PSoC™ 4 MCU: MSC self-capacitance touchpad tuning

This code example demonstrates how to use the CAPSENSE™ middleware to detect a finger touch position on a self-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 self-capacitance-based touchpad for optimum performance with respect to parameters such as reliability, power consumption, response time, and linearity using the CSD-RM sensing technique and CAPSENSE™ tuner GUI. Here, CAPSENSE™ sigma-delta (CSD) represents the self-capacitance sensing technique and RM represents the ratiometric method.

View this README on GitHub.

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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

Click the New Application link in the Quick Panel (or, use File > New > ModusToolbox™ Application). This launches the Project Creator tool.
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.
In the Project Creator - Select Application dialog, choose the example by enabling the checkbox.
(Optional) Change the suggested New Application Name.
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.
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 "PSoC™ 4: MSC self-capacitance touchpad tuning" application with the desired name "CSDTouchpadTuning" 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-csd-touchpad-tuning --user-app-name CSDTouchpadTuning --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/CSDTouchpadTuning" --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/CSDTouchpadTuning" --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

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
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
```
After programming, the application starts automatically.
To test the application, slide your finger over the CAPSENSE™ touchpad and observe that the user LED turns ON when touched and turns OFF when the finger is lifted.
You can also monitor the CAPSENSE™ data using the CAPSENSE™ tuner application as follows:

Monitor data using the CAPSENSE™ tuner

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.
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.
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
Click Connect or select Communication > Connect to establish a connection.
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.
Set the Read Mode to synchronized mode. Under the Widget View tab, you can see the touchpad widget highlighted in blue color when you touch it.

Figure 3. Widget view of the CAPSENSE™ tuner
You can view the raw count, baseline, difference count, status for each sensor, and touchpad position in the Graph View tab. For example, to view the sensor data for touchpad 0, select Touchpad0_Col0 under Touchpad0.

Figure 4. Graph view of the CAPSENSE™ tuner
The Touchpad View tab shows the heatmap view; it visualizes finger movement.

Figure 5. Touchpad view of the CAPSENSE™ tuner
Observe the Widget/Sensor Parameters section in the CAPSENSE™ Tuner window. Figure 5 shows the compensation CDAC values for each touchpad sensor element calculated by the CAPSENSE™ resource.
Verify that the SNR is greater than 5:1 by following the steps given in Stage 4 starting with Step 6.

Non-reporting of false touches and the linearity of the position graph indicate proper tuning.

Note: The touchpad performance can be further enhanced by configuring the board to connect the hatch pattern to the shield. To do so, see the kit user guide for the board connection settings. Ensure that you enable the shield signals in the CAPSENSE™ configurator as shown in Figure 6. Then, retune the touchpad following the tuning process explained in Tuning procedure.

Figure 6. Enabling shield signals in CAPSENSE™ configurator

Tuning procedure

Create custom BSP for your board

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”.
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 AN85951 – PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide to learn about the considerations for selecting each parameter value.

Figure 7. CSD touchpad widget tuning flow

Do the following to tune the touchpad:

Stage 1. Set the initial hardware parameters

Connect the board to your PC using the provided USB cable through the KitProg3 USB connector.
Launch the Device Configurator tool.

You can launch the Device Configurator in Eclipse IDE for ModusToolbox™ software from the Tools section in the IDE Quick Panel or 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.
In the CY8CKIT-041S MAX Kit, the touchpad pins are connected to both channel 0 and channel 1. Hence, make sure you enable channel 0 and channel 1 in the Device Configurator as shown in Figure 8.

Figure 8. Enable MSC channels in Device Configurator

Save the changes and close the window.
Launch the CAPSENSE™ configurator tool.

You can launch the CAPSENSE™ configurator tool in Eclipse IDE for ModusToolbox™ software from the 'CAPSENSE™' peripheral setting in the Device Configurator or directly from the Tools section in the IDE Quick Panel or in standalone 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™ software CAPSENSE™ configurator tool guide for step-by-step instructions on how to configure and launch CAPSENSE™ in ModusToolbox™ software.
In the Basic tab, note that a single touchpad Touchpad0 is configured as a CSD RM (Self-cap) and the CSD tuning mode is set as Manual tuning.

Figure 9. CAPSENSE™ configurator - Basic tab
Do the following in the General 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 trackpad, 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 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. Follow these steps:
  1. Under the System tab in the Device Configurator tool, select System Clocks > Input > IMO.
  2. Select 48 from the Frequency(MHz) dropdown 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 3).
- 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 10. CAPSENSE™ configurator - General tab in the Advanced tab
Go to the CSD Settings tab and make the following changes:
- Set Inactive sensor connection as Shield.
  
  Inactive sensors connected to Shield provide better performance in terms of SNR and Refresh rate (as the use of shield results in a reduction of sensor Cp) and can also be used if your design requires liquid tolerance.
- Set Shield mode as Active.
  
  MSC provides active and passive shielding. Active shielding is preferred for high-performance applications and passive shielding is preferred for low-power applications. Before enabling this option, ensure that your design has shield electrode(s).
- Set Total shield count as 0.
  
  This is equal to the number of shield electrodes in your design. It is zero when only the inactive sensors are shielded.
- Select Enable CDAC auto-calibration and Enable compensation CDAC.
  
  This helps in achieving the required CDAC calibration levels (85% of maximum count) for all sensors in the widget while maintaining the same sensitivity across the sensor elements.
Figure 11. CAPSENSE™ configurator - CSD Settings tab under the Advanced tab
Go to the Widget Details tab. Select Touchpad0 from the left pane and set the following:
- Maximum X-Axis position and Maximum Y-Axis position to 160 and 100 respectively, as it is a 16*10 touchpad.
- Column sense clock divider: Retain the default value (will be set in Stage 3)
- Row sense clock divider: Retain the 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: 110
  
  110 is a good starting point to ensure a fast scan time and sufficient signal. This value will be adjusted as required in Stage 5.
- 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.
Figure 12. CAPSENSE™ configurator - Widget details tab under the Advanced tab
Go to the Scan Configuration tab to select the pins and scan slots. Do the following:

Set the parameters in the Scan Configuration tab as shown in Figure 13.

Figure 13. Scan configuration tab
1. Configure channels for the row and column electrodes using the drop-down menu.
  
  As shown in Figure 13, the row and column pins are divided equally between channel 0 and channel 1.
2. Configure pins for the electrodes using the drop-down menu.
3. Configure the scan slots using the Auto-Assign Slots option.
  
  The summary section in the Scan Configuration tab shows 13 scan slots (for 26 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.
  
  Note: Row sensors cannot share a scan slot with a column sensor.
  
  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.
Click Save to apply the settings.

Stage 2. Measure the parasitic capacitance (Cp)

To determine the maximum row/column Cp, measure the Cp of each 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 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 and shield capacitances 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.

Use the Cy_CapSense_MeasureCapacitanceShieldElectrode() API to measure the total Shield capacitance (Cp) of the touchpad.

Note: Use the Cy_CapSense_SetInactiveElectrodeState() API to set the inactive electrode state to "Shield" before calling the above functions, as these functions use "Ground" as the default inactive electrode state irrespective of what is set in the configurator.

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:

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}/mt_ide_user_guide.pdf.
Place a breakpoint after the capacitance measurement.
In the Expressions window, add the Cp measurement variables: sense_cap, shield_cap_ch0, and shield_cap_ch1.

Read the status of the measurement through the return values sensor_meas_status and shield_meas_status in the Expressions window.
Click the Resume button (green arrow) to reach the breakpoint.

Note: 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/Shield capacitance measurement values obtained in debug mode

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

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

Kit	Maximum column parasitic capacitance (C_{P_Col}) in pF	Maximum row parasitic capacitance (C_{P_Row}) in pF	Total shield capacitance (Csh) in channel 0 in pF	Total shield capacitance (Csh) in channel 1 in pF	Maximum shield capacitance (Csh) in pF
CY8CKIT-041S-MAX kit	28	18	260	203	260

Stage 3. Calculate the sense clock frequency and init sub-conversions

Calculate the row and column sense clock frequencies using Equation 1, Equation 2, and Equation 3.

Equation 1. Max sense clock frequency from sensor capacitance

Where,
- F_{SW(Row)(Max,Cs)} and F_{SW(Col)(Max,Cs)} are the maximum row and column sense clock frequency based on sensor capacitance respectively.
- C_S(Row) and C_S(Col) are the maximum parasitic capacitances of the row and column electrodes respectively. Note: C_S = C_P when there is no finger present on sensor.
- R_Series is the maximum total series resistance which includes the 525-ohm (for CTRLMUX mode) internal resistance, the external series resistance (in CY8CKIT-041S MAX, it is 2 kilo-ohms), 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 pad and the device pin to reduce the radiated emission. ESD protection is built into the device.
Equation 2. Max sense clock frequency from shield capacitance

Where,
- F_{SW(Row)(Max,Cshield)} and F_{SW(Col)(Max,Cshield)} are the maximum row and column sense clock frequency based on shield capacitance respectively.
- C_sh is the maximum shield parasitic capacitance between channel 0 and channel 1.
- R_Series is the maximum total series resistance, which includes the 250-ohm (for CTRLMUX and active shield mode) internal resistance, the external series resistance (in CY8CKIT-041S MAX, it is 2 kilo-ohms), 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 pad and the device pin to reduce the radiated emission. ESD protection is built into the device.
Equation 3. Max sense clock frequency

F_swMAX = min(F_swMAX,Cs,F_{swMAX,Cshield})

From Equation 3, it is observed that the maximum sense clock frequency is chosen such that both the sensor and shield electrodes charge and discharge completely. Therefore, the minimum frequency value out of the two, i.e., based on sensor Cp and shield Cp is selected.

Note 1: If the LCR meter is not available, set an initial sense clock divider value and look at the charge and discharge waveforms of the sensor and shield 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 CSD 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 sensors and shield are not fully charging and discharging:

Figure 15. Incomplete charging and discharging

Ensure that the following conditions are also satisfied when selecting the sense clock frequency:

The auto-calibrated CDAC and Compensation CDAC value should lie in the valid range for the selected sense clock divider and Compensation CDAC divider. Verify this 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 to lower the electromagnetic interference, ensure that you select the sense 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.
If you want to scan Channel 0 and Channel 1 in the same scan slot simultaneously, the sense clock divider and the number of sub-conversions should be the same for both sensor elements.

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

Kit	R_SeriesTotal (Ω) for sensors	R_SeriesTotal (Ω) for shield	Maximum column Cp (pF)	Maximum row Cp (pF)	Total shield Csh (pF)	Maximum column sense clock frequency (kHz) based on sensor Cp	Maximum row sense clock frequency (kHz) based on sensor Cp	Maximum sense clock frequency (kHz) based on shield Csh	Actual column sense clock frequency (kHz)	Actual row sense clock frequency (kHz)
CY8CKIT-041S-MAX	2525	187.5	28	18	260	707	1100	1025	706	1000

Note 1: Here, all the unused sensor electrodes are ganged to form the shield electrode. R_SeriesTotal (Ω) for the shield is obtained by a parallel combination of the resistances (external + internal) of each unused sensor electrode (i.e., configured as "Shield").

Total resistance on each unused sensor line: 2000 + 250 = 2250

Number of unused sensors (per channel): 12

Therefore, parallel resistance obtained: 2250/12 = 187.5 Ω

Total shield capacitance Csh (per channel) is also calculated as a parallel combination of individual parasitic capacitances of the shield electrodes.

Note 2: Actual sense clock frequency value is chosen such that the divider is divisible by 4, to have all four scan phases for equal durations.

Note 3: The sense clock divider value, as given by Equation 4, is obtained by dividing HFCLK (48 MHz) by Maximum Column Sense Clock Frequency (kHz) and Maximum Row Sense Clock Frequency (kHz) calculated in Stage 3 (see Table 2) and choosing the nearest ceiling sense clock divider option in the Configurator.

Equation 4. Sense clock divider

In this case, column sense clock divider = 48000/707 = 68 and Row sense clock divider = 48000/1025 = 48.

Set the calculated value using the steps given in 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 CSD sensing method. In addition, also ensure that the shield waveform is probed and that it satisfies the condition given in the section Shield Electrode Tuning Theory in the AN85951 – PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide.

Calculate and set the Number of init sub-conversions using Equation 5 and the steps given in Step 6 in Stage 1

Note: Equation 5 is considering the default values of Cmod = 2.2 nF, Base % = 0.5 (50%), Auto-calibration % = 0.85 (85%). 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.

Equation 5: Number of init sub-conversions

Where,

VDDA = 5 V

Cs = Least self-capacitance value out of the sensors in pF (obtained in Stage2)

Stage 4. Obtain the cross-over point and noise

Program the board.
Check the calibration pass/fail status from the return value of the Cy_CapSense_Enable() function.
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.
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 3, the sense clock divider will be tuned to bring the CDAC values to the recommended range in this step.
- Click Touchpad0 in the Widget Explorer to view the Column reference CDAC value and Row reference CDAC value in the sensor parameters window as shown in Figure 16.
- Additionally, click each sensor element, for instance, Touchpad0_Col0 in the Widget Explorer to view the Compensation CDAC in the sensor parameters window as shown in Figure 16.
- If the reference CDAC values are within the range (20/Compensation CDAC Divider) to 255 and Compensation CDAC values are in the range 1 to 255, skip the next step.
Figure 16. CDAC value

See the AN85951 - PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide for the recommended guidelines on valid CDAC range (with and without compensation) to result in calibration PASS across multiple boards because of board-to-board variations.
Fine-tune the sense clock divider to bring the CDAC value within the range.

From the raw count equation (see AN85951 – PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide), it is evident that increasing the sense clock divider will decrease the reference CDAC value for a specific calibration percentage and vice-versa.
1. If the column reference CDAC value and row reference CDAC value are not in the recommended range, increase the column sense clock divider and row sense clock divider, respectively, 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_Col0 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 24 MHz.
7. Repeat Steps 1 to 6 until you obtain reference CDAC values in the range (20/Compensation CDAC Divider) to 255 and Compensation CDAC values are in the range 1 to 255.
  
  Note: As Figure 16 shows, CDAC values are in the recommended range when the Column Sense Clock Divider is 68 and Row Sense Clock Divider is 64. You can leave the sense clock divider to the value as shown in Step 8 of Stage 3.
Capture the raw counts of each sensor element in the touchpad (as shown in Figure 16) and verify that they are approximately (+/- 5%) equal to 85% of the MaxCount. See 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:
  - Display mode: Touch Reporting
  - Data type: RawCount
  - Value type: Current
  - Number of samples: 500
Figure 18. Rawcounts obtained on the touchpad view tab in Tuner window
Capture and note the peak-to-peak noise of each sensor element in the touchpad.
1. From the Widget Explorer section, select the widget Touchpad0.
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.
Figure 19. Noise obtained on the Touchpad View tab in Tuner window

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

Kit Max peak-to-peak noise for row sensors Max peak-to-peak noise for column sensors

CY8CKIT-041S-MAX 7 10
View the row and column sensor signals in the Graph View tab in the Sensor Signal graph display by swiping your finger across the touchpad from top to bottom and left to right respectively.
Firmly hold the finger (typically 8 mm or 9 mm) on the touchpad in the Least Touch Intensity (LTI) position (at the intersection of 4 nodes) as shown below. See AN85951 – PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide for more details on least touch intensity (LTI) position.

Figure 20. Least touch intensity (LTI) position

Note: Finger movement during the test can artificially increase 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
  Place the finger such that an equal signal is obtained in the two intersecting column and row sensors respectively (look at the heatmap displayed in the Touchpad View tab as shown in Figure 21).
  
  Note: The LTI signal is measured at the farthest point (not at the last column/row) of the touchpad from the sensor pin connection, where the sensors have the worst-case RC-time constant.
Figure 21. LTI position in Touchpad view

Row LTI Signal = (49 + 51 )/2 = 50, Column LTI Signal = (57 + 57)/2 = 57

Kit	Max peak-to-peak noise for row sensors	Max peak-to-peak noise for column sensors
CY8CKIT-041S-MAX	7	10

Stage 5. Use the CAPSENSE™ tuner to fine-tune sensitivity to achieve 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 around 10:1 SNR.

Ensure that the LTI signal count is greater than 50 and meets at least 5:1 SNR (using Equation 6).

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 at least 5:1 SNR.

Equation 6:

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 for row sensors and column sensors separately, using Equation 6.

Here, from Figure 19 and Figure 21,

SNR of column sensors = 57/10 = 6, SNR of row sensors = 50/7 = 7

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

Use Equation 7 to calculate the maximum number of sub-conversions:

Equation 7:

Max Nsub = 2^16/68 = 65536/68 = 963 (16-bit counter)

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

Equation 8. Scan time

Note: Total scan time is equal to the sum of initialization time and the scan time given by Equation 8.
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.

Verify 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 sensor initialization time, scan time (according to Equation 8), processing time, and tuner communication time, which can be verified using the tuner as shown in Figure 22.

Figure 22. Refresh rate measurement
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 refresh rate

Note: Refresh rate obtained here is with the tuner closed, as the 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 23 = 1 /2.16 ms = 463 Hz

Stage 6. Use 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 lower LTI signal (either Row or Column)
Noise Threshold: Twice the highest noise or 40% of the lower LTI signal (whichever is greater)
Negative Noise Threshold: Twice the highest noise or 40% of the lower LTI signal (whichever is greater)
Hysteresis - 10% of the lower LTI signal
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: Velocity parameter is not required for single-finger detection.

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

Parameter	CY8CKIT-041S-MAX
Number of sub-conversions	110
Finger threshold	40
Noise threshold	20
Hysteresis	5
ON debounce	3
Low baseline reset	30
Negative noise threshold	20

Applying settings to firmware

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 24. 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 self-capacitance (CSD-RM) based, 26-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 CSD-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.

Steps to set up the V_DDA supply voltage in Device Configurator

Open the Device Configurator from the Quick Panel.
Go to the System tab, select the Power resource, and set the VDDA value under Operating Conditions as shown in Figure 25.

Figure 25. Setting the VDDA supply in the System tab of Device Configurator

Note: PSoC™ 4100S Max Pioneer Kit has two onboard regulators - 3.3 V and 5 V. To use 3.3 V, place the jumper J10 at positions 2 and 3 and change the VDDA voltage and VDDD voltage in Device Configurator - Systems tab to 3300 mV (see Figure 24). 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 26. Device Configurator - EZI2C peripheral parameters

The following ModusToolbox™ software resources are used in this example:

Table 5. Application resources

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 27. 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: CE232273 - PSoC™ 4 MCU: MSC self-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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mtb-example-psoc4-msc-capsense-csd-touchpad-tuning/README.md