This circuit makes use of an optical coupler to isolate the telephone line. The circuit is from 1970s documentation. The components admit equivalents.
This circuit was found in an old American magazine for radio amateurs. The circuit is based on a...
The LDO series (Low Dropout) TPS80 from Texas Instruments (www.ti.com) can provide output voltages...
This circuit is from Motorola's 1990 Linear Databook. We can implement it with other operational...