How does a Soil moisture sensor works

The moisture of the soil plays an essential role in the irrigation field as well as in gardens for plants. As nutrients in the soil provide the food to the plants for their growth. Supplying water to the plants is also essential to change the temperature of the plants. The temperature of the plant can be changed with water using the method like transpiration. And plant root systems are also developed better when rising within moist soil. Extreme soil moisture levels can guide to anaerobic situations that can encourage the plant’s growth as well as soil pathogens. This article discusses an overview of the soil moisture sensor, working and it’s applications.

HOW SOIL MOISTURE SENSOR WORKS

The working of the soil moisture sensor is pretty straightforward.

The fork-shaped probe with two exposed conductors, acts as a variable resistor (just like a potentiometer) whose resistance varies according to the water content in the soil.

This resistance is inversely proportional to the soil moisture:

• The more water in the soil means better conductivity and will result in a lower resistance.
• The less water in the soil means poor conductivity and will result in a higher resistance.

The sensor produces an output voltage according to the resistance, which by measuring we can determine the moisture level.

Working principle of soil moisture sensor

• The above figure shows the working principle of the soil moisture sensor.
• Soil moisture sensor has two conducting plates. First plate is connected to the +5Volt supply through series resistance of 10K ohm and second plate is connected directly to the ground.
• It simply acts as a voltage divider bias network, and output is taken directly from the first terminal of the sensor pin, which is shown in figure above.
• The output will change in the range of 0 – 5 Volt, in proportion with change in content of water in the soil.
• Ideally, when there is zero moisture in soil, the sensor acts as open circuit i.e. infinite resistance. For this condition, we get 5V at the output.

Soil Moisture Sensor Pin Configuration

The FC-28 soil moisture sensor includes 4-pins

• VCC pin is used for power
• A0 pin is an analog output
• D0 pin is a digital output
• GND pin is a Ground

Specifications

The specification of this sensor includes the following.

• The required voltage for working is 5V
• The required current for working is <20mA
• Type of interface is analog
• The required working temperature of this sensor is 10°C~30°C

Soil Moisture Sensor Applications

The applications of moisture sensor include the following.

• Agriculture
• Landscape irrigation
• Research
• Simple sensors for gardeners