# Adafruit ItsyBitsy M0 Express > Compact 3.3V CircuitPython/Arduino board with ATSAMD21G18 Cortex M0+ at 48MHz, 32KB RAM, 256KB flash, 2MB SPI flash, 23 GPIO with 11 analog inputs, RGB DotStar LED, native USB. Measures 36mm × 18mm. ## Quick Facts - **Brand:** Adafruit - **Board Type:** dev-board - **Price:** ~$11.95 - **Product Readiness:** consumer - **CPU:** ATSAMD21G18 ARM Cortex M0+ - **CPU Architecture:** ARM Cortex-M0+ - **CPU Cores:** 1 - **RAM:** 32 KB - **Flash:** 256 KB - **Power:** 5V via Micro USB or LiPo battery via JST connector - **Operating Voltage:** 3.3V - **Dimensions:** 36mm × 17.8mm × 4.3mm - **Weight:** 2.7g ## Open Source - **Firmware:** Yes - **Schematics:** Yes - **PCB Layout:** Yes ## Compatible Firmware circuitpython, arduino ## Use Cases - wearable - usb-hid - education - prototyping - compact-controller ## Components - **ATSAMD21G18** (mcu): 32-bit ARM Cortex M0+ at 48 MHz with 256 KB flash, 32 KB SRAM, 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-itsybitsy-m0-express&source=md-export) - **W25Q16FW** (flash): 2 MB SPI NOR flash for CircuitPython code storage, accessible as USB drive. — [Datasheet](https://openhardware.directory/r?to=https%3A%2F%2Fwww.winbond.com%2Fresource-files%2Fw25q16fw%2520revj%252005182017%2520spi.pdf&ref=openhardware.directory&product=adafruit-itsybitsy-m0-express&source=md-export) - **APA102 DotStar** (led): Built-in RGB DotStar LED for status indication and light effects. — [Datasheet](https://openhardware.directory/r?to=https%3A%2F%2Fcdn-shop.adafruit.com%2Fproduct-files%2F2343%2FSK9822_FINAL.pdf&ref=openhardware.directory&product=adafruit-itsybitsy-m0-express&source=md-export) ## Protocols - **I2C**: SDA: D16, SCL: D17 - **SPI**: MOSI: D11, MISO: D12, SCK: D13, SS: D10 - **UART**: TX: D0, RX: D1 - **USB**: ## GPIO Map | Pin | Name | Type | Functions | |-----|------|------|-----------| | D0 | TX | UART | digital-input, digital-output | | D1 | RX | 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 | | D7 | 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 | | D16 | SDA | I2C | digital-input, digital-output | | D17 | 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 ItsyBitsy M0 Express is a compact CircuitPython and Arduino-compatible microcontroller board combining the ATSAMD21G18 ARM Cortex M0+ processor with 2MB of external SPI flash in a 36mm × 18mm package. It occupies the middle ground between the tiny Trinket and the full-sized Feather — smaller than a Feather but with significantly more I/O than a Trinket. The ATSAMD21G18 runs at 48 MHz with 256 KB of internal flash and 32 KB of SRAM. The 2MB SPI flash is accessible as a USB drive when running CircuitPython, enabling drag-and-drop code editing without any IDE. Hardware USB HID support allows the board to emulate keyboards, mice, MIDI devices, and mass storage devices. Seven capacitive touch pads, 11 analog inputs (including one DAC output), and 13 PWM channels give the board broad signal handling capability. A built-in red LED on pin 13 and an RGB DotStar LED provide immediate visual feedback for debugging and animations. The DotStar can be controlled from any pin using DMA for high-speed NeoPixel/DotStar chains. The board supports hardware SPI, I2C, and Serial, and can switch automatically between USB and battery power with the built-in power management circuit. The ItsyBitsy M0 Express is the ideal board for projects that need the CircuitPython ecosystem, moderate I/O count, and a smaller physical footprint than the Metro or Feather form factors — perfect for compact installations, wearables, and space-constrained enclosures. ## Where to Buy - [Adafruit](https://openhardware.directory/r?to=https%3A%2F%2Fwww.adafruit.com%2Fproduct%2F3727&ref=openhardware.directory&product=adafruit-itsybitsy-m0-express&source=md-export) — 11.95 ## Resources - [product page](https://openhardware.directory/r?to=https%3A%2F%2Fwww.adafruit.com%2Fproduct%2F3727&ref=openhardware.directory&product=adafruit-itsybitsy-m0-express&source=md-export) - [product](https://openhardware.directory/r?to=https%3A%2F%2Fwww.adafruit.com%2Fproduct%2F3727&ref=openhardware.directory&product=adafruit-itsybitsy-m0-express&source=md-export) - [documentation](https://openhardware.directory/r?to=https%3A%2F%2Flearn.adafruit.com%2Fintroducing-itsy-bitsy-m0&ref=openhardware.directory&product=adafruit-itsybitsy-m0-express&source=md-export) - [github](https://openhardware.directory/r?to=https%3A%2F%2Fgithub.com%2Fadafruit%2FAdafruit-ItsyBitsy-M0-Express-PCB&ref=openhardware.directory&product=adafruit-itsybitsy-m0-express&source=md-export) ## Tags `circuitpython`, `arduino`, `atsamd21`, `cortex-m0`, `adafruit`, `itsybitsy`, `express`, `compact`, `usb-hid` ## Images ![Adafruit ItsyBitsy M0 Express](https://nbg1.your-objectstorage.com/openhardware-directory/entities/adafruit-itsybitsy-m0-express/be7c40d306b6.jpg) ![Adafruit ItsyBitsy M0 Express](https://nbg1.your-objectstorage.com/openhardware-directory/entities/adafruit-itsybitsy-m0-express/d9176440a1f0.jpg) ![Adafruit ItsyBitsy M0 Express](https://nbg1.your-objectstorage.com/openhardware-directory/entities/adafruit-itsybitsy-m0-express/451d083434d9.jpg) --- [View full device page](https://openhardware.directory/devices/adafruit-itsybitsy-m0-express)