Problems with the new DHT12 Humidity sensor !

[JacquesBBB]

Hi All,

I have recently ordered 10 DHT12 sensors  on aliexpress.
which were presented  as improved form of DHT11.
After some preliminary testings, I have set up a more complete experiement with 9 sensors at the same time.

They give answers that are extremely different for the humidity. Not at all within the advertised specs of the  maker (AOSONG) which says 5% for the DHT11 (did not find the DHT12 datasheet)

The temp seems OK, but

I got   48%, 52%,  56%,  59%,  61%,  68%, 69%, 72%, 72%    for the Humidity output

so  a max difference of 24%  which is  huge.
I am presently claiming for a partial (50%) refund.

[singapol]

I have no experience either. but hope this helps: Check sampling period of DHT22. Datasheet says :
RH response time min. 6sec. max.15sec. typical -10sec. Also check your code. Are you using shielded wires as recommended? there is a way to rehabilitate sensor if contaminated, see datasheet.

DHT11 (Aosong) sensor specs:  https://akizukidenshi.com/download/ds/aosong/DHT11.pdf

DHT project:
http://www.micropik.com/PDF/dht11.pdf

 http://www.best-microcontroller-projects.com/dht22.html

http://playground.arduino.cc/Main/DHTLib

[kripton2035]

for me dht11 have always been not precise.
so better than dht11 can be ... less not precise ?
go and try the dht22 and you will have decent results.
then try sensirion sht11 and taste a real precision sensor (but for some 15 euros each !)

[JacquesBBB]

Thanks to all,

The sensors are new,  and just on the breadboard, so no problems of soldering, heating, deteriorating of any kind.
For the wiring,  I  believe that the present wiring is perfectly fine for these kind of low speed communication.

As an example, I have done the same experiment  with 5 brand new DHT22

Hum: 63.00 % 60.60 % 63.60 % 65.50 % 66.30 %     Temp: 24.80 C 23.70 C 23.40 C 22.90 C 23.10 C
Hum: 63.00 % 60.60 % 63.50 % 65.50 % 66.60 %     Temp: 24.80 C 23.70 C 23.40 C 22.90 C 23.20 C
Hum: 63.00 % 60.50 % 63.50 % 65.40 % 66.30 %     Temp: 24.80 C 23.70 C 23.40 C 22.90 C 23.10 C
Hum: 63.00 % 60.50 % 63.50 % 65.50 % 66.30 %     Temp: 24.80 C 23.70 C 23.40 C 22.90 C 23.10 C
Hum: 63.00 % 60.50 % 63.50 % 65.50 % 66.40 %     Temp: 24.80 C 23.70 C 23.40 C 22.90 C 23.10 C
Hum: 63.00 % 60.50 % 63.60 % 65.50 % 66.50 %     Temp: 24.80 C 23.70 C 23.40 C 22.90 C 23.10 C
Hum: 63.10 % 60.60 % 63.60 % 65.50 % 66.50 %     Temp: 24.80 C 23.70 C 23.40 C 22.90 C 23.10 C
Hum: 63.10 % 60.60 % 63.60 % 65.50 % 66.50 %     Temp: 24.80 C 23.70 C 23.40 C 22.90 C 23.20 C


and the  output is more reasonable :  less than 6 %   (± 3%)  variation among the sensors (close to the ± 2% of the  datasheet )/ 

I had tested once a DHT11 and found that  the output was not very good, but I had some expectations on the DHT12.
I am afraid it looks even worse.

I should try the sensirion, but up to  now, I  have not because of the price.  For a single one, its OK, but if you intend to have dozens of
them,  you like to have a cheaper one. I am afraid I will stick to the DHT22 (3$  vs 1$ for the DHT12).

I would be obliged if any one has a link to the real  datasheet of the DHT12.

Some tests on    the real precision of other humidity sensors are also welcome !

[kripton2035]

so why not use these dht22 ? they seems fine.

[mcauser]

Do you get the same results when you use the I2C interface?

Pin 1 - VCC
Pin 2 - SDA
Pin 3 - GND
Pin 4 - SCL

Don't forget to add pull ups on both SDA+SCL.

[Moseven]

The DHT11 and DHT22 are very inaccurate for the humidity. I have a DHT11 that says 31% when it should be 80%. For more accuracy a capacitive humidity sensor is needed. Adafruit has selected this one : https://www.adafruit.com/products/2857.

I don't know why the DHT11 and DHT22 are so inaccurate. Perhaps they are not calibrated, or the humidity-resistive part got a few chemical fumes. I think the DHT22 has a DS18B20 with a microcontroller inside. Therefor the temperature of the DHT22 is the only good thing.

[kripton2035]

from adafruit web site : https://learn.adafruit.com/dht/overview

DHT11

    Ultra low cost
    3 to 5V power and I/O
    2.5mA max current use during conversion (while requesting data)
    Good for 20-80% humidity readings with 5% accuracy
    Good for 0-50°C temperature readings ±2°C accuracy
    No more than 1 Hz sampling rate (once every second)
    Body size 15.5mm x 12mm x 5.5mm
    4 pins with 0.1" spacing

DHT22

    Low cost
    3 to 5V power and I/O
    2.5mA max current use during conversion (while requesting data)
    Good for 0-100% humidity readings with 2-5% accuracy
    Good for -40 to 125°C temperature readings ±0.5°C accuracy
    No more than 0.5 Hz sampling rate (once every 2 seconds)
    Body size 15.1mm x 25mm x 7.7mm
    4 pins with 0.1" spacing