RGB LED

What it is

Three LEDs in one small square package: a red, a green and a blue, each with its own 1 kΩ resistor on the board and its own pin on the header. Drive one and you get that colour. Drive two or three with PWM and the white diffuser blends them into one mixed colour.

It is common cathode and active high. The LED's three cathodes are joined to GND on the board, so a colour lights when its pin is HIGH. Sketches written for a common-anode LED, which send 255 minus each value, show the opposite colours here.

Three colours, three currents

There is no supply pin: each colour pin powers its own LED. The same 1 kΩ resistor sits on every colour, but red needs about 0.9 V less than green and blue, so it keeps more voltage for its resistor and draws more current:

All of them are far inside what any pin may supply. They are estimates from the LED's datasheet rather than measurements. The difference between the two rows is why a colour that looks right on an Uno leans pink on a 3.3 V board.

Which pin is which

Component side up, header at the bottom, reading left to right:

The back prints TK02 RGB LED and MIXES RED, GREEN, BLUE instead of pin names. Turned over, the square pad is on the right, and it is still GND.

Wiring, in four lines

1. GND to your board's GND.
2. RED to D9 on an Uno, GPIO 25 on an ESP32, GPIO 4 on an ESP32-S3, GP13 on a Pico.
3. GREEN to D10, GPIO 26, GPIO 5 or GP14.
4. BLUE to D11, GPIO 27, GPIO 6 or GP15.

All of those are PWM pins. Leave both NC pins unconnected. The classic ESP32 does not use GPIO 4, 5 and 6 like the S3, because its flash chip owns GPIO 6 to 11.

Example

// Uno: 9, 10, 11. ESP32: 25, 26, 27. ESP32-S3: 4, 5, 6. Pico: 13, 14, 15.
const int RED_PIN = 4;
const int GREEN_PIN = 5;
const int BLUE_PIN = 6;

// 0 is off, 255 is full. Common cathode: no "255 -" anywhere.
void setColour(int r, int g, int b) {
  analogWrite(RED_PIN, r);
  analogWrite(GREEN_PIN, g);
  analogWrite(BLUE_PIN, b);
}

void setup() {
  pinMode(RED_PIN, OUTPUT);
  pinMode(GREEN_PIN, OUTPUT);
  pinMode(BLUE_PIN, OUTPUT);
}

void loop() {
  setColour(255, 0, 0);    // red
  delay(1000);
  setColour(0, 255, 0);    // green
  delay(1000);
  setColour(0, 0, 255);    // blue
  delay(1000);
}

from machine import Pin, PWM
import time

# ESP32: 25, 26, 27. ESP32-S3: 4, 5, 6. Pico: 13, 14, 15.
red = PWM(Pin(4), freq=1000)
green = PWM(Pin(5), freq=1000)
blue = PWM(Pin(6), freq=1000)

def set_colour(r, g, b):
    # 0 is off, 255 is full. Common cathode: no "255 -" anywhere.
    red.duty_u16(r * 257)
    green.duty_u16(g * 257)
    blue.duty_u16(b * 257)

while True:
    set_colour(255, 0, 0)    # red
    time.sleep(1)
    set_colour(0, 255, 0)    # green
    time.sleep(1)
    set_colour(0, 0, 255)    # blue
    time.sleep(1)

Where to start

The handbook below is nine short articles, each with a working figure. The first colour is the whole build in four wires and a short sketch.

If you only read one, read why equal numbers are not white. It is the question everyone asks of an RGB LED, and the answer is not the one most people expect.

And if your colours look pink on an ESP32, why 3.3 V turns it pink works out why, and what numbers to use instead.