Abstract: This design uses the high-performance, low-power H12 series MCU produced by Freescale as the main control unit of the system. The US9111-006 pressure sensor is used as the front-end signal acquisition unit to design a new electronic sphygmomanometer . The design process of the electronic sphygmomanometer is described in detail through hardware design and software design. Finally, the test results of the electronic sphygmomanometer are given, and the data are analyzed and compared.
0 Preface
The continuous progress and development of human society, people's living standards are constantly improving, especially the pace of life of urban residents is also accelerating. In order to ensure the quality of life, people are paying more and more attention to their physical health. Traditional sphygmomanometers are simulated sphygmomanometers. These sphygmomanometers have many steps when measuring blood pressure. The accuracy of the measurement is limited, the environmental impact is great, and it is often calibrated. The use and maintenance of such sphygmomanometers is relatively cumbersome. In order to make the sphygmomanometer more convenient for users to use and maintain the sphygmomanometer, and to let more people learn to use the sphygmomanometer for simple blood pressure measurement, this paper designs a convenient operation. An accurate, maintenance-free, intelligent blood pressure measurement device to help people fight high blood pressure.
1 How does an electronic Blood Pressure Monitor work?
The electronic sphygmomanometer mainly comprises a cuff, an air pump, a deflation valve, a pressure sensor, a signal conditioning circuit, a liquid crystal display module and a control circuit. The basic principle is as follows. The cuff is first pressurized by the air pump, and the controller detects the feedback value of the pressure sensor until the air pressure in the cuff can cut off the arterial blood flow, at which time the air pump stops working. Then, the controller controls the deflation valve to open and slowly deflate. When the air pressure in the cuff is equal to the contraction pressure of the human heart, the arterial blood flow will circulate again, thereby changing the feedback value of the pressure sensor. The recorded pressure value is the systolic blood pressure of the human body (the highest blood pressure); keep the deflation valve continues to deflate slowly until the pressure sensor feedback signal does not change, then the recorded pressure value is the body's diastolic blood pressure (minimum blood pressure) ). Finally, the results obtained are displayed on the LCD.
2 system design
The electronic sphygmomanometer designed in this paper has the functions of: measuring the blood pressure value of the human body; recording the pulse value of the human body during the measurement process; visually displaying the measured value; and having an automatic control function.
According to the above functional requirements, the design scheme of the portable electronic sphygmomanometer is shown in Figure 1.
Figure 1 Block diagram of the electronic sphygmomanometer
As can be seen from Figure 1, the portable electronic sphygmomanometer is mainly composed of the following functional modules.
1. Main control unit: Mainly responsible for the coordination and synchronization of the operation of each functional unit in the whole measurement process of the electronic sphygmomanometer. In addition to this, there should be data processing capabilities that enable conversion between pressure and display values.
2. Drive circuit: It is mainly responsible for amplifying the output signal of the main control unit and switching to control the power component (air pump or bleed valve) to realize the function of charging and discharging the cuff.
3. Pressure sensor and signal conditioning circuit: It is mainly responsible for measuring the air pressure value in the inflatable cuff and converting it into an electric signal to be sent to the control unit.
4, liquid crystal display and function button unit: to provide users with a good human-computer interaction environment, according to the needs of users, the results will be displayed on the LCD panel.
5. System power supply unit: This unit is used to supply power to the entire system.
2.1 main control unit
The MC9S12XS128 is a low-power 16-bit microcontroller from the MC9S12 series from Freescale. The PWM unit of this microcontroller has 8 outputs, each of which can be set independently, and the control precision of each channel is 16 bits. In addition, the ADC unit of this microcontroller has two 10-bit AD conversion modules. And the microcontroller has a PLL (phase-locked loop) circuit inside, which can achieve a system execution rate of 40 MIPS by multiplying.
2.2 drive circuit
The driving circuit mainly recognizes and processes the control signal from the control unit, and then performs amplification to control the power component. The power unit in the electronic sphygmomanometer system is only the air pump and the bleed valve. The drive circuit mainly performs control of turning on and off the current flowing through the coil. Thus, the common emitter drive circuit is used to control the air pump and the bleed valve.
2.3 Pressure sensor
The pressure sensor mainly realizes the conversion of the air pressure value in the inflatable cuff into an electrical signal recognizable by the single chip microcomputer. The design uses the US9111-006 pressure sensor manufactured in Taiwan.
2.4 System power supply design
Consider that the electronic sphygmomanometer system is an analog-digital hybrid system. In this system, the analog circuit and the digital circuit should be divided and protected as much as possible to ensure the accuracy of the equipment operation.
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