This indicator with the integrated circuits CA3162E and 3161E was published in the July 1990 issue of Radio Electronics magazine. The circuit can be used as a basis for 3-digit projects.
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...