0 Preface Heart rate is a term used to describe the cycle of the heart, referring to the number of beats per minute of the heart, whichever is the first. Heart rate measurement is one of the commonly used medical examination items. Real-time accurate heart rate measurement is of great significance and wide application in clinical medicine, elderly physical signs monitoring and competitive sports. Under normal circumstances, there is a significant individual difference in heart rate in adults, generally 60 to 100 beats / min in quiet, an average of about 75 beats / min. Heart rate can vary depending on age, gender, and other physical conditions. The same person, when he is quiet or sleep, has a slow heart rate, and his heart rate increases when he is exercising, feeling emotional or sudden illness. Both tachycardia and slowness can affect your health, especially for the elderly and those with heart problems. Heart rate is a very important parameter. Therefore, accurate detection of heart rate is of great significance. This paper uses a small portable heart rate acquisition system based on piezoelectric ceramic sensor and ultra-low power MSP430 microcontroller. Figure 1 system structure diagram 1 system structure Heart rate is a very important physiological parameter of the human body. The traditional pulse diagnosis affects the accuracy of heart rate test because of its non-quantitative and subjective. In order to improve the accuracy of heart rate monitoring and the convenience of monitoring, the system adopts piezoelectric ceramic sensor and MSP430. The chip constitutes a test system, and the system hardware structure is shown in Figure 1. The temperature is collected by the ADC10 on-chip temperature sensor and can be displayed on the digital tube. At the same time, the signal collected by the SC0073 piezoelectric ceramic sensor is filtered and amplified, compared with the set pressure threshold, and the pulse wave signal is processed, and accurately counted and displayed according to the processing result. 1.1 Heart rate detection sensor At present, there are many instruments for detecting heart rate. Common types of test systems are based on pressure sensors, capacitive sensors, photoelectric sensors and electroacoustic sensors, but different sensors have different requirements for heart rate test sites. The common infrared-based sensor relies mainly on infrared detection of blood flow pressure fluctuation signals, that is, when the blood is transported to human tissue, the translucency of the tissue is reduced, and the translucency increases when the blood flows back to the heart. Fingertips are the most obvious. Although infrared detection is a good method of detection, it is not easy to carry for a long time due to factors such as washing hands and labor, and it is impossible to detect for a long time. In order to facilitate carrying for a long time, the system wrist structure design. In order to meet this requirement, this paper uses piezoelectric ceramic sheets to collect the pulse signal. Due to the heart beat, the pulse pressure fluctuation of the human wrist is relatively obvious. When the pulse beats, the piezoelectric ceramic sheet detects the corresponding signal. If the sensor is placed on the wrist, the sensor detects the pressure wave signal and performs pre-processing, then transforms it into a pulse signal, and then counts and displays it, thereby realizing the real-time detection of the heart rate. 1.2 MSP430 chip Because the heart rate detection system is oriented to families and hospitals, there are many empty nesters at present. Therefore, the chip selection uses ultra-small voltage and ultra-low power MSP430g2553 single-chip microcomputer, combined with piezoelectric ceramic sheets to collect pressure signals, thus achieving the size of the whole system. Miniaturized, wrist-worn design for 24 hours of real-time heart rate monitoring. MSP430 series MCU is a 16-bit MCU introduced by TI Company in the United States in 1996. This MCU is a hybrid MCU with a reduced instruction set and ultra-low power consumption. It has extremely low power consumption, rich on-chip and off-chip devices and convenient and flexible. The development method has become the first choice for many high-precision equipment electronic product design. 2 system hardware design The signal is processed by pre-amplifier amplification, low-pass filtering, etc., and amplified to a suitable amplitude and sent to AD for conversion into a digital signal. The acquisition system is controlled under the control of MSP430. In order to ensure stable and reliable operation of the acquisition system, the internal module circuits are all equipped with voltage regulator devices, which are characterized by quick start, convenience and safety. According to the characteristics of the heart rate signal, the system mainly includes the sensor interface circuit, signal acquisition, amplification and filtering circuit. The signal pre-stage should meet the following requirements: 1) High input impedance. The pulse signal detected by the sensor is an unstable weak signal. In order to reduce the influence of the internal resistance of the signal source, the input impedance of the amplifier must be increased. 2) The high common mode rejection ratio CMRR. The interference generated by the human body and the interference other than the measured parameters are generally common mode interference; 3) low noise, low drift; 4) high security to ensure the absolute safety of the human body. Figure 2 preamplifier circuit We specialize in developing and producing stretchers,anti-coronavirus products, first-aid product, Funeral Products, ward products, Diagnosis Device, emergency rescue product and so on. We supply one stop purchasing of Medical Equipment for all overseas customers. Soft Stretcher Medton Medical , https://www.medtonmedical.com
Design of human heart rate detection system based on MSP430 and piezoelectric sensor