Arduino - LED Bar Graph

Arduino Project: Potentiometer-Controlled LED Bar Graph

This project demonstrates a powerful and common pattern in physical computing: reading an analog sensor and visualizing its value using a series of digital outputs. We will build an LED bar graph that responds in real-time to the turning of a potentiometer.

Components Required

• 1 × Arduino Uno R3 or equivalent
• 1 × Breadboard
• 1 × 10kΩ Potentiometer (variable resistor)
• 8 × LEDs (any color)
• 8 × 220Ω Resistors (for current limiting)
• Jumper Wires

Circuit Connections

Carefully connect the components on the breadboard as described below. A resistor is essential for each LED to prevent damage.

1. Potentiometer:

• Connect one outer pin to the Arduino’s GND pin.
• Connect the other outer pin to the Arduino’s 5V pin.
• Connect the middle pin (the wiper) to Analog Pin A0 on the Arduino.

2. LEDs:

• For each of the 8 LEDs, connect the cathode (shorter leg) to the breadboard’s ground rail (which should be connected to Arduino GND).
• Connect the anode (longer leg) of the first LED to one end of a 220Ω resistor. Connect the other end of that resistor to Digital Pin 2.
• Repeat for the remaining 7 LEDs, connecting them via their own resistors to pins 3, 4, 5, 6, 7, 8, and 9 respectively.

The Sketch

Enter the following code into the Arduino IDE or your preferred editor. This code is designed to be readable and easily adaptable.

/*
  LED Bar Graph Controller

  This sketch reads an analog value from a potentiometer and lights up a
  corresponding number of LEDs in a bar graph fashion.

  It demonstrates arrays, for loops, analog input, and value mapping.
*/

// --- Constants for Configuration ---
const int analogSensorPin = A0; // Pin connected to the potentiometer's wiper
const int ledCount = 8;         // The total number of LEDs in our bar graph

// An array to hold the pin numbers for each LED. This makes the code scalable.
const int ledPins[ledCount] = {2, 3, 4, 5, 6, 7, 8, 9};


// --- Setup Function (runs once) ---
void setup() {
  // Use a for-loop to iterate through our array of LED pins
  // and set each one to be an output.
  for (int i = 0; i < ledCount; i++) {
    pinMode(ledPins[i], OUTPUT);
  }
  // Optional: Start serial communication for debugging
  Serial.begin(9600);
}


// --- Loop Function (runs repeatedly) ---
void loop() {
  // 1. Read the raw sensor value from the potentiometer (0-1023)
  int sensorReading = analogRead(analogSensorPin);

  // 2. Map the sensor's 10-bit range (0-1023) to the number of LEDs (0-8).
  // The map() function handles this conversion neatly.
  int ledsToLight = map(sensorReading, 0, 1023, 0, ledCount);

  // Optional: Print values to the Serial Monitor to debug and understand
  Serial.print("Sensor: ");
  Serial.print(sensorReading);
  Serial.print("\t -> LEDs to light: ");
  Serial.println(ledsToLight);

  // 3. Loop through the LEDs and turn them on or off.
  for (int i = 0; i < ledCount; i++) {
    // If the index 'i' is less than the number of LEDs we want to light,
    // turn this LED on.
    if (i < ledsToLight) {
      digitalWrite(ledPins[i], HIGH);
    } else {
      // Otherwise, turn it off.
      digitalWrite(ledPins[i], LOW);
    }
  }

  delay(10); // A small delay for stability
}

How It Works

The logic of the sketch is straightforward:

1. Read the Sensor: In each loop, analogRead() gets a value from 0 to 1023 from the potentiometer.
2. Map the Value: The map() function is key. It proportionally converts the sensor’s wide range (0-1023) into our smaller output range (0-8, the number of LEDs). This tells us how many LEDs should be lit.
3. Update the Display: A for loop efficiently iterates through all our LEDs. An if statement checks if a particular LED should be on or off based on the mapped value, and digitalWrite() sets its state accordingly.

Result & Extension Ideas

When you upload the sketch and turn the potentiometer, you should see the number of lit LEDs change, creating a smooth bar graph effect. From here, you can:

• Use a different sensor: Replace the potentiometer with a photoresistor (to measure light) or a temperature sensor.
• Change the display style: Instead of a bar graph, make only a single LED light up to indicate the level.
• Add PWM Fading: Modify the code to use analogWrite() to make the last active LED in the bar graph fade smoothly instead of just being on or off.