3. TECHNICAL BRIEF
3.3.5 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 21 switches, connected in a matrix of
5 rows by 5 columns and additional GPIO 35 for KEY_ROW5, as shown in Figure 3-x,
except for the power switch (KB1), which is connected independently. Functions, the row
and column lines of the keypad are connected to ports of AD6720. 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 AD6720 to identify the
pressed key.
21
Figure 3-7: LCD Interface Circuit
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