Interrupted tone converter

Abstract

A technique for converting specific dial tone signals received from a telephone exchange, such as those which indicate a Message Waiting, into formats that are readily recognized by telephones or adjunct devices is disclosed. A dial tone converter device is connected between the telephone exchange providing the dial tone signalling and a message indicator device (such as an integrated telephone or message display adjunct device) which does not recognize dial tone signals. Alternately, the dial tone converter device is connected in parallel with the message indicator device. Under normal conditions, the message indicator device is connected to the telephone exchange in a way that all types of signalling (including dialing, voice, and FSK) can pass to and from the exchange. At specific intervals when neither the telephone nor any extensions at the subscriber's number are in use, the dial tone converter engages the line such that the dial tone signal is provided by the telephone exchange. The converter device briefly monitors the dial tone signal, determines whether the dial tone signal conforms to a specific dial tone signal (such as interrupted or continuous tones), then disengages the line. The converter device then transmits the related information to the message indicator device in a format which will be recognized thereby.