開關(guān)抖動及消除設(shè)計

當(dāng)按下和釋放微動按鍵時，會由短時間的抖動現(xiàn)象才會到達(dá)想要的狀態(tài)。如下圖所示：

從上圖可知。按鍵抖動時間大概為150us。

在一些對按鍵抖動敏感的情況下需要進(jìn)行消抖設(shè)計，目前常見的消抖設(shè)計如下：

濾波電容

關(guān)于去抖硬件最簡單的方式并聯(lián)一顆100nF陶瓷電容,進(jìn)行濾波處理。

RC濾波＋施密特觸發(fā)器

要想更嚴(yán)謹(jǐn)設(shè)計消抖電路，會增加施密特觸發(fā)器，更大程度的保證后端不受按鍵抖動影響，電路如下：

分別來看按鍵閉合斷開時電路狀態(tài)：

開關(guān)打開時：

電容C1通過R1 D1回路充電,Vb電壓=Vcc-0.7為高電平,后通過反向施密特觸發(fā)器使Vout輸出為低。

開關(guān)閉合時：

電容C1通過R2進(jìn)行放電，最后Vb電壓變?yōu)?,通過反向施密特觸發(fā)器使Vout輸出為高。

當(dāng)按下按鍵出現(xiàn)快速抖動現(xiàn)象時，通過電容會使Vb點電壓快速變成Vcc或GND。在抖動過程時對電容會有輕微的充電或放電，但后端的施密特觸發(fā)器有遲滯效果不會導(dǎo)致Vout發(fā)現(xiàn)抖動現(xiàn)象。

此電路中D1的使用使為了限制R1 R2一起給C1供電，增加充電時間影響效果。如果減小R1的值會使電流增加，功耗較高。

專用消抖芯片

一些廠家會提供專用芯片，避免自搭電路的不穩(wěn)定性， 如美信-Max6816：

軟件濾波

軟件消除抖動也是很常見的方式,一般形式是延時查詢按鍵狀態(tài)或者中斷形式來消除抖動。

下面是Arduino的軟件消抖代碼：

/* 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();

}

}

審核編輯：湯梓紅