Using a 4046 PLL this circuit was obtained from the October 1994 issue of Electronics Now magazine. The circuit can be modified to generate signals at other frequencies.
This circuit generates sinusoidal signals between 300 and 3000 Hz. We find a 303 Circuits from the 90's....
This amplifier for audio transmission lines was found in a 1961 American publication. The critical...
Old phones with dials can be used in a simple home intercom system, as this circuit from Popular...