Abstract: A line circuit for a key telephone system using as the main operative components, two relays i.e. a ring relay and a combined off-hook and hold relay and an optical coupler and rectifier bridge combination. On a ring signal from the exchange, the optical coupler is activated to cause the energization of the ring relay. On a station of the line going off-hook, the conventional A lead ground operates the off-hook relay and causes de-energization of the ring relay. When a station of the line goes into hold, the circuit must differentiate this condition from a hang-up condition. This differentiation is performed by the coupler sensing the line voltage as low or high. The line voltage is high if the line loop is open indicating a hang-up condition. The line voltage is low if the line loop is still closed during the sensing period as a preliminary to the hold condition. The off-hook relay is held during this sensing operation so that the circuit may enter the hold condition when indicated.

Abstract: Disclosed is apparatus for providing a completely flexible arrangement for relating key telephone lines to stations and to provide special features as desired to selected stations and lines. A patch or jack panel is provided with appearances for each station and for each line or trunk. Interconnect or cross connect cords or cables may be secured between stations and lines to provide line appearances at the respective stations for each cross-connection made. Further provisions are made for providing line to station ringing on selected lines under power failure conditions and for providing selected class of service for selected lines. Use of this apparatus allows the interconnection of lines to key appearances to be made as desired on installation of the system, on location. In addition, changes can readily be made in the interconnections whenever such changes are required.

Abstract: A line circuit for a key telephone system using three relays, a line relay, a ring relay and a combined off-hook and hold relay. To control the energization of the ring relay and the off-hook and hold relay responsive to inputs from the exchange or from a station of the line, an operational amplifier network is used. Two amplifiers are used as individual relay drivers and two are used as comparators. The amplifiers of this network may be identical circuits as part of a quad circuit chip. On a ring signal from the exchange, a ring comparator amplifier is activated to energize the ring relay. On a station of the line going off-hook, the off-hook driver amplifier is activated directly to energize its relay. When a station of the line goes into hold, the off-hook and the hold comparator amplifier is activated to energize both the ring relay and the off-hook relay. The line relay is energized during only the ring and hold conditions, and is shunted against energization during the off-hook condition.