User Guide

NSB-9
System Module and User Interface CCS Technical Documentation
Page 36 Nokia Corporation Issue 1 04/03
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.
Figure 9: Engine qwerty keypad LED connection
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.
Engine qwerty
keypad LEDs
KLIGHT
VBAT
22R
VBAT
330R
470R