View source for Lesson 4--Microduino "LED Brightness and PWM"

{{Language|第四课--按钮PWM控制LED亮度}}
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==Objective==
LED has only two states on and off in other three experiment, now through button realize LED brightness light gradually and gradually out
That is PWM pulse width modulation. Adjusting digital signal (" 0 ", "1") within a period of time that is the time of the duty ratio, high level "1", the longer and more bright.

Detailed information for PWM, please refer to：
http://www.geek-workshop.com/thread-125-1-1.html

==Equipment==
*'''[[Microduino-Core]]'''
*'''[[Microduino-FT232R]]'''
*Other hardware equipment
**Breadboard Jumper            one box   
**Breadboard  	               one piece  
**LED Light-emitting diodes    one 
**220ohm resistor 	           one 
**Button                       one  
**USB Data cable               one


[[File:lesson3All1.jpg|600px|center|thumb]]

==Experimental schematic==
[[File:pwm schematic.jpg|600px|center|thumb]]
Buttons are used with internal pull-up and external pull-down, then connect to the digital I/O port D0-D13.
PWM must use I/O port D3,D5,56,D9,D10 and D11.

==Program==
<source lang="cpp">
int n=0;
void setup ()
{
  pinMode(2,INPUT);
  pinMode(7,INPUT_PULLUP);//Set to internal pull-up
  pinMode(11,OUTPUT);//The PWM only can use I/O port 3、5、11、9、10、11
}

void loop()
{
  int up =digitalRead(2);          //Read port 2's state
  int down = digitalRead(7);      //Read port 7's state   
  if (up==HIGH)                    
  { 
    n=n+5;                         
    if (n>=255) {
      n=255;
    }            //The max limitation is 255   
    analogWrite(11,n);   //Using PWM control the output of port 11, the range of the variable n is 0-255
    delay (300);
  } 
  if (down==LOW)             
  {
    n=n-5;
    if (n<=0) {
      n=0;
    }
    analogWrite(11,n); //Using PWM control the output of port 11, the range of the variable n is 0-255
    delay (300);
  }
}
</source>
===analogWrite（）usage===
*Usage：Write the simulation value to the specified pin
*grammar：analogWrite(pin, val)，pin：Microduino I/O port number；val：values from 0 to 255

==Result==
Left button to make LED brightness progressively decreasing, and the right button to make LED brightness incremental.
==Video==
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