Abstract: Within a key telephone system, there is provided a circuit for completing a direct signalling path from a first station to another station in the system. By depressing a button at the first station designated with identifying indicia of the other station, a direct speaking connection is made from the first station to the other station. The first station may be an attendant's position with direct key appearance for each station to which the attendant is to have direct access. In a preferred form, the called station has a loudspeaker associated with the station instrument. In this instance, a direct call results in a signalling tone directed to the loudspeaker, following which the attendant can converse with the speaker-equipped station. With an attendant's position, depression of a direct station key automatically places a line to which the attendant had been connected on hold.

Abstract: An intercommunication link for a multiple link key telephone system with a combination lamp-button on each handset for each available link. In each link, a line seeking intercom service is sensed to operate a relay in the link selected. A lamp flash signal on the lamp of the selected link is initiated. In this condition, all other links are disabled and none can be accessed when one link is in the lamp flashing condition. The called local number of the desired intercom station is dialed and when the called station line is answered, a second relay in the selected link operates to release the first relay. On operation of the second relay, a steady lamp indication is sent to both stations in the conversation. Other free links may be accessed at this time. Thus, only during this intercom signaling phase are the remaining free links affected.

Abstract: In key telephone systems where a plurality of stations have access to a line by merely depressing a line key, a circuit is provided to prevent that station from entering a busy line. The circuit uses a single relay per station to provide a normal condition of privacy for any line at a station to equipped. The circuit senses the condition of the line and on a busy condition, the station cannot access the busy line. By providing all stations of a key group with privacy circuits, all stations can have complete privacy on line calls. Privacy control is possible on less than all stations of a system and less than all lines by selective deployment of privacy circuits. Optionally, a privacy release button can be provided to allow a station to enable other stations to access that busy line. Protection has been built into the circuit against transient surges and the like.

Abstract: A circuit is provided for detecting the condition of a signalling output being applied by a line circuit to a key telephone and for responding to a predetermined condition of the line circuit. The detecting circuit provides a comparison with the signalling output to identify the signalling output and produce an indication based on the condition signalled by the output. The input to the lamp circuit comparator is compared for amplitude and wave form with a reference for passage of the output signal. With the circuit configuration disclosed, a large range of amplitudes may be used as a basis for comparison in a plurality of wave forms.