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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.
Circuit diagram
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.
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