Design of Photoplethysmography (PPG)-Based Respiratory Rate Measuring Device Through Peak Calculations

Respiratory rate is one of the essential components in measuring vital signs that convey information about health conditions and diagnoses to patients measured in breaths per minute (BrPM). Breaths per minute refer to the number of breaths taken by a person in one minute. The current clinical respiratory rate calculation method, i.e., a standard calculation by counting the number of chest movements, can cause patient discomfort, bias in counting, and waste the nurse’s time. This study aims to develop a tool for measuring respiratory rate by recording a one-minute photoplethysmography (PPG) signal non-invasively that is more comfortable and easier to use. The PPG signal obtained is first processed to remove unnecessary signal frequencies. The developed algorithm counts the number of peaks in the PPG signal to calculate the respiratory rate. It employs Zero-Phase Filtering to remove noise and motion artifacts (MA) on the signal to calculate the number of peaks in one minute. The device is designed using the MAX30102 sensor, XIAO ESP32-C3 controller, and TFT OLED display to show the measurement value. This tool uses a 3D case and Velcro tape on the sensor to reduce the possibility of a Motion Artifact appearing in the signal. The respiratory rate prediction test results obtained more than 94% accuracy with a maximum error of 3 BrPM in five subjects aged 15–48 years who were in good health. Based on the results, measuring respiratory rate from the PPG signal with a wearable device design can be a quite effective non-invasive solution and contribute to the medical world for measuring vital signs.