A 4 bit trainer from Germany - Busch Microtronic aka 2090

Here’s a demo of the trainer, which has a 4-bit TI processor:

Short description from the VCFb website:

At the beginning of the 1980s, there were various learning computer cases and kits in Germany in order to familiarize interested young people and adults with the functioning of a microcomputer on assembler and hardware level. The 1981 introduced Busch 2090, the result of the diploma thesis of the son of the CEO of the company Busch, was one of these microcomputers and was based on the 4-bit CPU Texas Instruments TMS-1600. This should be presented together with a tape emulator and PC cross assembler. In order to understand the interaction between the calculator (ALU), control unit (Control Unit), registers, memory, etc., even today 4-bit computers are ideal, since here in a manageable system this interaction not only theoretically but also practically can be researched. Second exhibit is therefore the 4-bit microcontroller " Martin Sauter

Big photo from this site:

Edit: more on this site:
25 Years of Home Computing! Or: My Road to Computers