Abstract: A talker speech level control circuit for controlling the level of an electric signal converted from a talker speech, includes an acoustic-electric conversion element for converting an acoustic input signal into an electric signal; a talker speech level detection circuit for detecting whether or not the speech level of an output signal from the conversion element is within an area representing a need for speech level control; and a talker speech level adjustment circuit responsive to a signal detected by the talker speech level detection circuit for controlling the electric signal level in accordance with the detected area within which the talker speech level falls.

Abstract: The present invention disclose a switching system including an exchange coupled to a plurality of central office lines and PBX's telephone lines, and a plurality of telephone sets. Each telephone set includes a side-tone adjusting circuit which adjusts a side-tone in response to a balanced impedance to obtain a suitable side-tone. When the exchange receives a speaking path selection request, representing one of the lines, from the telephone set, it determines one of a plurality of predetermined impedance information and makes a speaking path between the selected line and the telephone set. The telephone set selects one of the balanced impedances in response to the determined impedance information.

Abstract: A key telephone system including a key service unit, a plurality of key telephone station sets which are connected via speech lines for transmission of speech signals and via data lines for transmission of data, and a device provided at the key service unit for sending a predetermined discrimination signal to a selected key telephone station set via an associated speech line, whereby the key service unit sends key telephone station set information to the plurality of key telephone station set via the data lines, and each of the plurality of key telephone station sets derives its own key telephone station set information from the key telephone station set information sent via the data lines, on the basis of the discrimination signal sent via the speech line.

Abstract: A system allowing selective connection of various types of external apparatuses to a telephone set, which system comprises a plurality of switching circuits connected to the external apparatuses and a plurality of external apparatus interface circuit having mutually different characteristics and connected through the plurality of switching circuits to the external apparatuses, wherein any one of these switching circuits is turned on and at the same time the other circuits are turned off to selectively connect one of the interface circuits to one of the external apparatuses.

Abstract: An office line interface circuit includes a DC circuit for extracting a DC signal component from the office line current, an AC circuit for extracting an AC signal component from the office line current to supply the extracted AC signal component to the receiver of a telephone set, an impedance circuit switchably connected to the office line, and a switching circuit for connecting the impedance circuit to the office line when the extracted DC signal component exceeds a predetermined level to maintain at a substantially constant value the impedance of the office line as viewed from the telephone set. With this interface circuit, the sidetone preventing circuit for the telephone system can operate satisfactorily without complicating the construction under any office line condition.

Abstract: A signal communication apparatus is used for a telephone system having a plurality of unbalanced communication paths. A feedback line of each unbalanced communication path is connected to a ground level and each unbalanced communication path including a phase reversing transformer. The phase reversing transformer produces two induced currents in the connected path if a speech signal is transmitted through another path. The induced currents are cancelled due to mutual interference.

Abstract: A loud-speaker telephone set includes a switching control circuit to attenuate the incoming signal, during transmission, and to attenuate the outgoing signal, during reception, in order to prevent feedback from the loud-speaker to the microphone. An automatic gain control circuit is added which detects at least one of the incoming signal level and the outgoing signal level and which adjusts the attenuation of both the incoming and outgoing signals so as to reduce the attenuation change between reception and transmission below 20 dB and eliminate the unpleasant sensation, to a user, of large attenuation changes.

Abstract: In a circuit for driving a latching relay for use in a telephone set, a capacitor is charged from a battery, and when the capacitor is charged to a predetermined value, the capacitor is disconnected from the battery. Thereafter the latching relay is driven by the discharge current of the capacitor. With this circuit, it is possible to prevent unnecessary consumption of the battery.

Abstract: An output voltage of a first diode deriving out an office line voltage, and an output voltage of a second diode deriving out the voltage of a back-up battery are combined and then smoothed by a smoothing capacitor. The smoothed voltage is supplied to a control circuit. A voltage limiting circuit is connected to the input side of the first limiter for limiting the upper limit of the smoothed voltage. A switch circuit is provided which is rendered conductive at the time of talking and the at the time of sending out a dial pulse for combining the office line voltage with the combined voltage. A voltage limiting circuit is also provided which is enabled only at the time of talking and at the time of sending out a dial pulse for limiting the upper limit of the combined voltage.

Abstract: A telephone apparatus having the standard ten digit keys and two special keys, and in the handset the conventional switchhook. By manual operation of the two special keys and the switchhook the apparatus can be operated in any one of a plurality of modes, at least some causing transmission of stored sequences of digits in response to entry of an abbreviated address or in causing redialing. In one mode data signals are produced and transmitted in response to not only the digit keys but also the special keys as well. A controller operates the apparatus and is connected to a dial sender which converts the data signals into a multi-frequency signal which is transmitted by a telephone network to a repeater station.

Abstract: A terminal interface device comprises in-service detector connected to a plurality of CO lines leading to a main unit in a key telephone system and also connected to a terminal unit having a CO line interface, for detecting the in-service state of the respective lines, that is, whether the CO line is currently being used by the terminal unit and for sending an in-service signal indicative of the detected in-service state to the main unit of the system, and a switch controllably operated by a switching control signal generated from the main unit on the basis of the in-service signal and a signal indicative of the state of the CO lines in the main unit to connect one of the plural lines to the terminal unit.

Abstract: A telephone apparatus which can input character/symbol data. The apparatus has a keyboard including a plurality of numeral keys each assigned to characters/symbols, a mode change key for switching numerical mode to character/symbol mode, or vice versa and a special key for executing a predetermined sequence. After the apparatus has been set to the character/symbol mode, the numeral keys assigned for the characters/symbols and the special key are operated in the predetermined sequence, thereby inputting character/symbol data. The data are applied to a electronic calculator CPU, are outputted in the form of character/symbol pattern signals from a character generator, and are displayed by a display section in the predetermined sequence.

Abstract: The display device for a telephone set is designed to be capable of storing in advance the telephone number, person's name, company name, etc. of any desired (one or more) party (subscriber) through the numeric data input means and character data input means which typically use the dial keys of the telephone set, and proper software keys, recognizing the special dial operation made by the user via the specific software keys for telephoning, checking the memory whether the data corresponding to the dialed number is stored, reading the data from the memory if stored, and displaying in the display unit preferably giving the priority to the character data showing the name, company name, etc.

Abstract: This system is a key telephone system of a type setting operating data for controlling the operations of respective key telephone sets and the entire system by using the keys of the key telephone sets. This key telephone system has a plurality of key telephone sets and a main unit, and the main unit has first and second memories for storing the operating data. The main unit takes the first mode for operating the system in accordance with the operating data of the first memory and the second mode for setting the operating data. The second memory stores the reference operating data and transfers the data into the first memory as required.

Abstract: A key telephone system is provided which comprises: a plurality of key telephones; a key service unit; a plurality of transmission paths each including a first transmission cable for transmitting a voice signal between the key telephone and key service unit, a second transmission cable for transmitting a first control signal from the key telephone to the key service unit, and a third transmission cable for transmitting a second control signal from the key service unit to the key telephone; first, second and third transformers of which the primary windings are connected to the key telephone and the secondary windings to the first, second and third transmission cables; and fourth, fifth and sixth transformers of which the primary windings are coupled with the first, second and third transmission cables, respectively, and the secondary windings to the key service unit.