3.9 Keypad Switches and Scanning. LG KG291, KG290

3. TECHNICAL BRIEF

3.9 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 15 switches (Normal Key 12EA, Volume up down side key, camera side key), connected in a matrix of 5 rows by 3 columns, as shown in Figure 3-11, 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.

MAIN KEYPAD

CAMERA VOL_UP VOL_DOWN

KEY_ROW0

KEY_ROW1

KEY_ROW2

KEY_ROW3

KEY_ROW4

R317 680

VA303

(15pF)

VA304

(50pF)

R309

100ohm

R310

100ohm

1

KEY300

VA301

R617

100ohm

VA302

R618

100ohm

2

KEY301

3

KEY302

R321 680

VA305 4

KEY303

5

KEY304

6

KEY305

R324 680

VA306

7

KEY306

8

KEY307

9

KEY308

R329 680

VA331 *

STAR

0

KEY309

#

SHARP

R333 680

VA332

UKEY_ROW0

UKEY_ROW1

UKEY_ROW2

UKEY_ROW3

UKEY_ROW4

KEY_COL0

KEY_COL1

KEY_COL2

R335

R336

R337

680

680

680

Figure 3-11. Keypad Switches and Scanning

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