SIM808 module: GSM location command (AT+CIPGSMLOC=1,1) giving wrong value after execution of sending message command (AT+CMGS=+91xxxxxxxx)

Question

I wrote the code that if an interrupt is generated, get GSM location and send a message.

The first time the interrupt is generated, I got the correct GSM location using AT+CIPGSMLOC=1,1 and successfully sent a message using the AT+CMGS=+91xxxxxxxxcommand.

But the next time an interrupt was generated, AT+CIPGSMLOC=1,1 gave a wrong location. When I commented out the code to send a message, on every interrupt generated I am getting the correct GSM location. So it seems like the problem is occurring after sending a message. But I have no clue what exactly is going wrong. Following is my code.

Note: on restarting the module, I'm again getting the correct location the first time, before sending a message.

void setup() {
  mySerial.begin(9600);
  Serial.begin(9600);
  while (!Serial) {
  }
  // initialize the pushbutton pin as an input:
  pinMode(sensorPin, INPUT);
  // Attach an interrupt to the ISR vector
  attachInterrupt(0, pin_ISR, FALLING);
}

/////////***GSM RESPONSE***///////////
String DisplayGSMResponse() {
  if(mySerial.available()) {
    String gsm_input="";
    while(mySerial.available()) {
      gsm_input+= (char)mySerial.read();
    }
    gsm_input.trim();
    delay(1000);
    Serial.println(gsm_input);
    return gsm_input;
  }
}

void SendMessage(String mobNum,String Location) {
  Serial.println("Sending message..");
  mySerial.println("AT+CMGF=1");
  //Sets the GSM Module in Text Mode
  delay(2000);
  // Delay of 1000 milli seconds or 1 second
  DisplayGSMResponse();
  mySerial.println("AT+CMGS=\""+mobNum+"\"\r");
  // mobile Number
  delay(4000);
  DisplayGSMResponse();
  cleanBuffer();
  mySerial.print("test");
  // The SMS text you want to send
  delay(100);
  mySerial.println((char)26);
  // ASCII code of CTRL+Z
  delay(8000);
  DisplayGSMResponse();
}

void gprsInit() {
  if (isGPRSInit) {
    return;
  }
  Serial.println("GPRS INITIALIZING");
  mySerial.println("AT+SAPBR=3,1,\"CONTYPE\",\"GPRS\"");
  delay(2000);
  DisplayGSMResponse();
  mySerial.println("AT+SAPBR=3,1,\"APN\",\"INTERNET\"");
  delay(2000);
  DisplayGSMResponse();
  mySerial.println("AT+SAPBR=1,1");
  delay(8000);
  DisplayGSMResponse();
  mySerial.println("AT+SAPBR=2,1");
  delay(2000);
  DisplayGSMResponse();
  isGPRSInit = true;
}

void gprsterm() {
  mySerial.println("AT+SAPBR=0,1");
  delay(1000);
  DisplayGSMResponse();
  isGPRSInit = false;
}

String getGPS() {
  Serial.println("GETTING GPS LOCATION");
  String loc = "";
  String location = "";
  mySerial.println("AT+CIPGSMLOC=1,1");
  delay(3000);
  loc = DisplayGSMResponse();
  return location;
}

void loop() {
  if (buttonState == 1) {
    detachInterrupt(0);
    gprsInit();
    location = getGPS();
    SendMessage(mobileNumber, location);
    gprsterm();
    Serial.println("location = " + location);
    buttonState = 0;
    location = "";
    attachInterrupt(0, pin_ISR, FALLING );
  }
}

void pin_ISR() {
  buttonState = 1;
  Serial.println("interrupt");
}

EDIT: added gprsterm function.

Note: I removed the interrupt and called the code inside the loop function twice. The first time I got a correct result. The second time a wrong result. So it seems like the interrupt is not be causing the problem.

EDIT2: One interesting thing I found is that at my home it is showing correct results every time, but in the office it is showing a wrong location on second location call i.e after the SMS was sent and we get the GSM location using AT+CIPGSMLOC=1,1.

Answer 1

It might be due to the command giving the nearest cell tower location. And for sending SMS it might be shifting to a different cell tower depending on your network. This could maybe be easily checked using a different cell provider or as you said its working at your home so I believe I am correct in assuming this is the answer

Answer 2

Serial.println("location = " + location);

I think in upper line you should remove + sign from the code.