I haven't had a proper circuit diagram for FATCAT until now. Previously I've been getting by with a Fritzing breadboard sketch. It does the job as reference for my own use, but it doesn't connect up properly for every component.

I've taken a few hours to learn the basics of KiCad and have now finally made a "proper" circuit diagram. It's available in the Project Files section.

I can't guarantee there aren't any errors at this point. 

It did pass the "electric rules check". It throws some "pin not connected" errors, but those pins are intentionally left unconnected since that's how the actual device is meant to be built. 

The schematic omits the battery and boost module and just assumes it gets 5V from somewhere.

I'm not planning to make any custom PCB for FATCAT, but anyone who would like to do so is welcome to use this schematic as a starting point.