2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide CTMU Capacitive Touch Sensing Using CTMU

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2009 Microchip Technology Incorporated. All Rights Reserved.

2 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 2

3 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 3

5 CTMU Block Diagram CTMUCON CTMUICON External Edge Trigger Pins Current Source Timer1 OC1 Edge Control Logic A/D Converter Current Control Comparator 2 Input CTMU Control Logic Pulse Generation Logic A/D Conversion Trigger Comparator 2 Output Pulse Output Pin 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 5

6 CTMU Current Source Current Source Trimmable current source Range : 0.55 ua, 5.5 ua and 55 ua Trigger Starts/Stops Current Source Discharge CTMU To A/D Converter Current Source charges: Capacitive Touch circuitry A/D Converter Cap 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 6

7 CTMU Interface with ADC PIC MCU A/D PIC MCU A/D with CTMU Sensor 0 Current Source A/D Conversion Trigger CTMU C A/D Sensor 15 A/D Converter 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 7

8 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 8

9 Parts with CTMU Part Family Architecture No. Ch XLP? USB Pin Count Flash (kbytes) PIC18F87J90 8-bit 12 No No 64, PIC18F 46J11 8-bit 13 Yes No 28, PIC18F 46J50 8-bit 13 Yes Yes 28, PIC24FJ256GA1 16-bit 16 No No 64, 80, ,128,192,256 PIC24FJ256GB1 16-bit 16 No Yes 64, 80, ,128,192,256 PIC24FJ64GA1 16-bit 12 No No 28, 44 32, 64 PIC24FJ64GB bit 12 Yes Yes 28, PIC24F16KA bit 7, 9 Yes No 14, 20, 28 4, 8, 16 More to follow in PIC24F and PIC18F families 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 9

Microchip Cap Touch mtouch Sensing Solutions use

Oscillator) Touch sensor is the C in an RC

Measurement) Capacitor is charged for a fixed

VCap Vout VCs Frequency Measurement Voltage

10 Microchip Cap Touch mtouch 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. VCap Vout VCs Frequency Measurement Voltage Measurement 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 10

13 EE101 basics: How CTMU Works for Capacitive Touch 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 13

14 CTMU Touch Circuit Components I = C V t Trigger Current Source C P = C AD + C CIR + C SW = 30pF C F = 7pF Discharge CTMU V AD C F C SW C CIR C AD A/D Converter 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 14

15 Sample Calculations I = C V t I t C = V When un-touched I = 5.5µA t = 10µS C P = 30pF V = When touched I = 5.5µA t = 10µS C = C P + C F = 37pF V = C P = C AD + C CIR + C SW = 30pF C F = 7pF 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 15

17 Lab 1a Objective Gain a basic understanding of the CTMU control registers (CTMUCON & CTMUICON) Be able to set up the CTMU for cap touch 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 17

18 Lab 1a Instructions Part 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 PIC24FJ128GB Microchip Technology Incorporated. All Rights Reserved CTMU Slide 18

PIC24FJ256GB110 Data Sheet 2009 Microchip Technology

20 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 20

22 Lab 1a Solution //setup CTMU //CTMUCON CTMUCONbits.CTMUEN = 0; //make sure CTMU is disabled CTMUCONbits.CTMUSIDL = 0; //CTMU continues to run in idle mode CTMUCONbits.TGEN = CTMUCONbits.EDGEN = 0; 0; //disable edge delay generation mode //edges are blocked CTMUCONbits.EDGSEQEN = 0; //edge sequence not needed CTMUCONbits.IDISSEN = 0; //Do not ground the current source CTMUCONbits.CTTRIG = 0; //Trigger Output is disabled CTMUCONbits.EDG2POL = 0; //N/A since edges are blocked CTMUCONbits.EDG2SEL = 0x3; //Edge2 Src = OC1 (also N/A) CTMUCONbits.EDG1POL = 1; //N/A since edges are blocked CTMUCONbits.EDG1SEL = 0x3; //Edge1 Src = Timer1 (also N/A) //CTMUICON CTMUICON = 0x300; //55uA //or // CTMUICONbits.IRNG = 0x03; //55uA //optional CTMUICONbits.ITRIM = 0; //Nominal - No Adjustment 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 22

24 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 24

CTMU Full Waveform End Charge A/D Conversion Discharge Begin Charge 2009

27 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 27

29 Lab 2 Objective Perform 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 circuit 3. Wait for a fixed time period (2 us for this hardware) 4. Turn off Current Source to stop charging touch circuit 5. Perform A/D conversion to read voltage present on touch circuit 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 29

30 Lab 2 General Information: Project Files Open Lab2 C:\MASTERS\1337\Lab2 8KeyBoard.c CTMUcapsense.c Timer4.c 8KeyBoard.h CTMUcapsense.h Timer4.h 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 30

31 Lab 2 General Information: Main() Routine Start Initialization Timer 4 Sets this variable New Data to process? Y Stop Timer 4 Insures no interrupt while processing new data N Service USB Process New Cap Touch Data Lab 2 code here Service other application tasks Start Timer Microchip Technology Incorporated. All Rights Reserved CTMU Slide 31

32 Lab 2 General Information: Timer 4 ISR Setup in Init Timer 4 Interrupt (1 ms) Lab 2 Code Process CTMU Channel Flag is read by main routine Check for all CTMU Channels read All Channels Read? Y Reset Channel # Set Flag to process new data N Get ready for next interrupt Increment Channel to read Exit ISR 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 32

33 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 33

34 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 34

36 Lab 2 Solution #define loopcount 5 CTMUCONbits.EDG1STAT = 0; // Clear edge1 CTMUCONbits.EDG2STAT = 0; // Clear edge2 AD1CON1bits.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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 36

37 Lab 2 Questions??? Why use the highest current setting? Charges the Cap Touch Circuit the fastest Insures that PC board capacitor leakage is overcome 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 37

38 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 38

39 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 39

40 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 40

42 Averaging Algorithm Why is it needed? A cap touch button reading varies due to environmental changes The Slow Average Routine accounts for these variances 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 42

44 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. Counts Sensor Touched Floating Trip level Time Sensor Released Floating Released level Absolute Average 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 44

45 Button Detection Challenges Normal Button Detection React on button press React on button release Humidity/Temp variation Slow Average and detection level moves with change Counts Dirt/Sudden change Average Absolute Trip Time Counts Average Absolute Trip Time Power up with hand on sensor Average adjusts to prevent stuck button Adjust Average to new counts rate Counts Average Absolute Trip Time Counts Average Absolute Trip Time 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 45

46 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 46

47 Software Tips & Tricks #1 Use a software debounce routine Start A Read Sensor Unpressed_Count = 0 Y Sensor Reading Pressed? N Pressed_Count = 0 Pressed_Count > = 3? N Y Pressed Unpressed_Count > = 3? N Y Unpressed Pressed_Count++ Unpressed_Count++ A 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 47

48 Software Tips & Tricks #2 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% Condition 1 Condition 2 Unpressed Trigger % Change Req'd 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 48

49 Software Tips & Tricks #3 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% Condition 1 Condition 2 Unpressed Trigger % Change Req'd 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 49

50 Software Tips & Tricks #4 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 50

51 Software Tips & Tricks #5 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, (Avg = 50701) This allows better accuracy without having to use floating point math 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 51

52 Software Tips & Tricks #6 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 52

53 Software Tips & Tricks #7 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 53

55 CTMU What Else Can the CTMU Do? Time Measurement Capacitive Measurement Temperature Measurement Inductive Measurement DAC Applications PWM / Pulse Delay Applications 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 55

57 Time Measurement - CTMU Typical Applications Time Domain Reflectometry (TDR) Distance Measurement (laser or RF) Adaptive Cruise Control Safety Braking 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 57

58 Time Measurement - CTMU Back 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 58

Time Measurement - CTMU 2009 Microchip Technology

Time Measurement - CTMU Video Demonstration 2009 Microchip

61 Time Measurement - CTMU Resolution Calculations Assume I = 55uA C = C ADC + C PAD + C PIN + C STRAY = 15pF If VDD = 3.0V then V = 3/1024 = 2.93mV T = (15pF/55uA) * 2.93mV = 0.799nS 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 61

62 Calibration Time Measurement - CTMU 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 62

63 Time Measurement - CTMU Tips 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 63

66 Capacitance Measurement - CTMU Typical Applications Test Equipment Capacitor Meter Humidity Measurement Capacitive Microphone 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 66

67 Capacitance Measurement - CTMU 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 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 67

68 Capacitance Measurement - CTMU Calibration From EQ 3 C = C measure + C ADC + C PAD + C PIN + C STRAY For Calibration Let C measure = 0 C system = C ADC + C PAD + C PIN + C STRAY 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 68

69 Capacitance Measurement - CTMU 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 C system, and I in Eq Microchip Technology Incorporated. All Rights Reserved CTMU Slide 69

70 Capacitance Measurement - CTMU Method Two Add Precision resistor to board Measure the current using resistor and ADC Measure C system 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 70

71 Capacitance Measurement - CTMU 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)/ = 27.42pf Delta C = 0.08pF 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 71

73 Temperature Measurement - CTMU Typical Applications Thermostat control for homes Temperature monitoring of electronics Low cost medical thermometers 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 73

74 Temperature Measurement - CTMU Basic Diode Equation I = I 0 (e (qv/kt) -1) EQ 1 I/I 0 +1 = e (qv/kt) EQ 2 Ln(I/I 0 +1) = qv/kt EQ 3 Ln(I/I 0 +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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 74

75 Temperature Measurement - CTMU Temperature measurement 1N4007 1N4148 1N914 LED-D22 2N3904(NPN) LED-D27 2N3906(PNP) 2 1N ADC count (x256) Temperature 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 75

76 Temperature Measurement - CTMU Making a measurement Select ADC channel that diode is attached to Enable CTMU Set EDGESTAT1 Wait for settling time Read ADC Calculate Temperature 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 76

77 Temperature Measurement - CTMU Calibration From graphs we have a linear relation between T and V Take voltage measurements at two temperatures Calculate gain and offset 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 77

80 Inductance Measurement - CTMU Inductor Equations I = V DD /R(1 e (-TR/L) ) EQ 1 V 0 = V DD (1 - e (-TR/L) ) Where V 0 = IR EQ V 0 / V DD = e (-TR/L) EQ 3 -TR/L = B Where B=Ln(1 - V 0 / V DD ) EQ 4 L = -TR/B EQ 5 Note the linear relationship between T and L 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 80

81 Inductance Measurement - CTMU Resolution Calculations Assume: R = 1K V 0 = 1V V DD = 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 81

84 DAC Software Setup DAC using - CTMU 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 = T FULLSCALE * Vout / V FULLSCALE Sample AN0 With Sample and hold Hold Voltage 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 84

85 DAC Resolution Assumptions: DAC using - CTMU Full scale voltage is 2V Full scale time is 62.5ns *2 16 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 85

87 PWM / Pulse Delay - CTMU Typical Applications Blanking pulse for radar / sonar systems High frequency PWM Precision edge delay for test equipment 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 87

88 PWM / Pulse Delay CTMU Hardware Setup CTPLS Pulse Output Pulse Input CTED1 CTMU Comparator Input Current Source Comparator Out _ + CV Ref C DELAY 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 88

90 PWM / Pulse Delay - CTMU Setting 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 V DAC = T/T MAX 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 90

91 PWM / Pulse Delay - CTMU EDGE 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 91

92 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 C DELAY connected to comparator input 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 92

Requires scan of all buttons for a valid decode Can not differentiate two buttons pressed

94 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 94

95 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) R1 R2 R3 C1 C2 C3 C4 Q: What is the best optimization of sensor channels for a matrix? A: An Equal Number of Rows and Columns 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 95

96 Slider 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 100% PIC MCU Count 0% Left Sensor Raw Value Right Sensor Raw Value 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 96

98 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 98

99 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 99

100 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 together 2. 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 = Microchip Technology Incorporated. All Rights Reserved CTMU Slide 100

101 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? 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 101

102 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) 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 102

103 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 103

104 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 104

105 Lab 3 Solution // Is a keypad column/row pressed? if (currawdata[index] < (averagedata[index] - tripvalue[index])) { switch(index) { case 8: Col1 = 1; break; case 9: Col2 = 1; break; case 10: Col3 = 1; break; case 11: Col4 = 1; break; case 12: Row1 = 1; break; case 13: Row2 = 1; break; case 14: Row3 = 1; break; } else { } default: break; // If pressed criteria not reached, set to not pressed switch(index) { case 8: Col1 = 0; break; case 9: Col2 = 0; break; case 10: Col3 = 0; break; case 11: Col4 = 0; break; case 12: Row1 = 0; break; case 13: Row2 = 0; break; case 14: Row3 = 0; break; } } default: break; 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 105

106 Lab 3 Solution (cont d) //Decode the matrix buttons if(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, & Microchip Technology Incorporated. All Rights Reserved CTMU Slide 106

107 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 107

110 Lab 4 General Information 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 110

111 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 111

113 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 113

114 Lab 5 General Information Open, build, and run the Lab 5 project Launch the mtouch GUI Place the overlay on the 8 button daughter board 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 114

115 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 115

116 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 116

117 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 117

118 mtouch Resources mtouch Sensing Solutions Design Center: Capacitive Sensors by Larry K. Baxter ISBN 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 2009 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 118

Development Board PIC24F-based demo board DM164128 2009

119 Available Resources PICDEM Touch Sense 1 Development Board PIC16F-based demo board DM PICDEM Touch Sense 2 Development Board PIC24F-based demo board DM Microchip Technology Incorporated. All Rights Reserved CTMU Slide 119

Based 5 Cap Touch Keys OLED Graphics Display DM24001 2009

120 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 DM Microchip Technology Incorporated. All Rights Reserved CTMU Slide 120

122 Trademarks The 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 Microchip Technology Incorporated. All Rights Reserved CTMU Slide 122

Overview of Charge Time Measurement Unit (CTMU)

Overview of Charge Time Measurement Unit (CTMU) 2008 Microchip Technology Incorporated. All Rights Reserved. An Overview of Charge Time Measurement Unit Slide 1 Welcome to the Overview of Charge Time Measurement