Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 022~7000 1999-01-11
TECHNICAL FIELD
This is a divisional of Canadian Patent application 2,169,037 filed
February 7, 1996 entitled TRAFFIC INFORMATION SYSTEM USING LIGHT
EMITTING DIODES.
The subject invention relates to a trafffic control system of the type
including a traffic light that provides an illuminated signal for controlling the
movement of a vehicle.
BACKGROUND ART
Trafffic lights have been used since the early 1900's to control
10 vehicular traffic flow by advising drivers when and where to stop, proceed, turn,
etc. The growing use of traffic lights attests to their effectiveness in directing
traffic flow, reducing the incidence of accidents, and most recently to their utility in
controlling the flow of trafffic through large metropolitan areas when used in
conjunction with computer driven systems.
Interestingly, the modern trafffic light is no different today than it was
decades ago. The basic light still employs red, yellow and green filters over
incandescent lamps that are sequentially turned on and off by an
electromechanical timing switch or by more
76028-46E
CA 02257000 1999-01-11 ~'
modern solid state traffic controllers. Recent
developments in solid state lamps, i.e. light emitting
diodes tL.E.D.) have permitted the replacement of the
conventional incandescent-based traffic lights with
S L.E.D.-based traffic lights. Examples of L.E.D.-based
traffic lights can be found in United States Patent
numbers 4,729,076 and 5,136,287. The main advantages of
L.E.D.-based traffic lights over an incandescent-based
traffic lights are much lower power usage, i.e. higher
-10 luminous efCiciency~ and much longer lamp life. Other
than luminous efficiency and lamp life, othe- important
properties of light emitting diodes have nct yet been
utilized in traffic control systems. The present
invention incorporates improvements in traffic light
technology made possible by the use of light emitting
diodes.
S~RY OF ~ L~VS~'~lO~ ~ND ADVaNTAG~S
The present invention is a traffic control
system for controllins the movement of a vehicle by
providing a visual signal in the form of light rays and
for using the light rays to transmit digital
information. The sys~em comprises a traffic light
including a plurality of light emitting diodes for
~. .. .
CA 022~7000 1999-01-11
projecting light rays and a power supply for supplying
power to illuminate the diodes for a predetermined duty
cycle consisting of an ON period followed by an OFF
period short enough to be humanly imperceiva~le. The
present invention is characterized by a modulator for
varying the length of time of the duty cycle to trans~lt
the digital information.
The primary advantage of the present invention
is the provision of a traffic c~ntrol system that
utilizes the light e~itted from a traffic light to
optically transmit digital information to the driver of
a vehicle.
1~ Another advantage of the present invention is
the provision of a traffic light retrofit comprising a
plurality of light emit.ing diodes which can be used to
replace incandescent-based t_afric lights to thereby cut
energy and maintenance costs.
Another advantage of the present in~ention is
the provision of a L. E. D .-Dased traffic light having a
battery bac~-up for provldins emergency power.
.
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Another advantage of the present invention is
a traffic light system that utilizes the light emitted
from a traffic light to remotely detect and distinguish
a "red", "yellow", or "green" light.
s
~IG~JRES IN T~ D~WIN~S
Figure 1 is a perspective view of the traffic
control system of the present invention;
Figure 2 is a cross sectional view of the
traffic light retrofit of the present invention;
Figure 2A depicts another aspect of the
present invention;
Figure 3 is a cross sectional view of the
traffic light assembly taken about line 3 - 3 of Figure
l;
2~
Figure 4 is a schematic bloc~ diag am of the
electronic circuitry utilized in the present invention;
Figure 5 is a sc~ematic bloc.~ diagram of
additional circuit~y utilized in the present invention;
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Figure 6 is a signal diagram of amplitude
versus time depicting one modulation scheme utilized in
the present invention;
5Figure 7 is a schematic block diagram of the
receiver of the present invention; and
Figure 8 is a schematic bloc'; diagram of the
simpli~led receiver of the present invention.
DET~ILED DESC~IPTION OF T~F~ PREEE~ED E.~BODI~NT
Referring to Figure 1, the traffic control
system 10 of the present invention is shown. The
t~affic control system lO includes a road 12, a vehicle
14 traveling on the road 12 and a traffic light assembly
16 ope-atiYely associated with the road lZ. The traffic
light assembly 16 comprises at least one traffic light
ar lamp means 18 for providing an illuminated signal.
Typically, the traffic light assembly 16 includes red,
yellow and green traffic lights 17, 19, 21 for
projecting red, yellow and green light rays to signal
the driver of the vehlcle 14 to "stop", "yield", or
"go", respectively. ~owever, it is to be understocd
that while an intersection control light is depicted in
CA 02257000 1999-01-11 ~--
Figure 1, the benefits of this invention may be applied
to a variety of other applications such as pedestrian
c~ossing signals, e.g. WALR, DON'T WALX signals or any
other illuminated "traffic related" message for
controlling t_affic or simply providing information.
As shown in Figures 2 and 3, the preferred
embodiment of each traffic lih' o~ lamp means 18
includes a plurality of light e~it~ing diodes 24 for
trans~itting light rays from the t~affic light assembly
16. In other words, the red traf~ic light 17 comprises
a first set of light emitting diodes 17A for projecting
red light rays, the yellow traffic light 19 comprises a
second set of light emitting diodes 19~ for pro~ecting
yellow light rays, and the green traffic light 21
comprises a third set of light emitting diodes 21~ for
pro~ecting green ligh~ rays. Each traffic light 18
fur her includes d.c. power connection means 26 secured
to the traffic light 18 and elec'~ ically coupled to the
diodes 24 for receiving d.c. power. The traffic light
asse~bly 16 also includes a.c. power connection means Z8
seclred to the t-affic light 18 for receivin~ a.c.
power. The traffic light assembly 16 further includes
d.c. power supply means 30 securec to each t_affic light
Z5 18.
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Referring to Figure 4, d.c. p~wer supply means
30 is electrically coupled to and between the a.c. p~wer
connection means 28 and the d.c. pcwer connection means
26 for con~erting a.c. power received by the a.c. power
connection me~ 28 to d.c. power so that d.c. pawer is
supplied to said d.c. pawer connecti~n means 26. D.c
p~wer supply means 30 may be ~f con~entional linear or
switchmode design. D.c. power supply means 30 includes
a step-down transformer to bring the a.c. line vol~ages
of 120 - 140 volts down to approximately 3.5 volts and
a standard full or half wave rectifier to convert the
a.c power to d.c. power.
The traffic light assembly 16 is characterized
by a battery 32 re~ovably connected to the traffic light
18 for supplying d.c. pcwer to said d.c. p~wer
co~necLion ~c 26 to illu~ te the dicdes 24.
Preferably, the battery 32 is rec~argeable. For
example, battery 32 cculd include any sealed lead -
acid, nic~el - metal hydride, or lithium rec~argeable
batteries. The traffic light ~CcPmhly 16 further
c~y~ises battery charger means 33 secured to the
tr~ffic light 18 and elec~rically coupled to and between
the a.c. pawer connection means 28 and the d.c. power
connection m~nC 26 for recharging the battery 32.
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The interconnection ~f the backup battery 32
with the traffic light 18 is shown in Figure 4, and
essentially provides for a parallel power source with
the d.c. power supply means 30. Ordinarily, the output
voltage of d.c. power supply means 30 would be the same
as the rated operating voltage of the traffic light 18
and the nominal voltage of the battery 32. That is, if
the traffic light 18 were deslgned ~o operate at 12
Volts, then the battery 32 would also have a 12 Volt
output and would be charged at a comparable (slightly
higher~ voltage from bat'ery charser 33. The battery 32
does not supply power to the traffic light 18 until a
power failure, i.e. until a.c. pcwer from utility lines
is no longer being supplied to a.c. power connection
means 28.
Whenever a.c. utility power fails, the entire
function of the st~n~rd traffic controller is
compromised in addition to failure of the traffic lishts
th~celves. ~nless a contral uninte~L~ible power
supply is used to power both the traffic lights and the
controller, the lights may not be operated because the
crit~cal t~;ng function and sequencing normally
provided by the controller is not available. Therefore,
a specific aspect of this invention is to provide a
CA 02257000 1999-01-11
safety default condition whereby all the red stop lights
at an intersection are flashed whenever a.c. utility
power fails. The default condition effectively
establishes a four-way stop under battery power.
To implement the four-way stop default
condition, traffic lisht assembly 16 further comprises
a.c. power monitoring circuit means 3~ secured to each
traffic light 18 for monitoring a.c. power supplied to
the a.c. power connection means 28. A.c. power
monitoring circult means 34 is preferably included as
part of a pcwer pack 3S which also includes battery 32.
The power pac~ 35 may be attached to each traffic light
18 by various means. Monitoring means 34 monitors the
lS lamp c~rrent at all the traffic lishts (red 17, green 19
and yellow 21~ of t~e traffic light assembly 16. The
traffic lisht assembly 16 further comprises switch means
36 secured to each traffic light 18 for electrically
coupling the batt Q 32 to the d.c. power connection
means 26 in respanse to a trigger signal from the a.c.
power monitor~ng means 34 ~t u~p~ed by a predeter~ined
decrease in a.c. power supplied to the a.c. power
connection means 28. The traffic light ~Cc~mhly 16
further ~ L ises pulsating circuit means 38 secl~red to
2S each traffic light 18 and ele~L-ic211y coupled to the
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switch means 36 for causing the switch means 36 to
electrically couple the battery 32 to the d.c. pawer
connection means 26 at a predetermined frequency to
illuminate the diodes 24 at the predeter~ined frequency.
S Preferably, the pulsating means 38 is included as an
integral part of the pawer pac~ 35. If monitoring means
34 detects a loss of power to all traffic lights 18 of
traffic light assembly 16, switch mean~ 36 connects the
battery 32 to traffic light 18 and pulsating means 38
causes trafric light 18 to flash at the predeter~ined
frequency. Preferably, only the red traffic light 17 is
connected to the battery 32 upon a power loss so as to
create the default flashing red condition. A typical
flash duty cycle of 30~ will extend the battery 32 life
cycle to approximately 12 hours for a 24 Watt/Hr ra.ed
battery 32. Thus, the present invention allows low
cost, autonamous, rechargeable battery pac~s to be
adapted to L.~.D. - based traffic lanps in order to
pro~ide low cost emergency operation when line power
outages oczur, and to recharge automatic~lly upon
resumption of utility power.
A smzll, low pawer ra~io transmitter 40 may be
secured to the t-afflc light 18 to advise a cent~al
traffic engineerins office of power outases or other
CA 02257000 1999-01-11 ~ -~
problems. The radio transmitter 40 is electrically
coupled to the switch means 36 for transmitting a radio
wave in response to the trigger signal sent by
monitoring means 34. ~s shown in Figure 3, a digitally
s encoded radio transmitt_r 40 can ~e used to identify the
location of the malfunctioning traffic light assembly
16. Alternati~ely, a cable modem could be used to relay
this information. The traffic light-assembly 16 may
include delay means 42 secured to the traf.ic light 18
and electrically coupled to ~he radio transmitter 40 for
delaying the tr~n-cm;~csion of the emitted radio wave a
predetermined t~e after the switch m~c 3 6 recPives
the trigger signal. This delay is needed so that one
radio frequency may be utiliz~d by a number of t.affic
light assemblies without radio frequency collision by
any t-~o traffic light ~c-cPmhlies.
In the most si~ple configuration, all the
diodes 24 can be arranged on a disX, plate or printed
circu~t substrate so that all of the di~des 24 are
oriented in the same dm-ection. Preferably, the diodes
24 are mounted on circ~it board means 44. Circul' ~oard
means 44 comprises c~ a planar printed circuit ~oard
which includes c~nnection ~eans for elec~=ically
coupling the diodes 24 in a plurality of series circuits
- CA 02257000 1999-01-11
46 and for electrically coupling the series circuits 46
in parallel. Each series circuit 46 includes an e~ual
num~er of light emit~ing di~des 24.
s Each traffic light 18 further comprises a
traffic light housing 48. The light housing 48
comprises a hollow member 50 having a front open end 52
and a rear open end 54. The light housing 48 further
comprises a front cover 56 for covering the front end 52
and a rear cover 58 for covering the rear end 5~. The
diodes 24 are mounted within the hollow member 50
between the front and rear covers 56, 58. The front
cover 56 comprises a transp~Tent glass or plastic
material having a smooth auter surface 62. Transparent
glass is necessary to allow light rays emitted by the
diodes 24 to exit v~~tually un~mpe~ed and smooth surface
62 is preferrPd to avoid accumulation of dust and dirt.
m e front and rear covers 56, 58 for~ a hermetic seal
wit~ the hollow ~ ~ 50. The t~affic cu..~s~l syst~m
10 further c~ ises an ~CcDmhly housing 64 for housing
each traffic light 18. Each traCfic light 18 further
includes mounting r~nC 66 for removably mounting each
trafCic light 18 to t~e ~Cspmhly housing 64.
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The tra~fic light 18 is retrofitted to permit
the use of the lisht in existing traffic li5ht assP~bly
housings currently used to house incandescent traffic
lights. Fcr ease of implementation, the traffic lights
S 18 are preferably used with existing traff c lisht lens
filters, which are nor~ally stippled or equipped with
small lensatic ele ents to achieve correct beam
dispersion. These lens elements are ordinarily designed
to cperate in conjunction with a reflector and the quasi
point source of a filament lamp. While a planar array
of L.E.D.s w~ll operate satisfzctorily with existing
filters and lenses, a mcra effective lens is needed to
"fill-in" or illu~inate the spaces between diodes 24 and
to steer the light rays emitted from the diodes 24 to
the intended t~rget, such as the vehicla 14, to avoid
wasting an~ l sh~ ene-sy. To this end, each traffic
light 13 may include one or more ref-active elements 68
positioned bet-~een the diodes 24 and the front cover 56.
Refracti~e elements 68 act as a light ray steering means
to steer the light rays emittad by the diodes 24 to the
intended tarset. ~ltarnati~ely or in addition to
ref~active elements 68, a spacer member 70 positioned
betwean said circuit board means 44 and the d~cdes 24
can be used to p~int t~e dicdes Z4 in z pa-~icular
direction. The spacar m~mker 70 includes an an~led
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s~rfacP 72 against which the diodes 24 abut to
physically angle the diodes 24 relative to the road
surfaca 12.
Another aspect of this invention relates to
the ability of L.E.D. lamps to be pulsed at high rates;
i.e. to be turned on (illuminated) and off (not
illuminated) at hiSh rates. By pulsing L.E.D.'s at hi~h
rates, data can ke optically trans~itted from the
traffic light 18 to a remotely located photodetector.
Thus, the diodes 24 can be used to tr~nsmit information
to vehicle 14 such as announcing the presence of a
traffic lisht and transmitting map coordinates, street
names, directions or even trzffic advisories. Existing
incandescent t~afClc lights cannot be used to t~ansmit
digital data because the ther~al inertia of the
fllaments in these lamps precludes thP rapid modulation
of t~e supply current to cbtain detectable changes in
light ou~ . Ob~iausly, slow on - of~ modulation of
these lamps would be impractical as it would be annoying
and confusing to drivers. The perceived luminosity of
L.E.D. scurcas is a function of the average current that
powers the L.E.D. For ex~mple, a d.c. value of 20mA
might y~eld roughly the same percPived luminosity from
a L.E.D. as a s~uare wave (50% duty cycle) of 40mA peak
- CA 02257000 1999-01-11 ~
current. The actual modulation of L.E.D. traffic lamps
is rather simple, except for the fact that the percPi~ed
lu~inosity of the lamps- needs to be essentially
constant, as their main function is to visually alert
S drivers. Message transmission is a secondary function
that must not inter~ere with normal use. If the
percaived luminosity of each traffic light is to remain
c~nstant during operation, the average ~urrent delivered
to the respective diodes must be essentially constant
for periods greater than approximately 30 milliseconds.
This period corresponds to a flic~er frequency of a~out
33~z, which is perceptible by some humans.
Pulsing the dicdes 24 of the traffic light 18
allows the remote detection of the light rays
illuminated there~y as well as the identification of the
light rays, i.e., whether tie red, yellow, or green
traffic light 17, l9, 21 is on. To distinguish whether
eit~er the red, yellow, ar green traffic light 17, lg,
21 is ill~;nated, system 10 comprises a t~ansm~tt~r 20
including means for aptically transaitting data from one
of the traffic lights 18 of assP~hly 16 by turning the
first, second, and third set of diodes 17~, 19~, 21A on
and off at three dist nc_ fre~uencies. For example, the
fi_st set of light e~itting diodes 17A of the red
, .. ~ .......................................... . .
CA 02257000 l999-Ol-ll ---
16
traffic light 17 can be illuminated at 50 XHz, the
second set of light emitting diodes l9A of the yellow
traffic light 19 at 6~ X~z, the third set of light
emitting diodes 21A of the green traffic light 21 at so
~Hz In this manner, the traffic lights 17, 19, 21,
continue to serve their primary function of vlsually
alerting drivers to stop, yield, or go while allowing
the remote detecticn and identificatio~ of the lights
The system 10 further comprises receiver means
22 located at a location remote from the traffic light
assembly 16 For example, the recPiver means 22 can be
disposed on the vehicle 14, as shown in Figure 1, for
optically receiving the data transmitted by the
t ansmitter 2~ The receiver means 22 further includes
photo-detector mP~nc for converting the light rays
emitted by the red, ~reen, and yellcw traffic lights
into first, second and third ~LuuL signals of electric
c~rrent haYing first, second and third output
f-equencies, respecti~ely The rec~iver 22 further
inc~udes di2ferential means for differentiating the
first, second and thLrd output frequencies from each
other to deter~ine whether the red, yellow ~r green
t affic lisht is illu~inated The receiver 22 can be
.
- . ~
~ CA 02257000 1999-01-11 --
battery pawered, or pcwered by the electrical system of
the vehicle 14.
Within the scope of the present invention and
in addition to simple red, yellow and ~reen light
detection, the system 10 may include digital data
tr~n-cmission capability from the traffic light 18 to the
vehicle 14. One or all colors (red, yellow, green and
any turn signals, pedestrian ~essages, etc.) could be
driven by a digital ccde generator to relay a message to
oncoming vehicles, other tra~fic lights, or a central
traffic center. Typically, each traffic light (red 17,
yellow 19, and sreen 21) is "on" exclusively for a
certain time, therefore all traffic lights 17, 19, 21
facing one direction could share the same message
senerator which would then trans~it the same digital
code for each c~lor change. Alte~natively, each
individual traffic light 18 could be coded with a
"color" precursor co~e to per~it mora sophisticated
~co~i ng schemes at the remote recPivers 22. The data
rato ~ust ~e sufficiently high as to enable digital
message t-~n~iC~ion within a single flash of a f~chi~g
red or yellow traffic light 17, 19 in order to
accommodate virtually all t~affic signal continsencies.
The most a~propriate use for s1lch traffic light message
CA 02257000 1999-01-11
tr~n-cmi~sion capability w~uld be audible routing
di~ections. For example, upon approaching a given
intersection, the vehicle mounted receiver 22 might
announce, ~Eastbound Metro Parkway at Hayes". N~
directional ambiguity exists because the message is only
directed at oncoming traffic. Obviously, the
transmitter 20 would have to be proçrammed to deliver
the correct message, but this need be done only once, as
the light remains at the same location for many years.
If an L.E.D. lamp is required to maintain an
essentially constant, perceived output, the modulation
imparted to the L.E.D. must be suf'~iciently ~ast and
exhibit a constant a~erage duty cycle. Several digital
madulation schemes are capable of this limitation.
Pulse position modulation (PPM), phase shift ~eyed (PS~)
mcdulation and f-equency shl~t modulation (FS~) are
typical for~s of an essentially constant duty cycle
modulation. The F.S.~. modulation scheme is shown in
Figure 6, as it is amcng the simplest to implement, and
it is widely employed in wired and wireless
communication links. ~o distinct fre~uencies F1 and F2
are used to signal the digital l's and O's or mar~ and
space data that consti.ute the messase or data to ~e
2S transmitted. The ad~antage of using such a digital
~ . . ..
CA 02257000 1999-01-11 ----
.. 19
mcdulation scheme is that the average L.E.D. lamp
current (and power) r~m~ i n~ essentially constant
irrespective of the data. The reason for this is
readily apparent in the diagram depicted in Figure 6
S which indicates a constant 50~ duty cycle for any data
stream. The result of such modulation i5 that the
visible (perceived) brightness of the lamp is in~ariant,
while high rat~ digital data is being trans~itted ~r
even when no data is transmitted (all l's or o~s).
Ideally, the F.S.R. fre~uencies F1 and F2 representing
the digital l's or 0's would be separated by several
hundred Hertz or kilo Hertz to facilitate unambiguous
detection. Having the fre~uencies within a 10~ band
would allow a single tuned input amplifier to act as
preselec'or filter to the frecuency detectors.
Operating the L.E.D. lamps in the 10 to 20 R~z range may
be ad~antageous. This fre~uency band permits easy
differ_ntiation f-om high intensity discharge (~.I.D.)
lamps s~ch as street lights or neon lights. These light
sources may ha~e s;m;lar specLral characteristics as the
traffic lamps, and ther~y interfere with relia~le
detection of the traffic lights 18.
Referring to Figure 5, the transmitter 20 that
mcdulates the traffic light 18 is pcwered by the d.c.
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.
power supply means 30. A.c. pcwer from a conventional
traffic light controller in turn powers the d.c. power
supply means 30. The transmitter 20 comprises a non-
volatile local memory (E~P~OM~ or one time programmable
tO.T.P.~ memory chip 78 for electronically storing the
digital message to ~e transmitted. The message itself
could be coded in virtually any for~ such as ASCII or a
proprietary alphanumeric code. Additionally, digitally
coded, compressed voice communication could be
transmitted along wit~h the alphanumeric text or instead
of it facilitating the regeneratian of high quality
voice messages at the remote receiver 22. The
transmitter 20 furt~er comprises a mic-oprocessor 72 for
controlling the removal of the digital message stored in
the ~emory chip 78. The microprocessor 72 also controls
the tr~C~ission of the digital- message.
The tr~ncm;tter 20 further includes a solid
state switch 80. The solid state switch 80 converts the
coded digital ~~~ge developed by the ~i~o~Lo-essor 72
into F.S.~. for~at and thereafter transfers the F.S.g.
nodulated signal to the diodes 24 of the t_a~ric light
18. In other words, t~e switch 80 controls the power
from the d.c. power supply means 30 to supply power tc
illuminzte the dicdes 24 ~or a predeter~ined duty cycle
CA 02257000 1999-01-11 .~
co~.sistins c~ an ~'i re~~od foilowed hy 2~ o~r pericd
short enough to be humanly imperceivable. The
microprocessor 72 further includes modulator means for
varying the length of time of the duty cycle to t~ansmit
the digital information. Microprocessar 72 also
includes signal processor means for maintaining a
constant ratio between the ON and OFF periods as the
length of time of the duty cycle varies. Signal
processor mezns includes means for establishing a first
lens.h of time for the duty cycle to create a fi_st
digital sisnal cor-esponding to a digital "l" and for
estaklishing a secon~ length of time for the duty cycle
to create a second digital signal corresponding to a
digital "O". In other words, the first length of time
correspon~s to frecuency F1 and the second length of
time corresponds to freauenc~ F2;
The t_a-.ic light assem~ly 16 may ~nclude
power sensins mear.s 74 for sensing when d.c. pcwer is
delivered from the d.c. powe- supply means 30 and a
reset generator 76 for reset'ing the microproc~ssor 72
each time d.c. power is delive-ed to the traf.lc light
18 to initlate a new dlgital message secuer.ce. The
t_afCic light assembly 16 may also include ambie-.. light
Z5 sensor means 60 for varying the luminosity of the diodes
.
- CA 02257000 1999-01-11 t
24 in response to ambient light variations. Ambient
light sensor means 60 includes a photodetector 60
coupled to a power control element 82. Power control
element 82 controls the quantity of power delivered to
the diodes 24 in response to the level of ambient light
detected by the photodetector 60. For example, at
night, the voltage of the pulses delivered to the
tra fic light 18 may be reduced to dec-ease briahtness
to fu__her reduce power consumption while in bright
sunli5ht the sensor means 60 would cause the power
control element 82 to increase the voltage of pulses
delive_ed to the traffic lisht 18. The power control
elemen. 82 could consist of a linear voltage resulator,
o_ a low loss high frequency pulse width modulation
(~.W.~.) cont_oller, both or which are comme~cially
available devices. Note that if puIse control is
utilized to control lamp brightness, the operating
f-ecuency of such a device would have to be
significantly greater than t.~e modulation frecuencv in
order to nat af L ect the digital coding.
The companion receiver 22 receives the digital
infor~ztion transmitted by the diodes 24. Refer-ing to
Figure 7, receiver 22 consists of an o~tlcal wavelength
selecl-ve filter 84, a collec_ion lens 86, and a
:- CA 02257000 1999-01-11 .-
23
receiver photodetector 8$ coupled to a tuned amplifier
90 and a limiter 92. The photodetector 88 converts the
light rays emitted by the dicdes 24 into an output
signal cf electric current. The cptical wavelength
selective filter 84 allows only selective frequencies of
light, such as F1 or F2, to reach the photo detector 88.
The collection lens 86 directs the llght rays emitted by
the dlodes 24 to the photodetector 88. The ampll ie_ 90
ampliCies the output sicnzl. The amplifier 90 is
typically peaked to respond preferentially to the F.S.K.
f-ecuencies employed by the transmitter 2 0. F.S.K.
detection may be advantageously provided by a receiver
mlcroprocessor 94 whlch then also handles character
decoding (using nonvolatile resident memory) and the
lS messase dlsplay functlons. ~he receiver 22 further
c~mprises visual messase disolav means 96 for visually
displaying the digital infor~ation transmitted by the
diodes 24. Typically, a licuid c~stal, vacuum
fluorescent, L.E.D., or miniature C.R.T. display wauld
be used to display the messase trans~itted by the
traffic light 18. The receiver 22 may also be e~uipped
with a voice generation means 98 comprisins a speaker
means 99 for audibly conveyin5 the digital in~or~ation
._ans~it.ed by the dicdes 24. For voice message
zoplications, de~icated voice synthesis intesrated
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24
circuits would convert the digitized, transmitted voice
announcement back into human speech for review by the
driver. Modern linear predicti~e coding techniques and
specialized voice I.C.1s (as used in many toys) could be
used to simplify the delivery of audible messages of
several seconds duration.
Referring to Figure 8, a simplified alternate
receiver 22 1 is disciosed for use in detecting whether
the red 17, yellow 19, or green 21 traffic light is
illuminated. Rece1ver 2Z' conslsts of an optical
wavelength selective filter 84', a collection lens 86',
and receiver photodetector 88' coupled to a tuned
amplifier 90' and a limiter 92'. The receiver 22'
furthe- includes an alar~ generator 100 for driving a
s~ea~~ 9~'. As an example, the receiver 22' could be
set up to sound an alarm upon the detection of a red
lisht as transmitted by the first set of diodes 17A.
Once the reouisite hardware is installed in a
c-itical nl~m~er cf t~af,~ic lights 18 and ve~icles 14,
the t_~ffic control system 10 may be used to transmit
trafflc advis~ry messa~es. That is, the system 10 need
nct be limited to repetitive prerecorded messages. A
t_a-Ci_ lisht 18 positioned at specific points alon~ a
CA 02257000 1999-01-11
road 12, such as an intersection, may be directly
accessed by cable or a wireless link from a central
traffic authority to trans~it messages to passing
motorists. One method to accomplish such a ~unction
would be to download digital messa~e data to selected
tra~ic lights 18 for subsequent relay to passing
vehicles 12. Time-out or "sunset" provisions in the
sof.wzre or traffic light t_ar.smitter 20 hardware could
be i~?lemented to erase messages that were no longer
per_inent.
Another use for the tra~fic control syste~ 10
described herein involves the use of the digitally coded
tra~c lishts 18 as "signpcstsl' for vehlcular
1_ navicztion systems. Digitallv modulated tra~fic lights
18 could serve as convenient, low cost sign posts .or
vehicular navigation systems, whe e unambiguous loc-~tion
is essential. Traffic lights are ubi~uitous, and are
easily adapted to transmit dlgital location infor~ation
as well as ~ther data.
The invention has been described in an
illus.rative manner, and it is to be understood that the
ter~-nology which has been used is intended to be in the
CA 02257000 1999-01-11
26
nature of words of description rather than of
limitation.
Obviously, many variations and modifications
are possible in light of the above teachings. It is,
therefore, to be understood that within the scope of the
appended claims wherein reference numerals are merely
for convenience and are not to be in any way limiting,
the invention may be prac~iced otherwise than as
specifically described.
_ .
