This circuit shows how an Arduino controls an RGB LED using three output pins. An RGB LED contains three internal LEDs—Red, Green, and Blue—combined in one package. In this diagram, it is a common cathode type, meaning all the negative terminals are connected together and tied to ground.
Each color pin (R, G, B) is connected to a separate Arduino digital/PWM pin through a 220Ω resistor (R1, R2, R3). These resistors limit current and protect both the LED and the Arduino.
When the Arduino sends a HIGH signal to any pin, current flows through the resistor and the corresponding LED color turns ON. By using PWM (pins marked with ~), the brightness of each color can be adjusted. By mixing different brightness levels of Red, Green, and Blue, a wide range of colors can be produced.
For example:
Red + Green = Yellow
Red + Blue = Magenta
Green + Blue = Cyan
All three = White
This is the basic principle behind color mixing in displays and lighting systems.

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