This circuit was found in a 1977 documentation. It limits the voltage from a source using zener diodes on the rectifier bridge. It is an unusual configuration today.
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...