Bathroom fan with humidity control.

Hello, I am a complete newbie and need advice.
My planned project would be something like this.
2 computer fans
a humidity and temperature sensor.
A wall wart power supply.
A micro computer that is as small as possible.

I am thinking about using these parts.

Samsung old slow cell phone recharger.

2 Arctic F9 Silent fans

Not sure which controller but was thinking for fun to have a wifi connection to look at the data and play with the settings.

A humidity sensor but not sure what is the best option. Maybe this?
HiLetgo BME280 Atmospheric Pressure Sensor Temperature Humidity Sensor Breakout for Arduino

What have I over looked? What might I need.

PS I was a programmer so no fears there.


Computer fans are not really big enough to do the job IMHO there is also an issue on having electrics in bathrooms you need to check out.

Probably better to have a good sized extractor fan in the loft , together with all your parts - sense humidity on the fan inlet itself , nothing then in the bathroom , so safe. TBH a good sized fan on a timer does the job fine, but could be an interesting technical exercise.

Project looks doable though.

I agree. Mains electrical things in that environment can be dangerous and humodoty is really bad for all kinds of electronics. Buy a proper extractor fan controlled by a simple relay/SSD device.
There are such fans, powered by mains, that have built in humidity sensors but they cut off way too early in my opinion so controlling it Yourself gives a much better result. My control is manual, a mains switch using mains as a logic trigger for running. All according to specifications and installed by an outhorized electrician.

As long as the power adapter is kept in a dry spot, I don't see any real danger in this project. Components in the bathroom may not last too long due to corrosion, but that's not dangerous, that's just inconvenient. A simple inverted bucket case may do just fine. Cover the project, openings on the bottom, heated by the electronics themselves to just over ambient is all you need to keep moisture out.

Of course those fans are way too small to do something useful in a human sized bathroom, but that's another matter. A "slow charger" means not much current available, maybe not enough to run those fans.

MCU: WeMOS D1. Small, WiFi built in, 3.3V so very easy to work with the BME280. Placement of the sensor will be critical for the proper working of the project: switching on/off at appropriate times.

Some MOSFETs for switching the fans and done. A nice little demo/tinkering project.

I don't see how 12v to 3v project is going to be dangerous. We have lots of wall warts in the bathroom. They are made sealed. I have an electric shaver and also some toothbrushes and a clock, all run by wall warts.

Thanks for the advice about keeping at all dry!

Any advice about part choices.

For those that say the fans are not strong enough. Is there a chart somewhere about how much air needs to move to keep the bathroom dry?

Thanks everyone. Sorry I was slow about the reply. The forum had notifications turned off.

Have a look at a typical bathroom fan... compare the size of that to the size of those computer fans... that gives you a good idea.

Placement of the fan is also a factor in its effectiveness as most moisture comes from the shower.

If you only put the sensors in the bathroom and can blow dry air in while a vent out is open you avoid much.

Leave out the fancy stuff for version 2.

Sense temperature and humidity all the time but only act on info that trends in one direction or stays the same for at least 2-3 seconds. Look for noise, don't average it in.

What's the microcomputer for? Arduinos are microcontrollers which are in ways much neater.

Air changes per hour bathroom
It will give you a general idea.
Expect your fans to deliver HALF of their rated CFM.
Loss of flow through grills
Loss of flow due to open and unobstructed duct
Loss of flow by flex duct
Loss of flow by outside screen and grill.
Fans really bog down with any and everything.

Flow rate also tends to go down big time when you close the bathroom door (blocking the inflow of air).
Wind conditions no doubt also make a big difference - I've seen our bathroom fan spin at full speed while it was switched off... in the wrong direction. That wasn't even during a typhoon, just strong wind.