This circuit sounds when the input voltage drops below the value determined by the zener. The circuit is from a 90s American documentation.
This simple circuit uses a 200 µA galvanometer to measure voltages in three ranges. The circuit...
Today we can call this circuit a baby monitor. It is a microphone amplifier found in a publication by...
This circuit is from Motorola's Linear Interface ICs from 1993. The MC1723 is the equivalent of...