Following the American FCC rules, this 90s Radio Electronics circuit shows how to use a transformer to isolate the telephone line from an amplifier circuit.
This circuit was found in the National Semiconductor's Linear Applications of 1978. The circuit uses...
Found in a 1990 PE Hobbyst, this 4-digit circuit has a high response speed. The circuit is based...
This circuit was described in an article in the February 1993 Radio Electronics magazine. The...