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 activates an output, which can be a lock, only when a card containing the programmed code...
August 2017 - Texas Instruments is announcing the availability by Mouser Electronics of its new...
This circuit was obtained in a Popular Electronics of 1991. The magazine no longer exists, but the...