In this article, you will learn how to make a Soil Moisture Sensor easily. This soil moisture sensor, turns the indicator ON, when the soil is dry, it indicates to water the plant. Due to this reason, this circuit is also known as Plant Watering Indicator.
- 3V Power Supply
- Any NPN transistor
- 220K Ohm Resistor
- Few Wires
Soil Moisture Sensor Circuit
Soil Moisture Sensor Circuit Working
Dry soil offer high resistance and high voltage drop. As the soil gets wet, the conductivity of the soil increases, it leads to low resistance and low voltage drop. When the soil is wet, the low resistance path (which is lower than the LED branch) is established between Port 1 and Port 2. Then the current passes through 220K ohms resistor. When the soil is dry, it offers high resistance, resulting the current to flow the Red LED to glow.
This circuit indicates when the soil is dry and the plant needs watering. The circuit does not have a current-limiting resistor because the base resistor is very high and the current through the transistor is only 2mA. Don’t change the supply voltage or the 220k as these two values are correct for this circuit.
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