JPH0318385B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a branch telephone busy detection circuit used in automatic dialing devices and the like.

(Prior art) Automatic dialing devices, etc. that are used by connecting to a telephone line (office line) avoid sending invalid dials, and wait for a response from the other party before starting a call or sending a message, etc. Therefore, it has a function to prevent collision of incoming calls from the central office line and a function to detect response from the other party. Here, the central office line incoming call collision prevention function is to confirm that there is no incoming call within a predetermined time (several seconds) before dialing, and to monitor whether the polarity of the central office line reverses within that period. If there is no incoming call, the system will switch to dialing. The other party's response detection function is to check the other party's response by reversing the polarity of the central office line after dialing, and after confirming the response, a call can be started or a message can be sent.

FIG. 2 shows a circuit configuration of a detection circuit section of a conventional automatic dialing device 1 having the above-mentioned functions, where L ₁ and L ₂ are central office lines, and BT is a branch telephone. Further, the detection circuit section of the automatic dialing device 1 is
Parallel circuit of resistor R ₁ , contact h, contact p, and resistor
R ₂ and photocouplers PC _A and PC _B connected in antiparallel
It consists of a series circuit with an input circuit (light-emitting diode), a parallel circuit of a varistor VA, and this series circuit is connected between the station lines _L1 and _L2 . Note that the contact h operates in conjunction with the contact for closing the DC circuit during automatic dialing, and the contact p is for controlling the operation of the detection circuit. Although the output circuit (phototransistor) side of photo couplers PC _A and PC _B is not shown, signals indicating the on and off states of photo couplers PC _A and PC _B are extracted and connected to a microcomputer, etc. It's summery.

Therefore, prior to dialing, contact h is turned off and contact p is turned on, and the photo couplers PC _A and PC _B
(Depending on the polarity of the central office lines _L1 and _L2 , either one is activated.) is monitored for several seconds, and if there is no change, it is assumed that there is no incoming call and automatic dialing is performed. It should be noted that if the office lines L ₁ and L ₂ are disconnected, neither the photo couplers PC _A nor PC _B will operate, so dialing can be prevented from being performed in that case as well. Next, after the dial is sent out, the DC circuit is closed by the subsequent dial circuit, etc., and the voltage between the office wires L ₁ and L ₂ decreases, so the contacts h and p
Turn on both to increase the sensitivity and turn on the photocoupler.
The status of PC _A and PC _B is monitored, and if the status is reversed, it is determined that the other party has responded.

(Problems to be Solved by the Invention) The conventional circuit was configured and operated as described above, but when the branch telephone BT connected in parallel between the office lines L ₁ and L ₂ is in use. However, it has the disadvantage that the state cannot be detected, which may result in invalid dialing.
In other words, when the branch telephone BT is used, the voltage between the office lines L ₁ and L ₂ drops to the usual 48 V or below 22 V due to the DC circuit being closed, but the photo couplers PC _A and PC _B may not operate to some extent. In order to continue detecting the polarity even though it becomes stable, photocouplers PC _A and PC _B are used.
Information regarding the state of the branch telephone BT is not detected on the output circuit side of the branch telephone BT. Therefore, dialing may be performed while the branch telephone BT is in use, and there is a possibility that invalid dialing may occur.

(Object of the Invention) The present invention has been proposed in view of the above points, and its object is to be able to detect the state of a branch telephone by providing a minimum additional circuit to the conventional circuit. An object of the present invention is to provide a branch telephone busy detection circuit.

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a series circuit of two Zener diodes connected in anti-series and a first resistor, and a series circuit that is closed while the central line is closed. a parallel circuit with a first contact, a second contact that is closed when determining the polarity of the station line, a second resistor, an input circuit of two photocouplers connected in anti-parallel, and a varistor. The gist of the invention is to connect directly between the office lines and to detect signals relating to the usage status of the branch telephone and the polarity of the office line from the output circuit of the photocoupler.

(Examples) Hereinafter, the present invention will be described in detail with reference to the drawings showing examples.

FIG. 1 is a circuit configuration diagram showing one embodiment of the present invention, and shows an automatic dialing device as an example.
In the figure, automatic dialing device 1 is connected to central office lines L ₁ and L ₂
A branch telephone BT is connected in parallel to the central office lines L ₁ and L ₂ . The detection circuit section of the automatic dialing device 1 includes a parallel circuit of a series circuit of two Zener diodes ZD ₁ , ZD ₂ and a resistor R ₁ connected in reverse series, a contact h, a contact p, and a resistor R ₂ . and a photocoupler PC _A connected in antiparallel,
PC _B input circuit (light emitting diode), varistor VA
It consists of a series circuit with a parallel circuit, and this series circuit is connected between the station lines L ₁ and L ₂ . Note that the Zener diodes ZD ₁ and ZD ₂ are set to a value slightly higher than the voltage value (approximately 22 V) that drops when the branch telephone BT is used and the central office lines L ₁ and L ₂ are connected to direct current. In addition, the contact h operates in conjunction with the contact for closing the DC circuit during automatic dialing, and at this time, the DC resistance when closing the office line is connected and the voltage between the office lines decreases. If contact h remains open, photocoupler
Not enough current flows through PC _A and PC _B , making it impossible to detect polarity, so contact h is closed to increase sensitivity. Contact P is used to control the operation of the detection circuit, but normally this contact P is left open and meets the standards for DC resistance of the terminal equipment connected to the office line (1 MΩ or more when the office line is open, and when the office line is closed). 50~
300Ω), and the DC resistance at the time of break during dial pulse transmission is set to 100KΩ or more to correspond to the operating capacity of the central office exchange. On the other hand, the collectors and emitters of the phototransistors, which are the output circuits of the photocouplers PC _A and PC _B , are connected between the power supply +V and ground via resistors R _A and R _B , and the collectors and emitters of the phototransistors, which are the output circuits of the photocoupler PC A and PC _B , are connected between the power supply +V and the ground, and A signal corresponding to the on/off state of _B is extracted and sent to the microcomputer 2.
It is now entered into .

Therefore, if contact h is turned off and contact p is turned on before dialing, the branch telephone BT
is not used and there is no disconnection, a voltage of approximately 48V (48±5V) will occur between the station wires L ₁ and L ₂ , and the Zener diodes ZD ₁ and ZD ₂ will conduct and the resistances R ₁ , A current flows to the light emitting diodes, which are the input circuits of the photocouplers PC _A and PC _B , through the contact p and the resistor R ₂ depending on the polarity of the station wires L ₁ and L ₂ .
The polarities of the station lines L ₁ and L ₂ are determined from the collector voltages of the photo transistors that are the output circuits of the photo couplers PC _A and PC _B. In addition, when the branch telephone BT is used, the voltage between the office lines L ₁ and L ₂ drops to about 22V or less, so the Zener diodes ZD ₁ and ZD ₂ become non-conductive, and both photocouplers PC _A and PC _B operate. do not. Incidentally, even if the station lines L ₁ and L ₂ are disconnected, neither PC _A nor PC _B operates.

Therefore, prior to dialing, contact h is turned off and contact p is turned on, and the photocouplers PC _A and PC _B
If any of the above is confirmed to be operating, the status will be monitored for a few seconds, and if there is no change, it will be assumed that there is no incoming call and an automatic dial will be sent. Also,
If neither photocoupler PC _A nor PC _B works, the central office lines L ₁ and L ₂ are disconnected or the branch telephone BT is in use, so to prevent invalid dialing, do not send dials and wait. .

On the other hand, after the dial is sent out, the DC circuit is closed by the subsequent dial circuit, etc., and the voltage between the office lines L ₁ and L ₂ decreases, so both contacts h and p are turned on and the Zener diodes ZD ₁ and ZD ₂ , resistance R ₁
The circuit of photo coupler PC _A , PC _B is taken as shot.
The state of the device is monitored, and if the state is reversed, it is determined that the other party has responded.

(Effects of the Invention) As described above, the present invention includes a series circuit of two Zener diodes and a first resistor connected in anti-series, and a first contact that is closed while the station line is closed. A parallel circuit with a second contact that is closed when determining the polarity of the station line, a second resistor, an input circuit of two antiparallel-connected photocouplers, a varistor, and a parallel circuit are connected in series. Since it is connected between office lines and signals related to the usage status of the branch telephone and the polarity of the office line are detected from the output circuit of the photocoupler, only two Zener diodes are added compared to the conventional circuit. It is possible to detect the usage status of a branch telephone, and when applied to an automatic dialing device, etc., it is effective in preventing the occurrence of invalid dialing.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the branch telephone in-use detection circuit of the present invention, and FIG. 2 is a circuit diagram of a conventional polarity detection circuit. L ₁ , L ₂ ... central office line, BT ... branch telephone, 1 ... automatic dialing device, 2 ... microcomputer,
PC _A , PC _B ...photo coupler, ZD ₁ , ZD ₂ ...zener diode, h, p... contact, R ₁ , R ₂ , R _A , R _B
…Resistor, VA…varistor, +V…power supply.

Claims (1)

[Claims] 1. A series circuit of two Zener diodes and a first resistor connected in anti-series, a parallel circuit with a first contact that is closed when the central line is closed, and a parallel circuit that is closed when determining the polarity of the central line. A second contact, a second resistor, an input circuit of two antiparallel-connected photocouplers, and a parallel circuit of a varistor are connected in series and connected between the office lines, and a branch is formed from the output circuit of the photocoupler. A branch telephone-in-use detection circuit characterized by detecting a signal related to the telephone's usage status and the polarity of a central office line.