How can I create an automated GPS tracker using A9G AI Thinker module? - arduino

Question

I have an AI Thinker A9G module connected to an ESP8266 D1 mini. I have the following script to send and receive AT commands to/from the module. The idea is to get a SMS with the Google maps GPS location of the module onto my mobile phone.
// GPS tracker with AI Thinker A9G module and AZ Delivery D1 Mini ESP8266 module
#include <SoftwareSerial.h>
#define rxPin D7
#define txPin D8
SoftwareSerial A9modem(rxPin, txPin); // Pins D7 Rx and D8 Tx are used as used as software serial pins
String incomingData; // For storing incoming serial data
String gpsData; // For storing location data
char msg;
char call;
void setup()
{
Serial.begin(115200); // Baud rate for serial monitor
A9modem.begin(115200); // Baud rate for GSM shield
Serial.println("GPS/GSM A9G BEGIN");
Serial.println("Enter character for control option: ");
Serial.println("h : to disconnect a call");
Serial.println("s : to send a message");
Serial.println("r : to receive a message");
Serial.println("c : to make a call");
Serial.println("l : to read location");
Serial.println("d : to disconnect gps");
Serial.println();
delay(100);
// Set SMS mode to text mode
A9modem.print("AT+CMGF=1\r");
delay(100);
// Set GSM module to TP show the output on serial out
A9modem.print("AT+CNMI=2,2,0,0,0\r");
delay(100);
}
void loop()
{
ReceiveMessage();
gpsData = incomingData.substring(33, 52);
Serial.print("Location: ");
Serial.println(gpsData);
delay(2000);
if (Serial.available() > 0)
switch(Serial.read())
{
case 's':
SendMessage();
break;
case 'r':
ReceiveMessage();
break;
case 'c':
MakeCall();
break;
case 'h':
HangupCall();
break;
case 'l':
ReadLocation();
break;
case 'd':
DisconnectGps();
break;
}
}
void ReceiveMessage()
{
if (A9modem.available() > 0)
{
incomingData = A9modem.readString(); // Get the data from the serial port
Serial.print(incomingData);
delay(100);
}
}
void SendMessage()
{
A9modem.println("AT+CMGF=1"); // Sets the GSM Module into text mode
delay(1000); // Delay of one second
A9modem.println("AT+CMGS=\"xxxxxxxxxxxxx\"\r"); // Replace your mobile number here
delay(1000);
String sms = "http://maps.google.com/maps?q=" + gpsData; // Create the SMS location string
A9modem.println(sms);
delay(100);
A9modem.println((char)26); // ASCII code of CTRL+Z
delay(1000);
}
void MakeCall()
{
A9modem.println("ATD+xxxxxxxxxxxxx;"); // Replace your mobile number here
Serial.println("Calling "); // Print response over serial port
delay(1000);
}
void HangupCall()
{
A9modem.println("ATH");
Serial.println("Hangup Call");
delay(1000);
}
void DisconnectGps()
{
A9modem.println("AT+GPS=0");
Serial.println("Disconnect GPS");
delay(1000);
}
void ReadLocation()
{
A9modem.println("AT+GPS=1");
delay(1000);
A9modem.println("AT+LOCATION=2"); // Check location every two seconds
delay(2000);
}
So if I use the commands "l" and "s" in Arduino IDE serial monitor everything is working well but I don't know how to change the code in a way that I get a fully automated GPS tracker. The idea is the following: Power on starts the tracker. When gpsData string is not empty the first SMS will be send to my mobile phone. The next SMS follows 20 minutes later and so on until power is switched off. Could you help please?
Thanks in advance!

Answer 1

Finally I came up with this solution but I'm not very happy with it (it is working but I have to restart the module from time to time because there are no GPS data). There are 3 reasons for this: There is no error handling for the GPS function, I set the delays in a more ore less random way to get everything working but I don't know if the values make sense and I don't know if the substring() function is the best way to get the location from the serial response.
// GPS tracker with AI Thinker A9G module and AZ Delivery D1 Mini
ESP8266 module
#include <SoftwareSerial.h>
#define rxPin D7
#define txPin D8
SoftwareSerial A9modem(rxPin, txPin); // Pins D7 Rx and D8 Tx are used as used as software serial pins
String incomingData; // For storing incoming serial data
String gpsData; // For storing location data
int runGps = 1;
int sendSms = 0;
void setup()
{
pinMode(LED_BUILTIN, OUTPUT); // Use builtin LED for correct GPS status
Serial.begin(115200); // Baud rate for serial monitor
A9modem.begin(115200); // Baud rate for GSM shield
// Set SMS mode to text mode
A9modem.print("AT+CMGF=1\r");
delay(300);
// Set GSM module to TP show the output on serial out
A9modem.print("AT+CNMI=2,2,0,0,0\r");
delay(1000);
Serial.end();
delay(500);
}
void loop()
{
Serial.begin(115200);
ReceiveMessage(); // Start a new serial stream
gpsData = incomingData.substring(33, 52); // Strip all unnessesary data from the stream
Serial.print("Location: "); // Check if the location data are correct
Serial.println(gpsData);
delay(1000);
if(runGps == 1) { // Start GPS
ReadLocation();
delay(20000); // Wait for GPS to be ready
}
if(gpsData.length() == 19 && sendSms == 0) { // If the location string is correct send SMS
if (isdigit(gpsData.charAt(0))) { // Check if the stream starts with a number
SendMessage();
digitalWrite(LED_BUILTIN, HIGH);
delay(300);
digitalWrite(LED_BUILTIN, LOW);
delay(300);
digitalWrite(LED_BUILTIN, HIGH);
delay(300);
digitalWrite(LED_BUILTIN, LOW);
delay(300);
digitalWrite(LED_BUILTIN, HIGH);
}
}
if(runGps == 0 && sendSms == 1) {
runGps = 1;
sendSms = 0;
delay(6000); // Make sure that all SMS serial communication is over
while (A9modem.available()) {
A9modem.read(); // Delete all data from serial buffer
}
delay(300000); // If SMS was sent wait 5 minutes before running the main loop again
Serial.end();
delay(500);
}
}
void ReceiveMessage()
{
if (A9modem.available() > 0)
{
incomingData = A9modem.readString(); // Get the data from the serial port
Serial.print(incomingData);
delay(500);
}
}
void SendMessage()
{
sendSms = 1; // Stop starting the SendMessage function
A9modem.println("AT+CMGF=1"); // Sets the GSM Module into text mode
delay(1000);
A9modem.println("AT+CMGS=\"xxxxxxxxxx\"\r"); // Replace your mobile number here
delay(1000);
String sms = "http://maps.google.com/maps?q=" + gpsData; // Create the SMS string
A9modem.println(sms);
delay(500);
A9modem.println((char)26); // ASCII code of CTRL+Z
delay(500);
}
void ReadLocation()
{
runGps = 0; // Stop starting the ReadLocation function
A9modem.println("AT+GPS=1");
delay(1000);
A9modem.println("AT+LOCATION=2"); // Check location every two seconds
delay(2000);
}

Answer 2

Try turning ON the NMEA stream from the A9G. Say you want to get the NMEA data every t seconds, you can add and then call the following function once in the void setup()
void TurnOnNMEA(int t)
{
if(t > 3600)
t = 3600; // Because the max time is 3600s
A9modem.print("AT+GPSRD=");
A9modem.println(t);
while(!A9modem.available()); // wait till the A9G sends a response
char c;
while(A9modem.available())
{
c = A9modem.read();
Serial.print(c);
delay(2); // Time needed for the next character
}
}
This will start the NMEA data stream every t seconds which you can print using the following function,
void ReadNMEA()
{
char c; // Read each character from the stream as it comes
if(A9modem.available())
{
c = A9modem.read();
Serial.print(c);
delay(2); // Time needed for the next character
}
}
Parsing and decoding the NMEA is a bit tricky thing to do. There is a lot of information inside it and the decoding depends on what you want to do with it. If you just want the location, you can parse the $GNGGA line.
When parsing the data, DO NOT USE Arduino String() class. It is a very bad idea when handling this kind of stream. Instead, use char array.