Expensivo

A wireless version of the Cheapino: same shape and key layout, but with a nice!nano in each half, ZMK and Bluetooth between the halves. Not quite as cheap anymore, hence the name.

• 36 keys (3x5 + 3 thumb keys per half), MX hotswap sockets
• every key has its own pin on the nice!nano: no diodes, no matrix
• one reversible PCB for both halves: the left half is built on the front, the right half on the back
• LiPo battery, power switch and reset button on each half
• optional EC11 encoder on the right half
• 3D-printed case with an optional magnetic cover over the nice!nano

Parts per keyboard

Part	Qty	Notes
PCB	2	same board for both halves, see Ordering the PCB
nice!nano v2	2	or a compatible nRF52840 Pro Micro clone
Sockets + pins for the nice!nano	2 sets	12-pin single row; the case assumes the nano sits 4.9 mm above the PCB
LiPo battery	2	fits under the nano between the sockets, e.g. 301230 (3 x 12 x 30 mm); may stick out ~6 mm past the nano
MX switches	36
Kailh MX hotswap sockets	36	MX, not low profile
Slide switch PCM12SMTR	2	one per half
Tactile switch TL3342	2	reset, one per half
Keycaps	36
EC11 encoder	0-1	optional, right half only

For the case, per keyboard: 16 M2 heat-set inserts (4 mm long, 3 mm OD), 16 M2x5 countersunk screws, silicone bumpers (10 mm), 8 + 8 6x2 mm magnets (8 in the bottom plates, 8 for the two covers).

Building it

The PCB is reversible, so it matters which side you solder on:

• left half: everything on the front side (the side marked LEFT); hotswap sockets on the back
• right half: everything on the back side (marked RIGHT); hotswap sockets on the front
• the nice!nano goes on the same side as its label, components facing up
• bridge the four solder jumpers next to the nano's top pins on the side the nano is on (JP side), and leave the other four open
• the power switch and reset button have a footprint on each side; fit only the one on top
• battery to the pads below the nano, + and - are marked

The schematic shows how it is wired, including which nano pin ends up on which hole on each side.

Firmware

ZMK, built by GitHub Actions on every push (see the Actions tab for the .uf2 files). The left half is the central and has ZMK Studio enabled.

• keymap: config/expensivo.keymap
• shield: zmk/boards/shields/expensivo

To flash, double-tap reset and copy the matching .uf2 to the drive that shows up. Flash settings_reset first if the nanos were used before.

Case

OpenSCAD files in case/, see case/readme.md. The top frames print top face down without supports, so do the covers; the covers hold on with magnets and can be left off.

Ordering the PCB

scripts/gerbers.sh writes build/expensivo-jlcpcb.zip, ready for JLCPCB: 2 layers, 1.6 mm, default settings. 5 boards is two keyboards and a spare. Choose ENIG if you want the copper logo to stay shiny.

How it's made

Everything is generated by scripts, so edit those rather than the outputs:

Script	Makes
scripts/build.sh	the full board build: footprint, PCB, routing, DRC/ERC, schematic, case data
scripts/build_pcb.py	the PCB, starting from the Cheapino board: parts, nets, outline, logo
scripts/gen_nano_footprint.py	the reversible nice!nano footprint
scripts/gen_schematic.py	the schematic, from the PCB's parts and nets
scripts/gen_zmk.py	the ZMK shield pin lists
scripts/gen_case.py	PCB geometry for the OpenSCAD case
scripts/gerbers.sh	Gerbers and drill files for JLCPCB

The pin map shared by the PCB, schematic and firmware is in scripts/layout.py. Routing is done by Freerouting (downloaded on first run, needs Java). The scripts expect KiCad 8 in /Applications/KiCad.

License

This work is licensed under a Creative Commons Attribution license.