Adafruit METRO M0 Express - designed for CircuitPython [ATSAMD21G18]

The Adafruit Metro M0 Express brings 32-bit ARM power to the familiar Metro/UNO shield-compatible form factor. Powered by the ATSAMD21G18 ARM Cortex M0+ processor at 48 MHz, it offers 256 KB flash and 32 KB RAM — a massive upgrade over the ATmega328-based Metro. Designed from the ground up for CircuitPython, it also works seamlessly with the Arduino IDE.

With built-in native USB, the Metro M0 Express can act as a serial device, keyboard, mouse, or MIDI controller — no FTDI chip needed. The 2 MB SPI flash storage serves as a tiny drive for CircuitPython scripts, libraries, and data files. CircuitPython comes pre-loaded and ready to go.

Key Features

• ATSAMD21G18 ARM Cortex M0+ – 48 MHz, 256 KB flash, 32 KB RAM, 3.3V logic
• Native USB – Serial, keyboard, mouse, and MIDI support with no additional hardware
• 2 MB SPI Flash – On-board storage for CircuitPython scripts or Arduino data logging
• 25 GPIO Pins – 12 analogue inputs, 1 true analogue output, hardware SPI, I2C, and UART
• UNO Shield Compatible – Standard Metro/UNO form factor for plug-in shields
• Flexible Power – 7–9V DC (polarity protected) or Micro USB, with auto-switching and on/off switch
• UF2 Bootloader – Drag-and-drop firmware updates via USB storage mode
• CircuitPython Pre-Loaded – Ready to code out of the box
• Status LEDs + NeoPixel – Power (green), RX/TX, red LED, and an RGB NeoPixel

Ideal For

• CircuitPython beginners looking for a shield-compatible board
• Projects needing more power than an ATmega328 platform
• USB HID projects (keyboard, mouse, MIDI)
• Data logging with on-board flash storage

Package Contents

• 1× Adafruit Metro M0 Express (fully assembled with headers)
• 4× Rubber bumper feet

Resources

• Metro M0 Express Guide — Pinouts, Schematics & Code (Adafruit Learn)
• UF2 Bootloader Guide (Adafruit Learn)