View source for Lesson 5--Microduino “LED Brightness and Potentiometer PWM”

{{Language|第五课--电位器PWM控制LED亮度}}
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==Objective==
In the last lesson, we used a button to generate PWM to control the LED. Now, we will use a precision potentiometer to control the LED.
The difference between the two is that a button uses a digital signal (0 and 1) to control the LED. 
A potentiometer uses an analog signal to generate PWM which is a linear change of state, so the LED's brightness can be changed clearly and gradually.
Another downside of using a button is that electronic interference can cause unintended noise. That was why we had to add a pull-up/pull down resistor to our button.


[[File:lesson5All.jpg|600px|center|thumb]]

==Equipment==
*'''[[Microduino-Core]]'''
*'''[[Microduino-FT232R]]'''
*Other hardware equipment
**1x Box of breadboard jumper wires      
**1x Breadboard  	                 
**1x LED    
**1x 220Ω resistor 	         
**1x Precision potentiometer      
**1x USB Data cable              

==Experiment Schematic==
[[File:lesson 5-schematic.jpg|600px|center|thumb]]
*Connecting the Potentiometer <br>
The LED connects to any PWM output pin. The center pin of the potentiometer connects to analog ports A0 ~ A5. The potentiometer's other two pins connect to GND and 5V.
The analog interface can measure 0-5V, and analogRead() returns corresponding values 0-1024.

==Program==
<source lang="cpp">
void setup()
{
  pinMode(3,OUTPUT); //Choose the PWM output Port
}
void loop()
{
  int val= analogRead(A0);      //Read the analog port A0's value（voltage range is 0-5V,corresponding value is 0-1204）
  val = map(val, 0, 1023, 0, 255);
  //We want to map the analog value（0~1024）to（0~255) since the max PWM value is 255.
  analogWrite(3, val);
}
</source>
===map() function===
*Function: Maps a certain range of values to a different range
*Parameters: map(value, fromLow, fromHigh, toLow, toHigh)
**value: value to be mapped
**fromLow: Start value of source range
**fromHigh: End value of source range
**toLow: Start value of target range
**toHigh: End value of target range

==Result==
As you turn the potentiometer, the LED's brightness changes gradually.

[[File:lesson5Result1.jpg|600px|center|thumb]]
[[File:lesson5Result2.jpg|600px|center|thumb]]

==Video==
http://v.youku.com/v_show/id_XNzA5OTk1Mzky.html
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