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Choosing the Right Touch Technology
Incapacitating the sensors is difficult. Surface acoustic wave and infrared screens are most vulnerable; sticking chewed gum on the sensor or display, for example, will cause a perpetual false touch. Inadvertent touches to surface acoustic sensors can be caused by fluids or rain, but in real world applications this is seldom problematic; the electronic controllers are programmed to eventually ignore a constant touch and will reactivate much of the remaining sensed area. Infrared sensors can be triggered by reflections or sunlight, but pulsed sampling has all but eliminated these issues.
Accidental or intentional breakage is primarily a problem limited to hand-held or semi-portable equipment. As noted earlier, matrix and resistive touchscreens are the touch technology of choice for this class of products. (Of these technologies, matrix is often susceptible to breakage because it is the last technology still made entirely from plastics.
Power Consumption
Matrix and analog resistive technologies are the first choice when power is an issue, and are the only choice for hand-held applications. Both technologies can be made to work with the signal power from a COM port, thus obviating the need for external power supplies. Infrared touch consumes the most power and is applicable only to products where power is abundant.
Special Features
Touchscreens are often called upon to perform other functions. These include:
EMI and Tempest shields
Display brightness enhancement
Color filters and color changes
Contrast enhancement
Implosion shields
Privacy filters
Phosphor persistence filters.
Generally, any of these attributes can be incorporated easily into any touch technology. Infrared touch, however, has no sensor, glass or plastic panel over the display, and requires a separate, non-integrated solution.
Conclusion
Touch technology is as revolutionary a human-machine interface as is the ubiquitous mouse. For many applications - including industrial process control, medical and clean room equipment, hand-held devices, and kiosks - touch systems offer the best combination of functionality, cost, lifespan and ease-of-use. For designers, engineers and product developers, the choice of touch technology and vendor should include an analysis of these factors as well as the expertise, application experience, cost-delivery-quality track record, and flexibility of the various touch system vendors.
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