Keyboard pcb

KB79

Custom 79-key mechanical keyboard | Jonathan Li

KB79 is a custom 75% mechanical keyboard designed around an ATmega32A microcontroller. The project covers the complete hardware development process, including schematic design, PCB layout, component sourcing, fabrication, assembly, firmware integration, and testing.

The finished keyboard features USB-C connectivity, a rotary encoder for media controls, and a hybrid switch footprint designed for both Kailh Choc V2 low-profile and MX-style switches.

Overview

After using a 60% keyboard for several years, I wanted a compact layout that retained dedicated arrow keys and a function row without the additional size and keys of a tenkeyless keyboard. KB79 was designed around those requirements. Its 79-key layout includes a function row, arrow keys, Delete, Home, End, and Insert, alongside a rotary encoder for volume and playback controls.

The project also provided an opportunity to gain experience with KiCad and the complete PCB development workflow, from component selection and schematic capture to manufacturing, assembly, and hardware bring-up.

Features

• Custom 79-key, 75% layout
• ATmega32A-PU microcontroller
• 6 × 15 keyboard matrix
• USB-C connectivity using V-USB
• 16 MHz crystal
• Rotary encoder with volume and play/pause controls
• QMK firmware
• Hybrid Kailh Choc V2 / MX-style switch footprints
• Through-hole component construction
• FR4 switch plate and baseplate
• 2-layer, 1.6 mm PCB

Hardware & PCB Design

KB79 uses an ATmega32A-PU microcontroller and a custom 6 × 15 keyboard matrix. USB connectivity is provided through V-USB, allowing the ATmega32A to communicate with a computer over USB-C.

The PCB was designed in KiCad, including the keyboard matrix, component placement, trace routing, board geometry, and manufacturing preparation.

The PCB uses modified ScottoKeebs switch footprints, with additional mounting holes added to accommodate both Kailh Choc V2 low-profile and MX-style switches. The completed keyboard uses Kailh low-profile Cream switches; MX compatibility has not yet been physically tested.

The design primarily uses through-hole components, allowing the PCB to be assembled entirely by hand.

Fabrication & Assembly

Five bare PCBs were manufactured by JLCPCB. All electronic components were sourced separately through Taobao and hand-soldered without PCB assembly services.

The finished keyboard uses:

• Kailh low-profile Cream switches
• FR4 switch plate
• FR4 baseplate
• Low-profile spacebar stabilizer

The first PCB revision was successfully assembled and brought into operation without requiring a hardware revision.

Firmware

KB79 runs QMK firmware configured for the ATmega32A using V-USB and USBaspLoader.

The firmware configuration implements the custom keyboard matrix, keymap, USB interface, and rotary encoder functionality.

The encoder provides the following media controls:

• Clockwise: Volume Up
• Counterclockwise: Volume Down
• Press: Play/Pause

A secondary function layer (MO(1)) is included and currently reserved for future functionality.

Firmware configuration and source files are available in the firmware/ directory.

Bring-Up & Validation

Hardware and firmware bring-up involved testing USB connectivity, verifying the keyboard matrix, validating key mappings, and confirming rotary encoder operation.

Matrix configuration and USB enumeration issues were resolved through incremental testing, including simplified test keymaps and adjustments to the V-USB configuration.

The completed keyboard has been used regularly for two weeks without observed hardware or firmware issues.

Repository Structure

KB79/
├── LICENSE
├── README.md
├── firmware/
│   ├── builds/
│   │   └── handwired_kb79_default.hex
│   ├── keymaps/
│   │   └── default/
│   │       └── keymap.c
│   ├── keyboard.json
│   ├── readme.md
│   ├── rules.mk
│   └── usbconfig.h
├── hardware/
│   ├── fabrication/
│   │   ├── gerbers/
│   │   └── KB79_BOM.xlsx
│   └── kicad files/
│       ├── keyboard_pcb.kicad_pcb
│       ├── keyboard_pcb.kicad_pro
│       └── keyboard_pcb.kicad_sch
└── images/

The BOM includes component specifications and part numbers used for the build.

Attribution

Portions of the ATmega32A, USB/V-USB, and supporting circuitry were adapted from the open-source Mysterium TKL keyboard project by Cosey Fannitutti (CFTKB), licensed under the GNU General Public License v3.0.

KB79 features a separately developed keyboard matrix, physical layout, PCB placement and routing, component selection, assembly, and firmware integration.

Switch footprints were adapted from [ScottoKeebs](https://github.com/joe-scotto/scottokeebs?utm_source=chatgpt.com) by Joe Scotto, with two additional holes added for dual switch compatibility.

License

KB79 is distributed under the GNU General Public License v3.0. See LICENSE for details.