Patent GB-1504089-A (GB)
Title: Video conference system
IPC: H04N7/08
Filed: 1976-05-25
Abstract: 1504089 Video conference system A POIRIER G BUCHNER and G MARTEL 25 May 1976 [27 May 1975] 21508/76 Heading H4K A video conference system comprising a plurality of groups of conferees, each conferee being associated with a video telephone and a microphone, in which voice controlled switching is utilized; the address of the conferee producing the loudest speech signal and the address of the group containing this conferee are detected and used to connect the camera of the conferee to the image receivers of all the other conferees through a video switching circuit. Fig. 1, shows a video conference system having three groups A, B, C each associated with a control unit 1A, 1B, 1C respectively and are interconnected by a central control unit IN. For a system with only two groups, e.g. A and B, control unit IN is omitted and the groups are connected directly via a link 2-3. A typical group, Fig. 2, comprises conferees 9 1-5  associated with microphones 20 1-5  and video telephones 10 1-5  respectively. A loudspeaker 30, a camera 40 and a large image receiver 50 are common to all conferees. All the above equipment is connected to a control unit 1, which is connected to the control units of other groups, directly or through a central control unit IN, Fig. 1, through video links 3 and audio links 2. Audio link 2 may be a telephone line of a subscriber 4, switched by switch 5. The control unit 1 is shown in more detail in Fig. 3 in which the microphones 20 1-5  are connected to an audio splitting and isolating circuit 200 which supplies information to a duplexer 400 and a voice-voting circuit 300. The circuit 300 compares the inputs from each microphone and decides which one is louder and informs an address register and zero detector 500, which stores the address of this microphone. Every time the present address in the register changes, this address is stored as a past address. Both addresses are used by the switch control logic 600 to control a video switch 700 to enable the camera of the conferee with the loudest speech signal i.e. the speaker, and to connect the image receivers of all the other conferees to this camera; the image receiver of the speaker shows the previous speaker. If no conferee speaks for a predetermined time, say 10 sec., image receiver 50 is connected to the camera 40 (Fig. 2) of another group and a picture of the entire group is transmitted. The sum of all the signals in microphones 20 1-5  is sent to the other control unit, if two groups, or to the central control unit, if more than two groups by duplexer 400. If only two groups, each control unit compares the sum from the other and decides which group contains the speaker. If more than two groups, the sums from each group, 2A, 2B, 2C, Fig. 9, are connected to a voice voting circuit 1300 of the main control unit IN which in a manner similar to the control unit of Fig. 3 decides which group contains the speaker and through address register 1500 and switch control logic 1600 operates a video switch 1700 to enable the relevant group to interconnect the relevant camera to all the image receivers of all the groups. Each video telephone has means for photographing documents for transmission to other video telephones.