DHT11 temp too high !

hi, ive just started playing about with this so sorry for being a noob!

I've got one of the relatively cheap dht11 sensors from ebay so wasn't expecting much... I have got it working and outputting the values to my lcd.

the only thing is the temperature reading is a bit high...my room is about 15c and its reporting about 23c !?!?

is there anyway to calibrate ?

or am i using the wrong library (downloaded form adafruit) ?

cheers
onis

Check to make sure you have it wired correctly, I've learned the hard way they overheat (and melt) when miswired.

Let it sit running for a while, it may be something you've done to it to make it read high, ie, held it in your hand, or have it near a heat source. Use jumpers to locate it away from the reset of the project, see if that changes anything.

If it's always 8c over, then just subtract 8 from the reading.

Find a few known temp sources, and compare.

yup tried all that its deffo wired correctly and temp goes up and down.... just not quite right.

so maybe its just a cheap Chinese copy might try a dht22 or even splash out on a 44 as the temp accuracy is quite important in this project.........if fact it would be a matter of life and death !!!!!

Have an accurate thermometer handy?
Put both the thermometer and the dht11 in a refrigerator, when the temp gets to lowest point on the thermometer, record the dht11 and thermometer temp.
Then place the thermometer under a heat source at a distance where the temp will be under 122F(dht11 max. temp.).
When the thermometer rests at a high temp, place the dht11 in the same location and again record both resting temps.
You can use those recorded temps to calibrate the dht11 temp to the actual temp.

that sounds good but unfortunately i do not have a thermometer, i was using my house central heating thermostat as that's manually calibrated and pretty accurate, plus it felt cold so couldnt have been 23/24c...its under 10c here in London right now !

onisuk:
yup tried all that its deffo wired correctly and temp goes up and down.... just not quite right.

so maybe its just a cheap Chinese copy might try a dht22 or even splash out on a 44 as the temp accuracy is quite important in this project.........if fact it would be a matter of life and death !!!!!

Where do you source the 44's?

I can't find ANY 33's or 44's on the usual suspects (eBay, Amazon, Aliexpress, Bangood)
Thanks.

onisuk:
that sounds good but unfortunately i do not have a thermometer, i was using my house central heating thermostat as that's manually calibrated and pretty accurate, plus it felt cold so couldnt have been 23/24c...its under 10c here in London right now !

Something to consider is right now our heat is set for 70 F (21.1C) and the living room thermostat is reading 72 F (22.2C) . The thermostat is about 5 feet off the floor and today was a nice day so the furnace has not run. However, floor to ceiling is 8 feet (2.44 meters) and on some days I can measure a 8 - 10 degree difference between floor and ceiling and even that varies room to room.

The only way to know the actual error of the DHT 11 is as was mentioned, compare it to a known accurate temperature because less an accurate "known" you really have no way to know. You want a good thermometer of known accuracy for comparison.

Ron