I don’t mind the odd smell, but I thought I’d give this a go.

The main part of this is activated carbon, this is what’s going to remove the smell, but to make it more complicated I wanted to be able to switch this on and off so the output didn’t always go through it.
A simple vent would of done but I like the look of an iris.

Designed on CorelDraw, tested in cardboard first.
The bearing came from hard drive motors as they all seem to be the same size and reduced the friction somewhat.
To turn the iris I need a couple of points to reduce the side friction. Two Servos with some acrylic cut gears sorted this.

Gears were designed with use of this brilliant website https://woodgears.ca/gear_cutting/template.html
To drive the servos the cheapest option was a simple servo tester, £3 from ebay. Made a little box for it to sit in.

Smashed an Ikea cupboard about a bit up and sealed it. I divided it up internally so the iris would sit one side, the filter the other. The edges have draft sealer on and then I can screw a door on to it. Had to make a little viewing window though (video at bottom of page).


Mine was very dirty so I washed it, then cooked it in the oven. Because it’s so porous (the activated bit) it holds a lot of water, you need to be careful opening a hot oven after doing this, a lot of steam comes out….
  I used about 10kg

It works great reducing smells and as long as the iris works I don’t need to take the side door off, I can load up the carbon by popping off the top pipe and getting my hand in there.