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Cypress CapSense AN64846 Getting Started

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AN64846
®
Getting Started with CapSense
Document No. 001-64846 Rev. *X
Cypress Semiconductor
198 Champion Court
San Jose, CA 95134-1709
http://www.cypress.com

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  • Page 1 AN64846 ® Getting Started with CapSense Document No. 001-64846 Rev. *X Cypress Semiconductor 198 Champion Court San Jose, CA 95134-1709 http://www.cypress.com...
  • Page 2 (“Unintended Uses”). A critical component is any component of a device or system whose failure to perform can be reasonably expected to cause the failure of the device or system, or to affect its safety or effectiveness. Cypress is not liable, in whole or in part, and you shall and hereby do release Cypress from any claim, damage, or other liability arising from or related to all Unintended Uses of Cypress products.

  • Page 3: Table Of Contents

    Contents Introduction ................................7 How to Use this Guide ..........................7 Code Examples ............................7 Cypress CapSense Differentiation ....................... 7 CapSense Design Flow ..........................8 Document Conventions ..........................9 CapSense Technology ............................10 CapSense System Overview ........................10 2.1.1 Hardware Component ........................10 2.1.2...
  • Page 4 Contents 2.9.2 Proximity Sensing with CapSense ....................35 2.10 User Interface Feedback ........................... 35 2.10.1 Visual Feedback ........................... 35 2.10.2 Haptic Feedback ........................... 36 2.10.3 Audible Feedback ......................... 37 Design Considerations ............................. 39 Overlay Selection ............................39 3.1.1 Overlay Material..........................39 3.1.2 Overlay Thickness ........................
  • Page 5 Programmable CapSense Controllers ..................93 CapSense Resources ............................100 CapSense Design Guides and Application Notes..................103 Additional CapSense Resources ......................103 5.2.1 Cypress Document Manager ...................... 103 5.2.2 Website ............................103 Software Tools ............................105 5.3.1 Integrated Development Environments ..................105 5.3.2...
  • Page 6 Contents B.2.5 Vias on Sensors.......................... 118 B.2.6 Ground Plane/Mesh ........................118 B.2.7 Series Resistor ........................... 118 B.2.8 Shield Electrode.......................... 119 B.2.9 Guard Sensor ..........................119 Clearance Between Sensor and Ground ....................... 120 PSoC 1 In-Circuit Emulation (ICE) Pods ......................123 Evaluation Pods ............................

  • Page 7: Introduction

    Cypress’ robust CapSense solutions leverage our flexible Programmable System-on-Chip (PSoC) architecture, which accelerates time-to-market, integrates critical system functions, and reduces BOM cost. Cypress offers a wide range of configurable and programmable CapSense controllers. Configurable CapSense controllers are hardware or I configurable.

  • Page 8: Capsense Design Flow

    Therefore, this step is usually performed when the pre-production builds are available. Many of the CapSense devices support Cypress’s Auto-tuning algorithm called SmartSense that automatically sets parameters for optimal performance after the design phase and continuously compensates for system, manufacturing, and environmental changes.

  • Page 9: Document Conventions

    Introduction Figure 1-1. Typical CapSense Product Design Flow 1.5 Document Conventions Convention Usage Displays file locations, user entered text, and source code: Courier New C:\ ...cd\icc\ Displays file names and reference documentation: Italics Read about the sourcefile.hex file in the PSoC Designer User Guide. Represents menu paths: File >...

  • Page 10: Capsense Technology

    2. CapSense Technology < Cypress’ 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.
  • Page 11 CapSense Technology The capacitive sensor pads of a sensor board are formed by the PCB traces. The most common PCB format is a two- layer board with sensor pads and a hatched ground plane (see Ground Plane) on the top, and the electrical components on the bottom.

  • Page 12: Firmware Component

    Self-capacitance sensing is best suited for single-touch sensors, such as buttons and sliders. Cypress’s CapSense solutions use self-capacitance sensing because it enables efficient use of pins for single-touch sensors and sliders.
  • Page 13 CapSense Technology controller pin and the sensor pad, the vias through the circuit board, and the pin capacitance of the CapSense controller. is related to the electric field around the sensor pad. Although the following diagram shows field lines only around the sensor pad, the actual electric field is more complicated.

  • Page 14: Mutual Capacitance

    TrueTouch touchscreen solutions for automotive and home appliance applications. Contact your local Cypress sales office directly for more information. To find your local sales office, click here. ® AN64846 - Getting Started with CapSense...

  • Page 15: Capsense Sensing Technology

    The sensitivity of the CapSense sensor has units of counts-per-pF. Figure 2-11. Sensing Algorithm Output 2.3.2 CapSense with Sigma Delta Modulator (CSD) Cypress’s CSD method shown in Figure 2-12 uses a switched capacitor circuit on the front end of the system to convert...
  • Page 16 CapSense Technology Figure 2-13. Equivalent Resistor Model AMUXBUS AMUXBUS Two non-overlapping, out-of-phase clocks of frequency F (see Figure 2-14) control the switches SW and SW should be selected such that the sensor completely charges and discharges. Figure 2-14. Voltage Across Sensor Capacitance The continuous switching of SW and SW forms an equivalent resistance R...

  • Page 17: Capsense Tuning

    Tuning is required to maintain high sensitivity to touch and to compensate for process variations in the sensor board, overlay material, and environmental conditions. Many of the CapSense devices support SmartSense, Cypress’ Auto-tuning algorithm, which automatically sets parameters for optimal performance and continuously compensates for system, manufacturing and environmental changes.

  • Page 18: Definitions

    CapSense Technology 2.4.1 Definitions  Raw Count: As seen in Figure 2-19, 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.

  • Page 19: Smartsense Auto-Tuning

    CapSense Technology Figure 2-16. Hysteresis Finger Threshold + Hysteresis Finger Threshold Finger Threshold - Hysteresis Sensor OFF Sensor ON Sensor OFF 2.4.2 SmartSense Auto-Tuning 2.4.2.1 What Is SmartSense? Tuning the touch sensing user interface is a critical step in ensuring proper system operation and a pleasant user experience.
  • Page 20 CapSense Technology 2.4.2.3.1 Different Noise Levels in Different Designs SmartSense technology dynamically tunes itself (adjusts noise and finger thresholds) for different noise environments. Figure 2-17, Design A and Design B have different noise levels. To maintain a minimum SNR of 5:1, you must adjust the dynamic threshold.

  • Page 21: Signal-To-Noise Ratio (Snr)

    Thus, CapSense SNR, is defined as the ratio of signal (S) to noise (N). ������ = ��: �� Equation 11 Based on the experiments and knowledge from many CapSense applications, Cypress recommends a minimum SNR of 5:1 to ensure sufficient margin between noise and signal for robust ON/OFF operation. ®...

  • Page 22: Measuring Snr

    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 using the Cypress Bridge Control Panel and Miniprog3 or by using the Tuner...

  • Page 23: Buttons (Zero-Dimensional Sensors)

    CapSense Technology Figure 2-20. Several types of Widgets Button Sensor Slider Sensor Proximity Sensor 2.6.1 Buttons (Zero-Dimensional Sensors) CapSense buttons replace mechanical buttons in a wide variety of applications such as home appliances, medical devices, white goods, lighting controls and many other products. It is the simplest type of CapSense widget, consisting of a single sensor.

  • Page 24: Sliders (One-Dimensional Sensors)

    Shift, Ctrl, and Alt keys should be designed as individual buttons, or should be changed to a mutual-capacitance sensor design. See Mutual Capacitance to learn about Cypress products that support mutual-capacitance technology. 2.6.2 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.
  • Page 25 CapSense Technology Figure 2-24. Example Signal Pattern on a Linear Slider Segment Index Segment 2 has the maximum signal of 150 and its adjacent segments 1 and 3 have the signals of 100 and 110 respectively. Segments 0 and 4 do not have a signal since the finger is away from them. Now, the calculated centroid position is 51 (rounded) as shown in the following equation.

  • Page 26: Touchscreens And Trackpads (Two-Dimensional Sensors)

    CapSense Technology 2.6.2.3 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), as Figure 2-26 shows. Refer to the CapSense component datasheet to learn about the centroid equation for a radial slider.

  • Page 27: Sensor Construction

    CapSense Technology 2.7 Sensor Construction A capacitive sensor can be constructed using different materials depending on the application requirement. In a typical sensor construction, a conductive pad or surface that senses the user touches is connected to the pin of the capacitive controller using a conductive trace or link.

  • Page 28: Field Coupled Via Printed Ink

    In a CapSense design, false sensing of touch may happen due to the presence of a film of liquid or liquid droplets on the touch surface. Cypress’s CapSense sensing method can compensate for variation in raw count due to mist, moisture, water, ice, and humidity changes and provide a robust, reliable, CapSense operation.

  • Page 29: Effect Of Liquid Droplets And Liquid Stream On Capsense

    CapSense Technology When liquid droplets are present on the touch surface and if the shield electrode is implemented, the CapSense system can reliably work even in the presence of liquid droplets and report sensor ON/OFF status. When there is a liquid flow or a liquid pool on the touch surface, the CapSense system detects the liquid by using a guard sensor and disables the scanning for all other sensors in the system to prevent false triggers.
  • Page 30 CapSense Technology – Capacitance added by Liquid Droplet Figure 2-35. Effect of Liquid Droplet when the Hatch Fill Around the Sensor Is Connected to Ground To compensate the capacitance added by the liquid droplet to the CapSense circuitry, you should drive the hatch fill surrounding the sensor with the driven-shield signal.

  • Page 31: Driven-Shield Signal And Shield Electrode

    CapSense Technology Figure 2-37. Effect of Liquid Droplet when the Hatch Fill Around the Sensor Is Connected to the Driven Shield 2.8.2 Driven-Shield Signal and Shield Electrode The driven-shield signal is a buffered version of the sensor-switching signal, as Figure 2-38 shows.

  • Page 32: Effect Of Liquid Properties On The Liquid-Tolerance Performance

    CapSense Technology Figure 2-39. Capacitance Measurement with a Liquid Stream 560 Ω GUARD CapSense Controller SHIELD Liquid Stream Button Sensor Guard Sensor BTN1 BTN2 BTN3 Shield Electrode 2.8.4 Effect of Liquid Properties on the Liquid-Tolerance Performance In certain applications, the CapSense system has to work reliably in the presence of a variety of liquids such as soap water, sea water, and water with high mineral content.

  • Page 33: Proximity Sensing

    CapSense Technology Tune the guard sensor (if implemented) such that it is triggered only when there is a liquid stream. In the firmware, ensure that the sensors are not scanned when the guard sensor is triggered. Refer to the individual CapSense design guides for detailed procedures of how to tune the CapSense parameters to AN92239 –...
  • Page 34 CapSense Technology Gesture detection: Gesture detection is the technique of interpreting human body movements and providing gesture- type information to the device. Gesture-based user interfaces provide an intuitive way for the user to interact with the system, improving the user experience. Gesture detection is used in applications such as laptops, tablets, and mobile phones for controlling the user interface.

  • Page 35: Proximity Sensing With Capsense

    CapSense Technology Figure 2-45. Proximity Sensing Based on CapSense in a Soap Dispenser 2.9.2 Proximity Sensing with CapSense The proximity-sensing technique based on CapSense involves measuring the change in capacitance of a proximity sensor when a target object approaches the sensor. The target object can be a human finger, hand, or any conductive object.

  • Page 36: Haptic Feedback

    CapSense Technology programmable devices support different types of LCD technologies with pre-built components and user modules which provide APIs for displaying data with ease.  Character LCD with parallel interface - PSoC devices support interface with the Hitachi HD44780A LCD module. Figure 2-46 shows the typical connection for using the Hitachi HD44780A LCD module.

  • Page 37: Audible Feedback

    CapSense Technology Figure 2-48. Cypress Haptics Ecosystem Different haptic effects are created by varying the duration, frequency, and shape of the vibration profile. Vibrations are created by an actuator. The key requirements for an actuator are - Response time, Power consumption, Size, Form factor, Durability, and Vibration strength.
  • Page 38 CapSense Technology Figure 2-49. Implementing Audible Feedback for CapSense ® AN64846 - Getting Started with CapSense Doc. No. 001-64846 Rev. *X...

  • Page 39: Design Considerations

    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.

  • Page 40: Overlay Thickness

    Design Considerations 3.1.2 Overlay Thickness Sensitivity is inversely proportional to overlay thickness, as illustrated in Figure 3-1. Figure 3-1. Sensitivity Versus 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.

  • Page 41: Preventing Esd Discharge

    Design Considerations 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.

  • Page 42: Clamp

    Design Considerations 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.
  • Page 43 Design Considerations 3.3.1.1 General EMI/EMC Guidelines 3.3.1.1.1 Ground Plane In general, a proper ground plane on the PCB reduces both RF emissions and interference. However, solid grounds near CapSense sensors or traces connecting these sensors to the PSoC pins increase the parasitic capacitance of the sensors.
  • Page 44 Design Considerations Figure 3-6: Equivalent Circuit and Waveforms >= 10 R switching clock is the sum of the GPIO resistance and the external series resistance. C is the maximum capacitance of the sensor. For a given switching frequency, you must select the series-resistor value such that the sensor capacitor is charged and discharged fully.
  • Page 45 Design Considerations 3.3.1.1.3 Trace Length Long traces can pick up more noise than short traces. Long traces also add to C . Minimize trace length whenever possible. 3.3.1.1.4 Current Loop Area Another important layout consideration is to minimize the return path for current. A ground plane can lower the overall ground impedance, thus reducing the high-frequency ground bounce.
  • Page 46 Design Considerations Figure 3-9. Improper Current Loop Layout Isolated Ground Fill Ground Fill CapSense Sensor CapSense Path to Sensor Other Return Circuitry Path Figure 3-10 illustrates the proper layout for the previous example. The loop area is reduced by connecting the two grounded areas.
  • Page 47 Design Considerations Figure 3-11. Frequency Hopping  IMO dithering across sensor scans: IMO dithering or trimming can be done across different sensors. For example, the IMO frequency is swept over a range from 24 MHz to 22 MHz when the base IMO frequency is 24 MHz.
  • Page 48 Design Considerations Figure 3-12. Separating Noise Sources SMPS/LCD Inverter SMPS/LCD Inverter CapSense interface CapSense interface 3.3.1.2.2 EMC Feature CapSense User Modules and components with the EMC feature implement IMO dithering to scan each sensor. Each sensor is scanned at two or three different frequencies depending on the immunity level chosen for each sample for raw count.
  • Page 49 Design Considerations 3.3.1.3.2 System Oscillator Frequency (IMO) Lowering the system clock will significantly lower radiated emissions. However, lowering the system clock impacts the performance of your system because a low IMO can take more time to scan the sensors and perform the processing. Therefore, lower the system frequency depending on your application.
  • Page 50 Design Considerations 3.3.1.3.4 Slew Rate Control Figure 3-16 shows the impact of rise/fall time of a square wave on radiated emissions. Note that slowing the transitions introduces the cutoff point and damps the radiated-energy level. Internal clock signals of the CapSense controller are slew-controlled to reduce the radiated emission.
  • Page 51 Design Considerations Figure 3-17. Effect of Scan Time 3.3.1.3.6 Shield Signal The shield signal is driven on the hatch fill to reduce the parasitic capacitance of sensors for liquid tolerance and for proximity sensing. See the Shield Electrode and Guard Sensor section for more details.
  • Page 52 Design Considerations You can reduce emissions by the following techniques: 1. Reduce the size of the shield hatch fill to have a maximum of 10 mm from the sensors. Refer to the Shield Electrode and Guard Sensor section for more details. 2.

  • Page 53: Conducted Immunity And Emissions

    Design Considerations For CapSense applications, it is very important to have a clean power supply for CapSense devices to reduce problems related to radiated interference and emissions. Guidelines to filter the noise at the power supply of CapSense devices are given in the following section. It is recommended that you incorporate these guidelines to handle any EMC/EMI issues.

  • Page 54: Software Filtering

    Design Considerations 3.4 Software Filtering Software filters are one of the techniques of dealing with high levels of system noise. Table 3-6 lists the types of filters that are useful for CapSense. Table 3-6. CapSense Filter Types Type Description Application Average Finite impulse response filter (no feedback) with Periodic noise from power supplies...
  • Page 55 Design Considerations Figure 3-23. Average Filter Noise (16 Samples) Figure 3-24. 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.

  • Page 56: Iir Filter

    Design Considerations 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. Figure 3-25. IIR Filter Step Response The general equation for a first-order IIR filter is: ��...

  • Page 57: Median Filter

    Design Considerations Figure 3-27. 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.

  • Page 58: Jitter Filter

    Design Considerations Figure 3-29. 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.
  • Page 59 Design Considerations 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 reverted to the previous input plus or minus the threshold amount.

  • Page 60: Event-Based Filters

    Design Considerations 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 placed into a pocket, or the power supply voltage (V ) dropping suddenly in a camera phone when the camera flash circuit is being charged.

  • Page 61: Response Time Versus Power Consumption

    Design Considerations Figure 3-33. Instantaneous Current Where: I(t) = Instantaneous current = Active current = Sleep current = Active time = 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. ( ��...

  • Page 62: Proximity Sensing Design

    CapSense, works and describes the parameters that affect proximity-sensing distance. Evaluate how proximity sensing works: Use Cypress’s CY8CKIT-024 – CapSense Proximity Shield. Specify the proximity-sensing requirements: After evaluating the proximity sensor performance, specify the proximity-sensing requirements such as the required proximity-sensing distance, area available on the PCB for sensor construction, system power consumption requirements, and EMI/ESD performance.
  • Page 63 Design Considerations Figure 3-34. CapSense-based Proximity Sensing Design Start Understand Basics of Proximity Sensing Evaluate the Proximity Sensing Using a Kit Specify Proximity Sensing Requirements Study Feasibility and Select Part Design CapSense Schematic, Layout and Mechanical Structure Build Prototype Tune the Prototype Proximity Increase Sensor Size or Performance is...

  • Page 64: Proximity Sensor Design

    Design Considerations 3.6.2 Proximity Sensor Design A capacitive proximity sensor can be constructed using one of the following methods: Button: A button sensor, when tuned for high sensitivity, can be used as a proximity sensor, as shown in Figure 3-35 The proximity-sensing distance is directly proportional to the sensor area.

  • Page 65: Factors Affecting Proximity Distance

    Design Considerations Figure 3-37. CapSense-Based Proximity Sensing with PCB Trace (a) Bar Proximity Sensor (b) Loop Proximity Sensor Wire: A single length of wire works well as a proximity sensor. The proximity distance achieved with a wire loop sensor is higher compared to a PCB trace. But using a wire sensor is not an optimal solution for mass production because of manufacturing cost and complexity.
  • Page 66 Design Considerations  Size of the sensor: The proximity sensor size depends on various factors, such as the required proximity-sensing distance, presence of noise sources, and floating or grounded conductive objects. Noise sources and floating or grounded conductive objects reduce the SNR and the proximity-sensing distance. Therefore, large proximity sensors are needed to achieve the proximity-sensing distance required in your design.
  • Page 67 Design Considerations Table 3-8. Proximity Sensor Layout Recommendations Details Minimum Recommendation The sensor loop diameter or diagonal should be equal to or Start with a sensor loop diameter or greater than the required proximity-sensing distance if the ALP diagonal equal to the required filter is disabled.
  • Page 68 Design Considerations Figure 3-41. Electrical Field Propagation for a Single Sensor Configuration with a Solid Metal Object Figure 3-42. Using a Shield Electrode to Decrease the Metal Object’s Influence 3.6.3.2 Software Parameters  Resolution of CSD: The proximity-sensing distance is directly proportional to the resolution parameter of the CapSense sensing method.

  • Page 69: Pin Assignments

    Design Considerations Figure 3-43. Ground Loop Surrounding the Sensor for Improved ESD Performance CapSense Controller Proximity Loop Sensor Grounded Loop Having a ground loop around the sensor reduces noise in the proximity-sensor and provides a discharge path to the ground during ESD events but reduces the proximity-sensing distance. Therefore, there is a tradeoff between noise immunity and the proximity-sensing distance.
  • Page 70 Design Considerations 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.

  • Page 71: Pcb Layout Guidelines

    Design Considerations Figure 3-47. Not Recommended: C and LED Pins in Proximity PWM or other Communication Non- CapSense traces traces CapSense Controller Note that in PSoC1, using the P1.0 and P1.1 pins for LEDs or for communication purposes is not recommended. This is because, P1.0 and P1.1 pins are programming lines and upon power up, there will be a low pulse on the P1.0 and P1.1 pins.

  • Page 72: Board Thickness

    Design Considerations Figure 3-48. Two-Layer Stack-Up for CapSense Boards 3.8.3 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.

  • Page 73: Slider Design

    Design Considerations 3.8.5 Slider Design Figure 3-50 shows the recommended slider pattern for a linear slider and Table 3-9 shows the recommended values for each of the linear slider dimensions. Detailed explanation on the recommended layout guidelines are provided in the following sections.
  • Page 74 Design Considerations segment width and air-gap (i.e. dimensions “W” and “A” respectively, as marked in Figure 3-50) should follow the relation mentioned in Equation 3-25. Figure 3-51. Ideal Slider Segment Signals and Centroid Response Signal0 Signal1 Signal2 Signal3 Signal4 SLD0 SLD1 SLD2 SLD3...
  • Page 75 Design Considerations Figure 3-53. Finger Causes Valid Signal on More Than Two Segments when Slider Segment Width Is Lower Than Recommended 9 mm 4 mm Finger Threshold Noise Threshold SLD0 SLD1 SLD2 Equation 3-26. Centroid algorithm used by CapSense �� −...
  • Page 76 Design Considerations segment-width is too low, a finger may not be able to couple enough capacitance, and hence, none of the slider- segments will have a 5:1 SNR, resulting in a reported centroid value of 0xFF , as Figure 3-55 shows.
  • Page 77 Design Considerations Figure 3-57. Flat Spots (Nonresponsive Centroid) when Slider Segment Width Is Higher Than Recommended Signal0 Signal1 Signal2 Signal3 Signal4 Centroid SLD0 SLD1 SLD2 SLD3 SLD4 Finger Position Figure 3-58. Signal on Slider Segments when Slider Segment Width Is Higher Than Recommended 9 mm 12 mm Finger Threshold...
  • Page 78 Design Considerations if your application requires an ‘n’ segment slider, it is recommended to create n + 2 physical segments, as Figure 3-50 shows. If it is not possible to have two segments at the both ends of a slider due to space constraints, you can implement these segments in the top hatch fill, as Figure 3-59 shows.

  • Page 79: Sensor And Device Placement

    Design Considerations Equation 3-27. Relationship between minimum PCB length and slider length ������ ����������ℎ = ������������ ����������ℎ + 3 ∗ ������������ �������������� ��������ℎ + 2 ∗ ������ ������ If the available PCB area is lesser than that required per above equation, you can remove the dummy segments.

  • Page 80: Trace Length And Width

    Design Considerations 3.8.6.2 4-Layer PCB:  Place the sensors on the top layer of the PCB.  Route the sensor traces in the layer-2.  Place a hatch fill of 7-mil trace and 70-mil spacing and connect it to ground in layer-3. ...

  • Page 81: Crosstalk Solutions

    Design Considerations Figure 3-63. Routing of Sensing and Communication Lines 3.8.9 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.

  • Page 82: Leds Close To Capsense Sensors

    Design Considerations Figure 3-66. Filter Capacitor Solution for Crosstalk 3.8.10 LEDs Close to CapSense Sensors If LEDs are placed close to the CapSense sensors (within 4-mm distance), and if either end of the LED changes to a non-low impedance state at any point in time, the capacitance of the sensors changes between the On and Off states of the LEDs.

  • Page 83: Ground Plane

    Design Considerations 3.8.12 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.
  • Page 84 Design Considerations Figure 3-71 illustrates the schematic diagram with these recommendations. C1, C2, and C4 are decoupling capacitors and C3 is the CMOD capacitor. Figure 3-71. Example Schematics for Improved SNR CMOD Connector Figure 3-72 shows an example board layout diagram with placements of decoupling and CMOD capacitors and routing of ground and supply.

  • Page 85: Shield Electrode And Guard Sensor

    Design Considerations Figure 3-73. Important GND Nodes in CapSense Design CMOD CY8CMBR3xxx Connector (Sensor) Sensor 3.8.14 Shield Electrode and Guard Sensor A shield electrode is a hatched fill that is driven with a signal which is the replica of the sensor signal. A shield electrode is used for the following purposes: ...
  • Page 86 Design Considerations 3.8.14.2 Shield Electrode Construction for Liquid Tolerance As explained in the Liquid Tolerance section, by implementing a shield electrode and a guard sensor, a liquid tolerant CapSense system can be implemented. This section shows how to implement a shield electrode and a guard sensor. The shield electrode area depends on the size of the liquid droplet and the area available on the board for implementing the shield electrode.
  • Page 87 Design Considerations 3.8.14.3 Guard Sensor As explained in the Liquid Tolerance section, the guard sensor is a copper trace that surrounds all of the sensors, as Figure 3-75 shows. Figure 3-75. PCB Layout with Shield Electrode and Guard Sensor BTN1 BTN2 BTN3 The guard sensor layout should be placed such that:...

  • Page 88: 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 liquid tolerance.

  • Page 89: Capsense Selector Guide

    4. CapSense Selector Guide < Cypress is the world leader in capacitive sensing technologies. Our broad range of solutions provide robust noise immunity, enable quick time to market and system scalability, and have replaced more than 5 billion mechanical buttons over the past several years.
  • Page 90 ARM is the popular CPU choice for embedded applications as it allows portability across different vendors and scalability for complex application requirements. Cypress offers the ARM Cortex-M0 based PSoC 4 family and the ARM Cortex-M3 based PSoC 5LP family with different Flash and RAM combinations to suit your needs.

  • Page 91: Capsense Portfolio

    I C interface for configuration. These devices support up to 10 I/Os for buttons, LEDs, sliders, and operating voltage range of 2.4 V to 5.5 V. Cypress does not recommend these controllers for new designs.
  • Page 92 16-pin SOIC 16-pin QFN 8-pin SOIC 8-pin SOIC 48-pin QFN 32-pin QFN 32-pin QFN 16-pin QFN 16-pin QFN Contact Cypress to know the latest status of the products. ® AN64846 - Getting Started with CapSense Doc. No. 001-64846 Rev. *X...

  • Page 93: Programmable Capsense Controllers

    Programmable CapSense controllers are based on the PSoC platform and offer a rich set of analog and digital peripherals along with CapSense. Cypress provides a great deal of pre-built, production-ready, and GUI-configurable firmware components to speed-up your PSoC system design.
  • Page 94 CapSense Selector Guide Table 4-3. PSoC 4 Family Features Comparison Features/Device PSoC 4000- PSoC 4100- PSoC 4200- PSoC 4100 PSoC 4200 PSoC 4100 PSoC 4200 PSoC 4200 PSoC 4000 PSoC 4100 PSoC 4100S Plus Family Series Series Series M-Series M-Series BLE-Series BLE-Series L-Series...
  • Page 95 CapSense Selector Guide Features/Device PSoC 4000- PSoC 4100- PSoC 4200- PSoC 4100 PSoC 4200 PSoC 4100 PSoC 4200 PSoC 4200 PSoC 4000 PSoC 4100 PSoC 4100S Plus Family Series Series Series M-Series M-Series BLE-Series BLE-Series L-Series S- Series S-Series/PSoC 4100PS CSD ADC 12-bit SAR 12-bit SAR at...
  • Page 96 28-pin SSOP 45-pin WLCSP 48-pin TQFP 48-pin QFN Timer, Counter, PWM block Controller Area Network Contact Cypress to know the latest status of these products Wafer-Level Chip-Scale Package ® AN64846 - Getting Started with CapSense Doc. No. 001-64846 Rev. *X...
  • Page 97 CapSense Selector Guide Table 4-4. PSoC 5LP Family Features Comparison Features/Device Family PSoC 5200 PSoC 5400 PSoC 5600 PSoC 5800 Datasheet CY8C52XX CY8C54XX CY8C56XX CY8C58XX CPU and Speed ARM Cortex-M3 clocked up to 80 MHz Flash, SRAM, EEPROM Up to 256 KB, Up to 64 KB, 2 KB Total I/Os Up to 72 CapSense I/Os...
  • Page 98 CapSense Selector Guide Table 4-5. PSoC 3 Family Features Comparison Features/Device Family PSoC 3200 PSoC 3400 PSoC 3600 PSoC 3800 Datasheet CY8C324X CY8C346X CY8C366X CY8C386X CPU and Speed Single-Cycle 8051 clocked up to 50 MHz Single-Cycle 8051 clocked up to 67 MHz Flash, SRAM, EEPROM Up to 64 KB, Up to 8 KB, Up to 2 KB Total I/Os...
  • Page 99 CapSense Selector Guide Table 4-6. PSoC 1 Family Features Comparison Features/Device CY8C20XX7/S CY8C21X34/B CY8C20XX6A/S CY8C20XX6H CY8C24X94 CY8C22X45 CY8C28XXX CY8C20X34 Family Datasheet CY8C20XX7/S CY8C21X34/B CY8C20XX6A/S CY8C20XX6H CY8C24X94 CY8C22X45 CY8C28XXX CY8C20X34 CPU and Speed 24 MHz M8C 12 MHz M8C Flash/SRAM Up to 32 KB/ 8 KB/512 Up to 32 KB/ Up to 16 KB/...

  • Page 100: Capsense Resources

    5. CapSense Resources Cypress provides many resources to simplify the CapSense design process. To make it easier for you to find what you need from this rich selection, this section organizes the available documentation based on a typical workflow for a CapSense design.
  • Page 101 CapSense Resources I Want To Where To Go? Develop Firmware This step is applicable only to the programmable CapSense devices. Download a development environment. PSoC Creator for PSoC 3, PSoC 4, and PSoC 5LP systems. PSoC Designer for PSoC 1 systems. Refer to the Software Tools section to learn more.
  • Page 102 Programmable devices support various programmable digital and analog peripherals in addition to CapSense and require firmware development. Refer to the CapSense Selector Guide for details. Cypress’ SmartSense Auto-Tuning algorithm automatically sets sensing parameters for optimal performance and continuously compensates for system, manufacturing and environmental changes. ® AN64846 - Getting Started with CapSense...

  • Page 103: Capsense Design Guides And Application Notes

    (CDM) is an intuitive, Windows-based tool allowing users to navigate, filter, search, view, and manage Cypress documentation. CDM can directly open PDF and html pages. It allows you to select documents to download locally and to easily check for updates to those documents.
  • Page 104 Select the type of collateral you want, and type in your key words, as shown in Figure 5-2. Figure 5-1. Design Support in Cypress Website Figure 5-2. Cypress Web Search ® AN64846 - Getting Started with CapSense...

  • Page 105: Software Tools

    5.3.1.2 PSoC Designer PSoC Designer is a free Windows-based Integrated Design Environment (IDE) offered by Cypress for developing PSoC 1 systems. Develop your applications using a library of pre-characterized analog and digital peripherals in a drag-and- drop design environment. Then, customize your design leveraging the dynamically generated API libraries of code.

  • Page 106: Data Monitoring Tools

    KitProg, the on-board programmer integrated with the development kits. PSoC Programmer also provides APIs to develop your own application utilizing Cypress’ programmers and bridge devices in C, C#, Perl, and Python languages. Refer to the PSoC Programmer Component Object Model (COM) Interface Guide available under Program Files (x86)\Cypress\Programmer\Documents folder for more details.

  • Page 107: Ez-Click

    CapSense Resources 5.3.4 EZ-Click™ EZ-Click is a simple yet powerful software tool that enables development of CapSense MBR solutions. The tool allows you to configure, debug, monitor real time sensor output, and run production-line system diagnostics of all register-configurable CapSense MBR families. 5.3.5 Bridge Control Panel Bridge Control Panel is a Windows-based software tool installed along with PSoC Programmer.

  • Page 108: Capsense Express Development Kits

    – Excellent technical support is available online.  Technical Support – Cypress is committed to complete customer satisfaction. At our Quality website, you can find  Quality and Reliability reliability and product qualification reports.

  • Page 109: Springs

    A. Springs < 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 5-6.
  • Page 110 Springs  Influence of diameter on FTC Figure 5-8. FTC Versus Spring Diameter  Influence of wire thickness of the spring on FTC Figure 5-9. FTC Versus Wire Thickness of Spring 0,59 0,58 0,57 0,56 0,55 0,54 0,53 0,52 Wire Thickness of the Spring, mm ®...

  • Page 111: Mounting Springs To The Pcb

    Springs A . 1 . 1 M o u n t i n g S p r i n g s t o t h e P C B Figure 5-10 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.

  • Page 112: Capsense And Mechanical Button Combination

    Springs CapSense and Mechanical Button Combination The hollow space inside a spring can also be used as a mechanical button, as shown in Figure 5-12. Figure 5-12. CapSense and Mechanical Button Combination Touching such a button only triggers the sensor, while pressing the button activates both the sensor and mechanical button.
  • Page 113 Springs Figure 5-14. Cooktop Front Panel  ® AN64846 - Getting Started with CapSense Doc. No. 001-64846 Rev. *X...

  • Page 114: Schematic And Layout Checklist

    B. Schematic and Layout Checklist Schematic Checklist Refer to the PSoC 3 datasheet for PSoC 3 devices, refer to the PSoC 4 datasheet for PSoC 4 devices, and refer to PSoC 5LP datasheet for PSoC 5LP devices. Category Recommendations/Remarks Decoupling capacitor 0.1 µF Bulk capacitor 1 µF...

  • Page 115: R B

    Schematic and Layout Checklist Family Value Recommended 2.2 nF for CSD CY8C20xx6/A/AS 1.2 nF – 5.6 nF for CSA 5.6 nF-10 nF for PRS8 and PRS16 configuration. CY8C21x34 22nF- 47nF for Prescaler Configuration CY8C21x34 SmartSense, 10 nF CY8C24x94, CY8C22x45 5.6 nF-10 nF 1.2 nF –...

  • Page 116: Layout Checklist

    Schematic and Layout Checklist Layout Checklist Category Recommendations Buttons Shape Solid round or rectangle with curved edges Diameter/Diagonal 5 mm 15 mm 10 mm Air gap between button and 0.5 mm 2 mm Should be equal to overlay thickness. Hatch hatch can be connected to ground or shield.

  • Page 117: Buttons

    Schematic and Layout Checklist Category Recommendations Shield Size of shield fill Width of 1 cm Refer to Figure 3-74. Drive the shield only electrode around sensors when required such as in applications requiring liquid tolerance and proximity sensing. Shield pattern Use hatch fill instead of solid fill to reduce the parasitic capacitance of the shield electrode and to reduce the emissions.

  • Page 118: Overlay

    Schematic and Layout Checklist B . 2 . 3 O ve r l a y  Type (material): Do not use conductive materials as overlay since it interferes with the electric field pattern. Select a material with a higher dielectric constant. ...

  • Page 119: Shield Electrode

    Schematic and Layout Checklist Figure B-3. Series Resistor Placement B . 2 . 8 S h i e l d E l e c t r o d e Reduce the size of the shield fill (maximum 1 cm from the sensor). Limit the placement of the shield to only the selected sensors.

  • Page 120: Clearance Between Sensor And Ground

    C. Clearance Between Sensor and Ground The ground plane is placed on the same layer of the board as the buttons as shown in Figure C-1. The clearance between the button and ground plane plays an important role in the performance of the button. Electric field lines fringing between a button and the ground plane are illustrated in Figure C-2.
  • Page 121 Clearance Between Sensor and Ground The C Figure C-3 does not include the effect of the traces or vias. It is only the parasitic capacitance of the sensor pad. Figure C-3. Parasitic Capacitance, C , as a Function of Button-Ground Clearance and Button Diameter Note: The finger is not on the sensor.
  • Page 122 Clearance Between Sensor and Ground The capacitance, C , in Figure C-5 is the capacitance added by the touch of the finger. Total capacitance of the sensor pad and the finger is Cp + Cf. Figure C-5. Finger Capacitance, C , as a Function of Button-Ground Clearance and Button Diameter Note: The finger is on the sensor.

  • Page 123: Psoc 1 In-Circuit Emulation (Ice) Pods

    PCB via package-specific pod feet. The user guide and the quick start guide for the ICE kit are available here. Following are the pods available. Note that some of the following pod kits are not in stock but a web page is kept for accessing the documents. Contact Cypress technical support if you need help with a particular kit.

  • Page 124: Glossary

    Cypress’s touch-sensing user interface solution, which is the industry’s leading solution in sales. CapSense Mechanical Button Replacement (MBR) Cypress’s configurable solution to upgrade mechanical buttons to capacitive buttons. It requires minimal engineering effort to configure the sensor parameters and does not require firmware development. These devices include the CY8CMBR3XXX and CY8CMBR2XXX families.
  • Page 125 Glossary Debounce A parameter that defines the number of consecutive scan samples for which the touch should be present for it to become valid. This parameter helps to reject spurious touch signals. A finger touch is reported only if the Difference Count is greater than Finger Threshold + Hysteresis for a consecutive Debounce number of scan samples.
  • Page 126 Glossary Low Baseline Reset A parameter that represents the maximum number of scan samples where the Raw Count is abnormally below the Negative Noise Threshold. If the Low Baseline Reset value is exceeded, the Baseline is reset to the current Raw Count. Manual-Tuning The manual process of setting (or tuning) the CapSense parameters.
  • Page 127 Glossary Parasitic capacitance is the intrinsic capacitance of the sensor electrode contributed by PCB trace, sensor pad, vias, and air gap. It is unwanted because it reduces the sensitivity of CSD. Proximity Sensor A sensor that can detect the presence of nearby objects without any physical contact. Radial Slider A widget consisting of more than one sensor arranged in a specific circular fashion to detect the physical position of a finger.
  • Page 128 Glossary Signal-to-Noise Ratio (SNR) The ratio of the sensor signal, when touched, to the noise signal of an untouched sensor. Slider Resolution A parameter indicating the total number of finger positions to be resolved on a slider. Touchpad A Widget consisting of multiple sensors arranged in a specific horizontal and vertical fashion to detect the X and Y position of a touch.

  • Page 129: Revision History

    Revision History Document Revision History ® Document Title: AN64846 - Getting Started with CapSense Document Number: 001-64846 Revision Issue Date Origin of Change Description of Change 12/17/2010 SSHH New guide 03/04/2011 SSHH Multiple chapter enhancements for content and reader clarity 08/16/2011 SSHH/BVI Multiple section and table updates...
  • Page 130 Revision History Revision Issue Date Origin of Change Description of Change – added the benefits of CapSense over 01/19/2016 VAIR Updated Chapter 1 Introduction mechanical buttons.Added CapSense Design Flow. Updated Chapter 2 CapSense Technology. Updated the sections CapSense Sensing Technology, CapSense Tuning, CapSense...

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