LED Blinking

Interfacing LED Bar with Arduino UNO

Interfacing LED Bar with Arduino UNO demonstrates how an LED bar can be connected to an Arduino UNO board and controlled using digital output pins.

An LED (Light Emitting Diode) is a semiconductor device that emits light when it is forward biased.

An LED has two terminals:

• Anode (+) – positive terminal
• Cathode (−) – negative terminal

A current-limiting resistor is used while interfacing LEDs with the Arduino UNO to limit the current flowing through the LED.

Introduction to LED

LED stands for Light Emitting Diode.

An LED is a p-n junction diode that emits light when it is forward biased.

The typical characteristics considered for the LED in this practical are:

Parameter	Value
Required voltage	Approximately 1.7 V
Required current	5–20 mA

A current-limiting resistor is connected between the LED and the Arduino UNO to limit the current.

LED Bar

An LED bar consists of multiple LEDs arranged together in a single package.

In this practical, the LED bar contains 4 LEDs.

The LEDs can be controlled by applying suitable digital signals to their terminals.

The LED bar can have two commonly used configurations:

1. Common Anode
2. Common Cathode

Common Anode

In a Common Anode LED bar, the anode terminals of all the LEDs are connected together and connected to the positive supply VCC.

The individual LEDs are controlled through their cathode terminals.

Common Anode → VCC (+5 V)

By controlling the cathode terminals, the individual LEDs can be switched ON or OFF.

Common Cathode

In a Common Cathode LED bar, the cathode terminals of all the LEDs are connected together and connected to Ground (0 V).

The individual LEDs are controlled through their anode terminals.

Common Cathode → Ground (0 V)

By controlling the anode terminals, the individual LEDs can be switched ON or OFF.

Connections

The LED bar is interfaced with the Arduino UNO using four digital data pins.

Device	Pin	Arduino UNO	Function
LED Bar	Data Pin 1	D3	LED control
LED Bar	Data Pin 2	D4	LED control
LED Bar	Data Pin 3	D12	LED control
LED Bar	Data Pin 4	D13	LED control
LED Bar	VCC / Common Anode	+5V	Power
LED Bar	GND / Common Cathode	GND	Ground

Current Limiting Resistor

A current-limiting resistor is used with the LED to prevent excessive current from flowing through it.

The resistor is connected between the LED and the Arduino UNO output.

The resistor helps protect the LED and the Arduino UNO digital output from excessive current.

Safety Precautions

• First, make all the connections according to the circuit diagram.
• Check the LED bar configuration before connecting the supply.
• Use a suitable current-limiting resistor with the LEDs.
• Check the polarity of the LED bar.
• Ensure that the connections are correct before applying power.
• Then connect the Arduino UNO board to the PC or laptop.
• Do not connect the LED directly to an Arduino UNO digital output without suitable current limiting.

Interfacing Diagram Using Breadboard

The LED bar is connected to the Arduino UNO through the required data pins.

The LED bar's common terminal is connected according to its configuration.

For a Common Anode LED bar, the common anode is connected to the positive supply.

For a Common Cathode LED bar, the common cathode is connected to ground.

Configuration	Common Terminal	LED Control
Common Anode	VCC	Cathode terminals
Common Cathode	GND	Anode terminals

Algorithm

The following algorithm is used to interface and control the LED bar:

1. Start the Arduino IDE.
2. Declare integer variables for the four data pins of the LED bar.
3. In the void setup(), configure all the LED pins as OUTPUT.
4. In the void loop(), make all the LED pins HIGH.
5. Give a delay of one second.
6. Make all the LED pins LOW.
7. Give a delay of one second.
8. Repeat the process continuously.

The overall operation is:

Arduino UNO → Digital Output Pins → LED Bar → LEDs ON/OFF

Working

The Arduino UNO controls the LED bar using digital output pins.

During operation, the program alternately changes the state of the LED control pins.

First, all the required LED pins are made HIGH.

HIGH → LED control

After a delay of one second, all the LED pins are made LOW.

LOW → LED control

The process repeats continuously, causing the LED bar to change between its two output states.

Timing

The LED bar is controlled with a delay of one second between the first output state and the second output state.

The program uses a 1000 ms delay when the LEDs are HIGH and a 500 ms delay when the LEDs are LOW.

The sequence is:

All Pins HIGH → 1000 ms delay → All Pins LOW → 500 ms delay → Repeat

Program Codes

#define LED_PIN 3
#define LED_PIN1 4
#define LED_PIN2 12
#define LED_PIN3 13

void setup()
{
  pinMode(LED_PIN, OUTPUT);
  pinMode(LED_PIN1, OUTPUT);
  pinMode(LED_PIN2, OUTPUT);
  pinMode(LED_PIN3, OUTPUT);
}

void loop()
{
  digitalWrite(LED_PIN, HIGH);
  digitalWrite(LED_PIN1, HIGH);
  digitalWrite(LED_PIN2, HIGH);
  digitalWrite(LED_PIN3, HIGH);
  delay(1000);
  digitalWrite(LED_PIN, LOW);
  digitalWrite(LED_PIN1, LOW);
  digitalWrite(LED_PIN2, LOW);
  digitalWrite(LED_PIN3, LOW);
  delay(500);
}

Observation

After connecting the Arduino UNO to the LED bar and running the program, observe the LED bar output.

The LED control pins alternate between HIGH and LOW states.

The LEDs remain in the HIGH state for 1000 ms and in the LOW state for 500 ms.

The LEDs turn ON or OFF according to the configuration of the LED bar and the logic applied to its control terminals.

Result

The Arduino UNO successfully interfaces with the LED bar and controls the LED output using digital GPIO pins.

The LED bar output alternates between the two programmed states with a 1000 ms HIGH duration and a 500 ms LOW duration.