KXTIK-1004 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:
KXTIK-1004
Rev. 2
Dec-2011
KXTIK Embedded Applications
Orientation Detection Feature
The orientation detection feature of the KXTIK 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 KXTIK.
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 KXTIK 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 KXTIK 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.
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