RGB LED with Arduino — mix any colour with three PWM pins

#What you will build

An RGB LED that steps through six colours — red, orange, yellow, green, sky blue and purple — each for 0.8 seconds, forever. The serial monitor names each colour as it appears.

The same trick lights the "breathing" LED on a game controller, smart bulbs that change colour from your phone, and — with millions of tiny dots — every phone, TV and computer screen. Each pixel on your screen is a red, a green and a blue light mixed in different amounts.

#How it works

An RGB LED holds three LEDs under one milky lens: red, green and blue. This one is common cathode: the three share one minus leg (the longest), which goes to GND. Each colour has its own plus leg, its own 220 Ω resistor and its own PWM pin. More in how an RGB LED works.

Light adds up. Mixing light is not like mixing paint:

Each number is a PWM level from 0 (off) to 255 (fully on). With 256 levels for each of three colours, that is 256 × 256 × 256 ≈ 16.7 million combinations.

The three colours need different voltages, so with the same 220 Ω resistor they get different currents:

All three together: about 32 mA — fine, because each pin carries only its own colour.

#The wiring

The RGB LED's legs, from left to right: R, K (the longest), G, B.

1. Push the RGB LED in with its legs in 10e (R), 11e (K), 12e (G), 13e (B).
2. Red resistor (220 Ω) from 10d to 14d.
3. Green resistor (220 Ω) from 12c to 16c.
4. Blue resistor (220 Ω) from 13b to 17b.
5. Jumper wires: pin 9 → 14a, pin 10 → 16a, pin 11 → 17a, and 11a → GND.

#The code, line by line

const int RED = 9, GREEN = 10, BLUE = 11;

void setColor(int r, int g, int b) {
  analogWrite(RED, r);
  analogWrite(GREEN, g);
  analogWrite(BLUE, b);
}

void setup() {
  Serial.begin(9600);
}

void loop() {
  setColor(255, 0, 0);   Serial.println("red");    delay(800);
  setColor(255, 160, 0); Serial.println("orange"); delay(800);
  setColor(255, 255, 0); Serial.println("yellow"); delay(800);
  setColor(0, 255, 0);   Serial.println("green");  delay(800);
  setColor(0, 120, 255); Serial.println("sky");    delay(800);
  setColor(140, 0, 255); Serial.println("purple"); delay(800);
}

• const int RED = 9, GREEN = 10, BLUE = 11; names three pins in one line. All three are ~ pins.
• void setColor(int r, int g, int b) is your own function. It takes three numbers and does three analogWrites. Now one line sets a whole colour, and loop() stays short and readable.
• analogWrite(RED, r) sets the red brightness, 0–255. analogWrite makes the pin an output by itself, so setup() needs no pinMode.
• setColor(255, 160, 0) — full red plus some green makes orange. More green and it becomes yellow.
• setColor(140, 0, 255) — blue with some red is purple.
• Each line of loop() holds three statements: set the colour, print its name, wait 800 ms.

#Common mistakes

• Nothing lights at all. The longest leg is not on GND, or the LED is a common anode type (its shared leg must go to 5V and the numbers work backwards: 0 = full on).
• The colours are swapped. The legs are in a different order on your LED. Swap the wires, or swap the pin numbers in the first line.
• Only red works well; the mix looks too red. Normal: red gets more current (14 mA vs 9 mA). Lower the red number, e.g. setColor(200, 255, 0) for a truer yellow.
• A colour only turns fully on or off. That colour is on a pin without ~. Use 9, 10, 11 (or 3, 5, 6).

#Try these challenges

1. Add your favourite colour with setColor() and give it a name in the serial monitor.
2. Make white: all three at 255. Is it really white, or a bit pink?
3. Fade smoothly from red to blue with a for loop that counts from 0 to 255.
4. In the 3D lab, open the Code tab, change the purple line to setColor(255, 0, 255) and press Run.

#Check yourself

#Questions people ask

#What is the difference between common anode and common cathode RGB LEDs?

Common cathode shares the minus leg (to GND) and a HIGH pin lights a colour. Common anode shares the plus leg (to 5V) and a LOW pin lights a colour, so analogWrite(pin, 255 - value) fixes the code.

#Which Arduino pins can I use for an RGB LED?

Any three of the PWM pins marked ~: 3, 5, 6, 9, 10 and 11. This project uses 9, 10 and 11.

#Why does my RGB LED not make a pure white?

The three colours have different brightness for the same number, and the red die gets more current here. Turn red and green down a little until it looks white.

#How many colours can an Arduino RGB LED show?

256 levels for each of red, green and blue: about 16.7 million combinations — more than your eye can tell apart.

#What's next

So far the Arduino decides everything. Next, let the world decide: a light sensor turns on an LED when it gets dark in the night light project.

<iframe src="https://learnarduino.tech/?embed#/projects/rgb" title="RGB LED with Arduino — mix any colour with three PWM pins — live in 3D" width="100%" height="480" style="border:0;border-radius:12px" allow="fullscreen" loading="lazy"></iframe>

Last updated 2026-10-29