An Evaluation System for the TSL2560/61 Ambient Light Sensor
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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
