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| Alarm schematic |
materials:
555 timer IC
speaker - 8 ohms
10nF capacitor
aluminum foil touch plate (see above diagram)
2.2uF electrolytic capacitor
R1-3.9k ohms
R2-15k ohms
C-22nF or 0.022uF electrolytic capacitor
When it is raining the aluminum plate becomes wet, at that instant the 555 IC will start to to produces pulses (around 2kHz) to the speaker as an alarm.
You can visit links about 555 timer basics or 555 timer calculator for more info.
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