MPR121_10 FREESCALE [Freescale Semiconductor, Inc], MPR121_10 Datasheet - Page 30

• Manufacturer Part Number: MPR121_10
• Description: Proximity Capactive touch Senosr controller
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

MPR121
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After this averaging the filter reacts to Cases 1, 2, and 3.
ADVANCED CASES
advantage of some known properties to improve the functionality of the filter. These include direction of change, touch occurrence
and the rate of touch. The first four cases are still utilized but more functionality is added. The following cases described how
different settings are useful as opposed to what exactly the settings do, like cases 1-4.
Case 5
varying parameters for different directions of change. Since a touch can only be in the decreasing direction, it is usually best to
set the decreasing filter to be slower that the increasing one. This allows for automatic recovery from a bad baseline reading.
With an understanding of the basic cases, more advanced cases can be discussed. In a touch sensor system, we can take
The direction of change for a touch in the system is always negative. Thus the system takes advantage of this by allowing for
MHD = 1
NCL = 3
NHD = 1
FDL = 4
C. The repeated touch is easily handled since the baseline quickly adjusted; if it was slow, the second
A. As the touch occurs, the baseline is decreased slowly due to a non solid touch, but due to the slow
B. The baseline quickly snaps back to the initial value by having fast filtering in the positive direction
reaction, a touch is still detected.
touch would have resulted in a possible false negative for a touch detection.
Case 1
A
1
2
Case 2
3
B
Figure 32.
Figure 33.
1
C
2
3
Case 1
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Baseline
Data
Averaged
Data
Baseline
Data
Sensors