AVR-Chat

At 10:35 PM 7/14/04 +0000, you wrote:
> > The bigger issue I see is you are talking about an awful lot of
>data for
> > the students to analyze.  For the 1/min you are talking about 42000
> > points.  Will your spreadsheet (or whatever analysis program)
>handle
> > that?  And if it does will it do it w/o slowing to a crawl?  It
>would be
> > easy to create a dummy data file to check that out.
>
>
>oh, so you're saying there are leaves on those twigs ?

I'm not sure we've got to the leaves yet.  BTW, I just checked the 
spreadsheet I use for this sort of thing and it has a max of 8K rows.  If I 
want to seriously play with the data the program I use for that has an even 
smaller limit.



> > One last data question.  What are you trying to track with the
>brightness
> > measurement?  Do you really expect to see a significant change in 1
> > minute?  I would have guessed a 5 minute period made more sense
>(maybe even
> > longer at night).
>
>A bush in shade will see light when the blocking thing moves
>relitaive to the sun.  Imagine tree or tree trunk that acks like
>gnomon.  as the Earth rotates, the Gnomon will appear to move and the
>plant will be blocked for some period.
>
>How much sun a leaf gets from being in shade vs a cloudy day.  That
>sort of thing.

Yep, I'm just questioning the need for a 1 minute resolution.  Assuming you 
are at a reasonable mid latitude, taking measurements in the winter with 
the day getting no shorter than about 8 hours (I'm making this up as I go 
along). 1 minute represents 1/480 or a little more than 0.2% of the 
daylight hours.  Do you reasonably expect to see the difference from even a 
1% drop in light?  Or perhaps more to the point what is the minimum light 
difference you expect to cause a difference in what you are measuring?

In either case you will need a low pass filter to avoid aliasing (now we 
are getting to the leaves). Given the time scales the larger part of that 
is most effectively done in software.

You can quite easily track the average exposure during the sampling period 
(It could even be a no-linear 'average' like an RMS) without needing to 
store results from high frequency sampling.

What I'm getting at is if one plant is exposed to 50% intensity for 5 
minutes and another to 100% for 2.5 min and 0% for 2.5 minutes can you tell 
the difference in the plants responses?

Actually I wouldn't be surprised if you could get away with even longer 
sample intervals.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,
be they legal, genetic, or physical.  If you don't believe me, try to
chew a radio signal. "

                         Kelvin Throop, III