MMA8491Q

Sensors

Freescale Semiconductor, Inc.

13

3.6

Tilt angle

Tilt angles can be calculated from the g-value threshold using the equation below. The tilt threshold is 0.688g, which corresponds

to 43.5°. Figure 9 illustrates the tilt angle threshold.

•

When 0g acceleration is present on an axis, the tilt angle = 0°;

when 1g acceleration is present on an axis, the tilt angle = 90°.

•

When the tilt angle > the tilt threshold, the output for the axis is HIGH;

when the tilt angle

≤ the tilt threshold, the output for the axis is LOW.

Figure 9. MMA8491Q output is based on tilt angle and sensor g-value

Tilt Angle

g-value

1g

-------------------

⎝⎠

⎛⎞

asin

=

Horizontal

Reference

1g

Threshold = 0.688g

Ø

Threshold (g-value) = 0.688g

Projected g-value =

Tilt Angle φ = 55°

Horizontal

Reference

1g

0.688g

Horizontal

Reference

1g

0.688g

Output = 1

Tilt Angle φ = 30°

Output = 0

Tilt Angle φ = 70°

Output = 1

Ø

Ø