JP2004096408A - Video doorphone system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a video doorphone system for detecting a call from an entrance slave unit while a video image is displayed on a monitor of an indoor master unit with high accuracy without malfunction. <P>SOLUTION: A video demodulation circuit 25 of the indoor master unit compares a preset time with a pulse width of an output signal from a logic gate 31a of a first CMOS logic IC 31 the DC level of an input port of which is set to a level slightly higher than a midpoint level and allows a logic gate 35a of a second CMOS logic IC 35 to output a pulse with a prescribed time with respect to the input of a pulse longer than the set time, and an adder means 40 adds the output signal S6 to a video signal 36 after the detection so as to be capable of eliminating an undesired pulse outputted to a lower level side of a video synchronizing signal caused by the arrival of the call from the entrance slave unit while a video image is displayed on the monitor 21 of the indoor master unit and causing the output signal S6 to be a call signal component for allowing a CPU 28 to detect the call from a visitor during the display of the video image. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a television door intercom device, and more particularly, to a television intercom device that can detect a call from an entrance sub device in an indoor parent device in which an image captured by the entrance sub device is being displayed on a monitor.
[0002]
[Prior art]
Hitherto, as this kind of TV door intercom device, a TV intercom device having a configuration shown in a schematic external view of FIG. 5 has been proposed.
[0003]
In the schematic external view of FIG. 5, a call button 60, a camera 61, a child device microphone 62, and a child device speaker 63 are arranged on (a housing surface of) an entrance child device 51 normally installed at the entrance (entrance). ing. Illustration and explanation of a specific configuration of the entrance terminal 51 will be omitted.
[0004]
In the schematic external view of FIG. 5, a parent device speaker 70, a monitor 71, a handset 72 (constituting a communication device), and a hook switch 73 are arranged on (the housing surface of) an indoor parent device 52 which is usually installed indoors. The indoor master unit 52 is connected to the entrance slave unit 51 via transmission lines L51 and L52, respectively.
[0005]
As shown in the block diagram of FIG. 6, the indoor master unit 52 includes a master speaker 70, a monitor 71, a handset 72, a hook switch 73, a call detection circuit 74, a video demodulation circuit 75, and a master unit communication circuit. A master unit power supply circuit 77, a CPU 78, and an interface (hereinafter, referred to as a master unit I / F) 79 are provided.
[0006]
Further, as shown in the block diagram of FIG. 7, the video demodulation circuit 75 of the indoor master unit 52 includes a limiter amplifier 80, a delay circuit 81, a phase comparison circuit 82, a low-pass filter (low-pass filter) 83, and an embedding detection circuit 84. , An inverting circuit 85, an adding circuit 86 (constituting an adding means), and a video amplifier 87.
[0007]
In the conventional TV intercom apparatus configured as described above, a call operation by a visitor at the entrance, that is, a call button 60 of the entrance device 51 shown in the schematic external view of FIG. As a result, a ringing tone is sounded from the parent device speaker 70 of the indoor parent device 52 shown in the schematic external view of FIG. 5 and the block diagram of FIG. 6, and the image captured by the camera 61 of the entrance child device 51 is also displayed. When a visitor at the entrance presses the call button 60 of the entrance child device 51 (again) while the image is being displayed on the monitor 71 of the indoor parent device 52, the camera 61 of the entrance child device 51 After being modulated, the FM modulated signal S51 transmitted between the two lines of the transmission lines L51 and L52 to the video demodulation circuit 75 via the master unit I / F 79 of the indoor master unit 52 includes As shown in the explanatory diagram of FIG. M carrier intermittent occurs.
[0008]
Also, in the video demodulation circuit 75 of the indoor master unit 52 shown in the block diagram of FIG. 7, the limiter amplifier 80 amplifies the FM modulation signal S51 shown in the explanatory diagram of FIG. 8 to a logic level, and outputs the amplified FM modulation signal S52. Is input to the phase comparison circuit 82 as it is, and is also input to the phase comparison circuit 82 via the delay circuit 81 as the FM modulated signal S53 delayed for a predetermined time. Here, the FM carrier intermittent period generated in the FM modulation signal S51 is sufficiently longer than the delay time set by the delay circuit 81, so that the phase comparison circuit 82 outputs the low-pass filter 83 and the envelope signal. The video signal S54 output to the detection circuit 84 is fixed at the L (Low) level during the FM carrier intermittent period.
[0009]
Further, in the video demodulation circuit 75 of the indoor master unit 52 shown in the block diagram of FIG. 7, the video signal S55 passed through the low-pass filter 83 is demodulated through the video demodulation circuit, and then described in FIG. A large pulse is generated below the video synchronizing signal shown in the figure, and this pulse becomes noise, so that the luminance of the video displayed on the monitor 71 is largely changed or the synchronization is disturbed. Is added to an output signal S57 obtained by inverting the envelope detection signal S56 from the envelope detection circuit 84 via an inversion circuit 85 by an addition circuit 86, thereby obtaining the above-described video synchronization signal. Unnecessary pulses generated on the lower side can be removed, and the video signal S58 from the addition circuit 86 is converted to a video signal S59 amplified via the video amplifier 86. While being transmitted to the monitor 71, it is possible to detect the image output in the call from the visitor against CPU 78.
[0010]
[Problems to be solved by the invention]
However, in the video doorphone device of the conventional example, the video demodulation circuit 75 of the indoor master unit 52 performs the envelope detection / output inversion of the video signal S54 from the phase comparison circuit 82 via the envelope detection circuit 84 and the inversion circuit 85. For this reason, even with the amplitude pulse of the legitimate calling signal component, the envelope detection circuit 84 may malfunction to affect the video signal or cause the CPU 78 to detect an erroneous calling.
[0011]
In addition, the circuit structure of the embedding detection circuit 84 and the inversion circuit 85 constituting the video demodulation circuit 75 of the indoor master unit 52 is complicated, and there is a problem that a large board area is required.
[0012]
Further, when the video demodulation circuit 75 of the indoor master unit 52 causes the CPU 78 to detect a call during image output from the visitor, the CPU 78 performs special control to detect the carrier of the video signal S58 from the addition circuit 86. There were drawbacks that were needed.
[0013]
SUMMARY An advantage of some aspects of the invention is to solve the above-described drawbacks and detect an FM carrier discontinuity occurring in an FM modulation signal imaged / modulated by a front-end handset based on a pulse width of the FM modulation signal. Accordingly, it is an object of the present invention to provide a television intercom apparatus that can detect a call from an entrance slave while an image is being displayed on a monitor of an indoor master with a simple circuit configuration and with high accuracy without malfunction.
[0014]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the television doorphone device of the present invention is configured such that, when a call button of the entrance slave unit is pressed, a call is detected by the indoor master unit connected via the transmission line, and a ring tone is heard from the master speaker. The sound is sounded and the image taken by the camera of the entrance slave unit is displayed on the monitor of the indoor master unit, and a call is made between the communication device of the indoor master unit and the microphone and the speaker of the slave unit of the entrance slave unit. It is a TV door phone device. Further, the entrance device includes a video modulation circuit for modulating a video signal captured by the camera into an FM modulation signal. Further, the indoor master unit includes a video demodulation circuit for demodulating the FM modulation signal into a video signal. The video demodulation circuit further includes a first CMOS logic IC for setting the DC potential of the input port to which the FM modulation signal is input to a potential shifted from the midpoint potential, and a logic gate of the first CMOS logic IC. A comparing means for comparing the pulse width output from the control unit with a set time, a second CMOS logic IC for outputting a pulse of a fixed time in response to an input of a pulse longer than the set time, And the addition means for adding the output of the CMOS logic IC to the demodulated video signal, so that when the call button of the front door is pressed, the image generated when the FM carrier for making a call is interrupted. A pulse output below the synchronizing signal is removed, and the output of the second CMOS logic IC is used as a signal for detecting a call. That.
[0015]
According to such a TV door phone apparatus, the direct-current potential of the input port of the first CMOS logic IC of the video demodulation circuit of the indoor master unit is set to a potential slightly higher than the midpoint potential, so that the camera of the entrance slave unit can be used. Thus, the first CMOS logic can be driven without amplifying even a very small FM modulation signal that has been imaged and modulated via the video modulation circuit. Further, the pulse width of the output signal from the logic gate of the first CMOS logic IC is compared with a preset time, and a pulse of a predetermined time is inputted to the second CMOS logic IC in response to a pulse input longer than the preset time. Output from the logic gate, and the output signal and the video signal after detection are added through an adding means, so that the video generated when a call is made from the entrance slave unit while the video is being displayed on the monitor of the indoor master unit. Not only can unnecessary pulses output below the synchronization signal be removed, but also the output signal from the logic gate of the second CMOS logic IC has an L (Low) level during standby and an H (Low) level during calling. (High) level, which is a binary signal fixed at each level, so that a call signal component for making it easy for the CPU to detect a call during image output from the entrance slave unit. It made.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an example of a preferred embodiment to which the television door phone device of the present invention is applied will be described with reference to the drawings.
[0017]
FIG. 1 is a schematic external view of a television intercom apparatus according to an embodiment of the present invention as viewed from the front. Usually, the television intercom apparatus is installed at an entrance (entrance) and via a transmission line L1, L2. It is connected to the entrance slave unit 1 and is usually composed of an indoor master unit 2 installed indoors.
[0018]
In the schematic external view of FIG. 1, a call button 10 pressed by a visitor at the front door to call a resident in the room is provided on (the housing surface of) the entrance terminal 1, and a caller who has performed a call operation is provided. A camera 11 for capturing an image or an image near the entrance is arranged, and a sub-unit microphone 12 and a sub-unit speaker 13 used by a visitor to communicate with a resident are arranged.
[0019]
In addition, in the schematic external view of FIG. 1, the indoor parent device 2 (housing surface) is used to notify a resident of the room of a call from the entrance child device 1 by a visitor at the entrance. A main unit speaker 20 for sounding a ringing tone, a monitor 21 for displaying an image taken by the camera 11 of the entrance slave unit 1, and a resident used for making a call with a visitor. A call device, here, a handset 22 for making a handset call, and a hook switch 23 that is hooked off / on depending on whether the handset 22 is picked up or not are arranged.
[0020]
FIG. 2 is a block diagram showing a configuration of the television door phone apparatus according to the embodiment of the present invention.
[0021]
In the block diagram of FIG. 2, the entrance slave unit 1 modulates the above-described call button 10, camera 11, slave unit microphone 12, slave unit speaker 13, and a video signal captured by the camera 11 into an FM modulation signal. Video modulation circuit 14, a slave unit communication circuit 15 for forming a communication line between the slave unit microphone 12 and the slave unit speaker 13, and an interface 17 described later, and a later-described master unit power supply of the indoor master unit 2. A slave unit power supply circuit 16 for supplying DC power supplied from the circuit 27 to each component / circuit of the entrance slave unit as operating power, a call button 10, a video modulation circuit 14, and a slave unit communication circuit 15, an interface for forming a signal transmission line (communication line) between the slave unit power supply circuit 16 and the transmission lines L1 and L2, and a power supply line (hereinafter referred to as a slave); That I / F.) 17 and are provided.
[0022]
In the block diagram of FIG. 2, the indoor master unit 2 transmits the above-described master unit speaker 20, monitor 21, handset 22, hook switch 23, and calls from the entrance slave unit 1 during standby to the transmission line L1, A call detection circuit 24 for detecting based on a potential drop of a DC power supply superimposed in advance between two lines of L2, and a video signal which is a video signal to be output on the monitor 21 from the entrance terminal 1 A video demodulation circuit 25 for demodulating the video signal, a main unit communication circuit 26 for forming a communication line between the handset 22 and an interface 29 described later, and components / circuits of the indoor main unit and the entrance unit 1 A power supply circuit 27 for supplying DC power, a CPU 28 for controlling each component / circuit of the indoor master unit, and a call detection circuit. 24, a video demodulation circuit 25, a base unit communication circuit 26, an interface for forming a signal transmission line (communication line) between the base unit power supply circuit 27 and the transmission lines L1 and L2, and a power supply line, respectively A main unit I / F.) 29 is provided.
[0023]
FIG. 3 is a circuit block diagram showing a specific configuration of the video demodulation circuit 25 of the indoor parent device 2.
[0024]
In the circuit block diagram of FIG. 3, the video demodulation circuit 25 of the indoor master unit 2 converts the DC potential of the FM modulation signal input from the entrance slave unit 1 via the capacitor C1 into each of resistors R1, R2 connected in series. , An input port potential setting circuit 30 for setting to a predetermined potential caused by the resistance value of R3, and a DC power supply from the base unit power supply circuit 27 as an operating power source. An output from the first CMOS logic IC 31 for setting the DC potential of the FM modulation signal set to the potential to a potential slightly shifted from the midpoint potential and a logic gate 31a of the first CMOS logic IC 31 is provided. The time set with the pulse width of the FM modulation signal, here, a time set by the product of the resistor R4 and the capacitor C2 connected in parallel (hereinafter, referred to as a first set time) ), A NOR (Nor circuit) 33 for inverting an output signal from the logic gate 31a of the first CMOS logic IC 31, and an output of the NOR 33. The output signal from the gate 33a is used as a trigger to compare a fixed pulse width, here, a time set by the product of the resistor R5 and the capacitor C3 connected in parallel (hereinafter, referred to as a second set time). A pulse width setting circuit 34, a second CMOS logic IC 35 for outputting a pulse of a second set time in response to a pulse input longer than the first set time, and a first A delay circuit 36 for delaying the FM modulation signal output from the logic gate 31a of the CMOS logic IC 31 for a predetermined time; A phase comparison circuit 37 for comparing the phase of the FM modulation signal output from the logic gate 31a of the logic IC 31 with the phase of the FM modulation signal output via the delay circuit 36; A low-pass filter (low-pass filter) 38 for passing only a low-frequency band with respect to a video signal output from the VGA, a video amplifier 39 for amplifying the video signal passed through the low-pass filter 38, An adder circuit 40 is provided as an adder for adding an output signal from the logic gate 35a of the second CMOS logic IC 35 and a video signal amplified via the video amplifier 39.
[0025]
In the video demodulation circuit 25 of the indoor master unit 2 shown in the circuit block diagram of FIG. 3, one of the input ports of the first CMOS logic IC 31 has one of the input port potential setting circuits 30 (the series-connected resistors R1, R2, R3), the parent device I / F 29 is connected via the capacitor C1, the other input port is connected to the logic gate 35a of the second CMOS logic IC 35, and the logic gate 31a has the pulse width The resistor R4 constituting the identification circuit 32, one of the input ports of the phase comparison circuit 37, and the other of the input ports of the phase comparison circuit 37 are connected via the delay circuit 36, respectively. A resistor R4 and a capacitor C2 forming a pulse width discriminating circuit 32 are connected to one and the other of the input ports of the NOR 33, respectively. A resistor R5 forming a pulse width setting circuit 34 is connected to the output gate 33a. One of the input ports of the second CMOS logic IC 35 is connected to the input terminal via the input terminal. The other of the input ports of the second CMOS logic IC 35 is connected to a resistor R4 and a capacitor C2 constituting the pulse width discrimination circuit 32, respectively, and the logic gate 35a is connected to one of the input ports of the addition circuit 40. And the CPU 28 are connected to each other. The other output port of the addition circuit 40 is connected to the output port of the phase comparison circuit 37 via a low-pass filter 38 and a video amplifier 39. The output port of the addition circuit 40 is connected to the monitor 21. Is connected.
[0026]
Hereinafter, a specific operation of the TV door phone apparatus according to the embodiment of the present invention will be described with reference to the drawings.
[0027]
A call operation by a visitor at the entrance, that is, the call button 10 of the entrance slave unit 1 shown in the schematic external view of FIG. 1 and the block diagram of FIG. When a ringing tone is sounded from the main unit speaker 20 and an image captured by the camera 11 of the entrance unit 1 is being displayed on the monitor 21 of the indoor unit 2, the entrance destination is When the visitor at the location 1 presses (again) the call button 10 of the entrance device 1, the image is taken by the camera 11 of the entrance device 1 shown in the block diagram of FIG. After being modulated, the FM modulated signal S1 transmitted to the video demodulation circuit 25 via the slave unit I / F 17, the two lines of the transmission lines L1 and L2, and the master unit I / F 29 of the indoor master unit 2 includes As shown in FIG. 4, FM carrier interruption occurs.
[0028]
In the video demodulation circuit 25 of the indoor master unit 2 shown in the block diagram of FIG. 3, the input port potential setting circuit 30 connects the DC potential of the FM modulation signal S1 from the entrance slave unit 1 input via the capacitor C1 in series. A predetermined DC potential caused by the resistance value of each of the connected resistors R1, R2, R3, here, a half of the power supply voltage Vdd of the DC power supply from the base unit power supply circuit 27 shown in the block diagram of FIG. Also transitions to a slightly higher DC potential V1, and outputs the FM modulation signal S2 having the shifted DC potential V1 as a center value to the first CMOS logic IC31. In addition, the output from the logic gate 31a of the first CMOS logic IC 31 normally has a DC potential of の of the power supply voltage Vdd as a threshold, and becomes an H (High) level or an L (Low) level. When the DC potential of the FM modulation signal S2 is higher than the DC potential V1, the L level FM modulation signal S3 is output. On the other hand, when the DC potential of the FM modulation signal S2 is lower than the DC potential V1, the H level is output. An FM modulation signal S3 is output. The FM modulation signal S3 is not only stored in the capacitor C2 via the resistor R4 of the pulse width discriminating circuit 32, but also input as it is to the phase comparing circuit 37, and is also transmitted through the delay circuit 36 for a predetermined time (details). It is input to the phase comparison circuit 37 as a delayed FM modulation signal S4 (not described).
[0029]
In the video demodulation circuit 25 of the indoor master unit 2 shown in the block diagram of FIG. 3, the phase comparison circuit 37 determines the phase of the FM modulation signal S3 from the logic gate 31a of the first CMOS logic IC 31 and the phase from the delay circuit 36. The phase of the FM modulation signal S3 is compared. Here, the FM carrier intermittent period generated in the FM modulation signal S1 is sufficiently long as compared with the delay time set by the delay circuit 36, so that the phase comparison circuit 37 outputs the low-pass filter 38, The video signal S5 output to the addition circuit 40 via the video amplifier 39 is fixed at the L level during the FM carrier intermittent period.
[0030]
Further, in the video demodulation circuit 25 of the indoor master unit 2 shown in the block diagram of FIG. 3, the first CMOS during the carrier intermittent period shown in the explanatory diagram of FIG. The DC potential of the FM modulation signal S2 input to one of the input ports of the logic IC 31 is slightly higher than 電源 of the power supply voltage Vdd, and the FM modulation signal output from the logic gate 31a during the intermittent carrier period. Signal S3 is fixed at L level. Note that the period of the intermittent carrier is set to be sufficiently long as compared with the period of the carrier. For example, the frequency of the intermittent carrier is 12 MHz as compared with the carrier frequency of 12 MHz and the period of 0.083 μS, and the period is set to 33 μS. It has been set.
[0031]
In the video demodulation circuit 25 of the indoor master unit 2 shown in the block diagram of FIG. 3, the time (first set time) t1 set by the pulse width identification circuit 32 is the product of the resistor R4 and the capacitor C2. It is determined by a certain time constant, and is several times the period of the carrier of the FM modulation signal S3 from the logic gate 31a of the first CMOS logic IC 31, which is about 0.3 μS here, and carrier discontinuity occurs in the FM modulation signal S3. During this period, a pulse longer than the first set time t1 is input, so that the electric charge stored in the capacitor C2 is discharged, and the DC potential of one and the other of the input port of the NOR 33, the second One of the input ports of the CMOS logic IC 35 is at the L level, and the potential of the output port 33a of the NOR 33 is at the H level.
[0032]
In the video demodulation circuit 25 of the indoor master unit 2 shown in the block diagram of FIG. 3, a time (second set time) t2 set by the pulse width setting circuit 34 is a product of the resistor R5 and the capacitor C3. It is determined by a certain time constant, which is about 60 μS here, and the other potential of the input port of the second CMOS logic IC 35 is delayed by about 60 μS, which is the second set time t2, to become the H level. The output signal S6 from the logic gate 35a of the second CMOS logic IC 35 is fixed at the H level only during the second set time t2, and this output signal S6 is connected to one of the input ports of the first CMOS logic IC 31. , The adder circuit 40 and the CPU 28.
[0033]
In the video demodulation circuit 25 of the indoor master unit 2 shown in the block diagram of FIG. 3, the output from the logic gate 31a of the first CMOS logic IC 31 is output if any one of the input ports is at the H level. Since the signal is fixed at the L level, the output signal S6 from the logic gate 35a of the second CMOS logic IC 35 has the second set time t2 even if the carrier intermittent period generated in the FM modulation signal S1 is short. During the period, it always becomes H level.
[0034]
In addition, in the video demodulation circuit 25 of the indoor master unit 2 shown in the block diagram of FIG. 3, the addition circuit 40 outputs the FM modulation signal S5 amplified via the video amplifier 39 and the logic gate 35a of the second CMOS logic IC 35. By adding the output signal S6 to the monitor, an unnecessary pulse generated below the video synchronization signal shown in the explanatory diagram of FIG. 4 can be removed, and a monitor that outputs video based on the video signal S7 from the addition circuit 40 can be removed. In 21, the image at the time of calling during the image output from the entrance slave device can be output as a clear image in which a change in luminance and a disturbance in synchronization are prevented.
[0035]
Further, in the indoor master unit 2 shown in the block diagram of FIG. 2, the CPU 28 to which the output signal S6 from the logic gate 35a of the second CMOS logic IC 35 shown in the block diagram of FIG. A resident in the room, which has detected a call being displayed by a visitor at the entrance and sounds a ringing sound from the main unit speaker 20 and has confirmed the image displayed on the monitor 21 together with the call alert, is used by the handset 22. Is picked up and the hook switch 23 is hooked off, and under the control of the CPU 28 that detects this, the handset 22 used by the resident, the base unit communication circuit 25, the base unit I / F 29, and the transmission lines L1 and L2 are connected. Between two lines, the slave unit microphone 17 and the slave unit speaker used by the visitor via the slave unit I / F 17 of the entrance slave unit 1 and the slave unit communication circuit 15 3 is formed, and a voice signal is transmitted and received through the voice communication line to establish a voice call, that is, a handset voice call according to the resident in the room, and a handset voice according to the visitor at the entrance. Free calls can be made.
[0036]
In the TV intercom apparatus according to the embodiment of the present invention, a handset 22 for making a handset call is used as a communication device of the indoor master unit 2 used by a resident in the room to make a call with a visitor at the entrance. Is applied, and the CPU 28 detects the switching state of the hook switch 23 that is hooked off / on due to the presence / absence of picking up of the handset 22 to form a communication line. The base unit speaker 20 for sounding has a receiving function and a base unit microphone and a call button. These are connected to the base unit call circuit 25, and the CPU 28 which detects the pressing of the call button as a call response changes the call line. It is also possible to make a hands-free call by forming it, and in this case, it is applied to the above-described embodiment. Ndosetto 22 and the hook switch 23 is not required. In addition, the above-described communication device for performing the handset call and the communication device for performing the hands-free call can coexist in the indoor base unit 2. In this case, by providing the call switching unit, the resident in the room can use the handset communication. And hands-free communication can be selected.
[0037]
【The invention's effect】
As is apparent from the above description, according to the television intercom apparatus of the present invention, when a call is made from an entrance slave unit while an image is being displayed on the monitor of the indoor master unit, the FM carrier intermittent generated in the FM modulation signal is not interrupted. Is detected by the video demodulation circuit of the indoor master unit based on the pulse width of the FM modulation signal. Further, the output signal from the detection of the FM carrier interruption is a call signal component for detecting the call during the image output from the entrance slave unit, and not only can the call during the image output be detected with high accuracy, but also the signal generated at the time of the FM carrier interruption. Unnecessary pulses output below the video synchronization signal can be removed, and the image when the image is called out from the entrance slave unit is displayed on the monitor as a clear image with no change in luminance or disturbance of synchronization. This eliminates the need for a circuit for carrier envelope detection and output inversion applied in the conventional example, thereby simplifying the configuration by reducing the number of components.
[Brief description of the drawings]
FIG. 1 is a schematic external view of a television door phone apparatus according to an embodiment of the present invention as viewed from the front.
FIG. 2 is a block diagram illustrating a configuration of a television door phone device according to an embodiment of the present invention.
FIG. 3 is a block diagram showing a specific configuration of a video demodulation circuit of an indoor master unit in the television door phone apparatus according to the embodiment of the present invention.
FIG. 4 is an explanatory diagram for explaining signal processing performed in a video demodulation circuit of the indoor master unit in the television door phone apparatus according to the embodiment of the present invention.
FIG. 5 is a schematic external view of a conventional TV door phone apparatus viewed from the front.
FIG. 6 is a block diagram showing a configuration of an indoor parent device in a conventional TV door phone device.
FIG. 7 is a block diagram showing a specific configuration of a video demodulation circuit of an indoor parent device in a conventional TV door phone device.
FIG. 8 is an explanatory diagram for explaining signal processing performed in a video demodulation circuit of an indoor parent device in a conventional TV door phone apparatus.
[Explanation of symbols]
1 ... Entrance cordless handset
2. Indoor indoor master unit
10. Call button
11. Camera
12 ・ ・ ・ ・ ・ ・ ・ Microphone
13 ... Slave speaker
15 ... Video modulation circuit
20 ・ ・ ・ ・ ・ ・ ・ Main unit speaker
21 ... Monitor
22 ..... handset (communication device)
31 .. First CMOS logic IC
31a... Logic gate (of first CMOS logic IC)
32 .... Pulse width identification circuit (comparing means)
35... Second CMOS logic IC
40 ····· Addition circuit (addition means)
L1, L2 ... transmission line

Claims (1)

When the call button (10) of the entrance cordless handset (1) is pressed, a call is detected by the indoor master unit (2) connected via the transmission lines (L1, L2), and a ring tone is heard from the master unit speaker (20). Is sounded, and an image picked up by the camera (11) of the entrance slave unit is output to the monitor (21) of the indoor master unit, and the communication device (22) of the indoor master unit and the video of the entrance slave unit are displayed. A video door phone device for making a call between a slave unit microphone (12) and a slave unit speaker (13),
The entrance terminal includes a video modulation circuit (14) for modulating a video signal captured by the camera into an FM modulation signal.
The indoor master unit includes a video demodulation circuit (25) for demodulating the FM modulation signal into the video signal,
The video demodulation circuit includes a first CMOS logic IC (31) for setting a DC potential of an input port to which the FM modulation signal is input to a potential shifted from a midpoint potential, and the first CMOS logic. Comparing means (32) for comparing the pulse width output from the logic gate (31a) of the IC with a set time; and outputting a pulse of a fixed time in response to a pulse input longer than the set time. And a second CMOS logic IC (35) for adding the output of the second CMOS logic IC to the demodulated video signal. When a button is pressed, the second CMOS logic removes a pulse output below the video synchronization signal generated when the FM carrier for making a call is interrupted. TV door apparatus characterized by utilizing C output as signal for detecting said call.

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