Implementation of Adaptive Threshold for Peak Detection of Photoplethysmography Applied on Microcontroller

Heart rate (HR) is computed by counting how many a person's heart is beating in a minute. A photoplethysmography (PPG) that measures the changes in blood volume by implementing transmission or reflection of specific light color can be used to measure HR. HR measurement can be conducted using PPG by attaching the sensor to the wrist, earlobe or finger. The beat detection in HR measurement can be conducted by comparing the signal to the threshold for finding its peak. When the measured object has a slight movement, the signal will be shifted and it makes the peak difficult to be detected. To overcome this condition, an adaptive threshold can be applied by changing the threshold based on the shift of the signal. Several steps that are conducted in this study are sensor reading, digital filtering, thresholding, and heart rate calculation. The study shows that the adaptive threshold can change the threshold value based on the signal changes. Compared to Oximeter reading, the HR calculation can yield a good result.