Hi: I'm seriously thinking on tackling a permanent problem which is having a temp chamber to test some of my projects performance with temp. Since I need to lower the temp probably near 0 C or a bit lower for it to be really useful and with a fast temp change rate I think the best way is to use an existing working mini fridge??? and add a heating system such like a hair dryer or any other resistive element-fan combination that suits the purpose. I live in very hot weather so taking cold air from outside is just not possible. That way I will dodge the major task of building the cooling system by myself or even making any costly modifications to it. I'm planning on using a computer and Arduino to build the controls having a set of already preprogrammed temp change curves and modes and also some flexibility to manually program special modes and change parameters which will probably be needed; but that's still far away for now. The main concern I have and still have to resolve before continue planning is condensation, very common around here considering relative humidity is always high. Just to give you an idea how permanent it is, I have to clear my glasses everytime I go outside a place with AC even in what is supposed to be "winter". Since there will be electronics inside probably even Arduinos I want to prevent that. Do you think condensation will become a major problem? If so, will there be ways to mitigate that? Maybe I'm wrong and if done right by only opening the chamber when its hot, I won't have the problem; but how about with the door closed? Condensation will take place inside?. I think the sample can't get cold faster than the surroundings for condensation to occur; but the surrounding air can get hot faster than the sample when heating. Will recirculating the same inside air with a fan when in heating mode, will be better than opening windows and feed fresh air from outside?. I would like to have some help clarifying this point. Maybe it doesn't even matter to have some condensation. I don't know. Can Arduino sustain low temps??? I've heard of people sending Arduinos to the stratosphere; but I don't know the results. I don't want to put my Arduino inside the fridge without knowing of the possible outcomes. They have tried it all, so it probably happened already. Most of the people in this forum live in cold weather maybe they can tell what happens when they take their Arduinos for a walk and its -10C outside??? I would also be glad to get any other ideas and suggestions you may have. Since I haven't started with this yet, its better to get as much info as possible now that any thing can be changed, than later on in the process when I will have to modify already built things. Although far away in time, it will also be good to have an idea of which preprogrammed temp control modes maybe be good to have. I haven't think about that in detail yet; but again it will be good to have at least a general idea before hand. Any ideas or suggestions are welcomed. Maybe there are people here who have worked doing these things before or are interested in doing them.
If you're heating and cooling the chamber then you're inevitably going to be sucking in/blowing out air as the air contracts/expands. Even the best IP rated enclosures have this issue. The only solution I'm aware of for keeping that moisture out is a GORE(tm) vent; if you've ever disassembled a hard drive you might have noticed a white, rubbery sticker covering a vent hole -- that's GORE-TEX material. Unfortunately these vents appear to be unobtanium :(
For short periods you might want to look at silica gel dessicant. You can buy this in a color-changing form (pink to blue) when it becomes "moist" and can dry it out again with an oven.
I've had an ATTiny85 operating outdoors, covered but unprotected from the open air for almost two years now with no failures. Our temperatures here have been -20F (-6C) to 100F (38C).
Did not know about the GORE(tm) vent, very interesting. The silica I knew; but haven't made the connection. Glad you did it, it offers a real practical solution I haven't think about. Also good to know about your low temp experiences with Arduino. Everything is getting much clear now... Really thanks for your help and excellent explanation.