Touch screens – how it works

How Does It Work

This through non-conductive material capacitive touch sensing technology works using an electrical phenomenon called Projected Capacitance. When two electrically charged objects come near to one another without touching, their electric fields interact to form capacitance. In the case of the ViP Interactive foil projected capacitance forms between the user’s finger and the wires in the sensor grid. This “touch event” is detected, precisely measured, and passed on to the system for processing.

To better understand how this touch sensing technology works, let’s examine the construction of the capacitive used in the ViP Interactive foil:

* Insulating surface: A thin layer of clear polyester that protects the underlying sensor wires.

* Laminated sensor grid: The wires that form the sensor grid are made from copper and run horizontally and vertically through the sensor. To reduce the visibility of the grid, the wires are specially designed to tile the entire surface yet minimally overlap at the crossings. Each wire is a sensing element that connects to the touch controller chip. These wires sense and detect the user’s finger; information about x and y coordinates and this information is passed to the touch controller chip.

* Bottom substrate: Another thin layer of clear polyester that separates the sensor grid from the underlying surface to which it is applied.

When the user interacts with the ViP Interactive foil the following processes occur:

  • User’s input: The user initiates the touch event by interacting with the sensor grid through any non-metallic material layer (i.e. galls, acrylic, etc.)
  • Capacitance: The sensor wire grid captures information about the amount of capacitance on the x- and y-axes.
  • Measurement: circuits on the touch controller chip measure the capacitance on each sensor wire. This is equivalent to determining how hard the finger is pressing on, but it cannot tell where on the wire the finger is located. This is the z-axis. This information is used to determine the sensitivity of the sensor. In the case of the ViP Interactive foil this is used to adjust the distance of the projected capacitance field required to penetrate the chosen type and thickness of the non-conductive material.
  • Location: The location of the user’s finger on the grid is calculated by looking at the distribution and amount of capacitance on all of the wires. By examining this distribution of capacitance, the touch controller can determine the position of the finger. The points where the largest amount of capacitance on the x-axis and y-axis are mapped together pinpoint the location of the user’s input. By comparing the amount of capacitance on adjacent wires, a process referred to as “interpolation”, a more precise location is determined.
  • Processing: The touch controller board processes the information (about the pressure/location of the touch input) and passes it to the computer.
  • System response: Operating System/Application Software responds to the user’s input.
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