This circuit is for old telephones with analog lines. It was found in the May 1988 Radio Electronics magazine. The circuit is powered by the line signal voltaje.
This indicator makes use of an LM339 voltage comparator circuit that contains 4 internal...
This two-transistor amplifier can be used as power stage for intercom, experimental receivers,...
This circuit is from an old American publication, using transistors of the time and operating with a 48...