Patent Publication Number: US-2007114225-A1

Title: De-icing system for traffic signals

Description:
The present invention relates to LED traffic signals, and, more particularly, to a circuit for detecting and eliminating the buildup of snow and ice on the lenses of LED traffic signals.  
     SUMMARY OF THE INVENTION  
      Before light emitting diode (“LED”) traffic signals began replacing traffic signals using incandescent bulbs, the buildup of frozen matter, such as snow and ice, on the viewable faces or lenses of incandescent traffic signals was not an issue. Typically, the incandescent signals required an amount of power that was much larger than that required by LED traffic signals. The large amount of power used by incandescent traffic signals was converted to heat and dissipated through the face or lens of the traffic signal, resulting in the melting of most, if not all, snow and ice on the lenses of the incandescent traffic signals.  
      With the introduction of LED traffic signals, a significant reduction in power consumption over that used by incandescent signals was realized. The LEDs used in such signals convert the input power more efficiently and thus dissipate much less heat through the lens of the traffic signal. However, this significant improvement in power efficiency provided by the LED traffic signals eliminated the inherent benefit of the incandescent signals to reduce or eliminate the buildup of frozen snow and/or ice on the lenses of the traffic signals. This dangerous buildup of snow and/or ice on the LED signals has caused many accidents, and is a major concern for the safety of the motoring public.  
      Thus, it is desirable to provide a circuit that would detect and eliminate the buildup of ice or snow on the lenses of LED traffic signals.  
     BRIEF DESCRIPTION OF THE INVENTION  
      The present invention is directed to a circuit that detects and eliminates the buildup of frozen matter, such as snow or ice, on the viewable face or lens of an LED traffic signal. The circuit of the present invention monitors the ambient temperature within the traffic signal, and when the temperature falls below a certain set point where snow and/or ice accumulation can occur, the circuit begins looking for the buildup of snow and/or ice on the lens of the traffic signal. When the circuit detects the buildup of frozen matter, the circuit “warms” the face or lens of the traffic signal so as to defrost, and thereby eliminate, the frozen matter buildup. The circuit of the present invention uses a heating element or a plurality of elements that are mounted on, or in proximity to, the face or lens of the LED traffic signal to warm the face or lens of the signal. The heating elements are activated only when a sensor detects the buildup of frozen matter on the lens of the signal. The heating elements can be any device that produces heat when power is applied to them. Preferably, the heating elements are a plurality of high wattage resistors.  
      The circuit of the present invention includes a microcontroller that monitors ambient temperature within the LED traffic signal using an internal sensor. If the ambient temperature is above a temperature set point where ice and/or snow can form, the microcontroller takes no action. If the ambient temperature is below the set point, the microcontroller begins looking for the build-up of ice or snow on the lens of the LED traffic signal. Using an internal analog-to-digital converter that receives a signal from a photodiode light sensor, the microcontroller measures the ambient light level external to the signal. The measure of ambient light is used by the microcontroller as a baseline to reduce or eliminate false triggering of the circuits used to detect the buildup of ice or snow due to external light sources, such as sunlight, street lights, etc.  
      The circuits used to detect the buildup of ice or snow on the lens of an LED signal preferably include an infrared LED as a transmitter. The gain of the transmitter is continuously adjusted by the microcontroller using the ambient light level measurement received from the photodiode light sensor. Using an internal digital-to-analog converter, the microcontroller adjusts the gain of the infrared LED transmitter by adjusting the voltage applied to the base of a transistor that controls the operation of the infrared LED. This adjustment to the gain of the transmitter, in turn, controls the transmitting power of the infrared LED transmitter. Preferably, the microcontroller applies to the base of the transistor a 40 kHz signal modulated at 100 Hz, the signal being generated by the microcontroller.  
      Preferably, an infrared receiver looks for a signal that is reflected from the lens of the LED traffic signal. The reflected signal occurs when there is a buildup of ice and/or snow on the lens of the signal. When the reflected signal is received by the infrared receiver, it demodulates the transmitted signal and sends a 100 Hz signal to the microcontroller. The signal sent by the receiver is analyzed by the microcontroller to determine if it is a valid reflected signal, or if it is noise from an outside light source. The microcontroller determines if a signal is a valid reflected signal by counting the pulses received. If it is a correct count, ±5, then the signal is valid. If it is a valid reflected signal, the microcontroller then turns on the heating elements. For this purpose, the microcontroller turns on a triac, which applies AC power to the heating elements from an AC power source. Preferably, the heating elements are a series of high wattage resistors located near or on the lens of the traffic signal. However, it should be noted that other heating elements could be used, such as ceramic elements, resistive wire, resistive coatings, filaments, ultrasonic heaters, microwave signals, and Peltier thermoelectric devices. The heater will continue to heat the signal lens until the temperature measured by the microcontroller rises above a controlled set point, or the snow and ice condition no longer exists. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic drawing of the circuit of the present invention for detecting and eliminating the buildup of snow and/or ice on the lens of an LED traffic signal.  
       FIG. 2  is a simplified block diagram depicting the operation of the microcontroller in reading the ambient light level from a light sensor, using an analog-to-digital converter.  
       FIG. 3  is a side elevational view showing the operation of the infrared LED transmitter and the infrared LED receiver, in which a reflected signal is detected that indicates the presence of snow and/or ice on the lens of an LED traffic signal.  
       FIG. 4  is a simplified block diagram, showing the operation of the microcontroller in adjusting the transmitter power of the infrared LED transmitter.  
       FIG. 5  is a simplified block diagram showing the operation of the microcontroller in receiving a signal from the infrared receiver circuit, indicating the presence of snow and/or ice on the lens of the LED traffic signal.  
       FIG. 6  is a simplified block diagram showing the heater circuit used in the present invention for heating the signal lens to eliminate the buildup of snow and/or ice on the lens.  
       FIGS. 7A through 7   f  are plan and side elevational drawings showing alternative heating elements that can be used and locations of such heating elements relative to the lens of an LED traffic signal.  
       FIG. 8  is a simplified block diagram showing the voltage rectifying and regulating circuit for generating the power supply voltage for the circuit of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The present invention is directed to a circuit  10  for detecting the buildup of snow and/or ice on the lens of an LED traffic signal and for eliminating the buildup of the snow and/or ice from the lens of an LED traffic signal.  
      The heart of circuit  10  is a microcontroller  12 , which senses ambient temperature within the LED signal, initiates the function of looking for snow and/or ice buildup when the ambient temperature falls below a certain set point and initiates the operation of a heater to eliminate ice and/or snow when it is detected. Preferably, microcontroller  12  is a CY8C27143B programmable microcontroller manufactured, for example, by Cypress Semiconductor Corp. Microcontroller  12  is shown as component U 1  in the schematic of circuit  10  shown in  FIG. 1 , which includes an internal sensor to monitor the temperature within the LED signal.  
      As shown in  FIGS. 1 and 2 , the circuit  10  also includes an ambient light sensor circuit  14 , which uses a light sensing photodiode D 2  to detect the level of ambient light normally entering the lens of the LED traffic signal. Preferably, photodiode D 2  is, for example, a BPV10NF Light Sensor manufactured by Vishay. Microcontroller  12  monitors the temperature, using an internal sensor. Microcontroller  12  reads the ambient light level from the light sensor D 2  using an analog-to-digital converter  13  that is internal to microcontroller  12 . The monitoring of the ambient temperature by microcontroller  12  occurs at one-minute intervals. If the ambient temperature is above a set point where ice and snow can occur, microcontroller  12  takes no action. If the temperature is below the set point, microcontroller  12  will begin looking for a buildup of ice and/or snow.  
      Using the information obtained from ambient light sensor  14 , microcontroller  12  adjusts the gain of an infrared LED transmitter circuit  16  to reduce or eliminate false triggering due to external light sources, such as sunlight and streetlights. The information received by microcontroller  12  from ambient light sensor  14  is used as a baseline by microcontroller  12  to reduce or eliminate false triggering due to the external light sources.  
      Infrared LED transmitter circuit  16  includes an infrared light emitting diode D 1 , which functions as a transmitter. Preferably, diode D 1  is an LTE-4208C Infrared LED Emitter manufactured, for example, by Lite-On Technology Corporation. Microcontroller  12  adjusts the voltage on the base of a transistor Q 1 , which controls the forward bias of infrared LED D 1 , as transistor Q 1  is turned on. Transistor Q 1  is preferably a 2N3904 PNP transistor. As shown in  FIG. 4 , microcontroller  12  adjusts the voltage it applies to the base of transistor Q 1  using a digital-to-analog converter  23  that is internal to microcontroller  12 . By controlling the voltage applied to the base of transistor Q 1 , microcontroller  12  controls the power of transmitter circuit  16 . As also shown in  FIG. 4 , microcontroller  12  performs this function using a 40 kHz signal modulated at 100 Hz. This signal is generated by the microcontroller  12  and applied to the infrared LED D 1  through the emitter of transistor Q 1 . A 40 Khz signal modulated at 100 Hz is used for the transmitting function because the infrared receiver is tuned to 40 Khz. A 40 Hhz signal burst is modulated at 100 Hz to give the receiver time between bursts to reset itself. The benefit is noise immunity and lower susceptibility to the effects of ambient light.  
      As shown in  FIG. 3 , transmitter circuit  16  transmits an infrared signal  17 , which is directed towards the lens  19  of the LED traffic signal. When the signal  17  reaches the surface of signal lens  19 , if there is no buildup of ice or snow on lens  19 , signal  17  will migrate through lens  19  to the exterior of the LED traffic signal. Conversely, when signal  17  reaches the surface of lens  19 , if there is a buildup of ice and/or snow  11  on lens  19 , signal  17  is reflected back into the interior of the LED traffic signal, where it is received by receiver circuit  18 . Receiver circuit  18  includes an infrared receiver U 3 , which is preferably a model TSOP2140 integrated circuit manufactured by Vishay. When reflected signal  17  is received by receiver circuit  18 , it demodulates reflected signal  17 , and sends a 100 Hz signal to microcontroller  12 , as shown in  FIG. 5 . The 100 Hz signal received by microcontroller  12  is then analyzed by microcontroller  12  to determine if it is a valid reflected signal or noise from an external light source. If received signal  17  is a valid signal, then microcontroller  12  will turn on heater circuit  20  shown in  FIGS. 1 and 6 .  
      Microcontroller  12  turns on heater circuit  20  by turning on a triac U 2 , which applies AC power from an AC power source  22  to heating elements  21 . Preferably, heating elements  21  are a plurality of high wattage resistors R5-R16 connected in series between triac U 2  and the AC power source  22 . Although it should be noted, however, that other heating elements could be used, such as ceramic elements, resistive wire, resistive coatings, filaments, ultrasonic heaters, microwave signals, and Peltier thermoelectric devices. Regardless of the type of heating element used, microcontroller  12  would turn on triac U 2  to apply a voltage that turns on heater circuit  20 . Thus, for example, if heater circuit  20  were an ultrasonic heater, heater circuit  20  would be comprised of an ultrasonic emitter with its associated drive circuitry powered by triac U 2  under the control microcontroller  12 .  
      Heater circuit  20  continues to heat signal lens  19  until the temperature measured by microcontroller  12  through its internal sensor rises above the temperature set point, or the snow and/or ice condition on lens  19  no longer exists. In the latter case, signal  17  transmitted by transmitter circuit  16  is no longer reflected by snow and/or ice on lens  19  so as to be received by receiver circuit  18 .  
       FIGS. 7   a  through  7   h  are plan and side elevational drawings showing alternative heating elements  21  that can be used in heater circuit  20  and locations of such heating elements  21  relative to the lens  19  of an LED traffic signal  30 .  
       FIGS. 7   a  and  7   b  are plan and side elevational drawings, respectively, of an LED traffic signal  30  including heating elements  21  in the form of a plurality of resistive coatings  32  located on the lens  19  of traffic signal  30  and positioned in multiple iterations of a back and forth pattern across lens  19  to heat lens  19 . Preferably, resistive coatings  32  are connected in series between triac U 2  and the AC power source  22 .  
       FIGS. 7   c  and  7   d  are plan and side elevational drawings, respectively, of LED traffic signal  30  including heating elements  21  in the form of a resistive wire  34  located on the lens  19  of the traffic signal  30  and positioned in multiple iterations of a back and forth pattern across lens  19  to heat lens  19 . Preferably, resistive wire  34  is connected between triac U 2  and the AC power source  22 .  
       FIGS. 7   e  and  7   f  are plan and side elevational drawings, respectively, of LED traffic signal  30  including heating elements  21  in the form of a plurality of resistors  36 , shown as resistors R 5  through R 16  in the schematic of  FIG. 1 , and located substantially at the periphery of the circuit board  40  on which are mounted an array of light emitting diodes (not shown) used to provide the particular color light emitted by LED traffic signal  30  so as to be in close proximity to lens  19  to heat lens  19 . Preferably, resistors  36  are connected in series between triac U 2  and the AC power source  22 .  
       FIGS. 7   g  and  7   h  are plan and side elevational drawings, respectively, of LED traffic signal  30  including heating elements  21  in the form of a resistive wire  38  located on the lens  19  of the traffic signal  30  and positioned, to heat lens  19 , in a multi-loop circular pattern on lens  19  where such lens is in close proximity to the circuit board  40  on which the array of light emitting diodes are mounted. Preferably, resistive wire  38  is connected between triac U 2  and the AC power source  22 .  
      The power supply used by circuit  10  for its operation supplies a voltage of VCC, which is typically 5V DC. As shown in  FIG. 8 , AC voltage supplied by AC power supply  22  is fed into a bridge rectifier  24 , which rectifies the AC voltage signal and then feeds it to a voltage regulator  26  to then produce the DC supply voltage  28  labeled as VCC.  
      The circuit  10  of the present invention for detecting and eliminating the buildup of ice and/or snow from the lens of an LED traffic signal can be used with a single array of LEDs that form one of the signal lights of a traffic signal, such as the red, amber and green signals that are typically included in traffic signals. The circuit  10  can also be used with multiple arrays of LEDs that form the red, amber and green signals included in traffic signals. In the latter instance, it would be necessary to have an ambient light sensor circuit  14 , a transmitter circuit  16 , a receiver circuit  18 , and a heater circuit  20  for each of the LED arrays; however, a single microcontroller  12  could be used to interact with and control these circuits in each of the LED arrays.  
      While the invention has been described in connection with what is presently considered to be the preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.