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Capacitive sensing: Improved option for user interfaces

Handset user interfaces (UIs) are moving toward intuitive touch interaction. As users grow more technologically sophisticated and accustomed to these new handset designs, they will see that their options are best realized through capacitive technologies that bridge the gap between gesture-based controls and intuitive user interfaces.

Projected capacitance measurement devices are, in essence, solid state with no moving parts. Thus, they offer thinner profiles overall and more durability than electro-mechanical systems.

In most cases, a capacitive sensing system consists of three main functional blocks: an Analog Front End (AFE) for capacitive sensing; data processing and control; and an interface block for communications to a host processor. In actual implementation, the human finger forms one half of the parallel plate while the other parallel plate is connected to the sensor input of the chip.

A UI should enable the user to take advantage of the device's capabilities without being cluttered or difficult to use. It is important to have as many features and functions as possible, but present them to the user in a way that is not confusing. Also, transparent capacitive sensing designs over a display enable dynamic user interfaces that change according to the application being used. What's more, a device with innovative industrial design and sleek surfaces may be more attractive.

The second-generation LG Chocolate and Samsung Miniskirt are great examples of successful button-only designs. By being able to fit into a slim form factor, the design enables a usage model where the device could be used without exposing the keymat. This is useful when the user is not making a call. It is also a nice complement to the scrollwheel and helps to minimize UI crowding and increasing feature functionality.

These phones also demonstrate the tandem of touch and visual feedback. When inactive, the buttons are dark, but when touched or when the phone is open, the buttons illuminate.

A similar design can be found on the Nokia 6205, where a capacitive button solution was implemented on the exterior of the phone directly under the display to control settings on the media player. This clamshell phone can be operated without flipping it open.

The Samsung Soul clear array allows for dynamic icons and patterns to be displayed, each representing a different feature function. For example, when in music mode, music-related icons like play and pause will light up. When in camera mode, camera-related icons like zoom in and zoom out will light up.

However, the usage model of a typical button is preserved even though the buttons in this case are dynamic icons on the clear array. With this clear application, unique and dynamic icons and patterns were implemented to personalize the phone and make it unique.

The LG TRAX CU575 uses a 1D capacitive-enabled scrollbar on its exterior to control volume in music mode. Capacitive touch solutions for 1D scrolling have also proven useful in handheld devices where navigating through long lists is essential.

OEMs can also incorporate scrolling ballistics for speed-sensitive scrolling through log lists. Conventional mechanical scrolling methods such as scroll wheels and click-by-click button input are prone to wear.

The Samsung SGH-F480 Tocco and LG Prada handsets represent designs that use a clear 2D sensor display with both 1D scroll applications and 0D buttons integrated into it. A full touchscreen device using transparent projected capacitive sensing maximizes the real estate for multimedia- and feature-rich applications.

The camera application on the SGH-F480, in particular, greatly benefits from the dynamic on-screen controls enabled by the touchscreen. These designs can better incorporate the use of gestures and multifinger applications.

An integrated and customizable solution, such as Synaptics OneTouch, can help comprehend design challenges to maximize the advantages of capacitive sensing.


Albert Lee is a Strategic Applications Manager at Synaptics with more than 15 years of experience in the semiconductor and flat panel display industries.

Jimmy Lin is a Strategic Applications Engineer at Synaptics focused on developing and characterizing whole product collateral in support of Synaptics' extensive array of human interface products.

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