Note: Descriptions are shown in the official language in which they were submitted.
~3(~3~i4
1 APPARATUS FOR OPTICALLY COUPLING A TERMINAL
UNIT ~O THE PUBLIC TELEPHONE NETWORK ~HROUGH
A PAY TELEPHONE INSTRUMENT AND THE LIKE
BACKGROUND OF THE INVENTION
The present invention relates generally to
telephonic communications and deals more specifically with
communication on the public telephone network wherein a
user via a remote, portable, wireless terminal unit
establlshes a two-way optical communication path with a
coin operated telephone instrument and the like equipped
with the station unit of the invention.
Telephonic communication via the public telephone
network has grown substantially over the past few years as
the numbers of the traveling public become larger and as
more and more people become reliant on the ability to
communicate with others to gain their livelihood, such as,
for example, salesmen and the like. Such communication is
generally accomplished ucilizing the so-called pay or coin
operated telephone instrument and includes credit card and
the like type operated telephone instruments. In order to
meet the increased demand for access to the public
telephone network, the so-called cellular type telephone
service was introduced wherein a user is a~signed a
dedicated telephone number and may originate and receive
telephone calls by means of a cellular type telephone
13~37~9L
; 1 instrument cooperating with a mobile radio receiver.
Although cellular type telephone service permits a user to
place and receive a call from any location within a
cellular area from his own cellular telephone, cellular
telephone instruments and cellular telephone service are
relatively expensive and in some instances not available
in all geographic locations. Accordingly, the majority of
telephone callers still access the public telephone
network via conventional coin-operated, credit card and
the like type telephone instru~ents.
There are a number of disadvantages associated
with the æo-called "public pay phone" among which
disadvantages are concerns about the spread of viral
infectious diseases, bacteria and other contaminates that
may be present on the public pay telephone
handset~receiver.
Another disadvantage associated with public pay
telephones, particularly those located in an outdoor or
unprotected environment, is a user must necessarily be
-20 exposed to the effects of inclement weather, lack of
privacy, etc., when placing a call from such a located pay
telephone.
Yet a further disadvantage associated with pubic
pay telephones, especially in areas of high usage such as
airport, bus and train terminals, is the valuable wall and
floor space that is occupied by the large number of public
13V37~
1 pay telephones that are generally present to accommodate
the traveling public.
It is desirable therefore, to provide a
telephonic device that is portable and personal to a user
and which permits access to the pubic telephone network
while overcoming the above disadvantages and accordingly,
it is the general ob~ect of the present invention to
provide such a device.
SUMMARY OF THE INVENTION
In accordance with ~he present invention,
apparatus for accessing and connecting a user to the
public telephone network includes a station unit
associated with a coin operated, credit card and ~he like
pay telephone and a wireless, remote, portable terminal
unit. The station unit has two operative states which
permits the pay telephone to operate in a conventional,
normal manner when in one state. The station unit is
coupled optically to the wireless, remote terminal unit
when in the second state to complete a transmission path
between the handset of the terminal unit through the pay
telephone to the public telephone network. The handset
of the terminal unit includes a microphone, earpiece
receiver and keypad for dialing telephone numbers.
Supervisory and audio baseband frequency signals
are transmitted between the terminal unit and the station
1 ' ~,.;`
13~37~i~
1 unit via an energy beam, such as for example, a beam of
light in the infrared frequency spectrum. In one aspect
of the invention, a receiver~transmitter of the terminal
unit is aimed so to speak in the direction of the station
unit located at the pay telephone instrument. A telephone
call is originated from a terminal unit by operating a
switch which causes circuitry within the handset of the
terminal unit to produce an "off-hook" baseband fre~uency
supervisory signal which supervisory signal i8 converted
to an infrared signal and is transmitted to t~e station
unit. A photodiode or other optical receiving device at
the station unit senses and detects the infrared optical
signals and is coupled to supervisory circuitry within the
station unit. The supervisory circuitry generates the
proper "off-hook" signal to cause the station unit to
operate to its second state wherein the telephone line is
now coupled to the telephone instrument throuqh the
station unit. A dial tone signal is returned from the
public telephone network to the station unit which
converts the dial tone signal to an infrared optical
signal for transmission to the terminal unit. A
photodiode or other optical receiving device at the
terminal unit senses and detects the infrared optical
signal transmitted from the station unit and which sensed
signal is coupled to circuitry within the terminal unit.
The infrared optical signal is converted into an
electrical signal which is representative of the dial
' .~
13~3764
1 tone signal and which electrical signal is transformed by
the earpiece receiver into an audible signal as the
familiar audible dial tone indicating that a connection is
established between ~he pay telephone instrument and the
cen~ral office equipment of the public telephone network.
A telephone number is dialed on the keypad of the
handset and is transmitted via the infrared optical beam
to the station unit. The digits of the telephone number
are standard dual tone multi-frequency (DTMF) touchtone
signals. As is the case of the Roff hook" baseband
frequency signal the optically transmitted touchtone
signals are converted to an electric signal haviny the
corresponding touchtone freqencies for transmission on~o
the public telephone network and reception ultimately by
the central office equipment. In the above arrangement,
the user may tap in the desired telephone number and a
telephone credit card number in the normal manner on the
keypad to cause the central office telephone equipment to
validate and make the desired call connection in the same
way that a telephone number and credit card number entered
from a keypad directly on the pay telephone.
Since the pay telephone instrument need not be
accessible by a user, it may be mounted above the normal
floor space occupied by a convetional pay telephone ~hus
alleviating floor space problems in congested areas.
In one embodiment of the invention, the
receiver/transmitter of the terminal unit is arranged as a
~. ~
~3~376~
1 separate unit for attachment to the visor of an automoblle
which permits the receiver/transmitter to be aimed at the
station unit located in the vicinity of a pay telephone
instrument. In this arrangement, power is supplied to the
handset and receiver/transmitter from the vehicle's power
system.
In another aspect of the invention, the hand~et
and transmitter are arranged to be accommodated for
example, in a briefcase and is equipped with a battery for
portability. This embodiment is primarily intended to be
used in indoor areas such as airports, train and bus
termlnals wherein the pay telephone instrument equipped
with a station unit is not directly accessible by a user.
However, it will be understood that this embodiment may be
used equally as well in an outdoor environment.
BRIEF DESCRIPTIO~ OF THE DRAWINGS
Additional objects, features and advantages of
the present invention will become readily apparent from
the following written description and claims taken in
conjunction with the drawings wherein:
Fig. 1 is a perspective, somewhat conceptual
illustration showing the transmitter portion of the
terminal unit of the invention attached to an automobile
visor and aimed in the vicinity of the station unit of the
invention arranged to cooperate with a pay telephone.
~3~37i~1~
1 Fig. 2 is a somewhat perspective, exploded view of
the station unit embodying the present invention showing
one possible mounting arrangement with the pay telephone.
Fig. 3 is a somewhat perspective view of the
terminal unit embodying the present invention wherein the
energy beam receiver~transmitter unit is separate from the
handset containing the earpiece, microphone and keypad.
Fig. 4 is a schematic block diagram showing the
major functional components of the terminal unit of the
present invention.
Fig. 5 is a schematic block diagram showing the
major functional components of the station unit embodying
the present invention.
Fig. 6 is an electrical schematic circuit diagram
showing one possible implementation of the terminal unit
of the present invention.
Fig. 7 is an electrical schematic diagram showing
one possible implementation the station unit of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Turning now to the drawings and considering Figs.
1 and 2, Fig. 1 illustrates the receiver~transmitter unit
10 of a ~erminal unit 11 embodying the present invention
mounted on a visor 12 of an automobile and oriented such
that the receiver/transmitter unit 10 is aimed generally
,,.~.~
8 ~ 3~3764
l in the direction of a station unit associated with a coin
operated pay-type telephone instrument which can best be
seen in Fig. 2. In Fig. 2, the coin telephone instrument
is designated 14 and is mounted in a standard enclosure
unit 16. The station unit embodying the present invention
is designated 18 and is shown in a slightly exploded view.
The station unit 18 includes a base 20 and cover 22 which
enclose an electronic circuit board 24 upon which are
mounted electronic components 26,26 comprising the
circuitry of the station unit. The circuit board 24 also
includes a device such as, one or more light emitting
diodes (LEDs) 28, 28 for generating an energy beam for
example, an optical beam 30. The station unit 18 also
includes an optical sensing and detecting device such as a
- 15 photodiode 32 for receiving an energy beam, for example,
an optical beam 34 originated at the receiver/transmitter
unit 10. The station unit 18 also includes optical
filters 36 and 38 through which the optical beams 30 and
34, respectively pass. The optical filters 36 and 38
limit the energy sensed by the photodiodes and which
energy is in the form of visible or ambient light.
Turning now to Fig. 3, one embodiment of the
~erminal unit 11 is shown wherein the terminal unit 11
includes a handset 432, a receiver/transmitter unit 434
and a power plug 436. The handset 432 comprises a keypad
generally designated 116, a microphone buil~ into the
handset and generally designated 120 and an earphone
13(~3764
l generally designated 114 also built into the handset. The
power required for the circuitry within the handset 432
and the receiver~transmitter unit 434 is provided in the
case of a terminal unit designed for use with a vehicle
from a power plug 436 adapted to be inserted into the
cigarette lighter receptacle of the vehicle. Typically a
battery voltage potential from the vehicle is applied at
the tip 438 and ground reference potential is applied to
the side terminals 440 440. Both the battery voltage
potential and the ground reference potential are connected
to an electrical conduit 442 which carries the voltage and
ground reference potentials from the power plug 436 to the
handset 432. The handset 432 is in turn connected via a
conductor 444 to the receiver~transmitter 434.
The receiver~transmitter 434 includes in the
illustrated embodiment a visor clip 446 for attaching the
receiver/transmitter 434 to the visor of the vehicle. The
receiver/transmitter 434 also generates as illustrated
schematically in Figs. 1 and 4 an optical beam 34
produced by light emitting diodes (LEDs) located behind an
optical filter 33. The receiver~transmitter unit 434 also
includes optical detectors located behind an optical
filter 35 for sensing and detecting an optical beam 30
produced by the station unit (not illustrated in Fig. 3).
It will be understood that the handset and
receiver~transmitter unit 434 may be packaged as a single
integral unit and may also include an internally housed
. .
~3(~37~;~
1 battery. For example, the terminal unit may be packaged
to fit into a user's briefcase and to operate with a
station unit at a pay telephone instrument located in an
airport, railroad station, or other such area where pay
telephone instruments are generally located.
Turning to Figs. 4 and 5, Fig. 4 illustrates in
block diagram form the major functional component blocks
of the terminal unit and Flg. 5 illustrates in block
diagram form the major functional component blocks of the
station unit embodying tha present invention.~ Still
referring to Figs. 4 and 5, communication between the
terminal unit and the station unit occurs as follows. A
user generates a request for service via an "off-hook"
signal which is produced by an "off-hook" signal generator
represented by the function block 40 which generator
produces a baseband frequency signal at its output 42
which in turn is fed to the summing input 44 of an
amplifier represented by the function block 46. The
amplified "off-hook" signal is fed from the output 48 of
the amplifier 46 to the input of a buffer amplifier
indicated by the function block 50. The buffer amplifier
50 produces a signal at its output 52 which is coupled to
the input of one or more light emitting diode (LED) driver
circuit means represented by the function block 54. The
LED driver ciruit means 54 produces a signal at its output
56 which excites light emitting diodes (LEDs) represented
by the function block 58~ The LEDs produce an infrared
~3~3764
1 beam 34 which is representative of and carries the
baseband frequency information of the off-hook signal.
The infrared beam 34 is directed ~oward the
s~ation unit, shown in Fiy. 5 and passes through an
optical filter 38 which removes any unwanted portions of
the frequency spectrum associated with the surrounding
ambient light. The infrared beam 34 is sensed and
detected by a photodiode represented by the function block
32 and which photodiode produces an output voltage signal
on lead 60 which is proportional to and representative of
the "off-hook" signal. The output signal on lead 60 is
amplified and filtered by circuitry contained ~ithin the
function block 62. The filtered output voltage signal on
lead 64 is sensed and detected by an "off-hook" detector
circuit means contained within function block 66 and
generates an "off-hook" voltage signal at its ouput 68.
The detected "off-hook" voltage signal is used to
activate a relay driver circuit 70 whose output 72
operates a relay 74 which has a number of transfer
contacts to transfer the tip and ring of the telephone
line 76 to connect the telephone instrument 78 to a
two-wire to four-wire hybrid converter circuit means 80.
Leads 82, 82 are connected between the relay 74 and the
telephone instrument and leads 84, 84 are connected
between the relay and the hybrid circuit 80. In addition,
the detected "off-hook" signal is transmitted to an LED
driver circuit means represented by the function block 86
13~37~i~
l and which "off-hook" signal enables the LED driver circuit
means. Dial tone is produced by the telephone central
office equipment and is present across the tip and ring of
the telephone line 76. The dial tone voltage signal is
supplied to the hybrid converter circuit means 80 through
the relay 74 and leads 84, 84. The hybrid converter 80 is
connected to a transmit isolator circuit means 88 by lead
90 and which isolator circuit means couples the dial tone
voltage signal to an amplifier 92. The output 94 of the
amplifier 92 is fed to the LED driver circuit means 86
which ln turn produces a signal at its output 96 to excite
the LEDs 28, 28. The LEDs 28, 28 produce an infrared beam
30 which carries the baseband frequency dial tone signal.
As illustrated in Fig. 4, the infrared beam 30 is
sensed at the terminal unit by a detector 98. The signal
at the output 100 of the detector 98 is amplified and
filtered by circuitry within the function block 102 to
remove 60 hertz interference and which filtered signal is
outputted on lead 104 which lead 104 is coupled to an
amplifier 106. The output 108 of the amplifier 106 is
inputted into an amplifier and gain control circuit means
contained within the function block 110 and which has an
output 112 coupled to a receiver or earphone 114. The
earphone 114 converts the electrical signals on lead 112 to
an audio signal, in this case, a dial tone signal alerting
a user that a telephone number may now be dialed and that a
,. ~.~,
13~3764
l connection has been completed between the station and
terminal units.
A telephone number is dialed using dual tone
multi-frequency (DTMF) signals corresponding to standard
touchtone frequency signals via a keypad and touchtone
generator contained within the function block 116. The
touchtone baseband frequency signals are outputted on lead
118 which is coupled to the sensing input 44 of the
amplifier 46 and are processed for transmi~sion to the
station unit in the same manner as the "off-hook" signal
as explained above. Likewise, acoustic energy, such as
speech and the like, is sensed by a microphone 120 and
converted to electrical signals which appear at its output
122. The microphone output 122 is coupled to the summing
input 44 of the amplifi~er 46 and signals representative of
speech are processed and transmitted to the station unit
as explained above in conjunction with the sending of the
"off-hook" signal. The infrared beam 34 carrying voice or
- touchtone signals is sensed and detected at the station
unit in the same manner as the "off-hook" signal is
detected as explained above.
The signals representative of speech and
touchtone are also conditioned by the preamplifier and 60
hertz rejection circuitry contained in function block 62
and which conditioned signals are outputted on lead 64
which is connected to an amplifier 124. The output of
amplifier 124 is coupled via lead 126 to a receiver
. ~ ,
'!s~. J~
14 ~L3~37~i~
l isolator circuit means contained within function block
128. The receiver isolator circuit means 128 has an
output 130 coupled to the hybrid converter circuit means
80 which hybrid converter receives the baseband frequency
signals representative of speech and touch-tone. The
hybrid converter 80 couples the signals to the tip and
ring of the telephone line 76 via leads 84, 84 connected
through the transfer contacts of the relay 74.
Speech or other signals within the voice
fre~uency spectrum are coupled from the telephone line 76
through the transfer contacts of the relay 74 into the
hybrid converter circuit means 80. The signals are
coupled to the transmiter isolator circuit means 88 via
the output lead 90 of the converter and are inputted to
the amplifier 92 for amplification. The output 94 of the
amplifier 92 activates the LED driver circuit means 86
which in turn excites the light emitting diodes 28 to
produce an infrared energy beam 30 for transmission to the
terminal unit. As in the case of receiving a dial tone
signal as described above, the speech and other signals
carried by the infrared beam 30 are sensed and detected by
the detector 98 and ultimately presented to the earphone
114 for conversion into an acoustic signal.
Turning now to Figs. 6 and ~, an exemplary
electrical circuit implementation i5 illustra~ed for the
station and terminal units embodying the present
invention. Considering first the initiation of a
~3~3376t~
l telephone call ~y a user from a terminal unit, the
"off-hook" signal generator 40 illustrated in Fig. 4 is
shown within the dotted line box 40 in Fig. 6. The
circuitry comprising the generator 40 includes a high
speed binary ripple carry counter 132 having clock inputs
134 and 136 coupled to a crystal oscillator generally
designated 138 and having a crystal 140 whose oscillation
frequency is 3.58 megahertz. The counter 132 is reset
with a logical high voltage signal applied to the reset
lead 142 which prevents the counter from producing an
output pulse at its output lead 144 and which condition
corresponds to the terminal unit being in an ~on-hook or
idle condition. The logical high reset voltage signal is
supplied through operation of an ONtOFF switch 146 to its
ON position which switch has one terminal 148 connected to
the reset lead 142 and a second terminal 150 connected to
a voltage potentlal designated VCC thereby inhibiting the
counter 132. The contact 148 of the switch 146 is also
connected to the base 152 of a transistor lamp driver 154
through a resistor 156 to cause the transistor 154 to be
non-conductive. Upon operation of the switch 146 to its
OFF position, the voltage VCC is disconnected from the
terminal 148 causing the transistor 154 to become
conductive. The transistor has its emitter 158 connected
to the voltage source VCC and its collector 160 connPcted
to a ground reference potential 162 through an indicator
lamp 164 to light the lamp to indicate that the terminal
13(~3764
l is in an "off-hook" condition. In the "off-hoo~"
condition, the logical high reset voltage signal is
removed ~rom the reset terminal 142 which now enables the
counter 132. The counter 132 produces an output pulse at a
fre~uency of 27.968 kilohertz (28 KHz) at its output lead
144. It will be recognized that the 28 KHz "off-hook"
signal is generated continuously when the terminal unit is
in the "off-hook" condition.
The 28 KHz output signal on lead 144 is connected
to the summing input 166 of an operational amplifier 168,
the operation of which amplifier is well understood by
those skilled in the art. The output 48 of the amplifier
168 is coupled through a series capacitor 170 to the input
172 of a transistor buffer amplifier contained withln the
dashed line box 50 and which amplifier has an output 52
coupled to an LED driver circuit including transistors 176
and 180 as shown within the dashed line box 54. The
output 52 of the amplifier is coupled to the base 174 of
the transistor 176 and the base 178 of the transistor 180.
The transistors 176, 180 conduct concurrently and each
respectively excite a number of LEDs which are connected
in a parallel circuit arrangement. The collector 182 of
transistor 176 drives LEDs 184, 184 and the collector 186
of infrared transistor 180 drives the LEDs 188, 188. The
LEDs 184, 184 and 188, 188 produce an optical beam in this
case an infrared beam which carries the baseband frequency
information. The operation of the LEDs are generally well
~3~37~i~
l ~nown to those skilled in the art. The number of LEDs
selected, in this case 14, permits an operating range of
six to eight feet separation between the station unit and
the terminal unit.
Speech, supervisory and other information is
transmitted from the terminal unit in the form of an
infrared energy beam which is sensed and detected by a
detector shown within the dashed line box 98 and comprises
a photodiode 190 the resistance of which diode typically
varies in proportion to the intensity of the sensed light.
A voltage divider network is formed by the series
combination of resistor 192 and the photodiode 190
connected between the voltage source ~CC and ground
reference potential to provide a DC voltage at lead 194
which varies proportionally to the change in resistance of
the photodiode and which voltage is representative of the
variation in intensity of the infrared liqht transmitted
from the terminal unit. The DC voltage output signal on
lead 194 is inputted through a coupling capacitor 196 and
resistor 198 in series with the input 200 of an
operational amplifier 202 all of which components form a
part of a preamplifier and 60 hertz rejection circuit
contained within the dashed line box 102. The output 204
of amplifier 202 is coupled to the input of a further
amplifier contained within the dashed line box 106 and
which further amplifier comprises a coupling capacitor 206
in series with a resistor 208 connected to the input 210
18
13~3376~i~
l of an operation amplifier 212. The amplifier 212 has an
output 214 connected to the input of a transistor
amplifier contained within the dashed line box 110 and
which amplifier drives the earphone 114. The amplifier
110 comprises a transistor 216 arranged as an emitter
follower having a variable resistance 218 connected in
series between the emitter 220 of the transistor 216 and
one input 222 of the earphonP 114. A movable slider 224
is used to vary the resistance of the variable resistance
218 to control the magnitude of the earphone driving
voltage signal and accordingly, the acoustic volume
produced by the earphone 114. In addition, the variable
resistance 218 may be adjusted to compensate for
attenuation of the infrared energy beam transmitted from
the station unit and received by the terminal unit.
The touchtone signals used for dialing telephone
numbers are generated by cicuitry contained within the
dashed line box 116 and includes a keypad designated
generally 226 which has its keys arranged in the well known
telephone keypad matrix arrangement. The keypad 226 has
four outputs 228, 230, 232 and 234 representative of the
first through fourth rows, respectively and outputs 236,
238 and 240 representative of the three respective columns
of the keypad. The row and column output leads are coupled
to a dual tone multi-frequency generator 242 which decodes
the row/column combination identified through operation of
a given key on the keypad 226 to produce the touchtone
~3~37~i~
l frequencies corresponding to the number represented by that
key. The touchtone signals are outputted on lead 244 and
are coupled to the input 166 of the amplifier 168 and which
signals excite the LEDs 184,184 and 188,188 in the same
manner as the "off-hook" signal as explained above.
Speech or other acoustic signals are converted to
an electrical signal by the microphone 120. The
microphone 120 may be an electret or other electronic type
transducer well known to those skilled in the art. The
output 246 of the microphone 120 is coupled to the input
166 of the amplifier 168 through a coupling capacitor 248
in series with the input 166. Speech or other acoustic
signals converted to an electrical signal by ~he
microphone 120 are processed and transmitted in a si~ilar
manner as the "off-hook" signal and the touch-tone
signals.
At the completion of a call, the switch 146 is
operated to its ON position which connects the VCC voltage
potential to the reset lead 142 which resets the counter
132 and inhibits the generation of the 28 kilohertz
"off-hook" signal required to establish and maintain a
connection between the terminal and station units.
Likewise, the "off-hook" lamp 164 extinguishes because the
transistor 154 becomes nonconductive due to the
application of the VCC voltage potential to its base 152
through the resistor 156. The call may also be terminated
by operating a "Flash" switch 147 for the required time
~ .,
:1.3~37f~
l interval. The Flash switch 147 has one terminal 149
connected to the VCC voltage potential and a second
terminal 145 connected to the reset lead 142 so that
operation of the Flash swi~ch connects the VCC voltage
potential to the counter reset lead to inhibit the
generation of the 28 KHz signal. As explained in detail
below in the discussion of the station unit, the absence
of the 28 kilohertz signal causes the station unit to
terminate its connection between the telephone line and
the telephone instrument after a predetermined time
interval of approximately five seconds.
The infrared signals transmitted from the
terminal unit to the station unit are sensed and detected
by a photodiode 62 which produces a current having a
magnitude proportional to the intensity of the received
infrared signal. The photodiode 62 is coupled to the
input of a differential amplifier 250 which produces a
voltage signal at its output 252 which is the combined
baseband frequency audio signal and the baseband 28
kilohertz "off-hook" signal. The signal at the output 252
is further processed to reject 60 hertz interference and
is ampli~ied by the operational amplifier 254 contained
within the dashed line box 256. The output 258 of the
amplifier 254 is connected to a bandpass filter contained
within the dashed line box 260 and which filter is tuned
to pass the 28 KHz "off-hook" signal when the signal is
present to produce a voltage signal at the output 262 of
~1
13~3764
1 amplifier 264. The voltage signal present on the output
262 indicates that the 28 KHz "off-hook" signal is being
transmitted and is coupled through capacitor 266 to the
input 268 of a phase lock loop integrated circuit 270.
The phase lock loop integrated circuit 270 is well known
to those skilled in the art and typically identified by
the model number 567. The phase lock loop 270 is set to
detect the 28 KHz "off-hook" signal to produce a voltage
at its output 272 in response to the presence of that
"off-hook~ signal. The center frequency of the phase lock
loop 270 is set by selection of the proper resistance of
the series resistors 274 and 276 and the value of
capacitor 278. The resistor 276 is of the variable
resistance type and is used to precise~y adjust the free
running frequency of the oscillator within the phase lock
loop integrated circuit 270. The ouput 272 of the phase
lock loop 270 is coupled to the input of an inverting
buffer amplifier 280 shown in the dashed line bo~ 66b and
the junction of a resistor 282 and the capacitor 284. The
phase lock loop 270 produces a voltage output signal on
lead 272 in the presence of the 28 KHz signal to charge
the capacitor 284 and to cause the output 286 of the
amplifier 280 to produce a positive voltage. The output
286 of amplifier 280 is coupled to the base 288 of a
transistor 290 through a resistor 292. The positive
voltage at the output 286 causes the transistor 290 to
become conductive completing the connection between its
13~37~;~
l collector 294 and the emitter 296 which is connected to a
ground reference potential. The collector 294 of
transistor 290 is connected to one end of the coil 298 of
the off-hook relay 74 and the opposite end of the coil
being connected to a voltage potential VBB so that the
relay operates to transfer the tip and ring of a telephone
line to the station unit and disconnect the tip and ring
from the telephone instrument internal network when the
transistor 290 is conductive. In the illustrated example,
the tip and ring are connected to the transfer contact 300
and 302, respectively. In normal operation, the tip and
ring of the telephone line pass through normally closed
contacts 304 and 306, respectively to complete the circuit
from the telephone line to the telephone instrument's
internal components. In the presence of an off-hook
signal sent from the terminal unit and sensed by the
station unit as explained above, the relay 74 operates to
cause the transfer of the tip and ring to the normally
open contacts 308 and 310, respectively so that the tip
and ring of the telephone line are connected to the input
terminals 312 and 314, respectively of a two-wire to
four-wire hybrid circuit 316 shown within the dashed line
box 80. The two-wire to four-wire hybrid circuit 316 is
well known to those skilled in the telephony art and which
circuit converts a two-wire circuit to a four-wire circuit
using the well known phantom balancing circuit
arrangement.
~3q~37~;~
l The baseband audio frequency signals at the
output 258 of amplifier 254 are fed to the input 318 of
the receiver isolator circuit, shown within the dashed
line box 128 and which circuit includes a repeating
transformer 320 of the type typically used in the
telephone industry and which typically has a 600 ohm input
and 600 ohm output impedance and a one-to-one
transformation ratio. The voltage signals on lead 318
cause a current to flow in the winding 322 whlch induces a
voltage in the output winding 324. The output winding 324
is coupled to leads 326 and 328 respectively of the
two-wire to four-wire hybrid circuit 316, and accordingly
the tip and ring of the telephone line via the leads 312
and 314 connected through the transfer contacts of the
operated relay 74.
The baseband frequency audio signals on lead 258
are also coupled to the input 330 of an operational
amplifier 332 configured as a voltage follower and which
produces a voltage signal at its output 334 equal in
magnitude to the voltage at its input 330. The output 334
of the amplifier 332 is fed to a voltage doubler circuit
shown within the dashed line box 336. The voltage charges
the capacitor 338 of the voltage doubler to a voltage
approximately equal to twice the magnitude of the voltage
present at the output 334. The charging path is through a
capacitor 340 connected in series with the output 334 and
the junction of diodes 342 and 344, diode 342 having its
24
:i3~3764
cathode connected to one end of the capacitor 338 and the
diode 344 having its anode connected to the opposite end
of the capacitor 338 to charge the capacitor 338 so that
the voltage present at the end 346 of the capacitor is
twice the voltage at the output 334 of the amplifer 332.
The end 346 of the capacitor 338 is connected to
the input 348 of a bar display generator integrated
circuit 350 shown within the dashed line box 352. The bar
display generator 350 has a number of outputs 354, 356,
358, 360, 362, 364 each of which is connected to a
respective light emitting diode or other visual indicator
366, 368, 370, 372, 374 and 376 which LED's are shown
within the dashed line box 378. The bar display generator
350 provides an output voltage signal to one or more of
its outputs 354-364 to excite one or more of the
respective LEDs 366-376. The number of LED's that are
illuminated provide an indication of the signal strength
of an infrared energy beam received at the photodiode 62.
Accordingly, a user may determine by the number of LEDs
that are illuminated whether or not the terminal unit is
within proper operating range of the station unit.
Audio frequency signals such as dial tone and
speech present on the tip and ring of the telephone line
are converted for transmission to the terminal unit is
described as follows. Speech or other audio signals
present on the tip and ring of the the telephone line are
inputted to the two-wire to four-wire hybrid circuit 316
~3~37~
l via the input leads 312 and 314. The voltage signals are
coupled to a transmit isolator circuit shown in the dahsed
line box 88 in a well known manner and as described above
wherein audio signals are coupled to the input winding 380
; 5 of a one-to-one transformation ratio repeating transformer
382. The input winding 380 is connected across the output
terminals 384 and 386 of thé two-wire to four-wire hybrid
circuit 316. Voltage signals appearing across the input
winding 380 are transformed and induced in the output
windin~ 388 to develop a voltage potential across the
winding connected between lead 390 which is connected to a
ground reference potential and a second end 392 which
carries the voltage signals representative of the
information to be transmitted to the terminal unit. The
voltage signals on the output 392 are coupled through a
series resistor 394 and filtering capacitor 396 to the
base 398 of a transistor 400. The transistor amplifier
400 amplifies the signal received at its base 398 for
output on its collector lead 402 which is connected to an
LED driver circuit contained within the dashed line box
86. The LED driver circuit operates in a similar manner
to the LED driver circuit in the terminal unit. The LED
driver circuit includes transistors 406 and 408 which have
their respective bases 410 and 412 coupled to the
collector 402. The transistors 406 and 408 produce a
voltage signal at their respective collectors 414 and 416
to excite the LEDs 418,418 and 420,420 respectively.
13~37~i~
l The L~D driver transistors 406 and 408 are
disabled in the absence of the detection of the 28 KHz
"off-hook" signal which as discussed above, must be
received to operate the relay 74. The voltage signal
produced at the output 286 of the amplifier 280 no~ only
activates the relay driver circuit contained within the
dashed line box 90 but is also inputted to an inverting
amplifier 422. The amplifier 422 produces an enabling
signal at its output 424 which is connected to the gate
terminal 426 of a field effect transistor 428. The
transistor 428 is arranged as a switch to connect its
source terminal 430 which is coupled to the collector 402
of transistor 400 to a ground reference potential through
~ts drain terminal 432 in the presence of an enabling
lS voltage signal at its gate 426. When an "off-hook~
condition is detected by the station unit, the ground
reference potential is removed from the collector 402 of
the transistor 400 enabling it to drive the LED driver
transistors 406 and 408 which in turn excite the LEDs
418,418 and 420,420 to transmit the audio signals received
at the tip and ring via an infrared energy wave to the
terminal unit. The baseband frequency audio signal is
sensed and detected by the photodiode 190 contained within
the dashed line box 98 in the same manner as dial tone is
detected and as described above.
