PSoC™ 4: MSC CAPSENSE™ CSX button tuning

This code example demonstrates how to use the CAPSENSE™ middleware to detect a finger touch on a mutual-capacitance-based button widget in PSoC™ 4 devices with multi sense converter (MSC).

In addition, this code example also explains how to manually tune the mutual-capacitance-based button for optimum performance with respect to parameters such as reliability, power consumption, response time, and linearity using the CSX-RM sensing technique and CAPSENSE™ tuner GUI. Here, CAPSENSE™ CSX represents the mutual-capacitance sensing technique and RM represents the ratiometric method.

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Requirements

• ModusToolbox™ software v3.1 or later (tested with v3.1)
• Board support package (BSP) minimum required version: 3.0.0
• Programming language: C
• Associated parts: PSoC™ 4100S Max

Supported toolchains (make variable 'TOOLCHAIN')

• GNU Arm® embedded compiler v11.3.1 (GCC_ARM) - Default value of TOOLCHAIN
• Arm® compiler v6.16 (ARM)
• IAR C/C++ compiler v9.30.1 (IAR)

Supported kits (make variable 'TARGET')

• PSoC™ 4100S Max Pioneer Kit (CY8CKIT-041S-MAX) - Default value of TARGET

Hardware setup

This example uses the board's default configuration. See the kit user guide to ensure that the board is configured correctly to V_DDA at 5V (J10 should be at position 1 and 2). If you are using the code example at a V_DDA voltage other than 5 V, ensure to set up the device power voltages correctly for the proper operation of the device power domains. See Steps to setup the V_DDA supply voltage in Device Configurator for more details.

Software setup

This example requires no additional software or tools.

Using the code example

Create the project and open it using one of the following:

In Eclipse IDE for ModusToolbox™ software

1. Click the New Application link in the Quick Panel (or, use File > New > ModusToolbox™ Application). This launches the Project Creator tool.

2. Pick a kit supported by the code example from the list shown in the Project Creator - Choose Board Support Package (BSP) dialog.

   When you select a supported kit, the example is reconfigured automatically to work with the kit. To work with a different supported kit later, use the Library Manager to choose the BSP for the supported kit. You can use the Library Manager to select or update the BSP and firmware libraries used in this application. To access the Library Manager, click the link from the Quick Panel.

   You can also just start the application creation process again and select a different kit.

   If you want to use the application for a kit not listed here, you may need to update the source files. If the kit does not have the required resources, the application may not work.

3. In the Project Creator - Select Application dialog, choose the example by enabling the checkbox.

4. (Optional) Change the suggested New Application Name.

5. The Application(s) Root Path defaults to the Eclipse workspace which is usually the desired location for the application. If you want to store the application in a different location, you can change the Application(s) Root Path value. Applications that share libraries should be in the same root path.

6. Click Create to complete the application creation process.

For more details, see the Eclipse IDE for ModusToolbox™ software user guide (locally available at {ModusToolbox™ software install directory}/docs_{version}/mt_ide_user_guide.pdf).

In command-line interface (CLI)

ModusToolbox™ software provides the Project Creator as both a GUI tool and the command line tool, "project-creator-cli". The CLI tool can be used to create applications from a CLI terminal or from within batch files or shell scripts. This tool is available in the {ModusToolbox™ software install directory}/tools_{version}/project-creator/ directory.

Use a CLI terminal to invoke the "project-creator-cli" tool. On Windows, use the command line "modus-shell" program provided in the ModusToolbox™ software installation instead of a standard Windows command-line application. This shell provides access to all ModusToolbox™ software tools. You can access it by typing modus-shell in the search box in the Windows menu. In Linux and macOS, you can use any terminal application.

The "project-creator-cli" tool has the following arguments:

Argument	Description	Required/optional
--board-id	Defined in the <id> field of the BSP manifest	Required
--app-id	Defined in the <id> field of the CE manifest	Required
--target-dir	Specify the directory in which the application is to be created if you prefer not to use the default current working directory	Optional
--user-app-name	Specify the name of the application if you prefer to have a name other than the example's default name	Optional

The following example clones the "CSX button tuning" application with the desired name "CsxButtonTuning" configured for the CY8CKIT-041S-MAX BSP into the specified working directory, C:/mtb_projects:

project-creator-cli --board-id CY8CKIT-041S-MAX --app-id mtb-example-psoc4-msc-capsense-csx-button-tuning --user-app-name CsxButtonTuning --target-dir "C:/mtb_projects"

Note: The project-creator-cli tool uses the git clone and make getlibs commands to fetch the repository and import the required libraries. For details, see the "Project creator tools" section of the ModusToolbox™ software user guide (locally available at {ModusToolbox™ software install directory}/docs_{version}/mtb_user_guide.pdf).

To work with a different supported kit later, use the Library Manager to choose the BSP for the supported kit. You can invoke the Library Manager GUI tool from the terminal using make library-manager command or use the Library Manager CLI tool "library-manager-cli" to change the BSP.

The "library-manager-cli" tool has the following arguments:

Argument	Description	Required/optional
--add-bsp-name	Name of the BSP that should be added to the application	Required
--set-active-bsp	Name of the BSP that should be as active BSP for the application	Required
--add-bsp-version	Specify the version of the BSP that should be added to the application if you do not wish to use the latest from manifest	Optional
--add-bsp-location	Specify the location of the BSP (local/shared) if you prefer to add the BSP in a shared path	Optional

Following example adds the CY8CKIT-041S-MAX BSP to the already created application and makes it the active BSP for the app:

~/ModusToolbox/tools_{version}/library-manager/library-manager-cli --project "C:/mtb_projects/MSCCSXButtonTuning" --add-bsp-name CY8CKIT-041S-MAX --add-bsp-version "latest-v4.X" --add-bsp-location "local"

~/ModusToolbox/tools_{version}/library-manager/library-manager-cli --project "C:/mtb_projects/MSCCSXButtonTuning" --set-active-bsp APP_CY8CKIT-041S-MAX

In third-party IDEs

Use one of the following options:

• Use the standalone Project Creator tool:

  1. Launch Project Creator from the Windows Start menu or from {ModusToolbox™ software install directory}/tools_{version}/project-creator/project-creator.exe.

  2. In the initial Choose Board Support Package screen, select the BSP, and click Next.

  3. In the Select Application screen, select the appropriate IDE from the Target IDE drop-down menu.

  4. Click Create and follow the instructions printed in the bottom pane to import or open the exported project in the respective IDE.

• Use command-line interface (CLI):

  1. Follow the instructions from the In command-line interface (CLI) section to create the application.

  2. Export the application to a supported IDE using the make <ide> command.

  3. Follow the instructions displayed in the terminal to create or import the application as an IDE project.

For a list of supported IDEs and more details, see the "Exporting to IDEs" section of the ModusToolbox™ software user guide (locally available at {ModusToolbox™ software install directory}/docs_{version}/mtb_user_guide.pdf).

Operation

1. Connect the board to your PC using the provided micro USB cable through the KitProg3 USB connector on J8 as shown in Figure 1:

   Figure 1. Connecting the CY8CKIT-041S-MAX to a computer

   

2. Program the board using one of the following:

   Using Eclipse IDE for ModusToolbox™ software

   1. Select the application project in the Project Explorer.

   2. In the Quick Panel, scroll down, and click <Application Name> Program (KitProg3_MiniProg4).

   Using CLI

   From the terminal, execute the make program command to build and program the application using the default toolchain to the default target. The default toolchain is specified in the application's Makefile but you can override this value manually:

   make program TOOLCHAIN=<toolchain>
   

   Example:

   make program TOOLCHAIN=GCC_ARM
   

3. After programming, the application starts automatically.

4. To test the application, place your finger over the CAPSENSE™ button and notice that the user LED turns ON when touched and turns OFF when the finger is lifted.

5. You can also monitor the CAPSENSE™ data using the CAPSENSE™ tuner application as follows:

Monitor data using the CAPSENSE™ tuner

1. Open the CAPSENSE™ tuner from the Tools section in the IDE Quick Panel.

   You can also run the CAPSENSE™ tuner application standalone from {ModusToolbox™ software install directory}/ModusToolbox/tools_{version}/capsense-configurator/capsense-tuner. In this case, after opening the application; select File > Open and open the design.cycapsense file of the respective application, which is in the {Application root directory}/bsps/TARGET_<BSP-NAME>/config folder.

   See the ModusToolbox™ software user guide (locally available at {ModusToolbox™ software install directory}/docs_{version}/mtb_user_guide.pdf) for options to open the CAPSENSE™ tuner application using the CLI.

2. Ensure that the kit is in CMSIS-DAP bulk mode (KitProg3 status LED is ON and not blinking). See Firmware-loader to learn how to update the firmware and switch modes in KitProg3.

   3. In the tuner application, click on the Tuner Communication Setup icon or select Tools > Tuner Communication Setup. In the window that appears, select the I2C checkbox under KitProg3 and configure as follows:

      • I2C address: 8
      • Sub-address: 2 bytes
      • Speed (kHz): 400

      These are the same values set in the EZI2C resource.

   Figure 2. Tuner communication setup parameters

    <img src="images/tuner-comm-setup.png" alt="Figure 2"/>
   

   4. Click Connect or select Communication > Connect to establish a connection.

      Figure 3. Tuner Communication Setup parameters

      

   5. Click Start or select Communication > Start to start data streaming from the device.

      Figure 4. Start tuner communication

      

      The Widget/Sensor parameters tab gets updated with the parameters configured in the CAPSENSE™ configurator window. The tuner displays the data from the sensor in the Widget View and Graph View tabs.

   6. Set the Read Mode to Synchronized mode. Navigate to the Widget View tab, you can see the Button0 widget highlighted in blue color when you touch it.

      Figure 5. Widget view of the CAPSENSE™ tuner

      

   7. You can view the raw count, baseline, difference count and status for each sensor in the Graph View tab. For example, to view the sensor data for Button 1, select Button1_Rx0 under Button1.

      Figure 6. Graph view of the CAPSENSE™ tuner

      

   8. Observe the Widget/Sensor Parameters section in the CAPSENSE™ tuner window as shown in Figure 6.

   9. Switch to the SNR Measurement tab for measuring the SNR and verify that the SNR is above 5:1, select Button1 and Button1_Rx0 sensor, and then click Acquire Noise as shown in Figure 7.

      Figure 7. CAPSENSE™ tuner - SNR measurement: Acquire Noise

      

   10. Once the noise is acquired, place the metal finger at a position on the button and then click Acquire Signal. Ensure that the metal finger remains on the button as long as the signal acquisition is in progress. Observe the SNR is above 5:1.

       The calculated SNR on this button is displayed, as shown in Figure 8. Based on your end system design, test the signal with a finger that matches the size of your normal use case. Typically, finger size targets are ~8 to 9 mm. Consider testing with smaller sizes that should be rejected by the system to ensure that they do not reach the finger threshold.

       Figure 8. CAPSENSE™ tuner - SNR measurement: Acquire Signal

       

Tuning procedure

Create a custom BSP for your board

1. Create a custom BSP for your board having any device, by following the steps given in KBA231373. In this code example, it was created for the device "CY8C4149AZI-S598".

2. Open the design.modus file from {Application root directory}/bsps/TARGET_<BSP-NAME>/config folder obtained in the previous step and enable CAPSENSE™ to get the design.cycapsense file. CAPSENSE™ configuration can then be started from scratch as explained below.

The following steps explain the tuning procedure:

Note: See the section "Selecting CAPSENSE™ hardware parameters" in the PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide to learn about the considerations for selecting each parameter value.

Figure 9. CSX button widget tuning flow

Do the following to tune the button widget:

Stage 1. Set the initial hardware parameters

1. Connect the board to your PC using the provided USB cable through the KitProg3 USB connector.

2. Launch the Device configurator tool.

   You can launch the Device configurator in the Eclipse IDE for ModusToolbox™ software from the Tools section in the IDE Quick Panel.

   You can also launch it in stand-alone mode from {ModusToolbox™ software install directory}/ModusToolbox/tools_{version}/device-configurator/device-configurator. In this case, after opening the application, select File > Open and open the design.modus file of the respective application, which is in the {Application root directory}/bsps/TARGET_<BSP-NAME>/config folder.

   Note: If you are using the custom BSP with the Empty PSoC™ 4 starter application, use {Application root directory}/bsps/TARGET_<BSP-NAME>/config folder to open the design.modus file.

3. In the CY8CKIT-041S MAX kit, the button pins are connected to both channel 0 and channel 1. Hence, make sure to enable channel 0 and channel 1 in the Device Configurator as shown in Figure 10.

   Figure 10. Enable MSC channels in Device Configurator

   

   Save the changes and close the window.

4. Launch the CAPSENSE™ configurator tool.

   You can launch it in stand-alone mode from {ModusToolbox™ software install directory}/ModusToolbox/tools_{version}/capsense-configurator/capsense-configurator. In this case, after opening the application, select File > Open and open the design.cycapsense file of the respective application, which is in the {Application root directory}/bsps/TARGET_<BSP-NAME>/config folder.

   Note: If you are using the custom BSP with the Empty PSoC™ 4 starter application, use {Application root directory}/bsps/TARGET_<BSP-NAME>/config folder to open the design.cycapsense file.

   See the ModusToolbox™ software CAPSENSE™ configurator tool guide for step-by-step instructions on how to configure and launch CAPSENSE™ in ModusToolbox™.

5. In the Basic tab, note that two button widgets 'Button0' and 'Button1' configured as a CSX-RM (Mutual-cap).

   Figure 11. CAPSENSE™ configurator - Basic tab

   

6. Do the following in the General tab under the Advanced tab:

   • Set Scan mode as INTR driven.

   • Set Sensor connection method as AMUXBUS.

     Use AMUXBUS if your design has few number of sensors or if the sensors are connected to AMUXBUS pins.

     Note: For sensors using CSX-RM sensing mode with CTRLMUX as sensor connection method refer to the Touchpad code example.

   • Modulator clock divider is set to 1 to obtain the maximum available modulator clock frequency as recommended in the CAPSENSE™ design guide.

     Note: The modulator clock frequency can be set to 48,000 kHz only after changing the IMO clock frequency to 48 MHz, since the modulator clock is derived from the IMO clock. Do the following:

     1. Under the System tab in the Device Configurator tool, select System Clocks > Input > IMO.

     2. Select 48 from the Frequency(MHz) drop-down list.

   • Number of init sub-conversions is set based on the hint shown when you hover over the edit box. Retain the default value (will be set in Stage 3)

   • Check the Enable self-test library selection. This is required for sensor capacitance measurement using BIST.

   • Retain the default settings for all the filters. You can enable the filters later depending on the signal-to-noise ratio (SNR) requirements in Stage 4.

   The filters are used to reduce the peak-to-peak noise. Using the filters will result in higher scan time.

   Figure 12. CAPSENSE™ configurator - General settings

   

   Note: Each tab has a button Restore Defaults to restore the parameters of that tab to their default values.

7. Go to the CSX Settings tab and make the following changes:

   • Set Inactive sensor connection as Ground.

   • Set Number of reported fingers as 2 for two-finger detection.

   • Select Enable CDAC auto-calibration and Enable compensation CDAC.

     This helps in achieving the required CDAC calibration levels (40% of maximum count) for all the sensors in the widget while maintaining the same sensitivity across the sensor elements.

   Figure 13. CAPSENSE™ configurator - Advanced CSX settings

   

8. Go to the Widget Details tab. Select Button0 and Button1 from the left pane, and then set the following:

   • Tx clock divider: Retain default value (will be set in Stage 3)

   • Clock source: Direct

     Note: Spread spectrum clock (SSC) or PRS clock can be used as a clock source to deal with EMI/EMC issues.

   • Number of sub-conversions: 100

     100 is a good starting point to ensure a fast scan time and sufficient signal. This value will be adjusted as required in Stage 4.

   • Select Enable CDAC dither

   • Finger Threshold: 20

   • Noise Threshold: 10

   • Negative Noise Threshold: 10

   • Hysteresis: 5

     These values reduces the influence of baseline on the sensor signal, which helps to get the true difference-count. Retain the default values for all other threshold parameters; these parameters are set in Stage 5.

   Figure 14. CAPSENSE™ configurator - Widget details tab under the Advanced tab

   

9. Go to the Scan Configuration tab to select the pins and scan slots. Do the following:

   • Configure channels for the button electrodes using the drop-down menu.

     As seen in Figure 15, the button needs to be equally distributed between channel 0 and channel 1.

   • Configure pins for the electrodes using the drop-down menu.

   • Configure the scan slots using Auto-assign slots option or each sensor is allotted a scan slot based on the entered slot number.

     The summary section in the Scan Configuration tab is an indication of the distribution of scan of the sensor in each slot. Each slot allows simultaneous scanning of channel 0 and channel 1 if the Tx clock divider and the number of sub conversions are same. The basic recommendation for slot selection is to enter the slot number applicable which might help in achieving less scan time by parallel scanning.

     In CSX-RM sensing method, the Rx pin is scanned for each button. In the CY8CKIT-01S-MAX kit, the Rx pin in Channel 1 is shared between Button 0 and Button 1. Therefore, the summary section in the Scan Configuration tab shows that the Channel 1 is highlighted in Slot 0, and Slot 1 shows that Channel 1 is scanned.

     Note See AN85951 – PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide for more details on Scan slot allotment rules.

   • Check the notice list for warning or errors.

   Figure 15. Scan Configuration tab

   

10. Click Save to apply the settings.

Stage 2: Measure the parasitic capacitance (Cp)

Use one of the following options to determine the Cp of the sensor:

• Option 1: Using BIST API in CAPSENSE™ middleware

• Option 2: Using LCR meter

Option 1: Using BIST API in CAPSENSE™ middleware

While using this procedure, ensure that you have enabled the Enable self-test library option in the CAPSENSE™ configurator. After you obtained the Cp value, you can disable this option.

1. Estimate the Cp of the Tx and Rx electrode using the Cy_CapSense_MeasureCapacitanceSensorElectrode() function in firmware. The measured capacitance value is in femtofarad (fF).

2. Program the board in Debug mode.

   In the IDE, use the <Application Name> Debug (KitProg3) configuration in the Quick Panel.

   For more details, see the "Program and Debug" section in the Eclipse IDE for ModusToolbox™ software user guide: {ModusToolbox™ install directory}/docs_{version}/mt_ide_user_guide.pdf.

3. Place a breakpoint after the capacitance measurement.

4. In the Expressions window, add the Cp measurement variables (tx0_cp, tx0_cp_staus, rx0_cp, rx0_cp_status tx1_cp, tx1_cp_staus, rx1_cp, rx1_cp_status).

   The status of the measurement can also be read through the return value of the function in the Expressions window.

5. Click the Resume button (green arrow) to reach the breakpoint.

   Note that the function return value reads CY_CAPSENSE_BIST_SUCCESS_E and the measurement variables provide the capacitance value of the sensor elements in femtofarad as shown in Figure 5.

6. Click the Terminate button (red box) to exit Debug mode.

   Figure 16. Cp measurement using BIST

   

Option 2: Using LCR meter

Measure the Cp of the sensor electrode of the button using an LCR meter. The Cp should be measured between the sensor electrode (sensor pin) and the device ground.

Table 1. Cp values obtained for CY8CKIT-041S-MAX kit

Kit	Parasitic capacitance (CP) in pF
CY8CKIT-041S-MAX (Pin P11.2)	24
CY8CKIT-041S-MAX (Pin P0.3)	28
CY8CKIT-041S-MAX (Pin P0.1)	23

Stage 3: Calculate and set the Tx clock frequency and Init sub-conversions

1. Calculate maximum Tx clock frequencies using Equation 1

   Equation 1. Maximum Tx clock frequency

   

   Where, C_{P_Tx} and C_{P_Rx} are the parasitic capacitances of the Tx and Rx electrodes respectively. This value is obtained from Stage 2.

   R_{Series_Cp_Tx} and R_{Series_Cp_Rx} is the total series resistance of the Tx and Rx electrodes respectively, which includes the 525-ohm pin internal resistance, external series resistance (in CY8CKIT-041S-MAX, it is 2 kilo-ohm), and the trace resistance. Include the trace resistance if high-resistive material such as ITO, or conductive ink is used. The external resistor is connected between the sensor Tx/Rx electrode pad and the device pin to reduce the radiated emission. ESD protection is built into the device.

2. The Tx clock divider value, as given by Equation 2, is obtained by dividing HFCLK (48 MHz) by Maximum Tx clock frequency (kHz) calculated and choosing the nearest ceiling Tx clock divider option in the Configurator.

   Equation 2. Tx clock divider

   

   Table 3. Tx clock divider settings in configurator

   Development kit	Tx Cp (pF)	Rx Cp (pF)	RSeriesTx/Rx (ohm)	Maximum Tx clock frequency (kHz)	Tx clock divider setting in configurator
   CY8CKIT-041S-MAX (Tx-P11.2, Rx-P0.1)	24	23	2.525k	1650	30
   CY8CKIT-041S-MAX (Tx-P0.3, Rx-P0.1)	28	23	2.525k	1414	34

   Note

   • If you are explicitly using the PRS or SSCx clock source to lower electromagnetic interference, ensure that you select the Tx clock frequency that meets the conditions mentioned in the ModusToolbox™ software CAPSENSE™ configurator guide in addition to the above conditions. PRS and SSCx techniques spread the frequency across a range.

   • Actual Tx clock frequency value is choosen such that the divider is divisible by 2, in order to have all the 2 scan phases for equal durations.

     Table 3. Tx clock frequency settings for CY8CKIT-041S-MAX kit

     Development kit	Tx clock divider
     CY8CKIT-041S-MAX (Tx-P11.2, Rx-P0.1)	30
     CY8CKIT-041S-MAX (Tx-P0.3, Rx-P0.1)	34

3. The maximum frequency set should charge and discharge the sensor completely, which you can verify using an oscilloscope and an active probe. To view the charging and discharging waveforms of the sensor, probe at the sensors Tx electrode (or as close as possible to the sensors), and not at the pins or resistor. An example of proper and improper charging of the sensor Tx electrode is shown in Figure 17 and Figure 18 respectively. You can also use a passive probe which will add an additional parasitic capacitance of around 15pF and thus the tuning may be not optimal.

   Figure 17. Proper charge cycle of a sensor Tx electrode

   

   Figure 18. Improper charge cycle of a sensor Tx electrode

   

   Set the calculated value in the CAPSENSE™ configurator using the steps given in Step 8 in Stage 1, which ensures the maximum possible Tx clock frequency (for good gain) while allowing the sensor capacitance to fully charge and discharge in each phase of the MSC CSX sensing method.

4. Program the board.

5. Fine-tune the Tx clock frequency.

   1. Check the calibration pass/fail status from the return value of the function Cy_CapSense_Enable().

   2. Launch the CAPSENSE™ tuner to monitor the CAPSENSE™ data and for CAPSENSE™ parameter tuning.

   See the CAPSENSE™ tuner guide for step-by-step instructions on how to launch and configure the CAPSENSE™ tuner in ModusToolbox™ software.

   3. Ensure that the following condition is satisfied for the selected Tx clock frequency:

      • The auto-calibrated reference CDAC value should be within the range (10/Compensation CDAC Divider) to 255 and Compensation CDAC values are in the range 1 to 255. Verify this once the initial hardware parameters are loaded into the device.

        Note: If the reference CDAC value is equal to 1, ensure that the Compensation CDAC value is greater than or equal to 98.

      • Click Button0 in the Widget Explorer to view the Reference CDAC value in the Sensor Parameters window.

      • Also, click each sensor element, for example, Button0_Rx0 in the Widget Explorer to view the Compensation CDAC in the Sensor Parameters window.

      Refer to the CAPSENSE™ design guide for the recommended guidelines on valid CDAC range (with and without compenation) to result in calibration PASS across multiple boards due to board-to-board variations.

      Figure 19. Widget Explorer - button 0

      

      Figure 20. Widget Explorer - button 1

      

   4. If the above condition is not satisfied, fine-tune the sense Tx clock divider to bring the CDAC value within range.

      1. If the Reference CDAC value is not in the recommended range increase or decrease the Tx clock divider in the Widget hardware parameters window.

         Note From the raw count equation ( see AN85951 – PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide), it is evident that increasing the Tx clock divider will decrease the reference CDAC value for a given calibration percent and vice versa.

      2. Click To device to apply the changes to the device as shown in Figure 21.

         Figure 21. Apply changes to device

         

      3. Click each sensor element, for instance, Button0 in the Widget explorer.

      4. Observe the Reference CDAC value in the Sensing parameters section of the Widget Parameters window.

      5. Repeat steps 1 to 4 until you obtain Reference CDAC and Compensation CDAC in the recommended range.

   5. If the CDAC value is still not in the required range based on fine tuning the Tx clock divider then consider reducing the Modulator Clock Frequency to 24 MHz. The Tx clock frequency is dervied from Modulator clock frequency. Thus the corresponding Tx clock divider values needs to be updated.

   6. Actual Tx clock frequency value is choosen such that the divider is divisible by 2, in order to have all the 2 scan phases for equal durations.

   Note: As Figure 19 and Figure 20 shows, CDAC values are in the recommended range. You can leave the Tx clock divider to the value as shown in Step 2 of Stage 3.

   7. Capture the raw counts of each sensor (as shown in Figure 22) and verify that they are approximately (+/- 5%) equal to 40% of the MaxCount. See AN85951 – PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide for the MaxCount equation.

      Note: Calibration may fail if the obtained rawcounts is not within the targetted range.

      Figure 22. Verifying raw count calibration level

      

6. Calculate and set the Number of init sub-conversions using Equation 3.

   Note: Equation 3 is considering the default values of Cmod = 2.2nF, Base % = 0.5 (50%), Auto-calibration % = 0.85 (85%). If you intend to change any value, refer to the AN85951 – PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide to calculate the required number of init sub-conversions.

   Equation 3: Number of init sub-conversions

   

   where,

   VDDA = 5 V

   Tx Clock Divider - Calculated in previous steps.

   Cref_code - Reference CDAC code obtained from previous steps after fine tuning Tx clock divider. If there are multiple CSX widgets, select the code with least value.

   Here, Tx Clock Divider = 30, Reference CDAC = 4, VDDA = 5V. From Equation 3, Number of init-sub conversions = 4.

   Set this value in the CAPSENSE™ configurator. Then, re-program and open the tuner.

Stage 4: Use CAPSENSE™ tuner to fine-tune for required SNR and refresh rate

1. Update the number of sub-conversions.

   Do the following to update the number of sub-conversions:

   1. Update the number of sub-conversions (N_sub) directly in the Widget/Sensor parameters tab of the CAPSENSE™ tuner.

   2. Increase or decrease the number of sub-conversions by 10 and load the parameters to the device. The signal level is directly proportional to number of sub-conversion.

2. Measure SNR as mentioned in the Operation section. And tune until the minimum SNR of 5:1, and a signal count greater than 50 are achieved.

3. Skip this step if the following conditions are met:

   • Measured SNR from the previous stage is greater than 5:1.
   • Signal count > 50.

   If your system is very noisy (counts >20), do the following to set enable fitlers:

   1. Open CAPSENSE™ configurator from ModusToolbox™ software quick panel and select the appropriate filter:

      Figure 23. Filter settings in CAPSENSE™ configurator

      

      Note:

      • Add the filter based on the type of noise in your measurements. See ModusToolbox™ software CAPSENSE™ configurator guide for details.
      • The current example has SNR around 10:1; therefore, filters are not enabled.

   2. Reprogram the device to update filter settings.

Measure Refresh rate.

Refresh rate will impact overall power consumption and user experience of the device in CAPSENSE™ applications. You can measure the refresh rate by toggling one of the GPIOs in each sensor scan loop. Probing the GPIO (P10.4 on J3) on the Oscilloscope shows the refresh rate as shown in Figure 24.

Figure 24. Probing GPIO for refresh rate

Note: Refresh rate obtained here is with the CAPSENSE™ tuner closed, as CAPSENSE™ tuner is only used for the purpose of debugging and will not play a role in deciding the Refresh rate in the end application.

Refresh rate from Figure 24 = 1 /360 us = 2778 Hz

Note:

• Total scan time is equal to the sum of initialization time and the scan time given by Equation 4.

  Equation 4. Scan time

  

• Refresh rate is the reciprocal of sum of total scan time and procesing time.

If the Refresh rate meets your requirements, go to next step otherwise fine tune the number of sub conversions.

Stage 5: Use CAPSENSE™ tuner to tune threshold parameters

The software threshold is set for each widget based on the diff counts. Steps for setting the threshold for one of the widget is given below.

1. Switch to the Graph View tab and select Button1.

2. Touch the sensor and monitor the touch signal in the Sensor Signal graph as Figure 25 shows. Place the metal finger at all possible positions and use the least signal for setting the software threshold. Also ensure to ground the metal finger.

   Figure 25. Sensor signal when the sensor is touched

   

3. When the signal is measured, set the thresholds according to the following recommendations:

   • Finger threshold = 80 percent of signal

   • Noise threshold = 40 percent of signal

   • Negative noise threshold = 40 percent of signal

   • Hysteresis = 10 percent of signal

   • Debounce = 3

4. Set the threshold parameters in the Widget/Sensor parameters section of the CAPSENSE™ tuner.

   Figure 26. Widget threshold parameters

   

5. Apply the settings to the device and to the project by clicking To device and then To Project as Figure 27 shows, and close the tuner. The change is updated in the design.cycapsense file and reflected in the CAPSENSE™ configurator.

   Figure 27. Apply to project setting

   

6. Consider testing with metal finger with smaller sizes that should be rejected by the system to ensure that they do not reach the finger threshold. If your sensor is tuned correctly, you will observe the touch status go from 0 to 1 in the Status sub-window of the Graph View window as Figure 28 shows. The successful tuning of the button is also indicated by the LED in the pioneer kit; the LED is turned ON when the finger touches the button and turned OFF when the finger is removed.

   Figure 28. Sensor status in CAPSENSE™ tuner

   

7. Close the CAPSENSE™ tuner and launch CAPSENSE™ configurator. You should now see all the changes that you made in the CAPSENSE™ tuner reflected in the CAPSENSE™ configurator.

   Table 4. Software tuning parameters obtained based on sense for CY8CKIT-041S-MAX

   Parameter	Button 0	Button 1
   Signal	60	60
   Finger threshold	48	48
   Noise threshold	24	24
   Negative noise threshold	24	24
   Hysteresis	6	6
   ON debounce	3	3
   Low baseline reset	30	30

Debugging

You can debug the example to step through the code. In the IDE, use the <Application Name> Debug (KitProg3_MiniProg4) configuration in the Quick Panel. For details, see the "Program and debug" section in the Eclipse IDE for ModusToolbox™ software user guide.

Design and implementation

The project contains two button widgets configured in CSX-RM sensing mode. See the Tuning procedure section for step-by-step instructions to configure the other settings of the CAPSENSE™ configurator.

The project uses the CAPSENSE™ middleware (see ModusToolbox™ software user guide for more details on selecting a middleware). See AN85951 – PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide for more details on CAPSENSE™ features and usage.

The ModusToolbox™ provides a GUI-based tuner application for debugging and tuning the CAPSENSE™ system. The CAPSENSE™ tuner application works with EZI2C and UART communication interfaces. This project has an SCB block configured in EZI2C mode to establish communication with the on-board KitProg, which in turn enables reading the CAPSENSE™ raw data by the CAPSENSE™ tuner. See EZI2C - Peripheral settings.

The CAPSENSE™ data structure that contains the CAPSENSE™ raw data is exposed to the CAPSENSE™ tuner by setting up the I2C communication data buffer with the CAPSENSE™ data structure. This enables the tuner to access the CAPSENSE™ raw data for tuning and debugging CAPSENSE™.

The successful tuning of the button is indicated by an LED in the pioneer kit; the LED is turned ON when the finger touches the button and turned OFF when the finger is removed from the button.

Steps to setup the VDDA supply voltage in Device configurator

1. Open Device configurator from the Quick panel.

2. Go to the System tab. Select the Power resource, and set the set the VDDA value under Operating conditions as shown in Figure 29.

   Figure 29. Setting the VDDA supply in System tab of device configurator

   

Note: PSoC™ 4100S Max pioneer kit has two onboard regulators 3.3V and 5V. To use 3.3V, place the jumper J10 at positions 2 and 3. See the Kit user guide for more details.

Resources and settings

Figure 30. EZI2C settings

Table 3. Application resources

Resource	Alias/object	Purpose
SCB (I2C) (PDL)	CYBSP_EZI2C	EZI2C slave driver to communicate with CAPSENSE™ tuner
CAPSENSE™	CYBSP_MSC0,CYBSP_MSC1	CAPSENSE™ driver to interact with the MSC hardware and interface the CAPSENSE™ sensors
Digital pin	CYBSP_LED_BTN0,CYBSP_LED_BTN1	To show the button operation

Firmware flow

Figure 31. Firmware flowchart

Related resources

Resources	Links
Application notes	AN79953 – Getting started with PSoC™ 4 AN85951 – PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide
Code examples	Using ModusToolbox™ on GitHub Using PSoC™ Creator
Device documentation	PSoC™ 4 datasheets PSoC™ 4 technical reference manuals
Development kits	Select your kits from the evaluation board finder page.
Libraries on GitHub	mtb-pdl-cat2 – PSoC™ 4 Peripheral Driver Library (PDL) mtb-hal-cat2 – Hardware abstraction layer (HAL) library
Middleware on GitHub	capsense – CAPSENSE™ library and documents
Tools	Eclipse IDE for ModusToolbox™ – ModusToolbox™ software is a collection of easy-to-use software and tools enabling rapid development with Infineon MCUs, covering applications from embedded sense and control to wireless and cloud-connected systems using AIROC™ Wi-Fi and Bluetooth® connectivity devices.

Other resources

Infineon provides a wealth of data at www.infineon.com to help you select the right device, and quickly and effectively integrate it into your design.

Document history

Document title: CE231079 - PSoC™ 4: MSC CAPSENSE™ CSX button tuning

Version	Description of change
1.0.0	New code example. This version is not backward compatible with ModusToolbox™ software v2.1.
1.1.0	Updated the readme and tuning parameters
2.0.0	Code example is updated for ModusToolbox™ software v2.4. This version is not backward compatible with ModusToolbox™ software v2.3 or older version
3.0.0	Major update to support ModusToolbox™ software v3.0. This version is not backward compatible with previous versions of ModusToolbox™.
3.1.0	Updated to support ModusToolbox™ software v3.1 and CAPSENSE™ middleware v4.X.

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