Code development for heartbeat detection with inexpensive optical pulse sensors

Smart textiles with embedded electronics can be used to monitor body functions, e.g., during sports or for medical reasons. One of the main problems of such embedded electronics is their washability. A recent study therefore investigated the washability of different inexpensive optical pulse sensors, as they could be integrated into clothing to enable pulse measurements. To evaluate the measured data, microcontrollers can also be integrated into the garment, which is why an ATtiny85 microcontroller additionally underwent washing tests. The main part of this study concentrated on code development to improve heartbeat detection using inexpensive optical pulse sensors. While all sensors and microcontrollers remained unaltered by 10 washing cycles, significant differences in the quality of the inexpensive optical pulse sensors were found, depending on the producer. As the optimum hardware, a combination was defined of an ESP8266 D1 mini as the textile-integrated transmitter and an ESP32 with a 1.8’’ display to receive and show the measured data outside the garment. Pulse detection criteria were defined, which could be used to calculate the heart beats per minute (BPM) with high reliability. The tests and developments can be used as the base for a complete textile-integrated optical pulse measurement with mobile data storage and depiction.