Force sensors add 'touch' to any PC

Nijmegen, The Netherlands--Here's a self-contained, low-profile box that brings touch-input capability to computer monitors. Place DECtouch beneath the terminal, connect a serial data cable to the computer, plug in the power, and--Voila! The PC's video display becomes a touch-sensitive monitor. A simple calibration program translates touch locations into screen coordinates.

The system works as follows: The top of the unit mounts on three-dimensional springs, which allow movement in all directions relative to the unit's base. Internal sensors constantly measure the distance between the top and the base.

Each sensor consists of two parallel plates, one attached to the top, and one attached to the base. These plates form a capacitor. Two sets of sensor plates, mounted at a 45-degree angle, are located in each corner of the unit, for a total of eight sensors.

When you touch a monitor sitting on DECtouch, the force of the touch alters the distance between the unit's top and base--typically on the order of 0.001 inch. This difference changes the capacitance across each sensor, indicating movement in the x-, y-, and z directions, as well as roll, pitch, and yaw. The system then determines the level of force exerted to cause this movement, and the location where the force was applied.

To generate a baseline, an internal processor checks each sensor set approximately 40 times per second. This constant re-reading allows the system to filter out fluctuations in capacitance caused by temperature or humidity variations. Additional sensors detect the motion of the surface the system rests upon, protecting it from non-touch movements like vibration and sway.

"DECtouch can be used with any 12- to 19-inch monitor," says Eva Lilljegren, European Product Manager of Terminals and Input Devices. "And because the unit mounts beneath and is external to the monitor," she adds, "no regulatory agency approval or vendor warranties of the monitor are violated."

Additional details, Europe...Contact Components & Peripherals Business Unit, Digital Equipment Parts Center B.V., Box 6774, 6503 Nijmegen, The Netherlands, Tel: +31 80 529 911, FAX: +31 80 568 450.

Additional details, U.S. ...Norman Tremblay, Digital Equipment Corp., 2 Results Way, Marlborough, MA 01752-3011, (508) 467-7907, FAX: (508) 467-1926.