Abstract: This paper introduces the working principle of a microcontroller-based monitoring system for a grain cleaning test bench, and focuses on discussing the implementation methods of the system's hardware and software. The system adopts an 8051 microcontroller as its core control system, equipped with components such as an A/D converter, control circuit, display, and external data storage, thereby realizing real-time monitoring and display of airflow, speed, direction, and sieve vibration characteristics on the grain cleaning test bench. Keywords: Grain cleaning test bench; Microcontroller; Monitoring system In recent years, with the continuous development of China's economy and the continuous improvement of people's living standards, people have increasingly higher requirements for the quality of life. Therefore, the requirements for the working performance of grain cleaning machinery in grain cleaning operations have also increased. However, general grain cleaning machinery has limited functions, poor adaptability, or unstable technical performance. Therefore, we used the 8051 microcontroller and corresponding detection and conversion devices to design a monitoring system that is simple in structure, reliable in operation, precise in control, and inexpensive. This system utilizes the powerful functions and expandability of the microcontroller series to realize various real-time, effective, and multifunctional control operations on the grain cleaning test bench monitoring system. This system uses an 8051 microcontroller to monitor and control the main operating parameters of the cleaning test bench, which can improve the production efficiency and cleaning accuracy of the cleaning device, reduce grain loss, and improve its automation level. This paper discusses the design and implementation methods of the system. 1. Design of the Cleaning Test Bench This study focuses on the cleaning test bench, and the development of the monitoring system uses the cleaning test bench as the experimental equipment. Therefore, the design of the cleaning test bench is crucial. The cleaning test bench consists of a frame, conveyor belt, vibrating plate, sieve box, fan, motor, seed receiving box, and other components. The main dimensions and motion parameters of the cleaning test bench are shown in Table 1. Table 1. Main Dimensions and Motion Parameters of the Cleaning Test Bench [IMG= Main Dimensions and Motion Parameters of the Cleaning Test Bench]/uploadpic/THESIS/2007/12/2007121409523550628T.jpg[/IMG] 2. System Working Principle The cleaning test bench monitoring system is based on an 8051 microcontroller. Sensors detect operating parameters such as feed rate and fan speed, converting them into digital values ​​via an A/D converter. These values ​​are then processed by the 8051 microcontroller. Based on the actual feed rate, the system controls and adjusts the values ​​of various operating parameters to meet current operating needs. If the feed rate exceeds the limit (too high or too low), an indicator light illuminates, an alarm sounds, and the result is displayed on the screen. The system functional block diagram is shown in Figure 1. [IMG=System Functional Block Diagram]/uploadpic/THESIS/2007/12/20071214100359597679.jpg[/IMG] Figure 1 System Functional Block Diagram 3. System Hardware Design The system hardware adopts a control structure based on the 8051 microcontroller. This structure consists of sensors, signal processors, A/D (D/A) converters, control circuits, displays, and external data storage. The A/D converter uses the 12-bit successive approximation fast A/D converter AD547A. This type of converter can quickly convert parameters such as speed, pressure, and frequency. The measured parameter is detected and converted into a 0-2VDC signal, which is sent to the A/D converter to be converted into a digital quantity, and then sent to the 8051 for processing. The AD547A has the advantages of fast conversion speed, high accuracy, moderate price, and very convenient application. Since the AD544A has an internal clock, no external clock signal is required. Because the 74A outputs a 12-bit digital signal, the microcontroller needs to read the conversion result in two steps: first the high 8 bits, then the low 4 bits. The speed sensor uses a JN338 digital torque-speed sensor. This sensor employs two special toroidal rotary transformers to achieve energy input and torque signal output, and can simultaneously measure the rotational shaft speed. Therefore, this sensor can be used to achieve multi-parameter output of torque, speed, and shaft power. This sensor has advantages such as high measurement accuracy; strong anti-interference capability, no need for zeroing; high strength of the measuring elastic body, capable of withstanding 150% overload; high reliability, high signal-to-noise ratio, long service life; small size, light weight, and easy installation. The alarm interface circuit uses a control panel to set alarm lights and sound effects to achieve its function. The alarm lights have three levels: first, the light is off when the feed rate is normal; second, when the feed rate reaches the critical point, the system issues a warning, and the light turns green; third, when the feed rate exceeds the limit (too high or too low), the system alarms, the light turns red, and a siren sounds. The grounding light remains on during operation, indicating that the power supply is normal. In addition, we have adopted a series of anti-interference measures, such as digital filtering, to ensure that the system has high reliability and anti-interference capability. 4. System Software Design The microcontroller control system mainly receives control parameters from the host computer and completes the measurement and control tasks of various working parameters of the cleaning test bench. The system software design adopts a structured and modular design method to facilitate functional expansion. The program is programmed in assembly language. The program modules mainly include: main program, A/D conversion, digital filtering subroutines, etc. The main flowchart of the program is shown in Figure 2. Its software functions are: (1) Power-on self-test process, which mainly completes the system's hardware test; (2) System setting software process, which completes the setting of the rated value; (3) Data acquisition; (4) Data processing, comparison of data with the rated value and storage of early warning alarm signal data; [IMG=Main Flow of System Program]/uploadpic/THESIS/2007/12/2007121410040581492T.jpg[/IMG] Figure 2 Main Flow of System Program 5. Conclusion The innovation of this paper is that it integrates the detection, display and alarm functions of the working parameters of the cleaning test bench, and solves the problem of difficult system monitoring of the test bench fan and sieve. In terms of data acquisition and processing, the reliability design is strengthened. The cleaning test bench monitoring system based on 8051 microcontroller has the characteristics of simple circuit and convenient control.