps()
{
  while (nss.available())
  {
    if (gps.encode(nss.read()))
      return true;
  }
  return false;
}

The display is currently plugged into the main serial output for the arduino so it shows funny stuff when uploading to the board.

Mowcius

#2

Cool!

Is this part of a larger project? GPS for a clock seems a bit of overkill.

#3

Yes... This was just running when my normal radio controlled clock went flat and for some reason I had no AAs charged up!

It was interesting how quickly it picked up the time, and when I turned the receiver upside down, the time stopped...

It is part of a larger project but I'm not revealing it yet...

The clock currently is refreshing the time every 20 milliseconds. This means it is re-saving and recalling the GPS data every 20 milliseconds and with the million read/write cycle limit (minimum) on EEPROM, this would only last me just over 13 hours...

Is there any way I can save the data to RAM so I won't have this issue...

Mowcius

#4

Sorry, I don't see where you're using EEPROM?

-j

#5

Here in the library for TinyGPS:

/*
  TinyGPS - a small GPS library for Arduino providing basic NMEA parsing
  Copyright (C) 2008-9 Mikal Hart
  All rights reserved.

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public
  License along with this library; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

#include "WProgram.h"
#include "TinyGPS.h"

#define _GPRMC_TERM   "GPRMC"
#define _GPGGA_TERM   "GPGGA"

TinyGPS::TinyGPS()
:  _time(GPS_INVALID_TIME)
,  _date(GPS_INVALID_DATE)
,  _latitude(GPS_INVALID_ANGLE)
,  _longitude(GPS_INVALID_ANGLE)
,  _altitude(GPS_INVALID_ALTITUDE)
,  _speed(GPS_INVALID_SPEED)
,  _course(GPS_INVALID_ANGLE)
,  _last_time_fix(GPS_INVALID_FIX_TIME)
,  _last_position_fix(GPS_INVALID_FIX_TIME)
,  _parity(0)
,  _is_checksum_term(false)
,  _sentence_type(_GPS_SENTENCE_OTHER)
,  _term_number(0)
,  _term_offset(0)
,  _gps_data_good(false)
#ifndef _GPS_NO_STATS
,  _encoded_characters(0)
,  _good_sentences(0)
,  _failed_checksum(0)
#endif
{
  _term[0] = '\0';
}

//
// public methods
//

bool TinyGPS::encode(char c)
{
  bool valid_sentence = false;

  ++_encoded_characters;
  switch(c)
  {
  case ',': // term terminators
    _parity ^= c;
  case '\r':
  case '\n':
  case '*':
    if (_term_offset < sizeof(_term))
    {
      _term[_term_offset] = 0;
      valid_sentence = term_complete();
    }
    ++_term_number;
    _term_offset = 0;
    _is_checksum_term = c == '*';
    return valid_sentence;

  case '

Sorry, I did not realise that my it wasn’t obvious in my code,

From my understanding, all of this kind of stuff is using EEPROM:

_new_altitude = parse_decimal();

Is this the case? and if so then what can I do about it?

Mowcius: // sentence begin
   _term_number = _term_offset = 0;
   _parity = 0;
   _sentence_type = _GPS_SENTENCE_OTHER;
   _is_checksum_term = false;
   _gps_data_good = false;
   return valid_sentence;
 }

// ordinary characters
 if (_term_offset < sizeof(_term) - 1)
   _term[_term_offset++] = c;
 if (!_is_checksum_term)
   _parity ^= c;

return valid_sentence;
}

#ifndef _GPS_NO_STATS
void TinyGPS::stats(unsigned long *chars, unsigned short *sentences, unsigned short *failed_cs)
{
 if (chars) *chars = _encoded_characters;
 if (sentences) *sentences = _good_sentences;
 if (failed_cs) *failed_cs = _failed_checksum;
}
#endif

//
// internal utilities
//
int TinyGPS::from_hex(char a)
{
 if (a >= ‘A’ && a <= ‘F’)
   return a - ‘A’ + 10;
 else if (a >= ‘a’ && a <= ‘f’)
   return a - ‘a’ + 10;
 else
   return a - ‘0’;
}

unsigned long TinyGPS::parse_decimal()
{
 char *p = _term;
 bool isneg = *p == ‘-’;
 if (isneg) ++p;
 unsigned long ret = 100UL * gpsatol(p);
 while (gpsisdigit(*p)) ++p;
 if (*p == ‘.’)
 {
   if (gpsisdigit(p[1]))
   {
     ret += 10 * (p[1] - ‘0’);
     if (gpsisdigit(p[2]))
       ret += p[2] - ‘0’;
   }
 }
 return isneg ? -ret : ret;
}

unsigned long TinyGPS::parse_degrees()
{
 char *p;
 unsigned long left = gpsatol(_term);
 unsigned long tenk_minutes = (left % 100UL) * 10000UL;
 for (p=_term; gpsisdigit(*p); ++p);
 if (p == ‘.’)
 {
   unsigned long mult = 1000;
   while (gpsisdigit(++p))
   {
     tenk_minutes += mult * (*p - ‘0’);
     mult /= 10;
   }
 }
 return (left / 100) * 100000 + tenk_minutes / 6;
}

// Processes a just-completed term
// Returns true if new sentence has just passed checksum test and is validated
bool TinyGPS::term_complete()
{
 if (_is_checksum_term)
 {
   byte checksum = 16 * from_hex(_term[0]) + from_hex(_term[1]);
   if (checksum == _parity)
   {
     if (_gps_data_good)
     {
#ifndef _GPS_NO_STATS
       ++_good_sentences;
#endif
       _last_time_fix = _new_time_fix;
       _last_position_fix = _new_position_fix;

switch(_sentence_type)
       {
       case _GPS_SENTENCE_GPRMC:
         _time      = _new_time;
         _date      = _new_date;
         _latitude  = _new_latitude;
         _longitude = _new_longitude;
         _speed     = _new_speed;
         _course    = _new_course;
         break;
       case _GPS_SENTENCE_GPGGA:
         _altitude  = _new_altitude;
         _time      = _new_time;
         _latitude  = _new_latitude;
         _longitude = _new_longitude;
         break;
       }

return true;
     }
   }

#ifndef _GPS_NO_STATS
   else
     ++_failed_checksum;
#endif
   return false;
 }

// the first term determines the sentence type
 if (_term_number == 0)
 {
   if (!gpsstrcmp(_term, _GPRMC_TERM))
     _sentence_type = _GPS_SENTENCE_GPRMC;
   else if (!gpsstrcmp(_term, _GPGGA_TERM))
     _sentence_type = _GPS_SENTENCE_GPGGA;
   else
     _sentence_type = _GPS_SENTENCE_OTHER;
   return false;
 }

if (_sentence_type != _GPS_SENTENCE_OTHER && _term[0])
 switch((_sentence_type == _GPS_SENTENCE_GPGGA ? 200 : 100) + _term_number)
 {
   case 101: // Time in both sentences
   case 201:
     _new_time = parse_decimal();
     _new_time_fix = millis();
     break;
   case 102: // GPRMC validity
     _gps_data_good = _term[0] == ‘A’;
     break;
   case 103: // Latitude
   case 202:
     _new_latitude = parse_degrees();
     _new_position_fix = millis();
     break;
   case 104: // N/S
   case 203:
     if (_term[0] == ‘S’)
       _new_latitude = -_new_latitude;
     break;
   case 105: // Longitude
   case 204:
     _new_longitude = parse_degrees();
     break;
   case 106: // E/W
   case 205:
     if (_term[0] == ‘W’)
       _new_longitude = -_new_longitude;
     break;
   case 107: // Speed (GPRMC)
     _new_speed = parse_decimal();
     break;
   case 108: // Course (GPRMC)
     _new_course = parse_decimal();
     break;
   case 109: // Date (GPRMC)
     _new_date = gpsatol(_term);
     break;
   case 206: // Fix data (GPGGA)
     _gps_data_good = _term[0] > ‘0’;
     break;
   case 209: // Altitude (GPGGA)
     _new_altitude = parse_decimal();
     break;
 }

return false;
}

long TinyGPS::gpsatol(const char *str)
{
 long ret = 0;
 while (gpsisdigit(*str))
   ret = 10 * ret + *str++ - ‘0’;
 return ret;
}

int TinyGPS::gpsstrcmp(const char *str1, const char *str2)
{
 while (*str1 && *str1 == *str2)
   ++str1, ++str2;
 return *str1;
}


Sorry, I did not realise that my it wasn't obvious in my code,

From my understanding, all of this kind of stuff is using EEPROM:

**_new_altitude = parse_decimal();**

Is this the case? and if so then what can I do about it?

Mowcius
#6

Those are typical variables, which use RAM.

Using an underscore as the first character in the variable name is a convention to indicate variables that are private and only used inside the package/function/library.

tinyGPS doesn't use EEPROM.

-j

#7

Ok, thanks...

How do you know, just out of interest, and how do I make something in my own code save into RAM and not EEPROM, i'm a bit of a newbie at all of this stuff...

Mowcius

#8

Unless you are going to a fair amount of trouble to do so, nothing will be stored in EEPROM.

All variables are in RAM.

-j

#9

Ok, yeah I get it now, after reading up on EEPROM... That explains some things, and makes things much easier...

Thanks,

Mowcius

#10