DHT11 Humidity & Temperature Sensor with Blue Pill using STM32CubeIDE

Prerequisites

This project assumes you have already installed STM32CubeIDE. You need to have previously done a basic blink sketch with blue-pill using STM32CubeIDE. I have made a complete video from installing STM32CubeIDE to LED blink program. You can watch it by clicking this link. https://www.youtube.com/watch?v=kXg467nVd_A

Wiring Diagram

STM32CubeIDE Settings

Click RCC → High Speed Clock (HSE) to Crystal/Ceramic Resonator

Click Clock Configuration tab → HCLK (MHz) to 72

Click Pinout and Configuration tab

Click Timer → Click TIM1 →

Clock Source set to Internal Clock

Configuration → Parameter Settings →

Prescaler set to 71

Set PB9, PA1, PA4 and PA7 GPIO_Output

Additional code on top of STM32CubeIDE generated code

/* USER CODE BEGIN 0 */
#define DHT11_PORT GPIOB
#define DHT11_PIN GPIO_PIN_9
uint8_t RHI, RHD, TCI, TCD, SUM;
uint32_t pMillis, cMillis;
float tCelsius = 0;
float tFahrenheit = 0;
float RH = 0;

void microDelay (uint16_t delay)
{
  __HAL_TIM_SET_COUNTER(&htim1, 0);
  while (__HAL_TIM_GET_COUNTER(&htim1) < delay);
}

uint8_t DHT11_Start (void)
{
  uint8_t Response = 0;
  GPIO_InitTypeDef GPIO_InitStructPrivate = {0};
  GPIO_InitStructPrivate.Pin = DHT11_PIN;
  GPIO_InitStructPrivate.Mode = GPIO_MODE_OUTPUT_PP;
  GPIO_InitStructPrivate.Speed = GPIO_SPEED_FREQ_LOW;
  GPIO_InitStructPrivate.Pull = GPIO_NOPULL;
  HAL_GPIO_Init(DHT11_PORT, &GPIO_InitStructPrivate); // set the pin as output
  HAL_GPIO_WritePin (DHT11_PORT, DHT11_PIN, 0);   // pull the pin low
  HAL_Delay(20);   // wait for 20ms
  HAL_GPIO_WritePin (DHT11_PORT, DHT11_PIN, 1);   // pull the pin high
  microDelay (30);   // wait for 30us
  GPIO_InitStructPrivate.Mode = GPIO_MODE_INPUT;
  GPIO_InitStructPrivate.Pull = GPIO_PULLUP;
  HAL_GPIO_Init(DHT11_PORT, &GPIO_InitStructPrivate); // set the pin as input
  microDelay (40);
  if (!(HAL_GPIO_ReadPin (DHT11_PORT, DHT11_PIN)))
  {
    microDelay (80);
    if ((HAL_GPIO_ReadPin (DHT11_PORT, DHT11_PIN))) Response = 1;
  }
  pMillis = HAL_GetTick();
  cMillis = HAL_GetTick();
  while ((HAL_GPIO_ReadPin (DHT11_PORT, DHT11_PIN)) && pMillis + 2 > cMillis)
  {
    cMillis = HAL_GetTick();
  }
  return Response;
}

uint8_t DHT11_Read (void)
{
  uint8_t a,b;
  for (a=0;a<8;a++)
  {
    pMillis = HAL_GetTick();
    cMillis = HAL_GetTick();
    while (!(HAL_GPIO_ReadPin (DHT11_PORT, DHT11_PIN)) && pMillis + 2 > cMillis)
    {  // wait for the pin to go high
      cMillis = HAL_GetTick();
    }
    microDelay (40);   // wait for 40 us
    if (!(HAL_GPIO_ReadPin (DHT11_PORT, DHT11_PIN)))   // if the pin is low
      b&= ~(1<<(7-a));
    else
      b|= (1<<(7-a));
    pMillis = HAL_GetTick();
    cMillis = HAL_GetTick();
    while ((HAL_GPIO_ReadPin (DHT11_PORT, DHT11_PIN)) && pMillis + 2 > cMillis)
    {  // wait for the pin to go low
      cMillis = HAL_GetTick();
    }
  }
  return b;
}
/* USER CODE END 0 */

  /* USER CODE BEGIN 2 */
  HAL_TIM_Base_Start(&htim1);
  /* USER CODE END 2 */

 /* USER CODE BEGIN WHILE */
  while (1)
  {
    if(DHT11_Start())
    {
      RHI = DHT11_Read(); // Relative humidity integral
      RHD = DHT11_Read(); // Relative humidity decimal
      TCI = DHT11_Read(); // Celsius integral
      TCD = DHT11_Read(); // Celsius decimal
      SUM = DHT11_Read(); // Check sum
      if (RHI + RHD + TCI + TCD == SUM)
      {
        // Can use RHI and TCI for any purposes if whole number only needed
        tCelsius = (float)TCI + (float)(TCD/10.0);
        tFahrenheit = tCelsius * 9/5 + 32;
        RH = (float)RHI + (float)(RHD/10.0);
        // Can use tCelsius, tFahrenheit and RH for any purposes
      }
      if (TCI < 15) 
      {
        HAL_GPIO_WritePin(GPIOA, GPIO_PIN_7, 1);
        HAL_GPIO_WritePin(GPIOA, GPIO_PIN_4, 0);
        HAL_GPIO_WritePin(GPIOA, GPIO_PIN_1, 0);
      }
      else if (TCI < 25 ) 
      {
        HAL_GPIO_WritePin(GPIOA, GPIO_PIN_7, 0);
        HAL_GPIO_WritePin(GPIOA, GPIO_PIN_4, 1);
        HAL_GPIO_WritePin(GPIOA, GPIO_PIN_1, 0);
      }
      else 
      {
        HAL_GPIO_WritePin(GPIOA, GPIO_PIN_7, 0);
        HAL_GPIO_WritePin(GPIOA, GPIO_PIN_4, 0);
        HAL_GPIO_WritePin(GPIOA, GPIO_PIN_1, 1);
      }
    }
    HAL_Delay(2000);
    /* USER CODE END WHILE */

    /* USER CODE BEGIN 3 */
  }
  /* USER CODE END 3 */