STM32模拟I2C协议获取MLX90615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：

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；
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。

MLX90615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。MLX90615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。MLX90615内部有300KΩ的弱上拉，需要STM32侧也内部上拉才能更好的保证访问速度。否则会出现时序抖动错误。

MLX90615是更小体积的红外温度测温模块，与MLX90614两者相比有如下不同：

管脚排列顺序不同
从PWM进入I2C模式的控制时间长度不同,MLX90614需要大于1.44ms，MLX90615需要大于39ms
访问模块地址不同，除了默认0地址访问，另外的一个默认访问地址，MLX90614是0x5A, 而MLX90615是0x5B
访问温度数据存放的寄存器地址不同，MLX90614是0x07, 而MLX90615是0x27

硬件连接

这里用低成本的STM32F030F4P6开发板作为控制器，读取MLX90615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。

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MLX90615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。

MLX90615的规范文档里读时序有一个bug，多画了一个周期时钟，有这一个时钟周期时读出的温度数据，计算后的校准值和发送来的PEC值不一样，应当去掉这个时钟周期，读时序及该时钟周期指示如下图所示：

而MLX90614的规范文档里读时序是没有多这一个周期时钟，MLX90614的读时序如下：

PEC是MLX90615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MLX90615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MLX90615读操作的CRC-8校验函数如下：

uint8_t PY_CRC_MLX90615_READ(uint8_t daddr, uint8_t Raddr, uint8_t dl, uint8_t dh)
{   //Written by Pegasus Yu 2022/02/22uint64_t cdata = 0; //Computed total datauint16_t data_t = 0; //Process data of CRC computinguint16_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' searchinguint16_t index = 47;    //bit shifting index for CRC computinguint8_t rec = 0; //bit number needed to be compensated for next CRC computingcdata |= (((uint64_t)daddr)<<40);       //device write addresscdata |= (((uint64_t)Raddr)<<32);       //register access addresscdata |= (((uint64_t)(daddr+1))<<24);   //device read addresscdata |= (((uint64_t)dl)<<16);          //data LSBcdata |= (((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(main.c)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.********************************************************************************Written by Pegasus Yu in 2022*/
/* 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
__IO float usDelayBase;
void PY_usDelayTest(void)
{__IO uint32_t firstms, secondms;__IO 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)
{__IO uint32_t delayReg;__IO uint32_t usNum = (uint32_t)(Delay*usDelayBase);delayReg = 0;while(delayReg!=usNum) delayReg++;
}void PY_usDelayOptimize(void)
{__IO uint32_t firstms, secondms;__IO 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)
{__IO uint32_t delayReg;__IO uint32_t msNum = Delay/1000;__IO uint32_t usNum = (uint32_t)((Delay%1000)*usDelayBase);if(msNum>0) HAL_Delay(msNum);delayReg = 0;while(delayReg!=usNum) delayReg++;
}//MLX90615 I2C access protocol
#define us_num 10#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(50000) ;  //to enable i2c if previous mode PWMSCL_OUT_H;SDA_OUT_H;PY_Delay_us_t(2000000) ;
}void I2C_Start(void)
{PY_Delay_us_t(us_num) ;SDA_OUT_H;SCL_OUT_H;PY_Delay_us_t(us_num/2) ;SDA_OUT_L;PY_Delay_us_t(us_num/2) ;SCL_OUT_L;
}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) ;
}void I2C_Write_Ack(void)
{PY_Delay_us_t(us_num/2) ;SDA_OUT_L;PY_Delay_us_t(us_num/2) ;SCL_OUT_H;PY_Delay_us_t(us_num) ;SCL_OUT_L;SDA_OUT_H;}uint8_t I2C_Read_Ack(void)
{uint8_t status=0;SCL_OUT_L;PY_Delay_us_t(us_num/2) ;SDA_OUT_H;PY_Delay_us_t(us_num/2) ;status = SDA_IN;SCL_OUT_H;PY_Delay_us_t(us_num) ;SCL_OUT_L;SDA_OUT_L;return status;}void I2C_Send_Byte(uint8_t txd){for(uint8_t i=0;i<8;i++){PY_Delay_us_t(us_num/2) ;if((txd&0x80)>>7) SDA_OUT_H;else SDA_OUT_L;txd<<=1;PY_Delay_us_t(us_num/2) ;SCL_OUT_H;PY_Delay_us_t(us_num) ;SCL_OUT_L;}SDA_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/2) ;SDA_OUT_H;PY_Delay_us_t(us_num/2) ;SCL_OUT_H;rxd<<=1;if(SDA_IN) rxd++;PY_Delay_us_t(us_num) ;}SCL_OUT_L;SDA_OUT_H;if (rdack) I2C_Write_Ack();return rxd;
}uint8_t PY_CRC_MLX90615_READ(uint8_t daddr, uint8_t Raddr, uint8_t dl, uint8_t dh)
{   //Written by Pegasus Yu 2022/02/22uint64_t cdata = 0; //Computed total datauint16_t data_t = 0; //Process data of CRC computinguint16_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' searchinguint16_t index = 47;    //bit shifting index for CRC computinguint8_t rec = 0; //bit number needed to be compensated for next CRC computingcdata |= (((uint64_t)daddr)<<40);       //device write addresscdata |= (((uint64_t)Raddr)<<32);       //register access addresscdata |= (((uint64_t)(daddr+1))<<24);   //device read addresscdata |= (((uint64_t)dl)<<16);          //data LSBcdata |= (((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 0xB6(0x5B<<1) for MLX90615 default device addressI2C_Start();I2C_Send_Byte(daddr);I2C_Read_Ack();//I2C_Write_Ack();I2C_Send_Byte(ReaAd);//I2C_Write_Ack();I2C_Read_Ack();/* Don't add this erroneous clock timing, placed here just for reminder, from spec.PY_Delay_us_t(us_num) ;SCL_OUT_H;PY_Delay_us_t(us_num) ;SCL_OUT_L;*/I2C_Start();I2C_Send_Byte(daddr+1);I2C_Read_Ack();DataL=I2C_Read_Byte(1);DataH=I2C_Read_Byte(1);Pecreg=I2C_Read_Byte(0);I2C_Stop();Result |= (((uint32_t)DataH)<<24);Result |= (((uint32_t)DataL)<<16);Result |= (((uint32_t)Pecreg)<<8);Result |= PY_CRC_MLX90615_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(0x27);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)*0.02-273.15HAL_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_DIV8;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 */

例程下载

STM32F030F4P6工程(基于STM32CUBEIDE )下载
STM32F401CCU6工程(基于STM32CUBEIDE )下载

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–