Adafruit Feather STM32F405 Express

Overview

The Adafruit Feather STM32F405 Express is Adafruit's fastest CircuitPython-capable Feather board, powered by STMicroelectronics' STM32F405 ARM Cortex-M4F running at 168MHz. With a hardware floating-point unit, 1MB of onboard Flash, and 192KB of SRAM (128KB general-purpose + 64KB for program/cache), it handles demanding real-time tasks and rapid data processing that would bog down lower-speed microcontrollers.

The board follows the standard Feather form factor and pinout, maintaining compatibility with the entire catalog of FeatherWing accessories. A STEMMA QT/Qwiic connector on one end provides plug-and-play I2C connectivity to hundreds of sensors and displays without soldering. An onboard SD card socket using the SDIO 4-bit interface delivers high-speed storage access for logging or media applications. An additional 2MB SPI Flash chip provides code and asset storage separate from the SD card.

Power management follows the Feather standard: a USB-C connector handles both power and data, and a built-in LiPo charger (100mA) keeps a connected battery topped off when plugged in. A NeoPixel status LED gives visual feedback for custom user programs. The board operates at 3.3V logic throughout, though the 5V USB pin is accessible for powering peripherals.

Firmware support covers CircuitPython (Adafruit's recommended environment), MicroPython, and Arduino via the STM32duino community package. Hardware schematics are published under open-source licenses and available from Adafruit's product page.