[INFO] Compare Sensors DHT11, DHT22, Dallas DS18b20, BMP180

[Juan Pinto]

Hi all, I worked a long time with cheap DHT11 and DS18b20, now I added on 2 nodes (are on the same situation) with 4 sensors,  DHT11, DHT22, Dallas DS18b20 and BMP180.

What meassures:

DHT11 - Temperature, Humidity

DHT22 - Temperature, Humidity

Dallas  - Temperature

BMP    - Temperature, Barometric Pressure

Price: 

DHT11 ~0.5€

DHT22 ~2.5€

Dallas  ~0.4€

BMP    ~0.9€

PROS:

DHT11 - Cheap

DHT22 - Precise

Dallas  - Cheap, Precise

BMP    - Measure Presure

CONS:

DHT11 - Non Precise

DHT22 - Expensive

Dallas  - Not meassures Humidity

BMP    - Non Precise on Temperature Reading.

Conclusion: 

DHT11 is a cheap sensor that have Temperature and Humidity on the same sensor, but isnt have good readings, I suggest for reference values only.

DHT22 is a very good sensor, very precise readings, It cost more but if you want real Humidity values this is what you need, maybe you can put one or two (inside, outside of home) 

Dallas its precise and cheap, good to take many readings at home, can be connected one-wired. Suggested to meassure temperature on the different rooms.

BMP, note that the Temperature Sensor it's inside the electronics and this is why take readings about 3-4º higher than the real temperature, but its a good reference and I think its very important read the Barometric pressure, if this changes drastically the weather does. Isn't an expensive sensor and I suggest to have just one. 

Sorry if I not explained well, but I think this will be clear with this emoncms chart:

NOTE: DHT22 its the YELLOW LINE

http://emoncms.org/dashboard/view/comparativ?embed=1&apikey=defe9753dbe89afd85ac5fed65eb17e8

Regards

[Di Maio, Dario]

Good sharing!

From Mobile.

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[Marko S]

Juan what kind of thermometer and humiditiy-meter did you have for a reference to  compare against to the sensors measured? Did you compare just temperature or also humidity? Is DHT22 also best for humidity and how much difference is between 22 and 11 (I see 10-15% difference).

Dne ponedeljek, 07. december 2015 23.54.55 UTC+1 je oseba Dario Di Maio napisala:

[Juan Pinto]

Hi, Dallas Sensor its a good reference sensor, I don't have any other more precise.

 

On the Emoncms link you can see a chart with humidity values, DHT11 isn't a good sensor.

 

Regards.

 

 

 

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[Marko S]

But how do you know that Dallas sensor is giving the "right" value :D?

Dne sreda, 09. december 2015 16.07.25 UTC+1 je oseba Juan Pinto napisala:

[Juan Pinto]

Dallas is one of the most used sensors worldwide and they are more precise than other "comercial" sensors I have at home, don't need calibration and I tested with various and all give me the same value. 

 

I use thermistors on the 3d printer, calibrated to read precisely the values to read from ambient to 250º, I have the same reading on the printer and on the dallas too.

 

Regards

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[Andreas Karl]

Is there any humidity only sensor you can advise?

[Juan Pinto]

No :( if someone knows about other sensors please post here.

 

Regards

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[Artūrs Stīpnieks]

Nice information, thanks. It would be nice to see DHT21 data as well, they are cheaper then 22's, but more expensive than 11's. I haw couple of them, couple of 11's, but do not have any 22's (because they are quite expensive, and because I want to monitor every room (so the magic number I need is 14 + outside)), so I could not compare with that, but I could compare it with Dallas sensor in theory, but I haw very limited free time sadly.

[Electroguard]

Dallas has an accuracy of ± 0.5° between -10°C to +85°C and can measure extremes between -55°C to +125°C.
They are also the cheapest, and you could get your magic number 14 for less than 14 euros.

Use a DHT where you are also interested in humidity. Most sensors give readings well below freezing, but the low spec DHT11 only measures from 0 to 50 and with an accuracy of only ± 2°
The DHT21 and DHT22 both give ± 0.5° between -40°C to +80°C

The BME280 (not BMP180) is the most expensive, but if you also want one for reading barometric pressure (and why would you want more than one to do that), it gives pressure, humidity, and temp (-40 to +85°C) all in one.

[Juan Pinto]

I haven't a DHT21 to compare sorry.

 

To meassure temperature I suggest DS18B20, and if you want to have many sensors on the same node you can connecta various on the same PIN, this funcion it's only for Dallas, not DHT and others.

 

Thanks for the INFO Robin, I don't know about BME280

 

NOTE: You can see some strange readings on past days at emoncms, this was my tests and resets on the board, so isn't a problem with the sensors, just tests.

 

Regards

[Artūrs Stīpnieks]

I agree with Juan, good information, have not got the time to compare them all, thanks again.