Re: [Paparazzi-devel] BMP085 sensor temperature wiht large error

[Prof. Dr.-Ing. Heinrich Warmers]

Hi, Martin
Thanks for the fast correction.

Regards
Heinrich


Martin Mueller schrieb:

> Hi Helge,
>
> the extra noise is from reading the lower three bits of the pressure 
> result wrongly. They are in the higher bits of the XLSB, not the 
> lower, fixed in master:
>
> @@ -130,7 +130,7 @@ void baro_bmp_event( void ) {
>        /* get uncompensated pressure, oss=3 */
>        bmp_up = (bmp_trans.buf[0] << 11) |
>                 (bmp_trans.buf[1] << 3)  |
> -                bmp_trans.buf[2];
> +               (bmp_trans.buf[2] >> 5);
>        /* start temp measurement */
>        bmp_trans.buf[0] = BMP085_CTRL_REG;
>        bmp_trans.buf[1] = BMP085_START_TEMP;
>
> Thanks for looking into that.
>
> As the max conversion time is 25.5ms it could be run at 30Hz without 
> changes, maybe having the temp reading only once per second as 
> suggested in the spec. Some averaging could be done depending on the 
> frequency you need.
>
> Martin
>
> http://paparazzi.enac.fr/wiki_images/Bmp085_scp1000.png
> http://paparazzi.enac.fr/wiki_images/Bmp085_scp1000_fixed.png
>
>
> On 04.08.2011 11:36, Helge Walle wrote:
>
> > Hi,
> > To make sure that the sample rate is not set so high that it interferes
> > with the conversion time of the BMP sensor, I would need to check the
> > data flow with my logic analyzer.
> > I did not do that yesterday evening. However, Increasing freq from "8"
> > to "20" in .../paparazzi/conf/modules/baro_bmp.xml increased the data
> > flow and did not create any problems.
> > The code I used with my Arduino board that made better results was from
> > Sparkfun. I am quite determined to work through the code since I feel
> > sure that this is the right way to go.
> >
> > Regards,
> > Helge.
>
>
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