Complementary Filter

Be sure to check out the presentation on this filter at the bottom of this page.

Used the following to convert gyro and accel ADC readings to engineering units

Accelerometer Output (G) = (N-512) / 1024 * (double)10.78;
Gyro Output (radians) = (N-512) / 1024 * (double)28.783;

Implemented the complementary filter using the following equations

If filter term = tau / (tau + dt), where tau = time constant, dt = loop update rate:

rollAngle = (0.9615 * (rollAngle + (rollADC / 1024.0 * 28.783 * dt))) + (0.0385 * (rollAccADC / 1024.0 * 10.78)) * 57.2957795;
pitchAngle = (0.9615 * (pitchAngle + (pitchADC / 1024.0 * 28.783 * dt))) + (0.0385 * (pitchAccADC / 1024.0 * 10.78)) * 57.2957795;

Time Constant = 250ms, Control Loop = 10ms

• filter term = 0.9615
• when at rest observe noise to be 0.3 degrees
• very responsive
• appears to show 0.1 deg resolution

Time Constant = 500ms, Control Loop = 10ms

• filter term 1 = 0.9804, filter term 2 = 0.0196
• when at rest observe noise to be 0.2 degrees