Design of intelligent electronic blood pressure monitor based on LPC3250

　　This multifunctional electronic sphygmomanometer uses the oscillometric method for measurement. Its principle is to measure the vibration of the blood vessel wall caused by blood flow. During the cuff deflation process, as long as the pressure inside the cuff is the same as the blood vessel pressure, the vibration will be the highest. powerful. Its advantages are: easy to use, can be operated by one person alone, measurement values ​​are easy to record, and it is lightweight and easy to carry.

　　1 System working principle

　　Blood pressure refers to the lateral pressure of the blood in the blood vessel against the blood vessel wall per unit area, that is, the pressure. A normal heart is a powerful muscular organ that opens and contracts rhythmically day and night to allow blood to flow within the circulatory organ. When blood flows in blood vessels, whether the heart contracts or relaxes, it exerts a certain amount of pressure on the blood vessel walls. There are two types of blood pressure. One is systolic blood pressure, which means that when the ventricle contracts, the aortic pressure rises sharply and reaches the highest value in the middle of the systolic period. The arterial blood pressure value at this time is called systolic blood pressure, also known as "high pressure" The other is diastolic blood pressure, which refers to the drop in aortic pressure during ventricular diastole. The lowest value of arterial blood pressure at the end of diastole is called diastolic blood pressure, also known as "low pressure."

　　This multifunctional electronic sphygmomanometer uses the oscillometric method for measurement. Its principle is to measure the vibration of the blood vessel wall caused by blood flow. During the cuff deflation process, as long as the pressure inside the cuff is the same as the blood vessel pressure, the vibration will be the highest. powerful. Its advantages are: easy to use, can be operated by one person alone, measurement values ​​are easy to record, and it is lightweight and easy to carry.

　　2 Hardware design

　　2.1 Overall system structure

　　The overall structural block diagram of the multifunctional electronic blood pressure monitor system is shown in Figure 1, which mainly includes six major modules: LPC3250 main control module, power supply and reset module, detection module, LCD touch screen module, WiFi module, voice module and USB module.

　　2.2 Main control LPC3250

　　The main control adopts NXP's newly launched highly integrated LPC3250 microprocessor, which has the characteristics of high performance, high integration, low power consumption, etc., and is very suitable for the design requirements of this solution. It uses a 90 nm process and a powerful ARM926EJ-S core, clocked at up to 208 MHz, and has a full range of standard peripherals. These include a 24-bit LCD controller with a dedicated DMA controller to support STN and TFT panels; a three-channel 10-bit 400 kHz A/D converter with a touch screen interface; internal integration of up to 11 PWM channels; a USB OTG interface that can Connects host and devices at full speed; an external memory controller supporting DDR and SDR SDRAM, SRAM, FLASH and static devices. It fully meets the needs of this design. Only a few external chips can be added to realize the system functions, and the entire system can be reduced in size, power consumption, stability, and cost control.

　　2.3 Pressure sensor XFGN-6025KPGSR

　　The design adopts the new generation pressure sensor XFGN-6025KPGSR produced by Japan's Fujikura Company. It weighs only 0.35 g and is mainly used for portable electronic blood pressure monitors. It uses a precision thick-film ceramic chip and a nylon plastic package. It contains amplification, temperature compensation and preset The offset voltage and range are corrected, thereby improving the accuracy and stability of the measurement and eliminating the need for an amplification circuit. It directly converts blood pressure into an electrical signal of 0~4.5 V, and the corresponding blood pressure value is 0~25 kPa, that is, 0~187.5 mmHg, which matches the design requirements of the sphygmomanometer very well.

　　2.4 Filter MAX267

　　The measured analog signal must also be filtered and then A/D converted. Among them, filtering is used to filter out the DC component in the signal, power supply, high-frequency noise and power frequency interference caused by friction between the skin and the cuff, etc. This design uses Maxim's MAX267, which is one of the simpler of Maxim's many switched capacitor filter (SCF) chips. It contains two second-order SCFs and an op amp that have been fixed to the bandpass type and use the same Q parameter and frequency conversion ratio. By selecting appropriate feedback resistors and Q parameters, Butterworth or Chebyshev filters with different ripple rates can be formed. This greatly reduces the peripheral circuit, is flexible to use, and has far better performance than a filter circuit composed of an integrated operational amplifier, making it very suitable for this design.

　　3 Software design

　　3.1 Program flow

　　The software part is the core of the effective work of the system, and its program flow is shown in Figure 2. After the system starts, U-boot boots the embedded Linux, initializes related hardware and programs and enters the main menu. Among them, data query allows you to view past measurement results on the LCD, and the machine performs simple health analysis; network service, you can manually transmit the measured results to the hospital via WiFi, and have a simple conversation with the doctor; start testing, The sphygmomanometer enters the detection mode; system settings allow you to set the system time, network parameters, etc., and upgrade the system firmware; for personal information, you can enter your height, weight, gender, age and other information to facilitate the system to detect each person. The measurement data are managed individually and analyzed in a targeted manner.

　　3.2 Electronic blood pressure monitor detection mode process

　　When measuring blood pressure, the microprocessor PWM output controls the air pump to inflate, first inflate to the maximum rated value of the pressure sensor 25 kPa, that is, 187.5 mmHg, and then slowly deflate at a constant speed at a rate of about 3 mmHg per second, and adjust the cuff. Internal air pressure to automatically measure blood pressure. One A/D samples the DC component of the air pressure in the cuff to obtain systolic and diastolic blood pressure, that is, high and low pressure, and averages the heartbeat cycle to calculate the heart rate; the other A/D samples the AC component of the air pressure in the cuff and analyzes and calculates it. Finally, the instantaneous time position of systolic blood pressure and diastolic blood pressure is determined, the blood pressure pulse signal is received, the ADC is triggered to work, and the results of systolic blood pressure and diastolic blood pressure are calculated. The heart rate and blood pressure calculation flow chart is shown in Figure 3.

　　3.3 Design of database system

　　The data management of this design uses SQLite embedded database, which is a small and medium-sized embedded database developed by D. Richard Hipp in 2000. It can be easily used in embedded systems. Its source code is completely open and can Free for any purpose, including commercial purposes; it provides most support for SQL92, such as supporting multiple tables, indexes, transactions, views, triggers and a series of user interfaces and drivers, which is easy to use and fast. It also provides a rich database interface. After analyzing and optimizing the requirements, the ER diagram of the database system can be designed as shown in Figure 4. It comprehensively and accurately reflects the functional needs of users, can reduce the number of entity types and the number of attributes contained, and there is no redundancy between entity types.

　　3.4 System interface design

　　In the system interface, various commands are issued through the touch screen, and then displayed by the graphical interface through the connection to the database. The application window interface of this design is written and implemented using Qt. It is a cross-platform C++ graphical user interface application framework that is completely object-oriented, easy to extend, and allows real component programming. It is widely used in various embedded systems. in the product. Figure 5 is an interface designed using the lightweight cross-platform integrated development environment Qt creator. After powering on, first enter the main menu as shown in Figure 5(a), tap to start detection, and the system enters the detection menu as shown in Figure 5(b) to display the measured data. Considering the poor eyesight of the elderly, the fonts in this interface have been enlarged.

　　4 Conclusion

　　With the continuous improvement of living standards and the proportion of urban aging, the home-based and intelligentization of medical electronic equipment has gradually become a trend. This article gives a complete design solution for an intelligent electronic sphygmomanometer, which is different from traditional products that only have a single detection function. It has three major innovations: large-screen display and control; using the embedded database SQLite for data management; and connecting to the hospital through the network. Practical applications show that the system is small in size, low in power consumption, intelligent, and has fast detection speed. It realizes an integrated health detection network of individuals, instruments, and medical institutions, and is very suitable for home users, especially the elderly. If this program can be widely promoted and applied, it will produce immeasurable economic and social benefits.