The AngstromIO is an open-source development board measuring just 9.0 x 8.9 mm (0.35 x 0.35 inches), making it barely larger than its edge-mounted USB Type-C connector. Created by Dieu-de-l-elec, the board packs a Microchip ATtiny1616 microcontroller, two addressable SK6805-EC15 RGB LEDs, and access to I2C, UART, and UPDI programming interfaces despite its tiny footprint.

The ATtiny1616 runs at up to 20 MHz with 16KB flash, 2KB SRAM, and 256 bytes EEPROM. The USB-C port provides 5V power only, with no data lines connected to the MCU. Solder pads break out UPDI for programming, I2C (SDA and SCL), two GPIOs (PB2/TX and PA3), plus 5V and ground. Power consumption drops to 200nA in power-down mode. The board works with Arduino IDE using SpenceKonde's megaTinyCore, supporting libraries like Wire for I2C and tinyNeoPixel for LED control. Linux users should note that megaTinyCore requires the Arduino IDE downloaded directly from arduino.cc rather than from distribution package managers, which are known to cause compatibility issues with the core.

Since the ATtiny1616 uses UPDI for programming, the developer provides hardware files for a dual CH340-based programmer with two USB-C ports. This setup enables simultaneous UPDI programming and one-way serial debugging (TX only), letting you monitor serial output while flashing firmware. The CH340E chip includes cross-platform drivers that work on Linux. For command-line workflows, developers can use pymcuprog for UPDI programming on Linux, and PlatformIO provides an alternative to Arduino IDE with full ATtiny1616 support and SerialUPDI integration. The project also includes a larger CH32V003-based experimentation board with a built-in 4x5 charlieplexed LED matrix for learning multiplexing and the CH32V003 toolchain.

All schematics, PCB layouts, Gerber files, and sample code are available on GitHub as an open-source hardware project. The design shares similarities with PegorK's f32 ESP32-C3 board but focuses on AVR microcontrollers without built-in USB programming.