开关抖动及消除 |
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开关抖动及消除
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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：
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。
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：
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(); } }参考 Switch Bounce and How to Deal with ItSwitch DebouncingDebounce a Switch |
从上图可知。按键抖动时间大概为150us。
分别来看按键闭合断开时电路状态：
开关打开时：
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