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发表于: 2016-7-18 09:41:39 | 显示全部楼层

按键状态变化检测（State Change Detection）

在使用按键的过程中，经常会遇到要根据按键按下的次数来做一些处理。要做到这一点，我们需要知道按键的状态何时从关断变成闭合，并且记录下这样的状态变化发生的次数。这就是所谓的状态变化检测或者是边沿检测。本示例展示了如何来检测状态变化，将相关信息发送到串行监视器（ Serial Monitor），并且在四次状态变化时来点亮或熄灭LED指示灯。

所需硬件

- Arduino或者Genuino开发板

- 按钮开关

- 10k电阻

- 面包板

- 导线

电路连接方式

将三根导线连接到开发板。第一根导线将按键的一个引脚通过下拉电阻（用的是10k）连接到地。第二根导线将按键的另一个引脚连接到5V电源。第三根导线连接到数字IO引脚（2脚），通过该引脚来读取按键的状态。

当按钮处于开路状态（未按下）时，按键的两个引脚之间没有连接，所以该引脚连接到地（通过下拉电阻），并且读取时为低电平，或者0。当按键关闭（按下）时，两个引脚短接，使得该引脚连接到5V，因此读取时为高电平，或者1。

如果您断开数字I/O引脚的所有连接时，LED会无规律的闪烁。这是因为输入引脚处于悬浮状态，也就是说该引脚与电源或地之间没有固定的连接，并且会随机返回高电平或低电平。这就是为什么在电路中需要下拉电阻。

原理图

代码

下面的程序不断读取按键的状态。然后在主循环中与上次读取的按键状态进行对比。如果当前值与上次的按键状态不同，并且当前按键的状态为高电平，则表示按键从关断变成闭合。然后程序中增加一次按键按下的计数。

程序也检测按键按下的次数。如果该值是4的倍数，那么就会就将13脚的LED灯点亮。否则，LED熄灭。

/*
State change detection (edge detection)
Often, you don't need to know the state of a digital input all the time,
but you just need to know when the input changes from one state to another.
For example, you want to know when a button goes from OFF to ON. This is called
state change detection, or edge detection.
This example shows how to detect when a button or button changes from off to on
and on to off.
The circuit:
* pushbutton attached to pin 2 from +5V
* 10K resistor attached to pin 2 from ground
* LED attached from pin 13 to ground (or use the built-in LED on
most Arduino boards)
created 27 Sep 2005
modified 30 Aug 2011
by Tom Igoe
This example code is in the public domain.
http://www.arduino.cc/en/Tutorial/ButtonStateChange
*/
// this constant won't change:
const int buttonPin = 2; // the pin that the pushbutton is attached to
const int ledPin = 13; // the pin that the LED is attached to
// Variables will change:
int buttonPushCounter = 0; // counter for the number of button presses
int buttonState = 0; // current state of the button
int lastButtonState = 0; // previous state of the button
void setup() {
// initialize the button pin as a input:
pinMode(buttonPin, INPUT);
// initialize the LED as an output:
pinMode(ledPin, OUTPUT);
// initialize serial communication:
Serial.begin(9600);
}
void loop() {
// read the pushbutton input pin:
buttonState = digitalRead(buttonPin);
// compare the buttonState to its previous state
if (buttonState != lastButtonState) {
// if the state has changed, increment the counter
if (buttonState == HIGH) {
// if the current state is HIGH then the button
// wend from off to on:
buttonPushCounter++;
Serial.println("on");
Serial.print("number of button pushes: ");
Serial.println(buttonPushCounter);
} else {
// if the current state is LOW then the button
// wend from on to off:
Serial.println("off");
}
// Delay a little bit to avoid bouncing
delay(50);
}
// save the current state as the last state,
//for next time through the loop
lastButtonState = buttonState;
// turns on the LED every four button pushes by
// checking the modulo of the button push counter.
// the modulo function gives you the remainder of
// the division of two numbers:
if (buttonPushCounter % 4 == 0) {
digitalWrite(ledPin, HIGH);
} else {
digitalWrite(ledPin, LOW);
}
}

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电梯直达

【Arduino官方教程】数字处理示例（五）：按键状态变化检测 [复制链接]

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