Application Note

Bosch Sensortec

BlueBox Demo-Board for the digital sensors AN18002

SMB365 (acceleration) and SMD500 (pressure)

•Select Low-Power Mode [20]

•Select any acceleration range [21]

•Select Global Interrupt Mode [22]

•Put in global Hysteresis and Threshold digits [23]

•Start data acquisition [8]

•Accelerate, roll or tilt the BlueBox board while watching the interrupt LED [25]

Notes:

The triggering of an interrupt depends, in the first instance, on global Threshold value settings. The global Threshold can be assumed as the interrupt “switch-on” level which must be exceeded from at least one axis dependent acceleration signal. If any acceleration signal exceeds this value, an interrupt will be activated. If all signals are below the Threshold value again, the interrupt will be deactivated, provided that the Hysteresis value is set to zero, e.g.:

LED [25] = 1 if LSBX > Threshold OR LSBY > Threshold OR LSBZ > Threshold LED [25] = 0 if LSBX < Threshold AND LSBY < Threshold AND LSBZ < Threshold

In addition to the global Threshold value a global Hysteresis value can also be set. The Hysteresis can be assumed as the interrupt “switch-off” level, which must be under-run again from all signals, to deactivate the triggered interrupt. It relates directly to the before set Threshold value by a mathematical subtraction. The following example shows how to set up the global Threshold and Hysteresis values. The calculation corresponds to the 2g operation mode, e.g.:

LED [25] = 1

if LSBX > Threshold

OR

LSBY > Threshold OR LSBZ > Threshold

LED [25] = 0

if LSBX < Hysteresis

AND

LSBY < Hysteresis

AND LSBZ < Hysteresis

Threshold:

75d = 75 ⋅ 4LSB = 300LSB

 

∝

75 ⋅16mg = 1.2g

Hysteresis:

25d = 300LSB − 25 ⋅ 4LSB = 200LSB

∝

1.2g − 25 ⋅16mg = 0.8g

If Hysteresis is equal or above Threshold, the interrupt functionality will be disabled. For a total reset of the sensor internal interrupt information just switch to standby mode [20] and continue.

4.3.3SMB365 Low-Power Mode in independent interrupt conditions

Software and sensor offer the following features

Rev. 1.0

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