Here is a circuit of a rain detector switch using relay which can be used to switch off your electronic appliances outside the home when rainfall starts to prevent them from short circuit and damage and can also be used for many similar tasks. The circuit is using only few components and it can be operated
with 6 volts DC. The sensor can be made by your own by simply attaching the thin metal strips on a piece of plastic or wood but make sure to give 1mm gap between the strips, you can also make it by using verobaord.
Working of the Circuit:
Working of the circuit is simple the transistor BC547B is working as a switch. When the sensor detects water the transistor become switch on and hence the 6 volts starts passing through the transistor, which activates the 6 volts relay.