This project is an ongoing attempt to build a sleep monitoring device that lives embedded in a mouth guard or retainer. It is designed around tracking bite force, breathing, motion, and eventually more.

The goal was always a fully sealed, comfortable device with wireless data offload. Getting there is an ongoing iterative process while I pick up many skills along the way.

Iteration 1 — Proof of Concept

The first version was never meant to stay in the mouth for long. An ESP32 on a breakout board, a coin cell, an FSR for bite sensing, and a humidity sensor for breath detection — components glued together and embedded in a thermoformed retainer made with a dental vacuum forming machine.

Iteration 1 Top Iteration 1 Bottom

Rough as it was, it proved out the core measurements — bite events and breathing — and confirmed the form factor was viable enough to keep going.

Iteration 2 — First Custom PCB

The second version moved to a custom two-layer flexible PCB built around an nRF52. Added NOR flash for local data logging, an IMU for motion tracking, and a humidity sensor for breath. Also attempted PDM microphones for acoustic sensing — didn’t get those working this round.

The flex PCB sat embedded in a new thermoformed retainer, getting closer to something that could realistically be worn overnight.

Iteration 2 Boards Iteration 2 Potted

Iteration 3 — Rigid-Flex-Rigid

Iteration 3 BLE Board Iteration 3 Power Board

Iteration 3 Sensor Board

The current version is a three-board rigid-flex-rigid stack split into dedicated power, sense, and compute boards. The biggest change beyond the electronics is the form factor — instead of sitting on the roof of the mouth, the assembly now runs along the internal perimeter of the teeth, with some components wrapping to the outer face. A much more comfortable geometry for long wear.

Iteration 3 Electronics Iteration 3 Charging

Upgrades over iteration 2: wireless charging, a thermocouple replacing the humidity sensor for more direct thermal measurement, op-amps for improved sensor sensitivity, bone conduction microphones over PDM (with a PDM-to-I2S bridge), nrf5340 for more compute, and a larger NOR flash chip for extended logging. The whole assembly is fully sealed for long term intraoral exposure.