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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to telephone interfaced subscription cable
television systems and more particularly to those systems which distribute
both free and premium program channels where premium program requests by
the subscriber are made by telephone. Such systems can, for example, be
used in hotels or apartment complexes where, in addition to the
distribution of free broadcast program channels, there are also
distributed premium or special program channels for which the subscriber
is usually charged an additional fee for viewing.
2. Description of the Prior Art
Telephone interfaced cable television systems which utilize the
subscriber's telephone equipment for program requests have been used in
the past but they have not been entirely satisfactory or simple in
operation. Prior art systems generally require the use of a computer or
human operator for controlling and/or processing incoming subscriber
telephoned requests. In addition, prior systems which utilize signal
converters or program channel selectors at the subscriber terminal or
location require manual subscriber operation of the converter or selector.
Prior art systems also require a computer or other equipment at the
central station or head end for addressing each such subscriber located
device or terminal.
Because of the complexity of these prior art systems, the captial
investment cost for their initial installation, as well as the cost of
their operation and maintenance, are high and limit their use to
installations having a relatively large number of paying subscribers. The
use of such prior art systems in even large hotels are therefore not
generally profitable.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to
provide an improved telephone interfaced subscription cable television
system which requires a minimum of equipment and is simple in use and
automatic in operation.
It is another object of the present invention to provide a subscription
cable television system which is well adapted economically for use in
hotels, motels, and apartment complexes where the number of subscribers is
limited compared to large public cable systems.
It is yet another object of the present invention to provide a telephone
interfaced subscription cable television system having a subscriber
terminal which does not require subscriber adjustment to receive a desired
and selected one of a plurality of premium program channels.
It is a further object of the present invention to provide a subscription
cable television system in which the subscriber terminal equipment is
automatically adjusted to receive a subscriber selected program channel by
signals transmitted from the central station to the subscriber terminal
via the subscriber's telephone and associated telephone network.
It is yet a further object of the present invention to provide a telephone
interfaced cable television system in which the subscriber terminals do
not require addressing by the central station.
It is still another object of the present invention to provide a
subscription cable television system which utilizes the local telephone
network for the transmission of subscriber program request signals to the
central station and for the transmission of subscriber terminal enabling
signals from the central station to the subscriber terminals.
In addition, existing cable television systems utilizing a central station
which transmits television signals in non-standard frequency bands may be
easily converted to the telephone interfaced subscriber television system
described herein.
In accordance with the present invention, in one form, there is provided a
conventional coaxial cable television signal distribution network
interconnecting a central station and a plurality of subscriber terminals
and associated television sets. Certain of the television signals
trasmitted from the central station have frequencies corresponding to the
standard F.C.C. authorized television channels which, for example, can be
in the standard V.H.F. television band, channels 2 through 6 and 7 through
13. These signals may be received and viewed on the subscriber's standard
television set as transmitted from the central station without the
necessity of any additional frequency conversion or decoding and for
purposes of illustration in this specification are considered as "free"
program channels. Certain other of the television signals transmitted from
the central station have non-standard channel frequencies and can, for
example, be appropriately located midband in the V.H.F. band between the
standard channels 6 and 7. Again, for illustrative purposes, these
non-standard channels are considered in the specification as "premium" or
"restricted" program channels. For viewing of these premium program
channels on the subscriber's television set, they are converted in
frequency to a standard channel frequency capable of being received by the
television set, such as channel 12, for example. Thus, these non-standard
television signals are modified or converted to standard television
signals. It will be understood by those skilled in the art that scrambling
of the premium program television signals can be utilized without
departing from the spirit of the present invention.
Conversion of the premium channels is provided by a subscriber room
terminal which interfaces the subscriber's television set with the coaxial
cable signal distribution network. Conversion of any selected one of the
premium channels as may be desired by the subscriber is made automatically
upon a telephone dialed request by the subscriber to the central station.
Subscriber request for such premium program viewing is made by use of the
subscriber's telephone. A typical request in a hotel installed system
according to the present invention would comprise first, the dialing by
the subscriber or room guest, of a predetermined access digit followed by
the digits of the guest's room number and a special verification number or
digit known only to the quest of that room and last, the dialing of a
program number or digit corresponding to the particular premium program or
channel for which viewing is desired.
The central station includes conventional cable television R.F. head end
equipment for transmitting the television signals, including the
aforementioned premium program channels, via the coaxial cable
distribution network to each subscriber in the system. The central station
also includes at least one premium channel control and monitoring means
which accepts and processes the subscriber telephoned requests. The
control and monitoring means is interfaced with the telephone network
which, in the exemplified hotel installation, would comprise the hotel's
PABX system. Dialing of the access digit, which is known to all
subscribers, by a particular subscriber or room guest provides connection
of that subscriber's telephone with the control and monitoring means and
allows acceptance and processing of the remainder of the subscriber dialed
request digits by the control and monitoring means.
During the time period when the control and monitoring means is processing
a given subscriber's request, a busy signal is provided by the PABX system
to all other subscribers which at that time dial the access digit. This,
of course, indicates that the access digit should be redialed. The central
station can include a plurality of control and monitoring means to provide
the processing of requests from a plurality of subscribers simultaneously.
If a control and monitoring means is available at the time of the dialing
of the access digit by a given subscriber, the available control and
monitoring means will provide a ready tone or signal to the given
subscriber via his telephone, indicating that the control and monitoring
device is available for use by the requesting subscriber and that the
remainder of the request digits may be dialed by the requesting
subscriber.
The control and monitoring means upon receiving a satisfactorily dialed
subscriber request which includes the proper room and verification digits,
will respond by providing enabling signals to the requesting subscriber
telephone and room terminal via the telephone network. These enabling
signals in the one embodiment described herein comprise a pair of audio
tones which are inductively coupled from the subscriber telephone to the
subscriber room terminal. The enabling signals have frequencies that are
peculiar to the particular requested premium channel. A unique pair or
combination of tones is provided for each premium program channel
available for subscriber viewing.
The subscriber room terminal responds to the enabling signals by providing
a D.C. tuning voltage to a voltage or varactor tuned premium channel
converter within the subscriber room terminal. A different D.C. voltage
level is provided for each pair of enabling tones representing each of the
available premium program channels. The tuning voltage level is therefore
a function of the requested premium channel. The requested premium channel
is thus converted in frequency to one which is receivable by the
subscriber television set, such as channel 12 as stated in the
aforementioned example. For subscriber viewing of a premium channel, it is
only necessary that the subscriber television set be adjusted to a single
predetermined and known channel either prior to or after the dialed
request has been made; no other adjustment is required by the subscriber.
The television set can be a standard television receiver such as is sold
commercially for home use for receiving standard F.C.C. authorized
television signal channels.
The control and monitoring means, in addition to providing the enabling
signals to the subscriber room terminals, also provides signals to a tape
printer at the central station for maintaining a log or record of the
premium channel usage by each subscriber in the system. As an example, in
a hotel installation of the system there can be provided a printed record
of each premium program request including the guest room, verification,
and requested premium program channel numbers, as well as the date and
time of such request if desired.
The above objects of the present invention, as well as other objectives,
features, and advantages, will become more apparent from the following
description with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a pictorial view of the complete television program request and
signal distribution system illustrating the present invention in one form;
FIGS. 2A through 2C combined is a block diagram of a control and monitoring
station which can be used in the system of FIG. 1;
FIG. 3 is a block diagram of a subscriber room terminal which can be used
in the system of FIG. 1;
FIG. 4 is a simplified block diagram of a head end equipment which can be
used in the system of FIG. 1;
FIG. 5 illustrates a typical subscriber dialed program request of the
present invention in one form and the dialing sequence of the various
digits contained herein; and
FIG. 6 illustrates a typical recorded printout delivered by the printer
used in the system of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
For a better understanding of the present invention in one form thereof,
reference is made to the accompanying drawings. FIG. 1 is a pictorial view
of the complete television program request and distribution system
including a central station 1, one of a plurality of guest rooms 2, and a
PABX or private automatic telephone exchange equipment 3. Block diagrams
of the various component parts of the system shown in FIG. 1 are
illustrated in greater detail in FIGS. 2 through 4 and their operation in
the system will be disclosed herein later.
It should be understood that although the operation of the following
disclosed embodiment of the present invention is described in relation to
its use in a hotel or motel like environment, the invention is not so
limited. The system can for example, be used in apartment and multi-unit
condominium complexes as well as public cable television networks. In
addition, the use of the word "subscriber" in this disclosure is intended
to encompass house or hotel and motel room guests as well as apartment and
condominium tenants or owners and the like.
In the circuit descriptions which follow, reference to high and low level
signals denote respective types of 1, true, or presence and 0, false, or
absence logic signal states which are well known to those skilled in the
art. It should be understood, however, that the invention is not limited
in operation to the use of the logic signal states described and shown,
since those skilled in the art can readily adapt the various circuits
described to operate with the use of positive true and/or negative true
type logic.
The pulse duration and delay time periods illustrated in the herein
described embodiment of the present invention are typically based upon
utilization of telephone signals provided by telephone equipment complying
with well known telephone D.C. dial pulse and pulse train standards. As an
example, standard telephone dial pulses occur at a rate of 8 to 10 pulses
per second with each one of the pulses having a width of between 36 and
42% of a single pulse cycle. In addition, the minimum interdigital time is
600 milliseconds. It will be understood by those skilled in the art that
dial pulses having other than the standard characteristics can be used
with corresponding changes in the illustrated duration and delay times. In
addition, the disclosed system can be utilized with "touch-pad" type
telephones by replacing the dial pulse processing circuitry with
appropriate tone addressing circuitry.
Referring now again to FIG. 1, there is shown a central station 1 which
supplies and transmits free and premium program television signals to one
or more subscriber locations or guest rooms 2 by means of the coaxial
cable distribution network 4. The coaxial cable line taps 5 are
conventional and provide a means of supplying the television signals from
the coaxial cable network 4 to each of a plurality of guest rooms 2 and
associated equipment located within. In addition to a standard or
conventional television set 6 and telephone 7 which are normally provided
in each guest room 2, there is also provided in accordance with the
present invention, a subscriber room terminal 8, and a telephone signal
pickup means 9. The television signals from the coaxial cable line tap 5
are supplied to the subscriber room terminal 8 via the interconnecting
signal cable 10 whereupon they are either converted or unconverted in
frequency and supplied to the antenna input terminals 11 of the television
set 6 via the antenna signal cable 12. The A.C. line power cord 13 from
the television set 6 interconnects to the hotel A.C. power line (not
shown) within the subscriber room terminal 8. Telephone signals from the
telephone pickup means 9 are supplied to the subscriber room terminal 8 by
means of the interconnecting signal cable 14. The pickup means 9 shown in
FIG. 1 is intended to represent an inductive type of pickup; however,
other equally well known types may be used or the subscriber room terminal
can be "hard wired" directly into the PABX telephone system 3 in
accordance with accepted and standard telephone practices.
The central station 1 is comprised of a R.F. head end equipment 15 which
operates to provide radio frequency television signals to the coaxial
cable signal distribution network 4. The channel frequencies of the R.F.
television signals provided by the head end 15 are in two groups, the
first being in a frequency range normally receivable by the guest room
television set 6, and the second being in a frequency range not receivable
by the television set 6 without first being converted in frequency.
Television program material for distribution to guest room subscribers can
be supplied from public off-the-air television signals by means of
antennas 16, 17 as well as from the video tape equipment 18, 19 and/or
television camera equipment 20. The central station 1 of FIG. 1 also
comprises a control and monitoring station 21 and associated paper tape
printer 22. It should be understood, however, that the control and
monitoring station 21 and/or printer 22 can be physically located
elsewhere if convenience and desirability so dictate. The control and
monitoring station 21 is interconnected with the PABX telephone system 3
via an interconnecting telephone line 23. The control and monitoring
station 21 can also be connected to the head end equipment 15 via signal
cable 24, the purpose of which will herein later be described.
The PABX telephone system 3 is conventional and typically comprises line
switching equipment 25, in-house telephone lines 26 outside telephone
lines 27 which normally connect to a central telephone exchange (not
shown) outside the PABX system 3, one or more in-house or guest room
subscriber telephone sets 7 and its respective individual telephone line
28 and terminal block 29. The PABX telephone system 3 operates to provide
connection of the control and monitoring station 21 with a given one of
the subscriber telephone sets 7 upon a dialed access request from that
telephone set. Although a PABX telephone system or the like is utilized in
the television system of the present invention, such PABX equipments are
well known in the art and therefore a detailed explanation of its
operation is not given. The only requirement of the PABX system 3 is that
it be capable of providing the connecting of a given subscriber telephone
set 7 to the control and monitoring station 21 upon the subscriber dialing
of a predetermined access number and, after the resulting connection of
the subscriber telephone set 7 with the control and monitoring station 21
has been made, that the PABX system provide for any additional dialing
pulses originating from the given subscriber's telephone set 7 to be
transmitted to the control and monitoring station 21 for further
processing. It should be understood that the PABX system 3 can have the
capability of supplying more than one interconnecting telephone line 23 to
more than one corresponding control and monitoring station 21 in order
that access calls can be accepted simultaneously from more than one
subscriber telephone sets 7. This will provide for the simultaneous
processing of subscriber program requests from a plurality of subscribers
by a plurality of control and monitoring stations 21.
After the dialing of the predetermined access number by the subscriber, and
the resulting connection of the subscriber's telephone set 7 with the
control and monitoring station 21, any additional program request dialing
pulses from the subscriber's telephone set 7 will be processed by the
control and monitoring station 21. The control and monitoring station 21
will in turn send back to the subscriber telephone set 7 via the PABX
system 3, enabling signals for activation of the subscribers room terminal
8 as will herein later be described. The predetermined access number which
is dialed by the subscriber or room guest to gain access to the control
and monitoring station 21 is normally dictated by the PABX system 3 or
more specifically by the line switching equipment 25. This access number
may be any convenient digit such as for example, the number 6 could be
used in the embodiment of the present invention which is described herein.
The above described operation of the PABX system 3 upon the dialing of the
access number is much the same as that which normally occurs when one, for
example, dials a number 9 to gain access to an outside line 27 which
connects the dialed telephone set to a central telephone exchange outside
of the PABX system whereupon the central exchange processes any additional
dial pulses from the connected telephone set. It should be understood,
however, that the outside lines 27 or the central telephone exchange
located external from the PABX system 3 is not required for the operation
of the present invention.
Referring now in more detail to the combined FIGS. 2A through 2C, there is
shown a block diagram of the control and monitoring station 21. Referring
more specifically to FIG. 2A, the dialing of the access number at a given
subscriber telephone set 7 will provide connection of that telephone set 7
with the control and monitoring station 21, as previously described. A low
frequency telephone ringing signal provided by the PABX system 3 will
appear at the telephone line terminals 30 via the interconnecting
telephone line 23. This ringing signal is in turn applied through the
coupling capacitors 31 and 32 to the input of a ringing signal shaper
amplifier 33 where it is shaped and amplified. Amplifier 33 is normally
enabled to pass the ringing signal at its input to its output but can be
disabled or inhibited by application of an inhibiting signal at an inhibit
terminal 34. The signal appearing at the output of the shaper amplifier 33
representing the ringing signal is provided as an input signal to a
ringing signal detector 35. The detector 35 detects the presence of the
ringing signal at its input and in turn provides an output signal to a
relay driver 36. The detector 35 is capable of being latched to an ON
state by the presence of the ringing signal at its input and remains in
the ON state until it is reset by the application of a reset signal at its
reset terminal 37. The detector 35 provides an output signal to the relay
driver 36 during that time that the detector 35 is latched in the ON
state. The relay driver 36, in turn, provides activation of a relay 38,
thereby causing the contacts of the relay 38 to close from a normally open
condition whenever the relay driver 36 is supplied with an output signal
from the detector 35. The relay driver 36 can be a D.C. amplifier with the
electro-magnetic coil of the relay 38 in its output circuit. Thus, when
the PABX ringing signal is applied to the telephone line terminals 30, the
contacts of relay 38 are caused to close. The closing of these contacts
places the series combination of resistor 39 and the secondary winding 40
(FIG. 2C) of a tone amplifier output transformer 41, across the telephone
line input terminals 30 and associated telephone line 23. This resultant
electrical loading of the telephone line 23 is presented to the telephone
switching equipment 25 and indicates to the PABX equipment that there is a
"off-hook" condition or, in other words, that the control and monitoring
station 21 has accepted the incoming call represented by the ringing
signal.
The output signal from the ringing signal detector 35, in addition to being
applied to the input of the relay driver 36, is also applied to an input
of a 300 millisecond mono-stable multivibrator 42 and a 15 second delay
timer 43. The 300 millisecond mono-stable multivibrator 42 operates to
provide an output signal which changes to a high level state during a 300
millisecond time period duration after receiving its input signal from the
ringing signal detector 35. The 300 millisecond output signal from the
mono-stable multivibrator 42 is applied to the inhibit terminal 34 of the
ringing signal shaper amplifier 33 thereby preventing the ringing signal
shaper amplifier 33 from providing any additional ringing signals to the
input of the ringing signal detector 35 during the 300 millisecond time
period. The 300 millisecond output signal from the mono-stable
multivibrator 42 is also applied to a signal input terminal 44 of an OR
gate 45 (FIG. 2C) via the interconnecting lead 46 and to a signal input
terminal 47 of an OR gate 48.
Now referring to FIG. 2C, operation of the OR gate 45 in response to the
300 millisecond signal at its input terminal 44, provides the unclamping
of junction point 49, of a voltage control oscillator control circuit 50,
from a normally low or ground level to a level substantially equal to the
positive voltage level present at the supply voltage terminal 51. The
V.C.O. control circuit 50 is comprised of a series combination of diode 52
and resistors, 53, 54, 55, and 56, connected between ground level and the
supply voltage terminal 51. The unclamping of junction point 49 causes the
diode 52 to conduct, thereby providing a D.C. voltage to be applied to a
frequency control terminal 57 of a voltage controlled audio tone
oscillator or generator 58. The level of the voltage at the control
terminal 57, and thus the output signal frequency of the V.C.O. 58, is set
to a predetermined value by means of the adjustable resistor 54. The
output signal from the generator 58 is amplified by a tone amplifier 59
and passed by its output transformer 41 and interconnecting leads 60 to
the telephone line terminals 30 whereupon it is supplied as a ready-tone
to the requesting subscriber's room telephone set 7 via the telephone line
23 and PABX system 3. This ready-tone indicates to the requesting
subscriber that the control and monitoring station 21 has responded to the
incoming access request or ringing signal and is ready to process a
program request from the requesting room telephone set 7. In the
particular embodiment of the present invention described herein, the
dialed request must be made by the subscriber within a 15 second time
period following the ready-tone as will be later apparent. The output
signal frequency of generator 58 during the time period when the junction
point 49 is clamped to ground level, is far outside the passband of the
tone amplifier 59 and/or output transformer 41 and thus the unclamping of
junction point 49 by the OR gate 45 for all practical purposes enables
generator 58.
Now again referring to FIG. 2A, the OR gate 48 provides a reset output
signal on interconnecting lead 61 in response to the 300 millisecond
signal at its input terminal 47. This output signal is supplied to the
reset terminals (R) of the digit pulse accumulator 104, digit sequence
counter 90 and storage registers 96-100 shown in FIG. 2B via the
interconnecting lead 61 and provides for the resetting of these pulse
circuits to their initial states.
The 15 second delay timer mono-stable MV 43 operates to provide an output
signal 15 seconds after it receives the output signal from the ringing
detector latch 35. The output signal from the 15 second delay timer 43 is
supplied to a first signal input terminal 62 of an OR gate 63 and in
response to this signal, the OR gate 63 provides an input signal to a 3
second error beep timer mono-stable MV 64. The 3 second timer 64, upon
receiving the input signal from the OR gate 63, operates to provide at a
first output terminal 65, a first output signal having a 3 second time
duration and at a second output terminal 66 a second output signal which
is delayed for a 3 second time period after receiving the input signal
from the OR gate 63.
The first output signal from the 3 second timer 64 and appearing at the
output terminal 65 is supplied to a first input 67 of an AND gate 68 (FIG.
2C) via interconnecting line 69. A second input 70 of AND gate 68 is
provided by an error pulse multivibrator 71 which generates repetitive
pulses at a low frequency rate of, for example, 10 Hz per second. Thus 15
seconds after the detector 35 has detected the ringing signal, AND gate 68
will provide to OR gate 45 a low frequency 10 Hz per second pulsed signal
of 3 seconds time duration. This pulsed signal is supplied by OR gate 45
to the junction point 49 of the V.C.O. control circuit 50, thereby
enabling generator 58, as previously described, at the 10 Hz per second
rate for a time duration of 3 seconds. The output of generator 58 is
supplied as an error beep signal to the subscribers room telephone 7 as
previously described and indicates to the requesting subscriber as will
later be apparent, that an error in the subscriber request was made or
that the subscriber request was not received by the control and monitoring
station 21 within the required 15 second interval of time.
The second output signal from the 3 second timer 64 and appearing at the
output terminal 66 is supplied to a first input terminal 72 of an OR gate
73. The OR gate 73 in turn operates to provide an input signal to a second
input terminal 74 of the OR gate 48 whereupon the operation of the OR gate
48 provides an output signal on the interconnecting lead 61 for resetting
the pulse circuits shown in FIG. 2B as previously described. Thus, any
pulse circuits which may have been activated are again reset 18 seconds
after the ring detector 35 detects the PABX ringing signal and supplies an
output signal to the input of the 15 second delay timer 43.
The output signal from OR gate 73 which is supplied to the second input
terminal 74 of the OR gate 48 is also supplied to the reset terminal 37 of
the ring detector 35 whereby the ring detector 35 is also unlatched or
reset. The resetting of the ring detector 35, in turn, deactivates the
relay 38 which signals the PABX system 3 that the call is terminated and
that an "on-hook" condition exists.
Briefly summarizing the above described operation, the control and
monitoring 21 provides an off-hook condition to the PABX system 3 upon
detecting the ringing signal from the PABX system 3. A ready tone signal
is at this time provided and supplied to the PABX system 3 by the control
and monitoring station 21. A reset signal is also provided to the pulse
circuits of the control and monitoring station 21 for resetting the pulse
circuits to their initial states. At this point in operation the
subscriber would normally proceed with his dialing request, however, if
the subscriber fails to proceed with the dialing of his room,
verification, and program request numbers or fails to complete this
request within a 15 second time period immediately following the detection
of the ringing signal and the initiation of the ready tone, the control
and monitoring station 21 will provide to the PABX system 3 an error beep
signal of 3 seconds time duration commencing 15 seconds after the control
and monitoring station 21 detects the ringing signal. Immediately
following the 3 seconds time duration of the error beep signal and 18
seconds after the ringing signal has been detected, the ring detector
latch will be reset and a pulse reset signal will be provided to the pulse
circuits of the control and monitoring station 21 for resetting any of the
pulse circuits which may have been activated during the 15 second time
period.
It will be apparent that the pulse circuits of the control and monitoring
station 21 can be reset prior to the above described 18 second time period
by a signal at a second input terminal 75 of the OR gate 63 in which case
the 3 second error beep signal will be provided as previously described to
provide the operation of the OR gates 73 and 48 and the resulting presence
of a reset signal on the interconnecting line 61. It will later be
apparent that a signal at the second input terminal 75 of the OR gate 63
will be provided by an inverter amplifier 76 (FIG. 2B) whenever the
subscriber dialed room and/or verification numbers are not proper.
It will also be apparent that the pulse circuits of the control and
monitoring station 21 can be reset prior to the described 18 second period
of time, by a signal on a second input terminal 77 of OR gate 73. In this
case, however, the signal at the second input terminal 77 will not result
in providing the 3 second error beep signal prior to the pulse reset
signal on the interconnecting line 61. It will later be apparent that a
signal at the second input terminal 77 of the OR gate 73 can be provided
by the end of request decoder 78 (FIG. 2B) upon the completion of the
processing by the control and monitoring station 21 of a proper subscriber
room, verification and program request.
After the subscriber has dialed the access number and has received the
ready tone, he proceeds with the dialing of his room, verification, and
program request numbers. The resulting dial pulses from the requesting
subscriber's telephone set 7 are supplied to the telephone line terminals
30 of the control and monitoring station 21 by the PABX system 3, as
previously described. The telephone dial pulses present at the telephone
line terminals 30 are supplied to a dial pulse shaper 79 for clipping the
incoming dial pulses and for eliminating extraneous noises which may be
present on the telephone line.
Now referring to FIG. 2B, the output of the pulse shaper 79 (FIG. 2A) is
applied to the input of a second pulse shaper 80 via the interconnecting
lead 81. The pulse shaper 80 comprises a mono-stable multivibrator which
provides for each input dial pulse, an output signal pulse of 150
microseconds duration. Thus, the output of the pulse shaper 80 will
comprise a number of pulse trains, each train representing a different
digit or number dialed by the subscriber and each train comprising one or
more pulses. Therefore, for the herein stated example of a three digit
room number (435), a single digit verification number (1), and a single
digit program number (3), the output of the pulse shaper 80 would comprise
a series of five pulse trains with the number of pulses in each respective
train being 4, 3, 5, 1, and 3. The output of the pulse shaper 80 is
applied to a first input 82 of an AND gate 83. The AND gate 83 provides an
output signal for each 150 microsecond input pulse appearing at its first
input terminal 82, since the second input terminal 84 is normally at a
high level as will herein later be apparent. The output signal of AND gate
83 representing each incoming dial pulse to the control and monitoring
station 21 is applied to the input of a 300 millisecond mono-stable
multivibrator 85, as well as to the input of a digit pulse to binary
counter 86 and a first input terminal 87 of an AND gate 88. The second
input 89 of the AND gate 88 will be described later.
The 300 millisecond mono-stable MV 85 provides an output signal pulse of
300 milliseconds duration for each input pulse; however, since more than
one 150 microsecond input pulse from the AND gate 83 can occur within a
single 300 millisecond period, the output of the 300 millisecond
multivibrator 85 will, for all practical purposes, comprise a single
continuous high level pulse starting with the first 150 microsecond input
pulse and ending approximately 300 milliseconds after the last 150
microsecond input pulse of each pulse train received, representing each
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