Problem in serial communication between ESP32 and GSM A7670C

[naz2000]

I am using A7670C GSM breakout board with an ESP32.

Connections

• RX-TX
• TX-RX
• GND-GND

I am giving external power to the GSM module, 3.8 V according to the product description.

When I sent the AT command to GSM module, I don't get output on the serial monitor of the Arduino IDE.

The message is sent to a particular number successfully, but I don't receive the message from mobile.

This is my code:

#include <HardwareSerial.h>
#if defined(CONFIG_IDF_TARGET_ESP32)
    #define mySerial Serial2
#elif defined(CONFIG_IDF_TARGET_ESP32S2)
    #define mySerial Serial1
#elif defined(CONFIG_IDF_TARGET_ESP32S3)
   #define mySerial Serial2
#endif
String msg="";
void setup()
{
  Serial.begin(115200);
  delay(500);
  #if defined(CONFIG_IDF_TARGET_ESP32)
    mySerial.begin(9600);
 #elif defined(CONFIG_IDF_TARGET_ESP32S2)
    mySerial.begin(115200);
 #elif defined(CONFIG_IDF_TARGET_ESP32S3)
   mySerial.begin(115200, SERIAL_8N1, 18, 17);
 #endif
  delay(500);
  mySerial.println("ATI");
update_serial();
  delay(100);
  sent_sms();
update_serial();
  delay(100);
 RecieveMessage();
update_serial();
  delay(100);
   
}
void loop()
{    
  if (Serial.available()){
    char c = Serial.read();
    mySerial.write(c);
  }
 update_serial();
}

void update_serial()
{
    while(mySerial.available()) {
    Serial.print(mySerial.read());
  }
}

void sent_sms()
{
 mySerial.println("AT+CMGF=1");delay(500);
 mySerial.println("AT+CMGS=\"+91XXXXXXXXXX\"");delay(500);
 mySerial.print("test sent sms SIM7600");delay(500);
 mySerial.write(26);delay(500);
}

 void RecieveMessage() {
  mySerial.println("AT+CNMI=2,2,0,0,0"); // AT Command to receive a live SMS
  delay(1000);

I tried different baud rate also but I only got message on mobile with 115200 baud rate. i tried sofwareserial also but it didn,t work .

[horace]

how have you connected the A7670C to the ESP32?
how do you power the device?
note that the A149126_ADIY-SIM7670C-4G-Breakout-Board-V1.1_Datasheet.pdf states that Rx and TX are 1.8V logic??

[naz2000]

Thank you for the reply...
RX2(GPIO 16) and TX2(GPIO 17) connected alternate to GSM's RX and TX
ESP32 GND and GSM GND and external power supply GND are common.
I have circuit that convert the AC power supply to 3.3 Volt DC supply.
I am getting 3.2 V at RX pin of A7670 and 1.8 V at TX pin of A7670.

[horace]

think you require a 3.3V <> 1.8V level converter on the ESP32 serial to A7670C

[naz2000]

ok I will try it

[horace]

going back to your code in post 1 using Serial2 when I initialise Serial2 on an ESP32 I explicitly set the pins

#define RXD2 16
#define TXD2 17

void setup() {
  // Note the format for setting a serial port is as follows: Serial2.begin(baud-rate, protocol, RX pin, TX pin);
  Serial.begin(115200);
  Serial2.begin(115200, SERIAL_8N1, RXD2, TXD2);

it may help

[naz2000]

Thanks for the help!!!

[naz2000]

can I use voltage divider

[horace]

you can try a potential divider on the ESP32 3.3V Tx to A7670C 1.8V Rx
don't know if the A7670C 1.8V Tx will work with the ESP32 Rx

try it?

[naz2000]

ok, let me try i will be there ..after this

[naz2000]

I tried it but nothing was changed

[horace]

try with level converter otherwise you may have damaged the A7670C by inputting 3.3.V into the Rx

[naz2000]

I saw some method to make bi-directional voltage level shifter but I got 5v to3.3 logic level shifter .can anyone help me to make 3.3v logic level shifter to 1.8 v

[horace]

have a look at Sparkfun level converter - it states
This level converter also works with 2.8V and 1.8V devices

[naz2000]

now my GSM module work properly . I want help to set the time of GSM by NTP server using AT commands
I tried some AT commands

• this AT command set my time but i want to set the time automatically.

mySerial.println("AT+CCLK=\"24/04/02,16:14:00+20\"\r");delay(500);
  delay(100);
  update_serial();

• didn't work

mySerial.println("AT+CNTP=\"193.204.114.232\",20");delay(500);
  delay(100);
  update_serial();

I am following this pdf of AT commands
SIM7500_SIM7600_Series_AT_Command_Manual_V2.00.pdf (2.7 MB)

some more AT commands likes AT+CLTS=1(give me error message),AT&W do not set the time