Soil/Rain sensor module: S09
A module that generates an output voltage based on the resistance of the soil moisture or rain sensor and provides it to the analog or digital output pin.
Soil Moisture sensor:
A fork-shaped probe with two exposed conductors acts as a variable resistor whose resistance varies according to the water content in the soil.
Rain sensor:
The sensing pad with a series of exposed copper traces together acts as a variable resistor whose resistance varies according to the amount of water on its surface.