The circuit is from the 1994 National Semiconductor Linear Applications Handbook but can be implemented with more modern operational amplifiers. The power supply must be symmetrical.
This 2003 circuit serves to digitally show the intensity of a sound captured by a microphone....
The circuit shown in the figure makes it possible to control a stepper motor via a PC's serial port...
This circuit was found in an old American documentation. Its purpose is a proportional scanning signal...