Grain temperature detection technology is one of the four major technologies for grain storage in China. It can dynamically monitor the temperature change of warehouse grain and provide an important guarantee for the storage safety of grain. Due to the special environmental conditions of the reserve: when the grain enters the warehouse, some modules of the system (mainly the sensor module) are disassembled and reinstalled; the toxic gas H3P existing in the warehouse is easy to corrode electronic components, and the damaged sensor in the grain pile is not easy to replace. . Most of the grain detection systems currently used in food storage use wire transmission systems consisting of analog temperature sensors, multi-channel analog switches, A/D converters and single-chip microcomputers. This kind of temperature acquisition system needs to arrange a large number of temperature measuring cables in the warehouse, which is complicated to install and disassemble; at the same time, it is affected by the wire resistance and distributed capacitance, and the measurement error is relatively large, which is vulnerable to lightning strikes. Therefore, a design scheme of temperature detection system based on wireless sensor network is proposed. This scheme does not require any fixed network support, and the installation is simple and convenient, the system is stable and reliable, and the maintainability is good.
2 Wireless sensor networkA wireless sensor network is a wireless network composed of a large number of micro, intelligent, low-power sensors in a certain network protocol. Its purpose is to cooperatively perceive, collect and process the information of the perceived objects in the geographical area covered by the network, and distribute it to the observer. . It combines sensor technology, embedded computing technology, distributed information processing technology and wireless communication technology, and is becoming an emerging technology field, which is considered to be one of the most important technologies in the 21st century.
The wireless sensor network node has functions such as wireless communication, data acquisition and processing, and cooperation, and can be randomly or specifically arranged in the target environment, can acquire information of the surrounding environment, and work together to complete a specific task. The sensor node is mainly composed of functional modules such as a power management module, a sensor, a microprocessor, a memory, and a radio frequency module. The power management module provides the other functional units with the energy necessary for proper operation. The sensor is used to sense and acquire external information and convert it into a digital signal through a signal processing circuit. The microprocessor component is responsible for coordinating the work of various parts of the node, such as performing necessary processing, saving, and controlling the working mode of the sensor and the power supply. The RF module is responsible for communicating with other sensors or observers.
The whole system consists of several wireless temperature sensor nodes, measurement and control host and PC. The wireless temperature sensor nodes are distributed in the warehouse according to certain layout rules, and perform temperature data acquisition, preprocessing and transmission. The measurement and control host is composed of a wireless transceiver module nRF9E5 and an alarm device. It communicates with the PC through the external MAX232 conversion circuit. The measurement and control host transmits data, storage and commands to each node through wireless communication. The PC sends a function command to the measurement and control host and intelligently analyzes, displays and prints the temperature data collected by each node. Due to space limitations, this article mainly introduces the hardware structure and software design method of wireless temperature sensor nodes.
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