How to configure and use the STM32’s ADC Analog Watchdog feature
1. Introduction
In most of the STM32’s ADC (Analog Digital Converter), there is a feature called the Analog Watchdog. In this article we will learn how to configure it using the STM32CubeIDE tool and how to use it in an application.2. Prerequisites
- Hardware
- Micro USB cable used to power the Nucleo board from a host machine and to load the code into the STM32.
- Nucleo-L496
- Software: STM32CubeIDE
3. Theory
In this article we will use an STM32L496 Microcontroller. If you are using another STM32, please refer to the reference manual to check if there are any differences with what is presented in this article.First, let’s review the Analog Watchdog feature of the ADC. The analog watchdog monitors whether some channels remain within a configured voltage range (window).
You can define a low threshold and a high threshold as shown above which will define your “window” or guarded area. In this article we will use the AWD1 (Analog Watchdog 1) and enable it on a specific analog channel. We will use PA4 as the analog channel that will enable AED1. We will define a low and high threshold. A full range conversion for a 12-bit ADC bit is 4096.
For this article we will use the following thresholds:
High Threshold: 3000
Low Threshold: 1000
The AWD1 analog watchdog status bit is set if the analog voltage converted by the ADC is below the low threshold or above the high threshold. A potentiometer will be connected and used on PA4 to test the detection of the analog watchdog. We will enable the interrupt on the AWD1 to generate an interrupt if the converted value is outside the Analog Watchdog Window. If the converted value on the channel is outside the window, we will turn on the Nucleo board’s LEDs LD2 and LD3.
4. Steps
-
Open STM32CubeIDE
-
Create a new project using the NUCLEO-L496ZG board
-
Give a name to the project
-
Initialize all peripherals with their default mode settings by clicking on Yes
-
Configure ADC1
We will do a continuous conversion mode on channel 9 which is PA4.
The ADC1 can be found in the Pinout & Configuration Tab of the STM32CubeIDE under “Analog”.
-
Enable ADC1 Channel 9 which is an alternate function for PA4
-
Configure ADC1 Parameters settings
-
Change the sampling Time of channel 9
-
Enable Analog Watchdog 1
-
Configure the Analog Watchdog 1
High Threshold: 3000
Low Threshold: 1000
We will also enable the Interrupt mode so that an interrupt is generated when the converted channel is outside the defined window.
-
Enable ADC1 Interrupt
-
Generate Code
-
Add code
In main.c, add the declaration of these variables:
/* USER CODE BEGIN PV */ __IO uint16_t uhADCxConvertedValue = 0; /* Variable to report ADC analog watchdog status: */ /* RESET <=> voltage into AWD window */ /* SET <=> voltage out of AWD window */ uint8_t ubAnalogWatchdogStatus = RESET; /* Set into analog watchdog interrupt callback */ /* USER CODE END PV */
In USER CODE SECTION 4 add the call back function for the Analog WatchDog mode of the ADC:
/* USER CODE BEGIN 4 */
/**
* @brief Analog watchdog callback in non blocking mode.
* @param hadc: ADC handle
* @retval None
*/
void HAL_ADC_LevelOutOfWindowCallback(ADC_HandleTypeDef* hadc)
{
/* Set variable to report analog watchdog out of window status to main */
/* program. */
uhADCxConvertedValue = HAL_ADC_GetValue(&hadc1);
ubAnalogWatchdogStatus = SET;
}
/* USER CODE END 4 */
We need to add code to start the ADC Conversion.
/* USER CODE BEGIN 2 */
if (HAL_ADC_Start_IT(&hadc1) != HAL_OK)
{
Error_Handler();
}
/* USER CODE END 2 */
Now we add code on the main function to turn the LEDs LD2 and LD3 on or off depending on the Analog Watchdog event.
/* USER CODE BEGIN WHILE */
while (1)
{
/* Turn-on/off LED2 and LED3 in function of ADC conversion result */
/* - Turn-off if voltage is into AWD window */
/* - Turn-on if voltage is out of AWD window */
/* Variable of analog watchdog status is set into analog watchdog */
/* interrupt callback */
if (ubAnalogWatchdogStatus == SET)
{
HAL_GPIO_WritePin(GPIOB, LD3_Pin|LD2_Pin, GPIO_PIN_SET);
}
else
{
HAL_GPIO_WritePin(GPIOB, LD3_Pin|LD2_Pin, GPIO_PIN_RESET);
}
ubAnalogWatchdogStatus = RESET;
HAL_Delay(1);
/* USER CODE END WHILE */
-
Prepare your HW setup
-
Build the project, enter debug mode and run the code
After the project is built, enter a debug session and then click on the Resume icon to run the code.
Now if you change the potentiometer position you will see that the LEDs will turn on and off depending on whether the converted channel is outside the analog watchdog window or not.
5. Links
STM32CubeIDE - Integrated Development Environment for STM32 - STMicroelectronicsNUCLEO-L496ZG - STM32 Nucleo-144 development board with STM32L496ZG MCU, supports Arduino, ST Zio and morpho connectivity - STMicroelectronics
STM32L47xxx, STM32L48xxx, STM32L49xxx and STM32L4Axxx advanced Arm®-based 32-bit MCUs - Reference manual
Datasheet - STM32L496xx - Ultra-low-power Arm® Cortex®-M4 32-bit MCU+FPU, 100 DMIPS, up to 1 MB Flash, 320 KB SRAM, USB OTG FS, audio, external SMPS
