1. Low Cost Infrared Touch Screen Bezel for POS Systems Rohan Verma, Jeremy Taylor, Freddie Dunn III Georgia Institute of Technology School of Electrical and Computer Engineering October 19-23, 2009

2. Project Overview Optically driven bezel that affixes to a computer display to provide touch screen capabilities. Existing products are enhanced by retrofitting the bezel to displays. Product targets service industries whom seek to increase efficiency. Development costs and a production run of 5000 units totals $458,000 with a single unit cost of $91.60

3. Design Objectives Design a precision touch device with as few sensory components as possible Interprets single clicks, double clicks, and mouse drags USB is used as the communication mechanism between the MCU and PC and also serves to power the device –Plug and Play Bezel attaches to a 4:3 19” monitor

4. Building Blocks LEDs Microcontroller Bezel ADC USB PC Phototransistor

5. LED Circuit Design Used to create a plane of light Current divider to determine resistor values Account for voltage drop across the LEDs Incorporate an on/off transistor to allow for measures to be taken with in two states

6. Two sided LED configuration Problem areas / dark spots

7. 2.85” 4.5”6.2” 11.4” 15.2” LED Output Grid

8. Phototransistor Circuit Design Used to detect light levels Voltage across ADC input terminal and ground proportional to infrared light levels Voltage reference used to specify maximum voltage at the ADC input

9. Microcontroller Program Flow

10. PC/MCU Interaction USB 2.0 Interface 5V supply 500mA current limit – No external supply necessary Simplifies design – Plug-n-Play: OS supplied HID drivers

11. Evaluating Touches Store ‘base’ light intensity to determine if further processing required Strobe the LEDs to remove noise  Difference of the two readings for a given sensor forms the current light intensity at that sensor Hardcoded table of phototransistor values  Used to find relative finger placement  Extrapolate intermediate touch points from this table

12. Problems/Issues The original LEDs selected had too small of a sensitivity angle to be effective in this use Initial LED/Phototransistor orientation left “dead zones” on the screen Complexity of USB development

13. Demonstration Plan Bezel attached Bezel overlaid on LCD Bezel connected to PC through USB Power supplied through USB OS recognizes touch screen OS automatically recognizes the touch screen device OS should detect touch screen device as HID mouse – interpret touch as mouse click Pointer controlled by touch Slide finger  mouse pointer should follow Mouse clicks are detected at correct locations Distinguish between single and double click

14. Project Schedule Test and build prototype Test under different transceiver configurations Test under different ambient environments In progress Finish by 10/23 Design PCB and MCU Layout PCB Develop and optimize touch detection algorithm In progress Finish by 11/6 Interface with OS Utilize USB stack to enable MCU to talk to OS Debug any issues that may arise Finish by 11/20

15. Current Status Created/Programmed simple PIC microcontroller firmware – Working on ADC polling implementation LED/Phototransistor circuits fabricated and tests performed on them – Waiting on new LEDs/Phototransistors