This circuit was found in documentation from the 1970s. The transistor supports modern equivalents. L1 with C4 determines the frequency range of the signals that will be produced.
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...