Model M

^{_{Render may be of an outdated version, the images below are from a CI/CD render and are always up-to-date. Only compatible with nice!nano, other MCUs won't work}}

The Model K is a custom replacement controller designed to add BLE wireless functionality to classic IBM Model M keyboards. This controller can be hot-swapped into the original keyboard without destroying the original controller.

Features

• Fully wireless with BLE (Bluetooth Low Energy)
• Battery powered with 3+ weeks of battery life¹
• USB C for drag-and-drop programming, charging and wired use
• Compatible with IBM Model M 101/102 layouts (122-key compatibility uncertain as I do not own one yet)²
• Open source ZMK firmware, with CI/CD builds
• Works as a shield for the nice!nano, built on top of the Nordic nRF52840
• All components are THT and easy to solder/repair/replace
• Three high-frequency user-configurable pins

Hardware

PCB

The PCB is designed in KiCad 9. This repository has a CI/CD pipeline that automatically renders the schematic into a PDF/SVG and generates gerbers for JLCPCB and PCBWAY.

Components

See the automatically generated iBOM (you will need to download the .html file and open it in your browser for now).

For a full assembly, you will need:

• Model K PCB
• 2x 74HC595 shift register ICs, preferably with DIP-16 sockets (three for M122s)
• 3x 150R resistors for the LEDs (if you have any)
• 16x 1N4148 diodes (20 for M122s)
• 1x 6x3mm reset switch (GME for reference)
• A battery and its corresponding connector (on board is JST-PH 2mm and a 2.54mm pin header for power profiling)
• PCB Faston mount (GME for reference)
• Appropriate Trio-mate or Connfly connectors

Your keyboard might contain 16+12 or 16+8+4 connectors, make sure you order the ones you need! The board supports both of them.

Important

If you are using Connfly connectors, make sure to rotate them 180°! This sounds counter-intuitive, but your board will not work otherwise!

Assembly

TODO

Caution

Quadruple check the orientation of the battery! The nice!nano doesn't have reverse polarity protection and you will fry it.

Software

For now, see the modelk-zmk repository for the ZMK firmware. Might get merged into this repository.

Instalation:

• Download firmware from the modelk-zmk CI/CD builds (or click here for the latest firmware)
• Connect your nice!nano via USB
• Double-tap the reset button to enter bootloader mode (the little blue light should stay on)
• Your computer will detect a USB drive
• Drag and drop the firmware file (.uf2) onto this drive
• The nice!nano will disconect itself once the process is complete
• Enjoy a working wireless Model M!

My default, right alt switches to a function layer, where escape toggles USB/BT and F1-F3 toggles BT profiles and F6-F8 controls multimedia. You can, of course, completely redesign the layout.

Footnotes

1. currently ~3 weeks on a 400mAh battery with revision 0.3.1, will be better on newer boards ↩

2. Tested on: 1386716 ↩