Wearable Sensors System Prototype Design
Budget: £250 – £750 GBP
We are seeking an experienced wearable hardware + firmware engineer to design and build an MVP prototype of a non-invasive skin-worn sensing system that tracks local skin physiology signals and motion-based interaction patterns over time.
The goal is to collect trend data from multiple sensors and compute a composite risk / state score based on changes from user baseline.
This is a research / prototype device, not a regulated medical product.
System Overview
Two-part wearable system:
Skin Patch Sensor (placed near area of interest)
Wrist or Ankle Band (motion tracking)
Both devices communicate via Bluetooth Low Energy (BLE) to a phone or computer.
Skin Patch – Functional Requirements
Form factor
Thin adhesive patch (flex PCB preferred)
Skin-safe materials
Target thickness <5 mm (MVP tolerance OK)
Sensors (required)
Skin temperature (contact-based)
Local moisture / sweat proxy (humidity or impedance)
Chemical proxy (pH) using sweat interaction
Optical reflectance for redness / inflammation proxy (2–3 wavelengths acceptable)
Sampling targets
Temperature: ~0.2–1 Hz
Moisture/humidity: ~0.5–1 Hz
Optical reflectance: ~0.1–0.5 Hz
pH: periodic or sweat-event based
Example component options (flexible)
Temp: Maxim / TI digital temp sensor or thermistor
Moisture: Sensirion SHT series or impedance electrodes
pH: Colorimetric microfluidic patch + LED/photodiode OR potentiometric pH electrode
Optical: Red / Green / IR LEDs + photodiode (AFE acceptable)
Wrist / Ankle Band – Functional Requirements
Sensors
6-axis IMU (accelerometer + gyro)
Functions
Detect repetitive motion patterns
Extract features:
Event count
Duration
Intensity
Time-of-day clustering
Sampling
Raw IMU: ~50–100 Hz
On-device feature extraction preferred
Example IMUs
Bosch BMI270
TDK / InvenSense ICM series
Electronics & Firmware
MCU / SoC
Low-power BLE MCU (Nordic nRF52 class or equivalent)
Power
Patch: thin LiPo or coin cell
Band: coin cell or LiPo
USB or pogo-pin charging acceptable
Firmware responsibilities
Sensor sampling & filtering
BLE communication
Time sync between devices
Battery monitoring & fault handling
Data & Algorithms (MVP Scope)
Feature extraction
Temperature deviation from baseline
Moisture accumulation trends
Optical redness proxy trends
Motion-derived interaction metrics
Composite Output
Single 0–100 state / risk index
3–4 discrete stages (e.g., Stable → Elevated → Active → High)
All weights configurable (no hard-coded logic)
Output formats
CSV / JSON
Documented BLE characteristics
Deliverables
Hardware
Schematics
PCB (Gerbers)
BOM with estimated costs
Assembled prototypes (1–3 units)
Firmware / Software
Source code
Build instructions
Data protocol documentation
Documentation
System architecture diagram
Power consumption estimates
Calibration approach
Known limitations
Required Experience
Wearable electronics & BLE
Sensor integration
IMU signal processing
Low-power firmware design
Bonus
Skin-worn devices
Optical biosensing
Sweat or chemical sensing
The goal is to collect trend data from multiple sensors and compute a composite risk / state score based on changes from user baseline.
This is a research / prototype device, not a regulated medical product.
System Overview
Two-part wearable system:
Skin Patch Sensor (placed near area of interest)
Wrist or Ankle Band (motion tracking)
Both devices communicate via Bluetooth Low Energy (BLE) to a phone or computer.
Skin Patch – Functional Requirements
Form factor
Thin adhesive patch (flex PCB preferred)
Skin-safe materials
Target thickness <5 mm (MVP tolerance OK)
Sensors (required)
Skin temperature (contact-based)
Local moisture / sweat proxy (humidity or impedance)
Chemical proxy (pH) using sweat interaction
Optical reflectance for redness / inflammation proxy (2–3 wavelengths acceptable)
Sampling targets
Temperature: ~0.2–1 Hz
Moisture/humidity: ~0.5–1 Hz
Optical reflectance: ~0.1–0.5 Hz
pH: periodic or sweat-event based
Example component options (flexible)
Temp: Maxim / TI digital temp sensor or thermistor
Moisture: Sensirion SHT series or impedance electrodes
pH: Colorimetric microfluidic patch + LED/photodiode OR potentiometric pH electrode
Optical: Red / Green / IR LEDs + photodiode (AFE acceptable)
Wrist / Ankle Band – Functional Requirements
Sensors
6-axis IMU (accelerometer + gyro)
Functions
Detect repetitive motion patterns
Extract features:
Event count
Duration
Intensity
Time-of-day clustering
Sampling
Raw IMU: ~50–100 Hz
On-device feature extraction preferred
Example IMUs
Bosch BMI270
TDK / InvenSense ICM series
Electronics & Firmware
MCU / SoC
Low-power BLE MCU (Nordic nRF52 class or equivalent)
Power
Patch: thin LiPo or coin cell
Band: coin cell or LiPo
USB or pogo-pin charging acceptable
Firmware responsibilities
Sensor sampling & filtering
BLE communication
Time sync between devices
Battery monitoring & fault handling
Data & Algorithms (MVP Scope)
Feature extraction
Temperature deviation from baseline
Moisture accumulation trends
Optical redness proxy trends
Motion-derived interaction metrics
Composite Output
Single 0–100 state / risk index
3–4 discrete stages (e.g., Stable → Elevated → Active → High)
All weights configurable (no hard-coded logic)
Output formats
CSV / JSON
Documented BLE characteristics
Deliverables
Hardware
Schematics
PCB (Gerbers)
BOM with estimated costs
Assembled prototypes (1–3 units)
Firmware / Software
Source code
Build instructions
Data protocol documentation
Documentation
System architecture diagram
Power consumption estimates
Calibration approach
Known limitations
Required Experience
Wearable electronics & BLE
Sensor integration
IMU signal processing
Low-power firmware design
Bonus
Skin-worn devices
Optical biosensing
Sweat or chemical sensing