This circuit was found in the December 1977 issue of Radio Electronics magazine. The 4-digit circuit is based on TTL logic and must be powered by a voltage of 5 V.
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...