User Guide

PAMS
Technical Documentation
NME–3
Technical Information
Page 63
Issue 1 10/99
LCD Module
As display a passive, full dot matrix (48*84) Liquid Crystal Display module
in foil compensated super twisted nematic technology with integrated
driver from Phillips will be used. Size of the display is 39.5*34*3.5 mm.
The LCD display is working with 3V instead of 5V for the MCU and
therefore a level–shifter is needed between MCU and LCD display. Data
to be displayed will be transfered via a serial communication interface
from the MCU to the LCD display.
Back Light
The Back Light Dimming circuit is used to illuminate the keyboard and
LCD–Display depending from the backlight dimming signal of the car
(Kl.58g). For the HS only yellow green LEDs are used. Inside the RU a
MBUS message is generated and sent to the HS. The MCU of the HS will
then generate two PWM signals to control the back light dimming circuit.
Two PWM signals are generated to have the chance to illuminate
keyboard and LCD–Display in different ways if necessary. The LEDs are
driven by two constant current sources.
Mic/Speaker
As microphone an electret condenser microphone from Matsushita typ
WM–66EC110 will be used. The diameter of the microphone is 6mm.
The microphone signal is bandwidth limited and amplified and routed as
balanced signal to the RU. The needed reference voltage for biasing of
the OPs will be generated by an OP voltage follower out of the 5V supply
voltage. Also this 2.5V voltage is used for biasing of the microphone and
the microphone amplifier.
The balanced earpiece signal from the RU is bandwidth limited and
amplified and then routed thru the earpiece.
A Phillips earpiece typ WD 00918/32U will be used. The diameter is 23
mm.
HOOK Detection
For detection if the HS is inside or outside the cradle a hall detector is
used. The cradle contains there a permanent magnet, so if the HS is
inside the cradle the switch of the hall detector is closed and hook line is
connected to GND. The Hook line then goes to an interrupt input of the
MCU.
MBUS
The bidirectional MBUS between RU and HS is working at 2.8V. Inside the
HS the bidirectional MBUS is split into TX and RX direction and then fed to
one of the serial communication interfaces of the MCU. The split circuit
makes also the level shift from 2.8V to 5V which is needed by the MCU.
The prefered bit rate will be 9600 bit/s but can be speeded up to 19.2
kbit/s if needed by the SW to refresh the LCD display in a sufficient time.
(not needed at the moment, due to successful compression work of the
SW group)