Ring detector and telephone line monitoring system for telephone

Abstract

A circuit and system is provided in a telephone answering system and which monitors direct current voltage levels on the telephone line to distinguish between valid ring signals and dial pulses so that the telephone answering system will not attempt to answer when a local telephone is being dialed for an outgoing call. The circuit and system of the invention also responds to direct current voltage differentials on the telephone line, independent of the actual direct current voltage level, to cause the telephone answering system to return immediately to its automatic answer position in the event the calling party hangs up, or in the event the called party picks up, during the announcement interval (T1), or during the message recording interval (T2). This latter feature permits the telephone answering system immediately to return to its original condition in the presence of either of the two foregoing events, without wasting magnetic tape on blank messages, and without the calling party having to wait until the system goes through its entire (T1) and/or (T2) cycles in the event the called party picks up after the telephone answering instrument has answered a call.