cheaper temp / humidity sensor: DHT22

(10 posts) (6 voices)

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jbeale

I don't know if you've seen the DHT22 (AM2302) from Aosong Electronics. Runs on 3.3V, has a one-wire serial interface, and at under US$10, it's significantly less expensive than the SHT-11 sensor.

info.php?productsid=10167>

    Technical Specification:   Model DHT22
    Power supply:              3.3-6V DC
    Output signal:             digital signal via single-bus
    Sensing element:           Polymer capacitor
    Operating range humidity:  0-100%RH; temperature -40~80 Celsius
    Accuracy humidity:         +-2%RH(Max +-5%RH); temperature <+-0.5 Celsius
    Resolution or sensitivity: humidity 0.1%RH; temperature 0.1 Celsius
    Repeatability:             humidity +-1%RH; temperature +-0.2 Celsius
    Humidity hysteresis:       +-0.3%RH
    Long-term Stability:       +-0.5%RH/year
    Sensing period Average:    2s
    Interchangeability:        fully interchangeable
    Dimensions:                small size 14185.5mm; big size 22285mm


				Posted 14/11/2010 05:48:09


	
		
			
								
					jcw

				
			
			
				
Ah, great find - thanks! One-wire, eh? There's a plug for that, eh... coming up soon.
Unfortunately, there is one aspect which makes the DHT22 less useful for ultra low-power nodes: the current draw in standby mode is 40..50 µA, according to SparkFun, vs 1..2 µA for the SHT11.



				Posted 14/11/2010 17:43:44
			
		
	
	
		
			
								
					jbeale

				
			
			
				
If the SHT11 is the only other game in town, I'd guess it might still be worth the extra pin and another FET to power-switch the DHT22, for lowest power applications.



				Posted 15/11/2010 06:09:27
			
		
	
	
		
			
								
					jcw

				
			
			
				
Ah, that's a very good point. You don't need any extra components: an I/O pin can easily power a few mA. I'm thinking about using the IRQ pin for this: switched power, for low-power boards that can be turned off. The PIR cannot be turned off, but the DHT22 could indeed - just hook it up to IRQ, and tweak the code accordingly...



				Posted 15/11/2010 12:55:04
			
		
	
	
		
			
								
					jeroen

				
			
			
				
Is the SHT10 not almost the same as the SHT11 ?
The SHT10 is positioned as the low cost (volume) version.



				Posted 15/11/2010 16:23:19
			
		
	
	
		
			
								
					jcw

				
			
			
				
Yes, the SHT is the least accurate version of the SHT1x series. But it doesn't seem to be widely available, AFAICT. I've managed to get a good price on SHT11 in larger quantities, so it's not a show-stopper for me right now.



				Posted 15/11/2010 23:19:04
			
		
	
	
		
			
								
					erisan500

				
			
			
				
Be warned, This is NOT a OneWire sensor !!! It uses 1 wire, but NOT the OneWire protocol.



				Posted 19/11/2010 16:44:15
			
		
	
	
		
			
								
					jcw

				
			
			
				
> This is NOT a OneWire sensor !!!
Ah, thanks - good to know!



				Posted 19/11/2010 17:42:47
			
		
	
	
		
			
								
					adilson

				
			
			
				
There's an arduino lib here http://nethoncho.com/arduino/DHT22/



				Posted 19/01/2011 22:55:22
			
		
	
	
		
			
								
					agorts

				
			
			
				
Any progress with this? I am interested because of the very good price...



				Posted 26/01/2011 20:24:26