Road to Kwumsy K2 mod (part 1) - 米国で働く技術系サラリーマンのボヤキ on はてブロ

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I thought someone would make Handheld computer with it when I saw Kwumsy K2, full mechanical keyboard with touch screen first time.
There was a thread running on reddit too - I was expecting to see it in a month or 2.
...
well, after a year, nothing came up to the world.
Finding affordable 2nd hand one, I started my project, turning Kwumsy K2 as TRS-80 model 100 reborn.

Let's start from ingredients;

Kwumsy K2 keyboard + touch screen: for sure, we need it
Raspberry Pi Zero 2 W: this single board computer (SBC) enables linux based Raspberry Pi OS with HDMI, USB HID device and WiFi connection, very handy

Yeah, it works in dummy manner.

I plotted my build plan majorly with cable management - not to modify board, but to make custom cables to connect boards and other parts.
I bought a couple of cables and break-out boards;

mini-HDMI - HDMI cable: check link below, actually I bought several sorts, this is the easiest for hand-soldering
USB-A - micro-USB cable: anyone is fine, you must have some spares
micro-USB extension with chassis mount: check link below, I use it for USB power-bank charging
USB-C break-out board: check link below, it enables Kwumsy K2 keyboard control board - Raspberry Pi connection
USB-A break-out board: check link below, it is used for the board - USB power-bank connection
mini-HDMI break-out board: it is used for the reverse engineering and open/short check, if you are confident of your blue-wire work, you don't need it :-)

At last power management;

power button: anyone is fine as far as it fits into the space
USB power-bank (battery): I choose one in the below link, simply because of real estate

The most critical thing was to make a custom HDMI + USB -> USB-C cable in the project.
USB.org specifies USB-C HDMI alt mode, i.e. USB-C -> HDMI + USB - but the inbox cable is reverse of it, HDMI + USB -> USB-C.
Unless the inbox cable has some magic chip inside to do the magic, the inbox cable must be just a collection of wires.
I opened the inbox cable...

Yep, I am right and the cable is a dum collection of wires, all HDMI & USB are connected straight, the keyboard control board makes all the magic.

Next step was to find HDMI + USB -> USB-C "connector" pin to pin connection.
Break-out boards really help to figure out it - this is it.

If VBUS and GND are connected, Raspberry Pi can be powered from the keyboard control board.
Otherwise (my case) you can feed externally to both Raspberry Pi and the keyboard control board, as below.