Arduino 102 for intermediates 

Understanding the Common Cathode RGB LED

A common cathode RGB LED has four pins: one common cathode (negative terminal) and three anodes for the red, green, and blue LEDs. In this configuration, the common cathode is connected to a ground (GND), and the individual color pins (red, green, blue) are controlled by applying a voltage to each pin. By varying the intensity of each color using Pulse Width Modulation (PWM), you can create a wide range of colors by mixing the red, green, and blue light.

A Common Cathode RGB LED has four legs:

• Longest leg: Common cathode (connect to ground)

• Red leg: Connect to a PWM-capable digital pin (e.g., pin 11)

• Green leg: Connect to a PWM-capable digital pin (e.g., pin 10)

• Blue leg: Connect to a PWM-capable digital pin (e.g., pin 9)

Components Needed

• Arduino board (e.g., Arduino UNO)

• RGB LED (common cathode)

• 200-ohm resistors (three)

• Breadboard

• USB-B cable

• Jumper wires

Enter the following code into the Arduino IDE 

/* RGB LED TEST

  By. Fekadu Debebe

  April 21/2019

*/

//RGB LED pins (~PWM)

int green = 9;    //LED red

int blue = 10;    //LED green

int red = 11;     //LED blue

// Setup instructions

void setup()

{

  Serial.begin(9600); // serial monitor

  // Arduino pins input or output

  pinMode(red, OUTPUT);

  pinMode(green, OUTPUT);

  pinMode(blue, OUTPUT);

}

// Main loop

void loop()

{

  // PWM value from 0 to 255

  //Red, bright

  analogWrite(red, 255);  // 100% PWM

  analogWrite(green, 0);  // Green OFF

  analogWrite(blue, 0);   // Blue OFF

  delay(2000);            // wait for 2 sec

  // blue, bright

  analogWrite(red, 0);

  analogWrite(green, 0);

  analogWrite(blue, 255);

  delay(2000);

  //Green, bright

  analogWrite(red, 0);

  analogWrite(green, 255);

  analogWrite(blue, 0);

  delay(2000);

  // white, bright

  analogWrite(red, 255);

  analogWrite(green, 255);

  analogWrite(blue, 255);

  delay(2000);

}

You can also create a function to set the RGB color

// Define pins for the RGB LED

const int greenPin = 9;

const int bluePin = 10;

const int redPin = 11;

void setup() {

  // Initialize the pins as outputs

  pinMode(redPin, OUTPUT);

  pinMode(greenPin, OUTPUT);

  pinMode(bluePin, OUTPUT);

}

void loop() {

  // Set the RGB LED to red using the setColor subroutine

  setColor(255, 0, 0);  // Red

  delay(1000);

  setColor(0, 255, 0);  // Red

  delay(1000);

  setColor(0, 0, 255); // Red

  delay(1000);

  setColor(0, 0, 0); // Red

  delay(1000);

  //Add similar subroutine callouts

}

// Function to set the color of the RGB LED

void setColor(int red, int green, int blue) {

  analogWrite(redPin, red);

  analogWrite(greenPin, green);

  analogWrite(bluePin, blue);

}

Display control

In order to turn a specific segment, 5V will be supplied to the desired segment (A,B,C,D,E,F, or G). To get a digital number readout, the particular set of LEDs will be turned ON. For instance, to display the numerical digit 0, we will need to light up six of the LED segments (A,B,C,D,E,and F). Similarly, all the digits from ‘0 through 9’ and hexadecimal characters from ‘A through F’ can be displayed using a 7-segment display. 

​Wiring Diagram:

The attached GIF illustrates the wiring connections between the Arduino UNO and the seven-segment display. The seven segments (labeled a to g) and the decimal point (dp) are connected to the digital pins of the Arduino through resistors. 

Here is a typical pin configuration:

• DP -> Digital Pin 5

• Segment a -> Digital Pin 6

• Segment b -> Digital Pin 7

• Segment c -> Digital Pin 8

• Segment d -> Digital Pin 9

• Segment e -> Digital Pin 10

• Segment f -> Digital Pin 12

• Segment g -> Digital Pin 11

• Common Cathode -> GND