PSoC™ 4: MSC multi-touch mutual-capacitance touchpad tuning

This code example demonstrates how to use the CAPSENSE™ middleware to detect two-finger touch positions on a mutual-capacitance-based touchpad 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 touchpad 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™ crosspoint (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 5 V (J10 should be at positions 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 the "Steps to set up the V_DDA supply voltage in Device Configurator" section in this code example 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 "CAPSENSE™ MSC CSX touchpad tuning" application with the desired name "MSCCSXTouchpadTuning" 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-touchpad-tuning --user-app-name MSCCSXTouchpadTuning --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/MSCCSXTouchpadTuning" --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/MSCCSXTouchpadTuning" --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 FFC cable between J9 on the PSoC™ 4100S Max Pioneer Board and J2 on the capacitive sensing expansion board. Connect a USB 2.0 Type-A to Micro-B cable on J8 (USB Micro-B connector) as shown in Figure 1 to power the device.

   Figure 1. Connecting the CY8CKIT-041S-MAX kit with a capacitive sensing expansion board to a PC

   

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, slide your finger over the CAPSENSE™ touchpad 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™ 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 the Tuner Communication Setup or select Tools > Tuner Communication Setup and select the I2C checkbox under KitProg3 and configure the parameters as follows:

   • I2C address: 8
   • Sub-address: 2-Bytes
   • Speed (kHz): 1000

   These are the same values set in the EZI2C resource.

   Figure 2. Tuner communication setup parameters

   

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

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

   The tuner displays the data from the sensor in the Widget View, Graph View, and Touchpad View tabs.

6. Set the Read Mode to synchronized mode. Under the Widget View tab, you can see the touchpad widget sensors highlighted when you touch it.

   Figure 3. Widget view of the CAPSENSE™ tuner

   

7. You can view the raw count, baseline, difference count for each sensor, and touchpad position in the Graph View tab. For example, to view the sensor data for a single sensor in Touchpad0, select Touchpad0_Rx0_Tx0 under Touchpad0.

   Figure 4. Graph view of the CAPSENSE™ tuner

   

8. The Touchpad View tab shows the heat map view; it visualizes finger movement.

   Figure 5. Touchpad view of the CAPSENSE™ tuner

   

9. Observe the Widget/Sensor Parameters section in the CAPSENSE™ Tuner window. Figure 14 shows the compensation CDAC values for each touchpad sensor element calculated by the CAPSENSE™ resource.

10. Verify that the SNR is greater than 5:1 by following the steps given in Stage 4 starting with Step 6 in the Tuning procedure.

The linearity of the position graph, non-reporting of false touches, and no discontinuity in the line drawing indicate proper tuning.

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 is created for the “CY8C4149AZI-S598” device.

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 design.cycapsense file. Follow these steps to start the CAPSENSE™ configuration from scratch.

The following steps explain the tuning procedure.

Note: See the section "Selecting CAPSENSE™ hardware parameters" in the AN85951 – PSoC™4 and PSoC™6 MCU CAPSENSE™ design guide to learn about the considerations for selecting each parameter value.

Figure 6. CSX touchpad widget tuning flow

Do the following to tune the touchpad:

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.

3. In the CY8CKIT-041S MAX Kit, the touchpad pins are connected to both channel 0 and channel 1. Therefore, enable channel 0 and channel 1 in the Device configurator as shown in Figure 7.

   Figure 7. Enable MSC channels in Device configurator

   

   Save the changes and close the window.

4. Launch the CAPSENSE™ configurator tool.

   You can launch the CAPSENSE™ configurator tool in Eclipse IDE for ModusToolbox™ from the CAPSENSE™ peripheral setting in the Device configurator, or directly 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}/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.

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

5. In the Basic tab, note that a touchpad Touchpad0 is configured as CSX RM (Mutual-cap).

   In addition, add a button TouchpadInitWidget (with 1 Tx and 2 Rx) configured as the CSX RM sensing mode and move the widget to the top by clicking on Move up to be added to empty initialization slots as explained below.

   Note:

   • For sensors using the CSX RM sensing mode with CTRLMUX as the sensor connection method, initialization requires empty slots to be added. This is the workaround to the errata mentioned in the PSoC™ 4100S Max datasheet.

   • Choose the Inactive sensor connection as VDDA/2 and ensure to add empty scan slots before the first sensor scan (on both channel 0 and channel 1) for initializing the voltages on Rx lines to VDDA/2. This will be set in Step 7.

   • The Tx and Rx of the button can be ganged with any Tx and Rx pins of the respective channel of the touchpad. This will be configured in Step 9.

   Figure 8. CAPSENSE™ configurator - Basic tab

   

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

   • Set Scan mode as CS-DMA to enable autonomous scanning.

     For applications with a large number of sensors such as trackpads, automated scan using DMA helps scan multiple sensors autonomously, which helps in improved refresh rate and offloading the CPU.

     Ensure to do the required DMA settings in the Device configurator as described in the DMA connection settings for CS-DMA mode - KBA233869.

   • Sensor connection method is CTRLMUX by default for CS-DMA scan mode.

     Use CTRLMUX if your schematic has all the sensors on ctrlmux pins. CTRLMUX mode allows the MSC block to control the GPIO pins and removes the need for AMUXBUS to transfer CAPSENSE™ signals between GPIO and the MSC block.

   • Set the Modulator clock divider as 1 to obtain the maximum available modulator clock frequency as recommended in the AN85951 – PSoC™4 and PSoC™6 MCU 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 because 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 (it will be set in Stage 4).

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

   • Retain the default settings for all filters. You can enable the filters later depending on the signal-to-noise ratio (SNR) requirements in Stage 5.

     Filters are used to reduce the peak-to-peak noise. Use of filters results in higher scan time.

   Figure 9. CAPSENSE™ configurator - General sub-tab in the Advanced tab

   

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

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

   • Set the Inactive Sensor connection as VDDA/2 as explained in Step 1.

   • Set the 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 sensors in the widget while maintaining the same sensitivity across the sensor elements.

   Figure 10. CAPSENSE™ configurator - CSX settings tab under the Advanced tab

   

8. Go to the Widget Details tab.

   Select Touchpad0 from the left pane and then set the following:

   • Maximum X-Axis position and Maximum Y-Axis position to 160 and 100 respectively, as it is a 16*10 touchpad.

   • 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. The selected value should be set using the Widget Details tab in the CAPSENSE™ configurator.

   • Number of sub-conversions: 70

     70 is a good starting point to ensure a fast scan time and sufficient signal. This value will be adjusted as required in Stage 5.

   • Select Enable CDAC dither

   • Finger Threshold: 20

     Finger Threshold is initially set to a low value allowing the Touchpad View to track the finger movement during tuning.

   • Noise Threshold: 10

   • Negative Noise Threshold: 10

   • Hysteresis: 5

     These values reduce the influence of the 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 6.

   Select TouchpadInitWidget from the left pane and then set the following:

   • Tx clock divider: Retain the default value (it 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. The selected value should be set using the Widget Details tab in the CAPSENSE™ configurator.

   • Number of sub-conversions: 1

     1 sub-conversion is sufficient to initialize the touchpad widget.

   • Select Enable CDAC dither

   Figure 11. CAPSENSE™ configurator - Touchpad details in Widget details tab under the Advanced tab

   

   Figure 12. CAPSENSE™ configurator - TouchpadInitWidget details in the 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 the button TouchpadInitWidget:

   1. Configure channels for the Tx and Rx electrodes using the drop-down menu.

   Here, Tx0 is configured with MSC1, and Rx0 and Rx1 are configured with MSC1 and MSC0 respectively.

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

   Here, the Tx of the button is ganged with the Tx1 of the touchpad, Rx0 is ganged with Rx0 of the touchpad, and Rx1 is ganged with Rx5 of the touchpad.

   Configure the Touchpad widget:

   1. Configure channels for the Tx and Rx electrodes using the drop-down menu.

      The Rx and Tx pins are divided equally between MSC0 and MSC1.

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

   Configure the scan slots for both widgets using the Auto-Assign Slots option.

   The summary section in the Scan configuration tab shows 81 scan slots (for 162 sensors), with each channel scanning in each slot simultaneously. This helps to perform parallel scanning and reduces the total scan time.

   • Each sensor is allotted a scan slot based on the slot number.

   • The slots are assigned such that the sensors, which are under parallel scanning, are as far as possible from each other.

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

   • Check the notice list for warnings or errors.

     Figure 13. Scan configuration tab

     

10. Click Save to apply the settings.

Stage 2. Measure the parasitic capacitance (Cp)

To determine the maximum Tx/Rx Cp, measure the Cp of each Tx and Rx sensor element of the touchpad, between the sensor electrode (sensor pin) and device ground, using an LCR meter or using the built-in-self-test (BIST) library.

It can also be estimated by back-calculating for Cs (Sensor capacitance) using the CSD-RM Raw Count equation. See the Equation CSD-RM Raw Count in AN85951 – PSoC™4 and PSoC™6 MCU CAPSENSE™ design guide for the Raw Count equation.

Measure sensor capacitance using BIST:

Use the Cy_CapSense_MeasureCapacitanceSensorElectrode() API to measure the parasitic capacitance (Cp) of each touchpad sensor to determine the maximum Cp out of all the sensors.

If you are using the empty PSoC™ 4 starter application, you can copy the respective source code from this example’s main.c file to the main.c file of the application project. If you are using this code example, the required files are already in the application.

Do the following to determine the Cp values in debug mode:

1. 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™ software install directory}/docs_{version}/mtb_ide_user_guide.pdf.

2. Place a breakpoint after the capacitance measurement.

3. In the Expressions window, add the Cp measurement variable: sense_cap.

   Read the status of the measurement through the return value measure_status in the Expressions window.

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

   Note that the function return values read CY_CAPSENSE_BIST_SUCCESS_E and the measurement variables provide the capacitance of the sensor elements in femtofarads.

   Figure 14. Sensor capacitance measurement values obtained in debug mode

   

5. Click the Terminate button (red box) to exit debug mode.

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

   Kit	Maximum Rx parasitic capacitance (CP_Col) in pF	Maximum Tx parasitic capacitance (CP_Row) in pF
   CY8CKIT-041S-MAX kit	36	44

Stage 3. Calculate the Tx clock frequency

1. Calculate the Tx clock frequency using Equation 1.

   Equation 1. Max Tx clock frequency

   

   Where,

   • F_Tx is the Tx clock frequency.

   • C_{P_Tx} and C_{P_Rx} are the maximum parasitic capacitance of the Tx and Rx electrodes respectively.

   • R_SeriesTotal is the maximum total series resistance, which includes the 525-ohm internal resistance, the external series resistance (in CY8CKIT-041S-MAX, it is 2 kilo-ohms), and the trace resistance. Include the trace resistance if a high-resistive material such as ITO or conductive ink is used. The external resistor is connected between the sensor pad and the device pin to reduce the radiated emission. ESD protection is built into the device.

   Note 1: If the LCR meter is not available, set an initial Tx clock divider value and look at the charge and discharge waveforms of the sensor electrodes and iteratively change the divider using the CAPSENSE™ tuner and set a maximum frequency such that it completely charges and discharges in each phase of the MSC CSX sensing method.

   Note 2: 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 (or as close as possible to the sensors), and not at the pins or resistor.

   Note 3: Figure 15 shows the waveforms when the sensor is not fully charging and discharging:

   Figure 15. Incomplete charging and discharging

   

2. Ensure that the following conditions are also satisfied when selecting the Tx clock frequency and CDAC compensation divider:

   • The auto-calibrated CDAC and compensation CDAC value should lie in the valid range for the selected Tx clock divider and CDAC compensation divider. This should be verified after the initial hardware parameters are loaded into the device. See Step 3 (Ensure that the auto-calibrated CDAC is within the recommended range) of Stage 4 for more details.

   • If you are explicitly using the PRS or SSCx clock source for EMI/EMC tests, ensure that you select the Tx clock frequency that meets the conditions mentioned in the ModusToolbox™ CAPSENSE™ configurator guide in addition to the above conditions. PRS and SSCx techniques spread the frequency across a range. The maximum frequency set should charge and discharge the sensor completely, which you can verify using an oscilloscope and an active probe.

   • If you want to scan channel 0 and channel 1 in the same scan slot simultaneously, the Tx clock divider and the number of sub-conversions should be the same for both sensor elements.

   Table 2. Tx clock frequency settings for CY8CKIT-041S-MAX

   Kit	RSeriesTotal (kΩ)	Cp (pF)	Maximum Tx clock frequency (kHz)	Actual Tx clock frequency (kHz)
   CY8CKIT-041S-MAX	2525	44	900	888

Note 1: Actual Tx clock frequency value is chosen such that the divider is divisible by 2, to have two scan phases for equal durations.

**Note 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 in **Stage 3** (see **Table 2**) and choosing the nearest ceiling sense clock divider option in the configurator.
  
  **Equation 2. Tx clock divider**

  <img src="images/tx-clock-divider.png" alt="Equation 2" width="250"/>

  In this case, Tx clock divider = 48000/888 = 54.

Set the calculated value for both widgets TouchpadInitWidget and Touchpad0 using Step 8 in Stage 1, which ensures the maximum possible sense clock frequency (for good gain) while allowing the sensor capacitance to fully charge and discharge in each phase of the MSC CSX sensing method.

Stage 4. Obtain the cross-over point and noise

1. Program the board.

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

3. Launch the CAPSENSE™ tuner to monitor the CAPSENSE™ data and for CAPSENSE™ parameter tuning and SNR measurement.

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

4. Ensure that the auto-calibrated CDAC is within the recommended range.

   Note: Calibration may fail if the obtained raw count is not within the targeted range.

   As mentioned in Step 2 of Stage 2, tune the Tx clock divider to bring the CDAC values to the recommended range in this step.

   • Click Touchpad0 in the Widget Explorer to view the Reference CDAC value in the sensor parameters window as shown in Figure 17.

   • Additionally, click each sensor element (Touchpad0_Rx0_Tx0 for example) in the Widget Explorer to view the Compensation CDAC in the sensor parameters window as shown in Figure 16.

     Figure 16. CDAC value

     

   • If the reference CDAC value is within the range (10/Compensation CDAC Divider) to 255 and Compensation CDAC values are in the range 1 to 255, the following step is not required.

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

   See the AN85951 – PSoC™4 and PSoC™6 MCU CAPSENSE™ design guide for the recommended guidelines on valid CDAC range (with and without compensation enabled) to result in calibration PASS across multiple boards because of board-to-board variations.

5. Fine-tune the Tx clock divider to bring the CDAC value within the range.

   From Equation CSX-RM Raw Count in 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 percentage and vice versa.

   1. If the reference CDAC value is not in the recommended range, increase the Tx clock divider in the Widget Hardware Parameters window.

   2. Click To Device to apply the changes to the device as shown in Figure 17.

   3. Click each sensor element, for instance, Touchpad0_Rx0_Tx0 in the Widget Explorer.

   4. Observe the Compensation CDAC value in the Sensing Parameters section of the Widget/Sensor Parameters window.

   5. Click To Device to apply the changes to the device as shown in Figure 17.

      Figure 17. Apply changes to device

      

   6. If the CDAC values are still not in the required range, reduce the modulator clock frequency to the next lower value.

   7. Repeat Steps 1 to 6 until you obtain Reference CDAC values in the range (10/Compensation CDAC Divider) to 255 and Compensation CDAC values are in the range 1 to 255.

      Note: As Figure 16 shows, CDAC values are already in the recommended range. Therefore, you can leave the Tx clock divider to the value as shown in Step 2 of Stage 3.

6. Calculate and set the Number of init sub-conversions using Equation 3 and follow the steps given in Step 6 in Stage 1, with the values of SenseClockDivider and Reference CDAC value obtained.

   Equation 3: Number of init sub-conversions

   

   Where,

   VDDA = 5 V

   Tx Clock Divider - Calculated in Stage 3

   Cref_code - Reference CDAC code obtained in Step 4.

   Note: Equation 3 considers the default values of Cmod = 2.2 nF, Base % = 0.5 (50%), Clsb = 8.86 fF. If you intend to change any value, see the AN85951 – PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide to calculate the required number of init sub-conversions.

   Here, Tx Clock Divider = 54, Reference CDAC = 4, VDDA = 5 V. From Equation 3, Number of init-sub conversions = 3.

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

7. Capture the raw counts of each sensor element in the touchpad (as shown in Figure 18) and verify that they are approximately (+/- 5%) equal to 40% of the MaxCount. See Equation CSX-RM Raw Count in AN85951 – PSoC™4 and PSoC™6 MCU CAPSENSE™ design guide) for the MaxCount equation.

   1. Go to the Touchpad View tab and change the Display settings as follows:

      • Data type: RawCount

      • Value type: Current

      • Number of samples: 500

   Figure 18. Raw counts obtained on the Touchpad View tab in the tuner window

   

8. Capture and note the peak-to-peak noise of each sensor element in the touchpad.

   1. From the Widget Explorer section, select the Touchpad0 widget.

   2. Go to the Touchpad View tab and change the Display settings as follows:

      • Display mode: Touch Reporting

      • Data type: RawCount

      • Value type: Max-Min

      • Number of Samples: 500

      Capture the variation in the raw counts for 500 samples, without placing a finger (which gives the peak-to-peak noise) and note the highest noise.

      Note: Under Widget selection, enable Flip Y-axis and Swap XY-axes for proper visualization of finger movement on the touchpad.

      Figure 19. Noise obtained on the Touchpad View tab in the tuner window

      

      Table 3. Max peak-to-peak noise obtained in CY8CKIT-041S-MAX

      Kit	Max peak-to-peak noise
      CY8CKIT-041S-MAX	11

      
      

9. Firmly hold the finger (typically 8 mm or 9 mm) on the touchpad in the least touch intensity (LTI) position (at the intersection of four nodes) as shown below. See AN85951 – PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide for more details on the LTI position.

   Figure 20. Least touch intensity (LTI) position

   

   Note: Finger movement during the test can artificially increase the noise level.

   1. Go to the Touchpad View tab and change the Display settings as follows:

      • Display mode: Touch Reporting

      • Data type: DiffCount

      • Value type: Current

   2. Place the finger such that an almost equal signal is obtained in all four intersecting nodes (look at the heat map displayed in the Touchpad View tab as shown in Figure 18).

      Note: The LTI signal is measured at the farthest point of the trackpad from the sensor pin connection, where the sensors have the worst-case RC-time constant.

      Figure 21. LTI position in touchpad view

      

      LTI Signal = (67 + 67 + 66 + 70)/4 = 67

Stage 5. Use the CAPSENSE™ tuner to fine-tune the sensitivity for 5:1 SNR

The CAPSENSE™ system may be required to work reliably in adverse conditions such as a noisy environment. The touchpad sensors need to be tuned with SNR > 5:1 to avoid triggering false touches and to make sure that all intended touches are registered in these adverse conditions.

Note: For gesture detection, it is recommended to have approximately 10:1 SNR.

1. Ensure that the LTI signal count is greater than 50 and meets at least 5:1 SNR (using Equation 4).

   In the CAPSENSE™ Tuner window, increase the Number of sub-conversions (located in the Widget/Sensor Parameters section, under Widget Hardware Parameters) by 10 until you achieve this requirement.

   Equation 4: Measuring the SNR

   

   Where,

   • LTI signal is the signal obtained as shown in Figure 21

   • Pk-Pk noise is the peak-to-peak noise obtained as shown in Figure 19

   SNR is measured using Equation 4.

   Here, from Figure 19 and Figure 21,

   SNR = 67/ 11 = 6

   Note: Ensure that the Number of sub-conversions (Nsub) does not exceed the max limit and saturate the raw count.

2. Use Equation 5 to calculate the maximum number of sub-conversions:

   Equation 5: Max number of sub-conversions

   

   Max Nsub = 65536/54 = 1213 (16-bit counter)

   Nsub is also tuned to satisfy the refresh rate that is required.

   Equation 6. Scan time

   

   Note: Total scan time is equal to the sum of initialization time and the scan time given by Equation 6.

3. After changing the Number of sub-conversions, click Apply to Device to send the setting to the device. The change is reflected in the graphs.

   Note: The Apply to Device option is enabled only when the Number of sub-conversions is changed.

4. If the SNR condition is not achieved even with the maximum number of sub-conversions, enable filters in the General settings (go to the Advanced tab of the CAPSENSE™ configurator). This is generally not required for this kit.

Verify the refresh rate and response time

Response time of the touchpad can be visualized using LEDs to indicate toggling of sensor GPIOs when touched.

Refresh rate is a combination of the sensor initialization time, scan time (given by Equation 6), processing time, and the tuner communication time, which can be verified using the tuner as shown in Figure 22:

Figure 22. Measuring the refresh rate

You can also 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 23.

Figure 23. Probing GPIO for the refresh rate

Note: Refresh rate obtained here is with the tuner closed, because the tuner is used only for debugging and will not play a role in deciding the refresh rate in the end application.

The refresh rate from Figure 23 = 1 /8.2 ms = 121 Hz

Stage 6. Use the CAPSENSE™ tuner to tune threshold parameters

After confirming that your design meets the timing parameters, and the SNR is greater than 5:1, set your threshold parameters.

Note: Thresholds are set based on the LTI position because it is the least valid touch signal that can be obtained.

Set the recommended threshold values for the touchpad widget using the LTI signal value obtained in Stage 5:

• Finger Threshold: 80% of the LTI signal

• Noise Threshold: Twice the highest noise or 40% of the LTI signal (whichever is greater)

• Negative Noise Threshold: Twice the highest noise or 40% of the LTI signal (whichever is greater)

• Hysteresis

  Do the following:

  1. Place the finger in the LTI position.

  2. Set the Data type to DiffCount and the Value type to Max-Min in the Touchpad View tab.

  3. Record the maximum count value (Max_Count) of the selected 2x2 sensors.

     Figure 24. Obtaining the hysteresis

     

• Hysteresis: Max_Count/2 = 12/2 = 6

• ON Debounce: Default value of 3 (Set to 1 for gesture detection)

• Low Baseline Reset: Default value of 30

• Velocity: Default value of 2500

Note: For multiple finger detection, if the velocity value is low, two touches at different positions are considered to be two different finger touches. On the other hand, if it is set at a higher value, it is considered to be the same finger moving to a different position.

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

Parameter	CY8CKIT-041S-MAX
Number of Sub-conversions	70
Finger threshold	53
Noise threshold	26
Hysteresis	6
ON debounce	3
Low baseline reset	30
Negative noise threshold	26
Velocity	2500

Apply settings to firmware

1. Click Apply to Device and Apply to Project in the CAPSENSE™ Tuner window to apply the settings to the device and project, respectively. Close the tuner.

   Figure 25. Apply to Project

   

   The change is updated in the design.cycapsense file and reflected in the CAPSENSE™ configurator.

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 uses the CAPSENSE™ middleware; see the 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 of CAPSENSE™ features and usage.

The design has a ratiometric mutual-capacitance (CSX-RM) based, 160-element (10*16) CAPSENSE™ touchpad and EZI2C peripheral. The EZI2C slave peripheral is used to monitor the sensor data and touchpad touch position information on a PC using the CAPSENSE™ tuner available in the Eclipse IDE for ModusToolbox™ via I2C communication.

The firmware scans the touchpad widget using the CSX-RM sensing method and turns ON the corresponding LED when a finger touch is detected and sends the CAPSENSE™ rawcount, status, and position data over an I2C interface to the CAPSENSE™ Tuner GUI tool on a PC using the onboard KitProg USB-I2C bridge.

Set up the VDDA supply voltage in device configurator

1. Open the Device configurator from the Quick Panel.

2. Go to the Systems tab, select the Power resource, and set the VDDA value under Operating Conditions as shown in Figure 26.

   Figure 26. Setting the VDDA supply in the system tab of device configurator

   

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

Resources and settings

See the Operation section for step-by-step instructions to configure the CAPSENSE™ configurator.

Figure 27. Device configurator - EZI2C peripheral parameters

Table 5. Application resources

The following ModusToolbox™ resources are used in this example:

Resource	Alias/object	Purpose
SCB (I2C) (PDL)	CYBSP_EZI2C	EZI2C slave driver to communicate with CAPSENSE™ tuner GUI
CAPSENSE™	CYBSP_MSC0, CYBSP_MSC1	CAPSENSE™ driver to interact with the MSC hardware and interface the CAPSENSE™ sensors
Digital pin	CYBSP_USER_LED	To visualize the touchpad response

Firmware flow

Figure 28. 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™ software 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
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	ModusToolbox™ software – 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. PSoC™ Creator – IDE for PSoC™ and FM0+ MCU development

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: CE232275 - PSoC™ 4: MSC multi-touch mutual-capacitance touchpad tuning

Version	Description of change
1.0.0	New code example
2.0.0	Updated the code example to use ModusToolbox™ software v2.4
3.0.0	Major update to support ModusToolbox™ software v3.1 and CAPSENSE™ middleware v4.X

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