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matrix keyboard different diagrams

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svizoman

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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%
2nd 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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Yes you do but bear in mind that many PIC processors have switchable internal pull-up resistors (check for RBPU bit) so unconnected lines may go high without any additional resistors being needed.

Brian.
 

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