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.
Part Total Qty. Description Substitutions R1 1 1K 1/4 W Resistor R2 1 680 Ohm 1/4 W Resistor D1 1 1N4001 Silicon Diode BZ1 1 12V Buzzer S1 1 SPST Switch SCR1 1 C106B1 SCR 106CY SENSOR 1 See Notes MISC 1 Board, Wire, Case, PC Board (For Sensor)
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.