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I2C外设使用以光照传感器信息读取
I2C接口是很多传感器使用的通讯接口，在低功耗应用中，传感器的使用也是很普遍的。本文使用开发板的I2C接口来读取ISL29035光照传感器的数据。
1.硬件准备
通过查看原理图可知，PB8、PB9为Arduino接口上的I2C引脚。本文使用I2C接口与ISL29035光照传感器通讯，获得环境中的光照强度信息。
本文中使用到的传感器的原理图如图所示。
与传感器通讯的的I2C接口选择Arduino接口上的PB8和PB9，传感器模块和开发板的实物连接图如下图所示。
2.程序编写
首先，在STM32 CubeIDE中创建开发板的工程，选择根据开发板创建工程，
在CubeMX界面中会自动初始化开发板上的部分外设，比如串口、调试口、LED等，本文通过I2C1控制传感器，使用的PB8和PB9，选择对应管脚的复用功能，并在I2C的配置界面选择相应的I2C通讯参数，这里使用的参数是默认的配置。
完成上述操作后，保存配置并生成相应的外设初始化代码。
传感器ISL29035的功能框图如下图所示。
通过I2C向指令寄存器中写值，配置传感器的参数和控制传感器采样；从数据寄存器中读取采样的结果，用于计算光照值。驱动传感器工作需要实现以下几个函数。
- uint8_t DigitalLightISL29035_readRegister(uint8_t reg_address);
- void DigitalLightISL29035_writeRegister( int reg_address, uint8_t val) ;
- int DigitalLightISL29035_init(void) ;
- uint32_t DigitalLightISL29035_readIRLux(void);
其中的读取和写入寄存器的函数是驱动传感器工作的基础函数。这两个函数的具体实现如下。
- void DigitalLightISL29035_writeRegister( int reg_address, uint8_t val) {
- uint8_t ii[2]={0x00,0x00};
- ii[0] = reg_address;
- ii[1] = val;
- if (HAL_I2C_Master_Transmit(&hi2c1, (uint16_t)ISL29035_I2C_ADDRESS_W, ii, 0x02,10000) != HAL_OK)
- {
- /* Error_Handler() function is called when error occurs. */
- Error_Handler();
- }
- /*##- Wait for the end of the transfer #################################*/
- /* Before starting a new communication transfer, you need to check the current
- state of the peripheral; if it�s busy you need to wait for the end of current
- transfer before starting a new one.
- For simplicity reasons, this example is just waiting till the end of the
- transfer, but application may perform other tasks while transfer operation
- is ongoing. */
- while (HAL_I2C_GetState(&hi2c1) != HAL_I2C_STATE_READY)
- {
- }
- }
- uint8_t DigitalLightISL29035_readRegister(uint8_t reg_address) {
- uint8_t value;
- if (HAL_I2C_Master_Transmit(&hi2c1, (uint16_t)ISL29035_I2C_ADDRESS_W, ®_address, 0x01,10000) != HAL_OK)
- {
- /* Error_Handler() function is called when error occurs. */
- Error_Handler();
- }
- /*##- Wait for the end of the transfer #################################*/
- /* Before starting a new communication transfer, you need to check the current
- state of the peripheral; if it�s busy you need to wait for the end of current
- transfer before starting a new one.
- For simplicity reasons, this example is just waiting till the end of the
- transfer, but application may perform other tasks while transfer operation
- is ongoing. */
- while (HAL_I2C_GetState(&hi2c1) != HAL_I2C_STATE_READY)
- {
- }
- /* Read data back from the I2C slave */
- if (HAL_I2C_Master_Receive(&hi2c1, (uint16_t)ISL29035_I2C_ADDRESS_R, (uint8_t *)&value, 0x01,10000) != HAL_OK)
- {
- /* Error_Handler() function is called when error occurs. */
- Error_Handler();
- }
- /*##- Wait for the end of the transfer #################################*/
- /* Before starting a new communication transfer, you need to check the current
- state of the peripheral; if it�s busy you need to wait for the end of current
- transfer before starting a new one.
- For simplicity reasons, this example is just waiting till the end of the
- transfer, but application may perform other tasks while transfer operation
- is ongoing. */
- while (HAL_I2C_GetState(&hi2c1) != HAL_I2C_STATE_READY)
- {
- }
- return value;
- }
通过阅读传感器的数据手册可知传感器的寄存的分布如下图
通过向COMMAND-I和COMMAND-II指令寄存器中写入控制字，从而实现控制传感器的采样精度、采样时间、工作模式等。从DATA数据寄存器中读取转换完成的数据。
值得注意的一点是在数据手册中，ID寄存器的第7位需要在开始时确定其处于复位的状态。
配合数据手册中的信息，传感器的初始化函数如下：
- int DigitalLightISL29035_init(void) {
- uint8_t reg = 0;
- reg= DigitalLightISL29035_readRegister( CHIP_ID);//CHIP_ID->0x0f
- //Serial.println(reg, HEX);
- uint8_t chip_id = (reg >> 3) & 0x7;
- if (chip_id != 0x5) {
- return -1;
- }
- //清除BOUT位
- DigitalLightISL29035_writeRegister(CHIP_ID, reg & 0x7f);//CHIP_ID->0x0f
- //确保芯片处于停止模式
- DigitalLightISL29035_writeRegister( COMMAND_I, 0);//COMMAND_I->0x00
- //设置分辨率
- DigitalLightISL29035_writeRegister(COMMAND_II, full_scale_lux_range | (integration_time << 2) );//COMMAND_2->0x01
- //设置为单次模式
- DigitalLightISL29035_writeRegister( COMMAND_I, OPMODE_ALS_ONCE);//COMMAND_I->0x00
- return 0;
- }
- uint32_t DigitalLightISL29035_readIRLux(void) {
- uint16_t data = 0;
- uint8_t l, h;
- //设置为单次模式
- DigitalLightISL29035_writeRegister( COMMAND_I, OPMODE_ALS_ONCE);
- //等待时间
- if(integration_time==0)
- {
- HAL_Delay(105);
- }
- else if(integration_time==1 || integration_time==2)
- {
- HAL_Delay(7);
- }
- else if(integration_time==3)
- {
- HAL_Delay(1);
- }
- l=DigitalLightISL29035_readRegister(DATA_L);//DATA_L->0x02
- h=DigitalLightISL29035_readRegister(DATA_H);//DATA_H->0x03
- data=(h << 8) | l;
- uint32_t ranges=0;
- if(full_scale_lux_range==0)
- ranges=1000;
- else if(full_scale_lux_range==1)
- ranges=4000;
- else if(full_scale_lux_range==2)
- ranges=16000;
- else if(full_scale_lux_range==3)
- ranges=64000;
- uint32_t adc_count_max=0;
- if(integration_time==0)
- adc_count_max=65536;
- else if(integration_time==1)
- adc_count_max=4096;
- else if(integration_time==2)
- adc_count_max=256;
- else if(integration_time==3)
- adc_count_max=16;
- return ranges * (uint32_t)data /adc_count_max;
- }
- /* USER CODE BEGIN 2 */
- DigitalLightISL29035_init();
- HAL_Delay(500);
- lux = DigitalLightISL29035_readIRLux();
- printf("lux is %ld",lux);
- /* USER CODE END 2 */
- /* Infinite loop */
- /* USER CODE BEGIN WHILE */
- while (1)
- {
- HAL_Delay(1000);
- lux = DigitalLightISL29035_readIRLux();
- printf("lux=%ld\n",lux);
- /* USER CODE END WHILE */
- /* USER CODE BEGIN 3 */
- }
实际的运行效果如下所示。
3.总结
STM32的CubeMX工具和丰富的外设示例代码，可以帮助工程师快速完成应用的开发，实现系统原型的搭建。
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