Game Development Reference
Also a topic we'll soon discuss in detail, capacitive touch screens are very common on
today's smartphones. These touch screens operate by calculating the change in electrical
capacitance at the four corners of the screen when your finger influences the capacitive
nature of the circuits under the glass. The limitation is that whatever touches the screen
must be electrically conductive. If you insulate your fingers with gloves, the screen will
no longer be able to locate your touch. However, this can be solved with a few stitches
of conductive thread.
Infrared and Optical Imaging
Infrared touch screens use arrays of infrared LED and photodetectors to detect and
interpret an object breaking the path of a LED-photodetector pair. This uses line-
scanning techniques and is a very robust design.
Optical imaging techniques are relative newcomers to the touch screen scene whose big
advantage is that they are extremely scalable. They use imaging devices and light sources
to detect where the screen is being touched by interpreting any shadows cast by an object
through the thickness of the material.
Exotic: Dispersive Signal and Surface Acoustic Wave
Several other exotic touch screen technologies exist. We won't get into detail here, but
3M has a system that detects mechanical energy in glass caused by a touch. The amount
of vibration energy that reaches each sensor determines the position.
Another example of exotic screen input, surface acoustic wave technology detects
changes in the pattern of ultrasonic waves traveling along the surface of the screen.
Resistive Touch Screens
Resistive touch screens are classified as a passive touch screen technology because the
screen registers a touch without any active participation by the object touching the
screen. This is their major benefit over active technologies, such as capacitive touch
screens, as resistive screens can be activated by nonconductive objects like a pen or
gloved finger. In the past, resistive screens were limited to a single input, and that's the
type we'll describe, but they can be made to work with two or more simultaneous inputs,
also known as multitouch.