Abstract: An office line can be held by a holding path including a thyristor in response to operation of a manual operating hold switch during a call by a telephone set in a direct connection telephone system. A voltage drop on the office line due to an off-condition of any one of the telephone sets in the system caused thereafter can be detected by a capacitor and the thyristor is thereby turned off to release the office line holding condition. The office line holding condition is indicated by a light emission diode, and a hold sound signal is sent out to the office line during the office line holding condition.

Abstract: A key telephone system comprising a main equipment and a plurality of key telephones connected to the main equipment and comprising elements for operatively connecting another similar key telephone system. The main equipment in the key telephone system comprises a system call transmitting interface and a system call receiving interface which are connected through connecting lines to a system call receiving interface and a system call transmitting interface in a main equipment of another similar key telephone system, respectively. Each key telephone in both systems comprises an additional key for selecting the system call transmitting interface of its own main equipment. By use of the additional key in one key telephone, a speech path can be established between the one key telephone and another key telephone in another key telephone system through both main equipments and the connecting line.

Abstract: In a receiver receiving a time-division multiplex signal of a plurality of channels with each channel signal having a start signal part, an address signal, an error detecting code signal part, an information signal part, and a blank interval arranged in this order, a channel detecting circuit for detecting the channel signal assigned to the receiver is provided with a blank interval detecting circuit in addition to an address detecting circuit, in order to avoid an erroneous detection of the address detection circuit at a start condition of the receiver. Application of the multiplex signal to the address detecting circuit is prevented until the blank interval detection circuit initially detects one blank interval of the multiplex signal. At a start condition of the receiver, application of the multiplex signal to the address detecting circuit starts not at an intermediate time position in one channel signal but at the start signal part of a subsequent channel signal.

Abstract: Data signals in each channel over a plurality of sequential frames of a time division multiplex signal as received are temporarily stored in each channel memory, and are read out together from the channel memory at a given time to form a combined data signal. A start bit signal, a stop bit signal and an address signal corresponding to the channel are added to the combined data signal to form a start-stop synchronous fresh channel signal. The resultant N fresh channels are sequentially sent out to a common transmission line as a fresh time division multiplex signal with a reduced redundancy. A plurality of sub-equipments are connected to the common transmission line and take into the data signals of a channel assigned thereto according to the address data signal.

Abstract: A reproducer for reproducing a binary digital data signal from a signal received at a receiver side. A pulse train is detected from the received signal at a pulse detector. Each pulse in the pulse train sets a first D-type flip-flop, which is, in turn, cleared by a clear pulse produced by a second D-type flip-flop in response to a clock pulse just after the first D-type flip-flop is set. The output of the first D-type flip-flop is applied to a data input terminal of a third D-type flip-flop and is taken into the third D-type flip-flop by the same clock pulse. The clock pulse repetition frequency is synchronous with the binary digital data signal. Thus, the reproduced binary digital data signal is obtained on an output of the third D-type flip-flop.

Abstract: A circuit for obtaining a clock pulse synchronized to a data signal received at a receiving side, which has a plurality of clock pulses having a repetition frequency equal to that of a clock in a transmission side but being different from one another in phase. On reception of the first data bit of the received data signal, the timing of the first data bit is detected at a detection circuit in reference to the plurality of clock pulses. According to the detected timing, a selector circuit selects one of the plurality of clock pulses with a predetermined constant phase difference from the received data signal.The detection circuit comprises D-type flip-flops, and the selector circuit comprises AND gates.

Abstract: A pulse data signal and a DC power signal are transmitted over a pair of transmission lines interconnecting a main operating unit and telephone sets in a key telephone system. The main operating unit and each telephone set includes a pulse transmitting and receiving circuit and a transformer having a core and first and second pairs of opposed windings. The individual windings in the first winding pair are connected to input and output terminals, respectively, of the pulse transmitting and receiving circuit. One terminal of each individual winding in the second winding pair is connected to a transmission line. A DC power source is connected across the other winding terminals in the second winding pair in the main operating unit. In the telephone set, the other winding terminals in the second winding pair are connected with a power supply circuit which provides power to various component circuits in the telephone set.

Abstract: An equipment for interchanging time slots of time division multiplex signals on a plurality of highways. Data bit signals in respective time slots incoming on respective highways are one-bit delayed at one after another of the highways by shift registers of different stages and are converted into parallel data at respective serial-parallel converters. The parallel data of respective time slots are read out from the converters sequentially and are stored in different addresses in a speech memory over the entire frame of each highway in response to the sequential clock pulses. The data stored in the speech memory are read out at every intervals of adjacent clock pulses and are distributed to respective parallel-serial converters connected to different highways in response to the time intervals of the clock pulses. The addresses of the speech memory to be accessed in the read-out operations are obtained from an address control memory in which the address data are written by a central control unit.

Abstract: A key switch device having a key being depressable to allow a movable contact to come into contact with a pair of fixed contacts. The key is elastically supported in an opening of a housing plate and is prevented from slipping out of the opening by engagement with the key and the housing plate. The housing plate has a plurality of guide grooves formed in the inner surface of the opening in parallel with a center axis of the opening. A plurality of guide projections are formed on the lower side of the key and are slidably fitted into the guide grooves, respectively. The key can be smoothly and straightly moved along the center axis of the opening by a force applied to any point on the upper surface of the key without being inclined from the center axis.

Abstract: An automatic telephone hold releasing circuit for a plurality of telephone sets connected in parallel across a pair of wires of a subscriber's office line, which can automatically release a call placed on hold at one of the telephone sets even when the particular telephone set is on hold with its handset placed in the on-hook position. The circuit comprises means for detecting a voltage drop occurring in the voice-circuit when the handset of a telephone set other than that with which the call has been initially answered is unhooked, means for comparing the dropped voltage with a voltage present when the call was put on hold, and means responsive to an output of said comparing means for deenergizing a relay to open its contacts in response to the voltage drop and automatically release the initially answered telephone set.

Abstract: A ringing signal detection circuit for a subscriber's apparatus which is connected to a telephone office line together with an attached telephone set. An incoming signal on the telephone line is converted to a pulse signal with a repetition frequency twice the incoming signal by a full-wave rectifier and a differentiating circuit. The pulse signal is applied to a retriggerable mono-stable multivibrator through a photo-coupler and an inverter. The time period of a metastable state of the multivibrator by one trigger pulse is selected to be longer than the break period in the dial pulse signal but longer than a half cycle of the ringing signal. Therefore, the multivibrator is maintained at the high level for a longer time period at a time when the incoming signal is the ringing signal than the time when the incoming signal is the dial pulse signal.

Abstract: Telephone apparatus including a main unit and a plurality of loudspeaker type key telephone sets, in which a pair of office line call wires to be used solely for an office line call, a pair of audio signal wires to be used for calling and talking with a loudspeaker and a pair of data wires to be used for time-sharing transmission of control data extend from the main unit. The respective loudspeaker key telephone sets all connect in parallel to these three pairs of wires. A neutral potential point of the audio signal wire pair and a neutral potential point of the data wire pair are coupled, on the main unit side, to a D.C. power supply via a D.C. network and to loudspeaker drive systems connected to the audio signal wire pair via an A.C. network. The neutral potential points on the button-switch telephone set side connect to a D.C. constant voltage circuit in each telephone set via a D.C. network and to a talking network in the telephone set via a transfer switch.

Abstract: A key switch device having a plurality of keys and a plurality of light emission diode tips for indicating the keys operated, respectively. The diode tips are mounted and electrically connected to metal patterns formed on the same surface of a printed circuit on which fixed contact pairs are formed. In order to cover the diode tips, a transparent plate is overlaid on the printed circuit board and has lamp cover portions. The transparent plate is also provided with small upwardly opening funnel shaped slits at positions between adjacent lamp cover portions, whereby light from one light emission diode is prevented from leaking to a lamp cover corresponding to the adjacent light emission diode.

Abstract: An electronic key telephone set in an electronic key telephone system which is connected to the office line during the power failure by a power failure detecting relay in the key service unit having a common selection signal sender is provided with a circuit for detecting power failure to the key telephone system, additional contacts to respective keys of the key dial and a selection signal generator coupled with the additional contacts. The selection signal generator is connected to the voice signal pair line by a transistor which is turned on by a signal from the power failure detecting circuit during the power failure, and receives a D.C. power on the office line to be operable, so that a call may be generated from the key telephone set even during the power failure to the key telephone system. The signal from the power failure detecting circuit is fed to the transistor through a photo-coupler element.