Metro M0 Express - ATSAMD21G18
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Metro M0 Express - ATSAMD21G18

  • ATSAMD21G18 @ 48MHz
  • 3.3V Logic
  • FLASH: 256 Kb
  • RAM: 32Kb
  • 2 Mb FLASH SPI
  • USB bootloader
  • Ready for Arduino and MicroPython (CircuitPython)
€29.96 (tax incl.) €24.76 (tax excl.)
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Compatible Arduino and MicroPython with additional flash

Metro is a microcontroller boards serie from Adadruit that can be used with the Arduino IDE. This new Metro M0 Express board looks like a Metro 328 (an Arduino lime) but with a huge upgrade.

Instead of the ATmega328, this board is built around a ATSAMD21G18 chip, an ARM Cortex M0+.
This board is designed to support the CircuitPython! CircuitPython is a beginner-oriented flavor of MicroPython. CircuitPython is a small version of the popular Python programming language specifically for use with electronic and circuitry.

Metro M0 is also usable in the Arduino IDE and with MicroPython/CircuitPython.
Imagine an Arduino like board that can be programmed with Python... Whoaw!

The Metro M0's is beated with the Cortex M0 ATSAMD21G18 ARM processor, clocked at 48 MHz and a 3.3V logic. The Arduino Zero use the same processor, it includes 256K of FLASH (8x more than the Atmega328) and 32K of RAM (16x as much)! This chip has a built in USB native support so it has USB-to-Serial program & debug capability (so you don't need to use a FTDI-like chip).

  • Power the METRO with 7-9V DC or micro USB connector (5V USB source). The 2.1mm DC jack offer an on/off switch next to turn it off easily. The METRO will automatically switch between the power sources.
  • METRO has 25 GPIO pins, 12 of them are analog in. One of them is a true analog output.
    There's an hardware SPI bus, an hardware I2C bus and an hardware UART (serial port).
    They all use a 3.3V logic level.
  • Native USB. The Metro M0 has native USB support built inside the chip. When used to act like a serial device, the USB interface can be used by any computer to listen/send data to the METRO, and can also be used to launch and update code via the bootloader.
    The native USB support can also act like a keyboard, mouse or a MIDI device.
  • Four indicator LEDs and a NeoPixel. Can be used for easy debugging. Green LED: power. Two LED for the RX/TX signaling the data transmission over USB. A red LED connected to pin 13.
    A RGB NeoPixel is place next to the reset button that can be used for any purpose.
  • 2 MB SPI Flash for storage. You can use the SPI Flash chip like a very tiny hard drive.
    • When used in Circuit Python (microPython), the 2 MB flash acts as file storage for the python scripts, python libraries and other files.
    • When used in Arduino, the 2 MB flash can read/write files, like a little datalogger or SD card.  You can then use the Adafruit's helper program to access the files over USB.
  • Easy reprogramming. The board is pre-loaded with the UF2 bootloader. The UF2 looks like a USB storage key. The firmware on to program can be drag on the USB storage, no special tools or drivers needed! UF2 can be used to load up CircuitPython, PXT MakeCode or Arduino IDE (it is bossa-compatible)

Metro M0 Express for MicroPython

CircuitPython is still under development, Adafruit is working hard to make it awesome! Pick up an M0 Express if you want to try it out. The Adafruit support will be better at each realease!

Anyway, the Metro M0 is well supported in Arduino IDE, so you can use it as much as you like.

Technical details

  • LOGIC: 3.3V for logic and power
  • ATSAMD21G18 microcontroler clocked at 48MHz
  • USB bootloader, serial debugging port
  • FLASH: 256 Kb
  • RAM: 32Kb
  • FLASH SPI: 2 Mb additional flash wired on SPI
  • 32.768 KHz crystal for RTC and clock generation
  • Regulator: 3.3V with 500mA peak current
  • USB: USB native support
  • 25 GPIO pins (5 more than a Metro 328)
  • Hardware Serial
  • Hardware I2C
  • Hardware SPI
  • PWM outputs: almost all pins
  • Analog input: 6 x 12-bit ADC
  • Analog output: 1 x 10-bit DAC
  • Include a NeoPixel wired on pin #40
  • Like Arduino board, the Pin #13 is wired to a red LED
  • Power on/off switch
  • mounting holes (4)
  • Reset button
  • PCB: in black with gold plate on pads
  • Board size: 71mm x 53mm
  • Height (with the barrel jack): 13mm
  • Weight: 20g


Comes fully assembled with headers, tested, and with the UF2 bootloader loaded on. We also include 4 rubber bumpers to keep it from slipping off your desk. No soldering required to use, plug and play!


Check out our full guide for pinouts, schematics, drivers, instructions, Fritzing object, and more!