Lcd & Keypad Illumination - Nokia NSB-9 Service Manual

NSB-9
System Module and User Interface
LCD & Keypad Illumination
In NSB-9 white LEDs are used for LCD and keypad illumination. For LCD illumination
three LEDs are used and for keypad three in both qwerty sides and four in ITU-T keypad
(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, * and #), and three in engine control keys. Engine LEDs are con-
trolled by UEM KLIGHT and DLIGHT signals. Flip LEDs are controller by flip MCU, accord-
ing to flip serial interface messages.
Engine qwerty
keypad LEDs
Current through LEDs is controlled by transistor circuitry. External transistor driver cir-
cuitry is used as constant current source in order to prevent any change in the battery
voltage to be seen as varying LED brightness.
Page 36
Figure 9: Engine qwerty keypad LED connection
VBAT
22R
Nokia Corporation
CCS Technical Documentation
VBAT
470R
330R
KLIGHT
Issue 1 04/03