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Why can I get GPS fix while Im an GSM mode

userHead pierrot10 2014-09-14 09:56:59 3750 Views1 Replies
Good evening,

I still have difficulties to understand the user of gps and gsm mode. I am sorry.

I worked hard I can have good result.

Here is my code, where I am going to explain.

Note, now, I work wirh Leonardo board instead of UNO

Fiest I turn up the module. I will not past all function as the setup loop works fine
steup()
Code: Select all
void setup()
{
  // TURN THE SERIAL AT 9600 baut
  Serial.begin(baud_rate);              // Comm to PC
  while(!Serial);                       // while the serial stream is not open, do nothing:
  
  #ifdef LEONARDO
    Serial1.begin(baud_rate);           // Comm to GPS/GSM
    while(!Serial1);                    // while the serial stream is not open, do nothing:
  #endif
  
  delay(4000);                          // Wait for 4sec after begin
  
  if(debug)
  {
    Serial.println(F("\n******************************"));
    Serial.println(F("STARTING SYSTEM Read AT stream"));
    Serial.println(F("******************************"));
  }
  
  // SET THE PIN
  pinMode(pin_gsm,OUTPUT);              // Set the pins
  pinMode(pin_gps,OUTPUT);
  pinMode(pin_power,OUTPUT);
 
  powerUpModule:
  // POWER THE MODULE. THE powerUp function will attempt 4 time if AT does not return RDY
  if(powerUp(4))                       // Nb of attempt
  {
      // Enabling GSM mode
      gsm_enable();
     /*
       the gsm_enable does
        digitalWrite(pin_gsm,LOW);                //Enable GSM mode
        digitalWrite(pin_gps,HIGH);               //Disable GPS mode
       delay(2000);
     */

    
      // Staring GPS AT+CGPSPWR=1 AT+CGPSRST=0.
      if(start_gps())
      {
        readyToGo = true;
        if(debug)
        {
          Serial.println(F("\n***********")); 
          Serial.println(F("READY TO GO"));
          Serial.println(F("***********\n")); 
        }
      }
      else
      {
        // gps or rst does not return OK
        readyToGo = false;
        goto powerUpModule;
      }
  }
  else
  {
    // Could not be poweredUp
    if(debug) Serial.print(F("Could not powerup the module."));
    readyToGo = false;
  }
}
From now, I AM ON GSM MODE
Now the loop() loop does simply
Code: Select all
void loop()
{
  if(readyToGo)
  {
    if(debug) serialhwread();
     // Check the gps stat
     if(gps_stat() > 0)
     {
       // Display gps fixes
       gps_read();
     }
     delay(5000);
    
  } 
}
To understand my question, look at the two following function
Code: Select all
int gps_stat(void)
{ 
  if(debug) Serial.println(F("\n> Getting GPS Stat"));
  int val = 0;
  if(strstr(read_AT_string("AT+CGPSSTATUS?",3000),"OK") != NULL)
  {
    if(strstr(buffer,"+CGPSSTATUS: Location Unknown") != NULL) 
    {
      val=0;
    }
    if(strstr(buffer,"+CGPSSTATUS: Location Not Fix") != NULL)
    {
      val=1;
    }
    if(strstr(buffer,"+CGPSSTATUS: Location 2D Fix") != NULL)
    {
      val=2;
    }
    if(strstr(buffer,"+CGPSSTATUS: Location 3D Fix") != NULL)
    {
      val=3;
    }
  }
  else
  {
    if(debug) Serial.println(F("  Could not get GPS Stat"));
    val=0;
  }
  /*
  "Location Unknown": if GPS is not run
  "Location Not Fix": after GPS is run ,and haven’t fixed,
  "Location 2D Fix" : after GPS status is 2D fixed,
  "Location 3D Fix" : after GPS status is 3D fixed. 
  */
  if(debug_buffer)
  {
    Serial.println(F("------- Show buffer------"));
    Serial.println(buffer);
    Serial.println(F("-------------------------\n"));
  }
  
  return val; 

}
and
Code: Select all
// read data to gps_buf[] from GPS
static int gps_read () {
  
  read_AT_string("AT+CGPSINF=2",6000);
  Serial.println(F("------- Show buffer------"));
  Serial.println(buffer);;
  Serial.println(F("-------------------------\n"));
}
You can observe, I use the AT command
Code: Select all
AT+CGPSSTATUS?
AT+CGPSINF=2
After about 20sec, I got fixes while I never switch the GPS mode
Code: Select all
digitalWrite(pin_gps,LOW);                //Enable GPS mode
  digitalWrite(pin_gsm,HIGH);                //Disable GSM mode
  delay(2000);
But why!!!!!!

Does the gps mode is a way to receive the GPS fix automoticaly from Serial?
In my case, I can I switch S3 to GSM mode?

Then could you clearly telll me why I have to switch to GPS mode. I carefuly look at the Sketc exemple and particularely to http://www.dfrobot.com/wiki/index.php/G ... indication (The last, at the bottom "GPS Sample Code").
I observed that the GPS mode is enabled at the end of the start_up function, and it stay at the gps mode. I also never observed the command AT+CGPSINF= to get the GPS fixes.

Could you clarify me that. It would be very helpfully.

Many many thank

2014-09-15 19:16:41 Hi Pierrot,

In the older version, UART select is the switch of the GSM and GPS, but it is not very convenient to change its working mode. So if the switch in middle, you could control it via code.
In the USB debugging mode, if you want to check the GPS data, turn the switch to GSM side, and input AT command, then you need switch it GPS side to check the data in the monitor.
And for the GPS fix, I don't have information regarding this feature yet. It is better to check its datasheet.

Anyway, I find a library about this chip. maybe you can take a look. Wrote by marco
https://github.com/MarcoMartines/GSM-GPRS-GPS-Shield userHeadPic Grey.CC
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