With the rapid advancement of electronics and sensing technologies, temperature measurement and control have become essential in various fields such as civil engineering, industrial automation, and aerospace applications. Small, low-power, cost-effective, and highly reliable temperature sensors have gained significant attention. In real-world applications, temperature is a critical environmental factor, and accurate and timely monitoring and control are crucial for efficiency and safety. This paper presents a temperature acquisition and display system based on the AT89S51 microcontroller and the LM35 temperature sensor. The system is designed to offer high sensitivity, strong anti-interference capabilities, and stable and reliable performance.
1. System Structure and Working Principle
The temperature acquisition and display system consists of several key modules: a temperature sensing module, an A/D conversion module, a microcontroller unit (MCU) control module, a digital tube display module, and a download module. The system operates by first collecting ambient temperature data using the LM35 sensor. The output voltage from the LM35 is then amplified by a factor of 10 using the LM358 operational amplifier before being converted into a digital signal by the TLC549 A/D converter. This digital value is then processed by the AT89S51 microcontroller, which drives the digital tube to display the measured temperature. The system is capable of measuring temperatures within the range of 25°C to 80°C. The overall system is an open-loop control structure, as illustrated in Figure 1.
2. Core Hardware Circuit Design
The design of the system's core hardware includes the temperature acquisition module, A/D conversion module, MCU control module, digital tube display module, and download module.
2.1 Temperature Acquisition Module Design
As the first stage of signal input, the sensor plays a vital role in determining the overall performance of the system. Therefore, selecting the right sensor is crucial. In this system, the LM35 temperature sensor is used as the core component of the temperature acquisition module. It offers high accuracy and a wide linear operating range, with its output voltage directly proportional to the Celsius temperature. For every degree Celsius increase, the output voltage increases by 10 mV. The LM35 requires no external calibration and provides a typical room temperature accuracy of ±0.25°C. To enhance the signal strength, the LM35 is paired with an LM358 amplifier circuit, which amplifies the weak voltage signal by a factor of 10 before sending it to the microcontroller. The schematic diagram of the temperature acquisition module is shown in Figure 2.
2.2 A/D Conversion Module Design
The A/D conversion module uses the TLC549, a CMOS-based serial 8-bit analog-to-digital converter. It features an 8-bit switched capacitor successive approximation ADC with a conversion time of 17 microseconds and supports input voltages between 3V and 6V. The TLC549 only requires an input/output clock and a chip select (CS) signal for operation. Its maximum input frequency can reach up to 1.1 MHz. The schematic of the A/D conversion module is shown in Figure 3.
2.3 MCU Control Module Design
The AT89S51 microcontroller is chosen as the core of the MCU control module due to its low power consumption, high performance, and built-in 8K flash memory that allows for online programming. Unlike the 8031, which requires external memory expansion, the AT89S51 simplifies the system design and reduces complexity. The microcontroller processes the digital signal from the A/D converter and controls the digital tube display. The schematic of the MCU control module is shown in Figure 4.
2.4 Digital Tube Display Module Design
The digital tube display module is a key part of the system, enabling users to view the measured temperature in real-time. This module uses a standard 8-segment digital tube, driven by the microcontroller to display the temperature readings. The schematic diagram of the digital tube display module is shown in Figure 5.
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