Ring detector circuit for centrally located answering and recording equipment

Claim 1

Telephone answering and recording apparatus, connected to a telephone switching system serving a plurality of subscribers and including ringing signal generating means, said telephone answering and recording apparatus including a playback medium connectible to said switching system and adapted for playback of announcement messages through said switching system to at least one of said subscribers, and ringing signal detection means connected to said switching system and to said playback medium, said ringing signal detection means comprising: an optical isolator including an input circuit connected to said switching system; counting means including a plurality of outputs, a predetermined one of said outputs connected to said playback medium; and a comparator circuit connected between said optical isolator and said counting means, and including a circuit connection to a source of reference potential; said optical isolator operated to conduct output signals to said comparator circuit in response to receipt of ringing signals generated in said switching system; said comparator circuit operated in response to each output signal from said optical isolator of higher potential than said connected reference potential, to transmit an advance signal to said counting means; said counting means advanced in response to each advance signal received from said comparator to provide an operate signal sequentially at each of said outputs, until an operate signal is transmitted over said predetermined output to said playback medium; said medium operated in response to said received operate signal to play back an announcement message through said switching system to at least one of said subscribers.