PSOC™ 4: MSCLP low power self-capacitance touchpad

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 a 5th-generation low-power CAPSENSE™ (MSCLP).

In addition, this code example also explains how to manually tune the self-capacitance-based touchpad for optimum performance according to parameters such as reliability, power consumption, response time, and linearity using the CSD-RM sensing technique and CAPSENSE™ Tuner. Here, capacitive sigma-delta (CSD) represents the self-capacitance sensing technique and RM represents the ratiometric method.

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Requirements

• ModusToolbox™ v3.5 or later

• Board support package (BSP) minimum required version: 3.3.0

• Programming language: C

• Associated parts: PSOC™ 4100TP

Supported toolchains (make variable 'TOOLCHAIN')

• GNU Arm® Embedded Compiler v11.3.1 (GCC_ARM) – Default value of TOOLCHAIN
• Arm® Compiler v6.22 (ARM)
• IAR C/C++ Compiler v9.50.2 (IAR)

Supported kits (make variable 'TARGET')

• PSOC™ 4100T Plus CAPSENSE™ Prototyping Kit (CY8CPROTO-041TP) – Default value of TARGET

Hardware setup

This example uses the board's default configuration. See the kit user guide to configure the hardware to operate at the required operating voltage. To setup the device VDDA supply voltage, see section Set up the VDDA supply voltage and debug mode in Device Configurator.

This application is tuned to perform optimally at the default voltage. However, you can observe the basic functionality at other supported voltages.

Table 1. Kit user guide and supporting voltages

Kit	User guide	1.8 V	3.3 V	5 V
CY8CPROTO-041TP	PSOC™ 4100T Plus CAPSENSE™ Prototyping Kit guide	Yes	Yes	Yes*

Yes* - Kit default operating voltage.

Software setup

See the ModusToolbox™ tools package installation guide for information about installing and configuring the tools package.

This example requires no additional software or tools.

Using the code example

Create the project

The ModusToolbox™ tools package provides the Project Creator as both a GUI tool and a command line tool.

Use Project Creator GUI

1. Open the Project Creator GUI tool

   There are several ways to do this, including launching it from the dashboard or from inside the Eclipse IDE. For more details, see the Project Creator user guide (locally available at {ModusToolbox™ install directory}/tools_{version}/project-creator/docs/project-creator.pdf)

2. On the Choose Board Support Package (BSP) page, select a kit supported by this code example. See Supported kits

   Note: To use this code example 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. On the Select Application page:

   a. Select the Applications(s) Root Path and the Target IDE

   Note: Depending on how you open the Project Creator tool, these fields may be pre-selected for you

   b. Select this code example from the list by enabling its check box

   Note: You can narrow the list of displayed examples by typing in the filter box

   c. (Optional) Change the suggested New Application Name and New BSP Name

   d. Click Create to complete the application creation process

Use Project Creator CLI

The 'project-creator-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™ 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™ installation instead of a standard Windows command-line application. This shell provides access to all ModusToolbox™ 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 following example clones the "mtb-example-psoc4-msclp-low-power-csd-touchpad" application with the desired name "MSCLPlowpowerSelfCapTouchpad" configured for the CY8CPROTO-041TP BSP into the specified working directory, C:/mtb_projects:

project-creator-cli --board-id CY8CPROTO-041TP --app-id mtb-example-psoc4-msclp-low-power-self-capacitance-touchpad --user-app-name MSCLPSelfCapTouchpadTuning --target-dir "C:/mtb_projects"

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

Argument	Description	Required/optional
--board-id	Defined in the field of the BSP manifest	Required
--app-id	Defined in the 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

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™ tools package user guide (locally available at {ModusToolbox™ install directory}/docs_{version}/mtb_user_guide.pdf).

Open the project

After the project has been created, you can open it in your preferred development environment.

Eclipse IDE

If you opened the Project Creator tool from the included Eclipse IDE, the project will open in Eclipse automatically.

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

Visual Studio (VS) Code

Launch VS Code manually, and then open the generated {project-name}.code-workspace file located in the project directory.

For more details, see the Visual Studio Code for ModusToolbox™ user guide (locally available at {ModusToolbox™ install directory}/docs_{version}/mt_vscode_user_guide.pdf).

Arm® Keil® µVision®

Double-click the generated {project-name}.cprj file to launch the Keil® µVision® IDE.

For more details, see the Arm® Keil® µVision® for ModusToolbox™ user guide (locally available at {ModusToolbox™ install directory}/docs_{version}/mt_uvision_user_guide.pdf).

IAR Embedded Workbench

Open IAR Embedded Workbench manually, and create a new project. Then select the generated {project-name}.ipcf file located in the project directory.

For more details, see the IAR Embedded Workbench for ModusToolbox™ user guide (locally available at {ModusToolbox™ install directory}/docs_{version}/mt_iar_user_guide.pdf).

Command line

If you prefer to use the CLI, open the appropriate terminal, and navigate to the project directory. On Windows, use the command-line 'modus-shell' program; on Linux and macOS, you can use any terminal application. From there, you can run various make commands.

For more details, see the ModusToolbox™ tools package user guide (locally available at {ModusToolbox™ install directory}/docs_{version}/mtb_user_guide.pdf).

Operation

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

2. Program the board using one of the following:

   Using Eclipse IDE

   1. Select the application project in the Project Explorer

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

   In other IDEs

   Follow the instructions in your preferred IDE.

   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

   Note: After programming, you may see the following error message if debug mode is disabled, see Table 13 for the default debug configuration in the supported kits. Ignore the error or enable the debug mode to solve this error

   "Error: Error connecting Dp: Cannot read IDR"

4. To test the application, slide your finger over the CAPSENSE™ touchpad and notice that the LED mentioned in Table 2 turns on when touched and turns off when the finger is lifted

   Table 2. LED indications

   Scenario	CY8CPROTO-041TP	Status
   Touch (Column)	LED3	Brightness increases when the finger is swiped from left to right
   Touch (Row)	LED2	Brightness increases when the finger is swiped from bottom to top

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

   Monitor data using CAPSENSE™ Tuner

   a. Open CAPSENSE™ Tuner from the tools section in the IDE Quick Panel

   You can also run the CAPSENSE™ Tuner application in standalone mode from {ModusToolbox™ 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 present in the {Application root directory}/bsps/TARGET_APP_<BSP-NAME>/config/ folder

   See the ModusToolbox™ 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

   b. Ensure 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

   c. In the tuner application, click on the Tuner Communication Setup icon or select Tools > Tuner Communication Setup. In the window, select I2C 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 1. Tuner communication setup parameters

   
   

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

   Figure 2. Establish a connection

   
   

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

   Figure 3. Start tuner communication

   
   

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

8. Set the Read mode to Synchronized mode. Navigate to the Widget View tab and notice that the TOUCHPAD_SELF_CAP widget is highlighted in blue when you touch it

   Figure 4. Widget view of the CAPSENSE™ Tuner

   
   

9. 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_SELF_CAP, select TOUCHPAD_SELF_CAP_Col0 under TOUCHPAD_SELF_CAP

   Figure 5. Graph View tab of the CAPSENSE™ Tuner

   
   

10. The Touchpad View tab shows the heatmap view and the finger movement can be visualized on the same

    Figure 6. Touchpad view of the CAPSENSE™ Tuner

    

11. See the Widget/Sensor Parameters section in the CAPSENSE™ Tuner window. The configuration parameters for each touchpad sensor element calculated by the CAPSENSE™ resource are displayed as shown in Figure 6

12. Verify that the signal-to-noise ratio (SNR) is greater than 5:1 and the signal count is above 50 by following the steps given in Stage 4: Obtain noise and crossover point

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

Note: See the mtb-example-psoc4-msclp-low-power-csd-button to observe the power state transitions, and measure current at different power modes section. The Code Example also explains the scan time and process time measurements.

Tuning procedure

Create custom BSP for your board

1. Create a custom BSP for your board having any device, by following the steps given in the ModusToolbox™ BSP Assistant user guide

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

The following steps explain the tuning procedure.

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

The tuning flow of the proximity widget is shown in Figure 7.

Figure 7. CSD touchpad widget tuning flow

Do the following to tune the touchpad widget:

• Stage 1: Set the initial hardware parameters
• Stage 2: Set the sense clock frequency
• Stage 3: Measure sensor capacitance to set CDAC tuning mode
• Stage 4: Obtain noise and crossover point
• Stage 5: Fine-tune sensitivity to improve SNR
• Stage 6: Tune threshold parameters

Stage 1: Set the initial hardware parameters

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

2. Launch the Device Configurator tool

   Launch the Device Configurator in Eclipse IDE for ModusToolbox™ from the Tools section in the IDE Quick Panel or Standalone mode from the {ModusToolbox™ 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 present in the {Application root directory}/bsps/TARGET_APP_<BSP-NAME>/config folder

3. In the PSOC™ 4100T Plus kit, the touchpad pins are connected to CAPSENSE™ channel (MSCLP 0). Therefore, ensure that you enable CAPSENSE™ channel in the Device Configurator as shown in Figure 8

   Figure 8. Enable MSCLP channel in the Device Configurator

   

4. Save the changes and close the window

5. Launch the CAPSENSE™ Configurator tool

   You can launch the CAPSENSE™ Configurator tool in the Eclipse IDE from the CAPSENSE™ Peripherals tab in the Device Configurator or directly from the Tools section in the IDE Quick Panel. You can also launch it in standalone mode from {ModusToolbox™ 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 located in the {Application root directory}/bsps/TARGET_APP_<BSP-NAME>/config/ folder.

   See the ModusToolbox™ CAPSENSE™ Configurator user guide for step-by-step instructions to configure and launch CAPSENSE™ in ModusToolbox™

6. In the Basic tab, note that a single touchpad, TOUCHPAD_SELF_CAP is configured with CSD RM (self-cap) Sensing Mode

   Figure 9. CAPSENSE™ Configurator - Basic tab

   

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

   Table 3. Widget details

   Parameter	Setting	Comment
   CAPSENSE™ IMO Clock frequency (MHz)	46	Frequency of clock used as source for the CAPSENSE™ peripheral
   Modulator clock divider	1	Set to obtain the optimum modulator clock frequency
   Number of init sub-conversions	3	Set to ensure proper initialization of CAPSENSE™.

   Note: Retain the default settings for all regular and low-power widget filters. You can enable or update the filters later depending on the signal-to-noise ratio (SNR) requirements in Stage 5: Fine-tune for required SNR, power, and refresh rate

   Filters are used to reduce the peak-to-peak noise. However, using filters will result in a higher scan time.

   Figure 10. CAPSENSE™ Configurator – General settings

   

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

   
   

8. Go to CSD Settings tab and make the following changes:

   Table 4. Scan setting

   Parameter	CY8CPROTO-041TP	Comment
   Inactive sensor connection	Shield	Connects the inactive sensors (configured sensors which are not scanned in a given scan-slot) to the driven shield
   Shield mode	Active	The driven shield is a signal that replicates the sensor-switching signal. It helps to reduce sensor parasitic capacitance
   Total shield count	2	Selects the number of shield electrodes used in the design. Most designs work with one dedicated shield electrode, but some designs require multiple dedicated shield electrodes to ease the PCB layout routing or to minimize the PCB area used for the shield layer
   Raw count calibration level (%)	85	If the sensor raw count saturates (equals max raw count) on touch, reduce the raw count calibration level(%), which helps in avoiding saturation

   Figure 11. CAPSENSE™ Configurator – Advanced CSD Settings

   
   

9. Go to the Widget Details tab. Select TOUCHPAD_SELF_CAP from the left pane and then set the following:

   Table 5. Initial widget parameter setting

   Parameter	Setting	Comment
   Maximum X-Axis position	255	A touch on touchpad produces a position value from 0 to Maximum X-Axis position
   Maximum Y-Axis position	255	A touch on touchpad produces a position value from 0 to Maximum Y-Axis position
   Column sense clock divider	Default	Value will be set in Stage 2: Set sense clock frequency
   Row sense clock divider	Default	Value will be set in Stage 2: Set sense clock frequency
   Clock source	Direct	Direct clock is a constant frequency sense clock source. When you chose this option, the sensor pin switches with a constant frequency.
   Number of sub-conversions	12	Good starting point to ensure a fast scan time and sufficient signal. This value will be adjusted as required in Stage 5: Fine-tune for required SNR, power, and refresh rate
   Finger threshold	20	It is initially set to a low value which allows the Touchpad View to track the finger movement during tuning
   Noise threshold	10	Baseline is not updated when raw count is above baseline + Noise threshold
   Negative noise threshold	10	Baseline is not updated when raw count is below baseline - Negative noise threshold
   Hysteresis	5	Prevents sensor status toggling due to system noise
   ON debounce	3	Number of consecutive scans during which a sensor must be active so that a touch is reported

   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: Tune threshold parameters.

   Figure 12. CAPSENSE™ Configurator - Widget Details settings

   

10. To select pins and scan slots, go to Scan Configuration tab and do the following:

    Figure 13. Scan Configuration tab

    

    a. Configure pins for the electrodes using the dropdown menu

    b. Configure the scan slots using Auto-Assign Slots option. It will automatically reassigns all slots for sensors based on a widget and sensor order

    c. Check the notice list for warnings or errors

    Note: Enable the Notice List from the View menu if the notice list is not visible

11. Click Save to apply the settings

    See the CAPSENSE™ design guide for detailed information on tuning parameters

Stage 2: Set the sense clock frequency

The sense clock is derived from the modulator clock using a sense clock-divider and is used to scan the sensor by driving the CAPSENSE™ switched-capacitor circuits. Both the clock source and clock divider are configurable. The sense clock divider should be configured such that the pulse width of the sense clock is long enough to allow the sensor capacitance to charge and discharge completely. This is verified by observing the charging and discharging waveforms of the sensor using an oscilloscope and an active probe. The sensors should be probed close to the electrode, and not at the sense pins or the series resistor.

See Figure 14 and Figure 15 for waveforms observed on the shield. Figure 14 shows proper charging when the sense clock frequency is correctly tuned. The pulse width is at least 5 Tau, i.e., the voltage is reaching at least 99.3% of the required voltage at the end of each phase. Figure 15 shows incomplete settling (charging/discharging).

Figure 14. Proper charge cycle of a sensor

Figure 15. Improper charge cycle of a sensor

1. Program the board and launch CAPSENSE™ Tuner

2. Observe the charging waveform of the sensor as described earlier

3. If the charging is incomplete, increase the sense clock divider. Do this in CAPSENSE™ Tuner by selecting the sensor and editing the sense clock divider parameter in the Widget/Sensor Parameters panel

   Note: The sense clock divider should be divisible by 4. This ensures that all four scan phases have equal durations

   After editing the value, click the Apply to Device and observe the waveform again. Repeat this until complete settling is observed. Using a passive probe will add an additional parasitic capacitance of around 15 pF; therefore, should be considered during the tuning.

4. Click the Apply to Project so that the configuration is saved to your project

   Figure 16. Sense clock divider setting

   

5. Repeat this process for all the sensors and the shield
   Each sensor might require a different sense clock divider value to charge/discharge completely. But all the sensors which are in the same scan slot need to have the same sense clock source, sense clock divider and number of sub-conversions. Therefore, take the largest sense clock divider in a given scan slot and apply it to all the other sensors that share that slot

   Table 6. Sense clock divider settings obtained for supported kits

   Parameter	CY8CPROTO-041TP
   Sense clock divider	28

Stage 3: Measure sensor capacitance to set CDAC tuning mode

Generally the CDAC tuning mode is recommended to be set to Auto, however the appropriate tuning mode to use has some dependency on the sensor parasitic capacitance (Cp).

In order to avoid signal variation across devices in production, PSOC™ 4100T Plus devices have CDAC trim codes in SFlash (read-only). This code is used to scale the Reference CDAC and Fine CDAC parameters, which compensates for variations in the CDAC and brings down the overall signal variation across units.

This trimming is applicable only in the following scenarios,

• Only for CSD widgets (Regular and Low power)

• Sensor Cp is less than 4 pF

  Note: Check across all electrode of touchpad and if any of the electrode have Cp less than 4pF.

• Reference CDAC and Fine CDAC are set to Manual mode

  Note: Select CDAC tuning mode to Auto, if sensor Cp is above 4 pF. Also, for sensing methods other than CSD

1. Measure the sensor Cp using the CAPSENSE™ middleware, it provides Built-In Self Test (BIST) APIs to measure the capacitance of sensors configured in the application

   • Open CAPSENSE™ Configurator from Quick Panel and enable the library. See Figure 17

     Figure 17. CAPSENSE™ Configurator – Enable BIST library

     

   • Middleware API used to measure the capacitance of the CSD widget as follows:

      /* Measure sensor capacitance of the CSD widgets */
      Cy_CapSense_RunSelfTest(CY_CAPSENSE_BIST_SNS_CAP_MASK, &cy_capsense_context);

   See CAPSENSE™ library and documents for more details on BIST

   • Open the tuner and check the sensor Cp values. If Cp value is above 4 pF, set all CDAC parameters to Auto and proceed tuning. See Figure 19. Else, proceed with next the steps

     Note: It is recommended to disable the BIST library to achieve lower power consumption

     Figure 18. CAPSENSE™ Configurator – Read measured sensor Cp

     

2. Enabling CDAC scaling and setting manual CDAC values, if the sensor Cp is below 4 pF

   • Open CAPSENSE™ Configurator and start by setting all CDAC parameters to Auto

     Figure 19. CAPSENSE™ Configurator – Set CDAC Auto mode

     

   • Flash the device. Run the CAPSENSE™ Tuner and click apply to project button. This applies the auto calculated CDAC values to the project configuration

     Figure 20. CAPSENSE™ Tuner – Apply CDAC values

     

   • Close and reopen the CAPSENSE™ Configurator, and enable CDAC scaling as shown in Figure 21

     Figure 21. CAPSENSE™ Configurator – Enable CDAC scaling

     

   • Set Manual tuning mode only for Reference CDAC mode and Fine CDAC mode parameters, see Figure 22. You can see the CDAC values observed in Step 3 when CDAC was set to Auto

     Figure 22. CAPSENSE™ Configurator – Manual CDAC configuration

     

   • Flash the device with updated CAPSENSE™ configuration

   • Open CAPSENSE™ Tuner. Now you can see the scaled parameters after applying CDAC scaling

     Figure 23. CAPSENSE™ Configurator – Manual CDAC configuration

     

3. Use this as a base CDAC configuration and proceed with tuning

   For details about the CDAC trim, see the AN85951 – PSOC™ 4 and PSOC™ 6 MCU CAPSENSE™ design guide

Stage 4: Obtain noise and crossover point

To obtain the noise and crossover point, do the following:

1. Program the board

2. 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™.

3. Capture the raw counts of each sensor element in the touchpad as shown in Figure 24 and verify that they are approximately equal to 85% (± 5%) of the MaxCount. See AN234231 - PSOC™ 4 CAPSENSE™ ultra-low-power capacitive sensing techniques for the MaxCount equation

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

   Table 7. Display settings

   Parameter	Setting
   Display mode	Touch reporting
   Data type	RawCount
   Value type	Current
   Number of samples	1000

   Note: Under Widget selection, enable Flip X-axis for proper visualization of finger movement on the touchpad.

   Figure 24. Raw counts obtained on the Touchpad View tab in the Tuner window

   

4. Observe and note the peak-to-peak noise of each sensor element in the touchpad

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

   Table 8. Display settings

   Parameter	Setting
   Display mode	Touch reporting
   Data type	RawCount
   Value type	Max-Min
   Number of samples	1000

   Figure 25. Noise obtained on the Touchpad View tab in the Tuner window

   

   See the row and column having the highest raw counts without placing a finger (which gives the peak-to-peak noise) in the Touchpad View.

   b. Capture the accurate noise by following these steps:

   • Click on the highest value observed in the heatmap for Row

   • Click on SNR Measurement tab

   • Click on Acquire Noise

   • Repeat the above steps for the column as well

     Figure 26. Row noise obtained on the SNR Measurement tab in Tuner window

     
     

     Figure 27. Column noise obtained on the SNR Measurement tab in Tuner window

     
     

     Table 9. Maximum peak-to-peak noise obtained in CY8CPROTO-041TP kit

     Kit	Maximum peak-to-peak noise for row sensors	Maximum peak-to-peak noise for column sensors
     CY8CPROTO-041TP	46	48

   
   

5. Observe the sensor signal in the Graph View tab in the Sensor Signal graph display

   a. Select the columns in Widget Explorer as shown in Figure 21

   b. Firmly swipe the finger (6 mm) horizontally on the touchpad in the least touch intensity (LTI) position.
   Note the lowest crossover point observed under Sensor Signal

   c. Repeat the above steps for row by swiping the finger vertically on the touchpad in the LTI position

   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 28. Column signal obtained on the Graph View tab in Tuner window

   

   Figure 29. Row signal obtained on the Graph View tab in Tuner window

   

   Table 10. Sensor signal obtained in CY8CPROTO-041TP kit

   Kit	LTI signal for row sensors	LTI signal for column sensors
   CY8CPROTO-041TP	484	410

Stage 5: Fine-tune sensitivity to improve 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 greater than 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.

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

   In CAPSENSE™ Tuner window, increase the Number of sub-conversions (located in Widget Hardware Parameters > Widget/Sensor Parameters section) by 10 until you achieve at least 5:1 SNR.

   Equation 1. SNR

   

   Where,

   • LTI signal is the signal obtained as shown in Figure 28 and Figure 29

   • Pk-Pk noise is the peak-to-peak noise obtained as shown in Figure 25

   SNR is measured for row sensors and column sensors separately, using Equation 1.

   From the values derived from figures mentioned earlier, an example SNR calculation can be calculated as:

   SNR of column sensors = 340/45 = 7.55; SNR of row sensors = 358/51 = 7.01.

2. Update the number of sub-conversions

   a. Update the Number of sub-conversions (Nsub) directly in the Widget/Sensor parameters tab of the CAPSENSE™ Tuner

   b. PSOC™ 4 CAPSENSE™ devices with MSCLP have a built-in CIC2 filter. Enabling the CIC2 filter increases the resolution while maintaining the same scan time. See AN234231 - PSOC™ 4 CAPSENSE™ ultra-low-power capacitive sensing techniques for detailed information on the CIC2 filter. Enable the other filters based on the type of noise in your system. For Filter Descriptions refer to Table 11

   Table 11. Filters Description

   Filter	Description
   Median	Eliminates noise spikes from motors and switching power supplies.
   Average	Eliminates periodic noise (e.g., from power supplies).
   First order IIR	Software filter which eliminates high frequency Noise, Low coefficient results in lower noise but slows down response.
   Hardware IIR	Eliminates high frequency noise, Low coefficient means lower filtering, while higher response time.

   c. Current consumption is directly proportional to the number of sub-conversions. Therefore, decrease the number of sub-conversions to achieve lower current consumption

   Note: The number of sub-conversions should be greater than or equal to 8. They should not be increased beyond a certain limit such that the raw count does not increase more than 2¹⁶ (as it is a 16-bit counter).

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
   • Decrease the IIR filter coefficient if 5:1 SNR is not being achieved even with maximum Nsub

Stage 6: 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.

1. Set the recommended threshold values mentioned in Table 12 for the touchpad widget using the LTI signal value obtained in Stage 5: Fine-tune sensitivity to improve SNR

   Table 12. Software tuning parameters obtained

   Parameter	CY8CPROTO-041TP	Remark
   Number of sub-conversions	12	-
   Finger threshold	328	80% of the lower LTI signal (whichever is lower, row or column)
   Noise threshold	165	Twice the highest noise or 40% of the lower LTI signal (whichever is greater)
   Negative noise threshold	165	Twice the highest noise or 40% of the lower LTI signal (whichever is greater)
   Hysteresis	32	10% of the lower LTI signal
   Low baseline reset	30	30 (by default)
   ON debounce	3	Default

2. Apply the settings to the 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 30. 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 Eclipse 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™ user guide.

In other IDEs

Follow the instructions in your preferred IDE.

See Table 13 for the default debug configuration in the supported kits.

Table 13. Debug mode option status

Kit	Debug mode
CY8CPROTO-040T	Disabled
CY8CPROTO-041TP	Enabled

Design and implementation

The project contains a touchpad widget configured in CSD-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™ 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.

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 onboard KitProg, which in turn enables reading the CAPSENSE™ raw data by the CAPSENSE™ Tuner; see Figure 33.

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 touchpad is indicated by the user LED in the Prototyping; the LED3 brightness increases when the finger is swiped from left to right, and the LED2 brightness increases when the finger is swiped from bottom to top on the touchpad.

Set up the VDDA supply voltage and Debug mode in Device Configurator

1. Open Device Configurator from the Quick Panel

2. Go to the System tab. Select the Power resource and set the VDDA value under Operating Conditions as shown in Figure 31

   Figure 31. Setting the VDDA supply in the System tab of Device Configurator

   
   

3. see Table 13 for the default debug configuration in the supported kits. Enable the Debug mode to enable the SWD pins as shown in Figure 32

   Figure 32. Enable debug mode in the System tab of Device Configurator

   
   

Resources and settings

Figure 33. EZI2C settings

Figure 34. PWM settings

Table 14. Application resources

Resource	Alias/object	Purpose
SCB (EZI2C) (PDL)	CYBSP_EZI2C	EZI2C slave driver to communicate with CAPSENSE™ Tuner
CAPSENSE™	CYBSP_MSC	CAPSENSE™ driver to interact with the MSCLP hardware and interface the CAPSENSE™ sensors
Digital pin	CYBSP_USER_LED1, CYBSP_USER_LED2	To show the touchpad response with LED
PWM	CYBSP_PWM	To drive the user LED which visualizes touchpad response

Firmware flow

Figure 35. Firmware flowchart

Related resources

Resources	Links
Application notes	AN79953 – Getting started with PSOC™ 4 MCU AN85951 – PSOC™ 4 and PSOC™ 6 MCU CAPSENSE™ design guide AN234231 – PSOC™ 4 CAPSENSE™ ultra-low-power capacitive sensing techniques
Code examples	Using ModusToolbox™ on GitHub
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)
Middleware on GitHub	capsense – CAPSENSE™ library and documents
Tools	ModusToolbox™ – ModusToolbox™ software is a collection of easy-to-use libraries and tools enabling rapid development with Infineon MCUs for applications ranging from wireless and cloud-connected systems, edge AI/ML, embedded sense and control, to wired USB connectivity using PSOC™ Industrial/IoT MCUs, AIROC™ Wi-Fi and Bluetooth® connectivity devices, XMC™ Industrial MCUs, and EZ-USB™/EZ-PD™ wired connectivity controllers. ModusToolbox™ incorporates a comprehensive set of BSPs, HAL, libraries, configuration tools, and provides support for industry-standard IDEs to fast-track your embedded application 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: CE240430 - PSOC™ 4: MSCLP low power self-capacitance touchpad

Version	Description of change
1.0.0	New code example This version is not backward compatible with ModusToolbox™ v3.1
2.0.0	Major update to support ModusToolbox™ v3.3. This version is not backward compatible with previous versions of ModusToolbox™
3.0.0	Major update to support ModusToolbox™ v3.5. This version is not backward compatible with previous versions of ModusToolbox™

All referenced product or service names and trademarks are the property of their respective owners.

The Bluetooth® word mark and logos are registered trademarks owned by Bluetooth SIG, Inc., and any use of such marks by Infineon is under license.

PSOC™, formerly known as PSoC™, is a trademark of Infineon Technologies. Any references to PSoC™ in this document or others shall be deemed to refer to PSOC™.

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