exemplary embodiments of the present invention are now described with reference to the figures . reference numerals are used throughout the detailed description to refer to the various elements and structures . in other instances , well - known structures and devices are shown in block diagram form for purposes of simplifying the description . although the following detailed description contains many specifics for the purposes of illustration , a person of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the invention . accordingly , the following embodiments of the invention are set forth without any loss of generality to , and without imposing limitations upon , the claimed invention . the present invention relates generally to detection systems for use with tall vehicles such as trucks and tractor - trailer units for detecting and avoiding a stationary object such as a bridge or overpass located above a road . the present invention is essentially a two - part system that includes an exterior sensor component and an interior processing and control component . the exterior sensor component is typically mounted on the side mirror frame of a truck , tractor - trailer unit , or other tall and / or large vehicle . the interior control component is in electrical communication with the exterior sensor component and typically includes a digital controller unit that can be programmed with the height of the exterior sensor component and the height of the trailer that is being pulled or the truck that is being driven . when the vehicle approaches a potential obstacle or hazard , the operator of the vehicle slowly pulls the front portion ( i . e ., cab ) of the vehicle under the hazard and activates the overhead obstacle detection system of the present invention . the height of the obstacle relative to the height of the trailer is determined and reported to the vehicle &# 39 ; s operator . if the obstacle is lower than an acceptable height , and alarm sounds and the operator may avoid moving any farther forward . in this manner , the vehicle &# 39 ; s operator may avoid serious damage to the vehicle and / or the obstacle . this system addresses the problem of hazards , i . e . bridges , trestles , trees , that are unmarked or mismarked , or areas where new asphalt has been added ( up to several inches ) to the road bed and the height signs ( i . e . 12 ″, 12 ′ 6 ″) have not been changed accordingly . as previously indicated , a first general embodiment of this invention provides a collision avoidance system for use with moving vehicles ; a second general embodiment of this invention provides a system for preventing the collision of a moving vehicle with an overhead obstacle ; and a third general embodiment of this invention provides a method for preventing the collision of a moving vehicle with an overhead obstacle . with reference now to the figures , one or more specific embodiments of this invention shall be described in greater detail . with reference to fig1 - 6 , an exemplary embodiment of obstacle avoidance system 10 includes sensor assembly 20 , which is in electrical communication with processor 60 . as best shown in fig3 - 4 , sensor assembly 20 further includes sensor body 22 , which houses sensor 23 and level 24 . holding nut 25 attaches sensor body 22 to sensor base 26 , which includes top clamping portion 27 and bottom clamping portion 29 . top gasket 28 and bottom gasket 30 are included in sensor base 26 for purposes of stabilizing sensor assembly on mirror support 90 ( see fig5 ). bolts 31 and washers and nuts 32 are used to attach sensor base 26 to mirror support 90 . as best shown in fig2 , processor 60 includes led display 62 ( or another type of display ), control and display logic 64 , and audio alarm output 66 and may also include temperature compensation module 40 , signal amplifier 24 , signal comparator 44 , and power control 46 . connector cable 70 , which is typically a coaxial cable , is used to connect sensor assembly 20 to processor 60 . connector cable 70 may be provided in a variety of different lengths to accommodate different vehicle types , sizes , and dimensions . connector cables of 8 feet ( 2 . 44 meters ), 12 feet ( 3 . 68 meters ), or 16 feet ( 4 . 88 meters ) are compatible with this invention and other lengths are possible . in some embodiments , connector cable 70 includes quick - connectors , which permit cables of different lengths to be easily substituted for one another , as needed . power adaptor 80 is typically plugged into the cigarette lighter inside the cab of a vehicle and provides a source of electrical power to obstacle avoidance system 10 . in the exemplary embodiment of the present invention shown in the figures , sensor 23 is an ultrasonic sensor , and preferably an ultrasonic transducer . ultrasonic sensors are known as transducers when they both send and receive and work on a principle similar to radar or sonar which evaluates attributes of a target by interpreting the echoes from radio or sound waves respectively . ultrasonic sensors generate high frequency sound waves and evaluate the echo which is received back by the sensor . sensors calculate the time interval between sending the signal and receiving the echo to determine the distance to an object . systems typically use a transducer which generates sound waves in the ultrasonic range , above 20 , 000 hertz , by turning electrical energy into sound , then upon receiving the echo turn the sound waves into electrical energy which can be measured and displayed . ultrasonic transducers send and receive waves for many types of sensing . examples include distance , proximity , level , nondestructive evaluation , web break detection , counting , and security applications . they typically operate at their resonant frequency with various construction options , beam patterns , and power levels . ultrasonic transducers come in different styles for different applications and a variety of such transducers are compatible with the present invention . for example , plain general - purpose transducers , including air transducers , are available with no specialized features . more specialized styles are common as well , such as contact transducers for placing directly on the surface to be measured . dual element transducers have two elements in the transducer housing and allow the transmitter and receiver to operate independently . the elements are angled toward each other to create a reflective transmit / receive pathway . angle beam transducers include mounted transparent angle blocks and are often used for weld inspection and flaw detection . they typically utilize refracted shear waves to detect flaws throughout the depth of welded areas . immersible transducers are designed to be totally submerged in a liquid medium , most often fresh water . the protected element style has the transducer element protected for use on rough surfaces . delay line transducers are versatile , often with replaceable head options such as membranes and wear caps . they are used to gage or detect flaws such as delaminations in thin materials . shear wave transducers introduce shear waves into material without using an angle beam wedge . the ratio of shear wave components to longitudinal components can exceed 30 db . medical style transducers and housings are designed for specific medical applications . common features available for ultrasonic transducers are array configuration for connecting more than one transducer in series or parallel ; temperature compensation circuitry that compensates for sensitivities changing with ambient temperature ; and optional analog output . most transducers output analog voltage , but may have provisions for current loop output , etc . ultrasonic transducers that are potentially compatible with the present invention may be obtained from a variety of commercial sources such as maxbotics ( ez0 - 4 ), robotic electronics / devantech ( srf10 , srf08 , srf04 , and sr235 ), idec ( sa6a ), asl / seiz & amp ; viscarret ( usonic ), and sonaswitch ( minia and minis ). a variety of other ultrasonic devices are potentially compatible with obstacle avoidance system 10 . as will be appreciated by one of ordinary skill in the art , processor 60 may be any of a variety of commercially available or custom built signal processing units or central processing units that include signal processing capabilities as well as data processing and system control modules ( see fig2 ) in an exemplary embodiment , the operation range of the system is about 0 . 4 meter (+/− 0 . 1 meter tolerance ) to about 5 meters ( 16 . 4 feet ). in other embodiments , the upper limit of the operational range of the system is about 6 meters ( 20 feet ) or about 7 . 5 meters ( 25 feet ). other operational parameters are possible . features generally provided with or in the system include ( i ) a programmable distance for alarm signal ; ( ii ) a programmable offset ( subtraction ) to compensate for mounting position ; ( iii ) display type : led display for feet , inches convertible english / metric units ; ( iv ) power requirements : 12 v dc with female jack for dc power on display unit ; ( v ) operating current : 30 ma ( based on desired brightness of led ); ( vi ) interface : user keys for setting height , alarm position , english / metric mode ; ( vii ) installing distance between sensor and display : 3 to 6 feet horizontally ; and ( ix ) material : abs plastic and various metals . specifications for an exemplary interior control ( display ) unit are as follows : ( i ) operating voltage : 12v dc ; ( ii ) operating temperature : − 10 ° c . to 60 ° c . ; ( iii ) controller : microprocessor ; ( iv ) weight : approximately 150 grams . specifications for an exemplary exterior ( sensor ) unit are as follows : ( i ) operating voltage : 12 v dc ; ( ii ) operating temperature : − 10 ° c .-+ 60 ° c . ; ( iii ) sensor : ultrasonic transducer ; ( iv ) dimensions : baffle unit for sensor housing shown in fig1 ; ( v ) weight : approximately 120 grams . other system and component specifications are possible . with reference to fig6 , obstacle avoidance system 10 may be used according the following exemplary method . using sensor base 26 , sensor assembly 20 is mounted on the exterior of a vehicle in a location that allows sensor 23 to have a clear and unobstructed view ( i . e ., no impediments or blockages 45 ° from vertical ). no portion of the vehicle on which sensor assembly 20 is mounted should block the signal path of sensor 23 . sensor assembly 20 is then connected to processor 60 with connector cable 70 , which may be routed into the interior of the vehicle through a window vent or other access point . processor 60 is mounted inside the vehicle where it is easily visible and accessible by the operator of the vehicle . the height above ground level 100 at which sensor 23 ( sensor surface level 104 ) is mounted is measured ( e . g ., manually ) to determine reference height 106 . reference height 106 is then manually entered into processor 60 . the tallest portion above ground level 100 of the vehicle in which obstacle avoidance system 10 is installed is measured ( e . g ., manually or reference to printed height on vehicle or owner &# 39 ; s manual ) and entered into processor 60 . as the vehicle slowly moves under an overhead item ( i . e ., a potential obstacle ), sensor 23 is used to measure the overhead distance between the bottom of the overhead obstacle and the sensor itself . this distance is referred to as measured distance 110 , which is then stored in processor 60 . processor 60 is then used to calculate a measured height 108 of the obstacle , which is displayed by led 62 . measured height 108 is reference height 106 added to measured distance 110 . a visual and / or audible alarm is produced if the measured height 108 of the overhead obstacle is less than the height of the tallest portion ( e . g ., the trailer or portion of the vehicle behind the cab ) of the vehicle above ground level 100 . in this manner , the operator of a vehicle in which obstacle avoidance system 10 has been installed may avoid a collision with an overhead obstacle that is lower than the maximum height of the vehicle . in an exemplary embodiment , obstacle avoidance system 10 remains active while the cab portion of the vehicle passes completely under the overhead item and automatically shuts off when the potential obstacle has been cleared . obstacle avoidance system 10 typically remains active for one minute as the cab portion of the vehicle passes completely under the obstacle . another full minute of sensor activity can be obtained when the operator manually activates the sensor . during normal operation , the driver pushes an “ on ” button and obstacle avoidance system 10 measures for one minute and then shuts off . during that initial minute , the operator may push the on button again at any time to engage the system for another minute . in another exemplary embodiment , audio alarm output 66 produces an alarm and led 62 flashes if the height read by the sensor 23 is lower than reference height 106 . for example , if the height programmed into the unit is 13 ′ 0 ″ and the actual height of the obstacle is displayed as 13 ′ 1 ″, led 62 will show a constant 13 ′ 1 ″. if led 62 reads 13 ′ 0 ″ or below , the readout will blink on and off and the alarm will sound . in one embodiment of the present invention , when obstacle avoidance system 10 detects an overhead obstacle , the height of which is lower than the height of the tallest portion above ground level 100 of the vehicle in which obstacle avoidance system 10 is installed , the visual and audible alarms sound and the system locks into the lower height . upon locking into the lower height , the sensor stops taking measurements until the obstacle has been cleared and the unit has been manually reset by the user or until after a preprogrammed time delay ( e . g ., 3 - 4 seconds ) has passed . preventing obstacle avoidance system 10 from automatically resetting and beginning to take new overhead distance measurements provides a driver or operator with more time to become aware of a potentially dangerous overhead obstacle and respond accordingly . in this and other embodiments , the volume of the audible warning can be set to a level that allows it to be easily heard over the engine sound generated by the vehicle when being driven . while the present invention has been illustrated by the description of exemplary embodiments thereof , and while the embodiments have been described in certain detail , it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail . additional advantages and modifications will readily appear to those skilled in the art . therefore , the invention in its broader aspects is not limited to any of the specific details , representative devices and methods , and / or illustrative examples shown and described . accordingly , departures may be made from such details without departing from the spirit or scope of the applicant &# 39 ; s general inventive concept .