Cypress | CapSense CY8C20x36 | User guide | Cypress CapSense CY8C20x36 User guide

Cypress CapSense CY8C20x36 User guide
Getting Started with CapSense®
Document No. 001-64846 Rev.*I
Cypress Semiconductor
198 Champion Court
San Jose, CA 95134-1709
Phone (USA): 800.858.1810
Phone (Intnl): 408.943.2600
http://www.cypress.com
Copyrights
Copyrights
© Cypress Semiconductor Corporation, 2010-2013. The information contained herein is subject to change without notice.
Cypress Semiconductor Corporation assumes no responsibility for the use of any circuitry other than circuitry embodied in a
Cypress product. Nor does it convey or imply any license under patent or other rights. Cypress products are not warranted
nor intended to be used for medical, life support, life saving, critical control or safety applications, unless pursuant to an
express written agreement with Cypress. Furthermore, Cypress does not authorize its products for use as critical
components in life-support systems where a malfunction or failure may reasonably be expected to result in significant injury
to the user. The inclusion of Cypress products in life-support systems application implies that the manufacturer assumes all
risk of such use and in doing so indemnifies Cypress against all charges.
Trademarks
PSoC Designer™ and SmartSense™ are trademarks and PSoC®, CapSense®, and TrueTouch® are registered
trademarks of Cypress Semiconductor Corp. All other trademarks or registered trademarks referenced herein are property
of the respective corporations.
Source Code
Any Source Code (software and/or firmware) is owned by Cypress Semiconductor Corporation (Cypress) and is protected
by and subject to worldwide patent protection (United States and foreign), United States copyright laws and international
treaty provisions. Cypress hereby grants to licensee a personal, non-exclusive, non-transferable license to copy, use,
modify, create derivative works of, and compile the Cypress Source Code and derivative works for the sole purpose of
creating custom software and or firmware in support of licensee product to be used only in conjunction with a Cypress
integrated circuit as specified in the applicable agreement. Any reproduction, modification, translation, compilation, or
representation of this Source Code except as specified above is prohibited without the express written permission of
Cypress.
Disclaimer
CYPRESS MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARD TO THIS MATERIAL,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE. Cypress reserves the right to make changes without further notice to the materials described
herein. Cypress does not assume any liability arising out of the application or use of any product or circuit described herein.
Cypress does not authorize its products for use as critical components in life-support systems where a malfunction or failure
may reasonably be expected to result in significant injury to the user. The inclusion of Cypress product in a life-support
systems application implies that the manufacturer assumes all risk of such use and in doing so indemnifies Cypress against
all charges.
Use may be limited by and subject to the applicable Cypress software license agreement.
2
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
Contents
1.
Introduction.................................................................................................................................................................... 6
1.1
1.2
1.3
1.4
2.
How to Use This Guide .......................................................................................................................................... 6
Cypress‘s CapSense Documentation Ecosystem .................................................................................................. 6
Cypress CapSense Products................................................................................................................................. 8
1.3.1 Cypress CapSense Differentiation ............................................................................................................ 8
Document Conventions ......................................................................................................................................... 9
CapSense Technology ................................................................................................................................................ 10
2.1
2.2
2.3
2.4
2.5
2.6
2.7
Capacitive Sensing Methods ............................................................................................................................... 10
2.1.1 Self-Capacitance .................................................................................................................................... 10
2.1.2 Mutual-Capacitance ................................................................................................................................ 11
Self-Capacitance Equivalent Model ..................................................................................................................... 11
CapSense Sensing Technology .......................................................................................................................... 12
2.3.1 Sensing Methods .................................................................................................................................... 12
2.3.2 Capacitance Conversion......................................................................................................................... 12
2.3.3 CapSense with Sigma Delta Modulator (CSD) ....................................................................................... 13
2.3.4 CapSense Successive Approximation Electromagnetic Compatible (CSA_EMC) .................................. 14
CapSense Tuning ................................................................................................................................................ 15
2.4.1 Definitions ............................................................................................................................................... 15
2.4.2 Signal-to-Noise Ratio (SNR) ................................................................................................................... 16
2.4.3 Measuring SNR ...................................................................................................................................... 16
2.4.4 SmartSense Auto-Tuning ....................................................................................................................... 17
2.4.5 SmartSense_EMC (SmartSense Electromagnetic Compatible) ............................................................. 18
Sensor Types ...................................................................................................................................................... 19
2.5.1 Buttons (Zero-Dimensional Sensors) ...................................................................................................... 19
2.5.2 Sliders (One-Dimensional Sensors)........................................................................................................ 20
2.5.3 Touchscreens and Trackpads (Two-Dimensional Sensors) ................................................................... 22
2.5.4 Proximity (Three-dimensional Sensors) .................................................................................................. 22
Sensor Construction ............................................................................................................................................ 23
2.6.1 Field Coupled via Copper Trace (PCB) .................................................................................................. 23
2.6.2 Field Coupled via Spring/Gasket/Foam .................................................................................................. 23
2.6.3 Field Coupled via Printed Ink .................................................................................................................. 24
2.6.4 Field Coupled via ITO Film on Glass ...................................................................................................... 24
User Interface Feedback ..................................................................................................................................... 24
2.7.1 Visual Feedback ..................................................................................................................................... 24
2.7.2 Haptic Feedback ..................................................................................................................................... 28
2.7.3 Audible Feedback ................................................................................................................................... 29
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
3
2.8
2.9
3.
Design Considerations ............................................................................................................................................... 33
3.1
3.2
3.3
3.4
3.5
3.6
3.7
4
Water Tolerance .................................................................................................................................................. 31
CapSense System Overview ............................................................................................................................... 31
2.9.1 Hardware Component............................................................................................................................. 31
2.9.2 Firmware Component ............................................................................................................................. 32
Overlay Selection ................................................................................................................................................ 33
3.1.1 Overlay Material...................................................................................................................................... 33
3.1.2 Overlay Thickness .................................................................................................................................. 34
3.1.3 Overlay Adhesives .................................................................................................................................. 34
ESD Protection .................................................................................................................................................... 34
3.2.1 Preventing ESD Discharge ..................................................................................................................... 35
3.2.2 Redirect .................................................................................................................................................. 36
3.2.3 Clamp ..................................................................................................................................................... 36
Electromagnetic Compatibility (EMC) Considerations ......................................................................................... 37
3.3.1 Radiated Interference ............................................................................................................................. 37
3.3.2 Radiated Emissions ................................................................................................................................ 39
3.3.3 Conducted Immunity and Emissions....................................................................................................... 40
Software Filtering................................................................................................................................................. 41
3.4.1 Average Filter ......................................................................................................................................... 41
3.4.2 IIR Filter .................................................................................................................................................. 42
3.4.3 Median Filter ........................................................................................................................................... 44
3.4.4 Jitter Filter ............................................................................................................................................... 45
3.4.5 Event-Based Filters ................................................................................................................................ 47
3.4.6 Rule-Based Filters .................................................................................................................................. 47
Power Consumption ............................................................................................................................................ 47
3.5.1 Active and Sleep Current ........................................................................................................................ 47
3.5.2 Average Current ..................................................................................................................................... 47
3.5.3 Response Time versus Power Consumption .......................................................................................... 48
Pin Assignments .................................................................................................................................................. 48
PCB Layout Guidelines ....................................................................................................................................... 51
3.7.1 Parasitic Capacitance, CP ....................................................................................................................... 51
3.7.2 Board Layers .......................................................................................................................................... 51
3.7.3 Board Thickness ..................................................................................................................................... 51
3.7.4 Button Design ......................................................................................................................................... 51
3.7.5 Slider Design .......................................................................................................................................... 52
3.7.6 Sensor and Device Placement ............................................................................................................... 52
3.7.7 Trace Length and Width ......................................................................................................................... 52
3.7.8 Trace Routing ......................................................................................................................................... 53
3.7.9 Crosstalk Solutions ................................................................................................................................. 53
3.7.10 Vias......................................................................................................................................................... 54
3.7.11 Ground Plane ......................................................................................................................................... 54
3.7.12 Shield Electrode and Guard Sensor ....................................................................................................... 55
3.7.13 CapSense System Design with Single Layer PCB ................................................................................. 56
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
4.
CapSense Product Portfolio ....................................................................................................................................... 57
4.1
5.
CapSense Selector Guide ........................................................................................................................................... 59
5.1
6.
Selecting the Right CapSense Device ................................................................................................................. 59
CapSense Migration Paths ......................................................................................................................................... 63
6.1
6.2
6.3
6.4
7.
Cypress‘s CapSense Controller Solutions ........................................................................................................... 57
4.1.1 CapSense Express Controllers (Configurable Solutions) ....................................................................... 57
4.1.2 CapSense Controllers (Programmable Solutions) .................................................................................. 57
4.1.3 CapSense Plus (Programmable Solutions) ............................................................................................ 58
CY8C20x34 to CY8C20xx6A/H/AS ..................................................................................................................... 63
CY8C21x34/B / CY8C24x94 to CY8C20xx6A/H/AS ............................................................................................ 63
CY8C20xx6A/H/AS to CY8C21x34/B / CY8C24x94 ............................................................................................ 63
Pin-to-Pin Compatibility ....................................................................................................................................... 64
Resources .................................................................................................................................................................... 65
7.1
7.2
7.3
7.4
Website ............................................................................................................................................................... 65
Device Specific Design Guides............................................................................................................................ 65
Technical Reference Manuals ............................................................................................................................. 65
Development Kits ................................................................................................................................................ 65
7.4.1 Universal CapSense Controller Kits........................................................................................................ 65
7.4.2 Universal CapSense Module Boards ...................................................................................................... 66
7.4.3 CapSense Express Evaluation Kits for CY8C201xx ............................................................................... 66
7.4.4 CapSense Express Evaluation Kits for CY8CMBR2044 ......................................................................... 66
7.4.5 Evaluation Pods ...................................................................................................................................... 66
7.4.6 In-Circuit Emulation (ICE) Kits ................................................................................................................ 67
7.5 Demonstration Kit ................................................................................................................................................ 67
7.6 PSoC Designer .................................................................................................................................................... 67
7.7 PSoC Programmer .............................................................................................................................................. 68
2
7.8 I C-to-USB Bridge Kit .......................................................................................................................................... 69
7.9 Debugging/Data Viewing Tools ........................................................................................................................... 69
7.9.1 Bridge Control Panel............................................................................................................................... 69
7.9.2 MultiChart ............................................................................................................................................... 69
7.10 Design Support .................................................................................................................................................... 71
8.
Appendix ...................................................................................................................................................................... 72
8.1
8.2
Appendix A: Springs ............................................................................................................................................ 72
8.1.1 Finger-Introduced Capacitance .............................................................................................................. 72
8.1.2 Mounting Springs to the PCB ................................................................................................................. 73
8.1.3 CapSense and Mechanical Button Combination .................................................................................... 74
8.1.4 Design Examples .................................................................................................................................... 74
Document Revision History ................................................................................................................................. 75
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
5
1. Introduction
1.1 How to Use This Guide
®
This guide is an ideal starting point for those new to capacitive touch sensing (CapSense ) as well as for learning key
design considerations and layout best practices to ensure design success. In addition, you can use this guide to:

Become familiar with the technology underlying CapSense solutions

Understand important design considerations, such as layout, schematic, and EMI (Electro Magnetic Interference)

Become familiar with the CapSense product portfolio

Select the right device for your application

Migrate between CapSense devices

Become familiar with the many resources available to support your entire design cycle
When you are ready to design your application, consult the Design Guide specific to the CapSense device family you
have selected.
1.2 Cypress’s CapSense Documentation Ecosystem
Figure 1-1 and Table 1-1 summarize the Cypress CapSense documentation ecosystem. These resources allow you
to quickly access the information needed to complete a CapSense product design successfully. Figure 1-1 shows the
typical flow of a product design cycle with capacitive sensing; the information in this guide is highlighted in green.
Table 1-1 provides links to the supporting documents for each of the numbered tasks in Figure 1-1.
6
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
Figure 1-1. Typical CapSense Product Design Flow
1. Capacitive touch sensing basics
= Topics covered in this document
2. Specify system requirements and
characteristics
*
†
= Applicable for CY80MBR2xxx family of
devices
= Applicable for CapSense and CapSense
Plus programmable devices
3. CapSense device selection based
on needed functionality
Design for CapSense
4. Mechanical
design
6. PSoC Designer project
creation†
5. Schematic
capture and
PCB layout
7. Firmware
development†
8. CapSense tuning†
10. CapSense
configuration*
9. Programming PSoC
11. Preproduction build (prototype)
12. Test and evaluate system functionality and
CapSense performance
Performance
satisfactory
No
Yes
13. Production
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
7
Table 1-1. Cypress Documents Supporting Numbered Design Tasks of Figure 1-1
Figure 1-1 Task No.
1
Supporting Cypress CapSense Documentation
Getting Started with CapSense
Getting Started with CapSense
2
Device Family Specific CapSense Device Datasheets
Device Family Specific CapSense Design Guides
3
Getting Started with CapSense
4
Getting Started with CapSense
5
Getting Started with CapSense
6
PSoC Designer User Guides
Assembly Language User Guide
C Language Compiler User Guide
7
CapSense Code Examples
Device Family Specific Technical Reference Manuals
Device Family Specific CapSense Design Guides
Device Family Specific CapSense User Module Datasheets (CSA_EMC)
8
CapSense Data Viewing Tools -AN2397
CapSense Controller Code Examples Design Guide
Programmer User Guide
9
11
MiniProg3 User Guide
CapSense Code Examples
1.3 Cypress CapSense Products
Cypress CapSense solutions bring elegant, reliable, and easy-to-use capacitive touch sensing functionality to your
design. Our capacitive touch sensing solutions have replaced more than four billion mechanical buttons. Capacitive
touch sensing has changed the face of industrial design in products, such as cell phones, PCs, consumer electronics,
automotive features, and white goods. Cypress‘s robust CapSense solutions leverage our flexible Programmable
System-on-Chip (PSoC) architecture, which accelerates time-to-market, integrates critical system functions, and
reduces BOM costs.
1.3.1 Cypress CapSense Differentiation

Robust sensing technology

High noise immunity

High performance sensing across a variety of overlay materials and thicknesses

SmartSense™ Auto-Tuning technology

Proximity sensing

Water tolerant operation

Complete user interface solution including audio, visual, and haptics feedback

Low power consumption

Wide operating voltage range (1.71—5.5 V)

Small form factor packaging

Reduced BOM cost with integrated CapSense Plus features (ADC, DAC, timer, counter, PWM)
8
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
1.4 Document Conventions
Convention
Usage
Courier New
Displays file locations, user entered text, and source code:
C:\ ...cd\icc\
Italics
Displays file names and reference documentation:
Read about the sourcefile.hex file in the PSoC Designer User Guide.
[Bracketed, Bold]
Displays keyboard commands in procedures:
[Enter] or [Ctrl] [C]
File > Open
Represents menu paths:
File > Open > New Project
Bold
Displays commands, menu paths, and icon names in procedures:
Click the File icon and then click Open.
Times New Roman
Displays an equation:
2+2=4
Text in gray boxes
Describes Cautions or unique functionality of the product.
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
9
2. CapSense Technology
Cypress‘s CapSense controllers use changes in capacitance to detect the presence of a finger on or near a touch
surface, as shown in Figure 2-1. This touch button example illustrates a capacitive sensor replacing a mechanical
button. The sensing function is achieved using a combination of hardware and firmware. The following section
provides an overview of capacitive sensing technology and CapSense solutions.
Figure 2-1. Illustration of a Capacitance Sensor Application
2.1 Capacitive Sensing Methods
Capacitance can be measured between two points using either self-capacitance or mutual-capacitance.
Figure 2-2. Self-Capacitance and Mutual-Capacitance Methods
I
+
Vx _
Cx
Z
Tx
Self Capacitance
+
V1
_
Cx
+
V2
_
Rx
Mutual Capacitance
2.1.1 Self-Capacitance
Self-capacitance uses a single pin and measures the capacitance between that pin and ground. A self-capacitance
sensing system operates by driving current on a pin connected to a sensor and measuring the voltage. When a finger
is placed on the sensor, it increases the measured capacitance. Self-capacitance sensing is best suited for singletouch sensors, such as buttons and sliders.
Cypress‘s CapSense solutions use self-capacitance sensing. This approach makes efficient use of pins for single
touch sensors and sliders.
10
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
2.1.2 Mutual-Capacitance
Mutual-capacitance uses a pair of pins and measures the capacitance between those pins. A mutual-capacitance
system operates by driving a current on a transmit pin and measuring the charge on a receive pin. When a finger is
placed between the transmit and receive pins, it decreases the measured capacitance. The mutual-capacitance effect
is best suited to multitouch systems, such as touchscreens and trackpads.
®
Cypress‘s TrueTouch touchscreen solutions use mutual-capacitance sensing. See TrueTouch Touchscreen
Controllers to learn about these products. Cypress also offers trackpad solutions. Contact your local Cypress sales
office directly for more information. To find your local sales office, click here.
2.2 Self-Capacitance Equivalent Model
In a CapSense self-capacitance system, the sensor capacitance measured by the controller is called CX. When a
finger is not on the sensor, CX equals the parasitic capacitance of the system. This parasitic capacitance, CP, is a
simplification of the distributed capacitance that includes the effects of the sensor pad, the overlay, the trace between
the CapSense controller pin and the sensor pad, the vias through the circuit board, and the pin capacitance of the
CapSense controller. CP is related to the electric field around the sensor pad. Although Figure 2-3 shows field lines
only around the sensor pad, the actual electric field is more complicated.
Figure 2-3. CP and Electric Field
When a finger touches the sensor surface, it forms a simple parallel plate capacitor with the sensor pad through the
overlay. The result is called finger capacitance, C F, and is defined by Equation 1. CF is a simplification of a distributed
capacitance that includes the effects of the human body and the return path to the circuit board ground.
Equation 1
Where:
ε0 = Free space permittivity
εr = Dielectric constant of overlay
A = Area of finger and sensor pad overlap
D = Overlay thickness
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
11
Figure 2-4. CapSense System Equivalent Model
With a finger on the sensor surface, CX equals the sum of CP and CF.
Equation 2
2.3 CapSense Sensing Technology
2.3.1 Sensing Methods
There are a number of capacitive sensing methods currently in use across the electronics industry. Some of them
include:

Charge Transfer: The change in sensor capacitance introduced by a finger touch results in the change in charge
transfer between the sensor capacitor and the reference capacitor. These incremental charge packets are
transferred until a reference voltage is achieved on the reference capacitor, which indicates the presence of a
touch.

Relaxation Oscillator: A sensor capacitor is used to set its frequency directly. The capacitance introduced by the
finger touch is detected on the sensor by tracking the change in the frequency of the oscillator. When there is a
finger touch, the sensor capacitor increases and frequency of the oscillator decreases.

TX-RX: A source waveform is driven on the TX end of a mutual capacitance system and senses the response on
the RX end. The received signal reflects changes in sensor capacitance.

ADC: A current source generates a linear voltage ramp on a capacitor. This voltage is input to an analog
comparator circuit. The comparator‘s output is monitored and a counter increments whenever it transitions from
high to low.
Cypress‘s CapSense devices measure sensor capacitance using either CapSense with Sigma Delta modulator
(CSD) or CapSense Successive Approximation (CSA_EMC). Both methods are variants of the ADC method.
2.3.2 Capacitance Conversion
The CapSense algorithm converts the sensor capacitance into a digital count, called raw count. The raw count is
interpreted as either a TOUCH or NO TOUCH state for the sensor. The numerical value of the raw count is the digital
representation of the sensor capacitance, and increases as the capacitance increases. Sensitivity is a measure of
how much the output will change for a given change on the input. The sensitivity of the CapSense sensor has units of
counts-per-pF.
12
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
Figure 2-5. Sensing Algorithm Output
2.3.3 CapSense with Sigma Delta Modulator (CSD)
Cypress‘s CSD method uses a switched capacitor circuit on the front end of the system to convert the sensor
capacitance to an equivalent resistor. A Sigma-Delta modulator converts the current measured through the equivalent
resistor into a digital count. When a finger is on the sensor, the capacitance increases and the equivalent resistance
+decreases. This causes an increase in current through the resistor, resulting in an increase in the digital count.
The CSD method requires a single dedicated pin and a single external component, C MOD, or two dedicated pins and
two external components, CMOD and RB, depending on what CapSense controller family is selected.
Figure 2-6 shows the CSD configuration for the CY8C21x34 CapSense controller family, and the family requires two
external components and two dedicated pins.
Figure 2-6. CY8C21x34/B CSD Block Diagram
CY8C21x34/B
Vdd
Precharge
Clock
Sw1
Vref
Gnd
Sw2
AMUX Bus
Rbus
Cx
High-Z
input
Sigma-Delta
Converter
isensor
Rb
ibleed
Cmod
Getting Started with CapSense
®
= External Connection
Document No. 001-64846 Rev. *I
13
The CY8C20xx6A/AS/H family of CapSense controllers uses a single external component CMOD and a single
dedicated pin.
Figure 2-7. CY8C20xx6A/AS/H CSD Block Diagram
CY8C20x34/
CY8C20xx6A/AS/H
Vref
iDAC
Sw2
Rbus
ISENSOR
Cx
IDAC
Gnd
High-Z
input
Single
Slope ADC
AMUX
Sw1
IDIFF
Precharge
Clock
Cint(1.2nF)
= External Connection
2.3.4 CapSense Successive Approximation Electromagnetic Compatible (CSA_EMC)
Cypress‘s CSA_EMC method also uses a switched-capacitor circuit on the front end of the system to convert the
sensor capacitance to an equivalent resistor. An internal constant current source called the iDAC is calibrated with a
successive approximation procedure until an equilibrium voltage develops across the integration capacitor CMOD. This
equilibrium voltage is measured using a single slope ADC. When you place a finger on the sensor the capacitance
increases. Further, this causes the equilibrium voltage on CMOD to decrease and the ADC output increases that result
in an increase in the digital count.
The CSA_EMC method requires a single dedicated pin and a single external component, CINT, which is an integration
capacitor that is used by the single-slope ADC.
The CSA_EMC CapSense algorithm is developed to work well in the presence of RF interference. CSA_EMC is used
in applications where CapSense is exposed to conducted interference, AC noise, and other noise sources such as
inverters, transformers, and power supplies. For more detail on CSA_EMC CapSense, see Electromagnetic
Compatibility (EMC) Considerations.
14
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
Figure 2-8. CSA_EMC Block Diagram
CY8C20x34
Vref
Gnd
iDAC
AMUX Bus
Sw2
Rbus
High-Z
input
Single
Slope ADC
isensor
Cx
Sw1
idiff
Precharge
Clock
Cmod
= External Connection
For a detailed discussion of Cypress‘s CSD and CSA_EMC sensing methods, see the respective device design
guides. Table 5-1 shows the CapSense controller offerings and the sensing method supported for each. Table 5-2
compares these two CapSense sensing technologies in detail.
2.4 CapSense Tuning
Optimal CapSense system performance depends on board layout, button dimensions, overlay material, and
application requirements. These factors are discussed in Design Considerations. In addition to these factors,
switching frequency and threshold levels must be carefully selected for robust and reliable performance. Tuning is the
process of determining the optimum values for these parameters. Tuning is required to maintain high sensitivity to
touch and to compensate for process variations in the sensor board, overlay material, and environmental conditions.
Before we move further, a number of terms need to be defined to understand the tuning process.
2.4.1 Definitions

Raw Count: As seen in Figure 2-9, sensor capacitance is converted into a count value by the CapSense
algorithm. The unprocessed count value is referred to as raw count. Processing of the raw count results in
ON/OFF states for the sensor.

Baseline: The baseline is an estimate of the average sensor count level when the sensor is in the OFF state.
The baseline provides a reference level for the ON/OFF comparison.

Difference Count: Subtracting the baseline level from the raw count produces the difference count that is used
in the ON/OFF decision process. The actual baseline is dynamically adjusted by the user module to compensate
for environmental changes through a process called baseline update.
The thresholds are offset by a constant amount from the baseline level. The thresholds have the following functions:

Noise Threshold: If the difference count is below the noise threshold, then the baseline is updated.

ON Threshold (Finger Threshold + Hysteresis): If the difference count is increasing and exceeds the level of
(Finger Threshold + Hysteresis), then the sensor state changes from OFF to ON.

OFF Threshold (Finger Threshold - Hysteresis): If the difference count is decreasing and drops below the
level of (Finger Threshold - Hysteresis), then the sensor state changes from ON to OFF.
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
15
2.4.2 Signal-to-Noise Ratio (SNR)
Signal is a generic engineering term that can have many meanings. For the capacitive sensor application under
consideration for CapSense applications, signal is defined as the change in the average sensor output between the
OFF and ON states when the rising edge of the difference count starts below the noise threshold.
Noise is another term that has many meanings. The following discussion presents a definition of CapSense noise that
uses a simple mathematical model of the sensor output over time.
When the sensor is in the OFF state, the counts, X(t), can be modeled by an average count and a noise component.
X(t) = X0 + N0(t)
Equation 3

X0 is the average of X(t)

N0(t) is the noise component for t during the OFF state
The same model applies when the sensor is in the ON state.
X(t)= X1 + N1(t)

X1 is the average of X(t)

N1(t) is the noise component for t during the ON state
Equation 4
X0 is called the baseline level of the raw counts. The difference between X0 and X1 is called the signal, S.
S = (X1 - X0)
Equation 5
The noise components N0(t) and N1(t) are similar but not identical. For example, N1(t) usually contains a higher level
of AC line noise in finger sensing applications compared to N0(t). This occurs because the human body acts as an
antenna to 50 Hz and 60 Hz line noise, and the finger contact with the sensor overlay couples the noise into the
CapSense system.
We define the noise level N as the worst case measured peak noise in the OFF state.
N = max(N0(t)) = max(X(t))-X0
Equation 6
Thus, CapSense Signal-to-Noise Ratio, SNR, is defined as the ratio of signal (S) to noise (N).
SNR = S:N
Equation 7
For robust operation of CapSense, a minimum SNR of 5:1 is recommended.
Figure 2-9. Signal and Noise
2.4.3 Measuring SNR
SNR should be measured in the noise environment where CapSense is intended to be used. In other words, measure
the system SNR under worst-case noise conditions.
The first step in measuring SNR is to monitor the raw count for each sensor. This can be done using data logging to a
text file and plotting in a spreadsheet, or through the use of the Cypress MultiChart GUI tool and I2C-USB Bridge
(see chapter 7 - Resources for more details). Whatever the method, the raw count should be observed for SNR
16
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
measurement. The difference count should not be used in the measurement of SNR since it is a function of the
baseline update process, which involves filtering (filling the "bucket") and nonlinear threshold events.
Another factor to consider is how the signal is produced. The worst-case ON and OFF scenario should be used when
measuring SNR. If the system is designed to sense the presence of a finger, then measure SNR with a light touch of
the sensor area, and position the contact point slightly off-center. For automated testing, a worst-case finger touch
(0.1 pF) can often be simulated by an equivalent metal disc that is the size and shape of a small coin.
As an example of measuring SNR, consider the raw count waveform in Figure 2-9.
X0 = 5925 counts
X1 = 6055 counts
S = 130 counts
N = 5940 - 5925 = 15 counts
SNR = 130:15 = 8.6:1
2.4.4 SmartSense Auto-Tuning
2.4.4.1 What is SmartSense?
Tuning the touch sensing user interface is a critical step in ensuring proper system operation and a pleasant user
experience. The typical design flow involves tuning the sensor interface in the initial design phase, during system
integration, and finally production fine-tuning before the production ramp. Because tuning is an iterative process, it
can be time-consuming. SmartSense Auto-Tuning helps to simplify the user interface development cycle. Also, the
method is easy to use and reduces the design cycle time by eliminating the tuning process throughout the product
development cycle, from prototype to mass production.
2.4.4.2 What does SmartSense do?
SmartSense tunes each CapSense sensor automatically at power up and then monitors and maintains optimum
sensor performance during runtime. The number of parameters to be tuned is reduced from 17 in CSD to 4 with
SmartSense.

Power-up tuning—SmartSense tunes the parameters of each sensor based on the individual sensor parasitic
capacitance to get the desired sensitivity for the sensor.

Runtime tuning—Noise in the system is measured dynamically. The thresholds are adjusted accordingly for
each sensor to overcome false triggering due to dynamic variations in noise in the CapSense system.
2.4.4.3 How and where is SmartSense helpful?
SmartSense technology adapts for manufacturing variations in PCBs, overlays, and noise generators, such as LCD
inverters, AC line noise, and switch-mode power supplies and automatically tunes them out. SmartSense handles
changes in system environment, such as temperature, humidity, and noise sources such as RF, SMPS, LCD Inverter,
and AC line noise. In systems with special requirements or very high C P (greater than 45 pF), auto-tuning may not be
the ideal solution.
The following sections describe scenarios in which SmartSense is instrumental in adapting to the external noise. By
maintaining a robust signal-to-noise ratio, the false triggering of buttons is prevented.
2.4.4.3.1
Different Noise Levels in Different Designs
SmartSense technology dynamically tunes itself (adjusts noise and finger thresholds) for different noise
environments. In Figure 2-10, Design A and Design B have different noise levels. To maintain a minimum SNR of 5:1,
dynamic threshold adjustment is required. SmartSense does this automatically, which allows seamless transition from
one model to another with minimal or no tuning required.
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
17
Figure 2-10. Different Noise Levels in Design A and B Being Compensated Automatically
2.4.4.3.2
Noise Spikes during Production
SmartSense technology also automatically tunes out the noise spikes (in production) that may not be seen during the
design stage, as indicated in Figure 2-11. Noise spikes is a powerful feature prevents false button presses in the end
system, which prevents a failure analysis for a mass production design.
Figure 2-11. Finger Threshold Dynamically Adjusted to Prevent False Button Touches
2.4.5 SmartSense_EMC (SmartSense Electromagnetic Compatible)
In addition to the SmartSense Auto-Tuning algorithm discussed previously, the SmartSense_EMC user module
includes a unique algorithm to improve robustness of capacitive sensing algorithm/circuit against high-frequency
conducted and radiated noise.
Every electronic device must comply with specific limits for radiated and conducted external noise. These limits are
specified by several regulatory bodies (for example, FCC, CE, U/L, and so on). An excellent PCB layout design,
power supply design, and system design is mandatory for a product to pass the conducted and radiated noise tests.
In some instances, ideal design practices cannot be followed because of the cost and form factor limitations of the
18
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
product. SmartSense_EMC with superior noise immunity is well suited and useful for such applications to pass
radiated and conducted noise tests.
2.5 Sensor Types
Capacitive sensors can be broadly classified into four categories: buttons, sliders, touchscreens / trackpad, and
proximity sensors. Different sensor types cater to different market segments.
Figure 2-12. Types of Capacitive Sensors
Button (zero-dimensional)
Slider (one-dimensional)
Touchscreen and Trackpad (two-dimensional)
Proximity (three-dimensional)
2.5.1 Buttons (Zero-Dimensional Sensors)
CapSense buttons are used in a wide variety of applications including: home appliances, medical devices,
televisions, monitors, audio systems, photo frames, notebooks, home security systems, white goods, industrial
products, and lighting controls. To get higher reliability, lower cost, and appealing industrial design, use CapSense
buttons instead of mechanical buttons.
2.5.1.1 Simple Buttons
The simplest capacitive sensor consists of a copper pad connected to a CapSense controller pin with a trace. A
button is defined as the combination of the copper sensor pad and the nonconductive overlay material. The button is
surrounded by grounded copper hatch separated by an annular gap. Each button requires one I/O pin of the
CapSense controller.
Figure 2-13. Typical Simple Buttons
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
19
2.5.1.2 Matrix Buttons
In applications requiring a high number of buttons such as a calculator keypad or a QWERTY keyboard, capacitive
sensors can be arranged in a matrix. This allows a design to have more buttons than there are I/O pins on the
CapSense controller.
Figure 2-14. Typical Matrix Buttons
A matrix button design consists of two groups of capacitive sensors: Row sensors and Column sensors. When a
button is touched, it can be resolved by identifying the row and column sensors that are both in the TOUCH state.
The number of buttons supported by the matrix is equal to the product of the number of rows and the number of
columns.
Equation 8
Using a matrix button design can significantly reduce the number of I/O pins required. For example, the matrix in
Figure 2-14 implements 12 buttons, but requires only seven I/O pins for sensors. Additional dedicated pins need to be
assigned to external components, depending on the sensing method selected.
Matrix buttons can only be sensed one at a time. When more than one row or column sensor is in the TOUCH state,
then the finger location cannot be resolved, and the situation is considered an invalid condition. Some applications
require multiple buttons to be sensed simultaneously, such as a keyboard with a Shift, Ctrl, and Alt key. In this case,
the Shift, Ctrl, and Alt keys should be designed as individual buttons, or should be changed to a mutual-capacitance
sensor design.
2.5.2 Sliders (One-Dimensional Sensors)
Sliders are used for controls requiring gradual adjustments. Examples include a lighting control (dimmer), volume
control, graphic equalizer, and speed control. A slider is built using an array of capacitive sensors called segments
that are placed adjacent to one another. Actuation of one segment results in partial actuation of physically adjacent
segments. By using an interpolation method called a centroid, you can achieve a higher resolution than the number of
slider segments. In a typical application, a slider with five segments can resolve at least 100 physical finger positions
on the slider. High resolution makes for smooth transitions in light or sound as a finger glides across a slider.
2.5.2.1 Linear Sliders
In a linear slider, each CapSense controller I/O pin is connected to one slider segment. A zigzag pattern (double
chevron) is recommended for slider segments. This layout ensures that when a segment is touched, the adjacent
segments are also partially touched. Sensor data from multiple sensors improves the estimation of finger position.
The maximum number of slider segments is a function of the number of available CapSense controller pins and the
required response time.
20
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
Figure 2-15. Linear Slider
2.5.2.2 Diplexed Sliders
In a diplexed slider, each CapSense controller I/O pin is connected to two different slider segments. This allows a
design to have twice as many slider segments as there are I/O pins. For example, a diplexed 16-segment slider
requires only eight CapSense controller I/O pins.
Figure 2-16. 16-Segment Diplexed Slider
For a diplexed slider to work properly, the slider segments must be connected to the CapSense controller I/O pins in
a pre-determined order. The first half of the segments are connected to the CapSense controller I/O pins sequentially
(0, 1, 2 …7) and operate similar to a linear slider. The second half of the segments are connected to the same
CapSense controller I/O pins in a non-sequential order. This order exploits the fact that activation of one segment
results in partial actuation of neighboring segments. While slider actuation of one half of the slider results in aliasing
on to the other half, the levels will be scattered in the untouched half. Sensing algorithms search for strong adjacent
segment actuation and ignore scattered actuation to determine finger position on the slider accurately.
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
21
2.5.2.3 Radial Sliders
Radial sliders are similar to linear sliders in that finger position is estimated using data from adjacent sensors;
however, radial sliders are continuous (does not have a beginning or end).
Figure 2-17. Radial Slider
Area contacted by finger
2.5.3 Touchscreens and Trackpads (Two-Dimensional Sensors)
Cypress‘s TrueTouch touchscreen solutions use mutual capacitance sensing. For more information on these
products, see TrueTouch Touchscreen Controllers. Cypress also offers trackpad solutions. Contact your local
Cypress sales office directly for more information. To find your local sales office, click here.
2.5.4 Proximity (Three-dimensional Sensors)
Proximity sensors detect the presence of a hand or other conductive object before it makes contact with the touch
surface. Imagine a hand stretched out to operate a car audio system in the dark. The proximity sensor causes the
buttons of the audio system to glow through backlight LEDs when the user's hand is near. One implementation of a
proximity sensor consists of a long trace on the perimeter of the user interface, as shown in Figure 2-18.
Figure 2-18. Proximity Sensor
Proximity Sensor
Another way to implement a proximity sensor is by ganging sensors together. This is accomplished by combining
multiple sensor pads into one large sensor using firmware (see Firmware Component) to connect the sensors from
the internal analog multiplexer bus. Make sure you do not exceed the CP limit for the sensing method when ganging
sensors together.
22
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
2.6 Sensor Construction
2.6.1 Field Coupled via Copper Trace (PCB)
Figure 2-19. Field Coupled Using PCB
Features of a PCB-based design:

Most common implementation

Copper pads etched on the surface of the PCB act as sensor pads

Electric field emanates from the copper sensor pad to ground plane

No mechanical moving parts

A nonconductive overlay serves as the touch surface for the button

Ideal topology for simple flat panel designs

Low BOM cost
For more information on springs, see Appendix A: Springs.
2.6.2 Field Coupled via Spring/Gasket/Foam
Figure 2-20. Field Coupled via Spring
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
23
Features of a design based on springs/gaskets/foam:

Electrical field coupled from PCB to overlay using a compressed spring, or conductive gasket or foam

Conductive material itself acts as capacitive sensor pad

No mechanical moving parts. Springs and foam do not move

Coupled to touch sensor surface through nonconductive overlay

Any conductive overlay serves as the button touch surface

Ideal topology for curved, sloping, or otherwise irregular front panels

Ideal for designs where touch sensor surface is physically separated from silicon or mother board

Ideal for designs where CapSense and mechanical button combination is desired
For more information on springs, see Appendix A: Springs.
2.6.3 Field Coupled via Printed Ink
Features of a design based on printed ink:

Electric field coupled with printed patterns on a flexible substrate using conductive ink

High series resistance due to higher ohms-per-square of printed ink compared to copper

High parasitic capacitance due to thin PCB

No mechanical moving parts, but substrate is flexible

Coupled to touch sensor surface with a nonconductive overlay

Ideal topology for flexible front panels

Flexible PCB can be one-layer or two-layer film
2.6.4 Field Coupled via ITO Film on Glass
Features of a design based on ITO film:

Electric field coupled with printed or deposited patterns on glass

Higher series resistance of ITO films compared to copper and printed ink

No mechanical moving parts

Ideal topology for graphical front panels
2.7 User Interface Feedback
Effective user interface designs include some feedbacks to the user when they are using the capacitive touch sense
buttons. There are various forms of feedback, including visual, audio, and haptic (tactile). Depending on the user
interface design, multiple types of feedback can be used in combination.
2.7.1 Visual Feedback
LEDs and LCDs provide visual feedback.
2.7.1.1 LED-based Visual Feedback
Visual feedback is widely used in user interfaces. LEDs are used to indicate the status of buttons, sliders, and
proximity sensors. LEDs can implement different effects when the sensor status changes.
2.7.1.1.1
LED ON/OFF
In visual feedback‘s simplest form, LEDs are turned ON or OFF in response to a finger touch. General-purpose I/Os
are used to drive LEDs in either a sourcing or sinking configuration, as shown in Figure 2-21.
24
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
Figure 2-21. LED Sourcing and Sinking Configuration
VDD
R
Vsrc
CapSense Controller
Vsnk
CapSense Controller
LED
R
CapSense
button
LED
CapSense
button
Vsnk
Vsrc
VDD
VDD
ON
OFF
ON
OFF
t
ON
LED in Sourcing Mode
OFF
ON
OFF
t
LED in Sinking mode
2.7.1.1.2
Advanced LED Effects
For user interfaces that require sophisticated visual effects, a single hardware PWM or timer can be used to drive the
LEDs. By varying the duty cycle of the PWM output, you can achieve advanced effects, such as variable LED
brightness, fading, and breathing. A single hardware PWM or timer can be used to drive multiple LEDs.
2.7.1.1.3
LED Brightness
By varying the duty cycle of the PWM output, you can adjust the LED brightness as shown in Figure 2-22. This
enables adjusting your user interface brightness in response to ambient lighting conditions.
Figure 2-22. LED Brightness Control
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
25
2.7.1.1.4
LED Fading
By gradually changing the duty cycle between LED states, you can achieve a fading effect (see Figure 2-23). For
example, the LED appears to ―fade in‖ (from OFF to ON) when the duty cycle is increased in a series of small steps.
Figure 2-23. LED Fading
LED
100%
t
2.7.1.1.5
LED Breathing
Gradually increasing and decreasing the duty cycle between two levels on a continuous basis makes the LED appear
to ―breathe‖, as shown in Figure 2-24. LED breathing is useful when a system is in idle or stand-by mode. For
example, a power button can appear to breathe to alert the user that it is active and can be operated.
Figure 2-24. LED Breathing
LED Brightness
100%
t
ON
OFF
ON
OFF
Human Eye Sensitivity
The human eye‘s sensitivity to the brightness of a light source looks similar to a logarithmic function (Figure 2-25). To
provide a visible linear brightness change, change the PWM duty cycle in an exponential manner.
Figure 2-25. Human Eye Brightness Perception versus LED Luminous Flux
Visible
Brightness
Light Source
Brightness
26
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
The linear brightness levels are transferred to exponential duty cycle values using the lookup table. The following
expression is used for the conversion:
Equation 9
Equation 10
Figure 2-26 illustrates the table graphs at different values of parameter b. Note that NMAX is set to 255. This
expression converts an 8-bit unsigned byte value to the same range. The figure shows that the transfer characteristic
becomes more exponential as the b parameter increases.
Figure 2-26. LED Duty Cycle Conversion Table
LED Lookup table
250
b =0.005
b =0.014
b =0.023
200
b =0.032
Nout
b =0.041
150
100
50
0
0
50
100
150
200
250
Nin
2.7.1.2 LCD-based Visual Feedback
LCDs provide visual feedback for CapSense buttons and sliders. The main advantage of using an LCD is that it can
provide more information along with the feedback for each button press event. PSoC has built-in user modules for
driving Hitachi HD44780A LCD module. This user module supports high-level and low-level APIs that can directly
display data on the screen with ease. Figure 2-27 shows the typical connection for using the Hitachi HD44780A LCD
module.
Figure 2-27. Hitachi Dot Matrix LCD Pin Connections
2
PSoC can also control LCDs through I C. The I2CHW user module available in PSoC controls the GLK 24064-25 WB
2
graphics LCD. Sending the commands through the I C bus is simplified. The CSD user module is configured to scan
2
a set of buttons and any button press event initiates an I C transfer from the PSoC to the LCD as a feedback.
The typical circuit diagram for driving the GLK 24064-25 WB graphics LCD follows.
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
27
Figure 2-28. Implementing LCD Feedback with CapSense on CapSense Plus
2.7.2 Haptic Feedback
Haptic, or tactile, feedback uses vibration to let you know that the system has detected a finger touch.
Figure 2-29. Cypress Haptics Ecosystem
Vibrations are created by an actuator (DC motor) with eccentric rotating mass (ERM). When the end user touches a
CapSense button, a touch signal is sent to the CapSense controller. The CapSense controller processes the data
and drives the actuator to get a particular haptics effect. The CY8C20XX6H CapSense controller can generate 14
predefined haptics effects. PWM and Timer user modules are used to generate a haptics signal to drive the actuator.
The PWM signal is updated periodically. The Timer user module is used to generate a 5-mS periodic (for Hapticeffects generation) interrupt to update the effect that is currently being played. The Amplifier supplies the required
current to the actuator. The firmware can also generate the 5-mS timer to save a digital block, but this increases the
CPU load. The PWM user module is configured to generate output signals of frequency greater than 22 kHz to drive
the DC motor. This frequency is outside the audible range of the human ear.
The Haptics user module datasheet has more information about the 14 predefined haptics effects and also provides a
code example. This document is available at http://www.cypress.com/?rID=55635.
To know more about CY8C20xx6H, refer to the device datasheet at http://www.cypress.com/?rID=50279.
If you need a level 1 kit or any further assistance, contact capsense@cypress.com.
28
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
2.7.3 Audible Feedback
Audible feedback for CapSense buttons is implemented using a buzzer. The pulse-width modulator (PWM) is used to
output the PWM signal required for driving the buzzer as specified in the buzzer datasheet. The PWM user module
available in PSoC is used for this purpose. PSoC can implement CapSense through its CSA and CSD algorithms.
The CSD user module is configured to scan a set of buttons and sliders. When a button press event occurs, the
feedback is given by driving the buzzer at a particular intensity level. The circuit diagram for implementing the buzzer
feedback follows.
Figure 2-30. Implementing Audible Feedback for CapSense in CapSense Plus/CapSense Express Devices
2.7.3.1 CapSense with Audible Feedback Configuration
Select CSD and PWM8 user module from the user module list. Set the parameters for the CSD user module as
shown in Table 2-1. Calculate the PWM user module parameters based on the buzzer‘s resonant frequency. For
example, consider the buzzer CD1206 with a resonant frequency of 2.4 kHz. A 2.4-kHz PWM signal with a 50percent duty cycle is required to drive the buzzer to produce proper audio feedback.
Figure 2-31. PWM Clock Divider Calculation
To calculate the clock dividers to obtain a 2.4-kHz PWM output, see Figure 2-31.
The system clock is set to 24 MHz. The required PWM output frequency is 2.4 kHz. For this reason:
Equation 11
Where, N1 and N2 are the VC1 and VC2 clock divider values, respectively. Period Value is the value of period
register input to the PWM.
That means:
Equation 12
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
29
Rearranging the equation gives the following result:
Equation 13
The previous equation has various integral solutions. For simplicity, this example uses N1 = 4 and N2 = 10.
Substituting these values in the previous equation generates the values:
Equation 14
Thus, Period Value is 249. To have a 50-percent duty cycle, the Compare value for the PWM is set as:
Equation 15
User module parameters are matched as shown in the following table.
Table 2-1. PWM8 User Module Parameters
Parameter
Value
Name
PWM
Configuration
8 bit
Clock
VC2
Period
249
Pulse Width
125
Compare Type
Less than
Interrupt Type
Compare True
Clock Sync
Sync to SysClk
Note that the CSD user module automatically varies the clock dividers based on scan speed and resolution settings
of the CSD user module. Therefore, re-enter the clock dividers every time the PWM module is invoked by writing the
values directly to the configuration register OSC_CR1. For details about the Configuration register OSC_CR1, see
the Technical Reference Manual.
The clock dividers VC1, VC2, and VC3 vary with the CSD scan speed and resolution, as shown in Table 2-2 and
Table 2-3.
Table 2-2. Scan Speed versus VC1 Divider
Scanning Speed
VC1
Ultra fast
1
Fast
2
Normal
4
Slow
8
Table 2-3. Resolution versus VC2 and VC3 Clock Dividers
30
Resolution
Bits
VC2
VC3
9
8
16
10
8
32
11
8
64
12
8
128
13
8
256
14
8
256
15
8
256
16
8
256
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
2.8 Water Tolerance
Capacitive touch sensing is effective in applications where the touch sensing zone is exposed to moisture, rain, or
water drops. Such applications include automotive applications, outdoor equipment, ATMs, public access systems,
and portable devices such as cell phones, PDAs, and kitchen and bathroom applications. Two common triggers are
water droplets on sensors and the flow of water on the PCB. Shield electrodes and guard sensors (see Shield
Electrode and Guard Sensor for layout) help in achieving a water-tolerant capacitive sensing design. For more
information on the working of guard sensors and shield electrodes, see the CY8C21x34 Design Guide.

Water droplets: Use a shield electrode to prevent false triggering of buttons due to water droplets. Device
operation is guaranteed (sensors respond to finger touch) in case of water droplets.

Water stream: Use a shield electrode and guard sensor to prevent sensors from being triggered because of
water streams. Sensors do not respond to finger touch in the presence of water streams; only false triggering is
prevented.
2.9 CapSense System Overview
CapSense touch sensing solutions include the entire system environment in which they operate. This includes:

Hardware component, such as PCB and guard sensor

Firmware component to process the sensor data
2.9.1 Hardware Component
The CapSense controller resides within a larger system composed of a specially printed circuit board (PCB), and a
touch-surface called the overlay that protects the PCB.
Figure 2-32. Exploded View of the CapSense Hardware
The capacitive sensor pads of a sensor board are formed by the PCB traces. The most common PCB format is a twolayer board with sensor pads and a hatched ground plane on the top, and the electrical components on the bottom.
The electrical components include the CapSense controller and associated parts that convert the sensor capacitance
into digital counts. Figure 2-33 shows a cross-sectional view of a two-layer board stack-up.
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
31
Figure 2-33. Two-Layer Stack-up of a CapSense Board
Four-layer designs are an option when board area must be minimized. PCB layout plays a very important role in
CapSense system performance. Best practices are discussed in Design Considerations.
2.9.2 Firmware Component
Firmware is a vital component of the CapSense system that processes the raw count data and makes logical
decisions. The amount of firmware development required for your application depends on which CapSense controller
family that you select.
2
Devices from the CapSense Express family are fully configurable either through hardware or through I C and do not
require any firmware development on the CapSense controller itself. These devices are appropriate for systems
where the finger touch data is sent to a host for higher level processing; see Figure 2-34.
Figure 2-34. Example CapSense Express System Implementation
CapSense Controller
Sensors
Capacitance
Measurement
(Hardware)
Decision
Logic
(Firmware)
Non-CapSense
Actions
Host
Decision
Logic
Application
Functions
(Firmware)
Devices from the CapSense and CapSense Plus families are fully programmable. These devices allow complex
system level integration. These controllers can process the raw count data as well as perform other system functions.
See the CapSense Product Portfolio and CapSense Selector Guide for additional details. Cypress‘s PSoC Designer
accommodates firmware development in C and assembly language. See Resources for more information on this and
other tools.
32
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
3. Design Considerations
When designing capacitive touch sense technology into your application, it is important to remember that the
CapSense device exists within a larger framework. Careful attention to every level of detail from PCB layout to user
interface to end-use operating environment will enable robust and reliable system performance.
3.1 Overlay Selection
In a CapSense design, overlay material is placed over the sensor pad to protect it from the environment and prevent
direct finger contact.
3.1.1 Overlay Material
In the Self-Capacitance Equivalent Model section, Equation 1 shows the finger capacitance.
Where:
ε0 = Free space permittivity
εr = Dielectric constant of overlay
A = Area of finger and sensor pad overlap
D = Overlay thickness
The geometry of a CapSense system is more complex than a parallel plate capacitor. The conductors in the sensor
include the finger and PCB copper. However, like a parallel plate capacitor, CF is directly proportional to εr. High
dielectric constants lead to high sensitivity. Because air has the lowest dielectric constant, any air gaps between the
sensor pad and overlay must be eliminated.
Dielectric constants of some common overlay materials are listed in Table 3-1. Materials with dielectrics between 2.0
and 8.0 are well suited to capacitive sensing applications.
Table 3-1. Dielectric Constants of Common Materials
r
Material
Air
1.0
Formica
4.6–4.9
Glass (Standard)
7.6–8.0
Glass (Ceramic)
6.0
PET Film (Mylar®)
3.2
Polycarbonate (Lexan®)
2.9–3.0
Acrylic (Plexiglass®)
2.8
ABS
2.4–4.1
Wood Table and Desktop
1.2–2.5
Gypsum (Drywall)
2.5–6.0
Conductive material cannot be used as an overlay because it interferes with the electric field pattern. For this reason,
do not use paints that contain metal particles in the overlay.
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
33
3.1.2 Overlay Thickness
Sensitivity is inversely proportional to overlay thickness, as illustrated in Figure 3-1.
Figure 3-1. Sensitivity vs. Overlay Thickness
Both signal and noise are affected by the overlay properties. Table 3-2 lists the recommended maximum overlay
thicknesses for PSoC CapSense applications with an acrylic overlay material.
Table 3-2. Maximum Overlay Thickness with an Acrylic Overlay Material
Design Element
Max. Overlay Thickness (mm)
Button
5
Slider
2
Touchpad
0.5
3.1.3 Overlay Adhesives
Overlay materials must have good mechanical contact with the sensing PCB. This is achieved using a nonconductive
adhesive film. This film increases the sensitivity of the system by eliminating any air gaps between overlay and the
sensor pads. 3M™ makes a high performance acrylic adhesive called 200MP that is widely used in CapSense
applications in the form of adhesive transfer tape (product numbers 467MP and 468MP).
3.2 ESD Protection
Robust ESD tolerance is a natural byproduct of thoughtful system design. By considering how contact discharge will
occur in your end product, particularly in your user interface, it is possible to withstand an 18 kV discharge event
without incurring any damage to the CapSense controller.
34
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
Table 3-3. Overlay Material Dielectric Strength
Material
Breakdown Voltage (V/mm)
Min. Overlay Thickness at 12 kV (mm)
1200–2800
10
3900
3
Air
Wood – dry
Glass – common
7900
1.5
13,000
0.9
PMMA Plastic (Plexiglas )
13,000
0.9
ABS
16,000
0.8
Polycarbonate (Lexan )
16,000
0.8
Formica
18,000
0.7
28,000
0.4
PET Film (Mylar )
280,000
0.04
Polymide film (Kapton®)
290,000
0.04
Glass – Borosilicate (Pyrex®)
®
®
FR-4
®
CapSense controller pins can withstand a direct 2-kV event. In most cases, the overlay material provides sufficient
ESD protection for the controller pins. Table 3-3 lists the thickness of various overlay materials required to protect the
CapSense sensors from a 12-kV discharge as specified in IEC 61000-4-2. If the overlay material does not provide
sufficient protection, ESD countermeasures should be applied in the following order: Prevent, Redirect, Clamp.
3.2.1 Preventing ESD Discharge
Preventing the ESD discharge from reaching the CapSense controller is the best countermeasure you can take.
Make certain that all paths on the touch surface have a breakdown voltage greater than any voltage to which the
surface may be exposed. Also, design your system to maintain an appropriate distance between the CapSense
controller and possible sources of ESD. In the example illustrated in Figure 3-2, if L1 and L2 are greater than 10 mm,
the system will withstand 12 kV.
Figure 3-2. ESD Path
Mechanical Structure
Non Conductive
Material
ESD Event
ESD Event
L1
Air-Filled Space
L2
Exposed
mounting
hardware
CapSense
PCB
If it is not possible to maintain adequate distance, place a protective layer of a high breakdown voltage material
®
between the ESD source and CapSense controller. One layer of 5 mil-thick Kapton tape will withstand 18 kV. See
Table 3-3 for other material dielectric strengths.
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
35
3.2.2 Redirect
If your product is densely packed, it may not be possible to prevent the discharge event. In this case, you can protect
the CapSense controller by controlling where the discharge occurs. This can be achieved through a combination of
PCB layout, mechanical layout of the system, and conductive tape or other shielding material. A standard practice is
to place a guard ring on the perimeter of the circuit board. The guard ring should connect to chassis ground.
Figure 3-3. Guard Ring
CapSense
Controller
Ground with conductive
material on the perimeter to
direct discharge away from
CapSense controller
As recommended in PCB Layout Guidelines, providing a hatched ground plane around the button or slider sensor
can also redirect the ESD event away from the sensor and CapSense controller.
3.2.3 Clamp
Because CapSense sensors are placed in close proximity to the touch surface, it may not be practical to redirect the
discharge path. Including series resistors or special purpose ESD protection devices may be appropriate. Adding a
series resistor on the vulnerable traces is a cost-effective protection method. This technique works by splitting the
dissipation between the resistor and the controller. The recommended series resistance added to the CapSense
inputs is 560 ohms. More details are available in the Series Resistor section.
Figure 3-4. ESD Protection Using a Series Resistor
A more effective method is to provide special purpose ESD protection devices on the vulnerable traces. ESD
protection devices for CapSense need to be low capacitance. Table 3-4 lists devices recommended for use with
CapSense controllers.
Table 3-4. ESD Protection Devices
ESD Protection device
Manufacturer
Part Number
Input
Capacitance
Leakage
Current
Contact Discharge
maximum limit
Air Discharge
maximum limit
Littelfuse
SP723
5 pF
2 nA
8 kV
15 kV
Vishay
VBUS05L1-DD1
0.3 pF
0.1 µA <
+/-15 kV
+/-16 kV
NXP
NUP1301
0.75 pF
30 nA
8 kV
15 kV
36
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
3.3 Electromagnetic Compatibility (EMC) Considerations
EMC is related to the generation, transmission, and reception of electromagnetic energy that can upset the working of
an electronic system. The source (emitter) produces the emission and a transfer or coupling path transfers the
emission energy to a receptor, where it is processed, resulting in either desired or undesired behavior. Many
electronic devices are required to comply with specific limits for emitted energy and susceptibility to external upsets.
Several regulatory bodies worldwide set regional regulations to help ensure that electronic devices do not interfere
with each other. These regulations helps to prevent your computer from interfering with your television, or worse, a
hospital X-ray machine or ventilator, or corrupting the operation of a critical medical monitor.
CMOS analog and digital circuits have very high input impedance. As a result, they are sensitive to external electric
fields. Take adequate precautions to ensure their proper operation in the presence of radiated and conducted noise.
3.3.1 Radiated Interference
Radiated electrical energy can influence system measurements and potentially influence the operation of the
CapSense processor core. The interference enters the CapSense chip at the PCB level, through the sensor traces,
and through other digital and analog inputs.
The following sections discuss layout guidelines to minimize the effects of RF interference.
3.3.1.1 Ground Plane
In general, providing a ground plane on the PCB helps to reduce the RF noise picked up by the CapSense controller.
3.3.1.2 Series Resistor
Every CapSense controller pin has some parasitic capacitance, C P, associated with it. Adding an external resistor
forms a low-pass RC filter that can dampen RF noise amplitude.
Figure 3-5. RC Filter
External series
resistor
CapSense
Sensor
CapSense
Controller
Pins
Capacitance
Place series resistors within 10 mm of the CapSense controller pins.
3.3.1.2.1
CapSense Input Lines
The recommended series resistance for CapSense input lines is 560 ohms. Adding resistance changes the time
constant of the switched-capacitor circuit that converts CP into an equivalent resistor. If the series resistance value is
set larger than 560 ohms, the slower time constant of the switching circuit limits the amount of charge that can
transfer. This lowers the signal level, which in turn lowers SNR. Smaller values are better, but are less effective at
blocking RF.
3.3.1.2.2
Digital Communication Lines
2
Communication lines, such as I C and SPI, also benefit from series resistance and 330 ohms is recommended for
communication lines. Communication lines have long traces that act as antennae such as the CapSense traces. If
more than 330 ohms is placed in series on these lines, the voltage levels fall out of spec with the worst case
combination of supply voltages between systems and the input impedance of the receiver.
3.3.1.3 Trace Length
Long traces can pick up more noise than short traces. Long traces also add to C P. Minimize trace length whenever
possible.
3.3.1.4 Current Loop Area
Another important layout consideration is to minimize the return path for current. General system emission
suppression techniques include adding a decoupling capacitor network and reducing current loops. The current loops
create issues for both emission and immunity. A proper ground plane scheme can help reduce the path length. To
reduce the impact of parasitic capacitance, give hatched ground instead of solid fill near the sensors or traces. A solid
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
37
ground flood is not recommended within 1 cm of CapSense sensors or traces due to an increase in the parasitic
capacitance. Figure 3-6 shows an example of an improper grounding scheme. The layout greatly improves by
reducing the loop area.
Figure 3-6. Improper Ground Scheme and Ground Loop
2) Each output (and input) drives the AC
voltage out onto the PCB. Each signal
will have a loop area associated with it.
3) Cables magnify the problem as loop
areas are proportional to cable length
CapSense
Controller
On Board Driver
circiuts
External Circiuts
1) Decoupling loop inductance and
switching currents combine to create
an AC voltage on the local ground
In Figure 3-7, two sensors are surrounded by a ground plane that is connected to CapSense controller ground, while
a third sensor is surrounded by ground. The third sensor is connected to the other ground plane through the long
traces of other circuitry, which creates a large current loop. With this layout, the third sensor may be more susceptible
to radiated noise and have increased emissions. These two sections of ground are the same location on the
schematic, so they can potentially be one connected area with a better layout.
Figure 3-7. Improper Current Loop Layout
ISOLATED
GROUND
FILL #2
GROUND
FILL #1
CapSense
Sensor
PATH TO
SENSOR PAD
PCB
RETURN
PATH
CapSense
mC
OTHER
CIRCUITRY
Figure 3-8 illustrates the proper layout for the previous example. The loop area is reduced by connecting the two
grounded areas.
38
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
Figure 3-8. Proper Current Loop Layout
CONNECTED
PATH TO
SENSOR PAD
RETURN
PATH
CapSense
Sensor
CapSense
mC
GROUND
FILL
OTHER
CIRCUITRY
PCB
3.3.1.5 RF Source Location
When systems, such as computer monitors or digital photo frames, are designed with CapSense devices, make sure
you prevent noise from LCD inverters and switched-mode power supplies (SMPS) from upsetting the CapSense
system. A simple technique to minimize this kind of interaction is to partition the system with noise sources from
CapSense inputs, as demonstrated in Figure 3-9. Due to the practical limitations of product size, the noise source
and the CapSense circuitry may only be separated by a few inches. This small separation can provide the extra
margin required for good sensor performance compared to the case with close proximity between noise source and
CapSense.
Figure 3-9. Separating Noise Sources
Not Recommended
Recommended
Computer monitor
Computer monitor
SMPS/LCD Inverter
SMPS/LCD Inverter
CapSense interface
CapSense interface
3.3.2 Radiated Emissions
Figure 3-10 shows the impact of rise/fall time of a square wave on the radiated emissions. Note that slowing the
transitions introduces the cutoff point and damps the radiated energy level. The internal clock signals of the
CapSense controller are slew-controlled to reduce the radiated emission.
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
39
Figure 3-10. Impact of Slew Rate on Emissions
The CapSense sensing methods use a switched capacitor front end to interact with the sensors. Selecting a lowfrequency for the switched-capacitor clock helps you to reduce the radiated noise from the CapSense sensor.
3.3.3 Conducted Immunity and Emissions
The noise current generated by high-frequency switching circuits entering the system through the power and
communication lines is called conducted noise.
3.3.3.1 Board Level Solutions
Proper use of decoupling capacitors as recommended by the datasheet can limit the problem with conducted
emissions. For further protection, a passive filter can be used. Passive filter effectively limits not just the conducted
noise emitted but also the noise entering the system. Thus, it improves the conducted noise immunity of the system.
A pi-filter is a simple bidirectional low-pass filter. The two main types of pi-filters are the series inductor and the series
resistor. The series inductor pi-filter has two shunt capacitors and one series inductor configured similar to the Greek
letter π, as shown in Figure 3-11. The noise is filtered by all three elements (L1, C1, and C2) in both directions. The
bidirectional nature of the filter is important. Not only does it prevent the supply noise from affecting sensitive parts, it
can also prevent the switching noise of the part from coupling back onto the power planes.
Figure 3-11. Series Inductor Pi-filter
The values of the components are selected based on the frequency that needs to be attenuated.
3.3.3.2 Power Supply Solutions
The following guidelines help you to prevent conducted noise from entering your CapSense design:

Provide GND and VDD planes that reduce current loops

If the CapSense controller PCB is connected to the power supply by a cable, minimize the cable length and
consider using a shielded cable

To reduce high-frequency noise, place a ferrite bead around power supply or communication lines
40
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
3.4 Software Filtering
Software filters are one of the techniques of dealing with high levels of system noise. Table 3-5 lists the types of filters
that are useful for CapSense.
Table 3-5. CapSense Filter Types 49
Type
Description
Application
Average
Finite impulse response filter (no feedback) with
equally weighted coefficients
Periodic noise from power supplies
IIR
Infinite impulse response filter (feedback) with a step
response similar to an RC filter
High frequency white noise (1/f noise)
Median
Nonlinear filter that computes median input value
from a buffer of size N
Noise spikes from motors and switching power supplies
Jitter
Nonlinear filter that limits current input based on
previous input
Noise from thick overlay (SNR < 5:1), especially useful for
slider centroid data
Event-Based
Nonlinear filter that causes a predefined response to
a pattern observed in the sensor data
Commonly used to block generation or posting of
nonexistent events
Rule-Based
Nonlinear filter that causes a predefined response to
a pattern observed in the sensor data
Commonly used during normal operation of the touch
surface to respond to special scenarios such as accidental
multi-button selection
3.4.1 Average Filter
An average filter is a finite impulse response (FIR) filter with equal-weighted coefficients. The average filters work well
with periodic noise that is attenuated by spacing the samples out over one noise cycle. Sample spacing is not critical.
For example, power line noise can be anywhere from 50 Hz to 60 Hz. Without adjusting the sampling rate, the
average filter works well for 50-Hz and 60-Hz noise. Figure 3-12 shows a sample rate that is synchronized with a
simple periodic waveform. There is no feedback path in this filter.
Figure 3-12. Synchronized Sample Rate
The general equation for an average filter is:
–
Equation 16
Figure 3-13 and Figure 3-14 illustrate the results of using an average filter on real CapSense data using the 16sample filter equation:
–
Getting Started with CapSense
®
Equation 17
Document No. 001-64846 Rev. *I
41
Figure 3-13. Average Filter Noise (16 Samples)
Unfiltered
Filtered
Unfiltered
Filtered
Figure 3-14. Average Filter Finger Touch (16 Samples)
The previous examples are representative of power supply noise. The filter works well in this example because the
period of the noise is close to the length of the filter (N = 16). For more information about how to implement an
average filter, see the code example CSA Software Filters with EzI2Cs Slave on CY8C20xx6.
3.4.2 IIR Filter
Infinite impulse response filters (IIR) produce a step response similar to RC filters. IIR filters attenuate high-frequency
noise components and pass lower frequency signals, such as finger touch–response waveforms.
42
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
Figure 3-15. IIR Filter Step Response
The general equation for a first-order IIR filter is:
–
Equation 18
Figure 3-16 and Figure 3-17 illustrate the results of a first-order IIR filter on real CapSense data using the filter
equation with k = 16:
Equation 19
Figure 3-16. IIR Filter Noise
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
43
Figure 3-17. IIR Filter Finger Touch
Unfiltered
Filtered
Unfiltered
Filtered
For more information about how to implement an IIR filter, see the code example CSA Software Filters with EzI2Cs
Slave on CY8C20xx6.
3.4.3 Median Filter
Median filters eliminate noise spikes most commonly associated with motors and switching power supplies. In a
median filter, a buffer of size N stores the N most recent samples of the input. The median is then computed using a
two-step process. First, the buffer values are sorted from smallest to largest; then, the middle value is selected from
the ordered list. The buffer is scanned for the median with each update of the buffer. This is a nonlinear filter. The
general equation for a median filter is:
Equation 20
Figure 3-18 and Figure 3-19 show the results of a median filter on real CapSense data using the general filter
equation with N = 16.
Equation 21
Figure 3-18. Median Filter Noise Spike
44
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
Figure 3-19. Median Filter (16-sample) Finger Touch
For more information about how to implement a median filter, see the code example CSA Software Filters with
EzI2Cs Slave on CY8C20xx6.
3.4.4 Jitter Filter
3.4.4.1 Jitter Filter for Noisy Slider Data
The centroid function is used to estimate finger position on a slider. When the signal level is low, usually because of
thick overlay on the slider, the estimate of finger position will appear to shake and jitter even when the finger is held at
a fixed position. This jitter noise can be removed using a jitter filter. To do this, the previous input is stored in a buffer.
The current input is compared to the previous output. If the difference is greater than ±1, the output is changed by ±1
(matching sign), as shown in Equation 22. This is a nonlinear filter.
Equation 22
Figure 3-20 shows the results of applying a jitter filter applied to noisy centroid data.
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
45
Figure 3-20. Jitter Filter Applied to Noisy Centroid Data
Unfiltered
Filtered
3.4.4.2 Jitter Filter for Raw Counts
Although the jitter filter is intended for use with noisy slider data, it is also used with noisy buttons. If the change in the
current input exceeds a set threshold level, the output is changed to the previous input plus or minus the threshold
amount. The output is not changed if the current input changes by less than the threshold amount. The general
equation for a jitter filter applied to buttons is:
–
Equation 23
Figure 3-21 and Figure 3-22 shows the result of using a jitter filter on real button data with a large component of
periodic noise.
Figure 3-21. Jitter Filter for Button Noise
46
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
Figure 3-22. Jitter Filter for Button Finger Touch
Unfiltered
Filtered
Unfiltered
Filtered
For more information about how to implement a jitter filter, see the code example CSA Software Filters with EzI2Cs
Slave on CY8C20xx6.
3.4.5 Event-Based Filters
Event-based filters involve a special filtering method where a pattern observed in the sensor data causes a
predefined response in the CapSense system. The pattern in the data is triggered by an event, such as a handheld
product being placed into a pocket, or VDD dropping suddenly in a camera phone when the camera flash circuit is
being charged. One common response used with event-based filter is to block CapSense data transmission until the
pattern returns to normal. Another common response is to reset the level of the Baseline reference, defined in Signalto-Noise Ratio (SNR).
3.4.6 Rule-Based Filters
Rule-based filters are another special filtering method where a pattern observed in the sensor data causes a rulebased response in the CapSense system. Unlike the event-based filter, the rule-based filter acts on patterns in the
sensor data that are encountered during normal operation of the touch surface. The rule-based filter takes into
account special scenarios on how sensors are used. For example, with a set of radio channel selection buttons, two
buttons can be pressed accidentally, but only one should be selected. The rule-based filter sorts out this kind of
situation in a predefined way.
3.5 Power Consumption
Minimizing power consumption is an important design goal. For many CapSense systems, extending battery life is
critical to the success of the product. In systems that do not use batteries, power consumption still plays a role in
optimizing power supply designs to reduce costs and PCB area.
3.5.1 Active and Sleep Current
Active current is the current consumed by the device when all selected analog and digital blocks are enabled and the
CPU is running. In typical applications, the CapSense controller does not need to be in the active state all the time.
The device can be put into the sleep state to stop the CPU and the major blocks of the device. Current consumed by
the device in sleep state is called sleep current. Sleep current is much lower than the active current.
3.5.2 Average Current
In typical applications, sleep state can be invoked periodically to reduce power consumption. This means that during
a preset time period, the CapSense controller wakes up from sleep state, performs all necessary operations in the
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
47
active state (scan all sensors, update all baselines, check if any sensor is in the TOUCH state, and so on), and then
returns to sleep state. The resulting instantaneous current graph is shown in Figure 3-23.
Figure 3-23. Instantaneous Current
I(t)
IAct
ISlp
tSlp
tAct
t
T
Where:
I(t) = Instantaneous current
IAct = Active current
ISlp = Sleep current
tAct = Active time
tSlp = Sleep time
T = Time period of a cycle
The average current consumed by the device over a long period can be calculated by using the following equation.
Equation 24
The average power consumed by the device can be calculated as follows:
Equation 25
3.5.3 Response Time versus Power Consumption
As illustrated in Equation 25, the average power consumption can be reduced by decreasing I AVE or VDD. IAVE may be
decreased by increasing sleep time. Increasing sleep time to a very high value leads to poor response time of the
CapSense button. Because of this tradeoff between response time and power consumption, the application developer
must carefully select the sleep time based on system requirements.
In any application, if both power consumption and response time are important parameters to be considered, then, an
optimized method can be used that incorporates both continuous-scan and sleep-scan modes. In this method, the
device spends most of its time in sleep-scan mode where it scans the sensors and goes to sleep periodically as
explained in the previous section and thereby consuming less power. When you touch a sensor to operate the
system, the device jumps to continuous-scan mode where the sensors are scanned continuously without invoking
sleep and thereby giving very good response time. The device remains in continuous-scan mode for a specified
time-out period. If you do not operate any sensor within this time-out period, the device returns to the sleep-scan
mode.
3.6 Pin Assignments
An effective method to reduce interaction between CapSense sensor traces and communication and non-CapSense
traces is to isolate each by port assignment. Figure 3-24 shows a basic version of this isolation for a 32-pin QFN
package. Because each function is isolated, the CapSense controller is oriented such that there is no crossing of
communication, LED, and sensing traces.
48
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
Figure 3-24. Recommended: Port Isolation for Communication, CapSense, and LEDs
The CapSense controller architecture imposes a restriction on current budget for even and odd port pin numbers. For
a CapSense controller, if the current budget of an odd port pin is 100 mA, the total current drawn though all odd port
pins should not exceed 100 mA. In addition to the total current budget limitation, there is also a maximum current
limitation for each port pin. See the datasheet of the CapSense controller used in the application to know the
specification of that particular CapSense controller.
All CapSense controllers provide high current sink and source capable port pins. When using high current sink or
source from port pins, select the ports that are closest to the device ground pin to minimize the noise.
The following three examples demonstrate common pin assignment mistakes. In Figure 3-25, CapSense and nonCapSense traces are not isolated, and CapSense pins are far from ground. This is an example of a bad pin
assignment.
Figure 3-25. Not Recommended - CapSense and non-CapSense Pins in Proximity
X
PWM or other
Non-CapSense traces
VDD
X
Communication
traces
VDD
CapSense Controller
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
49
The example in Figure 3-26 achieves good isolation, but it has a bad pin assignment because the LEDs are placed
next to the ground pin. The CapSense sensors are assigned to the side of the chip that does not include ground. If
the CapSense pins are away from the ground pin, the impedance of the ground path increases, which in turn causes
the drive circuit‘s reference voltage to shift. This shift may lead to false triggering of sensors. For this reason, it is
recommended to have CapSense pins near the ground pin.
Figure 3-26. Not Recommended - LEDs and Ground Pins in Proximity
X
X
PWM or other
Non-CapSense traces
Communication
traces
CapSense Controller
VDD
Further, LEDs should not be placed close to CMOD/RB pin to avoid crosstalk as illustrated in Figure 3-26.
Figure 3-27. Not Recommended: CMOD/RB and LED Pins in Proximity
X
X
PWM or other
Non- CapSense traces
Communication
traces
Edra
w
Trial
Versi
on
Edra
w
Trial
Versi
on
Edra
w
Trial
Versi
on
Edra
w
Trial
Versi
on
Edra
w
Trial
Versi
on
Edra
w
Trial
Versi
on
CMOD / Rb
Edra
w
Trial
Versi
on
Edra
w
Trial
Versi
on
Edra
w
Trial
Versi
on
Edra
w
Trial
Versi
on
Edra
w
Trial
Versi
on
VDD
Edra
w
Trial
Versi
on
CapSense Controller
Note that using the P1.0 and P1.1 pins for LEDs or for communication purposes is not recommended. This is
because upon power up, there will be a low pulse on the P1.0 and P1.1 pins. For further clarity you can also refer to
the individual device design guides webpage having the sample schematics of all the CapSense devices:

CY8C21x34 design guide

CY8C20x34 design guide

CY8C20xx6A design guide
50
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
3.7 PCB Layout Guidelines
In the typical CapSense application, the capacitive sensors are formed by the traces of a printed circuit board (PCB)
or flex circuit. Following CapSense layout best practices will help your design achieve higher noise immunity, lower
CP, and higher signal-to-noise ratio (SNR). The CapSense signal drops off at high CP levels due to drive limits of the
internal current sources that are part of the CapSense circuitry. The long time constants associated with high C P are
another reason to avoid high CP.
3.7.1 Parasitic Capacitance, CP
The main components of CP are trace capacitance and sensor capacitance. C P is a nonlinear function of sensor
diameter, trace length, trace width, and the annular gap. There is no simple relation between C P and PCB layout
features, but here are the general trends. An increase in sensor size, an increase in trace length and width, and a
decrease in the annular gap all cause an increase in CP. One way to reduce CP is to increase the clearance between
the sensor and ground. Unfortunately, widening the gap between sensor and ground will decrease noise immunity.
3.7.2 Board Layers
Most applications use a two-layer board with sensor pads and a hatched ground plane on the top side and all other
components on the bottom side. The two-layer stackup is shown in Figure 3-28. In applications where board space is
limited or the CapSense circuit is part of a PCB design containing complex circuitry, four-layer PCBs are used.
Figure 3-28. Two-Layer Stackup for CapSense Boards
3.7.3 Board Thickness
FR4-based PCB designs perform well with board thicknesses ranging from 0.020 inches (0.5 mm) to 0.063 inches
(1.6 mm).
Flex circuits work well with CapSense, and are recommended for curved surfaces. All guidelines presented for PCBs
also apply to flex. Ideally, flex circuits should be no thinner than 0.01 inches (0.25 mm). The high breakdown voltage
®
of the Kapton material (290 kV/mm) used for flex circuits provides built in ESD protection for the CapSense sensors.
3.7.4 Button Design
The best shape for buttons is round. Rectangular shapes with rounded corners are also acceptable. Because sharp
points concentrate fields, avoid sharp corners (less than 90º) when designing your sensor pad.
Figure 3-29. Recommended Button Shapes
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
51
Button diameter can range from 5 mm to 15 mm, with 10 mm being suitable for the majority of applications. A larger
diameter helps with thicker overlays.
Annular gap size should be equal to the overlay thickness, but no smaller than 0.5 mm, and no larger than 2 mm. For
example, a PCB layout for a system with a 1-mm overlay should have a 1-mm annular gap, while a 3-mm overlay
design should have a 2-mm annular gap. The spacing between the two adjacent buttons should be large enough that
if one button is pressed, a finger should not reach the annular gap of the other button.
3.7.5 Slider Design
A typical slider pattern is shown in Figure 3-30. The recommended dimensions for slider design are in Table 3-6.
Figure 3-30. Typical Slider Pattern
Table 3-6. Slider Dimensions
Parameter
Min
Max
Recommended
Width of the Segment (A)
1.5 mm
4 mm
Equal to overlay thickness, but within the min/max limits.
Clearance between Segments ( B )
0.5 mm
2 mm
Equal to sensor to ground clearance
Height of the segment ( C )
7 mm
15 mm
12 mm
When any segment is scanned, the adjacent segments are grounded. To maintain uniformity, the two segments on
both ends of a slider should also be grounded. Therefore, for a design with a slider of ‗n‘ segments, there must be
actually n+2 segments. If the hatch around the slider is shielded instead of ground to achieve water tolerance, then
the last two segments should also be shielded. For more information, see Shield Electrode and Guard Sensor.
3.7.6 Sensor and Device Placement

Minimize the trace length from the CapSense controller pins to the sensor pad to optimize signal strength.

Mount series resistors within 10 mm of the controller pins to reduce RF interference and provide ESD protection.

Mount the controller and all other components on the bottom layer of the PCB.

Isolate switching signals, such as PWM, I C communication lines, and LEDs, from the sensor and the sensor
PCB traces. Do this by placing them at least 4 mm apart and fill a hatched ground between CapSense traces
and non-CapSense traces to avoid crosstalk.

Avoid connectors between the sensor and the controller pins because connectors increase CP and decrease
noise immunity.
2
3.7.7 Trace Length and Width
Minimize the parasitic capacitance of the traces and sensor pad. Trace capacitance is minimized when they are short
and narrow.

The maximum recommended trace length is 12 inches (300 mm) for a standard PCB and 2 inches (50 mm) for
flex circuits.

Trace width should not be greater than 7 mil (0.18 mm). CapSense traces should be surrounded by hatched
ground with trace-to-ground clearance of 10 mil to 20 mil (0.25 mm to 0.51 mm).
52
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
3.7.8 Trace Routing
Route sensor traces on the bottom layer of the PCB, so that the only user interaction with the CapSense sensors is
with the active sensing area. Do not route traces directly under any sensor pad unless the trace is connected to that
sensor.
2
Do not run capacitive sensing traces in close proximity to communication lines, such as I C or SPI masters. If it is
necessary to cross communication lines with sensor pins, make sure the intersection is at right angles, as illustrated
in Figure 3-31.
Figure 3-31. Routing of Sensing and Communication Lines
3.7.9 Crosstalk Solutions
A common backlighting technique for panels is to mount an LED under the sensor pad so that it shines through a
hole in the middle of the sensor. When the LED is switched on or off, the voltage transitions on the trace that drives
the LED can couple into the capacitive sensor input, creating noisy sensor data. This coupling is referred to as
crosstalk. To prevent crosstalk, isolate CapSense and non-CapSense traces from one another. In the case of
CY8C21x34/B, the crosstalk can also occur due to the coupling of the LED voltage transitions with the RB resistor. To
avoid this, isolate the RB trace from the non-CapSense traces. A minimum separation of 4 mm is recommended. A
hatched ground plane also can be placed between those traces to isolate them. LED drive traces and CapSense
traces (including RB trace) should not be routed together.
Figure 3-32. Not Recommended - LED and CapSense in Close Proximity
Figure 3-33. Recommended - LED and CapSense with Wide Separation
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
53
Another approach to reducing crosstalk is to slow down the rising and falling edges of the LED drive voltage using a
filter capacitor. Figure 3-34 shows an example circuit of this solution. The value of the added capacitor depends on
the drive current requirements of the LED; however, a value of 0.1 µF is typical.
Figure 3-34. Filter Capacitor Solution for Crosstalk
VDD
CapSense
Sensor
LED
Sensor
Port Pin
CapSense
Controller
LED
Port Pin
Series
resistor
Capacitor
3.7.10 Vias
Use the minimum number of vias to route CapSense inputs to minimize parasitic capacitance. The vias should be
placed to minimize the trace length, which is usually on the edge of the sensor pad, as shown in Figure 3-35.
Figure 3-35. Vias Placement on Sensor Pad
3.7.11 Ground Plane
Ground fill is added to both the top and bottom of the sensing board. When ground fill is added near a CapSense
sensor pad, there is a tradeoff between maintaining a high level of CapSense signal and increasing the noise
immunity of the system. Typical hatching for the ground fill is 25 percent on the top layer (7 mil line, 45 mil spacing)
and 17 percent on the bottom layer (7 mil line, 70 mil spacing).
Figure 3-36. Recommended Button and Slider Layout Top Layer
54
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
Figure 3-37. Recommended Button and Slider Layout Bottom Layer
3.7.12 Shield Electrode and Guard Sensor
Shield:


Shield-electrode copper-hatch recommendations

Top layer – 7-mil trace and 45-mil grid (15 percent fill)

Bottom layer – 7-mil trace and 70-mil grid (10 percent fill)

Only areas surrounding sensor pads and the CapSense controller should be grounded
Reduce the size of the shield patterns

The shield electrode pattern should surround the sensor pad and exposed traces, and spread no further
than 1 cm from these features. Spreading the shield electrode beyond 1 cm has negligible effect on system
performance. If board space is limited, the shield can spread less than 1 cm. In Figure 3-38, Sensor-1 shows
an example of a shield pattern surrounding a sensor pad and trace routed on the top layer. Sensor-2 shows
an example of a shield pattern with a sensor pad without a trace on the top layer.
Figure 3-38. Shield Electrode Pattern
PCB – Top Layer
Shield Electrode
Plane
1 cm
1 cm
Sensor-1
Getting Started with CapSense
®
1 cm
1 cm
Sensor-2
Document No. 001-64846 Rev. *I
55

Slow the edges of the shield waveform

Reduce the slew rate of shield electrode by adding a filter capacitor between the shield electrode port pin
and ground.
Guard Sensor:
The guard sensor is a copper trace that surrounds all of the buttons, as shown in Figure 3-39.
Figure 3-39. PCB Layout with Shield Electrode and Guard Sensor
PCB
Shield Electrode
Sensor Pads
Guard Sensor

The shield electrode pattern should surround the guard sensor pad and exposed traces, and spread no further
than 1 cm from these features.

The recommended shape for a guard sensor is rectangular with curved edges.

Recommended thickness of copper trace is 2 mm and distance of Copper trace to shield hash is 1 mm. This is a
general recommendation and will vary based on the design.
You can also refer to the individual device design guides webpage for sample layouts of all the CapSense devices:

CY8C21x34 design guide

CY8C20x34 design guide

CY8C20xx6A design guide
3.7.13 CapSense System Design with Single Layer PCB
Electronic product manufacturers face constant pressure to lower system costs. Several markets, including consumer
and home appliances, are switching to single layer PCBs to support their required product margins. Cypress‘s
CapSense controllers provide robust touch sensing on single layer PCBs, and their driven shield capability enables
longer trace length, proximity sensing, and water tolerance. CapSense delivers IEC (IEC 61000-6-1, IEC 61000-6-2)
noise compliant performance for accurate touch responses even in noisy environments using sophisticated firmware
algorithms. For more details on implementing CapSense touch sensing on single layer boards, contact
capsense@cypress.com.
56
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
4. CapSense Product Portfolio
®
Cypress‘s CapSense controller solutions are based on our Programmable System-on-Chip (PSoC ) platform and
offer a wide range of features.
4.1 Cypress’s CapSense Controller Solutions
Cypress is the world leader in capacitive sensing technologies and their broad range of solutions provides robust
noise immunity, enable quick time to market, and system scalability. With CapSense controllers, you can:

Replace mechanical components with simple CapSense buttons and sliders.

Reduce total BOM cost and form factor by integrating CapSense with other system components.

Optimize board space with our small form factor packaging (WLCSP, SOIC, and QFN).

Use our advanced sensing techniques for easy finger detection through 15 mm of glass or 5 mm of plastic.

Get to market more quickly using SmartSense Auto-Tuning.

Implement additional user interface functionality, such as LED effects, proximity and water rejection.
Cypress offers a wide range of configurable and programmable CapSense controllers. Configurable CapSense
2
controllers are hardware or I C configurable. Programmable devices provide complete flexibility to meet your exact
design requirements, including reducing BOM cost by integrating further system functionality. The different CapSense
device families are listed in the following sections.
4.1.1 CapSense Express Controllers (Configurable Solutions)
4.1.1.1 CY8CMBR20xx
The CY8CMBR20xx device features a wide operating voltage range, 1.71-V to 5.5-V operating voltage and CSD
2
capacitive sensing with SmartSense Auto-Tuning. These devices are hardware configurable; no I C is required.
4.1.1.2 CY8C201xx
CY8C201xx devices feature configurable I/Os that can be used as capacitive sensing inputs or as GPIOs for driving
LEDs, interrupt outputs, wake-up on interrupt inputs and other digital I/O functionalities. These devices support
2
register-based configuration through an I C interface.
4.1.2 CapSense Controllers (Programmable Solutions)
4.1.2.1 CY8C20x34, CapSense
CY8C20x34 devices feature CSA_EMC capacitive sensing and can implement up to 25 CapSense buttons.
4.1.2.2 CY8C20x36A, CapSense
CY8C20xx36A devices can operate at voltages as low as 1.71 V to 5 V; offer both CSA_EMC and CSD capacitive
sensing, SmartSense, and support up to 33 CapSense buttons.
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
57
4.1.3 CapSense Plus (Programmable Solutions)
Figure 4-1. CapSense Plus
System Functionality
ADC,
Comparators,
Noise
Filtering
2
I C, TX8,
UART, SPI,
USB
LED Effects,
Proximity,
Audio,
Haptics
PWM,
Counters,
Timers
CapSense
CapSense
Plus
CapSense Plus devices feature capacitive touch sensing and additional system functionality. Using CapSense Plus
devices can result in significant cost savings. Additional features include:

Feedback - LED, audio, haptics

Communication - I C, TX8, UART, SPI, USB

Digital functions - PWM, counters, timers

Analog functions - ADC, comparator

Bootloaders
2
4.1.3.1 CY8C20xx6A/AS, CapSense Plus
CY8C20xx6A/AS devices can operate at voltages as low as 1.71 V to 5 V, offer both CSA_EMC, CSD capacitive
2
sensing, SmartSense and SmartSense_EMC, and support up to 33 CapSense buttons, USB, I C, SPI, and up to
32-KB Flash memory.
4.1.3.2 CY8C21x34/B, CapSense Plus
CY8C21x34 devices feature CSD capacitive sensing and SmartSense sensing (CY8C21x34B) with advanced digital
and analog peripherals, are water tolerant, and can support up to 24 CapSense buttons.
4.1.3.3 CY8C24x94, CapSense Plus
CY8C24x94 devices feature CSD capacitive sensing, proximity sensing, are water tolerant, support a wide range of
2
interfaces (SPI, I C USB 2.0, and UART), and can support up to 44 CapSense buttons.
4.1.3.4 Dynamic Reconfiguration
Dynamic reconfiguration is a clever way to optimize total system cost. There are situations in which the number of
digital and analog blocks required by a particular application exceeds the resources of the chip. In these situations, it
may be possible to time-share the analog and digital blocks. The process of reusing analog and digital resources at
different points in time is called dynamic reconfiguration. If the application requires CapSense, an ADC, and a
counter, but not all at the same time, reconfiguring the hardware blocks dynamically will enable all features to be
implemented. For more information about dynamic reconfiguration, see the Cypress application note AN2104 –
PSoC 1 - Dynamic Reconfiguration with PSoC Designer.
58
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
5. CapSense Selector Guide
5.1 Selecting the Right CapSense Device
Several key system requirements must be considered when selecting the best CapSense device for your application.

Flash and RAM requirements

Operating voltage range

Configurable/Programmable

Number and type of capacitive sensors

Tuning method

Water tolerance

Feedback

Package size and pin count

Additional features, such as ADC, communication protocol, and timers
Figure 5-1 provides a high-level guide to the CapSense devices based on design requirements. Table 5-1 identifies
the key features for each CapSense product family. After completing the selection process, the next step in your
development cycle is to consult the more detailed design guide for the selected device. See the Device Specific
Design Guides.
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
59
Figure 5-1. Device Selection Tree
CapSense Family Portfolio
CY8CMBR2044, CY8C201xx, CY8C20x34,CY8C20xx6x,CY8C21x34/B,CY8C24x94
SmartSense_EMC for
superior noise immunity
Programmable
Low Power
Application
CY8C20xx6A
CY8CMBR20xx
Auto- Tuning
CY8C21x34B
Configurable
24 Sensors/GPIOs
4 Sensors & 4 GPOs
CY8CMBR2044
CY8CMBR2016
CY8C201xx
Configurable
16 Sensors & GPIOs
10 Sensors/GPIOs
24 Sensors/GPIOs
Proximity
5cm Range
2cm Range
CY8C21x34/B
CY8C24x94
CY8C21x34/B
CY820x34
CY8C20xx6A
CY8C24x94
44 Sensors/52GPIOs
24 Sensors/GPIOs
25 Sensors/GPIOs
Design Requirements
33Sensors/GPIOs
44 Sensors/52GPIOs
24 Sensors/GPIOs
Water Tolerance
CY8C20xx6A
CY8CMBR20xx
CY8C21x34B
CY8CMBR2044
CY8CMBR2016
CY8C201xx
CY8C21x34/B
CY8C24x94
CY8C21x34/B
CY8C20x34
CY8C20xx6A
CY8C24x94
CY8C21x34/B
CY8C21x34/B
CY8C24x94
44 Sensors/52GPIOs
Haptics
60
CY8C20xx6AS
CY8C24x94
CY8C20xx6H
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
Table 5-1. CapSense Sensing Method by Product Family
CapSense
User Modules
Product Family
CY8CMBR2044 CY8C201xx CY8C21x34/B CY8C20x34 CY8C20xx6A/H CY8C20xx6AS CY8C24x94
CSD
Yes
CSA_EMC
Yes
Yes
SmartSense
Yes
Yes
Yes (B)
Yes
Yes
Yes
Yes
Yes
Yes
SmartSense_EMC
Yes
Yes
Table 5-2. CapSense Key Features by Product Family
Product Family
CY8CMBR2044 CY8C201xx CY8C21x34/B CY8C20x34 CY8C20xx6A/H CY8C20xx6AS CY8C24x94
RAM (Bytes)
512
512
1 K/2 K
1 K/2 K
1K
Flash (Bytes)
8K
8K
8 K/16 K/32 K
16 K/32 K
16 K
2.4 V–5.25 V
2.4 V-5.25 V
1.71 V–5.5 V
1.71 V–5.5 V
3.0 V-5.25 V
Yes
Yes
Yes
Yes
Yes
Operating Voltage
1.71 V–5.5 V
2.4 V-5.25 V
Yes
Yes
Configurable
Programmable
Maximum Number
of Sensors
Buttons
Sliders
4
10
24
25
33
33
44
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Master and
Master and
Slave Interface
Slave
Interface
Master and
Slave Interface
Master and
Slave Interface
Master and
Slave
Interface
Master and
Master and
Slave Interface
Slave
Interface
Master and
Slave Interface
Master and
Slave Interface
Master and
Slave
Interface
Transmitter Software
Transmitter Software
UART
Proximity
HW Slave
I2C
Feature
SPI
UART
UART
Transmitter
- Software
Full speed USB
USB
Timer
8- to 32-bit
timer/counter
PWM
8- to 32-bit
deadband
option
LED
7-segment
support
7-segment
support
LCD
20x2 controller
interface
20x2
controller
interface
20x2 controller
interface
20x2 controller
interface
20x2
controller
interface
Emulation
Emulation
Emulation
Emulation
Emulation
EEPROM
16-bit timer
16-bit timer
I2C
Bootloader
®
8- to 32-bit
timer/counte
r
8- to 32-bit
7-segment
support
Tolerant
Water
Getting Started with CapSense
13-bit timer
Full speed
USB
Tolerant
I2C
I2C
Full speed USB
Document No. 001-64846 Rev. *I
I2C
I2C
Full speed
USB
61
Product Family
CY8CMBR2044 CY8C201xx CY8C21x34/B CY8C20x34 CY8C20xx6A/H CY8C20xx6AS CY8C24x94
Haptics
Feedback
Comparators
Yes
Yes
8- and 10-bit
ADC
Yes
Yes
8- and 10-bit
8- and 10-bit
7- to 13-bit
6,8 and 9-bit
DAC
Random
Sequencer
8- to 32-bit
pseudo
Amplifiers
Yes
2-pole band
and low
pass
Filter
Table 5-3. Comparison between CSD/SmartSense/SmartSense_EMC and CSA_EMC
Parameter
CSD/SmartSense/SmasrtSense_EMC
CSA_EMC
External Components
1-2
0-1
Sensitivity
+++
++
Noise Immunity
+++
++
Spread Spectrum Precharge Clock
Yes
No
Scanning Time Range
75 µs…23 ms
90 µs…1 ms
Water Proof Operation
++
-
Shield Electrode
+++
-
Buttons, Sliders, Touchpad‘s
+++
+++
Proximity
+++
++
Linear Transfer Characteristic
Yes
No
Power Consumption
++
+++
Sleep Support
+++
+++
Environment Changes Immunity
+++
++
[1]
[1] CSD, SmartSense, SmartSense_EMC have better immunity to external noise than CSA_EMC. However, CSA_EMC, immunity
against noise can be improved by selecting more number of scan frequencies .
62
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
6. CapSense Migration Paths
As a system evolves, it may require a CapSense controller with more advanced features. The following sections
describe possible migrations among CapSense controllers.
6.1 CY8C20x34 to CY8C20xx6A/H/AS
CY8C20xx6A/H/AS devices implement CSA_EMC using dedicated hardware similar to that in CY8C20x34.
Therefore, upgrading your design from CY8C20x34 to CY8C20xx6A/AS does not require any external hardware or
firmware changes, simply clone your PSoC Designer project to CY8C20xx6A/AS.
Advantages of CY8C20xx6A/H/AS over CY8C20x34:

More I/O pins

Wider operating voltage range

Lower power consumption

Immersion TS2000 Haptics Technology for ERM control
6.2 CY8C21x34/B / CY8C24x94 to CY8C20xx6A/H/AS
All three devices feature CSD capacitive sensing. CY8C20xx6A/H/AS devices implement CSD using dedicated
hardware as opposed to programmable digital and analog blocks as in CY8C21x34/B and CY8C24x94 devices.
Furthermore, CY8C21x34/B and CY8C24x94 devices use an external bleed resistor in the current measuring circuit,
whereas CY8C20xx6A/H/AS devices use an on-chip iDAC. These architectural differences necessitate different
external circuitry, user module parameters, and settings for similarly named parameters and APIs between the
devices.
Advantages of CY8C20xx6A/H/AS over CY8C21x34/B and CY8C24x94:

Eliminates an external hardware component

Wider operating voltage range

Lower power consumption

Immersion TS2000 Haptics Technology for ERM control
6.3 CY8C20xx6A/H/AS to CY8C21x34/B / CY8C24x94
All three devices feature CSD capacitive sensing. CY8C20xx6A/H/AS devices implement CSD using dedicated
hardware as opposed to programmable digital and analog blocks as in CY8C21x34/B and CY8C24x94 devices.
Furthermore, CY8C21x34/B and CY8C24x94 devices use an external bleed resistor in the current measuring circuit,
whereas CY8C20xx6A/H/AS devices use an on-chip iDAC. These architectural differences necessitate different
external circuitry, user module parameters, and settings for similarly named parameters and APIs between the two
devices. If the USB module is used in CY8C20xx6A, then migration is not possible to CY8C21x34/B.
Advantages of CY8C21x34/B and CY8C24x94 over CY8C20xx6A/H/AS:

Proximity up to 5 cm

Water tolerance
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
63
6.4 Pin-to-Pin Compatibility
When migrating from one device to another, PCB change is not required if you assign the same pin functionality to
the new device. If this is the case, then the two devices are pin-to-pin compatible. Table 6-1 gives information about
available device packages and pin-to-pin compatibility between the same packages of CY8C20x34, CY8C21x34/B,
CY8C20xx6A/AS, and CY8C24x94 devices.
Table 6-1. Pin-to-Pin Compatibility
Device
Package
CY8C20x34
CY8C21x34/B
a
CY8C20xx6A/H/AS
CY8C24x94
a
16 QFN
N
-
N
-
16 SOIC
N
N
-
-
24 QFN without USB
Y
-
Y
-
28 SSOP
Y
Y
-
-
30 WLCSP
N
-
N
-
Y
b
-
32 QFN without SMP
a.
b.
Y
Y
Pin 2 is different: CY8C20x34  P2[1], CY8C21x34/B  P2[3]. If Pin 2 is used, modify the firmware for migration.
Without USB
Symbols:
Y
pin-to-pin compatible (same package dimensions)
N
packages not pin-to-pin compatible
-
package not available
For more details, see the "Pin Information‖ section of the respective datasheets.
64
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
7. Resources
7.1 Website
At the Cypress CapSense Controllers website, you can access all the reference material discussed in this section as
well as device specific datasheets and design guides.
7.2 Device Specific Design Guides
Design guides are available for each CapSense family of devices. These documents are intended for design
engineers who are familiar with capacitive sensing technology and have selected a family of devices.
®

CY8C20x34 CapSense Design Guide

CY8C20xx6A/H CapSense Design Guide

CY8C21x34/B CapSense Design Guide

CY8CMBR2044 CapSense Design Guide
®
®
®
In addition to these device specific design guides, our CapSense Code Examples Design Guide is available to help
you design and evaluate CapSense applications quickly using our Development Kits.
7.3 Technical Reference Manuals
Cypress has created the following technical reference manuals to provide quick and easy access to information on
CapSense controller functionality including top-level architectural diagrams, register summaries, and timing diagrams.

CY8C201xx: Register Reference Guide

PSoC CY8C20x66, CY8C20x66A, CY8C20x46/96, CY8C20x46A/96A, CY8C20x36, CY8C20x36A Technical
Reference Manual (TRM)

CY8CPLC20, CY8CLED16P01, CY8C29x66, CY8C27x43, CY8C24x94, CY8C24x23, CY8C24x23A,
CY8C22x13, CY8C21x34, CY8C21x23, CY7C64215, CY7C603xx, CY8CNP1xx, and CYWUSB6953 PSoC®
Programmable System-on-Chip TRM

PSoC CY8C20x24, CY8C20x34 Technical Reference Manual (TRM)
®
®
7.4 Development Kits
7.4.1 Universal CapSense Controller Kits
Universal CapSense Controller Kits feature predefined control circuitry and plug-in hardware to make prototyping and
2
debugging easy. Programming and I C-to-USB Bridge hardware are included for tuning and data acquisition.

CY3280-20x34 Universal CapSense Controller

CY3280-21x34 Universal CapSense Controller

CY3280-20xx6A Universal CapSense Controller

CY3280-24x94 Universal CapSense Controller
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
65
Note CY3280-20x34 Universal CapSense Controller and CY3280-21x34 Universal CapSense Controller kits are
available only as a part of the CY3280-BK1 Universal CapSense Controller - Basic Kit 1.
7.4.2 Universal CapSense Module Boards
7.4.2.1 Simple Button Module Board
The CY3280-BSM Simple Button Module consists of ten CapSense buttons and ten LEDs. This module connects to
any CY3280 Universal CapSense Controller Board.
7.4.2.2 Matrix Button Module Board
The CY3280-BMM Matrix Button Module consists of eight LEDs as well as eight CapSense sensors organized in a
4x4 matrix format to form 16 physical buttons. This module connects to any CY3280 Universal CapSense Controller
Board.
7.4.2.3 Linear Slider Module Board
The CY3280-SLM Linear Slider Module consists of five CapSense buttons, one linear slider (with ten sensors), and
five LEDs. This module connects to any CY3280 Universal CapSense Controller Board.
7.4.2.4 Radial Slider Module Board
The CY3280-SRM Radial Slider Module consists of four CapSense buttons, one radial slider (with ten sensors), and
four LEDs. This module connects to any CY3280 Universal CapSense Controller Board.
7.4.2.5 Universal CapSense Prototyping Module
The CY3280-BBM Universal CapSense Prototyping Module provides access to every signal routed to the 44-pin
connector on the attached controller board(s). The prototyping module board is used in conjunction with a Universal
CapSense Controller board to implement additional functionality that is not part of the other single-purpose Universal
CapSense Module boards.
7.4.3 CapSense Express Evaluation Kits for CY8C201xx
CY8C3218-CAPEXP series of CapSense Express evaluation kits available for CY8C201xx family of devices enables
designers to replace mechanical buttons/sliders by implementing touch sensing designs with the CapSense touch
sensing family, CapSense Express. With Cypress's PSoC Designer visual embedded system design tool and
CapSense Express configuration tool, designers configure, monitor, and tune buttons or sliders, LEDs, and other
2
general purpose I/Os over I C in real time using a graphical user interface. The following are the lists of CapSense
Express evaluation kits available for CY8C201xx family of devices.

CY3218-CAPEXP1 CapSense Express Kit (Up to 10 I/O for Buttons) with CY8C20110 device

CY3218-CAPEXP2 CapSense Express Kit (Up to 10 I/O for Sliders) with CY8C201A0 device
7.4.4 CapSense Express Evaluation Kits for CY8CMBR2044
CY3280-MBR CapSense Express kit for CY8CMBR2044 device enables designers to replace mechanical buttons
with CapSense buttons. Designers can configure up to four CapSense buttons in hardware, eliminating the need for
software tools, firmware development, and chip programming.
7.4.5 Evaluation Pods
PSoC EvalPods are pods that connect to the ICE In-Circuit Emulator (CY3215-DK kit) to allow debugging capability.
They can also function as a standalone device without debugging capability. The EvalPod has a 28-pin DIP footprint
on the bottom for easy connection to development kits or other hardware. The top of the EvalPod has prototyping
headers for easy connection to the devices pins. The following are the evaluation pods available.

CY3210-CY8C20x34 PSoC Evaluation Pod (EvalPod)

CY3210-CY8C21x34 PSoC Evaluation Pod (EvalPod)

CY3210-CY8C20x36/46/66 PSoC Evaluation Pod (EvalPod)

CY3210-CY8C24x94 PSoC Evaluation Pod (EvalPod)
66
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
7.4.6 In-Circuit Emulation (ICE) Kits
The ICE pod provides the interconnection between the CY3215-DK In-Circuit Emulator via a flex cable and the target
PSoC device in a prototype system or PCB via package-specific pod feet. The kit guide and quick start guide for the
In-Circuit Emulator (ICE) Development Kit are available here. Following are the pods available.

CY3250-21X34QFN ICE Pod Kit to debug QFN CY8C21x34 PSoC devices

CY3250-24x94QFN ICE Pod Kit to debug QFN CY8C24x94 PSoC devices

CY3250-20246QFN ICE Pod Kit to debug CY8C20236/46A/46AS PSoC devices

CY3250-20346QFN ICE Pod Kit to debug CY8C20336/346A/346AS CapSense PSoC devices

CY3250-20666QFN ICE Pod Kit to debug CY8C20636/646/666A/646AS/666AS CapSense PSoC devices

CY3250-20566 ICE Pod Kit to debug CY8C20536/546/566A CapSense PSoC devices

CY3250-20466QFN ICE Pod Kit to debug CY8C20436/46/66/46AS/66AS CapSense PSoC devices

CY3250-20334QFN ICE Pods (2) to debug QFN CY8C20334 PSoC devices
Order replacement ICE pods here.
7.5 Demonstration Kit
The CY3235 - CapSense Proximity Detection Demonstration Kit allows quick and easy demonstration of a PSoC
CapSense-enabled device (CY8C21434) to accurately sense the proximity of a hand or finger along the length of a
2
wire antenna. The kit also includes the I C-USB Bridge, which allows hardware and software debugging of PSoC
2
applications by seamlessly connecting the PC's USB port to your application's I C interface.
7.6 PSoC Designer
Cypress offers an exclusive Integrated Design Environment, PSoC Designer. With PSoC Designer, you can configure
analog and digital blocks, develop firmware, and tune your design. Applications are developed in a drag-and-drop
design environment using a library of pre-characterized analog and digital functions, including CapSense.
PSoC Designer comes with a built-in C compiler and an embedded programmer. A pro compiler is available for
complex designs.
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
67
Figure 7-1. PSoC Designer Device Editor
7.7 PSoC Programmer
PSoC Programmer is a flexible, integrated programming application to program PSoC devices. PSoC Programmer
can be used with PSoC Designer and PSoC Creator to program any design on to a PSoC device.
Figure 7-2. PSoC Programmer
PSoC Programmer provides you a hardware layer with APIs to design specific applications using the programmers
and bridge devices. The PSoC Programmer hardware layer is explained in the COM guide documentation as well as
example code across the following languages: C#, C, Perl, and Python.
68
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
7.8 I2C-to-USB Bridge Kit
2
The CY3240-I2USB kit allows you to test, tune, and debug hardware and software by bridging the USB port to I C.
Populated with the CY8C24894 PSoC device, a wide variety of devices can be connected to the PC using this bridge
including:

EEPROMs

Real-time clocks

ADC/DAC converters

LCD displays

Regulated DC/DC converters

Port expanders

Other devices incorporating the I C interface
2
2
The number of devices that can be connected is constrained only by the I C address limit and physical ability of the
2
I C bus.
7.9 Debugging/Data Viewing Tools
Software tools are available for data viewing, debugging, and tuning CapSense applications. These tools can help
you monitor critical data, such as raw counts and CapSense parameters.
The debugging and data viewing tools are:

Bridge Control Panel

MultiChart
For more details on the tools, see the application note AN2397 – CapSense Data Viewing Tools.
7.9.1 Bridge Control Panel
2
2
Bridge Control Panel is a software tool used with CY3240 USB-I C Bridge to enable communication with I C slave
2
2
devices. The software tool is used to configure I C devices as well as acquire and process data received from I C
slave devices. The Bridge Control Panel helps in optimizing, debugging, and calibrating the target applications.
Figure 7-3. Bridge Control Panel
7.9.2 MultiChart
MultiChart is a simple PC tool for real-time CapSense data viewing and logging. The application allows you to view
data from up to 48 sensors, save and print charts, and save data for later analysis in a spreadsheet.
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
69
Figure 7-4. MultiChart User Interface
70
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
7.10 Design Support
Cypress has several support channels to ensure the success of your CapSense design.

Code Examples – Our vast collection of code examples will help get your design up and running fast.

Knowledge Base Articles – Browse technical articles by product family or perform a search on various CapSense
topics.

White Papers and Technical Articles – Learn about advanced capacitive touch interface topics.

Cypress Developer Community – Connect with the Cypress technical community and exchange information.

Video Library – Get up to speed with tutorial videos.

Quality and Reliability – Cypress is committed to complete customer satisfaction. At our Quality website, you can
find reliability and product qualification reports.

Cypress Design Partner Program – An expansion of our engineering capabilities providing customers with
access to design services and solutions from trusted and capable partners.

Cypress Developer Community – A very active online community to discuss technical issues.

Technical Support – Excellent technical support is available online.
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
71
8. Appendix
8.1 Appendix A: Springs
8.1.1 Finger-Introduced Capacitance
This section gives the influence of various physical parameters on finger-introduced capacitance in a CapSense
design with springs.

Influence of overlay thickness on Finger Touch added Capacitance (FTC) with springs is similar to that with solid
sensors
Figure 8-1. FTC versus Overlay Thickness
Introduced Capacitance, pF
1,2
1
0,8
0,6
0,4
0,2
0
0

2
4
6
8
Thickness of the Overlay, mm
Spring
Solid Sensor
10
12
Influence of height on FTC
Figure 8-2. FTC versus Spring Height
Introduced Capacitance, pF
0,6
0,5
0,4
0,3
0,2
0,1
0
0
72
5
10
15
20
Height of the Spring, mm
Document No. 001-64846 Rev. *I
25
30
35
Getting Started with CapSense
®

Influence of diameter on FTC
Figure 8-3. FTC versus Spring Diameter
Introduced Capacitance, pF
3
2,5
2
1,5
1
0,5
0
0

5
10
15
20
Diameter of the Spring, mm
25
Influence of wire thickness of the spring on FTC
Figure 8-4. FTC versus Wire Thickness of Spring
Introduced Capacitance, pF
0,59
0,58
0,57
0,56
0,55
0,54
0,53
0,52
0
1
2
3
4
Wire Thickness of the Spring, mm
5
6
8.1.2 Mounting Springs to the PCB
Figure 8-5 shows an example of spring mounting. This section discusses how to design spring sensors. Because
springs have higher side sensitivity, the neighboring spring sensors must be placed as far as possible from each
other to prevent false detections. Add a comparison level if the sensor pitch is small.
The requirements for the sensitive area of a spring are the same as the requirements for solid buttons. When using
thick overlays, the spring diameter must be larger than the overlay thickness by at least 2 or 3 times. The distance
between the PCB and the overlay must be 5 mm or more.
Figure 8-5. Spring Mounting Example
Overlay
> 5 mm
Overlay
Metal Spring
Solder
PCB
VIA Trace to PSoC
Sensing
Area
Solder point
Copper Ring
Copper-free
area
Trace to
VIAVIAPSoC
Metal Spring
LED for
BackLighting
Getting Started with CapSense
®
PCB
Document No. 001-64846 Rev. *I
73
Figure 8-6 shows examples of footprints for springs. Do not place solid grounds under the springs as this complicates
the spring soldering and increases the native capacitance of the sensors.
Figure 8-6. Proposed Spring Footprints
PCB
Trace to
PSoC
Spring Contour
Solder points
8.1.3 CapSense and Mechanical Button Combination
The hollow space inside a spring can also be used as a mechanical button, as shown in Figure 8-7.
Figure 8-7. CapSense and Mechanical Button Combination
Touching such a button only triggers the sensor, while pressing the button activates both the sensor and mechanical
button. In this case, preparatory actions such as backlighting, prompt showing, and others are possible only if the
sensor works. The final action is performed when both buttons work. For example, in a GPS navigation system,
touching a button shows only a hint and pressing the button takes an action.
8.1.4 Design Examples
Figure 8-8 and Figure 8-9 show project demonstrator examples for white goods applications.
Figure 8-8. Demo Cooktop
Figure 8-9. Cooktop Front Panel
74
Document No. 001-64846 Rev. *I
Getting Started with CapSense
®
8.2 Document Revision History
Revision
Issue Date
Origin of
Change
Description of Change
**
12/17/2010
SSHH
New guide
*A
03/04/2011
SSHH
Multiple chapter enhancements for content and reader clarity
*B
08/16/2011
SSHH/BVI
Multiple section and table updates
*C
12/07/2011
SSHH
Multiple chapter enhancements for content clarity
*D
04/27/2012
UDYG
Updated slider section. Updated PCB layout guidelines. Updated table 5-2. Corrected
phone number in the title page.
*E
07/19/2012
ZINE
Updated sample schematics and layouts.
Included information on layout/trace routing guidelines for CMOD, RB pin.
*F
08/31/2012
ZINE
Updated references to external documents
*G
10/16/2012
ZINE
Updated Section 3.1 (Overlay Selection) and moved Table 3-1 to Section 3.2.
*H
01/07/2013
SSHH
Updated Section 3.1. Added Section 3.7.13.
*I
03/07/2013
ZINE
Updated Section 2.7.2. Haptic Feedback.
Getting Started with CapSense
®
Document No. 001-64846 Rev. *I
75
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertising