Problems interfacing ESP32 to A9 Pudding GPRS module

[CyBaart]

For our project, we have a number of ESP32 nodes with a GPS chip and an RFM95 LoRa modules. I used the same ESP32 connections as the TTGO LoRa board for the GPS and RFM95 and they work well.

Next we want a cellular gateway to receive the data from the nodes and forward it via GPRS to ThingSpeak and decided to use the A9/A9G modules. I have been testing this out using a NodeMCU ESP32 module connected to the A9 with jumper cables. I have found that if I use the same TX/RX pins as the GPS on the nodes (IO12 and IO15) the pudding board does not start when power is applied but if I use IO16 and IO17, the A9 boots OK but the ESP32 resets everytime it tries to send an AT command to the A9. Now, I have had the A9 connected to my laptop via an FTDI cable and using AI-Thinkers serial tool, I have sent AT commands and received replies so I know the A9 is OK.

This is the info the ESP32 spits out on reboot

Code: Select all

ets Jun  8 2016 00:22:57

rst:0xc (SW_CPU_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:1
load:0x3fff0018,len:4
load:0x3fff001c,len:1044
load:0x40078000,len:10124
load:0x40080400,len:5856
entry 0x400806a8

Guru Meditation Error: Core  1 panic'ed (LoadStoreError). Exception was unhandled.
Core 1 register dump:
PC      : 0x400d0c8a  PS      : 0x00060730  A0      : 0x800d0d1a  A1      : 0x3ffb1f50  
A2      : 0x00000000  A3      : 0x3f400137  A4      : 0x000003e8  A5      : 0x3ffbfe78  
A6      : 0x3ffbfe60  A7      : 0x000007e8  A8      : 0x3f4001ed  A9      : 0x3ffb1f30  
A10     : 0x0000002b  A11     : 0x3f400137  A12     : 0x3ffbdbdc  A13     : 0x00000010  
A14     : 0x00000011  A15     : 0x00000008  SAR     : 0x00000018  EXCCAUSE: 0x00000003  
EXCVADDR: 0x3f4001ed  LBEG    : 0x4000c28c  LEND    : 0x4000c296  LCOUNT  : 0x00000000  

ELF file SHA256: 0000000000000000

Backtrace: 0x400d0c8a:0x3ffb1f50 0x400d0d17:0x3ffb1f80 0x400d1496:0x3ffb1fb0 0x400860dd:0x3ffb1fd0

and this is the sketch

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#define GPRSBAUD 115200        
#define GPRSTX 16             
#define GPRSRX 17
#define APN NXT17.net         //APN for Telit Sim

#define GPRSserial Serial2     //define GPRSserial as ESP32 Serial2 

char *response;

void setup()
{
  Serial.begin(115200);
  Serial.println();
  GPRSserial.begin(GPRSBAUD, SERIAL_8N1, GPRSTX, GPRSRX);
  delay(2000);
  if(sendAT("AT","OK", 1000))
	Serial.println(response);
  if(sendAT("AT+CREG?","OK", 1000))
	Serial.println(response);
}

void loop()
{
}


bool sendAT(char* ATcommand, char* expected, int timeout)
{
  uint8_t x=0;  
  unsigned long LoopStart = millis();
  bool Done = false;
  bool Good = false;
  int i;

  response="";
  //for(i=0; i<100; i++) response[i]=0;

  while( GPRSserial.available())
    GPRSserial.read();    // Clear the input buffer

  GPRSserial.println(ATcommand);    // Send the AT command
    
  
  do    // this loop waits for a response
  {
    if(GPRSserial.available() != 0)
    {
      response[x] = GPRSserial.read();
      x++;
      if (strstr(response, expected) != NULL)
        Done = true;
      if (strstr(response, "ERROR") != NULL)
      {
        Done = true;
        Good = false;
      }
    }
  }
  while((!Done) && ((millis() - LoopStart) < timeout));
  return Good;
}

Any suggestions as to why this is not working?

Thanks for any advice, Steve.