I am re-building the project I did some years ago. This time it will be much simpler (or so I thought).
I am using: Arduino DUE, Data logging shield + SD, 4x4 Keypad (from a phone, but it seems to work fine). It will be a phone-like experience (I have an amp and speaker ready).
When I connect the keypad through a Data logging shield, pin no. 7 would stop receiving the input. That means only the first two columns of the keypad numbers are functioning (1, 2, 4, 5, 7..).
But all tests show that pin 7 is working fine (e.g. button-LED test).
EDIT: It seems that the problem is somewhere else: changing the input to other pins - same result with only two columns working.
This is how I connect DUE to Data shield: Adafruit Data Logging Shield with DUE ... everything's OK!!!
Keypad code I am using to test: https://arduinogetstarted.com/tutorials/arduino-keypad
If I unplug all SPI pins from the shield - the input works sometimes. Very weird. I have tried with multiple shields and Arduinos - same result.
What could cause that? Thanks for any input