JP2654664B2 - TV intercom system - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a television intercom system, and more particularly, to a method for transmitting a signal between an intercom master unit having a monitor television and an intercom slave unit having a television camera. It relates to an improved television intercom system.

[Prior art] A TV camera is installed on the slave unit side, and a monitor TV is installed on the master unit side so that a call can be made at the same time as a call, so that the visitor's figure can be visually recognized inside the room by the intercom slave unit installed at the entrance. Television intercom systems capable of displaying images have been developed and used.

FIG. 8 is a block diagram showing the configuration of such a television intercom system. This system is configured by combining an intercom master unit 100 having a monitor television (not shown) installed indoors and an intercom slave unit 200 having a monitor camera (not shown) installed at the entrance. Both are connected by a single signal line 1 such as a coaxial cable. Power is supplied to the slave unit 200 from the master unit 100 side, and multiplex transmission of video, audio, and control signals is performed to communicate necessary information. It is configured to do this.

A more specific configuration will be described.
0 is a power supply circuit for the slave unit for supplying power to the slave unit 200 side.
101, a modulation unit 105 that modulates a high-frequency signal by an audio signal (shown as a microphone signal) amplified by a microphone (not shown) and a tone signal serving as a control signal of a camera provided on the intercom slave 200 side. The demodulation unit 104 demodulates the high-frequency signal transmitted from the 200 side to extract a calling signal and a voice signal. The high-frequency signal output from the modulation unit 105 is input to the demodulation unit 104 via the signal line l. A branching / mixing circuit 103 for outputting a high-frequency signal transmitted from the side, and a coil for superimposing the power supply current of the power supply circuit 101 for the child unit on the high-frequency signal of the branching / mixing circuit 103 and sending it to the child device 200 side from the signal line l. Power supply superimposing circuit 10 composed of L and capacitor C
The modulation section 105 inputs an output signal from a microphone signal amplification circuit 105b that amplifies a microphone signal to a certain level and an output signal from a tone signal generation circuit 105c to a modulation circuit 105a. The signal is used to modulate a high-frequency signal serving as a first carrier.
Then, a demodulation circuit 104a for demodulating a high-frequency signal from the demultiplexing circuit 103, and a slave 200
A tone signal detecting circuit 104c and a voice signal amplifying circuit 104b for extracting a calling signal and a voice signal transmitted from the side.
Is provided.

Further, the other intercom slave 200 is a modulation unit that modulates a high-frequency signal by a voice signal (shown as a microphone signal) amplified by a microphone (not shown) and a tone signal serving as a calling signal to the base unit 100 side. 204, a demodulation unit 205 that demodulates a high-frequency signal transmitted from the base unit 100 to extract a camera control signal and an audio signal, a high-frequency signal output from the modulation unit 204, and a video signal output from a television camera (not shown). And a demultiplexing circuit 203 for outputting a high-frequency signal to the demodulation unit 205, sending out the high-frequency signal of the demultiplexing and mixing circuit 203 to the signal line l, and
From the high-frequency signal sent from the 100 side,
In order to separate the power supply current, a power supply separation circuit 201 composed of a combination of a coil L ′ and a capacitor C ′ is provided, and a modulation unit 204 amplifies a microphone signal to a certain level by a microphone signal amplification circuit 204b. And the output signal from the tone signal generation circuit 204c are input to the modulation circuit 204a, and these signals are used to make the second carrier (a high-frequency signal that can be distinguished from the first carrier on the master unit side). It is configured to modulate the high frequency signal
The demodulation unit 205 includes a demodulation circuit 205a for demodulating a high-frequency signal from the demultiplexing / mixing circuit 203, a camera control signal from the demodulated signal, and a tone signal detection circuit 205c for extracting an audio signal. The configuration includes a signal amplification circuit 205b. The output end of the coil L 'of the power supply separating circuit 201 is connected to the camera power switch 202 and is supplied to the internal circuit of the slave as a slave power.

The connection terminals T1 and TG provided on the base unit side and the connection terminals T2 and TG provided on the base unit side are connected to the master unit 100 and the slave unit 200 with the core wire of the coaxial cable 1 and the shield jacket, respectively. The video, audio, and other control signals required for information communication are multiplex-transmitted between the two via the single signal line l.

In the system having such a configuration, when a call button (not shown) of the slave 200 is operated, a call signal is generated, and a tone signal is output from the tone signal generation circuit 204c of the modulation unit 204. The second carrier is FM-modulated with this tone signal. The modulated second carrier is sent to the parent device 100 side through the demultiplexing circuit 203 and the power supply separation circuit 201 and further via the coaxial cable l, and the FM-modulated signal is supplied to the power supply superposition of the parent device 100 side. The signal is applied to the demodulation unit 104 via the circuit 102 and the demultiplexing circuit 103,
When demodulated, the tone signal is detected by the tone signal detection circuit 104c, and a speaker (not shown) of the base unit 100 sounds as a calling signal.

In this way, the called base unit 100 responds with a timer (not shown) by sounding a speaker (not shown), and also operates a camera switch (not shown) for operating a monitor camera (not shown) on the child device 200 side. (Not shown) to generate a camera power control signal, output a tone signal from the tone signal generation circuit 105c, and send it to the modulation circuit 105a together with the responded output signal of the microphone signal amplification circuit 105b.
FM modulate the carrier. The FM-modulated first carrier is transmitted to the slave 200 through the demultiplexing circuit 103, the power supply superimposing circuit 102, and the coaxial cable l.

On the other hand, in handset 200 receiving this signal, the received signal is demodulated by demodulation unit 20 through power supply separation circuit 201 and demultiplexing / mixing circuit 203.
5, and further demodulates the FM modulated wave of the first carrier by the demodulation circuit 205a, amplifies the audio signal by the audio signal amplifying circuit 205b, and transmits the audio signal from the speaker (not shown) of the slave 200 to the master 100 side. A response is output. At this time, a tone signal is detected by the tone signal detection circuit 205c, and the camera power switch 202 is turned on to drive a television camera (not shown). When this television camera is driven, the video signal enters the demultiplexing / mixing circuit 103 of the parent device 100 via the demultiplexing / mixing circuit 203 and the coaxial cable l.
The image is sent to a monitor television (not shown) and projected.

The audio signal input from the microphone of the slave unit 200 is amplified by the microphone signal amplifier circuit 204b and input to the modulation circuit 204a in the same manner as the tone signal of the tone signal generation circuit 204c. FM modulation and demultiplexing / mixing circuit 20
3, through the power supply separation circuit 201 and the coaxial cable l,
Demodulation unit through the power supply superposition circuit 102 and the demultiplexer 103
After being sent to 104 and demodulated, the audio signal amplifier circuit 104c
And outputs a sound from a speaker (not shown) of base unit 100.

In such a television intercom system, the first carrier and the second carrier are selected to have a frequency higher than the video signal frequency band of the television camera in order to prevent interference. The power supply to be connected to the slave unit internal circuit from the constant voltage power supply circuit 101 provided on the base unit 100 side through the coil L and coaxial cable l of the power supply superposition circuit 102 and the coil L ′ of the power supply separation circuit 201 on the slave unit 200 side. Since the power is supplied to the television camera, if the fluctuation of the audio signal transmitted from the base unit 100 is large, the current consumption of the speaker of the slave unit driven by the power supplied from the base unit 100 is reduced. Fluctuations also increase.

As a result, the power supply superposition circuit 102 and the
Due to the impedance of the coils L and L 'of the power supply separation circuit 201 on the 0 side, a ripple voltage is generated on the cable l, causing problems such as disturbing the video signal.

For example, since the current consumption of the audio signal amplification circuit 205b normally fluctuates to about several mA to 100 mA, for example, the resistance components of the coils L and L 'of the power supply superposition circuit 102 of the parent device 100 and the power supply separation circuit 201 of the child device 200 Is 100Ω, (ripple voltage) = 100mA × 100Ω = 10V, and a ripple voltage of 10 volts is generated in the cable I. Normally, the video signal is about 1VP-P,
Since the ratio (the ratio between the desired signal and the interference signal) needs to be about 50 dB, if a large-level ripple voltage as described above is generated, the ripple voltage will be larger than the video signal and can be prevented by simple means. I will not be able to do it.

Further, in the circuit having the above configuration, the camera power switch 202 on the slave 200 is controlled by demodulating and detecting a tone signal transmitted by modulating the audio signal together with the audio signal from the base unit 100. , Master unit 100 side and slave unit 2
On the 00 side, a tone signal generation circuit 105c and a tone signal detection circuit 205c are required, and there is a problem that the circuit becomes complicated.

[Problem to be Solved by the Invention] The first invention proposed in view of the above situation is to control a driving of a television camera by controlling a current of a certain level supplied from a master unit to a slave unit by a television. It is intended to simplify the circuit configuration by changing the level between when the camera is driven and when it is not driven, detecting the level change on the slave unit side, and controlling the power supply of the television camera.

In the second invention proposed at the same time, a shunt regulator is provided on the slave unit, and the current consumption of the shunt regulator is changed in accordance with the change in the current consumption of the internal circuit on the slave unit. It is an object of the present invention to provide a video interphone system having a simple circuit configuration while removing a ripple voltage generated on a signal line connecting the video signal and a video signal without interference.

[Means for Solving the Problems] According to a first aspect of the present invention, which is proposed to achieve the above object, an intercom master unit having a monitor television and an intercom slave unit having a television camera have one signal. An improvement of a television intercom system in which video and audio signals required for information transmission are multiplex-transmitted by connecting via a line, wherein the interphone master unit is a constant-level constant current supplied to the slave unit side. A constant-current power supply circuit capable of variably controlling the power supply, and superimposing a constant-level current output from the variable constant-current power supply circuit on a high-frequency signal modulated with voice and other signals necessary for information transmission. And the variable constant-current power supply circuit switches and outputs a current level larger than normal when driving the television camera on the slave side. The intercom slave unit is used to separate the current from the variable constant current power supply circuit supplied from the master unit through the signal line from a high-frequency signal modulated by another signal necessary for information transmission. A power supply separation circuit is provided, and the current supplied from the master unit side is supplied to the internal circuit on the slave unit side including the television camera via the power supply separation circuit, and the level of the current separated by the power supply separation circuit is adjusted. A current detection circuit for determining the output level of the current supplied from the variable constant current power supply circuit by the current detection circuit, and actuating a camera power switch to drive the television camera. Features.

A second invention proposed at the same time is to connect an intercom master unit having a monitor television and an intercom slave unit having a television camera by one signal line, and to provide video and audio signals necessary for information transmission. The intercom master unit is provided with a variable constant current power supply circuit that can variably control a constant level constant current for supplying power to the slave unit side. The constant current output from the variable constant current power supply circuit is superimposed on a high-frequency signal modulated by voice and other signals required for information transmission and supplied to the slave unit side. The power supply circuit is configured to switch and output a current level larger than a normal level when the television camera on the slave unit side is driven. A power supply separation circuit for separating a constant level current from the variable constant current power supply circuit supplied from the master unit through the signal line from the high frequency signal is provided, and supplied from the master unit through the power supply separation circuit. And a current detection circuit for determining the current level separated by the power supply separation circuit, while supplying the current of a given level to an internal circuit on the slave unit side including a television camera connected in parallel with a shunt regulator. The current detection circuit determines the output level of the current supplied from the variable constant current power supply circuit, and operates the camera power switch to drive the television camera.

In a desirable mode of the second invention, the current detection circuit, the shunt regulator and the camera power switch of the intercom slave unit are integrated as a shunt regulator / camera power switch circuit.

[Operation] In the first aspect of the present invention, a variable constant current power supply circuit having high internal impedance is provided on the intercom master unit side, and the supply current of the variable constant current power supply circuit on the master unit side is switched by a camera power control signal. Is detected on the slave unit side and the camera power switch is controlled, so that it is not necessary to provide a tone signal generation circuit on the master unit side and a tone signal detection circuit on the slave unit side as in the conventional system.

According to the second aspect of the present invention, the shunt regulator is provided in parallel with the internal circuit of the slave unit including the television camera on the slave unit side. The power supply from the master unit to the slave unit is made constant, the fluctuation in current consumption on the slave unit is absorbed by the shunt regulator provided on the slave unit, and at the same time, the supply current value of the variable constant current power supply circuit is switched to power the camera. Since the switches are controlled together, the conventional system has a simplified configuration and the ripples are eliminated. In a desirable mode of the second invention, a composite circuit provided on the slave unit side for removing the ripple and controlling the power supply of the television camera can be realized by one circuit configuration.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of the present invention.

A variable constant current power supply circuit 1 for supplying a constant current to the master unit A and the slave unit B, and a video signal and an FM modulation wave from the slave unit B side are separated.
It has a branching / mixing circuit 5 for mixing, a demodulation unit 6 for demodulating the modulated wave split by the branching / mixing circuit 5, and a modulation unit 7 for generating an FM modulated wave to be sent from the master unit A to the slave unit B. ing.

On the other hand, the slave unit B has a coil L2 and a capacitor C2 that separate and output a constant current sent from the master unit A from a video signal or an FM modulation wave.
And a splitter / mixer circuit 8, a modulator 9 and a demodulator 10 which operate in the same manner as the splitter / mixer 5 on the master unit A side. The output from the circuit 2 is supplied from the output end of the coil L2 to the camera power supply via the camera power switch 4 and is also supplied as a slave power supply.
The output terminal of the capacitor C2 is connected to the above-described demultiplexing / mixing circuit 8.

Further, a current detection circuit 12 is provided on the slave unit B side, and power is supplied to the slave unit B and a television camera (not shown) through the current detection circuit 12. No tone generation circuit is provided, and no tone signal detection circuit is provided on the slave B side.

The variable constant current power supply circuit 1 provided on the base unit A is supplied with power from the power supply Vcc inside the base unit A,
1, a resistor R1 to R3, a Zener diode ZD1 and a switch S are connected as shown in the figure, and the switch S is connected to the Sb side when the television camera is driven by the camera power control signal of the master unit A side. When the motor is not driven, it is switched to the Sa side.

In such a variable constant current power supply circuit 1, if the Zener voltage of the Zener diode ZD1 is VZD1, when the switch S is switched to the Sa side, the resistor R2
Since R3 is connected in series, the current Ia supplied to the slave B is
Is Ia = VZD1 / (R2 + R3), and when the switch S is switched to the Sb side, the connection of the resistor R3 to the resistor R2 is released.
Is set to Ib = VZD1 / R2, and the constant current value supplied to the slave unit B is variably set according to the switching of the switch S, that is, the presence or absence of the camera power control signal.

On the other hand, the television camera (not shown) on the slave B side is configured to be supplied with power through the camera power switch 4 controlled by the output of the current detection circuit 12, and is provided on the master A side. The terminals T1 and TG and the terminals T2 and TG provided on the slave B side are connected to each other by one signal line l (for example, a coaxial cable).

The current detection circuit 12 provided in the slave B has a transistor Q2
And resistors R4 and R5 are connected as shown in the figure. When the camera power control signal is not output from the master unit A side, the master unit A
Since the supply current from the transistor Q2 is small, the voltage drop of the resistor R4 is necessary to turn on the transistor Q2.
The transistor Q2 is turned off without reaching the base-emitter voltage VBEQ2, and when the camera power control signal is output from the master unit A, the supply current increases from the master unit A, so that the voltage drop of the resistor R4 decreases by VBEQ2. Beyond the transistor Q2
Turns ON, and at this time, a current flows through the resistor R5,
The camera power switch 4 is turned on by the voltage between both ends, and the television camera is driven by being supplied with the current supplied from the variable constant current power circuit 1 via the camera power switch 4.

In such a configuration, since a tone signal for controlling the television camera on the slave B side is unnecessary, a tone generation circuit is not required on the master A side, and a tone signal detection circuit is not required on the slave B side. The configuration is simplified.

FIG. 2 shows a modulated wave on the base unit obtained by FM-modulating the first carrier sent from the intercom base unit A to the handset B side, and a child obtained by FM-modulating the second carrier sent from the handset B to the base unit A. FIG. 3 is an explanatory diagram showing a modulation wave on the device side and a frequency arrangement of a video signal sent from the slave device B to the master device A. FIG. 3 is a diagram showing an audio signal and tone transmitted between the master device A and the slave device B. FIG. 3 is an explanatory diagram illustrating a frequency arrangement of a signal. Audio signal is several hundred Hz to 10KH
It has a frequency band of about z, and the tone signals are 20 KHz signals so that the frequency bands do not overlap each other.

 Next, the operation of the intercom system will be described.

When a visitor operates a call button (not shown) of the intercom slave unit B provided at the entrance, a call signal is generated, and a tone signal is output from the tone signal generation circuit 9c of the modulation unit 9 and is transmitted to the modulation circuit 9a. FM modulation is performed on the input second carrier. The FM modulated wave is transmitted to the master A via the coaxial cable 1 through the branching / mixing circuit 8 and the power supply separating circuit 2.

In the master unit A, the internal impedance of the variable constant current power supply circuit 1 is very high, so that the modulated wave sent from the slave unit B is input to the branching / mixing circuit 5 through the capacitor C1,
Here, the frequency band of the second carrier of the slave unit modulated wave is demultiplexed and input to the demodulation unit 6, where it is demodulated into a tone signal by the demodulation circuit 6a, the tone signal is detected by the tone detection circuit 6c, and the calling signal and Then, a speaker (not shown) on the master unit A side sounds.

When the resident knows the visitor by this call signal, the master unit A
The microphone signal is input to a microphone signal amplifier circuit 7b of the modulation unit 7 by picking up and responding to a handset (not shown) provided on the side, and the microphone signal is FM-modulated by the modulation unit 7a on the first carrier. , Demultiplexing circuit 5 and capacitor C1
Through the coaxial cable 1 to the slave unit B side.

On the slave unit B side, the FM modulated wave transmitted from the master unit A side is input to the power supply separation circuit 2, the frequency band of the first carrier is split by the splitting / mixing circuit 8 and input to the demodulation unit 10. The demodulation circuit 10a demodulates the audio signal and the tone signal.
When the audio signal is amplified by the audio signal amplifier circuit 10b and the response of the master unit A is output from a speaker (not shown), the switch S of the variable constant current power supply circuit 1 of the master unit A is closed to the Sb side, and As described above, the camera power switch 4
Is turned on, and a constant current separated by the power supply separation circuit 2 is supplied to a television camera (not shown).

Thus, when the television camera is driven, the video signal is passed through the branching / mixing circuit 8 and the power supply separation circuit 2 of the slave unit B.
The signal is multiplex-transmitted through the coaxial cable 1 together with the FM modulated wave generated by the modulation unit 9 described later and sent to the master A side.

On the master unit A side, the multiplexed signal sent from the slave unit B side is input to the demultiplexing / mixing circuit 5 through the capacitor C1, and the split video signal is transmitted to a monitor television (not shown). The image of the visitor is displayed.

The audio signal of the slave unit B is amplified by the microphone signal amplifier circuit 9b, modulated by the modulation circuit 9a in the same manner as the tone signal, and transmitted to the master unit A through the coaxial cable l. A call is received by a handset (not shown) of A and a call is made.

FIG. 4 is a block diagram showing a second embodiment of the present invention. The same parts as those of the first invention are denoted by the same reference numerals, and description thereof will be omitted.

In this example, a variable constant current power supply circuit 1 is provided on the master unit A side, and a current detection circuit 12 is provided on the slave unit B side to supply power to the internal circuit of the slave unit B. A power control signal is generated and the switch of the variable constant current power circuit 1
When Sb is closed, the transistor Q2 of the current detection circuit 12
When turned on, the camera power switch 4 is turned on, and power is supplied to the television camera.

The internal circuit of the slave B has a shunt regulator 3
Are connected in parallel, and this shunt regulator 3
Is controlled in accordance with the current consumption on the side of the slave unit B, thereby preventing ripples from occurring on the coaxial cable l and eliminating interference with video signals and the like.

Here, the shunt regulator 3 includes a transistor Q,
A resistor R, a Zener diode ZD, and a capacitor C3 for increasing the stability of the Zener voltage VZD are connected in parallel with the resistor R. A current flows through the Zener diode ZD through the resistor R, and the voltage across the Zener diode ZD Is always maintained at VZD.

In such a shunt regulator 3, when the base voltage of the transistor Q is constant and the base-emitter voltage of the transistor Q is VBEQ, the emitter VE of the transistor Q is constant as VE = VZD + VBEQ.

Therefore, the current flowing through the transistor Q decreases when the current consumption of the internal circuit of the slave B and the television camera increases, and the transistor Q decreases when the current consumption of the internal circuit of the slave B and the television camera decreases. The current flowing through the cell increases, so that VE is always constant.

FIG. 5 is a block diagram in the case where the shunt regulator 3 on the slave B side, the current detection circuit 12 and the camera power switch 4 in the above embodiment are formed as a single circuit as a shunt regulator / camera power switch circuit 13. FIG.

FIG. 6 and FIG. 7 show circuit examples showing the detailed configuration of the circuit. The configuration of the circuit 13 shown in FIG. 6 will be described together with the operation. In the figure, the terminal I1 is supplied with a constant current separated by the power supply separation circuit 2, and the terminal O1 is connected to the internal circuit of the slave unit B. O2 is connected to a television camera (not shown). Transistor Q10, resistors R10, R11,
The shunt regulator 3 is composed of the Zener diode ZD10 and the capacitor C10. The camera power switch is driven.

When there is no camera power control signal (not shown) from master unit A, the supply current from variable constant current power supply circuit 1 is small,
Since the current shunted to the transistor Q10 is small, the resistance R
11 Voltage across is low, transistors Q11 and Q12 are off
State, and the current supply to the television camera is cut off.
However, when the camera power control signal is output, the supply current from the variable constant current power supply circuit 1 increases, so the collector current of the transistor Q10 also increases, the voltage across the resistor R11 increases, and the voltage increases across the diode D10 and the resistor R12. Transistor
A base current flows through Q11, turning on the transistor Q11 and turning on the transistor Q12 to supply power to the television camera. In the circuit 13, when power is supplied to the television camera at the same time when the transistor Q12 is turned on, the transistor Q1 is turned on.
In order to prevent the collector current of 0 from dropping and the voltage across the resistor R11 from dropping and turning off the transistor Q11, the transistor Q11 is configured to be self-held from the collector of the transistor Q12 through the diode D12 and the resistor R12. I have.

Then, if the camera power control signal on the master unit A disappears in this self-holding state, the supply current of the variable constant current power supply circuit 1 decreases, but since the power supply to the television camera is connected, the collector current of the transistor Q10 is connected. Decreases further,
Since the voltage across the resistor R11 also decreases, the base voltage of the transistor Q11 is clamped by the diode D11, the transistors Q11 and Q12 are turned off, and the power supply to the television camera is stopped. In this case, a Zener diode ZD11 having an appropriate Zener voltage is used to determine the ON / OFF voltage of the transistor Q11.

FIG. 7 shows another embodiment 13 'of the shunt regulator / camera power switch circuit 13. In the above circuit example, the Zener diode ZD11 is inserted between the emitter of the transistor Q11 and the ground. The difference is that the Zener diode ZD11 is inserted on the base side of the transistor Q11, and the operation is the same as described above.

[Effects of the Invention] According to the first invention, the drive control of the television camera can be realized with a simpler circuit configuration by detecting the current value of the variable constant current power supply circuit on the master unit side on the slave unit side. .

According to a second aspect of the present invention, in addition to the advantages of the first aspect of the invention, a ripple voltage on a signal line connecting an intercom master unit and a slave unit is removed, and a television intercom system having a simple circuit configuration with less interference is provided. Can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the first system of the present invention, FIGS. 2 and 3 are explanatory diagrams showing the frequency allocation of signals transmitted from the master unit and the slave unit, and FIG. FIG. 5 is a block diagram showing another embodiment of the system of the second invention, and FIG. 5 is a block diagram showing another example of the system of the second invention.
FIG. 6 and FIG. 7 are circuit diagrams showing details of the main part, and FIG. 8 is a block diagram showing the configuration of a conventional television intercom system. [Explanation of Symbols] A: Interphone master unit B: Interphone slave unit l: Signal line 1: Variable constant current power supply circuit 2: Power supply separation circuit 3: Shunt regulator 4: Camera power switch 12 Current detection circuit 13,13 '... Shunt regulator / camera power switch circuit

Claims (3)

(57) [Claims] An intercom master unit having a monitor television and an intercom slave unit having a television camera are connected by one signal line to multiplex and transmit video and audio signals necessary for information transmission. In the television intercom system, the intercom master unit is provided with a variable constant current power supply circuit capable of variably controlling a constant level constant current supplied to the slave unit, and a constant level constant current output from the variable constant current power supply circuit. The current is superimposed on a high-frequency signal modulated by voice and other signals necessary for information transmission and supplied to the slave unit, and the variable constant current power supply circuit controls the slave-side television camera. At the time of driving, it is configured to switch and output a current of a higher level than in a normal state. The intercom slave unit is supplied from the master unit side through the signal line. Power supply separating circuit for separating the current from the variable constant current power supply circuit from the high-frequency signal modulated by other signals necessary for information transmission, and supplied from the master unit side via this power supply separating circuit. And a current detection circuit for determining the level of the current separated by the power supply separation circuit, and the current detection circuit outputs the current from the variable constant current power supply circuit. A television intercom system, characterized in that the output level of the supplied current is determined, and the camera power switch is turned on and off to drive and control the television camera. 2. An intercom master unit having a monitor television and an intercom slave unit having a television camera are connected by one signal line to multiplex and transmit video and audio signals necessary for information transmission. In the television intercom system, the intercom master unit is provided with a variable constant current power supply circuit capable of variably controlling a constant current of a constant level for supplying power to the slave unit, and a constant output from the variable constant current power supply circuit. The level current is superimposed on a high-frequency signal modulated by voice or other signals necessary for information transmission and supplied to the slave unit. When driving the camera, a current of a higher level than that of a normal state is switched and output, and the intercom slave unit is connected to the master unit through the signal line. A power supply separation circuit is provided for separating a constant level current supplied from the variable constant current power supply circuit from the high frequency signal, and a constant level current supplied from the master unit through the power supply separation circuit. And a current detection circuit for determining a current level separated by the power supply separation circuit, and a configuration in which the shunt regulator is connected to the internal circuit on the slave unit side including the television camera connected in parallel.
A television interphone, wherein the current detection circuit determines an output level of a current supplied from the variable constant current power supply circuit, and turns on and off a camera power switch to control driving of the television camera. system. 3. The intercom slave unit wherein the current detection circuit, the shunt regulator and the camera power switch are combined by one circuit unit.
TV intercom system as described.