Found in a Popular Electronics from the 90s, it applies to the old answering machines that used tapes. It emits a warning beep on the drive.
In the figure we show another interesting application for integrated circuit 4001. This circuit...
This audibility or loudness control for sound equipment is from 1992 documentation. The circuit uses...
This circuit was found in an application note of the LTC1164 from Linear Technology of the 1990s....