Unable to read GSM serial response correctly

[yogeshshinde]

Hi,
I am using Atmega128 and Arduino ide in my project.
external crystal with 16MHz is used.
4G LTE module of sim a7672s is used with baud rate 9600.
change from 115200 to 9600 using the command.
GSM RX and TX connections are at pin 21 and 20 of Atmega128.
I am able to send commands but stuck in Rx response.

 String serial_data;
>   while (Serial1.available() > 0) {
>     serial_data = Serial1.readString();
>     Serial1.print(serial_data);
>   }

The terminal response is like this

> +CSQ: 21,99
> ONáhiM¥
>        bÊÊj
> 
> +CSQ: 21,99
> AT+CPMS="SM"
> +CPMS: 1,25,1,25,1,25
> 
> OK
> 
> +CSQ: 21,99
> ¡¥¨hiM¥
> +«ª¥5µòb?¨hiM¥
> +CSQ: 21,99
> Mmþmþmþm
> +CSQ: 21,99
> üþiM¥
>      bÊÊ

Unable to find the solution. Please help

[StefanL38]

try char and Serial1.read() instead of readstring

[paulpaulson]

Hello yogeshshinde

Take a view here to get some ideas:

SerialEvent | Arduino Documentation

Have a nice day and enjoy programming in C++ and learning.

[yogeshshinde]

Tried this.
But got almost same result

+CSQ: 19,99
¡¥¨¥
    Êb

+CSQ: 19,99
)Êj

+CSQ: 19,99

+CSQ: 19,99
9-¡ø+¡¥¨¥ÊbÊÊj

+CSQ: 19,99

+CSQ: 19,99
-¡ø+¡¥¨,99 ?¨¥
              ÊbÊÊj
h+¡¥¨,99 øÊj
+¡¥¨,99 øÊj

@paulpaulson

Take a view here to get some ideas:

https://docs.arduino.cc/built-in-examples/communication/SerialEvent

Have a nice day and enjoy programming in C++ and learning.

[StefanL38]

the characters that are printed to the serial monitor have high numbers.
One thing that can cause that is a wrong configuration of the serial parameters
baudrate
number of databits 5,6,7 ot 8 databits
parity even/uneven
number of stop-bits 0,1,2

what exact microcontroller-board are you using Atmea128 is a single chip not a completed board.
Is this your own custom PCB? / custom circuit-design
Well if yes you added a lot of parameters that should be checked each on his own.

If you reset the GSM-module to factory settings what is the default baudrate?
115200?

Do you have a device that is able to send/receive data at 115200 baud?
you need to check what bytes do you receive from the GSM-module
Ardiuno Mega, ESP32, a virtual COM-port to TTL-adapter?

A 24 Mhz 8 channel logic analyser would be very useful. They start at $10 on ebay
with such a logic analyser you can record the bitbanging and then let to the software the interpretation with different serial parameters like described above
best regards Stefan

[yogeshshinde]

@StefanL38

One thing that can cause that is a wrong configuration of the serial parameters
baudrate
number of databits 5,6,7 ot 8 databits
parity even/uneven
number of stop-bits 0,1,2

I have check response for 9600 and 115200 baud rate with changing of baud rate of GSM
Also check parameters. its 8 databits, no parity and stop bit 1. I also check same parameters of GSM module using commands.

@StefanL38

what exact microcontroller-board are you using Atmea128 is a single chip not a completed board.
Is this your own custom PCB? / custom circuit-design

It is custom PCB and check almost all parameters of datasheet.

@StefanL38

If you reset the GSM-module to factory settings what is the default baudrate?
115200?

Its 115200.

@StefanL38

Do you have a device that is able to send/receive data at 115200 baud?
you need to check what bytes do you receive from the GSM-module
Ardiuno Mega, ESP32, a virtual COM-port to TTL-adapter?

I am able to send commands and got correct response. Checked on PC using COM-port to TTL-adapter. Only problem is in reading that response.

@yogeshshinde

> +CSQ: 21,99
> AT+CPMS="SM"
> +CPMS: 1,25,1,25,1,25
> 

This is command sent and return response.

I also check if any problem in RX pin of atmega128 by removing connections of gsm and sending data using Realterm. It is able to read that data. Only problem is in GSM data.