[Gta04-owner] Using BMP085

Dr. H. Nikolaus Schaller hns at goldelico.com
Tue May 29 13:25:32 CEST 2012


Am 29.05.2012 um 13:16 schrieb Benjamin Deering:

> I did some work with temperature sensing on GTA02 for my ski wax chooser program.  I tried BMP085 mounted outside of the middle part of the case and still did not get good readings.  A later experiment showed that a lot of heat could transfer through the wires to affect the readings.  I ended up installing an MLX90614 infrared temperature sensor.  That works well.

Yes, the MLX90614 is a chip like what I think we should add to a future GTA04
release for doing reliable outside temperature measurements.

> 
> Pictures of BMP085 install, BMP085 test, and MLX90614 install:
> http://www.jeepingben.net/index.php?level=album&id=24
> http://www.jeepingben.net/index.php?level=album&id=26
> 
> Ben

BR,
Nikolaus

> 
> On 05/29/2012 05:55 AM, Denis Shulyaka wrote:
>> Hi,
>> 
>> 2012/5/29 Dr. H. Nikolaus Schaller<hns at goldelico.com>:
>>> 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).
>> What about temperature sensors inside gyro and accelerometer? Are the
>> chips mounted farther from the CPU?
>> 
>>> 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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