For analog lines, this circuit was found in the August 1994 issue of Electronics Now magazine. The transistors are common general-purpose types.
This circuit provides a signal when dialing occurs. The circuit is powered by the telephone line...
This simple injector and signal follower employs a high impedance headset. Transistors can be of...
This circuit uses a 6-bit A / D converter from Philips, and has its output compatible with most...