GB2239581A

GB2239581A - Door phone transmits image, voice, sync and power down same line

Info

Publication number: GB2239581A
Application number: GB9028152A
Authority: GB
Inventors: Hyun-Jong Choi; Eui-Duk Kim
Original assignee: Gold Star Co Ltd
Current assignee: LG Electronics Inc
Priority date: 1989-12-28
Filing date: 1990-12-28
Publication date: 1991-07-03
Also published as: JPH04140953A; KR910013025A; KR940000250B1; GB9028152D0; DE4042088A1

Abstract

The signal transmission device for a door phone is arranged so that signal frequencies of a voice signal and an image signal are separated between an indoor parent device A and a child device B on a front gate. The image signal from camera 3, the voice signal from microphone 5, a synchronization signal and a low frequency power are superposed, and the said four signals simultaneously are transmitted through a single line L6, so that installation of the door phone becomes convenient, resulting in lower cost and higher reliability. Ground line L7 is also provided. <IMAGE>

Description

1 r 1 A SIGNAL TRANSMISSION DEVICE The present invention relates to a

signal transmission device for a door- phone, more particularly to a signal transmission device for a door-phone which uses a signal line to transmit image, voice. power supply, and synchronizing signal simultaneously between an indoor parent device and a child device on a front gate.

Fig.1 is an overview diagram of a conventional signal transmission device for a door-phone which consists of an indoor parent device A having a transmitter/receiver 2, a beeper 7. and a monitor 1 and a child device B on a front gate having a camera 3, a speaker 4, a microphone 5, and a switch 6 whi,ch are connected to the indoor parent device A through an image signal line LL a voice signal line L2, a power supply line 1.3. a synchronizing signal line L4, and a ground line L5.

Turning now to an embodiment of the door-phone device having the above composition, when the switch 6 in the child device B on the front gate is pressed, the monitor 1 of the indoor Parent device A becomes activated and the beeper 7 starts to beep. llere, by lifting the transmaitter/receiver 2 up, it is possible to rey ize a visitor outside by seeing an image through the monitor 1 which takes the image from the camera in the child device B and by hearing a voice of the visitor which can be heard through the transmitter/receiver 2 in the indoor parent device A from the microphone 5 in the child device B. The voice from the indoor parent device A which is transferred to the child device A which is transferred to the child device B through the transmitter/receiver 2 can be heard through the speaker 4. At this time, a signal transmission is completed through Ll line if the signal is the image signal. When a signal is the voice signal, a transmission is made through L2 line, and when a signal is the power supply, a transmission is made through L3 line. A supply of the synchronizing signal from the child device B to the indoor parent device A is made through L4 line, and through the overall ground line LS, a signal communication is performed.

Generally, the parent device A is installed inside a house and the child device B is installed on the front gate. However, this requires five lines for a mutual signal transmission, causing a complication of an installation procedure and a high cost.

According the invention there is provided a device for transmitting voice and image signals between two stations, comprising means for transmitting the voice and image signals at different carrier frequencies, and means for superposing the image signal, the voice signal, a synchronization signal, and low-frequency power, in such a way that the said four signals can be transmitted simultaneously through a single line.

Embodiments of the present invention can provide a signal transmission system for a door-phone capable of simultaneously transmitting image, voice, power supply and synchronizing signals over a single signal line between a parent device installed inside a house and a child device set on a front gate, so that installation of the door-phone becomes simpler and cost is reduced.

3 BREIF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made. by way of example, to the accompanying diagrammatic drawings, in which:

Fig.1 is a conventional overview diagram of a signal transmission device for a door-phone; Fig.2 is an overview diagram of a signal transmission device for a door- phone according to the invention; Fig.3 is a detailed diagram of the signal transmission device on the door- phone according to the invention; and Fig.4 is a signal waveform plot accordini to the invention.

DETAILED DESCRIPTION

Referr.ing to Fig.2, the door-phone according to the present example includes an indoor parent device A, which has a monitor 1, a transmitter/receiver 2 and a beeper 7; and a child device B on a front gate. which has a camera 3, a speaker 4, a microphone 5, and switch 6, and is linked with the parent device through a line L6 and a ground line L7.

Turning now to more detailed description of the present ele with reference to Fig. 3, in the indoor parent device A. an alternating current from a power supply plug is applied to a rectifier 11 through a t 1 ' 4 transformer 10 in a power supply system 5, and an output of the rectifier 11. that is a supply voltage, is connected to a coupling circuit 12. Also, a signal from a receiver 14 goes through a low pass filter 15. and then modulates at a modulator 16 a signal inputted from a carrier generator 18 to add to the superposition circuit 12 after going through a high pass filter 17. In addition. an output from a synchronizing signal generator 13 is added to the superposition circuit 12, and a signal from a transmission line 27 is applied to a low pass filter 20 and a decoder 43 after going through a direct current cut-off device 21. An output of the low pass filter 20 is applied to a monitor 19 and an output of the decoder 43 is connected to the monitor 19 through a switch driver 42. An output of the direct current cut-offdevice 21 goes through a high pass filter 22. a demodulator 23. a low pass filter 24, and an amplifier 25 Sequentially and finally is connected to a receiver 26.

And in the child device B. a signal from the transmission line 27 is applied to a low pass filter 28, a synchronization divider 30, and a high pass filter 38. The low pass filter 28 isolates a power supply and applies the power to a camera 29. and the synchronization divider 30 isolates a synchronous signal and provides the synchronizing signal to the camera 29.

An output of the high pass filter 38 is connected to a speaker 41 through a demodulator 39 and a low pass filter 40. On the other hand, an output from the camera 29 is applied to a coupling circuit 31 through a low pass filter 32, and in addition, an output from a switch 44 is applied to the coupling circuit 31 through code signal generator 45. An output from a microphone 36 is applied to a modulator 34 through a low pass filter 35 while the modulator 34 receives an output from the carrier senerator37 to pass through a high pass filter 33 and to be connected to the superposition circuit 31. Here, the camera 29 consists of a highpressure generating circuit 29a which is driven by a power supply 29b and the synchronizing signal 29c, a deflection circuit 29d. and a pick-up tube 29e.

Hereinafter, an operational aspect of the present invention having the above composition is described.

As shown in Fig.2. the present invention requires an installation of the parent device A inside the house and the child device B on the front gate. When a visitor presses the switch 6 on the door-phone, the beeper 7 in the indoor parent dl-viee A beeps while turning the monitor 1 inside a house on. At this time, a person who is inside the house can pick the transmitter/receiver 2 up and talk to the visitor. The person inside the house can see the visitor from the monitor 1 since the camera 3 of the child device B takes a picture of the visitor's face and transmits to the indoor parent device A while the person inside talks to the visitor using transmitter/receiver 2. Because the voice, the image, and the power supply are transmitted through one signal line L6 and one ground line L7. an installation cost is reduced and a procedure of the installation becomes simpler.

Using Fig.3. and Fig.4 which are a block diagram and a waveform plot respectively, a detailed description will be given below. First, turning to a description of a superposing process for a power, a voice, and a

6 1 &L.

synchronizing signal at the indoor parent device A, an alternating current from the power supply plug through the transformer 10 goes through the rectifier 11 to become a direct current. and this direct current is applied to the superposition circuit 12. Synchronizing sigIals from the synchronizing signal generator 13 and voices from the receiver 14 in the indoor parent device A go through the low pass filter 15 to result iJa signal which contains only frequency components below ten kiloHertz. This low pass filtered signal is modulated wita carrier signal from the carrier signal generator 18 at the modulator 16. and then high- pass filtered 17 to add to the superposition circuit 12. Here, the transmission line 27 is made up of a pair lines of one signal line and one ground line. In order to transmit the power, the image, and the voice simultaneously an image band which is originally about 4 MHz should be reduced to 3MHz to display on a small screen. and a voice signal which has a frequency zone about 20 Hz to 15,000 Hz should go through a low pass filter to obtain a signal which contains frequency components lower than ten kilo Hertz since it has to he heard through the transmitter/receiver, and then delivered with the carrier signal. As shown in Fig.4. the image band a, the voice band b, and the power supply(frequency 0) c are superposed at the superposition circuit 12 to make the same frequency distribution as in Fig 4d and through a single pair of lines it is possible to transmit the voice. the image, and the power supply simultaneously.

In the child device B, the synchronising signal and the power through transmission line 27 go through the low pass filter 28 to isolate the 1 7 power. and the isolated power is applied to the power supply 29b in the camera 29. Through the synchronization divider 30. the synchronization signal is isolated and applied to the camera 29. When the camera 29 is operated. it takes an image of a visitor and the iiage is low pass filtered 32 with a low cut-off frequency three mega Hertz to deliver through the transmission line 27 to the superposition circuit 31. On the other hand, when a visitor presses the bell switch 44, a code signal is generated at the code generator 45 and through the superposition circuit 31 is delivered by the transmission line 27. Also, the voice of a visitor from the microphone is applied to the demodulator 34 after going through the low pass filter 36. and is demodulated with the carrier signal from the carrier signal generator 37. The demodulated signal goes through the high pass filter 33 and then is added to the superposition circuit 31 to transmit the image, the voice, and the power signals which have the same spectra as in Fig.4 through the transmission line 27.

From the signal from the child device B. components which do not contain the direct current are selected through the direct current cut-off device 21, and the code signal is generated by the switch which is pressed by a visitor. The code signal which is applied to the monitor through the switch driver 42 is detected by a decoder 43 to turn on the monitor 19.

1 8 On the other hand, the image signal goes through the low pass filter with cut-off frequency three mega Hertz to display an image of a caller on the monitor. The voice signal from the child device goes through the direct current cut-off device 21, and passes through the high pass filter 22 which passes frequency components higher than about 3.5 mega Hertz. The high pass filtered signal is demodulated at the demodulator 23, and then goes through a low pass filter 24 which passes frequency components lower than ten kiloNertz. Finally. the low pass filtered signal is amplified at an amplifier 25 and delivered to the receiver 26.

The voice signal from the parent device goes through the high pass filter 38 which has the same cut-off frequency 3.5 mega Hertz as the high pass filter in the child device B, and is demodulated by a demodulator 39.

The demodulated signal goes through a low pass filter 40 to remove high frequency noise components. and a voice from the parent device A com,,s out through the speaker 41 of the child device.

As described in the foregoing, the present invention has advantages that installation of the door-phone becomes tore convenient, cost is lower, and more reliable compared to conventional door-phones by using a pair of lines to transmit all signals instead of conventional five or six lines.

The foregoing description shows only preferred embodiments of the present invention. Various modifications are apparent to those skilled in the art without departing from the scope of the present invention which is only limited by the appended claims. Therefore, the embodiment shown and described are only illustrative, not restrictive.

7 1 1

Claims

WHAT IS CLAIMED IS:

1. A device for transmitting voice and image signals between two stations, comprising means for transmitting the voice and image signals at different carrier frequencies, and means for superposing the image signal, the voice signal, a synchronization signal, and low-frequency power, in such a way that the said four signals can be transmitted simultaneously through a single line.

2. A device as claimed in claim 1, in which the two stations are an indoor parent device and a child device for mounting at a gate.

3. A transmission device as claimed in claim 2, wherein the parent device A has a transmitting section and a receiving section; in which the transmitting section includes: a power supply for supplying power produced by rectifying an alternating current; a synchronizing signal generator for generating a synchronizing signal; a voice signal modulator for producing a modulated receiving voice; a superposition means for superposing the said power, the synchronizing signal and the voice signal for transmission on a transmission line; and in which the receiving section includes:

a direct current cut-off device for separating direct current from a code signal generated by actuation of a switch on the child device by a visitor, and from image and voice signals received from the child device B via the transmission line; a code signal processor for separating out the said code signal in order to activate a monitor; an image signal processor for producing an image of the visitor by separating out the image signal; and a voice signal processor for generating a voice of 1 the visitor through a receiver by separating out and demodulating the voice signal.

4. A transmission device as claimed in claim 2 or 3, wherein the child device B has a transmitting section and a receiving section, in which the transmitting section includes: a camera for taking an image of a visitor after receiving power from the parent device A and a synchronization signal; a code signal generator for generating a code signal when the visitor actuates a switch; a voice modulator for generating a modulated voice signal of the visitor; a superposition means for superposing the image signal from the camera, the code signal from the code signal generator, and the modulated voice signal from the voice modulator for transmission via the transmission line; and in which the receiving section includes:

a voice processor for generating a voice signal through a speaker after demodulating a voice signal delivered by said transmission line from the parent device A.

5. A transmission device as claimed in any preceding claim, in which the power transmitted is direct current power, the image signals are transmitted at frequencies below a predetermined frequency, and the sound signals are transmitted above the predetermined frequency.

6. A transmission device substantially as described herein with reference to Figures 2 to 4.

Published 1991 at Ihe Patent Office. State House. 66171 High Holborn. London WC1R47P. Further copies nay be obtained from Sales Branch. Unit 6. Nine Mile Point CwmfeUnfach. Cross Keys. Newport. NPI 7HZ. Printed by Multiplex techniques lid. St Mary Cray. Kent.

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