Whats the diy humidity thing called?

I remember seeing someone share a link to a diy box thing that helps control the humidity, raising it when its low and lowering it when its high. I have a humidifier that just crapped out on me and most the year I have to have a dehumidifier running, If its possible to build something that does both that would be great but I can't remember what the thing was called and am having a hard time looking it up.

Anyone know what it might be?

Humidistat. And you can build a digi for under 20 bucks....

Just a controller for a humidifier/dehumidifier for under 20 or the actual humidifier/dehumidifier + control that works both for 20?

Im considering just running my dehumidifier to drain into the humidifier and trying to hook up a fill setup like the toilet tank uses to make sure the humidifier keeps water in it and running an overflow for the humidifier to just drain out.