I would like to build a split-ortho computer keyboard. It would have 12 keys per side. Don’t worry too much about how to get a standard 104 key keyboard down to 24 keys. That’s software magic. But, I would like to have these all controlled off one controller, with a single cable between the two halves.

I really want to use a CAT6 patch cable as the cable, and it has 4 twisted pairs.

Assume the controller on the left side, and a cable to the right side. 12 keys on each side, and 8 cables.

I can use a switch matrix with some resistors to get a 3x4 grid of my switches, and this would use 7 cables. All good so far.

But, I also really want per-key RGB. This requires D-IN/D-OUT; VCC; GND. I could ground each side independently, so ok there. But unless there are some smarts, I only have 1 cable left and need more than that.

So the question to the community: are there any smarts that you can think of to complete the circuit?