MBUK Macro Pad Kit

Not sure that your soldering is the issue with 4th key.

After soldering this up I installed KMK (rather than QMK) as I wanted to be able to set up the macropad as a generic HID rather than a composite HID, and I reckon that KMK will be easier for that - haven't got that far yet. Just finished building the board and getting KMK to recognise the keys.

The problem I found with the RP2040 Pro Micro is that rather than just use digital GPIO pins (like GPIO2 thru GPIO9, all of which are free) the board uses 3x digital IO pins and 1x analog / digital IO pin (i.e. GPIO26). This appears to cause problems with KMK's scanning speed (and possibly QMK's) of the buttons where the analog / digital nature of GPIO26 makes this slower. I wasn't getting key presses with the 4th key either!

The simplest way that I could see to rectify this issue was to flip the port mappings so that GPIO26 (and the others) would act as outputs and GPIO21 would act as an input. Thus the mappings are:

keyboard.col_pins = (board.GP21,)
keyboard.row_pins = (board.GP23, board.GP20, board.GP22, board.GP26)

This enabled me to get output from all 4 keys.

As I said I've just done the basics so far (need to add macros, and present as basic HID) - if I find any other quirks I will update here provided Mechboards are OK with that!

As far as the soldering was concerned it was straightforward, although I did use some round pin strips to act as a socket for the RP2040 pro micro so that I could more easily remove the MCU board if needed. It would be nice if Mechboards could include these for ease. I also had to use some larger brass mounts to cater for the increased height of the socket approach.

My interactions with Mechboards have been good, and I would be happy to recommend them to others.

I got this kit to practice soldering and try out QMK before building something a bit more interesting. I learnt many things in the process, most importantly that my soldering still needs more practice.

I used a ProMicro RP2040 MCU, and this kit requires the firmware to be compiled with the flag -e CONVERT_TO=rp2040_ce on the compile command in order to generate the required .uf2. This wasn't obvious to me at all, but the support person responded to me quickly with this info.

Even then, *spoiler alert* I couldn't get the onboard LED to light as written, and decided to modify keyboard.json to specify the RP2040 and avoid the need for conversion. With the new mappings, the matrix is "cols": ["GP23", "GP20", "GP22", "GP26"],
"rows": ["GP21"]
and the LED pin is GP17. This worked a treat :)
I still don't have a functioning 4th key, but I suspect that is entirely related to said poor soldering.

General things about assembling the kit: I didn't push my switches in far enough before soldering so I've got issues with spacing. I had to cut short the pins to get the back on (but I think I would have anyway). The connectors on the MCU I used are really tiny and don't run to the edges, unlike Arduino style boards, and they were really hard to solder. I think next time I would test the circuits with a multimeter before attaching the MCU.

fun project to do but instructions are not super clear, recommend socketing the controller and this uses the handwired/mechboards_micropad layout on the qmk configurator

Nice little kit for practicing soldering, I had some clearance issues using a Pro Micro (ATMEGA32U4) & sockets but ii used some spare 5mm standoffs to give me some more space on the bottom and all was good.

Great little kit to get started on. Taught me that the direction you place the diodes in matters. Also taught me that it's useful to useful to get those sockets so you don't have to solder your controller on to the board. I'm ready for the next challenge now.