JPH09128948A - Phone call detection circuit and phone call recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phone call detection circuit which is capable of detecting phone call signals with high reliability and a phone call recording device. SOLUTION: A first output of a first signal line through a first resistor and a second output of a second signal line through a second resistor are connected through a third and a fourth resistor connected in series. Using the input section 3 in which the connection point between the third resistor and the fourth resister is grounded, the output obtained by reversing the above first output by a reversing section 5 is added with the buffer output of the second output buffered by a buffer section 7 by a summing circuit 6 to compare the summed output with the detection level of the comparison section and to output the above summed output when the above summed output exceeds the above detection level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a call detection circuit and a call recording device used for recording voice information on a telephone line or the like.

[0002]

2. Description of the Related Art Conventionally, in a call recording device for recording voice information on a public telephone line, recording is performed after detecting a call signal on a telephone line. In such a call recording device, a level detector 28 is connected to telephone lines (L1) and (L2) of telephones 26 and 27 connected to a central office 25 as shown in the schematic diagram of the telephone line of FIG. Then, the detected call signal is recorded in the recording device 29. FIG.
FIG. 6 is a circuit diagram showing a conventional level detector. The signal from the telephone line input to the input terminal (L2) 2 is input to the comparison unit 9 including a comparator via the resistor (R1) 30.

The input terminal (L1) 1 is connected to the earth line of the telephone line (potential as close as possible to the ground potential) and is connected to the power source voltage 0V through the resistor (R2) 31. . The output ends of the resistor (R1) 30 and the resistor (R2) 31 are connected by a resistor (R3) 32. The call signal is
It is compared with the detection signal level determined by the resistance values of the resistors R12 and R'13. When the signal from the telephone line exceeds a predetermined detection level, a call signal is output from the output terminal 14.

FIG. 9 is a diagram showing the signal level at the detection point (1) in FIG. FIG. 9A shows the resistance (R
2) When the 31 is grounded, the resistance R (R
2) shows the signal level when the output end of 31 is not grounded. In FIG. 9A, assuming that the detection level of the comparison unit 9 is −4.1V, the input terminal (L1) 1 is connected to the resistor (R).
2) When grounded via 31, the signal level during conversation becomes -3V, and the signal level when the receiver is placed is:
It becomes -5V. Therefore, it is possible to detect only the signal during the conversation. In FIG. 9B, the input terminal (L
2) When 2 is not grounded via the resistor (R2) 31, the signal level during conversation becomes -0.5V, and the signal level when the receiver is placed becomes -2.5V. Since these signal levels exceed the detection level of -4.1V, the signals during conversation cannot be discriminated.

[0005]

However, in the detection circuit for detecting the call signal level, it is necessary to ground the earth line of the public telephone line in order to detect the call signal with certainty. If it fluctuates, a predetermined voltage cannot be detected. Therefore, if the connection polarity of the level detector and the telephone line is incorrect, the call signal cannot be detected reliably.
An object of the present invention is to provide a call detection circuit and a call recording device capable of obtaining a highly reliable detection of a call signal.

[0006]

The present invention provides a call detecting circuit for detecting a call signal from a telephone line having a first signal line formed of a signal line and a second signal line formed of a ground line. The first output of the first signal line through the resistor of
The second output of the second signal line via the second resistor is connected to the first output and the second output via the third resistor and the fourth resistor connected in series. The input section in which the connection point of the resistance and the fourth resistance is connected to the ground potential, and the inverting section
The inverted output obtained by inverting the output of the above and the second output are added by the buffer output through the buffer unit in the addition unit, the addition output of the addition unit is compared with the detection level of the comparison unit, and the addition output exceeds the detection level. Occasionally, an addition output is output, and the third resistor and the fourth resistor
This is a call detection circuit capable of detecting a call signal by balancing the voltage of the telephone line with the middle point of the resistance of the above as the ground potential.

Further, the present invention is a call recording device comprising the above call detection circuit.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit explanatory diagram showing an embodiment of a call detecting circuit of the present invention. The input terminal (L1) 1 is connected to the earth line of the telephone line (potential near ground potential)
However, it is assumed that the signal voltage of the telephone line is applied to the input terminal (L2) 2. The ground line produces a predetermined voltage when the telephone handset is lifted. The ground voltage of the telephone line applied to the input terminal (L1) 1 is input to the inverting unit 5 formed of an inverting circuit via the resistor A4 of the input unit 3. The signal voltage applied to the input terminal (L2) 2 is input to the buffer unit 7 including a buffer circuit via the resistor B6 of the input unit 3. The output of the buffer unit 7 and the output of the inverting unit 5 are
The addition is performed by the addition unit 8 including an addition circuit. Then, the output of the addition unit 8 is input to the comparison unit 9 including a comparator circuit. The outputs of the resistors A4 and B6 are connected by a resistor A'10 and a resistor B'11 which are connected in series.

The addition output of the adder 8 input to the comparator 9 is compared with the detection level determined by the resistors R12 and R'13. When a signal with an addition output above the detection level is input, a call signal is output from the reproduction output terminal 14.

FIG. 2 is an explanatory view of the main part of the input section 3 of the call detection circuit of FIG. Input terminal (L1) 1 and input terminal (L
2) 2 is a resistor A4 and a resistor B6 having the same resistance value
A signal is input through the two lines, and further connected through resistors A'10 and B'11 in which the two lines are connected in series, and the output terminal B16 at the midpoint thereof is connected to the ground potential (0 V). ing. The output through the resistor A is output from the output terminal A17 and input to the inverting unit 5. The output via the resistor B6 is output from the output terminal C17 and input to the buffer unit 7. According to the present invention, a voice signal from a telephone line is differentially detected at a midpoint via a resistor, so that when two lines have a noise component in phase, the noise component can be canceled.

FIG. 3 is a diagram showing the signal level of the input section of the call detection circuit of FIG. 3A shows the output terminal B16 of the input section when it is grounded, and FIG.
It shows that 16 is not grounded. The output terminal A15 outputs -1.4 during a call and 60 mV when the output terminal B16 is grounded and the call is not in progress. On the other hand, from the output terminal C17, -1.8V during a call,
-3.1V is output when not in a call. When the input terminal (L2) 2 is grounded, the output terminal A15 outputs 0.2 V and the output terminal C17 outputs -0.2 during a call.
When V is output and no call is in progress, output terminal A15
To 1.6 V or -1.6 V from the output terminal C17. The same voltage having different polarities is output from the output terminal A15 and the output terminal C17. Therefore, it is necessary to set the detection levels of the same voltage having different polarities as the levels for detecting the call state.

FIG. 4 is a diagram showing output levels of the call detection circuit shown in FIG. In FIG. 4, the output terminal 1 of FIG.
4 shows an output level of 4. FIG. 4A shows the case where the output terminal B16 is grounded, and FIG. 4B shows the case where the output terminal B16 is not grounded. In both cases, -3.1V is output when not in a call, and when in a call,
-0.4V is output. This is because one of the outputs of the input section 3 is inverted by the inverting section 5 and the other output is not inverted and is added by the output section via only the buffer section 7 and the adding section 8, so that the output terminal 14 As for the output of, the voltage of one polarity is output. At this time, since the comparison unit 9 sets the voltage detection level to -1V, it can detect the call state by detecting that the call signal exceeds -1V. Even when the output terminal B16 is grounded and not grounded, the detection level is set to -1V to detect the voltage -0.4V during the call. This indicates that the busy state can be detected regardless of the polarity of the telephone line.

FIG. 5 is a block diagram when the call detection circuit of the present invention is applied to a recording device. The telephone line signal input to the input terminal 18 is detected by the call detector 19, and the detection signal of the call detector 19 is detected by the microcomputer 20. At this time, the audio signal is the AD converter 2
The data is AD (Analog Digital) converted by 1 and stored in the memory 22 for each predetermined data block. Then, the microcomputer 20 detects only the call signal by the call detector 19 to control the interface 23, and records only the call signal in the recording device 24. Further, if a power supply having a common electric potential at the output terminal B16 of the input section 3 of the call detector 19 is used, a call signal can be reliably detected even if a plurality of channels of the call detector 19 are provided.

FIG. 6 is an explanatory diagram showing signal levels when a telephone call is made and when a telephone call is received on the telephone line. When making a call, when the handset is lifted, the telephone line connected to the input terminal (L1) shifts the potential of −0.5V to −23V. The telephone line connected to the input terminal (L2) 2 is displaced from -49V to -28V. When a call is received, a bell signal is input to the telephone line connected to the input terminal (L2) 2, and the signal voltage greatly changes at brass minus 80V. When this call signal detects a predetermined voltage level, the microcomputer 17
D installed in the recording device 21 by activating the recording device 21
Recording medium such as AT (Digital Audio Tape) (not shown)
To record.

According to the present invention, the call detection circuit can be connected regardless of the polarity of the telephone line, and the voice signal during the call can be reliably detected. Therefore, the recording device can be operated by this detection signal. . Therefore, it is possible to reliably record only the audio signal in the recording device while monitoring the telephone line for a long time.

[0016]

According to the present invention, by the call detection circuit,
Since the call detection circuit can be connected regardless of the polarity of the telephone line and the call signal can be reliably detected, it is possible to provide a call detection circuit and a call recording device that can obtain a highly reliable detection of the call signal.

[Brief description of the drawings]

FIG. 1 is a circuit explanatory diagram showing an embodiment of a call detection circuit of the present invention.

FIG. 2 is an enlarged view of a main part showing an input section of an embodiment of the call detection circuit of the present invention.

FIG. 3A is a diagram showing an output level of the input section when the output terminal B of the input section of the embodiment of the call detecting circuit of the present invention is grounded. FIG. 6B is a diagram showing the output level of the input section when the output terminal B of the input section of the embodiment of the call detecting circuit of the present invention is not grounded.

FIG. 4A is a diagram showing an output level when an output terminal B of an embodiment of the call detecting circuit of the present invention is grounded.
FIG. 6B is a diagram showing an output level when the output terminal B of the embodiment of the call detecting circuit of the present invention is not grounded.

FIG. 5 is a block diagram showing an embodiment in which the call detection circuit of the present invention is applied to a recording device.

FIG. 6 is an explanatory diagram showing telephone calls and signal levels.

FIG. 7 is a schematic diagram of a telephone line.

FIG. 8 is a circuit diagram showing a conventional level detector.

9A is a diagram showing a signal level at a point (1) when a resistor (R2) 31 of the level detection circuit shown in FIG. 8 is grounded. FIG. 9B is a diagram showing the signal level at point (1) when the resistor (R2) 31 of the level detection circuit shown in FIG. 8 is not grounded.

[Explanation of symbols]

 1 Input Terminal (L1) 2 Input Terminal (L2) 3 Input Section 4 Resistance A 5 Inversion Section 6 Resistance B 7 Buffer Section 8 Addition Section 9 Comparison Section 10 Resistance A ′ 11 Resistance B ′ 12 Resistance R 13 Resistance R ′ 14, 18 output terminal 15 output terminal A 16 output terminal B 17 output terminal C 19 call detector 20 microcomputer 21 AD converter 22 memory 23 interface 24, 29 recording device 25 telephone station 26, 27 telephone 28 level detector 30 resistance (R1 ) 31 resistance (R2) 32 resistance (R3)

Claims (2)

[Claims] 1. A call detection circuit for detecting a call signal from a telephone line having a first signal line formed of a signal line and a second signal line formed of a ground line, in the call detection circuit, the first line including a first resistor. First output of the signal line, the second output of the second signal line via the second resistor, and the first output of the third resistor and the fourth resistor connected in series. And an output connected to the second output, and a connection point between the third resistor and the fourth resistor connected to a ground potential; an inverting output obtained by inverting the first output by an inverting unit; The output of No. 2 is added to the buffer output via the buffer unit by the adder unit, the added output of the adder unit is compared with the detection level of the comparison unit, and the added output is output when the added output exceeds the detection level. A call detection circuit characterized by outputting. 2. A call recording device comprising the call detection circuit according to claim 1.