04-09-2012, 03:01 PM
Touch Screen Technology Primer
[attachment=33331]
Introduction
Touch screens best suit applications that require frequent interaction with non-technical users or must work in
dirty environments. The devices are easy to use and can tolerate dirt and moisture that would quickly disable a
keyboard or a mouse. Some Touch screens can work through a 2-inch thick barrier. This feature can protect both
the system from user abuse and the user from the system’s environment. Compact designs can also benefit from
touch screen technology. Because Touch screens are integral to the display device, the screens eliminate the
need for a separate keypad. You can make hand-held devices with Touch screens as small as the display itself.
Touch screen technology comprises a variety of options that let you match the technology to your application. For
example, a touch screen’s sensor uses one of five mechanisms; resistance, capacitance, acoustics, optics, and
mechanical force. The first step in successfully applying Touch screens, therefore, is to understand these options.
The Types
Resistive Touch Screens use a thin, flexible membrane, usually polyester film (Mylar), separated from a glass or
plastic substrate by insulating spacers. The substrate surface and the facing membrane surface have transparent
metallic coatings that meet between the insulating spacers when the user’s finger or a stylus presses on the
screen, thus closing an electrical circuit. Four and five wire designs are available for sensing the position of the
touch.
In a four wire resistive touch screen, electrode arrays at opposite sides of the substrate can establish a one
dimensional voltage gradient across the substrate’s resistive indium-tin-oxide (ITO) coating. Similar electrodes
can establish an orthogonal gradient across the membrane’s ITO coating. Both sets of electrodes also allow the
ITO coatings to act as high-impedance probes. When a user touches a four wire system screen, the controller
establishes a gradient across the substrate. The controller then measures the voltage at the point of touch using
the membrane as a probe. Similarly, the controller establishes a gradient across the membrane and uses the
substrate as a probe. The two voltages provide the x and y coordinates of the touch point. The 4 wire type has the
advantage of being able to produce very small and simple construction touch panels ideally suited for hand-held
devices. They do not have a very long life span - usually 1 to 4 million touches.
Things to Consider
Once you understand the touch screen mechanisms, your next step is to consider the conditions under which
your system must work. Moisture, grease, dust, and other contaminants that have no effect on some touch
screens but can cripple others. You need to know if a bare finger, a gloved finger, a stylus, or any combination will
activate your system. Keep in mind also, the type of handling the system will receive. A system in a hospital will
receive more reasonable care than a public information kiosk, which is more susceptible to vandalism. Other
factors may also have a bearing on your applications.
By understanding basic touch screen technology and your operating environment, you can begin to evaluate the
range of choices. The comparison chart shows some of the tradeoffs for various touch screen options. Although
most of the technologies are comparable in price, Resistive touch screens are typically the least expensive
option. Four wire resistive Touch screens, however, are highly susceptible to wear out and all Resistive types are
susceptible to surface damage because of their flexible outer layer.
Conclusion
Touch screen technology will increase in significance as an I/O technique for user oriented embedded systems.
Vendors have been steadily reducing or eliminating the weaknesses in touch sensors as well as adding new
capabilities. This combination of steady improvement punctuated by innovation will continue to broaden the range
of applications that touch screens can serve.
With these improvements, touch screen technology has become a viable user interface for many embedded
systems. The inclusion of electronic ink services in Windows 9x indicates that touch screens will become a
dominant interface. You need only to carefully match the technology to the application environment.
[attachment=33331]
Introduction
Touch screens best suit applications that require frequent interaction with non-technical users or must work in
dirty environments. The devices are easy to use and can tolerate dirt and moisture that would quickly disable a
keyboard or a mouse. Some Touch screens can work through a 2-inch thick barrier. This feature can protect both
the system from user abuse and the user from the system’s environment. Compact designs can also benefit from
touch screen technology. Because Touch screens are integral to the display device, the screens eliminate the
need for a separate keypad. You can make hand-held devices with Touch screens as small as the display itself.
Touch screen technology comprises a variety of options that let you match the technology to your application. For
example, a touch screen’s sensor uses one of five mechanisms; resistance, capacitance, acoustics, optics, and
mechanical force. The first step in successfully applying Touch screens, therefore, is to understand these options.
The Types
Resistive Touch Screens use a thin, flexible membrane, usually polyester film (Mylar), separated from a glass or
plastic substrate by insulating spacers. The substrate surface and the facing membrane surface have transparent
metallic coatings that meet between the insulating spacers when the user’s finger or a stylus presses on the
screen, thus closing an electrical circuit. Four and five wire designs are available for sensing the position of the
touch.
In a four wire resistive touch screen, electrode arrays at opposite sides of the substrate can establish a one
dimensional voltage gradient across the substrate’s resistive indium-tin-oxide (ITO) coating. Similar electrodes
can establish an orthogonal gradient across the membrane’s ITO coating. Both sets of electrodes also allow the
ITO coatings to act as high-impedance probes. When a user touches a four wire system screen, the controller
establishes a gradient across the substrate. The controller then measures the voltage at the point of touch using
the membrane as a probe. Similarly, the controller establishes a gradient across the membrane and uses the
substrate as a probe. The two voltages provide the x and y coordinates of the touch point. The 4 wire type has the
advantage of being able to produce very small and simple construction touch panels ideally suited for hand-held
devices. They do not have a very long life span - usually 1 to 4 million touches.
Things to Consider
Once you understand the touch screen mechanisms, your next step is to consider the conditions under which
your system must work. Moisture, grease, dust, and other contaminants that have no effect on some touch
screens but can cripple others. You need to know if a bare finger, a gloved finger, a stylus, or any combination will
activate your system. Keep in mind also, the type of handling the system will receive. A system in a hospital will
receive more reasonable care than a public information kiosk, which is more susceptible to vandalism. Other
factors may also have a bearing on your applications.
By understanding basic touch screen technology and your operating environment, you can begin to evaluate the
range of choices. The comparison chart shows some of the tradeoffs for various touch screen options. Although
most of the technologies are comparable in price, Resistive touch screens are typically the least expensive
option. Four wire resistive Touch screens, however, are highly susceptible to wear out and all Resistive types are
susceptible to surface damage because of their flexible outer layer.
Conclusion
Touch screen technology will increase in significance as an I/O technique for user oriented embedded systems.
Vendors have been steadily reducing or eliminating the weaknesses in touch sensors as well as adding new
capabilities. This combination of steady improvement punctuated by innovation will continue to broaden the range
of applications that touch screens can serve.
With these improvements, touch screen technology has become a viable user interface for many embedded
systems. The inclusion of electronic ink services in Windows 9x indicates that touch screens will become a
dominant interface. You need only to carefully match the technology to the application environment.