This article looks at the latest touchscreen sensor technologies and the wide range of interfaces that the different technologies use. It also evaluates the different approaches for interfacing such sensors for human interfaces from three, four and five wire to USB, covering sensors and interfaces from Atmel, 3M, IR Touch Systems, and NKK Switches.
Resistive 4- and 5-wire touch sensors are the most popular and most common touchscreen technologies with about 75% market share, mainly due to their low costs and simple interface electronics.
The high volume of these screens requires a low-cost reliable interface, often with a low-power element. This can be provided through a range of analog features combined with low-power modes for portable, battery-powered applications.
Analog resistive touchscreens
Usually a resistive touchscreen consists of at least three layers (Figure 1). A flexible membrane made from PET film is suspended over a rigid substrate made from glass or acrylic, and both surfaces are coated with a transparent conductive film, usually Indium tin oxide (ITO). The conductive ITO layers are kept apart by an insulting spacer along the edges, and by spacer dots on the inner surface of the two ITO layers.