DHT11 accuracy

I want two temperature readings in my greenhouse, one inside and one outside. In the case of two DS18B20 sensors they have to be identified in order to assign them. That’s not impossible but if one sensor fails it is a major task to find the new identity and write it into the code - not possible if you don’t know code and haven’t an IDE!

I have a DHT11 reading internal humidity which produces a temperature reading simply. This offers a solution but the temperature reading isn’t accurate. Is it a known fault, is there a way to correct it or is the sensor faulty?

Neither.
The DHT11 is a poor quality sensor, especially with the humidity readings.
The DHT22 is better, but not brilliant.
What accuracy do you need with the humidity readings?
Good quality and accurate humidity sensors are fairly costly.
The SHT15 is a much better sensor.

DHT11 and accuracy: An oxymoron.

Well mauried, the humidity reading in a greenhouse doesn't need to be that accurate but it does need to be accurately repeatable. What I mean is that if a reading of 70% is given at one point, it will be 70% at every ensuing and equal point.

It is also necessary that in the event of a device failure, the replacement device will need to indicate 70% at the same point. Am I making myself clear?

this raises an important point that has only just occurred to me! If a device does fail the I2C address will have to be amended and most owners of the controller I have in mind won't be able to do that!

DHT11 and DHT22 are really poor sensors. I replaced nearly all DHT22 already. You can find Si7021 breakout boards for very cheap in asia. These sensors are really great and I also have one for measuring outside temperature and humidity. I can only recommend those sensors, they play in a different league!

These boards have an LDO and level shifter on board and thus can directly work with the 5V from Arduino:

Find attached a graph of todays temperature and humidity outside (I’m living at the foot of a small hill with forrest, it is really humid here). The DHT22 went into latch up very fast and didn’t get below 70% at some point anymore. Totally different with Si7021. Really calibrated, repeatable, interchangeable.

2016-04-03-si7021-out-day.png

I know this an old thread but Google showed me this as one of the results as I was figuring out the inaccuracy of my DHT11 sensors. It turns out my comparisons are correct.

However this thread got me intrigued by the Si7021. I always thought the BME280 is a better sensor overall. I Googled for comparison and found this result:
https://www.kandrsmith.org/RJS/Misc/Hygrometers/calib_many.html

Overall both sensors are good, but my recommendation still goes with the BME280.

Adrifran39:
Well mauried, the humidity reading in a greenhouse doesn't need to be that accurate but it does need to be accurately repeatable. What I mean is that if a reading of 70% is given at one point, it will be 70% at every ensuing and equal point.

Did you ever get an answer on that?
I know the consensus is that the DHT11 is dreadful, but I have a couple in the box and I'm wondering just how bad they are...

Try HTU21D/SHT21/Si7021 or AHT10. All of them are inexpensive and very accurate.

Read these
http://www.kandrsmith.org/RJS/Misc/Hygrometers/calib_dht22_dht11_sht71.html
http://www.kandrsmith.org/RJS/Misc/Hygrometers/calib_many.html

Don't waste your time on a necrothread from almost 4 years ago.

OP has no doubt already found a solution, or has moved on to other projects.