ESP32 Breathing Light

This project creates a breathing light effect using an Arduino Uno, where an LED gradually fades in and out in a smooth, continuous cycle. The effect is achieved through PWM (pulse-width modulation) on digital pin 9, which rapidly switches the LED on and off at varying rates to simulate dimming and brightening.

The guide includes a complete parts list, wiring diagram showing how to connect the LED with a protective resistor, and the Arduino firmware needed to produce the breathing effect. Assembly takes just a few minutes and requires only basic soldering skills.

Wiring diagram

Loading diagram…

Gather all the parts

Qty	Component
1	LED 红色 5 mm Standard 3mm/5mm through-hole LED. A current-limiting series resistor is added automatically.
1	Resistor 220 Ω，1/4 W Through-hole resistor (current-limiting in series with an LED)

Qty

Component

LED

红色 5 mm

Standard 3mm/5mm through-hole LED. A current-limiting series resistor is added automatically.

Resistor

220 Ω，1/4 W

Through-hole resistor (current-limiting in series with an LED)

Assemble it in 4 steps

1. 先断开 Arduino 的 USB 线

把 Arduino Uno 从 USB 线拔下，再把它放在面包板旁边。断电后接线可以避免金属跳线碰错位置时损坏板子。

先看清 Arduino 排针旁边印着的 D9 和 GND 标签。

2. 插入 LED

把红色 LED 插在面包板上，让两只脚落在不同的横排。较长的一只脚是正极；较短的一只脚、以及外壳边缘有平口的一侧是负极。

两只脚不要插在同一排，否则 LED 会被短接。
如果把 LED 的正负脚接反，它通常不会发亮。

3. 把 LED 负极接地

用一根黑色跳线，把 LED 的短脚所在横排接到 Arduino 的任意 GND 排针。这条线让电流能回到 Arduino。

Arduino 上标有 GND 的几个孔都可以使用。

4. 串入保护电阻并接到 D9

将 220 Ω 电阻的一只脚插到 LED 长脚所在横排；电阻另一只脚用一根跳线接到 Arduino 的 D9 排针。电阻没有方向，可以任意转向插入。

接线结果是：D9 → 电阻 → LED 长脚，LED 短脚 → GND。
D9 → 电阻（亮度控制和限流），电阻 → LED 长脚（保护 LED），LED 短脚 → GND（回流地线）。
不要省略 220 Ω 电阻；直接把 LED 接到 D9 和 GND 可能损坏 LED 或 Arduino 引脚。

Review all connections

1. Connections between "resistor_1" and "Arduino"

Function	resistor_1	Arduino
`digital`	P1 → D9 输出的亮度控制信号	GPIO 9
`digital`	P2 → LED ANODE	EXT

2. Connections between "led_1" and "Arduino"

Function	led_1	Arduino
`ground`	GND → LED 的回流地线	GND

Deploy the firmware

main.cppOpen in Schematik

// Arduino Uno breathing LED
// D9 drives the LED through a 220 ohm series resistor.
const uint8_t LED_PIN = 9;

uint8_t brightness = 0;
int8_t stepSize = 1;

void setup() {
  pinMode(LED_PIN, OUTPUT);
}

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

  brightness += stepSize;
  if (brightness == 255 || brightness == 0) {
    stepSize = -stepSize;
  }

  // A short pause makes the brightness change smoothly without busy-waiting.
  delay(12);
}