Note: Descriptions are shown in the official language in which they were submitted.
- . F. A. MIDDLETON ET AL 13-1
~LZ, L?~ 4978
SINGLE LINE TELE~H~NE CQMMUNICATI~N SYSTEM
BACKGROUND OF THE INVENTION
The present invention generally relates to a telephone
communication system and, in particular, relates to one such
telephone co~munication system having a line interface means
for establishlng communication with a single externally
provided pair of telephone wires and meansl associated wi~h
each o a plurality of telephone subsets, for establishing
communication between either another one of the plurality of
telephone subset or, via the line interface means, to the
single externally provided pair of telephone wires.
In recent years telephone subscribers in the United
States and other countries have become entitled to connect
their own equipment to externally provided telephone lines.
15 Consequently, a rapid expansion in residential oriented
telephone systems and equipment has been developing to satisfy
an ever growing number of needs related to such telephone
- communications.
F. A. MIDDLETON ET AL 13-1
124~378 - 2-
One particular identified need in such residences is the
ability to communicate between and among a plurality of
telephone subsets all being interconnected with the single
central office telephone line pair of wires that accesses the
. residence. In addition, o~her identified needs of subscribers
are similar to those of businesses having an independent
private automatic branch exchange (PABX). HoweYer, the
residential subscriber usually does not have the resources to
purchase such an exchange. Nevertheless~ numerous attempts
have been made to provide the PABX type features with systems
directed for sale in the residential market. This markett in
the field of telephone exchange equipment is unique in
requlring equipment that is considerably lower in cost than
past siMilarly ~unctioning equipment as well as requiring
relatively simpli~ied installation to allow the subscriber to
install the equipment without requiring a representative of a
telephone serYice company.
As it happens, this burgeoning market is not at all
limited to residences. For example, many small businesses,
such as hardware stores, drug stores, retail outlets and the
like, also have need for a communication system having many
PABX type features. In addition, a common characteristic in
many small businesses, in particular, ~n~3~ offices and
other professional offices, is the need to permit multiple
user access ~o a minimal number of telephone lines. The most
conventional arrangement is commQnly known as a "secretarial
system" where a telephone line is, in fact, shared between a
supervisor and a secretary. Typically, such secretarial
systems permit incoming calls to be screened by the secretary
lZ44978 _3_ F. A. MIDDLETON ET AL 13-1
and, in addition, allow intercommunication between the
secretary and the supervisor for local communications.
Present secretarial systems not only require specialized
telephone subsets but, additionally, require special wiring
for the intercommunication feature, i.e. usually about 10 to
25 pairs of wires. Although limited versions of telephone
communication systems exist, a vast majority of present
systems require individual interconnections to a master
control switch and thus are disadvantageous by requiring
either a rewiring cost upon installation and/or a prohibitive
cost penalty for the subsequent inclusion of additional
subsets.
In general, consumers of telephone communication systems
are confronted by one or more oE the following limitations
presently existing in conventional systems: that special
wiring is required; that the existing telephone subsets are
obsoleted; that the cost is excessive in consideration of a
residential market; that only limited performance is provided
in the event of power failures; that the available PABX type
features are limited; and that aEter installation, further
expansion and growth is difficult in time and/or expense.
SUMMARY OF THE INVENTION
Accordingly, it is one object of the present invention to
provide a telephone communication system providing
substantially all intercom and PABX type features to a
plurality of telephone subsets associated with a single pair
of telephone wires.
~2~97 !3
-4- 5993-159
This object is accomplished, at least in part, by a
single-line communication system, comprising: a wiring network
consisting of a single pair of wires, said single pair of
wires having an externally connected segment and an in-house
segment; a plurality of single-line subsets each connected to
said in-house segment of said single-line pair; means for
selectively providing connection between said externally con-
nected segment and said in-house segment; and means, inter-
connected between each said subset and said in-house segment,
for establishing direct communication between said subsets.
According to another aspect, the invention provides a
communication system for use with a single pair of wires, said
single pair of wires having an externally connected segment
and an in-house segment, said in-house segment having a plur-
ality of subsets interconnected therewith; satd system compris-
ing: means Eor selectlvely providing connection between said
externally connected segment and said in-house segment; means,
interconnected between each said subset and said in-house seg-
ment, for establishing direct communication between said sub-
sets, said subset communication means including a plurality ofstation adapter modules, each said station adapter module being
connected between one of said subsets and said in-house segment;
and means, associated with each said station adapter module,
for identifying said subset associated therewith, each said
station adapter module also including means for enabling a call
announcer in response to a signal from said subset identifying
means, and means for introducing a time-delay before said call
announcer is enabled, said delay being at least as long as the
time required for all identifiers to be received by said sub-
set identifying means.
" ~2~4~37~3
-4a- 5993-159
Other objects and advantages will become apparent to
those skilled in the art from the following detailed description
read in conjunction with the appended claims and the drawings
attached hereto.
BRIEF DESCRIPTION OF TH~ DRAWING
Figure 1 is a block diagram of a system embodying
the principles of the present invention;
Figure 2 is a generalized circuit diagram of a typi-
cal station adapter module for use as shown in Figure l;
Figure 3 is a generalized circuit diagram of one
embodiment of the line interface module for use as shown in
Figure l; and
: Figure 4 is another embodiment of a line interface
module for use as shown in Figure 1.
DETAILED DESCRIPTION OF THE INVENTION
A communication system, generally indicated at 10
in Figure 1 and embodying the principles of the present inven-
tion, includes a line interface module 12, serially inserted
between a single pair of externally connected
lY~ ~
F. A. MIDDLETON ET AL 13-1
~ 8 -5-
telephone wires 14 and a single pair of in-house telephone
wires 16, and a plurality of s~ation adapter modules 18, each
station adapter module 18 being connected between the single
pair of in-house telephone wires 16 and a telephone subset
20. The line interface module 12 in the preferred embodiment,
further includes a means 24 for connecting to a conventional
residential electrical outlet. In addition, the line
interface module 12 and the station adapter modules 18 are
provided with standard plug-in connectors 22 for connecting to
thc existing wiring, 14 and 16, and the subsets 20. Hence,
the line interface ~odule 12 and station adapter modules 18
can be readily installed by even the least experienced user.
For the purpose of the following description the single pair
o~ externally connected of telephone wires 14 can be
considered to be that palr of wires supplied by a telephone
service provider and, in general, connect to a central office
exchange. Further, the single pair of in-house telephone
wires 16 is, essentially, the telephone wiring of a residence
or similar building. The communication system 10, as more
fully discussed below, can be used with any type of telephone
subset 20 that, minimally, provides the user thereof with the
capability of going off-hook, dialing a number, going on-hook
and receiving an externally initiated telephone call. Por
example, as used herein, the term telephone subset 20 is
intended to include a rotary dial subset providing only plain
old telephone service (P.O.T.S.). In fact, the provision of
intercom and PABX type features in conjunction with such a
subset is a significant advantage of the communication system
10. As more fully discussed below the system 10 is,
. ~ ~
12 4497 8 6- F. A. MIDDLETON ET AL 13-1
preferably, provided with means 24 for connection to a
conventional residential wall outlet as a source of electrical
power.
In the preferred embodiment, each station adapter module
18 includes, as shown in Figure 2, means 26 for detecting when
the subset ZO associated therewith goes off-hook, means 28 for
detecting dial pulses presented on the in-house telephone
wires 16, means 30, responsive to the dial pulse detecting
means 28 9 for selectively signalling the presence of a call
directed to the associated subse~ ZO and means 32 for
~ s~h a rl~
ensuring privacy during~internal~or external calls involving
the subse$ 20 associated therewith. In addition, each station
adapter module 18 is proYided with a source 34 of d.c. power
that, as more fully discussed below is supplied by the line
interface module 12.
In one embodiment, the off-hook detector means 26 is
serially connected in one 36 of the in-house wires and the
privacy control means 32 is serially connected in the other 38
in-house wire. The privacy control 32, as more fully
discussed hereinafter, essentially determines the number of
subsets 20 that are off-hook by monitoring the voltage drop on
the in-house telephone wires 16. If 0, 1 or 2 subsets 20 are
off-hook the silicon control rectifier (SCR) switch 33 is
turned on by Zener diode circuit 35 and the subset 20 is
connected to the in-house wires 16. When a third subset 20
goes off-hook ~he resulting voltage is too low to turn on the
SCR switch 33 thereof and that subset 20 is not connected to
; the in-house wires 16. When a connection is made via the
above process, the off-hook detector 26 and 43 signals the
^ iZ44978 ~. A. MIDDLETON ET AL 13-1
control logic 60 that latches on $he privacy control means 32
so that the talking circuit to the local subset 20 remains
connected throughout the call.
As shown in Figure 2, for example, the off-hook detector
means 26 includes a resistor 40 in parallel with, for example,
a Zener diode 42 and comparator 43. Hence, when the local
subset 20 goes off-hook the impedance change caused thereby
causes the impedance of the off-hook detector means 26 to
change under the new biasing condition of the diode 42. As a
result, a signal is presented to a control portion 43 of the
means 30. The control portion 43 in conjunction with the
privacy control means 32 then, if no other subset 20 is
off-hook, connects the local subset 20 to the line interface
module 12 via the in-house telephone wires 16.
The dial pulse detecting means 28, in this embodilnent,
includes a bias resistor 44 in series with a Zener diode 46.
The diode 46 is also connected, via a rectifying diode 48,
across the pair of in-house telephone wires 16. Dial pulses
from remote subsets 20 are detected by the means 28 and
amplified by amplifier 50. The amplified signals are fed to
: the call signal selecting means 30.
The call signal selector means 30 includes a dial pulse
,~, counter 52, means~for identifying a local subset 20, an
.
interdigital pause timer 56, a master reset timer 58 and
control logic 60. Preferably, the dial pulse counter SZ is a
resettable counter that changes the output level on one output
line thereof in accordance with the pulse count received at
the input thereto. The dial pulse counter 52 can be readily
implemented by use of a CD 4017, manufactured and marketed by
~ Z 4 ~ 7 8 -8- F. A. MIDDLETON ET AL 13-1
RCA Corp. of Somerville, N. J., although functionally
equiYalent circui~s, or devices, can also be usedO The means
54 is in essence, a switch that connects the control logic 60
to one output port of the dial pulse counter ~4.
j,
Preferably, the switch is adapted to be accessible to and set
by the user and thus allows thç local subset 20 to be
identified as desired. Usually, for present residential type
purposes, the identification is limited to a single digit.
Thus, when the correct number of pulses is countecl by the dial
pulse counter 52, the control logic 60, in response to the
change in signal level at ~he switch, enables a call announcer
62. Any other number of pulses counted has no effect on the
control logic 60. As more fully discussed below, the fact
that the correct number of pulses identifying the local subset
20 is received hy the control logic 60 is only one condition
necessary to actlvate the call announcer 62. For example, the
call announcer 62 would not be activated, even if the correct
number o pulses were received, if the local subset 20 were
already off-hook.
The interdigital pause timer 56 is connected to the
control logic 60 and mandates that a preselected delay expire
before the call announcer 62 is activated. This timer 56 can
be implemented by an ICM 7555, manufactured and marketed by
Intersil of Cupertino, California. The interdigital pause
timer 56 is, in essence, a clock that is activated by the
rising edge of the first pulse received from ~he dial pulse
detecting ~eans Z8 and reset by subsequent pulses and provides
an output enabling signal to the control logic 6~ after a time
period T. Preferably, the time period T is set to allow the
F. A. MIDDLETON ET AL 13-1
~;~4~37~3 9
longest make cycle in a dial pulse sequence, i.e. T is set
equal to the expec~ed time between pulses plus a margin to
ensure accuracy. For example, T is set to about 40 msec in a
10 pulse per second dialer. Alternatively, the time period T
could be set so that, the digit "O" on a rotary dial subset
will have had time to be recorded by the counter 52. The timer
56 prevents partial readings from activating the call announcer
62. That is, the processing speed of the control logic 60 is
much faster than the time required for counting
pulses generated by a subset 20. Hence, the dialing of any
; digit greater than the identifying digit of the local subset 20
could, but for the interdigital pause timer 56, cause the false
announcement of an incoming call. The interdigital pause timer
56 is, preferably, resettable to zero to avoid
consecutively dialed digits being interpreted as the sum of
those digits.
The dial pulse counter 52 and the interdigital pause timer
56 are reset by the master reset timer 58. In this embodiment
the ~aster reset timer 58 is an ICM 7555, manufactured and
marketed by Intersil of Cupertino, California and includes a
preset time out after which a reset signal is generated to all
associated devices connected thereto. With this signal, the
master reset timer 58 resets all associated circuitry when the
local subset 20 goes on-hook.
The control logic 60, in this embodiment, includes an OR
gate 64, a flip-flop 66 and a NAND gate 68. By this
arrangement9 for incoming calls to the local subset 20, the
flip-flop 66 will only receive a call announcement signal when
the following conditions are met: a correct number of pulses
~ ~ 449 7 ~ -10- F. A. MIDDLETON ET AL 13-1
are received by the dial pulse counter 52 and the subset 20 is
on-hook. However, ~he call announcer 62 will be actiYated,
via the NAND gate 68, when the state of the flip-flop 66, as
per the privacy control means 32, indicates that the line,
i.e. the in-house wires 16, are not already in use by more
than one remote subset 20.
For outgoing calls, as determined by the local subset 20
going off-hook the control logic 60 is enabled by the off-hook
detector 26. If no other subset 20 connected to the in-house
wires 16 is off-hook, as determined by the privacy control 32,
the local subset 20 is connected to the in-house wires 16.
The line interface module 12 connects the i~-house
telephone wires 16 to the externally connected, or central
of~ce, telephone wires 14. One embodiment of the line
inter~ace module 12, as shown in Figure 3, lncludes, on the
central office side 70 thereof, a secondary surge protection
means 72 across the central office wires 14, a ring detector
74 in series with one of the central office wires 14, a ringer
simulator 76, a central office line hold circuit 78 and a
central office side relay 80.
The secondary surge protector circuit 72 includes a
resistor in series with a surge suppressor and is provided for
added protection in the event of electrical surges due to, for
example, lightning. The surge protector is a VlSOLAlOA,
manufactured and marketed by General Electric Corp. of Auburn~
N. Y. The ring detector 74 is, preferably, a CS8204, marketed
and manufac~ured by uherry Semiconductor of East Greenwich,
R. I~, or the functional equivalent thereof in con3un~ion
~;~ with an opto-coupler. The ringer simulator 76 is an ~ series
.
` ~Z44978 F. A. MIDDLETON ET AL 13-1
circuit connected on the subscriber side of the ring detector
74 across the central office wires 14. The ringer simulator
76 provides the proper impedance loading to enable the ring
de~ector 74 to function. For example, the capacitor 82 can
be 0.1 microfarad and the resistor 84 is about lOK ohms. The
central office line hold circuit 78 is, in essence, an LED
diode opto-coupler 86 and a holding resistor 88. In
operation, the central office side relay 80 is normally closed
and connected to the subscriber side 90 of the line adapter
module 12. However, when the relay coil 92 controlling -the
relay 80 is activated the central office line 14 is connected
to the hold circuit 78. When the hold circuit 78 is
activated, the subscriber side 90 is disconnected by the relay
80 and made available for local intercom use. The LED
optocoupler informs the microprocessor and subscriber that the
central office line is on hold.
The central office side 70 of the line interface module
12 is connected to the in-house wiring 16 by a subscriber
relay 94 the position of which is controlled by the relay coil
2G 96. When de-energized the relay 94 is arranged to secure
connection from the in-house wires 16 to the central office
side relay 80 and the central office line 14. Thus, in the
event of a power failure the central office wires 14 are
connected to the in-house wires 16 to, thus, provide plain
old telephone service (POTS) to the subscriber.
In addition, the subscriber side 90 includes a hook
switch and dial pulse detector 100, a dial tone
multi-frequency (DTMF) to dial pulse converter 102, a
-12~ 978 659~3~159
repertory dialer 104, means 106 for connect:ing to a source o~
power and a microcomputer 108.
The hook switch and dial pulse detector 100 provides
inputs to the microcomputer 108 that executes preprogrammed
instructions in accordance with the number of pulses received.
In one embodiment, the hook switch and dial pulse detector 100
are similar to the off-hook detector 26 and the dial pulse
detecting means 2S discussed above. The DTMF to dial pulse
, converter 102 monitors the subscriber in-house wires 16 and
allows both rotary and tone dial subsets to be used by the
subscriber. The reper-tory dialer 104 is a 525610, m~nuEac-tured
and marketed by AMI oE Santa Clara, California and, as more
fully discussed below, provides a memory 105 Eor a stored
calling Eeature as well as a repeat call Eeature under the
control oE the microcompu~er 108.
Another embodiment of a line interEace module 110
also useful in conjunction with the communication system 10
is shown in Figure 4. For the convenience of the reader,
elements that functionally correspond to previously recited
elements are assigned the same identifying numbers. In
general, the primary difference between the line interface
module 12 and the line interface module 110 as shown in
Figure 4 is that the line interface module 110 is coupled to
the externally connected wires 14 by a coupling transEormer
112. In this case, the central office side relay 80 is
closed only when a call i5 placed to the central office. On
an incoming call from the central office the ring~trip
; detector 74 sig~als the microprocessor to close the central
~ office side relay 80 to complete the voice path.
.~ ' .
~Z~4978 F. A. MIDDLETON ET AL 13-1
-13-
In one preferred embodiment, the communication system 10
is designed for up to nine station adapter modules 18 for a
given line interface module 12 when the communication system
10 is used for only intercom services and to about five
station adapters modules 18 when PABX type eatures are
provided. As used herein the phrase "PABX type features", or
the idiomatic equivalent thereof, is intended to encompass,
inter alia features such as: hold/call pick up; call transfer
between subsets; conference calls; calls coming from, or going
to, a central office exchange; maintaining telephonic
capability during a power outage; providing secondary
lightning protection; ringing on all subsets interconnected to
a single line; repertory dialing; memory dialing; and the
ability~to interface with either rotary dial pulse phones and
lS DTMF phones. In addition, the communication system 10, in a
manner similar to a PABX, also preserves the ability to use
existing types of subscriber premises equipment such as
cordless or decorative subsets, telephone answering machines,
or the likeO
The limitation to nine subsets 20 for an intercom only
system is dictated to the preference of using only a single
digit to identify a particular subset ~0. The tenth digit
would then function as the central office access identifier
digit. The limitation to five subsets 20 when PABX type
features are provided is responsive to the present regulation
that, in the even~ of a power failure, only five ringers can
be connected to the central office wires 14. It will be
understood that these limitations are for explanatory purposes
only and that, in fact, the system 10 is not so limited.
12~4978 F. A. MIDDLETON ET AL 13 1
~14-
To fully describe the operation of the system 10 the
following discussion is segmented int:o (a) an in-house call
and (b) an extraresidential incoming call. To make an
outgoing call the local subset 20 goes off hook and the
control logic 60 associated therewith is informed by the off
hook detector 26. If no other remote telephone is
simultaneously off hook, as determined by the privacy control
32, the local subset 20 is connected to the in-house telephone
wire 16. As discussed above, any single digit 0 through 9 may
then be dialed. For purposes of the present discussion the
digits will be assigned the following functions: 0, 1, 7, 8
and 9 will be recognized and handled by the line interface
module, 12 or 110, The function oE each will be more Çully
explained below. The dlgits 2 through 6 are, in this example,
local subset identifiers. Thus, when any single digit is
dialed by the local subset 20, all other dial pulse counters
52 of all the other station adapter modules 18 and the dial
pulse counter 100, of the line interface module 14~ receive
and count the digits. The digits 2 through 6 will be
recognized only by the properly assigned station adapter
module 18 and ignored by the line interface module 12. The
digits 0, 1, 7, 8 and 9 will be recognixed and handled by the
line interface module 12 described hereinafter. If a dialed
station adapter module 18 is connected to the in~house wires
169 the call announcer 62 associated therewith will be
activated and if that subset goes off hook a connection will
be established via the in-house telephone wires 16. At this
stage the priYacy control means 32 detects two subsets 20
;9L~97 ~ -15 F. A. l~lIDDLETON ET AL 13-1
off-hook and disallows any other subset 20 from being
connected to the in-house wires 16.
In this particular embodiment, lthe central o~fice wires
14 are seized when the digit 9 is dialed and, responsive
thereto, the line interace module lZ connects the in-house
relay 94 to the central office relay 80 and the caller
receives the central office dial tone. If the caller dials a
7 the repertory dialer 104 is activated and the last number
previously dialed is redialed according to a timing program
supervised by the microcomputer 108. If the digit 8 and a
second digit between 1 and 9 is dialed the repertory dialer
~ d~
104 is activated and dials a number from a memory~associated
therewith which number being designated by the second digit
dialed by the caller. In the event the digit 1 is dialed,
which digit 1 can also be accomplished for signalling purposes
by a conventional hook flash, the central office line relay 80
is switched to the hold circuit 78 thereby allowing
intercommunication to occur between, for example, a supervisor
and a secretary for incoming call announcement. The digit 0
is recognized by the microprocessor as an indication -to
disable the privacy controls 32 of all station adapter modules
18 for a predetermined period of time, for example, five
seconds. Such a feature then allows the signalling to each,
or any number, of the local telephone subsets 20, via the call
25- announcers 62 associated therewith, whereby a conference call
can be established between a select number of the local
subsets 20. After the predetermined period of time, the
privacy controls 32 are enabled and the conference call is
secure.
-~- lZ~4~78 F. A. MIDDLETON ET AL 13-1
-16-
To release the hold circuit 78~ the call receiving subset
20 goes on hook and the subset 20 to which the call is to be
transferred dials 9 to connect to central office line 14.
One technique, inter alia, to provide more diversified
features is to combine the "last number dialed" or "redialed"
function with the "repertory dialing" function since both of
these functions can include memory accessed by the
microcomputer 108. For example,, the digi~ 8 could be
assigned these features and a second digit dialed for
selecting either the last number dlaled, the repertory dialing
or the repertory dialing programming function. This technique
thus allows the dlgit 7 to be used to provide other features,
such as, access to a power line carrier system, such as a ~SR
interace.
For all incoming calls the line interface module 12 is
signalled with the normal ringing signal from the central
office wires 14. The ringing detector 74 releases the
in-house relay 94 connecting the ringing signal to the station
adapter modules 18 where the ringing signal rings on all local
subsets 20. When the central office senses one of the local
subset 20 going off hook, the incoming call is completed to
that subset 20.
The primary advantages of the communication system 10
lies in the modularity of the line interface module 12 and the
station adapter modules 18 being such that the purchaser can
not only perform the initial ins~allation but expand his
system as desired at any time in the future simply by adding
another subse~ 20 and an associated and uniquely identified
station adapter module 18. Thus, by use of the present system
` lZ44~78 F. A. MIDDLETON ET AL 13-1
-17-
a full range of PABX features as well intercom services can be
provided for residential or small businesses utilizing a
-` single pair of externally provided te!lephone wires ~
Although the present system has been described with
regard to a specific exemplary embodiment, it will be
understood that other configurations and arrangements may be
implemented ~hat nevertheless do not differ from the scope and
spirit of the present inven~ion. Consequently, the present
invention is deemed limited only by the appended claims and
the reasonable interpretation thereof.
