minecraft item frame not outputting redstone signal when item turned

I have an item frame on a block of emerald. In the item frame there is an anvil. I'm using vanilla Minecraft 1.9. When I turn the item in the item frame no signal comes out of the comparator. I have also placed a comparator behind the block. No difference.

Start

1 click

2 click4 click

After a few more clicks...

7 click all done

As you can see the piston never extended. Is there something I'm doing wrong?


Solution 1:

You have to put the comparator behind the block with the itemframe on it: enter image description here enter image description here