PSoC™ 4: MSCLP low-power self-capacitance button

This code example demonstrates an implementation of a low-power application including recommended power states and transitions, tuning parameter adjustments, and the method of tuning. This example uses a single self-capacitance-based button in multi-sense converter low-power (MSCLP), the 5th generation low-power CAPSENSE™ block, to demonstrate different considerations to implement a low-power design.

This examples also describes the procedure to manually tune the self-capacitance-based low-power widget for optimum performance, with respect to parameters such as power consumption and response time, using CSD-RM sensing technique and CAPSENSE™ Tuner.

View this README on GitHub.

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Requirements

ModusToolbox™ v3.2 or later

Note: This code example version requires ModusToolbox™ version 3.2 and is not backward compatible with v3.1 or older versions.
Board support package (BSP) minimum required version: 3.2.0
Programming language: C
Associated parts: PSoC™ 4000T

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™ 4000T CAPSENSE™ Prototyping Kit (CY8CPROTO-040T) - Default 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 use VDDA at 5 V.

Software setup

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

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).
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.
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 "MSCLP Low power CSD button tuning" application with the desired name "MSCLPSelfCapButtonTuning" configured for the CY8CPROTO-040T BSP into the specified working directory, C:/mtb_projects:

project-creator-cli --board-id CY8CPROTO-040T --app-id mtb-example-psoc4-msclp-low-power-csd-button --user-app-name MSCLPSelfCapButtonTuning --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).

Keil µVision

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

For more details, see the 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

Connect the board to your PC using the provided USB cable through the KitProg3 USB connector as follows:

Figure 1. Connecting the CY8CPROTO-040T kit with the PC
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
```
After programming, the application starts automatically.

Note: After programming, you see the following error message if debug mode is disabled. Ignore the error or enable the debug mode to solve this error.
```
"Error: Error connecting Dp: Cannot read IDR"
```
To test the application, observe the LED3 state change depending on the different low-power states based on the user interaction. Place your finger over the CAPSENSE™ button and notice that LED2 turns ON when touched, and turns OFF when the finger is lifted.

Table 1. LED3 state for different application power modes

Power mode state LED3

Active Blinks at a fast rate

Active low-refresh rate
(ALR) Blinks at a medium rate

Wake-on-touch
(WoT) Blinks at a slow rate
Verify that the application is transitioning to different power modes based on the user input conditions as follows:
- If there is no user activity for a certain time (ACTIVE_MODE_TIMEOUT_SEC = 10 s), the application transitions to ALR mode and the refresh rate is reduced to 32 Hz.
- Further non-activity for a certain time (ALR_MODE_TIMEOUT_SEC = 5 s) transitions the application to the lowest-power mode – the wake-on-touch mode, which scans the low-power widget at a low refresh rate (16 Hz).
Figure 2. Low-power mode state machine

Monitor data using the 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™ 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 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 for more information.

Ensure that the status LED is ON and not blinking. This indicates that the onboard KitProg3 is in CMSIS-DAP Bulk mode. See Firmware-loader to update the firmware and switch modes in KitProg3.
In the tuner application, click on the Tuner Communication Setup icon or select Tools > Tuner Communication Setup. In the window, select the I2C checkbox under KitProg3 and configure it as follows:
- I2C address: 8
- Sub-address: 2-Bytes
- Speed (kHz): 400
These are the same values set in the EZI2C resource.

Figure 3. Tuner communication setup parameters
Click Connect or select Communication > Connect to establish a connection.

Figure 4. Establish connection
Click Start or select Communication > Start to start data streaming from the device.

Figure 5. Start tuner communication

The Widget/Sensor Parameters tab is updated with the parameters configured in the CAPSENSE™ Configurator window. The tuner displays the data from the sensor in the Widget View and Graph View tabs.
Set the Read mode to Synchronized mode. Navigate to the Widget View tab and notice that the Button0 widget is highlighted in blue when you touch it.

Figure 6. Widget view of the CAPSENSE™ Tuner
Go to the Graph View tab to view the raw count, baseline, difference count, and status for each sensor. Observe that the low-power widget sensor (LowPower0_Sns0) raw count is plotted once the device completes the full frame scan (or detects a touch) in Wake-on-touch/WoT mode and moved to Active/ALR mode.

Figure 7. Graph view of the CAPSENSE™ Tuner
See Widget/Sensor parameters section in the CAPSENSE™ Tuner window as shown in Figure 7.
Switch to the SNR Measurement tab for measuring the SNR and verify that the SNR is greater than 5:1, and the signal count is above 50; select Button0 and Button0_Sns0 sensor, and then click Acquire noise as shown in Figure 8.

Figure 8. CAPSENSE™ Tuner - SNR measurement: Acquire noise

Note: Because the scan refresh rate is lower in ALR and WoT mode, it takes more time to acquire noise. Touch the CAPSENSE™ button before clicking Acquire noiseto transition the device to Active mode to receive the signal faster.
Once the noise is acquired, place the finger at a position on the button and then click Acquire signal. Ensure that the finger remains on the button as long as the signal acquisition is in progress. Observe that the SNR is greater than 5:1 and the signal count is above '50'.

The calculated SNR on this button is displayed, as shown in Figure 9. Based on the end system design, test the signal with a finger that matches the size of normal use case. Also, test using smaller size that will be rejected by the system to ensure that they do not reach the finger threshold.

Figure 9. CAPSENSE™ Tuner - SNR measurement: Acquire signal
To measure the SNR of the low-power sensor (LowPower0_Sns0), set the Finger threshold to max (65535) in Widget/Sensor Parameters as shown in Figure 10 for both Button0 and LowPower0 widgets. This is required to stop detecting a touch in low-power mode and ALR mode and to avoid state transitions to Active mode from both low-power mode and ALR mode. Use the Apply to Device option to set the modified parameters to the device instantaneously. But make the final configuration using the CAPSENSE™ Configurator.

Figure 10. CAPSENSE™ update finger threshold

Figure 11. Apply changes to device

Repeat steps 10 and 11 to observe the SNR and signal count as shown in Figure 12.

Figure 12. CAPSENSE™ Tuner - SNR measurement: low-power widget

Note : A 6-mm metal finger is used in this example for tuning.

Operation at other voltages

CY8CPROTO-040T supports operating voltages of 1.8 V, 3.3 V, and 5 V. Refer to the kit user guide to set the preferred operating voltage and refer to section setup the VDDA supply voltage and Debug mode.

This application functionalities are optimally tuned for 5 V. However, basic functionalities works on other voltages.

For better performance, it is recommended to tune the application with preferred voltages.

Measure current at different power modes

Disable the run time measurement, PWM LED, and tuner macros to measure the current used for CAPSENSE™ sensing in each power mode in main.c and disable the self test library from the CAPSENSE™ configurator as follows:
```
   #define ENABLE_RUN_TIME_MEASUREMENT      (0u)
   
   #define ENABLE_PWM_LED                   (0u)

   #define ENABLE_TUNER                     (0u)
```
Disable the self-test library from the CAPSENSE™ Configurator as follows:

Figure 13. Disable self-test library
Disable the debug mode (if enabled). By default, it is disabled. To enable, see the setup the VDDA supply voltage and Debug mode section. Enabling the debug mode keeps the SWD pins active in all device power modes and even during Deep Sleep. This leads to increase in power consumption.
Connect the kit to a power analyzer (KEYSIGHT - N6705C), using a current measure header to evaluate the low-power feature of the device as shown in the Figure 14.

Figure 14. Power analyzer connection
Control the power analyzer device through the laptop using a software tool called "Keysight BenchVue Advanced Power Control and Analysis".
Select the current measurement option from the instrument control setup. Then, select and turn ON the output channel as shown in Figure 15.

Figure 15. Current measurement setup
Capture the data using the data log option from the tool. The average current consumption is measured using cursors on each power mode as shown in Figure 16.

Figure 16. Current measurement
After reset, the application transitions to low-power states if there is no user activity, such as button touch detection, to reduce the power consumption as shown in Figure 17.

Figure 17. Power mode transition - no user activity

If the touch is detected in low-power states, the application transitions to Active mode with the highest refresh rate as shown in Figure 18.

Figure 18. Power mode transition - touch detection

Table 2. Measured current for different modes

Power mode	LED3 state	Refresh rate (Hz)	Current consumption (µA)
Active	Blinks at a fast rate	128	67
Active low-refresh rate (ALR)	Blinks at a medium rate	32	18
Wake-on-touch (WoT)	Blinks at a slow rate	16	3.1

Note : The above WoT current was measured on a kit having Deep Sleep current of 1.7 µA. If the kit has a Deep Sleep current of 2.5 µA (typical), the WoT current is expected to be ~4.4 µA.

Tuning procedure

Create a custom BSP for your board

Create a custom BSP for your board having any device, by following the steps given in the ModusToolbox™ BSP Assistant user guide. In this code example, it is created for the "CY8C4046LQI-T452" device.
Open the design.modus file from {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 then be started from scratch as follows.

Note: See the section "Selecting CAPSENSE™ hardware parameters" in AN85951 PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide to learn about the considerations for selecting each parameter value. In addition, see the "Low-power widget parameters" section in AN234231 - Achieving lowest power capacitive sensing with PSoC™ 4000T to learn about the considerations for parameter values specific to low-power widgets.

Figure 19. Low-power widget tuning flow

Do the following to tune the button widget:

Stage 1: Set the initial hardware parameters
Stage 2: Set the sense clock frequency
Stage 3: Fine tune for the required SNR, power, and refresh rate
Stage 4: Tune the threshold parameters

Stage 1: Set the initial hardware parameters

Connect the board to the PC using the provided USB cable through the KitProg3 USB connector.
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.
Enable the CAPSENSE™ channel in Device Configurator as shown in the Figrue 20 and save the changes.

Figure 20. Enable CAPSENSE™ in Device Configurator

Launch the CAPSENSE™ Configurator tool.

To launch the Configurator tool in Eclipse IDE for ModusToolbox™ from the "CAPSENSE™" peripheral setting in the Device Configurator or directly from the Tools section in the IDE Quick Panel.

The tool is launched in a 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, which is present 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™.
In the Basic tab, configure a Button widget Button0 and a low-power widget LowPower0 as a CSD-RM (self-cap) and set the CSD tuning mode as Manual tuning.

Figure 21. CAPSENSE™ Configurator - basic tab
Do the following in the General tab under the Advanced tab:
1. Select CAPSENSE™ IMO Clock frequency as 46 MHz.
2. Set the Modulator clock divider to 1 to obtain the maximum available modulator clock frequency.
3. Set the Number of init sub-conversions based on the hint shown when you hover over the edit box. Retain the default value.
4. Use Wake-on-Touch settings to set the refresh rate and frame timeout while in the lowest power mode (Wake-on-Touch mode). Set Wake-on-Touch scan interval (µs) based on the required low-power state scan refresh rate. For example, to get a 16-Hz refresh rate, set the value to 62500.
5. Set the Number of frames in Wake-on-Touch as the maximum number of frames to be scanned in WoT mode if there is no touch detected. This determines the maximum time the device will be kept in the lowest-power mode if there is no user activity. Calculate the maximum time by multiplying this parameter with the Wake-on-Touch scan interval (µs) value.
  
  For example, to get 10 s as the maximum time in WoT mode, set the Number of frames in Wake-on-Touch to 160 for the scan interval set as 62500 µs.
  
  Note: For tuning low-power widgets, the Number of frames in Wake-on-Touch must be less than the Maximum number of raw counts in SRAM based on the number of sensors in WoT mode as shown in Table 3.
  
  Table 3. Maximum number of raw counts in SRAM
  
  Number of low
  power widgets Maximum number of
  raw counts in SRAM
  
  1 245
  
  2 117
  
  3 74
  
  4 53
  
  5 40
  
  6 31
  
  7 25
  
  8 21
  
  Figure 22. CAPSENSE™ Configurator – general settings
6. Retain the default settings for all regular and low-power widget filters. To enable or update the filters later depending on the SNR requirements in Stage 3: Fine tune for required SNR, power, and refresh rate.The filters reduce the peak-to-peak noise, and using software filters results in a higher scan time.
Note: Each tab has a Restore Defaults button to restore the parameters of that tab to their default values.

Go to the CSD settings tab and make the following changes:

Set Inactive sensor connection as Shield.
Set Shield mode as Active.
Set Total shield count as 10.

To improve noise immunity, configure all unused sensor pins as shield.
Raw count calibration level(%) helps to achieve the required CDAC calibration levels (85% of maximum count by default) for all sensors in the widget, while maintaining the same sensitivity across the sensor elements. This can be reduced, if application reaches the saturation level on a touch event. Setting this to 70% for this application not to reach the saturation level on a touch event.

Figure 23. CAPSENSE™ Configurator - advanced CSD settings

Go to the Advanced > Widget Details tab. Select LowPower0 from the left pane, and then set the following:
- Sense clock divider: Retain the default value (this will be set in Stage 2: Set the sense clock frequency)
- Clock source: Direct
  
  Note: Use spread spectrum clock (SSC) or PRS clock as a clock source to deal with EMI/EMC issues. Take care of tuning-based on design recommendations. See AN85951 – PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide for more details on usage of different clock sources.
- Number of sub-conversions: 60
  
  '60'is a good starting point to ensure a fast scan time and sufficient signal. This value is adjusted as required in Stage 3: Fine tune for required SNR, power, and refresh rate.
- Finger threshold: 65535
  
  Finger threshold is set to maximum to avoid waking up the device from the WoT mode due to touch detection; this is required to find the signal and SNR.
- Noise threshold: 10
- Negative noise threshold: 10
- Low baseline reset: 10
- ON debounce: 3
  
  These threshold values reduce the influence of the baseline on the sensor signal, which helps to get the true difference count. These parameters are set in Stage 4: Tune threshold parameters.
  
  Next, select Button0 from the left pane, and repeat the same configuration for that sensor as well.
  
  Figure 24. CAPSENSE™ Configurator – Widget Details tab
Go to the Scan Configuration tab to select the pins and the scan slots. Do the following:

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

B. Configure the scan slots using the Auto-assign slots option. The other option is to allot each sensor a scan slot-based on the entered slot number.

C. Check the notice list for warnings or errors.

Figure 25. Scan configuration tab
Click Save to apply the settings.

Stage 2: Set the sense clock frequency

The sense clock is derived from the modulator clock using a 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 26 and Figure 27 for waveforms observed on the shield. Figure 26 shows proper charging when 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 27 shows incomplete settling (charging/discharging).

Figure 26. Proper charge cycle of a sensor

Figure 27. Improper charge cycle of a sensor

Program the board and launch CAPSENSE™ tuner.
Observe the charging waveform of the sensor as described earlier.
If the charging is incomplete, increase the sense clock divider. This can be done 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 button and observe the waveform again. Repeat this until complete settling is observed.
Click the Apply to Project button so that the configuration is saved to your project.

Figure 28. Sense clock divider setting
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.

Stage 3: Fine-tune for required SNR, power, and refresh rate

The sensor should be tuned to have a minimum SNR of 5:1 and a minimum signal of 50 to ensure reliable operation. The sensitivity can be increased by increasing number of sub-conversions and noise can be decreased by enabling filters.

Note: If sensor raw count saturates (equals Max Raw count) on touch, reduce Raw count calibration level(%). which helps in avoiding saturation.

The steps for optimizing these parameters are as follows:

Measure the SNR as mentioned in the Operation section.
If the SNR is less than 5:1 increase the number of sub-conversions. Edit the number of sub-conversions (N_sub) directly in the Widget/Sensor parameters tab of the CAPSENSE™ tuner.

Note: Number of sub-conversion should be greater than or equal to 8.
Load the parameters to the device and measure SNR as mentioned in Steps 10 and 11 in the Monitor data using the Tuner section.

Repeat steps 1 to 3 until the following conditions are met:
- Measured SNR from the previous stage is greater than 5:1
- Signal count is greater than 50

If the system is noisy (> 40% of signal), enable the filters.

This example has the CIC2 filter enabled, which increases the resolution for the same scan time. See AN234231 - Achieving lowest-power capacitive sensing with PSoC™ 4000T for detailed information on the CIC2 filter. Whenever CIC2 filter is enabled, it is recommended to enable the IIR filter for optimal noise reduction. Therefore this example has the IIR filter enabled as well.

Open CAPSENSE™ Configurator from ModusToolbox™ Quick Panel and select the appropriate filter as shown in Figure 29.

Figure 29. Filter settings in CAPSENSE™ Configurator
Enable the filter based on the type of noise in your system. See AN85951 – PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide for more details.
Click Save and program the device to update the filter settings.

Note : Increasing the number of sub-conversions and enabling filters will increase the scan time which in turn decreasing the responsiveness of the sensor. Increase in scan time also increases the power consumption. Therefore, the number of sub-conversions and filter configuration must be optimized to achieve a balance between SNR, power, and refresh rate.

Stage 4: Tune threshold parameters

Various thresholds, relative to the signal, need to be set for each sensor. Do the following in CAPSENSE™ tuner to set up the thresholds for a widget:

Switch to the Graph View tab and select Button0.
Touch the sensor and monitor the touch signal in the Sensor signal graph, as shown in Figure 30.

Figure 30. Sensor signal when the sensor is touched
Note the signal measured and set the thresholds according to the following recommendations:
- Finger threshold = 80% of the signal
- Noise threshold = 40% of the signal
- Negative noise threshold = 40% of the signal
- Hysteresis = 10% of signal
- Debounce = 3
Set the threshold parameters in the Widget/Sensor parameters section of the CAPSENSE™ Tuner:

Figure 31. Widget threshold parameters
For the LowPower0_Sns0 low power sensor, first configure the finger threshold to '65535' and wait for the application to enter Low-power mode. Since the finger threshold is set to maximum, touching the low-power button will not switch the application to Active mode. Repeat step 2 to 4 for the low-power button.
Apply the settings to the device by clicking Apply to Device.

Figure 32. Apply settings to device

After applying the configuration test the performance by touching the button. If your sensor is tuned correctly, you will observe the touch status go from 0 to 1 in the Status panel of the Graph View tab as shown in Figure 33. The status of the button is also indicated by LED2 in the kit; LED2 turns ON when the finger touches the button and turns OFF when the finger is removed.

Figure 33. Sensor status in CAPSENSE™ Tuner

Click Apply to Project as shown in Figure 34. The change is updated in the design.cycapsense file. Close CAPSENSE™ Tuner and launch CAPSENSE™ Configurator. All the changes in the CAPSENSE™ Tuner reflects in the CAPSENSE™ Configurator.

Figure 34. Apply settings to Project

Table 4. Sensor tuning parameters obtained for CY8CKIT-040T

Parameter	Button0	LowPower0
Signal	442	426
Finger threshold	353	340
Noise threshold	176	170
Negative noise threshold	176	170
Low baseline reset	30	30
Hysteresis	44	NA
ON debounce	3	3

Process time measurement

To set the optimum refresh rate of each power mode, we need to measure the process time of our application.

Follow these steps to measure the process time of the blocks of application code, while excluding the scan time.

Enable ENABLE_RUN_TIME_MEASUREMENT macro in main.c as follows:
```
#define ENABLE_RUN_TIME_MEASUREMENT (1u)
```
This macro enables the System tick configuration and runtime measurement functionalities.

Place the start_runtime_measurement() function call before your application code and the stop_runtime_measurement() function call after it. The stop_runtime_measurement() function will return the execution time in microseconds(µs).

   #if ENABLE_RUN_TIME_MEASUREMENT
      uint32_t run_time = 0;
      start_runtime_measurement();
   #endif

   /* User Application Code Start */
   .
   .
   .
   /* User Application Code Stop */

   #if ENABLE_RUN_TIME_MEASUREMENT
      run_time = stop_runtime_measurement();
   #endif

Run the application in Debug mode with breakpoints placed at the active_processing_time and alr_processing_time variables as follows:

   #if ENABLE_RUN_TIME_MEASUREMENT
      active_processing_time=stop_runtime_measurement();
   #endif
   and 
   #if ENABLE_RUN_TIME_MEASUREMENT
      alr_processing_time=stop_runtime_measurement();
   #endif

Read the variables by adding them into Expressions view tab.

Update related macros with above measured processing times in main.c as follows:

#define ACTIVE_MODE_PROCESS_TIME     (xx)

#define ALR_MODE_PROCESS_TIME        (xx)

Scan time measurement

The scan time is also required for calculating the refresh rate of the application power modes. The total scan time of all the widgets in this code example is 16 µs.

It can be calculated as follows:

The scan time includes the MSCLP initialization time, Cmod, and the total sub-conversions of the sensor.
To control the Cmod initialization sequence, set the "Enable Coarse initialization bypass" configurator option as listed in the following table: Table 5. Enable coarse initialization bypass

Enable coarse initialization bypass	Behaviour
TRUE	Cmod initialization happens only once before scanning the sensors of the widget
FALSE	Cmod initialization happens before scanning each sensor of the widget

Use the following equations to measure the widgets scan time based on coarse initialization bypass options selected:

Equation 2. Scan time calculation of a widget with coarse initialization bypass enabled
Equation 3. Scan time calculation of a widget with coarse initialization bypass disabled

where,

$n$ - Total number of sensors in the widget

$N_{init}$ - Number of init sub-conversions

$N_{sub}$ - Number of sub-conversions

$SnsClkDiv$ - Sense clock divider

$F_{mod}$ - Modulator clock frequency

$k$ - Measured Initialization time (MSCLP+Cmod).

This value of $k$ measured for this application is ~10 µs. It remains constant for all widgets.

The value of $k$ can be measured using oscilloscope as shown in Figure 35.

Figure 35. $k$ value measurement

Update the following macros in main.c using the scan time calculated. The value remains the same for both macros for this application.

#define ACTIVE_MODE_FRAME_SCAN_TIME     (xx)

#define ALR_MODE_FRAME_SCAN_TIME        (xx)

Note: If the application has more than one widget, add the scan times of individual widgets calculated.

Debugging

You can debug this project 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™ user guide.

By default, the debug option is disabled in the device configurator. To enable the debug option, see the Setup VDDA and Debug mode section. To achieve low power consumption, it is recommended to disable it.

Design and implementation

The project contains one button configured as a regular and low-power widget in CSD-RM sensing mode. See the Tuning procedure section for step-by-step instructions to configure other settings of the CAPSENSE™ Configurator.

There are two user LEDs used in this project. LED2 shows the button touch status: it turns ON when touched and turns OFF when the finger is lifted. LED3 shows the current low-power state of the application. See the following table for the LED3 response-based on the low-power state.

Table 6. LED3 state for different application power mode

Power mode state	LED3
Active	Blinks at a fast rate
Active low-refresh rate (ALR)	Blinks at a medium rate
Wake-on-touch (WoT)	Blinks at a slow rate

There are three power states defined for this project:

ACTIVE mode
Active low-refresh rate (ALR) mode
Wake-on-touch (WoT) mode

After reset, the device is in Active mode, and scans the regular CAPSENSE™ widgets with a high refresh rate (128 Hz). If user activity is detected in any other mode, the device is transferred to Active mode to provide the best user interface experience. This mode has the highest power consumption; therefore, your design should reduce the time spent in Active mode as much as possible.

If there is no user activity for a certain time (ACTIVE_MODE_TIMEOUT_SEC = 10 s), the application transitions to ALR mode. Here, the refresh rate is reduced to 32 Hz; this mode acts as an intermediate state before moving to the lowest-power mode (WoT mode). This mode can also be used for periodically updating baselines of sensors while there is no user activity for a long time.

Further non-activity for a certain time (ALR_MODE_TIMEOUT_SEC = 5 s) transitions the application to the lowest-power mode - Wake-on-touch mode, which scans the low-power widget at a low refresh rate (16 Hz) and processes the results without CPU intervention.

Note: An internal low-power timer (MSCLP timer) is available in CAPSENSE™ MSCLP hardware to set the refresh rate for each power mode as follows:

For ACTIVE and ALR modes: Use the Cy_CapSense_ConfigureMsclpTimer() function.
For WoT mode: Use the Wake-on-Touch scan interval in CAPSENSE™ Configurator.

The different power modes and transition conditions for a typical use case are as follows:

Figure 36. State machine showing different power states of the device

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.

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

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

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

Open Device Configurator from the Quick Panel.
Go to the System tab. Select the Power resource, and set the VDDA value under Operating conditions as follows:

Figure 37. Setting the VDDA supply in System tab of Device Configurator

By default, the Debug mode is disabled for this application to reduce power consumption. Enable the Debug mode to enable the SWD pins as follows:

Figure 38. Enable Debug mode in the System tab of Device Configurator

Resources and settings

Figure 39. EZI2C settings

Figure 40. PWM settings

Table 7. Application resources

Resource	Alias/object	Purpose
SCB (I2C) (PDL)	CYBSP_EZI2C	EZI2C slave driver to communicate with CAPSENSE™ Tuner
TCPWM	CYBSP_PWM	To show the power mode states
CAPSENSE™	CYBSP_MSC	CAPSENSE™ driver to interact with the MSC hardware and interface the CAPSENSE™ sensors
Digital pin	CYBSP_USER_LED2, CYBSP_USER_BTN	To show the button operation

Firmware flow

Figure 41. Firmware flowchart

Related resources

Resources	Links
Application notes	AN79953 – Getting started with PSoC™ 4 AN85951 – PSoC™ 4 and PSoC™ 6 MCU CAPSENSE™ design guide AN234231 – Achieving lowest-power capacitive sensing with PSoC™ 4000T
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) mtb-hal-cat2 – Hardware abstraction layer (HAL) library
Middleware on GitHub	CAPSENSE™ Middleware Library – CAPSENSE™ Middleware Library and documents
Tools	Eclipse IDE for ModusToolbox™ – ModusToolbox™ is a collection of easy-to-use software and tools enabling rapid development with Infineon MCUs, covering applications from embedded sense and control to wireless and cloud-connected systems using AIROC™ Wi-Fi and Bluetooth® connectivity devices.

Other resources

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

Document history

Document title: CE238886 – PSoC™ 4: MSCLP low-power self-capacitance button

Version	Description of change
1.0.0	New code example
2.0.0	Major update to support ModusToolbox™ v3.2 and CAPSENSE™ Middleware v5.0. This version is not backward compatible with previous versions of ModusToolbox™ software.

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Name		Name	Last commit message	Last commit date
Latest commit History 2 Commits
deps		deps
images		images
templates/TARGET_CY8CPROTO-040T/config		templates/TARGET_CY8CPROTO-040T/config
.cyignore		.cyignore
.gitignore		.gitignore
LICENSE		LICENSE
Makefile		Makefile
README.md		README.md
main.c		main.c

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PSoC™ 4: MSCLP low-power self-capacitance button

Requirements

Supported toolchains (make variable 'TOOLCHAIN')

Supported kits (make variable 'TARGET')

Hardware setup

Software setup

Using the code example

Create the project

Open the project

Operation

Monitor data using the Tuner

Operation at other voltages

Measure current at different power modes

Tuning procedure

Stage 1: Set the initial hardware parameters

Stage 2: Set the sense clock frequency

Stage 3: Fine-tune for required SNR, power, and refresh rate

Stage 4: Tune threshold parameters

Process time measurement

Scan time measurement

Debugging

Design and implementation

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

Resources and settings

Table 7. Application resources

Firmware flow

Related resources

Other resources

Document history

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PSoC™ 4: MSCLP low-power self-capacitance button

Requirements

Supported toolchains (make variable 'TOOLCHAIN')

Supported kits (make variable 'TARGET')

Hardware setup

Software setup

Using the code example

Create the project

Open the project

Operation

Monitor data using the Tuner

Operation at other voltages

Measure current at different power modes

Tuning procedure

Stage 1: Set the initial hardware parameters

Stage 2: Set the sense clock frequency

Stage 3: Fine-tune for required SNR, power, and refresh rate

Stage 4: Tune threshold parameters

Process time measurement

Scan time measurement

Debugging

Design and implementation

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

Resources and settings

Table 7. Application resources

Firmware flow

Related resources

Other resources

Document history

About

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License

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