The human body embodies an amazing array of senses. Musicians can hear the difference between a C and a C#, despite the fact that the two tones are only 15 Hz apart. Olympic rifle shooters can detect when their sights are misaligned by as little as two-thousandths of an inch. Sightless persons can read Braille—dots raised above the paper just two-hundredths of an inch and spaced one-tenth of an inch apart—at 400 words per minute using touch sensors in their finger tips.
When it comes to the design of human interface devices for today’s technology, senses are important factors. Device manufacturers are faced with the ongoing challenge of accommodating a conditioned expectation—that buttons or keys will move when depressed (perhaps as much as one-fourth to one-half of an inch), leading the brain to decrease the velocity of the finger to zero at the moment of contact.
The growing use of rigid flat screens, such as LCDs, under glass or plastic protective overlays has increased the need for improved touch solutions. The wrong sensory feedback can have sweeping negative effects, including difficulty of use, inaccurate communication of data, and—most ominous—physical impairments, such as repetitive stress injury (RSI), which are caused by the failure of buttons or keys to respond to the brain’s expectations. In addition, manufacturers of mobile consumer electronic (CE) devices in particular must consider other technical factors, including the need to reduce latency, reduce dependency on baseband processors, and lower cost and improve power consumption.
Recent trends in the integration of components have helped advance the CE industry toward capacitive-touch capabilities that address the conditioned expectations of users and the industry’s trend toward lower-cost, higher-performance solutions. This article will discuss the need for improved touch solutions, the alternatives available, and the benefits of an integrated approach to capacitive touch.
As technology evolves, so do consumer visions of what is “cutting edge.” A mobile handset or MP3 player with mechanical keys isn’t the trend of the future, and one with bubbled membrane keys would be an oddity at best. One human-machine interface (HMI) gaining considerable traction today in consumer and commercial/industrial segments is touch-centric input, whether display-based (e.g., touch screens), or non-display-based (e.g., buttons, sliders, and scroll wheels).
The research generated from membrane-type keys provides significant design findings for this latest generation of touch-based HMI due to the same fundamental challenges. When touch inputs are implemented on rigid flat screens, such as LCDs, or under glass or plastic protective overlays, such as in white goods or mobile handsets, there’s no “travel” to provide feedback to the user that a valid touch event has occurred. However, unlike membrane keys, it’s not practical to add travel through a bubble or other physical technique. New methods of feedback are required. With these touch inputs controlling more complex and essential product functions, this sensory feedback becomes even more critical in determining whether the new input methods enhance the users experience or detract from it.
A VARIETY OF FEEDBACK METHODS
Early on, membrane keys incorporated tactile feedback. But soon after, other types of feedback, such as visual and aural, were added. Today, multiple sensory feedback methods are commonplace; in fact, so much so that they’re often so subtle that they practically go unnoticed. However subtle, sensory feedback is important for many reasons.
The three senses involved in product sensory feedback—visual, aural, and touch—are used singularly and in combination. Depending on the application, one of these methods may be more effective than another. Often, it’s most effective to involve multiple senses, or all three. Studies conclusively show that sensory feedback improves user accuracy, makes using complicated products easier and quicker, and provides a better “emotional” response for the user.1
• Visual feedback: Human beings’ most developed sense is sight. Thus, incorporating visual feedback is desirable to producing positive results. Visual feedback appears in many forms, from simply illuminating an LED when a button press is detected to the more complex presentation of a scrolling phonebook display on a cellular phone in response to a touch slider.
The availability of high-resolution LCDs incorporating touch sensors has led to a plethora of visual responses to button presses and slider applications. Future technology applications have been announced by Microsoft and others that allow touches to perform heretofore complicated actions, such as sizing an image by simply “stretching” the image on the touch-sensitive display.
• Aural feedback: Another highly developed human sensory perception is hearing. Sounds have been used as a primary communication tool throughout history. Alarms virtually always incorporate a shrill sound to quickly grab everyone’s attention. Bells have been used to announce the current time to entire villages. And, of course, spoken language is the king of communication.
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