The game “Heart Rate” is based on an Arduino sketch and a heart rate detection sensor that works through capillarity and what is known as Photoplethysmogram.

This technique is based on the fact that oxygenated hemoglobin in arterial blood has the property of absorbing green light. The redder the blood (the higher the hemoglobin), the greater the absorption of green light. With each heartbeat, blood is pumped through the finger, causing a change in the amount of reflected light, which in turn produces a waveform at the output of the photosensor.

When the sensor detects the heartbeat (it takes up to 5 seconds to read the pulse), the app plays an audio file of a heartbeat and lights up a series of LEDs, rhythmically and consistently following the user’s heartbeat. Additionally, it triggers an animation, one by one, of a series of LED strips displayed in a folded shape (which mimics veins and arteries).

The installation uses the MAX30102 heart rate sensor model. This type of sensor operates on a principle called photoplethysmography, which utilizes one or more LEDs that emit light and a sensor that receives the light signal. The basic principle of the optical heart sensor is to pass light through the skin.

Our skin is composed of three distinct layers: the hypodermis, the dermis, and the epidermis.

The dermis is vascularized and contains many capillaries filled with blood. When the heart pumps blood, it slightly modulates the amount of blood present in the dermis.

Therefore, the principle is to send green light to the center of the capillaries, and based on the reflected light, the sensor will be able to determine blood flow and, consequently, heart rate.

In fact, this specific light was chosen to be absorbed by the blood. The blood pumped into the capillaries modulates the light, which is then re-emitted by the skin and detected by the heart rate monitor.

The signal is then processed by algorithms that separate the measurement noise from the heart rate. Depending on the activity performed, the results may vary in accuracy.