Hi,
I am using the nb-iot module with m5stack. The program is https://github.com/m5stack/M5-ProductExampleCodes/blob/master/Module/NB_IOT/Arduino/NB_IOT.ino

But I can't understand the mistake.
Can someone help me?

M5Stack Fire has occupied GPIO16 / 17 to connect with the PSRAM by default, it's conflict with TXD / RXD (GPIO16, GPIO17) of NB-IoT module. Therefore, when using the GPS module with the M5Stack Fire, you might have to cut the TXD and RXD from NB-IoT module and wire fly to another set of UART pin, if you gonna use the PSRAM.

What you need to do is that,

1. Cut the TXD and RXD from NB-IoT module;
2. Jump wire to other GPIOs, for example TX to GPIO5, RX to GPIO12;
3. Change the code according to the new GPIOs;
   Serial2.begin(115200, SERIAL_8N1, 12, 5);
4. Upload to play.

Cut is easy to do as there are ready made 0-ohm resistors that you can use.

Tested and this works!

Same issue here. The example code doesn't work at all: https://github.com/m5stack/M5-ProductExampleCodes/blob/master/Module/NB_IOT/Arduino/NB_IOT.ino

Code refers pin 5 in the setup and that pin is used in the schematics for serial line receive (and actually it is not connected as zero ohm resistor is missing). I think this code is just some kind of copy other M5Stack module examples and not suitable for this.

This module seems to be dead even I try to switch on power and reset as it have been guided in their website:

Power Operation:

Power On: GPIO2 stay HIGH for 2s
Power Off: GPIO2 stay HIGH for 8s
Power On: Button long-press for 2s
Power Off: Button long-press for 8s
Reset module: GPIO26 HIGH

In code level I have used following in setup:

pinMode(2, OUTPUT);
pinMode(26, OUTPUT);

digitalWrite(2, 1);
delay(3000);
digitalWrite(2, 0);

digitalWrite(26, 0);
delay(500);
digitalWrite(26, 1);
delay(500);
digitalWrite(26, 0);

When I send AT command to module. Sometimes it reply empty characters, but I am not sure is that just a noise.

Any help is appreciated!

Best regards, Jarkko