The presence of a low resistance between the terminals of the sensor causes this modulated oscillator to actuate, emitting sound through the speaker. Two oscillators are used, each with two NAND gates, obtaining a modulated signal. The activation of the first oscillator, which controls the second, is done with the presence of a low resistance in the sensor. For the integrated C-MOS this "low resistance" is in the order of a few megs, which means that the presence of moisture, the touch of fingers or even raindrops can trigger the circuit, with the emission of sound. In this circuit, amplifying steps can also be used with the connection at point (A).
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