Pulse Sensor

A pulse sensor is an electronic sensor developed to measure an individual’s heart rate or pulse in real time. These sensors typically operate on the principle of photoplethysmography (PPG), detecting changes in the amount of light reflected from or transmitted through tissue due to rhythmic variations in blood flow. The measured analog data is processed digitally through microcontroller platforms such as Arduino, ESP32, and STM32. As a result, pulse sensors are widely used in educational applications, health monitoring systems, wearable devices, and similar projects.

Working Principle

The majority of pulse sensors are based on photoplethysmography (PPG), a non-invasive optical technique that detects instantaneous changes in blood volume within the circulatory system. During each heartbeat (systole), the volume of blood in the arteries increases, altering the amount of light absorbed by the tissue. PPG sensors use a light source (LED) and a photodetector (such as a photodiode) to detect this change. The sensor is placed on areas with dense blood vessels, such as the fingertip, earlobe, or wrist. Light either passes through or reflects off the tissue and reaches the photodetector. Hemoglobin has the property of absorbing light at specific wavelengths. When blood vessels dilate during a heartbeat, light absorption increases, reducing the amount of light reaching the photodetector. During the relaxation phase of the heartbeat (diastole), absorption decreases and more light reaches the photodetector. The photodetector converts these variable light signals into analog electrical signals. The microcontroller processes these analog signals, converting them into digital data to determine the pulse rate.

Types of Sensors

There are numerous pulse sensors on the market with different operational principles and physical designs. The most commonly used types are optical PPG sensors, which fall into two main categories:

1. Reflective Sensors

The LED and photodetector are positioned on the same surface. When the sensor makes contact with the skin, light emitted by the LED reflects off the tissue and reaches the photodetector. This configuration is suitable for measurements on surfaces such as the fingertip or wrist.

2. Transmissive Sensors

The LED and photodetector are positioned opposite each other. Areas such as the fingertip or earlobe are placed between these two components. Light passes directly through the tissue to reach the photodetector. This configuration is preferred in some medical devices due to its superior signal stability.

Applications

Pulse sensors used in microcontroller-based projects have a wide range of applications:

• Wearable Technologies: Used for pulse measurement in prototypes of smartwatches, fitness bands, and similar health monitoring devices.
• Health and Fitness Applications: Enables monitoring of heart rate during exercise or at rest.
• Emotion and Stress Analysis: Metrics such as heart rate variability (HRV) can be analyzed to infer an individual’s stress level or emotional state.
• Educational Projects: Used by students and researchers seeking hands-on experience in electronics, biomedical engineering, and programming.
• Interactive and Artistic Applications: Integrated into projects that respond to the user’s heart rhythm with light, sound, or visual elements.