A split keyboard needs two sides.

Before ordering another PCB (for the right side), I want to make sure that the communication works. And luckily you always get two PCBs when ordering an assembled board, so I have two left sides. Enough to test (so stay tuned for another update with some results)!

Why do it like that? It gives me the chance to correct mistakes from the left side (see bodge wires posted earlier) and test an improved right side :)

From the beginning I prepared to cross Rx and Tx via solder jumpers so that I can run that test:

Maybe a bit over-engineered and in the meanwhile I found out that QMK supports half-duplex serial communication via a single wire, but I will give it a try. Unfortunately, I put these solder jumpers on the front side, which is inaccessible if I put the keyboard plate on.

Right next to the solder jumpers you can see the SMD footprint of the RJ12 connector. It is not that common for split keyboards, but I do like the fact that it doesn't expose blank pins like TRRS (which is indeed compact). I've seen a lot of people using USB-C but imho that's also wrong as it's not a standard conforming USB-C. Happy to hear suggestions!

Btw, did you recognize that the picture of this post already shows some 1.25U? I do like them a lot. Let me know your opinion about it~