**Photoplethysmographic Time-Domain Heart Rate Measurement Algorithm for Resource-Constrained Wearable Devices and its Implementationt**

#### **Marek Wójcikowski \* and Bogdan Pankiewicz**

Faculty of Electronics, Telecommunications and Informatics, Gda ´nsk University of Technology, 80-233 Gda ´nsk, Poland; bpa@eti.pg.edu.pl

**\*** Correspondence: marwojci1@pg.edu.pl; Tel.: +48-58-347-19-74

Received: 17 February 2020; Accepted: 21 March 2020; Published: 23 March 2020

**Abstract:** This paper presents an algorithm for the measurement of the human heart rate, using photoplethysmography (PPG), i.e., the detection of the light at the skin surface. The signal from the PPG sensor is processed in time-domain; the peaks in the preprocessed and conditioned PPG waveform are detected by using a peak detection algorithm to find the heart rate in real time. Apart from the PPG sensor, the accelerometer is also used to detect body movement and to indicate the moments in time, for which the PPG waveform can be unreliable. This paper describes in detail the signal conditioning path and the modified algorithm, and it also gives an example of implementation in a resource-constrained wrist-wearable device. The algorithm was evaluated by using the publicly available PPG-DaLia dataset containing samples collected during real-life activities with a PPG sensor and accelerometer and with an ECG signal as ground truth. The quality of the results is comparable to the other algorithms from the literature, while the required hardware resources are lower, which can be significant for wearable applications.

**Keywords:** heart rate; photoplethysmography; PPG; time-domain; wearable device
