Keyboard left

Hypothenar PCB

The v1 redesign — chip-direct nRF52840 module + I/O expanders, designed for JLCPCB PCBA assembly. See docs/v1-design.md (in the repo root) for architectural decisions and BOM rationale.

This directory is a work-in-progress. The PCB hasn't been drawn yet.

Repositories

• Primary: https://git.lyte.dev/lytedev/hypothenar-keyboard
• Mirror (GitHub): https://github.com/lytedev/hypothenar-keyboard
• Sibling model: thenar — the hand-solderable original this design derives from (GitHub mirror)

What's here

• ref-designguide-schematic/ — vendored copy of ebastler/zmk-designguide (CERN-OHL-P licensed). A reference schematic showing tested wireless-keyboard topologies: USB-C + ESD, TP4056 charge IC, XC6206 LDO, three different nRF52840 module options. This is our primary reference for the power tree and MCU section. Open ref-designguide-schematic/designguide-schematic.kicad_sch in KiCad to view.

• lib/kleeb/ — vendored MIT-licensed KiCad library from crides/kleeb. The only public source of the MS88SF3 nRF52840 module footprint + symbol (in lib/kleeb/mcu.pretty/ms88sf3.kicad_mod and the mcu.kicad_sym symbol library). Add this to KiCad's path when drawing the schematic.

• lib/marbastlib/ — CERN-OHL-P keyboard-focused KiCad library by ebastler. Used by zmk-designguide. Contains symbols + footprints for TP4056, XC6206, USB-C connectors, etc.

3D models from both libraries are stripped (~88 MB saved). Re-fetch the original repos if you want 3D viewer support.

Project skeleton

Two KiCad projects ready to open:

kicad/hypothenar-left/
  hypothenar-left.kicad_pro    # start with: nix develop -c kicad
  hypothenar-left.kicad_sch    # currently == designguide schematic (verbatim copy)
  hypothenar-left.kicad_pcb    # empty, will populate from netlist later
  sym-lib-table               # project-local symbol library wiring
  fp-lib-table                # project-local footprint library wiring

kicad/hypothenar-right/
  hypothenar-right.{kicad_pro,kicad_sch,kicad_pcb,sym-lib-table,fp-lib-table}

Open either project file (.kicad_pro) in KiCad and the kleeb + marbastlib libraries are wired up automatically — search the symbol browser for MS88SF3, TP4056, XC6206, USB_C etc. and they're all present.

Roadmap

1. Prune the designguide schematic to just what we want:

   • Keep: USB-C input + ESD, TP4056 charge IC, XC6206 LDO, one MCU module slot, Vsense divider (for battery reporting)
   • Delete: the other two MCU modules (Holyiot and Moko — we use the third slot for our MS88SF3), the alternative BQ24075 charge IC, the LED underglow circuit, the battery protection (DW01A/FS8205) — optional, depends on whether we want belt-and-suspenders
   • Replace: the Ebyte E73 module footprint slot with MS88SF3
   • Save. ERC should drop from 409 to <50.

2. Add the MCP23017 section (not in designguide):

   • Two MCP23017 ICs per half, I²C-connected to the MCU
   • Address straps for 0x20 and 0x21
   • 4.7 kΩ I²C pull-ups
   • Reset line tied to MCU GPIO
   • Reference: SolderedElectronics/IO-expander-MCP23017-breakout-hardware-design

3. Add the matrix section: 28 switches per half. With switch-per-pin topology, each switch has one pin → GPIO pin on one of the MCP23017s, other pin → GND. No diodes.

   • Will eventually come from the ergogen scaffold (regenerated for v1 without diodes); for now stub with a placeholder.

4. Add the rest of the per-half peripherals: scrollwheel encoder, Nice!View headers, slider switch, reset button.

5. Run ERC clean on the schematic.

6. Layout in KiCad: import netlist into the .kicad_pcb, place footprints in the chip area, then bring in the ergogen scaffold matrix and stitch the two together.

7. Routing: probably mostly by hand again (autoroute will hit similar plateaus as rc1).

8. Generate: gerbers + pick-place CSV + BOM CSV → submit to JLCPCB.

Working on this branch

v1 is a git branch off main. To work on v1:

jj edit v1                                       # check out v1 branch
jj new                                           # start a new commit
# ... edit files ...
jj describe -m "v1(...): what I changed"
jj git push --bookmark v1

main continues to be the validated rc1 design.

License notes

This repository bundles work under three licenses that are compatible with this project's MIT licence:

• ref-designguide-schematic/ — CERN-OHL-P v2 (ebastler/zmk-designguide)
• lib/kleeb/ — MIT (crides/kleeb)
• lib/marbastlib/ — CERN-OHL-P v2 (ebastler/marbastlib)

Both CERN-OHL-P and MIT permit redistribution + modification. Attribution preserved by keeping each library's original LICENSE file untouched.