I am interfacing a 4x3 keypad with LPC1778 using GPIO pins. These pins are 5V tolerant. Can I use zener diodes in the debouncing circuit?
Can I use zener diodes like this?
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A pre-wired matrix keypad pretty much requires debouncing in software. Adding diodes outside of the matrix will not help with de-bounce, neither will it help with "ghost rejection".
The diodes in your diagram might provide a diode-or function indicating that atleast one key is active, if the IO pin they are connected to has a pull-down on it. but for this they do not need to be zeners, any diode would work. eg: 1N4148