humidity sensors cheap and accurate

hello this is my 1st post but very doubtfully will be my last. I am looking for a low cost humidity sensor. It seems that the sht15 is a popular choice for the arduino, but 35-45 bucks each is a bit much. I have also come across the hope rf HH10D for 10 bucks, HUMTEMPSENS for 10 bucks , UPSI G-US.12 for 6.95, and the Humirel HS1101. I make beer wine cheese and am getting into growing indoors. I already can think of a multitude of uses for temp and humidity sensors but dont know where to start. If anybody has any recommendations for a cheap but somewhat accurate sensor please pass that info along. I read in some other site about a guy using the HUMTEMPSENS with an arduino. He said that it uses the same interface as the sht15. So does that mean it uses the same library? I am a newbie to the world of physical computing and my 1st arduino was shipped from adafruit yesterday. Well thanks for reading and I hope that we can find a solution to this issue. It seems I am not the only 1 looking for this solution. thanks

Humidity sensors are like clocks... if you only have one, you'll be perfectly satisfied with it.

Seriously, it depends on what you are going to do with the readings. First off, humidity is extremely difficult to measure with an electronic sensor. It's really best done the old fashioned way, with a wet-bulb thermometer.

I first became involved with humidity sensors during the design of a meat dry aging room for a restaurant. I used the SHT75 and have not been disappointed with the results. That sensor is relatively accurate and more important for the application, very repeatable. In fact, repeatability is probably most important for many applications.

I suggest you use several different grades(prices) of sensors, matching each one's characteristics to the individual application. And don't ever compare the readings. :)

thanks for the tip on never comparing readings. I have 2 humidity sensors that I was using in another project and comparing the readings drove me nuts. Where would be the best spot to get or look for humidity sensors. I go to digikey and search for humidity and get 20 pages of results. I am just looking to buy 1 for now but if it works out I'll buy a bunch. Any tips on the best source for sensors? thanks

I think the Sensirion SHT7X series sensors are a good value. They are about as accurate as you can get and you don't have to jump through any hoops to get that accuracy. They give you a digital output of relative humidity and temperature that has already been linearized via the built in calibration coefficients. If you take a look at how other sensors have to interface, you see that they require more signal conditioning and/or calibration. Interchangeability may also be a deciding factor for you.

My recommendation would be to purchase a SHT75 which comes pre-mounted on a tiny pcb and has easy to terminate leads. Unfortunately they are not carried by Digi-Key. I get mine from Newark for $35.18 in singles. That way you will have a reference standard against which you can evaluate less expensive sensors. You may even find that it is the most cost effective, in the long run.

Some of the really cheap sensors might do the job in some of your applications. If that's the case, you can use the SHT75 to calibrate them over the range you intend to use them.

By the way, I don't work for Sensirion nor do I own any stock in the company. :) I have just found their sensors to be a very good value by comparison to others.

http://www.sensirion.com/en/pdf/product_information/Datasheet-humidity-sensor-SHT7x.pdf

The Sensirion SHT11 may seem expensive at first but it does a lot of work for you. Parallax makes these pre-mounted as well. So, I also recommend these sensors. I have some arduino code I cobbled together for it posted somewhere in the forums.

The other cheaper sensors tend to have you assembling Instrumentation op amp and possibly a higher resolution A/D converter. By the time you have all that put together... you might be closer to the price of the Sensirion parts... but you won't get the digitally computed response send via modified I2C/SPI or whatever they want to call the interface.

I looked at a lot of parts just like you before I decide on the sensirion part... and now that I got it working quickly and easily... I'm happy I chose it.

I have several SHT-11 Sensirion temperature / humidity sensors mounted on a board with 0.1" male pins. I've been thinking about putting them on ebay.

You may like these: http://www.flickr.com/photos/flyboy19/3651924379/in/photostream/

thanks for all the responses. I probably will go with one of the Sensirion sensors. Every post I have read has said they are rock solid. That is a good idea to also get some other cheaper sensors and calibrate them with the Sensirion. As for flyboy, how much do you want for 1 or more. Or just let me know when you put them on ebay. I want to play around with one for orchid growing. thanks

I needed some humidity sensors to monitor the humidity in my pump house a while back, and found some on ebay. Problem was, they only sold a bag of about 50 or 100. It was only about 20 bucks for the whole bag (iirc), so if you send me your address I'll mail you one for free . ;)

Also, after much searching, I found a data sheet on them too. It's pretty cryptic but it helped with the coding and interfacing. I'll see if I can find it when I get home this evening. They seem to work pretty good with the Arduino, but who knows how accurate they really are.

Update: The datasheet for the SYH-2R is at http://www.rhopointcomponents.com/images/SYH-2R.pdf. The ones I have are the SYH-1, which is very similar.

Wow, at that price you could use them for pcb standoffs. :D

I'm curious to see the data sheet if you can find it.

thanks again everybody. god i luv the internet. Just a random unreleated topic. I have a thousand ideas and will have 1 arduino. How many boards do you guys have and do you just build them yourselves? I saw a cheapduino on the instructables site that costs 10 bucks each i think. Is that as cheap as it goes?