About Proximity sensing on the keyboard membrane

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zhangc
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I need to add a proximity sensor in the black identification part of the photo to realize proximity sensing. The wire on the film is made of carbon film or silver wire connected to the gold finger at the upper right corner, the gold finger connected to the PCB hard board, and the IC placed on the PCB. What are the requirements for this length of wiring?

 

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Vison_Zhang
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If you are going to paste the FPC onto the key film, then you need to make a double layer FPC, with a proximity ring on the top and a GND hatch (4 mil trace/32 mil grid, about 20* filling ratio) on the bottom to isolate interference between key signal and proximity signal.

The presence of the GND grid will significantly reduce the sensitivity of the proximity sensor, so you need to make the proximity sensor ring as large as possible (like 10mm x 20-30mm, etc.) within the structure allows. The proximity sensor ring electrodes are not limited in shape and electrode width should be 2 mm, 

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PandaS
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Hi @zhangc ,

As per the design guide any CapSense sensor the trace length should be within 300 mm for a
standard (FR4) & PCB 50 mm for flex PCB.

But try to avoid parallel traces next to sensor trace having fast switching signal.

You can refer this document for more information: https://www.infineon.com/dgdl/Infineon-AN85951_PSoC_4_and_PSoC_6_MCU_CapSense_Design_Guide-Applicati...

 

Warm regards,

Sobhit

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Vison_Zhang
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There are three black-marked areas,  do you want three independent proximity sensors to cover these three area or 1 proximity sensor to cover these three areas?

What's your proximity distance requirement?

How do you plan to design the proximity electrode, use silver wire and on the same layer as button wires?

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These three areas work independently,so it need three independent proximity sensors.The distance is controlled at about 4mm.I plan to make a separate FPC and paste it in this area.Thanks.

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Vison_Zhang
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First comment on KBA 750 replies posted 250 sign-ins

If you are going to paste the FPC onto the key film, then you need to make a double layer FPC, with a proximity ring on the top and a GND hatch (4 mil trace/32 mil grid, about 20* filling ratio) on the bottom to isolate interference between key signal and proximity signal.

The presence of the GND grid will significantly reduce the sensitivity of the proximity sensor, so you need to make the proximity sensor ring as large as possible (like 10mm x 20-30mm, etc.) within the structure allows. The proximity sensor ring electrodes are not limited in shape and electrode width should be 2 mm, 

Thanks for your suggestions.👍

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