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1 Microchip mtouch Solution Slide 1

2 Goal! Understanding advantage of Capacitive Sensor and applications Microchip mtouch Solution A principal of Capacitive Sensor CSM(Cap sensing Module) of PIC16F72x CVD(Cap Voltage Divide) of PIC16F193x Slide 2

3 Requirement Hardware mtouch 14Ch CVD Demo Kit ( Include PICKIT Serial Analyzer) MPLAB PICKIT3 Debugger/Programmer Acrylic Cover ( 1mm thickness ) Sotware MPLAB IDE V8.40 or Later Hi-Tech C V9.70 or Later mtouch Diagnostic Tool V2.5 or Later mtouch UART Monitoring Tool(Microchip Korea Supported) Slide 3

4 Input features Keypad, Switches, Buttons Touch sensitive keys Touch-screen Output features Segmented or Graphical LCD LEDs Buzzers, Speakers Typical Human Interface System Features Communication Protocols USB, RF Wireless, IrDA, CAN, RS-232 Slide 4

5 mtouch Solutions Buttons, Keys & Sliders Touch Screen Controllers Integrated USB, LCD & Graphical Display options Slide 5

6 On-chip Capacitive Sensing Methods 1. Capacitive Voltage Divider (CVD): AN1298 Uses only the on-chip Analog to Digital Converter (ADC) ADC Capacitance is used as reference to calculate external capacitance Offers high noise immunity as well as low emissions 2. Charge Time Measurement Unit (CTMU): AN1250 High speed, Flexible, Analog peripheral; Key Scanning time 4 µs Measures relative and absolute changes in capacitance Uses on-chip adjustable precision current source Works in conjunction with ADC 3. Capacitive Sense Module (CSM): AN1171 Uses Frequency based sensing Relaxation oscillator frequency changes depending on touch Operation during sleep All the above three methods require No External Components and thus reduce the BOM cost Slide 6

7 Part # DM Featuring: 4 Motherboards PIC16F bit MCU PIC18F46J50 8-bit MCU PIC24FJ64GB bit MCU PIC32MX795F512H 32-bit MCU 4 Sensor Daughter Boards NEW 2-Channel Slider 4-Channel Slider 8 Keys Direct Sense 12-Key Matrix PICkit Serial Analyzer Program & Debug mtouch Diagnostic Utility Price $99.95 New mtouch Capacitive Evaluation Kit Slide 7

8 CSM(Capacitive Sense Module) Slide 8

9 Capacitive Touch Principle Introduction of a finger produces a parallel capacitance (CF) Front Panel CF PCB Sensor Cs Ground Trace CP CP is the Parasitic capacitance CF is the Finger capacitance Cs is the total Sensor capacitance Sensor Capacitance (CS) = CP + CF Touch Sense Technology Slide 9

10 Physics Summary CF C = ε 0εr A d CP Sensor performance KEY PARAMETERS: Area, distance, material properties (ε r ) Slide 10

11 Cap Touch with PIC16F72X New Module called Capacitive Sense Module (CSM) Algorithms for touch detection are identical More Inputs 8 Channels on 28 pins 16 Channels on 40 pins Hardware Integration No external component required, Direct sensor interface Save 3 I/Os per sensor Choice of Timer 0, Timer 2 or WDT for time base Operation during Sleep Low power consumption More autonomous timing for servicing interrupt Slide 11

12 Built-in in SR-Latch Circuit PICmicro MCU CVREF 2/3 VDD 0.1µF 3KΩ 1KΩ VDD 1/4VDD + _ + _ C1 C2 TIMER0 S R Q Q C2OUT pin Parts: PIC16F616 PIC16F690 PIC16F887 TIMER1 T0CKI pin 120KΩ CS Slide 12

13 PIC16F72x Family Sensor 0 CPS0 PIC16F722/723/724/726/727 CAPOSC Module (Oscillator) Frequency Capture TMR1 TMR0 TMR2 CPS15 * 40-pin PIC MCU has 16 channels Built-in in SR-Latch Circuit PIC16F72x Family Slide 13

14 Operation & Measurement PIC16F72x TMR0 interrupt provides a fixed time base for measurement TMR1H:TMR1L Increment Frequency CSM TIMER1 MUX TIMER0 TMR0 0 0xFF time time CP TMR0 overflow Slide 14

15 Operation & Measurement PIC16F72x TMR0 interrupt provides a fixed time base for measurement TMR1H:TMR1L Increment Frequency CSM TIMER1 TIMER0 time MUX TMR0 0 0xFF TMR0 0 0xFF time CP TMR0 overflow Frequency slows down TMR0 overflow Slide 15

16 Operation & Measurement PIC16F72x TMR0 interrupt provides a fixed time base for measurement TMR1H:TMR1L Increment Frequency CSM TIMER1 MUX TIMER0 time TMR TMR TMR time CP Frequency slows up TMR0 overflow TMR0 overflow Slide 16

17 Operation & Measurement Use two timers Timer 0 = Sets fixed timebase, T Timer 1 = Captures edges to measure frequency Δf T T Timer 0 Interrupt 0 0xFF 0 0xFF 0 0xFF Slide 17

18 CVD(Capacitive Voltage Divide) Slide 18

19 CVD Measurement Principle - Resistive Voltage Divider Vref FORMULA : R1(10K) Reference resistor (Rref) Vx Vx / Vref = ( Rx Rx + Rref ) R2(10K) Unknown resistor (Rx) Ex) Vref is 5V Vx = 10K/(10K+10K) x 5V = 0.5 x 5 = 2.5V Slide 19

20 Measurement Principle - Capacitive Voltage Divider Vref FORMULA : C1(10pF) Reference Capacitor (Cref) Vx Vx / Vref = Cref ( Cx + Cref ) C2(10pF) Unknown Capacitor (Cx) Slide 20

21 CVD Measure Cycle CVD Measure steps: Step1 : Charge Cref, Discharge Cx Step2 : Divide Vref between Cref and Cx Step3 : Measure voltage Vx Slide 21

22 CVD Measure Cycle Step1(idle phase) Vref SW2 voltage divide SW3 charge Vx SW1 discharge C2(10pF) Unknown Capacitor (Cx) C1(10pF) Reference Capacitor (Cref) - SW1 is closed for Cx discharging and SW3 is closed for Cref charging. - SW2 is opened Slide 22

23 CVD Measure Cycle Step2(voltage divide) Vref SW2 voltage divide SW3 charge Vx SW1 discharge C2(10pF) Unknown Capacitor (Cx) C1(10pF) Reference Capacitor (Cref) - SW1 and SW3 are opened, SW2 is closed for voltage divide. - The voltage on C1 is now divided between Cref and Cx. Slide 23

24 CVD Measure Cycle Step3(measure voltage) Vref SW2 voltage divide SW3 charge VAVERAGE Vx SW1 discharge C2(10pF) Unknown Capacitor (Cx) C1(10pF) Reference Capacitor (Cref) - SW1,SW2 and SW3 are opened for measure voltage. (Vx) - Reducing all further changes on Vx. Slide 24

25 CVD Measure used to PICmicro(charge) Vref SW2 A/D multiplexer SW3 sample switch A/D Block Vx SW1 output transistor C2(10pF) Unknown Capacitor (Cx) C1(10pF) Reference Capacitor (Cref) All the switches and the reference capacitor are readily available inside of a PICmicro - Cref is Chold, Vref is digital I/O or FVR or DAC Slide 25

26 CVD Measure used to PICmicro(voltage divide) Vref SW2 A/D multiplexer SW3 sample switch A/D Block Vx SW1 output transistor C2(10pF) Unknown Capacitor (Cx) C1(10pF) Reference Capacitor (Cref) All the switches and the reference capacitor are readily available inside of a PICmicro - Cref is Chold, Vref is digital I/O or FVR or DAC Slide 26

27 Vref CVD Measure used to PICmicro(measure voltage) SW1 output transistor SW2 A/D multiplexer C2(10pF) Unknown Capacitor (Cx) SW3 VAVERAGE sample switch GODONE is Set A/D Block Vx C1(10pF) Reference Capacitor (Cref) All the switches and the reference capacitor are readily available inside of a PICmicro - Cref is Chold, Vref is digital I/O or FVR or DAC Slide 27

28 Capacitive Voltage Divider Using an ADC A sensor press increases parallel capacitance reducing VAVERAGE V AVERAGE = C AD (C AD + C S + C F ) * V DD VAVERAGE PRESS TIME to ADC CF CS CAD SENSOR Touch Sense Technology Slide 28

29 Basic Cap Touch System Slide 29

30 Basic Cap Touch System Signal Processing Signal Acquisition Decision Making Slide 30

31 Basic Cap Touch System Signal Processing Signal Acquisition Decision Making Signal Acquisition Sensor Design Board Layout Mechanical Design Get Reading Value Peripheral Management Pre-Processing Slide 31

32 Basic Cap Touch System Signal Processing Signal Acquisition Decision Making Signal Processing Set Trip Averaging Filter out noise RF Radiated Conducted Noise Slide 32

33 Basic Cap Touch System Signal Processing Signal Acquisition Decision Making Decision Making Press? Release? Which button? Slide 33

34 How to get started? Application notes AN Basic Overview of operation Webinar online AN Hardware and Layout of sensors Webinar online AN1103 Software Techniques for detecting buttons AN1104 How to get more buttons? AN1171 Using the CSM with PIC16F72X AN1202 Capacitive Sensing with a PIC10F AN1250 Microchip CTMU for Capacitive Touch Webinar Online TB3014 Low Power Cap Sensing with CSM NEW AN1254 Cap Touch Algorithm Simulation AN1268 Cap Touch using Period Measurement AN1286 Water Resistance Capacitive Touch NEW AN1298 Capacitive touch using ADC (CVD) Design Center: NEW NEW Slide 34

35 Thanks Slide 35