Keeb build log: BM40hsrgb

I am a big fan of colourful lights… whether they are neon, fairy, or ambi. I am also a big fan of custom mechanical keyboards. Unfortunately, I’ve never been able to bring those two interests together, as the boards that I’ve built were too fiddly or didn’t quite bring enough LEDs to the party. However, last month I came across an amazing keyboard build from /u/_GEIST_ on Reddit, which inspired me to have another go.

Digging into the specs of that build, I discovered that the relatively cheap BM40 PCB not only supported RGB underglow, but had the holy grail of individual LEDs per key… and that in the latest versions of the QMK keyboard software, you could get some really cool animations that would be triggered on each keypress (or release).

An unassuming beastie.

The parts

One of the big challenges of building custom mechanical keyboards is finding suitable parts for the project you want to build. Often, getting affordable cases can be tricky, and when you do find them, they are often of poor quality. There’s also the additional challenge of putting together the PCB with the required components. I have reasonable soldering skills, but having to connect up all of the resistors, diodes, and switches is an exercise in patience which I do not have… especially when you start to add in all of the LEDs. There’s also always the danger that you mess something up, and ruin the PCB, which is quite possible if you aren’t overly familiar with building keyboards. This is something I had managed to do fairly recently, and so I didn’t fancy experiencing another failure so soon after.

PCB + Case

Enter the BM40 board. Not only did this have all of the LEDs, and came with the components pre-soldered, it was also hot-swappable, which means that you can just click the switches into place, without having to solder them in. Brilliant. I picked up this, along with a case which had a diffused bottom panel to let the RGB lights shine through from KPRepublic on Aliexpress. The PCB connects via USB C, which is a nice touch.

Switches + Caps

When it comes to switches, I prefer really clicky keys. The clickier the better. However, that doesn’t always win you many popularity contests, and since my main keyboard has Cherry Blues in it, I decided to go for a more tacticle switch. I had read good things about the Holy Panda tactile switches, and found the Everglide Oreos, which claimed to be similar. If you aren’t familiar with keyboard nomenclature, this means that they wouldn’t be obviously ‘clicky’ to press, but would have some kind of a bump to them on the way down (as opposed to being ‘linear’, and therefore smooth). The other reason I went with these is because they had a smokey black casing, which would let the LEDs shine through.

For the keycaps, I went with my trusty flat DSA profile (rather than other profiles which are curved, or which have a shape change depending on the row and position of the key). I also selected the same kind of smokey black translucent colour to match the switches, and let the LEDs do their thing. I often use blank DSA caps as they are cheaper, and it means I can move them around my boards without having to worry about what is printed on them.

Annoyingly, I didn’t realise that the board was not made up of individual 1u keys like the Planck or Preonic… in the sense that it has a 2u space bar key. This meant that my 1u DSA caps wouldn’t fit. I found a temporary solid white 2u cap that I’ve put in place for now, but it’s not the correct profile, so I’ll need to revisit that. Finding a 2u translucent keycap in the DSA profile is proving easier said than done unfortunately.

Links + Cost

  1. BM40 PCB (Kit 1 with 2u stabilizers for the spacebar) – $37.52.
  2. Anodized aluminium JJ40 case (black version 2.0) – $70.90.
  3. Everglide Oreo tactile switches x70 – $45.60.
  4. Translucent black DSA keycaps x60 – £12.84.

The build

Putting the kit together was pretty easy. All you have to do is unscrew the bottom plate, hold the PCB in place and then connect the switches through the holes in the top of the case. However, there were a couple of stumbling blocks:

  1. There was no screws included to attach the PCB to the case, so the keys hold it in place. This makes getting it into position and not damaging the first few keys you attach a bit tricky.
  2. You need to install the keyboard spacer onto the PCB before you start attaching the keys. This means assembling it, which isn’t all that clear if you haven’t put one together before. After some frantic YouTubing I managed to figure it out, and had to take all the switches off again.

Flashing the software

The BM40 comes with its own software, but I immediately ditched it in favour of the de-facto standard QMK. There is no hardware reset button on the PCB to allow you to put it into DFU mode to flash the firmware, but there are two exposed points marked ‘RES’ which you can bridge with tweezers. This isn’t especially accessible given that the case is sealed up afterwards, so I made sure to include a soft RESET key on one of my custom layers.

I did run into a bit of an issue initially, where I couldn’t get some of the QMK functions to work, such as the all-important custom LED animations. With help from the aforementioned _GEIST_, who kindly sent me his config files, I realised that I had flashed the software with the QMK version provided by the keyboard manufacturer, which was out of date. Re-flashing with the bm40hsrgb settings provided with the latest QMK build (which I then customised), got everything to work as it should.

The Keymap

I already have a keymap set up which I have refined over time for my Planck – which is similar to the BM40, in that it has about the same number of keys, so I stuck with an evolution of that, which makes it easier to switch between the boards. I touch type, and don’t really use the bumps on the keys to indicate finger position, so having blank keycaps isn’t really an issue for me unless there are special characters or macros which I need to remember.

One of the cool things about having under-key LEDs is that theoretically I could code up a layout which maps certain colours to certain keys that I want to stand out. This isn’t something I’ve bothered looking into yet as I don’t feel like I need it, but it does make me think that I could build one of these boards as a dedicated MIDI controller, and change the keys depending on the notes of the scale. That’s probably a project for another day… but something I’m considering. Watch this space.

Anyway, here is how my keys are laid out at the time of writing. There are four layers. The first layer is the base layer. The other layers are accessed via a combination of keypresses, just like you would use the shift key to access capital letters on a ‘regular’ keyboard.

As well as the usual keys and media shortcuts, I have a bunch of custom shortcuts set up. For example, Alfred’s search has its own dedicated key on the base layer since I use it so often, as do my clipboard and bookmark managers. I also have keys specifically for copying, pasting, cutting; keys to copy the active URL in Chrome, and to strip down a long URL to its root (managed via Keyboard Maestro); and keys to perform tasks which become a bit trickier when you have a smaller board… like taking a screenshot.

I’ve uploaded my keymap to GitHub for those of you who want to see the actual code.

I’ve managed to configure things to change the colour of the keys temporarily when I activate layer 1 or 2, which is pretty useful. I can’t quite get it to work for the ‘adjust’ layer though, so if anybody has any tips on how to imrove the code, please let me know. I have a couple of ideas, but my brain is begining to melt looking at it, so I’ve given up for now.

RGB Animations

QMK’s built in RGB animations are awesome. Below I’ve uploaded a video running through some of the effects:

Note that I deliberately didn’t record sound, as there’s far too many people who will over-analyse the sound of the switches, and that’s one can of worms I didn’t want to open.

The Judgement

This is my fifth mechanical keyboard, and the third one that I’ve built (successfully) myself. It does feel a bit like cheating to say I built it, since it is hot-swappable and so couldn’t get much easier. However, it’s also probably my favourite. The case has a wonderful heft to it that the aluminium frame I have for my Planck doesn’t, and I love the LEDs. I had considered getting different coloured translucent keycaps, but the all-black colour scheme is so unassuming that it adds to their effect, and they are so bright that the cap colour doesn’t really matter when they are on. I’m really pleased with it overall, and glad _GEIST_ didn’t mind that I shamefully copied their idea. It is a bit of a shame that the underglow isn’t quite as prominent due to the solid black sides of the case, so as a minor point it would be great if there was a slight cutaway round the edges, but that’s just being petty.

The one thing that I’m not wild about is the choice of switches. While the Oreos are fine, they are very light, and not as tactile as I would like, at least not compared to the Outemu sky switches in my Planck. I end up bottoming out on them to such an extent that I may as well just have clicky keys in there, so I might end up changing them out at some point to find a better option… though they are growing on me. At the end of the day, having the option is the beauty of a hot-swappable board! Whatever happens, I definitely need to find a translucent 2u DSA keycap though, as the current one is driving me nuts. Even though the white looks pretty cool, it feels and sounds different to the rest of the board, and not in a good way.

Perhaps one other thing I should mention is that the LEDs run fairly hot. I guess that might be expected given how bright they are, but it does make me wonder about what their lifespan will be. On top of that, I will probably be making use of the auto LED off feature built into QMK to avoid any… accidental fires. Better safe than sorry. Of course, I could just run them at something less than maximum brightness, but where would the fun be in that?!

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