Out in Front

Low-cost touch pads cut power drain by 85%

The VersaPad touch pad from Interlink Electronics aims to overcome false-actuation and power-drain problems that occur with capacitive touch pads. False actuation—when your hand activates the pad by passing nearby—occurs frequently on most notebook PCs in which touch pads reside between a user and a keyboard. To solve this problem, the VersaPad uses force-sensitive resistors, like those in eraser-head pointing devices, in what Interlink calls "semiconductor touch-pad technology." The technology offers lower cost; insensitivity to humidity; ability to accept input from a hand, stylus, or pen tip; and a pad that can modulate its response as you vary the applied force. Interlink emphasizes that capacitive pads are humidity sensors, which cease to operate when wet. Capacitive pads also require you to point with your hand; they do not respond to input from a stylus or a gloved hand, which many industrial applications require.

The technology also lowers power drain, and Interlink further reduces the drain by putting the pad-support circuits into a "sleep" mode when nobody touches the pad for 1 sec. Capacitive pads cannot offer such a mode; if they did, they could not sense when someone tried to use the pad. Power drain is a problem in battery-powered devices, such as cordless IR keyboards; the VersaPad uses one-seventh the power of a capacitive pad. (Power drain is also a big issue in notebook PCs, but a capacitive touch pad uses only a small portion of a notebook's total power.)

Interlink expects the VersaPad to be less expensive than capacitive touch pads partly because of the lower cost of one of the VersaPad ICs. (This IC, or its counterpart in capacitive pads, comes from the pad vendor, which can mount it underneath the pad assembly or provide it for the PC manufacturer to mount on the motherboard.)

VersaPad is available as an OEM drop-in replacement for capacitive pads. A developer's evaluation kit costs $150. The company expects a retail price of less than $60 for an end-user mouse-replacement device that it plans to offer early in 1997. New software will take advantage of the pad's proportional response to force. With this software, you should, for example, be able to negotiate Windows menus more easily by varying the pressure you apply to the pad, thus varying the speed of the "elevators" adjoining the menu items.—by Dan Strassberg

Interlink Electronics, Camarillo, CA. (805) 484-8855, fax (805) 484-8889, http://www.interlinkelec.com.