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 astable multivibrator has an active cycle of 30,000: 1. We found it in a 1970 EEE. The...
This circuit was found in a 1969 Ferranti documentation. It can be implemented with modern...
The circuit in the figure is suggested by Linear Technologies (www.linear.com) and consists of a...