I designed a fully revertible modification for a Vornado 633DC fan so I could control it remotely over WiFi. The final result is concealed entirely within the fan’s housing, leaving no visible modification. If you’re interested in building one yourself, the schematic, BoM, and PCB design are all available here. In terms of firmware, I used ESPHome with an external component, for which the source code is available here. The rest of this post covers the research and development that went into the project.