inTouch Application Kit - Touch Wheel

XC83x
AP08128
inTouch Application Kit - Touch Wheel
Application Note
V1.0, 2012-02
Microcontrollers
Edition 2012-02
Published by
Infineon Technologies AG
81726 Munich, Germany
© 2012 Infineon Technologies AG
All Rights Reserved.
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AP08128
inTouch Application Kit - Touch Wheel
XC82x/XC83x
Revision History: V1.0 2012-02
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Application Note
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V1.0, 2012-02
AP08128
inTouch Application Kit - Touch Wheel
Table of Contents
1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2
2.1
2.2
Hardware & Program Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Program Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3
3.1
Sensing Touch on Wheel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Wheel Angle Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4
4.1
U-SPY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
inTouch_Wheel.ini . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Appendix - Schematics and Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Application Note
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AP08128
inTouch Application Kit - Touch Wheel
Introduction
1
Introduction
In today's Human-Machine Interface (HMI) designs, capacitive touch technology is now often more widely used
than traditional mechanical buttons. Capacitive touch technology is the more popular choice because it brings
flexibility, a high-level of customization, and a significant reduction in overall system cost.
The inTouch Application Kit is available to help learn about working with the advanced touch solutions provided
by Infineon. Step-by-step tutorials covers the basics of Infineon's touch solutions, while example application code
can be used to start developing new touch-related projects.
The inTouch Application Kit comprises of a mother board, supplied as a USB stick, and a number of daughter
boards. Figure 1 shows the USB stick with the Wheel daughter board.
Among the many different touch input elements that can be designed with capacitive touch technology, the touch
wheel is gaining popularity because of the intuitive control it provides. This application note describing the Wheel
daughter board, aims to highlight the ease of implementing a design with Infineon's touch solutions. Topics
covered include program flow and touch behavior.
Figure 1
inTouch Application Kit (USB Stick and Wheel board)
Application Note
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AP08128
inTouch Application Kit - Touch Wheel
Hardware & Program Flow
2
Hardware & Program Flow
This section describes the hardware used and the connections involved.
2.1
Hardware
Infineon’s XC836MT 2FRI (Figure 2) is used in this application. The XC836MT is embedded in the inTouch
Application Kit’s USB stick. For more details regarding the USB stick, please refer to AP08126: Infineon Touch
Solutions - inTouch Application Kit.
Figure 2
Infineon’s XC836MT 2FRI
The inTouch Wheel board (Figure 3) is available as a plug-in daughter board which is part of the inTouch
Application Kit.
Figure 3
Wheel Board
Application Note
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AP08128
inTouch Application Kit - Touch Wheel
Hardware & Program Flow
The inTouch Wheel board is a standard PCB with a 1mm thick plexiglas cover glued to the board. The touch wheel
is connected to 3 LEDTS pad inputs of the XC836. The centre button is connected to an LEDTS pad input of the
XC836. 12 indicator LEDs share 3 LEDTS column pins and 4 line pins of the XC836. The schematics are available
in the Appendix - Schematics and Layout.
Users can tap or dial the touch wheel and they can tap the centre button.
2.2
Program Flow
The inTouch Wheel board has four touch pads; one is used as a touch button and the remaining three form a wheel
for dialling. All 4 pads are handled by the XC836MT microcontroller’s LED Touch-Sense Control Unit (LEDTSCU)
which is a dedicated touch sense controller module. The method for measuring the pad capacitance is the
Relaxation Oscillator (RO) Topology.
For more information on the RO Topology, refer to the application note AP08126: Infineon Touch Solutions inTouch Application Kit.
In terms of interrupts, the Time Frame interrupt has the highest priority. In this service routine, touch sense related
tasks are performed each time pad capacitance has been measured. LED updates, which are performed in the
Time Slice interrupt, have low priority. The Timer 2 (T2) Overflow interrupt is given low priority due to its slow
frequency. The UART interrupt has low priority as it is not time-critical. Figure 4 provides an illustration of the
program overview.
low
Figure 4
TIMER 2 OVERFLOW
every 2ms
low
UART INTERRUPT
low
TIME SLICE
INTERRUPT
every 160μs
high
TIME FRAME
INTERRUPT
every 800μs
Wheel Angle
Calculation
Communication with
PC (send & receive
data)
LED settings
Touch Sense signal
processing
Centre Button touch
detection
RETI
RETI
RETI
RETI
Program Overview
The tasks performed in each interrupt service routine are further illustrated in the flowcharts that follow:
•
•
•
•
T2 Overflow Interrupt (Figure 5)
– The T2 module provides a slow time base by generating the T2 Overflow interrupt for calculations necessary
to handle the touch wheel.
UART Interrupt (Figure 6)
– The UART module, which is part of the XC800 core, is used for full-duplex UART communication with the
PC.
Time Slice Interrupt (Figure 7)
– The LEDTSCU module generates this interrupt after every LED column activation where the pattern for the
next LED column is loaded into shadow registers.
Time Frame Interrupt (Figure 8)
– The LEDTSCU module generates this interrupt after every measurement where signal processing and touch
detection take place.
Application Note
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AP08128
inTouch Application Kit - Touch Wheel
Hardware & Program Flow
Start
RETI
No
Startup over?
No
Calibrate wheel pads
Mode 1?
Yes
Centre Button
Touched?
Yes
Dim/Glow LEDs
based on direction of
wheel dial
Yes
Update LEDs based
on touch location
Yes
Calculate Wheel
Angle
No
Yes
Change Mode
Mode 0?
No
Condition wheel
signals
Update touched
location on wheel
No
Calculate Wheel
Amplitude
Figure 5
Wheel touched?
Timer 2 Overflow Interrupt Service Routine
Application Note
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AP08128
inTouch Application Kit - Touch Wheel
Hardware & Program Flow
Start
Receiver
Interrupt?
Yes
New
command?
Yes
Retrieve data
from buffer
No
No
Check button
selected
Transmitter
Interrupt?
Yes
Shift data out to
buffer
No
RETI
Figure 6
UART Interrupt Service Routine
Start
Figure 7
RETI
Time Slice Interrupt Service Routine
Start
Figure 8
Set LED LINE
and COMPARE
values
Mask LEDTS
ROM Library
flags for wheel
pads
LEDTS pads
signal processing
RETI
Time Frame Interrupt Service Routine
Application Note
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AP08128
inTouch Application Kit - Touch Wheel
Sensing Touch on Wheel
3
Sensing Touch on Wheel
This section describes how the LEDTSCU module of the XC836, complemented with a software library, control
the touch wheel. The algorithm for calculating the location of touch is also explained in the following section.
The main touch sensing functions, handled by software, are as follows:
•
•
•
•
•
Sample accumulation (ROM library)
Signal filtering and moving average calculation (ROM library)
Touch detection (ROM library)
Touch wheel calibration (user software in Flash)
Signal tuning (user software in Flash)
If properly configured, the LEDTSCU automatically measures the capacitance of the four pads. This capacitance
increases when a button is touched. A library function in ROM processes the capacitance signals and detects
touch on the centre button. It does so by accumulating 3 samples and low-pass filtering them to obtain a moving
average. The moving average filters noise and is used as a reference to detect sudden changes in capacitance.
When the button is touched or released, a corresponding pad flag in RAM will be set or reset. For more information
on the LEDTS ROM Library, please refer to the XC836 User’s Manual.
The pad flags for the wheel pads are unused (always cleared) and it is the moving averages (“pad averages”) that
are used instead to calculate the angle of the touch. The three pads are automatically calibrated to the same
sensitivity and resolution during startup. Once the pad averages are stable, an angle calculation algorithm is run
if the wheel is touched. The calculated angle is then used to determine the location of touch, and hence the LED
to be switched on.
3.1
Wheel Angle Calculation
The three touch pads are placed in a spatially interpolated manner (Figure 9).
Figure 9
Spatially interpolated wheel layout and abstraction
If the pads are calibrated to roughly the same sensitivity and the wheel is dialed clockwise with constant angular
speed and constant pressure (constant effective finger area), the pad average signals are expected to behave in
a linear manner in this model as seen in Figure 10.
Application Note
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AP08128
inTouch Application Kit - Touch Wheel
Sensing Touch on Wheel
Figure 10
Pad average signals of the three wheel pads during dialling
Values untouched_a, untouched_b and untouched_c are the pad average levels for pads A, B and C respectively
when they are not touched.
If the pads have roughly the same sensitivity, the three signals can be tuned to have a common untouched level
(Figure 11). The actual signals can be expected to look like those in Figure 12.
Figure 11
Pad average signals of the three wheel pads after tuning
Figure 12
Actual pad average signals after tuning
The, now common, untouched level is very high compared to the difference between touched and untouched
states. To make calculations easier, the signals are transformed near to zero by linear combinations which can be
represented by the formulae below. Figure 13 provides an illustration of the transformation. This transformation
also makes the transitions between angle sections smooth, which is especially important if the three pads have
different sensitivity or unstable untouched levels due to imperfect calibration or a changing environment.
A+B
X = -------------- – C
2
Application Note
A+C
Y = -------------- – B
2
11
B+C
Z = -------------- – A
2
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AP08128
inTouch Application Kit - Touch Wheel
Sensing Touch on Wheel
Figure 13
Combined pad average signals
The resulting X, Y and Z signals still have three distinct sections between 0 ° to 360 ° .
Section 1 (0ο to 120ο)
Before the transformation, Section 1 has three signals between UT and UT-MAXT (Figure 14). UT stands for the
untouched level and UT-MAXT stands for the signal level when the largest area of the respective pad is touched
(this happens at 0 ° , 120 ° and 240 ° ).
Figure 14
Section 1 before transformation
Application Note
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AP08128
inTouch Application Kit - Touch Wheel
Sensing Touch on Wheel
After the transformation, the X, Y and Z signals have much lower values (Figure 15). The angle axis has been
arbitrarily scaled from -1 to 2 in this region for convenience.
Figure 15
Section 1 after transformation
Signal X is constant low in this section so it does not participate in the angle calculation. The other two signals can
be described as:
MAXT
Y = ----------------- ϕ
2
MAXT MAXT
Z = ----------------- – ----------------- ϕ
2
2
MAXT
Y
If we rearrange Equation (1), we get ----------------- = ---- which we can substitute in Equation (2):
2
ϕ
Y Y
Z = ---- – ---- ϕ
ϕ ϕ
(1)
(2)
Y
Z = ---- ( 1 – ϕ )
ϕ
ϕ(Y + Z) = Y
Y
ϕ = -------------Y+Z
(3)
Z
ϕ = 1 – -------------Y+Z
(4)
One division is needed to calculate the angle; this operation needs the most computing performance. To minimize
the error, it is safer to use Equation (3) if Y is larger and Equation (4) if Z is larger.
Application Note
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AP08128
inTouch Application Kit - Touch Wheel
Sensing Touch on Wheel
An offset of 1 and a scaling factor of 2R are added to create a more usable calculated angle (Figure 16). R is for
resolution and corresponds to the number of left bitshifts on the numerator.
Section 1 Left
Section 1 Right
Figure 16
Z × 2R
ϕ = 2 × 2 R – ---------------Y+Z
Y × 2R
ϕ = ----------------- + 2 R
Y+Z
Section 1 after offsetting and scaling
Sections 2 and 3
In these two sections, the angle can be calculated in a similar way as described in Section 1, using the two nonconstant signals. Offsets of 4 and 7, and the same scaling factor, can then be added to sections 120 ° – 240 ° and
240 ° – 360 ° respectively to get a calculated angle of 0..9*2R for 0 ° .. 360 ° .
Section 2 Left
Y × 2R
ϕ = 5 × 2 R – ----------------X+Y
Section 2 Right
X × 2R
ϕ = ----------------- + 4 × 2 R
X+Y
Section 3 Left
X × 2R
ϕ = 8 × 2 R – ----------------X+Z
Section 3 Right
Z × 2R
ϕ = ---------------- + 7 × 2 R
X+Z
Figure 17 gives an illustration of the calculated angle across all 3 sections.
Application Note
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AP08128
inTouch Application Kit - Touch Wheel
Sensing Touch on Wheel
Figure 17
Calculated angle vs real angle across all sections
Figure 18
Actual calculated angle for a full round
Infineon provides a function library for angle calculation. The resolution, explained earlier, is user selectable from
1 to 8. The XC836M and XC836MT microcontrollers have a Multiplication/Division Unit (MDU) for hardware
acceleration. If the MDU is used for the division necessary to calculate the angle, the resolution is fixed at 8,
execution is faster and the code size is about 250 bytes smaller than without hardware acceleration. The
disadvantage is that the MDU increases the microcontroller’s current consumption by almost 1mA.
Application Note
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AP08128
inTouch Application Kit - Touch Wheel
U-SPY
4
U-SPY
For the inTouch Wheel board, one settings file, inTouch_Wheel.ini has been configured.
4.1
inTouch_Wheel.ini
This settings file (Figure 19) is customized to allow the user to monitor the calculated wheel angle, the brightness
level of the LEDs, the parameters of LEDTS ROM library and the Touch Wheel Library while running the
demonstration program.
Display Fields
Buttons
Progress Bar
Status Flags
Figure 19
inTouch_Wheel.ini User Interface
Buttons
In this settings file, the buttons allow the user to choose the signal(s) which they would like to monitor. The format
of the data transmitted for the buttons is in the following format (Table 1):
Table 1
Transmit Data Format for Buttons
D0
D1
Value (hex)
08
XX
Description
I.D. number
Button number
Application Note
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AP08128
inTouch Application Kit - Touch Wheel
U-SPY
The data received by the microcontroller will be used to determine the signals that will be transmitted to U-SPY for
display either as Status Flags (default) or on the Oscilloscope. The “off scope” button provides the option for the
user to return to the default display mode (status flags) after monitoring the signals on the oscilloscope.
Status Flags
The format of the transmitted data for the status flags is as follows (Table 2):
Table 2
Transmit Data Format for Status Flags
D0
D1
D2
Value (hex)
A3
XX
XX
Description
I.D. number
Mask (High Byte)
Mask (Low Byte)
The statuses of the LEDs received by USpy are masked before they are displayed as status flags. It is important
that the bits of a mask do not overlap with the bits of another mask. This is to ensure that status flags are not falsely
turned on. The masks used are as follows (Table 3):
Table 3
LED masks for Status Flags
Flag Index
8
12
13
14
15
11
Mask (hex)
0002
0004
0008
0010
0020
0040
265 to 0
1 to 24
25 to 48
49 to 72
73 to 96
97 to 120
Flag Index
7
3
2
1
0
4
Mask (hex)
0080
0100
0200
0400
0800
1000
121 to 144
145 to 168
169 to 192
193 to 216
217 to 240
241 to 264
Wheel Angle
(degrees)
Wheel Angle
(degrees)
Display Fields
The display fields output the calculated wheel angle and the current active mode. The mode can be toggled by
tapping on the touch wheel’s centre button. The format of the transmitted data for the display field is as follows
(Table 4):
Table 4
Transmit Data Format for Display Field
D0
D1
D2
D3
Value (hex)
A1
XX
XX
XX
Description
I.D. number
Display Field Index
Angle or Mode (High
Byte)
Angle or Mode (Low
Byte)
Progress Bar
The progress bar only becomes active in Mode 1 (Brightness Control Mode). The mode can be toggled by tapping
on the touch wheel’s centre button. The format of the transmitted data for the progress bar is as follows (Table 5):
Table 5
Transmit Data Format for Progress Bar
D0
D1
D2
D3
Value (hex)
A2
XX
XX
XX
Description
I.D. number
Progress Bar Index
Brightness Level
(High Byte)
Brightness Level
(Low Byte)
Application Note
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AP08128
inTouch Application Kit - Touch Wheel
U-SPY
Oscilloscope
The oscilloscope function allows the user to monitor up to 3 signals at a time (Figure 20). A total of 3 oscilloscopes
are available. However, we will display only 3 signals on 1 oscilloscope in this application. The format of the
transmitted data for the oscilloscope is as follows (Table 6):
Figure 20
U-SPY Oscilloscope
Table 6
Transmit Data Format for Oscilloscope
D0
D1
D2
D3
D4
D5
D6
D7
Value (hex)
A4
01
XX
XX
XX
XX
XX
XX
Description
I.D.
number
Scope
number
Signal 1
high byte
Signal 1
low byte
Signal 2
high byte
Signal 2
low byte
Signal 3
high byte
Signal 3
low byte
As mentioned in the previous section, the user is able to monitor six different types of signals in this settings file.
The signals displayed are as follows (Table 7: Wheel_A Mode, Table 8: Wheel_B Mode, Table 9: Wheel_C Mode,
Table 10: Wheel Avr Mode, Table 11: Angle, Amp Mode, Table 12: Centre Button Mode):
Application Note
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inTouch Application Kit - Touch Wheel
U-SPY
Table 7
Signals Displayed for Wheel_A Mode
Description
Colour
Table 8
Colour
Colour
Colour
Wheel_A Untouched Pad
Average Level
None
Green
Pink
Yellow
Signal 1
Signal 2
Signal 3
Wheel_B Current Pad
Average
Wheel_B Untouched Pad
Average Level
None
Green
Pink
Yellow
Signal 1
Signal 2
Signal 3
Wheel_C Current Pad
Average
Wheel_C Untouched Pad
Average Level
None
Green
Pink
Yellow
Signal 1
Signal 2
Signal 3
Wheel_A Current Pad
Average
Wheel_B Current Pad
Average
Wheel_C Current Pad
Average
Green
Pink
Yellow
Signal 1
Signal 2
Signal 3
Wheel Amplitude
Wheel Angle
None
Green
Pink
Yellow
Signal 1
Signal 2
Signal 3
Pad Total_TSCTR *
2DIVISORN
Pad Average
None
Green
Pink
Yellow
Signals Displayed for Angle, Amp Mode
Description
Colour
Table 12
Wheel_A Current Pad
Average
Signals Displayed for Wheel Avg Mode
Description
Table 11
Signal 3
Signals Displayed for Wheel_C Mode
Description
Table 10
Signal 2
Signals Displayed for Wheel_B Mode
Description
Table 9
Signal 1
Signals Displayed for Centre Button Mode
Description
Colour
Application Note
19
V1.0, 2012-02
20
D
C
2
1k5 R3
1
BZ1
1
8
6
4
2
20
18
16
14
12
10
KMTG1603
WHEEL_1
WHEEL_2
WHEEL_3
AN0
AN1
AN2
AN3
AN4
AN5
AN6
COL2
COL1
COL0
LINE6
LINE5
LINE4
LINE3
COL5 LINE2
COL4 LINE1
COL3 LINE0
WHEEL_C
19
17
15
13
11
9
7
5
3
1
2
2
R4 470R
R2 470R
R1 470R
3
3
4
4
LED7
green
Application Note
5
5
LED11
green
Figure 21
B
A
1
6
6
D
C
B
A
AP08128
inTouch Application Kit - Touch Wheel
Appendix - Schematics and Layout
Appendix - Schematics and Layout
inTouch Wheel Board Schematics
V1.0, 2012-02
LED12
green
LED10
green
LED9
green
LED8
green
LED6
green
LED5
green
LED4
green
LED3
green
LED2
green
LED1
green
AP08128
inTouch Application Kit - Touch Wheel
Appendix - Schematics and Layout
Figure 22
inTouch Wheel Board Component Bottom Layout
Figure 23
inTouch Wheel Board Top Layout
Application Note
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AP08128
inTouch Application Kit - Touch Wheel
Appendix - Schematics and Layout
Figure 24
inTouch Wheel Board Bottom Layout
Application Note
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AP08128
inTouch Application Kit - Touch Wheel
References
References
The list below provides resources that may be useful to the user.
1.
2.
3.
4.
5.
6.
7.
8.
User’s Manual - XC83x; 8-Bit Single-Chip Microcontroller
Application Note - AP08100 - Configuration for Capacitive Touch-Sense Application
Application Note - AP08110 - Design Guidelines for XC82x and XC83x Board Layout
Application Note - AP08113 - Capacitive-Touch Color Wheel Implementation
Application Note - AP08115 - Design Guidelines for Capacitive Touch-Sensing Application
Application Note - AP08121 - Infrared Remote Controller with Capacitive Touch Interface
Application Note - AP08122 - 16-Button Capacitive Touch Interface with XC836T
Application Note - AP08124 - XC82/83x Design Guidelines for Electrical Fast Transient (EFT) Protection in
Touch-Sense Applications
9. Application Note - AP08126 - Infineon Touch Solutions - inTouch Application Kit
10. Application Note - AP08127 - inTouch Application Kit - Buttons
11. Application Note - AP08129 - inTouch Application Kit - Touch Sliders
12. Application Note - AP08130 - inTouch Application Kit - LED Matrix
13. Link to XC83x-Series - www.infineon.com/xc83x
14. Link to Solutions for advanced touch control - www.infineon.com/intouch
Application Note
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V1.0, 2012-02
w w w . i n f i n e o n . c o m
Published by Infineon Technologies AG