2. R1R2 R3 R4 R5

3. R1R2 R3 R4 R5 AB C D How do you isolate the x,y coordinate? (x,y) OR (R1,R5) 1. Use the microcontroller to read the resistance between pairs of wires. 2. Use simultaneous equations to calculate the values of individual resistances.

4. Tri-State Logic HIGH: I/O pin OUTPUT, HIGH LOW: I/O pin OUTPUT, LOW HIGH IMPEDANCE: I/O pin INPUT

5. To Read Between Two Wires Digital I/O pin 1 Digital I/O pin 2 Digital I/O pin 3 Analogue Inputs 1 2 3 4 A B C D To Touch Panel

6. To Read Between Two Wires Digital I/O pin 1 Digital I/O pin 2 Digital I/O pin 3 READ FROM 3 1 2 3 4 A B C D HIGH LOW HIGH IMPEDANCE PASSES THROUGH R1, R3, R4

7. To Read Between Two Wires (Pin 1,HIGH) V+ (pin 3,LOW) 0V 100Ω fixed resistor (R f2 ) 100Ω fixed resistor (R f1 ) Panel Resistance (R p ) Analogue 3 A C

8. Use Simultaneous Equations D-A:R1+R3+R5 D-B:R2+R3+R5 A-B:R2+R1 A-D:R5+R3+R1 A-C:R4+R3+R1 C-D:R4+R5 (R1,R5)-Isolated coordinates

9. Too Many Pins! What Next?

10. The solution: Serial In Parallel Out Shift Registers 011000110 1 1 0 0 0 1 1 Chained Together!

11. Row Control Column Control

12. Matrix Schematic Benefit:Fewer pins than if connected individually. Problem:Can only have individual control of LEDs one row at a time.