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opendata-stuttgart / sensors-software

sourcecode for reading sensor data
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DHT22 and BMP180 together, which one will win in case of temperature? #227

Closed SunboX closed 6 years ago

SunboX commented 6 years ago

I want to use the DHT22 because I read it has the best accuracy.

For air pressure measurement I want to use the BMP180. But this one also has temperature measurement build in.

So if I use both together, which one will "win" in case of reporting temperature?

miskaknapek commented 6 years ago

Btw. I've been comparing results from DHT22 and BME280, and the BME280 is definitely better with humidity measurements.

On 20 June 2018 at 11:13, André Fiedler notifications@github.com wrote:

I want to use the DHT22 because I read it has the best accuracy.

For air pressure measurement I want to use the BMP180. But this one also has temperature measurement build in.

So if I use both together, which one will "win" in case of reporting temperature?

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SunboX commented 6 years ago

I guess, luftdaten.info will use the DHT22 temperature measurement. Because I read, that I have to tell that I'm also using the BMP180 so it will be manually added to the database. I guess this manually adding step makes sure, that the DHT22 temperature will be used?

PS: I also own a BME280... so if someone tells me, that it also works fine. I maybe use this one instead of the other both. Saves costs (for future sensors) and also saves some wiring.

miskaknapek commented 6 years ago

Thanks for the notes André.

I'm looking at the sensor data ( I'm sort of a data analytics person ) and will do a comparison between the BME280 and DHT22 for humidity data, one of these days…

Bests / m

On 21 June 2018 at 09:00, André Fiedler notifications@github.com wrote:

I guess, luftdaten.info will use the DHT22 temperature measurement. Because I read, that I have to tell that I'm also using the BMP180 so it will be manually added to the database. I guess this manually adding step makes sure, that the DHT22 temperature will be used?

PS: I also own a BME280... so if someone tells me, that it also works fine. I maybe use this one instead of the other both. Saves costs (for future sensors) and also saves some wiring.

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ricki-z commented 6 years ago

For the published data: all sensor data from registered sensors is published. So if both the DHT22 and the BMP180 are registered the temperature of both will be published. Graphs at Madavi.de: graphs are created for all sensors. Maps: there its a matter of implementation. Most maps (if the show temperature and humidity values) will prefer the temperature of the BMP180. But the may also show both. Sensor internal webserver: shows all values Displays (OLED, LCD) connected to the sensor: the order of preference for displayed values is DHT22 DS18B20 -> HTU21D -> BMP180 -> BMP280 ->BME280. So in your case the temperature values of the BMP180 is shown on the display.

SunboX commented 6 years ago

I read, that the temperature differs by 2°C between those both and that the DHT22 reports the more correct temperature.

Do you also have some time to look into this?

ricki-z commented 6 years ago

@SunboX How are they positioned? The temperature sensors should be placed as near as possible to one of the openings.

SunboX commented 6 years ago

I did not investigate both temperatures. It's just what I've read somewhere. My electronics is working, but I have to put everything together now. Maybe today. Thanks for tge hint with the positioning!

ricki-z commented 6 years ago

The slightly higher temperature was for the BME280 (temp., humidity, pressure). The Arduino library for this sensor sets a continuous operation mode as default. And this leads to the higher temperature. We have changed the mode so that the BME280 is only active when needed.

SunboX commented 6 years ago

Ok, I installed it now at it's final destination (with DHT22 and BMP180). Both sensors are close to each other and close to the opening of the airRohr:

https://opensensemap.org/explore/5b28d3891fef04001bd7dfae

The temperature values are slightly different. But it's ok for me, thanks for your help @ricki-z & @miskaknapek !

@miskaknapek I'm really interested in your evaluation. Can you give me a hint please when you are done? (andre.fiedler@me.com)