Variation in values from different DHT22 units

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Hi there, first time here. Hope I’m doing the right thing(s)

  • Already failed … as new user I can only post one inline image. :face_with_open_eyes_and_hand_over_mouth:

I have 3 DHT units.

All three in the same room within 100mm of each other.

2 are of the kind self contained using a ESP01-S (*Picture removed)
DHT & ESP01-S

The other is the type attached to a nodeMCU eps8266 as a separate unit. (*image also removed)
DHT22 for WES8266

The the bottom 3 in this image are the ones in question.
The ‘Workoom’ is the one attached to the NodeMCU as are the ‘Bar’ and ‘Master Bed’ this all seem to correlate with only minor differences between them and they are separated by by one floor each.

Screenshot 2023-11-13 at 15-19-32 User Dashboard – Home Assistant
Screenshot 2023-11-13 at 15-19-32 User Dashboard – Home Assistant540×844 21.8 KB

So to confirm the bottom three are in one room next to each other on a desk.
The others are in other parts of the house.

As can be seem there is 1.5 degree difference between Outside, Living and Workroom. Also there is about 15% humidity difference between the units.

Is anyone aware of any idiosyncrasies when using these units

TIA
Mike

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They are probably the bottom off the barrel (except for maybe DHT11) for accuracy, but if you calibrate them and apply filters to the sensor using your calibrated values, they are fine.

Google “calibrating DHT22” for some ideas. Temperature is relatively easy if you have an accurate thermometer. Humidity involves some mucking around with saturated brine solutions etc.
Also see Calibrate Linear and Calibrate Polynomial in Sensor Core:

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in my experience every sensor I have ever setup with esphome or tasmota has needed to be calibrated. I use a known good thermometer and calibrate to that. Those sensors ESP01-S are also notorious for giving dodgy readings as the sensors are heated up by the esp.

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Thanks all perfect solution, learning all the time!!
Thanks guys.