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Muri ONE: Low Profile Wireless TKL

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It's been a while so I thought I'd post another update. A lot has been going on lately.

First of all, PCB prototypes arrived and they look pretty great, it's awesome to finally be able to hold the product of my work:

Unfortunately, not assembled yet. The required mid-mount USB-C connector went out of stock seemingly everywhere so I'll only be getting them together with some remaining parts next week.
That said, I'm already very happy with the choc stabilizer holes coming out just right - I didn't have the actual stabilizers on hand yet and had to rely on some unofficial measurements I found online.
Then starts the challenge of actually implementing the remaining features. Speaking of which...

I have made the decision to embrace ZMK for this project. Generally, what scares me most about using open source projects is the politics, specifically when you as the user might have different short-term priorities than the project. I've been following them for a while and besides being a bunch of very nice people, their modular approach totally mitigates this risk of a diverging feature set, and actually would allow any third-party to draw from both ZMK core as well as your custom features should you go that route.

Finally, I have finalized the case design and will be ordering 3d prints for it soon. While I had the general design mostly figured out, it took a while to figure out the right hole placements and generally optimize it for CNC machining.
I also started working on actual keycaps, which would fit 19x19mm 1U spacing, rather than Kailh's 18x17mm thing. I played around with both a basic spherical and cylindrical designs, but ultimately ended up going for a hybrid of the two which I think should look the most pleasing of the three (especially with legends on it) and hopefully also feels good. I'll only be able to tell once I print them too.

Here's the three different profiles I made for comparison (top to bottom: spherical, combo, cylindrical):

So, what are the next steps?
For the near future, obviously getting the board assembled and flashing ZMK onto it.
That said, I'm probably also going to spend some time on some decent quality renders to get an interest check going as soon as I get the case prints and have validated the design.

Failure... the word. I really got ahead of myself there with that hint at getting an IC going.
But although the recent months have been a bit of a struggle, I've not given up on my project just yet and there's light at the end of the tunnel. So... what happened?

The case

Due to my lack of experience, it was very hard to find anyone willing to take on the project and when I did, the result was not what I had hoped for. The finish was so-so, the parts didn't actually fit together, nor did the PCB.
As I later found out, the core issue seems to be the sheer size of the part as well as relatively very little surface area on both top and bottom. Fine details and small tolerances didn't help either.

For my next prototype I will be looking at machining one myself from either wood or aluminium if it doesn't come out much more expensive. If I do go the 3d-printing route again, I'll split the model into multiple parts that can be glued together and most-likely do away with some features or details that are not necessary for functional validation of the design.

Speaking of functional validation, even though it came out the way it did, it was money well spent. Although I'm not able to assemble the whole thing using the parts I have, I was still able to get a feel for it and the verdict is:

- I'm really happy with how thin the case is (MX keys for comparison) and it feels almost exactly as good as I would've hoped for...
- ...'Almost' because the wrist-pad is way too narrow, it needs to be pushed out another 1.5-2cm so your fingers rest on the home row in the natural position.


For my first PCB I consider it a success. That said, it wasn't without it's own fair share of issues:

- Assembling the entire thing by hand was an absolute nightmare (ca. 450 smd parts) and as I later found out, I burned about 90% of the LEDs in the process.
- By mistake I used a 3.3V ESD diode for VBUS which led to me removing all the QFP chips and the bluetooth module looking for shorts. Putting them back evenly afterwards was a challenge.
- I also removed the USB port as part of that process and shorted one of it's D+/D- pins which caused data not to work.
- One of the debug output footprints I used (from official KiCAD library) was mirrored rendering it useless. Luckily I was precautious enough to add a second, different one just in case which worked just fine.

After working through all that, I did get ZMK flashed onto the board and validated what I could, even wrote a driver for the IS31FL3743A RGB matrix controller.
But once I decided I learned what there was to learn from this board, I switched my attention to designing the next version - adding features, simplifying the design and making it easier and cheaper to manufacture.
The new boards are already being manufactured and I'm hoping to be able to start working with them by the end of the month - and this time I checked the assembly option ;)

To point out some key changes:

- Added a battery fuel gauge for accurate battery level as well as temperature measurements.
- Added a 5-LED strip indicator above the navigation cluster for all your indication needs (bootloader, charging, caps lock or just pretty lights if you fancy).
- Backtracked on my idea of using two IS31FL3743A drivers and replaced them with a single IS31FL3741.
- Added a buzzer...
- ...and soft-shutdown capability for the power switch so your board can properly greet you when you turn it on or off.


I also finalized the keycap profiles - unfortunately the availability of full-size Choc compatible caps hasn't improved much in the last year - and will be printing them next week for some initial testing.

King Icewind:
Great work on your project! What are you using for a fuel gauge?

>Great work on your project! What are you using for a fuel gauge?

I'm using MAX17055 for the fuel gauge. There's a ready Zephyr driver for it and I believe some people have already successfully used it on their ZMK boards as well. I think it has best-in-class current consumption as well which is a nice bonus.

This weekend I decided to update the case to fix the wrist pad but I feel like the more I think about it the less excited I am by the design.
The wings make it very complex yet the effect isn't really felt that much because the keyboard is already so low profile.

So feeling somewhat inspired by the refreshing new iMac series I decided to draft up a quick new design for the case that's still compatible with my current PCB:

I removed the 'wings' and I went for a horizontal accent piece instead of two vertical ones.
Having just the angled part of the wrist pad be a different color helps keep things interesting instead of having just a big slab of metal - even though it's 2cm wider now. It's also narrower by about 18mm.
I'm thinking I could maybe even try engraving some sort of a low key pattern on it to make it even cooler. We'll see.

I'm feeling pretty pleased with the updated look and will continue working on it. What do you think?


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