Design And Algorithm Study Of Wrist-worn Heart Rate Monitor

Heart rate,as an important physiological parameter of human body,can be used to prevent and diagnose cardiovascular disease when it is monitored for a long time.The position of the heart rate monitor which designed by reflection-type photoplethysmography(PPG)technology is not restricted by the human body,and has a wide application prospect in the field of wearable equipment.The portability,real-time,low power consumption and anti motion artifact of the heart rate meter are taken into account,a wearable wrist watch was designed based on reflection-type PPG technology that can monitor heart rate in this paper.In order to extract the heart rate of human body in all kinds of motion,the PPG signal was analyzed and processed in this paper.First,the method of hardware and software combination was used to filter the high frequency and power frequency noise from PPG signals.That is,in order to solve the problem that the op amp will be saturated while the heart rate signal is amplified in the circuit amplification stage,the amplified signal was collected to the microcontroller by the analog to digital converter for low frequency digital filtering,then the filtered DC component was fed back to the input terminal,which a chebyshev II-type low-pass digital filter was designed with the aid of FDATool box.In addition,the adaptive filter was used to filter out motion artifacts that are difficult to eliminate in PPG signals,and the reference signal of motion noise was obtained by using three-axis accelerometer.In order to get the value of the step size parameter in a contradiction,a new variable step size LMS adaptive filtering algorithm based on adaptive filtering was proposed.That is,a new function relation was established between the step size and the error signal.The simulation results showed that the improved algorithm had better filtering performance.The hardware and software of the wearable cardio tachometer were designed to verify the validity of the algorithm for PPG signal processing and realize the real-time monitoring of heart rate.The hardware system contains PPG signal detection and amplification circuit,acceleration signal detection circuit,Bluetooth 4.0 circuit module,MCU control circuit and power system circuit.The software mainly includes the design of PPG signal processing flow and heart rate algorithm flow.The low-power sleep and low-power operation mode switching of the microcontroller STM32L152 CB was fully utilized to effectively reduce the power consumption of the system and improve its operating capacity.The waveform characteristics of different types of volume pulse wave were analyzed by using MATLAB software,and a universal heart rate algorithm was designed.Finally,based on the relevant experiments,the accuracy of heart rate monitor was measured in different preset environment(standing,walking and running).The experimental results show that the accuracy of the heart rate monitor is higher in steady state indicating that the improved adaptive filtering algorithm has good filtering effect.The test precision of the device is not high in a transient state,but the reaction time is not more than 3 seconds.In all experiments,the accuracy of the measuring results has reached about 90% which shows that the device can be able to complete the real-time monitoring of heart rate in a dynamic environment.