arduino ibox项目实战8－PWM实现LED灯渐变实验

armeasy

硬件平台：PC机一台，ibox卡片电脑一只，arduino扩展板一个，串联有电阻的LED灯外设一个

软件平台：WIN7操作系统，android4.0或android4.4系统

打开arduino的IDE开发工具，依次点击文件->示例->01.Basics->DigitalReadSerial，DigitalReadSerial的示例程序将会被打开，其源码如下：

1. int led = PWM0;           // the pin that the LED is attached to PWM0 = 5.
   
2. int brightness = 0;    // how bright the LED is
   
3. int fadeAmount = 80;    // how many points to fade the LED by
   
4. 
   
5. // the setup routine runs once when you press reset:
   
6. void setup() {
   
7.   // declare pin 5(PWM0) to be an output:
   
8.   pinMode(led, OUTPUT);
   
9. }
   
10. 
    
11. // the loop routine runs over and over again forever:
    
12. void loop() {
    
13.   // set the brightness of pin 5(PWM0):
    
14.   analogWrite(led, brightness);
    
15. 
    
16.   // change the brightness for next time through the loop:
    
17.   brightness = brightness + fadeAmount;
    
18. 
    
19.   // reverse the direction of the fading at the ends of the fade:
    
20.   if (brightness <= 0 || brightness >= 4095) {
    
21.     fadeAmount = -fadeAmount ;
    
22.   }
    
23.   // wait for 30 milliseconds to see the dimming effect
    
24.   delay(30);
    
25. }

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       从源码可以看出，程序通过pwm0口控制LED灯，通过analogWrite函数的传入参数brightness的渐变，实现PWM脉宽的调制，最终实现LED灯的渐亮渐灭的效果。

       将LED灯外设的负极接到PWM0口，正级接到3.3V电源口，运行arduino，可以发现，LED灯确实实现了渐亮渐灭的效果。