PSOC™ 4: MSCLP Inductive Sensing Touch over Metal Keypad-2

This code example demonstrates the implementation of inductive sensing based Touch-over-Metal(ToM) keypad buttons. This low-power application showcases recommended power states and transitions and the tuning flow for inductive sensing based buttons. This example uses the multi sense Inductive™ sensing low-power technology (MSCLP - 5th-generation low-power Inductive™) to demonstrate different considerations to implement a low-power design.

View this README on GitHub.

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Requirements

ModusToolbox™ v3.3 or later

Note: This code example version requires ModusToolbox™ v3.3 and is not backward compatible with v3.2 or older versions.

Board Support Package (BSP) minimum required version: 3.3.0
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 v6.22 (ARM)
IAR C/C++ Compiler v9.50.2 (IAR)

Supported kits (make variable 'TARGET')

PSOC™ 4000T CAPSENSE™ Multi-Sense Prototyping Kit (CY8CPROTO-040T-MS) - 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 VDD at 3.3 V.

Software setup

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

This example requires ModusToolbox™ CAPSENSE™ and Multi-Sense Pack to be installed.

Using the code example

Create the project

The ModusToolbox™ tools package provides the Project Creator both as 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 "mtb-example-msclp-isx-tom-keypad-4-buttons-demo" application with the desired name "CY8CPROTO_040T_MS_demo" configured for the CY8CPROTO-040T BSP into the specified working directory, C:/mtb_projects:

project-creator-cli --board-id CY8CPROTO-040T-MS --app-id mtb-example-msclp-isx-tom-keypad-4-buttons-demo --user-app-name CY8CPROTO_040T_MS_demo --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 USB cable between the CY8CPROTO-040T-MS Kit and the PC with the Keypad-2 extension board, as shown in Figure 1.

Figure 1. Connecting the CY8CPROTO-040T-MS 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 will see the following error message if the Debug mode is disabled. This can be ignored, or enabling debug will solve this error.

"Error: Error connecting Dp: Cannot read IDR"

Press any of the sensors with your finger; LEDs turn ON, indicating the activation of different Inductive Sensing based sensors as shown in Figure 2.

Figure 2. Pressing the CY8CPROTO-040T-MS Kit with the PC

Table 1. LED states for different sensors

Sensor pressed LED indication

ISX button 0 LED 0 turns ON

ISX button 1 LED 1 turns ON

All LEDs will be OFF when none of the sensor buttons are pressed.

Sensor pressed	LED indication
ISX button 0	LED 0 turns ON
ISX button 1	LED 1 turns ON

Monitor data using CAPSENSE™ Tuner

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

You can also run the CAPSENSE™ tuner application standalone from {ModusToolbox™ install directory}/ModusToolbox/tools_{version}/capsense-configurator/capsense-tuner. In this case, after opening the application, select File > Open and then 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.
Ensure that the status LED is ON and not blinking; this indicates that the onboard KitProg3 is in CMSIS-DAP Bulk mode. See the Firmware-loader to learn how 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 as shown in Figure 3.

Figure 3. Tuner communication setup

Select I2C 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 as shown in Figure 4.

Figure 4. Tuner Communication Setup parameters
Click Connect or select Communication > Connect to establish a connection.

Figure 5. Establish connection
Click Start or select Communication > Start to begin data streaming from the device.

Figure 6. 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 pressed widget is highlighted in blue as shown in Figure 7.

Figure 7. Widget view of the CAPSENSE™ Tuner
Go to the Graph View tab to view the raw count, baseline, difference count, and status of each sensor. To view the sensor data for the different ISX buttons, select Button0_Rx0_Lx0 under Button0 and so on, respectively (see Figure 8 ).

Figure 8. Graph view of the CAPSENSE™ Tuner for the ISX button
Observe that the low-power widget sensor (LowPower0_Rx0_Lx0) raw count is plotted after the device completes the full frame scan (or detects a press) in WoT mode and moves to Active/ALR mode.

Figure 9. Graph view of the CAPSENSE™ Tuner for the low-power widget
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 10:1, and the signal count is above 50; select Button0 and Button0_Rx0_Lx0 sensor, and then click Acquire noise as shown in Figure 10.

Figure 10. 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. Press the ISX button on the Keypad-2 extension board before clicking Acquire noise to 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 10:1 and the signal count is above '50'.

The calculated SNR on this button is displayed, as shown in Figure 11. Based on the end system design, test the signal with a finger press force that matches the size of normal use case. Also, test using lighter presses that will be rejected by the system to ensure that they do not reach the finger threshold.

Figure 11. CAPSENSE™ Tuner - SNR measurement: Acquire signal
To measure the SNR of the low-power sensor (LowPower0_Rx0_Lx0), set the Finger threshold to max (65535) in Widget/Sensor Parameters as shown in Figure 12 for all 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 12. CAPSENSE™ update finger threshold

Figure 13. Apply changes to device

Repeat steps 10 and 11 to observe the SNR and signal count as shown in Figure 14.

Figure 14. CAPSENSE™ Tuner - SNR measurement: low-power widget

Operation at other voltages

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

The functionalities of this application is optimally tuned for 3.3 V. Observe that the basic functionalities work across other voltages.

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

Tuning procedure

Create custom BSP for your board

Follow the steps shown in ModusToolbox™ BSP Assistant user guide to create a custom BSP for your board having any device. 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 "Tuning the inductive-sensing solution" in the AN239751 Flyback inductive sensing (ISX) design guide and the "Selecting CAPSENSE™ hardware parameters" in AN85951 – PSOC™ 4 design guide to learn about the considerations for selecting each parameter value. In addition, see the section "Low-power Widget parameters" in AN234231 – Achieving lowest power capacitive sensing with PSOC™ 4000T for more details about the considerations for parameter values specific to low-power widgets.

Figure 20. Low-power widget tuning flow

Do the following to tune the button widget:

Stage 1: Set the initial hardware parameters
Stage 2: Set the Lx clock divider
Stage 3: Fine tune for the required SNR, power, and refresh rate
Stage 4: Tune 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 Figure 21 and save the changes.

Figure 21. 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 the Button widgets and low-power widgets as ISX-RM as shown in the Figure 22 below.

Figure 22. 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 23. 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.

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

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

Raw count calibration level(%) helps to achieve the required CDAC calibration levels (35% of maximum count by default) for all sensors in the widget, while maintaining the same sensitivity across the sensor elements.

Figure 24. 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 Lx Clock Divider)
- Clock source: Direct
- 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 the other widgets from the left pane, and repeat the same configuration for that sensor as well.
  
  Figure 25. 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 26. Scan configuration tab
Click Save to apply the settings.

Stage 2: Set the Lx Clock Divider

The Lx clock is derived from the modulator clock using a clock-divider and is used to scan the sensor. The Lx clock divider should be configured such that the pulse width of the sense clock is long enough to allow the sensor inductance to accumulate its energy completely while preventing prolonged charging which will waste scan time. This is verified by observing the current waveforms of the sensor series resistance Rtx, using an oscilloscope and active probes.

Follow the steps as below to obtain the Lx Clock Divider value-

Find the expected/approximate value of the Lx Clock Divider using the following equation-

Equation 1. Lx Clock Divider Equation

Here,

Lx clock divider: Approximate value is obtained
$N_{tau}$: Settling constant. Set to 3 by default.
$Nphases$: Number of scan phases. Set to 4.
$F_{mod}(MHz)$: Modulator Clock Frequency in MHz. In this example, this is 46 MHz.
$L(uH)$: Obtain the inductance value using a LCR meter. For the buttons in this example, the value is around 34 uH.
$R_{stx}/R_{ext}$: The Tx resistor in series. 560 ohms in this kit.
$R_{switch}/R_{int}$: Internal switch resistance. The default value can be set as 100 ohms.
$Rinductor$: This value can be obtained using the LCR meter while obtaining the inductance value. It must be included when sensor is larger and can contribute to the total resistance value significantly.
Settling Shift: Provide a shift to consider actual settling time. Default value is 8. This can be changed based on oscilloscope observations.

This value serves only as a starting point for your measurements. Set this value in the CAPSENSE™ configurator as shown in the figure. Program the board.

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

Probe the Rtx resistor on both sides as shown in the figure. Then perform a math function on the oscilloscope to obtain the approximate current flowing through the resistor.

Calculate M1 = (Ch4 - Ch3) / Rstx On this kit the value of Rstx is 560 ohms.

Figure 27. Probing the series resistor
As shown in the figures below-

a. Ensure that the charging and discharging for the inductance is not incomplete. If so, increase the Lx Clock Divider.

b. Ensure that the inductance is not charging and discharging for a prolonged time. If so, decrease the Lx Clock Divider.

The Figure 28 and Figure 29 below show the two cases.

Figure 28. Improper charge cycle of a sensor with incomplete cycles

Figure 29. Improper charge cycle of a sensor with prolonged cycles

Obtain the Lx Clock Divider value where the charging and discharging are just completed as shown in the Figure 30 below.

Figure 30. Correct charge cycle of a sensor

Repeat this process for all the sensors. Each sensor might require a different Lx clock divider value to charge/discharge completely.

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

The sensor should be tuned to have a minimum SNR of 10:1 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.

The steps for optimizing these parameters are as follows:

Find the number of sub-conversions for each widget based on your Lx Clock Divider and scan time values (800 µs in this example).

$N_{sub}$ = $floor (Scan time * Lx Clock Frequency)$

where,

$Lx Clock Frequency$ = $F_{mod}$ (MHz) / Lx Clock Divider

$F_{mod}$ (MHz) = 46 MHz (default)
Measure the SNR as mentioned in the Operation section.
If the SNR is less than 10:1 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 10:1
- 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 31.

Figure 31. Filter settings in CAPSENSE™ Configurator
Enable the filter based on the type of noise in your system. See AN239751 - Flyback Inductive Sensing Design Guide and 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 32.

Figure 32. 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 33. Widget threshold parameters

Table 4. Sensor tuning parameters obtained for CY8CPROTO-040T-MS for Button0

Parameter	Button0	LowPower0
Signal	250	160
Finger threshold	200	100
Noise threshold	100	40
Negative noise threshold	100	40
Low baseline reset	30	30
Hysteresis	25	NA
ON debounce	3	3

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 34. 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 35. The status of the button is also indicated by LED1 in the kit; LED1 turns ON when the finger touches the button and turns OFF when the finger is removed.

Figure 35. Sensor status in CAPSENSE™ Tuner
Click Apply to Project as shown in Figure 36. 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 36. Apply settings to Project

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

$SnsClkDiv$ - The Lx clock divider for the widget

$F_{mod}$ - 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 37.

Figure 37. $k$ 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 the example to step through the code.

In Eclipse IDE

Use the <Application Name> Debug (KitProg3_MiniProg4) configuration in the Quick Panel. For more 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.

Design and implementation

The design has a ratiometric implementation of the following sensors:

Two Wake-on-Touch widget (2 elements), also called "Low-power Widget"
Two inductive sensing based button widgets (2 elements)

Following are the four LEDs used in this project:

LEDs 0 to 1 show the buttons' touch status: They are turned ON when the corresponding button is pressed and turned OFF when the finger is lifted.

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, the design should reduce the time spent in Active mode.

If there is no user activity for a certain period of time (ACTIVE_MODE_TIMEOUT_SEC = 10 s), the application transitions to ALR mode. Here, the refresh rate is reduced to 32 Hz; and hence 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 the baselines of sensors while there is no user activity for a long time.

Further non-activity for a certain time span (ALR_MODE_TIMEOUT_SEC = 5 s) transitions the application to the lowest-power mode, called the 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

Different power modes and transition conditions for a typical use case are shown in Figure 38.

Figure 38. 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 design guide and AN239751 - Flyback Inductive Sensing 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 using 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 shown in Figure 39.

Figure 39. 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 SWD pins as shown in Figure 40.

Figure 40. Enable the Debug mode in the System tab of Device Configurator

Resources and settings

Figure 41. EZI2C settings

Table 7. Application resources

Resource	Alias/object	Purpose
SCB (I2C) (PDL)	CYBSP_EZI2C	EZI2C slave driver to communicate with CAPSENSE™ Tuner
CAPSENSE™	CYBSP_MSC	CAPSENSE™ driver to interact with the MSC hardware and interface the CAPSENSE™ sensors

Firmware flow

Figure 42. Firmware flowchart

Related resources

Resources	Links
Application notes	AN79953 – Getting started with PSOC™ 4 AN234231 – PSOC™ 4 – Achieving lowest-power capacitive sensing with PSOC™ 4000T AN85951 – PSOC™ 4 design guide AN239751 - Flyback Inductive Sensing Design Guide
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 – 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: CE240147 – PSOC™ 4: MSCLP Inductive Sensing Touch over Metal Keypad-2

Version	Description of change
1.0.0	New code example
2.0.0	Major update to support ModusToolbox™ v3.3. This version is not backward compatible with previous versions of ModusToolbox™
2.1.0	Major update to support ModusToolbox™ v3.4. This version is not backward compatible with previous versions of ModusToolbox™

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