Smart Multi-Level Soil Moisture Sensing System

This paper presents a prototype design and construction of the smart multi-level soil moisture sensing system. The system consists of 3 3-level soil moisture probes whose length of each is adjustable. The soil moisture probe is equipped with the microcontroller unit, the solar panel, and the long range (LoRa) communication module. The capacitive sensing technique is chosen due to its satisfying accuracy, low cost, and low complexity. Each probe measures the response frequency due to capacitance variation associated with the soil moisture. The response frequency is then transmitted wirelessly over the long range wide area network (LoRaWAN) to the network server. The mathematical model of the actual moisture content (MC) vs measured response frequency was developed. The model was optimized to achieve the optimal correlation R-square of 0.8996. The measured moisture contents are validated by the actual ones. It is found that the average error is only ±2.87%MC. The web application is finally developed to display soil moisture contents.