Low humidity helps spread virus/bacteria over air.
The comfortable zone for humans depends on the temperature, here is what it looks like for most of us:
We own a ultrasonic humidifier, but it has no setpoint, just on/off with intensity setting. Also, I’d like it to work only in certain times, not all of the time, so that called for using the WiFi thermostat scheduling function, only re-worked to take the humidity as to determine on/off state rather than temperature:
I realize there are homes with exact opposite problem, i.e. humidity is too high. For that reason I have a “Dry” function to use with air drier as well so the relay will function using opposite logic i.e. activate when humidity is exceeded.
The project uses a DHT22
temperature sensor mounted to the side of the enclosure for better ventilation and reliable reading:
I threw in a ultra-cheap I2C OLED status display to get a visual reading. Milling the box so that the OLED shows was pretty nasty, hated it. I cut a piece of paper and placed it on top of the cover, below the transparent lid to cover up for the lousy milling job
For more detail: DIY Internet connected smart humidifier