So we got 'ca   cb' till now?
I think the 2nd image will give 3 characters.
I am assuming it is read clockwise of course.

So we will get something like: ca___cb

and using this: http://www.binaryhexconverter.com/hex-to-decimal-converter we will be able to get a 9 digit pass code.

1:


A and C appears pressed in this image.
Clockwise it is CA


3:




C and B appears pressed in the image.



Edit: To see this clearly, Right click and open in new tab both images and simply switch tabs quickly while looking at the coin. You will see the difference.