Parsing and comparing phone number data from sim800l

Projects Programming
1

Hi everyone,
I intend to build a sim800l gsm-based security device which is controlled by arduino nano. My goal in this scope is to check whether the received call to the gsm module is from a predefined number.

I was able to write a function to parse telephone number data from from serial. Output from sim800l is something like this.

+CLIP: "771234567",161,"",0,"",0

Below is the function I used.

String check_call(){
  String recieved_call_num ;
  if (sim800l.available()) {
    char c = sim800l.read();
    if (c == '\n') {
      String response = sim800l.readStringUntil('\n');
      if (response.indexOf("+CLIP:") != -1) {
        Serial.println("call detected");
        //Serial.println(response.indexOf(" "));
       recieved_call_num = response.substring(8,16);
       }
       return  recieved_call_num ;
    }
    
  
    }

}

But the problem is when i call the function it does not compare with the given number.

void loop()
{
  String number ="771234567";
if(number.equals(check_call())){
  Serial.println("Call received from a verified nuimber");
 
}
  

   
}

When i checked the "number" variable it is char[10] and the output of the check_call() function is a string. I also tried converting "number" variable to string and didn't work.

Are there any solution to this?

Thanks in advance for your help. :grinning:

here is the full code

#include <Arduino.h>
#include <SoftwareSerial.h>
SoftwareSerial sim800l(7, 3); 
String my_number = "+94771234567";
void shutdown(){
  while ((true))
  {
    /* code */
  }
  
}
void updateSerial()

{
  delay(500);
  while (Serial.available()) 
  {
    sim800l.write(Serial.read());//Forward what Serial received to Software Serial Port
  }
  while(sim800l.available()) 
  {
    Serial.write(sim800l.read());//Forward what Software Serial received to Serial Port
  }
}
void sendSMS(String phoneNumber, String message) {
  sim800l.println("AT+CMGF=1");  // Set SMS text mode
  updateSerial();
  
  sim800l.println("AT+CMGS=\""+phoneNumber+"\"");  // Start SMS sending mode
  updateSerial();
  sim800l.println(message);  // Send SMS content
  updateSerial();
  sim800l.write(26);  // Ctrl+Z to send SMS
  updateSerial();
  delay(5000);  // Wait for SMS to be sent
}
void call(String phone_num){
   sim800l.println("ATD" + phone_num + ";"); //  change ZZ with country code and xxxxxxxxxxx with phone number to dial
  updateSerial();
  //delay(20000); // wait for 20 seconds...
  //sim800l.println("ATH"); //hang up
  //updateSerial();
}
String check_call(){
  String recieved_call_num ;
  if (sim800l.available()) {
    char c = sim800l.read();
    if (c == '\n') {
      String response = sim800l.readStringUntil('\n');
      if (response.indexOf("+CLIP:") != -1) {
        Serial.println("call detected");
        //Serial.println(response.indexOf(" "));
       recieved_call_num = response.substring(8,16);
       }
       return  recieved_call_num ;
    }
    
  
    }

}
void setup()
{
  //Begin serial communication with Arduino and Arduino IDE (Serial Monitor)
  Serial.begin(9600);
  
  //Begin serial communication with Arduino and SIM800L
  sim800l.begin(9600);

  Serial.println("Initializing...");
  delay(1000);

  sim800l.println("AT"); //Once the handshake test is successful, it will back to OK
  updateSerial();
  sim800l.println("AT+CSQ"); //Signal quality test, value range is 0-31 , 31 is the best
  updateSerial();
  sim800l.println("AT+CCID"); //Read SIM information to confirm whether the SIM is plugged
  updateSerial();
  sim800l.println("AT+CREG?"); //Check whether it has registered in the network
  updateSerial();
    sim800l.println("AT+CMGF=1"); 
  updateSerial();
    sim800l.println("AT+CNMI=1,2,2,0,0"); // Decides how newly arrived SMS messages should be handled - correct
  updateSerial();
    sim800l.println("AT+CLIP=1" ); 
  updateSerial();
   
  //sendSMS(my_number,"Hello");
 // call(my_number);
  //sim800l.println("AT+CMGR=1"); 
}

void loop()
{
  String number ="771234567";
if(number.equals(check_call())){
  Serial.println("done");
  shutdown();
}
  
  //updateSerial();
   
}
2

It is a non-trivial problem, because the presentation of the number varies; eg,

Here it's just the number:

But here it's in International format:

So either you have to ensure that numbers are always in the same format, or you'll have to cope with the different formats.

Key to coping with both formats is to start comparing from the right-most digit, and work "backwards" to the left-most digit.

This is a common problem in telephone number handling - so some internet searching should find you general solutions...

3

Hey @awneil , Thanks for replying .

I am not trying to compare with that variable. I think that you picked the wrong variable. Pls, refer to the new variable that has been defined in the loop.

Here is the loop.

void loop()
{
  String number ="771234567";
if(number==check_call()){
  Serial.println("Call received from a verified nuimber");
 
}
  

   
}
4

But it's still an issue, and whatever code you come up with will need to handle it.