Rev 1.0
TSL2560/61 EVM
User’s Guide
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An Evaluation System for the TSL2560/61 LTD Ambient Light Sensor
ALS INTRODUCTION
TAOS’ Light-to-Digital (LTD) Ambient Light Sensor (ALS) solution can be used to automatically adjust
the brightness level of a computer display under a wide range of lighting conditions. As one of the
primary benefits of using TAOS’ ALS, battery life can be significantly extended by minimizing the
necessary power required to luminate a display under various lighting conditions. In PC notebooks,
for example, the display panel and inverter (which delivers the power to the display panel) comprise
approximately one-third (1/3) of the total power consumption. TAOS’ ALS helps control the display
backlight and keypad illumination in portable equipment like notebooks, PDAs, and cell phones. There
are other applications supported by the ALS which include street light control, security lighting,
sunlight harvesting, machine vision and automotive instrumentation clusters.
TAOS’ ALS can also help extend the longevity of the LCD lamp life by automatically controlling the
display brightness or luminance. Lamp life depends strongly on the lamp current and is directly
proportional to display brightness levels. Unnecessarily over-driving the display with high operating
currents and excessive brightness will prematurely degrade the lamp life of a display. Automatically
controlling the illuminance to extend lamp life is beneficial in a variety of applications:
Mobile users who frequently use notebook computers in different ambient lighting conditions
Digital monitors with on-screen controls to extend the display life and lower power consumption
Kiosks that continuously operate 24/7 in sunlight or artificial lighting
Automatically adjusting automobile display clusters (e.g. for navigation system) for safety to retain
the driver’s eyes on the road ahead at all times and eliminate glare to achieve better visibility at
night
Thirdly, since TAOS’ ALS closely approximates the response of the human eye, it can also help
improve visual performance. While eyestrain is not believed to permanently damage one’s eyes or
cause a loss of vision, it can be very uncomfortable and lead to a loss of productivity. Using TAOS’
ALS, excessive display brightness can be eliminated and productivity can be increased by maintaining
an optimal brightness level under various lighting conditions.
EVALUATION MODULE OVERVIEW
The TSL2560/61 EVM helps facilitate evaluation of the TAOS’ LTD ALS. A Universal Serial Bus (USB)
evaluation module is available which simply connects to the USB port of a personal computer.
Figure 1 is a picture of the USB evaluation module.
The TSL2560/61 device combines a visible light blocking photodiode with a broadband photodiode on
a single CMOS integrated circuit. This combination enables either device to be used to calculate light
intensity in lux over an effective 20-bit dynamic range with a 16-bit resolution without the use of an
expensive filter. Two integrating analog-to-digital converters (ADC) convert the photodiode currents
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to an SMBus (TSL2560) or I2C (TSL2561) digital output that represents the irradiance measured on
each channel. This output data can be input to a microprocessor where illuminance (i.e. ambient light
level) in lux is derived using an empirical formula. In general, the TSL2560 (SMBus interface) device
is intended for use in notebook and tablet PCs while the TSL2561 (I2C interface) device is ideal for
most other light-to-digital applications.
USB EVM HARDWARE AND DRIVER DESCRIPTION
The specification and system requirements for the hardware portion of the TSL2560/61 USB EVM
module follow:
System Requirements: Notebook or Desktop PC running Windows 98, 2000, NT4.0, XP
Host Connection: USB v2.0 using A-type connector
EVM Connection: Mini B-type connector
Software Installation: CD-ROM
After the mini-B connector is attached to the EVM using the enclosed USB cable, and subsequently
plugged into the USB port of the computer, a Wizard should appear instructing the user to load a USB
driver. The USB INF driver file is located in the FTDI directory on the CD-ROM and can be selected
using the ‘Browse’ button. Please note that if the FTDI USB driver installs automatically without
prompting the user to load the driver, then the FTDI USB driver will likely need to be updated. After
the software is executed, if an error message appears indicating that the "FTD2XX.DLL" could not be
found, then the USB driver will need to be updated. To update the driver with the proper file,
Click ‘Control Panel -> System -> Hardware -> Device Manager -> Universal Serial bus
controllers’
Highlight the appropriate FTDI driver in the list
Right mouse on the highlighted driver and select "Update". Note: The driver can found in
the FTDI directory on the CD-ROM
Fi
g
ure 1. TSL2560/61 EVM USB Evaluation Module
T
MB Dau
g
hterboard
USB Mini-B
Connector
EVM Motherboard
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GETTING STARTED
IMPORTANT: Before getting started, please review the “USB EVM Hardware and
Driver Description” section which contains information to insure that the proper USB
driver is loaded.
On most PCs, installation will automatically start when the CD-ROM is inserted into the drive. If the
installation does not begin:
Click Start
Click Run
Type D:\setup and press Enter. IMPORTANT: Use the appropriate drive letter in the above
command to install the software. CD-ROMs are commonly D:
The installation program will guide you through the product installation
Refer to the ReadMe file on CD for the latest installation instructions.
Two applications are loaded: “Automatic Brightness Control Demo” and “Device Utility”. Both
applications are discussed in the following pages.
AUTOMATIC BRIGHTNESS CONTROL DEMO
Software Description
To start the Automatic Brightness Control Demo application, click:
Start -> Programs -> TSL2560 USB EVM -> Automatic Brightness Control Demo
After the demo is executed, a “Monitor” dialog window (see below) will appear on top and an
application icon will appear in the system tray. The demo will continue to run until the monitor
application is closed.
The TSL2560/61 device can measure light levels ranging from approximately 0.1 lux to 40,000 lux.
No external circuitry is required for signal conditioning, and the integrating conversion technique used
in the ALS device eliminates the effect of fluorescent flicker, thereby increasing the stability of the
measurement.
The EVM application constantly monitors the ambient light level through the use of two photodiodes
on the TSL2560. One of the photodiodes (Channel 0) is sensitive to both visible and infrared light,
while the second photodiode (Channel 1) is sensitive primarily to infrared light. An integrating ADC
converts the photodiode currents to Channel 0 and Channel 1 digital outputs. Channel 1 digital output
is used to compensate for the effect of the infrared component of light on the Channel 0 digital
output.
Graphical User Interface (GUI)
The TSL2560 GUI is composed of three dialogs: Automatic Brightness Control Configuration,
Advanced, and Monitor. A fourth dialog (Main) is hidden and manages the ALS’ system tray icon,
menu, and profile selection.
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The Automatic Brightness Control Configuration dialog (see Figure 2) is the user’s primary
interface to configure the ALS environment. The dialog provides the capability to enable/disable
automatic brightness control, set two display brightness profiles, and open the Advanced
Configuration dialog. A default button is provided to reset the dialog back to the original settings.
The Configuration interface defines two display brightness profiles (i.e. two response curves) to
independently manage the lux-to-nits relationship between the current ambient light and display panel
luminance. The software provides the
AC
(for external power) and the
Batteries
display brightness
profiles to be configured. The
AC
Profile provides optimal viewing for varying ambient light
conditions. The purpose of the
Batteries
Profile is to extend the battery life by automatically dimming
(i.e. minimizing) the display luminance under equivalent ambient light conditions. Since it is
anticipated that the user will likely prefer optimal display aesthetics for some period of time when the
system is running on batteries, a pull-down menu is provide to allow the user to set the parameters of
the Batteries Profile to change from
AC
to
Batteries
profile when the power level is below a specified
percentage. Effectively, the profile becomes more aggressive (i.e. by minimizing the display
brightness) as battery life becomes more “critical”.
Note: The brightness range of the AC and Batteries Profile is bounded by the EVM software.
Since a “picture view” (see Automatic Brightness Control Monitor) is used to simulate the
display for a wide-range of platforms (e.g. notebooks, tablets, LCD monitors, etc.), an
approximate range of 20-140 nits was chosen to best simulate the dynamic range of the
display panel.
Fi
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ure 2. Automatic Bri
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htness Control Confi
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uration Dialo
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The Relative Power Savings is displayed on the Configuration dialog and is simply the relative power
savings between the
AC
and
Batteries
profiles at which the nit level of the LCD panel is set for each
profile.
The Advanced dialog (see Figure 3) displays three key TSL2560 options that directly affect how and
when the display backlight is adjusted when ambient light conditions change. The ALS software
automatically manages the LCD’s brightness using one of the two aforementioned brightness profiles.
A default button is provided to reset the dialog back to the original settings.
The three options that are exposed on the dialog include (1) Backlight Transition Speed, (2) Ambient
Light Threshold, and (3) Duration of Change Outside Threshold:
1. The Backlight Transition Speed specifically addresses the question of “How fast should
the backlight change?” The Backlight Transition Speed determines how fast (or slow) to
increment/decrement the display brightness steps from the current brightness step to the
target brightness step (according to the lux-to-nits response curve). This feature also
provides the capability of simulating the number of backlight steps to closely model the
ODM/OEM’s display brightness implementation. Up to 256 steps are supported.
2. Ambient Light Threshold describes the percentage change in ambient light condition to
detect. For example, small changes in ambient light can be filtered out while only
“significant” changes are detected.
Fi
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ure 3. Advanced Dialo
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3. The Duration of Change Outside Threshold is related to the Ambient Light Threshold.
Once an ambient light change exceeds the threshold, the change must persist for a
certain period of time. This feature filters large changes in light such as a shadow moving
across the light sensor and prevents display “bouncing.”
TAOS suggests exposing Backlight Transition Speed, Ambient Light Threshold, and Duration of
Change Outside Threshold on a user interface in order to provide some level of end-user
customization. Alternatively, the designer can hard-code these values to best fit their application.
The Advanced dialog also includes an ‘Option’ menu item which allows the user to select which
package type (TMB or chipscale) is being evaluated and whether to turn on/off the LEDs on the EVM.
When deriving lux, the lux equation is similar for both TMB and chipscale packages, but two distinct
equations are provided to optimize the illuminance value for the different package types. The LED(s)
on/off item is provided to eliminate the interference of the LED reflections at low light levels when the
EVM is covered. The green LED indicates power, and the red LED indicates if an interrupt event has
occurred. The LEDs will always be disabled at the start of the demo application and must be manually
selected in order to turn on the LEDs.
The TSL2560 application also supports a Monitor dialog (see Figure 4) that displays the illuminance,
channel 0 and channel 1 values, interrupt threshold, auto-range, and the display brightness setting of
a “simulated panel”. The remaining battery life and relative power (relative to maximum backlight
brightness) are also displayed.
Figure 4. Automatic Brightness Control Monitor Dialog
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The Monitor simulates display backlight control in a small panel box on the form. If the image is
clicked, the image will snap to the entire size of the display (“picture view”) to simulate the full screen.
Note: The EVM software performs a “picture view” update manually by manipulating the
picture image. Performance (i.e. image refreshing) will be directly impacted by the processor
speed since the USB EVM does not directly control the inverter, LCD monitor controller, nor
display graphic stack.
The Monitor receives notifications of changes from the Automatic Brightness Control object
whenever there is a change in the display brightness or whenever there is a change in the ambient
light condition. A change in the “simulated display brightness” directly updates the nits, backlight
step, relative power savings, and battery life. A change in the ambient light condition updates the
illuminance.
The Monitor dialog also includes a ‘Config’ menu item which allows the user to go directly to the
Automatic Brightness Control Configuration dialog (see Figure 2) and also close the demo
application.
Interrupt
The TSL2560 permits an SMB-Alert style interrupt and the TSL2561 supports a traditional style
interrupt that remains asserted until the firmware clears it. Channel 0 is used to trigger an interrupt
based upon a relative change in ambient light. When channel 0 crosses either the upper or lower
threshold as configured on the Advanced dialog, the Interrupt indicator will turn “red.” When an
interrupt is triggered, the EVM software will display the current state (i.e. threshold crossing), show
the new state (i.e. new ambient light reference point), clear the interrupt, and update the simulated
backlight accordingly.
Auto-Range
The TSL2560/61 EVM software supports two nominal integration times (402 ms and 101 ms) and both
the low gain (1x) and high gain (16x) modes as outlined in the datasheet. The EVM software
auto-ranges between the integration times and gain modes (see Timing Register in datasheet) to
optimize the setting under any given ambient light condition.
The software defaults to 402 ms and 16x gain (Normal Mode) to provide maximum resolution in
most artificial lighting conditions. If either photodiode channel saturates in this configuration, the
software will auto-range to 402 ms and 1x gain (Extended Mode). If the device saturates in this
subsequent configuration, the software will auto-range to 100 ms and 1x gain (Expanded Mode). In
general, these three configurations provide the best overall balance between resolution and dynamic
range under most ambient light conditions.
Illuminance (Lux) Derivation
Conventional silicon detectors respond strongly to infrared light, which the human eye does not see.
This can lead to significant error when the infrared content of the ambient light is high, such as with
incandescent lighting, due to the difference between the silicon detector response and the brightness
perceived by the human eye.
This problem is overcome in the TSL256x through the use of two photodiodes. One of the
photodiodes (channel 0) is sensitive to both visible and infrared light, while the second photodiode
(channel 1) is sensitive primarily to infrared light. An integrating ADC converts the photodiode
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currents to digital outputs. Channel 1 digital output is used to compensate for the effect of the
infrared component of light on the channel 0 digital output. The ADC digital outputs from the two
channels are used in the formula below to obtain a value that approximates the human eye response
in the commonly used illuminance unit of Lux:
Chipscale Package
For 0 < CH1/CH0 <= 0.52 Lux = 0.0315 X CH0 − 0.0593 X CH0 X ((CH1/CH0)1.4)
For 0.52 < CH1/CH0 <= 0.65 Lux = 0.0229 X CH0 − 0.0291 X CH1
For 0.65 < CH1/CH0 <= 0.80 Lux = 0.0157 X CH0 − 0.0180 X CH1
For 0.80 < CH1/CH0 <= 1.30 Lux = 0.00338 X CH0 − 0.00260 X CH1
For CH1/CH0 > 1.30 Lux = 0
TMB Package
For 0 < CH1/CH0 <= 0.50 Lux = 0.0304 X CH0 − 0.062 X CH0 X ((CH1/CH0)1.4)
For 0.50 < CH1/CH0 <= 0.61 Lux = 0.0224 X CH0 − 0.031 X CH1
For 0.61 < CH1/CH0 <= 0.80 Lux = 0.0128 X CH0 − 0.0153 X CH1
For 0.80 < CH1/CH0 <= 1.30 Lux = 0.00146 X CH0 − 0.00112 X CH1
For CH1/CH0 > 1.30 Lux = 0
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DEVICE UTILITY
Software Description
To start the Device Utility application, click:
Start -> Programs -> TSL2560 USB EVM -> Device Utility
The Device Utility program is included as a part of the EVM and is a separate application which
exposes key registers and control functions described in the TSL2560/61 datasheet. This utility
provides a knowledge of the low-level functionality of the TSL2560/61 device.
Graphical User Interface (GUI)
The Main dialog of the Device Utility application displays the illuminance (lux), raw channel values,
and relative position of the channel 0 value. The raw values are read from the ADC Channel Data
Registers (Ch-Fh) described in the TSL2560/61 datasheet. Since the TSL2560 has interrupt
capability, the upper and lower interrupt threshold values are also displayed along with the relative
position of the channel 0 value. Channel 0 is used to trigger an interrupt based upon a relative
change in ambient light.
When channel 0 crosses either the upper or lower threshold, the Interrupt indicator will turn “red.”
The interrupt will continue to be visible until it is reset using the adjacent ‘Clear’ button.
The Main dialog also includes an ‘Option’ menu item which allows the user to select which package
type (TMB or chipscale) is being evaluated and whether to turn on/off the LEDs on the EVM. When
deriving lux, the lux equation is similar for both TMB and chipscale packages, but two distinct
equations are provided to optimize the illuminance value for the different package types. The LED(s)
on/off item is provided to eliminate the interference of the LED reflections at low light levels when the
Fi
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ure 5. TAOS TSL2560/61 Device Utility Dialo
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EVM is covered. The green LED on the EVM hardware indicates power, and the red LED indicates if
an interrupt event has occurred. The LEDs will be enabled at the start of the utility and can be turned
on/off as an application preference from this menu item.
The Main form also supports the capability of logging the current state to a file from the ‘File’ menu
item. This feature is useful for studying the lux-to-nits relationship for a particular LCD panel. This
feature can be accessed from the menu. Simply enable logging and select the interval at which to log
the data.
The firmware version of the EVM is noted in the lower right hand corner on the status bar.
The Settings form exposes the following key TSL2560/61 device registers:
1. Control Register (0h): Primarily used to power up/down the TSL2560/61 device
2. Timing Register (1h): Controls the integration time and gain of the ADC channels
3. Interrupt Control Register (6h): Controls the interrupt capabilities of the device
4. Interrupt Threshold Registers (2h-5h): Stores the high and low trigger points for
the comparison function for interrupt generation
Fi
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in
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Dialo
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Fi
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sDialo
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