Application Note
BlueBox Demo-Board for the digital sensors
SMB365 (acceleration) and SMD500 (pressure)
Bosch Sensortec
AN18002
Rev. 1.0
Page 37
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7211RB11
.
•
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 LSB
X
> Threshold OR LSB
Y
> Threshold OR LSB
Z
> Threshold
LED [25] = 0 if LSB
X
< Threshold AND LSB
Y
< Threshold AND LSB
Z
< 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 LSB
X
> Threshold OR LSB
Y
> Threshold OR LSB
Z
> Threshold
LED [25] = 0 if LSB
X
< Hysteresis AND LSB
Y
< Hysteresis AND LSB
Z
< Hysteresis
Threshold:
g
mg
LSB
LSB
d
2
.
1
16
75
300
4
75
75
=
⋅
∝
=
⋅
=
Hysteresis:
g
mg
g
LSB
LSB
LSB
d
8
.
0
16
25
2
.
1
200
4
25
300
25
=
⋅
−
∝
=
⋅
−
=
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.
4.3.3 SMB365 Low-Power Mode in independent interrupt conditions
Software and sensor offer the following features
