Greenhouse control systems need to achieve three targets at the same time: low cost, high stability and the ability to implement complex control algorithm. Therefore, an automatic data acquisition and control system was designed based on RS-485 protocol in this paper. The system has three layers: the bottom layer consists of sensors and actuators, the middle layer is comprised of I/O nodes and the top layer is a main controller. An I/O node based on single chip microcomputer is responsible for executing commands of the main controller. The main controller based on ARM & Linux is in charge of scheduling of all commands. It controls temperature with hysteresis control algorithm. Firstly, the research status of hardware and topology structure was discussed, and their merits and drawbacks were found out. Secondly, an automatic data acquisition and control system was designed based on RS-485 protocol according to the needs of greenhouse control. Finally, the test process was analyzed and the running results were shown. This system was successfully used in our experimental greenhouse.

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