Note: Descriptions are shown in the official language in which they were submitted.
B ackg ro u nd o f th e I nvention:
T}le transmiSsion of images from an emitting station
to television sets is well known in the art. ~ut, it
has never been economically feasible for a person .seated
in front of a televislon set to have the op~iOJI oE wlr~-
less communication with the television station.
Consequently, the principal objective of this invention i9
to establish an improved medium by which a signal can
be se~t from the receiving set to the television station.
As a ccnsequence of this invention, it will be
possible to establish at any given moment who and how
many viewers observe the program, or to detect the
response of the television viewer to a specific question
that the television station may ask.
- lS Representative prior art relating to the interrogation
of T.V. receivers is U.S. Patent 3,769,579 - Oct. 30,
1973 to R. Ilarney for Cable Television Monitoring System,
which codifies a question on the T.V. signal for response
from the receiving station. However, this system is
limited to a small group of receivers each of which must
respond in a different frequency. Also, signals are sènt
out frame by frame and replies are limited in time to
vertical blanking pulse periods. This seriously limi~s
the numbers of receivinq stations that can be polled
in reasonably short time periods.
Another such system in U.S. Patent 4,290,141 -
Sept. 15, 1981 to R. E. Anderson et al. for Electronic
Voting System, which does not transmit questions from
the T.V. transmitter station. The transmission is in
the form of digitally coded signals modulated on a carrier
~ ~, " ~ ,
~,~ ,.
--2--
wave, thus requiring a broad band transmission system
at higll power and with complex transmitters and
receivers.
A further system in U.S. Patent 4,3g7,604 - Aug. 31,
l9B2 to M. Saito et al. for Bi-Directional Data
Communications System, is also limited in numbers of
receivers polled because of the time delays in communication
over long distances and does not transmit qUerie~ over
the T.V. signals. Also a separate transmission from the
T.V. signals is required for both queries and answers.
A modulated carrier is required for this as in Anderson
above.
In British 1,523,753 published Sept. 6, 1978 for
Two-Way Data Transmission System for Cable Television
Network, each subscriber is given a different "answer
delay" in response to a query signal transmitted to all
subscribers so that the subscribers can be identified in
a time multiplexing system. This system compensates for
propagation time by a separate time delay counter. A
digital communication system is required external to
the television signal requiring modulation of a carrier.
None of these systems are feasible for r-f transmission
of information by single unmodulated beeps of a
selected carrier frequency synchronously during T.V.
signal reception.
~:
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--3--
Disclosure of the Invention: '
Given the number o~ television sets in existence,
the simplest form ol implementation would be to produce
the response device as an accessory for the existing
televisions and later to include the device inside the
television set.
The electronic device which permits signals to be
sent from the television set to the television station
is a txansmitter of a radio frequency which will or will
not emit an r-f beep in response to a transmitted inquiry
to indicate whether the response is affirmative or not.
A keyset panel will permit viewer selected answers.
This beep responds to a question located in the T.V.
signal in the horizontal lines.
In order to prevent all of the devices from beeping
simultaneously, a different identification number will be
assigned to each response device produced, and a counting
circuit is placed in each device which only permits beep-
ing at a unique horizontal line location in response to a
question. This means that the answers will be ordered
according to the number of devices. The duration of the
response beeps is less than the time for one horizontal
line. Thus, if each response device is assigned a line
location, the T.V. signal is sent on 15750 horizontal
lines per second, 15750 answers can be received per second,
almost a million eacil minute.
Example of questions which can be asked:
Is the television set on?
Did the television viewer push button ~7
Reset the keys of the devices.
-'
'2~
--4--
It is logical to think that if the devices are
found at distinct distances from the transmitter, the
signals will take longer for some devices than for
othexs. In order to solve this, a circuit (depending on
the place of location and distance), may be incorporated
into the device to select the moment at which it must
transmit. This is simple, since the beeps have a
shorter duration than the intervals of the horizontal
line. Thus, zones of different kilometers in radius
from the television station can be identified for
different transmission times to zone coding for timing
response beeps.
On horizontal lines sent to the television viewers
a series of signals will be sent in timed order
identifiable by counting the horiæontal sync pulses of
the T.V. signal thus identifying each response device at
a particular time so that an identifiable response
unit will be obtained. Because of the single r-f
beep response signal only a simple transmitter will be
needed to emit a signal from every response device on
the same frequency.
These time multiplexed digital beeps lO/l) are
received at the transmitter and counted or processed by a
computer, which will process the information together with
the horizontal synchroniæation information to permit
identification of specific response device answers.
The inventlon in one broad aspect pertains to a bi-
directional television system permitting -television s-tati.ons to
ask questions by means of code superimposed on the video siynal
characterized by response units at television s.i.ynal reception
sites for answering those questions tuned to the i-:f frequerlc~ of
a television set receiving the video signal.
More particularly, the invention pertains to a bi-
directional television system permitting television stations to
ask questions and television signal receivers to answer those
questions wherein the questions are codified synchronously on the
television video signal. The improvement permits a large number
of receivers to be questioned for response from simplified
responders and comprises means at a transmission site for
transmission of a video signal hàving coded signal queries
constituting coded bits superimposed in selected horizontal line
- video positions and spaced at times permitting responses to be
received from receiver responder units in a predetermined
geographic area. Responder units at television set locations are
tuned to the video signal for processing the coded queries and
2n responding thereto to signify an answer wi.th a single r-f burst
timed to coincide with a designa-ted horizontal line uniquely
identifying each responder unit wherein all units respond with a
burst of the same frequency at a unique time slot following each
query wherein each responder unit and the transmitted video
signal provide identification of the distance ~travel time) of
the responder unit from the transmission site of the video
signal, and the responder units provide a response beep at a -time
compensating for signal transmit time from the transmission site
to the responder unit locations and back.
- .
-G-
More particularly the invention seeks to provide bi-
directional communication between a television station and
its viewers, in which:
All information (sound, video, data and sync~ frc7m
the T.V. station to the viewers is carried within the
standard frequency spectrum allowed for T.V. trarlsm;sxion.
All viewers within a typical metropolitan area can
communicate with the T.V. station (up to 78~,400 viewers
per minute in a 22.5 mile radius from the T.V. power
transmitter) in a fast and reliable form.
All information from the T.V. viewers to the T.V.
station is carried on a single radio frequency of low
bandwidth, using a time division multiplexing foxmat.
The viewers T.V. answer terminal is linked to the
T.V. station signal through the electromagnetic irradiation
of the intermediate frequency`(i-f) coming from signal
amplifiers of the T.V. set. Simplifying terminal construction
and improving operation as:
- The i-f signal is stronger than its r-f
counterpart at close distances from the T.V. set.
- The terminal has no need for a channel
selector and will always be tuned to the same channel
as the T.V. set, the terminal will work with any number
of T.V. stations.
- There is no need for interconnecting the
terminal to the T.V. alltelllla or to tlle T.V. set (no
installation).
- The terminal will work with any T.V. in the
house without need for re-connection.
- Each member of the family can have its own
terminal (without the need for complex wiring).
- The terminal can be portable.
~3112~
The system should work with T.V. signals carried
over the air and with T.V. signals carried through
cable simultaneously.
Th~ use of a single frequency for all communication
of viewers to the T.V. station makes it easier to obtRin
authorization and a hi~her radiated power permit. The
use of short time pulses makes it easier to construct
an inexpensive high power transmitter, as power dissipation
is not an issue in the short timè that the transmitter
operates.
.
srief Description of the Drawings:
The details of the invention are clearly shown in
the following description and in the accompanying
drawings, where similar reference symbols serve to show
related parts in the different figures.
Fiyure 1 shows a general block schematic diag~am of
the system afforded by this invention;
Figure 2 shos~s a }~loclc di~gram of the resp~nse
unit;
Figure 3 shows a diagram of the response timing circuit
for determining when the answer should be transmitted;
Figure 4 shows a typical diagram of the image query
signal and the answer signal;
Figure 5 is a diagrammatic system view with related
signals;
Figure 6 is a wavef`orm sketch of a video signal
encoded for operation in this system;
Figures 7 and 8 show even and odd fields of a T.V.
signal showing organization of the answer and query
signals;
Figure 9 is a diagrammatic view of the organization
of the 2~ control bits;
Figure 10 is a diagrammatic view with signal
sketches of the ask system;
Figure 11 is a diagrammatic view with signal sketches
of the answer system;
Figure 12 is a data bit organization chart;
Figure 13 is a system flow diagram for processing
answer signals;
Figure 1~ is a waveform sketch of a video signal
related with an answer pulse;
Figures 15 to 17 are charts explaining transit delay
line behavior of this system; and
Figure 18 shows groups of response units; ~s shown
with Figure 14.
': ~
2~
Detailed Description of the Invention:
_
In reference to the block diagr~m representation
in the drawings, the state of the electronic arts
necessary to implement the system is already well known
in the areas of television, radio communication and
computation employed.
The video signa] originates from a television
camera 1 or equivalent signal source. The audio signal
originates in a microphone 2 as a symbol of any equivalent
generator or audible signals. These signals are fed to
a T.V. transmitter 3. A tower 4 supports sending and
receiving antennas 5. The sending antenna emits the
television signal 6 through the air for capture by an
antenna 7 receiving T.V. signals 6 linking the response
unit 8 for communications between the television
viewers and the television station.
Using an antenna 10 an answer is transmitted from
the response device 8 to the station via air waves, using
beep signals 11 in Figure 4. These beeps will be captured
by receiving antenna 5 and response signal detector 13
tuned to the single beep frequency assigned for all of the
television viewers of a particular location. This detector
13 determines the pulse timing and thus identifies each
response unit 8, from the sync pulses of the television
signal.
In order to generate the questions for the response
device to answer, means 14 for inserting the questions
into the T.V. signal is capable of inserting a digital
code containing the question, as a sequence of single
digital bits inserted on each hori~ontal line (as
seen in Figures 6, 7 and 8).
--10--
The computer 15 will process the answers received by
the beep detector 13 obtaining the results desired to the
extent it has the necessary resources for doing this.
For example, in order to determine how many -television
sets are turned on, it only needs to add up the responses
over a specified number of frames. If the question
was: Tell me the names, addxesses and telephone numbers
of the television viewers which answered affirmakively
to the question asked by the announcer, this would require
the computer to have information provided by additional
means including a response unit owner address data bank.
The program of this computer will process
response beep signals received at a speed up to
15750 per second. Simultaneously the computer is counting
the horizontal synchronism, in such a way that the
horizontal line count corresponds to different responses,
received during a time period just after generating the
question. Thus, the first response corresponds to the
response code identification of a first television
viewer, the second, to the response code identification of
the second television viewer, and thus successively.
The maximum number of television viewers in the system
will be fixed by the number of horizontal lines
occurring between questions, as determined by the
, computer program and the nu~ber of response devices in
the system. For example, if five million television
viewers are wanted, and response devices are scheduled
for that number of television viewers, the questioning
period extends over intervals of five and a half minutes
during which horizontal lines are counted.
By way of a computer terminal 16 the questions can be
asked to the computer and the answer can be obtained from
the resulting responses.
.
.
~8~
-- 11--
To eliminate noise interference a remote transmitter
9 will be utili~ed. It will operate on the beep frequency
assigned for the television viewers of a particular
station. This r-f signal is transmitted using antenna 17
and it is a continuous r-f signal with a low amplitude
and it serves to eliminate noise interferenc~e in the
detector 13 by feeding a continuous signal to the autarnatic
fine tuning (aft) circuits of the beep detector 13.
The response units 8 permit the television viewers
to communicate with the television station. These units
(as shown in Figure 2) have a channel selector 8A to
select channels which the television viewer wishes to see.
The channel number selected 8B by the television viewer
is fed by a set of wires to the response unit in this
embodiment.
The question channel is tuned by channel selector 8C.
The responses will be emitted by the r-f beep
transmitter 8D (11, Figure 4), which transmits an r-f
carrier pulse with fixed amplitude. This circuit will
only transmit when the response circuit 19 indicates
a query has been made and the answer should be a beep.
Since this circuit will transmit a pulse of only 30 micro-
seconds high power can be achieved with low cost circuits,
also taking advantage of the narrow bandwidth of an
unmodulated carrier wave.
The response timing circuit 19 to de-termine when to
transmit is a fundamental part of the invention. This
circuit contains a counter and synchronizing circuit
in order to determine on what horizontal line the beep
is transmitted.
, ~
In ord~r to (]etermine when t.o transmit, .~ ~vice
colle num~er is requir~d sllc?l as a counter having ~I preset
count that mak~ the circuit 1.9 respond to a ~in~ry
CO~lllt reprQselltillq a numher from 256 to 8.3 mill:ion, w~llch
wi.ll be the :i.dent:iE.~catlon nulllber o~ that r~sE)or,s~ devl(f.-,
Tll~t circu:lt will. be presQt in the factory ~nd will not
aver be modified. Also, a further timing factor affecting
the moment of the transmission i~ the number of the
distance zone 8F. With this number the counter can be
set aheacl to compensate for trav~l time of the signal
through the air to the television station from "far ~way
response" units. This number can he built as collnter
preset switches so that the installer can place them
according to the location zone in which the response
device is found.
In order to make possible a decision from th~
television viewer to also b~ transmitted by the de~ice,
one or more keys 8G feed the de~ision of the television
viewer at a given moment. They could initially be of
two kinds: ~ne so that the television viewer can s~nd
his decision of "I like it", "good", "I accept",
"affirmative". Ana the other t~ se~a the decision o$:
"I don' t like it". "had", "1 refuse", "negative". In
order for the television viewer to push a mome~tary button
a storage circuit can be incorporated to store his decision
until the television station reset~. If the number of
keys were increased, more data coulcl be transmittecl.
The response timin~ l9 oE E`ic3u~es 2 and 3 receives
the codified T.V. signal of Fig~res 6~ 7, 8 from
receiver 8C. The sync generator 19A produces
hori~ontal tH), vertical (V1 synchroni~ati.on si~llals and
video imaqe (I) signal. These signals (H, v, I) a:re fed
to a query decoded l9B that decodes a digital code number
-13-
which represents the question sent out by the television
computer 15. This digital code number c~n be from O to
255 and it will be sent as bits of digital data codified
on horizontal lines as shown on Figures 6, 7 and 8.
In order to guarantee that a response is positioned
on the horizontal line, a generator of pulses 19E
generates impulses with a period equal to a tenth of the
h~xiz~ntal line and synchronizes these impulses with the
horizontal synchronization pulses (H) in the circuit l~E.
A counter circuit l9G starts counting in response to
start circuit l9F after receiving the question l9B and
stops the counting when the count for the particulax
response device which needs to be queried is reached.
At a point in time, the number in the counter l9G
will be equal to the comparison number of the circuit l~H.
This comparison number is composed by the code number 8E
minus the zone preset 8F. When both numbers are identical
the circuit 19I is activated. This circuit will limit
the pulse duration to 30 microseconds.
Decision block l9C will activiate r-f beep
transmiter 8D if and only if conditions to motivate an
answer to query on query decoaer 19B are met.
A digital to analog converter l9D is used to modulate
the power of the r-f beep according to the distance
zone 8F.
Reference to Figure 5 will show that the system of
Figures 1 to 4 is modified by having a response unit 8'
tuned to the i-f frequency 24 o~ the local T.V. set 23
and receiving the signal on its local antenna by being
located ad~acent the T.V. set. Thus, no wiring connection
or installation is required, nor any tuner.
The T.V. station sends a modified radio frequency
T.V. signal 6 that is received by plural T.V. sets 23.
Each T.V. set 23 pre-amplifies the signal and heterodynes
it with the output of a local variable oscillator converting
it to a standard intermediate frequency (i-f) o 45.75 M~Z
~28~1~6
(an EIA standard since 1950). The i-f signal is then
amplified by power i-f amplifiers, which radiate an
i-f signal 24 received by any one or more T.V. answer
terminals 8' which are close to the T.V. set 23.
Each T.V. answer terminal 8' sends radio frequenc~
pulses (r-f pulses) 11 back to the T.V. station.
At the T.V. station audio and video signals are
generated. ~he video signal 30 is modified by the T.V.
ask system 32 by encoding control and data bits accoxding
to instructions given to T.V. ask 32 by a personal
computer 15 in the manner aforesaid. The encoding format
is explained by Figures 6 to 8. Thus, each data
and control bit is encoded on a designated line as shown
in Figure 6, which shows preferred placement at the
beginning of the line which usually is on an area to the
left of the viewed video signal which is usually off-
screen.
These bits are inserted into even and odd fields of
a frame of 525 lines as shown in Figures 7 and 8. Thus,
the first 24 lines include the 24 bit ask code. The first
answer code of four bits is then at lines 35 to 38,
the 205th answer code is at lines 239-242, the 438th
answer code is at lines 501-504, etc. The overall
arrangement of the 24 control bits for this embodiment
is shown in Figure 9.
The modified video signal 31 is amplitude modulated,
and the audio signal 9 is frequency modulated by
the T.V. power transmitter 3, which also limits radiated
power and bandwidth to authorized standards, generating
the modified radio frequency T.V. signal 6.
, .
8~
-15-
Figure lO is a block diagram of the operating
principles of the T.V. ask system.
The T.V. ask system operates around a
single chip microprocessor 3~, typically widely available
chip 8748, which contains random access memory (RAM)
and eraseable programmable read only memory ~EPROM) for
program storage. The microprocessor 34 receives encoding
orders from a computer, via a standard serial communication
line 39 (EIA RS-23-C). A standard Universal Synchronous-
Asynchronous ~eceiver Transmitter unit (USART) 35 converts
serial encoding orders and communicates them to the micro-
processor 34 in parallel format, the microprocessor 34
receives the vertical and hori.zontal sync information
contained in the incoming video signal 30, from the sync
detection circuit 36. With sync information and the
encoding orders the microprocessor 34 activates the bit
insert circllit 37 which encodes data and control information
on the video signal 30 generating the modified video 31.
The microprocessor 34 also receives the received r-f
pulses ll, generated by plural T.V. answer terminals,
through a pulse detection circuit 38. The microprocessor
34 sends this data to the computex, to determlne how many
or which T.V. answer terminals answered with the r-f
pulses 11-
Figure ll is a block diagram illustrating the principles
of operation of a T.V. answer terminal 8'.
The T.V. answer terminal receives the i-f
signal 2~ radiated by the T.V. set 23. This signal passes
through an i-f amplifier 39/ and a video detector circuit
40, and further passes through a sync detector circuit
41, generating vertical ana horizontal sync pulses which
are fed to microprocessor 42- The video signal passes
also through a data detection circuit 43 which detects
a high/low level in the video signal and feeds the
information to microprocessor 42. As all data and control
26
~16-
information is encoded immediately after a horizontal
sync pulse (~igure 6), the microprocessor ~2 is able to
read all control and data bits encoded on the T.V.
; signal. With information read from keyboard 44, P~OM 45
~containing the unit ID number), data detector 43 and
sync detector 41, the microprocessor g2 activates LED's
47 and pulse power oscillator 48 using driver 46 to
transmit the response pulse 11.
The microprocessor operation is described in Figures
12 and 13. In Figure 12, a typical alignment of 28
control instructions is charted. With 24 bits in the
transmitted code word, sixteen bits ~1-16) are used for
identifying the frame member (0 - 64,535). The remaining
eight bits (17-24) are charted with bits 17-21
presenting 28 instruction choices. ~s may be seen,
instructi`ons 1 to 5 relate to groups, hereinafter
discussed. Instructions 6 to 9 can control keys in the
answer unit. Instructions 10-15, 19 to 23 and 27, 28
all give orders to transmit a beep under various conditions.
Instructions 16 to 18 ask for storage of the status
if keys A, B or C are actuated.
Controls in the answer system operate in the manner
of flow chart 13. Thus starting with detection of set
off or on conditions, the viaeo signal need be good for
processing, then the frame and ~uestion is passed onto
bus 50. On receipt of instructions 6, 7, etc. the control
function is executed in the answer system, such as by
turning on or off the latch keys, etc.
When instructions 1 to 5 are present, answer terminals
of that particular group transmit a r-f pulse that is used
to measure the total delay time by the travel time it
takes the signal from the T.V. station to the answer
terminal and the response pulse from the answer terminal
to the T.V. station. This delay data is encoded on the
T.V. signal and received and saved by the answer terminal.
-17-
With orders to transmit a beep (10, 11, etc.) signals
are processed via line Sl at appropriate timing if an
answer is keyed (52). Instruction 24 is used to show
the answer unit is working, for example, asking a response
at appropriate ID time on bus 53. The answering heep i5
timed to come in the center of the timed video line
identifying the answer unit as shown by Figure 14.
As there is a time delay for the T.V. signals to
travel from the T.V. transmitter location to the
T.V. receiver as described in Figure 15, and there is
also a time delay for the r-f pulse to travel from
T.V. receiver back to the T.V. station as described on
Figure 16, a total processable delay time described
on Figure 17 is for a maximim distance o~ 22.5 miles from
T.V. station in this describea embodiment. Thus, to
compensate for this delay, T.V. answer terminal should
send its r-f pulse up to 5 sync pulses before its
assigned response line. To do this each T.V. answer
terminal must know the distance that separates it from
the T.V. station. This is achieved by dividing all T.V.
answer terminals in five distance groups (see legend 1, 2,
3, 4, 5 in Figure 17) Thus, the T.V. ask system will
order all T.V. answer terminals in groups to send r-f
pulses by consecutively encoding instructions 1 to 5
of Figure 12 on the eight most significant bits of the
twenty-four control bits sent on each frame. By
computing the total delay time that it takes to receive
an answer from each terminal, the T.V. ask system will
encode a four bit delay data (described in Figure 17),
after the fifth, sixth, seventh, and eighth hori~ontal
sync pulses that follow the T.V. answer's assigned response
time. (As described on Pigures 7 and 8.) For example,
the terminal 1 will send a r-f pulse after receiving
instruction 1 (Figure 12) and frame 1 encoded on lines
1 to 24 (Figure 7~, and receiving sync pulse 30
~8~6
-18-
The r-f pulse will be received by the T.V. ask
system at any time (1 to F of Figure 17) between sync
pulse 30 and sync pulse 35 (of Figure 7). The T.V.
ask system will enclose a four bit message (1 to F)
after corresponding sync pulses 35, 36, 37 and 38.
When the T.V. answer terminal has received the four
bits of delay data it will proceed to light the ready led
47, and will store this value in its memory. The T.V.
answer terminal will use the delay data to send r-f
pulses in response to all instructions (except instructions
1 to 5) before its Assigned Response Line. This delay
compensation allows the T.V. ask system to receive r-f
pulses from each T.V. answer terminal exactly at the
~ssigned Response Line for each terminal.
Two or more T.V. stations can have access to T.V.
answer terminals, if they time share the r-f frequency.
This process is made more efficient if the T.V. ask
system of each T.V. station encodes the channel number
information on the T.V. signal and if each T.V. answer
terminal stores the delay data for each T.V. station.
In operation, the system performs generally in
the following way:
A transmitter ask operation sends out queries so
organized and synchronized on the video si~nal that it
identifies each receiver answer unit and the distance
between receiver and transmitter, measured by the travel
time of signals going and returning. Thus, the
delay data, plus a local answer unit identification
number permits a sin~le r-f beep from any unit to be
2~
--19--
sent at the proper time so that when received it can be
uniquely identified for processing answers to the queries.
A computer at the transmitter ask station can
identify the address of the xespondent, other data,
take a poll, or bill for use of special prograrns.
The receiver response unit is simplified by using
the T.V. set i-f radiation so that no tuners or wires
are necessary. It processes and times the answering beep
in response to variable key set or stored data at a time
slot identifying that particular unit. The response
transmitter o~ beeps is low cost and easily licensed at
narrow bandwidth, being required simply to produce an
r~f non-modulated burst. Thus, all T.V. viewers use the
same frequency to transmit answers. This is feasible by
time multiplexing the answers in time slots identified by
horizontal line counting, a`nd is operable over a large
distance because of the system compensation for travel
time of the signal. This time delay is automatically
evaluated.
The system is operable with cable or r-f transmission.
It can handle several answers (for classroom teaching or
the like) from one T.V. set.
A more detaile2 operational description follows for
the various key sub-systems.
-20-
T.V. ANSWER PROGRAM DESCRIPTION
Reference to Figure 13 will be helpful to follow
the sequence of operationg steps herein discussed.
STEP 1 - Verifies if a proper video signal _s bei~
received.
The following tests may be made:
a. 525 lines per frame.
b. 63.5 microseconds per line.
c. First vertical blanking internal between line
242.5 and line 263.5 with double sync pulses between line
242.5 and 245.5, signal inversion and double sync pulses
between line 245.5 and line 248.5, double sync pulses
between line 248.5 and the beginning of line 2Sl,
normalization lines and lines reserved for special purposes
between line 251 and line 263.5.
d. Second vertical blanking interval between the
beginning of line 505 and the end of line 525, with
double sync pulses in the first 3 lines, signal inversion
and double sync, sync pulses in the next 3 lines, double
sync pulses in the next 3 lines, and 12 lines for
normalization and reserved for special purposes.
If the received signal conforms to these standards
the receiving light emitting diode (LED) will be turned
on and the program will proceed to next step. (This
routine is designed to distinguish between a live l`.V.
station transmission and a home VCR reproduction of a
previous T.V. station transmission, a~ video cassette
recorders (VCR's) in home use today do not reproduce a
standard format during the vertical retrace interval.)
STEP 2 - Verifies if the vir3eo _ignal is encoded with
control codes in the first 24 bits of each frame.
a. An instruction or channel number in bits 17 to 24.
b. A progressive sequence of frame numbers on bits 1 to
16.
The program will remain in this state until it receives
a progressive sequence of at least SO frame numbers, and
" " , ' :
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126
until it receives the channel number (T.V. ask, will
always encode a channel number and a progressive sequence
of frame numbers when not encoding an instruction). The
program will store the channel number in memory and proceed
to the next step.
STEP 3 - The program checks if "delay time" for this
channel is stored in memory.
If "delay time" for channel being received is already
in memory it goes to Step 5 (Figure 13, line 54).
If "delay time" is not in memory it goes to Step 4.
STEP 4 - The program will remain in this step until
THE "instruction" in bits 1?-24 is equal to the "group
number" stored in the PROM (Figure 12).
When the "instruction" is equal to the "group number",
it will wait until the "frame" in bits 1-16 is equal to the
"assigned response frame" stored in the PROM 25.
The program will now count "lines" by counting
horizontal sync pulses (a special algorithm is provided
for counting lines during the vertical retrace interval),
when the "line number is equal to the "assigned response
line" stored in PROM, the program will trigger an r-f
pulse (line 51, Figure 13) to be sent to the air, the
program will then read the "delay data" on the 5th, 6th, 7th
and 8th lines after the "assigned response line", and store
this in memory as the "delay time" for the particular
channel number being received. The program now passes
to Step 5.
STEP 5 - The program turns on the "ready" LED,
indicating to the user that the equipment is all set for
receiving instructions and transmitting answers to those
instructions.
L12~
-22-
STEP 6 - The program reads the "instructions" on
bits 1~ to 24 of ~he "control bits", dependin~ on t~le
instruction (6 to 28, Figure 12). The program executes
a routine to perform the function ordered by each
instruction. Some of these routines do not transmit an
answer pulse to the T.V. station, the ones that do
transmit an r-f answer pulse to the T.V. station have
to compare the "frame bits" with the "assigned response
frame" on PROM, and when equal count lines by counting
horiæontal sync pulses (with a special routine for
counting lines during the vertical retrace internal) until
the line number is equal to the "assigned response time" in
PROM minus the "delay time" stored in memory for that
channel. At this time the program will activate the
circuitry for r-f pulse transmission.
~tilizing the multiprogramming capabilities of the
microprocessor used by T.V. answer, Steps 1 and 2 are
continuously being performed to detect any transmission/
reception errors (i.e. an interruption in the progressive
sequence of "frame bits" or a change in channel number).
3LX6
-23-
T.V. ASK PROGRAM DESCRIPTION
Reference is made to Figure 10.
Utilizing the multiprogramming features of the
microprocessor, the following routines will be operating
simultaneously and continuously:
I. Detecting the frame start from the video signal
and inserting the control bits with the following rules.
(a~ When there is no question to th T.V. answer,
it will be inserting the channel number in the instruction
bits and a progressive number in the frame bits (Figure 9).
(b) When there is a question to the T.V. answer,
it will insert, the instruction (Figure 12) into the
instruction ~its (Figure 9), and into the frame bits it
will insert a progressive sequential number.
(c) For the adjustment of the delay time, it will
insert the instructions 1 to 5 (Figure 12) and a
progressive sequential number into the frame bits of the
control bits. It will also insert the data bits that
contain the delay time ~Figures 7 and 8) into the video
signal. These data bits are calculated by measuring
the time elapsed between the moment in which
the horizontal pulse, (that corresponds to a particular
T.V. answer~ is assigned, and the time at which the
answer is received by the T.V. ask.
II. Detecting answers.
After inserting some instructions in the control bits
an r-f pulse counting routine will be activated. This
routine, besides counting pulses, stores the last 3 T.V~
answer frame numbers and response lines of answers
received (only 3, due to the si7e of the microprocessor;
with a bigger one, the number could be larger)~
Z~
-24-
III. Receiving information from the computer via
serial communication interface 49 (~igure lO).
(a) Receives the number of the instruction to
be sent to the T.V. answer. This instruction will be
transmitted to the routines that insert 'n the video
signal and receive the r-f pulse.
(b) Receives a command that asks how many
answers were there. This information is obtained from the
routines that are activated with questions that require
answers.
(c) A command that asks, which were the ~rame
numbers and response lines of the last 3 received answers.
If we analyze the instructions from Figure 12 we
can see that some of them store the answer in memory,
thus permitting it to eliminate those answers that were
not correct in the last "N" times.
Note: The list of questions in Figure 12 is only
an example of some of the possibilities. Adding more
instructions will permit many more applications and or better
ways to implement applications.
12~ K
DETAILED DESCRIPTION OF DELAY TIME ME~SUREMENT
Each T.V. answer terminal will answer to questions
encoded by the T.V. ask system coded on the T.V. signal
by sending r-f pulses. The pulse of each answer terrninal
should be received by T.V. ask system at a unique time
slot. For this purpose each T.V. answer terminal has a
unique assigned response line and assigned response frame.
The combination of 438 terminals per frame and up to
65536 different frames gives a potential of 28,704,768
unique T.V. answer terminals.
There is a delay time for the signal to travel from
the T.V. studio to the T.V. receiver response unit (Figure
15), and for the answer pulse to travel from T.V. response
unit to the T.V. station (Figure 16).
The delay time depends on the distance between the T.V.
station and T.V. receiver iocation, and it may be different
for each terminal. If we want the answer pulse from each
T.V. answer unit to be received by the T.V. ask system
at the T.V. station at the assigned response line, then
the T.V. answer unit should send the answer pulse when
the line that it is receiving is equal to the assigned
response line minus the delay time.
Each T.V. answer terminal must somehow know the delay
time. For this purpose a special dialog is provided between
the T.V. ask system and the T.V. answer terminals. On
this dialog T.V. ask encodes on the T.V. signal a
special instruction (instructions 1 to 5 of Figure 12)
ordering groups of terminals to transmit a pulse as soon
as they receive their assigned response line. The T.V.
ask system measures the delay time elapsed between the
moment in which it transmitted the assigned response line and
the moment in which it receives the answer pulse. This
elapsed time is the delay time. The T.V. ask system then
encodes this delay time as four bits of delay data on the
~l~8~6
-26-
5th, 6th, 7th and 8th lines after the assigned response
line (Figures 7, 8, 17). The T.V. answer unit will read
the delay data from the T.V. signal and it will store this
data in memory, In this way the T.V. answer unit will
now know the delay time.
As described on Figure 18, groups cluster answer
terminals with spaced assigned response lines. In this
way enough space is provided for the transmission of four
bits of delay data without overlappinq. However, as
there are five groups, the calibration cycle will require
five times more time than a normal question cycle.
This invention thus is directed to a bi-direction
television system of the type permitting television transmitting
stations to ask questions for television receivers to
answer, wherein the questions are codiEied synchronously on
the television video signal. Improvements o~fered by
this invention include:
(1) Operation of the system with all responder
units using a single r-f burst located on a designated
horizontal line uniquely identifying each responder unit,
where all units use the same frequency and are identi~ied
by a unique predesignated time slot occurring after a
single query is made by the transmitted video to all
responder units. This feature significantly simplifies
both the transmitter and responder systems.
(2) Coupling of the responder unit to the i-f
channel of an adjacent T.V. set, thereby to eli~inate
channel identification means and to permit radiation
couplding without wiring.
(3) Compensation of the system for signal transmit
time delays greater than one-half a horizontal line distance
away (3.75 miles) so that viewers at lon~ distances may be
included in the system. This compensation is automatically
made.
~8~
(4) The system is adaptable to classroom use since
several response units with individual identification may
be used with a single T.V. set.
Having therefore advanced the state of the art, -those
features of novelty believecl descriptive of the nature and
spirit of the invention are defined with par-ticular.ity
in the following claims.
