DIY Ereader - OpenPage

Overview

OpenPage is a dedicated, distraction-free reading device built around the LilyGo T5-4.7-S3 e-paper display.

It is designed to read .epub, .txt, and .cbz files directly from an SD card, offering a high-contrast 4.7-inch display. A standout feature is the “Daily Brief” mode, which uses the OpenAI API to generate and deliver a curated summary of current events straight to the device over WiFi.

Why I built it

I wanted a reading device that was completely under my control—no proprietary stores, no tracking, and no notifications.

The goal was to combine the longevity of e-paper with the extensibility of the ESP32, allowing for features like AI-powered summaries and custom layout engines that commercial devices don’t offer.

Build notes

• Custom Portrait Pipeline: Developed a rendering pipeline to work in a 540x960 portrait buffer on hardware that is landscape-native.
• Intelligent Power Management: Implemented a dual-sleep strategy using Light Sleep for instant wake during reading and Deep Sleep for long-term power savings.
• PSRAM Optimization: Heavy use of the ESP32-S3’s PSRAM to store framebuffers and large EPUB chapters without crashing.
• AI Daily Brief: Integrates OpenAI’s Responses API with web-search tools to generate offline-readable briefs stored on the SD card.

Parts / Stack

• Hardware: LilyGo T5-4.7-S3 (ESP32-S3, 16MB Flash, 8MB PSRAM).
• Firmware: C++/Arduino via PlatformIO.
• AI: OpenAI API (GPT-4o) for curated content.
• Storage: SD card for local library and bookmark persistence.

Challenges

• EPUB Pagination: Creating a fast, memory-efficient pager that handles word wrapping and image placement on an embedded chip.
• Battery Accuracy: Mapping the non-linear LiPo discharge curve to provide accurate percentage feedback during high-current WiFi tasks.
• Image Scaling: Implementing a grayscale-aware blitter to scale high-resolution CBZ and EPUB images for the 16-level grayscale display.

What’s next

• Enhanced Typography: Support for custom fonts and full text justification.
• WiFi Book Syncing: Wireless delivery of books via a local server or cloud integration.
• Local Dictionary: Long-press word lookups using an on-device database.
• UI Polish: Cover art previews in the book picker menu.