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Interface to 4x4 Keypad - how to scan the keypad correctly?

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Maverickmax

Maverickmax

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Interface to 4x4 Keypad

Hi

I am struggling to interface my 4x4 Keypad as I connected 4 rows and columns to P0H to P0H7 respectively. I tried to scan it but I kept getting incorrect data. How can I scan the keypad correctly?

I use column as output and row as input.

Please advise me asap

MM
 

Re: Interface to 4x4 Keypad

What is your reading sequence ?

Added after 54 seconds:

And the schematic

Added after 2 hours 22 minutes:

I imagine you are already doing the next:

Initial column value = 0

Set 1 to Column # 1
Read the input - If data != 0 then you have key(s) pressed
Set 0 to Column # 1

Set 1 to Column # 2
Read the input - If data != 0 then you have key(s) pressed
Set 0 to Column # 2

Set 1 to Column # 3
Read the input - If data != 0 then you have key(s) pressed
Set 0 to Column # 3

Set 1 to Column # 4
Read the input - If data != 0 then you have key(s) pressed
Set 0 to Column # 4

Delay to avoid bouncing
 

Re: Interface to 4x4 Keypad

Since I set the columns high and rows as input but each row has a pull-up resistor. So the inputs of row would be high. When key is depressed, say 1. The software will carry algorithm such as setting column to zero one by one. For example:

0111
1011
1101
1110

While key "1" is depressed and column number 1 set to zero which will override row 1 to zero. As button 1 releases, the 1st row will go back to one due to a pull-up resistor. Is that correct?

MM
 

Re: Interface to 4x4 Keypad

If you have pull-up resistors you cannot set the column to 1 to read each row.

But, to help you better, please send the schematics.
 

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