STM32使用PWM调光实现睡眠呼吸灯_pwm呼吸灯代码

引言

        在许多的智能手机和家用睡前床灯等场景上，或多或少都可以见到一个呼吸灯的影子。 本文中采用了PWM技术复刻这一呼吸灯效果。 

        在PWM调光屏幕上，调节亮度并不靠改变功率，而是靠屏幕的亮、灭交替。PWM调光屏幕点亮时并不是持续发光的，而是在不停地点亮、熄灭屏幕。当亮、灭交替够快时，肉眼就会认为手机一直在亮。

        在屏幕亮、灭的过程中，灭屏状态持续时间越长，屏幕给肉眼的观感就是亮度越低。点亮的时间越长，灭屏时间就相应减少，屏幕就会变亮。

        亮、灭交替的速度越低，对人眼造成不利影响的可能性就越大。但这并不是绝对的，因为每个人对于“闪烁”的敏感程度不同。比如看同一块PWM屏幕，有人没事，有人就会感到疲劳。如果你属于眼睛十分敏感的那部分人，你可能就需要使用高频PWM调光手机，甚至DC调光手机了。

一、PWM概述

1、PWM定义

        PWM叫脉冲宽度调制(Pulse Width Modulation)，通过编程控制输出方波的频率和占空比(高低电平的比例)，广泛应用在测量，通信，功率控制等领域(呼吸灯，电机)。

      脉冲：方波、频率（frequency）

      宽度：高电平宽度，占空比（duty）

占空比25%

占空比50%

占空比75%

如下所示，通过调节占空比，改变LED亮度以实现本文所描述的呼吸灯效果外，还可以通过调节占空比去控制舵机的转动角度。更深入的运用便是控制机械手、机械臂的运动。

调节亮度

占空比50%

占空比20%

控制舵机运转角度

二、STM32库函数

1、GPIO引脚映射函数----GPIO_PinAFConfig( )

/**
  * @brief  Changes the mapping of the specified pin.
  * @param  GPIOx: where x can be (A..K) to select the GPIO peripheral for STM32F405xx/407xx and STM32F415xx/417xx devices
  *                      x can be (A..I) to select the GPIO peripheral for STM32F42xxx/43xxx devices.
  *                      x can be (A, B, C, D and H) to select the GPIO peripheral for STM32F401xx devices. 
  * @param  GPIO_PinSource: specifies the pin for the Alternate function.
  *         This parameter can be GPIO_PinSourcex where x can be (0..15).
  * @param  GPIO_AFSelection: selects the pin to used as Alternate function.
  * @retval None
  */
void GPIO_PinAFConfig(GPIO_TypeDef* GPIOx, uint16_t GPIO_PinSource, uint8_t GPIO_AF);

2、初始化定时器的时间基准----TIM_TimeBaseInit( )

/**
  * @brief  Initializes the TIMx Time Base Unit peripheral according to 
  *         the specified parameters in the TIM_TimeBaseInitStruct.
  * @param  TIMx: where x can be  1 to 14 to select the TIM peripheral.
  * @param  TIM_TimeBaseInitStruct: pointer to a TIM_TimeBaseInitTypeDef structure
  *         that contains the configuration information for the specified TIM peripheral.
  * @retval None
  */
void TIM_TimeBaseInit(TIM_TypeDef* TIMx, TIM_TimeBaseInitTypeDef* TIM_TimeBaseInitStruct)

3、定时器通道1配置----TIM_OC1Init( )

/**
  * @brief  Initializes the TIMx Channel1 according to the specified parameters in
  *         the TIM_OCInitStruct.
  * @param  TIMx: where x can be 1 to 14 except 6 and 7, to select the TIM peripheral.
  * @param  TIM_OCInitStruct: pointer to a TIM_OCInitTypeDef structure that contains
  *         the configuration information for the specified TIM peripheral.
  * @retval None
  */
void TIM_OC1Init(TIM_TypeDef* TIMx, TIM_OCInitTypeDef* TIM_OCInitStruct)

注：

通道1:TIM_OC1Init

通道2:TIM_OC2Init

通道3:TIM_OC3Init

通道4:TIM_OC4Init

4、定时器通道1比较值----TIM_SetCompare1( )

/**
  * @brief  Sets the TIMx Capture Compare1 Register value
  * @param  TIMx: where x can be 1 to 14 except 6 and 7, to select the TIM peripheral.
  * @param  Compare1: specifies the Capture Compare1 register new value.
  * @retval None
  */
void TIM_SetCompare1(TIM_TypeDef* TIMx, uint32_t Compare1)

注：

通道1:TIM_SetCompare1

通道2:TIM_SetCompare2

通道3:TIM_SetCompare3

通道4:TIM_SetCompare4

三、函数配置说明

《stm32f4xx中文参考手册》.pdf P433

通用定时器TIM3到TIM5

TIMx_CNT由TIM_TimeBaseStructure.TIM_Period决定；

TIMx_CCR1由TIM_SetComparex(x:1、2、3、4)函数决定；

有效状态由TIM_OCInitStructure.TIM_OCPolarity决定；

频率值：由计数值决定
占空比：由比较值决定
注：要保持一定的占空比时，计数值（TIM_Period）发生变更，比较值（TIM_Pulse）也要发生变更

要设置的比较值 =（TIM_Period+1）* 占空比

TIM_TimeBaseStructure.TIM_Period = 100-1;		//输出脉冲的频率100Hz
......
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;		//通道工作在PWM模式1
......
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;	//有效状态为高电平
......
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;//输出状态使能
......
TIM_OCInitStructure.TIM_Pulse = 50;	//当前填写值决定了占空比
......

调整TIM1通道1的占空比为20%

TIM_SetCompare1(TIM3, 20);

四、PWM呼吸灯代码

  main.c

#include "stm32f4xx.h"
#include "mypwm.h"
 
int main(void)
{
 
	int i = 0;
	//NVIC_PriorityGroupConfig(NVIC_PriorityGroup_1);
 
	LED_TIM3_Init();
	LED_PWM1_Init();
	
	PAout(6) = 1;
	PCout(5) = 1;
 
	while(1)
	{
		//由暗到亮
		for(i=0; i<=100; i++)
		{
			TIM_SetCompare1(TIM3, i);
			TIM_SetCompare2(TIM3, i);
			delay_ms(20);
		}
		//由亮到暗
		for(i=100; i>=0; i--)
		{
			TIM_SetCompare1(TIM3, i);
			TIM_SetCompare2(TIM3, i);
			delay_ms(20);
		}
		
	}
	
	return 0;
}

  mypwm.c

#include "mypwm.h"
 
//LED初始化
void LED_TIM3_Init(void)
{	
	GPIO_InitTypeDef GPIO_InitStructure;
	
	/* TIM3 clock enable */
	RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);
	
	/* GPIOA clock enable */
	RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);
	
	/* GPIOC Configuration: TIM3 CH1 (PA6) */
	GPIO_InitStructure.GPIO_Pin   = GPIO_Pin_6;
	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); 
 
	/* GPIOC Configuration: TIM3 CH2 (PA7) */
	GPIO_InitStructure.GPIO_Pin   = GPIO_Pin_7;
	GPIO_Init(GPIOA, &GPIO_InitStructure); 
	
	/* Connect TIM3 pins to PA6 PA7 */  
	GPIO_PinAFConfig(GPIOA, GPIO_PinSource6, GPIO_AF_TIM3);
	GPIO_PinAFConfig(GPIOA, GPIO_PinSource7, GPIO_AF_TIM3);
	//熄灭所有灯
	PAout(6) = 1;
	PAout(7) = 1;
}
 
//LED的PWM配置
void LED_PWM1_Init(void)
{
	//NVIC_InitTypeDef NVIC_InitStructure;
	TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
	TIM_OCInitTypeDef  TIM_OCInitStructure;
	RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);
	
	/* Time base configuration */
	TIM_TimeBaseStructure.TIM_Period = 100-1; //100Hz  定时时间的配置，也就是配置重载值，而重载值会传递给计数值
	TIM_TimeBaseStructure.TIM_Prescaler = 8400 - 1;	  //配置分频值，确定定时器的时钟频率
	TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up; //向上计数，0->TIM_Period就会触发中断请求
	
	TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);
	
	/* PWM1 Mode configuration: Channel1 */
	TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
	TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
	TIM_OCInitStructure.TIM_Pulse = 50;	
	TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
	
	TIM_OC1Init(TIM3, &TIM_OCInitStructure);
	TIM_OC1PreloadConfig(TIM3, TIM_OCPreload_Enable);
	
	/* PWM1 Mode configuration: Channel2 */
	TIM_OCInitStructure.TIM_Pulse = 50;
	TIM_OC2Init(TIM3, &TIM_OCInitStructure);
 
	/* TIM3 enable counter */
	TIM_Cmd(TIM3, ENABLE);
	
//	NVIC_InitStructure.NVIC_IRQChannel = TIM3_IRQn;
//	NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
//	NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
//	NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
//	NVIC_Init(&NVIC_InitStructure);	
}

mypwm.h

#ifndef __MY_PWM_H
#define __MY_PWM_H
 
	#include "stm32f4xx.h"
    //位带操作
	#define PAout(n)  (*(uint32_t *)(0x42000000 +(GPIOA_BASE+0x14-0x40000000)*32 + n*4))
	#define PBout(n)  (*(uint32_t *)(0x42000000 +(GPIOB_BASE+0x14-0x40000000)*32 + n*4))
	#define PCout(n)  (*(uint32_t *)(0x42000000 +(GPIOC_BASE+0x14-0x40000000)*32 + n*4))
	
	#define PBin(n)   (*(uint32_t *)(0x42000000 +(GPIOB_BASE+0x10-0x40000000)*32 + n*4))
	#define PCin(n)   (*(uint32_t *)(0x42000000 +(GPIOC_BASE+0x10-0x40000000)*32 + n*4))
 
	void LED_Init(void);
	void LED_TIM3_Init(void);
	void LED_PWM1_Init(void);
	
#endif

注意：并不是每个GPIO引脚都可以进行TIM定时器配置，需要看ST官方的芯片手册，是否有对应的引脚复用功能。如下图所示的为STM32F407VET6芯片的部分截图。

普通IO也可以输出PWM，很少直接用MCU的IO口直接输出，因为那样需要消耗大量的MCU资源。