# Adafruit METRO M0 Express > Arduino Uno-compatible development board powered by ATSAMD21G18 Cortex M0+ at 48MHz with 256KB flash, 32KB SRAM, 2MB SPI flash, and CircuitPython pre-loaded. Features Arduino shield compatibility and native USB. ## Quick Facts - **Brand:** Adafruit - **Board Type:** dev-board - **Price:** ~$24.95 - **Product Readiness:** consumer - **CPU:** ATSAMD21G18 ARM Cortex M0+ - **CPU Architecture:** ARM Cortex-M0+ - **CPU Cores:** 1 - **RAM:** 32 KB - **Flash:** 256 KB - **Power:** 7-9V via DC barrel jack or 5V via Micro USB - **Operating Voltage:** 3.3V - **Dimensions:** 71mm × 53mm × 13mm - **Weight:** 20g ## Open Source - **Firmware:** Yes - **Schematics:** Yes - **PCB Layout:** Yes ## Certifications RoHS ## Compatible Firmware circuitpython, arduino ## Use Cases - prototyping - education - arduino-shield - data-logging - maker-projects ## Components - **ATSAMD21G18** (mcu): 32-bit ARM Cortex M0+ at 48 MHz with 256 KB flash and 32 KB SRAM, hardware native USB. — [Datasheet](https://openhardware.directory/r?to=https%3A%2F%2Fww1.microchip.com%2Fdownloads%2Fen%2FDeviceDoc%2FSAM-D21DA1-Family-Data-Sheet-DS40001882G.pdf&ref=openhardware.directory&product=adafruit-metro-m0-express&source=md-export) - **W25Q16FW** (flash): 2 MB SPI NOR flash for CircuitPython code, data logging, and file storage. — [Datasheet](https://openhardware.directory/r?to=https%3A%2F%2Fwww.winbond.com%2Fresource-files%2Fw25q16fw%2520revj%252005182017%2520spi.pdf&ref=openhardware.directory&product=adafruit-metro-m0-express&source=md-export) ## Protocols - **I2C**: SDA: D20, SCL: D21 - **SPI**: MOSI: D11, MISO: D12, SCK: D13, SS: D10 - **UART**: TX: D1, RX: D0 - **USB**: ## GPIO Map | Pin | Name | Type | Functions | |-----|------|------|-----------| | D0 | RX | UART | digital-input, digital-output | | D1 | TX | UART | digital-input, digital-output | | D2 | GPIO | — | digital-input, digital-output | | D3 | GPIO | — | digital-input, digital-output, pwm | | D4 | GPIO | — | digital-input, digital-output | | D5 | GPIO | — | digital-input, digital-output, pwm | | D6 | GPIO | — | digital-input, digital-output, pwm | | D7 | GPIO | — | digital-input, digital-output | | D8 | GPIO | — | digital-input, digital-output | | D9 | GPIO | — | digital-input, digital-output, pwm | | D10 | SS | SPI | digital-input, digital-output, pwm | | D11 | MOSI | SPI | digital-input, digital-output, pwm | | D12 | MISO | SPI | digital-input, digital-output | | D13 | SCK | SPI | digital-input, digital-output | | D20 | SDA | I2C | digital-input, digital-output | | D21 | SCL | I2C | digital-input, digital-output | | A0 | ADC/DAC | — | digital-input, digital-output, analog-input, dac | | A1 | ADC | — | digital-input, digital-output, analog-input | | A2 | ADC | — | digital-input, digital-output, analog-input | | A3 | ADC | — | digital-input, digital-output, analog-input | | A4 | ADC | — | digital-input, digital-output, analog-input | | A5 | ADC | — | digital-input, digital-output, analog-input | ## Available Software - **[CircuitPython]()** (open-source) - **[Arduino]()** (open-source) ## Description ## Overview The Adafruit METRO M0 Express is an Arduino Uno-compatible development board built around the ATSAMD21G18 ARM Cortex M0+ processor at 48 MHz. It follows the standard Arduino shield form factor, making it a drop-in upgrade for existing Arduino Uno projects while adding significantly more capability — including native USB, 2 MB of SPI flash for data logging or file storage, and CircuitPython out of the box. The board ships with CircuitPython pre-installed via the UF2 bootloader, so programming is as simple as dragging and dropping a .uf2 file or editing code.py on the mounted USB drive. Arduino IDE is fully supported as well, and the board appears as a standard Arduino-compatible device. Twenty-five GPIO pins provide six 12-bit analog inputs, one 10-bit DAC output, and hardware Serial, I2C, and SPI interfaces. Power flexibility is a key design feature: the METRO M0 can accept 7–9V DC via the barrel jack or 5V USB via Micro USB. A built-in NeoPixel on pin 40 and a power/RX/TX status LED array provide visual feedback. A power on/off switch is included on-board, and the board is fully assembled with headers, ready to use without soldering. With 256 KB of internal flash plus 2 MB of external SPI flash and 32 KB of SRAM, the METRO M0 Express has ample memory for CircuitPython scripts, data buffers, and audio samples, making it an excellent choice for education, prototyping, and intermediate-level maker projects. ## Where to Buy - [Adafruit](https://openhardware.directory/r?to=https%3A%2F%2Fwww.adafruit.com%2Fproduct%2F3505&ref=openhardware.directory&product=adafruit-metro-m0-express&source=md-export) — 24.95 ## Resources - [product page](https://openhardware.directory/r?to=https%3A%2F%2Fwww.adafruit.com%2Fproduct%2F3505&ref=openhardware.directory&product=adafruit-metro-m0-express&source=md-export) - [product](https://openhardware.directory/r?to=https%3A%2F%2Fwww.adafruit.com%2Fproduct%2F3505&ref=openhardware.directory&product=adafruit-metro-m0-express&source=md-export) - [documentation](https://openhardware.directory/r?to=https%3A%2F%2Flearn.adafruit.com%2Fadafruit-metro-m0-express&ref=openhardware.directory&product=adafruit-metro-m0-express&source=md-export) - [github](https://openhardware.directory/r?to=https%3A%2F%2Fgithub.com%2Fadafruit%2FAdafruit-Metro-M0-Express-PCB&ref=openhardware.directory&product=adafruit-metro-m0-express&source=md-export) ## Tags `circuitpython`, `arduino`, `atsamd21`, `cortex-m0`, `adafruit`, `metro`, `arduino-compatible`, `uno-form-factor` ## Images ![Adafruit METRO M0 Express](https://nbg1.your-objectstorage.com/openhardware-directory/entities/adafruit-metro-m0-express/31daca2b133b.jpg) ![Adafruit METRO M0 Express](https://nbg1.your-objectstorage.com/openhardware-directory/entities/adafruit-metro-m0-express/90f6322d6901.jpg) ![Adafruit METRO M0 Express](https://nbg1.your-objectstorage.com/openhardware-directory/entities/adafruit-metro-m0-express/7120bfc09fc6.jpg) ![Adafruit METRO M0 Express](https://nbg1.your-objectstorage.com/openhardware-directory/entities/adafruit-metro-m0-express/ab872e40fb9e.jpg) --- [View full device page](https://openhardware.directory/devices/adafruit-metro-m0-express)