Design Considerations
AN64846 - Getting Started with CapSense
®
Doc. No. 001-64846 Rev. *X
59
3.4.4.2 Jitter Filter for Raw Counts
Although the jitter filter is intended for use with noisy slider data, it is also used with noisy buttons. If the change in the
current input exceeds a set threshold level, the output is reverted to the previous input plus or minus the threshold
amount. The output does not change if the current input changes by less than the threshold amount. The general
equation for a jitter filter applied to buttons is:
𝑦[𝑖] = 𝑥[𝑖] – 𝑡ℎ𝑟𝑒𝑠ℎ𝑜𝑙𝑑, 𝑖𝑓 𝑥[𝑖] > 𝑦[𝑖 − 1] + 𝑡ℎ𝑟𝑒𝑠ℎ𝑜𝑙𝑑
Equation 22
𝑦[𝑖] = 𝑥[𝑖] + 𝑡ℎ𝑟𝑒𝑠ℎ𝑜𝑙𝑑, 𝑖𝑓 𝑥[𝑖] < 𝑦[𝑖 − 1] − 𝑡ℎ𝑟𝑒𝑠ℎ𝑜𝑙𝑑
𝑦[𝑖] = 𝑦[𝑖 − 1], 𝑜𝑡ℎ𝑒𝑟𝑤𝑖𝑠𝑒
and
show the result of using a jitter filter on real button data with a large component of periodic
noise.
Figure 3-31. Jitter Filter for Button Noise
Figure 3-32. Jitter Filter for Button Finger Touch
Unfiltered
Filtered
Unfiltered
Filtered
For more information about how to implement a jitter filter, see the code example
