[Solved] DHT Temperature offset

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Coudn’t find any Information of a temperature offset for the DHT with pimatic-homeduino?

I myself got the DHT11 which is not very accurate, but I have a wall Thermostat which usally is around 1.5-2° lower than the DHT11. So this could be a good way to use it to be more accurate?

Try to calibrate the information you got from you dht11 and the wall thermostat.
Calculate a calibration factor: WALL_TEMP / DHT11_TEMP
Then multiply the result from the DHT11 with the calibration factor.

Example:
DHT11_TEMP = 20°
WALL_TEMP = 18,6°

18,6° / 20 = 0,93
So you would have a calibration factor of 0,93.
20 * 0,93 = 18,6
21 * 0,93 = 19.53
etc…

Try if this works for you.

Thanks for the reply!

The other thermostat is one from my central heating. I cannot connect this at all with pimatic
So I only look for a way to set a static offset to my dht config.

Well it wasn’t meant to correct the value dynamicly, but to be calculated one time by yourself and to adjust the code of homeduino (dht.h) according to the result.
AFAIK there is no option in pimatic to calibrate results via config, but my knowledge is limited and the documentation of pimatic lag behind.

Okay, so I got you wrong

I know the value I want to put in, but I’d like to keep the device I created for the DHT and only add an offset.
Otherwise I will have to work with a variable, which I don’t like.

But it’s nothing too important, I just though I missed something since there is an offset for other devices.

Thank you anyway!

temp offset as well as humidity would be something for the feature request, not only for DHT, generally for temperature measuring imho.

I think we should implement a expressions field like the analog sensor

{
  "id": "homeduino-analog-sensor",
  "name": "AnalogSensor",
  "class": "HomeduinoAnalogSensor",
  "attributes": [
    {
      "name": "voltage",
      "unit": "V",
      "label": "Voltage",
      "pin": 14,
      "interval": 5000,
      "processing": "($value / 1023) * 5"
    }
  ]
}

The processing in Homeduino
https://github.com/pimatic/pimatic-homeduino/blob/master/homeduino.coffee#L940-L943

I will take a look on this.

I have pushed a commit to github for this.
I wait now for the answer from sweetpi.

https://github.com/pimatic/pimatic-homeduino/commit/51c2957a7f58b62738c2caaa9ceba6089c6c8bad

Tip: Don’t read the DHTxx sensors in an interval less then 30 seconds, else the sensor gets too hot and the temperature values are to high.

+1 for this! I’m currently using this:

{
      "id": "sensor1",
      "name": "Sensor 1",
      "class": "HomeduinoRFTemperature",
      "protocols": [
        {
          "name": "weather1",
          "options": {
            "id": 115,
            "channel": 1
          }
        }
      ]
    },
{
      "id": "kamers-links-temp",
      "name": "Kantoor & studio",
      "class": "VariablesDevice",
      "variables": [
        {
          "name": "Temperatuur kantoor",
          "expression": "($sensor1.temperature + 0.4)",
          "type": "number"
        }
      ]
    },

I think with the next update is this implemented.