JP2002009895A - Open-close detection circuit for telephone line - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an open-close detection circuit which can satisfy the leakage regulation of telephone lines and can detect the open-close states of the telephone lines by detecting the voltage between the lines. SOLUTION: A series circuit including a resistor R1, a variable capacitance diode VC and a resistor R2 is connected in parallel to the series connection of a hook switch 2 and a line transformer 3 connected to the telephone lines L1 and L2 respectively. Then a capacitance change detection circuit 5 detect the capacitance change of the diode VC for detecting the open-close states of lines L1 and L2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an open / close detection circuit for a telephone line, and more particularly to an open / close detection circuit used in a telephone or a facsimile for detecting whether or not a hook switch is pressed.

[0002]

2. Description of the Related Art As a simple method for detecting opening and closing of a telephone line by a hook switch, there is a method of detecting a current flowing through the telephone line using a photocoupler. However, in some countries, especially in Europe, the value of the DC resistance is determined by the telephone line standard, and it is not possible to use a photocoupler connected in series to the telephone line. Therefore, in a device for Europe, a current sensor using a high-sensitivity relay or a magnetic sensor is used for opening and closing a telephone line.

FIG. 3 shows an example using a high-sensitivity relay, and FIG. 4 shows an example using a current sensor. In FIG. 3, one telephone line L1 is connected to one end of a line transformer 3 via a coil of a high-sensitivity relay 1 and a hook switch 2,
The other end of the line transformer 3 is connected to the other telephone line L2. When the hook switch 2 is closed, a minute current flowing through one of the telephone lines L1 causes a current to flow through the coil of the high-sensitivity relay 1, and its contacts are closed to detect opening and closing of the telephone line.

In an example using the current sensor 4 shown in FIG.
One telephone line L1 has a current sensor 4 and a hook switch 2
And the other end of the line transformer 3 is connected to a telephone line L2. When the hook switch 2 is closed, a change in magnetic flux generated by a slight current flowing through one telephone line L1 is detected by the current sensor 4, and the detection signal is amplified and output.

In the example using the high-sensitivity relay shown in FIG. 3, the high-sensitivity relay itself is expensive and has a drawback that the response speed is slow because it is a mechanical type.

On the other hand, when the current sensor 4 shown in FIG. 4 is used, it is cheaper than the high-sensitivity relay 1, but it requires the use of special parts (sensor, coil, magnetic material). It cannot be cheap.

[0007]

As shown in FIGS. 3 and 4, the state (opening / closing) of the telephone line between the primary telephone lines L1 and L2 and the secondary device insulated by the line transformer 3 is shown. Can be detected by detecting the current flowing through the line,
Alternatively, it is necessary to detect the voltage. In the conventional techniques used so far, all of them detect a current flowing through a line, and it is difficult to detect a voltage. This is because the leakage current between the two telephone lines L1 and L2 is specified to be 10 μADC or less (in Japan), and even this transistor cannot operate at this current value. Further, if power is supplied from the secondary side by an insulating DC / DC converter, it becomes expensive by itself.

Accordingly, a main object of the present invention is to provide a telephone line open / close detection circuit which satisfies the leakage current regulation of a telephone line and can detect line open / close by detecting a voltage between the lines. .

[0009]

SUMMARY OF THE INVENTION The present invention relates to an open / close detection circuit for detecting the opening / closing of a hook switch in a telephone line connected to a line transformer via a hook switch. A series circuit including at least a variable capacitance diode connected in parallel to the series connection of the above, and detection means for detecting a change in the capacitance of the variable capacitance diode which occurs in response to a change in the voltage between the telephone lines by opening and closing the hook switch. It is composed.

Therefore, according to the present invention, it is not necessary to use special components by detecting a change in the capacitance of the variable capacitance diode in accordance with a change in the voltage between telephone lines, so that an inexpensive detection circuit can be configured.

A resistor is connected in series to the cathode and the anode of the variable capacitor, and the detecting means includes first and second terminals each having one end connected to the cathode side and the anode side of the variable capacitance diode. , An oscillation circuit that supplies an oscillation signal to the variable capacitance diode via the first capacitor, and a detection circuit that detects a change in the oscillation signal via the second capacitor.

Further, the detection circuit detects a change in the level of the oscillation signal as a change in the oscillation signal. Further, the detection circuit detects oscillation and non-oscillation or a change in oscillation frequency as a change in the oscillation signal.

Further, the detection circuit constitutes a filter by regarding the first capacitance, the variable capacitance diode and the second capacitance as one capacitor, and detects a change in the characteristics of the filter based on a change in the oscillation signal.

[0014]

FIG. 1 is a block diagram showing an open / close detection circuit according to an embodiment of the present invention.

In FIG. 1, a series circuit of a first resistor R1, a variable capacitance diode VC, and a second resistor R2 is connected in parallel to a series connection of a hook switch 2 and a line transformer 3. The cathode and anode of the variable capacitance diode VC are connected to the capacitance change detection circuit 5 via the first and second capacitances C1 and C2, respectively. C1 and C
2 provides insulation between the line and the equipment. The capacitance change detection circuit 5 internally generates an AC waveform by an oscillator, transmits the AC waveform through a first capacitance C1, a variable capacitance diode VC, a second capacitance C2, and outputs a variable capacitance diode VC.
Of the hook switch 2 is detected by detecting a change in the level of the AC signal due to a change in the capacitance of the hook switch 2.

As another method, the capacitance change detection circuit includes a first capacitance C1-a variable capacitance diode VC-a second capacitance C
2 may be regarded as one capacitor, and this capacitor may be oscillated as the oscillation capacity of the oscillator to detect oscillation, non-oscillation, or change in oscillation frequency. Further, the capacitance change detection circuit 5 regards the first capacitance C1−the capacitance VC of the variable capacitance diode−the second capacitance C2 as one capacitor, configures a filter circuit, and detects a change in filter characteristics with an AC signal. You can also.

FIG. 2 is a more specific circuit diagram of the open / close detection circuit of the present invention. In FIG. 2, telephone lines L1, L2
Is connected to the input side of the rectifier diode D via current limiting resistors R3 and R4, and the output side of the rectifier diode D is connected to the cathode and anode of the variable capacitance diode VC via current limiting resistors R5 and R6. The cathode of the variable capacitance diode VC is connected to the oscillation circuit 10 via the first capacitance L1.
Connected to the output of The anode of the variable capacitance diode VC is connected to the input of the detection circuit 11 via the second capacitance C2.

The oscillation circuit 10 includes two transistors TR
1 and TR2, a general oscillation circuit is used that oscillates by positively feeding back the output signal of the output transistor TR2 to the input of the input transistor TR1. However, the present invention is not limited to this, and an oscillation circuit may be formed using an operational amplifier or a logic circuit.

The AC level detection circuit 11 is constituted by using three transistors TR3 to TR5, and outputs a signal when the input signal level becomes higher than a predetermined level. This may also be configured using an operational amplifier or a comparator.

Next, the operation of the embodiment shown in FIG. 2 will be described. An AC signal is generated in the oscillation circuit 10, the AC signal is transmitted to the primary side via the first capacitor C1, and the AC signal is transmitted to the second capacitor C2 by the capacitance component of the variable capacitance diode VC. The voltage is transmitted to the secondary-side AC level detection circuit 11 by the second capacitor C2.

On the other hand, in the telephone line, the voltage between the two lines L1 and L2 changes in two states of opening and closing of the hook switch 2, so that the capacitance of the variable capacitance diode VC changes accordingly. Therefore, the level changes when the AC signal output from the oscillation circuit 10 is transmitted to the second capacitor C2. That is, the level changes due to a change in capacitance (change in impedance) of the variable capacitance diode VC. The change in the level of the AC signal is detected by the AC level detection circuit 11, and two states of opening and closing of the telephone lines L1 and L2 are detected.

Therefore, according to the embodiment of the present invention, since the components can be composed of a transistor, a variable capacitance diode, a capacitor and a resistor, it is not necessary to use special components and the configuration can be made inexpensively. In the conventional configuration,
In contrast to the need for a mechanical configuration such as a high-sensitivity relay, or the use of a ring-shaped core for the current sensor, it was difficult to reduce the cost. Since it can be configured using electronic components, a reduction in cost can be realized.

Further, in a conventional device using a high-sensitivity relay or a current sensor, the transmission from the primary side to the secondary side is performed by a magnetic field, and it is necessary to be aware of the influence of an external magnetic field.
In contrast to the monitor and the speaker which generate a magnetic field, this embodiment is not affected by the magnetic field in this embodiment.

Further, in a conventional high-sensitivity relay or current sensor, it is necessary to insert a coil in series in a line,
In contrast to the necessity of passing through a capacitor or a resistor in order to satisfy the line standard, in this embodiment, a detection circuit can be connected in parallel to the series connection of the hook switch 2 and the line transformer. And easily meet line standards such as insertion loss.

The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

[0026]

As described above, according to the present invention, a series circuit composed of a resistor and a variable capacitance diode is connected in parallel to the series connection of a hook switch and a line transformer to change the capacitance of the variable capacitance diode. Can be detected by detecting the opening and closing of the hook switch, the cost can be reduced by using inexpensive parts, and furthermore, since no magnetic field is used, there is no influence from an external magnetic field, and Since it is not necessary to connect the telephone line in series, the line standard can be sufficiently satisfied.

[Brief description of the drawings]

FIG. 1 is a block diagram of an open / close detection circuit according to an embodiment of the present invention.

FIG. 2 is a more specific circuit diagram of the open / close detection circuit according to one embodiment of the present invention;

FIG. 3 is a diagram showing an example of an open / close detection circuit using a conventional high-sensitivity relay.

FIG. 4 is a diagram showing an example of a conventional open / close detection circuit using a current sensor.

[Explanation of symbols]

2 hook switch, 3 line transformer, 10 oscillation circuit, 11 AC level detection circuit, L1, L2 telephone line, R1, R2 resistance, R3 to R6 current limiting resistance, D
Rectifier diode, VC variable capacitance diode, C1
First capacitance, C2 Second capacitance, TR1 to TR5 Transistors.

Claims (5)

[Claims] 1. An open / close detection circuit for detecting the opening / closing of said hook switch, wherein said telephone line is connected to a line transformer via a hook switch. A series circuit including at least a variable capacitance diode connected in parallel; and a detecting means for detecting a change in capacitance of the variable capacitance diode caused by a change in a voltage between the telephone lines by opening and closing the hook switch. , Telephone line open / close detection circuit. 2. A resistor is connected to each of a cathode and an anode of the variable capacitor, and the detecting means includes first and second terminals each having one end connected to a cathode side and an anode side of the variable capacitance diode. And an oscillation circuit that supplies an oscillation signal to the variable capacitance diode via the first capacitance; and a detection circuit that detects a change in the oscillation signal via the second capacitance. The telephone line open / close detection circuit according to claim 1, wherein 3. The circuit according to claim 2, wherein the detection circuit detects a change in the level of the oscillation signal as a change in the oscillation signal. 4. The circuit according to claim 2, wherein the detection circuit detects oscillation and non-oscillation or a change in oscillation frequency as a change in the oscillation signal. 5. The detection circuit according to claim 1, wherein the first capacitance, the variable capacitance diode, and the second capacitance are regarded as one capacitor to form a filter. 3. The circuit for detecting the opening and closing of a telephone line according to claim 2, wherein the detection is performed based on a change.