Converting a 103-key terminal Model M keyboard to a “fake ssk”.

References

• https://geekhack.org/index.php?topic=27272.0
• https://deskthority.net/viewtopic.php?t=21198
• https://scrausch.blogspot.com/2015/01/making-model-m-ssk.html
• https://www.reddit.com/r/MechanicalKeyboards/comments/2ds4wv/cleaned_and_converted_a_terminal_model_m_into_usb/
• https://www.reddit.com/r/MechanicalKeyboards/comments/2mca1p/model_m_restoration_rust_removal_plastidip/
• https://freematics.com/pages/software/arduino-builder/

Tools

• https://www.amazon.ca/gp/product/B00093GEJO/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
• http://www.leevalley.com/en/wood/page.aspx?p=58686&cat=1,42884
• https://www.canadiantire.ca/en/pdp/j-b-weld-clear-weld-epoxy-syringe-25-ml-0383803p.html#srp

Cut down the case

• remove the keycaps and unscrew the case screws
• measure and cut top case along each side of numpad
• measure and cut bottom case keeping flip foot and support rib (cut goes through rubber front foot hole; make sure the cut is the same width as the top plate)
• check pieces for fit
• sand, glue and clamp (used jb clear-weld epoxy)
• cut the 4th screw bracket from the junk section of top case
• glue screw bracket to new top case
• check top and bottom case for fit and alignment of screw holes
• trim sides of the leftmost/rightmost lock tabs on the top case if needed
• file down excess epoxy
• paint along the cut (?)

Cut the backplate and barrel plate

• remove the rivets from the backplate and separate the pieces
• take a photo of the hammer positions
• remove the hammers and put them in a jar
• glue ribs of the barrel plate if they’re cracking
• cut the steel backplate with a dremel
• cut the plastic barrel plate with a saw
• trim the rubber mat to match the barrel plate
• leave the membrane sheets intact, but snip the edges so they fold back easier
• drill a hole in the top right corner of the backplate to match the one in the top left (measure carefully)
• screw (/bolt) mod the barrel plate
• reassemble barrel plate, mat, membranes and backplate and screw (/bolt) them together

Specific tmk changes for a 3.3V pro micro and iso layout:

• change cpu speed to 8mhz
• comment KEYMAP and uncomment KEYMAP_101
• add k13 and k53 codes to keymap in 2 places
• add NUHS and NUBS to keymap

Compile the tmk converter

• download and install freematics arduino builder and mingw
• open mingw
• add freematics avr folder (containing avr-gcc.exe) to path if needed
• cd tmk_keyboard/converter/terminal_usb
• make

Flash pro micro via Freematics Arduino Builder

• open freematics arduino builder
• load the .hex file
• plug in the pro micro
• click COM1
• when the message appears in the console, short the RESET pin to GND twice (to enter bootloader)
• a new COM port should be found and the .hex will be flashed
• if you get a timeout error (no new port found), try repeatedly

Build the adapter

• cut the original cable where it enters the case
• use the short end with the internal connector for the controller (set aside the long remaining piece of cable with the rj45 end)
• save the rubber cable guard for reuse
• identify the wires based on hasu’s diagrams (5V, clock, data, and ground)
• solder the 4 wires from the original cable end to the pro micro
• for a 3.3V pro micro, ensure to solder the 5V line from the keyboard to RAW instead of VCC
• I soldered the shield connector from the cable to pro micro GND, but this might not be necessary
• attach the pro micro to the keyboard controller
• either use a panel mount microusb extension or some kind of strain relief for the usb cable (or you’ll damage either the usb port or the solder points on the pro micro)