Telephone, intercom and remote control system

Claim 1

In combination with a key service unit including a digital tone decoder; power supply; a 400 KSU; a utility telephone company interface; and a plurality of single line telephone instruments with digital tone dialing, a combined remote control, intercom and telephone system comprising: a telephone hookswitch sensing circuit operatively connected to said telephone instruments for triggering a tone decoder control circuit, conditioning the talk path gate circuit to energize with incoming calls when said telephone instrument is not in use, and canceling said conditioning at the termination of the call; a tone decoder control circuit operatively connected to said hookswitch sensing circuit responding to a telephone off hook and coupling the input of said tone decoder to the talk path of said telephone instruments; a time delay circuit operatively connected to the tone decoder control circuit to maintain operation of same for a predetermined time interval; a talk path gate circuit which shifts the operation of said telephones from intercom talk battery to said telephone interfaces in response to said tone decoder output or said 400 KSU circuits signaling of an incoming call, and cancels the operation of said tone decoder control circuit during tone signaling thru the telephone company network; a HOLD feature control circuit operatively connected to the output of said tone decoder and triggering the operation of said 400 KSU circuits initiating the condition of outside call holding; A bi-stable remote control circuit operatively connected to said tone decoder causing a maintained switch closure for operation of remote devices in one mode and a maintained open switch condition in the alternate mode, producing an audio hum on the talk path for approximately one second during the transition from closed to open switch conditions.