[嵌入式]STM32模拟I2C协议获取MLX90614红外温度传感器测温数据（Open Drain管脚配置）

STM32模拟I2C协议获取MLX90614红外温度传感器测温数据（Open Drain管脚配置）

STM32的GPIO管脚可以配置为Open Drain输出模式，并且有两个功能：

1. 可以设置内部上拉，因此对于I2C访问速度不是特别高的情况，可以不用外部I2C上拉电阻；
2. 虽然是Open Drain输出管脚，可以直接读取管脚电平状态，如同读取输入管脚而不必将输出管脚先切换成输入管脚。

MLX90614是无接触红外温度传感器，有DAA医疗级别高精度的型号，也有针对不同测温距离的型号，适合不同场景产品的应用。MLX90614可以采用PWM方式或者I2C方式进行数据获取，这里是模拟I2C的实现方式。

硬件连接

这里用低成本的STM32F030F4P6开发板作为控制器，读取MLX90614的温度数据。连接关系如下：

软件工程配置

这里采用STM32CUBEIDE开发环境和HAL库。首先建立STM32F030F4P6工程和配置时钟。测试中发现，如果HCLK高于4MHz（无论外部时钟源或内部时钟源），则代码里模拟I2C时序功能读到错误数据，即时序不能保证。推测是低端芯片的锁相环电路性能比较差，HCLK频率高了抖动反而比较大。因此将HCLK频率配置为4MHz。另外在STM32F3和STM32F4系列做同样代码测试，则没有HCLK频率配置高低引起问题，也说明了是STM32F0系列的性能问题。

然后配置PA5和PA6作为Open Drain输出带上拉，默认为高电平输出：

然后配置USART1用于串口数据输出：

保存并生成初始工程代码。

FLASH比较小的MCU需要设置“size”优化的编译模式，避免编译后的代码占用空间超过FLASH最大空间。参见 STM32 region `FLASH‘ overflowed by xxx bytes 问题解决 。

软件工程代码

代码里需要用到HAL工程微秒级延时，HAL库工程微秒延时的实现原理参考STM32 HAL us delay（微秒延时）的指令延时实现方式及优化。

代码里I2C_Init()初始化函数用于保证MLX90614进入I2C控制模式，然后在while循环里不断的读取温度并串口输出。

MLX90614的读时序如下图所示：

PEC是MLX90614发出的CRC-8校验字节，MCU侧可以将前面5个字节内容做CRC-8的计算，得到CRC-8的计算校验字节，和MLX90614发出的CRC-8校验字节比较，以判断传输和接收是否正确。因此设计了针对MLX90614读操作的CRC-8校验函数如下：

uint8_t PY_CRC_MLX90614_READ(uint8_t daddr, uint8_t Raddr, uint8_t dl, uint8_t dh)
{   //Written by Pegasus Yu 2022/02/22

	uint64_t cdata = 0; //Computed total data
	uint16_t data_t = 0; //Process data of CRC computing
	uint16_t crc_poly = 0x0107; //X^8+X^2+X^1+1 total 9 effective bits. Computed total data shall be compensated 8-bit '0' before CRC computing from 9-1=8.

	uint16_t index_t = 47;  ///bit shifting index for initial '1' searching
	uint16_t index = 47;    //bit shifting index for CRC computing

	uint8_t rec = 0; //bit number needed to be compensated for next CRC computing

	cdata |= (((uint64_t)daddr)<<40);       //device write address
	cdata |= (((uint64_t)Raddr)<<32);       //register access address
	cdata |= (((uint64_t)(daddr+1))<<24);   //device read address
	cdata |= (((uint64_t)dl)<<16);          //data LSB
	cdata |= (((uint64_t)dh)<<8);           //data HSB
	//8-bit '0' compensated into cdata so cdata involves 48 bits stored in 64-bit format.

	while(index_t>0)
	{
		if( (cdata>>index_t)&1 )
		{
			index = index_t;
			index_t = 0;

			data_t |= (cdata>>(index-8));
			{
				data_t = data_t ^ crc_poly;
			}

            while(index!=0xffff)
            {
    			if ((data_t>>7)&1) rec = 1;
    			else if ((data_t>>6)&1) rec = 2;
    			else if ((data_t>>5)&1) rec = 3;
    			else if ((data_t>>4)&1) rec = 4;
    			else if ((data_t>>3)&1) rec = 5;
    			else if ((data_t>>2)&1) rec = 6;
    			else if ((data_t>>1)&1) rec = 7;
    			else if ((data_t>>0)&1) rec = 8;
    			else rec = 9; ///

    			if((index-8)<rec)
    			{
    				data_t = data_t<<(index-8);
    				index = 0xffff;
    			}
    			else
    			{
        			for(uint8_t i=1;i<=rec;i++)
        			{
        				data_t = (data_t<<1)|((cdata>>(index-8-i))&1) ;
        			}

        			if(rec!= 9)
        			{
        				data_t = data_t ^ crc_poly;
        				index -= rec;
        			}
        			else
        			{
        				data_t = 0;
        				index_t = index-8-1;
        				index = 0xffff;

        			}

    			}


            }

		}
		else
		{
			index_t--;
			if(index_t<8) break;
		}
	}
	return (uint8_t)data_t;
}

代码设计上，通过串口将温度数据的高字节和低字节输出，可以对高字节和低字节按照公式计算，得到浮点格式的温度数据。主要的实现代码如下：

/* USER CODE BEGIN Header */
/**
  ******************************************************************************
  * @file           : main.c
  * @brief          : Main program body
  ******************************************************************************
  * @attention
  *
  * Copyright (c) 2022 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 */
/* USER CODE END Includes */

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

/* USER CODE END PTD */

/* Private define ------------------------------------------------------------*/
/* USER CODE BEGIN PD */
//us delay functions
float usDelayBase;
void PY_usDelayTest(void)
{
  uint32_t firstms, secondms;
  uint32_t counter = 0;

  firstms = HAL_GetTick()+1;
  secondms = firstms+1;

  while(uwTick!=firstms) ;

  while(uwTick!=secondms) counter++;

  usDelayBase = ((float)counter)/1000;
}

void PY_Delay_us_t(uint32_t Delay)
{
  uint32_t delayReg;
  uint32_t usNum = (uint32_t)(Delay*usDelayBase);

  delayReg = 0;
  while(delayReg!=usNum) delayReg++;
}

void PY_usDelayOptimize(void)
{
  uint32_t firstms, secondms;
  float coe = 1.0;

  firstms = HAL_GetTick();
  PY_Delay_us_t(1000000) ;
  secondms = HAL_GetTick();

  coe = ((float)1000)/(secondms-firstms);
  usDelayBase = coe*usDelayBase;
}

void PY_Delay_us(uint32_t Delay)
{
  uint32_t delayReg;

  uint32_t msNum = Delay/1000;
  uint32_t usNum = (uint32_t)((Delay%1000)*usDelayBase);

  if(msNum>0) HAL_Delay(msNum);

  delayReg = 0;
  while(delayReg!=usNum) delayReg++;
}


//MLX90614 I2C access protocol
#define us_num 5   //100kbps IIC
//#define us_num 50   //10kbps IIC

#define SCL_OUT_H HAL_GPIO_WritePin(GPIOA, GPIO_PIN_5, GPIO_PIN_SET)
#define SCL_OUT_L HAL_GPIO_WritePin(GPIOA, GPIO_PIN_5, GPIO_PIN_RESET)
#define SDA_OUT_H HAL_GPIO_WritePin(GPIOA, GPIO_PIN_6, GPIO_PIN_SET)
#define SDA_OUT_L HAL_GPIO_WritePin(GPIOA, GPIO_PIN_6, GPIO_PIN_RESET)
#define SDA_IN HAL_GPIO_ReadPin(GPIOA, GPIO_PIN_6)

void I2C_Init(void)
{
	SDA_OUT_H;
	SCL_OUT_L;
	PY_Delay_us_t(2000) ;  //to enable i2c if previous mode PWM
	SCL_OUT_H;
	SDA_OUT_H;
	PY_Delay_us_t(2000) ;
}

void I2C_Start(void)
{
	PY_Delay_us_t(us_num) ;
	SDA_OUT_H;
	SCL_OUT_H;
	PY_Delay_us_t(us_num) ;
	SDA_OUT_L;
	PY_Delay_us_t(us_num) ;
}

void I2C_Stop(void)
{
	SCL_OUT_L;
	PY_Delay_us_t(us_num) ;
	SDA_OUT_L;
	PY_Delay_us_t(us_num) ;
	SCL_OUT_H;
	PY_Delay_us_t(us_num) ;
	SDA_OUT_H;
	PY_Delay_us_t(us_num) ;
}

uint8_t I2C_Write_Ack(void)
{
	uint8_t status=0;

	SDA_OUT_H;
	PY_Delay_us_t(us_num) ;
	SCL_OUT_H;
	status = SDA_IN;
	PY_Delay_us_t(us_num) ;
	SCL_OUT_L;

	return status;
}

uint8_t I2C_Read_Ack(void)
{
	uint8_t status=0;

	SCL_OUT_L;
	SDA_OUT_H;
	PY_Delay_us_t(us_num) ;
	status = SDA_IN;
	SCL_OUT_H;
	PY_Delay_us_t(us_num) ;
	SCL_OUT_L;

	return status;
}


void I2C_Send_Byte(uint8_t txd)
{
    SCL_OUT_L;
    for(uint8_t i=0;i<8;i++)
    {
        if((txd&0x80)>>7) SDA_OUT_H;
        else SDA_OUT_L;
        txd<<=1;
        PY_Delay_us_t(us_num) ;
        SCL_OUT_H;
        PY_Delay_us_t(us_num) ;
		SCL_OUT_L;
    }
}

uint8_t I2C_Read_Byte(unsigned char rdack)
{
	uint8_t rxd=0;
    for(uint8_t i=0;i<8;i++ )
	{
    	SCL_OUT_L;
    	PY_Delay_us_t(us_num) ;
    	SCL_OUT_H;
        rxd<<=1;
        if(SDA_IN) rxd++;
        PY_Delay_us_t(us_num) ;
    }
    if (rdack) I2C_Read_Ack();

    return rxd;
}

uint8_t PY_CRC_MLX90614_READ(uint8_t daddr, uint8_t Raddr, uint8_t dl, uint8_t dh)
{   //Written by Pegasus Yu 2022/02/22

	uint64_t cdata = 0; //Computed total data
	uint16_t data_t = 0; //Process data of CRC computing
	uint16_t crc_poly = 0x0107; //X^8+X^2+X^1+1 total 9 effective bits. Computed total data shall be compensated 8-bit '0' before CRC computing from 9-1=8.

	uint16_t index_t = 47;  ///bit shifting index for initial '1' searching
	uint16_t index = 47;    //bit shifting index for CRC computing

	uint8_t rec = 0; //bit number needed to be compensated for next CRC computing

	cdata |= (((uint64_t)daddr)<<40);       //device write address
	cdata |= (((uint64_t)Raddr)<<32);       //register access address
	cdata |= (((uint64_t)(daddr+1))<<24);   //device read address
	cdata |= (((uint64_t)dl)<<16);          //data LSB
	cdata |= (((uint64_t)dh)<<8);           //data HSB
	//8-bit '0' compensated into cdata so cdata involves 48 bits stored in 64-bit format.

	while(index_t>0)
	{
		if( (cdata>>index_t)&1 )
		{
			index = index_t;
			index_t = 0;

			data_t |= (cdata>>(index-8));
			{
				data_t = data_t ^ crc_poly;
			}

            while(index!=0xffff)
            {
    			if ((data_t>>7)&1) rec = 1;
    			else if ((data_t>>6)&1) rec = 2;
    			else if ((data_t>>5)&1) rec = 3;
    			else if ((data_t>>4)&1) rec = 4;
    			else if ((data_t>>3)&1) rec = 5;
    			else if ((data_t>>2)&1) rec = 6;
    			else if ((data_t>>1)&1) rec = 7;
    			else if ((data_t>>0)&1) rec = 8;
    			else rec = 9; ///

    			if((index-8)<rec)
    			{
    				data_t = data_t<<(index-8);
    				index = 0xffff;
    			}
    			else
    			{
        			for(uint8_t i=1;i<=rec;i++)
        			{
        				data_t = (data_t<<1)|((cdata>>(index-8-i))&1) ;
        			}

        			if(rec!= 9)
        			{
        				data_t = data_t ^ crc_poly;
        				index -= rec;
        			}
        			else
        			{
        				data_t = 0;
        				index_t = index-8-1;
        				index = 0xffff;

        			}

    			}


            }

		}
		else
		{
			index_t--;
			if(index_t<8) break;
		}
	}
	return (uint8_t)data_t;
}

uint32_t Get_Temp_DATA( uint8_t ReaAd)
{
     uint8_t Pecreg = 0;
	 uint8_t DataL = 0 ,DataH = 0;
	 uint32_t Result = 0;

	 uint8_t daddr = 0x00; //0x00 or 0xB4(0x5A<<1) for MLX90614 default device address

	  I2C_Start();
	  I2C_Send_Byte(daddr);
	  I2C_Write_Ack();
  	  I2C_Send_Byte(ReaAd);
  	  I2C_Write_Ack();

	  I2C_Start();
	  I2C_Send_Byte(daddr+1);
	  I2C_Write_Ack();

  	  DataL=I2C_Read_Byte(1);
  	  DataH=I2C_Read_Byte(1);

  	  Pecreg=I2C_Read_Byte(1);
  	  I2C_Stop();

  	  Result |= (((uint32_t)DataH)<<24);
  	  Result |= (((uint32_t)DataL)<<16);
  	  Result |= (((uint32_t)Pecreg)<<8);
  	  Result |= PY_CRC_MLX90614_READ(daddr, ReaAd, DataL, DataH);
	  return Result;
}

/* USER CODE END PD */

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

/* USER CODE END PM */

/* Private variables ---------------------------------------------------------*/
UART_HandleTypeDef huart1;

/* USER CODE BEGIN PV */
float temperature_f;
uint32_t temperature_d;
uint8_t temprst[4];
/* USER CODE END PV */

/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_USART1_UART_Init(void);
/* USER CODE BEGIN PFP */

/* USER CODE END PFP */

/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */

/* 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_USART1_UART_Init();
  /* USER CODE BEGIN 2 */
  PY_usDelayTest();
  PY_usDelayOptimize();

  I2C_Init();
  PY_Delay_us(1000000);
  /* USER CODE END 2 */

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
	  temperature_d=Get_Temp_DATA(0x07);
	  temprst[0]= (temperature_d>>24)&0xff;
	  temprst[1]= (temperature_d>>16)&0xff;
	  temprst[2]= (temperature_d>>8)&0xff;
	  temprst[3]= (temperature_d>>0)&0xff;
      if(temprst[2]==temprst[3]) HAL_UART_Transmit(&huart1, temprst, 2, 2700);

      //HAL_UART_Transmit(&huart1, temprst, 4, 2700);

	  /*
	  temperature_f = (((float)((temprst[0]<<8)|temprst[1])) * 2 - 27315)/100;  //T= (DataH:DataL)*0.02-273.15
	  HAL_UART_Transmit(&huart1, &temperature_f, 4, 2700);
	  */
	  PY_Delay_us(2000000); //adjustable output delay


    /* USER CODE END WHILE */

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

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

  /** 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_ON;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSI;
  RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL8;
  RCC_OscInitStruct.PLL.PREDIV = RCC_PREDIV_DIV1;
  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_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV8;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;

  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_1) != HAL_OK)
  {
    Error_Handler();
  }
  PeriphClkInit.PeriphClockSelection = RCC_PERIPHCLK_USART1;
  PeriphClkInit.Usart1ClockSelection = RCC_USART1CLKSOURCE_PCLK1;
  if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit) != HAL_OK)
  {
    Error_Handler();
  }
}

/**
  * @brief USART1 Initialization Function
  * @param None
  * @retval None
  */
static void MX_USART1_UART_Init(void)
{

  /* USER CODE BEGIN USART1_Init 0 */

  /* USER CODE END USART1_Init 0 */

  /* USER CODE BEGIN USART1_Init 1 */

  /* USER CODE END USART1_Init 1 */
  huart1.Instance = USART1;
  huart1.Init.BaudRate = 115200;
  huart1.Init.WordLength = UART_WORDLENGTH_8B;
  huart1.Init.StopBits = UART_STOPBITS_1;
  huart1.Init.Parity = UART_PARITY_NONE;
  huart1.Init.Mode = UART_MODE_TX_RX;
  huart1.Init.HwFlowCtl = UART_HWCONTROL_NONE;
  huart1.Init.OverSampling = UART_OVERSAMPLING_16;
  huart1.Init.OneBitSampling = UART_ONE_BIT_SAMPLE_DISABLE;
  huart1.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;
  if (HAL_UART_Init(&huart1) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN USART1_Init 2 */

  /* USER CODE END USART1_Init 2 */

}

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

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

  /*Configure GPIO pin Output Level */
  HAL_GPIO_WritePin(GPIOA, GPIO_PIN_5|GPIO_PIN_6, GPIO_PIN_SET);

  /*Configure GPIO pins : PA5 PA6 */
  GPIO_InitStruct.Pin = GPIO_PIN_5|GPIO_PIN_6;
  GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_OD;
  GPIO_InitStruct.Pull = GPIO_PULLUP;
  GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_HIGH;
  HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

}

/* 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 */

完整STM32CUBEIDE工程下载：
https://download.csdn.net/download/hwytree/82030600

温度数据

可以通过PC串口工具获得温度数据，如：

16进制39C8，对应十进制14792，按照公式计算（14792*2-27315）/100=22.69℃。

–End–