Capacitive mtouch Sensing Solutions

Agenda Design Guidelines for: Copper Pad Size Circuit Traces Ground Plane Other Considerations LED Back-Lighting Effect Robust Design Conclusion Appendix Test Board Spec Test Condition Breakdown Voltage of panels materials 2010 Microchip Technology Korea AE Team. All Rights Reserved. Capacitive Touch Sensing Design Guide Slide 2

Capacitance A C ε = 0 ε r A d d ε0 εr A C d Permittivity of Free Space (8.854 Pico-Farad/meter) Relative Dielectric Constant (unit-less) Area of Plates (meters) Capacitance (Farads) Distance between plates (meters) 2010 Microchip Technology Korea AE Team. All Rights Reserved. Capacitive Touch Sensing Design Guide Slide 4

Pad Shape and Size 1 < Top > < Bottom > 20mm Touch Pad PIC16F726 Idle Touch % 1 616 550 10.714 2 645 600 6.977 3 675 641 5.037 4 665 637 4.211 5 663 636 4.072 800 700 600 500 400 300 200 100 0 <1> <2> <3> <4> <5> 12 10 8 6 4 2 0 Idle Touch % 2 15mm Touch Pad PIC16F690 Idle Touch % 1 548 484 11.679 2 580 528 8.966 3 612 575 6.046 700 600 500 400 300 200 100 14 12 10 8 6 4 2 Idle Touch % 3 10mm 4 600 570 5.000 5 595 568 4.538 0 <1> <2> <3> <4> <5> 0 4 5 8mm 5mm Touch Pad PIC10F206 Idle Touch % 1 186 170 8.602 2 193 180 6.736 3 200 192 4.000 210 200 190 180 170 160 10 8 6 4 2 Idle Touch % 4 198 191 3.535 5 197 191 3.046 150 <1> <2> <3> <4> <5> 0 2010 Microchip Technology Korea AE Team. All Rights Reserved. Capacitive Touch Sensing Design Guide Slide 7

Pads and Traces PICmicro MCU CVREF 2/3 VDD + _ C1 S Q Covering Plate 1/4VDD + _ C2 R Q sensor sensor 2 Via PCB Trace connects sensor to PIC MCU pin Sensing Trace as far away from other signals trace as possible (Do not route traces under any Sensor) 120KΩ C P1 120KΩ C P2 2010 Microchip Technology Korea AE Team. All Rights Reserved. Capacitive Touch Sensing Design Guide Slide 9

Other Trace Considerations Traces connected to Sensor pad Same Length (as short as possible) Same Thickness (as thin as possible) Parasitic capacitance sensor 1 sensor 2 sensor 3 Bottom View 2010 Microchip Technology Korea AE Team. All Rights Reserved. Capacitive Touch Sensing Design Guide Slide 10

Ground Plane Ground Plane for Sensor Pad - Sensor Pad Closed to Ground Plane, Capacitance Cp Increase (Sensor Sensitivity decrease) - Ground plane is needed for reducing the SNR (signal to Noise Ratio) - Open Mesh Ground to Minimize Parasitic Capacitance - Recommended Gap is 2~4 mm. Top Side Bottom Side Ground Plane for Traces - Traces Close to Ground Plane, Capacitance Cp Increase (Sensor Sensitivity decrease) - Ground plane is needed for reducing the SNR (signal to Noise Ratio) Sensor Pad Gap Ground Plane 2010 Microchip Technology Korea AE Team. All Rights Reserved. Capacitive Touch Sensing Design Guide Slide 12

Covering Plate Thickness Thinner covering plates increase sensitivity and accuracy C = ε 0 ε A r d CF CF 2010 Microchip Technology Korea AE Team. All Rights Reserved. Capacitive Touch Sensing Design Guide Slide 14

Dielectric Constant (εr) Material Air FR-4 Teflon Rubber Plexiglass Paper Glass Acryl Ceramic Vaseline Amber(fossil reson) ABS water Dielectric Constant(εr) 1 4.6 2.1 2.15 2.6 2.0~2.5 3.7~10 2.7 ~ 4.5 5.6 2.16 2.6 2.4 ~4.8 80.5 Covering Plate PCB C = - - - - - - - +++++++ Copper Pad ε 0 ε A r d Cover plate thickness and Its Dielectric Constant Play a large Part In Sensor Sensitivity. If you want to get high sensitivity, Cover plate s Material has a High Dielectric Constant. 2010 Microchip Technology Korea AE Team. All Rights Reserved. Capacitive Touch Sensing Design Guide Slide 15

LED Backlighting Issue Cover Plate PCB Touch Pad LED Touch Pad At nearby led a touch pad was cause led cross capacitance. It make the touch sensor less sensitive. To compensate a Led Cross Capacitance, Attached a 10nF Capacitor to transistor s Collector. 2010 Microchip Technology Korea AE Team. All Rights Reserved. Capacitive Touch Sensing Design Guide Slide 17

Robust Design: CSM Product PIC16F726 CAPOSC Module (Oscillator) Frequency Capture TMR1 CS TMR0 Resistor Value (ohm) PIC16F726 Idle Touch % 0 668 635 4.940 100 668 640 4.192 1K 667 640 4.048 5.1K 670 644 3.881 11K 673 648 3.715 56K 712 697 2.107 100K 722 716 0.831 740 720 700 680 660 640 620 600 580 0 100 1K 5.1K 11K 56K 100K 6 5 4 3 2 1 0 Idle Touch % 2010 Microchip Technology Korea AE Team. All Rights Reserved. Capacitive Touch Sensing Design Guide Slide 18

Robust Design : SR-Latch CVREF 2/3 VDD PIC16F690 1µF 300KΩ VDD 1/4VDD 100KΩ + _ + _ C1 C2 S R Q Q C2OUT pin TIMER0 TIMER1 T0CKI pin CS Resistor Value (ohm) PIC16F690 Idle Touch % 0 600 570 5.000 100 600 573 4.500 1K 600 574 4.333 5.1K 601 574 4.493 11K 603 575 4.643 56K 610 585 4.098 100K 624 602 3.526 630 620 610 600 590 580 570 560 550 540 0 100 1K 5.1K 11K 56K 100K 6 5 4 3 2 1 0 Idle Touch % 2010 Microchip Technology Korea AE Team. All Rights Reserved. Capacitive Touch Sensing Design Guide Slide 19

Robust Design : Simple Comparator Product PIC10F206 + C1 _ MMBD4148SE Band Gap(0.6V) CS 220K TMR0 Resistor Value (ohm) PIC10F206 Idle Touch % 215 210 4 3.5 0 198 191 3.535 100 198 192 3.030 1K 198 193 2.525 5.1K 203 198 2.463 11K 207 202 2.415 205 200 195 190 185 3 2.5 2 1.5 1 0.5 Idle Touch % 56K 210 207 1.429 100K 212 209 1.415 180 0 100 1K 5.1K 11K 56K 100K 0 2010 Microchip Technology Korea AE Team. All Rights Reserved. Capacitive Touch Sensing Design Guide Slide 20

Conclusion Design Considerations: Copper Pad Size Circuit Traces Ground Plane Covering Plate Other Considerations d LED Backlighting Issue Robust Design A C = ε 0 ε A r d 2010 Microchip Technology Korea AE Team. All Rights Reserved. Capacitive Touch Sensing Design Guide Slide 21

MCU Board Picture PIC16F726 Various Resistor PIC12F629 PIC16F690 Programmer Connector Push Button LEDs PIC10F206 Touch Ports Connector PIC24FJ128GA106 USB Jack PIC16F727 9V Adaptor Jack PICKIT Serial Connector Buzzer MCP1790 Jumper ( 5V or 3.3V ) MCP1700 2010 Microchip Technology Korea AE Team. All Rights Reserved. Capacitive Touch Sensing Design Guide Slide 23

Touch Board Picture < Top > < Bottom > 4 Zone Slide Pad Touch Pad Connector 2 Zone Slide Pad Touch Pad Connector 4X4 Matrix Pad Cap & Resistor Space for ESD/EMI Same Size(10mm), Different Pattern Same Pattern, Different Size 2010 Microchip Technology Korea AE Team. All Rights Reserved. Capacitive Touch Sensing Design Guide Slide 24

Test Condition Touch Pad Condition - Cover Material : Plastic - Cover Thickness : 3mm MCU Condition 1. PIC16F726( CSM Family ) - System Voltage : 5V - System Clock : Internal 4Mhz - Cap Button Scan Rate : 2.16mSec - CSM OSC Range Current : 18uA 2. PIC16F690( SR-Latch Family ) - System Voltage : 5V - System Clock : Internal 4Mhz - Cap Button Scan Rate : 2.16mSec 3. PIC10F206( Simple Comparator Family ) - System Voltage : 5V - System Clock : Internal 4Mhz - Cap Button Scan Rate : 10mSec 2010 Microchip Technology Korea AE Team. All Rights Reserved. Capacitive Touch Sensing Design Guide Slide 25

Breakdown Voltage of Panel s Materials Material Air Glass-Common Glass-Borosilicate Formica ABS Acrylic Polycarbonate FR-4 Nylon Lexan Breakdown Voltage [V/mm] 1200~2800 7900 13,000 18,000 16,000 13,000 16,000 27,000 16,000 15,700 2010 Microchip Technology Korea AE Team. All Rights Reserved. Capacitive Touch Sensing Design Guide Slide 26