Humidity sensor

Projects General Guidance
1

Hi all, Id like to add humidity sensing to my project.

I have never tried or even seen a humidity sensor so I'm a bit in the dark here. I don't want to spend much on them. Searching ebay I have come up with these..

http://www.ebay.co.uk/itm/4PCS-X-DHT11-Digital-Humidity-Temperature-Sensor-/200627851859?pt=LH_DefaultDomain_0&hash=item2eb65a1253#ht_4159wt_1163
http://www.ebay.co.uk/itm/2-Humirel-Humidity-Sensor-HS1101-Arduino-Hygrometer-/320743007075?pt=UK_BOI_Industrial_Automation_Control_ET&hash=item4aadc5e363#ht_2953wt_1048

One of them does temperature too but that is not really required although I could use that instead of NTC's

Are there any better options?

2

I have tried or even seen a humidity sensor so I'm a bit in the dark here

I suppose there is missing a "never" :wink:

But dont worry, its pretty straight forward :wink:

One of them does temperature too but that is not really required although I could use that instead of NTC's

Temperature is never a bad thing to measure, and it aint much more pricy, so ill go for the combined sensor..

Are there any better options?

Well, that depends on what you are planning to do with it? I have used those sensors before, and they have worked like a charm 8)

3

Thanks for fixing the typo :slight_smile:

That's re-assuring that you have used them already. I can't get the datasheet to load at the moment from the ebay listing - http://www.egochina.net.cn/eBay/Download/DHT11.pdf

how do you interface to the sensors?

4

Better check the DHT22 as it is more precise, For library and code - http://arduino.cc/playground/Main/DHTLib -

5

Actually i just realized it was the DHT22 i had used :slight_smile:

Go for it:-P

6

I haven't used the dht22, several DHT11s though and 1 out of the 5 I bought really deviates a lot. When the others tell humidity is 50 % or higher it never shows a humidity higher as 20 %. The others luckily don't differ more as 10% from each other, which is good enough for me.

The hs1101 is basically a variable capacitor, you'll need to integrate it in a circuit that outputs a frequency. By checking how high/low the frequency is you can calculate the humidity.

The DHT-11 (and I guess... DHT-22 as well) has a little more electronics inside. They need a power-supply and you can talk with it digital, all you need is an pull-up resistor, 1 free I/O-pin of your Arduino and library/software to talk with 'm.

For measuring temperature I think the DHT-11 is not the best idea. Reading 2 degrees C above and 2 degrees below the actual temperature using 5 sensors is quite a lot. It may be possible to adjust such differences for each individual sensor in a sketch, I simply bought a bunch of accurate temperature sensors and use those instead.

To those with a DHT22-sensor, is temperature measurement much better as the DHT11 ?

7

Used the DHT22 mainly for humidity, I recall it was quite slow in reacting on temperature changes.
For temperature I still prefer a DS18B20,
Played with some LM34's recently which work also quite well - These are 1F/10mV and I prefer them above the LM35 (1C/10mV) because they have a factor 1.8 higher precission for the same price :wink: