stm32f401rct6如何实现呼吸灯？

要实现呼吸灯效果，可以利用PWM（脉冲宽度调制）的技术。具体的实现步骤如下：

1. 初始化定时器TIM2，将其配置为PWM模式，设置PWM输出引脚的输出模式为推挽输出，并设置其输出频率和占空比。

2. 利用定时器的中断，周期性地调整PWM的占空比，使LED的亮度呈现出呼吸灯效果。

以下是一份示例代码，可供参考：

#include "stm32f4xx.h"

void TIM2_PWM_Init(uint32_t frequency, uint32_t duty_cycle)
{
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);

    GPIO_InitTypeDef GPIO_InitStructure;
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_5;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;
    GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
    GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
    GPIO_Init(GPIOA, &GPIO_InitStructure);

    GPIO_PinAFConfig(GPIOA, GPIO_PinSource5, GPIO_AF_TIM2);

    TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
    TIM_TimeBaseStructure.TIM_Period = 1000 / frequency - 1;
    TIM_TimeBaseStructure.TIM_Prescaler = 84 - 1;
    TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);

    TIM_OCInitTypeDef TIM_OCInitStructure;
    TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
    TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
    TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
    TIM_OCInitStructure.TIM_Pulse = duty_cycle * TIM_TimeBaseStructure.TIM_Period / 100;
    TIM_OC1Init(TIM2, &TIM_OCInitStructure);
    TIM_OC1PreloadConfig(TIM2, TIM_OCPreload_Enable);

    TIM_Cmd(TIM2, ENABLE);
    TIM_ITConfig(TIM2, TIM_IT_Update, ENABLE);
}

void TIM2_IRQHandler(void)
{
    static uint32_t duty_cycle = 0;
    static uint32_t direction = 1;

    if (TIM_GetITStatus(TIM2, TIM_IT_Update) != RESET)
    {
        TIM_ClearITPendingBit(TIM2, TIM_IT_Update);

        if (direction == 1)
        {
            duty_cycle += 5;
            if (duty_cycle >= 95)
            {
                direction = 0;
            }
        }
        else
        {
            duty_cycle -= 5;
            if (duty_cycle <= 5)
            {
                direction = 1;
            }
        }

        TIM_SetCompare1(TIM2, duty_cycle * TIM_GetAutoreload(TIM2) / 100);
    }
}

int main(void)
{
    TIM2_PWM_Init(100, 50);

    NVIC_InitTypeDef NVIC_InitStructure;
    NVIC_InitStructure.NVIC_IRQChannel = TIM2_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStructure);

    while (1)
    {
    }
}

该代码初始化了TIM2，将其配置为PWM模式，并设置其输出频率为100Hz，占空比为50%。在定时器中断中，周期性地调整PWM的占空比，使LED的亮度呈现出呼吸灯效果。