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

Working Principle

Most pulse sensors are based on the photoplethysmography (PPG) method, which is a non-invasive optical technique. This method relies on optically detecting instantaneous changes in blood volume within the circulatory system. During each contraction of the heart (systole), blood volume in the vessels increases, which changes the amount of light absorbed by the tissue. PPG sensors use a light source (LED) and a photodetector (photodiode, etc.) to detect this change. The sensor is placed on areas rich in blood vessels, such as the fingertip, earlobe, or wrist. Light reaches the photodetector by passing through or reflecting from the tissue. Hemoglobin has the property of absorbing light at certain wavelengths. When blood vessels expand during a heartbeat, light absorption increases, thus decreasing the amount of light reaching the photodetector. During the heart's relaxation phase (diastole), absorption decreases, and more light reaches the photodetector. The photodetector converts these varying light signals into analog electrical signals. The microcontroller processes these analog signals, converts them into digital data, and obtains the pulse information.

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Sensor Types

There are numerous pulse sensors on the market with different operating principles and physical designs. The most commonly used types are optical-based PPG sensors. These sensors are divided into two main categories:

1. Reflective Sensors

The LED and photodetector are located on the same surface. When the sensor touches the skin, light emitted from the LED reflects off the tissue and reaches the photodetector. This structure is suitable for measurements from 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 elements. Light passes through the tissue and directly reaches the photodetector. This structure is preferred in some medical devices due to its advantage in signal stability.

Application Areas

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

• Wearable Technologies: Used for pulse measurement in prototypes of smartwatches, fitness trackers, and similar health monitoring devices.
• Health and Fitness Applications: Heart rate can be monitored during exercise or at rest.
• Emotion and Stress Analysis: By analyzing metrics such as heart rate variability (HRV), inferences can be made about an individual's stress level or emotional state.
• Educational Projects: Used by students and researchers who want to gain practical experience in electronics, biomedical engineering, and programming.
• Interactive and Artistic Applications: Can be incorporated into projects featuring light, sound, or visual elements that react to the user's heart rhythm.