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This very simple circuit just uses a couple of resistors, a capacitor and the easily available 555 timer IC. The 555 is setup as an astable multi-vibrator operating at a frequency of about 1kHz that produces a shrill noise when switched on. The frequency can be changed by varying the 10K resistor.There are many variation [...]

This water level detector circuit diagram is a circuit that will produce an alaram when the water level reaches a present level. This circuit based on multivibrator wired around 555 IC timer. When there is no water up to probe A and probe B, it will be open circuit so the multivibrator will not produce [...]