Redesigning track layouts for increased resolution multi-touch screens

October 26, 2016 // By Ron Binstead
Standard touch-screens, as used in mobile phones, tablets, gaming tables, interactive digital signage, etc., comprise an orthogonal x/y array of horizontal and vertical conductive elements, where one set of "transmitting" elements has a signal or voltage that is sensed by a second set of "receiving" elements.

A change in signal strength, sensed at the intersecting nodes of any vertical and horizontal element, indicates the presence or absence of a finger at that point. Resistive touch-screens or touchpads may have a simple switch shorting the x and y elements at that point, whereas "projected capacitance" touch-screens or touchpads will show a change of capacitive coupling between the x and y elements.

Each node is scanned, one after the other, to determine the presence or absence of multiple fingers over the whole array. The density of these nodes determines how close together fingers can be while still being able to distinguish individual fingers.

Because vertical (x) elements can only ever intersect horizontal (y) elements, this arrangement restricts the number of nodes to the product of the number of rows and columns (x times y). This arrangement creates "non-touch" zones along two or three edges of the touch-screen (shown shaded in figure 1) where links are made between the conductive elements and the connector.

In the "Binstead Designs" arrangement there are no fixed receiving or transmitting conductive elements, each element being considered as both transmitting or receiving at different stages in the scanning cycle. All of the conductive elements run diagonal to the orientation of the touch-screen – see figure 2.

Each element starts at the connector edge and runs diagonally through the touch-screen to a second edge which is perpendicular to the connector edge. Here it changes direction and runs through the touch-screen again until it reaches a third edge, which is parallel to and opposite the connector edge. Even numbered elements run in one direction while odd numbered elements run in an opposing direction.

Conductive element 4, in figure 2, has been emphasised to illustrate the typical route of an element. This arrangement results in each element intersecting all the other elements, resulting in a significant increase in the number of intersections. It also eliminates any "non-touch" zones along the edges of the touch-screen.

Although this lattice layout leads to a staggered arrangement of intersecting nodes, as shown circled in figure 2, these can be rearranged into a good approximation of an orthogonal x/y array by distorting the conductive elements within the sensing area.