matrix keyboard different diagrams

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Svizoman

Joined Oct 23, 2016
9
Hi,

on internet I found different diagrams how to connect 4x4 matrix keyboard to a microcontroller.
this are the 4 different diagrams I found.
1st diagrams using ADC and voltage divider is understood 100%
2. diagram with no resistors I thin is false since having no sink resistors on the output means that voltage will stay even when pin will transition from logic 1 to logic 0.
3rd diagram with pull down resistors on the output pins is actually what I am thinking to make.
4th diagram is actually same as 3rd only in reverse and I think we can use internal weak pull ups instead of one on the PCB?

Do I understand those diagrams correctly?
 

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DickCappels

Joined Aug 21, 2008
6,640
Yes, you understand correctly. You can use the internal weak pullup if you are in a quiet electrical environment, that depends on the type of controller. The last one I made used that style but because of interference from some un-grounded AC equipment close to the keypad I had to use external pull-up resistors (2.2k).
 
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