DHT22 - 10x Photon power devices, only half reading correct humidity

Troubleshooting
1

Hey guys,
We have a board that contains the Photon and a few sensors (one of which being the DHT22). This is powered from a 12VDC power adaptor.

Out of 10x of these devices, half of them read the correct humidity, and the other half the humidity is generally off by up to 15%.
The temperature between all devices is always within 1/8 of a degree F.

We have multiple commercial temp/humidity sensors so we can verify what the real value is, and what the DHT22 gives us. Half of our devices humidity levels match the commercial devices, and half are off by 15%

One of the weird things is that the values all match… meaning all the ones that have good readings are all reading the identical value. All of the ones that have bad readings all have the identical bad reading.

All of the DHT22 sensors react to change in humidity and change in temperature, its just this humidity is off like I mentioned above.

Has anyone else had a similar experience with this, or know what might be the problem?
I am trying to determine if these sensors are just crap, or if there is something we are doing wrong?

Here is my schematic for power, photon, and dht22:

dht22_problem_1.jpg1756Ă—754 126 KB

Thanks again guys and any help is greatly appreciated!

EDIT:
This is the library we are using for reference:
https://github.com/russgrue/adafruit_dht_library

2

Is the raw data identical as well? I use a slightly modified version of https://github.com/liyanage/maxdetect-rht03-humidity-sensor in my code here to get the raw data (for checksumming, etc.) in addition to the usual output:

If data is coming in absolutely identical (and the data varies in lockstep as you described) then I’d suspect a code problem before a hardware thing (e.g., initializing several sensors and accidentally making them all point to the same single object)… post some code that exemplifies the problem.

1 Like
3

Hmm… does the “bad” reading follow the sensor? Try swapping a good and bad sensor.