On which principles does a capacitive touch screen work to enable detection of multiple triggers?

I understand that there are two layers; a driving layer and a sensing layer (with x or driving and y or sensing lines) that form a grid that when touched causes a trigger of some-sort.

How can it determine multiple touches, and what if your multiple touches effect the same driver or sensing line, how does it determine where those touches originated from?

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  • \$\begingroup\$ Multi-touch screens have x and y lines, x on one layer and y on the other, making up a grid. \$\endgroup\$ – Will Dec 9 '14 at 13:59
  • \$\begingroup\$ @Will yes, that's my understanding; in the linked article they call them driver and sensor lines. \$\endgroup\$ – Barnstokkr Dec 9 '14 at 14:06
  • \$\begingroup\$ My guess would be that the driving lines are multiplexed: there's only one on at the same time. That way you can see which sensing line reacts when which driving line is 'on' at that moment. This is also what's done on keyboards to save input pins (you need \$2\cdot\sqrt{n}\$ lines for \$n\$ buttons instead of \$n\$). \$\endgroup\$ – user17592 Dec 9 '14 at 14:28

If you are familiar with the keyboard matrix circuits, and know how it works. You can understand this kind of capacitive sensor well.

enter image description here

You know, in a 2-D map, any points are determined by (x,y). Points with same 'x' (or 'y') but different 'y' (or 'x') are recognized as different points.


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