WriteTouch Gives Pen Computers the Right Touch

Pen-based computing systems are often lauded for their intuitiveness, much of it a result of the way these systems encourage direct interaction and minimize the boundaries between person and machine. In these systems, the experience that people encounter is primarily shaped by two factors: the quality of the software, representing the logical portion of the system, and the digitizer, which greatly influences the physical impression.

In terms of the user experience, pen-based computing is perhaps a slight misnomer. In the best designed systems of the near future, people are equally likely to use their finger as a pen for certain types of input. Indeed, General Magic’s Magic Cap derives much of its friendliness by incorporating this idea into the basic design.

Getting the Right Touch

The problem today has centered on developing an accurate and affordable digitizer technology that combines these two modes of input, while at the same time reducing weight, thickness, and power consumption. However, the times are changing, accelerated by a new alliance known as WriteTouch between NCR Microelectronic, a division of AT&T Global Information Solutions, and Scriptel Holding, Inc.

WriteTouch is a cordless electrostatic digital pen (digitizer) technology that includes a sensor, digital stylus, controller, and associated drivers. When WriteTouch becomes available around the middle of 1995, OEMs will be able to use the digitizing technology to create a new generation of notebooks, handheld communicators, PDAs, and desktop conferencing systems.

The WriteTouch electrostatic technology represents a three year development effort by NCR and Scriptel, and features several improvements over two of the major systems currently in use: electromagnetic and membrane. Electromagnetic systems generally suffer due to interference from electrical noise generated by the LCD display. Likewise, membrane technology has its own shortcomings, including low transmissivity of light and the lack of proximity sensing that is useful in certain system designs.

WriteTouch Features

OEMs that select the WriteTouch technology will gain the benefits encompassed and protected by over 60 patents. These advantages include:

• Acceptable finger and pen input. Most systems concentrate on one at the expense of the other.
• Thinner and lighter display systems. The WriteTouch sensor adds only about 0.006 mils thickness to the system.
• Greater transmissivity. The design of the technology features fewer surfaces and air gaps, thereby reducing light reflection within the system and making the display easier to read.
• Better resolution and responsiveness. Together, these two factors will help improve drawing and handwriting accuracy, making the job of the software a bit easier.
• Smoother OEM integration. WriteTouch features built-in shielding from the LCD’s electrical noise.

A Bit of How it Works

WriteTouch uses a cordless electrostatic digital pen which generates an electric field. This field induces a current in the indium-tin-oxide (ITO) conductive layer that surrounds the LCD protective glass, causing the current to flow though connections at the four corners of the display. The system is able to detect the touch of a finger, as opposed to the stylus, by the extra capacitive load added to the ITO sensor by the finger.

The location of the stylus or finger is calculated using the controller chip by amplifying, filtering, and measuring the current flow at the four corners of the sensor. This enables the controller to determine the x and y coordinates, while accounting for any non-linearities that may come about due to variations in the ITO coating using data specific to each sensor panel.

After accurately determining the stylus or finger position, the controller forwards the coordinates and status information to the CPU. The status information includes such things as whether the pen is in proximity or in contact with the surface.

The final step is common to all systems. The software determines whether the user is writing digital ink or using the stylus for command input, such as selecting a menu item. Either way, the system responds by instructing the LCD to display the appropriate response.

The WriteTouch Package

The components that make up the WriteTouch system include a single chip controller, a stylus cartridge that is ready for custom housing, a pre-fabricated sensor panel, along with software drivers that are optimized for performance. ❑

NCR Microelectronics Products Division
Lea Schwartz
(303) 226-9550
1635 Aeroplaza Drive
Colorado Springs, CO 80916
(719) 596-5795
(719) 597-8225 (fax)

Scriptel Corporation
Edward Palmer
(614) 276-8402
4145 Arlington Plaza
Columbus, OH 43228
(614) 276-8402
(614) 276-7615 (fax)