JPH11146058A - Illegal speech prevention device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a speech of a general telephone set illegally in branch connection to a telephone line to which public telephone sets are connected. SOLUTION: A voltage of lines L1, L2 closed as a loop based on an off-hook operation of a public telephone set is detected and when it is 40 V or below, a transistor(TR) Q1 is turned off to open a DC loop of the lines L1, L2, and in the case that the line voltage after opening the DC loop is 40 V or below, it is judged that a general telephone set 100 is busy and an anti-parallel circuit 12 is used to short-circuit the lines L1, L2. Upon the receipt of a PB signal by a PB receiver during off-hook of the public telephone set, it is judged that the general telephone set makes dialing, the lines L1, L2 are similarly shortcircuited.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an unauthorized call preventing device for preventing a call of a telephone illegally connected to a telephone line to which a public telephone is connected.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing an example of a conventional public telephone. In FIG. 4, this public telephone is connected to a telephone line (hereinafter, line) L1 and L2, to which a diode bridge (DB) 1 is connected, and to an output side of the diode bridge 1, an incoming signal for detecting an incoming signal arriving at the lines L1 and L2. The detection circuit 2 is connected. A buzzer (B
Z) 3 is connected and rings when an incoming call arrives. Line L1,
A hook switch HS1 is connected to L2, and its contact is closed by off-hook to close the DC loop of lines L1 and L2. The diode bridge 4 converts voltages (L1; 0V (ground potential), L2; -48V) of the lines L1 and L2, which are DC-closed by the hook switch HS1, into a predetermined DC voltage. The DC voltage is applied to a power supply circuit 5 via a transistor Q1 for forcibly disconnecting the line, and is converted to a predetermined voltage V by the power supply circuit 5, and the control circuit 7, the dial circuit 8, the display unit 9, the operation unit 10 , And the coin processing unit 11.

[0003] When a call is made using such a public telephone, the user goes off-hook, inserts a coin, and operates a dial key of the operation unit 10 to dial the other party's telephone number, as is well known. Then, the operation dial number is detected by the control circuit 7 and sent to the dial circuit 8, and as a result, the dial circuit 8 outputs the line L as a dial signal.
1 and L2. As a result, the other party is called. Here, when the other party responds, the control circuit 7 controls the coin processing unit 11 to store one charge from the inserted coins as a call charge. While the call is continuing, the control circuit 7
Each time a billing signal is received by a billing signal receiving circuit (not shown) or every predetermined time by autonomous billing, a coin for one bill is stored from coins inserted, and when the balance is exhausted, the transistor Q1 is turned off and the line L1, L2 is forcibly disconnected to end the call.

As shown in FIG. 4, a general telephone 100 is connected to lines L1 and L2 to which such public telephones are connected.
Is connected, and the general telephone 100 dials a pay number to make a free call. For this reason,
Conventionally, such an illegal call is prevented by a branch call preventing device as disclosed in, for example, Japanese Patent Publication No. 7-52897.

That is, in the above-mentioned branch call preventing device, when the general telephone 100 connected to the lines L1 and L2 goes off-hook to make a call, the line voltage drops. Therefore, the intercept circuit 50 is provided on the public telephone side, and the intercept circuit 50 is provided. The circuit 50 detects a drop in the line voltage and transmits an interfering sound to the line side. Thereby, the general telephone 100
Even if the MF dial signal is sent from the side, it is not recognized as a dial signal by the exchange, and as a result, the ordinary telephone 100
Dialing is blocked. When the intercept circuit 50 detects a decrease in the line voltage, the lines L1 and L2 are short-circuited by a capacitor, and
This prevents transmission of the MF dial signal sent from the 0 side to the exchange side. Further, when the intercept circuit 50 detects a decrease in the line voltage, a DC current of a certain value or more is supplied to the line, and the dial pulse transmitted from the general telephone set 100 to the exchange is invalidated.

[0006]

However, in the above-described apparatus for preventing a branch call, if an off-hook operation is performed to make a call using a public telephone, the function of the intercept circuit stops. For this reason, there is a disadvantage that even if a public telephone is off-hook and a general telephone connected to the same line is off-hook and dialing, dialing is permitted, and free dialing using a general telephone with a pay number dial is allowed. There is a problem that calls can be made. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to prevent an illegal call by a general telephone after a public telephone is off-hook.

[0007]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a DC loop opening means for opening a DC loop of a closed line based on a capture operation of a public telephone, and a DC loop opening means. And line short-circuiting means for short-circuiting the line when the line voltage detected by the detecting means is lower than a predetermined voltage. Further, a receiving means for receiving a dial signal arriving on a line with a DC loop closed based on a capturing operation of a public telephone is provided, and the DC loop opening means opens the line when the dial signal is received by the receiving means. It is.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a first embodiment of a public telephone to which the present invention is applied. In this figure, a diode bridge (DB) 1 is connected to lines L1 and L2, and an incoming call detection circuit 2 for detecting incoming signals arriving at lines L1 and L2 is connected to the output side of diode bridge 1 in this public telephone. You. A buzzer (BZ) 3 is connected to the incoming call detection circuit 2 and sounds when an incoming call is received.

[0009] A hook switch HS1 is connected to the lines L1 and L2, and its contacts are closed by off-hook to close the DC loop of the lines L1 and L2. The diode bridge 4 outputs voltages (L1; 0 V (ground potential), L2; -48 V) of the lines L1 and L2, which are DC-closed by the hook switch HS1, to a subsequent circuit as a DC voltage. The DC voltage is supplied to a power supply circuit 5 via a transistor Q1 for forcibly disconnecting the line, and is converted into a predetermined voltage V by the power supply circuit 5, and the control circuit 7, the dial circuit 8, the display unit 9, the operation unit 10, The power is supplied to each of the coin processing units 11.

When a call is made using the public telephone constructed as described above, the user goes off-hook, inserts a coin, and operates a dial key of the operation unit 10 to dial the other party's telephone number, as is well known. Then, the operated dial number is detected by the control circuit 7 and sent to the dial circuit 8, and as a result, the dial circuit 8 sends it to the lines L1 and L2 as a dial signal. As a result, the other party is called. Here, when the other party responds and a billing signal arrives at the lines L1 and L2 from an exchange (not shown), the billing signal is received by a billing signal receiving circuit (not shown) and output to the control circuit 7. Then, the control circuit 7 controls the coin processing unit 11 to store one charge from the inserted coins as a call charge. While the call is in progress, every time a billing signal arrives, one coin is charged from the inserted coins as a call charge, and when the balance is exhausted, the transistor Q1 is turned off and the lines L1 and L2 are forcibly disconnected to terminate the call. Terminate.

As shown in FIG. 4, a general telephone 10 is connected to lines L1 and L2 to which such public telephones are connected.
0 is connected, and an unauthorized call by the general telephone 100 may be performed. For this reason, an anti-parallel circuit 12 is connected between the lines L1 and L2, and the anti-parallel circuit 12 is operated to prevent unauthorized calls of the general telephone set 100. FIG. 2 is a circuit diagram showing a detailed configuration of the anti-parallel circuit 12. The circuit 12 includes a diode bridge (DB) 21 that is connected to the lines L1 and L2 and outputs the voltages of the lines L1 and L2 to a subsequent circuit as a DC voltage, a battery BAT, a zener diode ZD1, and a capacitor C1.
The power supply circuit 22 of the circuit 12 including diodes D1 to D3 and resistors R1 to R3, and AND gates IC1 to IC
3, transistors Q2 to Q5, photocouplers pc1 to p
c4, diodes D4, D5, Zener diode ZD
2, ZD3, capacitors C2 and C3 and resistors R4 to R1
9 is provided for the main circuit 12 of the present circuit 12.

When the line is closed due to the off-hook of the public telephone, the voltage generated by the line current OFH flowing through the resistor R1 and the diode D1 is added to the voltage of the battery BAT and output as a voltage VBT to the main circuit. Is done. When the public telephone is on-hook, the voltage generated by the current ONF flowing through the resistor R2 and the diode D2 is added to the voltage of the battery BAT and output as the voltage VBT. Also,
When the line is short-circuited by the anti-parallel circuit 12 described later, the voltage of the battery BAT is output as the voltage VBT.

Next, the operation of the anti-parallel circuit 12 configured as described above will be described. First, when the public telephone is off-hook, the DC loops of the lines L1 and L2 are closed by closing the hook switch HS1 as described above, and the control circuit 7 is supplied with power and activated. In addition, due to this line connection, the output voltage of the diode bridge 21 which constantly outputs a voltage of approximately 48 V becomes 40 V or less. When the line voltage falls below 40V, the Zener diode Z
The line current Id does not flow through D2, so that the transistor Q3 changes from on to off.

When the transistor Q3 turns off, the output of the AND gate IC2 changes from "L" to "H" level,
As a result, the transistor Q5 is turned on. on the other hand,
When activated, the control circuit 7 outputs a drive signal a to the photocoupler pc2 to turn on the photocoupler pc2 in order to detect the states of the lines L1 and L2. In this case, the transistor Q connected in series with the photocoupler pc2
5 are on, the photocoupler pc4 connected in series to them is also on, and therefore the photocoupler pc
4 outputs an “L” level detection signal b to the control circuit 7 side. When inputting the "L" level detection signal b, the control circuit 7 recognizes that the voltages of the lines L1 and L2 have dropped.

In this case, the control circuit 7 cannot determine whether only the public telephone is off-hook and the line voltage is lowered, or whether the public telephone and the general telephone 100 are both off-hook and the line voltage is lowered. Therefore, the line forced disconnection transistor Q1 shown in FIG. 1 is turned off to open the DC loop of the lines L1 and L2 which are closed by themselves. Then, in order to detect the states of the lines L1 and L2, the drive signal a is similarly output to the photocoupler pc2 and the photocoupler p2 is output.
Turn on c2. Here, if the ordinary telephone 100 is off-hook, the line voltage has dropped because the DC loops of the lines L1 and L2 are closed, and the line current Id still does not flow. The transistor Q5 is turned on.

Accordingly, the photocouplers pc2 and pc4
Is turned on, the "L" level detection signal b is transmitted to the control circuit 7. Then, the control circuit 7 determines that the lines L1 and L2 are being used by the general telephone 100, and outputs a drive signal c to the photocoupler pc1. As a result, the photocoupler pc1 is turned on, so that the transistor Q2 connected thereto is also turned on, and the output terminal of the diode bridge 21 is short-circuited. As a result, the lines L1 and L2 are short-circuited. At this time, even if the general telephone 100 attempts to make a dial call, the dial signal is not transmitted to the exchange. Therefore, it is possible to prevent an unauthorized call of the general telephone 100 connected in parallel to the lines L1 and L2.

Note that the general telephone 100 is connected to the lines L1 and L2.
Is not connected, or is connected but not used, the line forced disconnect transistor Q1
Is turned off to open the DC loops of the lines L1 and L2, the line voltage is approximately 48 V, and therefore the line current Id
Flows. In this case, since the transistor Q3 is on, the transistor Q5 is off. At this time, even if the control circuit 7 outputs the drive signal a to the photocoupler pc2, the photocoupler pc2 does not turn on, and therefore the photocoupler pc4 does not turn on.
The level detection signal b is transmitted. The control circuit 7
When the "H" level detection signal b is input, the lines L1, L2
It is determined that the voltage has not dropped, and the line forced disconnection transistor Q1 is turned on again. Thereafter, the process returns to the normal process such as the dial transmission process based on the dial operation of the operation unit 10.

When the public telephone is on-hook and the general telephone 100 is off-hook to make a dial call, the line voltage is similarly reduced to 40 V or less, so that the line current Id does not flow and the transistor Q3 is turned off. When the transistor Q3 is turned off, the output of the AND gate IC1 changes from the "L" level to the "H" level, and one input of the AND gate IC3 connected thereto maintains the "H" level for a certain time. In this case, since the public telephone is in the on-hook state and the contact of the hook switch HS3 is open, the other input of the AND gate IC3 is at "H" level, so that the output of the AND gate IC3 is at "H" level. Become. This turns on transistor Q4,
The photocoupler pc3 connected in series with the transistor Q4 is also turned on to supply power from a power supply unit (not shown) to the control circuit 7 to activate the control circuit 7.

When the control circuit 7 is activated, the lines L1, L
In order to detect the state 2, the drive signal a is similarly output to the photocoupler pc2 to turn on the photocoupler pc2. In this case, lines L1, L2
Since the DC loop is closed, the line voltage has dropped, so that the line current Id does not flow and the transistor Q3
Is turned off, the transistor Q5 is turned on. Therefore, the photocoupler p connected in series with this
The “L” level detection signal b is transmitted to the control circuit 7 by turning on c2 and pc4. In this case, the control circuit 7 determines that the lines L1 and L2 are being used by the ordinary telephone 100 and outputs a drive signal c to the photocoupler pc1.
As a result, the photocoupler pc1 is turned on, so that the transistor Q2 connected thereto is also turned on, and the output terminal of the diode bridge 21 is short-circuited. As a result, the line L1,
L2 is in a short-circuit state, and illegal telephone call of the general telephone 100 can be prevented.

FIG. 3 is a block diagram showing a second embodiment of the present invention. Some public telephones turn off the transistor Q1 and forcibly disconnect the lines L1 and L2 when the non-operation state continues for a predetermined time (for example, 30 seconds) after the off-hook. Even if the lines L1 and L2 are forcibly disconnected and the lines L1 and L2 are captured again, the lines L1 and L2 are forcibly disconnected again if the non-operation state continues for a predetermined time. In such a case, it is conceivable that dialing is performed by the general telephone 100 during off-hook to the first forced disconnection of the public telephone or between the first forcible disconnection and the next forced disconnection, thereby enabling a free call. For this reason, in the second embodiment, the above-described anti-parallel circuit 12 is provided, and a general telephone is used by using a PB receiver 13 previously provided in the public telephone in order to perform communication with a center (not shown). This is to prevent 100 illegal calls. That is, when the public telephone goes off-hook and closes the DC loop of the lines L1 and L2, power is supplied to the PB receiver 13 in addition to the control circuit 7 and the like. When the control circuit 7 is powered on and activated, the PB receiver 13
To the operating state.

Here, when the off-hook operation and the dial operation are performed on the general telephone 100 side, the dial signal is received by the PB receiver 13 and transmitted to the control circuit 7. In this case, the control circuit 7 turns off the line forced disconnecting transistor Q1 and opens the DC loop of the lines L1 and L2 which are closed by itself. Then, a drive signal a is output to the photocoupler pc2 of the anti-parallel circuit 12 shown in FIG. 2 to turn on the photocoupler pc2. Here, if the general telephone 100 is off-hook, the lines L1, L2
Is closed, the line voltage is reduced, and the line current Id does not flow.
By turning off 3, transistor Q5 is similarly turned on.

For this reason, the photocouplers pc2 and pc4
Is turned on, the "L" level detection signal b is transmitted to the control circuit 7. When the control circuit 7 receives the "L" level detection signal b, it determines that the general telephone set 100 connected to the lines L1 and L2 has made a dial call to make an illegal call, and sends the drive signal c to the photocoupler pc1. Output. As a result, the photocoupler pc1 is turned on, the transistor Q2 connected thereto is also turned on, and the diode bridge 2 is turned on.
1 is short-circuited. As a result, the lines L1 and L2 are short-circuited. At this time, even if the general telephone 100 attempts to continue dialing, the dial signal is not transmitted to the exchange. Therefore, it is possible to prevent an unauthorized call based on dialing of the general telephone 100 connected in parallel to the lines L1 and L2.

After the control circuit 7 turns on the photocoupler pc1 and short-circuits the lines L1 and L2, the photocoupler pc1 is turned off and the lines L1 and L2
The short circuit between them is released, and a drop in line voltage due to the off-hook of the general telephone set 100 is detected. When it is detected that the line voltage is still low, the ordinary telephone 100
Is determined to be continuing, the photocoupler pc1 is turned on again to short-circuit the lines L1 and L2. Such an operation of the control circuit 7 is repeatedly performed at regular intervals until the line voltage is restored to the normal voltage. Then, when the line voltage returns to the normal voltage, the control circuit 7 turns off the photocoupler pc1 to release the short circuit between the lines L1 and L2, and turns on the line forced disconnection transistor Q1 to turn on the lines L1 and L2. A restoration process for closing the DC loop again is performed. Thereafter, the control circuit 7 detects a dial key operation of the operation unit 10 and shifts to a dial transmission process for transmitting a dial signal to the lines L1 and L2. In the present embodiment, an example is described in which the anti-parallel circuit 12 is built in a public telephone, but the anti-parallel circuit 12 may be provided outside the public telephone.

[0024]

As described above, according to the present invention, a DC loop opening means for opening a DC loop of a closed line based on a capture operation of a public telephone, and a DC loop after the DC loop is opened by the DC loop opening means. A detecting means for detecting the line voltage and a line shorting means for shorting the line when the voltage of the line detected by the detecting means is lower than a predetermined voltage are provided, so that the line is connected in parallel to the line to which the public telephone is connected. It is possible to accurately prevent a fraud such as connecting a general telephone to a public telephone and then off-hook the general telephone and dialing a pay number to make a free call. Further, receiving means for receiving a dial signal arriving on the line with the DC loop closed based on the capturing operation of the public telephone is provided, and when the dial signal is received by the receiving means, the line is opened and detected at this time. Line is short-circuited when the voltage of the line is lower than a predetermined voltage, so if a dial call is made from a general telephone connected in parallel to the line, the line is short-circuited immediately and the subsequent dial signal is sent. It is possible to prevent the unauthorized telephone call by the general telephone.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a public telephone to which the present invention is applied.

FIG. 2 is a circuit diagram of an anti-parallel circuit provided in the public telephone.

FIG. 3 is a block diagram showing a second embodiment of the public telephone.

FIG. 4 is a diagram showing an example of a fraudulent call in a conventional public telephone.

[Explanation of symbols]

1, 4, 21 ... diode bridge, 6 ... communication circuit, 7
... Control circuit, 12: Anti-parallel circuit, 13: PB receiver, 100: General telephone, Q1 to Q5: Transistor, L1, L2: Line (telephone line).

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Junichi Muroi 2-3-2 Shimomeguro, Meguro-ku, Tokyo Inside Tamura Electric Works, Ltd. (72) Inventor Osamu 2-3-3 Shimomeguro, Meguro-ku, Tokyo No. Tamura Electric Co., Ltd. (72) Inventor Isao Sato 2-3-2 Shimomeguro, Meguro-ku, Tokyo Inside Tamura Electric Co., Ltd.

Claims (2)

[Claims] 1. An unauthorized call preventing device for preventing a call of a telephone illegally connected to a telephone line to which a public telephone is connected, wherein the direct current loop of the telephone line is closed based on a capture operation of the public telephone. DC loop opening means for opening the DC loop, detecting means for detecting the voltage of the telephone line after the DC loop is opened by the DC loop opening means, and when the voltage of the telephone line detected by the detecting means is lower than a predetermined voltage And a line short-circuit means for short-circuiting the telephone line. 2. The receiving device according to claim 1, further comprising: receiving means for receiving a dial signal arriving at the telephone line with a DC loop closed based on a capturing operation of the public telephone, and wherein the DC loop opening means comprises the receiving means. And releasing the telephone line when a dial signal is received.