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 can be used as a shield as long as the power is supplied with voltage equal to that...
This simple megaphone is from old documentation, but uses still current components. The circuit is...
This simple telephone amplifier can be used as an auxiliary amplifier for additional listening, without...