This circuit was found in a 1985 documentation. It provides an audiovisual indication of the presence of moisture or water in the sensor. The circuit can be powered by voltages from 6 to 9 V.
In the figure we have the way to connect 6 solar cells in order to obtain higher voltage and...
This circuit has a maximum frequency of 10 kHz and a linearity better than 0.01%. The circuit is...
This circuit was obtained in a 1961 magazine, but it can be easily assembled today, as the...