[Tinkerphones] Fun with BME280 inside GTA04A5

Andreas Kemnade andreas at kemnade.info
Tue Sep 19 08:01:19 CEST 2017


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.

So the question is: does the hygrometer produce sane output when the gta04 case
is closed?

> 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?

> 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.

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

Regards,
Andreas
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