Abstract: This paper introduces a temperature intelligent control system based on the AT89C51 microcontroller, and elaborates on the basic principles, hardware composition, and corresponding software design of the system. Keywords: AT89C51 microcontroller, temperature control, hardware and software design I. Introduction For large public places such as laboratories that are extremely sensitive to temperature, this paper designs a temperature intelligent control system based on the AT89C51 microcontroller from a practical perspective to achieve good temperature control. Practice has proven that the system operates well and is economical and reliable. II. Hardware Composition: This system is mainly for temperature control in large public places such as laboratories. Therefore, the temperature we require is not a point, but a range. Thus, we set a temperature point, and set a hysteresis band near the upper and lower limits of this temperature point, as shown in the figure below. [align=center] Figure 1 Schematic diagram of temperature over-limit control[/align] In view of the above, this system uses the AT89C51 microcontroller as the core to form a closed-loop control system integrating temperature acquisition, processing, display, and automatic control. Its principle block diagram is shown in Figure 2. The hardware components shown in the diagram mainly consist of the following parts: microcontroller information processing, temperature acquisition, signal conversion, display, alarm, key tone, and control. [align=center]Figure 2: Block Diagram of Temperature Control System[/align] The specific operation is as follows: Temperature is acquired using an integrated temperature sensor. The signal is then converted from analog to digital by an operational amplifier, hold circuit, and A/D converter, and sent to the microcontroller for processing. A temperature range (upper and lower alarm values, upper limit, upper limit reset value, lower limit, lower limit reset value) is pre-input from the keyboard. The ambient temperature is detected by the temperature acquisition system and displayed by the digital display circuit. When the temperature exceeds the upper limit, the system activates the cooling equipment to lower the temperature. The number of devices activated is based on the percentage of the difference between the sampled temperature and the lower limit relative to the difference between the upper and lower limits. All devices are shut down only when the temperature falls below the upper limit reset value. The cooling equipment stops working. When the temperature is below the lower limit, the control method is the same as when it is above the upper limit. When the temperature is higher or lower than the alarm's upper or lower limit, the alarm sounds to remind staff that the temperature is too high or too low, allowing them to take appropriate measures. Specifically: 1. To improve the overall system operation, this system is designed with a matrix keyboard and a display composed of four LED digital tubes to show the real-time temperature value and the preset temperature value. 2. To improve the system's anti-interference capability, power detection and alarm circuits are designed on the basis of the original hardware to further improve the overall system functionality. 3. To ensure that the previously set parameters are not lost after a power failure, this system uses a serial EEPROM-24C02 to store the parameters before the power failure. The typical interface circuit of 24C02 and AT89C51 is as follows: [align=center] Figure 3 Interface circuit of 24C02 and AT89C51[/align] III. Software Design: For ease of debugging, this system mainly adopts a modular structure design, specifically composed of subroutines for keyboard, display, temperature acquisition, signal processing, A/D conversion, D/A conversion alarm, etc. Here is the main program flowchart, see Figure 4: [align=center] Figure 4 Main Program Flowchart[/align] Wherein, 1. This system uses a matrix keyboard and applies the key scanning method for recognition. Its program flowchart is shown in Figure 5: 2. In order to eliminate external interference to the sampling system, we use the anti-pulse interference averaging method, which is convenient to calculate, fast, and requires very little memory. 3. The temperature range in this system is set from 0℃ to 50℃, but the sampled value after A/D conversion corresponds to the voltage value of this temperature. Therefore, the standard conversion formula of this system is: After this calculation, the temperature range in the system is from 0℃ to 51℃. [align=center] Figure 5 Keyboard Program Flowchart[/align] IV. Conclusion: The design of the entire system is based on a microcontroller to realize the sampling, processing and control of temperature. This system is stable in operation, has high working accuracy, and can easily modify parameters through the keyboard, truly achieving intelligent temperature control. References [1] He Limin, ed. MCS-51 Series Microcontroller Application System Design System Configuration and Interface Technology. [2] Yang Zhonghuang and Huang Bojun, eds. 8051 Microcontroller Practice and Application. China Water Resources and Hydropower Press, June 2001. [3] Su Wenping, ed. New Electronic Circuits. Beijing University of Aeronautics and Astronautics. January 1999.