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Mutual capacitive button matrix design problems

Shawn L

Newbie level 1
Mar 8, 2023
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Hello everyone,

I would like to use a button matrix (see Fig.1 below) made up of 8 mutual capacitive buttons for an application. Fig.2 shows an example of a mutual capacitive button composed of two hollow square rings, the hollow square ring inside is RX electrode, the hollow square ring outside is TX electrode. But some problems came out when I tried to design touch button on PCB.
mutual capacitive matrix buttons.png

Fig.1 Mutual capacitive button matrix

Mutual Capacitive Button.png

Fig.2 Mutual Capacitive Button​

Firstly, how can I define the dimensions of a mutual capacitive button, which includes some related parameters, such as the width of RX electrode and TX electrode, the spacing (from the outer edge of RX electrode to the inner edge of TX electrode) between the two electrodes, and the outer edge length of TX electrode. Are there some factors about defining the dimensions of a mutual capacitive button? If the factors exist, then what are the quantity relations between these factors and the dimensions?

Secondly, I would like to know how to decide the separation (from the outer edge of TX electrode of a button to the same edge of the adjacent button) between two mutual capacitive buttons if supposing the separation of two buttons of same line and of same column are equivalent. Also, are there some experiences on designing this separation between two buttons can share with me?

Thanks in advance,

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