Development of a Low-Cost Soil Moisture Sensor Station for Hydrological Monitoring

The growing demand for high-resolution hydrological data necessitates innovative, scalable, and cost-effective monitoring solutions. This study presents the development of a low-cost soil moisture sensor station designed to address these challenges by leveraging advancements in open-source hardware and software.

The sensor station employs modified versions of commercially available capacitive soil moisture sensors, selected after a thorough review of existing technologies and preliminary evaluations to balance affordability and robustness. Built around the Raspberry Pi Pico microcontroller, the station features modular MicroPython programming, combined with a real-time clock (RTC) and an SD card module for robust data logging. Reconfiguration is streamlined through a JSON-based setup, avoiding the need for firmware modifications.

A custom-designed power supply unit, powered by a Li-Poly battery recharged using a 5W solar panel, ensures long-term operation. The station employs power-saving sleep modes during dormant periods, enabling continuous logging at intervals as low as 15 minutes even under suboptimal sunlight conditions in continental Europe, as per conservative estimates. Housed in a 3D-printed enclosure, the main control unit integrates ports for connecting up to three capacitive soil moisture sensors (3.3/5 V Analogue Out) at various depths, a (DHT 11) temperature and relative humidity sensor, and a UART interface for real-time access to runtime logs.

The affordability of the proposed design potentially allows for the deployment of multiple stations for the cost of a single commercially available system. This scalability is particularly critical for applications requiring dense sensor networks, such as watershed-scale studies, hydrological forecasting, or localized climate impact assessments. While acknowledging that the precision and robustness of such systems may not fully match commercial counterparts, this trade-off is expected to be offset by their adaptability and wide applicability in aforementioned cases.

Advancements in monitoring and communication technologies brought about by the "Industry 4.0" phenomena have been instrumental in enabling the design and development of this sensor station. By harnessing these innovations, the study demonstrates how innovative, cost-efficient technologies can be adapted for hydrological monitoring applications. This work wishes to not only showcase the potential of such advancements to bridge the technological and economic barriers in environmental monitoring but also wishes to highlight their role in addressing the growing gap between the demand for hydrological data and its availability.

This study aspires to facilitate and encourage further translation of advancements in monitoring and communication technologies from the "Industry 4.0" era into hydrological monitoring systems in the hope that such advancements could help democratize access to hydrological monitoring technologies, potentially addressing critical data gaps, and in-turn enabling better-informed water management and research practices.