Reading HDOP from NMEA GGA sentence via callback

dfrobot-l76k-i2c-hdop.ino

 /*!
  * based on getAllGNSS.ino
  * Added some code to read HDOP value.
  * Clavisound jul 24
  * @brief read all gnss data
  * @copyright Copyright (c) 2010 DFRobot Co.Ltd (http://www.dfrobot.com)
  * @license The MIT License (MIT)
  * @author ZhixinLiu([email protected])
  * @version V1.0
  * @date 2023-03-07
  * 
  * DEFAULT data:

$GNGGA,101747.000,,,,,0,00,25.5,,,,,,*7E
$GNGLL,,,,,101747.000,V,N*60
$GNGSA,A,1,,,,,,,,,,,,,25.5,25.5,25.5,1*01
$GNGSA,A,1,,,,,,,,,,,,,25.5,25.5,25.5,4*04
$GNGSA,A,1,,,,,,,,,,,,,25.5,25.5,25.5,2*02
$GPGSV,1,1,01,08,,,24,0*6A
$BDGSV,1,1,00,0*74
$GLGSV,1,1,00,0*79
$GNRMC,101747.000,V,,,,,,,170724,,,N,V*2A
$GNVTG,,,,,,,,,N*2E
$GNZDA,101747.000,17,07,2024,00,00*49
$GPTXT,01,01,01,ANTENNA OK*35

  * 
  * 
  * @url https://github.com/dfrobot/DFRobot_GNSS
  */

#include "DFRobot_GNSS.h"
//#include <NeoGPS_cfg.h>
//#include <NMEAGPS.h>

#define DEBUGINO 1
//NMEAGPS  gps;
//gps_fix  fix;

char nmeaBuffer[77];  // according to Google AI NMEA version 2.3 77 it's a safe choice
uint8_t nmeaIndex, nmeaStart, counterComma, indexHdop;
//char nmeaSentence[] = "GNGSA";     // comma in 17?
char nmeaSentence[6] = "GNGGA"; // comma in 8
uint16_t hdopNeoGPS; // multiply with 1000
char hdopTemp[] = "24.4";

#define NMEA_START    1
#define NMEA_NULL     0

// len is 32 most of the time because of arduino wire / i2c.
void hdop(char *data ,uint8_t len)
{

  for(uint8_t i = 0; i < len; i++){
    
    if ( data[i] == '$' && nmeaStart == NMEA_NULL ) {
      nmeaIndex = 0;
      nmeaBuffer[nmeaIndex] = '$';
      nmeaStart = NMEA_START;
    }

    // store characters one-by-one
    if ( nmeaStart == NMEA_START && data[i] != '$' && data[i] != '\r' ) {
      nmeaBuffer[nmeaIndex] = data[i];
    }
    
    // reset counter. We found end
    // TODO verify checksum
      if ( data [i] == '\r' ) { // dec: 10 line feed.  
      nmeaBuffer[nmeaIndex] = data[i];
      printMessage();
      }
    nmeaIndex++;
  }
}

void printMessage(){

  // In GSA is HDOP, VDOP, checksum.
  // in GGA HDOP is after 8th comma
  for ( uint8_t i = 1; i < 5; i++ ) {
    
    // Continue if we have match with nmeaSentence
    // we don't match; return.
    if ( nmeaBuffer[i] != nmeaSentence[i-1] ) { // i-1 because I don't store '$' in nmeaSentence
     // restart counters and abort.
     nmeaStart = NMEA_NULL;
     nmeaIndex = 0;
     return;
    }
  }

  #if DEBUGINO == 1
  Serial.print("\n");
  #endif

    // we have match. print
    counterComma = 0;
    indexHdop = 0;
    
    #if DEBUGINO == 1
    Serial.print("\nnmeaIndex:\t\t");Serial.println(nmeaIndex);
    #endif
    
    for ( uint8_t i = 0; i < nmeaIndex; i++ ) {

      // print message
      #if DEBUGINO == 1
      Serial.print(nmeaBuffer[i]);
      #endif

      // grab HDOP
      if ( (char)nmeaBuffer[i] == ',' ) { 
        counterComma++;
      }
      
      if ( counterComma == 8 ) {

          // when hdop is 25.5 we have five matches, including first ','
          if ( atoi(nmeaBuffer[i]) >= 0 || atoi(nmeaBuffer[i]) <= 9 || nmeaBuffer[i] == '.' ) {
          hdopTemp[indexHdop] = nmeaBuffer[i+1]; // Don't add the comma, store next character.
          indexHdop++;
        }
      }

/*
      // proccess via NeoGPS // FAILED
      if ( gps.decode(nmeaBuffer[i]) == NMEAGPS::DECODE_COMPLETED ) {
        if ( fix.valid.hdop ) {
        #if DEBUGINO == 1
        Serial.print("\n*NeoGPS hdop: ");
        Serial.print(fix.hdop);
        #endif
      }

      if ( fix.valid.time ) {
      #if DEBUGINO == 1
        Serial.print("\n*NeoGPS minutes: ");
        Serial.print(fix.dateTime.minutes);
        #endif
      }
    
      if ( fix.valid.date ) {
      #if DEBUGINO == 1
        Serial.print("\n*NeoGPS date: ");
        Serial.print(fix.dateTime.year);
        #endif
        }
      }*/
    }    


    // Delete garbage from i+1 above.
    hdopTemp[indexHdop-1] = '\0';
    hdopNeoGPS = atof(hdopTemp) * 1000;
    #if DEBUGINO == 1
    Serial.print("\nHDOP NeoStyle: ");Serial.print(hdopNeoGPS);
    Serial.print("\nhdopTemp: ");Serial.print(hdopTemp);
    #endif
    
    // restart counters.
    nmeaStart = NMEA_NULL;
    nmeaIndex = 0;
}

void callback(char *data ,uint8_t len)
{
  #if DEBUGINO == 1
  Serial.print("\nRaw callback len: ");Serial.println(len);
  #endif
  for(uint8_t i = 0; i < len; i++){
    /*
    if ( data [i] == '\r' ) {
    #if DEBUGINO == 1
      Serial.print("line feed");
      #endif
      
    }*/

   #if DEBUGINO == 1
   Serial.print(data[i]);
   #endif
   
  }

  /*
  #if DEBUGINO == 1
  Serial.print("\nInt callback: \n");
  #endif
  
  for(uint8_t i = 0; i < len; i++){
  #if DEBUGINO == 1
  Serial.print(" ");Serial.print((uint8_t)data[i]);
  #endif
  }
  */
}

#define I2C_COMMUNICATION  //use I2C for communication, but use the serial port for communication if the line of codes were masked

#ifdef  I2C_COMMUNICATION
  DFRobot_GNSS_I2C gnss(&Wire ,GNSS_DEVICE_ADDR);
#else
/* ---------------------------------------------------------------------------------------------------------------------
 *    board   |             MCU                | Leonardo/Mega2560/M0 |    UNO    | ESP8266 | ESP32 |  microbit  |   m0  |
 *     VCC    |            3.3V/5V             |        VCC           |    VCC    |   VCC   |  VCC  |     X      |  vcc  |
 *     GND    |              GND               |        GND           |    GND    |   GND   |  GND  |     X      |  gnd  |
 *     RX     |              TX                |     Serial1 TX1      |     5     |   5/D6  |  D2   |     X      |  tx1  |
 *     TX     |              RX                |     Serial1 RX1      |     4     |   4/D7  |  D3   |     X      |  rx1  |
 * ----------------------------------------------------------------------------------------------------------------------*/
/* Baud rate cannot be changed  */
  #if defined(ARDUINO_AVR_UNO) || defined(ESP8266)
    SoftwareSerial mySerial(4, 5);
    DFRobot_GNSS_UART gnss(&mySerial ,9600);
  #elif defined(ESP32)
    DFRobot_GNSS_UART gnss(&Serial1 ,9600 ,/*rx*/D2 ,/*tx*/D3);
  #else
    DFRobot_GNSS_UART gnss(&Serial1 ,9600);
  #endif
#endif

void setup()
{
  Serial.begin(9600);
  while(!gnss.begin()){
    Serial.println("NO Deivces !");
    delay(1000);
  }
  gnss.enablePower();      // Enable gnss power

/** Set GNSS to be used 
 *   eGPS              use gps
 *   eBeiDou           use beidou
 *   eGPS_BeiDou       use gps + beidou
 *   eGLONASS          use glonass
 *   eGPS_GLONASS      use gps + glonass
 *   eBeiDou_GLONASS   use beidou +glonass
 *   eGPS_BeiDou_GLONASS use gps + beidou + glonass
 */
  gnss.setGnss(eGPS_BeiDou_GLONASS);

}

void loop()
{
  
  //gnss.setCallback(callback);
  //gnss.getAllGnss();

  //strcpy(nmeaSentence, "GNGGA");
  gnss.setCallback(hdop);
  gnss.getAllGnss();

  /*strcpy(nmeaSentence, "GNRMC");
  gnss.setCallback(hdop);
  gnss.getAllGnss();
  */

  #if DEBUGINO == 1
  Serial.print("\nsats: ");Serial.print(gnss.getNumSatUsed());
  #endif
  delay(3000);
}