Conference video system

The system includes a plurality of conference seats, at each of which is a microphone. The system also includes a TV camera and a pivotable mirror which directs light from the conference seats to the TV camera. Each of the microphones is coupled through circuit elements to a servomotor(s) which positions the mirror to focus on the speaker and aims the camera's field of vision toward active audio. The electronic portion of the system utilizes the time two adjacent microphones receive a speaker's voice to generate a signal used to drive the servomotor to perform its mirror-positioning function.

BACKGROUND OF THE INVENTION 
Conference TV systems are known; however, each is subject to some 
criticism. Such known systems have one or more of the following faults: 
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1. High cost 5. Require cameramen 
2. Excessive complexity 
6. TV picture loses perspective 
of vision 
3. Require many TV cameras 
7. Delicate camera balancing 
4. Sensitivity to noise required 
8. Inability to simulate eye 
movement 
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SUMMARY OF THE INVENTION 
The present invention provides a conference TV system which overcomes the 
problems set forth above by utilizing a mirror, whose position is variably 
controlled by each speaker's microphone, to direct light rays from the 
speaker to the TV camera.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The system of the invention 10, referring to FIG. 1, includes a plurality 
of conference positions S1, S2, . . . Sn, positioned along a conference 
table 12 with a microphone M1, M2, . . . Mn provided at each conference 
location. Each microphone M is coupled through electronic circuitry 20 
including a microprocessor to an X-axis drive servomotor 30 (for panning) 
and an optional Y-axis drive servomotor 40 (for tilting) a mirror 50 to 
focus on an individual who is speaking into a microphone. The Y-axis drive 
servomotor would not be required in most systems. The mirror 50 directs 
light rays to a TV camera 60 which transmits its picture to a remote 
location on bus 70. The desired audio signal is fed out of the circuitry 
20 on bus 80. The distance from the mirror 50 to each microphone is 
preferably the same, e.g., 6 feet or so. (Otherwise, a zoom lens is added 
and controlled by the microprocessor to be described.) 
Referring to FIG. 2 for a more detailed description of the invention, each 
microphone M is connected to the input of an amplifier 90 and (1) to an 
audio mixer by lead 100 and (2) through a band pass filter 110 to limit 
room noise, a zero crossover detector 112, and single-shot multivibrator 
114 to a central processor (CPU) 130. Each detector 112 operates as a 
switch to signal the CPU on an interrupt request basis. One output of the 
central processor 130 is coupled by lead 140 to the X direction control 
motor 30 for mirror 50, and, if desired or needed, another output of the 
central processor is coupled by lead 150 to the Y direction control motor 
40 for mirror 50. 
The audio signal output from the central processor unit 130 appears on 
output lead 160. 
A conventional pulse proportional servosystem is used, in one embodiment of 
the invention, to operate the motors 30 and 40 to drive the mirror 50. 
Such a system uses pulse width to control the motor operation. 
The principles of the invention are illustrated in somewhat greater detail 
in FIG. 3, which shows each detector connected through its multivibrator 
114 to a counter 118 which may be a portion of the processor 130. 
In operation of the invention, when a conference participant, e.g. at 
position S2, speaks, his microphone M2 picks up his speech and a narrow 
pulse appears at the output of the filter 110, indicating the beginning of 
an utterance. A signal is coupled through the associated multivibrator 114 
to turn on the counter 118. Milliseconds later, the original utterance by 
the speaker at position S2 is detected by another microphone, e.g. at 
position S3, and this produces a signal which turns off the counter. The 
elapsed time is processed in the processor 130 to generate a signal whose 
length or time duration turns the mirror the proper amount to position it 
on the speaker at position S2. This time delay may range from zero to siz 
milliseconds. A zero delay indicates to the processor that the speaker's 
voice came from a position equidistant from two adjacent microphones. 
The system of the invention is shown in greater detail in FIGS. 4 and 5. 
When a vocal sound occurs at a microphone, the output of the associated 
zero-crossover detector 112 will become low, representing a negative-going 
pulse at one of the inputs to NAND gate 170. The resultant output of NAND 
gate 170 is inverted by gate 174 and fed to J-K flip-flop 180. At the same 
time, the positive pulse on the output of NAND gate 170 triggers one-shot 
multivibrator 184 whose purpose is to establish a nominal two-second 
window to count the elapsed time between the first microphone utterance 
and sound received from an adjacent microphone, said first microphone 
representing the gross vicinity of an utterance, and the delayed sound 
(received slightly later) representing the offset. When no one is talking, 
the one-shot multivibrator 184, after a time period determined by its 
components (e.g. 2 secs.), returns to its reset state and triggers 
one-shot multivibrator 188, thereby creating a negative-going pulse which 
has a time duration of about 1 us, and this sets the flip-flop 180 so that 
it is ready to make the next sampling operation. One-shot multivibrator 
188, therefore, provides a single sample of the beginning utterance, and 
inhibits further samples until the audio acitivity is discontinued for two 
seconds or someone else begins to speak. 
The purpose of the J-K flip-flop 180 is to condition either the "start" or 
"stop" latches 190 or 194 to detect the fist reporting microphone. The 
latch 194 is used to save the data corresponding to the second microphone 
which detects the original voice signal. The signals from the two 
reporting microphones and the two others are used as the most significant 
bits of an 8-bit word, representing the position of the speaker. The 
stepper motor driving the pivotable mirror will always follow this value 
plus or minus the offset contained in binary-coded decimal 4-bit counters 
198 or 200. 
Once the initial microphone audio signal is detected at one of the inputs 
of NAND gate 170 and latched into date latch 190, the flip-flop 180 
toggles to start counting up and down on counters 198 and 200. Clock 
pulses to the up-counter 198 and the down-counter 200 are fed from astable 
oscillator 202 which is enabled from start NAND gate 206, whose output 
will be high when either the Q output of multivibrator 184 or J-K 
flip-flop 189 is low, thereby permitting the odscillator 202 to generate 
pulses, and counters 198 and 200 to both count. This counting stops as 
soon as the second microphone audio signal is received. The microphone 
that causes the stopping is remembered in "stop" latch 194. In this way, 
counters 198 and 200 store the delay between reports. The start latch 190 
and stop latch 194 store the gross positional value. Counters 198 or 200 
compute the delay and are selected to subtract or add this offset to the 
most significant digit (MSD). 
Magnitude comparator 210 examines the value of date in latches 190 and 194 
and decides which 4-bits will be selected by data selector 214 to 
represent the most significant digits (MSD) of positional value based on 
the following algorithms: 
(A) If the second microphone report is smaller than the first report, the 
data value of stop latch 194 is represented as the MSD. The offset or 
least significant digit (LSD) is the value contained in counter 198. 
(B) If the second microphone report is larger than the initial report, the 
start data value contained in latch 190 represents the MSD. The offset 
(which is the least significant digit) is contained in "Down" counter 200. 
Data selector 218, also driven by magnitude comparator 210, is switched to 
select the corresponding LSD digits. 
Astable oscillator 202 has its frequency set to be such that sixteen clock 
output pulses divide the equivalent delay time between any two 
microphones. Therefore, the MSD value trapped by the start or stop data 
latches 190 or 194 are subdivided into sixteen parts to accurately 
position the mirror. 
The stepper motor driving the mirror is positioned to always track the 
digital 8-bit word out of the data processor. This tracking of the stepper 
is done with conventional binary comparison and tachometering of the 
mirror 50, to establish initial starting value when power is first 
applied. A simple pulse counter circuit compared to the 8-bit word is all 
this is required. The oscillator will always pulse the stepper driver 
until the equal output of the magnitude comparator is reached. 
Referring to FIG. 5, data bits B.sub.0 to B.sub.7 represent the positional 
value of the speaker's audio signal. These data bits come from data 
selectors 214 and 218, representing the MSD and LSD, respectively. This 
data is fed to magnitude comparator 300 which compares the value in two 
4-bit counters 310 (MSD) and 320 (LSD) containing the current mirror's 
position. There are three outputs from magnitude comparator 300. The 
output symbol &lt; means that the mirror must be moved, say, left until the 
output of the magnitude comparator is equal (=), while the symbol &gt; 
indicates that the mirror is, say, right of the correct position and the 
motor must be stepped right to cause the output to be =. Note that the 
output of comparator 300 is inverted by inverter 370 and presented to 
oscillator 330. When the value in the 4-bit counters differs from the data 
presented to the magnitude comparator, the inequality causes the 
oscillator 330 to provide output pulses to the mirror stepper motor and 
also to the counters 310 and 320. When they are equal, the oscillator 330 
is halted and the new positional value is reached. The "greater than" or 
"less than" signals to the driver condition the direction of stepping, 
while the oscillator 330 is enabled and causes the movement. 
It is noted again that module 130 may be a single microprocessor which is 
able to perform all of the necessary counting and timing functions 
required by the invention.