This interesting circuit was found in an 80's Electronic Engineering. The circuit has a 50% active cycle. R and C determine the generated frequency.
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...