JPS58105684A - Party line telephone discriminating circuit - Google Patents

Abstract

PURPOSE:To constitute all detecting circuits of the titled circuit into low power circuits and to minimize the scale of the circuit, by insulating a subscriber line from a telephone exchange with a photocoupler and linearly operating the photo coupler. CONSTITUTION:Photo couplers 4 and 10 and current limiting resistors 6 and 12 are connected between primary coils 8 and 13 of a hybrid transformer 7 connected to party line telephone sets 15 and 16 at a subscriber circuit side 1 and the positive side and the negative side of an office battery 3, respectively. Each of transistors 21 and 22 in each of the couplers 4 and 10 is connected to voltage comparators 28 and 30 at the exchange side, respectively. A resistance 23 and a variable resistance 24 which determine the current-voltage conversion gain of the couplers 4 and 10 are connected to the base of each transistor 21 and 22, and resistances 25 and 26 for outputting voltage are connected to the emitter. Then, a reference voltage is added to the comparator 28 and the output voltage of the coupler 4 is compared with the reference voltage, and the outputs of the couplers 4 and 10 are compared with each other at the comparator 10, and thus, it is automatically discriminated which subscriber makes the call or uses the line. Thus the scale of the circuit is minimized.

Description

[Detailed Description of the Invention] [Description of the Technical Field] The present invention relates to a communal telephone service in which one subscriber trunk line is shared by a plurality of subscribers. This invention relates to a communal telephone identification circuit that automatically identifies

[Description of prior art]

When providing a communal telephone service, it is necessary to determine which subscriber among the plurality of subscribers receiving the communal telephone service has made a call or is currently using the service. In stand-alone telephone services where one telephone is connected to one subscriber trunk line, the state of the subscriber who is making a call or in use can be ascertained by monitoring the telephone current in the subscriber trunk line.
In a communal telephone service in which a plurality of telephones are connected to a single subscriber trunk line, it is not possible to determine which of the communal subscribers is making a call or in use by simply monitoring the communication current of the subscriber trunk line.

Conventionally, when setting up a communal telephone service, when one telephone is taken off the hook (hereinafter referred to as "off-hook"), the telephone circuit is grounded with a resistance value that does not affect the voice signal. I'm trying to connect. As a result, the station is configured to be able to determine whether a telephone that is connected to the ground or a telephone that is not connected to the ground is used.

That is, the subscriber trunk line and the telephone circuit are used in a state where they are suspended from the ground. When the subscriber is off-hook in this state, a strong communication current flows through the subscriber's trunk line and B@KFi. However, when a telephone that is connected to the ground goes off-hook, the current on the subscriber relay line side (1M side) connected to the ground on the positive side of the nine batteries decreases, and conversely, the current on the subscriber relay line side (1M side) on the negative side of the assembled battery decreases. The current on the trunk line side (Ball) increases.When the talking currents of the AI/a and B lines are equal, the telephone that is not connected to the ground is in an off-hook state,
When the communication currents are different, it can be determined that the telephone connected to the ground is in an off-hook state.

A conventional community telephone identification circuit employs a method of monitoring the terminal voltage of the telephone current limiting resistor, instead of directly monitoring the communication current of the mu line and B@.

However, one of the current limiting resistors is connected to the positive terminal IN of the assembled battery.
One terminal is connected to (ground II) and the other terminal is connected to the negative electrode side, so there is a large potential difference between both detection terminals.

When the communication current increases, the detection voltage on the Mu line side decreases and the detection voltage on the B11I side increases, so the Bi line side and Bi! In order to detect the difference in the communication current of III, it is necessary to completely reverse the direction in which one of the detection voltages is used.

As described above, the conventional community telephone identification circuit requires the use of high-voltage active elements, requires a voltage reversal circuit, and has the disadvantage of increasing the circuit scale.

[Purpose of the invention]

The present invention improves on this point by using a 7-coupler to insulate the subscriber circuit and the exchange and operating it linearly, thereby making it possible to reduce the circuit size and to make it possible to reduce the cost of common telephones. The purpose is to provide an identification circuit.

[Summary of the invention]

In the present invention, the diode side of a photocoupler is inserted in series with each of two current limiting resistors of a current supply circuit that supplies current to a subscriber telephone, and the current flowing to the mu wire side and the B wire side of the subscriber circuit is is converted into a voltage on each transistor side of the photocoupler to provide insulation between the subscriber circuit and the inside of the exchange. The photocoupler output on the B line side is input to one input terminal of the first voltage comparator, and the other input terminal Ka reference voltage of the same comparator is connected. When it is detected that one of the subscribers is off-hook, the photocoupler output on the A line side is input to the second voltage comparator, and the other input terminal of the comparator is connected to the BIIj! A voltage obtained by lowering the output of the side photocoupler by a certain voltage is input, and the output of this second voltage comparator is used to detect the call or usage status of a telephone with a grounding circuit of a public telephone subscriber. It is characterized by

[Explanation based on examples]

An embodiment of the present invention will be described based on the drawings.

FIG. 1 is a diagram showing the main circuit configuration of a first embodiment of the present invention. FIG. 1 shows a case where there are two communal telephones. In FIG. 1, 1 indicates the subscriber circuit side and the 2Fi exchange side, respectively.

A diode 5 in a photocoupler 4 is connected to the positive electrode side of the assembled battery 3.
Seven nodes are connected. A telephone current limiting resistor 6 is connected to the cathode of this diode 50. This telephone current limiting resistor 6 is connected to the primary coil 8 of the hybrid transformer 7. AJi is connected to this secondary coil 8. Further, the cathode of a diode 11 in a photocoupler 10 is connected to the negative electrode side of the assembled battery 3. A telephone current limiting resistor 12 is connected to the anode of this diode 11. This telephone current limiting resistor 12 is connected to the primary coil 13 of the hybrid transformer 7. This negative side coil 13 has B+
II-bX connected. Community telephones 15 and 16 are connected between the mu wires and "ii, respectively. A bypass resistor 17 is connected to this community telephone 15, and the other end of this bypass resistor 17 is grounded. In other words, the telephone A capacitor 18 is connected between the current limiting resistors 6 and 12. r#i indicates the DC resistance value of the subscriber trunk line.

Further, a resistor 23 and a variable resistor 24 are connected to the transistor 21 in the photocoupler 4 and the transistor 22 in the photocoupler 1O, respectively, for determining the current-voltage conversion gain of the photocouplers 4 and 1o. ing. Further, resistors 25 and 26 for voltage output are connected to the emitters of the transistors 21 and 22, respectively.

The emitter of this transistor 21 is connected to the positive phase input terminal of a voltage comparator 28 and also to the anode of a diode 29. A reference voltage is connected to the negative phase input terminal of this voltage comparator 28. transistor 2
The emitter of voltage comparator 3o is connected to the positive phase input terminal of voltage comparator 3o. The diode 290 cand is connected to the negative phase input terminal of the voltage comparator 3o. Also the first
In the figure, a 31#i diode is connected to the negative power supply through a high resistance value resistor.

Now, when the shared telephone 16 is off-hook, the telephone current limiting resistance 6.12, the subscriber trunk line resistance (r+r),
A communication current determined by the telephone's internal resistance value and the station power supply voltage flows. At this time, the currents flowing through the photocoupler 4 and the diode 5.111I of IO become equal. Transistor 21 of this telephone RFi photocoupler 4.10
．． The voltage is converted on the 22 side and the photocoupler outputs v1, V2
is obtained. This photocoupler output V is given to the positive phase input terminal of the U voltage comparator 28, but the negative phase input terminal is given the nine reference voltage determined by the lower limit of the talking current when the telephone is off-hook. When the telephone 16 goes off-hook, the output of the voltage comparator 28 becomes low level. Note that it is possible to output a high level by a circuit connected to the next stage of this output type 1IIFi.

Moreover, at this time, if the photocoupler output v2 is adjusted by the variable resistor 24 so that it is equal to the photocoupler output v1, the negative phase input terminal of the voltage comparator 30 to which this photocoupler output v2 is given has 7 photocoupler outputs. When a voltage lower than the output v1 by the desired direction voltage of the diode 29 is applied, the output of the voltage comparator 30 becomes high level.

In this way, when the first cooperative talkie 16 goes off-hook, the output of the voltage comparator 28 becomes low level, and the output of the voltage comparator 30 becomes low level.
The output becomes high level. Therefore, the off-hook state is detected by the voltage comparator 28, and it is determined from the output of the voltage comparator 30 that the communal telephone 16 is being used.

Next, a case where the communal telephone 15 goes off-hook will be explained. The circuit of the communal telephone 15 is connected to the ground by a bypass resistor 17 inside the telephone to such an extent that the voice signal is not affected. When the communal telephone 15 goes off-hook, current flows into this circuit from the ground, the current flowing in the B wire of the subscriber trunk increases, and the current in the Mu wire decreases. As a result, the photocoupler output v1 increases and the photocoupler output cuff 2Fi decreases, but when the difference in potential between these two outputs becomes greater than the forward voltage of the diode 29, the output of the voltage comparator 30 is inverted and becomes a low level. Become.

When the utility telephone 15 is taken off-hook, the voltage comparator 28
The output becomes low level in the same manner as in the case of the community telephone 16. Also, the output of the voltage comparator 30 becomes a low level. Therefore, the off-hook state of communal telephone 15 can be detected by the output of voltage comparator 28, and it can be determined from the output of voltage comparator 30 that the communal telephone 15 is off-hook.

Here, the output of the voltage comparator 30 is active low, meaning that it is low level, but it can be active high if an inverting circuit is provided at the next stage.

FIG. 2 is a circuit diagram of the gI section according to the second embodiment of the present invention.

In the figure, 02 and O5 are direct current blocking capacitors/suzureri, and L is a letter coil.

The other points are similar to the first embodiment shown in FIG. 1, and the same reference numerals indicate the same parts.

Although the circuit for reducing the influence of the voice current flowing to the input side of this second implementation IPIIFi photocoupler 4.100 is different, the detection of the voice current of the public phone can be similarly understood, so detailed explanation will be omitted. do.

〔Effect of the invention〕

As described above, according to the present invention, the subscriber trunk line side and the calling or in-use detection circuit side are separated and insulated by a photocoupler, and all the detection circuits can be configured as low-voltage circuits. Furthermore, it has the advantage of being able to use low-power resistors, thereby reducing the number of circuit elements and making it more economical.

[Brief explanation of the drawing]

@1 Figure is a main circuit configuration diagram of the first embodiment of the present invention. FIG. 2 is a circuit diagram of a main part of a second embodiment of the present invention. l...Subscriber circuit positive, 2...exchange side, 3...station battery, 4, lO...7 automatic coupler, 7...hybrid transformer, 15.16...community telephone, 28. 3
0...Voltage comparator. Full 1 Figure

Claims (1)

[Claims] (1) Depending on whether the communication current flowing through the pair of subscriber lines is balanced with no leakage to the earth, or unbalanced due to leakage with the earth, the connection is made to the pair of subscriber lines. a community telephone identification circuit configured to detect which of two community telephones is in an off-hook state;
Two 7-channel automatic couplers are configured such that an input side diode is connected to each communication current path of the pair of subscriber lines, and a current corresponding to the magnitude of this communication current is generated in the output side transistor; A first comparison circuit that compares one output voltage of the photocoupler with a reference voltage, and a second comparison circuit that compares the output voltage with the other output voltage of the photocoupler. Community telephone identification circuit.