With the progress of the times, people's requirements for the quality of refrigerated and frozen food are constantly increasing. The changes in food appearance and nutrients are closely related to refrigeration and freezing temperatures. Different foods have their corresponding optimal cold storage or freezing temperature; different storage time requires setting different storage temperature. Therefore, it is necessary to develop a cold storage temperature monitoring system that meets the actual needs.
Based on the single bus technology, this article uses the computer serial port, single bus and serial port protocol conversion chip DS2480B and single bus digital temperature sensor DS18B20 to design a single bus temperature detection network. The system can meet the actual needs of various types of refrigerated and frozen foods, save electricity and manpower, and has functions such as temperature alarm, data storage, drawing dynamic and historical temperature curves, and modifying sensor data. Practical value.
1 Composition of cold storage temperature monitoring system
The system is mainly composed of five parts: DS18B20 digital temperature sensor module, MCU module, RS-485 transmission bus module, RS-485 / RS-232 conversion interface module, upper PC display and control module, as shown in Figure 1. The temperature data is collected by the DS18B20 and sent to the lower computer AT89C52, converted to RS-485 format, and then transmitted over a long distance using the 485 bus. The upper computer receives the temperature data through the RS-232 interface. Control information is also transferred in reverse through the same channel.
2 Hardware design of cold storage temperature acquisition system
2.1 Design of cold storage temperature detection and acquisition circuit
AT89C52 is a low-power, high-performance CMOS 8-bit microcontroller with 8K in-system programmable Flash memory. On a single chip, with a smart 8-bit CPU and in-system programmable
Flash is quite flexible and effective.
DS18B20 uses direct VCC power supply. The power supply voltage is the same as the power supply of the microcontroller. Among them, the data collected by DS18B20 is transmitted to the single-chip microcomputer through a data line, and the read / write operation of the single-chip microcomputer to the DS18-B20 is also realized through this pin. Due to the design requirements, 5 temperature measurement points need to be placed in each cold storage, so 5 temperature sensors are connected to a single bus, and 5 temperature data are measured, and the average value is calculated by the PC host computer software as the temperature of the cold storage. as shown in picture 2.
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