KXTI9-1001 Datasheet, PDF (39/54 Pages) List of Unclassifed Manufacturers – 2g/4g/8g Tri-axis Digital Accelerometer Specifications

± 2g / 4g / 8g Tri-axis Digital
Accelerometer Specifications
PART NUMBER:
KXTI9-1001
Rev. 2
Jul-2011
KXTI9 Embedded Applications
Orientation Detection Feature
The orientation detection feature of the KXTI9 will report changes in face up, face down, +/- vertical and +/-
horizontal orientation. This intelligent embedded algorithm considers very important factors that provide
accurate orientation detection from low cost tri-axis accelerometers. Factors such as: hysteresis, device
orientation angle and delay time are described below as these techniques are utilized inside the KXTI9.
Hysteresis
A 45° tilt angle threshold seems like a good choice because it is halfway between 0° and 90°. However,
a problem arises when the user holds the device near 45°. Slight vibrations, noise and inherent sensor
error will cause the acceleration to go above and below the threshold rapidly and randomly, so the
screen will quickly flip back and forth between the 0° and the 90° orientations. This problem is avoided
in the KXTI9 by choosing a 30° threshold angle. With a 30° threshold, the screen will not rotate from 0°
to 90° until the device is tilted to 60° (30° from 90°). To rotate back to 0°, the user must tilt back to 30°,
thus avoiding the screen flipping problem. This example essentially applies +/- 15° of hysteresis in
between the four screen rotation states. Table 23 shows the acceleration limits implemented for _T
=30°.
Orientation
0°/360°
90°
180°
270°
X Acceleration (g)
-0.5 < a_x < 0.5
a_x > 0.866
-0.5 < a_x < 0.5
a_x < -0.866
Y Acceleration (g)
a_y > 0.866
-0.5 < a_y < 0.5
a_y < -0.866
-0.5 < a_y < 0.5
Table 23. Acceleration at the four orientations with +/- 15° of hysteresis
The KXTI9 allows the user to change the amount of hysteresis in between the four screen rotation
states. By simply writing to the HYST_SET register, the user can adjust the amount of hysteresis up to
+/- 45°. The plot in Figure 2 shows the typical amount of hysteresis applied for a given digital count
value of HYST_SET.
36 Thornwood Dr. – Ithaca, NY 14850
tel: [phone] – fax:[phone]
www.kionix.com - [e-mail]
© 2011 Kionix – All Rights Reserved
438-2322-1107191455
Page 39 of 54