how to implement shield electrode in matrix capsense keypade

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Anonymous
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i want to design 7*7 capsense matrix keypade.as i found in one example matrix button is surrounded by hatch pattern of vss(ground) net on both side.and in capsense document its shown that to implement shield electrode surrounded hatch pattern should be connected to shield electrode pin.so its bit confusing should i connect ground net hatch pattern to shield electrode pin in my design ?

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4 Replies
Anonymous
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Hello,

   

The hatch pattern is connected to Shield pin if you want liquid tolerance in your design.

   

If you don't want liquid tolerance then it is recommended to connect the hatch pattern to GND.

   

 

   

Thanks,

   

Ranjith

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Anonymous
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Dose it affect the capsense detection if i implement shield electrode compare to case in which i connect hatch pattern to ground? i mean sensitivity because my kepade is 156mm*156mm in size so hatch pattern area of top and bottom is quite large.is single pin is capable for driving hatch pattern on both side?

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Anonymous
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Hello,

   

 

   

Usually the general implementation is to have hatch pattern connected to GND around the sensor. This is if you don't need Liquid tolerance in your design.Connecting the Hatch pattern to GND will increase the noise immunity.

   

But if you need water tolerance you need to connect this hatch pattern to Shield pin.

   

And if your design has long traces which will in turn increase the Cp then to reduce Cp you need to drive the hatch pattern in top and bottom layer by the shield signal.

   

Yes you can drive using a single shield pin on both the layers of hatch pattern.

   

 

   

Thanks,

   

Ranjith

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Anonymous
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if i want liquid tolerance should i connect both (top and bottom layer) hatch pattern to shield pin or only top layer hatch??

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