PSoC™ 6 MCU: SAR ADC low-power sensing - thermistor and ALS

This code example demonstrates low-power sensing of a thermistor and ambient light sensor (ALS) using the SAR ADC of the PSoC™ 6 MCU. This code example is supported only for devices that have an SAR ADC capable of operating in System deepsleep mode.

Sensor voltages are measured by the SAR ADC while the device is in System deepsleep mode resulting in a power-efficient solution.

In the code example, the temperature value in degree celsius and ambient light in percentage are displayed on the UART terminal every half second.

View this README on GitHub.

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Requirements

• ModusToolbox™ software v3.0 or later (tested with v3.0)

• Board support package (BSP) minimum required version: 4.0.0

• Programming language: C

• Associated parts: All CY8C62x4 parts

Supported toolchains (make variable 'TOOLCHAIN')

• GNU Arm® embedded compiler v10.3.1 (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™ 62S4 pioneer kit (CY8CKIT-062S4) - Default value of TARGET

Hardware setup

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

Software setup

Install a terminal emulator if you don't have one. Instructions in this document use Tera Term.

This example requires no additional software or tools.

Using the code example

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

In Eclipse IDE for ModusToolbox™ software

1. Click the New Application link in the Quick Panel (or, use File > New > ModusToolbox™ Application). This launches the Project Creator tool.

2. Pick a kit supported by the code example from the list shown in the Project Creator - Choose Board Support Package (BSP) dialog.

   When you select a supported kit, the example is reconfigured automatically to work with the kit. To work with a different supported kit later, use the Library Manager to choose the BSP for the supported kit. You can use the Library Manager to select or update the BSP and firmware libraries used in this application. To access the Library Manager, click the link from the Quick Panel.

   You can also just start the application creation process again and select a different kit.

   If you want to use the application for a kit not listed here, you may need to update the source files. If the kit does not have the required resources, the application may not work.

3. In the Project Creator - Select Application dialog, choose the example by enabling the checkbox.

4. (Optional) Change the suggested New Application Name.

5. The Application(s) Root Path defaults to the Eclipse workspace which is usually the desired location for the application. If you want to store the application in a different location, you can change the Application(s) Root Path value. Applications that share libraries should be in the same root path.

6. Click Create to complete the application creation process.

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

In command-line interface (CLI)

ModusToolbox™ software provides the Project Creator as both a GUI tool and the command line tool, "project-creator-cli". The CLI tool can be used to create applications from a CLI terminal or from within batch files or shell scripts. This tool is available in the {ModusToolbox™ software install directory}/tools_{version}/project-creator/ directory.

Use a CLI terminal to invoke the "project-creator-cli" tool. On Windows, use the command line "modus-shell" program provided in the ModusToolbox™ software installation instead of a standard Windows command-line application. This shell provides access to all ModusToolbox™ software tools. You can access it by typing modus-shell in the search box in the Windows menu. In Linux and macOS, you can use any terminal application.

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

Argument	Description	Required/optional
--board-id	Defined in the <id> field of the BSP manifest	Required
--app-id	Defined in the <id> field of the CE manifest	Required
--target-dir	Specify the directory in which the application is to be created if you prefer not to use the default current working directory	Optional
--user-app-name	Specify the name of the application if you prefer to have a name other than the example's default name	Optional

The following example clones the "mtb-example-low-power-sar-adc-thermistor-als" application with the desired name "LowPowerSarAdcThermistorAls" configured for the CY8CKIT-062S4 BSP into the specified working directory, C:/mtb_projects:

project-creator-cli --board-id CY8CKIT-062-WIFI-BT --app-id mtb-example-psoc6-low-power-sar-adc-thermistor-als --user-app-name LowPowerSarAdcThermistorAls --target-dir "C:/mtb_projects"

Note: The project-creator-cli tool uses the git clone and make getlibs commands to fetch the repository and import the required libraries. For more details, see the "Project creator tools" section of the ModusToolbox™ software user guide (locally available at {ModusToolbox™ software install directory}/docs_{version}/mtb_user_guide.pdf).

In third-party IDEs

Use one of the following options:

• Use the standalone Project Creator tool:

  1. Launch Project Creator from the Windows Start menu or from {ModusToolbox™ software install directory}/tools_{version}/project-creator/project-creator.exe.

  2. In the initial Choose Board Support Package screen, select the BSP, and click Next.

  3. In the Select Application screen, select the appropriate IDE from the Target IDE drop-down menu.

  4. Click Create and follow the instructions printed in the bottom pane to import or open the exported project in the respective IDE.

• Use command-line interface (CLI):

  1. Follow the instructions from the In command-line interface (CLI) section to create the application.

  2. Export the application to a supported IDE using the make <ide> command.

  3. Follow the instructions displayed in the terminal to create or import the application as an IDE project.

For a list of supported IDEs and more details, see the "Exporting to IDEs" section of the ModusToolbox™ software user guide (locally available at {ModusToolbox™ software install directory}/docs_{version}/mtb_user_guide.pdf).

Operation

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

2. Open a terminal program and select the KitProg3 COM port. Set the serial port parameters to 8N1 and 115200 baud.

3. Program the board using one of the following:

   Using Eclipse IDE for ModusToolbox™ software

   1. Select the application project in the Project Explorer.

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

   Using CLI

   From the terminal, execute the make program command to build and program the application using the default toolchain to the default target. The default toolchain is specified in the application's Makefile but you can override this value manually:

   make program TOOLCHAIN=<toolchain>
   

   Example:

   make program TOOLCHAIN=GCC_ARM
   

4. After programming, the application starts automatically. Confirm that the following is displayed on the UART terminal.

   Figure 1. Sensor readings in terminal

   

5. Touch the thermistor on the board and observe the change in the temperature readings on the terminal.

6. Block or increase the light over the ambient light sensor and observe the change in the percentage readings on the terminal.

7. Confirm that the user LED turns ON, when the light over the ambient light sensor is blocked.

Debugging

You can debug the example to step through the code. In the IDE, use the <Application Name> Debug (KitProg3_MiniProg4) configuration in the Quick Panel. For details, see the "Program and debug" section in the Eclipse IDE for ModusToolbox™ software user guide.

Note: On the CM4 CPU (Only while debugging), some code in main() may execute before the debugger halts at the beginning of main(). This means that some code executes twice - once before the debugger stops execution, and again after the debugger resets the program counter to the beginning of main(). See KBA231071 to learn about this and for the workaround.

Design and implementation

The SAR ADC is configured with three channels - two differential channels for the thermistor and one single-ended channel for the ambient light sensor. The interface circuit and the resources used in the device are shown in Figure 2.

Figure 2. Sensor interface

This example demonstrates a low-power sensing solution using the SAR ADC, which is configured to operate in System deepsleep mode. That is, while the CPU and other peripherals are turned OFF, the SAR ADC continues to scan the inputs and load the results into the FIFO. Scan is initiated by the timer configured to trigger the SAR ADC at a 400-Hz rate. The CPU wakes up only when the FIFO accumulates the configured number of samples; in this case, after accumulating 120 samples from 40 scans (120 samples / 3 channels). With the timer period of 2.5 ms (1/400), the CPU is woken up every 100 ms (40 x 2.5 ms).

The CPU reads the FIFO data every 100 ms, and passes it through first-order IIR low-pass filter algorithm. The filtered values are used to calculate the temperature in degree celsius and ambient light intensity in percentage. The user LED is turned ON or OFF depending on the ambient light intensity value. The calculated values of temperature and ambient light intensity are also sent over UART every 500 ms.

Figure 3. Flowchart

Figure 4. Timing diagram and average current calculation

The current consumed by the PSoC™ 6 MCU device can be measured on the kit at the appropriate header. See the kit user guide for details. The bench current measurement for different states of the firmware is shown in Table 1. Note that the thermistor circuit current is excluded from the readings. Current is calculated by setting the PSoC™ 6 MCU GPIO, driving the thermistor, to 0. In addition, to get current readings for different states, certain modifications are made in the main.c code as described in Table 1.

Table 1. Current measurement

State	Average current
Analog resources configured but SAR ADC conversion is not started (timer is disabled). Device is put to system deepsleep mode	8 µA
SAR ADC samples the input in system deepsleep mode every 2.5 ms, but FIFO interrupt is disabled which causes device to remain in system deepsleep mode	52 µA
Normal operation - FIFO interrupt is enabled which causes device to wake up periodically every 100 ms to process the ADC data and transfer the result over UART every 500 ms	74 µA

Figure 5. Captured current waveform

Resources and settings

This code example uses the custom configuration defined in the design.modus file located in the <application_folder>/templates/TARGET_<BSP-NAME>/config/design.modus folder. Important configurations are highlighted in Figure 6 to Figure 12.

Figure 6. SAR common parameters for all channels

Figure 7. SAR channel parameters

Figure 8. SAR global parameters

Figure 9. FIFO parameters

Figure 10. AREF, Deep Sleep Clock, LPOSC and timer parameters

Figure 11. Power parameters

Figure 12. Clock parameters

Table 2. Application resources

Resource	Alias/object	Purpose
SAR (PDL)	SAR	SAR driver to measure sensor voltages
SYSANALOG (PDL)	PASS	SYSANALOG driver for AREF, timer and deepsleep clock configuration
UART (HAL)	cy_retarget_io_uart_obj	UART HAL object used by retarget-io for debug UART port
GPIO (HAL)	CYBSP_USER_LED	User LED

Related resources

Resources	Links
Application notes	AN228571 – Getting started with PSoC™ 6 MCU on ModusToolbox™ software AN215656 – PSoC™ 6 MCU: Dual-CPU system design AN221774 – Getting started with PSoC™ 6 MCU on PSoC™ Creator AN210781 – Getting started with PSoC™ 6 MCU with Bluetooth® LE connectivity on PSoC™ Creator
Code examples	Using ModusToolbox™ software on GitHub Using PSoC™ Creator
Device documentation	PSoC™ 6 MCU datasheets PSoC™ 6 technical reference manuals
Development kits	Select your kits from the evaluation board finder
Libraries on GitHub	mtb-pdl-cat1 – PSoC™ 6 peripheral driver library (PDL) mtb-hal-cat1 – Hardware abstraction layer (HAL) library retarget-io – Utility library to retarget STDIO messages to a UART port
Middleware on GitHub	capsense – CAPSENSE™ library and documents psoc6-middleware – Links to all PSoC™ 6 MCU middleware emeeprom – Emulated EEPROM middleware
Tools	Eclipse IDE for ModusToolbox™ software – ModusToolbox™ software is a collection of easy-to-use software and tools enabling rapid development with Infineon MCUs, covering applications from embedded sense and control to wireless and cloud-connected systems using AIROC™ Wi-Fi and Bluetooth® connectivity devices. PSoC™ Creator – IDE for PSoC™ and FM0+ MCU development

Other resources

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

For PSoC™ 6 MCU devices, see How to design with PSoC™ 6 MCU - KBA223067 in the Infineon Developer community.

Document history

Document title: CE230699 - PSoC™ 6 MCU SAR ADC low-power sensing - thermistor and ambient light Sensor

Version	Description of change
1.0.0	New code example
2.0.0	Updated code to support version v2.X of the CY8CKIT-062S4 BSP
2.1.0	1. Updated flowchart and timing diagram 2. Updated the custom design file to use SAR personality v4.0
3.0.0	Major update to support ModusToolbox™ v3.0. This version is not backward compatible with previous versions of ModusToolbox™.

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