Adafruit’s METRO M0 Express board features an ATSAMD ARM Cortex-M0+. It is the first METRO board designed for use with CircuitPython, Adafruit’s beginner-oriented flavor of MicroPython, a small but full-featured version of the popular Python programming language created specifically for use with board level circuitry and electronics.  The METRO M0 is also programmable using the Arduino IDE and is designed in the familiar Arduino R3 style form factor.

At the METRO M0's heart is an ATSAMD21G18 ARM Cortex M0 processor, clocked at 48 MHz that employs 3.3 V logic levels. This MCU has 256 K of Flash and 32 K of RAM along with built in USB so it has USB-to-serial program and debug capability built in without the need for additional interface circuitry.

The METRO M0 Express board can be powered with 7 V to 9 V via the polarity protected DC power connector or via the micro USB connector from any 5 V USB source. The 2.1 mm DC power jack has a power switch next to it so you can turn off your setup easily and the METRO can switch between USB and DC power automatically.

A 2 MB SPI Flash storage chip is included on-board. When used in Circuit Python, the 2 MB Flash acts as storage for scripts, libraries, and files and when used in Arduino, users can read/write files to it for datalogging and with Adafruit’s helper program, access these files over USB.

The MCU comes pre-loaded with the UF2 bootloader, which causes the board to be recognized as a USB storage key. Simply drag firmware on to program, no special tools or drivers are needed. It can be used to load up CircuitPython, PXT MakeCode, or Arduino IDE (it is BOSSA-compatible).