Finally! a Cherry MX compatible upgrade for the infamous Mitsumi mylar keyboards that plague many unfortunate Texas Instruments TI-99/4A computers.

The upgrade consists of a new PCB and a handful of 3D printed parts. The original look is maintained by re-using the original key caps (and some other original parts). Add the switches of your choice and you're set! A brand new keyboard for your TI-99/4A.

Currently, the upgrade is designed for the Mitsumi keyboards since their mylar innards gives the most grief to TI-99 users. It is possible other TI-99/4A keyboard brands could be adapted to use this upgrade in the future, hower that would rely on community input.

The Gerber file for the KEYBOARD/4A-99 PCB is available in the /pcb directory. I recommend the PCB is ordered in black.

STLs for all 3D printed items are located under /stl.

Note: Not all STLs are required.

Check out the documentation for more details, including a bill of materials and full build process.

These are now available at:

For those outside the US, you can support the project by purchasing direct from my PCBWay project page.

Thanks to PCBWay for supporting this project.

All hardware designs and products you can find in this repository is licensed under CERN Open Hardware Licence Version 2 - Weakly Reciprocal