1337 CTMU Capacitive Touch Sensing Using CTMUcaxapa.ru/thumbs/245906/1337.pdfUse MPLAB® IDE breakpoints to look at cap touch values Add these variables to the watch window: curRawData[]

© 2009 Microchip Technology Incorporated. All Rights Reserved. 1337 CTMU Slide 1

1337 CTMUCapacitive Touch Sensing

Using CTMU


1337 CTMU Class Objectives

• When you complete this class you will:• Be familiar with the CTMU module• Use the CTMU for capacitive touch applications• Use tools to tune/optimize CTMU capacitive

touch applications• Use software techniques used for capacitive

touch sensing• Understand how to use the CTMU for time

measurement and other applications


Agenda: 1337 Cap Touch - CTMU� Introduction to the CTMU Module� Lab 1 – Setting up the CTMU for Cap Touch � Software to Implement Cap Touch� Lab 2 – Reading a Cap Touch Button� Other Uses for CTMU (Theory & Applications)� Advanced Cap Touch Topics� Lab 3 – Matrix Keypad Implementation� Tools for Cap Touch Application Tuning� Lab 4 – Setting up the mTouch™ GUI to tune

buttons� How Materials Properties Affect Cap Touch� Lab 5 – Use of Different Overlays and Re-tuning

the Application � Summary


What is the CTMU?

Charge Time Measurement Unit


CTMU Block DiagramCTMUCONCTMUCON

CTMUICONCTMUICON

Edge Edge Control Control LogicLogic

External Edge External Edge Trigger PinsTrigger Pins

Timer1Timer1OC1OC1 Pulse Pulse

Output Output PinPin

CTMU CTMU Control Control LogicLogic

A/D A/D Conversion Conversion

TriggerTrigger

Pulse Pulse Generation Generation

LogicLogic

Comparator 2 OutputComparator 2 OutputComparator 2Comparator 2InputInput

Current SourceCurrent Source

Current Current ControlControl

A/D ConverterA/D Converter


CTMU Current Source

To A/D Converter

CTMU

Current Source

Trigger Starts/Stops Current Source

Discharge

Current Source charges:Capacitive Touch circuitryA/D Converter Cap

Trimmable current sourceRange : 0.55 uA, 5.5 uA and 55 uA


PIC® MCU A/DPIC® MCU A/D with CTMUCTMU Interface with ADC

A/D Converter

Current SourceA/D Conversion Trigger

CTMU

Sensor 0

CCA/DA/D

Sensor 15


Uses for the CTMU� Capacitance Measurement (Relative)

� Capacitive Touch� Stud Finder

� Capacitance Measurement (Absolute)� Humidity Sensor� Capacitance Meter

� Resistance Measurement� Sensors

� Inductance Measurement� Inductive Touch

� Time Measurement� TDR Cable Length Measurement� Flow Measurement

� Temperature Measurement� Thermostat


Parts with CTMU

More to follow in PIC24F and PIC18F families…

Part Family Architecture No. Ch XLP? USB Pin Count Flash (kbytes)

PIC18F87J90 8-bit 12 No No 64, 80 128PIC18F 46J11 8-bit 13 Yes No 28, 44 64PIC18F 46J50 8-bit 13 Yes Yes 28, 44 64PIC24FJ256GA1 16-bit 16 No No 64, 80, 100 64,128,192,256

PIC24FJ256GB1 16-bit 16 No Yes 64, 80, 100 64,128,192,256

PIC24FJ64GA1 16-bit 12 No No 28, 44 32, 64PIC24FJ64GB004 16-bit 12 Yes Yes 28, 44 64PIC24F16KA102 16-bit 7, 9 Yes No 14, 20, 28 4, 8, 16


Microchip Cap TouchmTouch™ Sensing Solutions use two methods:� Frequency Measurement (Relaxation Oscillator)

� Touch sensor is the C in an RC oscillator

� Voltage Measurement (Charge Time Measurement) � Capacitor is charged for a fixed time and the voltage is measured.

Voltage MeasurementFrequency Measurement

Vout

VCap

VCs


How is the CTMU usedfor Capacitive Touch?


Theory of operation: Introduction of finger produces a parallel capacitance

CF

How Does it Work?

CP


How CTMU Works for Capacitive Touch

EE101 basics:� Instantaneous Current in a capacitor

i = C · dV/dt� If i = constant current, then

I = C · V/t I · t = C · V

� If I and t are held constant, as C increases, V must decrease


__

CTMU Touch Circuit Components

A/D Converter

Current Source

CADCCIRCSWCF

VAD

Discharge

Trigger

CTMU

I = C· Vt

CP = CAD + CCIR + CSW = 30pFCF = 7pF


Sample Calculations

CP = CAD + CCIR + CSW = 30pFCF = 7pF

__I = C· Vt

____I =C· Vt

• I = 5.5µA• t = 10µS• CP = 30pF

V = 1.833

• I = 5.5µA• t = 10µS• C = CP + CF = 37pF

V = 1.486

When un-touched

When touched


Lab 1: Setting up the CTMU for Cap Touch


Lab 1a Objective� Gain a basic understanding of the CTMU

control registers (CTMUCON & CTMUICON)� Be able to set up the CTMU for cap touch


Lab 1a InstructionsPart 1a: Find the CTMU setup in the

initialization routine:� Set Registers CTMUCON and CTMUICON for

Capacitive Touch sensing� Use PIC24FJ256GB110 Family Data Sheet

for CTMU register details� Actual Part we are using is PIC24FJ128GB106


PIC24FJ256GB110 Data Sheet


Lab 1a Tips� Use the highest current setting for the CTMU

(55 uA)� Make sure the current source is OFF� Enable the CTMU last in init routine


Lab 1a Result

� Compile, Program, and Run the project

� An LED should light when the ‘8’ key is touched


Lab 1a Solution//setup CTMU

//CTMUCONCTMUCONbits.CTMUEN = 0; //make sure CTMU is disabledCTMUCONbits.CTMUSIDL = 0; //CTMU continues to run in idle modeCTMUCONbits.TGEN = 0; //disable edge delay generation mode CTMUCONbits.EDGEN = 0; //edges are blockedCTMUCONbits.EDGSEQEN = 0; //edge sequence not neededCTMUCONbits.IDISSEN = 0; //Do not ground the current sourceCTMUCONbits.CTTRIG = 0; //Trigger Output is disabledCTMUCONbits.EDG2POL = 0; //N/A since edges are blockedCTMUCONbits.EDG2SEL = 0x3; //Edge2 Src = OC1 (also N/A)CTMUCONbits.EDG1POL = 1; //N/A since edges are blockedCTMUCONbits.EDG1SEL = 0x3; //Edge1 Src = Timer1 (also N/A)

//CTMUICON

CTMUICON = 0x300; //55uA//or// CTMUICONbits.IRNG = 0x03; //55uA//optional

CTMUICONbits.ITRIM = 0; //Nominal - No Adjustment


Lab 1b: What does it Look Like?


Lab 1b Objective� Observe the CTMU charging of a

Capacitive Touch Button� See a difference in the CTMU charging

waveform when a finger is touching the button


CTMU Full Waveform

Begin Charge

End ChargeA/D Conversion

Discharge


CTMU Waveforms Untouched & Touched

Not Touched

Touched


Lab 1b Summary

� A touch is visible on the oscilloscope� The CTMU current source charges the

cap touch button in a very linear manner� Leakage of the cap touch circuit can also

be observed on the oscilloscope


Lab 2: Reading a Cap Touch Button


Lab 2 ObjectivePerform the 5 basic steps to read a CTMU cap touch

button:1. Discharge Circuit to ensure a start from 0 Volts

(this has been done)2. Turn on Current Source to charge touch circuit3. Wait for a fixed time period (2 uS for this hardware)4. Turn off Current Source to stop charging touch

circuit5. Perform A/D conversion to read voltage present on

touch circuit


� 8KeyBoard.c� CTMUcapsense.c� Timer4.c� 8KeyBoard.h� CTMUcapsense.h� Timer4.h

Lab 2 General Information: Project Files

Open Lab2 – C:\MASTERS\1337\Lab2


Lab 2 General Information: Main() Routine

New Data to process?

Start

Initialization

Service USB

Service otherapplication tasks

N

Stop Timer 4

Process New CapTouch Data

Start Timer 4

Y

Timer 4 Sets this variable

Insures no interrupt whileprocessing new data

Lab 2 code here


Lab 2 General Information: Timer 4 ISR

Timer 4 Interrupt(1 mS)

Process CTMUChannel

All ChannelsRead?

Increment Channelto read

Exit ISR

N

Reset Channel #Set Flag to process

new data

Y

Setup in Init

Lab 2 Code

Check for all CTMUChannels read

Flag is read by main routine

Get ready for next interrupt


Lab 2 General Information: Application Software Design

•The main program loop processes the Cap Touch data after all of the channels have been scanned

•Timer 4 is used to read a CTMU channel on a 1 mS interval


Lab 2 Notes� Use MPLAB® IDE breakpoints to look at cap

touch values � Add these variables to the watch window:

� curRawData[] � tripValue[] � AverageData[]

� Tips� Read cap touch buttons multiple times for better

reliability and noise rejection� The slow averaging of the cap touch button values

allows environmental changes to be nulled out of the cap touch buttons

� The cap touch button trip point can be adjusted to allow for higher or lower sensitivity


Lab 2 Results

� Compile, Program, and Run the project� When any of the 8 keys are touched, a

corresponding LED should light


Lab 2 Solution#define loopCount 5CTMUCONbits.EDG1STAT = 0; // Clear edge1CTMUCONbits.EDG2STAT = 0; // Clear edge2AD1CON1bits.SAMP = 1; // Manually start ADC sampling

//////////////////////////////////////////////////////////////////////////////////////////CTMUCONbits.EDG1STAT = 1; // 2. Set edge1 - Start Charge//for (zvar = 0; zvar < loopCount; zvar++); // 3. Delay for CTMU charge time//CTMUCONbits.EDG1STAT = 0; // 4. Clear edge1 - Stop Charge//IFS0bits.AD1IF = 0;AD1CON1bits.SAMP = 0; //5. manually initiate an ADC conversion//while(!IFS0bits.AD1IF); // Wait for the A/D conversion to finish

///////////////////////////////////////////////////////////////////////////////////////immediateValue = ADC1BUF0; // Read value from the A/D conversion


Lab 2 Questions???

� Why use the highest current setting?� Charges the Cap Touch Circuit the

fastest� Insures that PC board capacitor

leakage is overcome


Lab 2 Questions???

� Why does the voltage vary from button to button?� Button distance from microcontroller� Button shape� Proximity to other buttons and board

traces


Lab 2 Questions???

� What is the response time of the cap touch buttons?� Timer 4 reads 1 cap touch channel

every 1 msec� 16 channels are read� 1msec x 16channels = 16 msec

response time


Lab 2 summary� Charging of cap touch buttons is

dependant on the amount of time the CTMU current source is enabled

� Reading of multiple cap touch buttons is easy; simply change the channel selected by the A/D converter and repeat the routine


Software DesignKey Points


Averaging Algorithm

� Why is it needed?� A cap touch button reading

varies due to environmental changes

� The Slow Average Routine accounts for these variances


Capacitance in Real WorldC

ount


Firmware Algorithm – Averaging

� Compare latest measured value with slow moving average� Automatically adjust for

environmental changes� Can also be ‘guarded’

average� Trip level is relative to

moving average� Other functions

implemented the same as normal buttons:� Debouncing� Touch and release� Etc.

Time

Cou

nts

AbsoluteAverage

SensorTouched

SensorReleased

‘Floating’Trip level

‘Floating’Released level


Button Detection Challenges

Time

Cou

nts

Dirt/Sudden change

Average adjusts to prevent‘stuck’ button

AbsoluteAverage

Trip

Time

Cou

nts

Humidity/Temp variation

Slow Average and detectionlevel moves with change

AbsoluteAverage

Trip

Time

Cou

nts

Power up with ‘hand on sensor’

Adjust Average to newcounts rate

AbsoluteAverage

Trip

Time

Cou

nts

Normal Button Detection

React on ‘button’press

AbsoluteAverage

Trip

React on ‘button’release


Software Tips & Tricks for Better Cap Touch Reliability

� Use a software debounce routine� Use a dynamic calculation of the cap touch

button trip point� Set all buttons as I/O pins (output, ‘0’ value)

except for the button being currently read� Shift the 10-bit A/D value to a 16-bit value� Freeze calculation of slow average when a

button press is detected� Reset the slow average value to the current

value when a button release is detected


Software Tips & Tricks #1

Start

Read Sensor

Sensor ReadingPressed?

Pressed_Count = 0

Unpressed_Count++

Unpressed_Count > = 3?

Unpressed

NUnpressed_Count = 0

Pressed_Count++

Pressed_Count > = 3?

Y

Pressed

Y

N N

Y

A

A

Use a software debounce routine



� As Environment changes the un-pressed value of the cap touch button, the trip value is a bigger/smaller percentage of the value read

� Example:1. First Condition

� Initial un-pressed value = 500� Assume fixed Trip value = 100� Required shift for press = 20%

2. Second Condition� Initial un-pressed value = 250� Same fixed Trip value = 100� Required shift for press = 40%

050

100150200250300350400450500

Condition 1 Condition 2

Unpressed

Trigger

% ChangeReq'd



� Re-calculate the Trip point values when the slow average is updated

� Use a fixed value for the trip point divisor:

1. First Condition (use 5 as a divisor)

� Initial un-pressed value = 500� Trip value = 500/5 (100)� Required shift for press = 20%

2. Second Condition (again, use 5 as a divisor)

� Initial un-pressed value = 250� Trip value = 250/5 (50)� Required shift for press = 20%

050

100150200250300350400450500

Condition 1 Condition 2

Unpressed

Trigger

% ChangeReq'd



� Setting all adjacent cap touch buttons to “ground” potential minimizes the amount of stray capacitance and stabilizes the reading of the cap touch button.� Set ADC pin configuration to all digital except channel

being read� Set TRIS bits for all channels except current channel to

output pins� Drive the outputs low, which effectively grounds the cap

touch button



� Shifting to a 16-bit value helps with the accuracy of the slow moving average Example:� Use 5 values for the average (10-bit)

807, 820, 761, 779, 794 (Avg = 792)� Use 5 shifted values (16-bit)

51648, 52480, 48704, 49856, 50816 (Avg = 50701)

This allows better accuracy without having to use floating point math



� Use for button functions that require a long hold time

Code Example: if(avg_delay[Index] == NUM_AVG)

{ if(buttonState[Index] ==PRESSED)

{// Skip average calculation.}

}* This is also known as a gated average



� Allows better response when a button is released

� Allows for better performance for repetitive button presses Example:if (curRawData[Index] > averageData[Index])

{averageData[Index] = curRawData[Index]; // If curRawData is above Average, reset to high average.

}

* This is the second half of the gated averaging method


What Else Can the CTMU do?


CTMUWhat Else Can the CTMU Do?� Time Measurement� Capacitive Measurement� Temperature Measurement� Inductive Measurement� DAC Applications� PWM / Pulse Delay Applications


1337 CTMUTime Measurement

Using CTMU


Time Measurement - CTMUTypical Applications� Time Domain Reflectometry (TDR)� Distance Measurement (laser or RF)� Adaptive Cruise Control� Safety Braking


Time Measurement - CTMUBack to CTMU basics� I = C(dV/dT) or EQ 1� dT = (C/I)dV Integrate EQ 2� If I and C are constants, then after

integration� T = (C/I)V + K EQ 3� In General K will be 0

� So T is proportional to V


Time Measurement - CTMU



VideoDemonstration


Time Measurement - CTMUResolution Calculations� Assume

� I = 55uA� C = CADC + CPAD + CPIN + CSTRAY = 15pF

� If VDD = 3.0V then V = 3/1024 = 2.93mV� T = (15pF/55uA) * 2.93mV = 0.799nS


Time Measurement - CTMUCalibration� Assume 0.01% Crystal� Using Software create two precision

times� Set CTED1, Set CTED2 (time 1)� Set CTED1, Nop, Nop, Set CTED2(time2)

� Use these two times to calculate the values for C/I and K in Eq 3

� No need to find exact values for C and I


Time Measurement - CTMUTips for Increasing Resolution� Use an external VREF of 2.5V

� T = (15pF/55uA) * (2.5/1024) = .666nS� Use an External High Resolution ADC

� Use an external 16 bit ADC� Assume capacitance is doubled to 30pF� T = (30pF/55uA) * (3.0/65536) = 24.9pS



PIC24F or PIC18FWith CTMU

16 BIT ADCANx

PORTx.[7:0]

Processor Interface

8


1337 CTMUCapacitance Measurement

Using CTMU


Capacitance Measurement - CTMU

Typical Applications� Test Equipment Capacitor Meter� Humidity Measurement� Capacitive Microphone



Back to CTMU basics� I = C(dV/dT) or EQ 1� dT = (C/I)dV Integrate EQ 2� If I and C are constant during the reading� C = (T*I)/V EQ 3



Calibration� From EQ 3

� C = Cmeasure + CADC + CPAD + CPIN + CSTRAY

� For Calibration Let Cmeasure = 0� Csystem = CADC + CPAD + CPIN + CSTRAY



Calibration Continued� Method One

� Using Software create two precision times� Set CTED1, Set CTED2 (time 1)� Set CTED1, Nop, Nop, Set CTED2 (time2)

� Use these two times to calculate the values for Csystem , and I in Eq 3



� Method Two� Add Precision resistor to board

� Measure the current using resistor and ADC

� Measure Csystem



Resolution� Assume:

� T = 500nS� V = 1V� I = 55uA� C = (55uA*500nS)/1V = 27.5pF� If Voltage Resolution is 3/1024 or 2.93mV � Then 1 bit delta is

� C = (55ua*500ns)/1.00293 = 27.42pf� Delta C = 0.08pF


1337 CTMUTemperature Measurement

Using CTMU


Temperature Measurement - CTMU

Typical Applications� Thermostat control for homes� Temperature monitoring of

electronics� Low cost medical thermometers



Basic Diode Equation� I = I0 (e

(qV/kT) -1) EQ 1� I/I0 +1 = e(qV/kT) EQ 2� Ln(I/I0 +1) = qV/kT EQ 3� Ln(I/I0 +1) = B EQ 4� T = qV/kB EQ 5� So Temperature T is proportional to V

voltage across the diode.� This relationship shown in the

following graph



Temperature measurement

0

10000

20000

30000

40000

50000

60000

0 20 40 60 80 100 120

Temperature

AD

C c

ount

(x25

6)

1N4007 1N4148 1N914 LED-D22 2N3904(NPN)LED-D27 2N3906(PNP) 2|| 1N914



Making a measurement� Select ADC channel that diode is

attached to� Enable CTMU� Set EDGESTAT1� Wait for settling time� Read ADC� Calculate Temperature



Calibration� From graphs we have a linear

relation between T and V� Take voltage measurements at two

temperatures� Calculate gain and offset


1337 CTMUInductance Measurement

Using CTMU


Inductance Measurement - CTMU

PIC24F or PIC18F with CTMU

CTED1

CTED2

VDD step Function

V0 Response Vo

T



Inductor Equations� I = VDD /R(1 – e(-TR/L)) EQ 1� V0 = VDD (1 - e(-TR/L)) Where V0 = IR EQ 2� 1 - V0 / VDD = e(-TR/L) EQ 3� -TR/L = B Where B=Ln(1 - V0 / VDD ) EQ 4� L = -TR/B EQ 5� Note the linear relationship between T

and L



Resolution CalculationsAssume:� R = 1K� V0 = 1V� VDD = 3V� T = 500nS� L = (-1000/-.405)*500nS = 1.233mH� For a delta of 0.8ns� L = (-1000/-.405)*500.8nS = 1.235mH� Resolution is 2uH


1337 CTMUDigital to Analog Converter

Using CTMU


DAC using - CTMU

PIC24 or PIC18 with CTMU

Sample And Hold

AN0

SAMPLE/HOLD

PORT I/O Pin

DAC OUT


DAC using - CTMUDAC Software� Setup

� Determine desired full scale Time and Voltage� Adjust current source to achieve full scale

voltage at full scale time� Implementation

� Discharge AN0 Pin� Charge AN0 for time T where

� T = TFULLSCALE * Vout / VFULLSCALE

� Sample AN0 With Sample and hold� Hold Voltage


DAC using - CTMUDAC Resolution� Assumptions:

� Full scale voltage is 2V� Full scale time is 62.5ns *216 or 4.096ms

� Therefore:� dV/dT = 2/4.096mS (or .488uV/nS)

� Since the minimum time step is 62.5nS resolution is .488uv*62.5 or 30.5uv


1337 CTMUPWM / Pulse Delay

Using CTMU


PWM / Pulse Delay - CTMU

Typical Applications� Blanking pulse for radar / sonar

systems� High frequency PWM� Precision edge delay for test

equipment


PWM / Pulse Delay – CTMU Hardware Setup

CTMU

_

+

CV Ref

Current Source

Comparator Input

CTED1

Pulse Input

Comparator Out

CDELAY

CTPLSPulse Output


PWM / Pulse Delay - CTMU

CTED1

INPUTS

OUTPUTS

Comparator In

CTPLS

CTMUCurrent Source


PWM / Pulse Delay - CTMUSetting up PWM/Pulse delay� Set TMGENEN bit = 1� Determine Ramp voltage at

maximum delay� Adjust CTMU current source to reach

Max Ramp Voltage at Max time� Program DAC for desired time delay

� VDAC = T/TMAX


PWM / Pulse Delay - CTMUEDGE Resolution� Assume:

� Full scale voltage of 2V� dV/dT 2V/uS

� With a 10 bit DAC minimum dV is 2/1024 or 1.95mV

� Therefore minimum dT is (1.95mV/2V)uS or .977nS


Summary of using the CTMU � Time Measurement

� Use CTED1 & CTED2 to start and stop CTMU current source� Time is represented by the voltage read by the ADC

� Temperature measurement� Single Diode only hardware needed� Basic Diode equation used; Temperature is proportional to voltage

� Capacitance Measurement� Use processor instruction cycle time as a fixed quantity� Capacitance is represented by the voltage read by the ADC

� PWM / Pulse Delay� Use Internal Comparator / Internal Reference Voltage� Delay Time is set by the CDELAY connected to comparator input


Advanced Cap Touch – Matrix Keys and Sliders


Paired Channel Method

� Expands 4 buttons to 10� 1, 3, 7, & 9 are whole buttons� 2, 4, 5, 6, 8, & 0 are paired

channel buttons� Paired press only produces ½

the capacitance shift � Requires scan of all buttons for

a valid decode� Can not differentiate two

buttons pressed from a paired press


Matrix Channels� A grid of ‘a’ rows by ‘b’

columns requires (a + b) channels, but implements (a x b) buttons

� Software determines button press after scanning all rows and columns

� Requires high speed scan (esp. for larger matrix)

C1 C2 C3 C4

R1

R2

R3

Q: What is the best optimization of sensor channels for a matrix?A: An Equal Number of Rows and Columns


Slider

Right SensorRaw Value

100%

0%

Left SensorRaw Value

Cou

nt

� Requires 2 Channels� Basic Equations:� Right Sensor

� % = 100 x (R/(L+R))� Left Sensor

� % = 100 x (1-(L/(L+R)))� Where L and R are the Delta from an

unpressed sensor

Triangular Copper Pads on PC Board

PIC® MCU


Lab 3: Matrix Keys Implementation


Lab 3 Objective� Be able to create an algorithm to decode a key

pad created using a matrix of cap touch buttons

� Take action upon cap touch button presses� Understand basic advantages and limitations of

using matrix cap touch buttons


Lab 3 General Information

� 7 Channels – 3 Rows x 4 Columns� Read all 7 channels normally� Decode the row and column; display the

depressed key� Located in MatrixDecode() function in

CTMUcapsense.c


Lab 3 Tips� Use channels 8 – 14 for the matrix keypad� Adjust trip points. Capacitance shift will be

lower for 2 reasons:1. Either 3 or 4 cap touch pads connected together2. Your finger is only touching ½ of a normal cap touch

button� Use LED1 – LED12 macros to display the keys

� LED1 = ON or LED1 = 1� LED1 = OFF or LED1 = 0


Lab 3 Questions?� Could Multiple button presses be detected?� Which tips & tricks can be used to improve

reliability of the matrix keypad?� How could you limit the key selection to a

single key? What would be the criteria for choosing the key?


Lab 3 Questions � Multiple button detection – possible but limited

to…� Buttons must be on same row or column� Software Algorithm must check for multiple

combinations (i.e. if a row is pressed, each column must be checked for a press)

� Other combinations are not allowed Example: Button 1 (row 1 column 1) & Button 6 (row 2 column 2) ALSO produces Button 2 (row 2 column 1) & Button 5 (row 1 column 2)


Lab 3 Questions ???

� Which tips & tricks can be used to improve reliability of the matrix keypad?� Use a software debounce routine� Use a dynamic calculation of the cap touch button trip

point� Set all buttons as I/O pins (output, ‘0’ value) except for

the button being currently read� Shift the 10-bit A/D value to a 16-bit value� Freeze calculation of slow average when a button press

is detected� Reset the slow average value to the current value when

a button release is detected


Lab 3 Questions???

� How could you limit the key selection to a single key? What would be the criteria for choosing the key?� Use an algorithm to find the most pressed row and

column � Lock out any further presses until the currently selected

button becomes unpressed


Lab 3 Solution// Is a keypad column/row pressed?if (curRawData[Index] < (averageData[Index] - tripValue[Index])) {

switch(Index){

case 8: Col1 = 1; break;




case 12: Row1 = 1; break;



default: break;}

}else // If pressed criteria not reached, set to not pressed{

switch(Index){








default: break;}

}


Lab 3 Solution (cont’d)//Decode the matrix buttonsif(Col1 != 0) //check column 1{

if(Row1 != 0){

LED1 = ON;}if(Row2 != 0){

LED5 = ON;}if(Row3 != 0){

LED9 = ON;}

}else{

LED1 = OFF;Nop();LED5 = OFF;Nop();LED9 = OFF;

}//repeat for columns 2,3, &4


Lab 3 Summary

� The CTMU is well suited for matrix key arrangements because of its high speed

� Matrix keys maximize the number of available buttons, while minimizing required I/O

� Matrix keys have limitations� Sensitivity is reduced from standard cap touch

buttons� Multiple button presses not able to be detected


Lab 4: Using the mTouch™ GUI


Lab 4 Objective

� Become familiar with using the mTouch™ GUI as a useful tuning tool for Capacitive Touch Applications


� Open Lab 4 Project in MPLAB® IDE; compile load and run

� Open the mTouch™ GUI -� Choose the “PIC24F CTMU Eval” Radio Button� Choose the “8 Button” Radio Button



Lab 4 Summary

� The mTouch™ GUI is a helpful tool for setting up and tuning cap touch applications

� The mTouch GUI has many features:� Viewing of cap touch values� Ability to adjust trip points on the target

application� Graphing of cap touch values� Logging of cap touch values� Ability to scale viewing for any cap touch button


Lab 5: Using Overlay Materials


Lab 5 Objective

� Discover how placing an overlay material on the cap touch button affects performance

� Learn how to adjust the cap touch application to compensate for the addition of the overlay



� Open, build, and run the Lab 5 project

� Launch the mTouch™ GUI� Place the overlay on the 8 button

daughter board


Lab 5 Summary

� Introduction of a covering material over a capacitive touch button greatly reduces its sensitivity

� Noise susceptibility is also increased� Software techniques described earlier in

this class are helpful in improving performance


1337 CTMU Summary� Today we covered:

� The CTMU module and how to use it for:� Capacitive Measurement� Time Measurement

� Designing a Cap Touch Application:� Setting up the CTMU for Cap Touch� Software Algorithms� Overlay Properties

� Using the mTouch™ GUI application as an application tuning aid


Other Related MASTERs Classes

� 1336 CTF – Capacitive Touch Fundamentals� Introductory Level Course� Tom Perme – Instructor� 2 hour course

� 1338 TSM – Touch Sensing Through Metal� Inductive Touch Class� Keith Curtis – Instructor� 2 hour course

� 1339 TSC – Touch Screen Controllers� Class covers: analog resistive, surface capacitive, and projected

capacitive touch screen technologies� Lance Lamont – Instructor� 2 hour course


mTouch™ Resources

� mTouch Sensing Solutions Design Center: www.microchip.com/mtouch� Capacitive Sensors by Larry K. Baxter

ISBN 0-7803-5351-X� AN1101 Basic Overview of operation

� Webinar online� AN1102 Hardware and Layout of sensors

� Webinar online� AN1103 Software Techniques for detecting buttons� AN1104 How to get more buttons?� AN1171 Using the CSM� AN1202 Using PIC10F for Capacitive Touch� AN1250 Microchip CTMU for Capacitive Touch Applications� DS39724 CTMU Ref Manual

http://www.microchip.com/mtouch


Available ResourcesPICDEM™ Touch Sense 1 Development Board• PIC16F-based demo boardDM164125

PICDEM Touch Sense 2 Development Board• PIC24F-based demo boardDM164128


Available Resources

mTouch™ Diagnostic GUI• For customizing the

Capacitive Touch Solution

MPLAB® Starter Kit for PIC24F• PIC24F Based• 5 Cap Touch Keys• OLED Graphics Display• DM24001


16F727

100 pt

255 pt

Matrix

Buttons

PKSA

USB 24FJ128GB106

(N-1)*100

$USD 84.95

DM183026: Cap Touch Eval Kit


TrademarksThe Microchip name and logo, the Microchip logo, dsPIC, KeeLoq, KeeLoq logo, MPLAB, PIC, PICmicro, PICSTART, rfPIC and UNI/O are registered trademarks of Microchip Technology Incorporated in the U.S.A. and other countries.

� FilterLab, Hampshire, HI-TECH C, Linear Active Thermistor, MXDEV, MXLAB, SEEVAL and The Embedded Control Solutions Company are registered trademarks of Microchip Technology Incorporated in the U.S.A.

� Analog-for-the-Digital Age, Application Maestro, CodeGuard, dsPICDEM, dsPICDEM.net, dsPICworks, dsSPEAK, ECAN, ECONOMONITOR, FanSense, HI-TIDE, In-Circuit Serial Programming, ICSP, ICEPIC, Mindi, MiWi, MPASM, MPLAB Certified logo, MPLIB, MPLINK, mTouch, nanoWatt XLP, Omniscient Code Generation, PICC, PICC-18, PICkit, PICDEM, PICDEM.net, PICtail, PIC32 logo, REAL ICE, rfLAB, Select Mode, Total Endurance, TSHARC, WiperLock and ZENA are trademarks of Microchip Technology Incorporated in the U.S.A. and other countries.

� SQTP is a service mark of Microchip Technology Incorporated in the U.S.A.� All other trademarks mentioned herein are property of their respective

companies.� © 2009, Microchip Technology Incorporated, Printed in the U.S.A., All Rights

Reserved.

Documents

1337 CTMU Capacitive Touch Sensing Using CTMUcaxapa.ru/thumbs/245906/1337.pdfUse MPLAB® IDE breakpoints to look at cap touch values Add these variables to the watch window: curRawData[]