Problems with the  new DHT12 Humidity sensor !  - Page 1
Forum section: electronics / beginners

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: July 28, 2016, 03:38:38 pm
content: 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, butI got 48%, 52%, 56%, 59%, 61%, 68%, 69%, 72%, 72% for the Humidity outputso a max difference of 24% which is huge.I am presently claiming for a partial (50%) refund.

author: singapol
author_rank: Frequent Contributor
timestamp: July 28, 2016, 06:21:19 pm
content: 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.pdfDHT project:http://www.micropik.com/PDF/dht11.pdfhttp://www.best-microcontroller-projects.com/dht22.htmlhttp://playground.arduino.cc/Main/DHTLib

author: kripton2035
author_rank: Super Contributor
timestamp: July 28, 2016, 07:47:58 pm
content: 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 !)

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: July 28, 2016, 08:17:49 pm
content: 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 DHT22Hum: 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 CHum: 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 CHum: 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 CHum: 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 CHum: 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 CHum: 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 CHum: 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 CHum: 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 Cand 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 ofthem, 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 !

author: kripton2035
author_rank: Super Contributor
timestamp: July 29, 2016, 06:34:07 am
content: so why not use these dht22 ? they seems fine.

author: mcauser
author_rank: Newbie
timestamp: August 05, 2016, 05:22:40 am
content: Do you get the same results when you use the I2C interface?Pin 1 - VCCPin 2 - SDAPin 3 - GNDPin 4 - SCLDon't forget to add pull ups on both SDA+SCL.

author: Moseven
author_rank: Newbie
timestamp: August 06, 2016, 03:04:33 am
content: 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.

author: kripton2035
author_rank: Super Contributor
timestamp: August 08, 2016, 07:56:16 pm
content: from adafruit web site :https://learn.adafruit.com/dht/overviewDHT11Ultra low cost3 to 5V power and I/O2.5mA max current use during conversion (while requesting data)Good for 20-80% humidity readings with 5% accuracyGood for 0-50°C temperature readings ±2°C accuracyNo more than 1 Hz sampling rate (once every second)Body size 15.5mm x 12mm x 5.5mm4 pins with 0.1" spacingDHT22Low cost3 to 5V power and I/O2.5mA max current use during conversion (while requesting data)Good for 0-100% humidity readings with 2-5% accuracyGood for -40 to 125°C temperature readings ±0.5°C accuracyNo more than 0.5 Hz sampling rate (once every 2 seconds)Body size 15.1mm x 25mm x 7.7mm4 pins with 0.1" spacing