Design of cardiopulmonary resuscitation system based on single chip microcomputer

1 Introduction

As we all know, it is of great significance to rescue patients with critical emergencies and sudden death caused by accidental injuries in a few minutes. The traditional artificial respiration and chest compression methods are often difficult to achieve the desired effect due to factors such as inaccurate pressing positions, incorrect force application methods, poor control of pressing depth, irregular pressing frequency, etc., and may even cause serious complications such as fractures, pneumothorax, and hemothorax. At the same time, mouth-to-mouth artificial respiration may also transmit diseases between patients and rescuers. Therefore, it is necessary to develop a portable intelligent cardiopulmonary resuscitation machine with rapid rescue, accurate positioning, and moderate compression. Its timeliness and accuracy can significantly improve the treatment effect and better solve the problems of manual cardiopulmonary resuscitation. At present, the most widely used cardiopulmonary resuscitation machine in China is the "Sabo" cardiopulmonary resuscitation machine of Michigan Instruments Company in the United States. There is still no domestically produced portable cardiopulmonary resuscitation machine in the domestic market. This article introduces a portable intelligent cardiopulmonary resuscitation system with Cygnal microcontroller as the control core.

2. Composition of the single-chip microcomputer cardiopulmonary resuscitation system

The structure diagram of the system is:

In the figure, 1 is a ventilation catheter, 2 is an opening valve, 3 is a gas storage cylinder, 4 is a pressure regulating valve, 5 is a solenoid valve, 6 is a pressure sensor, 7 is a single-chip controller, 8 is a solenoid valve, 9 is a cylinder, 10 is a piston, 11 is a spring, 12 is a pressure head, 13 is a solenoid valve, and 14 is a solenoid valve.

The system workflow is as follows:

1. Set the microcontroller parameters through the touch screen: pressing pressure, pressing frequency;

2. Open valve 2 and inflate gas storage cylinder 3;

3. The pressure regulating valve 4 and the solenoid valve 5 are opened, and the cylinder 9 starts to inflate and press;

4. Does the pressure sensor 6 detect whether the cylinder pressure has reached the limit? If not, continue to inflate;

5. When the pressure sensor 6 detects that the cylinder pressure reaches the preset value, the solenoid valve 5 is closed and the solenoid valve 8 is opened;

6. Exhaust the cylinder 9, and then go to step 3 for circulation;

In order to achieve the purpose of portability, the system uses high-pressure oxygen as power. It uses a double cylinder, one is a gas cylinder, and the other cylinder is equipped with a piston. The piston is pushed by gas to press the chest. Because there is a spring under the piston, the pressing depth and pressing pressure are adapted to each other. The deeper the depth, the greater the pressure. When the pressure in the cylinder reaches the preset value, the solenoid valve is opened to exhaust, thereby controlling the pressing pressure. The pressure regulating valve is controlled by a stepper motor to adjust the gas pressure of the cylinder. After the pressure regulating valve reduces the pressure, the gas pressure is high, and the cylinder with the piston is inflated quickly, otherwise it is slow. In this way, the frequency of pressing can be controlled. The cylinder has a baffle at the displacement of 50mm to prevent the piston from moving down, so that the cylinder wall shares part of the force. The maximum pressing depth is 50mm, which can effectively prevent the pressing depth from being too deep and causing rib fractures.

The oxygen discharged through the solenoid valve 8 is controlled by the opening and closing time of the solenoid valve 13 and the solenoid valve 14 according to the 5:1 compression-to-breathing ratio [5]. When the solenoid valve 13 is opened and the solenoid valve 14 is closed, the trachea is ventilated, and the tidal volume can be controlled by an external air bag. When the solenoid valve 13 is closed and the solenoid valve 14 is opened, the oxygen is discharged into the atmosphere. [page]

3 Hardware Design of Single Chip Microcomputer Control System

This system intends to use the C8051F020 microcontroller from the American CYGNAL company.

Figure 3. Circuit diagram of the microcontroller system structure

4 System power supply

The entire system is powered by a 12V battery pack, which is boosted to a 24V voltage to power the pressure sensor. After stepping down, a 5V voltage is obtained to power each driver chip. The microcontroller is powered by an AS1117 3.3V/800mA power supply. The pressure sensor outputs a 4-20mA current and cannot be directly connected to the microcontroller. It must be input into the microcontroller after passing through a conversion circuit. The solenoid valve only needs to provide a very short pulse level and is controlled by a ULN2803 driver chip powered by 12V DC. [9]

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5 Software Design

The system program is written in C51 and assembly language, with a modular structure, including the main program, interrupt service program and subroutine. The main program flow chart is shown in Figure 4. During the system initialization process, the watchdog timer is first allowed so that the program can enter the reset state in time when a "flight" occurs. Secondly, the external clock oscillator is initialized. In this system, considering the need for serial communication with the computer, an external PCF8563 clock chip is connected, and the clock source can be switched between the external clock source and the C8051F020 internal clock source. Then, by setting the cross switch control register, the counter/timer, serial bus, hardware interrupt, ADC conversion start input and other digital resources inside the microcontroller are configured to the port I/O pins. For detailed configuration methods, see references [06] and [07]. Then, C8051F020 opens the pressure regulating valve according to the input parameters, starts the stepper motor, queries the parameter table, determines the number of rotation steps, and starts pressurizing the cylinder. During the pressurization process, the pressure sensor is detected and the table is checked to determine whether the predetermined pressure is reached. Once reached, the opening and closing of the relevant solenoid valves are controlled, and the cycle is repeated. The interrupt service program mainly includes touch screen input interrupt and pressure sensor input interrupt. The subprograms include: stepper motor control program, solenoid valve switch program, data access program. The main program flow of the system is shown in Figure 4.

Figure 4 Main program flow chart

6 Conclusion

The test process shows that the system can meet the following technical requirements: a. Pressing frequency: 60-100 times/min, adjustable; b. Pressing pressure: 35-45kg, adjustable; c. Pressing depth: 2-6cm, adjustable. It can basically meet the actual use requirements.