How to Read Button with STM32 Nucleo-64 | STM32 Programming Tutorial 2

byee-diary • • 4 min read
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In this  STM Programming Tutorial we will use hal read function to read the button state and turn on or off a LED according to whether the button is low(when pressed) or high(not pressed). We will be using the STM32Cube IDE which uses internally GCC compiler for ARM to configure the STM32F401RE microcontroller peripherals, here the LED and button pins, the clock system and write the C  program code. The circuit diagram for this tutorial is shown below.

Button with STM32 Nucleo-64

In STM32Cube, we can use the hal read function HAL_GPIO_ReadPin()which is similar to digitalRead() function. The syntax of this hal read function is below:

HAL_GPIO_ReadPin(): Reads the input state of a pin.

Here we want to use this function to read the state of the button, low or high. To write the program first we have to set the PC8 as input pin through the STM32Cube Pin layout user interface. We can also apply label like BTN. Similarly we have to configure the LED pin also which is connected to pin PB1 which was covered in the guide LED blink with STM32 Nucleo-64 board with Hal Write function. Also we have to configure the pin name, state, pullup or pulldown or floating, speed etc. and regnerate the C code.

The part of the code that reads the button state and turns on/off the LED is below.

// Read the state of the button

if (HAL_GPIO_ReadPin(BTN_GPIO_Port, BTN_Pin) == GPIO_PIN_RESET)

{

// Button is pressed (grounded), turn the LED ON

HAL_GPIO_WritePin(LED_GPIO_Port, LED_Pin, GPIO_PIN_SET);

}

else

{

// Button is not pressed, turn the LED OFF

HAL_GPIO_WritePin(LED_GPIO_Port, LED_Pin, GPIO_PIN_RESET);

}

Note that the button pin was set to use internal pull up and so the logic in the above code should make sense.

The whole C program code to read the button and control a LED is below.

/* USER CODE BEGIN Header */
/**
  ******************************************************************************
  ee-diary.com
  ******************************************************************************
  */

/* Includes ------------------------------------------------------------------*/
#include "main.h"


/* Private variables ---------------------------------------------------------*/
UART_HandleTypeDef huart2;


/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_USART2_UART_Init(void);

int main(void)
{
  /* MCU Configuration--------------------------------------------------------*/
  /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
  HAL_Init();
  /* Configure the system clock */
  SystemClock_Config();
  /* Initialize all configured peripherals */
  MX_GPIO_Init();
  MX_USART2_UART_Init();
  /* Infinite loop */
  while (1)
  {
    // Read the state of the button
    if (HAL_GPIO_ReadPin(BTN_GPIO_Port, BTN_Pin) == GPIO_PIN_RESET)
    {
      // Button is pressed (grounded), turn the LED ON
      HAL_GPIO_WritePin(LED_GPIO_Port, LED_Pin, GPIO_PIN_SET);
    }
    else
    {
      // Button is not pressed, turn the LED OFF
      HAL_GPIO_WritePin(LED_GPIO_Port, LED_Pin, GPIO_PIN_RESET);
    }

    // Small delay to debounce the button
    HAL_Delay(50);
  }
}

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_SCALE2);

  /** Initializes the RCC Oscillators according to the specified parameters
  * in the RCC_OscInitTypeDef structure.
  */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
  RCC_OscInitStruct.HSIState = RCC_HSI_ON;
  RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;
  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_DIV2;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;

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

static void MX_USART2_UART_Init(void)
{
  huart2.Instance = USART2;
  huart2.Init.BaudRate = 115200;
  huart2.Init.WordLength = UART_WORDLENGTH_8B;
  huart2.Init.StopBits = UART_STOPBITS_1;
  huart2.Init.Parity = UART_PARITY_NONE;
  huart2.Init.Mode = UART_MODE_TX_RX;
  huart2.Init.HwFlowCtl = UART_HWCONTROL_NONE;
  huart2.Init.OverSampling = UART_OVERSAMPLING_16;
  if (HAL_UART_Init(&huart2) != HAL_OK)
  {
    Error_Handler();
  }
}

static void MX_GPIO_Init(void)
{
  GPIO_InitTypeDef GPIO_InitStruct = {0};

  /* GPIO Ports Clock Enable */
  __HAL_RCC_GPIOC_CLK_ENABLE();
  __HAL_RCC_GPIOH_CLK_ENABLE();
  __HAL_RCC_GPIOA_CLK_ENABLE();
  __HAL_RCC_GPIOB_CLK_ENABLE();

  /* Configure GPIO pin Output Level */
  HAL_GPIO_WritePin(LD2_GPIO_Port, LD2_Pin, GPIO_PIN_RESET);
  HAL_GPIO_WritePin(LED_GPIO_Port, LED_Pin, GPIO_PIN_RESET);

  /* Configure GPIO pin : B1_Pin */
  GPIO_InitStruct.Pin = B1_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_IT_FALLING;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  HAL_GPIO_Init(B1_GPIO_Port, &GPIO_InitStruct);

  /* Configure GPIO pin : LD2_Pin */
  GPIO_InitStruct.Pin = LD2_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
  GPIO_InitStruct.Pull = GPIO_NOPULL;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
  HAL_GPIO_Init(LD2_GPIO_Port, &GPIO_InitStruct);

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

  /* Configure GPIO pin : BTN_Pin */
  GPIO_InitStruct.Pin = BTN_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_INPUT;
  GPIO_InitStruct.Pull = GPIO_PULLUP; // Use pull-up resistor
  HAL_GPIO_Init(BTN_GPIO_Port, &GPIO_InitStruct);
}

void Error_Handler(void)
{
  __disable_irq();
  while (1)
  {
  }
}

#ifdef  USE_FULL_ASSERT

void assert_failed(uint8_t *file, uint32_t line)
{
}
#endif /* USE_FULL_ASSERT */

The following video shows how  to write the code in STMCube IDE, how to configure pins, how to apply label and the operation of the circuit showing how the code works.

In the video you can see that when the button is pressed, the LED turns on. This circuit was simulated in Proteus Software and the STM32 Nucleo64 Board simulation model can be downloaded for free from the link below.

Download STM32 Nucleo Simulation Model

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