Rain Detector

This circuit uses a sensor made of a small piece of etched PC board and a simple SCR circuit to detect rain and sound a buzzer. The SCR could also be used to activate a relay, turn on a lamp, or send a signal to a security system.

Schematic

This is the schematic of the Rain Detector

Parts

R1__________1K 1/4 W Resistor
R2__________680 Ohm 1/4 W Resistor
D1__________1N4001 Silicon Diode
BZ1_________12V Buzzer
S1__________SPST Switch
SCR1________C106B1 SCR
SENSOR______See Notes
MISC________Board, Wire, Case, PC Board (For Sensor)

Notes

1. The sensor is a small piece of PC board etched to the pattern showen in the schematic. The traces should be very close to each other, but never touching. A large spiral pattern would also work.

2. Make sure to use a loud buzzer.