SunFounder's Description of the Raindrop Sensor Module
Introduction When wired with a 5v supply, the power light will be on. When the sensor detects no raindrop, D0 is high and the indicator keeps out. Drop some water onto the sensor. The more drops, the lower value at A0. When the value of A0 is smaller than the value set, D0 will change from high to low and the indicator will light up.
Application It is widely used in the automatic wiper system, smart lighting system and sunroof system of automobiles.