Subject:
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Re: Light sensor initialization?
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Newsgroups:
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lugnet.robotics.rcx
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Date:
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Thu, 15 Jul 1999 14:25:02 GMT
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Viewed:
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2029 times
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Matthew's program takes one reading at initialization time to
determine a baseline value. Any reading that falls 7 units
below this is assumed to be a dark line.
I take a somewhat more conservative approach, taking 10
readings over one second and averaging them to get
a baseline value. This is done once at initialization.
I then detect a dark line by testing for a
reading that is 3 below the baseline. Here's the code I've
been using to calculate an average baseline value:
-----
#define NUMBER_OF_SAMPLES 10
int i;
int runningTotal;
int averageLight;
inline calibrateLightSensor {
// Take an average light reading.
i = 0;
runningTotal = 0;
while (i < NUMBER_OF_SAMPLES) {
runningTotal += LIGHT_SENSOR;
Sleep(10);
i += 1;
}
averageLight = runningTotal / NUMBER_OF_SAMPLES;
}
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Then I look for the black line with code like this:
if (LIGHT_SENSOR < averageLight - 3) {
It works well. I really like getting a baseline light value
at runtime, for two reasons:
1. You might want to run your robot at different times
of day and have it work right. Hardcoded values will
probably fail you here.
2. Different light sensors produce different readings
for the same amount of light. Doing a runtime calibration
increases the chances that your program can work on
someone else's robot.
There's really only one drawback: you have to assume that
your robot is over a white part of the driving surface
when the program runs. If it's over a black line, your
calibration will be all screwed up.
Jonathan
Matthew Miller wrote:
>
> Tim Rueger <rueger@io.com> wrote:
> > I'd like my 'bot to measure ambient light levels, and make light/gray/dark
> > decisions based on those levels. • [snip]
> > I'd like to avoid hard-coding these numbers. Has any one done this?
>
> Yes -- check out my RoboTag program at
> http://www.mattdm.org/mindstorms/robotag.shtml
>
> In RoboTag, the sensor is pointing at the ground, which is probably
> grey/brown/white, with black border lines. My program reads the light level
> at start, and assumes that it isn't on a line. This works well enough,
> assuming the operator knows this. (If you wanted to make it smarter, you
> certainly could.)
>
> --
> Matthew Miller ---> mattdm@mattdm.org
> Quotes 'R' Us ---> http://quotes-r-us.org/
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Message has 3 Replies:
 | | Re: Light sensor initialization?
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| (...) Wow. I feel I should point out that experimentally my method works 100% of the time. :) On the other hand, mine is a special-case application: the light sensor is used to read color values from a surface, which presumably will have very little (...) (25 years ago, 15-Jul-99, to lugnet.robotics.rcx)
| | | Re: Light sensor initialization?
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| (...) This is my inspiration for adding on-the-fly init code, btw. RoboTag uses two seperate robots, and it turns out that my friend -- the source of the second mindstorms kit -- has a light sensor which reads about 10 "darker" than mine. (25 years ago, 15-Jul-99, to lugnet.robotics.rcx)
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Message is in Reply To:
| | Re: Light sensor initialization?
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| (...) [snip] (...) Yes -- check out my RoboTag program at (URL) RoboTag, the sensor is pointing at the ground, which is probably grey/brown/white, with black border lines. My program reads the light level at start, and assumes that it isn't on a (...) (25 years ago, 14-Jul-99, to lugnet.robotics.rcx)
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