This code example demonstrates how to manually tune a self-capacitance (CSD)-based button widget in PSoC™ 4 devices using the CAPSENSE™ tuner. This document provides:

1. A high-level overview of the CSD widget tuning flow

2. An example to manually tune a CSD button widget

3. Details on how to use the CAPSENSE™ tuner to monitor the CAPSENSE™ raw data and fine-tune the CSD button for optimum performance

View this README on GitHub.

Provide feedback on this code example.

• ModusToolbox™ software v3.1 or later (tested with v3.1)

  Note: This code example version requires ModusToolbox™ software version 3.1 or later and is not backward compatible with v2.4 or older versions.

• Board support package (BSP) minimum required version: 3.0.0

• Programming language: C

• Associated parts: PSoC™ 4000S, PSoC™ 4100S, PSoC™ 4100S Plus and PSoC™ 4500S

• 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)

• PSoC™ 4100S Plus prototyping kit (CY8CKIT-149) - Default value of TARGET
• PSoC™ 4100S CAPSENSE™ pioneer kit (CY8CKIT-041-41XX)
• PSoC™ 4000S CAPSENSE™ prototyping kit (CY8CKIT-145-40XX)
• PSoC™ 4500S pioneer kit (CY8CKIT-045S)

This example uses the board's default configuration. See the kit user guide to ensure that the board is configured correctly.

Note: The PSoC™ 4 kits ship with KitProg2 installed. The ModusToolbox™ software requires KitProg3. Before using this code example, make sure that the board is upgraded to KitProg3. The tool and instructions are available in the Firmware Loader GitHub repository. If you do not upgrade, you will see an error like "unable to find CMSIS-DAP device" or "KitProg firmware is out of date".

This example requires no additional software or tools.

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

project-creator-cli --board-id CY8CKIT-041-41XX --app-id mtb-example-psoc4-capsense-csd-button-tuning --user-app-name CSDButtonTuning --target-dir "C:/mtb_projects"

~/ModusToolbox/tools_3.1/library-manager/library-manager-cli --project "C:/mtb_projects/CSDButtonTuning" --add-bsp-name CY8CKIT-149 --add-bsp-version "latest-v3.X" --add-bsp-location "local"

~/ModusToolbox/tools_3.1/library-manager/library-manager-cli --project "C:/mtb_projects/CSDButtonTuning" --set-active-bsp APP_CY8CKIT-149

Figure 1 gives a high-level summary on how to tune a CSD-based CAPSENSE™ button in PSoC™ 4 devices. See the “Manual tuning” section in AN85951 – PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide for information on the hardware and threshold parameters that determines the CAPSENSE™ touch performance.

Figure 1. High-level overview of CSD button tuning

This process involves the following stages:

• Stage 1: Set initial hardware parameters

• Stage 2: Measure SNR

• Stage 3: Modify hardware parameters or adjust filter settings

• Stage 4: Set the software threshold parameters using CAPSENSE™ tuner

Connect the board to your PC using the provided micro USB cable through the KitProg3 USB connector, and launch the CAPSENSE™ configurator.

See the "Launch the CAPSENSE™ configurator" section from the ModusToolbox™ CAPSENSE™ configurator guide.

In the Basics tab, you will find a single widget ‘Button0’ configured as a CSD button and the CSD Tuning method selected as Manual tuning.

Figure 2. CAPSENSE™ configurator - General settings

1. Navigate to the Advanced tab, and then select the General Settings sub-tab. Leave all the filter parameters at their default settings. Filters will be enabled depending on the SNR and system time requirements.

2. Select Enable self-test library to perform sensor capacitance measurement using the CAPSENSE™ middleware APIs in the firmware. See Step 3. Set the sense clock divider and sense clock source.

   Figure 3. CAPSENSE™ configurator - General settings

   

1. Select the Advanced tab and then select the CSD Settings sub-tab.

2. Configure the parameters as Table 1 and Figure 4 show.

   Table 1. Advanced tab - CSD settings

   Parameter	Value	Remarks
   Modulator clock divider	1 (To obtain the maximum allowed by the selected device)	A higher modulator clock frequency reduces flat spots, and increases the measurement accuracy and sensitivity. It also reduces the sensor scan time, which results in lower power consumption. Therefore, it is recommended to select the highest possible available modulator clock frequency.
   Inactive sensor connection	Ground (default)	Inactive sensors are connected to ground to provide good shielding from noise sources. Use the inactive sensor connection as shield for liquid-tolerant designs if your design contains a proximity sensor or if the adjacent sensors are being used to reduce Cp of sensors.
   IDAC sensing configuration	IDAC sourcing (default)	Choose IDAC sourcing mode because it is more susceptible to VDD noise compared to IDAC sinking mode. However, if you have clean/noise-free VDD, you may choose IDAC sinking mode for a higher SNR.
   Enable IDAC auto-calibration	Checked	Enabling auto-calibration allows the device to automatically choose the optimal IDAC value such that it calibrates the raw count of the sensor to 85 percent of its maximum value.
   Enable compensation IDAC	Checked	Enabling the compensation IDAC selects the dual-IDAC mode operation of the CSD. Dual-IDAC mode gives higher signal values compared to single-IDAC mode for fixed values of CAPSENSE™ parameters.
   Enable shield electrode	Unchecked (default)	Enable shield if your design requires a large proximity sensing distance, liquid tolerance, or if the shield is being used to reduce the Cp of sensors. Before enabling this option, ensure that the PCB has a shield electrode or hatched pattern connected to the device pin.

   
   

   Figure 4. CAPSENSE™ Configurator - Advanced CSD Settings

   

   Note: You can change the modulator clock frequency to 48 MHz only after changing the IMO clock frequency to 48 MHz. To do this, navigate to the System tab in the Device Configurator tool, select System Clocks > Input > IMO. Select 48 from the Frequency(MHz) dropdown list.

1. Navigate to the Advanced tab, and then select the Widget Details sub tab.

2. Set the sense clock divider and sense clock source per the following guidelines:

   • Sense clock divider

     In the CAPSENSE™ configurator, set the sense clock frequency in terms of the sense clock divider as shown in Equation 1:

     Equation 1. Sense clock divider

     

     Set the maximum possible sense clock frequency which will completely charge and discharge the sensor parasitic capacitance. Verify the charging and discharging of the sensor waveform with an oscilloscope by probing the sensor using an active probe.

     Use Equation 2 to compute the maximum sense clock frequency using the Cp of the sensor and the total series resistance R_Series. Note that the CAPSENSE™ configurator allows a maximum sense clock frequency of 6 MHz; therefore, you cannot set it above 6 MHz.

     Equation 2. Maximum sense clock frequency

     

     Cp is the parasitic capacitance of the sensor electrode.

     R_SeriesTotal is the total series resistance, which includes the 500 ohm pin internal resistance, the external series resistance (in CY8CKIT-149, it is 2 kilo-ohm), 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 and for ESD protection.

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

     • Option 1: Using the BIST API in CAPSENSE™ middleware

     • Option 2: Using an LCR meter

     Option 1: Using the BIST API in CAPSENSE™ middleware

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

     1. Estimate the Cp of the sensor electrode using the Cy_CapSense_MeasureCapacitanceSensor() function in firmware. The measured capacitance value is in femtofarad (fF).

     2. Program the board in Debug mode.

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

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

     3. Place a breakpoint after the capacitance measurement.

     4. In the Expressions window, add the Cp measurement variable sensor_cp.

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

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

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

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

        Figure 5. Cp measurement using BIST

        

     Option 2: Using an LCR meter

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

     Table 2. Sense clock divider settings in CAPSENSE™ configurator

     Development kit	Cp of sensor electrode (pF)	RSeriesTotal (ohm)	Maximum sense clock frequency (kHz)	Sense clock divider setting in configurator
     CY8CKIT-149 (Pin P4.5)	10	2.5K	4000	12
     CY8CKIT-145 (Pin P1.5)	9	1060	6000	8
     CY8CKIT-041-41xx (Pin P0.1)	44	1060	2144	23
     CY8CKIT-045S (Pin P4.4)	13	2.5K	1740	16

     
     

   • Sense clock source

     Select Auto as the sense clock source to automatically choose the correct spread spectrum clock (SSC) or PRS clock as the sense clock source to deal with EMI/EMC or flat spots issues.

3. Ensure that the following conditions are also satisfied when selecting the sense clock frequency and sense clock source:

   • The auto-calibrated IDAC value should lie in the mid-range (for example, 18-110) for the selected F_sw. If the auto-calibrated IDAC value lies out of the recommended range, ensure that F_sw is tuned such that IDAC falls within the recommended range. See Ensure that the auto-calibrated IDAC is within the recommended range.

   • If you are explicitly using the PRS or SSCx clock source, ensure that you select the sense clock frequency that meets the conditions mentioned in the ModusToolbox™ software CAPSENSE™ configurator guide.

Set the scan resolution to an initial low value of 10. This will be modified in Stage 3: Modify hardware parameters or adjust filter settings based on the signal-to-noise ratio (SNR) and system timing requirements.

Figure 6. Advanced tab - Widget Details

  1. Select the application project in the Project Explorer.

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

 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
  ```

1. Launch the CAPSENSE™ tuner.

   See the "Launch the CAPSENSE™ tuner" section from the ModusToolbox™ software CAPSENSE™ tuner guide.

2. Go to Tools > Tuner Communication Setup and set the parameters as Figure 7 shows. Click OK.

   Figure 7. Tuner Communication Setup

   

3. Click Connect.

   Figure 8. CAPSENSE™ tuner window

   

4. Click Start.

   Figure 9. CAPSENSE™ tuner start

   

   The Widget/Sensor Parameters tab gets updated with the parameters configured in the CAPSENSE™ Configurator window.

   Figure 10. CAPSENSE™ tuner window

   

5. Select the Button0 check box and Synchronized under Read mode, and then navigate to Graph View as Figure 11 shows.

   The Graph View shows the raw counts and baseline for Button0 in the Sensor data window. Ensure that the Raw counts and Baseline checkboxes are selected to view the sensor data.

   Figure 11. CAPSENSE™ tuner graph view

   

   Note: At this point, when the configured button is touched, you may or may not notice the touch signal in the Sensor Signal graph. The sensor may false-trigger which can be seen in the touch status going from 0 to 1 in the Status window.

As discussed in previous section, the sense clock frequency will be tuned to bring IDAC code to the recommended range in this step. Click Button0 in the Widget Explorer to view the IDAC value in the sensor parameters window as shown in Figure 12. If the IDAC value is within the range (18 to 110), this step is not required.

Increasing the sense clock divider will decrease the IDAC value for a fixed IDAC gain and calibration percent and vice versa.

Figure 12. IDAC value

1. Click Button0 in the Widget Explorer.

2. Increase or decrease the sense clock divider in the Widget hardware parameters window.

3. Click the To Device button to apply the changes to the device as shown in Figure 13.

   Figure 13. Apply changes to the device

   

4. Observe the Modulator IDAC and Compensation IDAC value in the Sensor Parameters section of the Widget/Sensor Parameters window.

5. Repeat steps 1 to 4 until you obtain the IDAC value in the range of 18 to 110.

   Note: As Figure 13 shows, IDAC values are already in the recommended range. Therefore, you can leave the sense clock divider to the value as shown in Table 2.

1. Switch to the SNR Measurement tab, select the Button0 sensor, and then click Acquire Noise as Figure 14 shows.

   Figure 14. CAPSENSE™ tuner - SNR Measurement: Acquire Noise

   

2. Once the noise is acquired, touch the button on the kit, and then click Acquire Signal. Ensure that the finger remains on the button as long as the signal acquisition is in progress.

   The calculated SNR on this button is displayed, as Figure 15 shows. Based on your end-system design, test with a finger that matches the size of your normal use case. Typically, finger size targets are ~8 to 9 mm.

   Figure 15. CAPSENSE™ tuner - SNR Measurement: Acquire Signal

   

Skip this stage if the following conditions are met:

• Measured SNR from the previous step is greater than 5:1
• Signal count is greater than 50
• Response time requirement are met

If the SNR is less than 5:1, do the following to increase the touch performance. The main parameters that influence SNR are scan resolution and filters.

It is best to find a balance between the resolution and filters to achieve proper overall tuning. If your system is very noisy (counts >20), you may want to prioritize adding a filter. On the other hand, if your system is relatively noise-free (counts <10), you should focus on resolution, as this will increase the sensitivity and signal of your system.

Scan resolution can be increased to increase the signal at a disproportionate rate to noise to improve the overall SNR. Increasing the resolution adds to the overall hardware scan time based on Equation 3.

Equation 3. Scan time

Do the following to update the scan resolution:

1. Update the scan resolution (N) directly in the Widget/Sensor Parameters tab of the CAPSENSE™ tuner.

2. Increase the scan resolution by one and repeat steps in Measure SNR until the minimum SNR of 5:1 and at least a signal count greater than 50 are achieved.

Firmware filters help to reduce noise without increasing the signal. Based on your noise type, you can enable a filter to improve SNR. Each filter will add additional processing time as well as memory use. If your system is very noisy (counts > 20), add a filter.

1. Open CAPSENSE™ configurator and select the appropriate filter as shown in Figure 16.

2. Reprogram the device to update filter settings.

   Note: Add the filter based on the type of noise in your measurements. See ModusToolbox™ software CAPSENSE™ configurator guide for details.

   Figure 16. Filter settings in CAPSENSE™ configurator

   

   Note: The current example has approximately 10:1 SNR; therefore, filters are not enabled.

   After setting the scan resolution and filter settings, check the total scan time based on Equation 3 to determine whether system requirements are met. This timing will impact the response time and is a crucial factor in the overall power consumption of the device in CAPSENSE™ applications.

   If the total sensor scan time meets your requirements, go to the next step.

   If not, adjust the tuning to speed up the scan time (decrease the scan resolution or increasing the F_MOD). If the SNR is greater than 10 on any sensor, lower the scan resolution or remove filters to decrease the scan time, but keep the SNR greater than 5:1. It is best to find a balance between the scan resolution and filters to achieve proper overall tuning.

3. Use Table 3 to set the hardware tuning parameters to achieve 5:1 SNR.

   Table 3. Final hardware tuning parameters to achieve 5:1 SNR (with firmware filters disabled)

   Development kit	Sense clock divider setting in configurator	Scan resolution
   CY8CKIT-149	12	11
   CY8CKIT-145	8	9
   CY8CKIT-041-41xx	23	11
   CY8CKIT-045S	16	10

   
   

After you have confirmed that your design meets the timing parameters, and the SNR is greater than 5:1, set your threshold parameters as follows:

1. Switch to the Graph View tab and select Button0 (CSD).

2. Touch the sensor and monitor the touch signal in the Sensor Signal graph.

   The Sensor Signal graph should show the signal as Figure 17 shows.

   Ensure that you observe the difference count (that is, the signal output) in the Graph View tab in Figure 17, not the raw count output for setting these thresholds. Based on your end system design, test the signal with a finger that matches the size of your normal use case. Typically, finger size targets are ~8 to 9 mm. Consider testing with smaller sizes that should be rejected by the system to ensure that they do not reach the finger threshold. Also ensure to ground the metal finger.

   Figure 17. Sensor signal when the sensor is touched

   

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

   • Finger threshold = 80 percent of signal
   • Noise threshold = 40 percent of signal
   • Negative noise threshold = 40 percent of signal
   • Hysteresis = 10 percent of signal
   • Debounce = 3

4. Set the threshold parameters in the Widget/Sensor Parameters section of the CAPSENSE™ tuner, as Figure 18 shows:

   Figure 18. Widget threshold parameters

   

   See Table 4 to set the threshold parameters in the CAPSENSE™ tuner for different development kits.

   Table 4. Threshold parameters for different development kits

   Development kit	Difference counts	Finger threshold	Noise threshold	Negative noise threshold	Hysteresis	Low baseline reset	Debounce
   CY8CKIT-149	80	64	32	32	8	30	3
   CY8CKIT-145-40XX	80	64	32	32	8	30	3
   CY8CKIT-041-41XX	60	48	24	24	6	30	3
   CY8CKIT-045S	80	64	32	32	8	30	3

   
   

5. Apply the settings to the device and to the project by clicking on the To Device icon and then the To Project icon as Figure 19 shows, and close the tuner.

   Figure 19. Apply settings to project setting

   

   If your sensor is tuned correctly, you will observe the touch status go from 0 to 1 in the Status sub-window of the Graph View tab as Figure 20 shows. The successful tuning of the button is also indicated by a user LED in the prototyping kit; the LED is turned ON when the finger touches the button and turned OFF when the finger is removed from the button.

   Figure 20. Sensor status in CAPSENSE™ tuner

   

6. Launch CAPSENSE™ Configurator. You should now see all the changes that you made in the CAPSENSE™ tuner reflected in the CAPSENSE™ Configurator.

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.

The project contains a single button widget configured in CSD sensing mode. See the "CAPSENSE™ CSD sensing method" section in the AN85951 – PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide for details on CAPSENSE™ CSD sensing mode. See the Operation section for step-by-step instructions to configure the other settings of the CAPSENSE™ configurator.

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

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

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

The successful tuning of the button is indicated by a user LED in the prototyping kit; the LED is turned ON when the finger touches the button and turned OFF when the finger is removed from the button. Figure 21 shows the firmware flow for this code example.

Figure 21. Firmware design

Figure 22. EZI2C Settings

Table 5. Application 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 title: CE230926 - PSoC™ 4 MCU: CAPSENSE™ CSD button tuning

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