Abstract: A waveform comparison and display system using a cathode ray tube, which is provided with a digital memory function for sequentially storing input signal levels in digital quantities and re-reading them out under control of desired clock pulses and with a display function for displaying on the cathode ray tube two waveforms obtained in outputs produced by high-speed switching of the input signal and an analog signal re-read out. The storing operation and the sweep operation of the cathode ray tube are controlled by a trigger signal synchronized with the input signal. The generation of the clock pulses is start-stop controlled in synchronism with the sweep. Accordingly, the two waveforms are displayed on the screen of the cathode ray tube in such a manner that they are stationary with respect to each other.

Abstract: A system for receiving a remote control signal in an automatic telephone answering device, in which the remote control signal is detected from a transmission line by the use of a remote control signal detector including a filter so that a message to the transmission line is sent out in response to the detected output of the remote control signal detector. The message from a line for sending the message to the transmission line is extracted after sufficiently attenuating the remote control signal by a directional circuit. The frequency components corresponding to the remote control signal are selected by a second filter from the message extracted, so that when the filter output of the second filter is obtained, transmission of the message to the transmission line is inhibited during the duration of the filter output of the second filter.

Abstract: An automatic telephone answering device, which sends out the contents of at least one recorded message to a calling party of a remote place upon arrival of a remote control signal from the calling party after the detection of a ringing signal sent over a communication circuit. In response to a first-received one of the remote control signal, a low-frequency signal generated from a low-frequency oscillator is recorded in a second channel developed on the same recording tape as a first channel for recording message in a forward direction for a predetermined period of time. A recording tape rewinding mechanism of the device is controlled to rewind the recording tape after completion of the recording of the low-frequency signal so that magnetic heads of the first channel and the second channel are opposite a position on the recording tape beyond the recorded position of the low-frequency signal but short of the end of a last recorded message.

Abstract: A ringing signal detector, which comprises a series diode clipper automatically biased by an input signal, a DC converter for converting the output of the series diode clipper to a DC level, a DC level detector for detecting the converted DC level to detect whether the input signal is a ringing signal or a dial pulse signal, thereby generating an output only when the input signal is the ringing signal.

Abstract: A rotary telephone dial, in which at least one shaft is fixedly planted on a base plate. A rotary member is rotatably mounted on the shaft. Another base plate is engaged with the free end of the shaft to support the shaft. One direction assembling can be performed as a result of the above structure. A finger moving compensation mechanism is provided to obtain a sufficent allowable range of finger moving. The spring retaining structure and the governor mechanism are improved to effectively reduce the number of parts and to realize simplification of the manufacturing process.

Abstract: A key telephone system, in which at least one CO line, at least one intercomm. line and control lines are arranged between a key service unit and a plurality of key telephone sets. The key service unit is provided with a scanning circuit for generating multiplexed code units indicating the connection state of each channel of said CO line and said intercomm. line in a time-division manner to scan the key telephone sets. The key service unit further includes means for transmitting the code unit to each key telephone set through said control lines. Each of the key telephone sets includes a decoder for decoding the code units thus transmitted to obtain individual indication signals indicating the states of each channel.

Abstract: A telephone set scanning type key telephone system, in which a plurality of key telephone sets are connected in parallel, to a key service unit through control lines composed of a display information line, key information line, a terminal selecting line and a clock line. Each key telephone set comprises a display memory, a key memory, a terminal coincidence circuit and a gate. The terminal coincidence circuit collates a selecting code transmitted thereto from the key service unit through the terminal selecting line and applies clock pulses transmitted thereto from the key service unit through the clock line to the gate to drive the display memory and the key memory only when the selecting code is coincident with the terminal number.

Abstract: An amplitude limiter, in which an input AC signal is applied to a first input of a differential amplifier and the output of the differential amplifier is positively fed back to a second input of the differential amplifier, so that an amplitude-limited output signal is derived from an output circuit coupled to the output terminal of the differential amplifier. A first diode is inserted in a line commonly connected to the feedback circuit and the output circuit of the differential amplifier to produce a positive periodic wave which is half-wave rectified from said input AC signal. A bias voltage set circuit is connected to the second input terminal of the differential amplifier to apply thereto a negative bias voltage to determine the negative limited level of the output of the differential amplifier. A second diode may be provided in the bias voltage set circuit in the direction of the bias current.

Abstract: A system for detecting the transmission direction of a signal on a two-say transmission line, in which a switch is inserted in the two-way transmission line while a signal detector is connected to the two-way transmission line at one side of the switch. Two signal detectors may be connected to the two-way transmission line at both sides of the switch respectively. If the switch has two selected contacts, the two signal detectors are connected to the selected contacts respectively. The switch is switched in response to the output of the signal detector or the outputs of the two signal detectors. The transmission direction of the signal on the two-way transmission line is detected in accordance with the state of the signal detector and the states of the two signal detector after the switching of the switch.

Abstract: A rotary dial device for a telephone set, in which an additional function of preventing a toll dialling is provided. In accordance with this invention, a contact is further attached to an usual dial to classify dial impulses so that when a number "1," one of numbers "2" to "9," and a number "0" are dialled, one, two and three pulses are produced respectively. The dialling function subsequent to the first dialling number "0" and the first and second dialling numbers "10" is effectively stopped by counting the classified pulses.

Abstract: A two tone generator using switching transistors in two LC resonance circuits each composed of a coil and a capacitor for producing a multifrequency signal in the form of two-tone signal by switching the value of the inductances of the coils in response to the control of push-button switches, in which only one make contact is actuated in response to the depression of each push button, so that the ON-OFF output of the contact is employed to control selected ones of switching transistors in each of the two resonance circuits for determining the oscillation frequencies of a two-tone oscillator associated with the two LC resonance circuits. The switching transistors comprises a first group of either NPN transistors or PNP transistors and a second group of NPN transistors or PNP transistors. The switching transistors are coupled with the two LC resonance circuits to switch the value of the inductance of each coil in response to the turning ON of the collector-emitter path thereof.

Abstract: A circuit for preventing impulse generation caused by operating a hook switch in a telephone set, in which the hook switch has a make contact and a break contact which are make-before-break contacts in going to the OFF-hook condition, and are break-after-make contacts in going to the ON-hook condition. A capacitor is charged through the make contact when it is closed in the OFF-hook condition. A transistor switching circuit is provided to turn ON by the charge on the capacitor so as to short-circuit between telephone line terminals of the telephone set when the break contact is closed in the ON-hook condition.

Abstract: An AC wave switching circuit in which the collector-emitter path of a switching transistor is inserted in series in the circuit loop of an AC signal to be switched. A control voltage source capable of flowing a DC current greater than a peak value of the AC signal current is connected across the base-emitter path of the switching transistor, so that the switching of the AC signal is performed by the voltage of the control voltage source without flowing any DC current in the collector-emitter path of the transistor. The collector-emitter path of another switching transistor may be connected in series or in parallel with the collector-emitter path of the first-mentioned switching transistor. At least one of a diode and a resistor may be included in the base-emitter path circuit of each switching transistor. The circuit loop may provide an output by transformer coupling or the capacitor coupling.