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MAX6675应用注意事项

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MAX6675应用注意事项当 CS 为高电平的时候开始转换 转换时间约为 220ms 当 CS 为低电平时 停止转换 通过 SO 读取转换结果

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MAX6675应用注意事项

注意：重定向c库函数printf到huart1，需要加入头文件#include “stdio.h”，同时勾选use MicroLIB选型，堆栈设置稍微大一些。
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1. MAX6675采样频率(建议不低于220ms，即0.22s)

  1. 当CS为高电平的时候开始转换，转换时间约为220ms，当CS为低电平时，停止转换，通过SO读取转换结果。否则，读取的数据一直为0或者不变。
  2. 配置SPI时序时，为MODE 0，即SCK空闲电平为0， 采集在上升沿(CPOA=0)，读取数据在下降沿。
  3. SPI通信速率必须小于4.3MHz，通常选取1-2MHz。
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    在这里插入图片描述
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2. 数字滤波

采集到的温度数据，要采用数字滤波，否则波动会比较大。滤波模式结合自身情况，合理选用。

3. 多通道MAX6675采集模式

4. 代码

4.1 max6675.h

#ifndef _MAX6675_H_  #define _MAX6675_H_ #include "main.h" #include "spi.h" //#define MAX6675_CS_Pin GPIO_PIN_0 //#define MAX6675_CS_GPIO_Port GPIOB extern SPI_HandleTypeDef hspi2; void SPI2_Init(void); void MAX6675_Init(void); //初始化max6675模块  uint8_t MAX6675_ReadWriteByte(uint8_t txData); //max6675模块读写一个字�? uint16_t MAX6675_ReadRawValue(void); float MAX6675_ReadTemperature(void); void MAX6675_CS(unsigned char choose); #endif

4.2 max6675.c

#include "max6675.h" #if 0 SPI_HandleTypeDef hspi2; /* SPI2 init function */ void SPI2_Init(void) { 
     hspi2.Instance = SPI2; hspi2.Init.Mode = SPI_MODE_MASTER; hspi2.Init.Direction = SPI_DIRECTION_2LINES; hspi2.Init.DataSize = SPI_DATASIZE_8BIT; hspi2.Init.CLKPolarity = SPI_POLARITY_LOW; hspi2.Init.CLKPhase = SPI_PHASE_1EDGE; hspi2.Init.NSS = SPI_NSS_SOFT; hspi2.Init.BaudRatePrescaler = SPI_BAUDRATEPRESCALER_256; hspi2.Init.FirstBit = SPI_FIRSTBIT_MSB; hspi2.Init.TIMode = SPI_TIMODE_DISABLE; hspi2.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE; hspi2.Init.CRCPolynomial = 10; if (HAL_SPI_Init(&hspi2) != HAL_OK) { 
     Error_Handler(); } } void HAL_SPI_MspInit(SPI_HandleTypeDef* spiHandle) { 
     GPIO_InitTypeDef GPIO_InitStruct = { 
    0}; if(spiHandle->Instance==SPI2) { 
     __HAL_RCC_SPI2_CLK_ENABLE(); __HAL_RCC_GPIOB_CLK_ENABLE(); /SPI2 GPIO Configuration PB13 ------> SPI2_SCK PB14 ------> SPI2_MISO PB15 ------> SPI2_MOSI */ GPIO_InitStruct.Pin = GPIO_PIN_13|GPIO_PIN_15; GPIO_InitStruct.Mode = GPIO_MODE_AF_PP; GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_HIGH; HAL_GPIO_Init(GPIOB, &GPIO_InitStruct); GPIO_InitStruct.Pin = GPIO_PIN_14; GPIO_InitStruct.Mode = GPIO_MODE_INPUT; GPIO_InitStruct.Pull = GPIO_PULLUP; //GPIO_NOPULL HAL_GPIO_Init(GPIOB, &GPIO_InitStruct); } } void HAL_SPI_MspDeInit(SPI_HandleTypeDef* spiHandle) { 
     if(spiHandle->Instance==SPI2) { 
     __HAL_RCC_SPI2_CLK_DISABLE(); /SPI2 GPIO Configuration PB13 ------> SPI2_SCK PB14 ------> SPI2_MISO PB15 ------> SPI2_MOSI */ HAL_GPIO_DeInit(GPIOB, GPIO_PIN_13|GPIO_PIN_14|GPIO_PIN_15); } } #endif //MAX6675 片选引脚初始化 void GPIO_Init(void) { 
     GPIO_InitTypeDef GPIO_InitStruct = { 
    0}; /* GPIO Ports Clock Enable */ __HAL_RCC_GPIOB_CLK_ENABLE(); HAL_GPIO_WritePin(MAX6675_CS_GPIO_Port, MAX6675_CS_Pin, GPIO_PIN_SET); /*引脚配置 */ GPIO_InitStruct.Pin = MAX6675_CS_Pin; GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP; GPIO_InitStruct.Pull = GPIO_PULLUP; GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_HIGH; HAL_GPIO_Init(MAX6675_CS_GPIO_Port, &GPIO_InitStruct); } / * @brief max66675模块初始化 * @param None * @retval None */ void MAX6675_Init(void) { 
     GPIO_Init(); //片选引脚初始化 // SPI2_Init(); //spi总线初始化 MX_SPI2_Init(); __HAL_SPI_ENABLE(&hspi2); } / * @brief max6675模块读写一个字节的数据 * @param txData：要发送的数据 * @retval 接收到的数据 */ uint8_t MAX6675_ReadWriteByte(uint8_t txData) { 
     unsigned char txdata,rxdata; txdata = txData; HAL_SPI_TransmitReceive(&hspi2,&txdata,&rxdata,1,1000); return rxdata; } / * @brief max6675模块读取测得的原始数据 * @param None * @retval 温度的原始数据 */ uint16_t MAX6675_ReadRawValue(void) { 
     uint16_t tmp; MAX6675_CS(1); // HAL_Delay(1); MAX6675_CS(0); // HAL_Delay(1); tmp = MAX6675_ReadWriteByte(0XFF); //read MSB tmp <<= 8; tmp |= MAX6675_ReadWriteByte(0XFF); //read LSB HAL_Delay(1); MAX6675_CS(1); if (tmp & 4) { 
     // thermocouple open tmp = 4095; //未检测到热电偶 } else { 
     tmp = tmp >> 3; } return tmp; } / * @brief max6675模块读取温度 * @param None * @retval 温度值（单位：℃） */ float MAX6675_ReadTemperature(void) { 
     return (MAX6675_ReadRawValue() * 1024.0 / 4096); } //MAX6675 片选控制 void MAX6675_CS(unsigned char choose) { 
     if(choose == 1) { 
     HAL_GPIO_WritePin(GPIOB, MAX6675_CS_Pin, GPIO_PIN_SET); } else { 
     HAL_GPIO_WritePin(GPIOB, MAX6675_CS_Pin, GPIO_PIN_RESET); } }

4.3 spi.h

/* USER CODE BEGIN Header */ / * @file spi.h * @brief This file contains all the function prototypes for * the spi.c file * @attention * * Copyright (c) 2023 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 */ /* Define to prevent recursive inclusion -------------------------------------*/ #ifndef __SPI_H__ #define __SPI_H__ #ifdef __cplusplus extern "C" { 
     #endif /* Includes ------------------------------------------------------------------*/ #include "main.h" /* USER CODE BEGIN Includes */ /* USER CODE END Includes */ extern SPI_HandleTypeDef hspi2; extern SPI_HandleTypeDef hspi3; /* USER CODE BEGIN Private defines */ /* USER CODE END Private defines */ void MX_SPI2_Init(void); void MX_SPI3_Init(void); /* USER CODE BEGIN Prototypes */ /* USER CODE END Prototypes */ #ifdef __cplusplus } #endif #endif /* __SPI_H__ */

4.4 spi.c

/* USER CODE BEGIN Header */ / * @file spi.c * @brief This file provides code for the configuration * of the SPI instances. * @attention * * Copyright (c) 2023 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 "spi.h" /* USER CODE BEGIN 0 */ /* USER CODE END 0 */ SPI_HandleTypeDef hspi2; SPI_HandleTypeDef hspi3; /* SPI2 init function */ void MX_SPI2_Init(void) { 
     /* USER CODE BEGIN SPI2_Init 0 */ /* USER CODE END SPI2_Init 0 */ /* USER CODE BEGIN SPI2_Init 1 */ /* USER CODE END SPI2_Init 1 */ hspi2.Instance = SPI2; hspi2.Init.Mode = SPI_MODE_MASTER; hspi2.Init.Direction = SPI_DIRECTION_2LINES; hspi2.Init.DataSize = SPI_DATASIZE_8BIT; hspi2.Init.CLKPolarity = SPI_POLARITY_LOW; hspi2.Init.CLKPhase = SPI_PHASE_1EDGE; hspi2.Init.NSS = SPI_NSS_SOFT; hspi2.Init.BaudRatePrescaler = SPI_BAUDRATEPRESCALER_128; hspi2.Init.FirstBit = SPI_FIRSTBIT_MSB; hspi2.Init.TIMode = SPI_TIMODE_DISABLE; hspi2.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE; hspi2.Init.CRCPolynomial = 10; if (HAL_SPI_Init(&hspi2) != HAL_OK) { 
     Error_Handler(); } /* USER CODE BEGIN SPI2_Init 2 */ /* USER CODE END SPI2_Init 2 */ } /* SPI3 init function */ void MX_SPI3_Init(void) { 
     /* USER CODE BEGIN SPI3_Init 0 */ /* USER CODE END SPI3_Init 0 */ /* USER CODE BEGIN SPI3_Init 1 */ /* USER CODE END SPI3_Init 1 */ hspi3.Instance = SPI3; hspi3.Init.Mode = SPI_MODE_MASTER; hspi3.Init.Direction = SPI_DIRECTION_2LINES; hspi3.Init.DataSize = SPI_DATASIZE_8BIT; hspi3.Init.CLKPolarity = SPI_POLARITY_LOW; hspi3.Init.CLKPhase = SPI_PHASE_2EDGE; hspi3.Init.NSS = SPI_NSS_SOFT; hspi3.Init.BaudRatePrescaler = SPI_BAUDRATEPRESCALER_64; hspi3.Init.FirstBit = SPI_FIRSTBIT_MSB; hspi3.Init.TIMode = SPI_TIMODE_DISABLE; hspi3.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE; hspi3.Init.CRCPolynomial = 10; if (HAL_SPI_Init(&hspi3) != HAL_OK) { 
     Error_Handler(); } /* USER CODE BEGIN SPI3_Init 2 */ /* USER CODE END SPI3_Init 2 */ } void HAL_SPI_MspInit(SPI_HandleTypeDef* spiHandle) { 
     GPIO_InitTypeDef GPIO_InitStruct = { 
    0}; if(spiHandle->Instance==SPI2) { 
     /* USER CODE BEGIN SPI2_MspInit 0 */ /* USER CODE END SPI2_MspInit 0 */ /* SPI2 clock enable */ __HAL_RCC_SPI2_CLK_ENABLE(); __HAL_RCC_GPIOB_CLK_ENABLE(); /SPI2 GPIO Configuration PB13 ------> SPI2_SCK PB14 ------> SPI2_MISO PB15 ------> SPI2_MOSI */ GPIO_InitStruct.Pin = GPIO_PIN_13|GPIO_PIN_14|GPIO_PIN_15; GPIO_InitStruct.Mode = GPIO_MODE_AF_PP; GPIO_InitStruct.Pull = GPIO_PULLUP; //GPIO_NOPULL，这是一个注意的地方，没有外部硬件上拉，改为内部上拉，不改也可以，不稳定 GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH; GPIO_InitStruct.Alternate = GPIO_AF5_SPI2; HAL_GPIO_Init(GPIOB, &GPIO_InitStruct); /* USER CODE BEGIN SPI2_MspInit 1 */ /* USER CODE END SPI2_MspInit 1 */ } else if(spiHandle->Instance==SPI3) { 
     /* USER CODE BEGIN SPI3_MspInit 0 */ /* USER CODE END SPI3_MspInit 0 */ /* SPI3 clock enable */ __HAL_RCC_SPI3_CLK_ENABLE(); __HAL_RCC_GPIOC_CLK_ENABLE(); /SPI3 GPIO Configuration PC10 ------> SPI3_SCK PC11 ------> SPI3_MISO PC12 ------> SPI3_MOSI */ GPIO_InitStruct.Pin = GPIO_PIN_10|GPIO_PIN_11|GPIO_PIN_12; GPIO_InitStruct.Mode = GPIO_MODE_AF_PP; GPIO_InitStruct.Pull = GPIO_NOPULL; GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_VERY_HIGH; GPIO_InitStruct.Alternate = GPIO_AF6_SPI3; HAL_GPIO_Init(GPIOC, &GPIO_InitStruct); /* USER CODE BEGIN SPI3_MspInit 1 */ /* USER CODE END SPI3_MspInit 1 */ } } void HAL_SPI_MspDeInit(SPI_HandleTypeDef* spiHandle) { 
     if(spiHandle->Instance==SPI2) { 
     /* USER CODE BEGIN SPI2_MspDeInit 0 */ /* USER CODE END SPI2_MspDeInit 0 */ /* Peripheral clock disable */ __HAL_RCC_SPI2_CLK_DISABLE(); /SPI2 GPIO Configuration PB13 ------> SPI2_SCK PB14 ------> SPI2_MISO PB15 ------> SPI2_MOSI */ HAL_GPIO_DeInit(GPIOB, GPIO_PIN_13|GPIO_PIN_14|GPIO_PIN_15); /* USER CODE BEGIN SPI2_MspDeInit 1 */ /* USER CODE END SPI2_MspDeInit 1 */ } else if(spiHandle->Instance==SPI3) { 
     /* USER CODE BEGIN SPI3_MspDeInit 0 */ /* USER CODE END SPI3_MspDeInit 0 */ /* Peripheral clock disable */ __HAL_RCC_SPI3_CLK_DISABLE(); /SPI3 GPIO Configuration PC10 ------> SPI3_SCK PC11 ------> SPI3_MISO PC12 ------> SPI3_MOSI */ HAL_GPIO_DeInit(GPIOC, GPIO_PIN_10|GPIO_PIN_11|GPIO_PIN_12); /* USER CODE BEGIN SPI3_MspDeInit 1 */ /* USER CODE END SPI3_MspDeInit 1 */ } } /* USER CODE BEGIN 1 */ /* USER CODE END 1 */

4.5 main.h

/* USER CODE BEGIN Header */ / * @file : main.h * @brief : Header for main.c file. * This file contains the common defines of the application. * @attention * * Copyright (c) 2023 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 */ /* Define to prevent recursive inclusion -------------------------------------*/ #ifndef __MAIN_H #define __MAIN_H #ifdef __cplusplus extern "C" { 
     #endif /* Includes ------------------------------------------------------------------*/ #include "stm32f4xx_hal.h" /* Private includes ----------------------------------------------------------*/ /* USER CODE BEGIN Includes */ /* USER CODE END Includes */ /* Exported types ------------------------------------------------------------*/ /* USER CODE BEGIN ET */ /* USER CODE END ET */ /* Exported constants --------------------------------------------------------*/ /* USER CODE BEGIN EC */ /* USER CODE END EC */ /* Exported macro ------------------------------------------------------------*/ /* USER CODE BEGIN EM */ /* USER CODE END EM */ /* Exported functions prototypes ---------------------------------------------*/ void Error_Handler(void); /* USER CODE BEGIN EFP */ /* USER CODE END EFP */ /* Private defines -----------------------------------------------------------*/ #define LED0_Pin GPIO_PIN_9 #define LED0_GPIO_Port GPIOF #define LED1_Pin GPIO_PIN_10 #define LED1_GPIO_Port GPIOF #define MAX6675_CS_Pin GPIO_PIN_0 #define MAX6675_CS_GPIO_Port GPIOB /* USER CODE BEGIN Private defines */ /* USER CODE END Private defines */ #ifdef __cplusplus } #endif #endif /* __MAIN_H */

4.6 main.c

/* USER CODE BEGIN Header */ / * @file : main.c * @brief : Main program body * @attention * * Copyright (c) 2023 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" #include "spi.h" #include "usart.h" #include "gpio.h" #include "stdio.h" #include "./max6675/max6675.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 */ /* USER CODE END PD */ /* Private macro -------------------------------------------------------------*/ /* USER CODE BEGIN PM */ /* USER CODE END PM */ /* Private variables ---------------------------------------------------------*/ /* USER CODE BEGIN PV */ uint16_t max6675_regValue = 0x0000; float max6675_temperature = 0.0; /* USER CODE END PV */ /* Private function prototypes -----------------------------------------------*/ void SystemClock_Config(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_SPI2_Init(); MX_SPI3_Init(); MX_USART1_UART_Init(); /* USER CODE BEGIN 2 */ MAX6675_Init(); printf("max6675\n"); /* USER CODE END 2 */ /* Infinite loop */ /* USER CODE BEGIN WHILE */ while (1) { 
     /* USER CODE END WHILE */ max6675_regValue = MAX6675_ReadRawValue(); max6675_temperature = (float)max6675_regValue*1024.0/4096.0; printf("max6675_regValue:%x, temperature:%.1f\n", max6675_regValue, max6675_temperature); HAL_Delay(1000); /* USER CODE BEGIN 3 */ } /* USER CODE END 3 */ } / * 函数功能: 重定向c库函数printf到huart1 * 输入参数: 无 * 返 回 值: 无 * 说 明：无 */ int fputc(int ch, FILE *f) { 
     HAL_UART_Transmit(&huart1, (uint8_t *)&ch, 1, 0xffff); return ch; } / * @brief System Clock Configuration * @retval None */ 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_SCALE1); / Initializes the RCC Oscillators according to the specified parameters * in the RCC_OscInitTypeDef structure. */ RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE; RCC_OscInitStruct.HSEState = RCC_HSE_ON; RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON; RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE; RCC_OscInitStruct.PLL.PLLM = 4; RCC_OscInitStruct.PLL.PLLN = 168; RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV2; RCC_OscInitStruct.PLL.PLLQ = 4; 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_PLLCLK; RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1; RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV4; RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV2; if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_5) != HAL_OK) { 
     Error_Handler(); } } /* 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 */

注意：重定向c库函数printf到huart1，需要加入头文件#include “stdio.h”，同时勾选use MicroLIB选型，堆栈设置稍微大一些。

5. 测试结果（要想波动小，加上数字滤波）

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