This analog telephone line extension circuit monitors when the line is in use. We found it in the November 1996 Electronics Now magazine.
This simple half-wave control using an SCR, which may be TIC106, has been obtained from a US...
I found this circuit in an English publication from 1989. This configuration can be mounted with...
This reader with TTL logic compatible output uses an LM139 comparator. The circuit was found in...