This circuit is from Texas Instruments documentation from the 1980s. The operatinal ones are from the era and the power supply must be symmetrical.
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...