Eidolon right

⚠️ Work in progress — do not build this yet. The PCB, case, and firmware have not been validated against a physical build. Things will change, things may be wrong. Watch the commits if you want to follow along, but don't order boards from these files yet.

Eidolon

eidolon /aɪˈdoʊlɒn/ noun An idealized image; a phantom or spectre of a person or thing. — from Greek εἴδωλον (image, idol, phantom)

A small column-staggered wireless split keyboard. 30 keys (5×3 + 2 thumb per half), Kailh Choc v1 switches, Seeed XIAO nRF52840 BLE, Totem-style clamshell case. Both halves are independent wireless units — no TRRS cable.

Built on the shoulders of

PCB

Left half	Right half

Case

Top — left	Top — right

Bottom — left	Bottom — right

Repository layout

pcb/              Ergogen source + routed KiCad files + gerbers
  eidolon.yaml      Ergogen config (geometry + nets)
  footprints/       custom Ergogen footprints
  build.js          local build wrapper (injects footprints)
  eidolon_left.kicad_pcb   routed left half
  eidolon_right.kicad_pcb  routed right half
  eidolon_left_gerbers.zip
  eidolon_right_gerbers.zip

case/             OpenSCAD case design
  eidolon_case.scad        top shell (both halves via -D right=true)
  eidolon_case_bottom.scad bottom shell
  stl/                     pre-generated STL files

PCB build (Ergogen)

Custom footprints live in pcb/footprints/, so use the wrapper rather than the ergogen CLI directly:

cd pcb
npm install       # once
node build.js     # -> pcb/output/

Outputs land in pcb/output/:

• outlines/board_left.svg|dxf, board_right.svg|dxf — board perimeters
• pcbs/eidolon_left.kicad_pcb, eidolon_right.kicad_pcb — both halves, footprints + nets placed (no routes)

On ergogen.xyz, paste each file in pcb/footprints/ into the web app's Footprints section under its filename (e.g. reset_button); eidolon.yaml then works as-is.

Layout

 pinky  ring  middle index inner
   ·    top    top   top   ·       (pinky has no top row; inner has no bottom)
 home  home   home  home  upper
 bot   bot    bot   bot   lower
                  thumbL thumbR    (-8°)

Pinky splayed 5°, ring splayed 3°; other columns straight. Choc spacing: 18 mm columns, 17 mm rows.

Wiring — COL2ROW diode matrix (XIAO BLE)

Each half is a fully independent wireless unit (own XIAO + battery, no TRRS), so the two halves carry independent pin maps. The columns are identical; the rows are assigned per half to keep each MCU's fan-out clean.

On the right half all four rows sit on the matrix-facing D7–D10 edge (D5/D6 spare), so only the five columns cross the MCU — the physical minimum. The two halves therefore need different MATRIX_ROW_PINS in firmware.

Power: battery + → RAW_BATT → slide switch → BATT → XIAO B+; battery − → GND.

Verify before fab: the XIAO pad→pin mapping lives in pcb/footprints/xiao_ble.js (surface-mount, mounted face-up over the PCB). It was corrected and checked against the XIAO datasheet and the TOTEM xiao-ble-smd-cutout footprint — re-confirm before ordering.

Mirrored halves, not reversible

The original Phantom is a single reversible PCB flipped for both hands. Eidolon generates a true left and right board. Because each half is an independent wireless unit with its own firmware, the halves do not share a pin map — the right half's MATRIX_ROW_PINS differ from the left's (see the per-half table above).

Case (OpenSCAD)

case/eidolon_case.scad is the top shell for both halves. The right half is the left mirrored (-D right=true).

openscad -o case/stl/eidolon_case_top_left.stl  case/eidolon_case.scad
openscad -D right=true -o case/stl/eidolon_case_top_right.stl  case/eidolon_case.scad
openscad -o case/stl/eidolon_case_bottom_left.stl  case/eidolon_case_bottom.scad
openscad -D right=true -o case/stl/eidolon_case_bottom_right.stl  case/eidolon_case_bottom.scad

Pre-generated STLs are in case/stl/.

Top shell features: keycap recess field, stepped 13.8 mm Choc plate holes, XIAO pocket with acrylic window rebate + USB-C cutout, battery pocket, power-switch wall slot, M2 bolt pockets.

Bottom shell

case/eidolon_case_bottom.scad nests inside the top from below. Geometry:

• z ∈ [−2.0, 0]: exterior plate (floor_t = 2.0 mm) matching the top case outer footprint
• z ∈ [0, 2.1]: nesting lip; PCB rests on the lip top at z = 2.1
• Per-switch hot-swap socket pockets cut into the lip — traced from the Kailh PG1350 socket silkscreen (plastic body plus both SMD pad rectangles), inflated by socket_clr = 0.6 mm
• Choc plastic-pin, power-switch-leg, and XIAO underside-joint clearance pockets in the lip
• M2 hex nut pockets (4.0 mm AF × 1.8 mm) at the four bolt positions
• Four Ø8.4 × 1.8 mm bumpon pockets in the underside (≥7.5 mm clear of the nut pockets)

Mounting hardware

MCU acrylic window

Cut a piece of 1.5 mm clear acrylic to drop into the XIAO rebate:

Angle the acrylic, slip the +y edge under the square lip (lip A), press the −y edge down past the chamfered lip (lip B). Remove the bottom shell to access the MCU.

Firmware

ZMK firmware for the Eidolon is available at jonnyirwin/zmk-keyboard-eidolon.

Deviations from the original Phantom

• Mirrored L/R instead of a single reversible board.
• BLE only — XIAO nRF52840, COL2ROW diode matrix, battery + slide switch; Pro Micro and TRRS removed.
• Diodes top-side, in each Choc south LED gap — hotswap sockets are the only underside component.
• Trackball omitted.
• Board outline is the original Edge.Cuts polygon with 1.5 mm corner fillets.