Electronic Design

These Touchscreen Pushbuttons Push You Right Back

A unique sensing system makes graphical interface buttons feel and respond like their mechanical anscestors.

Tactile feedback could add a layer of confidence as well as a more familiar feel to passive touchscreen applications. With that in mind, the TouchSense technology from Immersion (www.immersion.com) interfaces with the graphical buttons on a touchscreen to make them feel more like mechanical buttons.

Without affecting standard touchscreen functions, the system provides a fast tactile response, synchronizable with sound and image changes. It’s compatible with flat touchscreen sizes ranging from 2 in. to beyond 19 in. and supports a variety of sensing technologies, including capacitive, resistive, surface acoustic wave, and infrared.

Virtual buttons
The proprietary technology vibrates the touchscreen at varying frequencies, magnitudes, durations, and wave shapes, while application software controls tactile feedback. The software ensures that various on-screen objects and buttons maintain the desired feel.

Also, the software enables designers to program each button individually. One action button can provide a higher level of tactile feel, while buttons for other actions—no matter where they appear on the screen—could have a different feel.

Touching a particular button on the screen generates a signal to the touchscreen controller (see the figure). The controller determines the point of contact and sends the information to the application software, which in turn causes the TouchSense controller to deliver a preset tactile effect to the button.

The buttons can deliver a pulse sensation when lightly touched and a pushback response when pressed. A rockerswitch- like graphic can emit increasing or decreasing vibrations corresponding to changes in, say, motor or fan speed. Scrolling displays can elicit a stop sensation when reaching a first or last menu. Switch controls can deliver a pop effect. And, levers can provide a click response for each setting.

The company says that this higher level of interaction will open up more types of applications for active touchscreens. It will definitely make them more effective and reliable in certain environments, such as medical and industrial, where users may need to wear gloves. The largest market appears to be point-of-sale kiosks and ATM machines, usually installed in noisy locations.

Going mobile
Immersion’s technology is not limited to large touchscreen systems. Supporting touchscreen sizes up to 15 cm diagonal, TouchSense Mobile includes a TouchSense executable, a tactile effects library, an integration guide, software for the mobile end product, and a software development kit.

Instead of vibrating the touchscreen surface, the embedded software provides high-speed control over a standard vibration actuator such as those found in a cell phone. Pressing a button on the touchscreen drives the actuator to produce a preset vibration level. This programmed vibration, in turn, creates the perception of a mechanical button.

The streamlined integration process involves deploying the TouchSense runtime executable onto the mobile device’s microprocessor, which loads the tactile effects library into memory. The software-integration guide describes how to get the application programming interface (API) to retrieve tactile effects from the OEM host application. The mechanical-integration guide provides details for designing actuator-control circuitry.

Any application processor with about 1 MIPS of spare processing power with one or two free pulse-width modulation (PWM) lines and two available digital I/O lines will do. The TouchSense kernel requires a minimum trigger rate of 200 Hz every 5 ms when tactile effects are playing. The trigger can be a software interrupt, timer-triggered interrupt, or timed event.

The firmware and effects libraries require about 40 kbytes of ROM and 20 kbytes of RAM. The drive circuit requires about 4 by 3 mm or less of board space, depending on the components. It also consumes less than 1 mA of current during intense use, based on timings of 10 ms per touch and one touch per second.

GPS systems with the technology could reduce the amount of time drivers needs to look at the GPS device instead of the road ahead. Applications also include remote controls for home-entertainment systems, medical diagnostics, test-and-measurement equipment, portable terminals, games, and media players.

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