Summary of Fading an LED off and on using Arduino
This article demonstrates how to fade an LED on and off using the Arduino `analogWrite()` function with Pulse Width Modulation (PWM). The circuit connects an LED's anode to digital pin 9 via a 220-ohm resistor, while the cathode connects to ground. The code gradually adjusts the PWM value from 0 to 255 and back to create a smooth fading effect, controlled by a variable delay.
Parts used in Fading an LED:
- Arduino board
- Breadboard
- LED
- 220 ohm resistor
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, to create a fading effect.
Circuit
Connect the anode (the longer, positive leg) of your LED to digital output pin 9 on your Arduino through a 220-ohm resistor. Connect the cathode (the shorter, negative leg) directly to ground.
image developed using Fritzing. For more circuit examples, see the Fritzing project page
Schematic
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 calledbrightness. 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 55, then it’s set to 5. The next time through the loop, this change causesbrightness 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 program.
Fade
This example shows how to fade an LED on pin 9
using the analogWrite() function.
This example code is in the public domain.
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Hardware Required
- Arduino board
- Breadboard
- a LED
- a 220 ohm resistor
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How does analogWrite() create a fading effect?
It uses pulse width modulation (PWM) to turn a digital pin on and off very quickly. -
What is the correct way to connect the LED anode?
Connect the longer, positive leg of the LED to digital output pin 9 through a 220-ohm resistor. -
Where should the LED cathode be connected?
The shorter, negative leg should be connected directly to ground. -
What values represent the full range for PWM in this project?
0 represents all the way off, and 255 represents all the way on. -
How does the code change the direction of the fade?
If brightness reaches 0 or 255, the fadeAmount variable is changed to its negative value. -
Which part of the sketch controls the speed of the fade?
The delay at the end of the sketch controls the speed of the fade. -
Can I modify the fade speed?
Yes, you can try changing the value of the delay to see how it changes the program.
