Design of air purifier based on C8051F310 single chip microcomputer

0 Introduction

With the development of industry and society, global air pollution is very serious, and human health is facing the threat of "indoor air pollution". Therefore, people need a special air purification device - air purifier. Air purifiers have gone through two generations of products since their development. The first generation of products uses physical methods, that is, filtering, adsorption, magnetization, negative ions, etc. to eliminate smoke and dust. Its disadvantage is that it cannot eliminate pollution caused by odor, pathogens, viruses, microorganisms, etc. The second generation of products uses chemical reactions to produce ozone negative ions to purify the air, but ozone has an unbearable pungent smell, and ozone as a strong oxidant has certain harm to the human body. The air purifiers currently used in large quantities in China are produced at the cost of cutting down wood and making filters from special paper, which causes great damage to the ecological environment and increases consumer costs. If the filter is not replaced in time, the air purifier will not only fail to achieve the air purification function, but also become a source of pollution itself, causing secondary pollution. This article introduces an intelligent and efficient air purifier based on 51 single-chip microcomputer, which is an environmentally friendly, energy-saving, high-tech and economical product.

1 Overall design

1.1 Principle of high voltage electrostatic precipitator

High-voltage electrostatic dust removal is based on the principle that opposite charges attract and like charges repel. It uses electrostatic force to adsorb and settle charged dust in the air to achieve the purpose of dust removal.

When the gas containing dust particles passes through the high-voltage electric field formed between the cathode wire (also called corona electrode) connected to a high-voltage DC power supply and the grounded anode plate, corona discharge occurs at the cathode and the gas is ionized. At this time, the negatively charged gas ions move toward the anode plate under the action of the electric field force, and collide with the dust particles during the movement, making the dust particles negatively charged. The charged dust particles also move toward the anode under the action of the electric field force. After reaching the anode, they release the electrons they carry and the dust particles are deposited on the anode plate, thereby obtaining purified gas.

1.2 Overall design diagram of air purifier

The overall design block diagram of the air purifier is shown in Figure 1. The 51 single-chip microcomputer controls the operation of each component. When the air purifier is working, the wind speed generator starts to rotate, and the polluted air enters the purifier from the air inlet. After layers of purification, it finally becomes fresh air and flows out from the air outlet.

The front filter can filter out large particles in the air, including large dust particles, fluff and hair; the function of the high-voltage electrostatic dust removal unit is to absorb fine particles in the air, such as smoke, pollen, bacteria, viruses, etc.; the odor absorber is used to absorb common indoor odors and chemical gases to bring pleasant clean air; the wind speed generator has three working modes: high, medium and low wind, and the wind speed can be adjusted according to specific needs; the negative ion generator can release negative ions to make the air fresher and more pleasant.

The operation buttons can turn the air purifier on and off, and adjust the working mode of the air purifier. The indicator light will indicate the current working status of the air purifier. You can also turn on the night light to illuminate the room as needed.

In order to prevent secondary pollution of the air, the high-voltage electrostatic dust removal unit and the odor absorber should be cleaned or replaced regularly. The high-voltage electrostatic dust removal unit should be cleaned with tap water every two weeks, and the odor absorber should be replaced once a year. The time for cleaning and replacement is pre-set by the single-chip microcomputer. When the machine has been running for two weeks or a year, the corresponding indicator light will be lit and an alarm will sound to remind people to clean the high-voltage electrostatic dust removal unit or replace the odor absorber. After cleaning or replacement, you can operate the button to make the single-chip microcomputer reset the time.

2 Circuit Design

2.1 Selection of MCU

The single-chip microcomputer uses Silicon Laboratories' C8051F310, which is a fully integrated mixed-signal system-on-chip MCU chip. It mainly integrates SMBus/IIC, enhanced UART and SPI serial interfaces, single-ended/differential ADC, high-precision programmable internal clock oscillator, VDD monitor, internal power-on reset module, capture/compare module and programmable counter/timer array (PCA) with watchdog timer function and other functional components. C8051F310 uses Silicon Laboratories' patented high-speed CIP-51 microcontroller core, 70% of the instruction execution time is one or two system clock cycles; the operating voltage is 2.7~3.6V, the typical operating current is 5mA, and the power consumption is relatively low. In addition, this single-chip microcomputer also has 16kB of system-programmable FLASH memory, which can be used for non-volatile data storage.

2.2 Single chip microcomputer control circuit

The structural block diagram of the single chip microcomputer control circuit is shown in Figure 2.

P1.x~P3.x are common I/O ports of the microcontroller, and the maximum voltage that each port can withstand is 5V. In order to reduce interference, the pins that are not used temporarily should be grounded.
The microcontroller receives the indication signal sent from the key circuit, analyzes and processes it, and sends control signals to the wind speed adjustment circuit, status indicator circuit and other circuits to achieve the change of the working state of the air purifier.

3 Software Design

In order to improve the speed and real-time performance of the system, the software design of the system is all programmed in assembly language. The software adopts modular design, which is conducive to modification and debugging. The program is mainly divided into 5 parts: main program, timing interrupt service subroutine, wind speed adjustment subroutine, night light subroutine and negative ion generator subroutine. The main program first initializes each data register and peripheral circuit, and then enters the query state. When the key has a signal input, the corresponding subroutine is called. The LED indicator and buzzer are used to indicate the working status of the system.

The FLASH storage area is divided into two parts, which are used as the high-voltage electrostatic precipitator unit FLASH storage area and the odor absorber FLASH storage area respectively, and are used to store the working time of the high-voltage electrostatic precipitator unit and the working time of the odor absorber.

The design block diagram of the timing interrupt service subroutine is shown in Figure 3. The system generates an interrupt every 15 minutes, performs timing processing, and then returns to the main program.

In the wind speed adjustment subroutine, the system adjusts the machine to low, medium, high wind and shutdown states according to the number of button presses. In the low, medium and high wind states, the high-voltage electrostatic dust removal unit is in working state, and other buttons are in effective state; in the shutdown state, the high-voltage electrostatic dust removal unit is in a closed state, and other buttons are also inactive.

The design block diagram of the night light subroutine is shown in Figure 4. The night light switch button has two functions. When the button time is less than 3 seconds, the working state of the night light is changed; when the button time is greater than or equal to 3 seconds, the working time of the odor absorber is cleared.

The design of the negative ion generator subroutine is similar to that of the night light subroutine. First, determine whether the negative ion button pressing time meets 3 seconds. If not, turn on or off the negative ion generator and the negative ion generator indicator light and end and return to the main program; otherwise, erase the time in the FLASH storage area of ​​the high-voltage electrostatic dust removal unit and return to the main program.

4 Conclusion

The air purifier designed with 51 single chip microcomputer has the advantages of simple structure, reliable performance, energy saving and environmental protection. After many tests, the system works stably.