PaperMono Firmware Creates E-Ink Fridge Magnet Shopping List with Web App Sync

Project Overview

A new firmware project, PaperMono, has been released for the M5Stack PaperMono e-paper device. This firmware converts the device into a dedicated household shopping list that can be mounted on a fridge. The list remains synchronized with a companion mobile web application, allowing multiple users to manage items.

Technical Implementation

The PaperMono device, based on an ESP32-S3 with a 3.97-inch 480x800 e-paper touchscreen, runs approximately 2,400 lines of C++ code. The firmware handles e-paper refreshes using fast partial updates for taps, scrolling, and typing, with full refreshes every 10 partial updates to prevent ghosting. It includes a touch UI with an on-screen keyboard that suggests previously added items.

Connectivity and Power Management

The system uses low-power networking, activating Wi-Fi only during synchronization events: hourly, when the screen is tapped if the last sync is over 5 minutes old, or immediately after an edit. All other operations, including adding and ticking off items, work offline, with edits queued on flash until the next sync. Power management features include power-button shutdown, deep-sleep fallback, and automatic device shutdown at low battery voltage.

User Experience and Features

The shopping list displays items grouped by aisle, in a user-defined walking order. Users can tap items to tick them off or add new ones via the on-screen keyboard. The companion phone application allows other household members to add items. An optional server component, built with FastAPI and SQLite, stores the list and can use Claude Code CLI to sort new items into appropriate aisles.