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.
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
106CY
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.
Source: Electronics Lab
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