12/28/2025 - Initial Ideas + Schematic

Hello!

My inspiration from this project came straight from the HackPad page- I saw how much stuff I can add and thought that this would make for a great project to learn some REAL electrical engineering instead of whatever the hell I'm doing otherwise.

Idea

• As many keys as I can fit with my 11 inputs. (8)
• 4x4 RGB LED Matrix.
• 0.91in OLED display.
• Control various things from the keypad using the buttons on it, using the display to see what's happening.
• LED Matrix for cool decoration. No practical purpose. (I know this will be terrible to program, but here we are.)
• A rat drawn on the silkscreen of the PCB. (This is a REQUIREMENT. I will have no less.)

Schematic Prototype

Anyway, I've drafted a quick schematic (literally never used KiCad before but it's pretty intuitive), excuse the probably rookie mistakes, but I believe this is a good starting point.

Next Steps

Decide how I want to lay things out, route it, learn Fusion, get everything ready, hit order.

12/30/2025 - New Designs, Firmware, Getting Ready to Purchase!

Designs are approved, next is ordering everything as soon as I get some grants!

Final Designs

The final designs have changed dramatically from the initial designs. From discovering there is a 100x100mm limit and figuring out how to make a matrix out of the keys... a lot is different!

Specifically, the whole PCB is bordering on the size limit but is well within it, and has 12 keys instead of the original 8!

I experimented with the shape of the PCB, chamfering the edges to create a more distinct design, and putting a giant chamfer on the corner that doesn't have any components. I think it makes the design a lot more creative and makes it look interesting!

Case

Enough talking, here's some pictures! (Just imagine the PCB is blue... I couldn't figure out how to change it in Fusion)

Case + Cover:

I added a window on the left side of the cover, so you can see the LED matrix and silkscreen designs as well as the microcontroller. I would love to add acrylic to this window to make it more "premium" but I don't have access to a laser cutter or acrylic, so here we are. (I might experiment with a 3d printed diffuser for the matrix, we'll see)

You can see the slope on the bottom to make the whole thing angled (about 5deg):

You may also notice the screw holes in the PCB. I added them just in case, I don't think I'll be using them as the components should hold everything together. The screw holes in the case will definitely be used however to hold the lid on.

The hole for the OLED is absolutely too big, I measured it way more than 0.91in. It kinda depends on what model of OLED I get, so I'll adjust the design accordingly. Luckily, I have my own printer so it shouldn't be hard to iterate on the case.

Learning Fusion for this was really helpful and I now see just how much better it is than Tinkercad... (this would've taken DAYS in Tinkercad.)

PCB

Alright, here's the actually interesting stuff:

(Yes, the keys are actually connected to the diodes. The white line covers the traces.)

In total, I think I rerouted the PCB like 5 times and the schematic at least once. I've learned a lot though, I actually found it quite entertaining to route it!

You may notice the pin labels on the XIAO, that may or may not be completely unnecessary. Yes, they are but I like the verbosity and I think it will add some visual flare. Also useful for quicker debugging perhaps.

Yes, there are still mistakes. The routing may change one more time before sending it, as I have one more GPIO pin that I would like to use, or I might change the layout of the LED matrix.

Should I have used a ground layer? Absolutely. Could I figure out how to? No. That's for a later project, it shouldn't have a crazy effect on the final result.

Firmware

The firmware is currently in a very basic state. I'm using KMK as it meets my requirements (not that I like python), and will do everything I want. All it is right now is the keyboard controller, but it is there.

What's next?

Order stuff, assemble it, write some real firmware, get it working!

1/16/2026 - Soldering and firmware!

It's here!! It's finally here!!

The PCB and soldering iron finally arrived, and everything is soldered!!

The good, the bad, and the good

The good news is that nothing exploded the first time I turned it on, despite my terrible beginner solder joints!

Unfortunately, I made a fatal mistake in my routing that cost a large amount of time and effort.

You might not notice just by looking at the routing:

But if you look at the schematic...

Yep. I used the wrong symbol. Correct footprint though, but all the pin assignments are completely jumbled. There's unfortunately no good way to fix this without making new PCBs, as the only options are:
A) Mount the LEDs backward (you can't see the light) and do minor jumper soldering to make it work
B) Cut all the traces and make everything out of jumper wires

..yeah neither of those sound good, so unfortunately, we have to say goodbye to the beloved unnecessary LED matrix. I may reuse the LEDs in a future project though.

Anyway, back to the good! Everything else on the circuit board including the keys, microcontroller and OLED all work flawlessly! (although the OLED is actually upside down, but this is easy to fix in firmware)

The only other thing that went wrong is with the case.

1. The angle is way too shallow, I can't really see the OLED that well.
2. The microcontroller is a bit too tall and hits the lid, causing it to bulge and make some keys not push down all the way.

I'm thankful that all the issues I'm having are relatively fixable, minus the LEDs.

Firmware

KMK and Circuitpython were both very easy to set up! I got the OLED displaying things and the keys pressing actually keyboard buttons!

And saving the best for last, that piezo buzzer I installed last minute works really well! I made a nice startup tune and it adds to the quality a LOT!

Anyway, I'm gonna go fix a bunch of stuff.