This circuit is from a Hands-On Electronics from the 90s. The integrated amplifiers used are well known. The range is a few tens of meters depending on the resistance of the cables.
This circuit was found in Electronics Now. With it the dialing signals of a telephone are...
This circuit switches the brightness of the LED. We found it in an English documentation....
This circuit already explored in several diagrams in this section was found in a 90’s Popular...