Found in American documentation from the 1980s, this circuit can be designed with equivalent components. The microphone can be of the piezoelectric type.
This circuit activates a relay when the water reaches the sensors. The circuit is from a magazine...
The noise comes from the PN junction of a common silicon diode. Since no gain is given by the...
We have here an interesting audio preamplifier, which can be useful to those who are looking to...