I'm using an old small wine fridge for my cheese cave, and it doesn't have any temp or humidity displays. Since one of my other hobbies is electronics I looked through my junk drawer and found enough parts to build a temperature and humidity display using a DHT22 temp/humidity sensor. First thing I noticed was that my wine fridge was running too warm, so now I've got it down to 55 degrees F.
The next problem I need to solve is humidity. Putting a container with a wet sponge in the bottom of the fridge is wildy inconsistent depending on where I put the sensor, but I have't seen it get over 60%. My solution is to raid my junk drawer again for a small fan that I will place over the sponge container to circulate the moist air. I have a fan that runs pretty gently so it shouldn't disturb any mold cultures. Once I get the humidity up I'm going to attempt some St. Marcellin. I've only aged hard cheeses in the cave so far, mostly waxed cheddars.
Since I'm using a small AVR micro controller for the sensor and display I'm going to hook up the fan to it as well so the micro controller can turn the fan on if the humidity drops below a set point.
Total material cost of this project was $0 since I had all the parts lying around, but if I had to buy them it wouldn't be much more than $20. The most expensive part is the 2 line backlit LCD display at about $10. If I really want to get fancy I could hook up an IO pin on the micro controller to an AC relay, put the fridge on high, and let the controller cycle the power on and off to control temperature too, but I don't think I need to do that yet.
I love it when my hobbies cross pollenate!