XIAO SAMD21 Plus, powered by the Microchip ATSAMD21G18A ARM Cortex-M0+ processor, brings enhanced flexibility and expandability to the tiny and versatile XIAO SAMD21. While maintaining its low-power performance, Arduino compatibility, and compact footprint, the Plus variant features redesigned castellations and backside pad layout, offering 16 additional GPIOs, integrated Li-ion battery management, dedicated Reset and Boot buttons, and an onboard WS2812 RGB LED. It is ideal for advanced IoT projects, battery-powered wearables, embedded applications, and production-ready SoM designs.

Features:

Note:

This product is the Seeed Studio XIAO SAMD21 Plus, the upgraded variant of XIAO SAMD21 with 16 additional SMD GPIOs and integrated Li-ion battery management. The board and two 7-pin headers are included. No battery, USB cable, or other accessories are included.

Overview

Following the XIAO Plus design language established by XIAO nRF52840 Plus, XIAO nRF52840 Sense Plus, XIAO ESP32-S3 Plus, and XIAO RP2040 Plus, the new Seeed Studio XIAO SAMD21 Plus upgrades the flagship XIAO SAMD21 — the original thumb-sized Arduino board — with expanded GPIO resources, integrated Li-ion battery management, enhanced user interaction features, and a standardized backside layout.

Powered by Microchip's SAMD21G18A ARM Cortex-M0+ 32-bit processor, XIAO SAMD21 Plus brings enhanced flexibility and expandability to the tiny and versatile XIAO SAMD21. While maintaining all the powerful features including Arduino, MicroPython, and PlatformIO compatibility, the Plus variant features redesigned castellations and backside pad layout, offering 16 additional GPIOs, integrated Li-ion battery management, dedicated Reset and Boot buttons, and an onboard programmable WS2812 RGB LED. It is ideal for advanced IoT projects, battery-powered wearables, embedded applications, and production-ready SoM designs.

Production-Ready Design with FREE PCBA Support

As an addition to the Seeed Studio XIAO family,the XIAO SAMD21 Plus remains the classic XIAO design (thumb-size, SMD, stamp holes). All these features make it a perfect fit for either space-limited applications, or a production-ready System on Module (SoM) for your PCBA designs. Through our Fusion PCBA Sponsorship program, you can not only enjoy the lowest unit prices for all XIAO modules from our Fusion Open Parts Library, but also fabricate and scale your XIAO-based PCBA designs at low cost (30% off) with FREE Design for Manufacturing consulting services, streamlining your journey from prototype to production.

Note:

XIAO SoM User Manual open-sources all hardware and software materials of XIAO, providing professional product design guidelines to help you accelerate ideas off the ground, streamline product design, providing a seamless experience from module selection to mass production. You can check here to see more info.

Features:

High-Efficiency ARM Cortex-M0+ MCU
Powered by the Microchip ATSAMD21G18A ARM Cortex-M0+ processor running at 48MHz, XIAO SAMD21 Plus delivers an excellent balance between computing performance and ultra-low power consumption. Native USB support enables USB HID devices, MIDI controllers, USB serial communication, and numerous embedded USB applications. Fully compatible with Arduino, PlatformIO, CircuitPython, TinyGo, and other popular development ecosystems, it is suitable for projects ranging from STEM education to commercial embedded products.
Multi-Language Development Ecosystem
Start quickly with the Arduino IDE for rapid prototyping, develop efficiently with PlatformIO, or explore embedded scripting using CircuitPython and TinyGo. Backed by extensive community resources and comprehensive documentation, XIAO SAMD21 Plus provides a beginner-friendly experience while remaining flexible enough for professional development workflows.
Efficient Power Management
An onboard PMIC enables direct Li-ion battery connection with integrated charging management and 3V3/BAT backflow protection. The board can safely operate from USB power, battery power, or both simultaneously without requiring additional external charging circuitry, simplifying portable and battery-powered product design.
The integrated Charge LED provides intuitive charging status indication, making battery management easier during both development and daily use.
Expanded I/O for Advanced Applications
The redesigned backside layout introduces 16 additional GPIOs through 1.27mm-pitch SMD castellations, significantly expanding the available I/O resources while preserving the compact XIAO footprint.
These additional GPIOs allow developers to connect more sensors, peripherals, displays, and communication interfaces without relying on external GPIO expanders, making XIAO SAMD21 Plus especially suitable for custom carrier boards, advanced embedded applications, and production-ready System-on-Module (SoM) designs.
Universal Compatibility — Standardized Backside Layout
Following the unified XIAO Plus hardware standard, XIAO SAMD21 Plus adopts the standardized backside layout with aligned battery pads, debugger pads, and SMD castellations.
This standardized design ensures compatibility with current and future XIAO expansion boards, accessories, and custom carrier boards, allowing developers to migrate between different XIAO Plus modules with minimal hardware redesign.
Classic XIAO Form Factor
Despite the significant hardware upgrades, XIAO SAMD21 Plus retains the iconic 21 × 17.8 mm thumb-sized footprint and the familiar 2.54mm pin header layout.
Its compact size, lightweight design, and single-sided component placement make it ideal for wearable electronics, portable devices, robotics, sensor nodes, and space-constrained embedded applications.
Native Compatibility with the XIAO Ecosystem
XIAO SAMD21 Plus is fully compatible with the growing XIAO accessory ecosystem, including expansion boards, displays, Grove modules, CAN Bus modules, LoRa modules, LED Matrix, Round Display, Vision AI Sensor, ePaper Displays, mmWave sensors, GPS modules, relay modules, Bus Servo Drivers, and many more.
With standardized hardware interfaces across the XIAO family, developers can rapidly prototype ideas while benefiting from an extensive ecosystem that supports applications ranging from education to industrial IoT.

Specifications:

Product Name : Seeed Studio XIAO SAMD21 : Seeed Studio XIAO SAMD21 Plus
Chipset : Microchip SAMD21G18
Processor : ARM Cortex-M0+ processor runs at up to 48 MHz.
RAM : 32KB SRAM
Flash : 256KB Flash
Interface : GPIO Pin x14 : GPIO Pin x30

Digital Pin x11 : Digital Pin x27
Analog Pin x11 : Analog Pin x11
DAC x1 : DAC x1
I2C x1 : I2C x2
UART x1 : UART x1
SPI x1 : SPI x1
I2S ×1

Onboard : User LED x1 : RGB LED x1

Power LED x1 : Charge LED ×1
Status LEDs for Serial : Reset Button x1
Communication (TX/RX Indicators) x2 : Boot Button x1

Battery Management (PMIC) : None : Onboard PMIC
Power : Input Voltage (Type-C): 5V
Input Voltage (BAT): 5V
BAT-to-3V3 Backflow Protection : No : Yes
Working Temperature : -40°C ~ 85°C
Dimensions : 21 x 17.8mm
Software Compatibility : Arduino, PlatformIO, MicroPython, CircuitPython, Zephyr,and more to come
Varients : XIAO SAMD21 (Pre-Soldered)
XIAO SAMD21 3PCS Pack

Hardware Overview

PinOut

Applications:

STEM Education - Perfect for learning embedded programming, Arduino development, electronics, and ARM Cortex-M microcontrollers. Rich documentation and native USB support make it an excellent platform for beginners and educators.
USB HID Devices – Leverage the ATSAMD21 native USB peripheral to create custom keyboards, macro pads, game controllers, MIDI instruments, USB serial devices, and other Human Interface Device (HID) applications.
Wearable Electronics – The compact 21 × 17.8 mm footprint, onboard battery charging, and low-power MCU make XIAO SAMD21 Plus an excellent choice for smart badges, wearable sensors, health monitoring devices, and portable electronics.
Embedded Prototyping - With 16 additional GPIOs, developers can integrate more peripherals without external GPIO expanders, enabling faster prototyping of complex embedded systems while maintaining the familiar XIAO form factor.
Smart Home & Automation - Connect multiple Grove modules, displays, communication modules, and sensors to build automation controllers, environmental monitoring stations, lighting controllers, and edge computing devices.
Robotics – Suitable for educational robots, motor controllers, sensor hubs, and compact robotic platforms requiring reliable low-power control and flexible I/O expansion.
Human-Machine Interface (HMI) - The onboard WS2812 RGB LED together with dedicated Reset and Boot buttons provides convenient visual feedback and user interaction, making XIAO SAMD21 Plus well suited for compact control panels, interactive devices, and embedded user interfaces.
Battery-Powered IoT – The integrated PMIC and Li-ion charging circuit simplify the design of portable IoT devices, wireless sensor nodes, environmental monitoring systems, and remote data loggers.
Production-Ready SoM Design – Designed for board-to-board soldering through castellated edges, XIAO SAMD21 Plus serves as a production-ready System-on-Module (SoM). The additional GPIOs and standardized XIAO Plus layout simplify hardware migration from prototype to mass production.