Capacitive Low-Cost System for Soil Water Content Measurement in the IoT Precision Agriculture

The use of low-cost Internet of Things systems is a possible strategy to monitor the consumption of water used in agriculture even in countries that do not have good economic resources. In this paper, a low-cost system based on a new capacitive measuring approach of soil moisture is proposed. This solution exploits the sensor structure's capacitive properties to respond to the need to measure at the same time salinity and soil volumetric water content. To this purpose, a bi-functional system based on a modified commercial capacitive sensor and an AD5933 impedance converter integrated circuit is described. The considered frequency range for impedance measurements is equal to 10-100 kHz, which is a "low-frequency" range compared with typical operating frequencies of a professional system dedicated to water content measurements. For the sensor, a low-frequency Finite Element Modelling simulation of its electrical behavior has also been considered with the aim to understand how its measured admittance correlates with frequency, soil permittivity, and water conductivity.