How to Use RGB LED: Four Pin (Common Cathode): Examples, Pinouts, and Specs

An RGB LED with a common cathode configuration is a versatile electronic component that combines red, green, and blue light-emitting diodes in a single package. By adjusting the intensity of each color, it can produce a wide spectrum of colors, making it ideal for decorative lighting, signal indicators, displays, and any application requiring visual feedback or aesthetic enhancement.

• Mood lighting and ambient light control
• Color displays for information panels or signage
• User interface elements for electronic devices
• Art installations and stage lighting
• Educational projects and DIY electronics

• Forward Voltage (Typical): Red: 2.0-2.2V, Green: 3.0-3.2V, Blue: 3.0-3.2V
• Forward Current (Max): 20mA per color
• Luminous Intensity: Varies by color and current
• Viewing Angle: Typically around 120 degrees

1. Connect the common cathode pin (Pin 4) to the ground (GND) of your power supply or microcontroller.
2. Connect each anode pin (Pins 1, 2, and 3) to a current-limiting resistor, and then to the respective output pins on your microcontroller.
3. To turn on a specific color, provide a HIGH signal to the corresponding anode pin.
4. To create mixed colors, adjust the signal intensity (using PWM - Pulse Width Modulation) to each anode pin.

• Always use current-limiting resistors to prevent damage to the LEDs.
• The sum of currents through the individual LEDs should not exceed the maximum rating for the common cathode.
• Use PWM for dimming and color mixing to achieve the desired color output.
• Avoid static discharge and overvoltage, which can permanently damage the LEDs.

// Define the RGB LED pins
const int RED_PIN = 9;    // Red LED anode connected to digital pin 9
const int GREEN_PIN = 10; // Green LED anode connected to digital pin 10
const int BLUE_PIN = 11;  // Blue LED anode connected to digital pin 11

void setup() {
  // Set the LED pins as outputs
  pinMode(RED_PIN, OUTPUT);
  pinMode(GREEN_PIN, OUTPUT);
  pinMode(BLUE_PIN, OUTPUT);
}

void loop() {
  // Set the color to purple (Red + Blue)
  analogWrite(RED_PIN, 255);   // Full intensity for Red
  analogWrite(GREEN_PIN, 0);   // No Green
  analogWrite(BLUE_PIN, 255);  // Full intensity for Blue

  // Keep the color for 2 seconds
  delay(2000);

  // Turn off the LED
  analogWrite(RED_PIN, 0);
  analogWrite(GREEN_PIN, 0);
  analogWrite(BLUE_PIN, 0);

  // Wait for 1 second
  delay(1000);
}

• LED not lighting up: Check connections and ensure the common cathode is connected to GND. Verify that the current-limiting resistors are correctly sized and properly connected.
• Dim or uneven color output: Ensure that each LED receives the appropriate forward voltage and current. Adjust PWM values for balanced color mixing.
• LED burned out: This can occur due to excessive current. Always use current-limiting resistors and do not exceed the maximum forward current.

• Double-check wiring against the pin configuration table.
• Use a multimeter to verify the voltage across each LED and the current through each resistor.
• If using PWM, ensure that the microcontroller's pins support PWM and that the code is correctly implemented.

Q: Can I power the RGB LED directly from an Arduino pin? A: Yes, but you must use current-limiting resistors to protect the LEDs and the Arduino pins.

Q: How do I calculate the value of the current-limiting resistors? A: Use Ohm's Law: R = (V_supply - V_forward) / I_forward, where V_supply is the supply voltage, V_forward is the forward voltage of the LED, and I_forward is the desired forward current.

Q: What is PWM and how does it control the LED colors? A: PWM stands for Pulse Width Modulation. It controls the brightness of each LED by rapidly turning it on and off at a frequency high enough that the human eye perceives it as a continuous light with varying intensity.