Difference between revisions of "Lesson 4--Microduino "LED Brightness and PWM""

Objective

In the previous three lessons, the LED was either on or off. In this lesson, you will learn how to control an LED's brightness using a button and PWM. PWM stands for pulse width modulation. The circuit adjusts the ratio of digital signals ("0", "1") to create a certain brightness. For example, if there are more 1's (HIGH), then the LED seems brighter.

Equipment

• Microduino-Core
• Microduino-FT232R
• Other hardware equipment
  • 1x Box of breadboard jumper wires
  • 1x Breadboard
  • 1x LED
  • 1x 220ohm resistor
  • 1x Button
  • 1x USB Data cable

Experiment Schematic

One button is connected using internal pull-up and the other using external pull-down. They are then connected to I/O ports D0~D13. For the Microduino-Core, only D3, D5, D6, D9, D10, and D11 support PWM, so the user must connect the LED to one of those ports.

Program

int n=0;
void setup ()
{
  pinMode(2,INPUT);
  pinMode(7,INPUT_PULLUP);//Set to internal pull-up
  pinMode(11,OUTPUT);//PWM must use I/O ports 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);
  }
}

AnalogWrite() Usage

• Usage: Writes the simulation value to the specified pin
• Parameters: analogWrite(pin, val)
  • pin: Microduino I/O port number
  • val: values from 0 to 255

Result

Left button increases LED brightness and right button decreases LED brightness.

Video