Seeed XIAO nRF52840 Sense - User Manual

Getting Started with XIAO nRF52840Sense
As the advanced version of the board XIAO nRF52840, XIAO nRF52840
Sense has equipped a powerful Nordic nRF52840 MCU which is designed in a
Bluetooth 5.0 module, built around 32-bit ARM® Cortex™-M4 CPU with
Floating-Point Unit(FPU) operating at 64Mhz. With the capabilities of wireless
connection, it still remains the XIAO series classic form-factor of small and
exquisite which can be used for wearable devices and Internet of Things
projects. Furthermore, it only costs 5 μA in the deep sleep model and it
supports battery charge management because of the BQ25101 chip.
In addition, it carries two extra onboard sensors. One of them is a digital
microphone created through Pulse Density Modulation(PDM) module on the
nRF52840 chip. It can receive audio data in real-time which allows it can be
used for audio recognition. The board not only receives audio data but also
can speak through the MSM261D3526H1CPM microphone. The other one is
6-axis Inertial Measurement Unit(IMU) which can be applied in TinyML
projects like gesture recognition. These onboard sensors provide a great
convenience for users and the ultra-small size feature of the board has still
remained.
Same as XIAO nRF52840, XIAO nRF52840 Sense contains a wealthy
interface. The first thing to note is that the Near Field Communication(NFC) is

Summary

Product Features Overview

FCC Compliance and Integration

FCC Caution and Operational Notes

General warnings, important notes, and conditions for FCC compliance and equipment operation.

Radiation Exposure and Testing Requirements

Details FCC radiation exposure limits, installation guidelines, and additional testing requirements.

Overview

The XIAO nRF52840 Sense is an advanced version of the XIAO nRF52840 board, designed for a variety of applications including wearable devices and Internet of Things projects. At its core, it features a powerful Nordic nRF52840 MCU, integrated into a Bluetooth 5.0 module. This MCU is built around a 32-bit ARM® Cortex™-M4 CPU, which includes a Floating-Point Unit (FPU) and operates at 64MHz. This robust processing capability, combined with its wireless connectivity, allows the device to handle complex tasks efficiently while maintaining a compact and elegant form factor, consistent with the classic XIAO series design.

One of the key functional aspects of the XIAO nRF52840 Sense is its ultra-low power consumption. In deep sleep mode, it consumes only 5 μA, making it highly suitable for battery-powered applications where energy efficiency is critical. To further support such applications, the board incorporates a BQ25101 chip, which provides comprehensive battery charge management capabilities, ensuring reliable and extended operation.

The device is equipped with two additional onboard sensors that significantly enhance its functionality. The first is a digital microphone, which leverages a Pulse Density Modulation (PDM) module on the nRF52840 chip. This microphone is capable of receiving audio data in real-time, enabling applications such as audio recognition. Beyond just receiving audio, the board can also "speak" through the MSM261D3526H1CPM microphone, suggesting potential for interactive voice applications. The second onboard sensor is a 6-axis Inertial Measurement Unit (IMU), which can be utilized in TinyML projects for tasks like gesture recognition. These integrated sensors offer considerable convenience for users, expanding the range of potential applications without compromising the board's ultra-small size.

In terms of connectivity and interfaces, the XIAO nRF52840 Sense is well-appointed, mirroring the rich interface set of the XIAO nRF52840. A notable feature is the functional Near Field Communication (NFC) capability on the board, opening up possibilities for short-range wireless interactions. For user interaction and control, a tiny and elegant reset button is located on one side of the Type-C interface. On the opposite side, a three-in-one LED is integrated, alongside a power LED, providing visual feedback on the device's status.

The board offers a versatile array of input/output options, including 11 digital I/O pins that can function as PWM pins, and 6 analog I/O pins that can be used as ADC pins. It supports all three common serial communication protocols: UART, I2C, and SPI, facilitating integration with a wide range of peripherals and systems. Similar to the XIAO RP2040, it features an onboard 2 MB flash memory, which allows for programming using various languages and platforms such as Arduino, Micro Python, and Circuit Python.

The XIAO nRF52840 Sense is designed with single-sided components and a surface mounting design, contributing to its compact form factor and ease of integration into other systems. The device's ultra-small size, measuring 20 x 17.5mm, adheres to the classic XIAO series form factor, making it ideal for space-constrained applications.

For maintenance and compliance, the device adheres to FCC regulations. Any changes or modifications not expressly approved by the party responsible for compliance could void the user's authority to operate the equipment. The device complies with part 15 of the FCC Rules, meaning its operation is subject to two conditions: it must not cause harmful interference, and it must accept any interference received, including interference that may cause undesired operation. This equipment has been tested and found to comply with the limits for a Class B digital device, designed to provide reasonable protection against harmful interference in a residential installation. It generates, uses, and can radiate radio frequency energy, and if not installed and used according to instructions, may cause harmful interference to radio communications. However, there is no guarantee that interference will not occur in a particular installation. If the equipment does cause harmful interference, users are encouraged to try corrective measures such as reorienting or relocating the receiving antenna, increasing the separation between the equipment and receiver, connecting the equipment into an outlet on a circuit different from that to which the receiver is connected, or consulting a dealer or an experienced radio/TV technician for help.

The FCC Radiation Exposure Statement indicates that this equipment complies with FCC radiation exposure limits set forth for an uncontrolled environment and should be installed and operated with a minimum distance of 20cm between the radiator and the user's body.

For OEM/Integrators, the module has been tested and found to comply with part 15.247 requirements for Modular Approval. It can be applied in household electrical appliances, TV, and IP cameras. The input voltage to the module should be nominally 5VDC, with a typical value of 5VDC, and the ambient temperature should not exceed 85°C. The module uses a Chip Antenna for BLE with an antenna gain of 2.0dBi.

When the module is installed in a host device, the FCC ID label (Z4T-XIAONRF52840) must be visible through a window on the final device or when an access panel, door, or cover is easily removed. If not, a second label containing the text "Contains Transmitter Module FCC ID: Z4T-XIAONRF52840" must be placed on the outside of the final device. The FCC ID can only be used when all FCC ID compliance requirements are met.

The modular transmitter has been fully tested by the module grantee on the required number of channels, modulation types, and modes, so it should not be necessary for the host installer to re-test all available transmitter modes or settings. However, it is recommended that the host product manufacturer perform investigative measurements to confirm that the resulting composite system does not exceed spurious emissions or band edge limits, especially if a different antenna is used. Testing should also check for emissions due to the intermixing of emissions with other transmitters, digital circuitry, or the physical properties of the host product enclosure.

Integrating multiple modular transmitters requires special investigation, especially when certifications are based on stand-alone configurations. Host product manufacturers should not assume that certification of the modular transmitter absolves them of responsibility for final product compliance. If an investigation reveals a compliance concern, the host product manufacturer is obligated to mitigate the issue. Host products using a modular transmitter are subject to all applicable individual technical rules and general operating conditions to prevent interference. The operator of the host product will be obligated to stop operating the device until any interference has been corrected.

Additional testing against FCC Part 15B criteria for unintentional radiators is required for the final host/module combination to be properly authorized as a Part 15 digital device. The host integrator must ensure the final composite product complies with FCC requirements through a technical assessment or evaluation, referring to KDB 996369 guidance. For host products with a certified modular transmitter, the frequency range of investigation for the composite system is specified by rule in Sections 15.33(a)(1) through (a)(3), or the range applicable to the digital device as shown in Section 15.33(b)(1), whichever is the higher frequency range. During host product testing, all transmitters must be operating, enabled by publicly available drivers. If receive mode only is not possible, the radio should be passive (preferred) and/or active scanning, enabling activity on communication buses like PCIe, SDIO, or USB to ensure unintentional radiator circuitry is active. Testing laboratories may need to add attenuation or filters depending on the signal strength of any active beacons. Further general testing details can be found in ANSI C63.4, ANSI C63.10, and ANSI C63.26.

Seeed XIAO nRF52840 Sense Specifications