Adapt this: Buzzer

Published July 22, 2016

Fade an LED: Arduino Basics

Tired of the same old on-off, on-off action? Learn the power of PWM!

BeginnerProtip1 hour16,485

Things used in this project

Hardware components

Arduino 101

...or pretty much any other Arduino

LED (generic)

Resistor 100 ohm

Breadboard (generic)

Jumper wires (generic)

Hand tools and fabrication machines

Hardware 101 HW101 Marker

Story

Pretty light effects, standby modes, custom color hues... All possible when you can control the intensity of an LED! Bonus: you can adapt this tutorial to make annoying noises with a speaker. :)

This is our first introduction to PWM! Read on to find out about this powerful technique.

We're going to use the same LED/resistor setup as the Blink sketch – with one important difference: the LED should be attached to pin 9, or any other pin with a little tilde (~) mark next to it.

You can put the resistor on either side of the LED.

Load up the Fade example: File > Examples > Basics > Fade

CODE

First off, of course, you'll notice the brightness and fadeAmount variables. (This capitalization style is called camel case, one type of capitalization commonly used in code.)

Now, guess what? We're using an ANALOG function to write to a DIGITAL pin! The 0-255 brightness value (that's 2^8) is translated into switching the pin on and off, too fast for the eye to see. At a value of 127 (50% brightness), the LED will be on 50% of the time, off 50% of the time. And the actual length of those pulses gives PWM – pulse width modulation – its name.

So, we're changing brightness over time. First, we write its starting value of 0 to the led pin. (Yes, you can use variables for both the pin number and the brightness value!)

Next, add 5 brightness points (fadeAmount ), wait 30 milliseconds, and restart the loop. At this rate, the LED will reach full brightness in about a second and a half.

However, if we've hit max brightness, we also flip the sign of fadeAmount so that it's negative – fading back down to zero, -5 at a time, until it's completely off again. The || in the code signifies "or".

That's it!

Now try this:

Modify the "fadeAmount" value to make the effect faster or slower.

Grab red, green, and blue LEDs (or one RGB LED) and fade them at different rates. Put a sheet of paper over it as a diffuser, or point them at a wall, and see what colors you can make! (Note that different-colored LEDs may need different resistors, to keep Red from hogging all the brightness. More on this later!)

Adapt this: Buzzer

You can use PWM to control speakers, too, and produce "musical" tones at different frequencies. What happens if you swap out the LED and resistor for a small speaker...? (It may be very quiet!)

See the whole series of Hackster 101 tutorials on Hackster and YouTube

Code

Arduino example sketch: "Fade"

/*
 Fade

 This example shows how to fade an LED on pin 9
 using the analogWrite() function.

 The analogWrite() function uses PWM, so if
 you want to change the pin you're using, be
 sure to use another PWM capable pin. On most
 Arduino, the PWM pins are identified with 
 a "~" sign, like ~3, ~5, ~6, ~9, ~10 and ~11.

 This example code is in the public domain.
 */

int led = 9;           // the PWM pin the LED is attached to
int brightness = 0;    // how bright the LED is
int fadeAmount = 5;    // how many points to fade the LED by

// the setup routine runs once when you press reset:
void setup() {
  // declare pin 9 to be an output:
  pinMode(led, OUTPUT);
}

// the loop routine runs over and over again forever:
void loop() {
  // set the brightness of pin 9:
  analogWrite(led, brightness);

  // change the brightness for next time through the loop:
  brightness = brightness + fadeAmount;

  // reverse the direction of the fading at the ends of the fade:
  if (brightness == 0 || brightness == 255) {
    fadeAmount = -fadeAmount ;
  }
  // wait for 30 milliseconds to see the dimming effect
  delay(30);
}

Credits

Alex Glow

149 projects • 1592 followers

The Hackster team's resident Hardware Nerd. I love robots, music, EEG, wearables, and languages. FIRST Robotics kid.

Fade an LED: Arduino Basics

Things used in this project

Hardware components

Hand tools and fabrication machines

Story

Adapt this: Buzzer

Schematics

LED fade circuit

Code

Arduino example sketch: "Fade"

Credits

Alex Glow

Comments

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Fade an LED: Arduino Basics

Fade an LED: Arduino Basics

Things used in this project

Hardware components

Hand tools and fabrication machines

Story

Adapt this: Buzzer

Schematics

LED fade circuit

Code

Arduino example sketch: "Fade"

Credits

Alex Glow

Comments

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