FTIR TOUCH PANEL FOR A MOBILE DEVICE : Architecture and prototype evaluation

Abstract

This work was done in a company named TactoTek, which is specialized in embedding electronic components into 3D molded plastic. The technology allows curved touch interfaces produced cost efficiently by integrating infrared transmitters and receivers into molded plastic. How to design an optical touch application that runs on a microcontroller of limited power and processing resources providing touch functionality that meets today’s standards. The basic concepts of infrared detection and the frustrated total internal reflection (FTIR) phenomenon are gone through. The SW and HW architecture, signal processing and algorithms are described at high level.

A prototype device was developed with PC connectivity in order to read the runtime data to be displayed in the signal monitoring application and to feed the algorithm on computer. A simulator SW was developed to explore different kinds of methods for calculating touch points. The best algorithm candidate was integrated in a microcontroller providing digital interface for host device communication. The prototype’s performance and accuracy was evaluated by using a robot tester and other manual measurement methods. In the end the prototype device was integrated in a cell phone with a rebuilt mechanics.

The developed touch application has an accurate multi touch functionality and allows input to be given with gloved hands. In addition, a touch size, shape and relative pressure are calculated. This study proves that this technology has potential and it can compete with the existing technologies providing a good performance, accuracy and a multi-touch functionality. The challenge in the technology is the activation sensitivity compared to the capacitive, which does not need a physical contact for a touch activation. On the other hand the FTIR panel provides a more natural and secure input method for applications where unintentional touches should be avoided. This could be advantageous in consumer applications where usually buttons and switches have been used, for example household and automotive applications. In order to achieve an optimal solution, more studies are needed in the material, hardware and signal processing.