Tough touchscreen

Standard four-wire resistive touch-screen technology depends on a uniform Indium Tin Oxide (ITO) coating as a voltage divider. Operation entails applying a voltage gradient across the resistive surface of one layer and measuring the voltage on the other. Touch-screen life and positional accuracy depend on maintaining ITO uniformity on each substrate, andminimizing positional drift due to property changes.

The ITO voltage divider is difficult to apply uniformly, and it's resistance changes with temperature, humidity, general use, and abuse. The result is positional drift and a need for constant recalibration.

This design uses a proprietary deposited resistor instead of ITO as a voltage divider. The result is a more durable design that is less expensive to manufacture, and requires no recalibration. Eliminating the ITO results in higher process yields and a 10 to 20% cost savings.

Brian Heiser, CAM Graphics Co., 15 Ranick Drive, Amityville, NY 11701; (516) 842-3400.