Abstract: A method and apparatus to inform an online computer user of the presence of an incoming telephone call without disturbing an associated modem connection is disclosed. A telephony device is connected to a telephone line, modem and telephone set, and utilizes a Call Waiting service provided by the telephone company. Upon detection of a Call Waiting signal the telephony device generates a four second warbling tone to a piezoelectric sounder alert the user to the presence of an inbound telephone call. The user may answer or ignore the telephone call. Caller identifiers included in incoming calls may be used to alert the user of the origin of the incoming call before the user decides to accept or ignore the call. When the telephony device determines that the user has lifted the telephone set, it places the modem on hold, generates a signal displayed as a colored LED display, connects the telephone to the incoming tip/ring connection, thus establishing a connection to the caller.

Abstract: A telephone line bridging sensor circuit is provided which provides a variable output frequency signal to a microprocessor for measuring and storing the frequency count on a periodic basis. The circuit includes an isolation transformer to isolate the audio component of the telephone line from the sensing circuit. The loop current present in the telephone line is rectified through a full wave diode rectifier and the output of the rectifier is filtered and regulated to provide an input voltage to an astable, voltage controlled oscillator. As the current on the telephone line varies, the input voltage to the oscillator also varies a proportionate amount causing the output frequency of the oscillator to change accordingly.