按键防抖（Debounce）

按键在按下时，由于机械和物理特定的原因，经常会产生一些开关变换，而这些变换会让程序误认为是短时间内进行了多次按键。本示例展示了如何对输入信号进行防抖，也就是在一段短时间内进行两次检查来确保按键确实被按下。如果没有防抖的话，按下一次按键会产生很多不可预知的结果。示例代码使用了mills()函数记录按键按下经过的时间。

所需硬件

-    Arduino或者Genuino开发板

-    按钮开关

-    10K电阻

-    导线

-    面包板

电路连接方式

原理图

代码

以下代码基于Limor Fried的防抖方法，但是逻辑与她的示例相反。她的示例中，按键在闭合时返回低电平LOW，断开时返回高电平HIGH。而在本例中，按键按下时返回高电平，未按下时返回低电平LOW。

1. /*
   
2. Debounce
   
3. 
   
4. Each time the input pin goes from LOW to HIGH (e.g. because of a push-button
   
5. press), the output pin is toggled from LOW to HIGH or HIGH to LOW.  There's
   
6. a minimum delay between toggles to debounce the circuit (i.e. to ignore
   
7. noise).
   
8. 
   
9. The circuit:
   
10. * LED attached from pin 13 to ground
    
11. * pushbutton attached from pin 2 to +5V
    
12. * 10K resistor attached from pin 2 to ground
    
13. 
    
14. * Note: On most Arduino boards, there is already an LED on the board
    
15. connected to pin 13, so you don't need any extra components for this example.
    
16. 
    
17. 
    
18. created 21 November 2006
    
19. by David A. Mellis
    
20. modified 30 Aug 2011
    
21. by Limor Fried
    
22. modified 28 Dec 2012
    
23. by Mike Walters
    
24. 
    
25. This example code is in the public domain.
    
26. 
    
27. http://www.arduino.cc/en/Tutorial/Debounce
    
28. */
    
29. 
    
30. // constants won't change. They're used here to
    
31. // set pin numbers:
    
32. const int buttonPin = 2;    // the number of the pushbutton pin
    
33. const int ledPin = 13;      // the number of the LED pin
    
34. 
    
35. // Variables will change:
    
36. int ledState = HIGH;         // the current state of the output pin
    
37. int buttonState;             // the current reading from the input pin
    
38. int lastButtonState = LOW;   // the previous reading from the input pin
    
39. 
    
40. // the following variables are long's because the time, measured in miliseconds,
    
41. // will quickly become a bigger number than can be stored in an int.
    
42. long lastDebounceTime = 0;  // the last time the output pin was toggled
    
43. long debounceDelay = 50;    // the debounce time; increase if the output flickers
    
44. 
    
45. void setup() {
    
46.   pinMode(buttonPin, INPUT);
    
47.   pinMode(ledPin, OUTPUT);
    
48. 
    
49.   // set initial LED state
    
50.   digitalWrite(ledPin, ledState);
    
51. }
    
52. 
    
53. void loop() {
    
54.   // read the state of the switch into a local variable:
    
55.   int reading = digitalRead(buttonPin);
    
56. 
    
57.   // check to see if you just pressed the button
    
58.   // (i.e. the input went from LOW to HIGH),  and you've waited
    
59.   // long enough since the last press to ignore any noise:
    
60. 
    
61.   // If the switch changed, due to noise or pressing:
    
62.   if (reading != lastButtonState) {
    
63.     // reset the debouncing timer
    
64.     lastDebounceTime = millis();
    
65.   }
    
66. 
    
67.   if ((millis() - lastDebounceTime) > debounceDelay) {
    
68.     // whatever the reading is at, it's been there for longer
    
69.     // than the debounce delay, so take it as the actual current state:
    
70. 
    
71.     // if the button state has changed:
    
72.     if (reading != buttonState) {
    
73.       buttonState = reading;
    
74. 
    
75.       // only toggle the LED if the new button state is HIGH
    
76.       if (buttonState == HIGH) {
    
77.         ledState = !ledState;
    
78.       }
    
79.     }
    
80.   }
    
81. 
    
82.   // set the LED:
    
83.   digitalWrite(ledPin, ledState);
    
84. 
    
85.   // save the reading.  Next time through the loop,
    
86.   // it'll be the lastButtonState:
    
87.   lastButtonState = reading;
    
88. }

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