Biometric Sensor
Reads one or more biological signals (pulse, oxygen saturation, skin conductance, etc.) using optical or electrical front-ends, conditions and digitizes them, and streams the data over I²C/SPI to a host MCU.
Optical sensors shine red and IR LEDs through tissue and measure reflected light to compute SpO₂ and heart rate via photoplethysmography. Electrical sensors use precision instrumentation amplifiers to pick up µV-scale skin potentials (ECG, EMG, GSR).
In plain terms
A doctor's stethoscope and pulse-finger combined into a chip: it listens to your body's electrical and optical signals and reports them digitally.
Why designers use it
- Continuous health monitoring on smartwatches and fitness trackers.
- Pulse-oximetry in clinical and home medical devices.
- User authentication via heart-rate signature or skin conductance.
- Stress and sleep tracking through HRV and GSR baselines.
Best for
- Heart rate
- SpO₂
- ECG
- GSR
Key specifications
- Operating limits: Check the exact manufacturer's datasheet (A family name does not establish voltage, current, temperature or timing limits.)
- Pin assignment: Match the complete part and package code (A similar name or function does not guarantee the same wiring.)
- Mechanical fit: Use the exact package drawing (Check pad layout, dimensions and viewing direction before building.)
When not to use it
- Diagnostic-grade measurements without medical certification (FDA / CE-MDR) — consumer biometrics are informational, not medical.
- Tight skin-contact unavailable — optical PPG fails on loose wrist straps.
Common mistakes
- Underdriving the LEDs and getting a noisy PPG signal.
- Skipping a 50/60 Hz notch filter on ECG inputs and burying the QRS complex in mains hum.
Where you will find it
- Apple Watch combines a green-LED PPG (heart rate) with electrodes on the crown and back (Lead I ECG).
- Fingertip pulse oximeters in hospitals use red+IR PPG to compute SpO₂ continuously.
- Whoop straps measure HRV from wrist PPG to estimate recovery and strain.
A short history
The 2024 review Ninety years of pulse oximetry distinguishes Aoyagi's conceptual work in December 1972 from the prototype and public presentation in 1974. It also discusses Michio Kishi's contribution. Separating the idea, prototype and presentation avoids treating different milestones as contradictory invention dates. A teaching sensor module is not automatically a clinically validated pulse oximeter.