Note: Descriptions are shown in the official language in which they were submitted.
CA 02684532 2009-11-05
MULTIPLE ORIENTATION MOBILE ELECTRONIC HANDHELD DEVICE AND METHOD OF
AMBIENT LIGHT SENSING AND BACKLIGHT ADJUSTMENT IMPLEMENTED THEREIN
FIELD
[0001] The present application relates generally to electronic devices and
more particularly
to a method for automatically adjusting screen and keypad brightness on a
multiple orientation
mobile electronic handheld device.
BACKGROUND
[0002] The display screen on a mobile electronic handheld device may be
adjusted for
different operating environments. For handheld devices having a display whose
operation may
be enhanced via backlighting (e.g. a Liquid Crystal Display (LCD)), the
backlight should be very
bright in outdoor or sunlight conditions for the display to be readable,
whereas in normal indoor
or office conditions, the backlight should operate at medium brightness and in
dim or dark
conditions, the backlight should be at low intensity so as to avoid eye
strain.
[0003] Arrangements have been implemented in GPS displays and laptop
computers for
providing basic automatic screen and keypad backlighting adjustment, and for
providing
backlight adjustment of a display in mobile electronic handheld devices, such
as disclosed in co-
pending United States published patent application no. US-2007/0097065 Al,
published May 3,
2007, and entitled AUTOMATIC SCREEN AND KEYPAD BRIGHTNESS ADJUSTMENT ON A
MOBILE HANDHELD ELECTRONIC DEVICE.
[0004] Mobile electronic handheld devices conventionally include a light
sensor for sampling
ambient light conditions, on the basis of which display backlighting may be
adjusted for
readability in different operating environments (e.g. dimly lit environments,
normal indoor
environments and bright environments), for example as set forth in United
States patent no.
7,352,930, entitled SHARED LIGHT PIPE FORA MESSAGE INDICATOR AND LIGHT
SENSOR. The location of such light sensors on the device may be such that the
sensor
becomes covered, and therefore unreliable, in some circumstances. For example,
in handheld
devices with displays that operate in multiple orientations of the device
(e.g. portrait mode and
landscape mode), and which have a sensor disposed at a location on the device
where a user
may be inclined to grip the device in one of the orientations (e.g. landscape
mode), it is possible
1
CA 02684532 2009-11-05
that the user's finger(s) or thumb(s) may inadvertently cover and thereby
block the light sensor.
A mobile electronic device, and a method that can be carried out by the mobile
electronic
device, will be described below that may advantageously control display
backlight operation so
as to accommodate the possibility that the sensor may be blocked in certain
orientations of the
device.
SUMMARY
[0005] According to one aspect of an exemplary embodiment, there is provided a
method for
automatically adjusting backlight brightness on a mobile electronic device
capable of operating
in a DIM mode, an OFFICE mode and a BRIGHT mode, said device having a light
sensor, an
orientation sensor and a display. The exemplary method comprises obtaining
light level samples
from said light sensor; determining orientation of said device; and in the
event said backlight
brightness is in one of either OFFICE mode or BRIGHT mode, and the median
value of said
samples is less than a first threshold value and said device is in a first
orientation, then adjusting
the backlight intensity of said display to said DIM mode; in the event said
backlight brightness is
in one of either OFFICE mode or BRIGHT mode, and the median value of said
samples is less
than a first threshold value and said device is in another orientation then
continuing operation in
said OFFICE mode; in the event said backlight brightness is in DIM mode and
the median value
of said samples is greater than a second threshold value then adjusting the
backlight intensity of
said display to said OFFICE mode; in the event said backlight brightness is in
BRIGHT mode
and the median value of said samples is greater than said first threshold
value and less than a
third threshold value, then adjusting the backlight intensity of said display
to said OFFICE mode;
and in the event said backlight brightness is in one of either said DIM mode
or said OFFICE
mode and the median value of said samples is greater than a fourth threshold
value, then
adjusting the backlight intensity of said display to said BRIGHT mode.
[0006] According to another aspect of an exemplary embodiment, there is
provided a mobile
electronic device, comprising a light sensor; an orientation sensor; a
display; and a processor
connected to said light sensor, said display and said orientation sensor for
obtaining light level
samples from said light sensor; determining orientation of said device from
said orientation
sensor; and in the event said backlight brightness is in one of either OFFICE
mode or BRIGHT
mode, and the median value of said samples is less than a first threshold
value and said device
is in a first orientation, then adjusting the backlight intensity of said
display to said DIM mode; in
2
CA 02684532 2009-11-05
the event said backlight brightness is in one of either OFFICE mode or BRIGHT
mode, and the
median value of said samples is less than a first threshold value and said
device is in another
orientation then continuing operation in said OFFICE mode; in the event said
backlight
brightness is in DIM mode and the median value of said samples is greater than
a second
threshold value then adjusting the backlight intensity of said display to said
OFFICE mode; in
the event said backlight brightness is in BRIGHT mode and the median value of
said samples is
greater than said first threshold value and less than a third threshold value,
then adjusting the
backlight intensity of said display to said OFFICE mode; and in the event said
backlight
brightness is in one of either said DIM mode or said OFFICE mode and the
median value of
said samples is greater than a fourth threshold value, then adjusting the
backlight intensity of
said display to said BRIGHT mode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The method for automatically adjusting screen and keypad brightness on
a mobile
handheld electronic device will be better understood with reference to the
following description
and to the figures, in which:
[0008] FIG. 1 is a representation of a mobile electronic handheld device in
connection with
which a method for automatically adjusting screen and keypad brightness is set
forth in
accordance with one embodiment;
[0009] FIG.2 is a block diagram of certain internal components within the
mobile electronic
handheld device of FIG. 1;
[0010] FIGS. 3A and 3B show mobile electronic handheld device of FIG. 1 being
held in
orientations for operation of a display in portrait and landscape modes,
respectively;
[0011] FIG. 4 is a flowchart showing steps in a method for automatically
adjusting screen
brightness in the mobile electronic handheld device of FIG. 1;
[0012] FIG. 5 is a flowchart showing steps in the method of FIG. 3 when the
mobile electronic
handheld device is in DIM mode;
[0013] FIG. 6 is a flowchart showing steps in the method of FIG. 4 when the
mobile electronic
handheld device is in OFFICE mode;
[0014] FIG. 7 is a flowchart showing steps in the method of FIG. 4 when the
mobile electronic
3
CA 02684532 2009-11-05
handheld device is in BRIGHT mode;
[0015] FIG. 8 is a flow chart showing steps for controlling sample rate for
the methods of
FIGS. 4 - 7.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0016] Referring to FIGS. 1 and 2, a mobile electronic handheld device is
indicated generally by
the numeral 10. In the present embodiment, the device 10 is based on the
computing
environment and functionality of a wireless personal digital assistant. It
will be understood,
however, that the device 10 is not limited to a wireless personal digital
assistant. Other devices
are possible, such as desktop computers, cellular telephones, GPS receivers,
smart telephones,
handheld electronic gaming devices, and laptop computers. Referring again to
the present
embodiment, the device 10 includes a housing 12 that frames a display 31, a
speaker 33, a
message notification indicator 18, a multi-directional device touch sensitive
input 25 (touch
screen) to the display 31, and buttons 29. In a typical embodiment described
below, display 31
comprises Liquid Crystal Display (LCD), and may be called an LCD display. The
disclosure not
limited to embodiments in which display 31 is an LCD display, however. The
message
notification indicator 18 may be in the form of a light pipe having two
internal branches
terminating respectively in a Light Emitting Diode (LED) and an ambient light
sensor, as set forth
in United States patent no. 7,352,930, referred to above. The housing 12 may
be made from any
material or combination of materials that can provide structural integrity to
frame the various
components, to hold the components in a substantially stable relationship to
one another, and
can be stored, for example, in a holster (not shown) that includes an
attachment for attaching to
a user's belt.
[0017] FIG. 2 shows certain components within an exemplary embodiment of the
mobile
electronic handheld device 10, including a processor 20 connected to a read-
only-memory
(ROM) 21 that contains a plurality of applications executable by the processor
20 for enabling
each portable electronic device 10 to perform certain functions including, for
example, Personal
Identification Number (PIN) message functions, Short Message Service (SMS)
message
functions, address book and calendaring functions, camera functions, and
cellular telephone
functions. More particularly, processor 20 may execute applications within ROM
21 for
providing notification of events such as incoming calls and/or emails,
appointments, tasks, etc.
The processor 20 is also connected to a random access memory unit (RAM) 22 and
a persistent
4
CA 02684532 2009-11-05
storage device 23 to facilitate various non-volatile storage functions of the
portable electronic
device 10. The processor 20 receives input from one or more input devices,
including ambient
light sensor 36, user buttons 29 and an orientation sensor 40, such as an
accelerometer, for
detecting orientation of the device 10 (i.e. for operation in one of either
portrait mode or
landscape mode). A person of skill in the art will appreciate that other types
of orientation
sensors may be used, such as Hall Effect sensors, etc.
[0018] The processor 20 outputs to one or more output devices, including a
Liquid Crystal
Display (LCD) display 31, a backlight controller 26 and message notification
indicator 18. A
microphone 32 and phone speaker 33 are connected to the processor 20 for
cellular telephone
functions. The processor 20 is also connected to a modem and radio device 34.
The modem
and radio device 34 is used to connect to wireless networks and transmit and
receive voice and
data communications through an antenna 35.
[0019] Atypical backlight system comprises a backlight lighting source 37,
such as a series of
LEDs or a lamp located behind the display 31, and backlight controller 26 to
control activation of
the backlight 37. One example of a backlight controller is set forth in co-
pending United States
published patent application no. US 2007/0188438 Al, published August 16,
2007, and entitled
SYSTEM AND METHOD FOR ADJUSTING A BACKLIGHT LEVEL FOR A DISPLAY ON AN
ELECTRONIC DEVICE. The lamp may be fluorescent, incandescent,
electroluminescent or
other light source. The intensity of the backlight level may be controlled by
the controller 26 by
adjusting current or voltage, by selectively activating a selected number of
lighting sources (e.g.
one, several or all LEDs) or by selectively controlling the activation duty
cycle of the activated
lighting sources (e.g. a duty cycle anywhere between 0% to 100% may be used).
[0020] To assist with one method of adjusting the backlight level, light
sensor 36 is provided on
device 10. Sensor 36 is a light sensitive device which converts detected light
levels into an
electrical signal, such as a voltage. It may be located anywhere on device 10,
having
considerations for aesthetics and operation characteristics of sensor 36.
However as discussed
above, in one embodiment, an opening for light to be received by sensor 36 is
located on the
front cover of the housing of device 10 at a corner thereof (to reduce the
likelihood of blockage
the opening and thereby also blocking the sensor). In other embodiments,
multiple sensors 36
may be provided and controller 26 may operate to provide different emphasis on
signals
provided from different sensors 36. The signal(s) provided by sensor(s) 36 can
be used by a
circuit in device 10 to determine when device 10 is in a well-lit, dimly lit
or moderately-lit
environment, as discussed in greater detail below.
CA 02684532 2013-02-19
_
[0021] In one aspect, this disclosure sets forth an extension of the
specification in United States
patent no. 7701434, in describing a method for automatically adjusting
backlight brightness in a
multiple orientation mobile electronic handheld device.
[0022] As discussed above, the location of light sensor 36 on the device 10
may be such that
the sensor becomes covered, and therefore unreliable, in some circumstances.
For example,
when the device 10 is operated in portrait mode as shown in FIG. 3A, the
sensor 36 is
unobstructed so that accurate ambient light readings may be taken. However,
when the device
is operated in landscape mode as shown in FIG. 3B, the sensor it is possible
that the user's
finger(s) or thumb(s) may inadvertently cover and thereby block the light
sensor 36.
[0023] Reference is now made to FIG. 4, showing a flowchart of a method for
automatically
adjusting the backlight brightness of display 31 on the mobile handheld
electronic device 10 of
FIGS. 1 - 3. The method is implemented by an algorithm within an application
executable by the
processor 20 to correctly switch between three screen-specific ambient
lighting modes (referred
to herein as DIM, OFFICE and BRIGHT, respectively). In DIM mode, the display
31 backlight is
dimmed for low lighting environment. In OFFICE mode, the display 31 backlight
is set to a
brightness for an office environment. In BRIGHT mode, and the display 31
backlight is set at full
brightness, for legibility in bright sunlight. The DIM, OFFICE and BRIGHT
modes are
determined by detected ambient light conditions and operate to set the
backlight to appropriate
operating states, as discussed in greater detail below.
[0024] Each ambient lighting mode has a corresponding brightness/state value
as set forth in
Table A, where "%PWM" represents the duty cycle of a pulse width modulated
signal of variable
base frequency dependent on the specified duty cycle, and "Lux range"
represents the range of
ambient lighting intensity (measured in Lux units, where Lux represents the
amount of visible
light per square meter incident on a surface) in which each mode operates:
TABLE A
Screen Backlight DIM mode OFFICE mode BRIGHT mode
Mode
Lux range of ambient <70 16<Lux<4400 3000<Lux
lighting
Screen backlight 3%-6,5 /0PWM 10%-40`)/0PWM 100%PWM
brightness (based on 10%-100% (this "overdrives"
(based on 10%-
brightness defined in the backlight
100% brightness
Screen options circuit)
defined in Screen
screen)
options screen)
6
CA 02684532 2009-11-05
[0025] As indicated in Table A, the display 31 backlight is adjustable in 5
or 10 discreet
steps between 3% and 6.5% PWM, an additional 5 or 10 discreet steps between
10% and 40%
PWM and may also be set to 100% PWM Backlight brightness control also permits
a smoothly
and quick fade (-200ms) and a slow fade (1-1.5s) between any of these steps
(in addition to the
off state).
[0026] Upon starting the algorithm (step 50) when the device 10 is turned
on, the backlight
mode is normally initialized to an appropriate mode using the ambient lighting
sensed by the
light sensor 36 at that time. Next, light sensor samples are taken at set
intervals and maintained
in a buffer containing the five most recent samples at any given time (step
52). This buffer is
referred to as the sample window because it is a moving window such that when
each new
sample is received, the oldest sample in the window is discarded from the
buffer. The amount of
time between each light sensor sample determines the sampling rate. Atypical
sampling rate is
one sample per 1.2 seconds although in some situations the sampling rate may
be increased to
400ms temporarily for 5 samples to facilitate quick adjustment of the screen
backlight. At step
54, the median sample value is calculated by sorting all samples in the sample
window and
choosing the middle value (i.e. the third sample in the window).
[0027] When each sample is received, orientation of the device 10 is
detected using
accelerometer 40 (step 55), and a new median in the sample window is
calculated and
compared to various thresholds (step 56) to determine if a backlight
adjustment is necessary,
according to the detected orientation of the device (i.e. portrait or
landscape), as depicted in the
exemplary state Table B, where ADC represents Analog to Digital Converter
output values:
7
CA 02684532 2013-02-19
[0028] Table B:
Median Light Sensor Current Mode = Current Mode = OFFICE Current Mode =
BRIGHT
ADC Value DIM
Threshold 7 No Change Switch to DIM Switch to DIM
Orientation=Portrait
Threshold 7 No Change No Change No Change
Orientation=Landscape
Threshold 14 Switch to OFFICE No Change No Change
Orientation=Portrait
Threshold 14 Switch to OFFICE No Change No Change
Orientation=Landscape
Threshold 450 Switch to OFFICE No Change Switch to OFFICE
Orientation=Portrait
Threshold 450 Switch to OFFICE No Change Switch to OFFICE
Orientation=Landscape
Threshold 650 Switch to BRIGHT Switch to BRIGHT No Change
Orientation=Portrait
Threshold 650 Switch to BRIGHT Switch to BRIGHT No Change
Orientation=Landscape
[0029] The relationship between ADC threshold values expressed in Table B and
light intensity
values is as follows: ADC 7=16 Lux, ADC 14=60 Lux, 16 ADC = 70 Lux, 50 ADC =
250 Lux,
ADC 450 = 3000 Lux, and ADC 650 = 4400 Lux. Operation of the state Table B is
depicted in
the flowcharts of FIG. 4, 5 and 6.
[0030] Thus, as shown in FIG. 5, when the backlighting is in DIM mode(step
58), the median
sample value is compared (step 60) to a threshold value of 14 (70 Lux) and if
the value is
greater than 14 OFFICE mode of backlight operation is selected (step 62)
wherein the display
31 backlight is at a brightness for an office environment. However, if the
median sample value is
greater than 650 (step 64) then BRIGHT mode of backlight operation is selected
(step 66)
wherein the display 31 backlight is set to full brightness.
[0031] As shown in FIG. 6, when the backlighting is in OFFICE mode (step 68),
the median
sample value is compared (step 70) to a threshold value of 7 (16 Lux) and if
the value is less
than 7, a determination is made as to orientation of the device (step 71). If
the device is oriented
for operation in portrait mode, then DIM mode of backlight operation is
selected (step 72)
wherein the display 31 backlight is dimmed. Otherwise, the device is oriented
for landscape
8
CA 02684532 2009-11-05
mode, with the attendant risk that the sensor 36 is covered and therefore not
generating
accurate ambient light level samples, in which case backlight operation
continues in OFFICE
mode (step 68).
[0032] If the median sample value is greater than 650 (step 74) then BRIGHT
mode of
backlight operation is selected (step 76) wherein the display 31 backlight is
set to full brightness.
[0033] As shown in FIG. 7, when the backlighting is in BRIGHT mode (step
78), the median
sample value is compared (step 80) to a threshold value of 7 and if the value
is less than 7, a
determination is made as to orientation of the device (step 81). If the device
is oriented for
operation in portrait mode, then DIM mode of backlight operation is selected
(step 82) wherein
the display 31 backlight is dimmed. Otherwise, the device is oriented for
landscape mode, with
the attendant risk that the sensor 36 is covered and therefore not generating
accurate ambient
light level samples, in which case backlight operation switches to OFFICE mode
(step 86).
[0034] If the median sample value is less than 450 (step 84) then OFFICE
mode of
backlight operation is selected (step 86) wherein the display 31 backlight is
dimmed to a level
for an office environment.
[0035] From FIGS. 5 and 6, it will be noted that the threshold for changing
from DIM mode
to OFFICE mode is higher than the threshold for changing from OFFICE to DIM
mode. This
compensates for situations where the ambient lighting is hovering around a
particular threshold
value and prevents constant transitioning between backlight states. A similar
hysteresis is
integrated into the threshold values between the OFFICE and BRIGHT modes
(FIGS. 6 and 7).
[0036] By using the median sample in the sample window for mode-change
decisions, brief
lighting fluctuations (e.g. bright flashes lasting less than about 800ms) are
effectively filtered out
while still providing an acceptably quick response to entering an area with
bright sunlight or
pulling the device out of the holster in bright sunlight. Transitioning
through a dim environment
for less than about 5 seconds is also ignored because all five samples in the
sample window are
required to be less than the threshold value for the currently active mode to
affect a mode
change. Since it takes several seconds for a user's eyes to adjust to a dimmer
environment, the
LCD display 31 brightness is permitted by the algorithm to adjust gradually.
[0037] From the foregoing, it will be appreciated that backlight adjustment
may be provided
according to the methods set forth herein for multiple orientations of the
mobile handheld
electronic device 10, such as in landscape mode where a brighter backlight may
be used for
display of multimedia.
9
CA 02684532 2009-11-05
[0038] As shown in FIG. 8, light sensor samples are not taken (i.e. sleep
mode) while the
device 10 is off or in the holster (step 100) in order to save battery life
and because samples are
not likely to be valid because the light sensor is likely covered by an arm
(device 10 is in holster)
or in a bag or a pocket. When the light sensor software "wakes up" (step 102),
sampling and
backlight adjustment begins (step 106) with a fast sampling rate (400ms) for
the next five
samples. The first sample received is used to initialize the entire sample
window, if the second
sample is brighter than the first, then this value is used to initialize the
entire sample window. If
the third sample is brighter than the first two, then it is used to initialize
the sample window.
[0039] Thereafter, the normal sampling rate is one sample every 1.2 seconds
(step 108).
Preferably, each light sensor sample is actually an average of multiple quick
samples taken over
a period of about 9ms. More particularly, at least 8 ADC readings are taken
over a 9ms period
so that they can be averaged out so as to increase the reliability of each
sample and filter out
small variances in AC indoor lighting.
[0040] When the device 10 is pulled out of its holster, removed from a
pocket or bag, etc., it
is highly likely that the light sensor will be temporarily partially covered
by the user's hand or
shirt. This means that the first couple samples could be below the threshold
for transitioning to
DIM mode, even if the device 10 is operating in the OFFICE mode. Likewise, the
first couple of
samples could be indicative of OFFICE mode even though the device is in a
bright environment.
However, it is nearly impossible for a brighter sample to be received when the
device is in a dim
environment. Hence, as discussed above, the entire sample window is
initialized to the greatest
sample when the device 10 out of the holster.
[0041] If the display 31 turns off due to a system timeout or the power
button being pressed,
but the device 10 has not been yet been turned off or returned to its holster
(step 110), then light
sensor sampling reverts to sleep mode (step 100) provided the display 31 does
not turn back on
within the time it takes to receive the next five samples. This five sample
delay is provided
because the display 31 may time out while the user is reading the screen. It
is common for a
user to handle this situation by hitting a key to immediately wake up the
screen again (which
turns on the backlight). In this case, the sample window is not reset to sleep
mode. If the LCD
screen 4 stays off for more than a few seconds then the sample window is reset
to sleep mode
due to the likelihood that the device environment has changed.
[0042] Based on the foregoing, LCD display 31 brightness responds to a
change from a
dimmer to a brighter environment within 800ms to 2 seconds. This is the amount
of time that it
CA 02684532 2009-11-05
takes to receive three brighter samples (which sets the median of the 5-sample
window). The
first sample in a brighter environment triggers the fast 400ms sampling rate
(step 104).
However, it can take up to 1.2 seconds before the first sample is received.
LCD display 31
brightness responds to a change from a brighter environment to a dimmer mode
in about 6
seconds. It takes 5 consecutive samples in a dimmer mode to cause a transition
to the new
mode. When the display 31 backlight brightness is adjusted downwardly, the
backlight is slowly
faded to the new brightness level. This fading takes from about is to 1.5s.
[0043] In one embodiment of mobile electronic handheld device 10, the light
sensor 36 and
message indicator 18 (e.g. LED) share a common light pipe. If the sampling
algorithm of FIG. 7
requires a light sensor sample to be taken while the LED is on, then the
sample is delayed until
immediately after the LED turns off, unless the device 10 is in the process of
being pulled out of
its holster. In this case, an initial low light sample is "faked" if the LED
is on while removing the
device 10 from its holster, etc. so as not to delay turning on the LCD display
31 backlight (which
cannot occur until a sample has been received). Each LED on/off transition is
controlled so that
the state information can be provided to the automatic backlight software set
forth herein of LED
on/off transitions.
[0044] Preferably, coarse timers are used in the described method (e.g. +1-
12.5% variance).
The use of coarse timers minimizes the number of times the processor 36 must
wake up due to
timer events. Consequently, all times referred to in this specification are
characterized by a
possible error of +/-12.5%.
[0045] While the embodiments described herein are directed to particular
implementations
of the method for automatically adjusting screen brightness on a mobile
handheld electronic
device, it will be understood that modifications and variations to these
embodiments are within
the scope and sphere of the present application. For example, as indicated
above the
backlighting brightness adjustment methodology set forth herein is not limit
in its application to
handheld electronic devices but may advantageously applied to other electronic
devices such
as desktop computers, cellular telephones, GPS receivers, smart telephones,
portable gaming
devices, and laptop computers. Also, backlight adjustment may be controlled
based on device
orientations other than portrait and landscape (e.g. upside down, level,
etc.), or wherein the
sensor 36 is positioned at a different location on the device 10, where
possible obstruction of
the light sensor 36 may occur. Many other modifications and variations may
occur to those
skilled in the art. All such modifications and variations are believed to be
within the sphere and
scope of the present application.
11
