On Tue, 19 Sep 2017 18:46:03 +0200 "H. Nikolaus Schaller" <[email protected]> wrote:
> Hi, > > > Am 19.09.2017 um 18:38 schrieb Andreas Kemnade <[email protected]>: > > > > On Tue, 19 Sep 2017 08:42:21 +0200 > > "H. Nikolaus Schaller" <[email protected]> wrote: > > > >> Hi, > >> > >>> Am 19.09.2017 um 08:01 schrieb Andreas Kemnade <[email protected]>: > >>> > >>> Hi, > >>> > >>> On Sat, 16 Sep 2017 21:57:32 +0200 > >>> "H. Nikolaus Schaller" <[email protected]> wrote: > >>> > >>>> Hi, > >>>> since we a re a tinkerphones community, I just had > >>>> some fun with the GTA04A5 I want to share :) > >>>> > >>>> Maybe you know that there is a BME280 inside. It > >>>> is a combined barometer, thermometer, hygrometer > >>>> sensor chip. > >>>> > >>>> And it has full Letux kernel support so that it > >>>> works out of the box. > >>>> > >>> Well, to produce nice input there still needs to be some logic, > >>> Probably some power management logic. like suspend for some minutes to > >>> let the > >>> gta04 cool down and read then the sensor directly after suspend. > >> > >> That is easy: > >> > >> ./measure-suspend 300; cat > >> /sys/bus/iio/devices/iio:device5/in_humidityrelative_input > >> > >> Or integrate it into a new script that does similar things as > >> ./measure-suspend > >> for suspend + wakeup by RTC. > >> > >>> > >>> So the question is: does the hygrometer produce sane output when the > >>> gta04 case > >>> is closed? > >> > >> Yes, that would be nice if someone could find out. > >> > >>> > >>>> It was simple to do some readout: > >>>> > >>>> cat /sys/bus/iio/devices/iio:device5/in_humidityrelative_input > >>>> > >>>> Here is the full sequence when breathing upon > >>>> the sensor (of a board not installed in the case): > >>>> > >>>> root@letux:~# while true; do cat > >>>> /sys/bus/iio/devices/iio:device5/in_humidityrelative_input; sleep 1; done > >>>> 35.765625000 > >>> root@letux:/sys/bus/iio/devices/iio:device1# cat in_temp_input > >>> 39100 > >>> root@letux:/sys/bus/iio/devices/iio:device1# cat in_humidityrelative_input > >>> 78.563476562 > >>> > >>> Hmm, that does not make sense. 78% at 39 C. It was not in > >>> my pocket. It is in a train. So why it is so humid? > >> > >> Hm. Maybe the sensor needs calibration? More likely it is too much > >> influenced by the device temperature. > >> > >> Maybe printing temperature and humidity in a loop right after booting > >> shows some drift/correlation? > >> > > That should clearly be monitored. Of course I measure some innner device > > temperature and not outdoor temperature but I do not understand why a high > > device temperature would create a wrong humidity. Higher temperature -> air > > can store more vapour -> RH will go down. If I measure something I like to > > understand what I am actually measuring and how it is influenced. > > Well, the sensor might read different values at different temperatures but > same vapour amount. And there may be compensation algorithm in the chip or in > the driver which translates raw data to what we see. These compensation > values may be wrong if mounted inside the case and heated by the CPU. > Hmm, I get better values with a newer kernel... just tried 4.13. Regards, Andreas
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