On Fri, Jul 8, 2011 at 11:34 PM, Pedro Côrte-Real <[email protected]> wrote:
> On Fri, Jul 8, 2011 at 9:54 PM, Paul Alfille <[email protected]> wrote:
>> Thanks for the report -- I found the error with DS2409 aux/main directories.
>
> That's great, thanks! Is there anything else I should try to debug the
> humidity stuff? I've also just gotten a broken value for the pressure
> sensor so I suspect there is some generic timing bug in the way my
> installation work. Would any of the flextime/altUSB options be worth
> trying?

For some reason the hobbyboard humidity readings are particularly
prone to this. I've had almost 600 wrong readings in just a couple of
days. Anything else I can gather to help debug this?

One thing I did find odd in the code but is unrelated is that the
temperature compensation for the HIH4000 seems to be using the same
formula as for the HIH3600 instead of its different one as presented
here:

http://owfs.org/index.php?page=temperature-compensation

From ow_2438.c
FS_Humid_3600:
        humidity_uncompensated = (VAD / VDD - (0.8 / VDD)) / .0062 ;
        temperature_compensation = 1.0546 - 0.00216 * T ;
        OWQ_F(owq) = humidity_uncompensated / temperature_compensation ;

FS_Humid_4000:
        humidity_uncompensated = ((VAD/VDD) - 0.16) / 0.0062 ;
        temperature_compensation = 1.0546 - 0.00216 * T ;
        OWQ_F(owq) = humidity_uncompensated / temperature_compensation ;

Whereas from the owfs.org page

HIH3600:
RH = (Raw RH) /  ( 1.0546 - .00216 T )

HIH4000:
RH = (Raw RH) /  ( 1.0305 + .000044 T - .0000011 T^2 )

Copy/Paste error? The difference is significant, of the order of 2
percentage points of humidity, much larger than the actual temperature
compensation tends to be.

Pedro

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