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Sensors/MEMS??

Touchless gesturing paves way for innovative designs

Posted: 01 Oct 2011 ?? ?Print Version ?Bookmark and Share

Keywords:touchscreen? human interface? touchless gesturing?

There has been a significant evolution of human-machine interaction over the past decade brought about by enhancements in user interfaces and smart design. Many of these changes have focused around touchscreen interfaces with high-precision, low-power capacitive touchscreens at the forefront particularly in the handset market. Now, through advancements in human interface (HI) technology and design, infrared proximity sensors are poised to usher in the next user interface innovations centered on touchless gesturing.

Traditionally, infrared proximity sensing systems have incorporated legacy photo-detectors and photo-interrupters, which trigger based on motion or interruption respectively. These proximity sensing solutions are used extensively in automatic doors and lavatory dispensing systems, but the applications have been limited due to the sensor size, power and configurability. More advanced active proximity sensors offer exciting features and promise enhancements to consumer electronics and industrial products.

Next-generation infrared sensor offerings are not only smaller and lower power than previous offerings, but also have the ability to drive multiple infrared light emitting diodes (LEDs), thereby enabling advanced gesture inputs in multiple dimensions.

Single- to multiLED systems
Single-LED driver proximity sensors have been used in touchscreen handsets for many years and represent the highest-volume proximity sensor market, but their use has not been without issues. For example, although proximity sensors are used to deactivate handset touchscreens during calls to eliminate errant touches by the cheek, a quick web search reveals that many end-users are unhappy with proximity-sensor performance in their handsets. Accidentally muting calls, initiating conference calls and hanging up on callers are frequent mishaps caused by erroneous proximity sensor operation.

 proximity sensor

Figure 1: The Si114x proximity sensor is touted to enable multidimensional touchless gesture interfaces.

Why does a seemingly simple proximity-sensing system malfunction so frequently? The answer lies in the sensor design and configurability as well as the mechanical guidelines that accompany them. Many infrared proximity sensors are just that: dumb sensors that output raw data based on the signals received. The sensors do not have any onboard smarts to aid in distinguishing system noise from an actual signal, and they have trouble operating in environments with high ambient infrared content such as full sunlight or rooms lit by incandescent light bulbs for example. Furthermore, with industrial design taking an increasingly important role in the appeal of modern electronic systems, these proximity sensors are ill-suited to operate behind very dark overlays that limit the amount of visible and infrared light reaching the sensor.

The latest generation of proximity sensors addresses the shortcomings associated with poor proximity sensor operation. For example, the architecture of the Si114x sensors (figure 1) features multiple photodiodes coupled with analog-to-digital converter (ADC). This enables measurements with the infrared LED "on" for a fraction of the time (25.6 microseconds) of other sensor offerings. This LED on-time enables the sensor to determine and compensate for ambient infrared levels in the environment, and to better distinguish them from the actual proximity measurement.

Faster measurements also have the benefit of reducing overall system power. The infrared LED is the biggest contributor to a proximity system's power budget. Minimizing the time that the LED needs to remain on reduces the overall system power consumption. With 15 dynamically adjustable LED drive settings, the LED drive strength can be adjusted based on the ambient infrared conditions, thereby saving power and leading to a more energy-efficient design.

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