Here's a couple of photos of the shutter I'm currently using. It's made from a couple of bits of scrap card. One has a quite large hole cut in the center which fits over the pinhole (I didn't cut this very neatly – you can do better!) The other piece acts as the shutter and slides behind this, covering the pinhole. I stuck some black tape on the back of this shutter card.
here is how it looks like:
check out alspix blog for the most updated instructions