开关抖动及消除设计

当按下和释放微动按键时，会由短时间的抖动现象才会到达想要的状态。如下图所示：

从上图可知。按键抖动时间大概为150us。

在一些对按键抖动敏感的情况下需要进行消抖设计，目前常见的消抖设计如下：

    滤波电容

关于去抖硬件最简单的方式并联一颗100nF陶瓷电容,进行滤波处理。

    RC滤波＋施密特触发器

要想更严谨设计消抖电路，会增加施密特触发器，更大程度的保证后端不受按键抖动影响，电路如下：

分别来看按键闭合断开时电路状态：

开关打开时：

电容C1通过R1 D1回路充电,Vb电压=Vcc-0.7为高电平,后通过反向施密特触发器使Vout输出为低。

开关闭合时：

电容C1通过R2进行放电，最后Vb电压变为0,通过反向施密特触发器使Vout输出为高。

当按下按键出现快速抖动现象时，通过电容会使Vb点电压快速变成Vcc或GND。在抖动过程时对电容会有轻微的充电或放电，但后端的施密特触发器有迟滞效果不会导致Vout发现抖动现象。

此电路中D1的使用使为了限制R1 R2一起给C1供电，增加充电时间影响效果。如果减小R1的值会使电流增加，功耗较高。

    专用消抖芯片

一些厂家会提供专用芯片，避免自搭电路的不稳定性， 如美信-Max6816：

    软件滤波

软件消除抖动也是很常见的方式,一般形式是延时查询按键状态或者中断形式来消除抖动。

下面是Arduino的软件消抖代码：

/* SoftwareDebounce

 * 

 * At each transition from LOW to HIGH or from HIGH to LOW 

 * the input signal is debounced by sampling across

 * multiple reads over several milli seconds.  The input

 * is not considered HIGH or LOW until the input signal 

 * has been sampled for at least "debounce_count" (10)

 * milliseconds in the new state.

 *

 * Notes:

 *   Adjust debounce_count to reflect the timescale 

 *     over which the input signal may bounce before

 *     becoming steady state

 *

 * Based on:

 *   http://www.arduino.cc/en/Tutorial/Debounce

 *

 * Jon Schlueter

 * 30 December 2008

 *

 * http://playground.arduino.cc/Learning/SoftwareDebounce

 */

int inPin = 7;         // the number of the input pin

int outPin = 13;       // the number of the output pin

int counter = 0;       // how many times we have seen new value

int reading;           // the current value read from the input pin

int current_state = LOW;    // the debounced input value

// the following variable is a long because the time, measured in milliseconds,

// will quickly become a bigger number than can be stored in an int.

long time = 0;         // the last time the output pin was sampled

int debounce_count = 10; // number of millis/samples to consider before declaring a debounced input

void setup()

{

  pinMode(inPin, INPUT);

  pinMode(outPin, OUTPUT);

  digitalWrite(outPin, current_state); // setup the Output LED for initial state

}

void loop()

{

  // If we have gone on to the next millisecond

  if(millis() != time)

  {

    reading = digitalRead(inPin);

    if(reading == current_state && counter > 0)

    {

      counter--;

    }

    if(reading != current_state)

    {

       counter++; 

    }

    // If the Input has shown the same value for long enough let's switch it

    if(counter >= debounce_count)

    {

      counter = 0;

      current_state = reading;

      digitalWrite(outPin, current_state);

    }

    time = millis();

  }

}

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