What is a Pulse sensor?

A pulse wave is a change in the volume of a blood vessel that occurs when the heart pumps blood, and a pulse sensor is a detector that monitors this volume change.

To begin, there are four primary methods for determining heart rate: electrocardiogram, photoelectric pulse wave, blood pressure measurement, and phono cardiography. The photoelectric method is used by pulse sensors.

Heart Rate Measurement Method

Depending on the measurement method, photoelectric pulse wave sensors are classified into two types: transmission and reflection.

Transmission types measure pulse waves by emitting red or infrared light from the body's surface and detecting changes in blood flow as a change in the amount of light transmitted through the body during heartbeats.

Reflection-Type Pulse Sensor

Reflection-type pulse sensors (Optical Sensors for Heart Rate Monitor) emit infrared, red, or green light toward the body and use a photodiode or phototransistor to measure the amount of light reflected. Because oxygenated hemoglobin in the blood of the arteries absorbs incident light, we can measure the pulse wave signal by sensing the blood flow rate (change in blood vessel volume) that changes as the heart contracts over time.

Furthermore, because reflected light is measured, the range of suitable areas is not constrained as it is with transmission-type pulse sensors.

Reflection-Type Pulse Sensor - Operating Mechanism

Infrared rays contained in sunlight can affect pulse wave measurement using red or infrared light, preventing stable operation. As a result, use indoors or semi-indoors is advised.

Because a green light source with a high absorption rate in hemoglobin and less susceptibility to ambient light is preferred for outdoor pulse wave measurement (e.g., by smart watches), ROHM uses green LEDs as transmission light sources.

Pulse Sensor Applications-

In general, arterial blood oxygen saturation can be measured by looking at the period of fluctuation from the waveform obtained by measurements of the pulse wave sensor and observing the pulsation (variation) using the heart rate as well as both red and infrared waves (SpO2).

Furthermore, using data from pulse sensors should allow for the calculation of various vital signs such as HRV analysis (stress level) and vascular age via high-speed sampling and high-accuracy measurement. The pulse sensor can be interfaced to Arduino and a 16 X 2 display.