Smooth out the CMMotionManager acceleration readings with Low Pass Filter.

gistfile1.m

- (CMAcceleration)smoothOutAcceleration:(CMAcceleration)acceleration
{
    static CGFloat x0 = 0;
    static CGFloat y0 = 0;
    static CGFloat z0 = 0;
    
    const NSTimeInterval dt = (1.0 / 20);
    const double RC = 0.3;
    const double alpha = dt / (RC + dt);
    
    CMAcceleration smoothedAcceleration;
    smoothedAcceleration.x = (alpha * acceleration.x) + (1.0 - alpha) * x0;
    smoothedAcceleration.y = (alpha * acceleration.y) + (1.0 - alpha) * y0;
    smoothedAcceleration.z = (alpha * acceleration.z) + (1.0 - alpha) * z0;
    
    x0 = smoothed.x;
    y0 = smoothed.y;
    z0 = smoothed.z;
    
    return smoothedAcceleration;
}