That time I put a Teensy in a GMMK


This is copied straight from the original reddit post. I guess being redundant here and there helps with future insane people who look at their GMMKs and ask themselves “now how do I run QMK on this?” Also this is assuming that pcgamingrace never come out with a GMMK variant that runs on QMK.



I like the idea of trying out different switches type and tuning the layout of my keyboard to suit my needs, but at the same time I’m not enthusiastic about owning a million boards with different types of switches and layouts. GMMK it is then. I liked the GMMK TKL I got for pretty cheap, but I wanted the numpad for games like Space Engineers and GTA V. GMMK full size for me then, but to my dismay I discovered that V1 boards have LEDs that protrude from the PCB. This meant that all the switches I have minus the Kailh box ones would be barely held in with the plate while tilting awkwardly at the same time. I wasn’t able to tolerate this, and I can’t wait for the Kira from Input Club. Another person would just sell the GMMK v1 and get the v2 which will have flush LEDs, but y’all know what I chose. I actually placed an order for the v2 before discovering a GMMK with S/N 201605 on eBay with Zealios no less. The board was perfect for experimentation since it doesn’t even have the GUI for programming macros in the first place. Anything I do to it, if that worked, would actually make the board better. Without knowing any better, I decided to proceed ahead with buying the board along with a Teensy 2.0 ++

The build process:

****-up cascade. That summed everything up. I got the stock PCB matrix wrong which led to the stupid decision to mod the matrix. You don’t mod the matrix unless the traces were all oxidized to oblivion. I went ahead and commit various atrocities against the PCB which resulted in one of the most retarded keyboard matrices ever known to man. Still, I fixed the mistakes I made, and somehow everything work in the end. I’m not going into details with the actual steps since I think no sane person should do this mod to their GMMK, especially if theirs were made on or after Jan 2017.

Conclusion and future stuffs:

Board worked well enough at the moment. This entire wall of text was typed using the modded GMMK donning some silent Gat Red and Black. I’ll probably find a case from a broken full size keyboard and see if I can fit the GMMK pcb in that thing or not. While the existing case is fine enough as is (kinda think about it, the wires tacked onto the PCB acted as a sound dampener), I think there is space for improvement. The massive hole on the bottom of the case is something I’d like to patch up.


Behold v2.0

Board still works fortunately. Added foam wherever foam could fit. Tacked on a bunch of antiskid pads because I had a bunch. Also got myself a customized sticker. Actually went around to get the gaping hole on the back tidied up to look nicer. Overall a great keyboard. 10/10 would do something this ambitious again.


I remember this from Reddit, super interesting stuff. Do you think it would be possible in the future do have a controller that would add QMK to GMMK in the same fashion we have the Hasu controllers?


That’s awesome. And QMK is awesome!


That would be awesome! And if you actually do end up doing this, definitely open a PR!


Yes, QMK is truly awesome. I think I talked to you on the QMK channel one of those days about implementing GEST on TMK, didn’t I?


Yup. QMK is my passion. :slight_smile:
I’m pretty much always active in the QMK Gitter/Discord, and on /r/olkb. :slight_smile:


I am a huge fan of QMK myself, I need to up my programming skills to help more. One of the things I want to do is port the Hasu BT implementation over to QMK. I see that Hasu has all the BT code within the hhkb/rn42 folder. Shouldn’t be that hard to port over.

Let’s see if I can take a stab at it and I’ll bug you there on the Discord channel when I do if that’s OK :slight_smile: ?


That would be awesome! :slight_smile:
And yeah, it will be a bunch of work to convert it, I think.


I don’t think that’s possible since the MCU is on the same PCB as the matrix. Had it been on a separate PCB thing would have been easier.

Still, I’m toying with the idea of a 2nd GMMK with QMK board that still retain some use of the existing MCU for things QMK doesn’t do that well like per-key RGB LED control. Not sure if it’s even possible to have 2 MCUs control the same matrix without them frying one another.


I think the Anne Pro uses 2 MCUs IIRC. So it may be possible!