Ring

Swipe Smart Ring — Ring PCB

The main board for a BLE smart ring with IMU-based gesture input and capacitive touch. This repo contains the ring board KiCad project: PCB layout, schematic, and the custom footprints used by both.

Status: prototype, not yet fabricated or tested. Routed and verified in KiCad 9 — DRC clean: 0 errors, 0 warnings, 0 unconnected nets.

It's small — the board outline is 38 × 10 mm (about the footprint of a stick of gum).

The board isn't meant to stay flat. The middle 8 mm is a flex section: the rigid signet and BLE ends fold relative to each other there, so the board follows the curve of the finger inside the housing. In the housing the BLE end sits 115° around the ring from the signet, and the rigid ends stay flat — so the 8 mm flex takes that whole ~115° bend (about a 4 mm radius, well inside the material's 0.6 mm minimum).

A note on the rigid-flex: the flex zone is captured here as design intent — the layout is zoned signet (18 mm) / flex (8 mm) / BLE (12 mm) along the board's length, with the bend taken by the middle 8 mm. The ring.kicad_pcb itself is a flat 2-layer prototype; the actual rigid-flex stackup and coverlay callouts are left to the fabricator.

What this is

A 2-layer rigid-flex board that wraps around a finger. It carries a Nordic nRF52832 BLE SoC, a 6-axis IMU with built-in capacitive (Qvar) touch sensing, a haptic motor driver, indicator LEDs, and the spring contacts / connectors that mate with the ring housing.

The board is split into three zones along its length:

[ signet  18mm rigid ] —— [ flex 8mm ] —— [ BLE 12mm rigid ]
  battery + motor +                          ANNA-B112 module +
  LED arc + drivers                          antenna keepout + SWD

• Signet (rigid): battery and motor spring contacts, the two bicolor indicator LEDs (light-pipe aligned), the motor MOSFET and flyback diode, and the electrode-harness connector.
• Flex: the bend region that lets the rigid ends curve around the finger.
• BLE (rigid): the ANNA-B112 module with an antenna keepout, plus the SWD programming pads and the pogo-harness connector.

Key components

Full line-item list (passives, MPNs, prices) in bom.csv. The battery (Seiko MS920SE coin cell) and haptic motor are off-board — they sit in the housing and contact the spring pads — and are listed at the end of the BOM.

Design notes

• No LDO. VDD = VBAT throughout — the nRF52832 (1.7–3.6 V) runs directly off the coin cell (Seiko MS920SE, ~2.0–3.1 V).
• Motor runs off the battery rail directly, switched by Q1.
• Qvar touch uses the IMU's analog-front-end inputs through 500 Ω series resistors, with ESD diodes at the connector.
• Charging is resistor-limited from a 5 V pogo input (R3 = 2.2 kΩ → ~0.86 mA into the MS920).
• Layers, not vias. The fine-pitch parts (ANNA's inner pads, the LSM6DSV16X) are fanned out on 2 layers rather than escalating to 4-layer / via-in-pad. Vias are 0.3 mm (0.15 mm drill) — standard fab capability, sized so the LSM6DSV16X's 0.5 mm-pitch escapes clear the 0.127 mm rule.

The full product also includes a pogo charge-contact board, a Qvar electrode flex, and a USB-C dock — those are not part of this repo.

Opening it

Built with KiCad 9. Clone and open ring.kicad_pro, or open ring.kicad_pcb / ring.kicad_sch directly. Footprints are embedded in the board, and the custom.pretty library is included for editing.

• ring.kicad_pcb — routed PCB layout
• ring.kicad_sch — schematic
• ring.kicad_pro — KiCad project
• custom.pretty/ — custom footprints
• bom.csv — bill of materials for this board
• ring-schematic.pdf — schematic as a PDF (no KiCad needed)
• preview.png — rendered board, top and bottom (KiCad 9, 38 × 10 mm)
• preview-3d.png — 3D view of the rigid-flex fold at the flex zone
• fab/ — Gerbers and Excellon drill files (KiCad 9 export), ready to order

License

MIT — see LICENSE.