【RA-Eco-RA4M2开发板评测】基于MLX90614的红外测温(二)

5 红外测温枪实现

5.1 MLX90614温度读取

MLX90614是基于I2C的，根据MLX90614的读写时序，其核心函数如下。

/**
  * [url=home.php?mod=space&uid=2666770]@Brief[/url]  Mlx90614读寄存器
  * [url=home.php?mod=space&uid=3142012]@param[/url]  p_api_ctrl, regAddr, pReadData
  * @retval 返回值 0 表示正确， 返回1表示未探测到
  */
int8_t BSP_MLX90614_ReadReg(i2c_master_ctrl_t * const p_api_ctrl, uint8_t regAddr, uint16_t *pReadData)
{
    uint8_t writeBuf[1] = {0};
    uint8_t readBuf[3] = {0};
    uint8_t ValBuf[6] = {0};
    uint8_t prcRegVal = 0;
  
    ValBuf[0] = MLX90614_ADDR << 1;
    ValBuf[1] = (uint8_t)(regAddr);
    ValBuf[2] = (MLX90614_ADDR << 1) | 0x01;

    fsp_err_t err;

    writeBuf[0] = (uint8_t)(regAddr);

    err = R_IIC_MASTER_Write(p_api_ctrl, writeBuf, 1, true);
    R_BSP_SoftwareDelay(1, BSP_DELAY_UNITS_MILLISECONDS);
    err = R_IIC_MASTER_Read(p_api_ctrl, readBuf, 3 , false);

    R_BSP_SoftwareDelay(1, BSP_DELAY_UNITS_MILLISECONDS);

    err = R_IIC_MASTER_Write(p_api_ctrl, writeBuf, 1, true);
    R_BSP_SoftwareDelay(1, BSP_DELAY_UNITS_MILLISECONDS);
    err = R_IIC_MASTER_Read(p_api_ctrl, readBuf, 3 , false);
    if (err != FSP_SUCCESS)
    {
        return -1;
    }
    else
    {
        ValBuf[3] = readBuf[0];
        ValBuf[4] = readBuf[1];
        ValBuf[5] = readBuf[2];
        prcRegVal = CRC8_Calc(ValBuf, 5);
        if(prcRegVal == ValBuf[5])
        {
            *pReadData = (uint16_t)((readBuf[1] << 8) + readBuf[0]);
        }
    }
    return 0; /* 执行成功 */
}

/**
  * @brief  Mlx90614读取温度值
  * @param  p_api_ctrl
  * @retval 温度值
  */
float BSP_MLX90614_ReadTemp(i2c_master_ctrl_t * const p_api_ctrl)
{
    float temp;
    uint16_t data;

    if( 0 == BSP_MLX90614_ReadReg(p_api_ctrl, MLX90614_TOBJ1, &data))
    {
        temp = (float)(data * 0.02f - 273.15f);
    }
    else
    {
        temp = MLX90614_TEMP_READ_ERR_CODE;
    }
    
    return temp;
}

最后在Temperature任务中调用BSP_MLX90614_ReadTemp ()函数不断读取温度值。

5.2 MLX90614体温矫正

非接触式红外温度传感器测额温或是体表温度和实际体温是有一定的差异的。因此采用了迈来芯原厂提供的额温转体温参考算法来提高测温精度，以补偿后的温度作为人体体温输出。其核心算法如下：

/**
  * @brief  额温转体温算法
  * @param  ta为芯片内部温度，tf为额温
  * @retval tbody为体温
  */
float TF_to_Tbody(float ta, float tf)
{
    float tf_low, tf_high = 0;
    float tbody = 0;

    if(ta <= TA_LEVEL)
    {
        tf_low  = 32.66f + 0.186f*(ta-TA_LEVEL);
        tf_high = 34.84f + 0.148f*(ta-TA_LEVEL);
    }
    else
    {
        tf_low  = 32.66f + 0.086f*(ta-TA_LEVEL);
        tf_high = 34.84f + 0.1f*(ta-TA_LEVEL);
    }

    if((tf_low <= tf) && (tf <= tf_high))
    {
        //normal
        tbody = 36.3f + 0.5f/(tf_high - tf_low)*(tf - tf_low);
    }
    else if(tf > tf_high)
    {
        tbody = 36.8f + (0.829321f + 0.002364f*ta)*(tf-tf_high);
    }
    else if(tf < tf_low)
    {
        tbody =  36.3f + (0.551658f + 0.021525f*ta)*(tf-tf_low);
    }
    
    return tbody;
}