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Measuring Tilt using a Three Axis Solution
In order to define the angles of the accelerometer in three dimensions the pitch, roll and theta are sensed using all three outputs of the accelerometer. Pitch (ρ) is defined as the angle of the X-axis relative to ground. Roll (ϕ) is defined as the angle of the Y-axis relative to the ground. Theta (θ) is the angle of the Z axis relative to gravity.
http://www.freescale.com/files/senso...ote/AN3461.pdf
Here is the meat of the code:
Code:
solveangle:
'**********Solve for x angle ********************************************
if xresult < yresult + zresult then
dummy = 5000 'when x is smaller the following equation works best
xlong = (dummy * xresult) /(sqr((yresult*yresult) + (zresult*zresult)))
else 'keeps results accurate at near 0 and near 90 degree values
dummy =30 'when x is larger the following equation works best
xlong = (dummy * xresult*xresult) / ((yresult*yresult)+(zresult*zresult))
endif
y = xlong
x = dummy 'Assign x and y values for atan2 function
call atan2
xangle = 9000 - y
if yresult < xresult + zresult then
dummy = 5000 'when y is smaller the following eqauation works best
ylong = (dummy * yresult) / (sqr((xresult*xresult) + (zresult*zresult)))
else
dummy =30 'when y is larger the following equation works best
ylong = (dummy * yresult*yresult) / ((xresult*xresult)+(zresult*zresult))
endif
y = ylong
x = dummy '
call atan2
yangle = 9000 - y
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