This is a diagnostic cartridge for the ZX Interface 2.021, a new cartridge interface for the ZX Spectrum 16k/48k machines that includes a Sinclair joystick interface - just like the original. The cartridge slot have been expanded in order to expand the maximum cartridge size beyond the initial 16k using bank switching, mainly allowing me to create cartridges with just a handful of components. While you can use this a regular cartridge with the ZX Interface 2.021 interface, the diagnostic firmware I'm using is able to output system state to the LEDs - allowing you to debug a system that is running without a functioning display. There is a dedicated faceplate for this cartridge, this is also shown in the pictures.

I'll be creating a whole selection of cartridges for the interface, have a look at my PCBWay Shared Project for a filtered list of all shared projects that's related to this interface. 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 the diagnostic cartridge, it then reboots into standard ZX Basic before I play around with the bank switching scheme directly.