An ESP32 Cheap Yellow Display turns a microSD card into a standalone offline Wikipedia reader, with articles, images, and search available without an internet connection.
The project by Alun Morris uses the ESP32-2432S028 Cheap Yellow Display (CYD), with its 320×240-pixel ILI9341 display and XPT2046 touchscreen, to create a portable offline Wikipedia reader. Instead of connecting to the internet, the device stores the required encyclopedia data on a microSD card and retrieves articles directly from it.
The system is based on a Kiwix ZIM file containing the Simple English edition of Wikipedia. The recommended download is around 3.3 GB and contains roughly 285,000 articles. Before the data can be used by the ESP32, a Python-based preprocessor converts the ZIM archive into a binary database, cleans the article HTML and prepares images for the device’s limited memory.
The conversion process also reduces image sizes and changes their formats. Photos are stored as JPEGs, while diagrams use QOI, with thumbnails limited to 320×212 pixels. Articles are divided into 32 MB chunks and images into 4 MB chunks so that the ESP32 does not need to load large portions of the database into its roughly 300 KB of usable heap at once.
Search is handled through a fixed-width title index and a small sparse index kept in RAM. The latter contains one entry for every 64 articles and occupies only about 7 KB, allowing the firmware to locate the appropriate section of the larger index without scanning the entire database. The firmware is built with PlatformIO and uses TJpgDec for JPEG images and a QOI library for diagrams.
The processed database occupies about 10 GB, making a 16 GB microSD card a practical choice, while the CYD is reported to support cards up to 32 GB. The project requires only the ESP32-2432S028, a microSD card and a USB cable, with touchscreen calibration performed during the first boot and stored for later use. The complete firmware and preprocessing tools are available through Alun Morris’s project repository, making the setup reproducible for makers who need an offline reference device.
