rain drop sensor
Raindrop sensor is basically a board on which nickel is coated in the form of lines. As rain drops are collected on the circuit board, they create paths of parallel resistance that are measured via the op amp. The sensor is a resistive dipole that shows less resistance when wet and more resistance when dry The raindrop sensor module detects rainfall. It works on the principle of Ohms Law. (V=IR). When there is no rain the resistance on the sensor will be very high because there is no conduction between the wires in the sensor. The rain sensor works on the principle of total internal reflection.
An infrared light beams at a 45-degree angle on a clear area of the windshield from the sensor inside the car. When it rains, the wet glass causes the light to scatter and lesser amount of light gets reflected back to the sensor. A rain sensor is an automated device that shuts off your lawn irrigation system every time it rains. It is a relatively cheap device that can save up to 45% of your water bills, help protect the environment and conserve water