This circuit was found in an Electronic Engineering of the 80s. The circuit indicates when a telephone line is being used, being useful in case of extensions.
This circuit was obtained from a 90sLinear Technology documentation. It is a current source that...
This circuit is from an old American publication, using transistors of the time and operating with a 48...
This circuit was found in the January 1975 Radio Electronics magazine. The diodes are current...