Research on Communication Protocol for Global Mainstream Soil Moisture Sensors

This article focuses on the demand for sensor access in the sensing layer of the agricultural IOT. 12 soil moisture sensors from China, the United States, Germany, the United Kingdom, and Australia were selected, with the aim of directly connecting the sensors to the IOT. A comparative study was conducted on their communication interfaces and protocols. The 12 selected soil moisture sensors can be divided into three categories based on interface types: analog interface, SDI-12 interface, and RS485 interface. We conducted signal acquisition and communication protocol research on these three types of interfaces, and using the STM32 microcontroller as the platform, the data collection and conversion of these three interface sensors were programmed according to their respective communication protocols, and corresponding soil moisture data was obtained. Research has found that Modbus protocol is the simplest and most straightforward. SDI-12 protocol is second in complexity. Analog interfaces, rely on the calibration formula provided by the manufacturer or require self calibration for their measurement data accuracy.