1 Introduction
If the ambient temperature exceeds or falls below the limit, it will definitely affect people and equipment in the environment, and even cause huge losses to individuals and society. With the rapid development of single-chip technology, the use of single-chip design temperature control system has become the development of control technology. In this paper, a design scheme of temperature warning system based on single chip microcomputer is proposed and simulated by PROTEUS. The system can not only measure the temperature with high precision, but also monitor the temperature in real time and achieve over-temperature alarm, which has high practical value.
2. Overall plan of system design
The overall block diagram of this design scheme is shown in Figure 1. It consists of a single-chip microcomputer, a four-channel data acquisition module, a set of successful release modules, a human-computer interaction interface, and a system power supply.
The design system uses AT89C52 single-chip microcomputer as the control core, the data acquisition part is composed of temperature sensor DS18B20; the human-computer interaction interface is 4&TImes; 4 matrix keyboard input and LCD1602 liquid crystal display, which can conveniently input data and intuitive display. The system power supply is powered by a +5V power supply. The software part is programmed in C language to realize all the control functions of the design. The temperature warning system has a measurement range of -55°C to +125°C. The alarm function is implemented when the detected temperature is higher than the highest or lowest temperature setting.
3. Circuit design
3.1 Single Chip Microcomputer
The AT89S52 single-chip microcomputer is an enhanced product of the high-end AT89S series MCU introduced by ATMEL. AT89S52 is a low-power, high-performance CMOS8 for single-chip microcomputers. It contains 8K Bytes ISP and can read and write 1000 times of Flash read-only program memory. It is manufactured using ATMEL's high-density, non-volatile memory technology and is compatible with the standard MCS-51 command system and 80C51 pin structure. The on-chip integrates a general-purpose 8-bit CPU and ISP Flash memory unit. The AT89S52, a powerful microcomputer, provides a cost-effective solution for many embedded control applications.
3.2 Temperature acquisition circuit
The temperature information of the non-electrical signal obtained by the MCU must pass through the temperature sensor. The traditional temperature measurement mostly uses the thermistor as the temperature sensor. However, the thermal circuit has poor reliability and the measurement temperature accuracy is low, so the temperature is collected using the DS18B20 temperature sensor. The DS18B20 is a single digital temperature sensor chip from Dallas. The DS18B20 features small size, low power consumption, strong anti-interference ability, and easy microprocessor connection. The measurement range is -55°C~+125°C. The rate is 0.0625 ° C, and the temperature measurement standard is ± 0.5 ° C in the range of -25 ° C to + 85 ° C.
The DS18B20 has only three pins, one is grounded, one is connected to the power supply, and one is a digital input/output pin. Since the DS18B20 adopts a single bus structure, the four temperature sensors of the system are connected in parallel on the three lines, and the data input/output is connected to the P1 of the single chip microcomputer. 7 ports, need to connect a 4.7K resistor between the power supply and the digital input and output pins to achieve multi-point networking.
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