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Topic: Humidity sensor (Read 613 times) previous topic - next topic

dtokez

Feb 10, 2012, 01:09 pm Last Edit: Feb 10, 2012, 03:20 pm by dtokez Reason: 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?

kucza83

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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" ;)

But dont worry, its pretty straight forward ;)

Quote
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..

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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)


dtokez

Thanks for fixing the typo :)

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?


robtillaart


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

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

kucza83

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

Go for it:-P

Simpson_Jr

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 ?


robtillaart


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 ;)
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

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