A fan, a bathroom dehumidifier, or, as I like to call it, an AUTOMATIC FART EXTRACTOR.
I am very aware of the problems caused by excess moisture, like mold, and general degradation and decay, plus the health problems.
Costs and alternatives:
To use such a powerful microcontroller such as Arduino just to read a humidity sensor to switch on a fan might seem an overkill. And indeed it is. But in terms of costs, this project cost me almost nothing, except the work, of course, which I enjoyed very much. The fan was in my possession for free, the Arduino and the modules are dirt cheap, and the light switch casing also.
But what if I had to start from scratch, what my options would have been?
No.2 – if you already have an extractor and just want an automation for it, this humidity controller.
Set the lower limit, the upper limit, and it works. The down side is it doesn’t have a timer, so you’ll have to add this relay delay module, too.
No.1 – a proper fan with built in humidity sensor, timer, light sensor, even Bluetooth!
There are hundreds and thousands of humidity controller projects on the internet, and mine is one of them, no better, no worse. I just want to emphasis that is absolutely necessary, and how to implement such an idea.