AI Smart Ring based on nRF52840

Client

A wearable technology company creating a premium health-tracking smart ring that competes with wrist-worn fitness trackers in a smaller form factor.

Challenge

Packing a PPG heart rate sensor, IMU, temperature sensor, battery, and wireless charging into an 8mm-wide, 3mm-thick ring form factor without compromising sensor accuracy.

Product Concept & Architecture

We designed a custom flex-rigid PCB around the Nordic nRF52840. The ring houses an ams AS7058 PPG sensor (green/red/IR LEDs), a BMI270 IMU, and a TMP117 temperature sensor. A 30mAh Li-Po cell provides 7 days of battery.

Engineering Solution

The PPG firmware implements adaptive LED current control: the ring auto-adjusts LED brightness based on skin tone and perfusion, reducing power by 60% during sleep. On-device sleep staging uses a TinyML model (20KB) processing HR, HRV, and movement data. A daily readiness score combines sleep, HRV baseline, and temperature trend.

Result

Sleep staging accuracy of 82% vs. polysomnography (PSG). 7-day battery at typical usage. IP68 rating enables swim tracking.