Found in documentation from the 90s, this circuit triggers a relay with inductive signals applied to a link. The sensitivity depends on the frequency and the power supply depends on the relay used.
This triac circuit was found in the October 1987 Radio Electronics magazine. The triac is...
This circuit was found in a 1987 edition of the United States' Hands-On Electronics magazine. The...
We found this TTL circuit with the 7400 in the January 1975 Radio Electronics magazine. The power...