JPH11146097A - Public telephone set - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent free speech resulting from closing a DC loop of two lines connecting to an exchange by connecting a handset cord of a handset of a public telephone set to ground. SOLUTION: A transformer connects between one terminal and the other terminal of a handset cord and each output terminal of a speech circuit to isolate the handset code from lines L1, L2 in terms of DC. Furthermore, the other terminal of the handset cord and the line L2 are connected by a contact, and a control circuit 7 opens the contact when the off-hook state reaches an on-hook state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a public telephone which is connected to a public telephone line and charges a toll call.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing an example of a conventional public telephone operated by supplying power from an office. In FIG. 3, this public telephone has a telephone line (hereinafter, line) L
1, a diode bridge (DB) 1 is connected to L2,
An incoming detection circuit 2 for detecting an incoming signal arriving on the lines L1 and L2 is connected to the output side of the diode bridge 1.
A buzzer (BZ) 3 is connected to the incoming call detection circuit 2 and sounds when an incoming call is received. A hook switch HS1 is connected to the lines L1 and L2, and the contact is closed by off-hook to close the DC loop of the lines L1 and L2. The diode bridge 4 converts voltages (L1; 0V (ground), 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 coin processing unit 1
1 power supply.

[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 is stored for each billing from the inserted coins, and when the balance is exhausted, the transistor Q1 is turned off and the line L1, L2 is forcibly disconnected to end the call.

[0004]

As shown in FIG. 3, one end of a receiver R of a public telephone is connected to one end of a communication circuit 6 by one handset cord H1 via a capacitor C1, and the other end is connected to the other end. Is connected to the negative (-) potential output terminal of the diode bridge 4 (that is, the other end of the communication circuit 6). One end of the transmitter T is connected to the communication circuit 6 by one handset code H3 via the capacitor C2.
The other end is connected to the negative (-) potential output terminal of the diode bridge 4 via the other handset cord H4, similarly to the receiver R. That is, the receiver R
The other end of the transmitter T is DC-connected to the line side. On the other hand, among the lines L1 and L2 connected to the exchange, the line L1 has a ground potential. Therefore, the receiver R
When the wiring at the other end of the transmitter T is grounded to a ground potential as shown in FIG. 3, a line L as shown by a dotted line in FIG.
DC loops 1 and 2 are closed, and -4
The current Ig flows to the line L2 having a potential of 8V.

[0005] For this reason, there has been a problem that if the handset cords H2 and H4 connected to the other ends of the receiver R and the transmitter T are grounded during dialing from the public telephone and calling the other party, an illegal call is possible. That is, a pay phone number is dialed from a public telephone, and the handset cords H2 and H4 connected to the other ends of the receiver R and the transmitter T are grounded during the other party's call. Next, a hooking operation is performed to cause the public telephone to recognize that the call has been abandoned. In this case, even if the transistor Q1 is turned off for a certain period of time on the public telephone, the DC loop of the lines L1 and L2 is closed by the dotted line in FIG. Next, dial a free number from the public telephone. With this dial number, the mute of the transmitter T is released on the public telephone to enable a call, and since the dial number is not charged, the transistor Q1 is kept on without forcibly disconnecting the line. On the exchange side, the free number is ignored since it is a dial after the call has already been connected. In this way, there is a problem that a free call is made to the destination of the pay number dialed first.

[0006] In the case of a public telephone which receives a charging signal coming from the exchange side and charges, a handset code H2 connected to the other ends of the receiver R and the transmitter T as shown in FIG. If H3 is grounded via the capacitor C3, there is also a problem that illegal communication becomes possible. That is, a pay phone number is dialed from a public telephone, and the handset cords H2 and H4 connected to the other ends of the receiver R and the transmitter T are grounded via the capacitor C3 during the call of the other party.
In this case, the capacitor C3 is equivalent to a state where the capacitor C3 is connected between the lines L1 and L2 indicated by the dotted line in FIG. here,
When a charge signal arrives at the lines L1 and L2 from the exchange side by the other party answering the call, 16KHz or 12K
The billing signal of a high frequency of Hz passes through the capacitor C3, and cannot be received by a billing signal receiving circuit (not shown) disposed at a subsequent stage. Also, even if a billing signal arrives during a call, it cannot be received. For this reason, there has been a problem that free calls can be made.

As shown in FIG. 5, the general telephone 100 is connected between the ground and the handset cords H2 and H4 connected to the other ends of the receiver R and the transmitter T of the public telephone, and the public telephone is set in an on-hook state. There is also a problem that a free telephone call can be made with a general telephone by dialing off-hook with a general telephone. Therefore, an object of the present invention is to prevent the above-described illegal call on a public telephone.

[0008]

According to the present invention, there is provided a first line having a ground potential (L1).
And a second line having a potential lower than the ground potential (L
2) is connected to the line consisting of
A handset, one end of which is connected to the first output of the speech circuit and the other end of which is connected to the second output of the speech circuit and the line L2
A public telephone provided with a handset cord that is connected in a DC manner to the public telephone is provided with non-connection means for disconnecting the other end of the handset cord and the line in a DC manner. Further, the non-connection means is a transformer connected between one end and the other end of the handset cord and each output terminal of the communication circuit. Switching means for connecting the non-connection means between the other end of the handset cord and the line L2 by a contact, and control for controlling the contact of the switching means to open when the off-hook state of the public telephone is changed to the on-hook state. Means.

[0009]

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 according to the present invention. In the 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 the payphone. You. A buzzer (B
Z) 3 is connected and rings when an incoming call arrives.

A hook switch HS1 is connected to the lines L1 and L2, and the contact is closed by off-hook to close the DC loop of the lines L1 and L2. The diode bridge 4 converts voltages (L1; 0V (ground), 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 , Coin processing unit 11,
And as a power source for the charging signal receiving circuit 12.

When a telephone 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 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 partner responds and a billing signal arrives at the lines L1 and L2 from an exchange (not shown), the billing signal is received by the billing signal receiving circuit 12 via the transformer T3 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 for each bill as a call charge.
1 is turned off, the lines L1 and L2 are forcibly disconnected, and the call is terminated.

In this public telephone, both ends of the receiver R are connected to the transformer T via handset codes H1 and H2.
1 is connected, and the other side of the transformer T1 is connected to the communication circuit 6. One end of a transformer T2 is connected to both ends of the transmitter T via handset cords H3 and H4, and the other side of the transformer T2 is connected to a communication circuit 6
Connect to That is, by separating the handset cords connected to both ends of the receiver R and the transmitter T from the communication circuit 6 with the transformers T1 and T2 in a DC manner, the handset cords and the line side are separated in a DC manner. I do.

Therefore, even if the handset cord of the public telephone is grounded, a direct current loop is not formed in the lines L1 and L2 because the handset cord and the line side are DC-separated. For this reason, the following illegal calls due to the grounding of the handset cord can be prevented.

That is, the DC loops of the lines L1 and L2 are not closed as shown in FIG. 3 regardless of what kind of handset cord is grounded during off-hook and dialing a toll number on a public telephone and calling the other party. For this reason, the hooking operation is next performed on the public telephone, and the control circuit 7 detects this through the hook switch HS2 and turns off the transistor Q1 for a certain period of time, thereby disconnecting the line and transmitting this to the exchange. As a result, the exchange determines that the call made by dialing the toll number has been abandoned and disconnects from the call destination, thereby preventing free calls by dialing the toll number.

Also, as shown in FIG. 4, a capacitor C3 is connected between the handset cord and the ground, and the capacitor C3 allows the handset cord to be connected to the line side in a DC manner even if the charge signal from the exchange is to be passed. Due to the separation, the billing signal cannot be passed. Therefore, the charging signal from the exchange side is received by the charging signal receiving circuit 12 and transmitted to the control circuit 7,
The coins are stored according to this. As a result, it is possible to prevent a free call by a pay number dial.

Also, as shown in FIG. 5, when the general telephone 100 is connected between the handset cord and the ground, and an attempt is made to make an illegal call by off-hook and dialing of the general telephone 100, the line is disconnected when the general telephone 100 goes off-hook. DC loop cannot be closed. Therefore, it is possible to prevent a free call by the pay number dialing of the general telephone 100.

FIG. 2 is a block diagram showing a second embodiment of the present invention. The handset cords H2 and H4 connected to the other ends of the receiver R and the transmitter T, and the minus of the diode bridge 4 are shown. (-) Connect the transistor Q2 or the relay contact RL between the potential output terminals. Then, when the lines L1 and L2 of the public telephone are opened, the transistor Q2 is turned off or the relay contact RL is opened to release the DC coupling between the handset cords H2 and H4 and the line side.

Therefore, as shown in FIG. 3, even if the public telephone sets off-hook and dials a toll number to ground the handset codes H2 and H4 and close the DC loops of the lines L1 and L2 during the call of the other party, When a hooking operation is performed on the public telephone, the control circuit 7, which detects the hooking operation via the hook switch HS2, turns off the transistor Q1 for a certain period of time, and at this time, turns off the transistor Q2 or opens the relay contact RL. , The DC coupling between the handset cords H2, H4 and the line side is released, and the DC loop of the lines L1, L2 is released. As a result, the exchange determines that the call made by dialing the toll number has been abandoned and disconnects from the call destination, thereby preventing free calls by dialing the toll number.

[0019]

As described above, according to the present invention, L
Connected to a line consisting of two lines, 1 and L2,
A communication circuit, a handset, and a handset cord having one end connected to the first output terminal of the communication circuit, the other end connected to the second output terminal of the communication circuit, and DC-connected to the line L2. In such a public telephone, a disconnection means for disconnecting the handset cord from the line in a DC manner is provided, so that even if the handset cord is grounded, the handset cord and the line side are separated in a DC manner. Since no DC loop is formed in the lines L1 and L2, various illegal calls due to grounding of the handset cord can be prevented. In addition, since a transformer is connected between one end and the other end of the handset cord and each output terminal of the communication circuit as a non-connection means, unauthorized communication can be accurately prevented with a simple configuration. Switching means for connecting the other end of the handset cord and the line L2 by a contact is provided as non-connection means, and the contact of the switching means is controlled to be open when the off-hook state of the public telephone changes to the on-hook state. Since the DC loop of the line is opened, when a pay phone number is dialed by a public telephone and a free call is made by performing a hooking operation, the DC loop of the line is opened by the hooking operation, and therefore the toll number is released. You can prevent free calls by dialing.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a second embodiment of the public telephone.

FIG. 3 is a diagram showing a first example of an illegal call in a conventional public telephone.

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

FIG. 5 is a diagram showing a third example of an illegal call in a conventional public telephone.

[Explanation of symbols]

1, 4: diode bridge, 6: communication circuit, 7: control circuit, 12: billing signal receiving circuit, T1 to T3: transformer, Q1, Q2: transistor, RL: relay contact, R
... receiver (receiver), T ... transmitter (transmitter), H1 to H4 ... handset code, C1, C2 ...
Capacitors, L1, L2 ... lines (telephone lines).

 ──────────────────────────────────────────────────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 (3)

[Claims] 1. A telephone line comprising a first line having a ground potential and a second line having a lower potential than the ground potential, and a speech circuit, a handset, and one end of the speech circuit. A public telephone having a handset cord connected to a first output terminal and the other end connected to a second output terminal of the telephone circuit, and connected to the second line of the telephone line in a DC manner. A public telephone having disconnection means for disconnecting DC between the other end of the handset cord and the telephone line. 2. The public telephone according to claim 1, wherein said non-connection means is a transformer connected between one end and the other end of said handset cord and each output terminal of said communication circuit. 3. The non-connecting means according to claim 1, wherein the non-connecting means includes a switching means for connecting the other end of the handset cord and the second line of the telephone line by a contact, and an off-hook state of the public telephone is on-hook. Control means for controlling a contact of the switching means to be open when the state becomes a state.