I'm trying to get GPS coordinates and send them to my API through the GPRS SIM900 and GPS NEO-6M shields.

In setup(), I first start the GPRS shield and call the function that connects to the internet. Then in loop(), I start to capture GPS coordinates and finally I send to my API, but my code doesn't work with this logic. I'd like to connect once and get GPS coordinates and send them to the API many times making a tracking.

The app stops if I run the code. connectToInternet() in setup() and getGpsPosition() in loop(). The SIM900 shield connects but the NEO6-M shield does not display the coordinates. The GPS only captures the coordinates if I do not connect to the internet.

Could someone help me? Following is my code and printout of the response to AT commands.

#include <SoftwareSerial.h>
#include <TinyGPS++.h>
#include <inetGSM.h>

static const int RXPin = 4, TXPin = 3;
InetGSM inet;
TinyGPSPlus gps;
SoftwareSerial serialGps(RXPin, TXPin);
char msg[50];
boolean started = false;
const char* dataCoord = "";

void setup() {
  // Serial connection.
  Serial.print(F("------------------------------------------------- \r\n"));
  Serial.println(F("Starting App Tracking Arduino"));
  Serial.print(F("------------------------------------------------- \r\n"));
  // Turn on GPRS
  // Start configuration of shield SIM900 with baudrate.
  if (gsm.begin(2400)) {
    started = true;
  } else Serial.println(F("\nstatus=IDLE"));
  if (started)
  // Start configuration of shield GPS NEO-6M with baudrate.

void loop() {
  // This sketch displays information every time a new sentence is correctly encoded.
  while (serialGps.available() > 0)
    if (gps.encode(serialGps.read())) getGpsPosition();

  Power up
void powerUpGprs() {
  pinMode(9, OUTPUT);
  digitalWrite(9, HIGH);
  Serial.println(F("\nPower Up SIM900!"));

  Connect to Internet via GSM
void connectToInternet() {
  Serial.print(F("------------------------------------------------- \r\n"));
  Serial.print(F(" CONNECT TO INTERNET \r\n"));
  Serial.print(F("------------------------------------------------- \r\n"));
  //GPRS attach, put in order APN, username and password.
  if (inet.attachGPRS("zap.vivo.com.br", "vivo", "vivo"))
  //Read IP address.

  Get GPS position
void getGpsPosition() {
  Serial.print(F("------------------------------------------------- \r\n"));
  Serial.print(F(" GET POSITON \r\n"));
  Serial.print(F("------------------------------------------------- \r\n"));
  // geolocation
  TinyGPSDate &d = gps.date;
  TinyGPSTime &t = gps.time;
  char* timestamp;
  if (!d.isValid()) {
    timestamp = "00/00/0000 00:00:00";
  } else {
    char sz[32];
    sprintf(sz, "%02d/%02d/%02d %02d:%02d:%02d",
      d.day(), d.month(), d.year(),
      t.hour(), t.minute(), t.second());
    timestamp = sz;
  String position = String("");
  position.concat(String("timestamp=") + String(timestamp));
  position.concat(String("&latitude=") + String(gps.location.lat(), 6));
  position.concat(String("&longitude=") + String(gps.location.lng(), 6));
  position.concat(String("&altitude=") + String(gps.altitude.meters()));
  position.concat(String("&speed=") + String(gps.speed.kmph()));

  Send To API, The function inet.httpPOST(),
  this is submit method POST via http request
void send2Api() {
  Serial.print(F("------------------------------------------------- \r\n"));
  Serial.print(F(" SEND TO API\r\n"));
  Serial.print(F("------------------------------------------------- \r\n"));
  // Read until serial buffer is emapty.
  // TCP Client HTTP, send a POST request to the server and save the reply.
  int numdata = inet.httpPOST("api.myapp.com.br", 80, "/geolocations ", dataCoord, msg, 100);
  // Print the results.
  Serial.print(F("\nNumber of data received: "));
  Serial.print(F("\nData received: "));

If I connect to internet the GPS does not display the coordinates.

Run app with  connectToInternet() and getGpsPosition

But if I don't connect to internet the GPS displays the coordinates.

connectToInternet() function omitted


1 Answer 1


You are using 2 SoftwareSerial instances and you're losing bytes when you aren't listening to the other port. Also your inetGSM library uses pins 3 for RX with the SIM900 and in your Arduino sketch, pin 3 is also the Arduino TX pin to the GPS module. Therefore, anything sent by the Arduino over pin 3 is received by both modules. Confusion.

  • Use the GPS module with another pair of pins, maybe, 7 for RX and 8 for TX. Connect the GPS TX to 7 and its RX to 8.
  • Try adding: gsm._cell.listen(); right before this line:

    // Read until serial buffer is empty. gsm.WhileSimpleRead();

  • Also add serialGps.listen(); right before this line:

    // Print the results. Serial.print(F("\nNumber of data received: "));

Refer to this answer for more details.


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