The M2 IoT Modem is a 22 × 42 mm module in M.2 2242 format that adds Wi-Fi, Bluetooth and NB-IoT to your own hardware. An ESP32-PICO-D4 runs your firmware and drives a Quectel BC660K-GL NB-IoT modem with a soldered 1NCE eSIM, so the whole module is programmed from one processor with the Arduino framework, ESP-IDF or MicroPython. It suits products that must connect where there is no Wi-Fi: city and environmental monitoring, industrial equipment, asset tracking, farming or home automation.

M2 IoT Modem

Not for standard M.2 slots

The module uses the M.2 2242 mechanical format only. Its pinout is not compatible with the M.2 slots of laptops or SSD adapters: plugging it into one can damage the module and the host. Use it only with carrier boards designed for it.

Specifications

Feature	Specification
Form factor	M.2 2242 (22 × 42 mm), 4-layer PCB
Processor	ESP32-PICO-D4, dual-core Xtensa LX6 up to 240 MHz
Memory	4 MB SPI flash, 520 KB SRAM, 448 KB ROM, 16 KB RTC SRAM
Wi-Fi	802.11 b/g/n, 2.4 GHz
Bluetooth	v4.2 BR/EDR and BLE
NB-IoT modem	Quectel BC660K-GL (LTE Cat NB2), controlled with AT commands
NB-IoT bands	B1/2/3/4/5/8/12/13/17/18/19/20/25/28/66/70/85
SIM	1NCE eSIM (MFF2), soldered on board
Antenna connectors	2 × U.FL: WiFi-ANT (Wi-Fi and Bluetooth) and NB ANT (NB-IoT)
GPIO	10 ESP32 GPIOs at the connector, plus UART0 and GPIO0
Programming	Arduino framework, ESP-IDF or MicroPython, through UART0 of the ESP32
Peripherals	UART, SPI, I2C, I2S, LED PWM, pulse counter, GPIO, capacitive touch, ADC, DAC, TWAI

Power

Pin	Voltage	Use
VBUS (pins 1 and 2)	5 V	Power input.
+3.3V (pins 38, 49 and 54)	3.3 V	Output from the ESP32 supply rail, for references or low-power external circuits.

The modem supply is generated inside the module and is not available at the connector.

Inside the M2 IoT Modem

LEDs

LEDs of the module

LED	Color	Shows
LED1, modem power	Red	On while the BC660K-GL is powered.
LED2, network status	Yellow	NB-IoT network status, driven by the modem. The blinking pattern depends on the modem LED mode (AT+QLEDMODE).
LED3, TX	Blue	Blinks when the ESP32 sends data through UART0 (programming or serial console).
LED4, user	Red	Free for your firmware, on GPIO21. Set GPIO21 HIGH to turn it on.

Pinout

M.2 edge connector

Pins not listed are not connected.

M.2 pin	Signal	ESP32 GPIO	Notes
1, 2	VBUS		5 V power input.
3, 25, 40, 47, 51, 56, 63, 65, 67	GND		Ground.
4	TXD0	GPIO1	UART0 TX: console and programming.
6	RXD0	GPIO3	UART0 RX: console and programming.
8	IO0	GPIO0	Boot mode. Hold it LOW at reset to enter the download mode.
10	RESET	EN	ESP32 reset, active LOW.
20	TxBC-RxESP	GPIO4	Modem TXD to the ESP32.
22	RxBC-TxESP	GPIO13	ESP32 to the modem RXD.
24	IO12	GPIO12	ADC2, touch. Strapping pin: do not drive it HIGH at boot.
26	IO14	GPIO14	ADC2, touch.
28	IO27	GPIO27	ADC2, touch.
30	IO26	GPIO26	ADC2, DAC2.
32	IO25	GPIO25	ADC2, DAC1.
34	IO32	GPIO32	ADC1, touch.
36	IO33	GPIO33	ADC1, touch.
38, 49, 54	+3.3V		3.3 V output.
42	IO19	GPIO19
44	IO21	GPIO21	Shared with the user LED.
46	IO22	GPIO22
48	PWRKEY	GPIO23	Modem power key.
50	PSM_EINT	GPIO18	Wakes the modem from power saving mode.
52	RESET_BC	GPIO5	Modem reset.
66	BC_EXTERNAL_ENABLE		External power control of the modem.
68, 70, 72, 74	SIM_IO_EXT, SIM_RST_EXT, SIM_CLK_EXT, SIM_VDD		Connected to the on-board eSIM. Do not connect another SIM to them.

Modem control lines

Function	ESP32 GPIO	Behavior
Modem UART RX	GPIO4	Receives from the modem TXD, at 115200 baud by default.
Modem UART TX	GPIO13	Sends to the modem RXD.
PWRKEY	GPIO23	HIGH pulls the modem PWRKEY LOW (power on or off).
PSM_EINT	GPIO18	HIGH pulls the modem PSM_EINT LOW (wake up from power saving mode).
RESET	GPIO5	HIGH pulls the modem RESET LOW (hardware reset).

The control lines are inverted: a HIGH level on the GPIO activates the modem input. While the modem is in use, do not drive GPIO4, GPIO5, GPIO13, GPIO18 or GPIO23 from external hardware.

Connect it to Thinger.io

The ThingerNBCore class of the Thinger.io Arduino library connects the module over NB-IoT. It powers up the modem, applies the APN and network settings, waits for the network and keeps the connection to Thinger.io. To connect over Wi-Fi instead, use the module as any ESP32 board with ThingerESP32 (see Arduino).

Before you start

• A carrier board for the module, powered through VBUS, and a USB-to-UART adapter on its TXD0 and RXD0 pins. The module has no USB interface.
• Antennas on WiFi-ANT and NB ANT. Always connect the NB-IoT antenna before you use the modem.
• NB-IoT coverage of the 1NCE network where you deploy the module. Coverage and bands depend on the country and the operator.
• The Arduino IDE with the esp32 board package by Espressif Systems, or Visual Studio Code with PlatformIO.
• The thinger.io library and a TinyGSM library with Quectel BC660 support. The TinyGSM release in the Arduino Library Manager does not support the BC660: install it from github.com/alvarolb/TinyGSM.
• A device in Thinger.io, created as in Arduino. You need your username (YOUR_USER), the device ID (YOUR_DEVICE) and the device credentials (YOUR_TOKEN).

Upload the sketch

1. Select the board

   In the Arduino IDE, select ESP32 Dev Module. In PlatformIO, use the pico32 board.

2. Write the sketch

   Define THINGER_NB_M2CORE before the include, so the library uses the pins of this module. The 1NCE APN (iot.1nce.net, no user or password) is the default.

   main.cpp

   // #define THINGER_SERVER "YOUR_SERVER"  // only on a private instance
   #define THINGER_SERIAL_DEBUG
   #define THINGER_NB_M2CORE  // pins of the M2 IoT Modem
   
   #include <ThingerNBCore.h>
   #include <ThingerESP32OTA.h>
   
   #define PIN_USER_LED 21
   
   ThingerNBCore thing("YOUR_USER", "YOUR_DEVICE", "YOUR_TOKEN");
   ThingerESP32OTA ota(thing, 512);
   
   void setup() {
     Serial.begin(115200);
     pinMode(PIN_USER_LED, OUTPUT);
   
     // power up and configure the modem
     while (!thing.init_modem()) {
       delay(1000);
     }
   
     // user LED, controlled from Thinger.io
     thing["led"] << digitalPin(PIN_USER_LED);
   
     // modem and network information
     thing["modem"] >> [](pson& out) {
       out["modem"] = thing.get_modem_info();
       out["IMEI"] = thing.get_modem_imei();
       out["CCID"] = thing.get_sim_iccid();
       out["operator"] = thing.get_operator();
     };
   }
   
   void loop() {
     thing.handle();
   }

   On the free Cloud account, leave the THINGER_SERVER line commented: the library connects to the free Cloud server by default. On a private instance, uncomment it and replace YOUR_SERVER with your domain.

3. Upload it

   Hold GPIO0 (IO0) LOW while you reset the ESP32 with the RESET pin to enter the download mode, then upload the sketch. Open the serial monitor at 115200 baud to follow the connection.

The device shows as connected in Devices, with the led and modem device resources.

Network settings

Before init_modem(), set_apn() changes the APN for another SIM, set_preferred_bands() and set_preferred_operator() speed up the network search, and set_power_save(true) enables the modem power saving modes. The settings are stored in the modem and applied again only when they change.

To identify each module by the ICCID of its eSIM instead of a fixed device ID, see Use the SIM ICCID as device ID; on this module, keep #define THINGER_NB_M2CORE.

If the modem does not power on by itself, send a pulse on PWRKEY (GPIO23) before init_modem(). The timings are in the Quectel BC660K-GL hardware design document.

Resources

• Quectel BC660K-GL
• ESP32-PICO-D4 datasheet
• 1NCE IoT connectivity
• Arduino library reference

Disclaimer

INTERNET OF THINGER S.L. sells this module as a self-certified development kit, so it is not subject to the usual commercial homologation rules. The owner of the device is liable for any injury to third parties or damage to their property.