Here is my bonus cartridge! I mentioned here that I could have added another RAM bank to the 2x16K SRAM cartridge so here it is:

I added ROM 13(D) and made it selectable between ROM, RAM or disabled.

The screen shows ROM images loaded into banks 4, 5 and 13 (D).

The cartridge with an EPROM in position 13 and RAM in positions 0, 1 or 2, 3 and also in a Minus One 4, 5. It is handy getting that extra ROM slot with a basic Plus 1 or Minus 1.

If you would like to build one for yourself, everything you need including the Gerbers, BOM and Circuit Diagram are here - v3 Electron 2+1x16K SRAM.