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Touch Panel
ABCD
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C
D
A BR1 R2
R3R4
R5
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R1 R2
R3R4
R5
A B
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.
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Tri-State Logic
HIGH:
I/O pinOUTPUT, HIGH
LOW:
I/O pinOUTPUT, LOW
HIGH IMPEDANCE:
I/O pinINPUT
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To Read Between Two Wires
Digital I/O pin 1
Digital I/O pin 2
Digital I/O pin 3
Digital I/O pin 3
Analogue Inputs1 2 3 4
A
B
C
D To Touch Panel
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To Read Between Two Wires
Digital I/O pin 1
Digital I/O pin 2
Digital I/O pin 3
Digital I/O pin 3
READ FROM 31 2 3 4
A
B
C
D
HIGH
LOW
HIGH IMPEDANCE
HIGH IMPEDANCE
PASSES THROUGH R1, R3, R4
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To Read Between Two Wires(Pin 1,HIGH) V+
(pin 3,LOW) 0V
100Ω fixed resistor (Rf2)
100Ω fixed resistor (Rf1)
Panel Resistance (Rp)
Analogue 3
A
C
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Use Simultaneous Equations
D-A: R1+R3+R5D-B: R2+R3+R5A-B: R2+R1
A-D: R5+R3+R1A-C: R4+R3+R1C-D: R4+R5
(R1,R5)-Isolated coordinates
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Too Many Pins!
What Next?
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The solution: Serial In Parallel Out Shift Registers
01100011 01100011
Chained Together!
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Row Control
Column Control
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Matrix Schematic
Benefit: Fewer pins than if connected individually.Problem: Can only have individual control of LEDs
one row at a time.