Basics - Fading a LED


Basics - Fading a LED

Table of Contents

Objective

In this project, we will start to control the LED brightness analogly (not digitally1)touch base with the basics of running the board and provide simple visual feedback with a flashing LED.

Schematic Drawing

The 220 Ω resistor is a must, otherwise you will burn the LED.

Code

Header File

No header file needed.

Main File

The main file is saved as main.cpp under the [project root]/src folder.

#include <Arduino.h>

constexpr int ledPin = 32;
constexpr int pwmResolution = 12;           // 12-bit resolution
constexpr int maxBrightness = (1 << pwmResolution) - 1;  // 4095
int brightness = 0;                         // current brightness
int fadeAmount = 30;                        // step size (scaled for higher resolution)

void setup() {
  analogWriteResolution(pwmResolution);     // set ESP32 PWM to 12-bit (0–4095)
  pinMode(ledPin, OUTPUT);
}

void loop() {
  analogWrite(ledPin, brightness);

  brightness += fadeAmount;

  // Clamp to avoid LEDC overflow flicker at boundaries
  if (brightness <= 0) {
    brightness = 0;
    fadeAmount = -fadeAmount;
  } else if (brightness >= maxBrightness) {
    brightness = maxBrightness;
    fadeAmount = -fadeAmount;
  }

  delay(15);
}

We have "upgraded" the Arduino sample a lot. Let me explain:

  1. As ESP32 is more powerful in all aspects than the Arduino (8bit), we have a bigger range of "How bright a LED can be" (or "resolution"). We set this to int pwmResolution.
  2. Thus, the max brightness is set using bit-op.

The setup function

analogWriteResolution is new in ESP32 (or already there in Arduino?) and it sets the ESP32 PWM to 12-bit as defined.

The loop function

The loop controls the fading/shining of the LED.

We put some truncating control over the brightness. If we don't put this control, and when brightness+= fadeAmount exceeds the upper limit, we will see a "flickering" of the LED.

  1. To put it simple, "digital" control can only make the LED on or off; with "analog" control, we can make the LED shine with different brightness.  ↩

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