U.S. patent application number 15/174625 was filed with the patent office on 2016-12-08 for extended signaling system and method.
This patent application is currently assigned to Cottonwood Creek Technologies, Inc.. The applicant listed for this patent is Cottonwwod Creek Technologies, Inc.. Invention is credited to Dwight W. Kitchin, Alan K. Schott.
Application Number | 20160359334 15/174625 |
Document ID | / |
Family ID | 41799309 |
Filed Date | 2016-12-08 |
United States Patent
Application |
20160359334 |
Kind Code |
A1 |
Kitchin; Dwight W. ; et
al. |
December 8, 2016 |
EXTENDED SIGNALING SYSTEM AND METHOD
Abstract
Embodiments are described that include a "front end" device
located remotely from a local telephone location. The front end
filters DC and AC current on a telephone line to separate these
signals and passes a DC current through a low resistance Low Pass
Filter without traditional resistance or current limiting means.
The front end also provides signaling capability isolated from the
DC and audio channels by a High Pass Filter. Some embodiments also
include a "back end" unit located near a local telephone location.
The "back end" unit filters the DC and AC currents into at least
two DC current streams. One of the DC current streams provides
sufficient current to power a local telephone. The other stream(s)
provides current sufficient to power an auxiliary device. The "back
end" device may also provide signaling isolated from the DC and
audio channels that is complementary to the "front end"
signaling.
Inventors: |
Kitchin; Dwight W.; (Parker,
CO) ; Schott; Alan K.; (Centennial, CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Cottonwwod Creek Technologies, Inc. |
Centennial |
CO |
US |
|
|
Assignee: |
Cottonwood Creek Technologies,
Inc.
Centennial
CO
|
Family ID: |
41799309 |
Appl. No.: |
15/174625 |
Filed: |
June 6, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14086496 |
Nov 21, 2013 |
9362753 |
|
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15174625 |
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|
12553849 |
Sep 3, 2009 |
8594314 |
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14086496 |
|
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61191083 |
Sep 5, 2008 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B 3/548 20130101;
H02J 4/00 20130101; H04M 19/005 20130101 |
International
Class: |
H02J 4/00 20060101
H02J004/00; H04B 3/54 20060101 H04B003/54 |
Claims
1. A method of providing direct current (DC) through a telephone
line, the method comprising: providing direct current (DC) in a
power signal; filtering the power signal with a first low pass
filter that provides a low equivalence resistance toward the DC and
attenuates alternating current (AC) signals; after the filtering:
transmitting the power signal through a telephone line; filtering
at least a first portion of the power signal with a second low pass
filter that provides a low equivalence resistance toward the DC and
attenuates AC signals; and passing the output from the second low
pass filter to an input of a power supply.
Description
I. RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/086,496, titled "EXTENDED SIGNALING SYSTEM
AND METHOD," filed Nov. 21, 2013, which is a continuation of U.S.
patent application Ser. No. 12/553,849, now U.S. Pat. No.
8,594,314, titled "EXTENDED SIGNALING SYSTEM AND METHOD," filed
Sep. 3, 2009, which is hereby incorporated by reference in its
entirety, and which claims the benefit of U.S. Provisional Patent
Application Ser. No. 61/191,083, titled "EXTENDED SIGNALING SYSTEM
AND METHOD" filed on Sep. 5, 2008, which is hereby incorporated by
reference in its entirety.
II FIELD OF THE INVENTION
[0002] The present invention relates to a device and method to
enable a finite electrical power source to deliver more power to
the point of use over a defined transmission channel and provide
additional signaling capability between the termination points of
the defined transmission channel.
III. BACKGROUND OF THE INVENTION
[0003] Traditionally, "plain old telephone service" or "POTS" has
been facilitated using a low voltage, low current combination of DC
and AC signals transmitted over the telephone network to a local
telephone. This has been sufficient to power the functionality of a
simple telephone and to generate, transmit, and receive modulated
AC signals for voice transmission. The electrical current necessary
to enable operation of a local telephone is typically about 25
milliamps.
[0004] Modern telephones have an expanded array of features such as
visual displays, speakerphones, recording/messaging, portable
handset and other capabilities. The power necessary to enable these
capabilities exceeds what is available from the telephone network
at a local telephone. Simply stated, telephone network current is
not sufficient to power anything but the telephone itself. As a
result, one or more additional external power supply units are
required to furnish the necessary capability. Frequently, these
power supply units take the form of AC/DC adaptors that are plugged
into a standard 110 AC wall socket and the output of which is
connected to the telephone or peripheral devices. These so-called
"wall-warts" provide the additional power required to support the
added functions/capabilities and devices (e.g., battery operated
wireless handset) associated with the telephone.
[0005] Likewise if electronic "data" services, such as ISDN or DSL,
are to be transported on the same pair of conductors to, or near
to, the local telephone instrument, yet another "wall-wart" is
almost certainly required to power the associated modem device. For
convenience these telephone instruments and modem power sources are
referred to as being "AC line powered."
[0006] While wall-warts are unsightly and cumbersome they are
acceptable for most purposes to provide the additional power (i.e.,
power beyond what is supplied by the CO/CB/SLC/IAD/PBX over the
telephone network) to AC line powered devices.
[0007] Nevertheless, there are situations where some
telephone-related capability or feature is desired that requires
additional power but is located in an environment where AC line
power is not available. This can be the case wherever wiring was
put in place specifically for telephone applications. Existing
incarceration facilities, particularly older prisons and jails, are
one example of such an environment. These institutions typically
provide POTS telephone services as an amenity for the inmates to
conduct necessary and/or interpersonal communications with those on
the "outside." Recently, such institutions have desired to
supplement POTS service with additional capabilities. For example,
it is highly desirable to increase the accuracy of inmate
identification required to access outside phone service by using
fingerprint, barcode, RFID, or other types of readers that can
identify or verify the inmate by thumb print, palm print, voice
print, retinal scan, or another idiosyncratic physical
characteristic, or information embedded within a wristband. It is
also desirable to enable a telephone with visual two-way camera and
picture capability so that the phone can be used as a vehicle for
remote visitation from a site near to or far from that of
incarceration to avoid excess prisoner movement.
[0008] Penal institutions are also finding it increasingly
desirable to provide limited Internet or more commonly a restricted
service Intranet access to inmates for purposes of accessing an
inmate account, conducting transactions, etc., all of which require
a modem or similar device to connect to the Intranet via the
telephone network. All of these peripheral devices require
additional power. A typical peripheral device may require about
60-70 milliamps at some low voltage such as 3-12 VDC. When one or
more of these peripheral devices are desired, power requirements
may exceed more than 125 milliamps. The equivalent power required
for these devices is far in excess of the 25 milliamps available
and intended to operate the telephone itself. The DC current
available from the telephone network typically barely exceeds the
18-20 milliamp minimum requirement recommended for reasonable
conversation quality.
[0009] Due to the understandably unique requirements of such
facilities, certain infrastructure features available in other
buildings, e.g., crawl spaces, hollow walls, AC outlets, are simply
not permitted adjacent to or near the physical locations where a
telephone or telephone and data device may be desired or needed.
Absent the access that may be available in a more typical structure
the cost of rewiring for example from a 25-pair cable distributed
to many cell blocks and individual station locations to separate
CAT-5 cables is simply cost prohibitive, often by orders of
magnitude. Likewise the cost to provide new AC power near to the
required location, and provide that power source with appropriate
physical security for both the outlets, the `wall-warts`, and the
low voltage from the warts to the actual instruments is usually
little short of astronomic. And neither option, even if financially
possible, could be accomplished in a time frame similar to that
required in a commercial building situation due to the security,
controlled access, and physical detritus and debris related to such
an undertaking.
[0010] Nevertheless, there are emerging pressures (e.g., service
delivery, social pressure, cost containment, and manpower reduction
reasons) to provide newer telephony related and additional service
delivery instruments to these same facilities and difficult
locations.
[0011] In the absence of available AC power, there are two possible
solutions. First, replace the existing POTS, or POTS-like wire pair
with either a larger gauge wire or greater number of conductors to
each telephone to reduce the resistance to current and facilitate
the delivery of greater power to the telephone location. For
example, a single UTP could be replaced with a full CAT5 quad pair
cable. In many inmate or similar facilities, this is not realistic
or perhaps even possible for many of the same reasons that it is
not possible to supply AC power.
[0012] More recently, it has been proposed to "bleed" a small
amount of excess current not required for powering the telephone to
charge one or more local batteries that would then be used to
provide power to the device (e.g. fingerprint reader) supplying the
supplemental capability or feature. This implementation has the
disadvantage of requiring a `recharge` time period between
instances of device use and cannot be relied upon to provide
adequate power in situations of high-use or unexpected use
patterns. Using a fingerprint reader as an example, the taking of a
fingerprint reading and transmitting that information through the
network for verification would result in at least some discharge of
the battery while powering the fingerprint reader. Since the
fingerprint reader is likely to require much more power than is
available from the telephone line to charge the battery, the state
of the battery charge will be diminished and will eventually,
through constant use, be unable to provide adequate power to
operate the fingerprint reader. The device user must now wait some
period of time until the battery has time to recharge to a usable
threshold before the user can continue his use of the device. A
simple misdial of the telephone number and subsequent redial by the
user could possibly cause enough discharge of the supply battery to
fail the redial attempt which is deemed to be unacceptable
operation for most applications.
[0013] The use of various example identification enhancement
devices mentioned above entails a variety of, typically low speed,
controls and communications protocols to, for example, enable and
disable a device, provide operational instructions to the device
user, and the communication of results or other output from the
device to a decision making point such as a centralized control
system.
[0014] In the current implementations of many of these devices they
are always powered whether needed or not, instructions to the user
are often provided by playback of a verbal recording from a
centralized control system, and the device results are transmitted
via DTMF or other audible signaling means. The local telephone
instrument is commonly utilized to provide the user instructions
which tends to extend the call setup time but in any case prevents
the use of the local telephone for its primary purpose when being
used to provide instructions. Likewise when the external device
such as a biometric characteristic reader is reporting its findings
by the use of DTMF tones additional time is required within the
overall call setup process. It is no longer an over-zealous concept
to deactivate power using devices when not actively performing a
function but most current biometric devices will, at best, move to
some form of lower power state when not actively performing their
respective biometric functions but generally have no means to
deactivate when not required for a particular, or over an extended,
period of time. The use of DTMF signaling to communicate results
can have the additional disadvantage of providing audible clues to
inmates in a penal institution situation or for third parties to
record otherwise secure information. In either case the information
can later be mimicked or used for unintended purposes.
[0015] Accordingly, a need exists to supply additional power over
the existing delivery system infrastructure to provide greater
power at the local telephone location to enable both the normal
operation of the telephone and additional capabilities, features or
devices. Likewise a need exists to provide some level of control
and signaling over that same delivery system that does not use the
bandwidth originally provided for telephone conversations. It is
with respect to these and other considerations that embodiments of
the present invention have been made. Although relatively specific
problems have been discussed, it should be understood that
embodiments of the present invention should not be limited to
solving the specific problems identified in the background.
IV. SUMMARY OF THE INVENTION
[0016] The deficiencies of the prior art are solved using the
method and system of the present invention. In embodiments, the
invention enables a finite source of DC and AC current typically
provided to enable use of a telephone to deliver more current
through a previously defined transmission channel between the
source and the local telephone and also provides a mechanism to
exchange telephony and non-telephony related signals, in the form
of states or data, between a distribution location and equipment
associated with the local telephone or telephony related
instrument. While the typical -48 VDC powered telephone line is
only sufficient to provide about 25 milliamps of DC current to a
local telephone instrument over its existing infrastructure, the
invention in embodiments permits that same -48 VDC level to deliver
a current in excess of 25 milliamps to the same telephone or
instrument location over the same existing wiring and
infrastructure while adding additional signaling capabilities. This
is accomplished by employing a "front end" device typically located
at a point in the transmission channel remote from the local
telephone such as at the service entrance of the network into the
building or at an appropriate distribution frame. The front end
performs several functions including filtering the DC and AC
current on the transmission channel to separate these signals and
passing the DC current through a low ESR (equivalent series
resistance) LPF (Low Pass Filter) without traditional additional
resistance or current limiting means and resettable fuses to
prevent damage to the source of DC and AC current in the event of a
short circuit or other overload condition. Typically, the fuses
replace one or more series resistances or other devices that are
generally employed to protect the network from electrical short
conditions, but have the disadvantage of adding significant
resistance to the flow of electrical current. The front end also
provides an audio (speech frequency range) channel for telephony
communications use isolated from the DC path by a BPF (Band Pass
Filter) as well as a high frequency (out of band) signaling
capability isolated from the DC and audio channels by a HPF (High
Pass Filter). The system also employs a "back end" unit located at
a point on the transmission channel at or near the local telephone
location. The "back end" unit splits the DC and AC currents into at
least two DC current streams. One of those streams provides
sufficient current to power the local telephone. The other
stream(s) provides current sufficient to power additional
capabilities, features or devices associated with the local
telephone, such as a biometric reader. The back end unit also
splits the AC signals into an audio channel, via a LPF, for
telephony conversation purposes as well as to an out-of-band
signaling channel, via a HPF, for state and/or data signaling
purposes. By use of this methodology and system, the same power
source can deliver 40-60 milliamps or more to the local telephone
and associated peripheral devices instead of the usual 25 milliamp
current. By the application of a power conversion subsystem the
extra current not utilized by the local telephone is converted to a
lower voltage but yet higher current which is made available to
external devices such as the example biometric reader. For example,
the system can provide 100 milliamps or more at 5 volts to such an
external device associated with a local telephone or similar use
device over 4000 feet of standard 24 AWG UTP in addition to one or
more out-of-band signaling channels and still provide normal
telephone communication capabilities.
[0017] This summary is not intended to identify key features or
essential features of the claimed subject matter and should not be
used to narrow the scope of the claimed subject matter. This
summary is provided only to generally provide a description of some
of the embodiments of the present invention.
V. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a schematic showing a typical POTS system for
delivering "land line" service to a local telephone. It is labeled
as "prior art" because it existed prior to the present
invention.
[0019] FIG. 2 is an overall schematic of an embodiment of the
present invention showing how the major functional blocks are
interconnected to provide the electrical, audio, and signaling
terminations.
[0020] FIG. 3 is a circuit schematic showing in more detail an
example implementation of one embodiment of the Head-End of the
present invention.
[0021] FIG. 4 is a circuit schematic showing in more detail an
example implementation of one embodiment of the Tail-End of the
present invention.
[0022] FIG. 5 is a flow diagram depicting one embodiment of the
signaling operations as may be implemented at the Head-End of the
present invention.
[0023] FIG. 6 is a flow diagram depicting one embodiment of the
signaling operations as may be implemented at the Tail-End of the
present invention.
VI. DETAILED DESCRIPTION OF THE INVENTION
[0024] The principles of the present invention may be further
understood by reference to the following detailed description and
the embodiments depicted in the accompanying drawings. Note that
like items in multiple figures have like item numbers.
[0025] FIG. 1 is a simplified depiction of a traditional "plain old
telephone system" ("POTS") telephone subscriber circuit including
pertinent elements at a Central Office ("CO"), the "outside plant,"
and at the location of the end customer instrument, i.e., "local
telephone" and any peripheral functions or devices. It is provided
as context in that it represents: (a) how telephone current is
provided to the local telephone in the absence of the present
invention and (b) the electrical relationship of major on-premises
components. FIG. 2 is a depiction of an embodiment of the invention
which: (a) provides electrical, audio, and signaling termination
for the subscriber location as seen by the traditional POTS network
and (b) shows the arrangement of circuit elements which provide the
additional power and functionality which will be then conveyed to
the terminating equipment end of the complete system.
[0026] FIG. 1 depicts a very high level view of a subscriber
telephone instrument 20, the "Serving Wire Center" 1 ("SWC") for a
specific customer, the subscriber premises 12 where the telephone
instrument 20 is located, the telephone line 11 connecting the two
locations, and the customer premises inside wiring telephone line
17 that provides all but the final few inches or few feet of
connectivity to telephone instrument 20. The serving wire center 1
is very commonly referred to as the "Central Office" ("CO") even
though the specific equipment that pertains to the specific
subscriber may actually be located at some point physically closer
to the subscriber for example within a "Remote Terminal" ("RT"), a
"Subscriber Loop Carrier" ("SLC") installation, or from a "Channel
Bank" ("CB") which may be located within the subscribers or a
nearby building or in a "Controlled Environment Vault" ("CEV") near
the subscribers location. In most cases regarding the above
examples, the equipment and functions mentioned may belong to the
Local Exchange Carrier ("LEC"). For purposes of the present
invention, the functionality of the SWC may also be provided by any
other modern communications mechanism including, for example, an
"Integrated Access Device" ("IAD"), a "residential gateway"
("RGW"), a "Private Branch Exchange" ("PBX"), an "Inmate
Communications Control System" ("ICC S"), or any other system
appropriate to the purpose as may be recognized by one skilled in
communication arts. Further, such equipment may well not be owned
or operated by the LEC but rather may belong to an entity
associated with the physical premises or some unrelated third
party. In that context, the following is a brief description of
POTS features and items that provide context for the present
invention.
[0027] The SWC requires a power source to run everything within its
own confines but traditionally also provides the subscriber loop
bias current to each customer such that the subscriber no longer
has to provide their own individual battery system, as was the case
prior to this practice being adopted as a standard practice. This
core power source 2 comprises major elements such as AC mains
powered battery chargers, optionally a backup generator in case of
AC mains interruption, storage battery systems that provides
uninterrupted power to operationally critical systems, including
the loop bias current to the subscribers, and the "ring generators"
("RG").
[0028] The SWC may be thought of as having two very basic types of
equipment to provide normal operations. The common equipment and
systems 3 include all shared and non-subsrcriber specific equipment
and functionality. The subscriber dedicated equipment including the
"Subscriber Line Interface Circuit" ("SLIC") 4, current and voltage
limiting, fusing protection, surge and lightening protection
equipment 9, and the final subscriber "Tip and Ring" terminals 10,
including the equipment, wiring, and functionality that is
duplicated for and dedicated to individual subscribers. The various
forms of equipment power for the common equipment is indicated by
signal 5, while the battery and ringing voltages provided to each
subscribers SLIC are indicated by signal 6. Those skilled in the
art will recognize that among the functions within the SLIC
subsystem is, as mentioned above, the limiting of the loop current
to the subscriber terminals 10. Most often the SLIC is configured
such that the current drawn from the SLIC will not exceed
approximately 100 milliamperes (mA) if the subscriber pair is
directly shorted together. Those skilled in the art will recognize
that, primarily due to line resistance between terminals 10 and
terminals 13, the actual off-hook loop current will normally be
substantially less that the 100 mA limit and that the "Outside
Plant" ("OP") is normally engineered to provide at least 18 mA loop
current on the longest lines. Experience has shown that the most
common range of off-hook loop currents is 22 mA to 35 mA. Signal 8
refers to the two-wire, typically "unshielded twisted pair"
("UTP"), associated with the physical wires carrying bias current,
ringing voltage, signaling, and bi-directional voice frequencies
between the SWC and the subscriber. Signal 7 refers to a set of
physical and electrical signals which are often in significantly
different formats as compared to those appearing on signal 8.
Signal 7 includes many uni-directional signals to convey voice
frequency signals, and control signals as are appropriate for the
implementation of the SWC in question.
[0029] Signal 11 is simply a representation of all of the OP wiring
and possible equipment used to implement the transportation of the
signals available at the SWC terminals 10 to the subscriber
location 12. The telephone service provider is normally responsible
for appropriate protection to the subscribers internal wiring from
the anticipated effects of lightning, high voltage transmission
line induced voltages, accidental connection of undesired voltages,
etc., from the OP wiring 11. Protection is indicated in the SWC by
protection equipment 9 connected between the subscriber side "Tip
and Ring" terminals 10 and the SWCs internal "Tip and Ring" signals
8, and indicated in the subscriber location elements 12 by
protection equipment 14 connected between the SWC side "Tip and
Ring" terminals 13 and the subscribers on-premises "Tip and Ring"
signals 15.
[0030] The subscriber connection 19 to the local telephone
instrument 20 may be the only apparent connection, as far as the
subscriber is concerned, between the telephone service provider
system and the telephone instrument 20. Those skilled in the art
are aware that within the borders of the subscriber location 12
there exists a few physical elements that are normally transparent
to the users of the telephone instrument 20. Elements pertinent to
the present invention include the functional point of demarcation
16 ("DEMARC") between the LEC and customer premises equipment
("CPE") including perhaps a first distribution frame often referred
to as the Main Distribution Frame ("MDF") which would be in near
proximity to the DEMARC, inside wiring 17 ("IW"), which may include
one or more additional intermediate distribution frames ("IDF"),
leading eventually to some sort of jack, punch-down block, or other
termination connection point indicated as point 18 in the figure,
and finally, the connection 19 to the telephone instrument 20
itself. For reference purposes, those skilled in the art recognize
that a conventional telephone instrument 20 embodies both audio or
conversation, transceiver functionality, and also certain AC
(alternating current) related capabilities such as customer
alerting, Ringing, and certain DC (direct current) related
functionalities of which the existence of loop current, or the
on-hook or off-hook status of the telephone instrument, and the
range of values of the amount of current when the instrument is in
its off-hook state is relevant to the present invention. Those
skilled in the art will understand that the foregoing is only a
brief description of selected elements of a traditional telephone
circuit and is not intended to be comprehensive, but rather to
provide reference points for the description of the embodiments of
the present invention that follows.
[0031] FIG. 2 provides a depiction of an arrangement of elements
that describes an embodiment of the present invention.
[0032] FIG. 2 includes a depiction of an arrangement of elements
that operating together may be referred to as the "Head End" ("HE")
or "front end" functionality in one embodiment of the present
invention. Subscriber Tip and Ring signal 15' is the same signal as
its corresponding signal in FIG. 1. As previously stated, it is an
object of the present invention to provide additional power and
functionality and to make this additional power and functionality
available at the local telephone location. This improved power can
be delivered even if a traditional telephone instrument is not
actually employed at that location or if the telephone is not
employed for the traditional purpose of voice "telephone"
communications. In other words, the increased power can be used to
enable some communications device or one or more other instrument
or capabilities employed with, or in lieu of, the local telephone.
Communications devices examples include telephones, speaker phones,
non-telephone, yet telephone-like instruments, such as a video
phone or non-telephone-like devices that may optionally include
telephone communications features such as a computer or
microcontroller based display and user interface device primarily
intended to access data or inmate related services. Some of these
communications devices may traditionally be AC line powered
devices.
[0033] FIG. 2 also includes a depiction of an arrangement of
elements that operating together may be referred to as the "Tail
End" ("TE") or "back end" functionality in one embodiment of the
present invention. Local telephone instrument Tip and Ring signals
19' and the local telephone instrument 20' are the same elements
and signals as their corresponding elements and signals in FIG.
1.
[0034] FIG. 2 also includes elements 16', 17', and 18' which are
the same IW functionalities as those presented in FIG. 1.
[0035] It may now be recognized that FIG. 2 HE elements 21 thru 43
are, in an embodiment of the present invention, interposed between
signal 15 and terminal 16 of FIG. 1 as indicated by their like
elements 15' and 16' in FIG. 2. Likewise, it may now be recognized
that the FIG. 2 TE elements 70 thru 90 are, in an embodiment of the
present invention, interposed between terminal 18 and signal 19 of
FIG. 1 as indicated by their like elements 18' and 19' in FIG. 2.
As indicated in FIG. 2, telephone instrument 20' does not have an
unimpeded sequence of direct electrical continuity between signals
15' and 19'.
[0036] Those skilled in the art may now follow the signals and
mechanisms provided by the present invention as depicted in the
embodiment presented in FIG. 2.
[0037] In an embodiment of the present invention, FIG. 2 indicates
that a telephone instrument 20' is located at its original or local
location and uses some "last inch" cable to provide connectivity of
signal 19' to what it perceives as a SLIC or "Foreign Exchange
Station" ("FXS") signal. This signal, in terms of DC voltage range,
bias current, on-hook and off-hook control signaling, and optional
alerting or ringing signals are functionally provided by a
plurality of mechanisms now to be described.
[0038] In FIG. 1, the bias current, or "Talk Battery", is provided
to telephone 20 from the distant source 2 without regard to the
actual equipment, capabilities, purpose, or location of SWC, or
alternative entity 1, keeping in mind that this bias current is
typically around 25 milliamps at telephone 20. Likewise, the
alerting or ringing voltage for telephone 20 is provided from the
distant source 2, while the on-hook or off-hook status of telephone
20 is detected, from the SWCs point of view, by distant element 4.
In FIG. 2 it can be appreciated by those skilled in the art that
the SWC provided bias current may not be directly communicated
through the elements depicted all the way to telephone 20. Those
skilled in the art will also appreciate that SWC generated
alerting, or ringing voltages, may not be directly communicated
through the elements depicted all the way to telephone 20.
Likewise, one skilled in the art would appreciate that the on-hook
or off-hook status of 20 may not be directly communicated through
the elements depicted all the way back to the SWC loop current
detector. A more detailed examination of FIG. 2 will explain how
the previously mentioned current and signal equivalents may be
provided.
[0039] In the embodiment shown in FIG. 2, bias and signaling
voltages and currents are communicated via signal 15' between the
SWC function and the "Foreign Exchange Office" ("FXO") port 21 of
the HE portion. These voltages and currents are then communicated
by signal 22 to relay function 23 whose operation will be seen by
one skilled in the art as being analogous to the hookswitch
function in a traditional telephone instrument. However, a major
difference between the traditional operation and that of the
embodiment shown in FIG. 2 is that in the embodiment, the
subscriber does not have physical or direct control of the hook
switch function provided by relay function 23.
[0040] Relay function 23 is depicted in its on-hook state and thus
voltages appearing on signal 15' will be communicated via relay
function 23 and signals 22 and 25 to Ring Detector 24. Signal 26 is
representative of the current ringing state of signal 15' and
communicates this state information to Signal Transceiver and
Controller 27 ("STC"). An alerting signal from the SWC
functionality will thus be detected by Ring Detector 24 and
forwarded via signal 26 to STC 27. Assume for the purposes of this
description that this embodiment of the present invention is
expected to forward the SWC alerting state to the local telephone
20'. This may not be the case in another embodiment such as in an
embodiment intended for use with an inmate telephone control system
where incoming calls would normally not be expected, nor would such
calls normally be extended towards an inmate accessible telephone
instrument. In the example embodiment, signal 26 does not directly
cause an audible, visual, or other conventional ringing
indication.
[0041] The STC may, depending upon the needs of a particular
embodiment, encode a new signal 42 onto a higher frequency carrier
where this carrier frequency is greater than the traditional
telephony sampling frequency of 8,000 samples per second.
Preferably, the carrier may be some multiple of 4 KHz. Those
skilled in communications art will understand that should some of
the energy of this carrier frequency reach the SWC voice frequency
digital encoding device, e.g. a CODEC, then that energy, due to the
effective under-sampling per Nyquist's theory, would result in an
aliased or phantom frequency energy within the 0 to 4 KHz voice
frequency range. This potential effect is minimized when the
carrier frequency is a multiple of 4 KHz as the resulting aliased
signal will be near zero Hz and thus be inaudible to persons on the
related telephone call. To further attenuate any potential unwanted
energy from the STC within the voice frequency communication
frequencies, a "High Pass Filter" 43 ("HPF") may be provided. This
is not intended to limit the carrier frequency to some multiple of
4 KHz, as HPF 43 may be configured to provide adequate isolation
between the voice frequency range and the desired carrier
frequency. For example, an HPF 43 required to adequately attenuate
carrier frequency energy above 20 KHz may be implemented.
Alternatively, it may be convenient to use two or more carrier
frequencies where each carrier frequency is also a multiple of 4
KHz, or may have no special relationship to 4 KHz, so long as HPF
43 provides adequate isolation between the voice frequency range
and the selected carrier frequencies. Moreover it may be convenient
to use one or more carrier frequencies in each direction, i.e., one
or more carrier frequencies from HE to TE (as described later), and
the same or a different one or more carrier frequencies from TE to
HE. The output of HPF 43 is coupled to a common bus 35 that
provides for the combining of signals, which will be described
below, onto a single wire pair so as to provide novel
capabilities.
[0042] While the following will be more completely described,
please assume that an appropriate off-hook representation signal,
again encoded onto the high frequency carrier previously described,
or encoded onto yet another useful carrier frequency arrangement,
is sent from the TE system depicted in FIG. 2 and thus appears on
the common signal bus 35 of FIG. 2. When the encoded signal
presently being considered passes through HPF 43, it will appear to
STC 27 on signal 42, which is a bidirectional signal, where STC 27
may receive the signal, decode the command, and in response to the
command, send signal 29 to relay coil 28 causing relay contacts 23
to connect signal 15' to signal 32 and thus to coupler element
31.
[0043] Coupler 31 provides three principal functions: first, to
provide DC loop termination toward the SWC; second, to couple
traditional voice frequency energy in the range of approximately
300 Hz to 3500 Hz bi-directionally between signals 32 and 33; and
third, to provide DC isolation between signals 32 and 33. This
coupler may be either passive, if some small insertion loss is
acceptable, or active if there is a requirement to compensate for,
and thus minimize any voice frequency artifacts. Another function
of coupler 31 is to, under abnormal conditions, attenuate the
relatively high ringing voltages from passing through to signal 33
which is primarily intended to be limited to traditional voice
frequency energy. Normally relay 23, 28 prevents ringing voltage
from reaching coupler 31. To further ensure this is accomplished, a
"Band Pass Filter" ("BPF") 34 may be provided prior to coupling
signal 33 to the common signal bus 35.
[0044] As mentioned previously, coupler 31 provides DC loop current
termination towards the SWC. Those skilled in the art will
recognize that with this arrangement there is no bias power
available to power either the HE STC 27 or the telephone instrument
20' that the subscriber would presumably use. Therefore, the
embodiment of the present invention shown in FIG. 2 provides a
novel arrangement to satisfy those needs, but also to provide new
and additional capabilities that will become evident. A master
power element 36, as depicted in FIG. 2, may be an AC line powered
supply, a battery, perhaps some other DC power source, or a
combination of these configured to supply a DC voltage to power
signal 37 to an effect somewhat similar to the SWC battery
function.
[0045] Those skilled in the art will understand that the power
signal 37 appears very much like a large capacitor which would
effectively short out or highly attenuate virtually any AC signals
such as voice frequency or higher frequency signals, if those
signals were to be connected directly to power signal 37. Those
skilled in the art will recognize that the BORSCHT functions, and
particularly the battery feed to the hybrid of a SWC SLIC function,
is intended to prevent this non-DC shorting effect. In the
embodiment shown in FIG. 2, the traditional BORSCHT functions are
foregone and only a "Low Pass Filter" 38 ("LPF") is used to prevent
non-DC signal attenuation and to provide a non-current limited DC
bias to the signal passed from LPF 38 to common signal bus 35 to
novel effect. Elements 36 and 38 together are provided to present a
relatively low "equivalent series resistance" ("ESR") towards the
signal passed from LPF 38 to common signal bus 35 at DC and a high
ESR generally for AC signals including AC signals at voice
frequencies and above. Although this arrangement may hint at those
advantages later to be described, it also presents some potential
problems. If signal 35 were to be directly connected to HE output
terminals 16' and if the terminals 16' were shorted, there would
exist the same sort of over currents that would exist if a SWC did
not provide current limiting to its own subscriber circuits
[0046] The protection fuses in traditional protection element 9 in
FIG. 1 are chosen to protect against major faults such as
inadvertent connections to AC mains (110/220, etc.) but are not
intended to specifically limit the SWC loop current to 100
milliamps as that is accomplished by the battery feed resistors of
the SLIC. In embodiments of the present invention, a useful current
limit may be provided with "precise" fuses or a current foldback
circuit. Protection element 39 in FIG. 2 may also provide lightning
protection similar to that provided by element 9 in FIG. 1.
[0047] FIG. 2 also depicts an arrangement of elements that operate
together to form what may be referred to as the "Tail End" ("TE")
or "back end" functionality of the present invention. IW telephone
line 17' in the figure carries the higher DC current capability
presented by the HE as previously described as well as voice
frequency energies and the higher frequency carrier encoded
bi-directional signals as previously discussed. The signals on IW
telephone line 17', which may be considered a modified form of Tip
and Ring signals, appear on the TE terminals 18' and may be
connected to protection element 71. Protection element 71 would
conveniently have many characteristics similar to those of
protection element 39 including a low ESR throughout its design
current range as well as lightning and induced voltage protection
and excessive current limiting as its function would be most
beneficial if IW telephone line 17' were either relatively long,
perhaps thousands of feet, or if it traversed open distances
between buildings where lightning or power lines may induce
undesirable voltage or currents into it, or both. One skilled in
the art will recognize that in many cases protection elements 71 or
39, or both, would not be necessary in a particular embodiment. For
example, if power source 36 implementation includes the current
foldback characteristic previously mentioned, then fuse elements
49, 50 of FIG. 3 are not required for short circuit protection
purposes which would result in the overall ESR of the HE being
reduced by the ESR due to these fuses. With this in mind, it may be
seen that the DC voltage, voice and carrier frequency energies on
IW telephone line 17' are coupled to common signal bus 72 which is
functionally somewhat similar to common signal bus 35. The
embodiment shown in FIG. 2 also contains element 73 which is a LPF
with characteristics substantially similar to those of LPF 38. LPF
73 then couples primarily only the DC portion of the signal on
common signal bus 72 to the input sides of local power source 75.
Note that power source 75 may conveniently be implemented as one or
more "switch mode power supplies" ("SMPS") depending upon the needs
of the specific implementation. Power source 75 is provided to
supply any local bias power such as to STC 77 and to provide some
limited amount of power to an external device or system such that
external device or system does not require a local, generally AC
mains derived, power source. If a specific implementation requires
different voltages either for functions internal to the IL or for
the TE circuitry and for an optional auxiliary device, then local
power source 75 may be composed either of appropriate individual
power conversion elements or a single conversion system with
multiple outputs as would be appropriate for the implementation. In
any case, it is appropriate to configure the local power source
such that an overload condition presented to the auxiliary power
signal 88 could be appropriately managed and yet would not
interfere with any other TE operational capability.
[0048] Element 78 in FIG. 2 is a LPF whose upper frequency
characteristics would normally match the similar characteristics of
BPF 34. Element 78 is a LPF so that the DC component of the signal
on common signal bus 72 may be utilized to provide bias current to
a telephone instrument such as 20' should such be connected to
telephony output terminals 87. Since the power source for the
signal on common signal bus 72 derives from the low resistance
source 36, 37 a local current limiting means is provided by a
Constant Current Limiter ("CCL"), an element of 80. Per previously
noted experience, the CCL may conveniently be configured to
provide, for example, 22 to 30 mA to a telephone instrument 20'
when in its off-hook configuration. Thus signal 79 contains: (1) DC
voltage with its current limited only by the resistance of LPF 38,
telephone line 17' and resistances within, and protection limits of
optional elements 39 and 71; (2) the voice frequency energy path
needed for telephone 20' while the CCL controls that loop current
at signal 86 to its preconfigured value.
[0049] An Off-Hook Detector, an element of 80, is provided to sense
when a telephone instrument 20' is in its off-hook configuration.
The status of the on-hook or off-hook configuration is reflected by
the state of signal 88 being presented to STC 77. STC 77 would
encode this onto a signal sent towards the HE STC 27 in a manner
similar to that described earlier for the ring detection signal
being encoded and sent from STC 27 towards STC 77. Likewise, when
STC 77 receives a signal from STC 27 interpreted as ringing from
the SWC, STC 77 would activate signal 85 to enable an optional
local ringer 84. Optionally, ringer control signal 83 may enable
Ring Generator ("RG"), an element of 80, which may activate a
conventional ringer device in telephone 20', should one exist. If
an RG is not provided in a particular implementation, then the AC
characteristics of signal 86 are the same as those of signal 79,
else signal 86 has the additional capability of including the
ringing voltage provided by the RG. Signal 86 is the TE local
telephony signal, voltage, and current set presented to output
terminals 87.
[0050] In a similar manner the off-hook encoded signal sent from
STC 77 to STC 27 may now be recognized by STC 27 which would
utilize signal 29 to activate relay coil 28 to energize relay
contacts 23 to effectively connect coupler 31 towards the SWC or
appropriate SWC-like equipment as an off-hook event.
[0051] It is now apparent that the above descriptions explain how
the embodiment of the present invention shown in FIG. 2 may
advantageously use the low ESR characteristic of the HE to provide
an auxiliary power source at the TE location. First, the HE device
may provide significantly more power to its output terminals 16'
principally due to the low ESR of the HE design. Further, a
telephone instrument 20' connected to the TE device will only use a
relatively small portion of the current potentially available at
the TE device input terminals 18'. The difference between the
current, and thus power, available at TE input signal 70, and the
actual power consumed by telephone instrument 20', is thus
available to one or more power supplies such as power source 75.
With the one or more local power supplies such as power source 75
being implemented with modern high efficiency SNIPS designs, this
additional power permits a new range of capabilities and features
to be provided at a location normally considered limited to the
availability of a simple telephone instrument without providing any
new wiring or AC mains to the location.
[0052] Further, the expected functions of traditional ringing and
off-hook signaling have been effectively preserved such that the
SWC, or whatever provides that function, would not be materially
affected by provisioning of these new capabilities.
[0053] Further, one skilled in the art may appreciate that the
additional signaling capabilities afforded by the out-of-band
signaling channels may permit either additional types of signals to
be exchanged between the HE and TE locations, or more secure
communication of sensitive signals previously exchanged as DTMF or
other forms of in-band signaling, or both. One example of signals
that may benefit from this additional security are credit card or
personal account access codes.
[0054] As described in connection with FIG. 2, the carrier
frequency or frequencies that are used to convey signaling
information between the HE and TE portions of embodiment of the
present invention are also related to the frequency discriminate
filters identified as HPF's 43, 81 in FIG. 2. Alternatively, it is
possible to use one or more carrier frequencies that fit below the
normal telephony voice frequencies for example in the range of 5 Hz
to 120 Hz as the carrier frequency or frequencies instead of, or in
addition to, the higher frequencies previously described. In the
case of such low frequencies carriers filters 43 and 81 would be
configured as Band Pass Filters instead of High Pass Filters for
those carriers. Because such low frequencies might be heard by the
persons using the overall system for voice communications it may be
necessary to include a Band Reject or Notch Filter along with the
BPF 34 and LPF 78 functionality to reduce or eliminate
objectionable artifacts related to such low frequency carriers. If
both low and high frequency carriers are used within the same
system each frequency range requires its own frequency discriminate
filters of appropriate configuration.
[0055] A particularly useful choice for such a low frequency
carrier is 60 Hz since CODECs associated with SLIC functions
typically already contain band reject or notch filters to minimized
anticipated 60 Hz hum coupled from AC mains carried on wires which
may run parallel to telephone lines. This also applies to a carrier
frequency of 120 Hz.
[0056] To appreciate the benefits of embodiments of the present
invention it is helpful to consider the practical power normally
delivered to a telephone instrument with the power that may be
delivered to the same location by use of embodiments of the present
invention.
[0057] Assume for these first examples that the Voltage source is
-48 VDC.
[0058] Further, in the traditional POTS case, assume that the ESR
of the SLIC is a fixed 480 Ohms. In a hypothetical case, please
also assume that the telephone instrument was unconstrained and was
able to choose any equivalent resistance for the sole purpose of
maximizing the power it could use. Further, let us assume that the
telephone instrument was located at zero feet from the SWC SLIC
terminals such that the total line related resistance was 0 Ohms.
In such a case, the telephone instrument would choose to match the
source resistance of 480 Ohms and one-half of the source voltage
would appear across the telephone instrument resulting in a loop
current of 50 mA and 1.2 Watts being dissipated by the telephone
instrument and another 1.2 Watts being dissipated in the ESR of the
SLIC. Thus, the absolute maximum power that a traditional SLIC
circuit can deliver to a traditional telephone instrument under
these hypothetical ideal conditions is 1.2 Watts.
[0059] In another hypothetical case assume that the SLIC ESR was
replaced by a constant current source of ideal compliance and
configured to deliver 22 mA under all loop resistances and within
the available source voltage. Again let us assume that the
telephone instrument was located zero feet from the SWC SLIC
terminals such that the line resistance was 0 Ohms. In such a case,
the telephone instrument would choose to have a resistance which
would place all of the available voltage across its own terminals.
Since that voltage is 48 volts, the instrument would choose 2182
Ohms which would result in just less than 1.06 Watts being
dissipated by the telephone. Similarly, if the constant current
source was configured to supply 30 mA the chosen resistance would
be 1600 Ohms and the power dissipated would be 1.44 Watts.
[0060] The real world will neither have zero length lines nor
telephones that have only a requirement to maximize power
dissipated. Real telephone lines are typically 24 AWG copper which
exhibits a resistance of about 50 Ohms per thousand feet for a
twisted pair.
[0061] Assume now again the traditional -48 VDC source and 480 Ohm
ESR and that the line length were 1000 Ft but the telephone
instrument was still free to ideally choose its ESR to maximize the
power it dissipates. This results in a 530 Ohm phone with just less
than 1.09 Watts being dissipated. At 4000 Ft the result would be a
680 Ohm phone with just under 850 milliwatts dissipation. With a
constant current source of 22 mA from the -48 VDC source and 1000
Ft of 24 AWG UTP, the phone would chose to have 2132 Ohms
resistance with maximum power would be 1.03 Watts while at 4000 Ft
the phone would chose 1982 Ohms resistance with a dissipation of
less than 960 milliwatts. Similarly, for a 30 mA source, the 1000
Ft power would be less than 1.4 Watts and at 4000 Ft about 1.26
Watts with respective phone resistances of 1550 and 1400 Ohms.
[0062] It is instructive to compare an embodiment of the present
invention to see what may be provided to the telephone instrument
location from the same -48 VDC level and then estimate the power
available for other purposes beyond that required by the telephone
instrument itself.
[0063] Assuming that the ESR of the Head End of the embodiment is
about 60 Ohms and then repeat the above calculations related to
that configuration. If the line length were zero, and there were no
current limiting at all, then the telephone instrument along with
any additional circuitry desiring to use the excess power would
choose an equivalent total resistance of 60 Ohms which would result
in 9.6 Watts being available at the telephone instrument location.
As the telephone itself requires only about 100 milliwatts to
operate, almost 9.5 Watts would be available for the additional
circuitry. But in the embodiment if we choose to describe the
source current limiting fuses as being limited, in one example, at
100 mA, then the phone would choose to have 420 Ohms resistance and
the maximum power available would be about 4.2 Watts leaving 4.1
Watts available for the additional circuitry.
[0064] One skilled in the art would appreciate the value of
embodiments of the present invention even when the maximum current
is limited to 100 mA and the additional advantage of choosing a
somewhat higher maximum current limit. Likewise, if the source
voltage was selected to be a voltage higher than 48 Volts, one can
appreciate the yet higher power available for use by additional
circuitry for otherwise identical line lengths or similar power
over greater line lengths. Without listing all details as above, in
embodiments, the present invention would provide the following
approximate total power capability at various source voltages and
telephone line lengths while retaining a 100 mA current limit. At
75 VDC Talk Battery: 6.4 Watts at 1000 Ft, 4.8 Watts at 4000 Ft,
and 3.8 Watts at 6000 Ft. At 100 VDC Talk Battery: 8.9 Watts at
1000 Ft, 7.4 Watts at 4000 Ft, and 6.4 Watts at 6000 Ft. At 120 VDC
Talk Battery: 10.9 Watts at 1000 Ft, 9.4 Watts at 4000 Ft, and 8.3
Watts at 6000 Ft. Considering the same voltages and telephone line
lengths but limiting the loop current to less than 550 mA, and in
most cases less than 400 mA is the actual current expected, then at
75 Volts the total power capability deliver to the Tail End would
be 12.7, 5.3, and 3.8 Watts respectively. From 100 VDC one would
expect to have 22.5, 9.5, and 6.8 Watts available respectively.
Finally, from 120 VDC one would expect to have up to 32.4, 13.6,
and 9.8 Watts available respectively. In all the above cases, the
power is made available under ELV/SELV conditions.
[0065] It will be apparent to one skilled in the art that
embodiments of the present invention satisfy the needs and
objectives outlined in the background and enables considerable
flexibility for novel functionalities at heretofore unpowered
physical locations that have at least a single pair of telephone
communications cable available.
V. EXAMPLE
[0066] The componentry described with respect to FIG. 2 was
embodied in "front end" and "back end" circuit boards shown in more
detail in FIGS. 3 and 4 respectively. FIG. 3 and FIG. 4 merely
illustrate one implementation of an embodiment of the present
invention.
[0067] Referring first to FIG. 3, an example implementation of the
HE portion of an embodiment of the invention. One skilled in the
art will appreciate that in many cases several HE circuit blocks
may be conveniently configured into a single assembly such that
several TE locations might be served from a single HE location.
While that was the case for the physical HE devices assembled, it
is also convenient to consider a HE description as if it were a
stand alone device as we shall do here.
[0068] Power source 36' is provided both for the "Talk Battery"
("TB") and for the bias requirements of the signaling and control
electronics. In the example construction, the TB selected was a
traditional -48 VDC obtained from a custom power supply. A suitable
commercially available isolated AC input, DC output power supply is
a VPS-25-48 available from CUI Inc of Tualatin, Oreg. Likewise, the
bias voltage in the example construction was obtained from the
custom power supply. A suitable commercially available isolated
DC-DC power supply is a VWRBS1-D48-S5-SIP available from CUI Inc of
Tualatin, Oreg. In this case, the TB supply also powers the bias
supply. It is convenient to connect the outputs of these separate
DC power supplies such that the overall result provides an SELV
configuration along with a static drain resistor to earth ground.
Referring now to FIG. 3, this arrangement is indicated by the AC
line input cable 44 providing mains power to the isolated output 48
VDC power supply, a portion of 45. The traditional polarity for the
TB is obtained by designating the more positive output terminal of
the 48 VDC supply as "common" signal 66 while the more negative
terminal provides TB signal 46. Rather than connecting the "common"
terminal directly to earth ground as is normal practice in SWCs and
similar equipment, the implementation provides a static charge
bleed resistor 68 so that the resulting TIP and RING voltages may
cover the International Electrotechnical Commission ("IEC") Extra
Low Voltage ("ELV") range and retain a Safety Extra Low Voltage
("SELV") rating as contact with either TIP or RING terminal or
electrically conductive point does not have a direct path through
earth ground back to source 45. A suitable value for resistor 68
would be in the range of 100K Ohms to 1 Meg Ohm. A suitable surface
mount device ("SMD") for this resistor is Vishay CRCW1206510KJNEA.
As previously mentioned, the bias power supply, a portion of power
supply 45, may conveniently be powered by the TB voltage source so
that if a physical battery would be connected from 46 to 66, and a
suitable isolated battery charger were to be used in place of the
suggested precision voltage source described above, then all
operating functions remain active in the event of an AC power loss.
It is convenient to connect the more negative output terminal of
the bias supply to "common" signal 66 and the more positive output
terminal of the bias supply to "Vcc" signal 67.
[0069] Item 38', Low Pass Filter, serves to permit the passing of
DC voltage and current from signal 46, 66 onto signal 35'. More
specifically, this LPF serves to protect the AC electrical signals
existing on signal 35' from the shunting effect of the low
capacitive reactance of capacitor 47 and that of the Talk Battery
power source portion of 45. Thus LPF 38' provides significant
reactance at voice and signaling frequencies while providing a low
ESR in series from signal 46, 66 to signal 35'. In the
implementation this is accomplished by the use of a split inductor
where half of the windings are in series with each the physical
electrical conductors making up signals 46, 66 and 35'. These
winding are connected, or phased, such that the two inductances act
in concert like a single total inductance with capacitor 47
appearing across the apparent center of the inductors halves. An
advantage of this split inductance arrangement is that while there
is no true low resistance "ground" reference point as there would
be in a traditional SWC, inductor 48 and capacitor 47 in concert
provide excellent voice and high frequency isolation between
multiple channels of a multi-HE configuration. A suitable SMD
capacitor for 47 is 220 .mu.F, 100V part number EMVY101GDA221MMH0S
available from United Chemi-Con of Rosemont, Ill. A suitable
inductor would have significant inductance and low DC resistance
for each winding. As a suitable inductor was not commercially
available, a custom inductor was designed and constructed on a
small physical sized core and bobbin. The inductance of each
winding was about 2.5 H with a DC resistance of less than 12 Ohms.
A suitable inductor would be part number 11-5415A available from
Tranex of Colorado Springs, Colo.
[0070] Items 39', Protection Circuit, must take into account the
low ESR nature of the main power source of the implementation. The
primary function of this protection circuit is to limit current
into or out of either terminal of the output conductor pair to a
value that will protect the above main power source should the
output conductors be shorted together, to ground, or to some
unintended external power source. For the purposes of the example
implementation, the short circuit current limit was selected to be
about 100 mA. Appropriate devices for this purpose are resettable
fuses 49 and 50 so that service may be automatically restored
following an event causing the fuses to open in order to protect
the system. Suitable resettable fuses for this purpose are Raychem
(TYCO) part number TS250-130-RA available from TYCO Industries of
Menlo Park, Calif. If the TB supply of power source 36'
implementation includes the current foldback characteristic
previously mentioned, then fuse elements 49, 50 are not required
for short circuit protection purposes.
[0071] Contact from an inadvertent source to either TIP or RING
must be accommodated safely and the most likely such source may
have a voltage as high as 200 V peak such as from a 110 VAC hot
lead. Due to the ground isolation provided by the implementation,
such a voltage has only one return path back to its own ground
reference that being through resistor 68. With the example 510 K
Ohms and -48 VDC TB values, the maximum current due to a 110 VAC
hot lead touching the TIP lead somewhere would be less than 400
microamps or less than 500 microamps if touching the RING lead.
[0072] As any fuse, including those utilized in this example,
requires a finite amount of time to react to an over-current
condition additional protection may be warranted to protect the
system from the effects of very brief events such as from voltages
induced by nearby lightning strikes. If an implementation is
concerned about the possibility of such induced voltages, then
additional protection in the form of automatically resettable
overvoltage clamp 53 is prudent. These devices typically present no
effects upon the circuit until a high voltage appears on one or
both of the output conductors. The devices then quickly transition
to a low resistance state shunting the abnormal voltage to an
appropriate reference point. As these devices typically and
intentionally have quite low on-state forward voltages some small
resistance 51, 52 in series with each terminal will tend to limit
the inrush current. These resistors should be closely matched so as
to minimize longitudinal balance errors and should be able to
dissipate the small but finite amount of power they would likely
experience during a fault condition. An appropriate value for these
resistors is 10 Ohms, 1%, and 0.5 Watt rated. Suitable SMD
resistors for this purpose are Dale (Vishay) part number
CRCW201010R0FKEF available from Vishay Intertechnology of Malvern,
Pa. If the induced voltage persists long enough the combination of
voltage clamp 53 and series resistors 51, 52 may give the
resettable fuses 49, 50 time to open as well. A suitable active
voltage clamp is Littlefuse part number P1101CA2L available from
Littelfuse of Des Plaines, Ill.
[0073] Item 21', Connector, is most often an industry standard
telephony connector. A single Tip and Ring pair would thus
typically use an RJ-11 style jack while a 24 channel (24 Tip and
Ring pairs) would thus typically use a 25 pair ribbon connector. A
suitable SMD device for a single channel connector is Molex part
number 085513-5014 available from Molex Corporation of Lisle, Ill.
A suitable insulation displacement device for 24 channels is AMP
(TYCO) part number 554090-1 available from TYCO Industries of Menlo
Park, Calif.
[0074] Item 23', 28', Relay, should meet typical telephony relay
requirements and use as little operating power as practicable. This
relay is most commonly a DPDT (2 Form C) type with a low power
magnetically biased coil. The coil voltage rating should be
compatible with the electrical drive available from the controller,
Item 27'. If the controller is configured to operate from a 5 VDC
bias voltage, then a suitable relay is NAIS (Panasonic) part number
TXS2SA-4.5V available from Avnet Electronics of Phoenix, Ariz.
[0075] Item 24', Ring Detector, may be a circuit commonly comprised
of an optocoupler of the `AC` input variety in combination with a
capacitor to couple the ringing voltage to the optocoupler input
LEDs while blocking any DC current through the optocoupler LED and
a resistor in parallel with the optocoupler LEDs such that in
combination with the reactance of the capacitor at the ringing
frequency ensures that a real ringing voltage is present before the
transistor output of the optocoupler is activated. A suitable
optocoupler is NEC part number PC2915-1-F3 which exhibits a nominal
LED forward voltage drop of 1.1 V and is available from California
Eastern Laboratories of Santa Clara, Calif. An appropriate value
for the shunting resistor is 10K Ohms and may be a SMD 1/16 W due
to the voltage limiting action of the optocoupler LEDs. A suitable
SMD resistor is Yageo part number RC0805J-0710KL available from
Yageo USA of San Jose, Calif. To ensure ringing voltage detection
down to 60 Vrms the capacitor should be at least 270 nF and 250 V.
A suitable SMD capacitor is Panasonic part number ECW-U2274KCV
available from Digikey of Thief River Falls, Minn. A suitable
output transistor pull up resistor may have a value of 10 K Ohms. A
suitable SMD resistor is Yageo part number RC0805J-0710KL available
from Yageo USA of San Jose, Calif.
[0076] Items 27', Signal Transceiver and Controller, is a circuit
comprised of a programmable microcontroller containing digital
logic and analog device elements in addition to a programmable
controller, random access memory for short term memory uses and
programmable flash memory for program, configuration and
operational settings. STC 27' is provided with resistors 62-65 to
bias input signals for analog functions within the working limits
of the microcontroller device. An appropriate microcontroller is
Cypress Semiconductor part number CY8C27443-24PVXI available from
Cypress Semiconductor of San Jose, Calif. Configuration and
programming tools are provided by Cypress Semiconductor for this
series of microcontrollers. Appropriate SMD resistors are Yageo
part number RC0805J-0710KL available from Digikey of Thief River
Falls, Minn.
[0077] Item 31', Coupler, provides several functions including DC
termination of the SWC loop current, DC voltage isolation between
the SWC provided voltage and loop current, and bi-directional voice
frequency coupling of audio signal energy between the SWC and the
internal system side of the coupler element. The coupling element
would ideally cause no insertion loss into this last function.
However, in many applications the small insertion loss due to the
use of a quality transformer is justifiable as compared to the cost
and complexity of a lossless bi-directional coupling mechanism such
as a transformer, or transformers, along with amplifiers and likely
hybrid circuitry used to compensate for the inherent transformer
losses while preventing self oscillation. If the SWC function is
actually provided by an IAD or channel bank arrangement, it is
likely possible to adjust these units to externally compensate for
the small inherent insertion loss of a single transformer design.
The example implementation implements the coupler element based
upon a single transformer design where in the transformer 54 is
implemented as a 600:600 Ohm split primary and split secondary
design. This transformer, as implemented in the present example,
must operate satisfactorily while sustaining the net DC bias
current of the SWC loop current termination. A suitable transformer
was not found to be generally available from commercial sources.
Thus custom transformers were constructed to meet these criteria. A
suitable transformer would be part number 17-7183 available from
Tranex of Colorado Springs, Colo. The center terminals of each side
of this transformer are bypassed for voice frequency coupling
purposes by 2.2 .mu.F, 100 Volt, film capacitors. It should be
noted that the voice frequency coupling (DC blocking) capacitor 56
on the secondary side of the transformer works in concert with the
components of item 34' to provide the band pass nature of item 41'.
Suitable SMD capacitors for this purpose are Arcotronics part
number LDEEF4220JB0N00 available from Kemet Corporation of
Simpsonville, S.C. The side of the transformer associated with DC
termination of the SWC loop, referred to as the primary side of the
transformer, also requires a resistor or resistors in parallel with
the afore mentioned capacitor to provide DC termination of the SWC
current loop when relay 23' is in the off hook state. The SWC
termination impedance "Z" 55 may be implemented by a complex
impedance. In many cases however, especially when the effective
length of 15'' is relatively short, simple DC resistance to
terminate the current loop of the SWC and a parallel capacitance to
minimize loss of AC coupling through the transformer is
functionally effective. This resistance must be low enough to
guarantee off hook detection by the SWC at maximum loop 15'' length
while being high enough to limit the current in the primary of the
coupling transformer according to the DC current limitation of the
transformer design when loop 15'' electrical length is short. The
present example chose to use six 100 Ohm, 0.25 Watt SMD resistors
in series for a total of 600 Ohms, 1.5 Watts. Suitable SMD
resistors are Yageo part number RC1206FR-07100RL available from
Yageo USA of San Jose, Calif.
[0078] Item 34', Band Pass Filter, serves to pass voice frequencies
bi-directionally between signals 22' and 35' via coupler 31' when
relay contacts 23' are in an off-hook state while simultaneously
blocking DC current from passing through the secondary of
transformer 54 of coupler 31'. The DC blocking, or high pass
component of this band pass filter is conveniently provided by the
2.2 .mu.F capacitor 56 within coupler 31' circuit previously
described.
[0079] BPF 34' frequency characteristics are implemented in the
present example by a pair of small inductors 58, 59 placed in
series with the electrical conductors comprising the signals 33'
and 35' in FIG. 3, along with an appropriate corresponding
capacitor 57 across the electrical conductors of signal 33' in FIG.
2. For the prototype circuits it was determined that the most
advantageous values of these components are 18 mH for inductors 58,
59 and 68 nF, 100V, 5% film for capacitor 57. Suitable inductors
are Coilcraft part number RFB0810-183L available from Coilcraft of
Cary, Ill. A suitable SMD capacitor is Panasonic part number
ECW-U1683JC9 available from Digikey of Thief River Falls, Minn.
[0080] Item 43', High Pass Filter, serves to effectively pass the
high frequency carrier frequencies bi-directionally between signals
42' and 35' of FIG. 3 while blocking DC voltages and any potential
interference from voice frequencies appearing on signal 35'.
[0081] HPF 43' is implemented in the present example by a pair of
small capacitors 60, 61 connected in series with the electrical
conductors comprising the signals 69, which is substantially
similar to signal 35', and 42 in FIG. 3. For the prototype circuit
it was found that the most advantageous value is 330 nF, 100V, 10%
film for capacitors 60, 61. Suitable SMD capacitors are Panasonic
part number ECW-U1C334KC9 available from Digikey of Thief River
Falls, Minn.
[0082] Connector 16'' is most often an industry standard telephony
connector. A single Tip and Ring pair would thus typically use an
RJ-11 style jack while a 24 channel (24 Tip and Ring pairs) would
thus typically use a 25 pair ribbon connector. A suitable SMD
device for a single channel connector is Molex part number
085513-5014 available from Molex Corporation of Lisle, Ill. A
suitable insulation displacement device for 24 channels is AMP
(TYCO) part number 554090-1 available from TYCO Industries of Menlo
Park, Calif.
[0083] Although connector 30' may be defined by a specific
application, in order to provide for signals 41', a common
connector that may be easily configured to a suitable size is a
right angle header such as AMP 4-103801-0 available from TYCO
Industries of Menlo Park, Calif.
[0084] Referring now to FIG. 4, an example implementation of the TE
portion of an embodiment of the invention. One skilled in the art
will appreciate that in many cases a single TE circuit block may be
associated with a single telephone instrument 20'' location.
However, it may also be convenient to configure two or more TE
circuit blocks within a single assembly such as may be useful in a
multi-user kiosk application.
[0085] Further, one skilled in the art may appreciate an
arrangement where two or more TE circuits blocks may connect via
one or more IW telephone line 17''' pair to a single HE circuit
block so long as the audio frequency channels, which would
effectively be in parallel, are either not utilized or that this
parallel operation is beneficial, or at least not detrimental, to
the end application and that the signaling encoding is such that
the presumed, but optional, external devices connected to their
respective signaling connectors 90' in FIG. 4 may beneficially
utilize the common HE external signal 41 and connector 30 of FIG.
2.
[0086] Further one skilled in the art may appreciate that with an
appropriate configuration of signals 89 and an appropriate one or
more connector 90 of FIG. 2 multiple external devices may
conveniently share the power and signaling capabilities afforded by
the present implementation. One example of such an implementation
is the beneficial operation of two or more biometric or other
identification equipment associated with a single telephone 20'
location. In embodiments, identification equipment may include a
biometric device, a barcode scanner, a magnetic strip reader, a
radio frequency identification tag reader, a camera, or a
microphone. Examples of biometric devices that may be implemented
at the location of telephone equipment 20' include but are not
limited to a fingerprint reader, an iris scanner, a retina scanner,
and a palm scanner.
[0087] Connector 18'' is most often an industry standard telephony
connector. A single Tip and Ring pair would thus typically use an
RJ-11 style jack. A suitable SMD device for a single channel
connector is Molex part number 085513-5014 available from Molex
Corporation of Lisle, Ill.
[0088] Optional item 71', Protection Circuit, must take into
account the low ESR nature of the main power source of the
implementation. The primary function of this protection circuit is
to limit current through the terminals of the input conductor pair
70' to a value that will protect the TE circuitry should some
unintended external power source be connected across terminals 18''
or the conductors of IW 17'''. If particular implementation and
installation conditions preclude such an event, fuse elements 91,
92 may be omitted. For the purposes of the example implementation,
the current limit was selected to be about 100 mA. Appropriate
devices for this purpose are resettable fuses 91 and 92 so that
service may be automatically restored following an event causing
the fuses to open in order to protect the system. Suitable
resettable fuses for this purpose are Raychem (TYCO) part number
TS250-130-RA available from TYCO Industries of Menlo Park,
Calif.
[0089] Contact from an inadvertent source to either TIP or RING
conductors of IW 17'' must be accommodated safely and the most
likely such source may be from a voltage as high as 200 V peak such
as from a 110 VAC hot lead. Due to the ground isolation provided by
the present implementation such a voltage has no return path to
earth associated with the TE.
[0090] As any fuse, including those utilized in this example,
requires a finite amount of time to react to an over-current
condition, additional protection may be warranted to protect the
system from the effects of very brief events such as from voltages
induced by nearby lightning strikes. If an implementation is
concerned about the possibility of such induced voltages then
optional additional protection in the form of automatically
resettable overvoltage clamp 95 is prudent. These devices typically
present no effect upon the circuit until a high voltage appears
across the input terminals 18''. The devices then quickly
transition to a low resistance state shunting the abnormal voltage
to an appropriate reference point. As these devices typically and
intentionally have quite low on-state forward voltages some small
resistance 93, 94 in series with each terminal will tend to limit
the inrush current. These optional resistors should be closely
matched so as to minimize longitudinal balance errors and should be
able to dissipate the small but finite amount of power they would
likely experience during a fault condition. An appropriate value
for these resistors is 10 Ohms, 1%, and 0.5 Watt rated. Suitable
SMD resistors for this purpose are Dale (Vishay) part number
CRCW201010R0FKEF available from Vishay Intertechnology of Malvern,
Pa. If the induced voltage persists long enough the combination of
voltage clamp 95 and series resistors 93, 94 may give the
resettable fuses 91, 92 time to open as well. A suitable active
voltage clamp for this example circuit would have a standoff
voltage of 70 Volts ensuring a breakdown voltage no higher than 90
Volts. A suitable SMD device for this purpose is Vishay part number
SMAJ70A available from Vishay Intertechnology of Malvern, Pa. If an
implementation and installation is not concerned about inadvertent
differential voltages appearing across IW 17'' conductors then
items 93, 94, 95, and perhaps 91 and 92 may be omitted.
[0091] Items 73', Low Pass Filter, similarly serves to permit the
passing of DC voltages and current from signal 72' onto signal 74'.
More specifically, this LPF serves to protect the AC electrical
signals existing on signal 72' from the shunting effect of the low
capacitive reactance of the input circuitry of power sources 75'.
Thus LPF 73' provides significant reactance at voice and signaling
frequencies while providing a low ESR in series from signal 72' to
signal 74'. In the implementation this is accomplished by the use
of a split inductor 96 where half of the windings are in series
with each the physical electrical conductors making up signals 72'
and 74'. These winding are connected, or phased, such that the two
inductances act in concert like a single total inductance with the
input capacitor 97, along with any additional input capacitance of
power sources 75', appearing across the apparent center of the
inductors halves. A suitable inductor would have significant
inductance and low DC resistance for each winding. As a suitable
inductor was not commercially available, a custom inductor was
designed and constructed on a small physical sized core and bobbin.
The inductance of each winding was about 2.5 H with a DC resistance
of less than 12 Ohms. A suitable inductor would be part number
11-5415A available from Tranex of Colorado Springs, Colo. A
suitable SMD capacitor for 97 is 220 .mu.F, 100V part number
EMVY101GDA221MMH0S available from Untied Chemi-Con of Rosemont,
Ill.
[0092] LPF items 38' of FIGS. 3 and 73' of FIG. 4 thus have
basically the same criteria of providing low resistance to DC
signals while providing significant reactance to voice and
signaling frequencies. For items 48 of FIGS. 3 and 96 of FIG. 4, an
inductor with a resistance in the 10 to 20 Ohm range and an
inductance of around one half Henry per winding has been found to
be satisfactory for this purpose.
[0093] Local Power Source 75' must operate from the available DC
input voltage and provide a low voltage bias source, typically 5.0
VDC or 3.3 VDC, but may be some other voltage or set of voltages as
may be convenient, for the electronic components and circuitry
required to implement the active functions of the implementation.
As such, this voltage/power converter must be able to operate from
the voltage provided by item 42 of FIG. 2 which may be a nominal
-48 VDC. One skilled in the art will recognize that even if item 42
of FIG. 2 is a nominal -48 VDC, particularly if 42 of FIG. 2 is
implemented as a storage battery and battery charger , this source
voltage may vary over a range of perhaps 40 VDC to near 60 VDC. Due
to the resistive losses inherent in Item 17'', the input voltage
seen by Item 75' may be substantially lower than even this, perhaps
as low as 10 to 20 VDC. Therefore, 75' must be of as high an
efficiency as practicable and in the implementation is implemented
as a Buck type switch mode power controller. Due to the potentially
wide range of input voltages seen by this controller, the
controller must be able to operate over this same input range of
voltages, such as an example of 10 to 60 VDC. It is further
desirable for this controller to require a minimum of `external to
the controller` components such as external switching transistors.
A suitable controller for this purpose is National Semiconductor
part number LM5574MT available from National Semiconductor of Santa
Clara, Calif. A suitable inductor for use with this controller in
this application is a dual winding inductor connected such that one
winding is utilized as the buck inductor as described in National
Semiconductor application notes for this controller while the
second winding is configured to provide the operating bias voltage
for the controller. A suitable SMD inductor for this purpose is
Coiltronics (Cooper Bussmann) part number DRQ74-151-R available
from Cooper Bussmann of St. Louis, Mo. One skilled in the art will
appreciate that if two or more separate voltages are required for
such bias supplies, then either separate, parallel input, SMPSs may
be used, or generally it would be more practical to set the SMPS to
deliver the highest such voltage and then use small linear
regulators to drop this voltage to the remaining lower bias
voltages.
[0094] Low Pass Filter 78' serves to pass voice frequencies
bi-directionally between signal 72' and elements of 80'. In
contrast with BPF 34' in FIG. 3, LPF 78' must pass DC current as
this current is required to power a telephone or similar function
instrument 20'' if such an instrument is used by the
application.
[0095] Items 34' in FIGS. 3 and 78' in FIG. 4 otherwise have
similar frequency characteristics and are implemented in the
present example by the same components as those described for BPF
34' in FIG. 3. For reference, suitable inductors are Coilcraft part
number RFB0810-183L available from Coilcraft of Cary, Ill. A
suitable SMD capacitor is Panasonic part number ECW-U1683JC9
available from Digikey of Thief River Falls, Minn.
[0096] Item 80', Constant Current Limiter, Ring Generator, and
Off-Hook Detector, item 80 in FIG. 2, is shown in more detail being
depicted as separate functions Constant Current Limiter 103, Ring
Generator 108, and Off-Hook Detector 109.
[0097] Constant Current Limiter 103 is provided in the
implementation by the application of a voltage regulator of
sufficient power dissipation and input voltage capability
configured as a constant current source including a small resistor
to set the desired current, an appropriate capacitor as required by
the regulator for stability, and a larger audio frequency bypass
capacitor in parallel with the resulting circuit to provide an
electrically noise free current source. A suitable linear regulator
for this purpose is National Semiconductor LM337T available from
National Semiconductor of Santa Clara, Calif. A resistor of 56.2
Ohms, 1%, is used in the implementation to configure this regulator
as a 22 mA current source (no current will flow if item 20'' is not
connected and on hook). A suitable SMD resistor is Yageo part
number RC0805FR-0756R2L available from Yageo USA of San Jose,
Calif. A suitable SMD capacitor for stability is Kemet part number
T491A105M016AT available from Kemet Corporation of Simpsonville,
S.C. A suitable SMD capacitor for electrical noise suppression is
Chemi-Con part number EMVE101ADA330MJA0G available from United
Chemi-Con of Rosemont, Ill. If the source voltage made available
from 36 of FIG. 2 is greater than 48 volts, an LM337 could be
forced to dissipate more power than that for which it is specified
and this function would be replaced by, for example, a SMPS
regulator configured to provide the same resulting current.
[0098] Item 84', Option Ring Indicator, if needed by the intended
application, may by implemented by the use of a pair complementary
outputs of item 77' to drive a ceramic resonator at the resonators
design frequency. A suitable ceramic resonator is Kyocera part
number KBS-20DB-2P-0, available from Kyocera International of San
Diego, Calif., which is designed to operate at 2 KHz and up to 10 V
peak to peak. In this case, the controller would provide both the
driving pattern and voltage to produce an appropriate audible
signal.
[0099] Ring Generator 108, if needed by the intended application,
may be implemented by a custom circuit such as an appropriate
circuit based upon use of Unitrode part number UCC3752 available
from Texas Instruments of Dallas, Tex. or based upon use of
Supertex part number HV430 available from Supertex of Sunnyvale,
Calif. It may be convenient to simply use an off the shelf ring
generator module for this function. A suitable module is PowerDsine
part number PCR-SIN06V48F00 available from Microsemi of Irvine,
Calif.
[0100] Off-Hook Detector 109 may be a circuit comprised of an
optocoupler in combination with a resistor in parallel with the
optocoupler LED such that the combination requires at least 5 mA,
by standard practice, before the LED causes the optocoupler output
transistor to activate. The LED, with parallel resistor, is
connected in series with one lead of the telephone output connector
observing the required polarity of the LED. A suitable SMD
optocoupler is NEC part number PC2913-1-F3 which exhibits a nominal
LED forward voltage drop of 1.1 V available from California Eastern
Laboratories of Santa Clara, Calif. An appropriate value for the
shunting resistor for use with this optocoupler is 160 Ohms and may
be a SMD 1/8 W device due to the voltage limiting action of the
optocoupler LEDs along with the 22 mA current limit provided in the
implementation. A suitable SMD resistor is Yageo part number
RC0805FR-07160RL available from Yageo USA of San Jose, Calif. A
suitable output transistor pull up resistor may have a value of 10
K Ohms. A suitable SMD resistor is Yageo part number RC0805J-0710KL
available from Yageo USA of San Jose, Calif. If longitudinal
balance is particularly critical in a particular application, then
it may be advisable to use two optocouplers as above, along with
each optocoupler LED shunt resistor, where one optocoupler is in
series with each of the telephone output leads observing LED
polarity requirements. These optocoupler output transistors may be
connected in parallel in this case and share a single pull up
resistor and signal connection to the associated controller
77'.
[0101] Connector 87' may be an industry standard telephony
connector. A single Tip and Ring pair would thus typically use an
RJ-11 style jack. A suitable SMD device for a single channel
connector is Molex part number 085513-5014 available from Molex
Corporation of Lisle, Ill. However, particularly if the device used
as instrument 20'' is something other than a standard telephone,
some other type of connector may be more suitable.
[0102] High Pass Filter 81' is functionally the same as HPF 42' in
FIG. 3 and thus may utilize the same components. For reference,
suitable SMD capacitors are Panasonic part number ECW-U1C334KC9
available from Digikey of Thief River Falls, Minn.
[0103] STC 77' is functionally similar to and uses the same or a
microcontroller similar to that suggested for STC 27' in FIG. 3.
STC 77' is provided with resistors 112-115 to bias input signals
for analog functions within the working limits of the
microcontroller device. For reference, an appropriate
microcontroller is Cypress Semiconductor part number
CY8C27443-24PVXI available from Cypress Semiconductor of San Jose,
Calif. Configuration and programming tools are provided by Cypress
Semiconductor for this series of microcontrollers. Appropriate SMD
resistors are Yageo part number RC0805J-0710KL available from
Digikey of Thief River Falls, Minn.
[0104] Item 90', Connector, would typically be application
dependent so as to provide a physical connector most convenient for
the intended installation or user. As the implementation
anticipates that the auxiliary output voltage to be within SELV
limits, and even commonly to be less than 15 VDC at the power
connector, if separate from any auxiliary signal termination, may
be of the common pin and sleeve type. A suitable connector is CUI
part number PJ-102A available from CUI Inc of Tualatin, Oreg.
However, if the external device also utilizes the additional
signaling capabilities, then a more suitable connector would likely
accommodate both the auxiliary output voltage and unidirectional or
bidirectional signal or signals 89' in a single physical device. A
common connector that may be easily configured to a size suitable
for a specific implementation is a right angle header such as AMP
4-103801-0 available from TYCO Industries of Menlo Park, Calif.
[0105] One skilled in the art will appreciate that the preceding
example, including several component specifications, was intended
to utilize a TB voltage of -48 VDC as described. If, however, the
additional benefits afforded by a design utilizing a higher TB
voltage, for example, up to the 120 VDC ELV limit, then appropriate
component and sub-circuit ratings would have to be selected to be
compatible with the higher voltage chosen.
[0106] Referring now to FIG. 5, an example implementation of the
primary firmware functions of the HE portion of an embodiment of
the invention. It is convenient to assume that the auxiliary or
external device signaling functions are likely to occur either more
frequently, at a greater rate, or should be more responsive to
update requests than, for example, the needs relating to basic
telephony functions such as ringing or on or off hook transitions.
Thus FIG. 5 depicts a simplified overall flow diagram that gives
priority to the exchange of external device (auxiliary) signals
between connectors 30 and 90 of FIG. 2.
[0107] Head End flowchart FIG. 5 depicts the execution logic of a
Head End device embodiment. The start point for the logic is the
Begin symbol 200 that is the logical equivalent of the End symbol
211, the designation of the endless logic loop
[0108] Item 200 is the entry point for implementation of the
firmware functions of the HE portion of an embodiment of the
invention. The overall process described below may be executed
within STC 27' of FIG. 3. The upper portion of FIG. 5 depicts an
embodiment of a mechanism to address changes occurring at the HE
and to encode and forward those changes to a TE embodiment.
Likewise, the lower portion of FIG. 5 depicts an embodiment of a
mechanism to address encoded signals received from a TE embodiment
and to decode those signals to specific signals related to items
within or connected to the HE embodiment.
[0109] As indicated in the figure, a first decision point 201
determines if any input signals of signal 30' of FIG. 3 associated
with an external, that is an auxiliary, device have changed during
the interval since the prior execution of the process herein
described. If a change has occurred as determined by 201, then
process step 202 is executed wherein the change detected, or the
resulting new state, is encoded by STC 27' of FIG. 3 onto the one
or more carrier signals, and functionally transmitted onto IW 17''
of FIG. 3 towards STC 77' of FIG. 4. When process 202 is complete
control passes to decision 203. If decision 201 determines that no
input signals of signal 30' have changed then control passes
directly to decision 203 without executing process 202.
[0110] If decision 203 determines that the state of Ringing
Detector signal 26' of FIG. 3 has changed then process 204 is
executed wherein the change detected, or the resulting new state,
is encoded by STC 27' of FIG. 3 onto the one or more carrier
signals, and functionally transmitted onto IW 17'' of FIG. 3
towards STC 77' of FIG. 4. When process 204 is complete control
passes to decision 205. If decision 203 determines that signal of
signal 26' has not changed then control passes directly to decision
205 without executing process 204.
[0111] Decision 205 determines if new encoded signals have arrived
from IW 17'' of FIG. 3. If decision 205 determines that no new
encoded signals are available to decode then control passes to 211,
and the entire process embodiment of FIG. 5 is complete. If
decision 205 determines that some new encoded signals are available
to decode then control passes to 206.
[0112] Decision 206 determines if the new encoded signals include
new information or new states directed towards an external or
auxiliary device connected to connector 30' of FIG. 3. If decision
206 determines that no new signals are directed towards an external
or auxiliary device then control passes to 208. If new encoded
signals directed towards an external or auxiliary device are
determined to be available then process 207 will decode the new
signal or signals onto output signal portions of signal 30' of FIG.
3. When process 207 is complete control passes to decision 208.
[0113] Decision 208 determines if the new encoded signals include a
request to activate or deactivate relay 23' of FIG. 3 in the HE
embodiment. If decision 208 determines that a request to deactivate
relay 23' of FIG. 3 has been received, then process 209 will cause
signal 29' of FIG. 3 to de-energize relay coil 28' of FIG. 3 to
effectively disconnect coupler 31' of FIG.3 from the SWC signals on
signal 15'' of FIG. 3. When process 209 is complete control passes
to decision 211, and the entire process embodiment of FIG. 5 is
complete. If decision 208 determines that a request to activate
relay 23' of FIG. 3 has been received then process 210 will cause
signal 29' of FIG. 3 to energize relay coil 28' of FIG. 3 to
effectively connect coupler 31' of FIG.3 to the SWC signals on
signal 15'' of FIG. 3.When process 210 is complete control passes
to decision 310 and the entire process embodiment of FIG. 5 is
complete.
[0114] Referring now to FIG. 6, an example implementation of
firmware functions of the TE portion of an embodiment of the
invention. With assumptions similar to those mentioned above, FIG.
6 depicts a simplified overall flow diagram that gives priority to
the exchange of external device (auxiliary) signals between
connectors 30 and 90 of FIG. 2.
[0115] Head End flowchart FIG. 6 depicts the execution logic of a
Tail End device embodiment. The start point for the logic is the
Begin symbol 200 that is the logical equivalent of the End symbol
211, the designation of an endless logic loop.
[0116] Item 300 is the entry point for implementation of the
firmware functions of the TE portion of an embodiment of the
invention. The overall process described below may be executed
within STC 77' of FIG. 4. The upper portion of FIG. 6 depicts an
embodiment of a mechanism to address changes occurring at the TE
and to encode and forward those changes to a HE embodiment.
Likewise, the lower portion of FIG. 6 depicts an embodiment of a
mechanism to address encoded signals received from a HE embodiment
and to decode those signals to specific signals related to items
within or connected to the TE embodiment.
[0117] As indicated in the figure, a first decision point 301
determines if any input signals of signal 89' of FIG. 4 associated
with an external, that is an auxiliary, device have changed during
the interval since the prior execution of the process herein
described. If a change has occurred as determined by 301, then
process step 302 is executed wherein the change detected, or the
resulting new state, is encoded by STC 77' of FIG. 4 onto the one
or more carrier signals, and functionally transmitted onto IW 17'''
of FIG. 4 towards STC 27' of FIG. 3. When process 302 is complete
control passes to decision 303. If decision 301 determines that no
input signals of signal 89' have changed then control passes
directly to decision 303 without executing process 302.
[0118] If decision 303 determines that the state of Off-Hook
Detector signal 88' of FIG. 4 has changed, then process 304 is
executed wherein the change detected, or the resulting new state,
is encoded by STC 77' of FIG. 4 onto the one or more carrier
signals and functionally transmitted onto IW 17''' of FIG. 4
towards STC 27' of FIG. 3. When process 304 is complete control
passes to decision 305. If decision 303 determines that no input
signals of signal 88' have changed, then control passes directly to
decision 305.
[0119] Decision 305 determines if new encoded signals have arrived
from IW 17''' of FIG. 4. If decision 305 determines that no new
encoded signals are available to decode then control passes to 310,
and the entire process embodiment of FIG. 6 is complete. If
decision 305 determines that some new encoded signals are available
to decode, then control passes to 306.
[0120] Decision 306 determines if the new encoded signals include
new information or new states directed towards an external or
auxiliary device connected to connector 90' of FIG. 4. If decision
306 determines that no new signals are directed towards an external
or auxiliary device then control passes to 308. If new encoded
signals directed towards an external or auxiliary device are
determined to be available then process 307 will decode the new
signal or signals onto output signal portions of signal 89' of FIG.
4. When process 307 is complete control passes to decision 308.
[0121] Decision 308 determines if the new encoded signals include a
request to activate or deactivate alerting equipment that may be
included in the TE embodiment. If decision 308 determines that no
new alerting function change signals are included in the new
signals then control passes to 310. If decision 308 determines that
new alerting function change signals are included in the new
signals then process 309 will enable, disable, or cycle the
alerting, or ringing embodiments that may be included in the TE
embodiment via signal 83' and/or signal 85' of FIG. 4. When process
309 is complete control passes to decision 310, and the entire
process embodiment of FIG. 6 is complete.
[0122] The foregoing description has been provided with particular
reference to deployment of the invention in an incarceration
institution. However, the invention may have numerous other
advantages. For example, it can be deployed to reduce or eliminate
"wall-warts" associated with peripheral telephone devices in a
home. It can be used to enable peripheral devices efficiently in
other environments where rewiring would not be as economical. For
example, it can be used to enable camera capability at a remote
existing telephone used for screening access to a physical
facility, e.g., a commercial manufacturing facility or office
structure, the main gate of a ranch, compound or other real estate
of significant size or even with an intercom used at the door of a
residence. The invention may be useful in many other
applications.
* * * * *