working of 4x4 matrix keypad

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here's a simple writeup
https://www.8051projects.net/keypad-interfacing/introduction.php

the need for 4x4 keypad is to use less lines for the 16 switchs. normal method shown uses only 8 lines.

4 lines are output from uC, and connect to each column
4 lines are input to uC and connect to each row.

now first energise 1st column with 5v. other columns are all kept low. then read all the rows. If some key is pressed in that column, the input will have that as high, otherwise low. this way we know which key(s) is pressed in that column.

now very quickly we do exact same thing with 2nd column, then 3rd, then 4th. each time reading in the rows and seeing which is high, and which is low.

easy no ?
 

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