Humidity-temperature sensing and relay control

Hello everybody, I have a telescope and I want to shield the parts from high humidity and avoid low temperatures. I have a dehumidifier and a thermal pad and I would like to connect them to sensors that would control when they would be turned on or off. I have very small experience with electronics (some course in college about a decade ago) but I can find my way around a breadboard and I can program (not a developer, a matlab guy, but you get the meaning..) So I was thinking about plugging an arduino to a temperature/humidity sensor and control the two devices with a relay. I am not looking for a ready solution (I am sure I ll find something if I keep searching the forum - just been here for 10 minutes) I just have one or two general questions, the most important one being , Which components and which arduino? Searching the net I find many different choices for arduino and dont get me started on the temperature/humidity sensors. So, to begin with, which arduino do you think would be more appropriate for such a task, taking in mind first that I want to avoid overkill? Secondly, does it really matter which sensor I buy? (Considering ease of use when programming them and accuracy more or less. But ok, I dont need the readings to be 100% accurate.. ) They way I think about the whole setup is this : 1. Arduino 2. Breadboard and cables etc 3. Two relays for switching on and off the devices 4. A temperature/humidity sensor (or different sensors ?) 5. Two knobs for inputing the desired values (one for humidity and one for temperature) - something else would be better perhaps? please advise if possible. 6. perhaps an lcd screen?? Am I in the right path with this? Thanks in advance for any help.

P.S : In case you DO think this, NO I am not a college student,neither a schoolboy looking for easy answers for a project. :D Thanks again Steven - Greece

Hi Steven, Sounds like you are on the right track. I would go with an Arduino Uno. Also, I have used the following temperature sensor (TMP36) and it is easy to use. http://www.adafruit.com/products/165. I have not really done anything with humidity, but you could get one sensor that combine both like the SHT15. http://www.sparkfun.com/products/8257 You should be able to avoid using knobs and just program in the desired temperature & humidity level as well. Good luck.

Thanks a lot for the swift reply. Well, regarding the sensor, $40 seems a bit steep.. I found this looking around, and it seems a good choice too -pricewise at least : . Anybody used that? : http://www.sparkfun.com/products/10167

I would need some help with the relays too because all I know now is "I need two relays" .. :S any suggestions? The one device whose characteristics I remember operates in 12vdc , ~3.5A. The heating pad, I dont remember.. Something like this perhaps? http://www.sparkfun.com/products/100

Sorry for the -most probably- extremely naive and beginner's questions guys. And thanks again

Hi there, I am new to arduino just like you and working on a very similar project, namely, humidifier controller relay. Opposite to yours, I would like a place to be humidified. I would like to set a humidity level by up-down buttons and see the current and set levels on a screen. When the level goes below the set level the relay turns the humidifier on and when reaches the set level then the relay shuts the humidifier down.

When it comes to choices here, the standard Uno is more expensive, and really not as convenient to integrate as a Nano. Both are effectively the same chip and pinout, but you can buy nanos for about $2 on the internet, solder pins to them, and plant them nicely in a circuit board.

A nice sensor is the DHT11 or DHT22 (more accurate), which integrates with a 1 wire interface to the Nano (arduino), and has a very simple library to use with Arduino.

As for Nano's if you buy one, buy a few. You'll find uses for them.

I used DHT22 for one of my project. Like jrdroner said, Nano is a good fit for projects because of the small footprint in a board.