Development of hardware solution for disinfection machine control system

As we all know, air is not only a necessary condition for human survival, but also an important medium for spreading diseases. At present, there are 41 major infectious diseases in the world, 14 of which are transmitted through the air, accounting for the first place in the spread of infectious diseases. SARS, which brought huge losses to humans in 2003, was mainly transmitted through the air through droplets. The air environment around us is full of harmful bacteria, viruses, organic (or inorganic) pollution particles, toxic dust, etc. Therefore, the sterilization and disinfection of air is of great significance for the prevention and treatment of diseases and health. In order to create a fresh and healthy working and living environment, it is of great practical significance to design an automatic instrument that can not only purify fresh indoor air, eliminate odors such as smoke and musty, but also dynamically kill bacteria in the air.

1. Selection of Air Sterilization and Disinfection Scheme

There are three main methods for air disinfection: ozone, ultraviolet rays and chemicals. Ozone is a colorless, non-residual, slightly odorous gas with strong disinfection and bactericidal effects, and is called a "green disinfectant". Ozone is a broad-spectrum, high-efficiency fungicide recognized around the world. It can quickly kill bacteria and viruses in the air, and quickly restore it to oxygen after sterilization without any residue or secondary pollution. Using ozone to disinfect ambient air is one of the most efficient, convenient and fast ways at present. In addition, ozone has a strong deodorizing ability, which can remove peculiar smells such as smoke, fishy smell, and odor in the air, and achieve the purpose of purifying the air. However, high-concentration ozone has certain harm to the human body. It can stimulate the human respiratory tract and cause respiratory diseases; it can cause human neurotoxicity, dizziness, headache, and vision loss. Therefore, in the design of the disinfection machine, we have controlled the generation time and concentration of ozone, and researched and designed a catalytic device for eliminating ozone to avoid the generation of high-concentration ozone, so that ozone disinfection can be carried out in an environment with people.

Ultraviolet rays also have the function of sterilization and disinfection. Ultraviolet disinfection has the characteristics of high efficiency, broad spectrum, low cost, long life and no secondary pollution. It is an internationally recognized mainstream disinfection technology. The ultraviolet sterilizing band is mainly between 200nm and 300nm, among which the 253.7 nm wavelength has the strongest bactericidal ability. After the fungus absorbs the ultraviolet energy, it will cause the chain break between the DNA nucleoproteins and cause the bacteria to perish.

When designing the disinfection machine, we designed ozone and ultraviolet light as double disinfection, and installed a high-efficiency carbon filter in the machine, which can effectively remove dust and impurities in the air, second-hand smoke, oil fume and other peculiar smells. Therefore, the disinfection machine has triple sterilization and disinfection functions, which can purify the air while sterilizing and disinfecting.

2. Design of disinfection machine control system

In the design of the control system of the disinfection machine, there are mainly three control modules, which realize remote control, automatic control of ozone and ultraviolet rays and the operating status of the fan under different working modes through the relay group, air quality detection, and liquid crystal display. The block diagram of the control system is shown in Figure 1, and its core is the ATMEGA8 single-chip microcomputer. ATMEGA8 is a high-performance, low-power 8-bit AVR high-end microcontroller launched by ATMEL. The chip of ATMEGA8 integrates a large-capacity memory and a rich and powerful hardware interface circuit inside. It has all the performance and characteristics of a high-end single-chip microcomputer, but its price is only comparable to that of a low-end single-chip microcomputer. Its high performance and low price make it highly competitive in the product market, and its application fields are very broad.

The whole system is controlled by remote control. According to different indoor environments and anti-virus effects, the system is divided into three working modes: "fresh", "standard" and "strong". The default "standard" mode is turned on, and the user can operate the remote control according to the environment after turning on the machine; real-time display of the indoor air quality and system operating status on the LCD provides a convenient operation interface for the user; the machine can set the running time and shut down at a fixed time; it has an alarm Cue the lifetime replacement function of the UV system, catalytic filter and ozone generating system.

2.1 Input module design

The input module is mainly for receiving and controlling the remote controller. In the infrared receiving circuit, the integrated infrared receiver HS0038 is used, and the output terminal outputs a high level when it is static. When the infrared signal is received, the negative pulse data signal is output according to the data waveform of the infrared signal. In the circuit design, the "OUT" end of the infrared receiver is connected to the single-chip microcomputer through the pin PB0 (ICP1), and the trigger signal of the infrared remote control receiver is captured by the input capture unit of the T/C.

2.2 Output module design

The output module mainly has two parts: liquid crystal display and relay group control.

The output part of the control relay is driven by a high withstand voltage and high current Darlington transistor ULN2003 chip. The control of the relay group should realize the control of the fan, ultraviolet lamp and ozone generator, so that they can automatically start and run in different working modes. In the fresh mode, the fan runs at low speed, in the standard mode, the UV lamp and the fan run at low speed, in the powerful mode, the fan runs at high speed, and the ozone generator and the UV lamp are turned on. Considering that high-concentration ozone is harmful to the human body, the running time of the ozone generator in the powerful mode is controlled by the program, which is turned on every 30s and continues to run for 15s. The disinfection and sterilization effect of ozone avoids its harm to the human body.

The liquid crystal display part mainly displays parameters, as shown in Figure 5, which can display three working modes, indoor dynamic air quality conditions and corresponding image representations, life prompts and set timer shutdown time. Among them, the indoor air quality is interpreted by the freshness and cleanliness index, and the number of cells of the progress bar corresponding to each index and the corresponding smiling face, sad face and crying face are used to display the quality of the air quality, which is very intuitive. In the design of the control system, the LCD driver HT1621 is mainly used to drive and control the liquid crystal display. HT1621 is a new segment LCD driver chip, which can drive 4-digit 128-segment LCD.

2.3 Detection module design

The indoor air quality is monitored in real time by QS-01 air quality sensor and PPD4NS smoke sensor. QS-01 is a tin dioxide semiconductor gas sensor that can detect a variety of polluting gases with high sensitivity and good sensing characteristics. From the experiment and the characteristics of the sensor, it is known that the pollution degree of the air quality is proportional to the voltage value of the resistor RL, that is, the higher the voltage value, the higher the pollution degree and the worse the air quality.

The detection of smoke and dust adopts the PPD4NS dust sensor imported from Japan, which can detect tiny particles above 1mm with high sensitivity and stably. PPD4NS is based on the same light scattering principle as the particle counter. The light pulse generated by each particle scattered under the light is converted into an electrical pulse with a large signal amplitude through a photoelectric converter. When there is no particle, the dust sensor outputs a high level, and when there is particle, the sensor outputs a negative pulse signal. In the circuit design, the sensor signal output terminal is connected to the external interrupt INT0 input terminal of the microcontroller, and the concentration of particulate matter per unit time is determined by measuring the duration of the negative pulse. Through debugging, the number of progress bars corresponding to the cleanliness index of different particle concentrations can be determined.

2.4 Software Design

The software mainly controls the function realization of each module, and mainly completes the infrared remote control signal reception, liquid crystal display, working mode operation status (that is, the switch status of the relay group), air quality detection, timing shutdown, and reading and writing EEPROM to realize life prompt, etc. Functional control. The entire control system has many task threads, and each subprogram module is organically organized mainly through the main program. The subroutine mainly includes work mode selection, liquid crystal display, A/D conversion processing, smoke detection interrupt, infrared remote control receiving interrupt, timing interrupt and other parts.

Summarize

After being put into use, the sterilizer runs stably and reliably, and its functions fully meet the design requirements. The device with AVR microcontroller as the core control system has the advantages of stable operation, convenient operation and low cost. The sterilizer can be used in family bedrooms, living rooms, offices and medical environments, and has a very broad market prospect.

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