Note: Descriptions are shown in the official language in which they were submitted.
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A POWER LINE TELEPHONE EXTENSION SYSTEM
HAVING TRANSMITTING CODED SIGNALS
BETWEEN PHONES IN THE SYSTEM,
_
FULL DUPLEX CONFERENCING, CALL HOLD,
5~ULTI-TELEPHONE EXTENSIONS AND INTERCOM
Background Art
The present invention relates to apparatus for
remote signaling to a telephone line over the available
AC power line. More particularly, the present invention
provides a telephone extension system for communicating
over the AC power line between telephones of the system
and a conventional telephone subscriber telephone line.
U.S. Patent No. 3,949,172 which issued April 6,
1976, entitled "Telephone Extension System Utilizing
15Power Line Carrier Signals", which is assigned to the
same assignee as the present application, describes a
system for doing very much the same thing as the system
described in the present application. That patent
describes a main (or master) station that couples the
20subscriber's telephone line to his AC power Iine and a
special extension telephone that plugs into his AC power
line at any convenient receptacle and is used to make and
receive telephone calls in a conventional manner. In
that patent, the extension telephone includes a hand set
2swith a microphone at one end and an earphone at the other
with separate lines from each. The line from the
microphone feeds a radio frequency (RF) transmitter and
the line to the earphone comes from an RF receiver. A
corresponding RF transmitter and RF receiver are provided
30at the main station. These transmitter-receiver --
combinations enable full duplex signalling of voice and
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other signals between the main station and the extension
telephone over the AC power line.
The power line, RF carrier extension telephone
system in Patent No. 3,949,172 is not immune to
interference from RF signals (in the same RF frequency
range) on the AC power line that come from other sources,
such as another telephone subscriber's power~line carrier
extension telephone system. It is an object of the
present invention to provide such a power line carrier
10 telephone extension system with improved protection
against interferences by RF signals from other sources on
the same AC power line.
Also, the system in Patent No. 3,949,172 is not
immune to eavesdropping by others who have access to the
15 same AC power line. It is another object to provide
protection against such eavesdropping.
Signalling for other purposes than ordinary
telephone usage between a conventional subscriber's
telephone line and various kinds of transmit-receive
20 devices over the available AC power line are described in
U.S. Patent No. 4,058,678, entitled "Remote Signaling to
a Telephone Line Using Power Line Carrier Signals" (also
assigned to the same assignee as the present
application). That patent describes a system whereby
25 appliances or other electrical equipment on the AC power
line at a premises can be controlled by an incoming
telephone call to the premises. The incoming telephone
call brings control signals to the premises and these
signals are carried by an RF carrier over the power line
30to the location of an appliance, for example, to turn the
appliance on or off. The same patent describes a system ~ ~
for sending an alarm from the premises For example, a
fire detector in the premises plu~ged into the power line
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sends an RF alarm signal over the power line to the
telephone where it initiates operation of the telephone
to call a predetermined number and deliver a pre-recorded
message. Clearly, other RF signals from other sources on
the same power line may interfere with the intended
signals or cause a false or unintended response at the
appliance. The interfering signals may interfere by
accident or chance or the interference may result from
intentional mischief by another on the same power line.
10 In any case, the interference is to be avoided and such
mischief frustrated as much as possible. It is another,
object of the present invention to provide a technique of
signalling over the AC power line that prevents such
interference.
15 It is another object of the present invention to provide
an improved method and means of transmitting voice and
data signals over a conventional AC power line at a
typical telephone subscriber premises, whereby
interference and mischief caused by signals from other
20 sources on the same power line are avoided.
The power line, P~ carrier extension telephone
system in Patent No. 3,949,172 provides for a main (or
master) station and one extension telephone that plugs
into the AC power line at a power line receptacle. That
25 system can accommodate more than one extension telephone
and if all transmit at the same extension RF carrier
frequency, the main can respond to any_one of them.
However, the single receiver at the main can respond to
only one extension carrier at a time. A specific embodi-
30 ment described in the present invention provides such a
power line carrier telephone extension system including ~-
several extension telephones that all can operate at the
same time and engage in full duplex communication with
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each other and with the telephone line on telephone calls
placed or received by any of the telephones of the system
and all can initiate telephone line call hold.
It is a further object of the present invention to
provide in such a multi extension telephone system as
described in the specific embodimeIIt hereof, means
whereby all of the e~tension telephones are capable of
initiating telephone line call hold.
In conjunction with any of the above objects, it is
10 further object to provide a secured communication system
wherein the system signals are coded to distinguish them
and the analog signals accompanying them from interfering
signals.
It is another object to provide a multi telephone
15 extension system for a telephone subscriber's premises
wherein system phones are capable of initiating telephone
line call hold, conferencing between the system phones
and other functions, such as the I, P and S functions
described herein, over a two element intra-premises
20 transmission line.
It is desirable where two or more of such systems
are installed in a premises to integrate them with a
single main station. Therefore, it is another object of
the present invention to provide a technique of integrat-
25 ing such systems so that the satellite stations of bothsystems can be operated simultaneously.
It is another object of the present_invention to
provide a technique of integrating or combining several
such meter reading systems with each other and/or with an
30 appliance control and/or an alarm system such as
described above so that a single main station at the ~-
telephone line serves all the systems.
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It is an object of the present invention to provide
a power line carrier telephone extension system including
several extension telephones that all can operate at the
same time and engage in full duplex communication with
5 each o-ther without going on the telephone line
(Intercom), while at the same time, any of the system
telephones not engaged in such intercom communication can
place or receive calls from the telephone line.
It is another object to provide means for signalling
l0tO the system telephones while they are engaged in
intercom communication, that an outside telephone call is
received so that any or all of those telephones can
answer the outside call.
It is another object to provide a multi-telephone
15extension system for a telephone subscriber's premises
capable of Intercom and conferencing between the system
phones and capable of other functions, such as Hold,
Privacy and Special functions, as they are defined
herein, over a two element intra-premises transmission
20line between phones of the system.
Disclosure of the Invention
The present invention is applicable to simplex or
duplex communication between remote transmit-receive
(TX-RX) devices over the available power line in a
2spremises or over a two element intra-premises
transmission line. The communicated signals are
processed before transmission and upon reception to
eliminate or block at the receiver interfering or
mischievous signals from other sources. The remote TX-RX
30device may be a telephone or it may be a data lin]c modem, _
or a utility meter specially equipped to respond to
interrogation signals from the telephone line by
transmitting back meter data signals. In a preferred
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embodiment of the present invention, the system transmits
voice and/or other data over the AC power line by modu-
lated RF carrier.
The preferred embodiment, described in detail herein
is a telephone system for use with a conventional tele-
phone line at a subscriber's premises, using the avail-
able AC power line in the premises for transmitting voice
and/or data signals simultaneously in both directions
(full duplex) between the several extension telephones of
10 the system and the subscriber's telephone line. In this
embodiment, the extension telephones of the system plug
into conventional AC power line receptacles at the
premises. Thus, this telephone extension system is
particularly sensitive to RF signals from other sources
15 on the same power line. For example, an AC power main
services many premises and the only barrier to RF signals
on the power main between the main and the power line in
a premises may be the elec~ric meter of the premises.
This barrier is usually no greater than barriers within
20 the premises such as across the two phases of the
premises power line. Thus, RF launched into the ~C power
line at a premises is likely to flow to the main and into
the power line of a neighboring premises and interfere
with a power line communications system in the neighbor-
25 ing premises, and visa-versa.
It is a particular object of the present invention
to provide such a telephone extension system including
several extension telephones all communicating over the
power line that is normally available at a telephone
30 subscriber's premises, which provides all conventional
telephone usages. ~~-
It is another object to provide for a conventional
telephone line at a telephone subscribers premises that
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is also a private system for communicating with the
telephone line, via the available power line in the
premises and not subject to power line interference.
It is another object to provide for a conventional
5 telephone line, a subscriber end data link or modem which
is private, for communicating with the telephone line via
the available power line in the premises.
It is another object to provide a full duplex
private multi-extension communication system for communi-
cating with the conventional telephone line to a premises
through the available power line at the premises.
In conjunction with any of the above objects, it is
further object to provide such a secured communication
system wherein the system signals are coded to
15distinguish them from interfering signals and the codes
are readily set by the user.
Other objects, features and advantages of the
present invention will be apparent in view of the
following descriptions of specific embodiments which
20represent the best known uses of the invention and are
described herein with reference to the drawings.
Brief Description of the Drawin~s
Figure 1 is an electrical block diagram showing a
generic transmit-receive system for transmitting voice
25and/or other data signals over conventional AC power line
such as at a typical residence and incorporating means
for coding the signals and analyzing the received coded
signals to enable readily distinguishing the received
signals from interfering signals;
30 Figure 2 shows waveforms A to D as illustrations of __
the technique of coding;
Figure 3 is an electrical block diagram showing a
generic, multi-station, ,ull duplex system for
transmitting voice and/or other data sisnals over a
conventional AC power line such as at a typical residence
and incorporating the features shown and described with
reference to Figs. 1 and 2:
Figure ~ is a pictorial representation of a power
line carrier telephone extension system incorporating
features of the present invention and including a main
~elephone and one or more extension telephones that
communicate with each other and the telephone line over
10 the AC power line and have Intercom (I~, Hold (H),
Privacy (P) and Special (S1 features of operation in
addition to al.l conventional telephone operations;
Figure 5 is an electrical block diagram showing the
principle electrical subsystems of the main telephone of
15 the system;
Figure 6 is an electrical block diagram showing the
principle electrical subsystems of one of the extension
telephones of the system;
Figures 7 to 11 are tables showing the status of
20 operation of the main (M) and extension (El and E2)
telephone subsystems for functions and routines including
the following: communicating in the telephone line (TL)
mode; M, El, and/or E2 in the intercom (I) mode; placing
a TL call on hold (H), imposing privacy (P) between two
25 phones in the I mode or between any phone and the TL; and
using the special (S) function for automatic redialing of
last number dialed and automatic dialing from a repertory
of stored telephone numbers. In particular, these
figures show:
Fig. 7 - Answer call from TL by El or E2;
Place call to TL by El or E2; and ~-
Conference El, E2 and ~-l on TL call.
Fig. 8 - I mode between ~l and El and/or E2;
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g
I mode between E1 and E2; and
I mode between El and E2 while M on TL
Fig. 9 - H the TL while M and E1 and/or E2 in I
H the TL while El and E2 in I.
Fig. 10 - P between M and TL;
P between M and E1 and E2 and TL;
P between El and E2 and TL; and
P between M and TL, while El and E2 in I.
Fig. 11 - S used by M - last nurnber redial;
S used by M - dial stored number;
S used by E1 or E2 ~ last number redial;
and
S used by El or E2 ~ dial stored numberO
Figure 12 is an electrical diagram showing the main
15 telephone power line coupler circuit, for connecting the
main telephone to the power line;
Figure 13 is an electrical diagram showing the
extension telephone power line coupler circuit that
connects an extension telephone to the AC power line;
Figure 14A, B, C, D, and E show electrical details
of the key pad in the main telephone; and
Figures 15A, B and C show electrical details of the
key pad in an extension telephone;
Figures 16 and 17 show electrical details for the
25 extension address set switches at the main and extension
telephones, respectively; and
Figure 18 shows electrical details of the dual
(dial) tone multi frequency (DTMF) main and system
generators in the main telephone.
30 Best Mode of Carrying Out the Invention
Description of Generic Embodiments of the Invention --
.,
l~hile the present invention has particular use in a
power line carrier telephone extension system to reduce
the effects of interfering RF signals on the power line
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whether they are from neighboring power line carrier
telephone extension systems or from other sources or
mischievous signals intentionally launched into the AC
power line to interfere with the user's power line
5 carrier telephone line extension system, it should be
understood that the techniques applied in the specific
embodiment described herein have useful application in
any transmission line system, local area network system,
or, other power line carrier systems. For such general
10application, a generic embodiment of the present
invention is described herein.
Simplex Two Station System
Turning first to Figure l there shown a block
diagram of a power line transmit-receive (TX-RX) system
15for the simplest case, simplex signalling ~rom one
station on the AC power line in a premises to another
station on the AC power line (or on any two element,
intra-premises transmission line). As wil' be shown in
connection with Figure 1, the first station, the
20transmitter station 201 generates analog signals and
digital CODE signals including, for example, an address
byte, a code byte and a checksum byte, combines this CODE
with the analog signals and transmits the combination as
DATA by RF carrier over the AC power line 202 in the
25premises. The other station, the receiver station 203,
first detects the RF carricr and then demodulates the
received signal, and detects and examines the CODE and
sends the code byte and the analog part of the signal on
to a utilization device depending on whether or not the
30following conditions are met: _
(a) the RF power level of the detected carrier is at ~-
a prcdetermined minimum value;
(b~ in-the CODE, the address and code bytes match
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the checksum byte;
(c) the address byte satisfies the stored address at
the receiver; and
(d) the code byte ma~ches one of the stored codes at
the receiver.
Figure 2 shows a set of waveforms A to D that
illustrate one technique of screening undesirable
interfering signals by coding transmitted data. In
Figure 2, waveform A shows a transmission interval,
10 called the TX interval that is ordered at the transmitter
station 201. ~aveform B shows a complete signal interval
called the T~DATA interval, within the TX interval.
TXDATA includes analog voice signals called VOICE follow-
ing the code message called CODE. TXDATA begins for a
15 few milliseconds with the special CODE signals. The TX
and TXDATA normal or "resting" state (off) is high when
the transmitter is turned off. The transmitter 201TX is
ordered to send a TXD~TA message when the CODE message
from the transmitter (TX) computer 208 goes low and
20 remains there for five milliseconds (5 ms). This indi-
cates to the transmitter that a voice message, VOICE, is
coming from the source 204. After this 5 ms interval,
the transmitter returns high for no less than 5 ms and
the next falling edge is the start of the first bit of
25 the CODE, called a CODE CELL.
Consider, for example, where the RF carrier
frequency is 120 KHz and, the CELL is 156 cycles long.
Waveform C shows waveform B expanded in time and waveform
D shows a CELL of C expanded in time. The CODE CELL
30Width is then 1.3 ms. Then, let the pulse width of each
cell be modulated 33%/66~ as shown in waveform D. This ~ ~
gives a minimum pulse width of 0.43 ~s. Then, let the
CODE protocol be: address byte, code byte and checksum
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byte, each eight CELLS long. Furthermore, in this
protocol, unused CELLS of the address will be zero. The
checksum seed is 00. So all three bytes add to zero
ignoring the carry. This gives a CODE message length of
~24x1.3) + 5 milliseconds = 37 milliseconds at the
beginning of the VOICE message.
At the receiver 203RX, after filtering in filter
214, RF carrier threshold detection in 220, demodulating
in 216 and filtering in 217, the received CODE is ready
10 for examination and is in the same ~orm as sent. This
means that the polarity of the impulses of the CODE is
the same as sent. The receiver at 203 continually
monitors reception of RF carrier and in the absence of
carrier, produces a high signal similar to the high shown
15by the waveform B. The receiver program responds to a
low from its monitor, indicating that RF carrier in the
system band pass at a predetermined minimum power level
is present, and when this low occurs, it immediately
switches to a receiving routine. The receiving routine
20recognizes all front edges of the demodulated RF carrier,
beginning at the start of the CODE message. First, it
inte~rates from 33% to 66% of the width of each received
CODE CELL and decides if the CELL is a binary one or
zero. If the integrated level for a CELL is high, then
25the CELL is a zero, and if it is low, then the CELL is a
one.
The CELL width, 1.3 ms, and integration over 0.43 ms
of this width is suitable for eliminating a certain kind
of RF noise that can come from the user's premises, as
30well as from outside the user's premises, and is produced
typically by light dimmers hat have silicon control ~-
rectifiers (SCR) as the controllable variable element
therein for controlling power--to a light, because such
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SCR's typically produce impulses a few microseconds
duration at 8.33 ms intervals. The receiver has high
immunity to such noise from SCR's, because the CEI,L
integration action is much slower than the SCR impulse
5 duration, integration is over a much longer intervai
(0.43 ms) than the impulse interval and the intervals
between impulses is much longer than a CE~1 width. The
received VOICE portion OF THE DATA does not interfere
with the CODE, because of the lower modulation level of
10VoICE.
Turning again to Figure 1, the transmitter station
201 includes a source of sig~al 204 which may be analog
voice or other data and a signal compressor 206 that
enhances transmission by compressing the amplitude level
5Of the source signals which has advantages in a frequency
modulated carrier transmission system. To the output of
the compressor 206, in summing circuit 207, is added the
CODE and so VOICE and CODE are combined as shown in
waveform 2B to form the TXDATA signal. As mentioned
20above, the CODE may be, for example, the 3 byte code
shown in waveform 2C and include the address byte, the
code byte, and the checksum byte, each eight bits long,
occupying 37ms of the total TXDATA message. This message
is fed to the transmitter RF oscillator and modulator 209
25and the modulated carrier is fed to the transmitter power
amplifier 211 via switch 210 which is controlled by the
transmitter (TX~ computer 208. By this switch the TX
computer turns the transmitter 201TX, on and off,
depending on a predetermined criteria met by the signal
30from the source.
The output from the transmitter, in line 211a from ,~-
power amplirier 211 is fed to the premises AC power line
202, via the transmitter power line coupler 212. This
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coupler may perform as a filter-directional coupler and
include an absorbing load to protect the transmitter from
RF from the power line.
At the receiver, station 203, RF from the
5 transmitter is coupled from the power line 202 by coupler
213 and fed to the receiver 203~X that includes an input
filter 214 (which may, for example, be a band pass
filter), to limiter 215 and demodulator 216. The output
of the demodulator, called RXDATA, is fed through output
10filter 217 (which may, for example, be a low pass
filter)to two stages of audio amplifiers, 218 and 219 and
from the second stage to expander 225, via switch 224,
producing the receiver output in line 225a. From the
output of the second stage audio amplifier 219, the
15received RXDATA is compared with a reference signal level
by code detect circuit 222 that adjusts the pulse level
of the RXCODE portion of RXDATA so that it is suitable to
feed to the receiver (RX) computer 223. Meanwhile the
received RF in the output of the band pass input filter
20214 is processed by a carrier level detection circuit
and switching amplifier 220 that produces a carrier
status on/off signal suitable for the RX computer 223. A
similar signal from the carrier level detection circuit
220, the squelch signal, is fed to code detect circuit
25222 to squelch its output in case the RF carrier status
level is off. Thus, the receiver up to this point
screens the received carrier power level and squelches
any detected CODE in case the RF level criteria is not
met.
30 The RX computer 223 is programmed to perform the --
examination of the received message RXCODE that includes -~
the address byte, code byte and the checksum byte. The
computer integrates from 33% to 66~ OL each CODE CELL
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and decides if the CEL~ is a zero or a one. It then adds
the address, code and checksum bytes (without carry) and
if the sum is zero, it produces an enable; or if not
zero, it produces a disable signal that turns switch 224
5 off. In addition to this, the receiver computer examines
the contents of the address byte, the contents of the
code byte and it compares them with preset numbers in the
computer. If they both compare, i.e., match up, then
the disabled-enable signal to switch 224 is not changed.
10However, if they do not compare and the signal to the
amplifier is enable, then that signal is switched to
disable. In this way, the computer checks the received
address and code to be sure that it is received as sent
and then correlates them against stored address and code
15numbers and if the check and the correlations are all
satisfied, the RXDATA is fed through switch 224 to
expander circuit 225 and then to voice signal utilization
device 226. At the same time tor instead) the correlated
code byte may cause the computer to send an initiating
20signal to the code byte utilization device 227.
All signals in the output of the second stage audio
amplifier 219 are fed to expander circuit 225, producing
the receiver output that is fed to the signal utilization
device 226. The function of the expander is to return
25the full dynamic range of the received data (VOICE)
signals and so compensate for the compression that
occurred at the transmitter. Between the switch 224 and
expander 225 may be included a summing circuit (not
shown) for adding to the VOICE signals any other signals
30Or tones that are appropriate, in view of the overall
uses and functions of the system. Such tones and signals -~-
may be stored or generated in the RX comDuter and are -
selected depending on the code byte of the received
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signal. Adding signals in this way is a function of the
RX computer in the specific embodiment of the present
invention, a power line carrier telephone extension
system, that is described in detail herein.
Full Duplex Multi Station System
The generic signalling technique described with
reference to Figures 1 and 2, as already mentioned, has
particular application and use in a premises such as a
residence, in a system within the residence that signals
over the available AC power line and so the system
requires screening against interfering signals that may
originate from neighboring premises on the same power
line main. The techniques described herein have appli-
cation to a multi-station system in the premises that
is capable of simultaneous full duplex signalling be-
tween all of the stations of the system and so each
station includes a transmitter and a receiver and a
computer with pre-stored programs for encoding, decod-
ing and controlling the transmitter and receiver in
accordance with the techniques shown and described
with reference to Figures 1 and 2. Such a full duplex,
multi station (more than two) system is shown in
Figure 3. The transmitters and receivers in Figure 3
may be constructed and operate the same as the
transmitter 201TX and the receiver 203RX of Figure
1 and, where that is the case, they are referred
to by those reference numbers without further detail.
The station computers in Figure 3 are all referred to as
TX-RX computers which means that they perform all of the
functions of the TX computer 208 and the RX computer 223
in Figure 1 with respect to the associated transmitter
and receiver. This is the case for all of the TX-RX
computers except the main TX-RX computer for the main
station which will be described further hereinbelow.
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Turning to Figure 3 there is shown a typical
power main 301 that includes three wires, the neutral
302 and the power wires 303 and 304 at phase one ~01)
and phase two (02) . The phases are, for example, 180
apart and the RMS voltage from the neutral to either
of the phases is 120 volts at 60 Hz and so the RMS
from phase one to phase two is 240 volts. Note that
for illustration purposes, 120 volts 60 Hz iS shown
herein, the system is equally applicable to, for ex-
ample, 240 volts 50 H2 application or other mains
distribution voltages. From the power main 301, a three
wire line 305 feeds the premises through the premises
electrical power meter 306 to the premises AC power
line, denoted generally 202 ( as also in Figure 1). For
15 purposes of illustration, the power line 202 is rep-
resented by three wires, the neutral 202~, the phase
one wire 20201 and the phase two wire, 202~2. Within
the premises are six satellite stations, herein called
stations I, II, III, IV, V and the main, called M, that
20 all couple to one or the other phase of the premises AC
power line 202. The stations I to V are denoted 311 to
315 and the M station is denoted 316.
The stations I to V may all be identical except
for the carrier frequency that each transmits, referred
25 to herein as RF carrier frequencies or channels Fl to F5
respectively. Hence, only station I, denoted 311, will
be described herein in detail. Station I includes a
transmitter (like transmitter 201TX) and a receiver like
(203RX of Figure 1) and so the transmitter and receiver
30 at the station bear the same reference number as inFigure
1. The transmitter and receiver are controlled and support-
ed by a computer with a stored program that does all the
functions and controls that the TX computer 208 and the
RX computer 223 perform in Figure 1 and so the computer
at the station is referred to as a TX-RX computer and is
denoted 208/223. The source of signal and the utilization
device at the station may be the same as source 204 and
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utilization device 226 in Figure 1 and so they bear the
same reference numbers. The coupler 307 from station I
to the AC power line 202 couples RF from the transmitter
to the power line, it couples RF from the power line to
5 the receiver and it may draw power from the line for a
power supply (not shown) for the transmitter, receiver
and computer at the station. The construction of this
coupler 307 is described herein with reference to the
specific embodiment, a power line telephone extension
10system, particularly with reference to Figure 13.
Each of the other stations I to V are substantially
identical TX-RX combinations as at station I, except that
they each transrnits at a different carrier frequency.
For example, station I ~ransmits the carrier frequency
15F1, station II transmits the carrier frequency F2, and so
forth. All of these stations receive the same carrier
frequency, Fm, from the main station at location 316.
Hence, the only difference between stations I to V may be
that they transmit on different channels. Otherwise,
20they all send signals from their station source and they
all use signals at their station utilization device and
the transmission and reception is full duplex between all
stations. Clearly, at any of the stations, any of these
features may be omitted and the transmission and/or
25reception at any station may be simplex or a station may
transmit only or receive only, depending on the purposes
of the total system.
At the main station 316 the transmitter 201T that
transmits on carrier frequency Fm, may be substantially
30the same as the transmitters at the stations I to V and
the same as transmitter 201T in Figure 1, except that ,~~
there is no switch like switch 205 controlling signals to
the compressor 206, because the function of the main
transmitter is not just to transmit signals generated at
the main station. The main transmitter's function is
also to relay to the receivers at all (or some) of the
other stations of the system the received data from any
5 of the transmitters of the other stations of the system.
Hence, the transmissions from the station I to V are all
received at the main station by the individual channel
receivers 321 to 325, respectively, and all data received
is combined and immediately transmitted by the main
10station transmitter 201TX to all of the stations.
Therefore, the input to transmitter -201TX is the combined
outputs of the receivers 321 to 325, plus any signals
generated at the main station from the main source 326.
The output of the main transmitter 201TX is coupled to
15the power line 202 by the main power line coupler 327.
The construction of this coupler is described herein with
reference to the specific embodlment, a power line
telephone extension system and shown in Fig. 12.
Each of the channel receivers at the main station
20316 is constructed and operates substantially as receiver
203RX already described with reference to Figure l.
Hence, the receivers 321 to 325 each include a band pass
input filter 214, a limiter 215, a demodulator 216, a low
pass input filter 217, a first stage audio amplifier 218,
25a second stage audio amplifier 219, a CODE detect circuit
222 and a carrier level detector circuit 220 that
squelches the CODE detect circuit output to the RX
computer when received RF carrier power level falls below
a pre-determined level and feeds an RF carrier status
30signal to the RX computer. The CODE and RF status
control lines from these receivers to the main TX-RX -
computer 330 are the same as the control lines from
receiver 203RX, to RX computer 223 and these lines carry
~Z~66~9
-20-
control signals that function just as already described
with reference to Figure 1.
At any of the receivers 321 to 325, when the
received RF power level compares satisfactorily with a
reference level, the detected RXCODE is fed to the main
TX-RX computer 330, via OR circuit 331. In the main
computer the TXCODE is correlated with stored signals and
if it correlates with the stored signals, the computer
immediately enables the corresponding receiver by an
10 enabling signal to the receiver output switch 331. This
switch feeds the receiver output to summing circuit 340
that sums the switch outputs of all of the receivers 321
to 325, as those outputs are controlled by the computer.
The output of summing circuit 340 is amplified by audio
15 amplifier 341 and fed to expander circuit 342 that has
the same function as expander circuit 225 in Figure 1u
The main TX-RX computer 330 is responsive to all of
the same inputs and performs all of the same functions
and controls as the TX and RX computers 208 and 223 in
20 Figure 1, It performs these functions for the main
transmitter 201TX and for all of the channel receivers at
the main station; and, in addition, it may store
predetermined data signals that may be tones, numbers,
VOICE or COD~ and are fed into the system for
25 transmission to the stations I to V at summing circuit
207 in the main transmitter 201TX, or they may be fed to
the main station VOICE utilization device 343 via line
343a or the main station CODE utilization device 346; via
line 346a, depending upon the code signals received from
30 the other five stations and/or depending upon a signal
initiated at the main station from the main source 326, -
fed to the computer via line 326a. Also, at the same
time (or instead) the correlated code byte may cause the
1216~689
-21-
computer to send an initiating signal to the code byte
utilization device 346.
At the main station, the received channel VOICE
signals from the expander circuit 342 are fed to the main
5 transmitter 201TX via summing circuit 344 and the
transmitter input amplifier 345. The purpose of summing
circuit 344 is to combine such VOICE signals originating
at the main station from the main source 326 with the
received VOICE signals for transmission to the other five
10stations~
The power line carrier systems in both Figures 1 and
3 are presented herein as generic systems, inasmuch as
they teach techniques of signalling that can be used for
any of a number of different specific applications.
15Figure 1 shows and describes a simplex unidirectional
signalling system including just two stations, one
transmits only and the other receives only. Figure 3, on
the other hand, teaches a system including a multitude of
stations all of which both transmit and receive full
20duplex and all stations can conference together and draw
upon signals stored in the main station computer for
transmission to all or selected of the other stations
depending on the address in the CODE that accompanies the
signal. Common techniques incorporated in both of these
25examples include the techniques for screening the
received signals to eliminate interfering signals whether
they originate from within the premises where the system
is used or from outside of the premises from, for
example, a neighbors premises that connects to the same
30power main 301, on the same side of the power main
transformer 301a as the premises in question. That
screening is described in detail with reference to the
6G89
-22-
operation of the system in Figure 1 and applies also in
Figure 3.
Where the power main 301 provides two phases as
shown in Figure 3, a premises that takes power from the
5 main is likely to take power from both of the phases and
so some of the electrical outlets (receptacles) in the
premises will access one phase of the power line while
others will access the other phase and so within that
premises, some of the stations are likely to plug into
10 one phase while other stations plug into the other phase.
The stations plugged into the same phase have a
relatively low attenuation transmission path between
them, whereas stations plugged into different phases have
a relatively higher attenuation transmission path between
15 them. The screening by code and address and checksum
signals, described herein, afford assurance that
interfering signals in the receiver band from a
neighboring premises will be rejected.
DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION
Figure 4 illustrates a power line carrier telephone
extension system that includes three telephones on one
telephone line sometimes referred to as a 1 x 3
telephone system. This system provides conventional
telephones services which may be either rotary dial or
25 Touch Tone type, at several locations along the AC power
line available at a telephone subscriber's premises.
Other uses include sending and/or receiving voice or data
or alarm or control signals by RF carrier over the
conventional AC power line for any purpose, including all
30purposes mentioned in this application.
As shown in Figure 4, the subscriber's premises has -
a telephone line 1 which usually consists of four wires
(not shown) called the tip line, the ring line, earth
1~166~9
ground and a fourth line for special party line ringing
circuits. The ring line is usually red, the tip line is
green, the earth ground is black and the fourth line is
yellow. As a rule, three of these lines, the tip, ring
5 and ground, connect to "on line" conventional telephones
at the premises and also connect to telephone line wall
jacks 2.
- In a conventional telephone system at a subscribers
premises, extension telephones connect to the telephone
lOline at the wall jack by merely plugging them in and any
such extension phone can engage an incoming telephone
call and can place a telephone call to the telephone
line. The system described herein provides the same
service and, in addition, provides features called:
15Intercom (I~, Hold (H3, Privacy ~P) and Special (S), that
are described more fully hereinbelow. These are all in
addition to the feature that the extension telephones of
the system can be used at any of the available AC power
receptacles in the premises and so their use is not
20restricted to where a telephone line wall jack is
provided.
In Figure 4 access to the subscriber's telephone
line 1 is at the telephone wall jack 2. The main IM)
telephone 3 of the system plugs into the jack 2 by a
25conventional (modular) telephone plug 4 at the end of
line 4a and also plugs into a nearby AC power line outlet
5 by an AC power adapter plug 6 at the end of power cord
6a. By these connections, the subscriber's telephone line
1 is linked to his AC power line, which is denoted
30generally 10. At any of the other AC power outlets
(receptacles) on his AC power line 10, the system ~~-
extension telephones can be used. For example, at 11,
extension (El) telephone 12 plugs into the power line 10
~Z16689
-24-
by its AC power adaptor plug 15, via its power cord 15a.
Similarly, at another AC power outlet 16, the system
extension (E2) telephone 17 plugs into the power line by
AC power adaptor plug 20, via its power cord 20a. The
5 system extension telephones 12 and 17 may be the same in
construction and operation except for the specific RF
carrier frequency F1 or F2 and address signals that are
set in each in conjunction with similar settings in the
main telephone 3.
In opera-ion, an incoming telephone call ring signal
in the telephone line 1 is processed through the M
telephone 3, which transmits a ring signal by the main RF
carrier frequency, Fm, (channel m) over the power line 10
and it is received by the system El and E2 phones, 12 and
1517, causing them to ring. This incoming call can be
answered by any of the system telephones, or all can
simultaneously engage the incoming call and communicate
with each other. Thus, the incoming caller and all the
system telephones can conference together. In addition,
20the incoming call is not terminated at the subscriber's
location until all of the system telephones are on hook
(cradled). Furthermore, any of the system telephone can
place a call to the telephone line, just as any
conventional phone places a call, by the phone going off
25hook and signalling the call number by using the phone's
key pad (buttons); and before, during or after this
signaling, the other phones of the system can go off hook
and join in the call. Thus, the normal operation of the
system illustrated in Figure 4 is much the same as
30conventional extension telephone operation, with the
added feature and advantage that the extension telephones ~-
of the system can be located in the premises at any
convenient AC power outlet.
:~Z~6689
-25-
Main Telephone Circuits
Turning next -to Figure 5 there is shown an overall
electrical block diagram of the system main telephone
circuits. Some of the block sub-systems shown in Figure
5 5 are shown also in greater detail in other figures that
are denoted in the blocks. Some parts of these
sub-systems are shown in more than one of the detail
figures. This is done intentionally as an aid in
understanding the details. Wherever a given part appears
lOin any figure, it bears the same reference number.
All signals that are transmitted between the main
(M) and extension (E1 and E1) phones of the system are
transmitted by RF carrier (Fm, Fl or F2~ and are called
system signals. The transmission of svstem signals is
15denoted TXDATA and the reception RXDATA,
The main telephone 3 circuits include a telephone
line inter ace subsystem 21 that connects directly to the
subscriber's telephone line 1, via plug 4 and jack 2.
The interface 21 includes a telephone line network 22
20that is a multi-port directional coupler similar to the
network used in conventional telephones. The interface
provides an appropriate impedance across the telephone
line and directs incoming and outgoing voice signal
between the system and the telephone line. It also
25switches signals between the system main and the E1 and
E2 phones subject to the position of the main phone hook
switch 23. More particularly, interface 21 feeds the
main telephone ringer drive circuit 24 directly from the
telephone line and feeds the main transmitter subsystem
3025 from the telephone line and the main receivers (MRX)
26 via the multi-port system network 27 (also a ~-
directional coupler) and referred to herein as the system
hybrid. The MTX 25, in turn, feeds ring, voice and data
~2~6689
-26
(VOICE) and CODE system signals through the main power
line coupler circuit 28 to the AC power line 10.
The ports of network 22 are: input port r~Ic/Dl;
output port MEp; and input-output port TL that connects
5 to the telephone line via diode bridge 22a and the 55
relay switch 33. The parts of hybrid 27 are: input port
MRXN (line 26) output port MTX to an input of
transmitter; and input-output port TL that connects to
the telephone line via C relay switch 34.
As mentioned above, ringer circuit 24 responds, to
ring signals on the telephone line and, preferably, it
gets all of its power for responding to these signals
from the telephone line. In response to the ring
signals, it drives the main telephone annunciator (ring
15speaker) 30 via speaker transformer 30a.
The main speaker 30 is also energized by intercom
signals from the main TX-RX computer 31 when the computer
decodes an intercom signal from one of the extension
phones in the system. This intercom signal and power
20supply voltage from voltage regulator 32 energize the
speaker through the drive circuit 24 to produce an
audible sound, such as a buzz.
The main power line coupler circuit 28 is a reactive
circuit and, in fact, a transformer. However, it should
25be understood that this coupling between the AC power
line and the telephone line can be capacitive as well as
inductive..
The MRX subsystem 26 receives RF carrier signals
from the power line coupler 28 that originate from the
30system El and E2 telephones and the received signals that -_
pass tests for RF power level and CODE are fed by line '-
26a through the directional coupler 27, of interface 21,
to the telephone line 1. Among the system signals that
~Z~66~9
-27-
may be received, originating from one of the system
extension telephones, are command or status signals.
They are strictly CODE signals including the code byte,
like the extension hook signal and key pad signals.
5 These are fed from receivers 26 to the main TX-RX
computer subsystem 31 and initiate special actions at the
main telephone as are described more fully hereinbelow.
The main TX-RX computer 31 processes all system
signals between the main and extension phones. More
10particularly, it processes all initiating and terminating
signals from the telephone line including ring signals,
processes all signals from the system extension
telephones, processes the main telephone hook swi.ch
signal derived from hook switch 23, processes all signals
15from the main key pad 32, controls the subset (SS) relay
switch 33, the carrier (C) relay switch 34 and the hold
(H) relay switch 35, (all in the telephone line interface
21), turns the main transmitter 25 on and off, adds CODE
to the analog VOICE transmitted by the main transmitter
20and controls the system dual tone multi-frequency (DTMF)
generator 36, depending on coded key pad signals received
at the main from an extension.
In this processing, the main computer performs logic
functions on all CODE signals received from the
25extensionS as described above with reference to Figs. 2A
to 2D and it generates and adds CODE to all signals
transmitted by the main transmitter and, unless the CODE
that accompanies a received signal satisfies
predetermined criteria programmed in the main computer,
30the received signal is not recognized, even if it is at
the RF carrier frequency F1 or F2 and the received RF ~-
power level is sufficient.
1;2 ~6689
-28-
Extension Telephone Circuits
An extension telephone (E~ or E2) circuits are shown
in Eigure 6. These circuits include the extension power
line coupler circuit 41 that may be constructed and
function the same as the main power line coupler 28. All
signals transmitted by main transmitter 25 (called system
signals) and fed through coupler 28 over the AC power
line 10 are fed via the extension power line coupler 41
to the extension receiver 42. The first part of a signal
10 transmitted by the main transmitter is the CODE that
includes an address byte and a code byte. For example,
beginning with the extension telephone on-hook, the first
signal may be a telephone line ring signal. That ring
signal is simply an address byte, code byte and check-sum
15 byte (the CODE) that are detected at the extension
receiver 42 by CODE detector circuit 222 that feeds
detected CODE to the extension TX-RX computer 46. If
this CODE passes the logic tests at the computer, the
computer turns on the ringer circuit 47 that drives the
20 annunciator (ring speaker) 48 via transformer 48a and so
the extension phone "rings".
Thus, an initial received signal at the extension
receiver 42, the ring signal, received while all system
phones are on-hook, is processed by the extension
25 computer which turns on the extension ringer circuit 47
that drives the speaker 48 producing an audible sound.
When the extension phone is answered by lifting its
handset 49, the extension hook switch 50 produces an
off-hook signal that is fed to computer 46. In response
30 to this, the computer turns on the extension transmitter
44 which transmits the extension off-hook CODE signal ~`-
(containing the off-hook code byte) generated by computer
46 on the extension RF carrier frequency, through coupler
41 to the power line 10 to the main phone receiver.
~216~i89
-29-
Thereafter, at the main phone, the extension off-hook
CODE is detected and processed and the telephone line
loop for the extension is closed by actuating both the
subset (SS) and carrier (C) relays 33 and 34 (as shown in
5 Fig. 5) and the main transmitter is turned on again,
beginning another main telephone line TXDATA phase which
consists of CODE followed by signals from the telephone
line. The telephone line signals are conducted via
relays 33 and 34 arld hybrid 27 to the main transmitter
1025. All of these signals are received at the extension
receiver 42, processed in 46 and the telephone line
signals fed to the extension earphone 51. Meanwhile,
audio signals from the extension phone microphone 52 are
fed to the extension transmitter where CODE from the
15extension computer 46 is added and begins another
extension microphone T~DATA phase.
All of the above described may occur as described
while the main phone is on-hook, or after the main and
the other extension phone go off-hook after the extension
20Of discussion. Thus, all audio signals from the
microphones of all phones of the system that are off-hook
are fed to the telephone line and all telephone line
signals are transmitted to the earphone of all phones of
the system that are off hook.
The main and the extension circuits shown in Figures
5 and 6 are for the most part symmetrical with respect to
each other. For example; note the following:
Main Circuits Extension Circuits
transmitter 25 transmitter 44
30 receiver 26 receiver 42
ringer drive 24, speaker 30 ringer drive 47, speaker 48
key pad 32 key pad 53
power line coupler 23 power line coupler 41
~2~66~
-30-
As will be seen from detailed descriptions of these
circuits, some of these main subsystems circuits are
interchangeable with their equivalent extension subsystem
circuits. For example: the power line couplers 28 and
5 41 can be identical; the transmitters can be the same
except they generate different carrier frequencies, and
the receivers can be the same except their input filters
are tuned to different frequency bands.
Conventional Telephone Functions
The main and extension telephones in the systems
perform all the functions of conventional single line
telephones in current use by subscribers with one or more
extension telephones. These are:
(1) placing an outside call by any of the phones;
~2) receiving an outside call by any of the
telephones;
(3) conferencing between any and all of the
telephones on an outside call; and
(4) an outside call is held so long as any one of
the telephone receivers is off hook (and in the
telephone line (TL) mode).
In addition, so long as an outside call is held because
one of the system extension phones remains off hook,
either or both of the extension phones can be unplugged
25from the power line and moved and then plugged in again
without terminating the outside call. The outside call
can be terminated only by one of the system phones, while
plugged in, going on hook while the other phones of the
system are either already on hook or not plugged in.
30This feature is intrinsic to the system whether the -_
system includes the Intercom II), Hold (H), Privacy ~P) ,~-~
or Special (S) functions.
lZ~
Additional Telephone Functions
The main and extension telephone computers 31 and
46, shown in the electrical block diagrams of Figures 5
and 6 perform all of the processing, logic, tests and
5 controls already described with reference to those
figures in response to signals input to the computers to
accomplish the conventional functions of the telephones
described above. Additional telephone functions of Hold
(H), Intercom II), Privacy (P) and Special (S), described
10hereinbelow, can be added to this performance. In the
performance of these additional functions, the computers
store many values and parameters that are preset therein
and they generate CODE, control and tone signals as will
be more fully described below. In particular, the
15computers perform processing, logic, and tests and store
all of the signals as described above with reference to
both of the generic embodiments of the present invention
shown and illustrated by Figures l to 3 and the specific
embodiment shown by Figures 4 to 6, as they are described
20so far. With reference to the generic embodiments, those
are the values and parameters stored and the functions
performed by both the TX computer 208 and the RX
computer 223 and the full duplex, multi-station
performance as described with reference to Figures 1 to
253. With reference to the specific embodiment shown and
described so far with reference to Figures 4 to 6, the
full duplex, multi-telephone performance ~a 1 x 3
telephone system) and the technique of encoding all
transmitted signals with CODE including an address byte,
30code byte, and checksum byte, the protocol of the --
encodement and the technique of screening the detected RF -_~
carrier at a receiver first for RF power level and then
testing the CODE is all substantially the same as in the
generic embodiments. Hence, in the following detailed
-
~2~6~i89
-32-
description of the operations of the specific ernbodiment
incorporating the additional functions of H,I,P and S,
reference is sometimes made to the generic embodiments
and all that is described and shown therein is
5 incorporated in the specific embodiment.
The specific embodiment includes the additional
functions (features) H, I, P and S that have already been
mentioned and identified. These additional functions are
all accomplished and provided for in the specific
l0embodiment substantially entirely through the programming
of the main computer 31 in the main telephone and the
extension computer 46 in each of the extension telephone
and, except for a very few exceptions, there are no
additional electronic components or subsystems in the
main or extension telephones that serve specifically to
accommodate these additional functions. Before
describing the structure and operation of the main and
extension systems to perform these additional functions
(in additional to conventional functions), the H, I, P,
20 and S functions are very briefly described below as an
aid to understanding their uses and benefits.
Hold - H
Each phone in the system has a Hold key or button,
H, that when pressed puts an outside call on hold if the
25 particular phone is off-hook and in the telephone line
(TL) mode (not in the I mode); and, provided further,
that that phone is the only one in the system that is
off-hook. The H is released by the same phone that
placed the outside call on hold, going on-hook and then
30 off-hook, or by any phone in the system that is off-hook, -_
switching from the I to the TL mode. H can also be ~
engaged by any of the extension phones, while engaged in
an outside call, upon being unplugged from the power line
~2~66B~
during the call. This unplugging behaves just like
pressing the Hold button and going on-hook.
Intercom - I
Each phone in the system has an Intercom button,
`denoted I or I/TL which flips the phone between the I and
TL modes. In general the system is in either the TL or I
mode at all times depending upon activation of the I
button. An exception to this is that an extension phone,
cannot go to the TL mode and place an outside call while
the main phone is in the I mode.
While any one of the system telephones is in the I
mode, which is accomplished by taking the phone off-hook
and pressing the I button, the other phones in the system
can be signalled that they are being called for an I
communication. This is done by the phone that is
off-hook and in the I mode pressing "1", "2", or "O" on
its key pad. The "1" is to call extension phone El, "2"
is to call extension phone E2 and "O" is to call the main
phone (M) and each press of the button causes several
buzzes (BUZ) at the phone being called for an I mode
communication. Also, in this way, any of the phones can
intercom buz~ themselves.
Privacy - P
Each of the phones in the system has a Privacy
button on the key pad denoted P. Pressing this button
"locks out" any of the other phones in the system that
are on-hook. In other words, it stops additional phones
in the system from joining in the same mode ~I or TL) as
the phone that initiated P. The system does this by not
enabling the microphone (Mic) and the ear phone (Ep) of
the locked out phone,if the locked and phone is an -
extension phone; or not coupling the network 22 to the
hybrid 27, if the locked out phone is the main phone.
~2~G6~il9
- 34 -
To this situation, the main computer may add
an error beep or tone if it is informed that any of
the phones in the system that have been locked out
by the privacy action come off-hook. This beep enters
the communication to the phone or phones engaged in the
privacy communication (either in the I or TL mode) and
alerts those phones that the locked out phone wishes
to join in. The beep is initiated by the locked out
phone, by the operator of that phone pressing "1",
"2", or "0" on the keypad and the operator of the
phone that is so buzzed may then cancel the P situa-
tion by merely pressing his P button.
Special - S
Each of the phones of the system has a Special
function button on the key pad denoted S. Included
among the S features of the system is the following:
either of the extension phones can silence the ring
at that extension made by an incoming telephone call
and can silence any and all intercom buzzes. This is
accomplished at the extension phone by coming off-
hook and then, while in the TL mode, pressing the S
and * buttons on the key pad.
Another Special feature is the storage in
each of the computers of the telephone of the last
number dialed by that phone. Each phone in the system
stores in its computer the last number that was
dialed by that phone. For example, a typical use
of this feature is when a telephone call is made by
the phone and it gets a busy signal back and then the
phone is hung up. Thereafter, the operator of that
phone coming off-hook can redial that last number
dialed by merely pressing the S button and then the
"0" button. Redialing is speed dialed at about
seven digits per second.
i21661E~9
The main phone can also store a repertory of many
other telephone numbers. The number of telephone numbers
that can be stored depends on the power of the main
computer. For example, it may store twelve additional
5 numbers with a maximum of 160 digits, the last number
dialed at the main being included among these digits. In
that particular case, the numbers that are stored in the
main telephone computer are entered into storage in the
main computer by the operator thereof as follows: first
lOcoming off-hook; then pressing the S bu-tton; then the "#"
button; then one of the twelve buttons in the top three
rows of the key pad (see Figure 14A); and then pressing
the specific telephone number to be entered by pressing
that number in the sequence of keys of the pad. Entry of
5the stored number can be stopped by either the main phone
going on-hook or by pressing any of the feature buttons
I, H, P or S. Automatic or speed dialing from this
repertory of stored numbers can then be done from any of
the telephones in the system, by that phone coming
200ff-hook, pressing the S button and then pressing any of
the buttons in the top three rows of buttons on the key
pad (see Figures 14A and 15A). It should be noted that
these buttons that initiate dialing of the stored
telephone numbers include the I, H and P buttons.
In the event there is no more storage capacity left
in the main computer for storing telephone numbers, the
computer will either ignore the additional numbers that
are attempted to store or it may produce an error beep to
the earphone of the main phone.
Clearly, in the event of AC power failure, unless
the main telephone is equipped with batteries, the stored 4~-
telephone numbers will be lost- Also, in such a case, if
the main telephone is unplug~ed from the AC power line,
~2~6~
- 36 -
the stored telephone numbers will be lost. In the
extension telephones, the last number dialed that is
stored therein is lost in the event of power failure
or if the telephone is unplugged from the power line,
unless the extension is also equipped with battery
power.
With this general understanding of the I, H,
P and S features, now consider the following descrip-
tion of the sequences of operations performed by the
main (M) and extension (El and E2) phone systems, sub-
systems and computers.
System Operations - Conventional & Additional
Conventional operation of telephones in the
system is defined herein to include placing or receiving
an outside call by the main or either of the extensions
and conferencing by any two or all of the three phones
with an outside call. These functions are described
as routines and subroutines performed by the sub-
systems in the M, El and E2 telephones. These con-
ventional telephone performance routines and subrou-
tines are listed in the function table in Fig. 7 and
are stored as computer programs in the computers in-
cluded in the present system. For each of these
routines the system inputs, subsystems activated and
signals produced and transmitted are listed in the
table as an aid to understanding operation of the
system.
Nomenclature
Systems, subsystems and functions are abbreviated in
the table and the following description as follows:
Systems Touch Pad Routines
.
Main M Dial Call Numbers for Out-
side or Intercom Call D
First Extension El Actuate Intercom Button
Second Extension E2 Actuate Hold Button H
Actuate Privacy Button P
Telephone Llne TL Actuate Special Button S
Power Line PL
5 i~
12~L6689
-37-
Subsystems Main Ext. 1 Ext. 2
Hook Switch MHk ElHk E2Hk
Network 22 Ntwk - -
Hybrid Circuit 27 Hybd
5 Ringer Drive Circuit MRng ElRng E2Rng
Transmitter MTX ElTX E2TX
Receiver Channel 1 MRX1
Receiver Channel 2 MRX2
Receiver Channel M - ElRX E2RX
10 Subset Relay 33 SS
Carrier Relay 24 C
Hold Relay 35 H
Main MDTMF 37 MDTMF - -
System DTMF 38 SDTMF
15Dial Key Pad MKP ElKP E2KP
Microphone MMic ElMic E2Mic
Earphone MEp ElEp E2Ep
TX Routines RX Routines
Turn On Transmitter TX Produce RF Carrier RF
20Add CODE CD Status Signal
Transmission of Received Detect CODE CD
Signals RX Receiver Out Enable En
Transmit DTMF DTMF System DTMF Signal DTMF
Add Tone (E1, E2) Tn
Note that the same nomenclature applies to systems,
25subsystems and routines at each of the phones, except
that at the extensions El and E : M is replaced by E1 or
E2; there is no RX input into the transmitter, but
instead there is the extension handset microphone (Mic)
input enabled, referred to as MicEn; the output of the
30receiver enables the handset earphone (Ep) and when
enabled is called EpEn; and a tone is sometimes added to
the output of the receiver and indicatea as Tn. At both
the main and the extensions, intercom signalling is
referred to as a buzz (BUZ) and indicated as the function
35BUZ. The above symbols are used to describe systems,
subsystems and routine functions as columns along the top
of the table and are also used to define the routines, ~-
subroutines and responses as rows along the left side of
the table.
~216~
-38-
Before describing these routines for performing the
conventional and additional functions (defined herein),
consider the telephone line interface subsystem 21 shown
in Fig. 5 and its operation to effect the I and TL modes
and H for various combinations of M, El and E2 engaged in
I and TL modes. The table below shows columns that
represent the status of the subset (SS) relay 33~ carrier
~C) relay 34, hold (H) relay 35, main hookswitch (MHK)
33, network (Ntwk) 22 and hybrid (Hybd~ 27 for the
10 routines listed as rows. The status of each circuit is
indicated as + or -. For the relays, the + indicates,
that the relay is actuated and the - that it is not
actuated, for the main hookswitch the + indicates off
hook and the - indicates on hook and for the network and
15hybrid the + indicates that it is active to conduct
signals between the telephones of the system and the
telephone line in the I or TL mode, whereas - indicates
that it is not so active.
12~661B9
-39-
Telephone Line Interface Ope_ations
C SS H MHk Ntwk Hvbd TL
M--TL - - - + ~ -
M--TL, (El ~ E2) - I - - - + +
5 (M ~ El)--TL + - - + ~ + TL
(M + El + E2)---TL + - - + ~ ~ TL
(El + E2)--TL + + - - - + TL
H--TL, (M + E23 - I - + + + ~+~ (+~
I 12
H--TL, (M + El) - I - + + + ~+)--(+~
1 12V
10 H--TL, (M + El + E2) - I - + + + ~+~
1 12V
H--TL, (El + E2) - I - - +
Nothing
_
As shown by the table above, when M and El and/or
E2 are in the I mode together, Ntwk and Hybd are both +
15 and in series with 12 volts from the power supply across
the series. The table also shows that when M and El
and/or E2 are in the TL mode, Ntwk and Hybd are both
activated and in parallel across the telephone line.
When any of the routines listed in the table are called
20 for, the main TX-RX computer 31 is programmed by received
CODE and other inputs to the computer to control the C,
SS and H relays as indicated in the table. For this - ~-
purpose, zs shown in Fig. 5, the computer 31 outputs
lL2~66~
~40-
include signals in lines denoted C, SS and H to relay
control amplifiers 34a, 33a and 35a that control the
solenoids 34b, 33b and 35b of the relays 34, 33 and 35,
respectively.
Conventional Function Operation
Refer next to Fig. 7 along with Figs. 5 and 6 and
the interface operations table above. The table in Fig.
7 shows the routines and subroutines and responses, @ M,
E1 and E2, for performing conventional functions by
the three phones of the system. The functions shown by
the table in Fig. 7 are:
Answer call by El;
Place call by El; and
Conference ~E1 + E2 + M) -- TL.
For these routines a + under the column of subsystem or
function indicates that the subsystem or function is
active and a blank indicates that it is not active (the
same as a minus). Under Place Call by El, the first
subroutine is El - Off Hook, which is an input command
into the system and El responds by TX and CD. In
response to this, at M, RXl receives RF and CD and
computer 31 actuates C and SS and turns on transmitter 25
to TXCD to El through the Hybd. Here, it should be
noted that when C and SS are both +, Hybd is connected
across TL and the CD transmitted to E1 is received at
El (as indicated by R @ El) where El receives RF
and CD and, as a result, the computer 46 at E1 sends an
EpEn signal to its receiver 42 and sends a TX and an
~icEn signal to its transmitter 44. The effect of all
this is to store at the main computer 31 the off hook
status o E1, connect hybrid 27 across the telephone -
line 1, turn on the transmitter at E1 and enable the
microphone and earphone in the handset at E1 and so the
1216~
-41-
operator at E1 hears a telephone line dial tone from
the telephone line in his earphone indica~ing that he may
then dial a number.
The next subroutine is El-Dial, which is an input
5 command at E1 and is initiated by the operator punching
keys on keypad 53 that are fed to El computer 46 which
turns them into CODE (CD) that is transmitted by
transmitter 44 to M. The response at M is to receive the
CODE including the code byte for the number dialed at
10 E1, detect it and feed the detected CODE to the main
computer 31. In this process denoted R @ M, RXl output SJ_
is disabled and the system DTMF 36 converts the received ~c
code to dial tones that are sent in line 36a to the
output of receivers 26 and fed in that output to hybrid =~
15 27, to the telephone line. The same tones are also fed - -
to the input of main transmitter 25 and sent back to
El, where they are received at the earphone of El as
tones and so the operator at El can hear the tones he
is dialing. This is indicated in the table by R @ El.
20 Thereafter, when the dialed call goes through, the
routine Place Call by El is completed.
The next routine shown in the table in Fig. 7 is
Answer Call by E1. This routine begins with the input
command Rng at M which transmits ring code to El and
25E2. The R @ El is to receive the ring code and
process it in the computer 46 producing a signal in line
47a to turn on drive circuit 47 that drives the speaker
48. These signals in line 47a from the computer cause
the speaker to produce a distinct audible sound
30indicating an outside call ring. The next subroutine is - -
El-off hook which commences with the off hook input
command at E1 and E1 transmits CD indicating this
status. The R @ M is to received that CODE, enable RX1
~Z~66~g
-42-
and actuate C and SS placing Hybd across the TL. In
addition, the main transmits CODE to E1 and the R @
E1 upon receiving this is to enable the Mic and Ep at
E1. When that occurs, the status E1-TL is achieved
and so E1 has answered the incoming telephone call.
The routine for conferencing (Conf) between E1,
E2 and M and the telephone line continues from the
status of El-TL. The first step in this routine is
E2-Off hook and then M-Off hook. The subroutines and
responses involved in these procedures can be followed
~rom the table.
I Mode Operations
The table in Fig. 8 shows the routines, subroutines
and responses to accomplish each of the following:
(M + El + E2) I
(El + E2)--I
(E1 + E2)-I, M-TL
M - Off HK Which activates Hk and Ntwk at M;
M - I When M presses the I button, which
activates Hybd and relay SS so that
MHk, Ntwk, Hybd and SS are all
activated which connects Ntwk and
Hybd in series across 12 V, as
illustrated by the operation table on
page 34;
M - DlE1 When M presses the I button, it turns
on TXm, transmitting CD1 (for BUZ),
addressed to El. (Note that when
MTXm CD, the RX input to MTX is from
Hybd);
R @ E1 The response at E1 is to receive RXm, ,~
detect the CD1 ~for BUZ) and actuate
the E1 ring drive 47 with a BUZ
-~3~
signal and so E1 is buzzed for an
intercom communication;
E1 - Off Hk When E1 goes Off Hk, it turns on TXl,
transmitting CD (for El - Off Hk);
R @ M The response at M is to receive, RX1,
detect the CD (for E1 - Off Hk) which
causes TXM to send CDl taddreSsed to
E1) for MicEn and EpEn at El;
R @ El The response at El is to RXm, detect
the CD1 and MicEn and EpEn; and so
the
M + El - I Routine status is achieved.
M DlE2 When M presses the 2 button, it turns
on TXm transmitting CD2 (for BU~)
addressed to E2;
R @ E2 The response at E2 is to receive RXm,
detect the CD2 (for BUZ) and activate
E2 ring drive 47 with a BUZ signal
and so E2 is buzzed for an intercom
communication;
E2 - Off Hk When E2 goes Off Hk, it turns on TX2,
transmitting CD (for E2 - Off Hk)
R @ M The response at M is to receive RX2,
detect the CD (for E2 - Off Hk) which
causes TXm to send CD2 (addressed to
E2~ for MicEn and EpEn at E2;
R @ E2 The response at E2 is to RXm, detect
the CD2 and MicEn and EpEn; and so
the
30 M + El + E2 - I Routine status is achieved. .-
The second series of routines starts from the ~_
routine status M + El + E2 - I and the purpose is to
achieve El + E2 - I. This done as follows:
~Z~6~ 9
-~4-
M On Hk When M goes On Hk, the M Hk, Ntwk and
Hybd are deactivated and relay SS is
deactivated so that the outputs of
MRXl and MRX2, combined at 340 are
fed directly through Hybd 27 as RX to
the input of MTXM and El and E2
remain in intercom; and so
El + E2 - I Routine status is achieved.
The third series starting from El + E2 - I, is to
10 achieve El + E2 - I, M - Tl. This is done as follows:
M Off Hk When M goes Off Hk, while E1 and E2
are in I, Ntwk is activated, but the
Hybd is not activated, because relay
C is not activated (when activated, C
relay couples one side of Hybd to the
telephone line). At M, the Ep
receives dial tone from the TL, via
the Ntwk.
M Dl Tl When M gets dial tone, M dials (Dl)
an outside number and, presumably,
the call is answered; and so
El + E2 - I, M - Tl Routine status is achieved.
In the first of this series of routines, the starting
routine status is with Ml, El and E2 all on-hook. In the
251ast of these routines, the starting point is with E1
and E2 in the I mode when an incoming ring signal from
the telephone line occurs, whereupon M comes off hook to
answer the incoming call. Having followed the routines,
subroutines and responses described in detail with
30reference to the conventional functions in the table in
Fig. 7 and being mindful of the operation of interface 21 ~_~
as shown in the table on page 34, one should have no
problem in following all steps in detail shown in Fig. 8.
-
~21661~9
-4~-
H Function Operations
The table in Fig. 9 describes the routines,
subroutines and responses for performing the following
uses of the H feature:
H - TL by M and (M + E~
H - TL by El and (El + E2) - I
H - TL by M and (El + E2) - I
It should be noted here that any time the telephone line
is in hold, whether initiated by the main or an
10 extension, Ntwk and Hybd are both active and in series
wlth 12 volts from the power supply across the series
while the hold relay impedance 35c is across the
telephone line. In this situation any combination of
intercom calls can be made between M, El and E2.
15 During the H-TL status, any of the above intercom
situations are possible, however, only M, being not
engaged in I (the last situation) can come off hook into
the TL mode and cancel the H. This means that if while
H-TL, M and El are in I and E2 comes off hook, I is
20 cancelled and all three phones are placed in the TL mode.
P Function Operations
Various P function routines are shown in the table
in Fig. 10. These routines include the following:
P between M and TL
P between M, El and TL
P between El and TL
P between El, E2 and TL
P between M and TL while ¦El and E2) - I.
In any of the above situations, the system phone that is
30 locked out can come off hook and alert the others that it
wishes to join in. This is done simply by the locked out
phone coming off hook and the operator pressing 1, 2 o~ 0
on the keypad to signal whichever of the other phones it
~2~668~
- 46 -
wishes to request that the lock out be cancelled. This
routine is shown in the last of the above ~isted. It
should be noted that when M and El are in the I mode
and either of them initiates P, that E2 is lock out
and so if E2 comes off hook it is locked out of the I
and it has no access to TL. On the other hand, if E
and E2 are in the I mode and either presses P, the
main M is locked out of the I, but if M comes off
hook it is automatically in the TL mode and M can
then be switched by its operator to the I mode and
request to join the intercom. This sequence is also
shown in Fig. 10.
S Function Operations
The S function is initiated by any of the
phones by coming off hook in the TL mode and the opera-
tor pressing the S button. It is used to either redial
the last number dialed by that phone or to dial out
one of the stored telephone numbers among a repertory
of stored telephone numbers stored a~ the main com-
puter. Several routines involving the S feature are
described in the table in Fig. 11~ They include the
following:
S by M - last number redial;
S by M - dial repertory number,
S by E1 - last number redial,
S by El - dial repertory number.
M and E Computers and Codes
The CODE part of the transmitted data (TXDATA)
including Address Byte, Code Byte and Checksum syte
shown by the waveforms in Fig. 2 is suitable for the
power line carrier telephone extension system des-
cribed herein as the specific embodiment and shown
particularly by the electrical block diagxam in Figs.
5 and 6. As this CODE is used in the present embodi-
ment of the telephone extension system, the Address
Byte is an ~3 bit binary number of which the user manually
~;~3L66~9
- 47 -
sets 4 bits and the other 4 bits are fixed (or preset
in production). ~ote, however, that any number "N" of
bi.ts may be advantageously used in the present inven-
tion. The user sets 4 bits of the El address and 4
bits of the E2 address by the address set switches 38
at the main telephone. The user then sets the same
4 bits of the El address in address set switches 54
at El and the same 4 bits of the E2 address in address
set switches 54 at E2. By setting the address set
switches in this way, the transmitted Address Byte
that is part of the transmitted CODE from a telephone
matches the Address Byte that will be recognized in
received CODE at the telephone for which the trans-
mission is intended and unless the received CODE in~
cludes that Address Byte, the receiving telephone's
computer will not allow its receiver to respond to
the DATA that accompanies the CO~E.
This technique of setting the Address Byte
provides versatility and assures that the Address Bytes
set at M will be matched to those at El and E2, even
if the user does not set anything, because the bits set
in production will provide sufficient address. For ex-
ample, for a given system of M, El, and E2, the 4 bits
of the El and the E2 addresses set in production (at
the factory) may be the bits: 1000 and 0100, respec-
tively, and the manual set switches in the phones all
begin at 0000. This system will perform in all res-
pects as described herein, even if the user ~customer)
fails to set the switches, because the El address set
at both El and M will be 1000000 and the E2 address set
at both E2 and M will be 01000000. Clearly, however,
it is necessary where the user elects to set four bits
of the addresses of El and E2 that he sets El the same
at M and El and he sets E2 the same at M and E2.
It is also clear that the -four bits manually set by the
..~
-
~2~ iB9
-48-
user can be the same for E1 and E2 and the system
will still perform in all respects as described herein
~because the factory set bits will be different). Thus,
the bits (four bits for El and four bits for E2) that
5 can be manually set at M could be accomplished by a
single set of four switches that manually set the same
four bits for El and E2j and, correspondingly the
same four bits would be manually set in El and E2.
An advantage may lie in having the user manually set all
10the system phones the same and refer to the setting as
the user's address.
The first purpose of the Address Byte is to
distingu~sh data transmitted from M, by RF carrier Fm as
intended for E1 or E2 (or both). Another purpose is
15to distinguish between system data on Em and signals from
other systems also on Fm. For example, if the
probability of neighboring premises with such telephone
extension systems both having the same Fm is 1:10; then
the probability that both will have the same Fm and the
20same factory set four bits for El or E2 is 1:10 x
2:24 or 1:80; and the probability that both will have
the same Fm, the same factory set four bits and the same
manually set four bits for E1 or E2 is 1:80 x 2:2
or 1:640.
The Code Byte part of CODE is generated by the
computer in each phone depending on commands by each
phone and commands received at that phone from the other
phones and stored in the computer. As already described
with reference to Fig. 2 the Checksum Byte merely
30confirms that the Address and Code Bytes are received as ~
sent. With this format in mind, M, E1 and E2 Code 4-
Bytes for various commands can be set up as shown in the
table 2 belowO
12~6689
-49-
Extension (E)1st 5 ~its Main (M)
Command/MessageCode Byte Command~Message
E Of~ Hk 11111 EnMic-On
E On Hk 01111 EnMic-Off
E On I 10111 EnEp-On
E Off I 00111 EnEp-Off
E Dl 1 10000 MDl 1
E Dl 2 01000 MDl 2
E Dl 3 1l000 MDl 3
E Dl 4 00100 MDl 4
E Dl 5 10100 MDl 5
E Dl 6 01100 MDl 6
E Dl 7 11100 MDl 7
E Dl 8 00010 MDl 8
E Dl 9 10010 MDl 9
E Dl 0 01010 MDl 0
E Dl * 11010 MDl *
E Dl ~ 00110 MDl #
E On H 11011 M On H
E Off H 01011 M Off H
E On P 10011 M On P
E Off P 00011 M Off P
E On S 11101 M On S
Examination of the routine tables for performing the
25 various functions of the telephone system and shown in
figs. 7 to 11, reveals that when a transmitter in any of
the phones transmits CODE, the input to the transmitter
(from the receivers in the main or from the microphone in
an extension) are disabled and immediately following the
30 transmission of CODE, if transmission continues, the
input to the transmitter is enabled again. This is shown
also by Fig. 2: during the 31.68 milliseconds that CODE
is transmitted, VOICE is not transmitted. Clearly this
31.68 milliseconds is not perceived as an interruption by
35 the user, because the period is so brief.
M And E Power Line Couplers (Adapter Plugs)
The main telephone power line coupler circuit 28 is -
shown in some electrical detail in Fig. 12 and the .~~
extension power line coupling circuit 41 is shown in Fig.
40 13. These figures shown circuit details of parts of the
~2~68C9
-- 50 --
coupling circuits in the phones and parts in the
adapter plug. In both cases the power line of, for
example, 110 VAC stops at the adapter plug and so the
cord (see Fig. 4) from the phone to the adapter plug,
5 which can be of considerable length to allow freedom
of movement of the telephone even while it is plugged
in, carries all power and RF signals between the phone
and the power line and all of this is at relatively
low voltage and low power and so the phone itself is
intrinsically a safer instrument than it would be if
the cord carried 110 VAC into the phone envelope.
Turning first to Fig. 12, for the main phone,
the power line coupling circuit 28 of Fig. 5 is com-
prised of the RX-TX transformer 61M located inside the
15 main phone envelope, the cord 6a from the main phone
and the adapter plug 6 that plugs into a conventional
AC power line receptacle. The adapter plug 6 contains
circuitry of the coupler as is necessary to insure
that the mains supply, i.e., 110 VAC is isolated from
20 the telephone at the plug.
Ihe output of the main transmitter (MTX) power
amplifier to 211, iS fed to the RX-TX transformer 61M
and the inputs to each of the channel 1 and channel 2
receivers (MRX-l and MRX-2 in 26 ) is taken from this
25 transformer. In particular, the main RX-TX transformer
includes a primary coil 62M and secondary 63M, the out-
put of the transmitter being coupled to one side of this
primary via the variable inductance 64M and capacitance
65M in series and the other end of primary goes to
ground. A thermistor 66M is connected across this
primary to maintain a low primary impedance when the main
transmitter (MTX) is "off`'. When the transmitter MTX is
"on", the thermistor 66M heats up and its resistance in-
creases. Conversely, when the transmitter MTX is `'off"
1L2~66fl9
-51-
the resistance of thermistor 66M decreases. The inputs
to each of the receivers M26 and 2 are coupled in series,
as shown, with the secondary 63m of the RX-TX transformer
and this coupling is into the band pass filters of the
5 two receivers and may be by coupling coils in the filters
(as shown). Thus, the secondary 63 is in series with the
inputs of the two receivers across the terminals 2 and 4
of the main phone that connec-t to terminals 2 and 4 of
the cord 6a. The other end of this cord, at the adapter
lOplug 6 that correspond to the terminals 2 and 4 is across
the secondary 67M of transformer 68M in the plug and in
the primary 69 of that transformer connects to the power
line 10, one end of that being connected to the power
line via capacitor 71M. By this structure the
15transmitted RF from the main is launched into the power
line and RF signals carried by the power line are coupled
from the power line to the two receivers in the main
phone.
The main phone power supply, regulator 32 provides
20all operating power for the main phone except power
derived from the telephone line for operating parts of
the telephone line interface system 21 and for operating
the main DTMF 37 as already described. The power supply
32 produces 12 volts and 5 volts DC for operating the
25systems and subsystems in the main phone. Power to
regulator 32 comes from transformer 72M in the adaptor
plug. The primary side 73M of that transformer connects
directly across the power line and the secondary has a
center tap that is carried by cord 6a to terminal 3 in
30the main phone that provides the main phone ground while
the two ends of the secondary are connected together via ~ -
diodes 75M, as shown, providing rectified positive
voltage that is carried by cord 6a to terminal 1 in the
1216~ 9
-52-
main phone and terminal 1 feeds the input to voltage
regulator 32. Thus, regardless how the adaptor plug is
plugged into the power line 10, terminal 1 gets full wave
rectified positive voltage for the main phone regulator.
5 In order to insure that the DC level at the output of the
transmitter and at the input of the regulator is the same
and yet block RF flow between the two, RF choke 76M is
provided which short circuits DC and blocks RF ~shunts it
to ground).
The power line coupling circuit 41 in the extension
telephone (Fig. 6) is shown in detail in Fig. 13. This
circuit also includes parts in the extension telephone
envelope, parts in the adaptor plug 15 and the cord 15a
from the phone to the plug. The principle parts of this
15circuit are the RX-TX transformer 61E in the extension
phone, the cord 15a and the two transformers 68E and 72E
in the adaptor plug 15. The parts included herein may be
the same and have the same functions as the equivalent
parts described above with reference to the main power
20line coupling circuit 28. Similar parts bear the same
reference number followed by M or E. The only
substantial difference between this coupling for the main
and the extension phones, is that the extension has only
a single receiver, ERXn, (a channel m receiver) instead
250f two receivers. Clearly it is of some advantage that
adaptor plug 6 and its cord 6a for the main phone be
identical to adaptor plug 15 and its cord 15a for an
extension phone, inasmuch as the cords and plugs are then
interchangeable.
M and E Kevpads
The main phone keypad (29 in Fig. 5) carry the ~_~
operating buttons as shown. These include the
conventional telephone Touch Tone 1 through 9, 0, *, and
~6~
-53-
# buttons, and in addition to these it carries the
intercom (I), the hold (H), the privacy (P), and the
Special function (S) buttons. A pictoral view of the
keypad 29 is shown by Fig. 14A. ~lectrical diagrams 14B
5 and 14C and their associated tables 14D and 14E,
respectively, show the system and telephone line
operating functions of the main keypad. The telephone
line operation described by Figs. 14C and 14E occur when
the main telephone is operated outside of the system;
lOmore particularly when it is operated without AC power
and while plugged into the telephone line only. For this
operation, all power to the phone is derived from the
telephone power line and the operation is essentially
conventional.
For con~Tentional operation, only the conventional
keys l to 9, O, *, and # are operational through pins 1
to 8 of the output terminal board 29a of the keypad. The
interconnections between these pins, accomplished by
- pressing the various keys of the pad, are listed in the
20table in Fig. 14E and shown diagrammatically by Fig. 14C.
For example: when key 1 is pressed, row 1 and column 1
are connected and so pins 2 and 3 are connected; when key
2 is pressed, row 1 and column 2 are connected and so
pins 2 and 5 are connected and so forth. Thus, upon
25pressing each of the keys in the touch pad, different
combinations of rows and columns are connected (short
circuited). These rows and columns are denoted R1, R2,
R3, R4 and Cl, C2, and C3 herein. Clearly, when R3
connects to C2 the indication is only that key 8 is
30pressed. This telephone line operation of the main
keypad activates only the main DTMF 37 (see Fig. 5) and ~~
so the connection from the key~ad to the main DTMF is of
only Rl, R2, R3, R4, C1, C2, C3 and Common.
~LZ1661B9
-54-
Turning next to Figs. 14D and 14E there is shown the
operation of the main keypad in the system mode when the
main is plugged into the power line and the systems and
subsystems of the main are energized by the main
regulator 32. In this case, all of the keys including
the I, H, P, and S keys are active and the actuation of
these keys is defined by R1, R2, R3, R4, C1, C2, C3, C4
and the Common. In this case pins 9 to 17 of the output
pad 29a are also activated and so all 17 output pins of
10 the pad 29a are activated. For example, when key 1 is
pressed, pins 2 and 3 are connected and also pins 16 and
13 are connected. When the I is pressed, none of the
pins 1 to 8 are connected, but pine 9 to 16 are
connected.
The connections between the main keypad 29 pins 1 to
17 and the main DTMF 37 and the connections to the system
DTMF 36 and the main computer 31 are explained further
hereinbelow with reference to Fig.16, which describes
also the operation of the address code set switches 38 in
20 the main phone.
The extension keypad 53 shown in Fig. 6, the
electrical connections between the keys and the output
pins of the keypad output terminal board 53a are
illustrated by Figs. 15A, 15B, and 15C. For the
25 extension, there is only system operation, because the
extension phone is not operable unless plugged into the
power line and so all sixteen keys on the pad are
operable at all times. Here, the output pins are denoted
1 to 9 and they connect to the rows Rl to R4 and columns
30 and C1 to C4 as listed in the table in Fig. 15C. Thus,
when key 1 is pressed, pins 9, 3, and 8 are short ~_
circuited and when key S is pressed, 2ins 9, 4, and 7 are
short circuited, and so forth.
6689
-55-
Here again, as for the main telephone keypad, the
keypad outputs are designated by their row and column
symbol rather than the pin and the pin designation is
described only with reference to these figures. The pin
5 designation is not carried through in the descriptions of
operations of the keypad system elsewhere herein. The
electrical connections between the extension keypad 53
and the extension computer 44 and extension address set
swi~ches 54 is described more fully herein~elow with
lOreference to Fig. 17.
M and E Address Code Set Switches
At the main phone, four bits of the address bytes of
E1 and E2 are set by the switches 38 and at each of
the Extension phones, the same four bits are set by the
15address switches 54. The purpose of these settings is
discussed above. Briefly, the purpose is to give the
user the opportunity to change the addresses. The
occasion might arise to change the addresses in the event
of interference from other sources, such as a neighbors
20power line telephone system of the same design as the
users.
It is convenient at both the main and the extension
to set the four bits of the addresses into the computer
using the same lines that feed the key signals from the
25keypad into the computer and this is the way it is done
at both the main and extension.
Turning first to Fig. 16 there is shown the main
keypad 29, main DTMF 37, system DTMF 36 and the extension
address set switches 38. There are two banks of these
30switches 38a and 38b, of which 38a is for setting the
four bits of the address of E1 and 38b is for setting ,~-
four bits of the address of E2. All the switches, when
closed, draw current through a diode, denoted generally
-
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39, when transistor 40 is enabled by a signal in line 40a
from the main computer. This enable signal occurs very
briefly every time the main computer is reset and the
main computer is reset every time there is an
5 interruption of power from the power line to the
telephone, followed by a continuation again of power.
~ence, whatever the switches are set at, just before the
telephone is plugged into the power line, that setting is
stored in the computer. It is convenient to feed that
10setting into the computer via the lines denoted Rl to R4
and Cl to C4 from the keypad. In the main telephone, as
shown in Fig. 16, all eight of the lines, Rl to R4 and C1
to C4 are used. Immediately following initiation of
power from the power to the telephone, the transistor 40
15is no longer enabled and the switches play no part and
have no effect on the signal flow between the main keypad
29, the system DTMF 36, the main DTMF 37 and the computer
25.
Operation of the address set switches 54 at the
20extension is much the same as the address set at the
main, except that only a single bank of four switches is
reguired. As shown in Fig. 17 the bank of four switches
54a feed through diodes 55 and transistor 56 when the
transistor is enabled by a signal in line 56a from the
25Computer~ In this case it is convenient to feed the
impulse from the switches to the computer 46 via lines Rl
to R4 from the extension keypad 53.
Main and Svstem DTMF
As shown in Fig 5, the main phone contains the
30system DTMF 36 that generates the conventional dual tones
(Touch Tones~ for dialing to the telephone line and the ~`~
main (or subset~ DTMF 37 for doing the same. It should
be noted that while the system shown herein uses a DTMF,
1~66~9
those skilled in the art will recognize that any suitable
telephone signalling device may be substituted herein
and, specifically, that a rotary dial device or a
combination of tone or dial telephone signalling
5 apparatus may be used in the system.
The main DT~F feeds the telephone line interface 21
and is powered by the telephone line. It operates in
conjunction with the main key pad 32, network 22 and hook
switch 23, feeding tones to; one of the primary windings
1022C of the network as the tones are dialed (called for)
at the key pad. Details of these circuits and the
connections and couplings between them are shown by Fig.
18. That figure shows details of network 22, hybrid 27,
main hook switch 23 and the C, SS and H relay switches.
15The parts of network 22 and hybrid 27 are identified.
In Figure 18, the tip line ia connects through
subset (SS) relay 33 and switch 23-3 of the hook switch
set 23 to the balanced diode bridge circuit 21a. The
ring line lb connects through SS relay 33 directly to the
20diode bridge. Whichever line (the tip or ring) is at a
positive voltage level with respect to the other is fed
through the bridge to the Vbb terminal of the main DTMF,
37 and, correspondingly, whichever line is negative is
fed through the bridge to the ground terminal, Vss of
25DTMF 37. In this way DTMF 37 is powered from the
telephone line.
When DTMF 37 receives control input signals in lines
Rl to R4 and C1 to C3 from the main key pad 32, it
produces the appropriate tone combinations in output line
30 37a to the secondary winding 22c, and across capacitor
22d of network 22. ---
~ hese dial tones are coupled by transformer actions
to the secondary 22e, which is across the tip and ring
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- 58 -
lines via the SS relay 33, and so the dial tones from the
main subset are transmitted to the telephone line. A
center top 22g on the primary 22e feeds the main handset
29 earphone 29 Ep. The main microphone 29 Mic also feeds
across the primary winding 22c when handset 29 is off
hook, except when dial tones are produced in the output
of DTMF 37. The dial tones squelch the Mic via line 22f
by turning on a transistor in the Mic (not shown). Thus,
the main earphone produces audible dial tones and the0 main microphone is cut off when the operator dials.
Conclusions
The Generic embodiment of the present invention
described herein with reference to Figures 1 - 3 has
useful application to just about any power line carrier
communication system and particularly those systems that
operate within a residential premises where interference
is likely to be present. Furthermore, some of the tech-
niques for implementing Intercom, HOLD, PRIVACY, etc.
have useful application in a conventional telephone sys-
tem having extension telephones that do not use the powerline to communicate between phones of the system, but
uses a two wire telephone line between jacks in the
premises. The specific embodiment of the present inven-
tion incorporates the coding and decoding techniques,
because certain commands are implemented using code
words. The specific embodiment of the present invention,
a power line telephone extension system is described to
show the full use of all advantages of the Generic Em-
bodiment in the power line telephone extension system.
In addition, the specific embodiment teaches fully the
implementation and use of additional or new features
referred to as Hold, Intercom, Privacy, and Special.
Those additional features are described along with
the operation and
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12~668'~
-59-
implementation to effect them to show fully the problems
overcome and the advantages to be obtained by the
practice of the present invention as set forth in the
appended claims.
Equivalents
Glearly other specific embodiments and some varia-
tions of the Generic Embodiments will be apparent to
those skilled in the art without departing from the
spirit and scope of the invention as set forth in the
ed claims,
