Introduction

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.

Only Mitsumi boards?

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 hardware

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

New version: v1.1

Verion 1.1 adds support for re-using the original alpha-lock switch. The original switch provides much greater throw than the replacement I used in v1.0. As a result, the keycap adapters for v1.1 are slightly taller to match the taller alpha lock key. Also, the mounts are slightly slimmer.

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.

Purchasing options

KEYBOARD/4A-99 PCBs and kits are available on my Tindie store:

<a href="https://www.tindie.com/products/visrealm/keyboard4a-99"><img src="https://d2ss6ovg47m0r5.cloudfront.net/badges/tindie-larges.png" alt="I sell on Tindie" width="200" height="104"></a>

Also (more convenient for North America)

<a href="https://www.arcadeshopper.com/wp/store/#!/Keyboard99-Mitsumi-membrane-replacement-PCB-only/p/648592668"><img width="640" src="https://www.arcadeshopper.com/wp/wp-content/uploads/2016/01/Arcadeshopper-horizontal-Web-logo-1024x147.jpg"></img></a>

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

Detailed build instructions

Also check out the documentation for more details.

Thanks

Thanks to PCBWay for supporting this project.

Gallery

Licence

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