This circuit for light modulated in frequency (FM) was found in documentation of the 90s. SUS is uncommon today, but transistors admit equivalents.
Old phones with dials can be used in a simple home intercom system, as this circuit from Popular...
This circuit was found in the July 1992 issue of Radio Electronics magazine. The circuit has a...
This simple circuit indicates if the polarity of a load is reversed when it is connected to a...