---
title: "M66-IOT Board"
description: "## Basic Overview The **M66-IoT board** is an optimized and feature-rich development board, making it an excellent choice for getting started with the **Quectel M66 module**. It is designed to simplify IoT prototyping and supports a wide range of applications,…"
url: "https://eicut.com/wiki/development-boards/2g-3g-4g-5g/m66-iot-board/"
updated: "2026-02-15"
category: Development Boards / 2G / 3G / 4G / 5G
---

# M66-IOT Board

## Basic Overview

The **M66-IoT board** is an optimized and feature-rich development board, making it an excellent choice for getting started with the **Quectel M66 module**. It is designed to simplify IoT prototyping and supports a wide range of applications, including **solar-powered solutions** through its integrated MPPT solar charging circuit.

## Feature List

Key highlights of the board include:

- Built-in **Bluetooth antenna**
- **USB-to-Serial converter** with Micro-USB port for easy debugging and programming
- **Battery socket and charging circuit** for Li-Po batteries, with charge status LED indicator
- **MPPT-based solar charger**, enabling efficient energy harvesting for off-grid deployments

In addition, the board integrates several useful sensors:

- **Temperature and humidity sensor**
- **Ambient light sensor**
- **3-axis accelerometer**

Other features that enhance its versatility:

- **64 Mbit (8MB) flash memory (W25Q64)**
- **Microphone and speaker outputs**
- **External watchdog timer**
- **OLED interface support**
- **Level shifters on all I/O pins**

With this comprehensive set of features, the M66-IoT board provides a **powerful, all-in-one platform** that goes far beyond typical development boards—ideal for building and testing next-generation IoT solutions.

## Board Resources

### Function Description

The main component and interface placement of the evaluation board is shown in the following figure:

![annotated layout EICUT M66-IOT Board](https://eicut.com/wp-content/uploads/2025/10/image1_11zon-1-2-1024x681.webp)
**Top view**

![EICUT M66-IOT board underside](https://eicut.com/wp-content/uploads/2025/10/image2_11zon-1-2-1024x803.webp)
**Bottom view**

 

| NO. | Name | Comment |
| --- | --- | --- |
| **1** | USB Type-C Connector | The USB port, connected to a CH343P USB-to-Serial converter, is used for programming and communication with the PC. |
| **2** | Reset Button | Pressing this button will reset the power supply of the entire board. |
| **3** | BLE Antenna | — |
| **4** | Battery Switch | You can use this switch to connect or disconnect the battery. |
| **5** | Li-Po Charger | Charger circuit for Li-Po battery, suitable for a 200 mAh battery; this LED indicates the charging status. |
| **6** | GSM Antenna | You can use a 2G antenna with a 50 Ω impedance, connected via a UFL connector. |
| **7** | 6-axis accelerometer sensor | Interfaced with the M66 module via I²C and includes a dedicated interrupt (INT) pin for event-driven operation. |
| **8** | SHT40 | The temperature and humidity sensor interfaces with the M66 module using the I²C communication protocol. |
| **9** | LEDs | Two LEDs: one for network status (Net Light) and one user LED (connected to the RTS pin). |
| **10** | Main UART M66 Selector | This switch allows toggling the main UART between the GPIO pins and the USB interface. |
| **11** | Watchdog Disable Circuit | External watchdog implemented using the TPS3823 chip. Note: if the WDG reset jumper is removed, you must reset the watchdog through the RTS pin. |
| **12** | Light Ambient Sensor | Ambient light sensor implemented using the BH1750 chip. |
| **13** | OLED Connector | Dedicated connector for connecting an OLED display via the I²C interface. |
| **14** | Solar MPPT Circuit | High-efficiency solar charging circuit with MPPT technology for optimal energy harvesting. |
| **15** | User Key Button | — |
| **16** | SIM1/SIM2 or SD Card Socket | Use either two SIM cards, or one SIM card and one microSD card. |
| **17** | Microphone and Speaker Output | Standard AUX output is supported. |
| **18** | 8 MB SPI Flash | 8 MB flash memory using the W25Q64 chip. |
| **19** | External Battery Socket | — |
| **20** | Level Shifter | — |
| **21** | USB to Serial Converter | — |

 

### Board Interfaces

The detailed assignment of the peripheral interfaces on the evaluation board is as follows:

| NO. | Name | Silkscreen | Comment |
| --- | --- | --- | --- |
| **1** | +5V | +5V | — |
| **2** | +3.3V | +3.3V | — |
| **3** | VDD_EXT | +VEXT | — |
| **4** | PCM_SYNC | MISO | Use only for SPI communication, and make sure to use a dedicated CS (Chip Select) pin. |
| **5** | PCM_IN | SCK | Use only for SPI communication, and make sure to use a dedicated CS (Chip Select) pin. |
| **6** | PCM_OUT | MOSI | Use only for SPI communication, and make sure to use a dedicated CS (Chip Select) pin. |
| **7** | PCM_CLK | CE | — |
| **8** | Auxiliary TXD | A-TXD | — |
| **9** | ADC | ADC | — |
| **10** | Auxiliary RXD | A-RXD | — |
| **11** | PWR KEY | PWR | — |
| **12** | GND | GND | — |
| **13** | +3.3V | +3.3V | — |
| **14** | Main TXD | M-TXD | Set the UART selection switch to "UART ON GPIO" to make the UART pins accessible. |
| **15** | Main RXD | M-RXD | Set the UART selection switch to "UART ON GPIO" to make the UART pins accessible. |
| **16** | Debug TXD | D-TXD | — |
| **17** | Debug RXD | D-RXD | — |
| **18** | RFTXMON | RFTX | — |
| **19** | RI | SCL | — |
| **20** | DCD | SDA | — |

###  Board Dimensions

The main pin placement of the evaluation board is shown in the following figure:

![EICUT M66-IOT board dimensions ](https://eicut.com/wp-content/uploads/2025/10/image3_11zon-1-2.webp)
**Mechanical layout with full dimensions: board size 58.5 × 39 mm**

  🔗Tip

• To program the board, slide the switch to the "**UART ON USB**" position and connect the USB cable to begin programming.

• The SPI interface pins are shared with the onboard flash memory. It is recommended not to use these pins for other purposes to avoid conflicts.

• The battery switch simply connects or disconnects the battery from the circuit; it does not control charging or power regulation.

## Resource Download

- [M66-IOT Schematic](https://eicut.com/wp-content/uploads/2025/10/M66-IOT.pdf)
- [Quectel_M66_GSM_Specification_V1.4](https://eicut.com/wp-content/uploads/2025/05/Quectel_M66_GSM_Specification_V1.4.pdf)
- [Quectel_M66_Hardware_Design_V1.2](https://eicut.com/wp-content/uploads/2025/10/Quectel_M66_Hardware_Design_V1.2-1.pdf)

## FAQ

    What is the M66-IoT Development Board?

An all-in-one, feature-packed platform built around the ultra-small **Quectel M66 OpenCPU** module — perfect for battery/solar-powered IoT projects with integrated sensors, MPPT charging.

    Can it run completely off-grid with solar power?

Yes — includes a true **MPPT solar charger**, Li-Po charging circuit (with status LED), and battery switch. Just connect a small solar panel (5–6 V) and a Li-Po battery.

    Which sensors are built-in?

• **SHT40** – High-accuracy temperature & humidity
 • **BH1750** – Ambient light sensor
 • **6-axis IMU** (accelerometer + gyroscope) with interrupt pin
 All connected via I²C to the M66.

    How do I program and debug it?

Slide the **UART switch to “UART ON USB”** → connect **USB-C** → opens as a COM port (CH343P). No external programmer needed. Default baudrate: **115200**.

    Can I use the main UART on GPIO pins instead of USB?

Yes — move the **UART selector switch to “UART ON GPIO”** to route main TX/RX to the breakout pins (M-TXD / M-RXD).

    Is there external flash memory?

Yes — **8 MB (64 Mbit) W25Q64 SPI flash** is included for data logging, OTA firmware, or file storage. Note: SPI pins are shared — do not use them for other devices without proper CS management.

    Does it support Bluetooth?

Yes — M66 has **Bluetooth 4.0 LE** with an onboard high-performance chip antenna.

    Can I connect an OLED display?

Yes — dedicated **4-pin 0.96″/1.3″ OLED header** (VCC/GND/SDA/SCL) is provided (3.3 V I²C).

    Is there an external watchdog?

Yes — hardware watchdog using **TPS3823** chip. Can be disabled with a jumper if needed. When enabled, you must periodically toggle the RTS pin or the board will reset.

    What are the board dimensions?

**58.5 × 39 mm** with mounting holes — fits perfectly in small enclosures or on prototyping shields.

[![M66 Open CPU IOT DB Supporting GSM/GPRS/Bluetooth/Display/Audio](https://eicut.com/wp-content/uploads/2025/10/Frame-37_11zon-273x300.webp)](https://eicut.com/product/m66-open-cpu-iot-db/)