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Getting Started with CapSense

Document No. 001-64846 Rev. *I 45

Figure 3-19. Median Filter (16-sample) Finger Touch

For more information about how to implement a median filter, see the code example CSA Software Filters with

EzI2Cs Slave on CY8C20xx6.

3.4.4 Jitter Filter

3.4.4.1 Jitter Filter for Noisy Slider Data

The centroid function is used to estimate finger position on a slider. When the signal level is low, usually because of

thick overlay on the slider, the estimate of finger position will appear to shake and jitter even when the finger is held at

a fixed position. This jitter noise can be removed using a jitter filter. To do this, the previous input is stored in a buffer.

The current input is compared to the previous output. If the difference is greater than ±1, the output is changed by ±1

(matching sign), as shown in Equation 22. This is a nonlinear filter.

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  Equation 22

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 

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Figure 3-20 shows the results of applying a jitter filter applied to noisy centroid data.

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