How to Configure STM32L4 Sleep Modes with RTC for 1Hz Sensor Polling

Introduction

In this tutorial, we will guide you through the process of configuring the STM32L4 microcontroller to enter low-power sleep modes, utilizing the Real-Time Clock (RTC) for a 1Hz sensor polling mechanism. This method is essential for battery-operated devices, enabling extended battery life while maintaining functionality.

Prerequisites

• Basic understanding of embedded systems and STM32 microcontrollers.
• STM32L4 development board (e.g., Nucleo or Discovery).
• STM32CubeIDE installed on your computer.
• Familiarity with C programming.

Parts/Tools

• STM32L4 development board
• USB cable for programming
• Optional: Sensor for polling (e.g., temperature sensor)

Steps

1. Set Up Your Development Environment
   • Open STM32CubeIDE.
   • Create a new STM32 project for your specific STM32L4 board.
2. Configure the RTC
   • In the STM32CubeMX perspective of STM32CubeIDE, enable the RTC peripheral.
   • Set the RTC to use the LSI (Low-Speed Internal) oscillator for low-power operation.
   • Configure the RTC to trigger an interrupt every second:

   RTC_HandleTypeDef hrtc;
   hrtc.Init.HourFormat = RTC_HOURFORMAT_24;
   hrtc.Init.AsynchPrediv = 127; // Configure for 1Hz
   hrtc.Init.SynchPrediv = 255;
   HAL_RTC_Init(&hrtc);

3. Configure Low-Power Sleep Mode
   • Set up the sleep mode in your main application code:

   void enter_low_power_mode(void) {
       HAL_PWR_EnterSLEEPMode(PWR_MAINREGULATOR_ON, PWR_SLEEPENTRY_WFI);
   }

4. Implement RTC Interrupt Handler
   • Create the RTC interrupt service routine (ISR) to handle the wakeup event:

   void RTC_IRQHandler(void) {
       HAL_RTC_AlarmIRQHandler(&hrtc);
   }

   • After waking up, read your sensor data:

   void HAL_RTC_AlarmAEventCallback(RTC_HandleTypeDef *hrtc) {
       read_sensor_data(); // Function to read the sensor data
       enter_low_power_mode(); // Return to low power mode
   }

5. Write Sensor Data Reading Function
   • Implement the function to read data from your sensor:

   void read_sensor_data(void) {
       // Code to read sensor data
       // e.g. HAL_I2C_Master_Receive() or similar
   }

Troubleshooting

• RTC Not Triggering: Ensure the RTC is properly configured and initialized. Check the LSI clock is stable.
• Microcontroller Not Entering Sleep Mode: Verify that all peripherals not needed during sleep are disabled.
• Sensor Data Not Updating: Check the sensor connection and I2C/SPI configurations.

Conclusion

By following this tutorial, you have successfully configured the STM32L4 to utilize low-power sleep modes with RTC wakeup for efficient 1Hz sensor polling. This approach not only optimizes power consumption but also ensures that your application remains responsive. Experiment with different sleep modes and configurations to further enhance your device’s efficiency.