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Touch or Touchless? That Is the Question



Capacitive and resistive touchscreen interface technology used in smartphones and other popular consumer electronic devices is just now becoming mainstream, but alternatives are starting to emerge based on dramatic advances in human interface design. Now comes the question: Which of these technologies – touch or touchless gesturing – should be used in a design?

Touch

Touch-type gesturing – using a finger or stylus to work a display – allows consistently high resolution and extremely high refresh rates. While touchscreens are primarily used in consumer-facing devices like iPads, ATM machines and self-service checkouts today, they are also suitable for industrial settings because they are not affected by noise, lighting or other harsh environmental elements found in these settings.

An added bonus for designers is the flexibility of touch-gesture applications. Designers can program the device interface to look and act however they want, and make updates and upgrades quickly and easily on-site where the machine resides.

Touchless

If broad-based gestures – such as a hand movement from left to right or front to back – are required, a touchless sensor may be a better fit.

Touchless sensing is used in applications like bathroom dispensing units and automatic doors that use motion or interruption to create a response. Many more applications can benefit from a touchless approach, but until recently many were unable to leverage the technology due to sensor size and power requirements.

Today, low-power touchless sensor ICs have a significantly smaller footprint, yet are powerful enough to drive multiple LEDs and enable gesture input in multiple directions. This opens up the possibility for many new applications including ones in the medical field.

For example, minimizing contact in a hospital system helps reduce the spread of disease. During a procedure, a surgeon may need to refer to a text while doing an experimental procedure. If the information was transferred to an electronic format the surgeon could “scroll” through the pages by gesturing at a screen; the surgeon wouldn’t have to come in direct contact with any surface. Touchless gestures are generally accepted from up to six inches from the object so this application could be easily integrated into existing surgical room technology.

Advancement

Single-LED driver proximity sensors represent the highest-volume of proximity sensors used today. The mechanical design, however, still presents challenges. For instance, proximity sensors used in handsets are often blamed for disconnected of cell phone calls and accidental call-muting. These previous-generation sensors often do not have the ability to distinguish system noise from real signal, and they have specific problems in certain environments such as sunlight or incandescent light bulb-lit rooms, or when the amount of visible and infrared light is limited.

Advances in proximity sensors address these specific issues by adding multiple high-sensitivity photodiodes and a high-precision ADC so that the infrared LED is on for a shorter time. This allows the sensors to adjust for ambient infrared levels in the environment that are not part of the proximity measurements they are tasked to take. Similar advances in power reduction now allow LED drive settings to vary based on the existing ambient infrared conditions instead of consistently setting LEDs at power-wasting maximums. When combining these multi-LED proximity sensors with host capacitive touch-sense microcontrollers, touchless gesturing now has the computational it needs to interpret infrared sensor output.

Silicon Labs recently announced a sensitive, power-efficient and long-range proximity sensor. Available in a 2 x 2-mm package, the sensors enable sophisticated proximity sensing and touchless interfaces for use in handsets, eReaders, netbooks, tablets, personal media players, toys, office equipment, industrial controls, and security systems. Silicon Labs is not the only company working on this challenge. Cypress Semiconductor indicates that they have also been working on touchless gesturing for the past six months.

Conclusion

For designers, using a touchscreen solution is still very flexible. Touchless, in comparison, is not as mature. When designing a touchless solution, mechanical aspects such as controlling the amount of metal, considering the geometry - making sure there’s enough space for adequate sensors, and making sure there is enough directionality in the sensor are all important physical and mechanical design considerations.

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