DHT22/AM2302: Wrong values

ESPHome
1

Hi all,

I have ordered some DHT22 at Aliexpress (https://de.aliexpress.com/item/1005005203616199.html). Unfortunately the measurement is quite bad:

Measured → Real values:
Temperature:

  • 16.4 → 8.2
  • 19.4 → 16
  • 19.6-> 19.6
    Humidity:
  • 48.8 → 65
  • 50.2 → 59
  • 50.9 → 55

My sensor is connected to an ESPCam, powered with 3,3V and has a 4,7K pullup. The config looks as followed:

sensor:
  - platform: dht
    pin: 15
    temperature:
      name: $friendlyname Temp
      filters:
        - sliding_window_moving_average:
            window_size: 15
            send_every: 15
    humidity:
      name: $friendlyname Humidity
      filters:
        - sliding_window_moving_average:
            window_size: 15
            send_every: 15
    update_interval: 15s
    model: AM2302

I have tried different models (dht22, …) in the config and also checked if the pullup has any impact. Temperature impact from other components, light, sun, whatever can get excluded (5cm cable outside the casing).

Anybody any idea what I can do else?

2

Have a look what you get on logs.
Be aware that your readings are not realtime (15x15s).

SHT3x or SHT4x

3

Thanks for the hint.

The logs dont tell anything special:

[D][dht:042]: Temperature 21.9°C Humidity 59.2%

I have tried it also without the filter, no changes…

4

If you don’t get errors on logs, there’s not a lot to do. It’s crap. But usually temperature readings are reasonable and you can use calibrate_linear filter to improve results. Humidity readings are not accurate enough to be usable.
If you get 16.4 → 8.2, just throw it to the trash and get SHT.

5

DHT22 sensors aren’t the most accurate but they’re not this bad:

Even the DHT11 isn’t that bad.

And the bad temperature reading will affect the relative humidity measurement.

How close is your sensor to the ESP board?

The wifi modules on the boards heat up considerably which affects the sensor.

Also second vote for the

Though even that will have trouble with self heating if you put it close tot he ESP.

1 Like
6

How close is your sensor to the ESP board?
I first had the same thought. But I have created and printed a new casing which places the sensor completely outside of the case with >1cm space to the casing where the ESP is located in. So i thing that should be fine.

Well then I think I need to get a new one …