Since Hall effect Keyboards/Switches took basically the whole gaming industry over, and I want to equip one of my endgame keebs with a Hall effect pcb, does anyone know if any company sells/plans to sell 65% Pcbs that will fit in the likes of a Keycult 65 or SingaKBD Kohaku???

Dear Community,

I recently came across an interesting channel on youtube, someone building a completely custom analog keyboard, even designing and 3D printing their own switches (You can see the keyboard here: https://www.youtube.com/watch?v=sFR6E_Ejot0&t=2659s).

I got inspired and decided I really want a custom analog keyboard of my own now. Making custom switches and cases is a bit too much for me though so I am planning to put this PCB in a Keychron Q1. I plan to then swap out the switches for lekker switches (those found in the increasingly popular Wooting analog hall effect keyboards, and also for sale separately), and swap the included PCB for my own to work with the lekker switches. These switches just have a magnet connected to the stem, and no contacts like most regular keyboard switches. I mostly followed the guide from riskable (the video I mentioned), but things became a lot harder when I realized he used a blackpill breakout board. I believe this wouldn't fit in the Q1 case, (nor any other 75% cases with a knob I could find). So I then also had to include a microcontroller in my design (I chose the STM32F411CEU6 or STM32F401CEU6 since those are used on the blackpill board). I used a 2-layer board to keep things as simple as possible for myself.

Getting an LED to light up from a battery has been my only experience with electrical engineering until now, so this was quite a challenge for me. I expect many beginner mistakes in my design, but would love to learn, since I really enjoy engineering.

GOALS

The board should:

- have hall effect sensors to measure the distance all keys have been pressed in.

- be able to connect to a pc via USB-c 2.0 connection.

- have an acceptably high sample rate.

- be programmable via ST-link and/or preferably USB.

- have a rotary encoder.

- be accurate enough in measuring key depression (preferably 0.1mm steps or smaller, but anything up to 0.3mm is pretty acceptable to me).

SOURCES

Since this is my first time designing PCB, I relied heavily on youtube video guides.

These are the guides by the person who initially inspired this project of mine:

• https://www.youtube.com/watch?v=TfKz_FbZWLQ

• https://www.youtube.com/watch?v=sFR6E_Ejot0

I also found Phil's Lab's videos to be quite helpful, especially this one on STM32 PCB design:

• https://www.youtube.com/watch?v=aVUqaB0IMh4

DESIGN & UNCERTAINTIES

Firstly, I want to say I am aware the positioning of my microcontroller is pretty terrible. It's kind of annoying that I only came to this conclusion late into the process of designing the PCB. So I figured before making drastic changes to a board that could be fundamentally flawed, I should get someone else to look at it. In the next iteration, I would place the microcontroller somewhere in the middle up top, or on the top right, next to the USB-c port. This depends on what I should prioritize, the distance to the analog multiplexers or the USB port (if it's placed in the middle, it would still be quite far from the USB port, since the board is around 320mm wide).

The next thing I'm not so sure about, is the placement of some resistors and capacitors, for example, the resistors for the rotary encoder (R8 and R11). Do I need to place these next to the microcontroller instead of just placing them anywhere along the trace? I assumed since there's a direct uninterrupted connection between the IC and the rotary encoder, it wouldn't matter where I placed them. However, for decoupling capacitors for the IC, the documentation mentioned they should be placed as close to the IC as possible, so that made me unsure.

I was also a bit confused about USB inrush currents. The documentation mentioned you could have at most 10uF worth of capacitors on the VBUS line. However, as you can see in my design, I have 2.2uF, then a ferrite bead, followed by another 24.2uF. Will the resistance from the ferrite bead be enough to fix the issue, or is this setup just wrong? A guide I followed on youtube (I couldn't find it anymore) just directly connected the AMS1117 with its 22uF capacitors directly to the VBUS line, without a ferrite bead. I found this strange since it isn't within spec according to the datasheet.

Additionally, I'm not sure if using 2 ferrite beads is necessary. I used one for the 5V, and another for the analog 3.3V line. Do I need both or should I remove the one on the 5V line? If so, what should I do about inrush current?

Another uncertainty of mine is the handling of analog signals. The hall effect sensors all give an analog signal, which I've read you have to be a little more careful around with routing, so I tried to maximize the distance between traces. I hope this is enough to make this system at least usable. Would something similar to the sensitivity of a Wooting keyboard be possible? (They advertise 0.1mm measurement precision) I will try to increase precision through firmware, but obviously, firmware can't always solve bad design.

Perhaps a small remark, but something that confused me nonetheless. The footprint of the STM32 microcontroller I'm using has a ground connection in the middle of the IC, I connected this to ground through a single connection, is this the correct way of doing this? I couldn't find how I should handle this connection on the datasheet.

Finally, I also want to mention that while I tried my best to look everything up when it comes to safety and protection, many things seemed quite complicated and I just ended up not integrating them (yet). For example, I wanted to add a fuse on the VBUS line, just to be safe, but then I realized that might not be the best idea because of inrush current. Any advice on how to integrate more safety measures into the board? And is it even necessary, or is the ESD protection on the USB data lines enough?

IMAGES

The 3D view is lacking a model for the rotary encoder. I plan on using an EC11. It's the one used in the Q1 keyboard's original PCB, so it should fit perfectly.

I also didn't include a model for the USB port because, in the final design, I will replace it with a ribbon cable connector, so I can connect it to the original daughterboard included with the keyboard (the daughterboard has a toggle switch which I won't be using, and the USB port).

The 4-pin STL-Link connector is something I put in because one of the guides I followed advised me to add it even though I have a boot button. When putting the PCB in the case I will probably snip the pins shorter or bend them out of the way to make them fit under the plate.

I deduced the location of the mounting holes from the plate file which can be found on the official Keychron website (https://www.keychron.com/pages/q1-keyboard-plate-file-1). The other holes next to the backspace, enter and spacebar are for screw-in stabilizers.

If I wasn't clear enough on certain things, or you have any more questions, don't hesitate to ask!

Any feedback/advice, of any kind, relating to the design, component selection, project, post and my questions is greatly appreciated!

Thanks in advance!