Firmware for the M5Stack PaperMono e-paper device turns it into a household shopping list that lives on the fridge and stays in sync with a phone web app over Wi-Fi. The device, built on an ESP32-S3 with a 3.97-inch 480×800 e-paper touchscreen, runs about 2,400 lines of C++. It features fast partial screen updates, an on-screen keyboard with item suggestions, and low-power networking that syncs hourly or after each edit while working offline otherwise. A FastAPI server with SQLite store sits between the device and phone browser, optionally using Claude Code to auto-sort new items into aisles. The repository includes platformio firmware, a web UI, and hardware documentation with pin maps and I²C addresses.

The project was fully vibe-coded with Claude Code, with the creator admitting it is the first home-built project used day-to-day. Features include grouped lists by walking order, tap-to-tick functionality, and deep-sleep power handling with a safe shutdown sequence. The device remembers every added item in a catalog driving suggestions on both screens.

Key capabilities include optional Claude-driven aisle assignment, offline editing queued to flash, and a frontlight off by default. The firmware documentation details the bring-up sequence for the power IC, IO expander, panel, and touch controller in a known-good order.