A single transistor amplifier is used at the output of the UM66 IC for amplifying the audio output to drive an 8 ohms speaker. An LED is also used to show the visual indication of raining.
The circuit is using a hand built sensor, it can be made by many techniques for example you can make it simply by attaching thin wires on a 3 to 6 inches square plastic piece, make sure to give 1 to 3 millimeter gap between all wires. The max operating voltage of the circuit is 4.5 volt DC. For operating with higher voltage like 6, 9 or 12 volt a zener diode of 3.3V with a resistor will be required before the UM66 IC.
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