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# LED Bar Graph Using Arduino

In this project, you’ll combine what you’ve learned in the previous led projects to create a led bar graph that you can control with a potentiometer.

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Parts Required

• Arduino board
• Jumper wires
• 9 LEDs
• 50k-ohm potentiometer
• 9 220-ohm resistors

How It Works

A bar graph is a series of LEDs in a line, similar to what you might see on an audio display. It’s made up of a row of LEDs with an analog input, like a potentiometer or microphone. In this project, you use the analog signal from the potentiometer to control which LEDs are lit. When you turn the potentiometer one way, the LEDs light up one at a time in sequence, as shown in Figure 1-1(a), until they are all on, shown in Figure 1-1(b). When you turn it the other way, they turn off in sequence, as shown in Figure 1-1(c).

FIGURE 1-1: The LEDs light up and turn off in sequence as you turn the potentiometer.

THE BUILD

1. Insert the LEDs into the breadboard with their shorter, negative legs in the GND rail. Connect this rail to Arduino GND using a jumper wire.

2. Insert a 220-ohm resistor for each LED into the breadboard, with one resistor leg connected to the positive LED leg. Connect the other legs of the resistors to digital pins 2–10 in sequence, as shown in Figure 1-2. It’s important that the resistors bridge the break in the breadboard as shown.

 LEDS ARDUINO Positive legs Pins 2–10 via a 220-ohm resistor Negative legs GND

Figure 1-2: Circuit diagram for the bar graph

3. Place the potentiometer in the breadboard and connect the center pin to Arduino A0. Connect the right outer pin to +5V and the left potentiometer pin to GND.

 POTENTIOMETER ARDUINO Left pin GND Center pin A0 Right pin +5V

4. Upload the code in “The Sketch” below.

### The Sketch

The sketch first reads the input from the potentiometer. It maps the input value to the output range, in this case, nine LEDs. Then it sets up a for loop over the outputs. If the output number of the LED in the series is lower than the mapped input range, the LED turns on; if not, it turns off. See? Simple! If you turn the potentiometer to the right, the LEDs light up in sequence. Turn it to the left, and they turn off in sequence.

/* By EA. This example code is in the public domain.
http://www.arduino.cc/en/Tutorial/BarGraph */

const int analogPin = A0; // Pin connected to the potentiometer
const int ledCount = 9;   // Number of LEDs
int ledPins[] = {2,3,4,5,6,7,8,9,10}; // Pins connected to the LEDs

void setup() {
for (int thisLed = 0; thisLed < ledCount; thisLed++) {
pinMode(ledPins[thisLed], OUTPUT); // Set the LED pins as output
}
}

// Start a loop
void loop() {
int ledLevel = map(sensorReading, 0, 1023, 0, ledCount);
for (int thisLed = 0; thisLed < ledCount; thisLed++) {
if (thisLed < ledLevel) { // Turn on LEDs in sequence
digitalWrite(ledPins[thisLed], HIGH);
}
else { // Turn off LEDs in sequence
digitalWrite(ledPins[thisLed], LOW);
}
}
}