A reverse-engineered protocol reference for the PicPak 4-colour e-ink photo frame. Captured against firmware V0.4.1 by combining BLE HCI snoop logs from the official Android app with APK decompilation.
This document describes the wire protocol only — what bytes go on the BLE characteristics, in what order, and what they mean. It is enough to write a custom uploader, downloader, or device manager in any language.
If you are publishing your own client based on this, you may want to be explicit that you are not affiliated with the manufacturer.