I've just updated Latest schematics adding an optional EEPROM extension.
It is very simple:
With the optional EEPROM extension MegaDrum may have 2-32(depending on EEPROM IC used) times more persistent memory to store Configs/Drum maps. As an example, in my tests with the EEPROM extension using 24LC256 (32Kbyte) can store 33 Configs/Drum Maps with MaxInputs set to 56.
I will publish a new MegaDrum firmware with the support for the EEPROM extension today or tomorrow.