In view of the shortcomings of the previous electronic sphygmomanometer, the design of an intelligent electronic sphygmomanometer based on the programmable system-on-a-chip (SOPC) is introduced. The method of blood pressure measurement adopts the oscillometric method based on the inflation process. The system uses the Cyclone II series of low-cost FPGAs, and embedded NNIOS II soft core as the core processor, which can automatically measure blood pressure, information display, data storage, view and delete historical data. Due to the adoption of FPGA, the circuit design is simplified, the reliability and stability of the system are improved, and the system has strong scalability, which is beneficial to system upgrade.
Blood pressure is an important physiological parameter reflecting the state of the cardiovascular system. Appropriate blood pressure is a necessary condition for maintaining normal metabolism of the human body. With the continuous improvement of people's living standards and the aging of the city, people's awareness of self-care is gradually increasing. The electronic sphygmomanometer has the advantages of low cost, miniaturization and high degree of automation. Nowadays, it has become a must-have health care product for families. People's favor. SOPC (Programmable System-on-Chip) is a flexible and efficient SOC solution proposed by Altera Corporation. Programmatic logic is used to place the entire system on a piece of silicon called SOPC. It can perfectly combine MCU, DSP and FPGA, and has very good development prospects.
1 Human blood pressure measurement principle 1.1 Blood pressure measurementThere are many blood pressure measurement methods, and the most commonly used non-invasive blood pressure measurement methods are Korotkoff and oscillometric methods. The design of this paper is based on the oscillometric method of aeration. The oscillometric based inflation measurement is just the inverse of the deflation measurement. As shown in Figure 1, during the pressure increase (inflation), the static pressure and the oscillating wave of the gas in the cuff are detected. The oscillating wave originates from the vessel wall. Beat. When the pressure is small, before the cuff static pressure is less than the diastolic pressure Pd, the arterial wall has fully expanded during the diastolic phase, and the tube wall rigidity increases, so the amplitude is maintained at a small level. As the pressure increases, when the cuff pressure is higher than the systolic pressure Ps, the artery is compressed, and at this time, a small oscillation wave appears due to the impact of the proximal pulse; when the cuff static pressure is equal to the average pressure, the amplitude reaches the maximum. Value; the cuff pressure corresponding to the envelope of the oscillating wave indirectly reflects the arterial blood pressure.
Heart rate refers to the number of beats per minute of the heart. Since the heart is consistent with the pulse of the pulse, the heart rate can be measured while measuring blood pressure. The heart rate is measured by determining the peak value of the pulse wave, and then calculating the heart rate based on how many pulse waves are measured within a certain period of time.
2 hardware design of SOPC systemThe hardware design block diagram of the SOPC system is shown in Figure 2.
This part of the circuit consists of FPGA chip, memory and other peripheral components, is the core part of signal processing. An embedded microprocessor system including the CPU, memory interface, and I/O peripherals is built by the SOPC Builder hardware development environment. After completing the system design, you can use SOPC Builder to generate the system. The following figure shows the system content configuration built in SOPC Builder.
The EPCS device controller core is added to the SOPC system. The purpose of this is to make full use of the system resources, and to solidify the FPGA configuration data and the Nios II software program into the EPCS chip, saving more space for the Flash chip. Store measurement results. At this time, the reset address of the Nios II processor should be set to the base address of the EPCS controller. When the system is reset, the program that is solidified into the EPCS chip will be automatically downloaded to the SDRAM for operation.
Figure 4 is a top-level block diagram of the SOPC system generated by the SOPC Builder hardware development environment.
2.2 Pressure measurement circuit 2.2.1 Pressure sensor selectionThe pressure sensor of this design selected the MPXV5050GP pressure sensor manufactured by Motorola. It contains a signal op amp inside, has a signal regulation function, has a good linearity, can directly convert the pressure of the arterial blood to the blood vessel wall into an electric signal of 0.2 to 4.7V, and the corresponding blood pressure value is 0 to 375 mmHg. Very well matched to the design requirements of the sphygmomanometer.
2.2.2 Design of the drive circuitThe signal for controlling the operation of the air pump and the solenoid valve is issued by the FPGA. The working drive current required by the air pump is 450 mA, the solenoid valve is 75 mA, and the digital I/O output current of the FPGA cannot meet the requirements. Therefore, in order to provide suitable driving current for the air pump and the solenoid valve, the Darlington tube array ULN2803 driving circuit is used to drive the air pump and the solenoid valve to work. The ULN2803 can output 500mA, using the first and second paths of the ULN2803 to drive the solenoid valve and the air pump, and the third drive an LED to indicate the pulse wave signal. As shown in Figure 5.
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