This project uses Logitech K380 keyboard and fully replaces its internal logic, equipping it with cool features like the ZMK keyboard firmware, USB and an integrated Li-Ion battery.
This project was born out of the need for a very robust but lightweight keyboard and my custom key layout needs. I wanted a keyboard where one doesn't need an extra casing when it is squeezed between your laptop and books inside an already struggling backpack without losing the comfort of key layers, macros, tap-dance and more.
The choice fell on the Logitech K380, as it is easy to source, cheap (for a custom keyboard), has a build in on/off switch and already very robust. Additional perks are the membrane switches, which I personally prefer over normal MK switches and are essentially indestructible.
The actual logic inside the original K380 is contained on a small PCB in the upper left corner (from the top) with the key matrix attached using an FPC cable. This makes it really easy to trash it and put your own PCB inside. The Li-Ion battery also fits snugly in the previous AAA battery compartment.
The hardware folder contains the schematic and PCB for the mod-chip. It uses an
nRF52840 processor for wireless (and wired) connectivity, uses WS2812 for status LEDs
and integrates a sensible Li-Ion charging IC. Except for the newly added USB port and
a few more LED colors, the mod is essentially indistinguishable from the outside.
The only part of the mod, that requires a bit more effort besides potentially soldering the PCB, is the drilling on the case for the USB-C port. In my first revisions also integrated a completely oversized Li-Ion battery which didn't fit into the battery bay without some subtractive manufacturing.
- nRF52840 - a low power, but feature-rich wireless IC
- ZMK support
- easy to integrate
- replaces AAA batteries with a Li-Ion battery
- a fully functioning USB port, for charging, connecting and programming
- RGB status LEDs
Besides not being able to really mix up the keyboard layout, the biggest problem there is with the keyboard is the lack of phantom key blocking. The keyboard matrix itself lacks any kind of diodes - presumably to save on costs - and is such prone to ghosting. In normal use one doesn't really notice that, as the vendor firmware only supports three key presses at a time and the key matrix traces are routed all over the place, so that common key combinations won't result in ghost key presses.
Before you start editing the hardware here, you should install the marbastlib plugin into your KiCad. It contains the footprints and 3D models for the HolyIoT board.
Otherwise, feel free to go. But if you want to contribute anything to the main hardware, please open an issue first. I'm currently a bit unsure how collaboration could work with KiCad projects as merging changes isn't really trivial here.