Laura,

Stuart has it right.  You need to change paradigms here.  You have been
"calibrating" by changing your code to select a new threshold level.

Calibration as normally handled by NXT-G is a process where you in effect
provide a sample dark color to the brick and tell the brick to consider that
color, and anything darker to be 0.  i.e. the light sensor functions on that
brick will now return 0 anytime this or a darker color is encountered.
 Likewise you provide a sample light color and tell the brick to consider
that color and anything lighter or brighter to be 100.  i.e. use of the
light sensor functions will now return 100 anytime this or lighter is
encountered.

So now you've really accomplished 2 things.  You have set low and high
levels for the present conditions and you have probably increased the
resolution slightly. (uncalibrated values of, for example only, maybe 23 to
84 gives you a range of about 51, where a calibrated 0 to 100 gives you a
range of 100).  The thing you are counting on as part of this overall
calibration process is you will probably be able to use 50, at least as your
threshold level between black lines and white background, regardless of
field and lighting conditions.

Execution the calibrate functions will create a persistent file on your
brick.  You can turn the brick on and off, and so long as you don't run the
calibrate functions again or erase the little calibrate file, your brick
will stay calibrated to the conditions that were there when you executed the
calibrate functions.

There still may be times when you use a threshold level other than 50, but
that will likely be when you are try to find a boundary of some middle (not
black or white) color.  And again it will probably be able to be kept
constant so long as you keep re-calibrating each time you go to a field.

Calibrate can run entirely on the brick so you don't need to take any
computer to the field.  My kids have calibrate on the brick when they go to
the field for their competition run.  About the first 10 seconds of their
setup time at the field is running their calibrate program.

My kids wrote their own calibrate program which displays instructions on the
brick as it is running.  They used it as an example in their programming
workshop and hence have posted the code on cougarrobot.com Here's a direct
link to the short article and program ->
http://www.cougarrobot.com/index.php?option=com_content&view=article&id=82:calibrate-program&catid=38:nxt-g-programming-workshop&Itemid=76

I hope this helps,
Best Regards,
Jamie Diamond

<http://www.cougarrobot.com/index.php?option=com_content&view=article&id=82:calibrate-program&catid=38:nxt-g-programming-workshop&Itemid=76>

On Thu, Nov 4, 2010 at 10:03 AM, Stuart & Lori Roll <[log in to unmask]>wrote:

>
> The calibration issue is this... you want your light sensor to give you a
> reading of 0 for black and 100 for white but under varying conditions, you
> might get some other range - say 23 to 84.  By calibrating the sensor you
> can get it back to 0-100 under your current conditions.  Remember of course
> that these are inexact measurements which is why the sensor blocks have you
> look for "greater than" or "less than" values.
>
> Using sensor calibration you can adjust your robot to handle different
> environmental conditions without changing your programs at all.
>
> For more info, instructions on how to use the standard calibration program
> and other optional programs, try this page<http://www.nxtprograms.com/line_follower/steps.html#calibrate>
> .
>
> Stuart
>
>
>  *From:* Laura Dysart <[log in to unmask]>
> *Sent:* Thursday, November 04, 2010 9:24 AM
> *To:* [log in to unmask]
> *Subject:* Re: [VADCFLL-L] calibration
>
> My team is using light sensor- they have been taking the average of white
> and black readings and imputing that theshold into their program. How can
> they callibrate at the tournament when they can't have a computer at the
> table to adjust the threshold if necessary?
> Thanks
>
> Laura Dysart
>
>
> On Nov 4, 2010, at 9:11 AM, Ralph Grove <[log in to unmask]> wrote:
>
>  The form is available at
> <http://www.usfirst.org/uploadedFiles/Community/FLL/Events/TeamInfoSheet.pdf>
> http://www.usfirst.org/uploadedFiles/Community/FLL/Events/TeamInfoSheet.pdf
> .
>
> You should bring four copies to the tournament - one for registration and
> one for each of the judging panels.
>
> Ralph
>
>
> On 11/4/10 9:00 AM, Annelise Ware wrote:
>
> When I did the tournament last year, we had to fill out a team information
> form to hand to all of the judges.  It had a list of every member of our
> team and answered four questions about our overall experience.  Are we doing
> that list this year?  If so, where might I find the form as a pdf or jpg?
>  Please forgive me if this has already been answered.
> Smiles,
>   *Annelise Ware*
> RES Coach
>
>
>
>
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> --
> Ralph F Grove, PhD
> Professor, Graduate Director
> James Madison University Department of Computer Science
>
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