This is an easy to use digital soil moisture sensor. Just insert the sensor in the soil and it can can measure moisture or water level content in it. It gives a digital output of 5V when moisture level is high and 0V when the moisture level is low in the soil. 
The sensor includes a potentiometer to set the desired moisture threshold. When the sensor measures more moisture than the set threshold, the digital output goes high and an LED indicates the output. When the moisture in the soil is less thatn the set threshold, the output remains low. The digital output can be connected to a micro controller to sense the moisture level. The sensor also outputs an analog output which can be connected to the ADC of a micro controller to get the exact moisture level in the soild.
This sensor is great for making water gardening projects, water sensing, etc.
 
Specifications:-
 
Operating voltage: 3.3V~5V
Dual output mode,analog output more accurate
A fixed bolt hole for easy installation
With power indicator (red) and digital switching output indicator (green)
Having LM393 comparator chip, stable
Panel PCB Dimension: Approx.3cm x 1.5cm
Soil Probe Dimension: Approx. 6cm x 3cm
Cable Length: Approx.21cm
VCC: 3.3V-5V
GND: GND
DO: digital output interface(0 and 1)
AO: analog output interface