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.
Based on common unijunction transistors, this 1968 General Electric circuit is powered by 12 V. |...
This circuit of the 80's makes use of components of the time. The circuit is from an American...
This is the conventional protection system for a low resistance analog instrument (millameter or...