But that was at the end of the interview... I was lucky, what I did in my last job perfectly matched what they needed to be done, so I didn't have to advertise myself that much.

Well, just be careful how you place that bit in the interview. Yes, it shows technical skill if the HR person is willing to look at it that way. But it's so "strange" a pastime that it might just as well put you in the "nerd" box, and many HR / manager types don't like them that much.