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In lugnet.robotics.handyboard, Ben Jackson writes:
> In lugnet.robotics.handyboard, Jean-Michel Mongeau writes:
> > Does anyone how I could create a lookup table or an algorithm to convert the
> > output of the Sharp GP2D02 (0 to 255 = byte) to values between 10 and 80 cm,
> > which is the reading capability of the IR?
>
> You mean like value = 10 + ((70 * b) / 256) ?
>
> --Ben
Actually, the GP2DO2's output is not at all linear. Plotting the output
against the actual distance will show an exponential curve. Each one is
slightly different so what I do is to make up a little table in Excel like:
0,0
70,10
116,15
142,20
155,25
163,30
169,35
176,40
180,45
Cells A1 and B1 are the constants in the equation Dist = A*B^reading.
The data from actual measurements starts in row 2, where the first column is
the reading and the second column is the actual distance measured in
centimeters. Then I put in a third column (C) that has an exponential equation
of the form +$A$1*($B$1^(A2/10))and a fourth column (D) that subtracts the
actual reading from the calculated one:
+ABS(B2-C2)
and finally, at the bottom of the fourth column I have a single cell which sums
up these error values:
+SUM(D2..D9)
Use the Excel solver to calculate the optimal value in cells A1 and B1 which
will minimize the value in the summed error cell.
Once you have these two values you can use them in an IC program like the one
shown below. The variable GP2D02_15 is an integer set by the assembly code.
The constants in the equation are ones that I had Excel calculate for my
GP2D02. In my experience, most of them will have at least slightly different
values.
float distance;
while(1)
{
f = 1.55931 * (1.018606 ^ (float) GP2D02_15);
printf ("distance is %f\n",f);
msleep(200L);
}
If the spreadsheet description wasn't clear enough, email me and I'll copy the
actual spreadsheet for you.
Barry
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Message has 1 Reply:
 | | Re: GP2D02 conversion
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| (...) Sorry for two messages about the same subject but after playing around a bit more with it I got better results. Here is the spreadsheet to calculate the constants to convert the GP2D02 output to centimeters: 0.1233 1.0320 9.3078 GP2D02 Actual (...) (25 years ago, 15-Jan-00, to lugnet.robotics.handyboard)
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