I'm confused in the capacitive sensors footprint design

[fjrg76]

Hi,

In this video it's stated that the interdigitated shapes for buttons must be avoided (18:07):

Best Practices for Capacitive Sensors Designs - YouTube 

but in the other side the NXP boards OM40001 and OM 13081 (LPCXpresso804 development kit and LPC824 touch solution, respectively) use such shapes (please see the attached image).

At first sight the stand alone capacitive sensors are using the same approach of that in such boards, so the question is: Which approach should I use for a new design based upon LPC8xx mcu's? Maybe I'm wrong thinking in that both products are the same (standalone and implementation based on mcus) that's way I ask to the experts.

Thank you!!

[soledad]

Hi,

I suggest to check the following application note,

https://www.nxp.com/docs/en/application-note/AN12082.pdf 

this application note discussed the LPC84x Cap Touch implementation and the Cap Touch Sensor design consideration to have a good cap-touch sensing operation.

Have a great day,
Sol

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[fjrg76]

Very nice AN, but it didn't answer my original question.

If demo boards from NXP are using the interdigitated shape, then I should too! I guess this approach applies for microcontrollers that already include the touch capability (or are using a software library) whereas the standalone touch/proximity sensor chips, like the PCF8883, use a technology other than the aforementioned. Then I need to read about it!

Just a short question unrelated to the original: Can I use the sensor approach for mcu's for sensing liquids like water in an on/off fashion? Is that possible?

Thanks!!!