Keypad Switches And Scanning - LG MG295 Service Manual

3.8 Keypad Switches and Scanning

The key switches are metal domes, which make contact between two concentric pads on the keypad
layer of the PCB when pressed. There are 27 switches (Normal Key 23EA, Volume up down and
camera side key, PWR down side key), connected in a matrix of 6 rows by 5 columns, as shown in
Figure 3-11, except for the power switch (END), which is connected independently. Functions, the row
and column lines of the keypad are connected to ports of AD6721. The columns are outputs, while the
rows are inputs and have pull-up resistors built in. When a key is pressed, the corresponding row and
column are connected together, causing the row input to go low and generate an interrupt. The
columns/rows are then scanned by AD6721 to identify the pressed key.
R302
680
POWERKEY
KEY_ROW0
KEY_ROW1
KEY_ROW2
KEY_ROW3
KEY_ROW4
2V8_VEXT
KEY_ROW5
KEY_COL0
KEY_COL1
KEY_COL2
KEY_COL3
KEY_COL4
Copyright © 2007 LG Electronics. Inc. All right reserved.
Only for training and service purposes
CAMERA
CN300
1
2
3
END
4
5
END
R321 680
R325 680
R328 680
R333 680
R336 680
R337
100K
R338 680
R339 680
R340 680
R341 680
R342
680
R343 680
Figure 3.8 Keypad Switches and Scanning
VOL_UP VOL_DOWN
R311 R312 R313
100ohm
100ohm 100ohm
1 2 3
SW300 SW301 SW302
SW303 SW304 SW305
4 5 6
SW306 SW307 SW308
7 8 9
* SW309 SHARP
* 0 #
T
T
- 31 -
3. TECHNICAL BRIEF
Side Key
CLR FAV
CLR FAV
LEFT
LEFT MENU MENU
UP SEL
UP
SEL
RIGHT SEND
RIGHT
SEND
DOWN CONF
DOWN
CONF
LGE Internal Use Only