Design of medical ozone therapy instrument based on ATmega8L-8PI microcontroller

Overview

As an efficient cold sterilization method, ozone has been widely used in all walks of life. Ozone, which has efficient and rapid sterilization effect, is widely used in hospital environment disinfection, preoperative disinfection and other aspects, and its therapeutic effect is better than other traditional sterilization therapeutic devices. Therefore, it is of practical significance to develop an ozone therapy 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 microcontroller as the control core. Although it can also achieve the required functions, the execution speed is slow. In a 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. Problems such as these are highlighted. For this purpose, this article uses an AVR high-end microcontroller from ATMEL to improve the control system and improve the performance of the whole machine.

Principles and methods of ozone generation

There are many ways to generate ozone. At present, the production of ozone in industry mainly adopts the corona discharge method. 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 extremely strong electric field forces, gas molecules collide and accelerate, and oxygen ions and oxygen molecules and oxygen ions react 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 instrument 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 output. At the same time, the single-chip microcomputer 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) structure 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, which is 10 times faster than ordinary microcontrollers.

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

Ozone generator module

According to the safety performance requirements of home medical treatment 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 standard flow rate ≥1.5L/min. When the technology allows, the flow rate can be increased to 2L/min, and the ozone concentration is standard. The gas flow rate of the latter 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 be almost ignored outside a certain range.

Power supply module The

power input is AC 220V/50Hz; the power output needs to power 4 parts:
* The working power supply of the microcontroller - DC +5V;
* The working power supply of the ozone generator - AC 220V/50Hz;
* The working power supply of the air pump - AC 220V/50Hz;
* The working power supply of the relay - 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 microcomputer, and also have a certain interference with the +5V DC stable power supply; the air pump module will cause electromagnetic interference, which is attached to the signal transmission line through radiation coupling, which may cause malfunction and inaccurate control; the electromagnetic waves in the space and various interferences in the working environment will be added to the power input end. In addition, the mains power is not a pure 220V AC power supply, and it will also be accompanied by some spikes. Therefore, a large number of anti-interference measures are adopted in the design of the power supply.

LED and keyboard module

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

All I/O lines of the AVR single-chip microcomputer have settable pull-up resistors, so they can be directly grounded 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, key function subroutine, printing subroutine, etc. After the source code is compiled into 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 and resets, it first calls the initialization subroutine to define the input and output of the relevant IO ports and initialize the parameters; then it scans the keyboard (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 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, instruction redundancy, sleep anti-interference, etc. The software anti-interference measures plus hardware anti-interference technology are reliable guarantees for the stable realization of the functions of medical therapeutic devices.

EMC test of therapeutic device

The safety performance and anti-interference performance of the designed "medical ozone therapeutic device" were tested using the full-function computer-type 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 therapeutic device introduced in this article 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 therapeutic device designed in this article is stable and reliable, the system has strong anti-interference ability, is portable and practical, and provides a convenient and effective home treatment plan for patients with gynecological diseases.

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