Rearview mirror with integrated microwave receiver

An inventive rearview mirror assembly is disclosed in which a microwave antenna is mounted so as to receive transmissions from one or more satellites through the front windshield of the vehicle. The microwave antenna may be tuned to receive satellite transmissions from a position identification system constellation of satellites, such as GPS or GLONASS. Additionally, the microwave antenna may be tuned to alternatively or additionally receive transmissions from at least one communication satellite, such as a CD radio satellite. In addition to the inventive rearview mirror assembly, an inventive electrical control system is disclosed that may be used as a navigation system, an electrochromic rearview mirror control system, a head lamp control system, a tire pressure monitoring and display system, a temperature sensing and display system, a vehicle compass system, a vehicle data recorder system, and/or a vehicle odometer verification system. In each of the above systems, new parameters are made available by the microwave antenna to perform control operations not previously performed.

BACKGROUND OF THE INVENTION 
The present invention generally relates to a rearview mirror for a vehicle 
and to microwave receivers and antennas. More specifically, the present 
invention relates to electrochromic rearview mirror assemblies and control 
systems, vehicle navigation systems, satellite-to-vehicle communuications, 
vehicle compass systems, vehicle head lamp control systems, vehicle 
temperature sensing and display systems, and vehicle tire pressure sensing 
and display systems. 
Vehicle position identification systems are known and commonly used in 
vehicles for purposes relating to vehicle navigation and tracking systems. 
Currently, two such position identification systems that are in use are 
GPS and GLONASS, both of which utilize a constellation of satellites that 
transmit microwave signals towards the earth that, in turn, are received 
by a ground-based microwave receiver and used to determine the position of 
the receiver on the earth's surface. Such systems are capable of a very 
high degree of accuracy. As a result, a great deal of research has been 
conducted to construct navigation systems that may be readily incorporated 
into a vehicle. 
Position identification systems have also been used in vehicles with 
respect to communication systems, particularly emergency communication 
systems, whereby a vehicle occupant making an emergency call using a 
cellular telephone need not actually know the vehicle's exact location in 
order to have emergency vehicles dispatch to that location. Examples of 
such systems include the ONSTAR.RTM. system from General Motors 
Corporation and the AUTOLINK.RTM. system available from Johnson Controls, 
Inc. Other uses of position identification systems in vehicles include the 
use of position information to identify the time zone that the vehicle is 
currently in, and the use of such position data to determine which zone of 
magnetic variance the vehicle is in for purposes of calibrating an 
in-vehicle electronic compass. See U.S. Pat. Nos. 5,724,316 and 5,761,094, 
respectively. 
Despite all the research that has been conducted and all the literature 
that has been generated relating to the use of position identification 
systems in vehicular applications, little consideration had been given to 
the practicalities of where to mount the microwave antenna that is to 
receive the microwave signals from the satellites. Published International 
Application No. WO 97/21127 discloses the mounting of two separate 
microwave antennas in the two external rearview mirror housings of the 
vehicle. While there are two microwave antennas located in the external 
rearview mirror housings, the system receiver circuit is located in the 
interior of the vehicle. The separation of the receiver circuit from the 
antennas introduces significant manufacturing difficulties. Coaxial cable 
typically used to connect the antenna to the receiver is expensive and 
difficult to handle in a manufacturing process, since it cannot be kinked 
and is relatively difficult to terminate. Furthermore, such coaxial cable 
typically has a relatively expensive push-on or screw-on type connectors 
that connect it to the system receiver circuit and/or microwave antenna. 
Additionally, vehicle manufacturers have expressed an unwillingness to 
require their assembly line workers to connect the components using such a 
coaxial connector. 
Locating a microwave antenna in the external rearview mirror housings is 
also disadvantageous because of the likelihood that dirt, moisture, snow, 
and humid air may readily reach the microwave antenna and adversely affect 
its performance. Also, because the reception of microwave signals by the 
microwave antennas is adversely affected by any metallic or other 
electrically conductive materials that may exist between the satellites 
and the antenna, it is necessary to utilize two separate antennas to allow 
for a sufficient field of view of the satellites so as to accurately 
determine the vehicle's position. Obviously, the need for this additional 
antenna significantly adds to the cost of implementing such a system, 
particularly when one takes into account the need to run two separate 
coaxial cables to the system receiver circuit. Further, even with a 
separate antenna mounted in each of the two exterior rearview mirrors, the 
overall field of view of the system is still restricted by the sides and 
roof of the vehicle. 
While WO 97/21127 further suggests that the antenna could additionally be 
positioned within the bezel of an interior mirror of the vehicle, doing so 
is not preferred because the interior mirror bezel is movable with respect 
to the passenger compartment, which may introduce error in the vehicle 
position measurements. Further, WO 97/21127 additionally states that 
metallic coatings on the vehicle windshield may interfere with the 
operation of a receiving antenna when mounted in an interior rearview 
mirror assembly. Additionally, like the configuration where the receiving 
antennas are mounted in the two exterior mirrors, the mounting of the 
receiving antenna in the interior rearview mirror bezel also presents 
manufacturing problems associated in connecting the antenna with the 
receiver, which apparently is mounted in the vehicle instrument panel. 
SUMMARY OF THE INVENTION 
Therefore, it is an aspect of the present invention to solve the above 
problems by mounting a microwave antenna in a location within a vehicle 
where it is protected from rain, dirt, and snow, and where the antenna has 
the least obstructed field of view of the sky. It is an additional aspect 
of the present invention to provide a location for mounting the microwave 
antenna where the corresponding microwave receiver may also be mounted, so 
as to eliminate difficulties in running a connecting coaxial cable 
therebetween. Further, it is an aspect of the present invention to mount a 
microwave antenna in a location within a vehicle, where its reception is 
least likely to be affected by the conductive body structure of the 
vehicle and where it may be mounted in an aesthetically pleasing location. 
It is another aspect of the present invention to provide an assembly 
incorporating a microwave antenna that is compatible with standard 
manufacturing practices and that can be readily retrofit into the vehicle 
or installed by a dealer. 
The present invention achieves these and other aspects and advantages by 
mounting a microwave antenna in a mounting bracket of an inside rearview 
mirror assembly of a vehicle. Accordingly, an inside rearview mirror 
assembly of the present invention comprises a mounting bracket adapted to 
be mounted to a vehicle in a location proximate to or on the windshield of 
the vehicle, a mirror bezel coupled to the mounting subassembly, a mirror 
mounted in the mirror bezel, and a microwave antenna mounted to the 
mounting bracket proximate the windshield. In a most preferred 
construction, the rearview mirror assembly of the present invention 
further includes a microwave receiver circuit having at least a portion 
thereof mounted to the mounting bracket, with the microwave receiver 
circuit being electrically coupled to the microwave antenna. 
Other inventive features are described below that relate to vehicle and 
vehicle accessory control that is responsive to vehicle position data. 
Other inventive features also described below relate to the provision of a 
microwave receiver for receiving microwave signals and information from 
other types of communication satellites in an automobile environment. More 
specifically, some inventive aspects of the present invention that are 
described more fully below include an electrochromic mirror control 
system, a head lamp control system, a navigation system, a tire pressure 
monitoring system, a temperature sensing and display system, a vehicle 
compass system, a vehicle "black box" data recorder, and a vehicle 
odometer verification system. 
These and other features, advantages, and objects of the present invention 
will be further understood and appreciated by those skilled in the art by 
reference to the following specification, claims, and appended drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As discussed above, certain aspects of the present invention relate to the 
mounting of a microwave antenna to the mounting bracket of a vehicle 
inside rearview mirror assembly. As also described above, there are 
various other aspects of the present invention that relate to the use of 
information obtained from satellites through the microwave antenna in 
various vehicle and vehicle accessory control systems. While the mounting 
of the microwave antenna to the mounting bracket of an inside rearview 
mirror assembly is the most preferred location for mounting the microwave 
antenna, certain of the other aspects of the invention may be accomplished 
irrespective of where the microwave antenna is actually mounted in the 
vehicle. Accordingly, the following description is broken into separate 
headings, each relating to different aspects of the present invention. 
1. Preferred Structural Features of the Present Invention 
A. Preferred Antenna Mounting 
An inside rearview mirror assembly constructed in accordance with the 
present invention is shown in FIGS. 1-5. FIG. 1 shows the general mounting 
of rearview mirror assembly 10 to the inside surface of a front windshield 
20 of a vehicle 25. FIGS. 2A and 2B show two different exemplary rearview 
mirror assembly constructions with which the present invention may be 
implemented. More specifically, rearview mirror assembly 10a shown in FIG. 
2A is designed to be mounted directly to windshield 20, whereas rearview 
mirror assembly 10b shown in FIG. 2B is mounted to the roof of the 
vehicle. As will be apparent to those skilled in the art, the present 
invention may be implemented in virtually any inside rearview mirror 
assembly regardless of its particular construction. 
In general, rearview mirror assemblies include a bezel 30 that may have a 
wide variety of the possible designs, such as, for example, the bezel 
taught and claimed in U.S. Pat. No. 5,448,397. Rearview mirror assemblies 
also include a mounting bracket 35 that attaches bezel 30 to the vehicle. 
Such mounting brackets typically include a mounting foot 36 that is 
directly mounted to the vehicle and to a mirror stem 38 that extends 
between mounting foot 36 and bezel 30. As apparent from a comparison of 
FIGS. 2A and 2B, the structure of mounting foot 36 and mirror stem 38 may 
vary considerably from one rearview mirror assembly to the next. For 
example, mirror stem 38 may be pivotally mounted to mounting foot 36 as 
shown in FIG. 2A or fixedly attached to mounting foot 36 as shown in FIG. 
2B. Additionally, bezel 30 is typically pivotally attached to mirror stem 
38. Such pivotal attachments allow the driver to move and position the 
mirror so as to allow the driver to a have a clear field of view towards 
the rear of the vehicle. 
While all rearview mirror assemblies include a mirror 40 (FIG. 5) mounted 
in bezel 30, mirror 40 may be a simple prismatic mirror or may be an 
electrochromic mirror having a reflectivity that may be automatically or 
manually varied. 
Rearview mirror assemblies may also include a display 45 housed within 
bezel 30 or housed within mounting foot 36. Such a display may be 
laterally or vertically spaced from mirror 40 as shown in FIG. 2A, or may 
be provided behind mirror 40 so as to project information through mirror 
40. 
As best shown in FIGS. 2A, 3, and 4, a microwave antenna 50 may be mounted 
within mounting foot 36 of mounting bracket 35 of rearview mirror assembly 
10. 
As best shown in FIG. 3, mounting foot 36 includes a mounting portion 52 
and an antenna housing portion 54. Mounting portion 52 may be constructed 
to have virtually any conventional structure used to mount a rearview 
mirror to a windshield 20 or other structure of the vehicle. For purposes 
of example, the structure of mounting portion 52 is shown as being 
configured to attach to a mounting puck or button 56 that is attached to 
the inside surface of windshield 20 using an adhesive. Puck 56 includes an 
inclined edge surface 57 and a threaded aperture 58 formed in the surface 
of puck 56 opposite that which is adhered to windshield 20. Mounting 
portion 52 thus has an aperture 60 for engaging puck 56. One edge 62 of 
aperture 60 is a sloped profile so as to engage incline edge surface 57 of 
puck 56. In this manner, the size of aperture 60 is slightly smaller than 
the area of the surface of puck 56 that is opposite that which is secured 
to windshield 20. To then secure mounting portion 52 to puck 56, a set 
screw 66 is slid into an aperture 64 formed in mounting portion 52 and 
turned so as to thread into threaded aperture 58 on puck 56. Again, it 
should be noted that the specific structure illustrated in FIG. 3 is 
provided for purposes of illustration only, and the present invention is 
not limited by the particular structure utilized to secure mounting foot 
36 to windshield 20 or to any other portion of the vehicle. 
Antenna housing portion 54 of mounting foot 36 may be integrally formed 
with mounting portion 52 or formed as a separate component that may be 
attached to mounting portion 52. Antenna housing portion 54 includes an 
aperture 70 having a generally square, rectangular, or round shape or any 
other shape for accommodating the particular shape of antenna 50. Aperture 
70 is provided so as to open towards windshield 20 through which microwave 
signals from satellites may pass to reach microwave antenna 50. Antenna 50 
is preferably mounted in aperture 70 so as to be substantially parallel 
to, and slightly spaced apart from, the inner surface of windshield 20. 
The structure of antenna 50 will be discussed further below under the 
heading "Preferred Antenna Construction." 
As shown in FIG. 3, a foam pad 72 or other non-conductive substrate may be 
placed within antenna housing portion 54 between antenna 50 and the inside 
surface of windshield 20. Foam pad 72 is provided to prevent moisture or 
any debris from coming between antenna 50 and windshield 20. Also, by 
using a black or gray foam pad 72, antenna 50 may be covertly hidden from 
viewing from the outside of the vehicle and thus allow for antenna 50 to 
be mounted behind windshield 20 and yet maintain an aesthetically pleasing 
appearance. The foam pad should preferably be made of a material with low 
moisture absorption and low loss factor at microwave frequencies. Closed 
cell polyethylene foam or GORE-TEX.RTM. are two possible materials. The 
adhesive used to attach the foam should ideally be applied only to the 
perimeter of the antenna or pad as adhesives typically have much poorer 
moisture absorption and dielectric properties than the dielectric 
materials themselves. Alternatively, an O-ring could be used around the 
perimeter of the antenna to prevent moisture or any debris from coming 
between the antenna and windshield. 
By extending antenna housing portion 54 from mounting portion 52 in a 
direction upward towards the upper region of windshield 20, antenna 
housing portion 54 may be located behind the tinted upper band on 
windshield 20 and thereby be more covertly hidden from view outside the 
vehicle. In the event that microwave antenna 50 is to be mounted behind a 
windshield made of conventional low-E glass, the electrically conductive 
layers within the low-E glass windshield should be masked out in the 
region behind which antenna 50 is to be mounted. In this manner, the 
conductive layers in the low-E glass will not interfere with the reception 
of satellite transmissions. Alternatively, a cut that electrically 
separates an area of the conductive low-E coating and forms a parasitic 
antenna element could be used. Such cuts can be made by a masking or laser 
cutting operation. 
As shown in FIG. 4, antenna mounting portion 54 may also be configured to 
include a gasket 74 provided about the periphery of aperture 70, so as to 
provide for additional protection against moisture or debris coming 
between windshield 20 and antenna 50. 
In addition to providing space for accommodating antenna 50, mounting foot 
36 may also be configured to provide sufficient space for a receiver 
circuit 80 printed on a circuit board 82. Circuit board 82 may thus be 
mounted directly behind antenna 50 in antenna mounting portion 54, so as 
to minimize the length of antenna connector 84 that extends between 
antenna 50 and printed circuit board 82. By providing sufficient space for 
both antenna 50 and receiver circuit 80, both these components may be 
prefabricated and fixedly mounted to one another prior to mounting an 
antenna housing portion 54. Thus, antenna 50 may be connected to receiver 
circuit 80 without requiring any coaxial cable or its associated 
connectors. 
Because receiver circuit 80 converts the signals received by antenna 50 
into signals that may be transmitted over conventional wires, the 
information obtained from the satellite signals may be transmitted to 
other components in the vehicle via the vehicle bus or by discrete 
connections. More specifically, if a display 45 or additional circuitry, 
such as a control circuit for an electrochromic mirror or electronic 
compass, is mounted in bezel 30, receiver circuit 80 may be coupled to 
such circuitry via a connector line 85 that may be run between mounting 
foot 36 and bezel 30 outside of mirror stem 38 or internally through 
mirror stem 38 as disclosed in U.S. patent application Ser. No. 09/123,682 
now U.S. Pat. No. 5,984,482. Additionally or alternatively, data processed 
by receiver circuit 80 may be transmitted via line 86 to other electrical 
systems within the vehicle. Another alternative would be to transmit the 
data by infrared light or a low power RF transmitter. Mirror assembly 10 
may include a shroud 88 that extends from mounting foot 36 to the vehicle 
headliner, so as to provide a covert channel for running cabling 86 
between rearview mirror assembly 10 and the remainder of the vehicle. 
While a specific and preferred antenna structure is described below, it 
will be appreciated by those skilled in the art that the mounting of 
microwave antenna 50 within mounting foot 36 may be accomplished 
regardless of the specific construction or type of microwave antenna 50 
that is mounted therein. 
B. Preferred Antenna Construction 
Having described a preferred mounting for a microwave antenna within a 
vehicle, a preferred antenna structure will now be described with further 
reference to FIGS. 3 and 4. Microwave antenna 50 is preferably constructed 
as a patch antenna including a dielectric substrate 90 having a layer of a 
conductive material provided on one side of dielectric substrate 90 so as 
to form a resonant patch 92. Antenna 50 further includes a layer of 
electrically conductive material on the opposite side of dielectric 
substrate 90, which forms a conductive ground plane 94 for antenna 50. 
Antenna 50 may be constructed using materials that are conventional and 
well known for such use in such fixed-frequency patch antennas. 
Resonant patch 92 may have a generally square shape with dimensions 
selected so as to tune antenna 50 to a resonant frequency at which 
particular satellites are transmitting. For example, GPS satellites 
transmit at 1.57542 GHz and GLONASS satellites transmit at 1.60256 to 
1.61550 GHz, and CD radio satellites transmit at 2.31 to 2.36 GHz. The 
manner by which a patch antenna may be tuned to these frequencies is well 
known in the art. Because the windshield glass 20 forms a dielectric cover 
over antenna 50, the patch resonant frequency is slightly reduced from its 
free space value. To compensate for the effect of the glass, the patch 
dimensions or corners 95 of resonant patch 92 may be trimmed to compensate 
for this reduction in resonant frequency caused by windshield 20. 
Although microwave antenna 50 is shown as having a generally planar 
construction, the antenna could be provided on a non-planar substrate 
thereby allowing greater flexibility in the mounting of antenna 50. Also, 
resonant patch 92 need not have a generally square shape but may be 
circular, rectangular, or fractal or have any shape known in the art 
provided it may be tuned to receive the desired satellite transmissions. 
If resonant patch 92 is rectangular, two major resonant frequencies 
corresponding to the average X and Y dimensions may be used to 
simultaneously receive microwave transmissions in two different frequency 
bands. Thus, for example, microwave antenna 50 could be configured to 
simultaneously receive both GPS and GLONASS transmissions so as to allow 
calculation of vehicle position using satellites from both position 
identification systems. Other possibilities include tuning the antenna to 
receive GPS transmissions and to receive CD radio satellite transmissions. 
Such CD radio transmissions may then be supplied to the audio system of 
the vehicle. As will be apparent to those skilled in the art, microwave 
antenna 50 could be dimensioned so as to be tuned to the resonant 
frequency of other satellite transmissions to receive information from 
such satellites that may be of particular use by the electrical systems of 
the vehicle or that may be displayed or played back to the vehicle 
occupants. 
Receiver circuit 80 may optionally be attached to the ground plane surface 
94 on antenna 50. One preferred implementation uses a four-layer printed 
circuit board with layers assigned as follows: resonant patch, antenna 
ground plane, receiver ground plane/secondary signal layer, and a last 
layer including the receiver primary signal layer and component mounting. 
It will be appreciated, however, that receiver circuit 80 may be mounted 
elsewhere, such as in bezel 30 behind mirror 40. If such an implementation 
is used, however, a coaxial cable would need to extend from mounting foot 
36 to bezel 30. Nevertheless, the length of the coaxial cable would be 
relatively short and could be readily connected between antenna 50 and 
receiver circuit 80 by the OEM manufacturer of the rearview mirror 
assembly, so as to eliminate the need for the end manufacturer to run and 
connect any such coaxial cable. Further, the mounting of the microwave 
antenna and receiver circuit in the same vehicle accessory assembly also 
allows for the system to be readily retrofit or installed by an auto 
dealer. For example, if the microwave antenna is mounted in the housing of 
an exterior rearview mirror as disclosed in WO 97/21127, the microwave 
receiver circuit is preferably mounted in the same housing thereby 
eliminating the need for running expensive coaxial cable therebetween. 
2. Vehicle and Vehicle Accessory Electrical Control System 
Having described the preferred mechanical mounting structure and preferred 
microwave antenna construction, a preferred electrical control system 100 
is described below with reference to FIGS. 6 and 7. Electrical control 
system 100 includes a microprocessor 110 that is interconnected to various 
components as described below, and programmed to perform various 
monitoring and control functions as also described in more detail below. 
The present invention generally includes a microwave antenna 50 coupled to 
a receiver circuit 80 via a connector 84. As shown in FIG. 6, receiver 
circuit 80 includes an RF circuit 112 and a correlator 114, which may be 
constructed using conventional GPS or general microwave receiver circuitry 
(no correlator need be used in a general purpose receiver). The 
informational signal obtained from any satellite transmissions received by 
antenna 50 are thus processed by receiver circuit 80 and supplied to 
microprocessor 110 via line 85. As used and described herein, the term 
"microwave receiver" shall refer to microwave antenna 50 and receiver 
circuit 80. The microwave receiver is labeled with reference number 115. 
When microwave antenna 50 is tuned to receive satellite transmissions from 
GPS satellites, receiver 115 receives and supplies to microprocessor 110 
data identiying the satellites from which transmissions are received, as 
well as a clock signal from each of the different satellites. In a manner 
well known in the art, microprocessor 110 may process this data to 
identify the position of the vehicle in terms of its latitude, longitude, 
and altitude. Insofar as clock signals are received from the various 
satellites, receiver 115 also serves as a source of a clock signal that 
may be used to determine the time of day. Further, insofar as the 
information obtained from receiver 115 may be used to calculate the 
vehicle's change of position over time, receiver 115 also serves as a 
source of data from which the vehicle velocity and distance of travel may 
be ascertained. 
If, on the other hand, microwave antenna 50 is tuned to receive signals 
from one or more CD radio satellites, microwave receiver 115 serves as a 
source of a CD quality satellite radio broadcast transmission, which may 
then be supplied to an audio system 162 (FIG. 7) via a discrete connection 
provided through discrete connection interface 118. As yet another 
alternative, microwave receiver 115 could supply its audio signal directly 
to the vehicle audio system without first supplying it through 
microprocessor 110. The audio or other data may also be transmitted via an 
infrared or low power RF link. Audio could be transmitted directly to the 
vehicle's radio from the mirror on a vacant channel with a low power 
transmitter. This would be particularly useful in aftermarket and retrofit 
applications. 
As discussed above, microwave receiver 115 may be configured such that 
microwave antenna 50 receives signals from both GPS satellites and CD 
radio satellites, in which case microwave receiver 115 would serve as a 
source of a wide variety of information and audio signals. Moreover, to 
the extent that microwave receiver 115 could be tuned to receive satellite 
transmissions from other communication satellites, such information may be 
passed to microprocessor 110 and displayed on a display 45 or other 
displays 166 (FIG. 7) connected to vehicle bus 117. Additionally, such 
information, if provided as a GPS or audio signal, may be transmitted to 
audio system 162 as described above with respect to CD radio signals. 
Further still, such information may be simply used and processed by 
microprocessor 110 or otherwise transmitted by radio frequency (RF) or 
infrared (IR) signals to other vehicle components or nonvehicle devices 
via transmitter 134. The information transmitted may be derived from 
either the microwave receiver or vehicle bus. Information derived from the 
vehicle bus may be particularly useful for troubleshooting and diagnostic 
purposes. Transmission of diagnostic data would typically be activated by 
a special vehicle startup sequence such as holding a radio or mirror 
button or buttons depressed while starting the vehicle. 
As shown in FIG. 6, microprocessor 110 may optionally be connected to one 
or more electrochromic mirrors 120. Specifically, when microwave receiver 
115 is mounted in an interior rearview mirror assembly, microprocessor 110 
is preferably coupled at least to the interior electrochromic mirror and 
optionally to external electrochromic mirrors 144, which may be coupled 
thereto by discrete connection or via vehicle bus 117. As will be 
described in moire detail below, microprocessor 110 may be programmed to 
change the reflectivity of the electrochromic mirror(s) 120, 144 in 
response to information obtained from an ambient light sensor 122, a glare 
sensor 124, as well as any of the other components coupled to 
microprocessor 110 either directly or through vehicle bus 117. As well 
known in the art, ambient light sensor 122 is preferably mounted in a 
bezel of a rearview mirror assembly in a forward-looking location so as to 
be exposed to the light conditions in front of the vehicle, whereas glare 
sensor 124 is typically mounted in bezel 30 in a rearward-facing position 
so as to sense glare from head lamps of vehicles behind the vehicle. The 
detailed manner by which microprocessor 110 may control electrochromic 
mirror(s) 120 is described below under the heading "Electrochromic Mirror 
Control System." 
Electrical control system 110 may also include a memory device 100 coupled 
to microprocessor 110. Memory device 126 may be external to microprocessor 
110 or internal, depending upon the need for additional memory. Memory 126 
may be volatile or non-volatile also depending upon the various components 
that are utilized in the electrical control system. For example, if the 
vehicle is equipped with an electronic compass 128 also provided in the 
rearview mirror assembly, some of the memory 126 would preferably be in 
the form of non-volatile memory so as to store calibration data 
accumulated by compass 128 and processed by microprocessor 110. 
As shown in FIG. 5, rearview mirror assembly 10 may include a plurality of 
user-actuated switches 130 that provide user input information to 
microprocessor 110. Such switches may cause microprocessor 110 to change 
information displayed on display 132 or to deactivate the electrochromic 
mirrors 120, to name just but a few functions that may be affected through 
user actuated switches. 
As will be explained in further detail below, electrical control system 100 
may include a transmitter 134, preferably an IR transmitter, for 
transmitting an IR signal into the interior passenger area of the vehicle. 
This IR signal may include any data or other information intended for 
portable electronic devices that may be located in the passenger area. 
Electrical control system 100 may also include a receiver 136 intended to 
receive RF signals or the like, from remotely located transmitters such as 
a remote keyless entry (RKE) transmitter or tire pressure monitoring 
sensors, as will be explained in more detail below. 
As will become apparent to one skilled in the art from the description of 
the various functions below, electrical control system 100 may include 
various combinations of the elements identified above and shown in FIG. 6, 
and thus need not include each and every element described above. Further, 
although each of the elements shown in FIG. 6 may be housed within 
rearview mirror assembly 10, some or all of the components may be provided 
in other remote locations and transmit and receive information from 
microprocessor 110 over vehicle bus 117. Further, the various components 
that may be mounted in rearview mirror assembly 10 may be mounted in 
either mounting foot 36 or bezel 30 with appropriate electrical 
connections made therebetween. 
FIG. 7 shows an example of some systems and other electrical devices within 
the vehicle that may be connected to vehicle bus 117, and hence in 
electrical communication with microprocessor 110 and the various 
components that are connected to microprocessor 110. Specifically, the 
following are a few examples of the components that may be coupled to 
vehicle bus 117: interior lights 140, head lamp controller 142, external 
rearview mirrors 144, navigation system 146, tire pressure monitoring 
system 148, climate control system 150, speedometer 152, odometer 154, 
clock/display 156, temperature sensor 158, engine control system 160, 
audio system 162, and various other switches 164 and other display devices 
166 that may be located throughout the vehicle. The specific manner by 
which microprocessor 110 interacts with the components shown in FIG. 7 is 
described below. 
A. Electrochromic Mirror Control System 
Electrochromic rearview mirrors are known in the art which have a 
reflectivity that is automatically varied based upon light levels sensed 
by a rearward-facing glare sensor and a forward-facing ambient light 
sensor. In general, the advantages offered by such electrochluomic mirrors 
are to prevent the light reflected from the mirrors from greatly exceeding 
the light levels the driver sees from the front of the vehicle. For 
example, at nighttime a driver's eyes would become acclimated to 
relatively low light levels, and thereby be much more sensitive to the 
light emitted from a vehicle's head lamps to the rear of the vehicle that 
is reflected off the mirrors towards the driver's eyes. Such a head lamp 
glare not only is a nuisance, but may also adversely impact the driver's 
night vision. On the other hand, during daylight hours the light from a 
rearward vehicle's head lamps would present much less of a problem, since 
the driver's eyes are already acclimated to bright light, and therefore, 
it is not desirable to darken the mirrors and lower their reflectivity in 
such circumstances. It is therefore the primary objective of the control 
system for such electrochromic mirrors to maintain a reflected level of 
light to the driver's eyes that is no greater than, and approximately the 
same as, the light levels seen by the driver in the forward direction of 
the vehicle. 
Electrochromic mirrors and control systems for those electrochromic mirrors 
are well known in the art and are described in U.S. Pat. No. 4,902,108, 
entitled "SINGLE-COMTMENT, SELF-ERASING, SOLUTION-PHASE ELECTROCHROMIC 
DEVICES SOLUTIONS FOR USE THEREIN, AND USES THEREOF," issued Feb. 20, 
1990, to H. J. Byker; Canadian Patent No. 1,300,945, entitled "AUTOMATIC 
REARVIEW MIRROR SYSTEM FOR AUTOMOTIVE VEHICLES," issued May 19, 1992, to 
J. H. Bechtel et al.; U.S. Pat. No. 5,128,799, entitled "VARIABLE 
REFLECTANCE MOTOR VEHICLE MIRROR," issued Jul. 7, 1992, to H. J. Byker; 
U.S. Pat. No. 5,202,787, entitled "ELECTRO-OPTIC DEVICE," issued Apr. 13, 
1993, to H. J. Byker et al.; U.S. Pat. No. 5,204,778, entitled "CONTROL 
SYSTEM FOR AUTOMATIC REARVIEW MIRRORS," issued Apr. 20, 1993, to J. H. 
Bechtel; U.S. Pat. No. 5,278,693, entitled "TINTED SOLUTION-PHASE 
ELECTROCHROMIC MIRRORS," issued Jan. 11, 1994, to D. A. Theiste et al.; 
U.S. Pat. No. 5,280,380, entitled "UV-STABILIZED COMPOSITIONS AND 
METHODS," issued Jan. 18, 1994, to H. J. Byker; U.S. Pat. No. 5,282,077, 
entitled "VARIABLE REFLECTANCE MIRROR," issued Jan. 25, 1994, to H. J. 
Byker; U.S. Pat. No. 5,294,376, entitled "BIPYRIDINIUM SALT SOLUTIONS," 
issued Mar. 15, 1994, to H. J. Byker; U.S. Pat. No. 5,336,448, entitled 
"ELECTROCHROMIC DEVICES WITH BIPYRIDINIUM SALT SOLUTIONS," issued Aug. 9, 
1994, to H. J. Byker; U.S. Pat. No. 5,434,407, entitled "AUTOMATIC 
REARVIEW MIRROR INCORPORATING LIGHT PIPE," issued Jan. 18, 1995, to F. T. 
Bauer et al.; U.S. Pat. No. 5,448,397, entitled "OUTSIDE AUTOMATIC 
REARVIEW MIRROR FOR AUTOMOTIVE VEHICLES," issued Sep. 5, 1995, to W. L. 
Tonar; and U.S. Pat. No. 5,451,822, entitled "ELECTRONIC CONTROL SYSTEM," 
issued Sep. 19, 1995, to J. H. Bechtel et al. While the control systems 
utilized in such electrochromic mirror systems are generally effective, 
such control systems may nevertheless be further improved by reducing 
their susceptibility to variations in ambient light levels that may be 
sensed by the forward-facing ambient light sensor. For example, lights 
from spaced-apart streetlights may cause the control system to 
periodically change the reflectivity of the mirror each time it passes 
under a streetlight. While some of the above patents disclose control 
systems that average readings from the ambient light sensor so as to 
reduce the system's responsiveness to such changes in ambient light 
levels, such systems typically use a fixed time average, which may or may 
not be of sufficient duration so as to prevent the mirror reflectivity 
from being changed in response to periodic changes such as those 
introduced by streetlights or head lamps of oncoming traffic. 
It is also important to ensure that any external electrochromic mirrors are 
not darkened during daylight hours because electrochrornic mirrors are 
susceptible to irreversible damage when exposed to ultraviolet (UV) 
radiation when in a darkened, less reflective state. Because a control 
system may be tricked into believing that it is nighttime and that the 
external electrochromic mirrors may be darkened when the vehicle has 
merely gone under an overpass, entered a tunnel, or when the sun is 
obscured by some other obstructions, it is possible that the external 
electrochromic mirrors could be exposed to harmful UV radiation from the 
sun when the obstruction is moved or when the vehicle moves relative to 
the obstruction so that the sunlight once again strikes the vehicle's 
external mirrors. 
Accordingly, it is an aspect of the present invention to provide a control 
system that overcomes some of the problems experienced by prior art 
control systems. Specifically, it is an aspect of the present invention to 
provide additional information to a control circuit for an electrochromic 
mirror, with which the control circuit can make better decisions how to 
darken the mirror. To achieve these and other aspects and advantages, an 
electrochrornic rearview mirror system constructed in accordance with the 
present invention preferably includes a control circuit adapted to be 
coupled to a source of a clock signal and being configured to determine 
whether it is daytime or nighttime based upon the clock signal received 
from the clock source. The control circuit being further configured to 
generate and supply a reflectivity control signal to the electrochromnic 
mirror(s) 120 to thereby control the reflectivity of the electrochromic 
mirror(s), whereby the control circuit controls the reflectivity 
differently in response to light levels sensed by the glare sensor 124 
when the control circuit determines that it is nighttime. Further, the 
electrochromic rearview mirror system preferably includes a microwave 
receiver 115 for receiving signals from satellites in the sky over the 
vehicle to thereby track the location of the satellites relative to the 
vehicle and monitor the presence or absence of a signal received from each 
of the satellites. The control circuit is coupled to the microwave 
receiver and is configured to determine what portions of the microwave 
receiver's view of the sky over the vehicle are blocked by a potentially 
light blocking/filtering obstruction based upon a determination of whether 
a signal is or is not being received from one or more of the satellites. 
The control circuit may then control the reflectivity of the 
electrochromic mirror(s) as a function of the light level sensed by the 
glare sensor and the portions of the sky above the vehicle that are 
potentially obstructed by a light blocking/filtering structure. 
The electrochromic rearview mirror system of the present invention may also 
be implemented according to another aspect by coupling the control circuit 
to a source of vehicle velocity data and configuring the control circuit 
to control the reflectivity of the electrochromic mirror(s) differently in 
response to light levels sensed by the glare sensor depending upon the 
velocity of the vehicle as determined from the vehicle velocity data. 
Preferably, the control circuit referenced above includes microprocessor 
110 (FIG. 6), which is programmed to perform the functions outlined 
generally in the flowcharts shown in FIGS. 8A and 8B. 
FIG. 8A shows the general control loop 200 that microprocessor 110 performs 
in controlling electrochromic mirror(s) 120. Control loop 200 begins with 
microprocessor 110 reading the analog voltage levels applied to its ports 
by ambient light sensor 122 and glare sensor 124. Ambient light sensor 122 
and glare sensor 124 may be implemented with photo cells that vary their 
output voltage level directly or indirectly in response to the light 
levels they are currently sensing. Next, in step 204, microprocessor 110 
filters the ambient and glare sensor output values based on the time of 
day, the on and off state of the lights inside the vehicle, the on and off 
state of the head lamps of the vehicle, light history of the ambient and 
glare sensors, and the amount and rate of change of sky and sun blockage. 
The specific manner by which microprocessor 110 filters these values in 
step 204 is described in more detail below with reference to FIG. 8B. 
Once microprocessor 110 has filtered the values received from sensors 122 
and 124, it calculates a glare value in step 206 by generally comparing 
the filtered ambient light level to the filtered glare level. Next, in 
step 208, microprocessor 110 adjusts the level of the reflectivity control 
signal(s) applied to electrochromic mirror(s) 120. Microprocessor 110 then 
loops back to step 202 to again read the values of sensors 122 and 124, 
and continues to loop through steps 202 to 208 to continuously monitor the 
sensed light levels and control the reflectivity of the electrochromic 
mirror(s). 
FIG. 8B shows the general process by which microprocessor 110 performs the 
filtering steps outlined in step 204 of FIG. 8A. As shown in FIG. 8B, 
microprocessor 110 starts the filtering process in step 210, whereby it 
initializes variables that are utilized in the subsequent steps. 
Microprocessor 110 then determines whether it is daytime in step 212. 
Microprocessor 110 may determine whether it is daytime based upon a clock 
signal it receives from one of a variety of possible sources of such a 
clock signal. The clock signal may be delivered to microprocessor 110 via 
the vehicle's clock 156 or may be supplied by an internal clock within 
microprocessor 110. Preferably, however, the source of the clock signal is 
microwave receiver 115, which receives such a clock signal from the 
satellites of a position identification system. Microwave receiver 115 is 
preferred since it also provides information from which the vehicle's 
current position may be determined. Such vehicle position information may 
then be used to access a look-up table to determine what time zone the 
vehicle is in and to determine the daylight hours for the vehicle's 
current position for that particular time of year. Thus, microprocessor 
110 may determine whether it is daytime at the vehicle's current location 
without having to rely upon the ambient light levels sensed by ambient 
light sensor 122, which may not accurately reflect whether or not it is 
daytime. For example, the vehicle may be parked in a well lit parking ramp 
at nighttime, or the vehicle may be parked in a dimly lit garage during 
the daytime. 
If microprocessor 110 determines that it is daytime in step 212, it sets a 
flag so as to not darken the external electrochromic mirrors 144 
regardless of the light levels sensed by ambient light sensor 122 or glare 
sensor 124. Thus, if the vehicle is parked in a dimly lit garage during 
the daytime, the external mirrors cannot be darkened and thus can not be 
damaged when the driver moves the vehicle out of the garage into the 
direct sunlight. Conversely, the external rearview mirrors will be allowed 
to be darkened when it is not daytime despite the fact that the vehicle 
may be located in a well lit parking ramp, where head lamps on vehicles to 
the rear may otherwise be a nuisance to the driver. It should be noted 
however, that the microprocessor could nevertheless be programmed to allow 
the external electrochromic mirrors to be darkened during daylight hours 
particularly if improvements are made to electrochromic mirrors that make 
them less susceptible to damage from UV radiation. In such a case, the 
microprocessor could be programmed to change the way it filters the data 
it uses to control the darkening of the mirrors during daylight. For 
example, the microprocessor could lengthen the time period during which 
the ambient light levels are averaged during daylight hours. 
Alternatively, the thresholds used to determine the extent to which the 
mirrors are to be darkened could be changed based upon a determination of 
whether it is day or night. 
In addition to preventing the outside rearview mirrors from becoming 
darkened when it is daytime, microprocessor 110 also lengthens the time 
period during which the output of forward-facing ambient light sensor 122 
is averaged when it is daytime (step 216). By lengthening the time period 
during which the ambient light level is averaged during daytime, 
microprocessor 110 will be less likely to overreact to a sudden darkening 
of the ambient light level as would be the case when the vehicle travels 
or is stopped under an overpass or under some other obstruction, such as a 
dense tree or other light-blocking obstruction. 
If microprocessor 110 determines in step 212 that it is not daytime, or if 
microprocessor 110 determines that it is daytime and has performed steps 
214 and 216, microprocessor 110 then determines whether the head lamps of 
the vehicle are on in step 218. Microprocessor 110 may determine whether 
the head lamps are on by communicating with a head lamp controller 142 via 
bus 117, or it may be able to determine if the head lamps are on if 
microprocessor 110 is configured to automatically control the head lamps 
as discussed below under the next heading. 
If the vehicle head lamps are not on, microprocessor 110 proceeds to 
execute step 220, otherwise microprocessor 110 first offsets the sensed 
ambient light value by a predetermined amount so as to account for the 
fact that the sensed ambient light level is artificially higher as a 
result of the light produced by the head lamps. 
In step 220, microprocessor 110 checks whether there are any interior 
lights that are on that would affect the light level sensed by the 
rearward-facing glare sensor 124. If there are no interior lights on, 
microprocessor 110 proceeds to step 224. If microprocessor 110 determines 
that there are interior lights that are on, it first clears the 
electrochromic mirror(s) in step 226 prior to proceeding to step 224. 
Microprocessor 110 clears the mirrors in this instance so as to maximize 
the reflectivity, since interior lights that are turned on during 
nighttime already make it difficult to see outside the vehicle let alone 
if the reflectivity of the mirrors are substantially reduced in response 
to the artificial light levels sensed by glare sensor 124. 
In step 224, microprocessor 110 monitors the velocity of the vehicle and 
increases the time period during which the ambient light level is averaged 
with slower vehicle velocities. Microprocessor 110 receives data from 
which the vehicle velocity may be ascertained from a source of data that 
may include the vehicle speedometer 152 or microwave receiver 115. 
Microprocessor 110 utilizes vehicle velocity to vary the control of the 
electrochromic mirrors, since the electrochromic mirror control system of 
a vehicle traveling slowly under spaced-apart streetlights or in the face 
of oncoming traffic would otherwise be more susceptible to those changes 
in light level than would that of a vehicle traveling at a higher velocity 
that is exposed to those same lighting conditions. More specifically, the 
electrochromic mirror control system of a vehicle that is either stopped 
or moving very slowly beneath a streetlight would otherwise sense a 
relatively high level of ambient light over a sufficiently long period for 
microprocessor 110 to determine that it is relatively light outside, 
whereas a car that is quickly moving underneath the same streetlight would 
not be as significantly impacted by the sensing of the streetlight. 
Referring back to FIG. 8B, microprocessor 110 next performs step 228, 
whereby it determines whether there is a rapid change in the sensed 
ambient light level beyond a threshold level established by a stored 
hysteresis. If there is no rapid forward change, microprocessor 110 simply 
returns to the main control loop and performs steps 206 and 208. If 
microprocessor 110 determines that there has been a rapid change in the 
sensed ambient light level, it determines in step 230 whether there is an 
increasing amount of sun and sky blockage. If microprocessor 110 
determines that there is not an increasing amount of sun and sky blockage, 
it returns to the main control loop and executes steps 206 and 208. If the 
amount of sun and sky blockage is increasing, microprocessor 110 first 
shortens the time period during which the ambient light level is averaged 
in step 232 prior to returning to step 206 of the main control loop. 
Microprocessor 110 preferably determines whether there is an increasing 
amount of sun and sky blockage based upon information obtained by 
microwave receiver 115 from the GPS satellite constellation. The GPS 
constellation is a group of satellites that are in roughly 12-hour orbits, 
inclined 55.degree. from the Equator, spaced every 60.degree. around the 
Earth. Every satellite is constantly sending data that indicates where all 
the other satellites are in the sky. Thus, once microwave receiver 115 
locks onto one satellite, it knows where to look for all the other 
satellites of the constellation. In an ideal situation, microwave antenna 
50 can "see" the whole sky and receive data from every satellite in view 
of the antenna. However, the vehicle may be located where microwave 
antenna 50 cannot "see" part of the sky. For example, the GPS signals will 
not penetrate or go around most buildings. The satellites that are behind 
these buildings cannot be "seen" by microwave antenna 50, and microwave 
receiver 115 cannot get data from them. Thus, the fact that a satellite is 
up in the sky but cannot be "seen" at a given time is useful information 
that may be taken into account when controlling the reflectivity of the 
electrochromic mirror(s). Specifically, there typically has to be a reason 
a satellite that is up in the sky cannot be detected. For example, metal 
objects usually block the GPS signal. Most buildings, tunnels, bridges, 
etc., will block GPS signals. The information that these objects are there 
can be used as will be described below. For example, a vehicle's climate 
control system may use the information to determine where the sun is, how 
it is hitting the car, and if the sun is blocked by an object. Such sun 
load sensing is now commonly performed with multiple IR sensors. By using 
GPS data in combination with a single IR sensor, equivalent or better sun 
load sensing performance could be obtained at less cost in a GPS equipped 
vehicle. For electrochromic mirror control as well as head lamp control, 
the combination of ambient light information and object detection produces 
a more robust control algorithm. 
Microprocessor 110 may thus be programmed to store the position information 
of each of the satellites from which receiver 115 receives such a signal, 
and then may compare this information to the signals it later receives so 
as to determine whether there may be an obstruction that is preventing 
reception of a signal from one of the satellites. For example, as a 
vehicle approaches an overpass, a progression of the satellites in the 
portion of the sky in front of the vehicle will have their signals blocked 
by the upcoming overpass, but will progressively reappear as the vehicle 
approaches and travels under the overpass. Microprocessor 110 may thus 
monitor the presence or absence of signals received from the various 
satellites in the sky over the vehicle and store their history, so as to 
ascertain whether there are any obstructions in any particular portion of 
the sky that may affect the ambient light levels sensed by ambient light 
level sensor 122. Thus, if microprocessor 110 determines in step 228 that 
there is a rapid change in the light level detected by sensor 122 and that 
there is an increasing amount of sun and sky blockage based upon the 
history of signals received from the satellites in the sky overhead, 
microprocessor 110 may determine that the rapid change in light level was 
caused by a temporary light blocking/filtering obstruction and then 
control the reflectivity of the electrochromic mirrors accordingly. 
If, on the other hand, the amount of sun and sky blockage does not suggest 
that the rapid change in ambient light level is the result of a temporary 
blockage, but is the result of an approaching larger blockage, 
microprocessor 110 would shorten the time period in which the ambient 
light is averaged so as to increase the responsiveness of the control 
system to increases in light levels sensed by glare sensor 224. 
Microprocessor 110 may determine that the amount of sky blockage is 
increasing by determining that more and more of the signals from the 
satellites are being blocked and not subsequently received despite the 
movement of the vehicle. Such sky blockage may be indicative of an 
approaching mountain range, tunnel, tall buildings, or a parking ramp, 
because such increasing sky and sun blockage would indicate that the rapid 
drop in ambient light level is not subsequently going to rapidly increase. 
While the above system is described as detecting either the absence or 
presence of signals from the satellites to determine sky blockage, it is 
possible to determine sky blockage by detecting the strength of the 
signals from the satellites. 
As apparent from the above description, the inventive electrochromic mirror 
control system controls the reflectivity of the electrochromic mirror(s) 
in response to parameters not previously considered for electrochromic 
mirror control. Because some of the parameters relied upon in the 
inventive system may be obtained from vehicle components other than 
microwave receiver 115, it will be appreciated by those skilled in the art 
that the inventive electrochrornic mirror control system may be 
implemented without utilizing microwave receiver 115, although certain 
features of the present invention relating to determining sky blockage 
would not then be available. 
Although the preferred mounting for microwave antenna 50 and microwave 
receiver circuit 80 has been described above as being in the mounting foot 
of a rearview mirror assembly, microwave receiver 115 may be mounted in 
any other location within the vehicle, and the data utilized by 
microprocessor 110 in controlling electrochromic mirror(s) 120 may be 
obtained through vehicle bus 117 or through a discrete connection. As will 
also be appreciated by those skilled in the art, the inventive 
electrochromic mirror control system may be implemented without use of 
components other than electrochromic mirror(s) 120, ambient light sensor 
122, glare sensor 124, microprocessor 110, and optionally microwave 
receiver 115. 
B. Head Lamp Control System 
Vehicle electrical control systems are known that automatically control the 
vehicle's head lamps in response to sensed ambient light levels. Such head 
lamp control systems have typically been incorporated in rearview mirrors 
since the rearview mirror assembly provides a convenient location for 
mounting a photocell that is pointed at the sky to measure ambient light. 
The reason rearview mirror assemblies are used for such mounting is that 
it provides an unobstructed view of the sky and is not subject to blockage 
by papers, etc . . . as when the sensor is in the dash. 
Head lamp control systems suffer from many of the same problems of 
conventional electrochromic mirror control systems insofar as they both 
rely upon the light levels sensed by a single forward-facing ambient light 
sensor. As with electrochromic mirror control systems, head lamp control 
systems may be fooled into believing it is daylight when parked or 
traveling slowly under a streetlight or parking ramp, while also being 
fooled into believing it is nighttime when parked in the shadow of a 
light-obstructing structure. To avoid turning the head lamps on and off, 
the detected ambient light level is often filtered/averaged over a time 
period. However, such averaging and filtering does not always reliably 
control the head lamps. 
Therefore, it is an aspect of the present invention to provide a head lamp 
control system that more reliably controls the head lamps. The head lamp 
control system of the present invention achieves this aspect and other 
advantages by controlling the head lamps not only in response to light 
levels sensed by an ambient light sensor, but also in response to the 
amount of sky blockage, the vehicle velocity, and/or a clock signal that 
identifies the time of day. With reference to FIGS. 6 and 7, the head lamp 
control system of the present invention preferably includes microprocessor 
110, ambient light sensor 122, and a connection of microprocessor 110 to 
the head lamps or a head lamp controller or control switch 142. As 
generally known in the art, ambient light sensor 122 is typically a 
separate sensor from the ambient light sensor used to control an 
electrochromic mirror. The system also preferably includes a microwave 
receiver 115 coupled to microprocessor 110 for providing information from 
which the vehicle velocity, time of day, and amount of sky blockage may be 
determined. The head lamp control system may, but need not, include any of 
the other components shown in FIGS. 6 and 7. As an alternative or 
additional element to microwave receiver 115, microprocessor 110 may 
include a connection to the vehicle speedometer 152 and/or the vehicle 
clock/display 156. Having described the general structure of the head lamp 
control system, the inventive control process is described below with 
reference to FIGS. 9A through 9C. 
FIG. 9A shows the main control loop 300 executed by microprocessor 110 to 
control the head lamps of the vehicle. Control loop 300 begins in step 302 
in which microprocessor 110 determines the ambient light level and filter 
parameters in accordance with the subroutine procedures outlined in FIGS. 
9B and 9C. Subsequently, microprocessor 110 compensates and filters the 
sensed ambient light level in step 304 and then compares the filtered and 
compensated ambient light level to a threshold, so as to determine whether 
the sensed and adjusted ambient light level is low enough to turn on the 
head lamps. If the light level is not low enough, microprocessor 110 turns 
the head lamps off in step 306 or otherwise maintains the head lamps in 
their off state. On the other hand, if the sensed and adjusted ambient 
light level is low enough, microprocessor 110 issues a signal over bus 117 
or another discrete connection to the head lamp controller 142 causing the 
head lamps to be turned on or otherwise maintained in their on state (step 
310). Once microprocessor 110 has executed either step 308 or step 310, it 
loops back to reexecute steps 302 through 306 following a delay period 
established in step 312. Such a delay period may be terminated in response 
to an interrupt signal that is generated on a periodic basis to either 
wake up microprocessor 110 or otherwise interrupt another process 
performed by microprocessor 110. Moreover, delay 312 may simply correspond 
to the amount of time it takes for microprocessor 110 to perform other 
routines relating to control of an electrochromic mirror or other 
components in the vehicle. 
FIG. 9B shows the general process by which microprocessor 110 determines 
the ambient light level and the filter parameters in step 302. 
Microprocessor 110 begins this subroutine in step 314 by recording the 
previously sensed ambient light level and then determining the ambient 
light level currently sensed by ambient light sensor 122 (step 316). 
Microprocessor 110 then records the previous sun and sky blockage data in 
step 318 prior to proceeding to step 320 by which microprocessor 110 
determines the current sun and sky blockage based upon information 
obtained from microwave receiver 115. As described above in the preceding 
section, microprocessor 110 may determine the amount of sun and sky 
blockage by keeping track of the history of signals received from the 
satellites in the sky. 
In step 322, microprocessor 110 adjusts the head lamp filter parameters 
based on the velocity of the vehicle, time of day, amount of sky and sun 
blockage, the rate of change of sky and sun blockage, amount of ambient 
light, and the ambient light history. The specific manner by which the 
filter parameters are adjusted is described below with reference to FIG. 
9C. After executing step 322, microprocessor 110 adjusts the filter for 
special cases, such as a detection that power has just been turned on or 
off and whether the transmission is in or out of reverse gear. The 
specific manner by which the filter is adjusted for these special cases is 
disclosed in U.S. Pat. No. 5,666,028 issued to Bechtel et al. 
Subsequently, microprocessor 110 returns to step 304 of main control loop 
300 and performs the functions described above. 
FIG. 9C shows the specific manner by which microprocessor 110 adjusts the 
head lamp filter parameters identified in step 322. Microprocessor 110 
begins this subroutine in step 32.6 by adjusting the filter parameters to 
make it harder to change the state of the head lamps with slower vehicle 
velocities. More specifically, microprocessor 110 increases the time 
period during which the ambient light level is averaged with decreasing 
vehicle velocity. Thus, for example, a vehicle passing under a bridge 
during the day and a street light at night are anomalies that the 
algorithm should filter out. The velocity of the vehicle determines the 
time the vehicle spends by these anomalies, and therefore should influence 
the parameters of the averaging and filtering algorithm. 
Next, in step 328, microprocessor 110 biases the filter parameters, such 
that it is easier to turn the head lamps on and harder to turn the head 
lamps off during nighttime and so that it is easier to turn the head lamps 
off and harder to turn the head lamps on during the day. As discussed 
above in the preceding section, microprocessor 110 may determine whether 
it is nighttime or daytime based upon a clock signal that represents the 
current time of day. This clock signal may be obtained from the vehicle 
clock 156 or from microwave receiver 115, which receives a clock signal 
from the satellites of a position identification system. As also discussed 
above, microprocessor 110 may access a look-up table or otherwise 
calculate the hours during which daylight is expected for the identified 
current location of the vehicle for the present time of year. 
Microprocessor 110 may thus use this information and the current time of 
day to determine whether it is currently daytime or nighttime. 
After step 328, microprocessor 110 executes step 330 in which it determines 
whether ambient light is rapidly decreasing beyond a threshold window. If 
the ambient light is rapidly decreasing beyond the threshold window, 
microprocessor 110 executes step 332 in which it determines whether sky 
blockage is increasing and the position of the blockage in direction of 
travel indicates that the blockage will continue to increase. If the sky 
blockage is increasing and will continue to increase, microprocessor 110 
adjusts the filter parameters to make it easier to change the state of the 
head lamps (step 334). If the sky blockage is not increasing or if it is 
increasing but will not continue to increase, such as the case of when the 
vehicle is approaching an overpass, microprocessor 110 slowly returns the 
filter parameters to nominal values (step 336) prior to returning to step 
324 of subroutine 302. The reason the filter parameters are adjusted in 
step 334 to make it easier to change the state of the head lamps when sky 
blockage is increasing and will continue to increase and when ambient 
light is rapidly decreasing is that it is likely that the vehicle is 
approaching a tunnel, in which case one would like the head lamps to 
respond more rapidly to the decrease in ambient light levels. On the other 
hand, if the decrease is caused only by a temporary blockage, such as an 
overpass, one would not want their head lamps to be turned on rapidly in 
response to the decrease in ambient light. 
To allow a vehicle's head lamps to more rapidly turn off when emerging from 
a tunnel, microprocessor 110 may check in step 338 whether the ambient 
light is rapidly increasing beyond a threshold window. If the ambient 
light is neither rapidly decreasing (step 330) nor rapidly increasing 
(step 338), microprocessor 110 executes step 336, whereby it slowly 
returns filter parameters to nominal values and returns to step 324 (FIG. 
9B). On the other hand, if the ambient light is rapidly increasing beyond 
the threshold window, microprocessor 110 executes step 340, whereby it 
determines whether the sky blockage is decreasing and the position of the 
blockage and direction of travel indicates that the blockage will continue 
to decrease. If the sky blockage is not decreasing or is decreasing but 
will not continue to decrease, microprocessor 110 executes step 336 and 
slowly returns the filter parameters to nominal values prior to returning 
to step 324 (FIG. 9B). On the other hand, if the sky blockage is 
decreasing and will continue to decrease, microprocessor 110 adjusts the 
filter parameters to make it easier to change the state of the head lamps 
(step 342). Thus, if the vehicle is emerging from a tunnel, the ambient 
light would rapidly increase and the sky blockage would decrease and 
continue to decrease, such that microprocessor 110 would make it easier to 
turn the head lamps off upon emerging from the tunnel or other large 
obstruction. After executing one of steps 334 or 342, microprocessor 110 
returns to step 324 to make further adjustments prior to executing step 
304 and main control loop 300, whereby the ambient light levels are 
compensated and filtered using the parameters set in step 302 prior to 
determining whether or not to turn the head lamps on or off. The 
above-noted process is then continued indefinitely, so long as the vehicle 
is operating. 
While a specific process is described above for controlling head lamps of a 
vehicle, it will be appreciated by those skilled in the art that other 
processes may be employed without departing from the spirit and scope of 
the present invention. For example, any prior art process such as that 
disclosed in U.S. Pat. Nos. 5,666,028 or 5,451,822 issued to Bechtel et 
al., may be modified to utilize any of the information made available 
through implementation of the present invention, to improve the manner in 
which the head lamps are controlled. 
C. Navigation System 
Navigation systems are currently drawing much attention for use in 
automobiles generally due to the availability and access to GPS satellite 
positional data. While some navigation systems have been commercially 
implemented, such systems are often quite expensive and difficult to 
accommodate within the interior of a vehicle, where the displayed 
information can be readily viewed by the driver without unduly distracting 
the driver from his or her driving. Other difficulties in implementing 
navigation systems relate to the provision of a large amount of data 
showing the detailed level of road map information in all or specific 
regions of the country. Largely, however, such navigation systems are not 
in widespread use due to the relatively expensive price associated with 
such systems. 
The present invention overcomes many of the difficulties noted above by 
providing a relatively simple and inexpensive navigation system. 
Additionally, the inventive navigation system may be readily retrofit in 
any existing vehicle. Further still, the navigation system of the present 
invention allows the use of a conventional laptop computer, so as to 
provide portability of the more expensive component of the navigation 
system between a user's different vehicles. These aspects of the present 
invention are achieved by providing an IR transmitter 134 (FIG. 6) that is 
coupled to microprocessor 110, so as to transmit an IR signal including 
vehicle position data as received from microwave receiver 115 when 
configured to receive signals from a position identification system, such 
as GPS or GLONASS. By transmitting the IR signal in NMEA format using a 
standard IrDA protocol, the IR signal may be readily picked up by most 
laptop computers available on the market today that include an IR port for 
receiving data transmitted in an IR signal. In this manner, the data 
obtained from GPS satellites or the like may be directly transmitted via 
the IR signal into the passenger compartment to any one or more laptop 
computers, which may use the information while executing a program such as 
MICROSOFT MAP.TM. or MICROSOFT EXPEDIA STREETS 98.TM. so as to display on 
the computer screen a moving map showing the present location of the 
vehicle. Thus, the present invention would work with a wide variety of 
available laptop computers, as well as a wide variety of different 
navigational programs presently available on the market. Insofar as many 
people now own or have access to such laptop computers and insofar as such 
navigational programs are relatively inexpensive, the present invention 
provides an inexpensive navigational system that may be upgraded at any 
time through the upgrading of any navigational software, while also 
allowing the computer and display device of the navigation system to be 
used for a wide variety of other purposes as such laptop computers are 
already employed. 
While laptop computers have been contemplated for use as a navigation 
system when physically connected to a GPS receiver, such GPS receivers are 
typically not mounted in the vehicle, but are separate physical devices 
that require an electrical power connection separate from that of the 
computer. While such setups offer much of the same advantages as the 
present invention, they cannot always be implemented, since some vehicles 
only include a single power outlet. Additionally, the added physical 
connections that are required to connect the GPS to a power outlet of the 
vehicle and to a serial port of the laptop computer can become quite 
cumbersome and limit the locations in which the laptop computer may be 
positioned so as to allow the driver or other vehicle occupants to readily 
view the display screen on the computer. The present invention, on the 
other hand, would allow the laptop computer to be operated without any 
external connections when operating on the power supplied by its internal 
rechargeable battery. 
The prior systems utilizing a separate GPS receiver physically connected to 
a laptop computer also do not provide other advantages offered by the 
present invention--namely, the use of the data from the GPS receiver by 
other components within the vehicle. As described above and in further 
described below, the data from microwave receiver 115 may be used to more 
accurately control various electrical components within the vehicle. 
Further, the transmitted IR or RF signal may be used by other electronic 
devices within the vehicle, such as a cellular telephone, if equipped with 
an IR or RF receiver. Such information would be particularly useful should 
it become necessary for a vehicle occupant to make an emergency telephone 
call when the vehicle occupant does not know their present location. By 
making such vehicle position information available to the cellular 
telephone, this information may be automatically transmitted to an 
emergency service operator whenever an emergency call is made using a 
telephone within the passenger compartment. 
While the microwave receiver 115, microprocessor 110, and transmitter 134, 
which would be used to implement the inventive navigation system, have 
been described above as being located within a rearview mirror assembly, 
it will be appreciated by those skilled in the art that the advantages 
offered by the inventive navigation system may be obtained regardless of 
the location of these components. Moreover, each of the components may be 
remotely located from each other within the vehicle. However, to enable 
the system to be readily retrofit into an existing vehicle, it would be 
preferable to include these components in a single vehicle accessory 
housing. For example, provided these accessories are located within a 
rearview mirror housing, one could simply replace their existing rearview 
mirror assembly with one incorporating the inventive components and 
thereby obtain the benefits of the present invention without requiring any 
further reconfiguration of the electrical control system within the 
vehicle. 
It is further noted that the location of transmitter 134 along a bottom 
surface of bezel 30 serves as a very convenient and effective location for 
mounting the transmitter, so as to enable it to transmit the IR signal 
throughout the front portion of the passenger compartment where a laptop 
computer 21 (FIG. 1) would likely be located. The transmitter, however, 
could also be located remotely in center portion of the vehicle headliner 
proximate a dome or map lights, so as to enable transmission of the IR 
signal to a back seat of the vehicle. With transmitter 134 remotely 
located, microprocessor 110 could transmit the vehicle position data over 
a discrete connection or via vehicle bus 117. Further, it should be noted 
that more than one IR transmitter may be positioned within the vehicle so 
as to more widely disperse the transmission of the vehicle position data 
as contained in the IR signals. 
According to another aspect of the present invention, a navigation system 
may also be provided by displaying navigation-related information on a 
display 45 mounted on rearview mirror assembly 10. Such information could 
prompt the driver to "turn left now" or to "continue to proceed north," or 
provide similar directions. Further, mirror assembly 10 could include 
indicator lights positioned behind a transparent insignia etched in the 
reflective surface of mirror 40. For example, the mirror may have right 
and left arrows 170 and 172 etched in its reflective surface, such that 
the activation of an indicator light behind such insignias would advise 
the driver to turn left or right at an upcoming intersection. 
Microprocessor 110 may process the vehicle position data and access map 
information so as to control the indicators or provide the navigation 
prompts in any manner known in the art. 
According to yet another aspect, the navigation system of the present 
invention may be used to provide the vehicle position information to a 
separate navigation system 146 via vehicle bus 117. Thus, provided the 
navigation system 146 is configured so as to be capable of receiving 
vehicle position data over a vehicle bus, the microwave receiver 115 may 
be mounted in a rearview mirror assembly, and preferably in the mounting 
foot of a rearview mirror, and supply the received information to the 
navigation system regardless of its location within the vehicle. 
D. Tire Pressure Monitoring System 
Electrical systems in vehicles are known that monitor the tire pressure of 
each of the vehicle's tires and either provide a warning when the sensed 
tire pressure is abnormal or simply display the sensed tire pressure to 
the driver. Such systems typically include a pressure sensor mounted 
inside each of the tires of the vehicle for sensing the pressure and 
transmitting a signal representing the sensed tire pressure over a 
wireless link to a central receiver. A control circuit coupled to the 
receiver either controls the display to display the sensed tire pressures 
or compares the sensed tire pressures to threshold levels, so as to 
determine whether a tire pressure abnormality exists (i.e., whether the 
sensed tire pressure is too low or too high). When the tire pressure in 
any tire is abnormal, the control circuit would then activate an 
indicator, which may be an audio or visual warning, so as to advise the 
driver of the abnormality. 
While the above-noted tire pressure monitoring systems generally work 
effectively, the accuracy of the systems would be improved by taking into 
account the altitude of the vehicle, since the altitude affects the 
relative readings of the tire pressure. 
Accordingly, it is an aspect of the present invention to provide a tire 
pressure monitoring system that determines the vehicle's current altitude 
and adjusts the sensed tire pressures as a function of the current 
altitude. To take into account the vehicle's current altitude, the control 
circuit used in the tire pressure monitoring system of the present 
invention is adapted to be communicatively coupled to a source of data 
from which the vehicle's current altitude may be determined. As described 
above, microwave receiver 115 may serve as a source of such data when it 
is tuned to receive transmissions from satellites of a position 
identification system such as GPS. 
The pressure monitoring system of the present invention may then use the 
adjusted tire pressures so as to operate a display, such as display 45, to 
display the adjusted tire pressures or to operate display 45 or some other 
indicator whether audio or visual, to indicate when an abnormal tire 
pressure exists based upon a comparison of the adjusted tire pressures to 
at least one threshold value. The at least one threshold value may include 
a low tire pressure threshold and/or a high tire pressure threshold. 
In the most preferred embodiment, the control circuit is implemented using 
microprocessor 110, and the source of altitude information is microwave 
receiver 115. The receiver used to receive the signals from the tire 
pressure sensors mounted in the tires may be receiver 136 that may be 
mounted in a common housing, such as a rearview mirror assembly, with 
microprocessor 110 and microwave receiver 115. Further still, 
microprocessor 110 may utilize display 45 to display tire pressure, or may 
activate some other indicator that may be provided behind the mirror or 
may transmit an activation signal over vehicle bus 117 to some other 
display 166 that is also coupled to bus 117. It should also be noted that 
the receiver of the tire pressure monitoring system as well as the control 
circuit may be remotely located from microwave receiver 115, whereby the 
altitude information is transferred to tire pressure monitoring system via 
bus 117. Additionally, the altitude information may be used to adjust the 
threshold levels at which a warning is issued rather than adjusting the 
sensed tire pressure. 
In addition to using the altitude information for tire pressure sensing and 
monitoring, the altitude information could also be transmitted over 
vehicle bus 117 to other vehicle systems, such as the engine control 
system. 
E. Temperature Sensing and Display System 
Electrical systems for sensing and displaying exterior temperature are well 
known in the art. Such systems typically include a temperature sensor 
mounted so as to be exposed to the external air, while being electrically 
coupled to a control circuit located inside the vehicle, which processes 
the temperature information obtained from the sensor and displays the 
information on a display that is typically located on the display of an 
overhead console, inside rearview mirror, or instrument panel of the 
vehicle. Because the temperature sensed by the temperature sensor is 
affected by the velocity of the vehicle, such systems typically obtain 
vehicle velocity data from the speedometer of the vehicle, so as to 
compensate the temperature reading from the external sensor to account for 
the velocity of the vehicle. If the temperature display is located in the 
overhead console or inside the rearview mirror, it becomes a practical 
necessity that the vehicle speedometer be configured so as to provide the 
vehicle speed on the vehicle bus, so that the control circuit for the 
temperature sensing and display system can take the velocity into account 
when compensating the external temperature reading. Additionally, a common 
location for the external temperature sensor is in front of the radiator. 
This sensor becomes inaccurate if the vehicle is stopped for a relatively 
short period of time, since heat from the radiator will cause the 
temperature sensor to read high. If the vehicle is turned off long enough 
for the radiator to cool, the sensor will become accurate again. 
Typically, the radiator cooling period is around 2 hours. Present practice 
is to use an analog timer circuit to determine if the vehicle has been in 
operation in the last two hours. If so, the last known temperature before 
the car was switched off is displayed rather the inaccurate sensor 
reading. The displayed temperature is then updated at slow rate for a 
fixed period of time corresponding to the time required for the sensor to 
again accurately register ambient temperature. With the availability of 
data from the bus or GPS, a separate analog timer is no longer required. 
The fixed time delay can be shortened at higher vehicle speeds if speed is 
known. 
The temperature sensing and display system of the present invention does 
not require that the vehicle speedometer output the vehicle velocity onto 
a vehicle bus or that any other discrete connection between the vehicle 
speedometer be made to the control circuit of the inventive system. The 
inventive temperature sensing and display system includes a temperature 
sensor 158 mounted to the vehicle for sensing the temperature external to 
the vehicle and for generating a signal representing the sensed external 
temperature, a microwave receiver 115 for receiving transmissions from 
satellites of a position identification system constellation, and for 
generating vehicle position data from the satellite transmissions, a 
control circuit such as a microprocessor 110 coupled to the temperature 
sensor, and microwave receiver for determining the velocity of the vehicle 
based upon changes in the vehicle position data per unit of time. The 
control circuit receives the signal generated by the temperature sensor 
and adjusts the sensed external temperature reading as a function of the 
vehicle velocity so as to generate an external temperature display signal. 
The inventive temperature sensing and display system further includes a 
display 45 coupled to the control circuit for receiving the external 
temperature display signal and displaying the adjusted external 
temperature. To adjust the sensed external temperature reading, the 
control circuit may utilize any conventional algorithm. 
As will be appreciated by those skilled in the art, temperature sensor 158 
may be coupled to microprocessor 110 through vehicle bus 117 or through a 
discrete connection. Further, if microprocessor 110 is coupled to vehicle 
bus 117, microprocessor 110 may transmit the external temperature display 
signal to another display 166 located remotely within the vehicle via 
vehicle bus 117. Further, microwave receiver 115 may be remotely located 
from microprocessor 110 and provide the vehicle position data over vehicle 
bus 117 or through a discrete connection. 
The particular use of velocity information that is ascertained from the 
vehicle position data of microwave receiver 115 is advantageous over 
utilizing the speed from speedometer 152 insofar as microprocessor 110 may 
use the same vehicle velocity data for other control functions, such as 
taking the velocity into account when controlling electrochromic mirror(s) 
120 or the vehicle head lamps 142. Moreover, the vehicle velocity obtained 
from the data supplied from microwave receiver 115 may also be used to 
verify the accuracy of speedometer 152. 
F. Vehicle Compass System 
Electronic vehicle compass systems are known that include electronic 
compass sensors for sensing the earth's magnetic field, and generate an 
electrical signal representing the vehicle's direction of travel based 
upon the sensed magnetic field. Such systems are typically calibrated 
based upon sensor readings obtained while driving the vehicle through one 
or two closed loops. Such calibration techniques are also well known and 
described in U.S. Pat. No. 5,761,094. These known electronic compass 
systems compensate the compass sensor readings based upon the calibration 
data as well as other filtering parameters, and display the current 
vehicle heading on a display device commonly provided in the overhead 
console or interior rearview mirror of the vehicle. One of these 
parameters is used to adjust the vehicle heading based upon a geographical 
zone of variance in which the vehicle is currently located. Typically, a 
user is required to manually input in which zone the vehicle is currently 
located. U.S. Pat. No. 5,761,094, however, utilizes vehicle position data 
obtained from a GPS receiver to determine the vehicle's current location 
and to determine which zone of variance the compass system should use to 
further compensate the sensed vehicle heading. 
As noted above, the prior art electronic compass systems all utilize some 
form of device that senses the earth's magnetic field. Such sensing 
devices are relatively expensive and must be mounted in particular 
locations within the vehicle so that the sensors are not adversely 
affected by the metal structure of the vehicle, which may introduce errors 
to the magnetic sensors. Such magnetic sensors are also susceptible to 
errors resulting from driving over railroad tracks and driving in large 
cities. Further, the compasses must be calibrated for each different model 
vehicle in which it is mounted, since the body style of these different 
model vehicles may have differing effects on the way in which the compass 
sensors sense the earth's magnetic field and sense the vehicle's current 
heading. 
The compass system according to the present invention overcomes the 
problems noted above with respect to conventional electronic compass 
systems. According to one aspect of the present invention, the compass 
system includes an electronic compass sensor for sensing the earth's 
magnetic field and for generating an electrical signal representing the 
vehicle's direction of travel based upon the sensed magnetic field, a 
microwave receiver for receiving transmissions from satellites of a 
position identification system constellation and for generating vehicle 
position data from the satellite transmissions, a control circuit coupled 
to the electronic compass sensor and to the microwave receiver for 
determining the vehicle's direction of travel from the vehicle position 
data received from the microwave receiver, adjusting the vehicle's 
direction of travel as identified by the electronic compass sensor using 
calibration data, comparing the vehicle's direction of travel as 
determined using the vehicle position data with the vehicle's direction of 
travel as received from the electronic compass, and recalibrating the 
compass system when the vehicle's direction of travel as determined by 
both the microwave receiver and the adjusted electronic compass sensor 
readings are not the same. The compass system further includes a vehicle 
direction indicator, such as display 45, coupled to the control circuit 
for advising a vehicle occupant of the vehicle's direction of travel. 
If combined with a magnetic sensor, the GPS heading data may be used to 
provide continuous calibration correction for the magnetic sensor, 
allowing placement of the magnetic sensor in a non-fixed location, such as 
inside the movable portion of the rearview mirror assembly. Magnetic, 
angle rate, speedometer, odometer, or other inertial sensor data can then 
be used to supplement GPS data when buildings or other environmental 
obstacles interfere with reception of the GPS satellite constellation. 
According to yet another aspect of the present invention, the inventive 
compass system does not include an electronic compass sensor or any other 
form of sensor that senses the earth's magnetic field, but instead 
utilizes vehicle position data that is derived from transmissions received 
from satellites of a position identification system constellation 
utilizing a microwave receiver that is mounted in the vehicle. By 
utilizing the vehicle position data that is available from microwave 
receiver 115, a control circuit including microprocessor 110 may use this 
data to directly determine the vehicle's current heading, which is 
subsequently displayed on display device 45. Thus, the inventive 
electronic compass system may be constructed without utilizing an 
electronic compass sensor, and may therefore provide accurate vehicle 
heading information independent of the earth's magnetic field and its 
inherent anomalies when sensed by a sensitive electronic compass sensor. 
Accordingly, much of the expense of providing such magnetic field sensors 
may be eliminated. 
G. Vehicle "Black Box" Data Recorder 
Vehicle data recorders, also known as a "black box," have been used in 
automobiles. Such data recorders record time-stamped vehicle data 
including vehicle speed, vehicle direction, position of the vehicle, 
application of the vehicle brakes, and/or air bag deployment. This 
time-stamped data may then be read from memory to enable law enforcement 
officials to reconstruct the scene of an accident in a manner similar to 
how such black boxes are used in reconstructing the events immediately 
preceding an airplane crash. Such automobile data recorders contemplate 
the use of a clock signal from the vehicle's clock for purposes of placing 
a time stamp on the data that is stored in memory. This data may be stored 
in a circular first-in-first-out manner so that data covering the most 
recent fixed time period is stored in memory. The data recorder would stop 
recording upon detection that the airbags have deployed or upon detection 
of impact by impact or other inertial detectors otherwise located within 
the vehicle. 
Additionally, these data recorders could record intermittent events, such 
as the number of times the car goes over 100 mph. Thus, when the user 
brings the car in for warranty work, the dealer can determine how this car 
is being abused. 
One problem with these types of systems is that the vehicle clock may not 
be set to the correct the time when a crash occurs. This is particularly 
problematic when more than one vehicle is involved and the clocks on both 
vehicles are set to different times. Thus, the times that are stored in 
memory may be subject to corruption by a user who purposely sets a time 
that is, for example, five minutes faster or five minutes slower than the 
correct time of day. 
The present invention overcomes the above-noted problems associated with 
automobile data recorders by utilizing a clock signal obtained from at 
least one satellite for purposes of time stamping the vehicle-generated 
data that is recorded in the vehicle's data recorder memory. The 
satellites of the GPS constellation currently transmit the time of day as 
derived from an atomic clock so as to be highly accurate. By utilizing the 
clock signal from satellites in this manner, the time stamps on the 
vehicle data contained in two different vehicles involved in a single 
crash would then be accurately synchronized and thus provide a more 
accurate representation of the events that occurred immediately preceding 
the accident. Furthermore, because the clock signal is coming from an 
external source, the data recorder of the present invention would not be 
as susceptible to user corruption as would be the prior contemplated data 
recording systems. 
The inventive data recorder system may be implemented using portions of 
electrical control system 100 (FIG. 6). Specifically, the data recorder 
could be implemented using microwave receiver 115, microprocessor 110, 
memory 126, a vehicle bus interface 116 coupled to a vehicle bus 117, or 
alternatively a discrete connection interface 118 that is discretely 
connected to the various sources of vehicle-generated data to be stored in 
the data recorder. Further, the data recorder could include a battery 
back-up (not shown) for maintaining power to memory 126 in the event of 
other power disruption caused by the accident. The components of the data 
recorder are preferably mounted in a rearview mirror assembly, but may 
also be mounted in any other location within the vehicle. Further, the 
various components making up the inventive data recorder system may be 
commonly housed in a single housing or remotely located throughout the 
vehicle. 
In addition to transmitting GPS data, IR or RF transmitter 134 may also be 
used to transmit anything off the vehicle network. For example, most 
diagnostic ports are under the hood of the vehicle. If the vehicle is in a 
front end collision (most common type), the diagnostic port under the hood 
is hard to access. Because it may be very desirable to get accident data 
out of a car (direction traveled, recent speeds, etc.), the transmitter 
could transmit IR/RF signals to a hand held receiver that supplies the 
accident data to either the police or a technician. 
H. Vehicle Odometer Verification System 
By law, all automobiles are required to include an odometer if used within 
the United States. As well known, odometers provide an accumulated 
distance of travel over the lifetime of the vehicle. Because of the 
potential for individuals and used car dealers to fraudulently roll back 
the odometer, much effort has been made to ensure that the odometers are 
tamper proof. Nevertheless, there remains a concern that a sufficiently 
skilled individual may nevertheless be able to roll back an odometer on a 
vehicle and commit fraud on the purchaser of the vehicle. Also, odometers 
sometimes malfunction and do not record the distance traveled correctly or 
even at all. 
The present invention ameliorates the above concerns by providing a vehicle 
odometer verification system, whereby a control circuit is coupled to a 
microwave receiver so as to receive vehicle position data that is 
transmitted to the receiver from satellites of a position identification 
system constellation. The control circuit utilizes the vehicle position 
data to determine and accumulate vehicle distance of travel. The control 
circuit may use this information to verify the odometer reading or may 
additionally or alternatively store the accumulated distance of travel 
data so computed in a memory device. In this manner, a purchaser of a used 
vehicle or a law enforcement officer may confirm that the reading on the 
vehicle's odometer is accurate by reading the accumulated distance of 
travel computed by the control circuit from its connected memory device. 
The inventive vehicle odometer verification system may be implemented using 
microwave receiver 115, microprocessor 110, and memory 126 of electrical 
control system 100. Additionally, if microprocessor 110 is to compare and 
verify the reading of the vehicle's odometer, microprocessor 110 would be 
somehow coupled to the vehicle odometer 154 either via vehicle bus 117 or 
via a discrete connection. 
The above description is considered that of the preferred embodiments only. 
Modifications of the invention will occur to those skilled in the art and 
to those who make or use the invention. Therefore, it is understood that 
the embodiments shown in the drawings and described above are merely for 
illustrative purposes and not intended to limit the scope of the 
invention, which is defined by the following claims as interpreted 
according to the principles of patent law, including the doctrine of 
equivalents.