Design of Portable Digital Blood Pressure Monitor Based on AT89C51 Single Chip Microcomputer

introduction

At present, due to unscientific eating habits and unhealthy living habits, people are prone to various diseases, and hypertension, as one of the diseases, has seriously threatened the health of modern people. How to detect hypertension as early as possible has become the primary issue for people to fight against hypertension. There are many kinds of digital sphygmomanometers at present, but most of them do not have automatic reporting and autonomous monitoring functions. The portable digital sphygmomanometer designed in this paper is a simple-to-operate pressure measuring device that provides convenience for family health care. Its active reporting and overpressure monitoring functions provide great convenience, especially for the elderly and blind people with poor eyesight.

2. Digital blood pressure monitor system design block diagram

2.1 Working Principle of Digital Sphygmomanometer

This sphygmomanometer uses the oscillometric method to measure blood pressure. Its pressure measurement process is the same as the Korotkoff sound method. The cuff is pressurized to the occipital artery to block the blood in the blood vessel, and then the pressure is slowly reduced. At this time, the fluid in the blood vessel pulses due to pressure. The oscillometric method is to use an instrument to identify the small pressure pulses transmitted from the arm to the cuff, and distinguish them to obtain the blood pressure value. There are two main methods for determining blood pressure using the oscillometric method: the mutation point criterion and the fixed ratio calculation method. This system design uses the fixed ratio calculation method. Its determination method is to first find the maximum amplitude value Amax of the pressure pulse wave. The blood pressure DC component value corresponding to the transient position with an amplitude of 0.5Amax before the maximum value is the systolic pressure. The blood pressure DC component corresponding to the transient position with an amplitude of 0.8Amax after the maximum value is the diastolic pressure, as shown in Figure 1.

2.2 System overall block diagram

The system hardware mainly includes: AT89C51 single chip microcomputer, pressure sensor (BP01), air pump, filter amplifier circuit, keyboard module, LCD display module, voice prompt module, etc. The specific structure block diagram is shown in Figure 2.

Specifically, the pressurization button on the keyboard module sends a signal to the microcontroller to start the air pump to inflate the cuff; the pressure sensor collects the human body fluid pulse wave as the signal source. After the amplification and filtering circuit, it is transmitted to the microcontroller for data processing. Finally, the blood pressure is displayed, the voice reading and the overpressure reminder are performed. After completion, the deflation valve switch controlled by the microcontroller is used to quickly discharge the gas in the cuff.

3. Software Design

This software uses a mixed programming of assembly and C language, including inflation, judgment, deflation, data calculation and comparison, display and other subroutines, which can reliably collect useful signals and separate interfering physiological signals. The main process of the system is shown in Figure 3, where the pressure measurement mode is the default mode in the mode selection. During the measurement process, the standard for abnormal blood pressure is: systolic pressure> 140mmHg or systolic pressure<95mmHg. Diastolic pressure> 90mmHg or diastolic pressure chart<45mmHg. When the blood pressure is abnormal, the voice will report the abnormal reason.

4 Conclusion

This paper systematically gives the design principle and scheme of a portable digital blood pressure meter. This system is based on the AT89G51 single-chip microcomputer as the control core, and is designed with pressure sensors, amplifier and filter circuits, charging and discharging circuits, voice alarm circuits and other peripheral circuits. It has high practical value.