DHT11 moisture sensor failure modes?

H

halleffector

Member

• Jul 30, 2016

• #1

I have a DHT11 to measure the moisture in a room. I've noticed that what previously registered as above 90 now is read as around 10! The value still increases if it gets more humid, but obviously what values I used to define when it is humid and not are no longer valid.

What causes it to degrade like this? Is it simply not a quality product meat for use over time? This has only been in use for a month. But I noticed this was a gradual deterioration.

What should I get instead? I need a reliable sensor.

 

ericgibbs

Well-Known Member

Most Helpful Member

• Jul 31, 2016

• #2

hi,
I use the DHT22 sensor.
Which PIC or MCU type are you using.?

E

 

K

KeepItSimpleStupid

Well-Known Member

Most Helpful Member

• Jul 31, 2016

• #3

Not sure what your using it for, but do you know about the comfort chart?

**broken link removed**

 

S

schmitt trigger

Well-Known Member

Most Helpful Member

• Aug 1, 2016

• #4

I use this one...gives you both temperature and RH. Simple I2C interface.

https://www.adafruit.com/products/1899

 

dr pepper

Well-Known Member

Most Helpful Member

• Aug 1, 2016

• #5

Very recently I pligged a dht22 in backwards, temp still works but the humidity reads 1%.

 

H

halleffector

Member

• Aug 2, 2016

• #6

ericgibbs said:

hi,
I use the DHT22 sensor.
Which PIC or MCU type are you using.?

E

Click to expand...

I'm just using an Arduino Nano.

 

H

halleffector

Member

• Aug 2, 2016

• #7

KeepItSimpleStupid said:

Not sure what your using it for, but do you know about the comfort chart?

**broken link removed**

Click to expand...

This is probably it. Probably just a silly user mistake on my part, nothing wrong with the sensor. I had just moved it when I did the reading, and the sensor was mounted with hot glue. To move it I had to heat up the hot glue again, which probably introduced a huge skew into the readings. Although, from the chart it seems like I should have read _more_ humidity, not less, if it was really hot. But perhaps the heat also just made it really dry?

It works as before again now though. So either it was just an intermittent failure or a user mistake.

Thanks.

 

dr pepper

Well-Known Member

Most Helpful Member

• Aug 2, 2016

• #8

I've just been working on the project that uses the Dht22, having blown the '22 I modded the code to read a Dht11 which I have a few of, and I found that the execution time for the code that reads the Dht11 is much longer than the '22, so much so I had to reduce the read rate to once every 30s to prevent the code from getting ugly.

I read somewhere that silicone can hurt the humid sensor in the Dht, must be some kind of poly or something, some chemist here might know.

 

S

schmitt trigger

Well-Known Member

Most Helpful Member

• Aug 3, 2016

• #9

Not only the DHT sensors are affected by chemical attacks, I once had a bad experience with a HDC1008 which was ruined by the solder flux.

 

dr pepper

Well-Known Member

Most Helpful Member

• Aug 3, 2016

• #10

Had to look that one up, its a more professional version of a dht and board mounted.
The datasheet for the dht implies there is a one wire ds18b20 inside, the actual sensor is just a thermistor by the looks of it, so either the black blob on the board contains a ds substrate or it isnt a ds temp sensor.

 

throbscottle

Well-Known Member

• Aug 4, 2016

• #11

Silicone releases acetic acid fumes when it cures. Probably that.