Backlight And Illumination; Ambient Light Sensor - Nokia RM-235 Service Manual

RM-235
System module and user interface

Backlight and illumination

When the backlight is enabled, the LED drive TPS65102 (N1451) is set to voltage mode by setting the ENVM
input high, this overrides the I2C control from the camera processor and sets the output to a constant 5V.
The TCA6507 switches the outputs P0 to P6 low depending on which group of LEDs are required to be on.
The current is set by the resistors on these inputs. The driver circuit made up from transistor pair V2499 is
required to ensure that the limits of the Navi Key LED forward voltage is achieved as this can not be guaranteed
from the TCA6507.
The display backlighting is sourced from the constant current regulator N2301and enabled from the PWM
300 output from Betty. The current is set by the 33R resistor to ground.
Figure 53 Display backlighting control

Ambient Light Sensor

In order to optimise user interface legibility, the display and UI illumination brightness is controlled by the
handset according to the ambient lighting conditions. The ambient light level is measured by the handset
using the Ambient Light Sensor/Detector N6502 which communicates to the engine via the I2C interface:
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