The soil moisture sensor is commonly used in smart agriculture or other garden automation projects to measure the moisture content present in the soil. It consists of 4 pins in which two pins, Vcc and Gnd are connected to supply voltage. The remaining two pins are digital (D0) and analog (A0) are the output pins. When the moisture content present in the soil goes beyond the threshold level, the output of the digital pin (D0) will go low (the output of the digital pin is either logic 0 or 1). The threshold value of the sensor module can be set by varying the onboard potentiometer. The analog output pin can be used to calculate the approximate level of moisture content present in the soil.
When purchased, a single unit of soil moisture sensor module will be shipped with the sensor probes and the measurement module. The sensor probe will be dipped in the soil and connected to the measurement module. The measurement module will compare the measured value with the set threshold value (can be set using 10k pot) using the LM393 OP-Amp comparator and provide output on the digital pin. Both the sensor probe and measurement module is shown below.
SPECIFICATIONS OF THE SOIL MOISTURE SENSOR
1.Operating voltage (Vcc): 3.3V to 5V
2.Analog Output voltage: 0 to 4.2V@ Vcc = 5V
3.Digital Output Voltage: 0V or 5V @ Vcc=5v
4 Current consumption: 32mA
Because of the presence of the onboard Lm393 comparator circuit, you can also directly use the soil moisture sensor in your project without connecting a microcontroller unit (MCU) to it. When the moisture content of the soil is higher than the threshold value, the digital output of the moisture sensor is logic 0 (0V). The output from the digital pin can be used to drive an LED or a buzzer circuit.
You can also connect the Digital and Analog Output pins with a microcontroller like Arduino to built measure and monitor the soil moisture sensor and build interesting projects.
Additional Resources
1.Interfacing Soil Moisture Sensor with Arduino
2.Automatic Plant Irrigation using Arduino
3.IoT based Smart Farming using Arduino