Capacitive Button

Making your own components and patterns, organizing and using libraries.
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Haz
Posts: 12
Joined: 27 Aug 2011, 16:33

Capacitive Button

#1 Post by Haz » 17 Apr 2020, 10:34

Hi,

I am making a capacitive sensor button and have the shape completed, but gives me errors because I made it up of a few touching pads which I am sure is not the right way.
It is a mutual capacitance button, so the outer pad is a single pad, and the inner one (looks like an H) is another pad. so only 2 pads are needed.
I made it by putting multiple rectangular pads, and when I got to the PCB, I get all these errors, which are valid, but don't know how to get over them. Functionally it will work, but I don't like errors on my designs.

Any step by step guide I can refer to?

thanks,
H-
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Tomg
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Posts: 1571
Joined: 20 Jun 2015, 14:39

Re: Capacitive Button

#2 Post by Tomg » 17 Apr 2020, 15:23

Draw two separate filled polygons on the Signal layer. Draw the outer polygon with a gap, then close the gap by moving the pertinent points until a butt-joint is achieved. Convert each filled polygon to a pad (right-click > Convert to Pad).
draw.png
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Tom

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KevinA
Posts: 487
Joined: 18 Dec 2015, 15:35

Re: Capacitive Button

#3 Post by KevinA » 17 Apr 2020, 17:14

LOL - I've always thought the pentagon on the tool bar was for drawing a pentagon! More Tomg gems

Haz
Posts: 12
Joined: 27 Aug 2011, 16:33

Re: Capacitive Button

#4 Post by Haz » 17 Apr 2020, 17:21

You guys are great! It worked. I just learned something new.
thank you for the quick response.
H-

Tomasina
Posts: 1
Joined: 22 Apr 2020, 03:33

Re: Capacitive Button

#5 Post by Tomasina » 22 Apr 2020, 04:07

Which IC processes this sensor?
I am confused by the shape of the pads. For single sensors it is not recommended to use this shape, the round shape will shows great efficiency.
See docs:
-SEMTECH Capacitive Touch Sensing Layout Guidelines.pdf
-AN2934 Capacitive Touch Sensor Design Guide.pdf
-AN447 Printed Circuit Design Notes for Capacitive Sensros.pdf

Haz
Posts: 12
Joined: 27 Aug 2011, 16:33

Re: Capacitive Button

#6 Post by Haz » 23 Apr 2020, 08:37

This is a Cypress PSoC.

The sensor design is mutual capacitance not self-capacitance which most others do. Although the sensor can do both, I use mutual capacitance given its immunity to noise, and most importantly, I need to send through 2-3mm plastic and off the main board. Meaning my sensors are on one board, and my PSoC MCU is on another.
I am using PSoC6 which is a great part. Other much smaller PSoCs are able to do the same.
https://www.cypress.com/products/cypres ... chnologies
If you look at the CapSense tab on this page you will see the difference.

There are many more shapes of sensors, depending on your application and the environment it is in.

H-

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