Research On CAN Bus-based Distributed Greenhouse Control System

With the rapid development of computer software and hardware technology, electronic technology, sensor technology, and the widespread application of the large-scale integrated circuit and high-speed digital processing chips, fieldbus controlling technology are developing gradually from centralized to distributed form. In recent years, fieldbus technology has a very wide range of applications in our country. Especially the CAN-Bus technology, because of its superior capability, high reliability and low price, is one of the world's most widely used fieldbus. Therefore, the research on CAN fieldbus technology becomes an important issue in the development of modern communication technology. At the same time, greenhouse is a highly efficient technology in agriculture (By greenhouse technology, we can control the growth of crops, so as to achieve the goals of highyield, high quality and efficiency of crops). In order to meet China's national policy of " rejuvenate the country through science and technology", research on the application of bus technology in greenhouse monitoring field is of great practical significance.First, the paper introduces the research of the domestic and foreign environmental monitoring system for greenhouse and its application status. Based on analyzing the design demand of greenhouse environment system, and comparing several kinds of fieldbuses, the paper presents the design of communication system by using CAN-Bus as the communicational method, and using the CAN2.0 technical specifications in the frame structure.In this paper, the greenhouse monitoring system based on the CAN-Bus is composed of the monitored equipment, monitor subsystem, monitor host, top PC and so on. The monitored equipment is the equipment to be monitored. Monitor subsystem collects the data from the monitored equipment, transmits the data to the monitor host by CAN-Bus, and then transmits the data to top PC after the processing of monitor host.The design uses PIC18F4580 unit with integrated CAN-Bus controller as the main controller, which simplifies the hardware and software designs of system. The system hardware mainly includes: system feed circuits, digital input/output circuits, simulation input circuits, master-controlling CPU, data-collecting circuits, CAN-Bus interface circuit, data-displaying circuit, RS232 and external communications interface circuits and so on. In the part of software design, the flow of main program, the CAN-Bus communication module, the data collection and processing module and warning module are introduced respectively. The paper also discusses several interferences to system and its corresponding protection methods, which can improve the antijamming ability of the system effectively.