Capacitive Soil Moisture Sensor V1.2

A capacitive soil moisture sensor measures soil moisture by detecting changes in capacitance, providing corrosion-resistant, reliable, and precise readings, making it ideal for automated plant watering and agricultural applications.

A capacitive soil moisture sensor operates using the principle of capacitance. The sensor probe contains two electrodes embedded in a PCB, forming a capacitor with the soil acting as the dielectric material. When soil moisture changes, its dielectric constant changes, which affects the charging time of the capacitor. This change is converted into an analog voltage output by the sensor’s onboard circuitry, often including a 555 timer chip, a rectification and smoothing stage, and a voltage regulator. The voltage typically varies from around 1.5V (wet soil) to 3V (dry soil) when powered at 5V and can be read by an analog input on a microcontroller such as Arduino or ESP32

Unlike resistive sensors that measure soil conductivity and corrode over time, capacitive sensors are corrosion-resistant, have longer life spans, and cause no electrical damage to plants. They also offer more consistent readings in different soil types and are less affected by fertilizers or short-term electrical interference

• Operating Voltage: 3.3–5.5 V DC
• Operating Current: < 5mA
• Analog Output: Voltage proportional to soil moisture (wet → low, dry → high)