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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates generally to telephone data transmission
systems, and more particularly to a dial-in data transmission system which
allows a central computer, for example, to access a remote data set, such
as an electronic publication storage device, a television polling system,
a computer data base subscriber data set, or a utility meter or plurality
of utility meters located in a business or residence, via non-dedicated
telephone lines and communicate with that remote data set without
substantially interfering with normal use of the subscriber's telephone.
Even more particularly, the present invention relates to dial-in data
transmission systems wherein the data device to be accessed dials up a
central computer via telephone lines to communicate with the computer at a
selected time and stands by to detect calls from the central computer at
other selected times.
The present invention finds application in many areas, one of which, for
instance, might be a shop by computer system where it might be necessary
to transmit information to and from an individual subscriber's data set
connected to an information storage device. Another might be the field of
utility usage data retrieval, wherein a central computer accesses a remote
data set which has stored therein data corresponding to the electrical or
gas or other utility usage at the remote location. Thus, the present
invention is useful for allowing a utility to read a utility meter located
at a remote location, for example an electric meter or a gas or water
usage meter. Still another application might be remote control of heating,
ventilating and air-conditioning equipment through telephone lines, as for
instance, in a utility's load management program. Although the invention
will be described for use with telephone lines, it will be apparent to one
skilled in the art that the invention can also be used with transmission
media other than telephone lines.
Various systems are presently known which allow central computers to access
individual subscriber's data sets via non-dedicated telephone lines. For
example, see U.S. Pat. Nos. 4,126,762, 4,104,486, 4,394,540 and 4,345,113.
In the 4,104,486 and 4,394,540 patents, the telephone is isolated from the
telephone line during a selected time window. In U.S. Pat. No. 4,126,762,
in one embodiment, a time window is utilized. In another embodiment,
sequential ringing signals, having a different time spacing than signals
from a normal telephone call condition a remote terminal to intercept the
ringing signals and to provide selective connection of a data accumulator
to the telephone line. It is preferable to use the subscriber's existing
telephone line rather than install a separate dedicated line to provide
access to the data set. Thus, systems of this type require that the
telephone line be available for use both by ordinary persons and by
computers calling the subscriber. Requirements of systems of this type are
that when computer calls are received, the call is automatically
transferred to a data set and the telephone preferably should not ring.
In applicant's prior U.S. Pat. No. 4,345,113, an automatic telephone
message intereption system is described which permits the use of a single
telephone line for both ordinary personal use and for receiving calls from
a computer, wherein computer calls are automatically transferred to the
subscriber's data set without ringing the subscriber's telephone. An
ordinary (non-computer) call made to the subscriber, would, however, be
answered by the automatic telephone message interception system described
in this U.S. patent even if no one were present at the subscriber's
telephone. The caller would thus be charged for a brief call even though
no actual person answered the phone.
The subscriber could, of course, solve this problem by shutting off the
automatic system if the telephone is to be left unattended, but the data
set could not be accessed by the computer while the system was shut off.
The need thus existed for a system which both allows a central computer to
access the subscriber's data set via a non-dedicated telephone line and
which allows normal operation of the telephone by both the subscriber and
other persons calling the subscriber. In particular, such a system should
allow a computer to access the subscriber's data set without ringing the
subscriber's telephone and should allow persons to call the subscriber at
any time without being charged for the call if the telephone is unanswered
by a person.
Applicant's prior U.S. Pat. No. 4,469,917, issued Sept. 4, 1984, describes
an apparatus which satisfies the above need.
In U.S. Pat. No. 4,469,917, a system and apparatus is described for
connecting a central computer to a remote subscriber's data set using the
subscriber's non-dedicated telephone line during a preselected window in
time. 27 Furthermore, in applicant's prior U.S. Pat. No. 4,578,534, the
apparatus described in U.S. Pat. No. 4,469,917 was modified to permit
connection of the central computer at any time to a remote subscriber's
data set using the subscriber's non-dedicated telephone line and without
interference of any sort with normal use of the subscriber's telephone
other than suppression of the first ring of an incoming call.
In the system of U.S. Pat. No. 4,469,917, the apparatus therein described
detects a ringing signal on the telephone line during a preselected window
in time during which the subscriber's data set is connected to the
telephone line and the subscriber's telephone instrument is disconnected.
The apparatus does nothing until the ringing signal stops, indicating that
the caller has hung up. The apparatus then causes the data set to dial up
the central computer and proceed to transmit or receive data during the
time window.
In the device described in applicant's prior U.S. Pat. No. 4,578,534, the
telephone instrument is normally disconnected from the telephone line. The
central computer issues a ringing signal preferably having a single ring
burst, and a device described in that patent detects the single ring burst
and triggers a data set to dial-up the central computer and provide data
over the telephone line to the central computer. If a ringing signal with
more than one ring burst is detected, then the device recognizes that the
call is not from the central computer and disconnects the data set from
the telephone line and connects the telephone instrument to the telephone
line, enabling the telephone to ring and the user to answer the call.
Because the telephone is normally disconnected, if a ringing signal with
only one ring burst is detected, the telephone subscriber never hears the
call from the central computer.
In a further development, applicant's prior U.S. Pat. No. 4,654,868, the
apparatus described in U.S. Pat. No. 4,578,534 was modified in order to
allow its use in applications where more than one data set or data device
is located at the remote location. For example, in U.S. Pat. No.
4,654,868, an apparatus is described where a plurality of consumption
level devices, for example, electricity, gas and water meters, are
interrogated at the remote location by a central computer
Accordingly, the above patents describe various apparatus for allowing the
central computer to access a remote data set via, for example, telephone
lines. In applicant's estimation, the simplest system for allowing a
central computer to access a remote data set, for example, to read a
utility meter, is the so-called "dial-in" system wherein the meter
interface device (data set) is connected directly across the telephone
line, and a clock in the interface device causes the interface to dial the
central computer's telephone number at a particular time each month and
transmit the meter reading to the computer. Applicant's prior U.S. Pat.
No. 4,469,917 describes a modified example of this type of device,
improved to prevent interference with the subscriber's use of the
telephone device at any time, even when the computer is communicating with
the data set, and which allows a computer first to call the data set
during a time window with the data set not answering but subsequently
calling the computer back (in contrast to the simple dial-in system
wherein the data set merely calls the central computer at the preselected
time), and wherein a clock is utilized to disconnect the telephone
instrument from the transmission line during predetermined time intervals
allowing the computer to call the data set with the data set not answering
but subsequently calling the central computer to provide communication
during that time interval.
The major disadvantage of time-synchronized dial-in systems is the
inability of the computer to establish contact with the data set at any
time other than that programmed by the clock. Thus, for example, if a
house or business is sold and the seller's utility account must be closed
out, a meter reader must be dispatched to take a final reading on the day
of the sale if that day does not coincide with the programmed time. This
can be a time-consuming and expensive task, especially considering that in
many areas of the country, 20% of the houses change hands each year.
Accordingly, it would be advantageous if a system could be provided which
would allow a central computer access to a remote data set not only at the
preselected time (for example, once a month), but also during a
preselected interval in time as required by the needs of the central
computer, for example, a utility required to read a utility meter on a
particular day.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a dial-in
data transmission system wherein a central computer can access a remote
data set via telephone lines.
It is a further object of the present invention to provide such a dial-in
data transmission which allows a central computer access to a remote data
device at preselected times on, for example, a monthly basis, and also at
more frequent intervals.
It is furthermore an object of the present invention to provide a dial-in
data transmission system having the capability to allow a central computer
to access the remote data device during specified intervals in time on a
frequent basis, such that, during these additional time intervals, the
subscriber's use of the telephone is substantially unimpaired.
It is yet still a further object of the present invention to provide such a
dial-in data transmission system utilizing the time independent data
transmission system described in U.S. Pat. Nos. 4,578,534 and 4,654,868.
It is furthermore an object of the present invention to provide a dial-in
data transmission system which is particularly suitable for providing
access by a central computer to remote data devices such as utility
meters.
The above-described deficiencies of the dial-in system wherein a remote
data device is programmed to dial up the central computer at a preselected
time can be cured if the remote data device can also standby at a common
time each day to receive instructions, if necessary, from the central
computer. Such a standby capability can be provided by suitably coupling
the time independent data transmission system (TIDTS) described in U.S.
Pat. No. 4,578,534 with a conventional dial-in data transmission system
wherein the data device is programmed to dial up the central computer at a
preselected time. Accordingly, the conventional dial-in system is modified
by programming the clock circuit of the dial-in system to insert the TIDTS
circuit between the data device and the telephone line for a period of
time each day (a period common to the data devices at all locations) and
preferably in the middle of the night, so as to interfere with normal
telephone usage as little as possible.
Thus, the central computer can call any particular data device, or several
data devices in succession, on any particular day, and hang up after one
ring, in accordance with the time independent data transmission system
described in U.S. Pat. No. 4,578,534. The data device called will then
call the computer back and will transmit the particular data, for example,
a meter reading, in accordance with the teachings of U.S. Pat. No.
4,578,534. As noted in U.S. Pat. No. 4,578,534, a call from a person
during the standby period will be coupled to the telephone instrument
after the first ring, the first ring having been suppressed by the time
independent data transmission device (TIDTD). The telephone instrument may
be used at any time by lifting the handset, even if the computer and data
device are in communication, as will be described below. Additionally, by
utilizing the time independent data transmission system described in U.S.
Pat. No. 4,654,868, the present invention can be applied to the accessing
of a plurality of data devices at a remote location.
The above and other objects of the present invention are achieved by an
apparatus coupling a telephone data set at a first location to a telephone
transmission line connected to a telephone instrument and for enabling
communication of data between the data set and a second location over the
telephone transmission line comprising first switching means coupling the
telephone instrument and the data set to the telephone transmission line
in a first state of the first switching means, clock means coupled to the
data set through the switching means in the first state of the switching
means and for providing a trigger signal to the data set to cause the data
set to communicate data over the telephone transmission line to the second
location periodically at a predetermined time, and further for placing the
switching means into a second state periodically during a predetermined
time interval, data transmission means coupled to the telephone
transmission line and further coupled to the telephone instrument and the
data set through the first switching means, and having a data set line
connected to the data set through the switching means when the switching
means is in the second state, the data transmission means normally
connecting the data set line to the telephone transmission line, the data
transmission means further having a telephone instrument line connected to
the telephone instrument through the switching means when the switching
means is in the second state, the data transmission means disconnecting
the data set line from the telephone transmission line and connecting the
telephone instrument line to the telephone transmission line in response
to any of selected ones of a plurality of first electrical signals
transmitted on the telephone transmission line, the first signals each
being indicative of a call from a caller on the telephone transmission
line, the data transmission means preventing disconnection of the data set
in response to a selected one of the first signals, the data transmission
means further comprising means for detecting any of the first electrical
signals transmitted on the telephone transmission line without answering
the call and for generating a second electrical signal when any of the
first electrical signals on the telephone transmission line has
terminated, indicating that the caller has hung up, the data set being
adapted to communicate data to the second location via the first switching
means over the data set line when the switching means is in the second
state during the predetermined time interval and further via the data
transmission means and the telephone transmission line in response to the
generation of the second electrical signal after the selected one of the
first electrical signals has terminated.
Other objects features and advantages of the invention will be apparent
from the detailed description below.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in greater detail in the following detailed
description with reference to the drawings in which:
FIG. 1 shows the dial-in data transmission system having standby capability
according to the present invention useful in allowing a central computer
access to a remote data set;
FIG. 1a shows in more detail the time independent data transmission device
of U.S. Pat. No. 4,578,534 suitably modified as utilized in the device
shown in FIG. 1;
FIG. 1b shows the operation graphically of a part of the time independent
data transmission device shown in FIG. 1a;
FIG. 2 shows the dial-in data transmission system having standby capability
shown in FIG. 1 modified for use so as to allow a central computer to
access more than one data device at a remote location;
FIG. 2a shows the arrangement of the time independent data transmission
device according to U.S. Pat. No. 4,654,868 for allowing a central
computer to access more than one data device at a remote location; and
FIG. 2b shows the time independent data transmission device of FIG. 1a
modified in accordance with FIG. 2 which allows the central computer to
access a plurality of data devices at a remote location.
DETAILED DESCRIPTION
With reference now to the drawings, FIG. 1 shows basically the arrangement
of the time-synchronized dial-in data transmission system having standby
capability according to the present invention. The data transmission
system includes a time independent data transmission device (TIDTD) 110,
which will be described in greater detail below and is described in U.S.
Pat. No. 4,578,534.
Telephone line 20, which comprises a pair of conductors, is coupled to the
TIDTD 110. A telephone instrument 40 is coupled alternatively to the
telephone line 20 and to telephone instrument line 91 coupled to the TIDTD
110, via a first portion 95a of a three-pole switch 95 operated by a clock
30. A data set 10 is coupled to a data device 122, for example, an
electric utility meter. The output 58a of the data set 10 is coupled
alternatively to the TIDTD 110 via a data set line 58 and to the telephone
line 20 via a second portion 95b of the three-pole switch 95. The data set
also has a trigger input 112a which is coupled alternatively to the TIDTD
110 via a trigger line 112 and to the telephone line 20 via a third
portion 95c of the three-pole switch 95. The TIDTD 110 trigger line 112
provides a signal to switch 95c for use in activating the data set 10 to
dial up the central computer when the central computer calls during the
data set's standby time period, as will be explained in greater detail
below. The TIDTD 110 data set line 58 comprises a line on which the output
of the data set 10 is provided when the data set dials up the central
computer during the standby time period. Telephone instrument line 91
couples the telephone instrument to the telephone line 20 via the TIDTD
110 during the standby period. At other than the standby period the
telephone instrument 40 and data set 10 are directly coupled to the
telephone line 20 by the switch 95.
In FIG. 1, all lines shown are schematic and are intended to depict signal
flow lines. Thus, the lines shown may actually comprise a conductor pair,
even though only one line is schematically shown in FIG. 1. Furthermore,
each switch portion 95a, 95b and 95c would actually comprise a two pole
switch, one pole for each conductor of the pair. The same is true with
respect to FIG. 2, to be discussed below.
Clock 30 generates a trigger pulse on line 33 at a predetermined time on a
periodic basis, for example, on a once a month interval, which is supplied
to data set 10 trigger line 112a via switch portion 95c when the switch 95
is in its normal position, as shown in FIG. 1. In the normal position of
switch 95, the telephone line 20 is coupled directly to the telephone
instrument 40 and to the output 58a of the data set 10. Accordingly, at
the predetermined time, for example, once a month, the clock 30 provides a
trigger pulse to data set 10, thus causing data set 10 to dial up the
central computer and provide data to the central computer via the output
58a.
The initial output of data set 10 is a dial up routine provided over the
telephone lines to the central computer, which then allows the central
computer to communicate with the data set and retrieve the data stored in
the attached device 122, for example, a water, gas, electric or other
utility meter. During the computer-data set communication at the
predetermined time, the user cannot utilize telephone instrument 40
because of the ongoing communication between the central computer and the
data set 10. However, this is not a significant problem, since it occurs
only once a month and only for a brief period of several seconds.
In order to allow the central computer to communicate with the data set 10
at other than during the time period at the predetermined time once a
month, clock 30 also executes a standby switching cycle on a more frequent
basis, for example, once a day, as shown by the dotted lines 31. Thus, for
example, once a day, preferably in the middle of the night, clock 30
switches switch 95 into its second position, such that the telephone
instrument 40 is connected via line 91 to TIDTD 110, the output 58a of the
data set 10 is connected via line 58 to the TIDTD 110 and the trigger
input 112a of the data set 10 is connected to trigger line 112 of the
TIDTD 110. Accordingly, the data set and telephone instrument are removed
from direct communication with the telephone line 20 and can only
communicate with the telephone line through the TIDTD 110 during the
standby period.
The purpose of the TIDTD 110 is fourfold. First, it allows the central
computer to call the data set during the standby period with a preselected
number of rings and allows the data set to dial up the computer. Second,
it allows the user complete access and use of his telephone during the
standby period, regardless of whether the computer is communicating with
the data set. Third, it allows outside calls, i.e., noncomputer calls, to
be directed to the telephone instrument 40 so that they can be answered by
the telephone user during the standby period (of course when the central
computer is not already communicating with the data set). Fourth, the
TIDTD prevents a call from a human caller from being answered during the
standby period if the telephone user is not at home.
The TIDTD 110 as modified is shown in detail in FIG. 1a and its operation
is also described in U.S. Pat. No. 4,578,534. Its operation will be
explained herein for convenience.
The TIDTD 110 includes a ring detector and trigger circuit 50, a ring
signal counting circuit 80, and a subscriber priority circuit 34. Data set
10, as shown in FIG. 1, is coupled via lines 58 and 112 to the TIDTD 110,
and in particular, to the subscriber priority circuit 34 and to the ring
detector and trigger circuit 50, respectively. Telephone instrument 40 is
coupled to the subscriber priority circuit 34 via telephone instrument
line 91. The telephone lines 20 are coupled to the ring signal counting
circuit 80 and the ring detector and trigger circuit 50. Data set 10 is
normally connected to the telephone line 20 through a first dual set of
contacts 60 (a and b) of a relay 61.
The central computer is preferably programmed to provide only one ringing
signal or ring burst over the telephone transmission line. In the
preferred embodiment, if only one ringing signal is detected, the
telephone instrument 40 will remain disconnected, the data set will remain
connected and the subscriber's data set will be triggered to dial up the
central computer and communicate with the computer. Two way communication
is contemplated, i.e., the data set may, for example, both receive data
from the computer and transmit data to the computer. Additionally, because
of the subscriber priority circuit 34, the subscriber may regain use of
the telephone instrument during data transmission simply by lifting the
telephone receiver, as will be explained below.
Furthermore, if desired, the subscriber priority circuit can also be
employed to allow the subscriber to regain use of the telephone instrument
during the brief once a month period of communication between the computer
and data set by suitable connection and switching of the subscriber
priority circuit as will be evident to a person of skill in the art.
If ring signal counting circuit 80 detects the commencement of a second
ring burst in the incoming call, it triggers the latch coil 62 of the
relay 61 and thus connects the subscriber's telephone instrument 40 to the
telephone line by allowing contacts b and c of contact 60 to make. The
data set is thus disconnected and the subscriber's telephone connected
which then proceeds to ring and can be used normally. Thus, the TIDTD 110
will suppress the first ring of any call received by the TIDTD 110. If a
second ring burst does not follow the first ring burst, the data set
remains connected to the telephone line and is caused to dial up the
central computer, as will be described in more detail below. Thus, the
TIDTD 110 assumes that if only one ring occurs, the central computer
called. In the event that the central computer did not call but only one
ring is sensed, the data set will still dial up the central computer, but
the central computer will be programmed properly to know that it had not
called and thus would ignore or reject the call.
Ring signal counter circuit 80 resets itself after each call. After any use
of the telephone instrument has been completed, the data set is once more
connected to the telephone line by the relay 61 which ha been unlatched by
the operation of the subscriber priority circuit 34, to be described in
more detail below.
Thus, for selected ones of the ringing signals having more than one ring
burst, the data set is disconnected and the telephone instrument
connected. For a selected one of the ringing signals, i.e., preferably a
ringing signal having only one ring burst, the data set remains connected
and the telephone instrument disconnected.
The ring signal counter circuit 80 essentially may be an RC circuit
disposed across the telephone lines as shown in FIG. 1 comprising a
resistor R, a capacitor C, diode D, resistor BR and gas discharge tube GT.
The time constant is chosen to charge the capacitor C through resistor R
and diode rectifier D to approximately one-half of the ring signal voltage
on the first ring and to a higher voltage on the second ring as shown in
FIG. lb. The higher voltage is sufficient to trigger a gas discharge tube
GT in series with the latch coil 62 of relay 61, thus energizing the latch
coil and connecting the telephone instrument to the telephone line while
disconnecting the data set from the telephone line. A diode 84 is placed
between the pulse amplifier and shaper 35, to be described below, and the
latch coil 62, to prevent pulses from the circuit 80 from feeding back
into circuit 35. A high resistance bleeder resistor BR discharges the
capacitor slowly after each single-ring call from the central computer and
between successive rings from a non-computer caller, as shown in FIG. 1b.
Other types of counting circuits could obviously be used for this purpose.
For example, the gas discharge tube could be replaced by a semi-conductor
device, e.g., a threshold sensitive zener diode in series with a resistor
coupled across the resistor BR, the junction of the zener diode and the
resistor being coupled to the base of a switching transistor having its
emitter-collector path in series with latch coil 62. Furthermore, other
circuits could be used, such as filter circuits and appropriate digital
logic counters.
The operation of ring detector and trigger circuit 50 will now be
explained. When the central computer calls, or if anyone else calls, the
ring signal on the telephone line will charge capacitor 36 through
rectifying diode 38 and isolating resistor 42. Contacts 44 operated by
relay coil 46 of relay 45 will, therefore, close once relay coil 46 is
energized. Resistor 48 and capacitor 36 have a time constant chosen so
that capacitor 36 remains sufficiently charged between successive rings of
the same call and coil 46 remains energized. When the | | |
