Incorporating a Capacitive Touch Interface into
Your Design
Renesas Electronics America Inc.
© 2012 Renesas Electronics America Inc. All rights reserved.
Renesas Technology & Solution Portfolio
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© 2012 Renesas Electronics America Inc. All rights reserved.
Microcontroller and Microprocessor Line-up
2010
2012
1200 DMIPS, Superscalar
32-bit
 Automotive & Industrial, 65nm
 600µA/MHz, 1.5µA standby
1200 DMIPS, Performance
 Automotive, 40nm
 500µA/MHz, 35µA deep standby
500 DMIPS, Low Power
 Automotive & Industrial, 90nm
 600µA/MHz, 1.5µA standby
165 DMIPS, FPU, DSC
 Industrial, 40nm
 200µA/MHz, 0.3µA deep standby
165 DMIPS, FPU, DSC
 Industrial, 90nm
 200µA/MHz, 1.6µA deep standby
8/16-bit
25 DMIPS, Low Power
 Industrial, 90nm
 1mA/MHz, 100µA standby
 Industrial & Automotive, 150nm
 190µA/MHz, 0.3µA standby
44 DMIPS, True Low Power
10 DMIPS, Capacitive Touch
 Industrial & Automotive, 130nm
 144µA/MHz, 0.2µA standby
 Industrial
Automotive, 130nm
Wide
Format&LCDs
 350µA/MHz, 1µA standby
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Embedded Security, ASSP
© 2012 Renesas Electronics America Inc. All rights reserved.
‘Enabling The Smart Society’
 Challenge:
“Embedded designs are increasingly being incorporated in
new, innovated interfaces. How can the engineer keep up
with the increased demand for users desires for enhanced
user interfaces.”
 Solution:
“Let’s investigate one of those highly desired interfaces, capacitive
touch!”
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© 2012 Renesas Electronics America Inc. All rights reserved.
Agenda
 Touch Basics
 What is ‘Capacitive Touch’
 Detection methods
 Simple touch sensing
– Transforming analog to digital
 Renesas Touch Solution
 Hardware implementation
 Software overview
 Available Solution
 Capacitive Touch Lab
 Q&A
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© 2012 Renesas Electronics America Inc. All rights reserved.
Touch Basics
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© 2012 Renesas Electronics America Inc. All rights reserved.
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What is Capacitive Touch?
 Solution Components
 Flat, non-conductive surface
 Capacitive circuitry
– Electrode pads
– Connecting circuits
– Springs or other conductive elements
 Detection system
– Measures change in capacitance
 Touch Detection
 Capacitance change = touch?
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© 2012 Renesas Electronics America Inc. All rights reserved.
Touch Sensing Model
 Based on plate capacitance model
 C = cap. in farads (F).
 A = plate area
 d = distance between plates
 k = dielectric constant
 E = permittivity of free space
 Basic Operation
 Object detected = 1 plate
 Electrode = other plate
 Typically:
 Bigger object = bigger plate area = bigger cap change
 Large electrodes = bigger plate area = more sensitive
 Thicker dielectric = less change in C = less sensitive
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© 2012 Renesas Electronics America Inc. All rights reserved.
Types of Capacitive Touch Detection Methods
Mutual Capacitance *



Power Consumption:
Medium/High
Emissions: Medium/High
Immunity: Medium/High
Renesas Method
Self Capacitance *

Power Consumption:
Low

Emissions: Low

Immunity: Medium
* Attributes may vary depending on implementation
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© 2012 Renesas Electronics America Inc. All rights reserved.
Capacitive Sensing
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Simplified Hardware Circuit
 Major components…
Charge Circuit
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Circuit Control
© 2012 Renesas Electronics America Inc. All rights reserved.
Capacitance Detection
Touch
Electrode
Circuit Operation
 Charge circuit…
Vct
Cr
Cx
Rc
Cc
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Circuit Operation
 Waveform process
RC charge formula
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Circuit Operation
 Quick discharge…
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Vct
Circuit Operation
RC discharge formula
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© 2012 Renesas Electronics America Inc. All rights reserved.
Circuit Operation
 Charge re-distribution…
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© 2012 Renesas Electronics America Inc. All rights reserved.
Vct
Circuit Operation
 Charge re-distribution…
Charge re-distribution… Charge re-distribution
Vct = Vc * (Cr / Cr + Cx)
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© 2012 Renesas Electronics America Inc. All rights reserved.
Circuit Operation
 Continue process till
Test if Vct below Vref
No = Count channel up
Yes = Cycle complete
Charge re-distribution…
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Circuit Operation
 Repeat discharge and re-distribution
Test if Vct below Vref
No = Count channel up
Yes = Cycle complete
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© 2012 Renesas Electronics America Inc. All rights reserved.
Touch Detection
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Effect of Touch
Adding ‘object’ adds capacitance
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Touch Sampling
 Quicker re-distribution/discharge
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Touch…Analog to Digital
 Tracking counts vs. time
‘Counts’
Time
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Touch…Analog to Digital
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© 2012 Renesas Electronics America Inc. All rights reserved.
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Touch-Sensor Control Unit
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© 2012 Renesas Electronics America Inc. All rights reserved.
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Why Develop Hardware?
 How could we control
the switches shown in
the diagram?
 Would our timing need
to be accurate?
 How would you
measure the discharge
curve voltage?
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© 2012 Renesas Electronics America Inc. All rights reserved.
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T-SCU (Touch-Sensor Control Unit)
 T-SCU performs:
 Sequencing and timing of
the charge/discharge
 Key scanning
 High-frequency filtering
 Interrupt Generation
 Data Transfers
T-SCU
– DTC or DMA
 T-SCU Features
 Up to 36 channel sense
capability
 Single, scan, or selective
scan modes
 S/W or H/W scan kickoff
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© 2012 Renesas Electronics America Inc. All rights reserved.
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R8C T-SCU CPU Utilization
 R8C/3xT SCU performs touch scanning autonomously
 In software solution, CPU is utilized 100%
Softwarebased
solution
R8C/3xT
Option A
R8C/3xT
Option B
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CPU Active
(Touch Scanning)
CPU Active
(System Functions)
CPU
System Functions
CPU
SCU
Scanning + Data Transfer
CPU
Not Operating
SCU
Scanning + Data Transfer
CLK
…
© 2012 Renesas Electronics America Inc. All rights reserved.
CPU Active
(Touch Post
Processing)
Less than
15% of
total CPU time
(20MHz)
T-SCU Scan Sequence
T-SCU Data Transfer to RAM Buffer
SCSTRT
(Start bit)
Ch 0 Measure
T-SCU Operating
Ch 1 Measure
Ch 2 Measure
T-SCU Interrupt
T-SCU DTC Ch
2
User Code
running
T-SCU DTC Ch
1
T-SCU Operating
Touch SW Processing
T-SCU Operating
User Code
running
User Code
running
T-SCU DTC Ch 0
Complete scan example using Ch 0 to Ch 2
Scan is started by program
Note: Time for operations not to scale
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© 2012 Renesas Electronics America Inc. All rights reserved.
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T-SCU Data Storage
 Count data is transferred by
DTC to RAM Buffer
 Start address of buffer is
set in T-SCU Destination
Register
Example
• Scan channel 0-2 in ascending order
• T-SCU Destination Register = 0C00h
start
Measure Ch 0
 Dedicated RAM
Measure Ch 1
Measure Ch 2
0C00h
0C01h
0C02h
0C03h
0C04h
0C05h
0C06h
0C07h
0C08h
0C09h
0C0Ah
0C0Bh
CH0 dataA
CH0 dataD
CH1 dataA
CH1 dataD
CH2 dataA
CH2 dataD
T-SCU Interrupt
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T-SCU Low Power Operation
 Core can be in “Wait” mode
 T-SCU trigger from Timer for sampling interval
 Once scan is completed DMA (not DTC) transfers data to
RAM
 Utilizes a special SDMA block
 DMA interrupt “wakes” MCU on transfer complete
 Touch determination made
 No touch MCU back to sleep
 Touch - MCU services button
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© 2012 Renesas Electronics America Inc. All rights reserved.
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Low-power Example
Example using Timer as Trigger
T-SCU
T-SCU not operating
touch
detection
Touch Data
processing
normal process
Power
Consumption
T-SCU
T-SCU not operating
Touch Data
processing
Wait mode
Wait mode
touch
detection
Timer
trigger
Enable T-SCU
(via S/W)
Start trigger
(internal)
T-SCU DMA transfers touch data to RAM Buffer so
MCU does not wake up until DMA Interrupt occurs
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© 2012 Renesas Electronics America Inc. All rights reserved.
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Flexible Tuning Capability
 Dual Comparison Capacitor
● Aids in tuning flexibility
● Selectable via H/W register
● Reconfigurable during operation
Long electrodes
Choose Cr1 (CHxA1)
Rr
CHxA0
Cr0
CHxA1
CH
Selector
Cr1
CHxB
Rc
CHxC
Cc
Shorter electrodes
Choose Cr0 (CHxA0)
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© 2012 Renesas Electronics America Inc. All rights reserved.
Improving Noise immunity
 20MHz Sample Clock
 Decreased measurement cycle
 reduces noise influence
 Larger internal registers
 Higher count values
Touch waveform with noise influence
Noise influence
Inverter Noise
Correct level
Measure point @20MHz clock
High speed sample clock is effective
for reducing noise
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© 2012 Renesas Electronics America Inc. All rights reserved.
Renesas Touch Software
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© 2012 Renesas Electronics America Inc. All rights reserved.
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Implementation Overview
User Application
 Three Distinct Layers
Application
Application Layer
Layer
 Renesas API covers:
 T-T-SCU Driver
Tscu_mode
SetTscuMode
Slider position
 Auto Calibration
 Low-level functions/data
can be accessed as well
from any level
Slider
Position
Detection
Wheel
Position
Detection
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© 2012 Renesas Electronics America Inc. All rights reserved.
SetTscuDcen
Touch
position
Detection
Drift Correction
Measurement value
output
Auto Calibration
Reference Value
Calculation
S/W Noise Filter
H/W
H/W interface
interface Layer
Layer
H/W Noise Filter
 Full-source code available
Drift On/Off
Functional
Functional Implementation
Implementation interface
interface Layer
Layer
 User Application
 Typical interface thru
‘USER API’
Sensor On/Off
GetSliderPosition GetWheelPosition GetTouchOnOff
 Basic Touch Decision
 Slider/Wheel
Wheel position
TSCU Driver
Touch API Configuration
 Touch API Overview
 Base API and User API
– Base API controls TT-SCU measurement and low-level touch
decision
– User API allows setup and acquisition of touch data from
application level
 Five (5) Source Files Needed
 touch_control.c
 touch_user_API.c
 touch_interrupt.c
 slider_control.c
 wheel_control.c
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© 2012 Renesas Electronics America Inc. All rights reserved.
Touch API Functionality
 Major ‘Base API’ Functions
 Data movement and TT-SCU interrupt process
 Low-level touch decision
 Drift correction
 Automatic calibration
 Multi Touch Cancellation
 New ‘User API’ Functions
 Wheel position detection
 Slider position detection
 Start/Stop of TT-SCU measurement
 Drift compensation enable/disable
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© 2012 Renesas Electronics America Inc. All rights reserved.
Touch API Features
 Drift Compensation
 Monitors continuously
 Reduces environmental effects
 Suspended if touched
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© 2012 Renesas Electronics America Inc. All rights reserved.
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Integrated Wheel Processing
 Configurable Wheel Setting
 Uses updated wheel shapes
 4 or 8 channels selectable
 Positional
 The range of the position value is
from zero to 72
 When the value is zero the wheel
is not touched
 API variable returns information
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© 2012 Renesas Electronics America Inc. All rights reserved.
Integrated Slider Processing
 Configurable Slider
 6 channels implementation
 Configurable Resolution
– Currently up to 256 positions
 Features
 Reports position on touch
 User code determines direction
 API variable returns information
for processing
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© 2012 Renesas Electronics America Inc. All rights reserved.
CH0
CH1
CH2
CH3
CH4
CH5
Renesas Touch Solution
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© 2012 Renesas Electronics America Inc. All rights reserved.
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R8C/3xT-A Features
 CPU Core
Program Flash
up to 128KB
 16-bit R8C CPU Core with built-in
hardware multiplier
 Single-cycle memory access
SRAM
Memory
up to 10KB
Data Flash
up to 4KB
 Touch T-SCU
 Up to 36 channels
 ~8 ms for scanning 36 channels
 Tuning dependent
 Memory
 ROM: up to 128KB
 SRAM: up to 10KB
DTC
T-SCU
Touch
Clock Generation
Internal, External
DMA
POR, LVD
System
Event Link
Controller
ADC
 Power Supply
 1.8V to 5.5V
 Clocks
 Hi-Speed and Low Speed OCO
 XCIN and XIN
Interrupt Controller
Debug
Register Protect
Safety
Clock
10-bit, 20 ch
Analog
On-Chip
Voltage Reference
 Package
 80 pin LQFP (14x14)
Low Speed
Low
Speed
Mode
Mode
Power
Management
Wait
Mode
Wait Mode
STOP Mode
STOP
SRAMMode
On
SRAM On
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CRC
1 x I 2C
 20 channels, 10-bit
 SPI, UART, I2C (SSU block), LIN
Monitoring
Single-Wire
 Analog
 Communication
Program Code
Protect
© 2012 Renesas Electronics America Inc. All rights reserved.
1 x Timer
8-bit
3Timers
x Timer
16-bit
WDT
1 x SSU
SPI
Compatible
Communication
3x UART
7, 8-bit
1 x LIN
1ch
Renesas Touch Evaluation Kit
 Renesas Demo Kit for
R8C/36T-A
 Full featured development
platform
 Includes E1debugger
 HEW IDE environment and
trial compiler
 Touch software source
included
 Workbench tuning tool
included
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© 2012 Renesas Electronics America Inc. All rights reserved.
Touch Application Notes
 Application notes
 Hardware Design
 Power Supplies
 Noise
 Tech Briefs
 Humidity
 Temperature
 Design Guides
 Tuning Guidelines
 Layout Recommendations
 Spring Usage
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© 2012 Renesas Electronics America Inc. All rights reserved.
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Advanced Tuning Tools
Intuitive GUI
Measurement
Parameter Setting
Circuit Modeling
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© 2012 Renesas Electronics America Inc. All rights reserved.
Questions?
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© 2012 Renesas Electronics America Inc. All rights reserved.
‘Enabling The Smart Society’
 Challenge:
“Embedded designs are increasingly being incorporated in
new, innovated interfaces. How can the engineer keep up
with the increased demand for users desires for enhanced
user interfaces.”
 Solution:
“Let’s investigate one of those highly desired interfaces, capacitive
touch!”
 Do you agree that we accomplished the above statement?
51
© 2012 Renesas Electronics America Inc. All rights reserved.
Renesas Electronics America Inc.
© 2012 Renesas Electronics America Inc. All rights reserved.