Easy Touch ET-604 User Manual

Kari Severinkangas FTIR TOUCH PANEL FOR A MOBILE DEVICE Architecture and prototype evaluation

10 FIGURE 2. Touch market forecast by technology in 2012 (IDTechEx 2012, date of retrieval 8.9.2013) There are many different methods

11 from the other layer by measuring the voltage level. The resistive touch allows input with any object, but in most devices only sin

12 light is transmitted. There must be an air gap between the touch window and the display. There is one company, named FlatFrog, that has been devel

13 The touch module manufacturer assembles the components (transmitters, receivers and controller IC) on a foil and molds the wavegu

14 chosen, because from an HW design point of view it is an easier component to integrate compared to a photodiode. Photodiode and pho

15 2 FTIR AND HW OPERATION 2.1 Total internal reflection The FTIR phenomenon has been known at least from the times of Isaac Newton (Zhu et al. 1

16 the detector chip surface and it decreases to zero at 90 degrees (light parallel to the chip surface). Naturally, the material of

17 FIGURE 5. FTIR touch panel In order to achieve a narrow dead band and a low cost design, the component count and signal routings to MCU must

18 FIGURE 6. Phototransistor measurement circuit Theoretical rise and fall times for a phototransistor are around 15 µs. In practise it is challeng

19 The measurement with photodiodes is similar to phototransistors, except that the current is much smaller, thus the voltage to be measured o

FTIR TOUCH PANEL FOR A MOBILE DEVICE Architecture and prototype evaluation

20 Figure 9 shows how the analog signal is read. The blue toggling line tells when LED is switched on. In this example case a phototransistor takes a

21 to the calibration levels. When a threshold level is passed, a touch is detected. Because of dirt and water (or liquids) a slow calibration task m

22 3 ARCHITECTURE 3.1 Functional architecture Figure 11 shows the main functions of the FTIR touch controller. The touch controller provides an i

23 normalized and pre-processed for the touch algorithm (touch detection). Self-calibration is an important function as it adjusts the sen

24 3.3 Verification and architecture choices Architecture is validated by prototyping and using iterative SW development methods. Also some quality

25 circuits are combined in a single package, containing MCU, memory, peripherals and passive components. The selected HW configurati

26 • Fast ADC converting time providing 1-2 Msps performance (12-16 bit). • 16 kb of RAM • 64 kb of Flash Today a 32-bit processor is a goo

27 4 SW ARCHITECTURE 4.1 Overview The HW requirements dictate very much the SW requirements. The SW binary size, the dynamic memory and the avail

28 The HW driver represents the low level SW stack, which interfaces with MCU. The C Algo (algorithm) component does the actual touch

29 the test SW reads the touch controller (n touch events) and stores the output to the database. Another option is to store the raw measurement data

3 ABSTRACT Oulu University of Applied Sciences Master Degree Program in Information Technology Author: Kari Severinkangas Title of Master’s t

30 There are three relevant interrupts: SysTick, timer and I2C. The FreeRTOS scheduler uses ARM SysTick (system timer) interrupt for scheduling an in

31 4.4 Algorithm 4.4.1 Choosing algorithm The algorithm can be qualified by accuracy, speed and scalability. The scalability has vari

32 5 RESULTS 5.1 Prototype HW and SW The prototype HW used in the project is a sandwich solution containing a MCU part on one circuit board and

33 with the touch panel’s coordinate system. For that reason the offset errors were first corrected in the results. Anyhow offsets were very small +-

34 FIGURE 16. Absolute errors in touch area (values in mm) Various tests were run and the overall result can be seen in the next table (table 5).

35 TABLE 5. Comparison of simulation and robot testing Simulation worst case (mm) Robot worst case (mm) Average distance error 0,64 0,65 Max distan

36 FIGURE 17. Example of a 10 * 16 test scan (values in mm) 5.4 MCU Performance The tested prototype was not configured to give the best possible

37 The algorithm processing does not take much time. When running CPU at 48 MHz and using 3 fingers, the algorithm processing time is around 6ms, whi

38 The dynamic memory consumption was measured by using API functions of FreeRTOS and by observing memory from the debugger. The measured RAM

39 6 SUMMARY The project proved that it is possible to implement a multi touch device by using TactoTek’s patented FTIR touch. The

4 TABLE OF CONTENTS TERMS AND ABREVIATIONS 6 PREFACE 7 1 INTRODUCTION 8 1.1 Scope 8 1.2 Technology 8 1.3 Touch technologies and markets 9

40 On the other hand the FTIR panel provides a more natural and secure input mechanism for applications where unintentional touches

41 LIST OF REFERENCES Benson, H. 1995. University Physics. New York: John Wiley & Sons Inc. Cohen, R., Small, J. 2013. Lambert’s law. 4physics.

42 APPENDICES INTERRUPTS AND TASKS APPENDIX 1 LED offRead ADCEnable Algo taskTimer InterruptSelect next LED and ReceiverA

43 CORTEX-M FEATURES COMPARISON APPENDIX 2

44 PROTOTYPE HW AND ROBOT TESTER APPENDIX 3

45 TESTING RESULTS APPENDIX 4

46 DEMO APPLICATION APPENDIX 5

5 4.4.1 Choosing algorithm 31 4.4.2 Algorithm interface 31 5 RESULTS 32 5.1 Prototype HW and SW 32 5.2 Test set-up 32 5.3 Touch accuracy

6 TERMS AND ABREVIATIONS ADC Analogue to Digital Converter. ARM Advanced RISC Machines, small microprocessor for embedded devices. DAC Dig

7 PREFACE In 2012 I had a great chance to start working at TactoTek to develop a touch technology based on a new manufacturing concept. Thanks to

8 1 INTRODUCTION 1.1 Scope TactoTek is a spin-off company from VTT (Finnish research center) that develops a novel FTIR (Frustrated Total Inter

9 TactoTek’s manufacturing process (Pat. FI 121862B) is very simple and cost-efficient, LEDs, photodiodes, controls and wiring are put on a foil subs