Big difference between DHT22 and BMP/E280

opendata-stuttgart / sensors-software

sourcecode for reading sensor data

572 stars 310 forks source link

Big difference between DHT22 and BMP/E280 #665

Open jsturm opened 4 years ago

jsturm commented 4 years ago

I have 2 temp sensors next to each other installed in my airrohr: DHT22 and BMP/E280 The readings are verry different.

Is this normal? The DHT22 seams to show the more realistic values, compared with the values of the local meteorological station.

Achim

zoomx commented 4 years ago

BMP280 and BME280 are known to overestimate temperature so datasheet and Bosh site describe them as Perssure sensor and Pressure and Humidity sensor. BME280 has better perfomance on Humidity than DHT22 http://www.kandrsmith.org/RJS/Misc/Hygrometers/calib_many.html https://wiki.liutyi.info/display/ARDUINO/v9+Sensors+Board

ricki-z commented 4 years ago

The overestimation for the BMp/E280 is only in "normal" (continuous) measurement mode. In continuous mode the Bosch sensors will become warm and the measured temperature is getting higher. This can be disabled and we do this in our firmware. Take a look at this device: https://api-rrd.madavi.de/grafana/d/q87EBfWGk/temperature-humidity-pressure?orgId=1&var-chipID=esp8266-1027427 The temperature of the BME280 is lower than those of the DHT22.

stickybyte commented 4 years ago

@ricki-z how is that working in the firmware? I dont see a switch for that.

zoomx commented 4 years ago

This instruction bmx280.takeForcedMeasurement(); (about line 2698 in main sketch) mean that measure is done only when requested. See datasheet.