LED Control with Arduino

Introduction

In this lesson you will learn:

How LEDs work
How to calculate the right resistor
Programming different light patterns
Control through a computer

Safety Warning!

● Always use a resistor to protect your circuits
● Ensure the correct polarity
● Avoid exposing the LED to direct current

Ohm's Law for Resistor Calculation

To calculate the resistor needed to protect your LED, use the following formula:


R = (Vcc - Vd) / I

Where:

R is the resistor value in ohms (Ω).
Vcc is the supply voltage (e.g., 3.3V, 5V, 9V, or 12V).
Vd is the forward voltage of the LED (which varies by color).
I is the nominal current of the LED, usually around 20mA (0.02A).

Resistor Calculation for Different LED Colors

Below is the resistor value required for different LED colors based on various supply voltages.

Color	Forward Voltage (Vd)	Ω (3.3V)	Ω (5V)	Ω (9V)	Ω (12V)
Infrared	1.4V	150Ω	270Ω	510Ω	680Ω
Red	1.8V	100Ω	220Ω	470Ω	680Ω
Orange	2.1V	100Ω	200Ω	470Ω	680Ω
Yellow	2.2V	100Ω	200Ω	470Ω	680Ω
Green	3.2V	10Ω	150Ω	330Ω	560Ω
Blue	3.5V	-	100Ω	330Ω	560Ω
Violet	3.6V	-	100Ω	330Ω	560Ω
White	3.8V	-	100Ω	330Ω	560Ω

Programming Examples


// Basic Blinking Example
const int ledPin = 9;

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

void loop() {
  digitalWrite(ledPin, HIGH);  // Turn LED on
  delay(1000);                 // Wait for one second
  digitalWrite(ledPin, LOW);   // Turn LED off
  delay(1000);                 // Wait for one second
}


const int ledPIN = 9;
int option;

void setup(){
  Serial.begin(9600);
  pinMode(ledPIN, OUTPUT);
}

void loop(){
  if (Serial.available() > 0) {
    char option = Serial.read();
    if (option >= '1' && option <= '9') {
      option -= '0';
      for(int i = 0; i < option; i++) {
         digitalWrite(ledPIN, HIGH);
         delay(100);
         digitalWrite(ledPIN, LOW);
         delay(200);
      }
    }
  }
}


const int ledPIN = 5;
byte outputValue = 0;

void setup() {
   Serial.begin(9600);
   pinMode(ledPIN, OUTPUT);
}

void loop() {
   if (Serial.available() > 0) {
      outputValue = Serial.read();
      if(outputValue >= '0' && outputValue <= '9') {
         outputValue -= '0';
         outputValue *= 25;
         analogWrite(ledPIN, outputValue);
      }
   }
}