Note: Descriptions are shown in the official language in which they were submitted.
~ ~ r r /~ r~ r PCTIUS94101570
WO 94/18780
I
A Telephorle System and Adapter Therefor
FIELD OF THE INVENTION
This invention relates to telephone systems of the kind permitting
at least one external telephone line to be connected to a plurality of internal
users, one of whom may make external calls whilst still allowing the
5 remaining internal users to make internal calls.
BACKGROUND OF THE INVENTION
Small telephone exchanges, such as are commonly provided in
offices and the like, permit a plurality of internal users to make outside calls10 via one or more outside lines and also to use the system as an internal
intercom whereby they can call one another internally. In such systems,
each internal extension has a unique identity code which must be dialled in
order to call the respective extension. Normally, some special number, such
as "9", must be dialled in order to obtain an outside line.
1~ A large number of such systems exists, each providing a variety
of features, but all existing systems require that the internal exchange is
coupled to the outside line and then to each of the internal extensions
separately in a radial arrangement. This requirement renders the installation
of such systems costly, since each internal extension must be separately
'~O wired to the internal exchange, an operation which is labor-intensive, time- consuming and inconvenient.
WO 94/18780 PCT/US94/01570
2~S6~S 2
Many small businesses and domestic installations have extension
telephones which are commonly coupled to a single outside line. This
provides the convenience of being able to answer the telephone in more than
one location, but does not provide an intercom facility whereby a user in one
room can call another user in a different room via the telephone network.
So far, the only way to provide such a facility has been to install an internal
exchange of the type described above: a fact which has clearly militated
against the widespread use of such systems, particularly for domestic
situations.
Systems have been proposed for at least partially addressing this
requirement. For example, U.S. Patent No. 4,8"1,319 (Middleton et al.)
discloses a single line telephone communication system for the provision of
four intercom services and/or PABX-type features to a plurality of subsets.
Each subset is provided with a station adaptor adapter for coupling it to a
15 single pair of in-house wires and additionally there is required a line
interface adapter connected between the in-house wires and an external line.
The arrangement proposed by Middleton et al. obviates the need for much
of the complex wiring associated with other systems, since each telephone
subset is connected in parallel to the in-house wires and does not need to
O be separately wired to the line interface. There is, thus, only one internal
connection to the line interface. This notwithct~ntling, the line interface
itself must be connected to the external line, and this cannot be done without
installing the system: something which is probably beyond the capabilities
of the average domestic user.
''~ U.S. Patent No. 4,893,334 (Parnello) discloses an intercom system
for use with a plurality of telephones on a single extension, including a
single master station and a plurality of slave stations. The master station is
connected so as to interrupt the telephone line pair to and from a central
exchange. Each slave station is preferably associated with a handset that is
WO 94/18780 21 ~ ~ ~ 6 ~ PCT/US94/OlS70
on the extension. When the extension is not being used for intercom service
or for an outside call, any telephone handset on the extension that has a
keypad can initiate a signal that is received and decoded in the master unit.
When the master station receives such a signal, it disconnects the line to the
telephone exchange from the extension and connects the telephone exchange
to a circuit that detects incoming calls so that they can be signalled to users.The master station also sends a signal to each slave station that enables the
intercom function.
In such an arrangement, the master station serves a similar
function to the line interface shown by the Middleton et al. in that it must
be connected between the external telephone wires and the internal system.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a telephone
system, particularly one suitable for small business and residential use,
which requires no interface with the incoming telephone line and therefore
obviates the need for speçi~li7ed installation.
According to the invention, there is provided a telephone system,
compnsing:
at least two telephone outlet sockets coupled to a telephone line across
which there is applied a d.c. voltage,
a respective telephone extension unit for coupling to the telephone line,
and
a respective switching means connected between each one of the
telephone outlet sockets and the corresponding telephone extension unit
coupled thereto and switchable between a first position in which the
telephone extension unit is directly connected to the telephone outlet socket
and a second position wherein the telephone extension unit is a.c. coupled
wo g~/18780 2 ~ ~ ~ 6 6 5 PCT/US94/01570
to the telephone outlet socket so as to block said d.c. voltage from the
telephone extension unit;
the system further including in respect of each telephone extension
unit:
call si~nalling means for sending a call signal to another telephone
extension unit,
a call signal detector for detecting said call signal sent by a remote
telephone extension unit and producing a call detection signal,
a call indication means responsive to the call detection signal for
generating a call indication signal,
a status indication means responsive to a status of the system for
producing a respective status indication signal,
an actuation means for producing an actuation signal, and
a control unit coupled to the status indication means, the actuation
mç~n~, the call signal detector, the call indication means, the call ~ign~llin~
means and the switching means and being responsive to the status indication,
the actuation and the call detection si~n~lc, for o~e.alhlg the call indication
means, the call sign~lling means and the switching means.
The invention also incorporates within its scope an adapter which
may be connected between each extension telephone and its respective
telephone outlet socket in a conventional multi-extension system sh~rin,e a
common telephone line, so as to convert all of the telephone extension units
thus connected to a telephone system having all of the features of a
conventional PABX system. Such an adapter incorporates therein a control
circuit for providing all of the facilities normally associated with such
systems and therefore necess~rily duplicates some of the components which
are in any case provided in more sophisticated telephones. Alternatively, the
telephone itself may be modified so as to include therein all of the special
features of the adapter, in which case the adapter can be dispensed with.
WO 94/18780 ~ 6~ PCT/US94/01570
BRIEF DESCRIPIION OF THE DRAWINGS
In order to understand the invention and to see how the same may
be carried out in practice, some preferred embodiments will now be
described, by way of non-limiting example only, with reference to the
5accompanying drawings, in which:
Fig. 1 is a block diagram showing functionally a system according to
the invention;
Fig. 2 is a circuit diagram showing schematically an adaptor for use
with the system shown in Fig. 1;
10Fig. 3 is a block diagram illustrating how a controller shown in Fig. 2
may be incorporated into the system shown in Fig. 1; and
Figs. 4 to 10 are flow diagrams showing the principal operating steps
associated the adaptor shown in Fig. 2.
15DETAILED DESCRIPIION OF PREFERRED EMBODIMENTS
Fig. 1 shows a system, desi~n~ted generally as 10, comprising
three pairs of telephone lines 11, 12 and 13 connected to a central office
exchange 14. The telephone lines 11, 12 and 13 are commonly connected
to a telephone 15 via an adaptor 16 and, in similar manner, an answering
20m~chine 17 is connected to the telephone lines 11, 12 and 13 via an
adaptor 18.
The telephone line 11 corresponds to the normal tip and ring lines
which are commonly connected to multiple-extension telephone sets in a
domestic installation, wherein only one telephone extension may initiate an
25external telephone call, no intercom facility being provided. Such a
connection is replese-lted by a telephone 19 which is directly connected to
the telephone line 11. In contrast to this, there is shown a telephone 20
which is connected to the telephone line 11 via an adaptor 21. Likewise, a
telephone-operated door lock 22 is connected to the line 11 via an adaptor
WO 9`1/18780 ~ ' PCT/US94/01570
2~5665 6
'3; a modem 24 is connected to the telephone line 11 via an adaptor 5;
a fax machine 26 is connected to the telephone line 11 via an adaptor 27
and remotely-operated appliances 28 and 29 are connected to the telephone
line 11 via an adaptor 30. A control unit 31 is commonly coupled to the
telephone line 11 for controlling the sequence in which all automatic
extension units are controlled as will be explained in greater detail below
with particular reference to Fig. 3 of the drawings.
All of the adapters shown in Fig. 1 are provided with an outlet
(constituting a line coupling means) shown schematically as 32 for coupling
to a telephone outlet socket designated schematically as 33 and is also
provided with an inlet tconstituting an extension coupling means) designated
schematically as 34 for coupling to the corresponding telephone. Thus, each
adaptor is connected to the telephone line 11 by unplugging the correspond-
ing telephone or other appliance therefrom, connecting the adaptor in its
place via the line coupling means 32 and then connecting the telephone or
other appliance. All of the adapters are subst~nti~lly identical but for minor
modifications which are dictated by the type of appliance connected thereto.
Thus, the adaptor 21 through which the telephone 20 is connected to the line
11, is provided with an internal ringer whilst the adaptor 16, by means of
which the telephone 15 is connected to one of the three lines 11, 12 and 13,
has no internal ringer. Similarly, the adaptor 23, by means of which the
door lock 22 is controlled, also has no internal ringer but is provided with
a controlled switching device (not shown).
Referring now to Fig. 2 of the drawings, a particular configuration
of the adaptor 27 shown in Fig. 1 will now be described. Tip and ring
connections of the incoming telephone line 11 are connected, via the line
coupling means 32 (see Fig. 1), to respective diodes 40a and 40b, across
which are coupled respective opto-couplers 41a and 41b such as m~nllf~r-
tured by the Motorola Company under the catalog name 4N28. The emitters
WO 94/18780 ~ ~ 5 ~ ~ 6 5 PCT/US94tO1570
of the opto-couplers 41a and 41b are connected, via respective rectifier
diodes 42a and 42b to a common bus 43. A DTMF Transceiver 44 is
connected to the bus 43 and is also connected across the telephone line 11
via respective capacitors 45a and 45b. Similarly, a ring detector 46 is
connected to the bus 43 and is also connected across the telephone line 11.
The telephone extension unit 20 is coupled across the telephone
line 11 via a pair of normally-closed 2-pole, 2-throw switch contacts 47a
and 47b, respectively operated by a relay A. Corresponding normally-open
contacts 48a and 48b are connected to a ring driver 49 which is also
connected to the common bus 43. The normally-open contact 48a is also
connected to a Local Off Hook Detector 50 which is coupled to a power
supply 51 via a primary winding of a coupling transformer 52.
A Ring Notch Filter and Ring Tone Generator 53 is connected
across the secondary winding of the coupling transformer 52 and is also
connected, via a pair of normally-open contacts 54a and 54b of a relay B
across the telephone line 11, an a.c. coupling capacitor 55 being connected
between the normally-open relay contact 54a and the telephone line 11 so
as to de-couple the d.c. voltage from the Ring Notch Filter and the Ring
Tone Generator 53 and hence form the telephone extension unit 20. The
output of the Local Off Hook Detector 50 is coupled via a rectifier diode 56
to the common bus 43.
Also coupled across the telephone line 11 is a bridge rectifier 57
having respective positive and negative output rails 58a and 58b. Connected
across the positive and negative output rails 58a and 58b are two voltage
dividers comprising, respectively, resistors 59a, 59b and 60a, 60b. An
inverter 61 is connected at its input to the common connection between the
resistors 59a and 59b, whilst an inverter 62 has an input connected to the
common junction of the resistors 60a and 60b. Respective oulE,uls of the
inverters 61 and 62 are coupled to a micro-controller 63.
WO 94/18780 21 ~ ~ 6 ~ ~ PCT/US94/OlS70
The positive output rail 58a of the bridge rectifier 57 is connected
to an Audio Sign~lling Device 64 which is responsively coupled to the
micro-controller 63. A manually operated push-button switch 65 is
connected to the micro-controller 63, as is an LED 66. A switch contact
5 67 is responsively coupled to the micro-controller 63 for operating the
remotely-controlled appliance 28 (shown in Fig. 1).
The system 10 is energized by a source of d.c. electricity typically
provided via a rectified domestic a.c. supply. There is provided a back-up
power supply shown schematically as 68, typically constituted by an internal
10 battery, for powering the internal circuit in the event that the domestic a.c.
supply fails.
The operation of the circuit will now be explained. The diodes
40a and 40b, in conjunction with the opto-couplers 41a and 41b and the
rectifier diodes 42a and 42b, constitute an Fxten.~ion On~Off Hook Detector
15 and Pulse Detector which is coupled across the telephone line 11 for
detecting an off-hook condition in any one of the telephone extension units
coupled to the line 11 and producing a general off hook signal. The diodes
40a and 40b are connecte~ in parallel to the respective opto-couplers 41 and
41b so as to be plurality independent and the configuration is symmetrical
20 with regard to the tip and ring connections so that the circuit functions
correctly regardless of the order in which the tip and ring connections are
connected to the line coupling means.
The capacitors 45a and 45b serve for a.c. coupling the DTMF
Transceiver 44 to the telephone line 11, whilst the capacitor 55 serves for
25 a.c. coupling of a speech signal on the telephone line 11 to the Ring Notch
Filter and Ring Tone Generator 53.
Sign~lling an inter-communication between the telephone
extension units, of which only the extension unit 20 is shown in Fig. 2, is
achieved by a.c. coupling of audio signals, both speech via the capacitor 55
WO 94/18780 2~ 6 5 PCT/US94/01570
9
and DTMF via the capacitors 45a and 45b, to the telephone line 11. The
a.c. coupling for inter-communication with the system 10 is accomplished
by depressing the manual push-button switch 65 prior to the lifting of the
handset. Thus, depressing the push-button switch 65 results in a.c.
5 connection between the telephone extension unit 20 and the telephone line
11 via the transformer 52 and the capacitor 55. This is achieved by ch~nging
the state of the relay A whereby the telephone extension unit 20 is de-
coupled from the telephone line 11 and connected instead to the normally-
open relay contacts 48a and 48b. In this condition, the power supply 51
10 supplies d.c. speech voltage to the telephone extension unit 20 through the
primary winding of the transformer 52.
The push-button switch 65 having been depressed, a so-called
"smart code" is transmitted and the handset of the extension unit 20 may
now be lifted and an extension number of another internal extension unit
15 may be dialled either in pulse or DTMF within a predetermined time period
(e.g. five seconds) whereby the "smart code", followed by the dialled
extension number is received by all other adapters coupled to the system via
their respective DTMF Transceivers 44 and the a.c. coupling capacitors 45a
and 45b. Only the dialled extension adaptor will a.c. couple its telephone
20 extension unit, responsive to the dialled extension number, by ch~nging the
state of its relay B, whereupon its d.c. speech voltage will be supplied by the
corresponding supply 51 within its own adaptor 27 in.cte~d of via the
telephone line 11. At the same time, all the other extension units in the
system whose respective adapters do not recognize the dialled extension
25 number will, under control of their respective micro-controllers 63, change
the state of their respective relays A so as to disconnect their extension units20 from the telephone line 11 so as to prevent their eavesdluppillg on the
internal conversation between the internal caller and the internally-dialled
extension number.
WO 94/18780 PCT/US94/01570
6~ lo
In a similar manner, other internal extension units within the
system can be allowed to join an existing conversation, so as to allow
conference calls, by any one of the existing participants pressing his push-
button switch 65 and ~liallin~ another unit's extension number. If, subsequent
5 to effecting an internal call, an external call is received, then a pilot tone is
generated by the Ring Tone Generator 53 and will be heard by all internal
participants, so as to indicate the presence on the line of an external call.
As will be explained later with particular reference to Fig. S of the drawings,
upon pressing the push-button switch 65, the status of the relays A and B
10 is now changed whereby the relay B, having been previously connected, is
now disconnected, whilst relay A, having been previously connected to the
normally-open contacts 48a and 48b, is now connected to the normally-
closed contacts 47a and 47b. By this means, the d.c. speech voltage is
disconnected from all the participating internal extension units, which are
15 now connected directly to the external line 11. By virtue of having
disconnected the Ring Tone Generator 53, the ring tone is interrupted and
by virtue of connecting the extension units directly to the telephone line 11,
the external call will now be received.
A light-emitting diode (LED) 66 is responsively coupled to an
20 output of the micro-controller 63 so as to give a visual indication when,
during an existing call, the current telephone extension unit 20 is on-hook
whether in EXIERNAL or INTERCOM mode. In such condition, relay A in
the current telephone extension unit 20 is switched such that the telephone
extension unit 20 is d.c. de-coupled from the telephone line 11, whilst relay
25 B is also disconnected so that the current telephone extension unit 20 is also
a.c. de-coupled from the telephone line 11. This situation, (constituting a
third position of the switching means) is thus indicated by the LED 20 when
min~ted
WO 94/18780 ~ 1 5 ~; 6 ~ ~ PCT/US94/01570
11
D.c. power is supplied to the system via the power supply 68
which is a typically derived from a recti~led a.c. domestic supply backed up
by an internal rechargeable battery. In the event of a failure of the domestic
a.c. supply, all of the adapters are connected through their respective
extension units 20 to the telephone line 11 and, although the system 10 no
longer functions as an internal exchange system, the extension units 20 will
nevertheless continue to operate as regular extension units.
The diodes 40a and 40b in conjunction with the opto-couplers
41a and 41b and the rectifier diodes 42a and 42b constitute an Extension Off
10 Hook and Pulse Dial Detector 70 which serves two functions. First, it
detects whether the extension unit 20 is off-hook. Secondly, when the
telephone extension unit 20 employs pulse t~ ng~ the dialled pulses are
detected by the Extension Off Hook and Pulse Dial Detector 70 and fed to
the micro-controller 63 which instructs the DTMF Transceiver 44 to
15 transmit the dialled pulses in DTMF. The Local Off Hook Detector 50
detects a local off-hook condition when the extension unit 20 is connected
in INTERCOM MODE.
The bridge recti~ler 57 in conjunction with the voltage dividers
59a, 59b and 60a, 60b and the inverters 61 and 62 constitute a General Off
20 Hook and Zero Volt Pulse Detector 72, which generates a General Off Hook
signal whenever a handset of any of the extension units within the system
10 is lifted, or a zero volt pulse was sent down the telephone line 11 by
another extension unit.
The transforrner 52 in conjunction with the Ring Notch Filter and
25 Ring Tone Generator 53, the Relay B and the capacitor 55 together
constitute an a.c. coupling circuit 73 for connecting the extension unit 20 to
the telephone line 11 when a connection to another internal extension unit
is required during INTERCOM MODE.
WO 9~118780 PCT/US94/01570
2~5~S 12
The rectifler diodes 42a, 42b and 56 constitute OR-gates for the
Local Off~Hook Detector 50, the Extension Off Hook and Pulse Dial
Detector 70, respectively, so that in the event of any of these detectors
generating appropriate detection .sign~l~, a Local Off Hook signal is fed via
S the common bus 43 to the micro-controller 63.
The voltage across the bridge recti~ler 57 between the positive
and negative output rails 58a and 58b thereof is approximately 50V d.c., this
being the d.c. voltage across the telephone line 11. On the other hand, the
voltage which must be supplied to the inverters 61 and 62, as well as to the
10 micro-controller 63, should be no greater than approximately 5V d.c. If the
handset of an extension unit is lifted, then the voltage across the telephone
line 11, throughout the whole system 10, falls from the original value of
50V d.c. to approximately 10V d.c.. Thus, this drop in voltage may be
employed in order to determine a General Off Hook condition.
In a practical embodiment reduced to practice, the values of the
resistors 59a and S9b are respectively 50 MQ and S MQ, such that the
voltage at their common junction is approximately SV when all the handsets
are closed and the voltage across the telephone line 11 is therefore 50V d.c.
In this situation, the voltage at the output of the invelLer 61 is 0 (logic
20 LOW). If now one of the handsets in the system is lifted, then the voltage
appearing across the telephone line 11 falls from approxim~tely 50V d.c. to
approximately 10V d.c., whereupon the voltage appearing at the common
junction of the resistors S9a and S9b falls to somewhat less than lV d.c. and
the output of the inverter 61 now goes to logic HIGH. Thus, the voltage
25 divider S9a and S9b in conjunction with the inverter 61 constitute a General
Off Hook Detector for producing a General Off Hook signal whenever any
of the handsets of the extension units 20 in the system 10 is lifted.
The value of the resistor 60a is 50 MQ and the value of the
resistor 60b is 30 MQ. Thus, when all of the handsets are closed and the
WO 94/18780 ~ 6 ~ ~ PCT/US94/01570
13
voltage across the telephone line 11 is 50V d.c., the voltage appearing across
the common junction of the resistors 60a and 60b is approximately 30V d.c.
However, such a voltage cannot exist in practice, because the inverter 62
connected to the common junction of the resistors 60a and 60b is a CMOS
5 circuit, having internal protection diodes which clip the voltage to a
maximum of SV d.c. The high values of the resistors 60a and 60b ensure
that only minimal current flows to the inverter 62 (so as not to damage the
internal protection diodes) and under normal conditions, the voltage
appearing across the common junction of the resistors 60a and 60b is
10 therefore clipped to 5V d.c.
If the voltage across the telephone line 11 now drops to IOV d.c.,
then the voltage at the input of the inverter 62 falls to 6V d.c. (from the
theoretical value of 30V d.c.) and, consequently, the output of the inverter
62 remains LOW. Even if more than one handset in the system 10 is lifted
15 simultaneously, resulting in the line voltage falling from 10V d.c. to a
somewhat smaller value, the voltage appearing at the common junction of
the resistors 60a and 60b is still sufficiently high to ensure that the output
of the inverter 62 remains LOW.
However, when any handset is lifted and, at the same time, the
20 telephone line 11 is temporarily shorted, then the voltage appearing across
the common junction of the resistors 60a and 60b falls to zero and, in this
case, the voltage appearing at the output of the inverter 6' goes to HIGH.
The telephone line 11 may indeed be temporarily shorted when the push-
button switch 65 is depressed, under control of the micro-controller 63, or
25 upon lifting or replacing the handset of the extension unit 20 in INTERCOM
MODE. Thus, the voltage divider 60a, 60b in conjunction with the inverter
62 constitutes a 0-10 and 10-SOV pulse detector which produces a detection
signal whenever the push-button switch 65 is depressed and it is required
to awaken the DTMF Transceivers in all of the rem~ining adapters.
WO 94118780 - PCT/US94/01570
2~6~ 14
The switch 67 operates under control of the micro-controller 63
to control the remotely-controlled appliance 28 in order that the appliance
can be enabled or disabled remotely by telephone. The audio sign~lling
device 64 is typically constituted by a beeper, buzzer or loudspeaker to give t
S an audio signal or a vocal announcement when addressed under control of
the micro-controller 63. The DTMF Transceiver 44, the Ring Detector 46,
the Ring Driver 49, the Local Off Hook Detector 50, the Ring Notch Filter
and Ring Tone Generator 53 and the Audio Sign~lling Device 64 are all
standard components well-known to those skilled in the art and therefore
10 not requiring any further description. The operation and the progr~mming
of the micro-controller 63 will be described in detail below with particular
reference to the flow diagrams shown in Figs. 4 to 10 of the drawings.
It should be noted that in the adaptor 27 shown schematically in
Fig. 2, the DTMF Transceiver 44 remains dormant (i.e. inoperative) until
15 awakened by the zero volt pulse which is produced on de~res~illg the push-
button switch 65 or upon lifting or replacing the handset in INTERCOM
MODE. It then operates under control of the micro-controller 63 to perform
whatever function is required, whereafter it is again (under control of the
micro-controller 63) disabled until subsequently reawakened by another
20 pulse. This is necessary particularly when the adaptor 21 is operated by the
internal battery 68 since, whilst most of the components in the adaptor 21
require very little current when not operational, the DTMF Transceiver 44
has a current drain of 10 Ma which would drain the internal battery 68
within appro~im~tely only two weeks. By rendering the DTMF Transceiver
25 45 operational only when required, the life of the internal battery 68 may be increased to apprnximately two years since the current drain of the
rem~inin~ components is of the order of only 20-30,uA.
Additionally, by awakening the DTMF Transceiver 44 only when
it is required to transmit or receive DTMF signals, it can be ensured that a
WO 94/18780 2 ~ ~ ~ 6 6 5 PCT/IJS94/01570
~ 15
DTMF signal sent over the telephone line 11 will have no effect unless the
DTMF Transceiver 44 of the respective adaptor ''1 has first been awakened
by depressing the push-button switch 65. This is important in the situation
where an internal user answers an external call and transfers the call to
5 another internal extension by depressing the push-button switch 65 (so as
to awaken the DTMF Transceiver 44) and then di~lling the appro~liate
internal extension number. The corresponding DTMF code thus generated
will not only be transmitted to the internal extension but will, in fact, also
be transmitted over the telephone line 11. It would obviously be undesirable
10 to cause the transmitted DTMF signal to alert an internal extension at the far
end having the same extension address code as the local extension to whom
the call is to be transferred. However, in practice, this cannot happen
because although the DTMF signal is indeed transmitted over the telephone
line 11, it is not received by the DTMF Transceiver at the far end since this
15 remains dormant, no awakening signal having been transmitted thereto.
Fig. 3 illustrates in more detail the controller 31 shown in Fig. 1
for allowing connection and control of all automatic answering extension
units connected to the telephone line 11. The controller 31 can be coupled
to a plurality of telephone lines, if desired.
The controller 31 comprises a DTMF/PULSE line interface 75
connected to the telephone line 11. An Off Hook Detector 76 and a Ring
Detector 77 are likewise coupled to the telephone line 11 as well as being
connected to a micro-controller 78 to which is also coupled a DTMF
receiver 80. A Fax/Modem Signal Detector 81is connected to the telephone
line 11 as well as to the micro-controller 78. The circuit is powered by a
power supply 82 which can either be derived from a rectified domestic a.c.
supply or, alternatively, can be derived from an internal battery back-up.
The controller 31 operates as follows. The Ring Detector 77
detects an external ring on the telephone line 11 and awakens the micro-
WO 94/18780 ~15 ~ 6 6 5 PCT/US94/01570
16
controller 78. The micro-controller 78 allows sufficient time, for example,
four rings, for a local subscriber to lift the handset of the extension unit
coupled thereto whereafter, if the local handset is not lifted, the controller
31 connects a 600Q load across the telephone line 11 so as simulate an off-
hook condition. A false ring signal, of different frequency, is generated by
the DTMF/PULSE Line Interface 75 and transmitted along the telephone
line 11. By such means, an external caller receives the i~ ,les~ion that the
extension is on-hook.
However, if the remote caller is a machine, such as a facsimile
or modem, it will ignore the false ring signal, will detect the off-hook state
of the local extension unit and will start sending its h~n~lch~ke protocol
signals. The Fax/Modem Signal Detector 81 in the controller 31 identifies
the type of service required by the remote caller according to its h~nc~sh~ke
protocol signals in order to determine whether the remote caller should be
connected to a local facsimile m~chine, computer modem, remotely-operated
appliance, and so on. If none of the above signals is detected within a
predetermined time, e.g. three seconds, the controller 31 assumes that the
local answering rn~chine service is required and sends an a~,"~.iate control
signal to the micro-controller 78 which, in turn, produces an appropriate
"smart code" for addressing the corresponding telephone extension unit.
Figs. 4 to 10 describe in detail the logic in accordance with which
the micro-controller 63 (Fig. 1) operates. Fig. 4 shows a MAIN routine
(100) which is executed continuously in order to determine the status of the
respective adapter and which branches to subroutines as and when required.
Specifically, at step 101, an initi~li7~tion procedure is invoked
whereby the status of the relays A and B is checked and, if necessary, they
are returned to their respective reset states as shown in Fig. 2. All internal
flags are likewise reset.
WO 94/18780 PCT/US94/01570
21~5S~
~ 17
At step 10 ', the status of the General Off Hook Detector 7'' and
the Local Off Hook Detector 50 is determined. A negative response to step
10 implies either that an external handset has been lifted, in which case the
General Off Hook Detector 72 produces a signal whilst the Local Off Hook
5 Detector 50 does not or, alternatively, that no local handsets have been
lifted, in which case no signal is produced by either the General Off Hook
Detector 72 or the Local Off Hook Detector 50. In either case, at step 104
a check is determined as to whether the General Off Hook Detector 72 has
produced a signal. If so, this implies that another handset within the system
10 has been lifted, in which case control branches at step 105 to the EXrERNAL
SLAVE routine which is described in greater detail below with reference to
Fig. 6 of the drawings.
If at step 104 no signal is detected by the General Off Hook
Detector 72, then at step 106 a check is performed to determine whether the
15 push-button switch 65 in the local handset has been depressed. If so, then
at step 107 a single beep is initiated and control branches to the INTERCOM
MASTER routine, which is described in greater detail below with particular
reference to Fig. 7 of the drawings.
If the push-button switch 65 has not been depressed, then at step
20 108 a check is determined as to whether a pulse has been detected and, if
so, control branches at step 109 to the INTERCOM SI~VE routine which is
described in greater detail below with particular reference to Fig. 8 of the
drawings. If no pulse is detected, then at step 110 a check is determined as
to whether a ring signal has been detected by the Ring Detector 46. If so,
2~ then at step 111 the "RING" flag is set for four seconds and control
branches to the beginning of the loop at step 102.
If, however, at step 102 signals are detected from both the
General Off Hook Detector 72 and the Local Off Hook Detector 50, this
means that the current handset has been lifted, which can be due to one of
wo 91/18780 ~ 6 ~ S PCTrUS94/01570
two reasons. Either the local handset wishes to initiate a call or, alternative-ly, an external call was received by the local handset and the call has been
answered. Therefore, at step 112 the status of the "RING" flag is deter-
mined which, as has been explained, is set as soon as the Ring Detector 46
S detects a ring signal owing to an incoming call. If the "RING" flag is OFF,
then control branches at step 113 to the EXIERNAL MASTER routine at step
200. Otherwise, control branches at step 114 to the EXrERNAL M~STER
routine at step 202.
Referring now to Fig. S of the drawings, the principal steps of the
EXTERNAL ~LASTER routine 200 Will be described. At step 201 the
INTERCOM FLAG is reset, if necessary, and the push-button switch 65 is
disabled for five seconds. lt will be recalled from the description of Fig. 4
above, that step 201iS executed only if the "RING" flag is OFF, implying
that the local handset wishes to initiate a call. As will be explained below,
15 the function of the push-button switch 65 is to initiate intçrn~1 calls and, in
this mode, it must be depressed before the handset is lifted and not
afterwards. Therefore, in order to avoid any possible confusion whereby a
user may forget and depress the push-button switch 65 after lifting the
handset, the push-button switch 65 is disabled for a short time period, so
that inadvertent depression of the push-button switch 65 is of no conse-
quence. However, after a five second time period, the push-button switch
65 is enabled once again so as to permit the user to transfer a call or to
invoke conference calls during a conversation.
At step 202 the status of the General Off Hook Detector 72 is
25 determined and, if no signal is detected thereby, then at step 203 control
branches to the MAIN routine at step 100, as shown in Fig. 4. If a signal is
detected by the General Off Hook Detector 72, then at step 204 the status
of the Local Off Hook Detector 50 is determined. If no signal is received
thereby, then at step 205 the status of the General Off Hook Detector 72 is
WO 94/18780 PCT/US94/01570
21S~665
19
again determined in order to check for the possibility that the local handset
was lifted and then immediately returned. Under these circumstances, no
General Off Hook signal is detected and so, at step 205A, control branches
once again to the MAIN routine at step 100. If a General Off Hook signal
S is still detected at step 205, then control branches at step 205B to the
EXTERNAL SLAVE routine described below with reference to Fig. 6 of the
drawings.
However, if a Local Off Hook signal is detected, this means that
the local handset has not been replaced and so, at step 205C, a check is
10 performed to determine whether a "smart code" has been received by the
current adapter from a remote internal adapter. Such a "smart code" may
be sent when a local subscriber lifts his handset for the purpose of m~king
an outside call and finds that the line is engaged owing to the present
external call. In this case, the other adapter is an EXTERNAL SLAVE and, as
15 will be explained below with particular reference to Fig. 6 of the drawings,
he can send an "alert" signal in order to warn the EXTERNAL MASTER that
he wishes to use the outside line. In such case, the EXTERNAL MASTER has
two options: he can either immediately depress the push-button switch 65
in order to initiate a "smart code" whereby the EXTERNAL SLAVE may
20 immediately be connected; or, alternatively, a ten second grace period will
elapse, whereafter the EXTERNAL SI~VE will be connected anyway.
This logic is reflected at step 205E, where a ten second timer is
set, during which period beeps are heard in the EXTERNAI, MASTER's adapter
and at step 207 a check is performed in order to determine whether the
25 EXTERNAL M~STER has depressed his push-button switch 65 in order to
allow connection of the EXTERNAL SLAVE. If not, then the loop repeats
from step 202. If, however, at step 207 the push-button switch 65 has been
depressed or, alternatively, if at step 206 the ten second time period has
termin~te~l, then the beeps are termin~te-l and the push-button switch is
WO 94/18780 PCT/US94/01570
6 6 ~ 20
enabled so as to produce the effect of the push-button switch 6~ having
been depressed. Then, the output of step . 07 is affirmative and at step 208
the beeps are termin~ted, DTMF is awakened and a "smart code" constituted
by a pulse followed by e.g. "#" is generated so as to allow the EXTERNAL
5 SLAVE to join the conversation. The ten second time delay thus provides
discrete connection by an EXrERNAL SI~VE in the event that the EXrERNAL
MASTER does not grant him prior entry by appropriate tr~n~mi~sion of the
"smart code". In effect, there are now two EXIERNAL MASTERS in the
system corresponding to the current handset and the handset which has just
10 joined the conversation.
In the logic described so far, the second EXIERNAL MASTER
joined the conversation at his initiative by sending an interrupt signal.
However, according to an alternative scenario, the EXIERNAL MASrER,
corresponding to the current handset who is engaged in an external call, may
15 decide on his own initiative to involve another local handset. This is
accomplished by depiessillg the push-button switch 65 in order to send a
"smart code", after which the local extension number of the desired
extension unit is dialled.
At step 209, having already established that the push-button
20 switch is depressed, having awakened DTMF and set the five second timer
(at step 208), a check is now performed in order to determine whether the
Local Off Hook signal is detected. This test is necessary, notwithst~n~iing
the fact that a Local Off Hook signal has already been detected at step 204
because if the current handset operates using pulse ~ lling, then the Local
25 Off Hook signal will appear to oscillate between ON and OFF every 0.05 s.
Thus, if at step 209 no Local Off Hook signal is detecte~, then at step 210
a check is performed in order to deterrnine whether the local handset used
pulse ~ lling and, if so, at step 211 the dialled code is converted from
WO 94/18780 ~ ~ 5 5 6 ~ 5 PCT/US94/01570
21
pulse to DTMF, the DTM~ signal is sent down the line, DTMF is killed and
control branches to step 20''.
Otherwise, control branches to step '12, which checks whether
a General Off Hook signal is detected, as well as the Local Off Hook signal
5 which has already been established at step 209. I~ not, then the current
handset (which is the EXrERNAL MASTER) is the only handset in the system
which is off-hook and control branches at step 213 to the MAIN loop 100
already described with reference to Fig. 4 of the drawings. However, if a
General Off Hook signal is detected then, at step 214, a further check is
10 determined as to whether the Local Off Hook signal has been detected. This
further check is necessary because the current handset, having dialled
another internal extension, may have done so in order to transfer the external
call thereto and may therefore have now replaced his handset. In this case,
of course, no Local Off Hook signal will be detected and the current h~n~l~et
15 changes status from EXIERNAL MASTER to E~TERNAL SLAVE and control
branches at step 215 to the EXIERNAL SLAVE routine 300 which will be
described in greater detail below with reference to Fig. 6 of the drawings.
However, if at step 214 a Local Off Hook signal is ~letected, then
at step 216 the status of the push-button switch 65 is deterrnined. This will
20 be deplessed if the current handset is still in the process of transferring a call to another internal extension via DTMF and, in this case, control
branches to step 208. Otherwise, at step 217, the elapsed time period is
determined and if the five second time period has not yet elapsed control
branches to step 209 and the loop repeats. Otherwise, when five seconds
25 has elapsed, control branches to step 202.
Referring now to Fig. 6 of the drawings, the E;XIERNAL SLAVE
routine 300 will be described. As has already been explained in some detail
with reference to Fig. S of the drawings, an EXrERNAL SLAVE is any
internal extension which is on-hook whilst a conversation is in progress
W094/18780 PCT~S94/01570
21~5~5 22
between an outside caller and at least one EXTERNAL MASTER. The
EXTERNALSLAVE routine 300 allows for the possibility that the EXrERNAL
SLAVE may interrupt the EXIERNAL MASTER as described previously or,
alternatively, may be dialled by the EXIERNAL MASrER either for the
5 purpose of transferring the external call to the EXIERNAL SLAVE or for
allowing him to participate in the conversation.
On entry to the EXIERNAL SLAVE routine 300, relay A in the
EXrERNALSLAVE adapter is reset such that the telephone extension unit 20
is connected to the telephone line 11. Therefore, relay A is now set at step
10 301 in order to disconnect the extension unit from the line wh reupon, at
step 302, the status of the General Off Hook Detector is determined. If no
General Off Hook signal is detected, then the EXTERNAL MASTER which
went off hook has subsequently gone on-hook and so at step 303 relay A
is reset, the push-button switch 65 in the local adapter is enabled and
15 control branches to the MAIN routine 100 described above with reference to
Fig. 4 of the drawings.
Otherwise, if a General Off Hook signal is detected, then the
EXTERNAL MASTERis still connected and at step 302A the status of the
push-button switch 65 in the local adapter is determined. If this is
20 depressed, then at step 302B a single beep is emitted, followed by a "smart
code" comprising a zero volt pulse followed by e.g. DTMF "A". A series
of DTMF beeps is also produced so as to provide a status indication to the
EXTERNALSI~VE. At the same time, the smart code is transmitted to the
EXIERNAL MASTER and causes a series of DTMF beeps to be produced
25 therein so as to provide corresponding status indication to the EXTERNAL
MASTER. As has been explained previously, a ten second timer is now
initiated and a BREA~ FLAG is set. Step 302C checks whether the ten
second time limit has elapsed, in which case at step 30 'D, relay A is reset,
thereby connecting the local handset to the line whereupon the loc.al
WO 94/18780 2 ~ ~ 5 ~ ~ ~ PCT/US94/01570
23
telephone extension unit becomes an EXI ERNAL MASTER and control
branches to step 202 (Fig. 5). If the ten second time limit has not yet
elapsed, then at step 304 a check is determined as to whether a pulse has
been received having been sent down the telephone line 11 from the
S EXIERNAL MASTER in order to connect the local extension unit to the
conversation even before the ten second time limit has elapsed. If no such
pulse is detected, then control branches to step 302 and the loop repeats.
Otherwise, at step 305, DTMF is awakened for one second in order to allow
sufficient time for an interrupt signal constituted by e.g. DTMF "~" sent by
10 the EXIERNAL MASTER to be detected at step 306. Again, if no such signal
is detected, control branches to step 302. Otherwise, at step 307 the status
of the BREAK FLAG iS determined and if it is set then, at step 307B, the
DTMF beeps which were initiated at step 302B to give an indication to the
EXIERNAL SLAVE are stopped, relay A is reset and control branches to the
1~ EXTERNAL MASTER routine at step 202 (see Fig. 5).
If at step 307 the BREAK FI~G iS not set, this means that the
EXIERNAL MASTER has attempted to call the local extension unit on his
own initiative without having been requested to do so by the local extension
unit. In this case, at step 307C a five second timer is set and steps 308 to
20 309 constitute a loop which checks whether any DTMF digit was receivèd.
At the end of the five second time period, if no DTMF digit has been
received, then at step 310 DTMF is killed and control reverts to step 302.
If, at step 308, a DTMF digit is received, then step 311 checks
whether the received DTMF digit corresponds to the code of the current
25 adapter. If not, then step 312 checks whether the received DTMF code is
"0". If not, then at step 313 DTMF is killed and control reverts to step 302.
However, if DTMF code "0" is received, then step 314 checks whether an
additional DTMF digit is received and, if so, the received DTMF digit is
stored at step 315, DTMF is killed and control branches to step 316 which
WO 94/18780 PCT/US94/01570
~1~S~65 24 ~
initiates the CONNECT ROUTINE described in detail below with reference to
Fig. 9 of the drawings. If at step 314 no additional DTMF digit is received,
then step 317 allows for step 314 to be repeated if the five second time
period has not elapsed or, alternatively, step 318 causes control to branch to
step 310, which kills DTMF and reverts control to step 302. If, at step 311,
the received code corresponds to the address code of the current handset
then, again, the CONNECT ROUTINE iS initiated so as to enable connection
of the addressed telephone extension unit to the telephone line, thereby
ch~nging its status from an EXTERNAL SLAVE to an E~'TERNAL MASTER.
The significance of step 312, which checks whether the received
DTMF code is "0", and associated steps 314 and 315, which allow for a
subsequent DTM~ digit to be stored, will become clear when the CONNECT
ROUTINE is described with reference to Fig. 9 of the drawings. However,
briefly at this stage, it allows for the EXIERNAL MASTER to call a desired
EXI`ERNAL SLAVE by sending a specific number of beeps corresponding to
the address code of the desired EXrERNAL SI~VE to all EXIERNAL SI~VES,
any one of which can then be lifted by an internal user who recognizes the
code as his extension number. In contrast to this, ~i~lling only the DTMF
digit of the desired adapter will cause only that adapter to ring and if the
user is in a dirr~rellt room he will receive no indication of the attempted
transfer.
Fig. 7 shows the logic associated with an INTERCOM l\~ASTER
routine 400 which is invoked when an extension unit depresses the push-
button switch 65 prior to lifting the handset, thereby informing the system
that an internal call is to be dialled.
At step 401, various injti~li7~tion steps are effected and, in
particular, DTMF is awakened and a pulse followed by e.g. "~" is sent down
the telephone line, whereafter DTMF is killed. Relay A is set so as to
change the coupling of the extension unit to the telephone line from direct
WO 94/18780 2 :1 ~ 5 6 6 ~ PCT/US94/01570
25
coupling to a.c. coupling via the transformer 52 and the capacitor 54a. At
step 40, the General Off Hook signal is tested. If ON, this means that
another extension unit has already lifted its handset and so at step 403 the
timer is reset and the E~TERNAL SLAVE routine 300 is invoked as described
5 above with reference to Fig. 6 of the drawings. Otherwise, only the handset
of the current extension unit has been lifted and at step 404 the output of the
Ring Detector 46 is evaluated. If ON, an external call is on the line and at
step 405 the timer is reset and control branches to the MAIN routine 100,
shown in Fig. 4. If no RING signal is detected, then at step 406 the status
10 of the Local Off Hook Detector 50 is determined. If ON, then the local
handset has been lifted and at step 407 relay B is set, DTM~ is awakened
and a DTMF code e.g. "C" is sent for incrementing a USER'S COUNT
variable stored in all of the adapters as will be described below. At the
same time, a five second timer is set. Otherwise, if at step 406 no Local
15 Off Hook signal is detected, this means that although the push-button switch
65 was depressed, the hand set was not lifted and step 408 allows the loop
to be repeated until the five second time period has elapsed whereupon, at
step 409, if the handset has still not been lifted control branches to the l\~AIN
routine 100 shown in Fig. 4.
However, if the handset were lifted within the five second time
period, then an intçrnal extension code may now be dialled in order to call
another internal extension. Thus, step 410 checks whether the current
telephone extension unit employs pulse dialling and, if not, at step 411 the
presence of a DTMF signal is checked. If no DTMF signal is detected then,
at step 412, the status of the Local Off Hook Detector is again checked and,
if affirmative, step 413 checks for a Ring signal to allow for the possible
arrival of an external call. If no Ring signal is detected, then step 414
checks whether the five second time period has termin3te(1, in which case
control branches to step 434, which will be described in greater detail belo~v.
WO 91/18780 21 S ~ 6 ~ ~ PCT/US94/01570
26
Otherwise, the loop is repeated either until the five second time period
elapses or until the loop exits owing to one of the following conditions.
It should be noted that the USER'S COUNTER iS incremented in
respect of every adaptor in the system 10 whenever a local handset is lifted
5 and the system is in INTERCOM MODE. Consequently, before an external
call may be received, it is necessary to reset the USER'S COUNTER in all of
the adapters in the system. Thus, if at step 413 a Ring signal is detected,
then step 416 checks whether the push-button switch 65 is depressed for the
purpose of accepting the external call. If the push-button switch 65 is
10 depressed, then at step 417 one beep is sent, relay B is reset, the INTERCOM
FLAG (set at step 401) is reset, relay A is reset and control branches to the
MA~N routine 100 shown in Fig. 4 whereby the INTERCOM MASTER iS d.c.
connected to the telephone line 11 thereby becoming EXIERNAL MASTER
so as to allow reception of the external call. Since the EXIERNAL MASTER
15 is off-hook, the General Off Hook Detector 72 produces a General Off
Hook signal, responsive to which the USER'S COUNTER iS reset in all of the
telephone extension units.
If, at step 416, the push-button switch 65 is not depressed, then
control branches to 410 where the loop is repeated either until the push-
20 button switch 65 in the local extension unit is depressed or, alternatively,until owing to the termination of the five second time period, control
branches to step 434. If, at step 412, no Local Off Hook signal is detected,
this means that the local handset has been replaced. Therefore, at step 418
DTMF is awakened, a disconnect code "D" is sent, DTMF is killed, the
25 USER'S COUNT iS decremented in all of the adapters and relay B is reset.
If, at step 419, the USER'S COUNT is greater than "0" then, at step 420, the
current control unit branches to step 525 of the INTERCOM SLAVE routine
which is described below in greater detail with particular reference to Fig. 8
of the drawings. Otherwise, if the USER'S COUNT iS "0", this means that all
WO 94/18780 PCT/US94/01570
27 ~ 6~
the local handsets have been replaced, including the current handset, and
therefore at step 421, relay A is reset, the INTERCOM FLAG set at step 401
is reset and control branches to the MAIN routine 100 shown in Fig. 4.
At step 410, if the test for pulse dial is affirmative, then at step
S 422 the pulses are converted to DTMF signals, a fifteen second timer is set
and beeps are sent along the line. At step 423 the fifteen second timer is set
and the beeps are sent if the current handset operates under DTMF. Step
424 chec}~s whether the DTMF code is "C" (i.e. Connect). If not, step 425
checks whether the Local Off Hook signal has been detected. If so, then
step 426 checks whether the Ring Detector 46 has detected a Ring signal
and, if not, step 427 checks whether the push-button switch 65 has been
depressed. If not, step 428 checks whether the fifteen second time period
has termin~teA, the loop starting from step 424 being repeated until the
fifteen second time period termin~t~. If, at step 427, the push-button
switch 65 is depressed, then step 429 resets the fifteen second timer, sends
a pulse followed by e.g. "it", whereupon control branches to step 410
permitting another internal extension to be dialled by the INTERCOM
MASTER.
If, at step 428, the fifteen second time period has elapsed, then
step 430 kills DTMF, stops the beeps and returns control to step 434. If at
step 424, a Connect code (e.g. DTMF "C") is detected, then step 431 resets
the timer, stops the beeps and increments the USER'S COUNT in respect of
all adapters in the system, whereupon conkol branches to step 434. If in
step 426, a Ring signal is detected, then step 432 e~mines the status of the
push-button switch 65. If the push-button switch 65 is depressed, then step
433 branches to step 417 so as to allow the external caller to make
connection.
- If at step 434 a pulse is detected, this indicates that another
internal extension unit (constituting an INTERCOM SLAVE) wishes to join the
WO 94118780 PCT/US94/01570
21~66S 28
conversation and has depressed the push-button switch on its handset for
alerting INTERCOM MASTER of its desire to make connection. If no pulse
is detected, then step 435 checks whether the Local Off Hook signal is
detected and, if so, step 436 checks whether a Ring signal has been detected.
If not, the possibility exists that another internal extension unit wishes to
make connection and has alerted the INTERCOM MASTER of this by
depressing its push-button switch, thereby setting a BREAK FLAG at step
445B. Step 436A checks whether the BREAK FLAG iS set, in which case the
INTERCOM MASTER has ten seconds to permit the connection, failing which
the INTERCOM SI~VE will, in any case, effect the required connection. Step
436B checks whether this ten second time period has elapsed, in which case,
step 437C resets the BPcEAK FLAG, stops the beeps and returns control to
step 434. Otherwise, if the ten second time period has not yet termin~te-l,
the status of the push-button switch 65 in the INTERCOM MASTER iS
checked. If it is not depressed, then control returns to step 434. Otherwise,
at step 438 a single beep is generated, the beeps are then stopped, a five
second timer is set, DTMF is awakened, a pulse followed by e.g. "~" is sent
and control reverts to step 410, permitting the INTERCOM MASTER to dial
the extension code for effecting the required connection with the respective
INTERCOM SLAVE.
If at step 434 a pulse is detected, this could either be due to the
fact that another INTERCOM MASTER participating in the internal conversa-
tion wishes now to disconnect or, alternatively, the reverse: an INTERCOM
SLAVE wishes to connect. In either case, step 442 awakens DTMF and sets
a one second timer for receiving a DTMF code. Steps 443, 444, 445 and
445A check for the arrival within the one second time period of DTMF
codes e.g. "C", "D" and "A" for effecting Connection, Discormection and
Alert, respectively, of an INTERNAL SLAVE handset. If a Connect code is
received, then step 446 increases the USER'S COUNT and passes control to
WO 94/18780 21 ~ 5 ~ 6 ~ PCT/US94/01570
29
step 434, the loop being repeated until the local handset is replaced and
control branches to step 418. If a Disconnect code is received, then the
USER'S COUNT is decreased and control branches to step 419. If an Alert
code is received then, at step 445B, a ten second timer is set, the BREAK
S FLAG is set and beeps are sent down the telephone line so as to alert the
INTERCOM MASTER that a currently disconnected extension unit (INTERCOM
SLAVE) wishes to make connection. Control then passes to step 434.
Fig. 8 describes the INTERCOM SLAVE routine 500 which parallels
the INTERCOM MASTER routine 400 described above with reference to Fig. 7
10 of the drawings. Therefore, not all steps are described in detail even though,
for the sake of completeness, all relevant steps are shown in the figure.
At the outset, it will be recalled that the INTERCOM SLAVE
routine 500 is executed in one of two conditions: either the INTERCOM
MASTER wishes to call a disconnected handset (INTERCOM SLAVE) for
15 participation in an existing conversation; or, alternatively, the IN~ERCOM
SI~VE on its own initiative wishes to join a conversation by sending an
Alert signal. In either case, at step 501 a one second timer is set an DTMF
is awakened, whereafter step 502 checks for the presence of a DTMF "~"
code. If absent, the loop is repeated until step 503 determines the one
20 second time period has elapsed whereafter, at step 504, DTMF is killed and
control branches to the MAIN routine 100 (Fig. 4). However, if at step 502
a DTMF "#" code is detected, then step 504 sets a five second timer and
awakens DTMF. Step 506 checks for the presence of a General Off Hook
signal whose presence, of course, indicates that one of the extension units
25 is connected to the external line. In such conditions, it is not a~lmi~sible for
other extension units to intercommunicate via the INTERCOM MODE and so,
at step 507, the USER'S COUNT is reset, relay B is reset and control branches
- to the EXIERNAL SI~VE routine 300 described above with reference to Fig.
6 of the drawings.
WO 94/18780 ~ ; PCT/US94/01570
If at step 506 no General Off Hook signal is detected, then step
508 checks for receipt of a DTMF "C" code sent by the INTERCOM MASTER
for connecting the INTERCOM SLAVE handset. If no DTMF "C" code is
detected, then step 509 causes the loop to be repeated until the five second
5 time period for effecting the desired connection termin~tes, whereupon at
step 510 DTMF is killed and control branches to the MAIN routine 100 (Fig.
4). Otherwise, if a DTMF "C" code is detected, then step 511 sets relay A
so as to connect the extension unit to the line via the transformer 52 and the
capacitor 55, a six second timer is set, DTMF is awakened and the USER'S
10 COUNT is incremented. By this means, the fact that another extension unit
has gone off hook, thereby increasing by one the number of off-hook
handsets, is recorded in the adaptor of the current INTERCOM SLAVE and
ensures that all adapters are, at all times, updated as to the number of
handsets which are off-hook in the INTERCOM MODE. This iS important
15 because, in INTERCOM MODE, there is no General Off Hook signal and
therefore the only way to determine whether any of the handsets is off-hook
is to keep a constant tally in all of the adapters of the number of handsets
which are off-hook. Only when this number equals zero is it known that
all handsets have been returned, thereby allowing control to branch to the
20 MAIN routine 100 (Fig. 4).
Steps 512 to 520 allow the INTERCOM SLAVE to monitor an
extension code dialled by an INTERCOM MASTER and to effect the required
connection if the dialled extension code corresponds to the extension code
of the INTERCOM SLAVE. If the dialled extension number is preceded by
25 "0", then a number of beeps corresponding to the dialled extension will be
heard at all INTERCOM SI~VES in the system. For example, if the
EXl~ERNAL MASTER wishes to dial extension S, then either DTMF "5" can
be dialled directly, in which case only the addressed extension unit will ring;
or, alternatively, DTMF "05" can be dialled, in which case all on-hook
wo 94/18780 2 ~ 5 5 6 ~ ~ PCT/USg4/01570
31
adapters in the system will emit five beeps for so long as the timer is set,
or until one of the INTERNAL SLAVE handsets is lifted. As has been
explained above with reference to the EXIERNAL SLAVE routine, this permits
a user to identify that he is being called even when he is not in his room
S and, further, allows him to join the conversation by lifting any of the on-
hook handsets: not necessarily his own.
Steps 521 to 524 check whether a DTMF "D" code or a DTMF
"C" code is received, indicating that an INTERNAL MASTER has disconnected
or that another INTERNAL SLAVE has connected, respectively, the USER'S
10 COUNT being adjusted accordingly.
Control branches to step 525 in the event that no DTMF code was
received and the five second time period has elapsed. In this case, step 525
kills DTMF and step 526 checks whether a General Off Hook signal is
detected. If so, then step 527 resets the USER'S COUNT, resets relay B and
branches to the EXrERNAL SI~VE routine 300 (Fig. 6). If, at step 526, no
General Off Hook signal is detectecl, then step 528 checks for the presence
on the line of a 0V pulse followed by ";~" which, it will be recalled, are
produced by an INTERCOM MASTER d~plessillg its push-button switch 65
prior to ~liallin~ the extension code of a INTERNAL SLAVE to which
20 connection is required. If, at step 529, the BRE~K El,AG iS not set, this
means that the INTERNAL MASTER initiated the connection, in which case
a five second timer is set, DTMF is awakened and control reverts to step
512, allowing the INTERCOM MASTER to dial the required extension code.
Otherwise, if at step 529 the BREAK FLAG iS set, this means that the current
25 adapter initiated the connection by sending an Alert signal and that the
INTERCOM MASTER responded within the ten second time period so as to
allow the INTERCOM SLAVE to effect the required connection. In this case,
control branches to step 534, wherein the DTMF beeps are stopped and relay
B is set, thereby connecting the current telephone extension unit which thus
WO 9~/18780 PCT/US94/01570
21S~6~ 32
ceases to be an INTERCOM SLAVE and becomes instead an INTERCOM
MASTER, control branching to step 434 in the INTERCOM MASTER routine
(see Fig. 7).
Fig. 9 shows the CONNECT routine 600 which is called by the
S EXTERNAL SLAVE and INTERCOM SLAVE routines described above with
reference to Figs. 6 and 8 of the drawings. At step 601 a fifteen second
timer is set for allowing connection of the current extension unit within a
fifteen second time period. At step 602, DTMF is killed whilst step 602
distinguishes between the current adapter being addressed directly by
10 f~iallin~ its extension code only or, alternatively, to its being addressed by
first ~ 11ing "O". If at step 603 no "smart code" is detected, then step 603A
checks for the presence on the line of DTMF "D" denoting disconnection of
an INTERNAL MASTER extension unit. If DTMF "D" is cletectecl, then step
603B checks whether the USER'S COUNT iS zero, in which case the beeps are
15 stopped and conkol branches to the MAIN routine 100 (see Fig. 4).
Otherwise, step 603D stops the beeps and reverts control to the INTERCOM
SLAVE routine 500 shown in Fig. 8. If, at step 603A, no DTMF "D" code
is detected, then step 604 checks for the present of the Local Off Hook
signal and, if this is absent, step 604A checks the status of the INTERCOM
20 ~I~G. If this is not set, then the system 10 is not in the INTERCOM MODE
and so step 604B checks whether a General Off Hook signal is detected. If
not, step 604C stops the beeps and restores control to the MAIN routine 100
(Fig. 4).
Otherwise, if a General Off Hook signal is detected, this means
25 that the CONNECT routine has been called by the EXIERNAL SLAVE routine
300 (Fig. 6). Regardless of which routine calls the CONNECT routine 600,
the loop is repeated, as required, until the fifteen second time period
termin~tes or until step 603 detects a "smart code", or until step 604 detects
a Local Off Hook signal. If at step 605 the fifteen second time period has
WO 94/18780 2 1~ ~ 6 ~ ~ PCT/US94101570
33
terminated, then step 606 stops the beeps and steps 607, 608 and 609 cause
branching to step 525 of the INTERNAL SLAVE routine or to step 300 of the
EXTERNAL SLAVE routine, depending on which of these two routines called
the CONNECT routine in the ~lrst place.
If at step 603 a "smart code" is detected, then steps 610, 611 and
612 revert control to step 501 of the INTERCOM SLAVE routine or to step
305 of the EXTERNAL SLAVE routine, again depending on which of these
two routines called the CONNECT routine. Otherwise, if at step 604 a Local
Off Hook signal is detected, then steps 613, 614 and 615 stop the beeps and
enable the push-button switch. Further, step 614 sets relay B, increases the
USER'S COUNT, and sends DTMF "C" for connecting the INTERCOM SI~VE,
whereupon control branches to step 434 of the INTERCOM MASTER routine
shown in Fig. 7. Otherwise, for an EXIERNAL SLAVE, relay A is reset and
control branches to the EXIERNAL MASTER routine.
In the system described so far, the default condition is EXTERNAL
MASTER such that any extension unit can initiate an external call by lifting
the handset so as to couple the extension unit directly to the outside line 11,
whereupon an external extension number can be dialled. In this configura-
tion, depressing the push-button switch prior to lifting the handset puts the
adaptor into INTERCOM MODE.
Ho~ er, it will readily be appreciated that this is merely a
design choice and it is equally feasible for the default condition to be the
INTERCOM MODE in which the default condition for an extension unit is
INTERCOM MASIER such that EXTERNAL MASTER must be selected by
lifting the handset and ~ lling "9", for example.
Fig. 10 shows the principal steps which are invoked in such an
arrangement in a so-called MAIN NORMALLY DISCOMNECTED routine 700.
Step 701 initializes the adaptor, disconnects relay A and connects relay B,
and sets the INTERCOM FLAG. Thereafter, step 703 checks whether a Local
WO 94/18780 PCT/US94/0157û
2 1 ~ 34
Off Hook signal is detected and, if not, step 704 checks whether a 0V pulse
is detected on the line. If not, step 705 checks whether the Ring Detector
has detected a ring signal and, if not, step 706 checks whether a General Off
Hook signal has been detected. If at step 704 a 0V pulse is detected, this
S means that an INTERCOM MASTER wishes to call one of the on-hook
extension units and control therefore branches, at step 707, to the INTERNAL
SLAVE routine at step 501. Otherwise, if at step 705 a ring signal is
detected, then at step 708 relay B is disconnected and relay A is connected,
and control branches to the EXIERNAL MASTER routine. If at step 706 a
10 General Off Hook signal is detected, this means that another handset has
initiated an external call and in order to ensure privacy, step 709 disconnects
relay B and branches to step 302 of the EXIERNAL SLAVE routine shown in
Fig. 6.
If at step 703 a Local Off Hook signal is detected, then conkol
15 branches to step 710 wherein the status of the push-button switch is
determined. If this is not depressed, then step 711 checks whether "9" was
dialled. This caters for the situation wherein all the local extension units arenormally connected in INTERCOM MODE and an outside line is obtained by
first ~ lling ~9". If no "9" is detected, then step 712 checks whether a
20 Local Off Hook signal is detected so as to check whether the handset of the
current extension unit has been replaced, in which case control reverts to
step 703. If at step 710 a push-button signal is detected, then step 716
sends a "smart code" followed by DTMF "C" and control branches to the
INTERCOM MASTER routine shown in Fig. 7. Otherwise, if at step 711 the
25 "9" is detected, this means that an outside line has been dialled and step 717
disconnects relay B, connects relay A and branches to step 202 of the
EXIERNAL MASTER routine.
If at step 713 a zero volt pulse is detected, then at step 718
control branches to step 501 of the INTERCOM SLAVE routine (Fig. 8).
WO 94/18780 ~ i 6 ~ 5 PCT/US94101570
Otherwise, if at step 714 no Ring signal is detected, then step 715 checks
whether a General Off Hook signal is detected. If not, then control reverts
to step 703.
The presence of a Ring signal at step 714 indicates that an
5 external call is on the line, in which case step 719 disconnects relay B,
connects relay A and reverts control to the EXrERNAL MASTER routine (Fig.
5). If at step 715 a General Off Hook signal is detected, this means that an
external call is already in progress, in which case step 720 disconnects relay
B and reverts control to step 302 of the EXrERNAL SLAVE routine,
10 whereupon the current extension unit ceases to be an INIERCOM MASTER
and becomes instead an EXrERNAL SLAVE.
Although the invention has been described with particular
reference to a telephone system providing access to both external and
internal extensions, it may also be used for internal-only systems such as
15 field telephones and the like. For example, field telephones provide a singleinternal line connected to a plurality of extensions which do not have
extension numbers. To "dial" an extension, a handle is usually turned or a
button depressed, and this generates a call signal which is heard by all the
interconnected extensions. Such a system offers no privacy because all
20 extensions can participate in the conversation merely by lifting their
respective handsets.
By connecting the extensions to the intern~l line via the adapter
according to the invention, a field telephone of this kind can be converted
into an intercom system wherein each extension has a unique extension
25 number and privacy is ensured during a conversation between two or more
users such that other users (i.e. "slaves") cannot hear the conversation by
lifting their handsets. Since the system is intern~l only, the coupling
- provided by the adapters may be a.c. or d.c. It should be understood,
however, that the adapters which are required for such a system are merely
WO 94/18780 PCT/US94/01570
~15~6~ 36
a simp ified form of the adapter described in detail above with particular
reference to Fig. of the drawings. Specifically, in the simplified adapter
for use with a field telephone system, the relay B, the transformer ~, the
Local Off Hook Detector 50 and the General Off Hook Detector 7 ' can all
S be dispensed with, and the micro-controller logic altered accordingly.
The preferred embodiment allows for addressable extension units
which each have a unique extension number. However, it will be under-
stood that this is not m~n~tory and can be dispensed with in such situations
as the conventional field telephone just described or where, for example,
10 only two extensions are connected to the line.
Furthermore, although in the preferred embodiment the a.c.
coupling circuit includes a transformer and a capacitor, it will be understood
that other configurations, such as a single capacitor, are also suitable.
It will also be understood that the DTMF codes e.g. "#", "A", "C"
15 and "D" which are employed for call transfer as well as alerting, connecting
and disconnecting of extension units are by way of example only. Other
DTMF codes may equally well be employed consistent with the detailed
logic described above.
It will further be appreciated that, whilst relays A and B are
20 shown in the preferred embodiment for operating the various switches, solid
state components such as triacs can be used in~tead In order to comply
with telephone company regulations, such triacs should preferably be
disabled when energized.
It will equally well be appreciated that although the remotely-
25 operated switch 67 is shown as normally open, it can also be normallyclosed. Likewise, multi-pole, multi-throw switches can be controlled
remotely and the switch can be electro-mechanical or solid state or, indeed,
any type of switch.
WO 9~/18780 ~~66~ PCT/US9~/01570
37
It should also be noted that the invention includes within its scope
a modified telephonic device including therein all the relevant components
described above with respect to the adapter. Obviously, in such case the
- adapter can be dispensed with. Furthermore, combining the adapter within
S the telephonic device itself avoids unnecessary duplication of those
components, such as an extension off hook detector, an audio sign~lling
device and so on, which are required within the adapter but are provided in
any case within telephonic device. In the context of the specification and
appended claims, the term "telephonic device" includes within its scope any
10 device connected to a telephone line such as, for example, a telephone
extension unit, a f~ccimile m~c.hine, an auto answering machine and so on.
The invention thus provides for a comprehensive telephone
exchange system to be constructed merely by plugging an adaptor between
each telephone extension unit and a corresponding telephone outlet socket,
15 there being no requirement to install an interface unit at the point where the
telephone line enters the system. Although the logic has been described in
detail for connecting telephone extension units to the system in either an
EXTERNAL or INTERCOM mode, it will readily be appreciated that the
telephone extension unit can be replaced, as required, by a f~c.simile
20 m~c.hine, a modem, an answering m~rhine, a remotely-operated appliance,
and so on. In such case, a standard telephone extension unit can be
addressed by ~ llin~ the a~ployliate extension code or any of these
appliances can be ~cce.cced in response to a~pr)pliate remote h~ncl.ch~ke
protocols or, in the case of an answering machine, in the absence of a
25 handset being lifted within a predetermined number of rings.
