STM32 ve NTC Sensörü İle Sıcaklık Ölçme

Posted on 19 Ağustos 2019 by Mehmet Topuz

Sıcaklığa bağlı olarak direnci değişen devre elemanlarına Termistör denir. İki farklı çeşidi vardır. “Negative Thermocouple” ifadesinin kısaltması olan NTC ve “Positive Thermocouple” ifadesinin kısaltması olan PTC . İkisinin de sıcaklığa bağlı olarak direnci değişir. Farkları ise birinin direnci sıcaklık ile artar iken diğerinin azalmasıdır.

NTC: Sıcaklık arttıkça direnci azalır.
PTC: Sıcaklık arttıkça direnci artar.

Bu direnç değişimleri doğrusal değildir. Bu yüzden sıcaklık hesaplamaları yapılırken bazı formüllerden yararlanılır. Bu formüllerden biri Stein-Hart denklemidir.

Stein-Hart Denklemi

Bu denklemde “R” değişkeni “T(kelvin)” derecede ölçülen NTC‘nin direnç değeridir. Bu formülü kod içerisinde kullanabilmemiz için A,B ve C katsayılarını bilmemiz gerekir. Bu katsayılar NTC sıcaklık-direnç tablosuna göre hesaplanır. NTC tablosundan 3 farklı derece seçip ve bu derecelerin karşılığı olan direnç değerlerini formülde yerine yazarak 3 adet 3 bilinmeyenli denklem elde edilir. Buradan A,B ve C katsayıları bulunarak formüle yazılabilir. Ben hazır hesaplanmış olan katsayıları kullandım. Ayrıca linkteki siteden NTC sıcaklık-direnç tablosundan seçeceğiniz üç farklı değer için kendiniz A,B ve C katsayıları hesaplatıp kullanabilirsiniz.

NTC Bağlantısı

STM32 ile NTC arasındaki bağlantı yukarıdaki gibi yapılabilir. 10k‘lık NTC yine 10k bir direnç ile pull-down bağlantı yapılarak ADC pinine bağlanmıştır.

Formüle dikkat edilecek olursa sıcaklık değerini hesaplayabilmek için NTC’nin direncini bilmemiz gerekir. Yukarıdaki bağlantıda gerilim bölücü mantığından yola çıkarak NTC’nin direnci rahatlıkla hesaplanabilir. Fakat denklem sadeleştirildiği zaman sadece ADC’den okunan 12 bitlik değeri bilmemiz yeterlidir.

Yukarıdaki denklemde görüldüğü gibi gerilim bölücüden yola çıkarak NTC nin direnci hesaplanabilir. Burada görüldüğü gibi ADC referans voltajı ve NTC nin besleme voltajı birbirini götürürür. Denklem sadeleştiği zaman aşağıdaki fonksiyondaki gibi olur.

double Thermistor(int analogValue){

 double temperature;
 temperature = log(((40950000 / analogValue) - 10000));// 4095 ADC çözünürlüğü(12 bit)
 temperature = 1 / (0.001129148 + (0.000234125 + (0.0000000876741 * temperature * temperature)) * temperature);
 temperature = temperature - 273.15;
 return temperature;
}

double Thermistor(int analogValue){

double temperature;

temperature = log(((40950000 / analogValue) - 10000));// 4095 ADC çözünürlüğü(12 bit)

temperature = 1 / (0.001129148 + (0.000234125 + (0.0000000876741 * temperature * temperature)) * temperature);

temperature = temperature - 273.15;

return temperature;

}

NOT: Denklemde dikkat ettiyseniz logaritmik işlem yapılmaktadır. Bunu yapabilmek için “math.h” kütüphanesi projeye dahil edilmelidir.

ADC’ den okunan değer bu fonksiyona gönderildiğinde geriye sıcaklık bilgisini derece cinsinden döndürmektedir.

CubeMx Ayarları

STM32-NTC Kodlarının Tamamı

/**
  ******************************************************************************
  * File Name          : main.c
  * Description        : Main program body
  ******************************************************************************
  ** This notice applies to any and all portions of this file
  * that are not between comment pairs USER CODE BEGIN and
  * USER CODE END. Other portions of this file, whether 
  * inserted by the user or by software development tools
  * are owned by their respective copyright owners.
  *
  * COPYRIGHT(c) 2019 STMicroelectronics
  *
  * Redistribution and use in source and binary forms, with or without modification,
  * are permitted provided that the following conditions are met:
  *   1. Redistributions of source code must retain the above copyright notice,
  *      this list of conditions and the following disclaimer.
  *   2. Redistributions in binary form must reproduce the above copyright notice,
  *      this list of conditions and the following disclaimer in the documentation
  *      and/or other materials provided with the distribution.
  *   3. Neither the name of STMicroelectronics nor the names of its contributors
  *      may be used to endorse or promote products derived from this software
  *      without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
  ******************************************************************************
  */
/* Includes ------------------------------------------------------------------*/
#include "main.h"
#include "stm32f1xx_hal.h"

/* USER CODE BEGIN Includes */
#include <math.h>
/* USER CODE END Includes */

/* Private variables ---------------------------------------------------------*/
ADC_HandleTypeDef hadc1;

/* USER CODE BEGIN PV */
/* Private variables ---------------------------------------------------------*/
int adc_raw,temp;
/* USER CODE END PV */

/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_ADC1_Init(void);

/* USER CODE BEGIN PFP */
/* Private function prototypes -----------------------------------------------*/
double Thermistor(int analogValue){

 double temperature;
 temperature = log(((40950000 / analogValue) - 10000));
 temperature = 1 / (0.001129148 + (0.000234125 + (0.0000000876741 * temperature * temperature)) * temperature);
 temperature = temperature - 273.15;
 return temperature;
}
/* USER CODE END PFP */

/* USER CODE BEGIN 0 */

/* USER CODE END 0 */

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_ADC1_Init();

  /* USER CODE BEGIN 2 */
	HAL_ADC_Start(&hadc1);
  /* USER CODE END 2 */

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
		
		adc_raw = HAL_ADC_GetValue(&hadc1);
		temp = Thermistor(adc_raw);
		HAL_Delay(200);
  /* USER CODE END WHILE */

  /* USER CODE BEGIN 3 */

  }
  /* USER CODE END 3 */

}

/** System Clock Configuration
*/
void SystemClock_Config(void)
{

  RCC_OscInitTypeDef RCC_OscInitStruct;
  RCC_ClkInitTypeDef RCC_ClkInitStruct;
  RCC_PeriphCLKInitTypeDef PeriphClkInit;

    /**Initializes the CPU, AHB and APB busses clocks 
    */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
  RCC_OscInitStruct.HSEState = RCC_HSE_ON;
  RCC_OscInitStruct.HSEPredivValue = RCC_HSE_PREDIV_DIV1;
  RCC_OscInitStruct.HSIState = RCC_HSI_ON;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
  RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL7;
  if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
  {
    _Error_Handler(__FILE__, __LINE__);
  }

    /**Initializes the CPU, AHB and APB busses clocks 
    */
  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
                              |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
  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_2) != HAL_OK)
  {
    _Error_Handler(__FILE__, __LINE__);
  }

  PeriphClkInit.PeriphClockSelection = RCC_PERIPHCLK_ADC;
  PeriphClkInit.AdcClockSelection = RCC_ADCPCLK2_DIV4;
  if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit) != HAL_OK)
  {
    _Error_Handler(__FILE__, __LINE__);
  }

    /**Configure the Systick interrupt time 
    */
  HAL_SYSTICK_Config(HAL_RCC_GetHCLKFreq()/1000);

    /**Configure the Systick 
    */
  HAL_SYSTICK_CLKSourceConfig(SYSTICK_CLKSOURCE_HCLK);

  /* SysTick_IRQn interrupt configuration */
  HAL_NVIC_SetPriority(SysTick_IRQn, 0, 0);
}

/* ADC1 init function */
static void MX_ADC1_Init(void)
{

  ADC_ChannelConfTypeDef sConfig;

    /**Common config 
    */
  hadc1.Instance = ADC1;
  hadc1.Init.ScanConvMode = ADC_SCAN_DISABLE;
  hadc1.Init.ContinuousConvMode = ENABLE;
  hadc1.Init.DiscontinuousConvMode = DISABLE;
  hadc1.Init.ExternalTrigConv = ADC_SOFTWARE_START;
  hadc1.Init.DataAlign = ADC_DATAALIGN_RIGHT;
  hadc1.Init.NbrOfConversion = 1;
  if (HAL_ADC_Init(&hadc1) != HAL_OK)
  {
    _Error_Handler(__FILE__, __LINE__);
  }

    /**Configure Regular Channel 
    */
  sConfig.Channel = ADC_CHANNEL_0;
  sConfig.Rank = 1;
  sConfig.SamplingTime = ADC_SAMPLETIME_55CYCLES_5;
  if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)
  {
    _Error_Handler(__FILE__, __LINE__);
  }

}

/** Configure pins as 
        * Analog 
        * Input 
        * Output
        * EVENT_OUT
        * EXTI
*/
static void MX_GPIO_Init(void)
{

  /* GPIO Ports Clock Enable */
  __HAL_RCC_GPIOD_CLK_ENABLE();
  __HAL_RCC_GPIOA_CLK_ENABLE();

}

/* USER CODE BEGIN 4 */

/* USER CODE END 4 */

/**
  * @brief  This function is executed in case of error occurrence.
  * @param  None
  * @retval None
  */
void _Error_Handler(char * file, int line)
{
  /* USER CODE BEGIN Error_Handler_Debug */
  /* User can add his own implementation to report the HAL error return state */
  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

/**
  * @}
  */ 

/**
  * @}
*/ 

/************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE****/

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/**

******************************************************************************

* File Name : main.c

* Description : Main program body

******************************************************************************

** This notice applies to any and all portions of this file

* that are not between comment pairs USER CODE BEGIN and

* USER CODE END. Other portions of this file, whether

* inserted by the user or by software development tools

* are owned by their respective copyright owners.

* Redistribution and use in source and binary forms, with or without modification,

* are permitted provided that the following conditions are met:

* 1. Redistributions of source code must retain the above copyright notice,

* this list of conditions and the following disclaimer.

* 2. Redistributions in binary form must reproduce the above copyright notice,

* this list of conditions and the following disclaimer in the documentation

* and/or other materials provided with the distribution.

* 3. Neither the name of STMicroelectronics nor the names of its contributors

* may be used to endorse or promote products derived from this software

* without specific prior written permission.

* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"

* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE

* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE

* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR

* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER

* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,

* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE

* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

******************************************************************************

/* Includes ------------------------------------------------------------------*/

#include "main.h"

#include "stm32f1xx_hal.h"

/* USER CODE BEGIN Includes */

#include <math.h>

/* USER CODE END Includes */

/* Private variables ---------------------------------------------------------*/

ADC_HandleTypeDef hadc1;

/* USER CODE BEGIN PV */

/* Private variables ---------------------------------------------------------*/

int adc_raw,temp;

/* USER CODE END PV */

/* Private function prototypes -----------------------------------------------*/

void SystemClock_Config(void);

static void MX_GPIO_Init(void);

static void MX_ADC1_Init(void);

/* USER CODE BEGIN PFP */

/* Private function prototypes -----------------------------------------------*/

double Thermistor(int analogValue){

double temperature;

temperature = log(((40950000 / analogValue) - 10000));

temperature = 1 / (0.001129148 + (0.000234125 + (0.0000000876741 * temperature * temperature)) * temperature);

temperature = temperature - 273.15;

return temperature;

}

/* USER CODE END PFP */

/* USER CODE BEGIN 0 */

/* USER CODE END 0 */

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_ADC1_Init();

/* USER CODE BEGIN 2 */

HAL_ADC_Start(&hadc1);

/* USER CODE END 2 */

/* Infinite loop */

/* USER CODE BEGIN WHILE */

while (1)

{

adc_raw = HAL_ADC_GetValue(&hadc1);

temp = Thermistor(adc_raw);

HAL_Delay(200);

/* USER CODE END WHILE */

/* USER CODE BEGIN 3 */

}

/* USER CODE END 3 */

}

/** System Clock Configuration

void SystemClock_Config(void)

{

RCC_OscInitTypeDef RCC_OscInitStruct;

RCC_ClkInitTypeDef RCC_ClkInitStruct;

RCC_PeriphCLKInitTypeDef PeriphClkInit;

/**Initializes the CPU, AHB and APB busses clocks

RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;

RCC_OscInitStruct.HSEState = RCC_HSE_ON;

RCC_OscInitStruct.HSEPredivValue = RCC_HSE_PREDIV_DIV1;

RCC_OscInitStruct.HSIState = RCC_HSI_ON;

RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;

RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;

RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL7;

if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)

{

_Error_Handler(__FILE__, __LINE__);

}

/**Initializes the CPU, AHB and APB busses clocks

RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK

|RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;

RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;

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_2) != HAL_OK)

{

_Error_Handler(__FILE__, __LINE__);

}

PeriphClkInit.PeriphClockSelection = RCC_PERIPHCLK_ADC;

PeriphClkInit.AdcClockSelection = RCC_ADCPCLK2_DIV4;

if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit) != HAL_OK)

{

_Error_Handler(__FILE__, __LINE__);

}

/**Configure the Systick interrupt time

HAL_SYSTICK_Config(HAL_RCC_GetHCLKFreq()/1000);

/**Configure the Systick

HAL_SYSTICK_CLKSourceConfig(SYSTICK_CLKSOURCE_HCLK);

/* SysTick_IRQn interrupt configuration */

HAL_NVIC_SetPriority(SysTick_IRQn, 0, 0);

}

/* ADC1 init function */

static void MX_ADC1_Init(void)

{

ADC_ChannelConfTypeDef sConfig;

/**Common config

hadc1.Instance = ADC1;

hadc1.Init.ScanConvMode = ADC_SCAN_DISABLE;

hadc1.Init.ContinuousConvMode = ENABLE;

hadc1.Init.DiscontinuousConvMode = DISABLE;

hadc1.Init.ExternalTrigConv = ADC_SOFTWARE_START;

hadc1.Init.DataAlign = ADC_DATAALIGN_RIGHT;

hadc1.Init.NbrOfConversion = 1;

if (HAL_ADC_Init(&hadc1) != HAL_OK)

{

_Error_Handler(__FILE__, __LINE__);

}

/**Configure Regular Channel

sConfig.Channel = ADC_CHANNEL_0;

sConfig.Rank = 1;

sConfig.SamplingTime = ADC_SAMPLETIME_55CYCLES_5;

if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)

{

_Error_Handler(__FILE__, __LINE__);

}

/** Configure pins as

* Analog

* Input

* Output

* EVENT_OUT

* EXTI

static void MX_GPIO_Init(void)

{

/* GPIO Ports Clock Enable */

__HAL_RCC_GPIOD_CLK_ENABLE();

__HAL_RCC_GPIOA_CLK_ENABLE();

}

/* USER CODE BEGIN 4 */

/* USER CODE END 4 */

/**

* @brief This function is executed in case of error occurrence.

* @param None

* @retval None

void _Error_Handler(char * file, int line)

{

/* USER CODE BEGIN Error_Handler_Debug */

/* User can add his own implementation to report the HAL error return state */

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

/**

* @}

/**

* @}

/************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE****/

STMStudio programı yardımı ile “temp” isimli sıcaklık değişkeninin değerini gözlemleyebilirsiniz. Eğer daha sağlıklı bir sıcaklık değeri okumak isterseniz basit bir yazılımsal filtre uygulayabilirsiniz. Örneğin; 20 defa ADC değeri okuyup bunun aritmetik ortalamasını alıp Thermistor() fonksiyonuna gönderebilirsiniz.

İyi Çalışmalar…

Okunma Sayısı: 3.875

STM32 ve NTC Sensörü İle Sıcaklık Ölçme

CubeMx Ayarları

STM32-NTC Kodlarının Tamamı

Mehmet Topuz

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