How to make a ThumbsUp! keyboard wireless

ThumbsUp! keyboards can be made wireless. 

Not all of them, but those driven by ProMicro controller.
There are multiple options, so far I only used one of them, the nice!nano v2 with ZMK-based firmware.

Nice!nano is a drop-in replacement for AtMega32U4-based ProMicro units.
It got a compatible pinout and is quite simple to use.

Here is how it looks fully assembled:

These are the parts: nice!nano v2 in the middle, the battery on the left and the pin headers on the right. Also there is a power switch on the PCB - it physically disconnects the battery from MCU/USB.

I use pin headers/sockets to allow MCU swap. The default/standard sockets are too tall, so I have to pull the pins from headers and cut them so they are flush with the board surface. Make sure solder balls are small enough to allow the raisers/connectors to actually connect.

Notice the MCU goes components towards PCB.

Make sure the B+ and B- holes are not used, they are added in nice!nano, but the ProMicro does not have them. There are other pins that connect MCU to battery.

The battery is hidden under MCU. Battery terminals are soldered to the board. There is a power switch visible in other pictures that disconnects the battery from the circuit.

There is plenty of space under MCU, the battery has to be affixed by a double-sided tape, or by a roll of scotch tape - with the sticky side out from both sides. Here it is like it looks like, the battery is suspended between MCU and PCB with two cylinders of scotch tape:

ZMK firmware for nice!nano is provided in the same dropbox folder with other files. Look for thumbsupv9-nice_nano_v2-zmk_20240401215300.uf2

By default firmware supports up to 4 bluetooth profiles, i.e. the board can be switched between 4 devices. Luckily there is a ZMK fork with mouse key support, that is the board can be used to move the mouse pointer and use the mouse buttons in the same way they are used in the QMK-based ThumbsUp! keyboards. Unfortunately there is no Cirque ProGlide touchpad support yet.

UPDATE 20240627: Some of the boards (i.e. all the newer versions v5, v8, v8b, v9) need a power switch installed, it is in the bottom right corner in the picture below.
That switch disconnects the battery from nice!nano. You can order it from Mouser: https://www.mouser.ca/ProductDetail/655-1825232-1

Note that the battery will charge only when the switch is the ON position, towards the center of the board.