[Gta04-owner] Using BMP085

Dr. H. Nikolaus Schaller hns at goldelico.com
Tue May 29 11:35:21 CEST 2012


Hi Neil,

Am 29.05.2012 um 11:18 schrieb Neil Jerram:

> Neil Jerram <neil at ossau.homelinux.net> writes:
> 
>> Hooray, it works, thank you:
>> 
>> gta04:~# echo bmp085 0x77 > /sys/bus/i2c/devices/i2c-2/new_device
>> gta04:~# find /sys -name "*pressure*"
>> /sys/devices/platform/omap/omap_i2c.2/i2c-2/2-0077/pressure0_input
>> gta04:~# cat /sys/devices/platform/omap/omap_i2c.2/i2c-2/2-0077/pressure0_input
>> 92192
> 
> I've been looking now at temperature too
> (/sys/devices/platform/omap/omap_i2c.2/i2c-2/2-0077/temp0_input).
> 
> I'm getting 33 degrees C [1], although the actual temperature in my
> house is only 16 degrees C.  Is that because the temperature reported is
> intentionally that *inside* the GTA04, and hence reasonably higher than
> ambient?  If so, is 33 degrees a reasonable temperature to be measuring

Yes.

> inside the GTA04?

Yes. It can go up to 45-50 degrees if the CPU is running at full power.
The BMP085 is mounted directly near the CPU and the PCB also
distributes the heat of other high-power components (WLAN). 

The temp measurements of the BMP085 are done for compensating the
pressure readings and are not intended to indicate the correct outside temp.

Maybe, we can try to use a thermopile sensor in some future device.

> 
> [1] To be precise, I mean that ((VALUE + 5) / 10) = 33, where VALUE is
> `cat /sys/devices/platform/omap/omap_i2c.2/i2c-2/2-0077/temp0_input`.
> 
> Regards,
>        Neil
> 

BR,
Nikolaus



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