Design and implementation of medical ozone therapy instrument based on AVR microcontroller

　　Overview

　　As an efficient cold sterilization method, ozone has been widely used in all walks of life. Ozone, which has high efficiency and rapid sterilization, is widely used in hospital environment disinfection, preoperative disinfection, etc., and its therapeutic effect is better than other traditional sterilization therapeutic devices. Therefore, it is of practical significance to develop an ozone therapy device product that is stable, easy to use, and portable, and provide patients with gynecological diseases with a convenient and effective way to treat at home.

　　At present, similar products on the market all use 80C51 single-chip microcomputer as the control core. Although it can also realize the required functions, the execution speed is slow. In the long-term working environment, especially under the interference of the internal high-power air pump module and ozone generator of the ozone therapy device, the system power consumption is high, the anti-interference performance is poor, and the system performance is unstable. For this reason, this paper adopts an AVR high-end single-chip microcomputer of ATMEL Company, improves the control system, and improves the performance of the whole machine.

　　Principles and methods of ozone generation

　　There are many ways to produce ozone. Currently, the main method of producing ozone in industry is corona discharge. The basic principle is shown in Figure 1.

　　Figure 1 Basic principle of ozone generator

　　In an ozone generator, a pair of electrodes are separated by a dielectric (usually glass) and an air gap (usually oxygen-containing gas). When an AC high voltage is applied, as the voltage value increases, corona discharge occurs in the air gap, the gas is ionized, and the concentration of oxygen ions in the gap increases sharply. Under the action of an extremely strong electric field, gas molecules collide and accelerate, and oxygen ions react with oxygen molecules and with each other to generate ozone.

　　According to the frequency of the power supply, it can be divided into: industrial frequency ozone generator, medium frequency ozone generator and high frequency ozone generator.

　　System overall structure design

　　The medical ozone therapy system is based on the ATmega8L-8PI high-performance microprocessor, and is mainly composed of a power module, an ozone generator, an air pump module, serial communication, an LED display circuit, and a keyboard, as shown in Figure 2. The single-chip microcomputer controls the operation of the ozone module and the air pump module through relay outputs, and also controls operations such as LED display and keyboard input.

　　Figure 2 Overall block diagram of the control system

　　ATmega8L-8PI microprocessor

　　ATmega8L-8PI is a high-performance, low-power 8-bit microcontroller based on AVR RISC (Reduced Instruction Set) architecture produced using low-power CMOS technology. The processor has a controllable power-on reset delay circuit and a programmable undervoltage detection circuit, 18 internal and external interrupt sources, and 5 sleep modes. 32 working registers and a rich instruction set are connected together, so that most instructions are executed in only one clock cycle. Therefore, ATmega8 can achieve a performance of nearly 1 MIPS/MHz, and its running speed is 10 times higher than that of ordinary microcontrollers.

　　The chip integrates 8KB of Flash program memory, 512B of EEPROM, supports ISP and IAP programming, programmable program encryption bits, 3 PWM channels, 8-way 10-bit ADC, 2 8-bit timers/counters with pre-scaling, 1 16-bit timer/counter with pre-scaling, a programmable watchdog timer with RC oscillator, etc.; as well as I2C, SPI, and UART interfaces, which can receive programs downloaded from the RS-232 interface of the host computer. It only needs a few external devices such as a crystal oscillator and a reference power supply to work, which greatly facilitates the development and research of the system.

　　Ozone generator module

　　According to the safety performance requirements of home medical therapeutic devices specified in national standards GB9706.1-1995 and GB4343.2-1999, the ozone generator module we selected has a power supply of AC220V/50Hz, a power of 13W, and an output of 100~200mg/h. According to the selection of different function buttons, the ozone concentration is adjustable and automatically adjusted by the function control program. The therapeutic device has four functions: air disinfection, ozone water treatment, vaginitis treatment, and cervicitis treatment. In the first two functions, the gas flow rate is a standard flow rate ≥1.5L/min. When technology permits, the flow rate can be increased to 2L/min, and the ozone concentration is standard. The gas flow rate of the last two functions is 1~1.2L/min, and the ozone concentration is increased.

　　According to the principle of ozone generation, the high voltage interference generated by the ozone generator in this system cannot be ignored. This high voltage will mainly interfere with the stability of the linear power supply through conduction coupling, and at the same time cause certain interference to the high-frequency component in the control system - the single-chip microcomputer.

　　Air pump module

　　According to relevant requirements, the selected air pump power supply is AC220V/50Hz industrial frequency power supply, with a power of 5~9W and an air output of 1.2L/min. The working principle is to generate power by driving a special diaphragm through electromagnetic oscillation. Compared with the ozone generation module, this module generates less interference. Because the voltage is low, the electric field interference is not strong; in terms of magnetic field interference, the working core of the motor will affect other modules through leakage magnetic field. However, since the frequency of the magnetic field is not high and has not reached the MHz level, the magnetic field interference can almost be ignored outside a certain range. [page]

　　Power Module

　　The power input is AC 220V/50Hz; the power output is used to power four parts:

　　*The working power supply of the microcontroller is DC +5V;

　　* Working power supply of ozone generator: AC 220V/50Hz;

　　* Working power of air pump: AC 220V/50Hz;

　　*Relay working power supply – DC +12V.

　　The quality of the power module design is directly related to the working stability of the single-chip system. In this design system, the design of the power module has the following problems: the high voltage of the ozone generator will affect the work of the single-chip, and also have some interference with the +5V DC stable power supply; the air pump module will cause electromagnetic interference, which will be attached to the signal transmission line through radiation coupling, which may cause malfunction and inaccurate control; the electromagnetic waves in space and various interferences in the working environment will be added to the power input end, and the mains power is not a pure 220V AC power supply, and it will also be accompanied by some spike waves. Therefore, a large number of anti-interference measures are adopted in the design of the power supply.

　　LED and Keypad Modules

　　The keyboard can be used to set various working modes. For example, when the vaginitis treatment key is selected, the program automatically switches to the ozone concentration and default working time for vaginitis treatment. Users can also set the length of treatment time by themselves through the keyboard.

　　All I/O lines of the AVR microcontroller have configurable pull-up resistors, so they can be directly connected to ground without connecting resistors; when the keyboard is not pressed, all inputs are high level. If one of the keys is pressed, the corresponding port of the key will be pulled down to a low level input.

　　System software design

　　In this system, ATmega8L-8PI is written and compiled in C language under ICCAVR environment. It mainly scans the keyboard, reads the keyboard status, and outputs various statuses to the four-digit digital tube for display. At the same time, MCU outputs the control signal to the power board. It includes the main program, keyboard scanning subroutine, display subroutine, each key function subroutine, printing subroutine, etc. After the source code is compiled into an Intel hexadecimal file, it can be directly loaded into the flash/electrically erasable program memory in the ATmega8L-8PI chip through the UART serial port, and can be debugged and modified online, which greatly improves the development efficiency. The main program flow chart is shown in Figure 3.

　　Figure 3 Main program flow chart.

　　After the main program starts resetting, it first calls the initialization subroutine to define the input and output of the relevant IO ports and initialize the parameters; then it performs keyboard scanning (including de-jitter processing), and then executes the corresponding function according to the keyboard key code value. When the work is completed, it enters the sleep state. If there is no operation for more than a certain period of time, the system will also be in the sleep state, which greatly reduces power consumption.

　　In terms of software, software anti-interference measures are also adopted, such as watchdog, command redundancy, sleep anti-interference, etc. The software anti-interference measures plus hardware anti-interference technology are reliable guarantees for the stable function of medical therapeutic devices.

　　EMC testing of therapeutic devices

　　The safety performance and anti-interference performance of the designed "medical ozone therapy device" were tested using the full-function computer-based tolerance tester TRANSIENT-2000. The functional test results and anti-interference performance test results are shown in Table 1 and Table 2 respectively.

　　Conclusion

　　The medical gynecological ozone therapy device introduced in this paper uses the high-performance AVR microcontroller ATmega8L-8PI as the main control center, simplifies the circuit, saves costs, and adopts various hardware and software anti-interference measures to effectively improve the system operation speed and stability. The test results show that the medical gynecological ozone therapy device designed in this paper operates stably and reliably, has strong anti-interference ability, is portable and practical, and provides a convenient and effective home treatment plan for patients with gynecological diseases.

　　references:

　　1. Wei Xu et al., Research on improving the efficiency of ozone generator discharge chamber, New Technology of Electrical Engineering and Power, 1998.2: 46-49

　　2. Tang Jie, Research and development of series resonant DBD type ozone generator power supply, Hunan University Press, 2004.

　　3. Bao Xiurong, Wang Nan, Characteristics and Application of AVR Microcontroller, Inner Mongolia Science and Technology and Economic Publishing House, 2004.6: 51-52

　　4. Gou Jiazhi, Anti-interference design of single-chip microcomputer measurement and control system, Journal of Chongqing Technology and Business University (Natural Science Edition), 2005, 22(1): 59-62.

　　5. Zhao Xiaohui, Research on anti-interference measures of single-chip microcomputer in intelligent instrument, Journal of Liaoning Teachers College, 2002, 4(3): 93-95. 

　　6. Huang Yongjun, Zhang Xuezhong, Xie Xingang, Research on the reliability of single-chip embedded system, Agricultural Mechanization Research, 2005, (3): 89-91.