User Guide

System Module LG4 and Grip Module LS4 CCS Technical Documentation
Page 30 ¤Nokia Corporation Issue 2 11/02
Ambient Light Sensor
Ambient Light Detector (ALD) is used as a power saving feature.
Ambient Light Detector (ALD) measures illuminance on the display (ambient light). User
can select the limit, above which display backlight is not needed. In practice, two limits
are used in software to produce hysteresis. Hysteresis is needed to prevent backlight
from blinking. Backlight can be switched ON only when ambient light level is below
lower limit. Backlight is switched OFF, when ambient light level exceeds higher limit.
Figure 17: Ambient light sensor implementation
Optical
Lense
UEM
Ambient
Light
Pull-up
resistor
100 kOhm
VFlash1
2.78 V
Phototransistor
Siemens
LS
NTC-
Resistor
Pull-up
resistor
100 kOhm
VANA
2.78 V
VCXOTEMP