For the house fan project I have an iris v2 subtract sensor on every window and the fan is controlled by a GE paddle switch.
I wrote an app to control the automation.
I also have the netatmo weather station. Using that my custom app will tell me when the conditions outside are perfect for opening the house. And when those conditions change to outside of my parameters, it turns off the fan and tells me it is time to close the house.
So this one is fairly simple yet it’s going to end up costing me about $500 when it’s all said and done.
We have three cats and their litter box is in a basement storage room with my tools and a bunch of shelving units, stuff in plastic containers, etc. I put a little cat through wall door between the basement and that room so the door doesn’t have to actually be open. Well there’s two issues, the first is there’s no air circulation and the second is that cat litter dust eventually starts to cover everything in the room. We tried covered litter boxes (cats hated them), tucking in a corner and trying to isolate as much as possible, etc, but nothing worked.
So my bright idea was to build a floating wall above the litter box, which is where our water main and stuff is anyway, and then on the bottom of that floating wall put a vent with a filter. Duct the vent up to the ceiling and put a in line vent fan on it plugged into a smart outlet. Hook up a motion sensor and when there’s motion the fan kicks on, pulls the air from above the litter box, filters it, and ejects it back into the same room.
Well that ended up into adding a electric box in that area and then since there was a vent going to a room above I decided to add a booster fan to that air duct and T it off so that room can get some air from the furnace. And then I said well if I’m already making that floating wall to enclose the water main and stuff I might as well finish off that wall, and the wall next to it, etc, etc.
With two young kids running around and a full time job I’m on month 5 of this project. 
Yeah, sometimes these projects get away from us. We just took out some old carpet and put in a new vinyl floor, which was very good, but now of course it makes the old paint look shabby. And that might lead to new closet doors because the old paint didn’t come evenly up to the cabinets. All of which would make a big project even bigger, so I’ve decided to live with shabby paint for now! But it was a struggle. LOL!
You can see what your cats think, but most litter box motion-triggered mechanisms have a delay of about 15 minutes between the time motion is detected and the time the motor starts. That gives time for the cat to get out of the box again and avoid startling them on their way in.
You may have already planned on that, but I just wanted to mention it. Our cat is fine with a covered box and an automatic rake, but only with the delay. 
We were also really surprised at how much difference a scatter mat made at cleaning the cats’ paws as they came out of the litter box. But it only worked once we had the hooded boxes so we could put the mat right where they would come out. Of course you could put scatter mats around all four sides of the box if necessary.