First test whether any key is pressed down. Connect power to rows, so they are High level. Then set all the rows R1-R2 as Low and then detect the status of the columns. Any column of Low indicates there is key pressing and that the key is among the 4 keys of the column. If all columns are High, it means no key is pressed down. Next, locate the key. Since the column in which the pressed key lies is identified, knowing the line would finalize the testing. Thus, set the rows as Low in turns until any is unveiled accordingly – other rows will still be High.
Now the row can be identified. Detect the status of each column in turns. The column tested Low is the one intersecting with the line – their cross point is just the key pressed.

Package Includes:

1 * 2 x 2 Matrix 4 Push Button Keyboard Module