JPH0383475A - Interphone for multiple dwelling house - Google Patents

Abstract

PURPOSE:To constitute a transmission line from an entrance equipment to an inhouse equipment connected to the branching terminal of an arbitrary brancher by connecting the input terminal of each brancher to a sending terminal at standby time or at the time of emergent notification and connecting the input terminal of any one of the branchers to a branching terminal at the time of a call. CONSTITUTION:At the standby time or at the time of emergent notification, input terminals 51 of respective branchers B1, B2 and B3 is connected to sending terminals 52 and thus, a trunk line is constituted from an entrance equipment G through a repeater R and the branchers B1, B2 and B3 to an inhouse equipment J4. At the time of the call, a select signal is transmitted from the entrance equipment G through the repeater R to controllers C1, C2 and C3. When the select signal for selecting the inhouse equipment J2 is applied to the controllers C1, C2 and C3, switching operation is executed so that only the brancher B can connect the input terminal 51 to a branching terminal 53. Thus, the transmission line is constituted from the entrance equipment G through the repeater R and branchers B1 and B2 to the inhouse equipment J2.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an intercom for apartment complexes, which can be used between an entrance device installed in a common entrance or a manager's room and a housing device installed in each dwelling unit. This device is suitable for making phone calls.

[Prior Art] A schematic configuration of a conventional dark-colored intercom with a TV is shown in FIG. 4. When a visitor operates the call switch 24 provided on the entrance device G, the impedance Z.

A resistor R1 is connected in parallel to the housing unit J, a ringing signal is transmitted to the housing unit J, and a ringing tone is emitted from the ringing speaker 3 of the housing unit J. When the resident answers the ring tone by pressing the response switch 4, power is supplied to the television camera 21 installed in the entrance device G via the power line f, and the video signal is transmitted via the coaxial cable 10. The video is transmitted to the housing device J, and the video is displayed on the monitor TV 1. In addition, the audio signal from the handset 2 of the housing unit J is transmitted to the signal line 12 for telephone calls.
is transmitted to the entrance device G, and the resident's voice is output from the speaker 22 via the audio transformer 29 of the entrance device G. On the other hand, the visitor's voice signal inputted by the microphone 23 of the entrance device G passes through an audio amplifier 26, a coupling capacitor 27, a bridge circuit 28, and two audio transformers, and then is transmitted to the dwelling unit via a signal line e for communication. J, and the visitor's voice signal is output from the handset 2 of the dwelling unit J. This allows the visitor and the resident to communicate over the phone, and also allows the resident to see the visitor. Incidentally, an emergency lamp 25 is connected to the entrance device G via a resistor R2, and an emergency call line 2. It is possible to report abnormalities in the house to the front door via the system.

In this conventional example, in order to connect the housing unit J and the entrance unit G, a coaxial cable 1° for video signal transmission and a power line 13 are used.
, a signal line 12 for calls and calls, a ground line and an emergency call line 1. A four-core cable is used. For this reason, the wiring of transmission lines is complicated, and if, for example, only 2-core or 4-core cables for intercom calls are installed during construction, the wiring must be redone when additional TV cameras are installed. There was a problem.

Figures 5(a) and 5(b) show a schematic configuration of another conventional example. This system is constructed by combining a dwelling unit J with a monitor TV 1 installed inside the dwelling unit and an entrance unit G with a TV camera 21 installed at the entrance, both of which are connected using a dedicated cable such as a coaxial cable. They are connected by a transmission line l. Power is supplied to the entrance unit G side from the housing unit J side, and video, audio, and control signals are multiplexed and transmitted to communicate necessary information.

To explain the more specific configuration, the dwelling unit J is the entrance unit G.
F of the calling signal transmitted in response to the operation of the calling switch 24 of the entrance device G.
One ring detection circuit that demodulates the M-modulated wave, a ring tone generation circuit 20 that amplifies the demodulated ring tone and makes the ring tone sound from the ring speaker 3, a voice modulation circuit 17 that FM modulates the voice signal, and an entrance device G. an audio demodulation circuit 13 that demodulates an FM modulated signal sent out to extract an audio signal; a handset 2 that includes a microphone and a speaker for communications; an audio amplifier 14, 15 that constitutes a communications circuit that includes the handset 2; and a sidetone prevention circuit. 16. A video signal output circuit 11 that takes out the video signal sent out from the entrance device G and outputs it to the monitor television 1, and inputs the FM modulation signal output from the audio modulation circuit 17 via the bandpass filter 18, The FM modulated signal sent from the entrance device G is outputted to the audio demodulation circuit 13 via the bandpass filter 12, and the video signal sent from the entrance device G is outputted to the video signal output circuit 11 via the video filter 10. , furthermore, the power superimposing circuit 8
A balanced input/output circuit 9 is provided for transmitting the supply voltage to the entrance device G. The audio modulation circuit 17 is configured to perform FM modulation on the transmitted audio signal from the handset 2 and send it out to the transmission line l through the balanced input/output circuit 9. itj that demodulates the FM modulated signal and outputs the audio of the entrance device G from the handset 2
In addition, the video signal transmitted from the entrance device G is output from the balanced input/output circuit 9 to the video filter 10, after being amplified by the video signal output circuit 11, and then output to the monitor television 1. It is. A transmission line short-circuit protection circuit 6 and an open detection circuit 7 are added to the power supply superimposition circuit 8.

Moreover, when the response switch 4 is operated, the control circuit 5 is operated, the power supply superimposing circuit 8 is operated, and power is supplied to the entrance device G.

On the other hand, the entrance device G includes an audio demodulation circuit 38 that demodulates the FM modulated signal sent from the housing device J and extracts an audio signal;
Audio modulation circuit 40 that modulates the audio signal from the microphone 23
, a calling signal generating circuit 43 that generates a calling signal in response to the operation of the calling switch 24, an operating state determining circuit 42 that determines the operating state and can generate a calling signal if the call is not in progress, and a voice modulation circuit An FM modulated signal outputted from the circuit 40 via the bandpass filter 41, an FM modulated signal outputted from the calling signal generation circuit 43, and an FM modulated signal outputted from the television camera 21 to the video filter 30 and the video signal output circuit 31.
A balanced input/output circuit 32 inputs a video signal outputted through the transmission line 1 and sends a multiplexed transmission signal to the transmission line 1, and outputs an FM modulated signal to the audio demodulation circuit 38 via a bandpass filter 37; A non-polarizing circuit 33 for non-polarizing the connection with the entrance device G, and a balanced input/output circuit 3 from the modulated signal sent from the housing unit J via the transmission line l.
The power supply separation circuit 34 is provided for separating the power supply of the entrance device G via the power supply terminal 2. The power supply voltage separated by the power supply separation circuit 34 is used as a camera power supply and a circuit power supply via a power switch circuit 35 and a shunt regulator 36. The audio modulation circuit 40 FM-modulates the audio signal input from the microphone 23 and amplified by the audio amplifier 26 and sends it to the housing unit J via the balanced input/output circuit 32. It is configured to demodulate the FM modulated signal from the circuit 32, amplify it in the audio amplifier 39, and output audio from the speaker 22.

In this intercom system, the dwelling device J and the entrance device G are connected by a pair of transmission lines 1 made of coaxial cables, etc., and the video, audio, and video necessary for information communication are transmitted between the two via this transmission line 1. The configuration is such that other control signals are multiplexed and transmitted.

FIG. 6 shows the frequency division state of the signal transmitted via the transmission line 1 in this system.

As shown in the figure, the FM modulated wave of the audio signal sent from the housing device J to the entrance device G is transmitted at the first carrier frequency,
The FM modulated wave of the voice signal sent from the entrance device G to the dwelling unit J is transmitted at the second carrier frequency, and the FM modulated wave of the calling signal is transmitted at the third carrier frequency. The frequency is set to be higher than the video signal frequency band of the television camera that is transmitted over the band.

Note that the power supply voltage is superimposed as a DC component, and these are multiplexed and transmitted via a dedicated transmission line l.

By the way, when such a system is used in an apartment complex with a large number of dwelling units, it is necessary to use multiple units in order to make a call between the common entrance (or the manager's room) and one of the unit units. It is necessary to switch the voice line by some means. For example, a method may be considered in which control is performed so that only the residential unit that is on a call can transmit a frequency assigned for transmitting audio signals. In this type of receiver, each residential unit is always connected to the common entrance unit, so it is necessary to use a dedicated branch or distributor to match the impedance of the transmission line. On the other hand, it is also possible to use a method in which only the selected dwelling unit is switched and connected to the entrance unit, and the other dwelling units are separated from the entrance unit. In this method (see Japanese Patent Application No. 01-88678), a transmission line switch may be provided instead of a branch or divider for impedance matching of the transmission line. A connected transmission line and a transmission line each connected to a plurality of dwelling units are wired, and any one dwelling unit is switched and connected to the entrance unit.

[Problems to be Solved by the Invention] However, when a star wiring switch like the one described above is installed between the entrance unit and a plurality of housing units, the installation locations of each housing unit are dispersed, so the switch There was a problem in that the wiring from the to each unit became long, and the total wiring length became long. Furthermore, since a large number of transmission lines are concentrated in one switch, the wiring becomes complicated and wiring errors are likely to occur during construction. Furthermore, the star wiring switch has a problem in that it is difficult to perform simultaneous broadcasting in an emergency.

The present invention has been made in view of the above points, and its object is to reduce the total wiring length in an intercom for apartment complexes that selectively connects one of a plurality of dwelling units to an entrance unit. In addition to shortening and simplifying wiring,
The purpose is to easily realize simultaneous broadcasting in an emergency.

[Means for Solving the Problems] In order to solve the above-mentioned problems, in the intercom for collective housing according to the present invention, as shown in FIGS. + , J2 * J3 +
In an intercom that multiplex transmits at least an audio signal and a video signal between... using a pair of transmission lines l,
A plurality of branches B having an input terminal 51, a sending terminal 52, and at least one branch terminal 53.

B2+k... are connected in cascade so that the feed terminal is connected to the input terminal of another branch, and the input terminal of the cascaded first-stage branch is connected to the transmission line leading to the entrance switch, making the cascade connection. Connect the feed terminal of the final-stage branch switch to the termination means, and connect the branch terminals of the plurality of branch switches to transmission lines connected to different residential units. Connect the emergency call device H to the sending terminal, connect the input terminal of the turnout to the send terminal during standby or emergency call, and connect the input terminal of any one turnout according to the selection signal given from the outside during a call. The device is characterized in that controllers C+, C2, C:l, . . . are provided for switching connection to the branch terminals.

Here, the controllers C+, C2, Cx, . . . switch the input terminals of the turnouts B1 + B 21 B 31 . Connecting. This controller CI, C
The selection signal or cancellation signal given to 21C31... may be transmitted via a signal line different from the transmission line,
It is preferable that the voice signal during one call, which may be multiplexed transmitted through the transmission line, is transmitted by a signal modulated with a carrier wave, and the voice signal at the time of emergency call is transmitted by a baseband signal. In a system configured to supply DC voltage to a transmission line, the emergency alarm device disconnects the internal notification circuit from the transmission line when the DC voltage level on the transmission line is high, and disconnects the internal notification circuit from the transmission line when the DC voltage level is low. Preferably, a switch circuit is provided for connecting a circuit to the transmission line.

Note that the terminating means connected to the feed terminal of the cascade-connected final stage branch may be a housing unit or may be a terminating resistor.

[Function] In the present invention, in this way, a plurality of branches B + , B 2 , B 3 , . The terminals are connected in cascade so that they are connected to the input terminals of other turnouts, and the input terminal of the cascaded first-stage turnout is connected to the transmission line leading to the entrance switch. Since the input terminal of the turnout is connected to the sending terminal as shown in Fig. 2, it is possible to construct a main line from the entryway through all the turnouts to the termination means. Therefore, in the event of an emergency, simultaneous broadcasting can be performed to all the emergency notification devices H connected on this main line.

In addition, when making a call, the input terminal of one of the branching devices is switched to the branching terminal as shown in Figure 2, so that one of the dwelling units connects to the entrance device via the transmission line.
Since the device is connected in a pair-to-one manner and other residential units are separated from the transmission line, there is no risk of deterioration in speech quality due to impedance mismatching or the like.

Furthermore, at the end of a call, by switching and connecting the input terminal of the branch to the sending terminal, it is possible to reconfigure the main line from the entrance switch to the terminating means via all the branches, as shown in FIG. This turnout B,,B2. B...
Controller ClIC2+C31 for controlling the switching operation of
... is preferably each branch B + , B 2B
3 +..., and the branchers B, , B2 . Controls the switching operation of B, .

In this intercom system, the video signal and audio signal are multiplexed through a pair of transmission lines, so when the video signal is transmitted as a baseband signal, the audio signal is modulated on a carrier wave with a higher frequency than the video signal. It will be transmitted as a signal. However, in emergencies, video signals are often unnecessary, and multiplex transmission systems do not always work well, so it is preferable to transmit audio signals in emergencies using baseband signals. By doing so, the emergency alarm device H can be realized with a simple configuration.

More detailed configuration and operation of the present invention will be made clearer in the following description of the embodiments.

[Example] FIG. 3 is a block diagram of one embodiment of the present invention.

First, the entrance device G consists of a doorbell D with a camera and a dwelling unit selection unit S. The configuration of the camera-equipped door phone D is as follows:
The structure is the same as that of the entrance device G in the conventional TV intercom shown in the figure, and the video signal and the audio signal can be multiplexed and placed on the transmission line e. In order to reduce power consumption, power is not supplied to this camera-equipped door phone D when it is on standby (when not talking), and power is supplied from repeater R via transmission line l only when it is in operation. It is composed of The dwelling unit selection unit S selects a plurality of dwelling units J, , J2 . J...
・It is a device for selecting one from the entrance device G side, and is equipped with a numeric keypad T for selection. The selection signal of the dwelling unit on the entrance device G is a DTMF (Double Modulated Tone) used in electronic button telephones, etc.
e Frequency) signal.

This selection signal may be superimposed on the audio signal from the entrance device G, or may be transmitted on a different carrier wave from the audio signal from the entrance device G, or the DTMF signal may be transmitted on a different signal line. The operating power of the dwelling unit selection unit S may be superimposed on the signal line and supplied from the repeater R, but in this embodiment, the operating power of the dwelling unit selection unit S is supplied from the door phone D with a camera. It is supplied independently.

Housing equipment Jl, J2. J3. . . . has the same configuration as the conventional housing unit J shown in FIG. In the configuration shown in FIG. 1, two housing units J2 are provided, but
Either one is connected to the branch B2 by a switch K. In addition, each housing unit J l r J2. J3+・
... supplies a low DC voltage onto the transmission line l in the standby state, and a high DC voltage on the transmission line l in the operating state.
configured to supply the top.

The repeater R transmits the selection signal generated by the dwelling unit selection unit S in the entrance device G to the controller C1 via a dedicated signal line.
, C2, C3, . Based on this selection signal, the controllers C+, C2, C3,...
+, Bx, B), . . . Moreover, the repeater R relays the signal on the transmission line e connected to the entrance switch G to the input terminal 51 of the first branch B1.

The branch B has an input terminal 51, a feed terminal 52, and a branch terminal 53. The input terminal 51 is selectively connected to either the sending terminal 52 or the branching terminal 53.

Other branches B2+B3+... have similar configurations. The feed terminal of the first turnout B1 is connected to the input terminal of the second turnout B2, and the feed terminal of the second turnout B2 is connected to the input terminal of the third turnout B. The feed terminal of the third branch B3 is connected to an input terminal of a fourth branch (not shown) or to a termination means.

The terminating means may be a terminating interphone whose characteristic impedance is equivalent to the transmission line 1, or may be another housing unit J4.

An emergency notification device H is connected to an input terminal or a sending terminal of at least one branch. The configuration of this emergency alarm device H is shown in FIG. 1 and will be explained. In the figure, 60 is a DC relay, and 61 and 62 are its contacts. The input terminal of the emergency alarm H has a coupling capacitor 63.64 and a contact 61.62.
The twelfth winding of the audio transformer 67 is connected through the twelfth winding. A speaker 68 for emergency notification is connected to the secondary winding of the audio transformer 67. Further, the excitation coil of the DC relay 60 is connected to the input terminal of the emergency alarm H via choke coils 65 and 66 for cutting off high frequency waves. When the level of the DC voltage applied from the transmission line between the input terminals of the emergency alarm device H becomes high, the DC relay 6
0 is energized and the contacts 61 and 62 are opened, thereby disconnecting the reporting circuit consisting of the audio transformer 67 and the speaker 68 from the transmission line. Further, when the level of the DC voltage applied from the transmission line between the input terminals of the emergency alarm device H becomes low, the excitation of the DC relay 60 is released, and the contacts 61.6
2 closes. As a result, the reporting circuit consisting of the audio transformer 67 and the speaker 68 is connected to the coupling capacitor 63.6.
4 to the transmission line. When making an emergency call, the audio signal is transmitted as a baseband signal from the repeater R or the entrance device G onto the transmission line, so the audio signal can be output from the speaker 68 without providing demodulation means to the emergency call device H. . Note that the audio signal at the time of emergency call may be an evacuation guidance broadcast or a simple alarm sound. can be easily created.

Next, the switching operations of the switches B + , B 2 , and B 3 will be explained with reference to FIGS. 1 and 2.6 First,
When on standby or when making an emergency call, as shown in FIG.
are connected to the sending terminal 52, and thereby the gateway device G is connected to the repeater R1, the branching device B, , B2 . After B., Judoki, J.

(or the terminating means) is constructed. Also, during a call, the controller C+,
A selection signal is transmitted to C2 and Cs. Now, housing equipment J2
If a selection signal for selecting is given to the controller CC2,C, only the branch B2 performs a switching operation to connect the input terminal 51 to the branch terminal 53, as shown in FIG. As a result, a transmission line is formed from the entrance device G to the dwelling device J via the repeater R1 and the branching devices B, B2.

The repeater R is equipped with a voltage discrimination circuit for monitoring the voltage of the transmission line connected to the first branch B, detects the voltage level of the DC component on this transmission line, and depending on the detection result, The 0 turnout switch B2, which discriminates between the operating state and the non-operating state of the housing unit, performs the above switching operation, and the relay R switches the housing unit J2
After the connection is made, a door device call signal is transmitted from the entrance device G or the repeater R to the dwelling device J2. As this calling signal, as explained in the conventional example, a carrier wave of a special frequency may be transmitted, or the transmission line voltage may be set below a certain value,
Alternatively, the calling signal may be transmitted by short-circuiting the transmission line. At +[tll of the dwelling unit J2, the calling signal is received and the operation is started, and the circuit for power supply is activated. Increase the voltage level of the DC component of transmission 8.1. As mentioned above, the residential unit supplies a low DC voltage to the transmission line l even in the standby state, but in the operating state, the DC voltage of the transmission line l is set higher than in the standby state. . In the emergency notification device H, which is closer to the entrance device G than the turnout B2, the DC relay 60 is energized by this increase in DC voltage, contacts 61 and 62 are opened, and the notification circuit is disconnected from the transmission line. Further, in the repeater R, the level of the DC voltage is monitored by a voltage discrimination circuit to detect the start of operation of the dwelling unit. When the start of operation of the dwelling device is detected, the power superimposing circuit of the repeater R operates, and power is supplied to the camera-equipped door intercom D of the entrance device G. Therefore, when power is supplied to the camera-equipped door phone D, the dwelling unit is always connected normally and starts operating normally. For this reason, the FM in the camera-equipped door phone D
There will never be a situation where the FM modulated wave from the residential unit is not supplied to the audio demodulation circuit of the system, and no abnormal noise will occur.

Here, while the first dwelling unit is being selected and called using the entrance unit G, inconvenience may occur if another dwelling unit is called. In other words, while the first unit is ringing, the second
If a door unit is called, multiple units may respond at the same time, but since the door unit can only talk to one unit, it is preferable to prohibit calling another unit. Therefore, in this embodiment, after the first dwelling unit is selected and called, selection of another dwelling unit is not accepted until the end of the call. Specifically, until the end of the call is detected by the voltage discrimination circuit of the repeater R, even if the repeater R receives a selection signal from the dwelling unit selection unit S,
This is not relayed to controllers C, , C2, and C3.

When the call ends, the DC voltage of the transmission line 1 is set to a standby voltage on the residential unit side, so the level of the DC voltage of the transmission line 1 decreases. In the emergency alarm H, the DC relay 60 is de-energized due to this drop in DC voltage, and the contacts 61 and 62
is closed and the reporting circuit is connected to the transmission line. Also,
In the repeater R, the level of the DC voltage of the transmission &11 is monitored, and the selection of the dwelling unit is canceled by detecting a fall in the voltage. Specifically, from the repeater R to the controllers C,,C
,.

Sends a release signal to C1, and all branches B l + B
2 +B to the standby connection state shown in FIG. However, in this embodiment, since an FM audio demodulation circuit is used in the camera-equipped door intercom D, the power superimposing circuit in the repeater R is Stop the operation and use the camera-equipped doorbell D at the entrance device G.
The power supply is shut off first to prevent abnormal noise from occurring.

By the way, there may be a vacant line in the transmission line from the turnout B2 to the housing unit J2, or there may be a break in the transmission line leading to the housing unit J2.
If the voltage is not normal, the voltage of the transmission line from the first branch B to the repeater R will not reach the specified voltage even after connecting the branch B2 to the unit J2. In device R, after a selection signal switches branch B2, if the voltage of transmission line e does not reach the specified voltage even after a certain period of time (for example, 1 second), a release signal is forcibly generated. And all the switches B + , B 2 ,
B3 is returned to the standby connection state shown in Figure 1. In this case, the rise in voltage of the transmission line connected to unit J2 is not detected, so the power superimposition circuit of repeater R is connected to the doorbell with camera. If the power supply operation to D is not started, that is, in this embodiment, the dwelling unit is connected normally and has not started operating normally, the power supply to the camera-equipped door intercom D in the entrance device G is turned on. It is configured so that there is no such thing.

The above operation has been described for the case where the dwelling unit J2 is selected, but it goes without saying that the same operation occurs when the dwelling unit Jl or J is selected. In addition, the number of turnouts and housing units is not limited to the examples,
The number can be any number.

Note that the turnouts B, B2. B, controller C+, C2
, C3's operating power supply is entrance device G, repeater R1 switch K,
Housing equipment J 3. It does not matter whether the power is supplied from either J2+J3, a dedicated power supply line may be provided for the operation power supply, or a power supply superimposed on the transmission line may be used.Furthermore, the normally open contact A relay circuit with a normally closed contact and a common contact is used as a changeover switch of a branch, and the normally open contact is connected to the branch terminal, the normally closed contact is connected to the feed terminal, and the common terminal is connected to the input terminal. When used, the common contact returns to a normally closed contact simply by cutting off the power supply to the relay circuit, making it easy to return to the standby state in which the input terminal is connected to the sending terminal.

In the above embodiment, a dedicated signal line is provided to transmit the selection signal or the cancellation signal to the controllers C+, C2, and C), but multiplex transmission may also be performed using the transmission LA1. In this case, It is sufficient to add a fourth carrier frequency to the multiplex transmission signal shown in Fig. 6 and transmit the selection signal or cancellation signal by modulating this fourth carrier frequency. However, the multiplex transmission system will not work well in an emergency. Because there is no limit,
It is preferable that the release signal in an emergency is transmitted as a baseband signal.If the frequency of this release signal is set lower than the horizontal synchronization signal of the video signal transmitted as a baseband signal during normal times, it is possible to transmit the video signal during normal times. can be prevented from being mistaken as a release signal.

In addition, in the embodiment, a repeater R is provided between the entrance device G and the first branch B, but if the function of this repeater R is included in the entrance device G, the repeater R may be omitted. .

[Effects of the Invention] As described above, in the present invention, turnouts having an input terminal, a feed terminal, and a branch terminal are connected in cascade so that the feed terminal is connected to the input terminal of another turnout. , during standby or emergency call, connect the input terminal of each turnout to the feed terminal,
When making a call, the input terminal of one of the turnouts is connected to the branch terminal, so from the entrance unit connected to the input terminal of the first turnout to the residential unit connected to the branch terminal of any turnout. At this time, other residential appliances are disconnected from the transmission line, so good transmission quality can be obtained. Furthermore, each branch can be connected with a feed wiring, so the branch Simultaneous emergency broadcasting can be easily performed to all emergency alarm devices connected to the input terminal or sending terminal of the system. Further, by using feed wiring instead of the conventional star wiring, the total wiring length is shortened and the wiring becomes easier.

Note that if the audio signal for an emergency call is transmitted as a baseband signal, the emergency call can be made even if the multiplex transmission system does not work well in an emergency.

Further, since it is not necessary to provide the emergency alarm device with a demodulating means, the configuration of the emergency alarm device becomes simpler.

Furthermore, in an intercom system in which the DC voltage level of the transmission line is set high during a call, deterioration in transmission quality can be prevented by configuring the system so that the notification circuit of the emergency alarm device is disconnected from the transmission line upon detection of this DC voltage.

[Brief Description of the Drawings] Figures 1 and 2 are block diagrams for explaining the operation of an embodiment of the present invention, Figure 3 is a block diagram showing the overall configuration of the same, and Figure 4 is a block diagram of the conventional example. Schematic configuration diagram, Figure 5 (,) and (
b) is a block diagram of a housing unit and an entrance unit in other conventional examples, respectively, and FIG. 6 is an explanatory diagram showing an example of frequency division on a transmission line used in the same. B + , B 2 , B s are turnouts, C,, C,
, C, is the controller, G is the entrance device, H is the emergency alarm device, J l
, J2. J 3. J- is a housing unit, and l is a transmission line.

Claims (6)

[Claims] (1) In an intercom that multiplex transmits at least an audio signal and a video signal between a doorway unit and a dwelling unit using a pair of transmission lines, a plurality of branchers each having an input terminal, a sending terminal, and at least one branch terminal. are connected in cascade so that the feed terminal is connected to the input terminal of the other branch, and the input terminal of the cascaded first stage branch is connected to the transmission line leading to the entrance switch, and the cascaded terminal is connected to the input terminal of the other branch. The feed terminals of the plurality of turnouts are connected to the terminating means, and the branch terminals of the plurality of turnouts are each connected to a transmission line connected to a different dwelling unit, and at least one
An emergency call device is connected to the input terminal or sending terminal of two turnouts, and when on standby or when making an emergency call, the input terminal of the turnout is connected to the send terminal, and when making a call, either one of the turnouts is connected according to the selection signal given from the outside. An intercom for an apartment complex, characterized by being provided with a controller that switches and connects an input terminal of a turnout to a branch terminal. (2) The intercom for apartment complexes according to claim 1, wherein the voice signal during a call is transmitted by a carrier wave modulated signal, and the voice signal at the time of emergency call is transmitted by a baseband signal. (3) The intercom for apartment complexes according to claim 1, wherein the signal given to the controller is transmitted via a signal line different from the transmission line. (4) The intercom for apartment complexes according to claim 1, wherein the signals given to the controller are multiplexed and transmitted via the transmission line. (5) The apartment building according to claim 4, wherein the video signal is transmitted by a baseband signal, and the signal given to the controller at the time of emergency call is transmitted at a frequency lower than the horizontal synchronization frequency of the video signal. Intercom. (6) The emergency alarm device disconnects the internal notification circuit from the transmission line when the DC voltage level on the transmission line is high;
2. The intercom for an apartment complex according to claim 1, further comprising a switch circuit that connects an internal notification circuit to the transmission line when the DC voltage level is low.