Wearable Health Tracker
Ultra-compact PCB, BLE firmware, and iOS/Android companion app for continuous health monitoring.
What we delivered (snapshot)
- Miniaturised 4-layer flex-rigid PCB integrating PPG, SpO₂, accelerometer, and BLE 5.2.
- Ultra-low-power firmware with adaptive sampling and secure BLE data streaming.
- React Native companion app for iOS and Android with real-time charting and history.
The Challenge
A digital health startup needed to bring a continuous health-monitoring wearable from concept to a V1 prototype suitable for user testing with 50 participants. The device had to unobtrusively capture heart rate, SpO₂, and activity data simultaneously while lasting 5 days on a single charge.
The form factor constraint was a standard 22 mm watch-band slot, making PCB miniaturisation the primary engineering challenge. The companion app needed to present data accessibly to non-technical users and connect via BLE without user pairing steps.
Constraints
Timeline
18 weeks (Blueprint Sprint + prototype)
Budget Band
£45k–£65k (PCB + firmware + app)
Technical Constraints
- Maximum PCB area: 22 × 15 mm (flex-rigid)
- Battery life target: 5 days at 30-second HR sampling
- BLE advertising without explicit pairing
- Not regulated as a medical device (wellness use only)
Our Approach
- 1
Fit check & constraints clarification
Confirmed wellness (non-medical) scope, selected Maxim MAX86916 sensor cluster, reviewed flex-rigid fabrication options.
- 2
Requirements & acceptance criteria for V1
Defined accuracy bands (HR ±5 bpm, SpO₂ ±3%), battery test protocol, and app data display requirements.
- 3
Architecture & risk register
Risk flagged on flex-rigid yield; recommended 2 PCB revisions budget. BLE stack compatibility matrix.
- 4
Design & build
Simultaneous PCB layout, enclosure cavity design, firmware + app development with Bluetooth Low Energy data protocol.
- 5
Integration & validation
Wrist-worn bench testing, power profiling, and app connectivity testing on iOS 17 and Android 13.
- 6
Handover package
All repos, Gerbers, app store submission guide, and recorded handover session.
What We Delivered
- Schematic and 4-layer flex-rigid PCB (22 × 15 mm)
- Gerbers, BOM, and flex-PCB fabrication notes
- Two design revision notes
- Nordic nRF52840 firmware source
- BLE data protocol specification
- Power profiling report and OTA update module
- Watch shell enclosure CAD (SolidWorks)
- Assembly exploded-view drawing
- DFM recommendations for SLA prototype and injection mould
- React Native companion app source (iOS + Android)
- BLE service/characteristic documentation
- App Store and Google Play submission checklist
Outcome
"V1 prototype hardware and app delivered within 18 weeks. Initial user testing session ran with 20 participants — device achieved target battery life and all participants successfully paired with the app without support intervention."
Handover
- Hardware design files, firmware repo, and app repo
- BLE protocol spec and integration notes
- App submission checklist and build scripts
- Recorded handover walkthrough
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