I've grown fond of cartridge formats in my later years, mostly because of the feeling you get by browsing a case of cartridges, selecting something and then popping it in the slot for an instant load. There are certainly more modern options available, but they mostly don't provide the ability to physically slot in a cartridge. For that you need a Sinclair ZX Interface 2, a RAM Turbo interface or a Kempston Pro Joystick interface - somewhat easily done as long as you have deep pockets. For the game cartridges, you definitely won't get anywhere with the sort of holes I've got in my pockets so I had to design a few of those as well.

So I started building a new ZX Interface 2-compatible interface instead, a sort of ZX Interface 2021. Except I couldn't exactly call it that, I built it using cheap and easy to assemble through-hole components so I decided that calling it 2.021 would fit the project a lot better. Neither did I want to keep the originals 16K limitations, so I extended the length of the cartridge with more pins so that in theory you could build a cartridge with up to 4x 512K ROM storage (that's 4 megabytes in total). The bank switching is built into the interface, meaning that the cartridges built for them only require a few components.

This is the actual module, there is a separate faceplate that goes on top for added rigidity as well as supporting the cartridge. I'll be creating a whole selection of cartridges and other expansions for it, have a look at my PCBWay Shared Project (click the link to filter for projects related to this). For documentation, including the BOM, build instructions as well as everything else that you'd need - check out the github-repository.

I put together a small video, no words so far - mainly as I don't really do much of those in person. It goes through starting up the ZX Spectrum computer with a diagnostic cartridge, it then reboots into standard ZX Basic before I play around with the bank switching scheme directly.