Abstract: The disclosed four-wire to two-wire converter employs a pair of dual detector opto-isolator circuits to both linearize the converter transfer characteristic and eliminate signal feedback between ports. This is accomplished by feeding back the signals transmitted by the transmit portion of the four-wire port through the auxiliary detector of the opto-isolator circuit connected across the two-wire port to prevent signal feedback to the receive portion of the four-wire port. This opto-isolator feedback arrangement eliminates the need for complex feedback and impedance matching circuitry thereby enabling direct connection of the opto-isolator circuits to the communication paths while also rendering the converter circuit transparent to signals appearing thereon.

Abstract: The disclosed energy control system employs the serving electronic stored program PBX to regulate the operation of energy consuming devices located throughout a hotel/motel or office building in accordance with one or more modes of operation as offered by an algorithm stored in the PBX memory. This is accomplished by equipping each guest room or office with a control circuit to regulate the operation of the energy consuming devices located in that room. These control circuits are activated by the presence of an audio frequency tone on the telephone line associated with the room. To minimize the impact of this scheme on the traffic capacity of the PBX time division switching network, all activated control circuits are concurrently connected to a single time slot, which supplies the required audio frequency tone.