In-Depth: How Soil Moisture Sensor Works and Interface it with Arduino

The soil moisture monitoring system operates by measuring changes in electrical conductivity within the soil using a dual-probe sensing element. When the sensor forks are placed into soil, the water content present in the surrounding earth acts as a resistive medium; wetter soil allows more electrical current to flow between the probes, while dry soil presents higher resistance. The attached LM393 voltage comparator module processes this raw resistive variation. It features both an analog output (AO) pin and a digital output (DO) pin. The analog output provides a continuous voltage level that fluctuates inversely with the moisture content, which can be read directly by an analog-to-digital converter pin on the Arduino board. Simultaneously, the LM393 comparator compares the analog signal against a user-adjustable threshold set via an onboard potentiometer. If the soil moisture crosses this preset threshold, the digital output pin changes state from HIGH to LOW (or vice versa), providing a straightforward trigger mechanism. By writing a sketch in the Arduino IDE, you can read these values through jumper wires, enabling the Arduino to monitor precise soil hydration levels or trigger external hardware based on the sensor state.