Telephone device, telephone line monitoring device and method

1. Field of the Invention

The present invention relates to landline telephones, and particularly to a landline telephone line monitoring device and method for preventing a telephone line of a landline telephone device from being used by an unauthorized person.

2. Description of Related Art

Landline telephone devices are ubiquitous. A landline telephone device uses wiring to convey sound information from one landline telephone device to another landline telephone device or to convey sound information to a mobile phone via a wired and a wireless network. However, the wiring, of landline telephones, is usually exposed outside of buildings, thus the wiring can be surreptitiously tapped into by an unauthorized person. Referring to FIG. 6 , an illicit phone connected to a telephone line at an outdoor location is shown. Thus, an unauthorized person would be able to use the telephone services of the legitimate subscriber of the telephone line, while the legitimate subscriber is liable for all the service payments.

Therefore, an improved telephone device, a telephone line monitoring device and method are needed to address the aforementioned deficiency and inadequacies.

A telephone line monitoring device for preventing a telephone line from being tapped illicitly is provided herein. The telephone line monitoring device is connected to a telecommunications network via the telephone line, and is adjacent to a telephone device using the telephone line. The telephone line monitoring device includes a rectifying circuit, a first controller, a second controller, a load booster, and a first switch circuit. The rectifying circuit is used for generating a corresponding direct current voltage according to an effective voltage of the telephone line. The first controller is configured for generating a first control signal when the direct current voltage is lower than a predetermined voltage. The second controller is configured for detecting an operating state of the telephone device and generating a second control signal when the telephone device is operated. The load booster is used for pulling down the effective voltage of the telephone line when enabled. The first switch circuit is configured for disabling the load booster whenever receiving the second control signal, and enabling the load booster when receiving the first control signal while not receiving the second control signal. A related telephone line monitoring method and a telephone device are also provided.

Other advantages and novel features of the present invention will become more apparent from the following detailed description of preferred embodiment when taken in conjunction with the accompanying drawings.

FIG. 1 illustrates a block diagram showing a telephone system including a telephone line monitoring device in accordance with a first exemplary embodiment.

FIG. 2 is a detailed block diagram of the telephone line monitoring device.

FIG. 3 is another detailed block diagram of the telephone line monitoring device.

FIG. 4 is a circuit of the telephone line monitoring device of FIG. 3 .

FIG. 5 illustrates a block diagram showing a telephone device in accordance with a second exemplary embodiment.

FIG. 6 illustrates a block diagram showing a conventional telephone system, wherein the telephone line is used by an illicit telephone.

Reference will now be made to the drawings to describe a preferred embodiment of the present telephone device, the telephone line monitoring device and method.

Referring to FIG. 1 , in a first exemplary embodiment, a telephone system includes a landline telecommunication device (telephone for short) 200 placed indoors and connected to a telecommunications network (not shown) via a telephone line (phone line for short). The phone line powered by a power supply include a tip wire A and a ring wire B. The tip wire A is connected to a tip terminal of the telephone 200 . The ring wire B is connected to a ring terminal of the telephone 200 . An illicit phone 300 is connected to the phone line. The telephone system further includes a telephone line monitoring device 100 (monitoring device for short) connected to the phone line and adjacent to the telephone 200 .

The monitoring device 100 is configured for preventing the phone line from being used by the illicit phone 300 , and generating an audible alarm when detecting the illicit phone 300 . When the illicit phone 300 is in use, a value of the effective voltage applied to the phone line changes, from −50 volts to −9 volts, for example. So, when the effective voltage drops and the telephone 200 is not in use (being operated), this may indicate that the illicit phone 300 is in use. In the embodiment, the monitoring device 100 pulls down the effective voltage applied to the phone line, and outputs the audible alarm when detecting the illicit phone 300 . The pulled down effective voltage is low enough to affect operation of the illicit phone 300 , and may even affect normal operations of any additional phone devices connected to the phone line.

Referring to FIGS. 2 and 3 , the monitoring device 100 includes a rectifying circuit 10 , a first controller 20 , a second controller 30 , a first switch circuit 40 , and a load booster 50 .

The rectifying circuit 10 is configured for generating a corresponding direct current (DC) voltage according to an effective voltage of the phone line. In operation, when the phone line is free or in use, a negative DC power supply powers the phone line, the rectifying circuit 10 converts the negative DC voltage into a positive DC voltage. When there is an incoming call, an alternating current (AC) ringing voltage (75 volts for example) is supplied to the phone line so as to ring a bell (not shown) in the telephone 200 , the rectifying circuit 10 converts the AC ringing voltage into a corresponding DC voltage.

The first controller 20 is configured for generating a first control signal when the DC voltage outputted by the rectifying circuit 10 is lower than a predetermined voltage. The second controller 30 is configured for detecting an operating state of the telephone 200 and generating a second control signal when the telephone 200 is being operated. The method for detecting the operating state of the telephone 200 may include step of detecting an on/off state of a hookswitch of the telephone 200 , or detecting whether there is current flowing through the telephone 200 , etc. When the hookswitch of the telephone 200 is closed (on-state), this means that the telephone 200 is being operated. When there is a current flowing through the telephone 200 , this also means that the telephone 200 is being operated. In the exemplary embodiment, the method for detecting the operating state of the telephone 200 is to detect whether there is a current flowing through the telephone 200 .

The load booster 50 is configured for pulling down the effective voltage of the phone line when enabled. The load booster 50 is a high voltage powered electrical device. In the exemplary embodiment, the load booster 50 is a multivibrator circuit with an electro-acoustic transducer.

The first switch circuit 40 is configured for disabling the load booster 50 when receiving the second control signal, and enabling the load booster 50 when receiving the first control signal while not receiving the second control signal. That is, the first switch circuit 40 disables the load booster 50 when the telephone 200 is being operated, and enables the load booster 50 so as to prevent the illicit phone 300 from being operated.

Referring to FIG. 4 , the rectifying circuit 10 includes four diodes D 1 , D 2 , D 3 , D 4 that form a full-bridge rectifier.

The first controller 20 includes a sampling circuit 22 , a comparator U 1 , and a reference voltage circuit 24 . The sampling circuit 22 includes a first zener diode DZ 1 , a first resistor R 1 , and a second resistor R 2 . A cathode of the first zener diode DZ 1 is connected to the rectifying circuit 10 , and an anode of the first zener diode DZ 1 is connected to the an end of the first resistor R 1 . Another end of the first resistor R 1 is connected to an end of the second resistor R 2 and the inverting input terminal of the comparator U 1 . Another end of the second resistor R 2 is grounded. The reference voltage circuit 24 includes a second zener diode DZ 2 , a first capacitor C 1 , a third, a fourth, and a fifth resistors R 3 , R 4 , R 5 . An end of the fifth resistor R 5 is connected to the rectifying circuit 10 , and another end of the fifth resistor R 5 is connected to a cathode of the second zener diode DZ 2 , an end of the third resistor R 3 , and the anode of the first capacitor C 1 . An anode of the second zener diode DZ 2 , and a cathode of the first capacitor C 1 are grounded. Another end of the third resistor R 3 is connected to an end of the fourth resistor R 4 and the non-inverting input terminal of the comparator U 1 . Another end of the fourth resistor R 4 is grounded. An output terminal of the comparator U 1 is connected to the second controller 30 and the first switch circuit 40 via a sixth resistor R 6 . A zener voltage of the first zener diode DZ 1 should be lower than the high voltage of the phone line, and higher than the low voltage of the phone line. A zener voltage of the second diode DZ 2 should be lower than the low voltage of the phone line.

The second controller 30 includes a second switch circuit 32 and a third switch circuit 34 . The second switch circuit 32 includes a fifth diode D 5 , an eleventh resistor R 11 , and an NPN type fourth bipolar junction transistor (BJT) Q 4 . An emitter of the fourth BJT Q 4 is connected to the tip wire A of the phone line and an end of the eleventh resistor R 11 , a base of the fourth BJT Q 4 is connected to the tip terminal of the telephone 200 and another end of the eleventh resistor R 11 . A collector of the fourth BJT Q 4 is connected to a cathode of the fifth diode D 5 , and an anode of the fifth diode D 5 is connected to the first switch circuit 40 . The third switch circuit 34 includes a sixth diode D 6 , a twelfth resistor R 12 , and an NPN type fifth BJT Q 5 . An emitter of the fifth BJT Q 5 is connected to the ring wire B and an end of the twelfth resistor R 12 , and a base of the fifth BJT Q 5 is connected to the ring terminal of the telephone 200 and another end of the twelfth resistor R 12 . A collector of the fifth BJT Q 5 is connected to a cathode of the sixth diode D 6 , and an anode of the sixth diode D 6 is connected to the first switch circuit 40 .

The first switch circuit 40 includes an NPN type first BJT Q 1 and a light-emitting diode (LED) D 7 . The base of the first BJT Q 1 is connected to the first controller 20 and the second controller 30 , the emitter of the first BJT Q 1 is grounded, and the collector of the first BJT Q 1 is connected to a cathode of the LED D 7 and the multivibrator circuit 50 . An anode of the LED D 7 is connected to the rectifying circuit 10 via a resistor.

The multivibrator circuit 50 includes a second capacitor C 2 , a third capacitor C 3 , a ninth resistor R 9 , a tenth resistor R 10 , a PNP type second BJT Q 2 , an NPN type third BJT Q 3 , and an electro-acoustic transducer DY. A base of the second BJT Q 2 is connected to the first switch circuit 40 via a resistor, an emitter of the second BJT Q 2 is connected to the rectifying circuit 10 , and a collector of the second BJT Q 2 is grounded via the tenth resistor R 10 . The second capacitor C 2 and the ninth resistor R 9 are connected in series between the base of the second BJT Q 2 and a collector of the third BJT Q 3 . The third capacitor C 3 is connected between the base and collector of the second BJT Q 2 . A base of the third BJT Q 3 is connected to the collector of the second BJT Q 2 , the collector is connected to a terminal of the electro-acoustic transducer DY, and an emitter is grounded. The other terminal of the electro-acoustic transducer DY is connected to the rectifying circuit 10 . In the exemplary embodiment, the electro-acoustic transducer DY is a loud speaker.

In the exemplary embodiment, the effective voltage (absolute value) of the DC voltage is a high voltage, about 50 volts, when the phone line is free, and a low voltage, about 9 volts, when the phone line is busy (the phone is being operated). In the first controller 20 , a zener voltage of the first zener diode DZ 1 is 12 volts, a resistance of the first resistor R 1 is 800 kilohms, a resistance of the second resistor R 2 is 100 kilohms, a zener voltage of the second zener diode DZ 2 is 5 volts, a resistance of the third resistor R 3 is 100 kilohms, and a resistance of the fourth resistor R 4 is 50 kilohms. Thus, a threshold voltage V 1 of the comparator U 1 can be calculated according to the following formula (1):

V 1=5 volts* R 4/( R 3+ R 4)=5 volts*50/(50+100)=1.67 volts   (1)

In operation, when the phone line is free, the effective voltage (absolute value) of the phone line is 50 volts. The DC voltage outputted by the rectifying circuit 10 is 50 volts too, higher than the zener voltage of the first zener diode DZ 1 . Thus, the first zener diode DZ 1 is enabled (turned on), the voltage at the node between the first zener diode DZ 1 and the first resistors R 1 equals to 38 volts (that is 50 volts minus 12 volts), and the voltage at the node between the first resistor R 1 and the second resistor R 2 and the inverting input terminal of the comparator U 1 equals to about 4.22 volts, in other words, higher than the threshold voltage of the comparator U 1 . As a result, the comparator U 1 outputs a low voltage that is nearly 0 volts, the first BJT Q 1 is disabled (turned off), and the multivibrator circuit 50 is disabled.

When the phone line is used, the effective voltage of the phone line reduces to 9 volts. The DC voltage outputted by the rectifying circuit 10 is 9 volts too, lower than the zener voltage of the first zener diode DZ 1 . Thus, the first zener diode DZ 1 is disabled, a voltage supplied to the inverting input terminal of the comparator U 1 equals to 0 volts, in other words, lower than the threshold voltage of the comparator U 1 . As a result, the comparator U 1 outputs a high voltage (that is the first control signal) that is nearly 5 volt.

If the telephone 200 is being operated, a current flows through the tip terminal and the ring terminal of the telephone 200 , and because one wire of the phone line (the tip wire A or the ring wire B) is always lower than or equals to 0 volts at any time, one of the BJTS Q 4 , Q 5 is enabled. Thus, a voltage supplied to the base of the first BJT Q 1 is pulled down to 0 volts or lower (this is the second control signal). As a result, the first BJT Q 1 is disabled, and the multivibrator circuit 50 is disabled.

When the phone line is used by the illicit phone 300 , and the telephone 200 is not operated, there is no current flowing through the tip terminal and the ring terminal of the telephone 200 , the BJTS Q 4 , Q 5 will not become enabled (turn on). Thus, the 5 volts voltage outputted by the comparator U 1 is transmitted through the sixth resistor R 6 to the base of the first BJT Q 1 . The first BJT Q 1 is enabled, as a result, the LED D 7 emits light to indicate that the phone line is used by the illicit phone 300 , and furthermore, a low voltage that equals to 0 volts is transmitted to the base of the second BJT Q 2 . As a result, the BJTS Q 2 , Q 3 is enabled, the multivibrator circuit 50 begins to work, and the electro-acoustic transducer DY is enabled to output an audible alarm to alert that there might be an illicit telephone tapped-in to the phone line. Meanwhile, the effective voltage of the phone line is pulled down so as to prevent the illicit phone 300 from being operated. The pulled down effective voltage is lowered such that it cannot drive any telephones.

In other embodiments, any of the BJTS can be replaced by other controllable switches, such as Field-Effect Transistors (FETs). The LED D 7 can be omitted.

Referring to FIG. 5 , in a second exemplary embodiment, the monitoring device 100 is integrated in a telephone 400 . The monitoring device is connected to a communication unit 402 of the telephone 400 .

It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.