Suggested by a Popular Electronics from the 90s, this circuit triggers an external load, relay or recorder, when the telephone line receives a call, thus enabling its recording.
This circuit was found in a European documentation from 1964. The circuit makes use of components of...
This circuit consists of a design improvement that we have previously published (1982), obtaining a new...
This adjustable circuit from 0 to 200 nA was found in a 90's EDN. The components can still be...