[Tinkerphones] Fun with BME280 inside GTA04A5

H. Nikolaus Schaller hns at goldelico.com
Tue Sep 19 08:42:21 CEST 2017


> Am 19.09.2017 um 08:01 schrieb Andreas Kemnade <andreas at kemnade.info>:
> Hi,
> On Sat, 16 Sep 2017 21:57:32 +0200
> "H. Nikolaus Schaller" <hns at goldelico.com> 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 at letux:~# while true; do cat /sys/bus/iio/devices/iio:device5/in_humidityrelative_input; sleep 1; done
>> 35.765625000
> root at letux:/sys/bus/iio/devices/iio:device1# cat in_temp_input
> 39100
> root at 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?

>> Does this trigger new ideas for user interfaces?
> humidity + pressure + temperature is nice for weather forecasts if
> that are outdoor values. You can calculate the dewpoint.
> The dewpoint is a good estimation of the temperature the next morning.
> So you are not surprised too much if it becomes cold.
> You can also estimate the lower cloud base with that.

Nice ideas!

> That is the reason why I have a hih6130-family device with some flow of air
> attached to my bicycle.


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