•

Paul Rodolf P. Castor

Published June 14, 2026

Time Project: Clock Using RT-Spark

A simple digital clock made using the RT-Spark Development Board with the STM32F407ZGT6 microcontroller.

IntermediateFull instructions provided2 hours16

Things used in this project

Hardware components

RT-Spark Development Board

Breadboard (generic)

Jumper wires (generic)

LED (generic)

Resistor 220 ohm

Oscilloscope

Software apps and online services

STM32CubeIDE

STM32CubeMX

Story

Introduction

This project demonstrate how timer interrupts can be used to keep track of time in an embedded system. Instead of using an external LCD module, the project uses the built-in LCD of the RT-Spark board.

The timer interrupt runs every 1 millisecond and continuously updates the hour, minute, second, and millisecond values. Every 100 milliseconds, the LCD is refreshed to show the latest time.

An LED is also used as a visual indicator. It flashes every second and slowly fades out using PWM control. The brightness starts at 100% and decreases to 0% during the first 600 milliseconds of each second.

This project shows how multiple peripherals can work together to create a simple but useful embedded application.

Built-in LCD setup

Create a new STM32 project.
Select the STM32F407ZGT6 MCU and keep the default settings.
Configure PF9 as GPIO Output.

Generate the code.

Turn on the LCD backlight in the program.

When powered on, the LCD backlight should light up, confirming that the display is receiving power.

LCD backlight testing:

LCD Communication Setup

After testing the backlight, the LCD communication interface was configured.

Set PD3 as LCD_RST.
Enable FSMC in STM32CubeMX.

Import the LCD libraries.Download the needed header and source files for the built-in LCD setup.

Source files (.c) = ProjectName/Core/Src

1 / 2 • Header files (.h) = ProjectName/Core/Inc

Generate the code and initialize the LCD.

LCD testing

After initialization, text and graphics can be displayed on the built-in LCD.

Software Setup

The built-in LCD of the RT-Spark board was used to display the clock, while timers were configured to handle timekeeping and LED fading.

1 / 6 • PF9 was configured as a GPIO Output pin. This pin controls the LCD backlight and allows the display to become visible after initialization, while PD3 was assigned as LCD_RST for the LCD reset signal.

The timer interrupt runs every 1 ms and performs the following:

Updates the current time.
Requests an LCD update every 100 ms.
Controls LED brightness using PWM.
Flashes the LED every second.

The main loop checks if an LCD update is requested. If the flag is set, the latest time values are displayed on the LCD.

When the interrupt sets the lcd_update, the latest time values are displayed on the LCD.

Hardware Setup

The LED is controlled using PWM to create the fading effect.

Result

The display was refreshed every 100 milliseconds, making the clock update smoothly and accurately. A timer interrupt running every 1 millisecond handled the timekeeping in the background, ensuring that the clock remained precise. At the same time, an external LED flashed once every second and gradually dimmed until it turned off, creating a smooth fade-out effect using PWM.

Testing with Oscilloscope

An oscilloscope was used to check the PWM signal generated by the STM32F407ZGT6. The waveform showed that the signal was working correctly and changing as expected. As the PWM duty cycle decreased, the LED became dimmer until it eventually turned off. This confirmed that the timer and PWM settings were configured properly and that the LED fade-out effect was working successfully.

Conclusion

This project successfully created a simple clock using the STM32F407ZGT6 microcontroller and the RT-Spark board's built-in LCD. The system was able to display the elapsed time accurately while using timer interrupts to keep track of time and PWM to create a smooth LED fading effect.

Schematics

Code

Main code

/* USER CODE BEGIN Header */
/**
  ******************************************************************************
  * @file           : main.c
  * @brief          : Main program body
  ******************************************************************************
  * @attention
  *
  * Copyright (c) 2026 STMicroelectronics.
  * All rights reserved.
  *
  * This software is licensed under terms that can be found in the LICENSE file
  * in the root directory of this software component.
  * If no LICENSE file comes with this software, it is provided AS-IS.
  *
  ******************************************************************************
  */
/* USER CODE END Header */
/* Includes ------------------------------------------------------------------*/
#include "main.h"

/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */
#include "drv_lcd.h"
#include "stdio.h"
/* USER CODE END Includes */

/* Private typedef -----------------------------------------------------------*/
/* USER CODE BEGIN PTD */

/* USER CODE END PTD */

/* Private define ------------------------------------------------------------*/
/* USER CODE BEGIN PD */

/* USER CODE END PD */

/* Private macro -------------------------------------------------------------*/
/* USER CODE BEGIN PM */

/* USER CODE END PM */

/* Private variables ---------------------------------------------------------*/
RTC_HandleTypeDef hrtc;

TIM_HandleTypeDef htim2;
TIM_HandleTypeDef htim3;

SRAM_HandleTypeDef hsram1;

/* USER CODE BEGIN PV */
volatile uint8_t updateled = 0;
volatile uint8_t lcd_update_requested = 0;

volatile uint16_t global_time = 0;

RTC_TimeTypeDef sTime = {0};
RTC_DateTypeDef sDate = {0};
/* USER CODE END PV */

/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_TIM2_Init(void);
static void MX_FSMC_Init(void);
static void MX_TIM3_Init(void);
static void MX_RTC_Init(void);
/* USER CODE BEGIN PFP */

/* USER CODE END PFP */

/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */
void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim) {
	if(htim->Instance == TIM2) {
		updateled = 1;
	}

	if(htim->Instance == TIM3) {
		global_time++;

		if(global_time >= 1000) {
			global_time = 0;
		}

		if(global_time % 100 == 0) {
			lcd_update_requested = 1;
		}
	}
}

void ledFade(uint16_t system_ms) {
    uint32_t duty_cycle = 0;

    // Use the absolute system time instead of a local counter
    if(system_ms <= 600) {
        duty_cycle = 159 - ((159 * (uint16_t)system_ms) / 600);
        __HAL_TIM_SET_COMPARE(&htim2, TIM_CHANNEL_1, duty_cycle);
    } else {
        // Explicitly keep the LED off from 601ms to 999ms
        __HAL_TIM_SET_COMPARE(&htim2, TIM_CHANNEL_1, 0);
    }


	}


void lcdUpdate() {
	HAL_RTC_GetTime(&hrtc, &sTime, RTC_FORMAT_BIN);
	HAL_RTC_GetDate(&hrtc, &sDate, RTC_FORMAT_BIN);

	char timeINlcd[20];

	sprintf(timeINlcd, "%02d:%02d:%02d:%03d", sTime.Hours, sTime.Minutes, sTime.Seconds, global_time);

    lcd_set_color(GREEN , BLACK);
	lcd_show_string(8, 100, 32, timeINlcd);
}
/* USER CODE END 0 */

/**
  * @brief  The application entry point.
  * @retval int
  */
int main(void)
{

  /* USER CODE BEGIN 1 */

  /* USER CODE END 1 */

  /* MCU Configuration--------------------------------------------------------*/

  /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
  HAL_Init();

  /* USER CODE BEGIN Init */

  /* USER CODE END Init */

  /* Configure the system clock */
  SystemClock_Config();

  /* USER CODE BEGIN SysInit */

  /* USER CODE END SysInit */

  /* Initialize all configured peripherals */
  MX_GPIO_Init();
  MX_TIM2_Init();
  MX_FSMC_Init();
  MX_TIM3_Init();
  MX_RTC_Init();
  /* USER CODE BEGIN 2 */
  HAL_TIM_Base_Start_IT(&htim2);
  HAL_TIM_Base_Start_IT(&htim3);

  HAL_TIM_PWM_Start(&htim2, TIM_CHANNEL_1);

  drv_lcd_init();
  lcd_clear(GREEN);
  /* USER CODE END 2 */

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
    /* USER CODE END WHILE */

    /* USER CODE BEGIN 3 */
	  if(updateled == 1) {
		  updateled = 0;
		  ledFade(global_time);
	  }

	  if(lcd_update_requested == 1) {
		  lcd_update_requested = 0;
		  lcdUpdate();
	  }

  }
  /* USER CODE END 3 */
}

/**
  * @brief System Clock Configuration
  * @retval None
  */
void SystemClock_Config(void)
{
  RCC_OscInitTypeDef RCC_OscInitStruct = {0};
  RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};

  /** Configure the main internal regulator output voltage
  */
  __HAL_RCC_PWR_CLK_ENABLE();
  __HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE1);

  /** Initializes the RCC Oscillators according to the specified parameters
  * in the RCC_OscInitTypeDef structure.
  */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI|RCC_OSCILLATORTYPE_LSI;
  RCC_OscInitStruct.HSIState = RCC_HSI_ON;
  RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;
  RCC_OscInitStruct.LSIState = RCC_LSI_ON;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE;
  if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
  {
    Error_Handler();
  }

  /** Initializes the CPU, AHB and APB buses clocks
  */
  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
                              |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_HSI;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;

  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_0) != HAL_OK)
  {
    Error_Handler();
  }
}

/**
  * @brief RTC Initialization Function
  * @param None
  * @retval None
  */
static void MX_RTC_Init(void)
{

  /* USER CODE BEGIN RTC_Init 0 */

  /* USER CODE END RTC_Init 0 */

  RTC_TimeTypeDef sTime = {0};
  RTC_DateTypeDef sDate = {0};

  /* USER CODE BEGIN RTC_Init 1 */

  /* USER CODE END RTC_Init 1 */

  /** Initialize RTC Only
  */
  hrtc.Instance = RTC;
  hrtc.Init.HourFormat = RTC_HOURFORMAT_24;
  hrtc.Init.AsynchPrediv = 127;
  hrtc.Init.SynchPrediv = 255;
  hrtc.Init.OutPut = RTC_OUTPUT_DISABLE;
  hrtc.Init.OutPutPolarity = RTC_OUTPUT_POLARITY_HIGH;
  hrtc.Init.OutPutType = RTC_OUTPUT_TYPE_OPENDRAIN;
  if (HAL_RTC_Init(&hrtc) != HAL_OK)
  {
    Error_Handler();
  }

  /* USER CODE BEGIN Check_RTC_BKUP */

  /* USER CODE END Check_RTC_BKUP */

  /** Initialize RTC and set the Time and Date
  */
  sTime.Hours = 0x0;
  sTime.Minutes = 0x0;
  sTime.Seconds = 0x0;
  sTime.DayLightSaving = RTC_DAYLIGHTSAVING_NONE;
  sTime.StoreOperation = RTC_STOREOPERATION_RESET;
  if (HAL_RTC_SetTime(&hrtc, &sTime, RTC_FORMAT_BCD) != HAL_OK)
  {
    Error_Handler();
  }
  sDate.WeekDay = RTC_WEEKDAY_FRIDAY;
  sDate.Month = RTC_MONTH_JUNE;
  sDate.Date = 0x5;
  sDate.Year = 0x26;

  if (HAL_RTC_SetDate(&hrtc, &sDate, RTC_FORMAT_BCD) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN RTC_Init 2 */

  /* USER CODE END RTC_Init 2 */

}

/**
  * @brief TIM2 Initialization Function
  * @param None
  * @retval None
  */
static void MX_TIM2_Init(void)
{

  /* USER CODE BEGIN TIM2_Init 0 */

  /* USER CODE END TIM2_Init 0 */

  TIM_ClockConfigTypeDef sClockSourceConfig = {0};
  TIM_MasterConfigTypeDef sMasterConfig = {0};
  TIM_OC_InitTypeDef sConfigOC = {0};

  /* USER CODE BEGIN TIM2_Init 1 */

  /* USER CODE END TIM2_Init 1 */
  htim2.Instance = TIM2;
  htim2.Init.Prescaler = 99;
  htim2.Init.CounterMode = TIM_COUNTERMODE_UP;
  htim2.Init.Period = 159;
  htim2.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
  htim2.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;
  if (HAL_TIM_Base_Init(&htim2) != HAL_OK)
  {
    Error_Handler();
  }
  sClockSourceConfig.ClockSource = TIM_CLOCKSOURCE_INTERNAL;
  if (HAL_TIM_ConfigClockSource(&htim2, &sClockSourceConfig) != HAL_OK)
  {
    Error_Handler();
  }
  if (HAL_TIM_PWM_Init(&htim2) != HAL_OK)
  {
    Error_Handler();
  }
  sMasterConfig.MasterOutputTrigger = TIM_TRGO_RESET;
  sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
  if (HAL_TIMEx_MasterConfigSynchronization(&htim2, &sMasterConfig) != HAL_OK)
  {
    Error_Handler();
  }
  sConfigOC.OCMode = TIM_OCMODE_PWM1;
  sConfigOC.Pulse = 0;
  sConfigOC.OCPolarity = TIM_OCPOLARITY_HIGH;
  sConfigOC.OCFastMode = TIM_OCFAST_DISABLE;
  if (HAL_TIM_PWM_ConfigChannel(&htim2, &sConfigOC, TIM_CHANNEL_1) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN TIM2_Init 2 */

  /* USER CODE END TIM2_Init 2 */
  HAL_TIM_MspPostInit(&htim2);

}

/**
  * @brief TIM3 Initialization Function
  * @param None
  * @retval None
  */
static void MX_TIM3_Init(void)
{

  /* USER CODE BEGIN TIM3_Init 0 */

  /* USER CODE END TIM3_Init 0 */

  TIM_ClockConfigTypeDef sClockSourceConfig = {0};
  TIM_MasterConfigTypeDef sMasterConfig = {0};

  /* USER CODE BEGIN TIM3_Init 1 */

  /* USER CODE END TIM3_Init 1 */
  htim3.Instance = TIM3;
  htim3.Init.Prescaler = 15;
  htim3.Init.CounterMode = TIM_COUNTERMODE_UP;
  htim3.Init.Period = 999;
  htim3.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
  htim3.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;
  if (HAL_TIM_Base_Init(&htim3) != HAL_OK)
  {
    Error_Handler();
  }
  sClockSourceConfig.ClockSource = TIM_CLOCKSOURCE_INTERNAL;
  if (HAL_TIM_ConfigClockSource(&htim3, &sClockSourceConfig) != HAL_OK)
  {
    Error_Handler();
  }
  sMasterConfig.MasterOutputTrigger = TIM_TRGO_RESET;
  sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
  if (HAL_TIMEx_MasterConfigSynchronization(&htim3, &sMasterConfig) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN TIM3_Init 2 */

  /* USER CODE END TIM3_Init 2 */

}

/**
  * @brief GPIO Initialization Function
  * @param None
  * @retval None
  */
static void MX_GPIO_Init(void)
{
  GPIO_InitTypeDef GPIO_InitStruct = {0};
  /* USER CODE BEGIN MX_GPIO_Init_1 */

  /* USER CODE END MX_GPIO_Init_1 */

  /* GPIO Ports Clock Enable */
  __HAL_RCC_GPIOF_CLK_ENABLE();
  __HAL_RCC_GPIOA_CLK_ENABLE();
  __HAL_RCC_GPIOE_CLK_ENABLE();
  __HAL_RCC_GPIOD_CLK_ENABLE();
  __HAL_RCC_GPIOG_CLK_ENABLE();

  /*Configure GPIO pin Output Level */
  HAL_GPIO_WritePin(BACKLIGHT_LCD_GPIO_Port, BACKLIGHT_LCD_Pin, GPIO_PIN_RESET);

  /*Configure GPIO pin Output Level */
  HAL_GPIO_WritePin(RESET_LCD_GPIO_Port, RESET_LCD_Pin, GPIO_PIN_RESET);

  /*Configure GPIO pin : BACKLIGHT_LCD_Pin */
  GPIO_InitStruct.Pin = BACKLIGHT_LCD_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  HAL_GPIO_Init(BACKLIGHT_LCD_GPIO_Port, &GPIO_InitStruct);

  /*Configure GPIO pin : RESET_LCD_Pin */
  GPIO_InitStruct.Pin = RESET_LCD_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  HAL_GPIO_Init(RESET_LCD_GPIO_Port, &GPIO_InitStruct);

  /* USER CODE BEGIN MX_GPIO_Init_2 */

  /* USER CODE END MX_GPIO_Init_2 */
}

/* FSMC initialization function */
static void MX_FSMC_Init(void)
{

  /* USER CODE BEGIN FSMC_Init 0 */

  /* USER CODE END FSMC_Init 0 */

  FSMC_NORSRAM_TimingTypeDef Timing = {0};

  /* USER CODE BEGIN FSMC_Init 1 */

  /* USER CODE END FSMC_Init 1 */

  /** Perform the SRAM1 memory initialization sequence
  */
  hsram1.Instance = FSMC_NORSRAM_DEVICE;
  hsram1.Extended = FSMC_NORSRAM_EXTENDED_DEVICE;
  /* hsram1.Init */
  hsram1.Init.NSBank = FSMC_NORSRAM_BANK3;
  hsram1.Init.DataAddressMux = FSMC_DATA_ADDRESS_MUX_DISABLE;
  hsram1.Init.MemoryType = FSMC_MEMORY_TYPE_SRAM;
  hsram1.Init.MemoryDataWidth = FSMC_NORSRAM_MEM_BUS_WIDTH_8;
  hsram1.Init.BurstAccessMode = FSMC_BURST_ACCESS_MODE_DISABLE;
  hsram1.Init.WaitSignalPolarity = FSMC_WAIT_SIGNAL_POLARITY_LOW;
  hsram1.Init.WrapMode = FSMC_WRAP_MODE_DISABLE;
  hsram1.Init.WaitSignalActive = FSMC_WAIT_TIMING_BEFORE_WS;
  hsram1.Init.WriteOperation = FSMC_WRITE_OPERATION_ENABLE;
  hsram1.Init.WaitSignal = FSMC_WAIT_SIGNAL_DISABLE;
  hsram1.Init.ExtendedMode = FSMC_EXTENDED_MODE_DISABLE;
  hsram1.Init.AsynchronousWait = FSMC_ASYNCHRONOUS_WAIT_DISABLE;
  hsram1.Init.WriteBurst = FSMC_WRITE_BURST_DISABLE;
  hsram1.Init.PageSize = FSMC_PAGE_SIZE_NONE;
  /* Timing */
  Timing.AddressSetupTime = 1;
  Timing.AddressHoldTime = 15;
  Timing.DataSetupTime = 60;
  Timing.BusTurnAroundDuration = 0;
  Timing.CLKDivision = 16;
  Timing.DataLatency = 17;
  Timing.AccessMode = FSMC_ACCESS_MODE_A;
  /* ExtTiming */

  if (HAL_SRAM_Init(&hsram1, &Timing, NULL) != HAL_OK)
  {
    Error_Handler( );
  }

  /* USER CODE BEGIN FSMC_Init 2 */

  /* USER CODE END FSMC_Init 2 */
}

/* USER CODE BEGIN 4 */

/* USER CODE END 4 */

/**
  * @brief  This function is executed in case of error occurrence.
  * @retval None
  */
void Error_Handler(void)
{
  /* USER CODE BEGIN Error_Handler_Debug */
  /* User can add his own implementation to report the HAL error return state */
  __disable_irq();
  while (1)
  {
  }
  /* USER CODE END Error_Handler_Debug */
}
#ifdef USE_FULL_ASSERT
/**
  * @brief  Reports the name of the source file and the source line number
  *         where the assert_param error has occurred.
  * @param  file: pointer to the source file name
  * @param  line: assert_param error line source number
  * @retval None
  */
void assert_failed(uint8_t *file, uint32_t line)
{
  /* USER CODE BEGIN 6 */
  /* User can add his own implementation to report the file name and line number,
     ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */
  /* USER CODE END 6 */
}
#endif /* USE_FULL_ASSERT */

Credits

MA REGINE BERMUDO

7 projects • 0 followers

Paul Rodolf P. Castor

57 projects • 9 followers

Time Project: Clock Using RT-Spark