Is it to monitor a two player game or is it to act as an opponent?Resistors are placed on the column or row pins of the matrix depending on how you wire it up.
Monitor a two player game.
This implies two different color pieces - red/black, white/black, whatever - else how would the players keep track of who's who? Yet, curiously, you seem indifferent to having distinguishing colors for the virtual board. Please explain.
Yes that would work. Because of the position of the diodes I would suggest that the rows have resistors connected to ground and the Arduino input, and the columns have the walking one on them.
If you have a red piece on square A1, that piece disappears and one appears on B2, what's the chance that the colour has changed?
Probably nil. But, after nine moves how is one to determine at a glance which pieces belong to which player if there's no color difference?
Sorry, what do you mean by "walking ones"?