This 1967 Raytheon circuit uses a Raystor, an optical coupler with a lamp and an LDR. The circuit can be adapted to use another type of coupler.
This circuit for conventional lines was obtained in a 1996 documentation. The circuit uses common...
This tube circuit was found in the magazine 73 for radio amateurs in an issue from the 1980s. Note...
September 2016 - can already be found at Mouser Electronics new integrated circuit from Texas...