CA2254271A1 - Traffic control system using light emitting diodes - Google Patents
Traffic control system using light emitting diodes Download PDFInfo
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- CA2254271A1 CA2254271A1 CA002254271A CA2254271A CA2254271A1 CA 2254271 A1 CA2254271 A1 CA 2254271A1 CA 002254271 A CA002254271 A CA 002254271A CA 2254271 A CA2254271 A CA 2254271A CA 2254271 A1 CA2254271 A1 CA 2254271A1
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Abstract
A traffic control system (10) including a road (12), a vehicle (14) traveling on the road (12) and a traffic light assembly (16) operatively associated with the road (12) is disclosed. The traffic light assembly (16) comprises at least one traffic light or lamp means (18). The traffic light (18) includes a plurality of light emitting diodes (24) for projecting light rays to the vehicle (14) to provide the driver of the vehicle (14) with a visual signal. The system (10) further comprises a transmitter (20) including a power supply (30) and a modulator (72) for turning the diodes (24) on and off at a rate that is imperceivable to humans while optically transmitting information to a receiver (22) disposed on the vehicle (14).
Description
CA 022~4271 1998-11-09 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 traffic control system of the type including a trafffic light that provides an illuminated signal for controlling the movement of a vehicle.
BACKGROUND ART
Tramc 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 trafffic 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 traffic 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 CA 022~4271 1998-11-09 .
modern solid state traffic controllers. Recent developments in solid state lamps, i.e. light emitting diodes (L.E.D.) have permitted the replacement of the conventional incandescPnt-based traffic lights with 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 luminous efficiency, and much longer lamp life. Other than luminous efficiency and lamp life, other important properties of light emitting diodes have not 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~NMaRY OF T~E lNv~NllON AND ADVaN~AGgS
The present invention is a traffic control system for controlling 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 system comprises a traffic light including a plurality of light emitting diodes for CA 022~4271 1998-11-09 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 imperceivable. The present invention is characterized by a modulator for varying the length of time of the duty cycle to transmit the digital information.
The primary advantage of the present invention is the provision of a traffic control system that utilizes the light e~itted from a traffic light to optically transmit digital information to the driver of a vehicle.
Another advantage of the present invention is the provision of a traffic light retrofit comprising a plurality of light emitting diodes which can be used to replace incandescent-based traffic lights to thereby cut energy and maintenance costs.
Another advantage of the present invention is the provision of a L.E.D.-based traffic light having a battery back-up for providing emergency power.
CA 022~4271 1998-11-09 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.
~IGtJ}~ES IN T~E DRAWINGS
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;
Figure 4 is a schematic block diagram of the electronic circuitry utilized in the present invention;
Figure 5 is a schematic bloc~ diagram of additional circuitry utilized in the present invention;
CA 022~4271 1998-11-09 Figure 6 is a signal diagram of amplitude versus time depicting one modulation scheme utilized in the present invention;
SFigure 7 is a schematic block diagram of the receiver of the present invention; and Figure 8 is a schematic bloc~ diagram of the simplified receiver of the present invention.
DE~ILED DESCRIPTION OF T~2 P~E~E~RED E~BOI)IMENT
Referring to Figure 1, the traffic control system 10 of the present invention is shown. Ihe traffic control system 10 includes a road 12, a vehicle 14 traveling on t~e road 12 and a traffic light assembly 16 operatively associated with the road 12. The traffic light assembly 16 comprises at least one traffic light or 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 vehicle 14 to "stop", "yield", or "go", respectively. However, it is to be understood that while an intersection control light is depicted in , CA 022~4271 1998-11-09 Figure 1, the benefits of this invention may be applied to a variety of other applications such as pedestrian crossing signals, e.g. WALK, DON'T WALX signals or any other illuminated "traffic related" message for controlling traffic or simply providing information.
As shown in Figures 2 and 3, the preferred embodiment of each traffic light or, lamp means 18 includes a plurality of light emitting diodes 24 for transmitting light rays from the traffic light assembly 16. In other words, the red traffic 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 l9A for projecting yellow light rays, and the green traffic light 21 comprises a third set of light emitting diodes 21A for pro~ecting green light rays. Each traffic light 18 further includes d.c. power connection means 26 secured to the traffic light 18 and electrically coupled to the diodes 24 for receiving d.c. power. The traffic light assembly 16 also includes a.c. power connection means 28 secured to the traffic light 18 for receiving a.c.
power. The traffic light assembly 16 further includes d.c. power supply means 30 secured to each traffic light 18.
Referring to Figure 4, d.c. power supply means 30 is electrically coupled to and between the a.c. power connection means 28 and the d.c. power connection means 26 for con~erting a.c. power received by the a.c. power connection means 28 to d.c. power so that d.c. power is supplied to said d.c. power connection m~nC 26. D.c power supply ~s 30 may be of conventional linear or swit~hmo~e design. D.c. power supply means 30 includes a step-down transformer to bring the a.c. line voltages of 120 - 140 volts down to approximately 3.5 volts and a st~n~rd 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 removably connected to the traffic light 18 for supplying d.c. power to said d.c. power connaction means 26 to ~ ;n~tP the diodes 24.
Preferably, the battery 32 is rechargeable. For example, battery 32 could include any sealed lead -acid, nic~el - metal hydride, or lithium rechargeable batteries. The traffic light ~Scamhly 16 further CO~L ises battery charger means 33 secured to the traffic light 18 and electrically coupled to and between the a.c. power connection means 28 and the d.c. power connection ~e~c 26 for recharging the battery 32.
The interco~nection of 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 ou~L
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 des gned to 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 battery charger 33. The battery 32 does not supply power to the traffic light 18 until a power failure, i.e. until a.c. power 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~Ard traffic controller is c~L~mised in addition to failure of the traffic lights themselves. ~nless a central uninte~L~ible power supply is used to power both t~e traffic lights and the controller, the lights may not be operated because the critical timing function and se~uencing normally provided by the controller is not available. Therefore, 2S a specific aspect of this invention is to provide a 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 circuit means 34 is preferably included as part of a power pac~ 35 which also includes battery 32.
The power pac~ 3S may be attached to each traffic light 18 by various means. Monitoring means 34 monitors the lamp current at all the traffic lights (red 17, green 19 and yellow 21) of the traffic light assembly 16. The traffic light assembly 16 further comprises switch means 36 secured to each traffic light 18 for electrically coupling the battery 32 to the d.c. power connection means 26 in L~ se to a trigger signal from the a.c.
power monitoring means 34 prompted by a predetermined decrease in a.c. power supplied to the a.c. power connection means 28. The traffic light assembly 16 further comprises pulsating circuit means 38 secured to each traffic light 18 and electrically coupled to the switch means 36 for causing the switch means 36 to electrically couple the battery 32 to the d.c. power connection means 26 at a predetermined frequency to illuminate the diodes 24 at the predetermined frequency.
Preferably, the pulsating means 38 is included as an integral part of the power pac~ 35. If monitoring means 34 detects a loss of power to all traffic lights 18 of traffic light assembly 16, switch means 36 connects the battery 32 to traffic light 18 and pulsating means 38 causes traffic light 18 to flash at the predetermined 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 rated battery 32. Thus, the present invention allows low cost, autonomous, rechargeable battery packs to be adapted to L.E.D. - based traffic lamps in order to pro~ide low cost emergency operation when line power outages occur, and to recharge automatically upon resumption of utility power.
A small, low power radio transmitter 40 may be secured to the traffic light 18 to advise a central traffic engineering office of power outages or other problems. $he radio transmitter 40 is electrically coupled to the switch means 36 for transmitting a radio wa~e in response to the trigger signal sent by monitoring means 34. As shown in Figure 3, a digitally encoded radio transmitter 40 can be used to identify the location of the malfunctioning traffic light assembly 16. Alternatively, a cable modem could be used to relay this information. The traffic light-assem~ly 16 may include delay means 42 sec~red to the traffic light 18 and electrically coupled to the radio transmitter 40 for delaying the tr~nC~i~sion of the emitted radio wave a predetermined time after the switch means 36 receives the trigger signal~ This delay is needed so that one radio frequency may be utilized by a number of traffic light assemblies without radio frequency collision by any two traffic light assemblies.
In the most simple configuration, all the diodes 24 can be arranged on a dis~, plate or printed circu~t substrate so that all of the diodes 24 are oriented in the same direction. Preferably, the diodes 24 are mounted on circuit board means 44. Circl~it board means 44 comprises of a planar printed circuit board which includes ro~nection means for electrically coupling the diodes 24 in a plurality of series circuits 46 and for electrically coupling the series circuits 46 in parallel. Each series circuit 46 includes an equal num~er of light emitting diodes 24.
Each traffic light 18 further comprises a traffic light housing 48. The light housing 48 comprises a hollow member S0 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 54. The diodes 24 are mounted within the hollow member 50 between the front and rear covers 56, 58. The front cover 56 comprises a transparent glass or plastic material having a smooth outer surface 62. Transparent lS glass is necessary to allow light rays emitted by the diodes 24 to exit virtually unimpeded and smooth surface 62 is preferred to avoid accumulation of dust and dirt.
The front and rear covers 56, 58 form a hermetic seal with the hollow member 50. The traffic ~o~ol system 10 further comprises an assembly housing 64 for housing each traffic light 18. Each traffic light 18 further includes mounting means 66 for removably mounting each traffic light 18 to the ass~mhly housing 64.
The traffic light 18 is retrofitted to permit the use of the light in existing traffic light assembly housings currently used to house incandescent traffic lights. For ease of implementation, the traffic lights 18 are preferably used with existing traffic light lens filters, which are normally stippled or equipped with small lensatic elements to achieve correct beam dispersion. ~hese lens elements are ordinarily designed to operate 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 satisfactorily with existing filters and lenses, a more effective lens is needed to "fill-in" or illuminate the spaces between diodes 24 and to steer the light rays emitted from the diodes 24 to lS the intended target, such as the vehicle 14, to avoid wasting any 1 Sht energy. To this end, each traffic light 18 may include one or more refractive elements 68 positioned between the diodes 24 and the front cover 56.
Refractive elements 68 act as a light ray steering means to steer the light rays emitted by the diodes 24 to the int~n~e~ target. Alternatively or in addition to refractive elements 68, a spacer member 70 positioned between said circuit board means 44 and the diodes 24 can be used to point the diodes 24 in a partic~llar direction. The spacer member 70 includes an angled . ~ . . . ~ .
surface 72 against which the diodes 24 abut to physically angle the diodes 24 relative to the road surface 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 high rates. By pulsing L.E.D.'s at high rates, data can be optically transmitted from the traffic light 18 to a remotely located photodetector.
Thus, the diodes 24 can be used to transmit information to vehicle 14 such as announcing the presence of a traffic light and transmitting map coordinates, street names, directions or even traffic advisories. Existing incandescent traffic lights cannot be used to transmit digital data because the thermal inertia of the filaments in these lamps precludes the rapid modulation of the supply current to obtain detectable changes in light o~L~L. Obviously, slow on - off modulation of these lamps would ~e impractical as it would be annoying and confusing to drivers. The perceived lllmi~ocity of L.E.D. sources is a function of the average current that powers the L.E.D. For example, a d.c. value of 20mA
might yield roughly the same perceived luminosity from a L.E.D. as a square wave (50~ duty cycle) of 40mA peak ., ~
current. The actual modulation of L.~.D. traffic lamps is rather simple, except for the fact that the perceived luminosity of the lamps needs to be essentially constant, as their main function is to visually alert S drivers. Message tr~ncm;Csion is a secondary function that must not interfere with normal use. If the perceived luminosity of each traffic light is to remain constant during operation, the average ~l~rrent delivered to the respective diodes must be essentially constant for periods greater than approximately 30 milliseconds.
This period corresponds to a flicker frequency of a~out 33Hz, which is perceptible by some humans.
Pulsing the diodes 24 of the traffic light 18 allows the remote detection of the light rays illuminated thereby as well as the identification of the light rays, i.e., whether the red, yellow, or green traffic light 17, 19, 21 is on. To distinguish whether either the red, yellow, or green traffic light 17, 19, 21 is illuminatod, system 10 comprises a transmitter 20 including means for optically transmitting data from one of the traffic lights 18 of assembly 16 by turning the first, second, and third set of diodes 17A, l9A, 21A on and off at three distinct frequencies. For example, the first set of light emitting diodes 17A of the red traffic light 17 can be illuminated at 50 KHz, the second set of light emitting diodes l9A of the yellow traffic light 19 at 65 KXz, the third set of light emitting diodes 21A of the green traffic light 21 at so S RXz. In this manner, the traffic lights 17, 19, 21, continue to serve their primary function of visually alerting drivers to stop, yield, or go while allowing the remota detPction and identification 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 receiver means 22 can be disposed on the ~ehicle 14, as shown in Figure 1, for optically receiving the data transmitted ~y the transmitter 2~. The receiver means 22 further includes photo-detector means for converting the light rays emitted by the red, green, and yellow traffic lights into first, ~co~ and third ~L~ signals of electric ~u~ L having first, second and third output frequencies, respecti~ely. ~he recaiver 22 further includes differential means for differentiating the first, second and third output fre~uencies from each other to deter~ine whether the red, yellow or green traffic light is illuminated. ~he recei~er 22 can be ~attery powered, or powered by the electrical system of the vehicle 14.
Within the scope of the present invention and in addition to simple red, yellow and green light detection, the system 10 may include digital data trAn~mi~sion capability from the traffic light 18 to the vehicle 14. One or all colors (red, yellow, green and any turn signals, pedestrian messages, etc.) could be driven by a digital code generator to relay a message to oncoming vehicles, other traffic lights, or a central traffic center. Typically, each traffic light (red 17, yellow 19, and green 21) is l'on" exclusively for a certain time, therefore all traffic lights 17, 19, 21 lS facing one direction could share the same message generator which would then transmit the same digital code for each color change. Alternatively, each individual traffic light 18 could ~e coded with a "color" precursor code to per~it mor~ sophisticated ~co~;n~ schemes at the remote receivers 22. The data rate must be sufficiently high as to ena~le digital message transmission within a single flash of a flAsh;ng red or yellow traffic light 17, 19 in order to acco~odate virtl~ally all traffic signal contingencies.
The most a~yLo~Liate use for such traffic light message CA 022~427l l998-ll-09 tr~C~iscion capability would be audible routing directions. For exampl~, upon approaching a given intersection, the vehicle mounted receiver 22 might announce, "Eastbound Metro ~arkway at Hayes". No directional ambiguity exists because the message is only directed at oncoming traffic. Obviously, the transmitter 20 would have to be programmed 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, percaived output, the modulation imparted to the L.E.D. must be sufficiently fast and exhibit a constant average duty cycle. Several digital modulation schemes are capable of this limitation.
Pulse position modulation (PPM), phase shift keyed (PSX) modulation and frequency shift modulation (FSX) are typical forms of an essentially constant duty cycle modulation. m e F.S.~. modulation scheme is shown in Figure 6, as it is among the simplest to i~plement, and it is widely employed in wired and wireless cv ~r,;cation links. Two distinct frequencies F1 and F2 are used to signal the digital l's and 0's or mark and space data that constitute the message or data to be transmitted. The advantage of using such a digital .
modulation scheme is that the average L.E.D. lamp current (and power) rPm~; n~ essentially constant irrespective of the data. The reason for this is readily apparent in the diagram depicted in Figure 6 which indicates a constant 50~ duty cycle for any data stream. The result of such modulation is that the visible (perceived) brightness of the lamp is invariant, while high rate digital data is being transmitted or even when no data is transmitted (all l's or 0's).
Ideally, the F.S.K. frequencies F1 and F2 representing the digital 1'S or 0's would be separated by several hundred Hertz or kilo Hertz to facilitate unambiguous detection. Having the frequencies within a 10% band would allow a single tuned input amplifier to act as preselector filter to the frequency detectors.
Operating the L.E.D. lamps in the 10 to 20 KHz range may be ad~antageous. This frequency band permits easy differentiation from high intensity ~is~h~rge (H.I.D.) lamps such as street lights or neon lights. ~hese light sources may ha~e si~ r spectral characteristics as the traffic lamps, and thereby interfere with reliable detection of the traffic lights 18.
Referring to Figure S, the transmitter 20 that modulates the traffic light 18 is powered by the d.c.
power supply means 30. A.c. power 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 (EEPROM) or one time programmable (O.T.P.) memory chip 78 for electronically storing the digital message to be transmitted. The message itself could be coded in virtually any form such as ASCII or a proprietary alphanumeric code. Additionally, digitally coded, compressed voice communication could be transmitted along with the alphanumeric text or instead of it facilitating the regeneration of high quality voice messages at the remote receiver 22. The transmitter 20 further comprises a microprocessor 72 for controlling the removal of the digital message stored in the memory chip 78. The microprocessor 72 also controls the transmission of the digital message.
The transmitter 20 further includes a solid state switch 80. The solid state switch 80 converts the coded digital message developed by the mi~.o~ocessor 72 into F.S.~. format and thereafter transfers the F.S.~.
modulated signal to the diodes 24 of the traffic light 18. In other words, the switch 80 co-.L ols the power from the d.c. power supply means 30 to supply power to illuminate the diodes 24 for a predete~ined duty cycle __ . ., _ . ., CA 022~4271 1998-11-09 consisting cf a~ ~ Fe~iod foilowed ~y 21' OFF period short enough to be humanly imperceivable. The microprocessor 72 further includes modulator means for varying the length of time of the duty cycle to transmit the digital information. Microprocessor 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 means includes means for establishing a first length of time for the duty cycle to create a first digital signal corresponding to a digital "1" and for establishing a second length of time for the duty cycle to create a second digital signal corresponding to a digital "0". In other words, the first length of time corresponds to frequency F1 and the second length of time corresponds to frequency F2;
The traffic light assembly 16 may include power sensing means 74 for sensing when d.c. power is delivered from the d.c. power supply means 30 and a reset generator 76 for resetting the microprocessor 72 each time d.c. power is delivered to the traffic light 18 to initiate a new digital message sequence. The traffic light assembly 16 may also include ambient light sensor means 60 for varying the luminosity of the diodes CA 022~4271 1998-11-09 _,_ 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 traffic light 18 may be reduc~d to decrease brightness to further reduce power consumption while in bright sunlight the sensor means 60 would cause the power control element 82 to increase the voltage of pulses delivered to the traffic light 18. The power control element 82 could consist of a linear voltage regulator, or a low loss high frequency pulse width modulation (P.W.M.) controller, both of which are commercially available devices. Note that if pulse control is utilized to control lamp brightness, the operating frequency of such a device would have to be sign~ficantly greater than the modulation frequency in order to not affect the digital coding.
The companion receiver 22 receives the digital information transmitted by the diodes 24. Referring to Figure 7, receiver 22 consists of an optical wavelength selective filter 84, a collection lens 86, and a CA 022~4271 1998-11-09 receiver photodetector 88 coupled to a tuned amplifier 90 and a limiter 92. The photodetector 88 converts the light rays emitted by the diodes 24 into an output signal of electric current. The optical 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 light rays emitted by the diodes 24 to the photodetector 88. The amplifier 90 amplifies the output signal. The amplifier 90 is typically peaked to respond preferentially to the F.S.K.
frequencies employed by the transmitter 20. F.S.K.
detection may be advantageously provided by a receiver microprocessor 94 which then also handles character decoding (using nonvolatile resident memory) and the message display functions. The receiver 22 further comprises visual message display means 96 ~for visually displaying the digital information transmitted by the diodes 24. Typically, a liquid crystal, vacuum fluorescent, L.E.D., or miniature C.R.T. display would be used to display the message transmitted by the traffic light 18. The receiver 22 may also be equipped with a voice generation means 98 comprising a speaker means 99 for audibly conveying the digital information transmitted by the diodes. 24. For voice message applications, dedicated voice synthesis integrated CA 022~4271 1998-11-09 circuits would convert the digitized, transmitted voice announcement back into human speech for review by the driver. Modern linear predictive coding techniques and specialized voice I.C.'s (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' is disclosed for use in detecting whether 10the red 17, yellow l9, or green 21 traffic light is illuminated. Receiver 22 I consists 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' further includes an alarm generator 100 for driving a speake- 99'. As an example, the receiver 22' could be set up to sound an alarm upon the detection of a red light as transmitted by the first set of diodes 17A.
20Once the requisite hardware is installed in a critical nl~mher of traffic lights 18 and vehicles 14, the traffic control system 10 may be used to transmit traffic advisory messages. That is, the system 10 need not be limited to repetitive prerecorded messages. A
traffic light 18 positioned at specific points along a CA 022~4271 1998-11-09 ---road 12, such as an intersection, may be directly accessed by cable or a wireless link from a central traffic authority to transmit messages to passing motorists. One method to accomplish such a function S would be to download digital message data to selected traffic lights 18 for subsequent relay to passing vehicles 12. Time-out or "sunset" provisions in the software or traffic light transmitter 20 hardware could be implemented to erase messages that were no lonser pertinent.
Another use for the traffic control system 10 described herein involves the use of the digitally coded tra'fic lights 18 as "signposts" for vehicular navigztion systems. Digital~y modulated traffic lights 18 could serve as convenient, low cost sign posts for vehicular navigation systems, where unambiguous location is essential. Traffic lights are ubiquitous, and are easily adapted to transmit digital location information as well as other data.
The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the CA 0225427l l998-ll-09 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 practiced otherwise than as specifically described.
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 traffic control system of the type including a trafffic light that provides an illuminated signal for controlling the movement of a vehicle.
BACKGROUND ART
Tramc 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 trafffic 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 traffic 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 CA 022~4271 1998-11-09 .
modern solid state traffic controllers. Recent developments in solid state lamps, i.e. light emitting diodes (L.E.D.) have permitted the replacement of the conventional incandescPnt-based traffic lights with 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 luminous efficiency, and much longer lamp life. Other than luminous efficiency and lamp life, other important properties of light emitting diodes have not 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~NMaRY OF T~E lNv~NllON AND ADVaN~AGgS
The present invention is a traffic control system for controlling 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 system comprises a traffic light including a plurality of light emitting diodes for CA 022~4271 1998-11-09 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 imperceivable. The present invention is characterized by a modulator for varying the length of time of the duty cycle to transmit the digital information.
The primary advantage of the present invention is the provision of a traffic control system that utilizes the light e~itted from a traffic light to optically transmit digital information to the driver of a vehicle.
Another advantage of the present invention is the provision of a traffic light retrofit comprising a plurality of light emitting diodes which can be used to replace incandescent-based traffic lights to thereby cut energy and maintenance costs.
Another advantage of the present invention is the provision of a L.E.D.-based traffic light having a battery back-up for providing emergency power.
CA 022~4271 1998-11-09 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.
~IGtJ}~ES IN T~E DRAWINGS
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;
Figure 4 is a schematic block diagram of the electronic circuitry utilized in the present invention;
Figure 5 is a schematic bloc~ diagram of additional circuitry utilized in the present invention;
CA 022~4271 1998-11-09 Figure 6 is a signal diagram of amplitude versus time depicting one modulation scheme utilized in the present invention;
SFigure 7 is a schematic block diagram of the receiver of the present invention; and Figure 8 is a schematic bloc~ diagram of the simplified receiver of the present invention.
DE~ILED DESCRIPTION OF T~2 P~E~E~RED E~BOI)IMENT
Referring to Figure 1, the traffic control system 10 of the present invention is shown. Ihe traffic control system 10 includes a road 12, a vehicle 14 traveling on t~e road 12 and a traffic light assembly 16 operatively associated with the road 12. The traffic light assembly 16 comprises at least one traffic light or 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 vehicle 14 to "stop", "yield", or "go", respectively. However, it is to be understood that while an intersection control light is depicted in , CA 022~4271 1998-11-09 Figure 1, the benefits of this invention may be applied to a variety of other applications such as pedestrian crossing signals, e.g. WALK, DON'T WALX signals or any other illuminated "traffic related" message for controlling traffic or simply providing information.
As shown in Figures 2 and 3, the preferred embodiment of each traffic light or, lamp means 18 includes a plurality of light emitting diodes 24 for transmitting light rays from the traffic light assembly 16. In other words, the red traffic 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 l9A for projecting yellow light rays, and the green traffic light 21 comprises a third set of light emitting diodes 21A for pro~ecting green light rays. Each traffic light 18 further includes d.c. power connection means 26 secured to the traffic light 18 and electrically coupled to the diodes 24 for receiving d.c. power. The traffic light assembly 16 also includes a.c. power connection means 28 secured to the traffic light 18 for receiving a.c.
power. The traffic light assembly 16 further includes d.c. power supply means 30 secured to each traffic light 18.
Referring to Figure 4, d.c. power supply means 30 is electrically coupled to and between the a.c. power connection means 28 and the d.c. power connection means 26 for con~erting a.c. power received by the a.c. power connection means 28 to d.c. power so that d.c. power is supplied to said d.c. power connection m~nC 26. D.c power supply ~s 30 may be of conventional linear or swit~hmo~e design. D.c. power supply means 30 includes a step-down transformer to bring the a.c. line voltages of 120 - 140 volts down to approximately 3.5 volts and a st~n~rd 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 removably connected to the traffic light 18 for supplying d.c. power to said d.c. power connaction means 26 to ~ ;n~tP the diodes 24.
Preferably, the battery 32 is rechargeable. For example, battery 32 could include any sealed lead -acid, nic~el - metal hydride, or lithium rechargeable batteries. The traffic light ~Scamhly 16 further CO~L ises battery charger means 33 secured to the traffic light 18 and electrically coupled to and between the a.c. power connection means 28 and the d.c. power connection ~e~c 26 for recharging the battery 32.
The interco~nection of 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 ou~L
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 des gned to 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 battery charger 33. The battery 32 does not supply power to the traffic light 18 until a power failure, i.e. until a.c. power 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~Ard traffic controller is c~L~mised in addition to failure of the traffic lights themselves. ~nless a central uninte~L~ible power supply is used to power both t~e traffic lights and the controller, the lights may not be operated because the critical timing function and se~uencing normally provided by the controller is not available. Therefore, 2S a specific aspect of this invention is to provide a 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 circuit means 34 is preferably included as part of a power pac~ 35 which also includes battery 32.
The power pac~ 3S may be attached to each traffic light 18 by various means. Monitoring means 34 monitors the lamp current at all the traffic lights (red 17, green 19 and yellow 21) of the traffic light assembly 16. The traffic light assembly 16 further comprises switch means 36 secured to each traffic light 18 for electrically coupling the battery 32 to the d.c. power connection means 26 in L~ se to a trigger signal from the a.c.
power monitoring means 34 prompted by a predetermined decrease in a.c. power supplied to the a.c. power connection means 28. The traffic light assembly 16 further comprises pulsating circuit means 38 secured to each traffic light 18 and electrically coupled to the switch means 36 for causing the switch means 36 to electrically couple the battery 32 to the d.c. power connection means 26 at a predetermined frequency to illuminate the diodes 24 at the predetermined frequency.
Preferably, the pulsating means 38 is included as an integral part of the power pac~ 35. If monitoring means 34 detects a loss of power to all traffic lights 18 of traffic light assembly 16, switch means 36 connects the battery 32 to traffic light 18 and pulsating means 38 causes traffic light 18 to flash at the predetermined 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 rated battery 32. Thus, the present invention allows low cost, autonomous, rechargeable battery packs to be adapted to L.E.D. - based traffic lamps in order to pro~ide low cost emergency operation when line power outages occur, and to recharge automatically upon resumption of utility power.
A small, low power radio transmitter 40 may be secured to the traffic light 18 to advise a central traffic engineering office of power outages or other problems. $he radio transmitter 40 is electrically coupled to the switch means 36 for transmitting a radio wa~e in response to the trigger signal sent by monitoring means 34. As shown in Figure 3, a digitally encoded radio transmitter 40 can be used to identify the location of the malfunctioning traffic light assembly 16. Alternatively, a cable modem could be used to relay this information. The traffic light-assem~ly 16 may include delay means 42 sec~red to the traffic light 18 and electrically coupled to the radio transmitter 40 for delaying the tr~nC~i~sion of the emitted radio wave a predetermined time after the switch means 36 receives the trigger signal~ This delay is needed so that one radio frequency may be utilized by a number of traffic light assemblies without radio frequency collision by any two traffic light assemblies.
In the most simple configuration, all the diodes 24 can be arranged on a dis~, plate or printed circu~t substrate so that all of the diodes 24 are oriented in the same direction. Preferably, the diodes 24 are mounted on circuit board means 44. Circl~it board means 44 comprises of a planar printed circuit board which includes ro~nection means for electrically coupling the diodes 24 in a plurality of series circuits 46 and for electrically coupling the series circuits 46 in parallel. Each series circuit 46 includes an equal num~er of light emitting diodes 24.
Each traffic light 18 further comprises a traffic light housing 48. The light housing 48 comprises a hollow member S0 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 54. The diodes 24 are mounted within the hollow member 50 between the front and rear covers 56, 58. The front cover 56 comprises a transparent glass or plastic material having a smooth outer surface 62. Transparent lS glass is necessary to allow light rays emitted by the diodes 24 to exit virtually unimpeded and smooth surface 62 is preferred to avoid accumulation of dust and dirt.
The front and rear covers 56, 58 form a hermetic seal with the hollow member 50. The traffic ~o~ol system 10 further comprises an assembly housing 64 for housing each traffic light 18. Each traffic light 18 further includes mounting means 66 for removably mounting each traffic light 18 to the ass~mhly housing 64.
The traffic light 18 is retrofitted to permit the use of the light in existing traffic light assembly housings currently used to house incandescent traffic lights. For ease of implementation, the traffic lights 18 are preferably used with existing traffic light lens filters, which are normally stippled or equipped with small lensatic elements to achieve correct beam dispersion. ~hese lens elements are ordinarily designed to operate 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 satisfactorily with existing filters and lenses, a more effective lens is needed to "fill-in" or illuminate the spaces between diodes 24 and to steer the light rays emitted from the diodes 24 to lS the intended target, such as the vehicle 14, to avoid wasting any 1 Sht energy. To this end, each traffic light 18 may include one or more refractive elements 68 positioned between the diodes 24 and the front cover 56.
Refractive elements 68 act as a light ray steering means to steer the light rays emitted by the diodes 24 to the int~n~e~ target. Alternatively or in addition to refractive elements 68, a spacer member 70 positioned between said circuit board means 44 and the diodes 24 can be used to point the diodes 24 in a partic~llar direction. The spacer member 70 includes an angled . ~ . . . ~ .
surface 72 against which the diodes 24 abut to physically angle the diodes 24 relative to the road surface 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 high rates. By pulsing L.E.D.'s at high rates, data can be optically transmitted from the traffic light 18 to a remotely located photodetector.
Thus, the diodes 24 can be used to transmit information to vehicle 14 such as announcing the presence of a traffic light and transmitting map coordinates, street names, directions or even traffic advisories. Existing incandescent traffic lights cannot be used to transmit digital data because the thermal inertia of the filaments in these lamps precludes the rapid modulation of the supply current to obtain detectable changes in light o~L~L. Obviously, slow on - off modulation of these lamps would ~e impractical as it would be annoying and confusing to drivers. The perceived lllmi~ocity of L.E.D. sources is a function of the average current that powers the L.E.D. For example, a d.c. value of 20mA
might yield roughly the same perceived luminosity from a L.E.D. as a square wave (50~ duty cycle) of 40mA peak ., ~
current. The actual modulation of L.~.D. traffic lamps is rather simple, except for the fact that the perceived luminosity of the lamps needs to be essentially constant, as their main function is to visually alert S drivers. Message tr~ncm;Csion is a secondary function that must not interfere with normal use. If the perceived luminosity of each traffic light is to remain constant during operation, the average ~l~rrent delivered to the respective diodes must be essentially constant for periods greater than approximately 30 milliseconds.
This period corresponds to a flicker frequency of a~out 33Hz, which is perceptible by some humans.
Pulsing the diodes 24 of the traffic light 18 allows the remote detection of the light rays illuminated thereby as well as the identification of the light rays, i.e., whether the red, yellow, or green traffic light 17, 19, 21 is on. To distinguish whether either the red, yellow, or green traffic light 17, 19, 21 is illuminatod, system 10 comprises a transmitter 20 including means for optically transmitting data from one of the traffic lights 18 of assembly 16 by turning the first, second, and third set of diodes 17A, l9A, 21A on and off at three distinct frequencies. For example, the first set of light emitting diodes 17A of the red traffic light 17 can be illuminated at 50 KHz, the second set of light emitting diodes l9A of the yellow traffic light 19 at 65 KXz, the third set of light emitting diodes 21A of the green traffic light 21 at so S RXz. In this manner, the traffic lights 17, 19, 21, continue to serve their primary function of visually alerting drivers to stop, yield, or go while allowing the remota detPction and identification 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 receiver means 22 can be disposed on the ~ehicle 14, as shown in Figure 1, for optically receiving the data transmitted ~y the transmitter 2~. The receiver means 22 further includes photo-detector means for converting the light rays emitted by the red, green, and yellow traffic lights into first, ~co~ and third ~L~ signals of electric ~u~ L having first, second and third output frequencies, respecti~ely. ~he recaiver 22 further includes differential means for differentiating the first, second and third output fre~uencies from each other to deter~ine whether the red, yellow or green traffic light is illuminated. ~he recei~er 22 can be ~attery powered, or powered by the electrical system of the vehicle 14.
Within the scope of the present invention and in addition to simple red, yellow and green light detection, the system 10 may include digital data trAn~mi~sion capability from the traffic light 18 to the vehicle 14. One or all colors (red, yellow, green and any turn signals, pedestrian messages, etc.) could be driven by a digital code generator to relay a message to oncoming vehicles, other traffic lights, or a central traffic center. Typically, each traffic light (red 17, yellow 19, and green 21) is l'on" exclusively for a certain time, therefore all traffic lights 17, 19, 21 lS facing one direction could share the same message generator which would then transmit the same digital code for each color change. Alternatively, each individual traffic light 18 could ~e coded with a "color" precursor code to per~it mor~ sophisticated ~co~;n~ schemes at the remote receivers 22. The data rate must be sufficiently high as to ena~le digital message transmission within a single flash of a flAsh;ng red or yellow traffic light 17, 19 in order to acco~odate virtl~ally all traffic signal contingencies.
The most a~yLo~Liate use for such traffic light message CA 022~427l l998-ll-09 tr~C~iscion capability would be audible routing directions. For exampl~, upon approaching a given intersection, the vehicle mounted receiver 22 might announce, "Eastbound Metro ~arkway at Hayes". No directional ambiguity exists because the message is only directed at oncoming traffic. Obviously, the transmitter 20 would have to be programmed 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, percaived output, the modulation imparted to the L.E.D. must be sufficiently fast and exhibit a constant average duty cycle. Several digital modulation schemes are capable of this limitation.
Pulse position modulation (PPM), phase shift keyed (PSX) modulation and frequency shift modulation (FSX) are typical forms of an essentially constant duty cycle modulation. m e F.S.~. modulation scheme is shown in Figure 6, as it is among the simplest to i~plement, and it is widely employed in wired and wireless cv ~r,;cation links. Two distinct frequencies F1 and F2 are used to signal the digital l's and 0's or mark and space data that constitute the message or data to be transmitted. The advantage of using such a digital .
modulation scheme is that the average L.E.D. lamp current (and power) rPm~; n~ essentially constant irrespective of the data. The reason for this is readily apparent in the diagram depicted in Figure 6 which indicates a constant 50~ duty cycle for any data stream. The result of such modulation is that the visible (perceived) brightness of the lamp is invariant, while high rate digital data is being transmitted or even when no data is transmitted (all l's or 0's).
Ideally, the F.S.K. frequencies F1 and F2 representing the digital 1'S or 0's would be separated by several hundred Hertz or kilo Hertz to facilitate unambiguous detection. Having the frequencies within a 10% band would allow a single tuned input amplifier to act as preselector filter to the frequency detectors.
Operating the L.E.D. lamps in the 10 to 20 KHz range may be ad~antageous. This frequency band permits easy differentiation from high intensity ~is~h~rge (H.I.D.) lamps such as street lights or neon lights. ~hese light sources may ha~e si~ r spectral characteristics as the traffic lamps, and thereby interfere with reliable detection of the traffic lights 18.
Referring to Figure S, the transmitter 20 that modulates the traffic light 18 is powered by the d.c.
power supply means 30. A.c. power 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 (EEPROM) or one time programmable (O.T.P.) memory chip 78 for electronically storing the digital message to be transmitted. The message itself could be coded in virtually any form such as ASCII or a proprietary alphanumeric code. Additionally, digitally coded, compressed voice communication could be transmitted along with the alphanumeric text or instead of it facilitating the regeneration of high quality voice messages at the remote receiver 22. The transmitter 20 further comprises a microprocessor 72 for controlling the removal of the digital message stored in the memory chip 78. The microprocessor 72 also controls the transmission of the digital message.
The transmitter 20 further includes a solid state switch 80. The solid state switch 80 converts the coded digital message developed by the mi~.o~ocessor 72 into F.S.~. format and thereafter transfers the F.S.~.
modulated signal to the diodes 24 of the traffic light 18. In other words, the switch 80 co-.L ols the power from the d.c. power supply means 30 to supply power to illuminate the diodes 24 for a predete~ined duty cycle __ . ., _ . ., CA 022~4271 1998-11-09 consisting cf a~ ~ Fe~iod foilowed ~y 21' OFF period short enough to be humanly imperceivable. The microprocessor 72 further includes modulator means for varying the length of time of the duty cycle to transmit the digital information. Microprocessor 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 means includes means for establishing a first length of time for the duty cycle to create a first digital signal corresponding to a digital "1" and for establishing a second length of time for the duty cycle to create a second digital signal corresponding to a digital "0". In other words, the first length of time corresponds to frequency F1 and the second length of time corresponds to frequency F2;
The traffic light assembly 16 may include power sensing means 74 for sensing when d.c. power is delivered from the d.c. power supply means 30 and a reset generator 76 for resetting the microprocessor 72 each time d.c. power is delivered to the traffic light 18 to initiate a new digital message sequence. The traffic light assembly 16 may also include ambient light sensor means 60 for varying the luminosity of the diodes CA 022~4271 1998-11-09 _,_ 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 traffic light 18 may be reduc~d to decrease brightness to further reduce power consumption while in bright sunlight the sensor means 60 would cause the power control element 82 to increase the voltage of pulses delivered to the traffic light 18. The power control element 82 could consist of a linear voltage regulator, or a low loss high frequency pulse width modulation (P.W.M.) controller, both of which are commercially available devices. Note that if pulse control is utilized to control lamp brightness, the operating frequency of such a device would have to be sign~ficantly greater than the modulation frequency in order to not affect the digital coding.
The companion receiver 22 receives the digital information transmitted by the diodes 24. Referring to Figure 7, receiver 22 consists of an optical wavelength selective filter 84, a collection lens 86, and a CA 022~4271 1998-11-09 receiver photodetector 88 coupled to a tuned amplifier 90 and a limiter 92. The photodetector 88 converts the light rays emitted by the diodes 24 into an output signal of electric current. The optical 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 light rays emitted by the diodes 24 to the photodetector 88. The amplifier 90 amplifies the output signal. The amplifier 90 is typically peaked to respond preferentially to the F.S.K.
frequencies employed by the transmitter 20. F.S.K.
detection may be advantageously provided by a receiver microprocessor 94 which then also handles character decoding (using nonvolatile resident memory) and the message display functions. The receiver 22 further comprises visual message display means 96 ~for visually displaying the digital information transmitted by the diodes 24. Typically, a liquid crystal, vacuum fluorescent, L.E.D., or miniature C.R.T. display would be used to display the message transmitted by the traffic light 18. The receiver 22 may also be equipped with a voice generation means 98 comprising a speaker means 99 for audibly conveying the digital information transmitted by the diodes. 24. For voice message applications, dedicated voice synthesis integrated CA 022~4271 1998-11-09 circuits would convert the digitized, transmitted voice announcement back into human speech for review by the driver. Modern linear predictive coding techniques and specialized voice I.C.'s (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' is disclosed for use in detecting whether 10the red 17, yellow l9, or green 21 traffic light is illuminated. Receiver 22 I consists 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' further includes an alarm generator 100 for driving a speake- 99'. As an example, the receiver 22' could be set up to sound an alarm upon the detection of a red light as transmitted by the first set of diodes 17A.
20Once the requisite hardware is installed in a critical nl~mher of traffic lights 18 and vehicles 14, the traffic control system 10 may be used to transmit traffic advisory messages. That is, the system 10 need not be limited to repetitive prerecorded messages. A
traffic light 18 positioned at specific points along a CA 022~4271 1998-11-09 ---road 12, such as an intersection, may be directly accessed by cable or a wireless link from a central traffic authority to transmit messages to passing motorists. One method to accomplish such a function S would be to download digital message data to selected traffic lights 18 for subsequent relay to passing vehicles 12. Time-out or "sunset" provisions in the software or traffic light transmitter 20 hardware could be implemented to erase messages that were no lonser pertinent.
Another use for the traffic control system 10 described herein involves the use of the digitally coded tra'fic lights 18 as "signposts" for vehicular navigztion systems. Digital~y modulated traffic lights 18 could serve as convenient, low cost sign posts for vehicular navigation systems, where unambiguous location is essential. Traffic lights are ubiquitous, and are easily adapted to transmit digital location information as well as other data.
The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the CA 0225427l l998-ll-09 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 practiced otherwise than as specifically described.
Claims (7)
1. A traffic light assembly (16) for controlling the movement of a vehicle (14), said assembly (10) comprising:
traffic light means (18) comprising a plurality of light emitting diodes (24) for transmitting light rays form said traffic light assembly (16);
d.c. power connection means (26) secured to said traffic light means (18) and electrically coupled to said diodes (24) for receiving d.c. power;
a.c. power connection means (28) secured to said traffic light means (18) for receiving a.c. power;
d.c. power supply means (30) secured to said traffic light means (18) and electrically coupled to and between said a.c. power connection means (28) and said d.c. power connection means (26) for converting a.c. power received by said a.c. power connection means (28) to d.c. power so that d.c. is supplied to said d.c. power connection means (26);
and characterized by a battery (32) removably connected to said traffic light means (18) for supplying d.c. power to said d.c. power connection means (26) to illuminate said diodes (24).
traffic light means (18) comprising a plurality of light emitting diodes (24) for transmitting light rays form said traffic light assembly (16);
d.c. power connection means (26) secured to said traffic light means (18) and electrically coupled to said diodes (24) for receiving d.c. power;
a.c. power connection means (28) secured to said traffic light means (18) for receiving a.c. power;
d.c. power supply means (30) secured to said traffic light means (18) and electrically coupled to and between said a.c. power connection means (28) and said d.c. power connection means (26) for converting a.c. power received by said a.c. power connection means (28) to d.c. power so that d.c. is supplied to said d.c. power connection means (26);
and characterized by a battery (32) removably connected to said traffic light means (18) for supplying d.c. power to said d.c. power connection means (26) to illuminate said diodes (24).
2. The traffic light assembly (16) of claim 1 further comprising a.c. power monitoring circuit means (34) secured to said traffic light means (18) for monitoring a.c.
power supplied to said a.c. power connection means.
power supplied to said a.c. power connection means.
3. The traffic light assembly (16) of claim 2 further comprising switch means (36) secured to said traffic light means (18) for electrically coupling said battery (32) to said d.c.
power connection means (26) in response to a trigger signal from said a.c. power monitoring means (34) prompted by a predetermined decrease in a.c. power supplied to said a.c. power connection means (28).
power connection means (26) in response to a trigger signal from said a.c. power monitoring means (34) prompted by a predetermined decrease in a.c. power supplied to said a.c. power connection means (28).
4. The traffic light assembly (16) of claim 3 further comprising pulsating circuit means (38) secured to said traffic light means (18) and electrically coupled to said switch means (36) for causing said switch means (36) to electrically couple said battery (32) to said d.c. power connection means to illuminate said frequency so as to (26) at a predetermined frequency diodes (24) at said predetermined minimize consumption of power from said battery (32).
5. The traffic light assembly (16) of claim 3 further comprising transmitter means (40) secured to said traffic light means (18) and electrically coupled to said switch means (36) for transmitting a radio wave in response to said trigger signal.
6. The traffic light assembly (16) of claim 5 further comprising delay means (42) secured to said traffic light means (18) and electrically coupled to said transmitter means (40) for delaying the transmission of said radio wave from said transmitter means (40) a predetermined time after said switch means (36) receives said trigger signal.
7. The traffic light assembly (16) of claim 1 further comprising battery chargermeans (33) secured to said traffic light means (18) and electrically coupled to and between said a.c. power connection means (28) and said d.c. power connection means (26) for recharging said battery (32).
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/386,816 | 1995-02-08 | ||
| US08/386,816 US5633629A (en) | 1995-02-08 | 1995-02-08 | Traffic information system using light emitting diodes |
| CA002169037A CA2169037C (en) | 1995-02-08 | 1996-02-07 | Traffic control system using light emitting diodes |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002169037A Division CA2169037C (en) | 1995-02-08 | 1996-02-07 | Traffic control system using light emitting diodes |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2254271A1 true CA2254271A1 (en) | 1996-08-09 |
Family
ID=25678332
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002254271A Abandoned CA2254271A1 (en) | 1995-02-08 | 1996-02-07 | Traffic control system using light emitting diodes |
| CA002257000A Expired - Fee Related CA2257000C (en) | 1995-02-08 | 1996-02-07 | Traffic control system using light emitting diodes |
Family Applications After (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002257000A Expired - Fee Related CA2257000C (en) | 1995-02-08 | 1996-02-07 | Traffic control system using light emitting diodes |
Country Status (1)
| Country | Link |
|---|---|
| CA (2) | CA2254271A1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2399206A (en) * | 2003-03-05 | 2004-09-08 | Qinetiq Ltd | Signalling system with visible and non visible signals |
-
1996
- 1996-02-07 CA CA002254271A patent/CA2254271A1/en not_active Abandoned
- 1996-02-07 CA CA002257000A patent/CA2257000C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2257000C (en) | 2002-06-11 |
| CA2257000A1 (en) | 1996-08-09 |
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