This circuit is part of an oscilloscope project with the PC. Its purpose is to record a peak in a signal that is to be displayed. We found it in the Radio Electronics magazine of February 1990.
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...