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Arduino - LED - Fade
In this tutorial, we are going to learn:
- Arduino fades LED by using delay() function
- Arduino fades LED by using millis() function
- Arduino fades LED by using ezLED library
※ NOTE THAT:
This tutorial provides in-depth knowledge that helps you understand the working principle. To make it easy, you can use Arduino - LED library.
Hardware Required
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About LED
Pinout
LED includes two pins:
- Cathode(-) pin: needs to be connected to GND (0V)
- Anode(+) pin: is used to control LED's state
How It Works
After connecting the cathode(-) to GND:
- If connecting GND to the anode(+), LED is OFF.
- If connecting VCC to the anode(+), LED is ON.
- If generating a PWM signal to the anode(+), the brightness of LED is changed according to PWM value. PWM value varies from 0 to 255. The bigger PWM value is, the brighter LED is. The smaller PWM value is, the darker LED is.
- If PWM value is 0, it is equivalent to GND, therefore, LED is OFF
- If PWM value is 255, it is equivalent to VCC, therefore, LED is fully ON
※ NOTE THAT:
For most of LED, it needs to use a resistor between the anode(+) and VCC. The value of the resistor depends on the specification of LED.
Arduino - fade LED
Some of Arduino pins can be programmed to generate PWM signal. We can fade LED by connecting LED's anode(+) pin to an Arduino's pin, LED's cathode(-) to GND, and programming generate PWM on the Arduino's pin.
Wiring Diagram
This image is created using Fritzing. Click to enlarge image
How To Program
- Configure an Arduino's pin to the digital output mode by using pinMode() function. For example, pin 9:
pinMode(9, OUTPUT);
- Set brightness of LED by generating the corresponding PWM signal by using analogWrite() function:
analogWrite(9, brightness);
Where the brightness is a value from 0 to 255.
Arduino Code - Fade Example from Arduino IDE
Quick Steps
- Connect Arduino to PC via USB cable
- Open Arduino IDE, select the right board and port
- Copy the below code and paste it to the Arduino IDE
/*
* Created by ArduinoGetStarted.com
*
* This example code is in the public domain
*
* Tutorial page: https://arduinogetstarted.com/tutorials/arduino-led-fade
*/
#define LED_PIN 9 // the Arduino PWM pin connected to the LED
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_PIN, OUTPUT);
}
// the loop routine runs over and over again forever:
void loop() {
// set the brightness of pin 9:
analogWrite(LED_PIN, 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);
}
- Click Upload button on Arduino IDE to upload code to Arduino
- See the brightness of LED
Code Explanation
Read the line-by-line explanation in comment lines of code!
How to fade-out LED in a period without using delay()
/*
* Created by ArduinoGetStarted.com
*
* This example code is in the public domain
*
* Tutorial page: https://arduinogetstarted.com/tutorials/arduino-led-fade
*/
#define LED_PIN 9 // the Arduino PWM pin connected to the LED
#define FADE_PEDIOD 3000 // fade time is 3 seconds
unsigned long fadeStartTime;
// the setup routine runs once when you press reset
void setup() {
pinMode(LED_PIN, OUTPUT); // declare pin 9 to be an output
fadeStartTime = millis();
}
// fade-in in loop, and restart after finishing
void loop() {
unsigned long progress = millis() - fadeStartTime;
if (progress <= FADE_PEDIOD) {
long brightness = map(progress, 0, FADE_PEDIOD, 0, 255);
analogWrite(LED_PIN, brightness);
} else {
fadeStartTime = millis(); // restart fade again
}
}
How to fade-in LED in a period without using delay()
/*
* Created by ArduinoGetStarted.com
*
* This example code is in the public domain
*
* Tutorial page: https://arduinogetstarted.com/tutorials/arduino-led-fade
*/
#define LED_PIN 9 // the Arduino PWM pin connected to the LED
#define FADE_PEDIOD 3000 // fade time is 3 seconds
unsigned long fadeStartTime;
// the setup routine runs once when you press reset
void setup() {
pinMode(LED_PIN, OUTPUT); // declare pin 9 to be an output
fadeStartTime = millis();
}
// fade-in in loop, and restart after finishing
void loop() {
unsigned long progress = millis() - fadeStartTime;
if (progress <= FADE_PEDIOD) {
long brightness = map(progress, 0, FADE_PEDIOD, 0, 255);
analogWrite(LED_PIN, brightness);
} else {
fadeStartTime = millis(); // restart fade again
}
}
Video Tutorial
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Challenge Yourself
Change the brightness of LED using potentiometer . Hint: Refer to Arduino - Potentiometer.
Additional Knowledge
- PWM signal generated by analogWrite() function fades a LED. That is because it's high-frequency PWM. If we create a customized function (required advanced knowledge), which generates low-frequency PWM signal, LED will be blinked instead of faded.
- Summary: PWM signal can be used in Arduino to: control servo motor, control DC motor, make sound using a piezo buzzer, fade LED, blink LED ...
