Weird oscillation with DHT22

ESPHome
1

I have a couple of nodemcus with DHT22 as temperature and humidity sensors. I am observing weird oscillations in the temperature history when the temperature should be relatively constant like this:

dht

The amplitude of the oscillation is ~ 3F and the period is ~ 25 minutes. I don’t think it’s the period of my AC coming on. I am collecting data every 30 seconds. Can’t really see this in the humidity data just noise is ± 1%, which I would expect.
I tried moving average filters, but that didn’t really do anything.

Anyone have an idea what’s going on and how to fix this?

2

How close are your sensors to your nodemcus?

The nodemcu generates a bit of heat.

You could try this config:

  - platform: dht
    pin: D5
    model: DHT22
    update_interval: 15s
    temperature:
      name: "Lounge Room Temperature"
      filters:
        - sliding_window_moving_average:
            window_size: 15
            send_every: 15
            send_first_at: 15
    humidity:
      name: "Lounge Room Humidity"
      filters:
        - sliding_window_moving_average:
            window_size: 15
            send_every: 15
            send_first_at: 15

Gives updates about every 3 minutes which I find is plenty for room temperatures.

3

The nodemcus are too close, but I can’t really find a good 3D printed cases where that is not the case (maybe pun intended). I use this and this case.

But it turns out I was wrong: I covered the sensor to shield it from any air movement and the oscillations went away.

Thanks for your help.