A small charge is placed on the electrodes and electrical resistance through the sensor is measured. As water is used by plants or as the soil moisture decreases, water is drawn from the sensor and resistance increases. Conversely, as soil moisture increases, resistance decreases.
How do you connect a soil moisture sensor?
Connect the two pins from the Sensor to the two pins on the Amplifier circuit via hook up wires. Connect the Vcc from the Amplifier to the 3.3V pin on the Arduino and the Gnd pin to the Gnd pin on the Arduino. Now connect the Analog Data Pin to the A0 pin on the Arduino (Since I'm interested in Analog Data).
How do you install a moisture sensor?
https://www.youtube.com/watch?v=wx5FhYMusj4
How do you connect a capacitive soil moisture sensor?