Fading a LED

Demonstrates the use of analog output to fade an LED.

This example demonstrates the use of the analogWrite() function in fading an LED off and on. AnalogWrite uses pulse width modulation (PWM), turning a digital pin on and off very quickly with different ratio between on and off, to create a fading effect.

Hardware Required

  • Arduino board

  • LED

  • 220 ohm resistor

  • hook-up wires

  • breadboard

Circuit

Connect the anode (the longer, positive leg) of your LED to digital output pin 9 on your board through a 220 ohm resistor. Connect the cathode (the shorter, negative leg) directly to ground.

simplefade bb

Schematic

simplefade pin9 schem

Code

After declaring pin 9 to be your

ledPin
, there is nothing to do in the
setup()
function of your code.

The

analogWrite()
function that you will be using in the main loop of your code requires two arguments: One telling the function which pin to write to, and one indicating what PWM value to write.

In order to fade your LED off and on, gradually increase your PWM value from 0 (all the way off) to 255 (all the way on), and then back to 0 once again to complete the cycle. In the sketch below, the PWM value is set using a variable called

brightness
. Each time through the loop, it increases by the value of the variable
fadeAmount
.

If

brightness
is at either extreme of its value (either 0 or 255), then
fadeAmount
is changed to its negative. In other words, if
fadeAmount
is 5, then it is set to -5. If it's -5, then it's set to 5. The next time through the loop, this change causes
brightness
to change direction as well.

analogWrite()
can change the PWM value very fast, so the delay at the end of the sketch controls the speed of the fade. Try changing the value of the delay and see how it changes the fading effect.

Learn more

You can find more basic tutorials in the built-in examples section.

You can also explore the language reference, a detailed collection of the Arduino programming language.

Last revision 2015/07/29 by SM

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