Mission 04 · Stage 1

LED Chaser

loop index drives a moving pattern

Light one segment at a time on a bar graph using a loop index.

Pin connections

Part 1		Part 2
Arduino pin 2	→	LED bar graph A1
Arduino pin 3	→	LED bar graph A2
Arduino pin 4	→	LED bar graph A3
Arduino pin 5	→	LED bar graph A4
Arduino pin 6	→	LED bar graph A5
Arduino pin 7	→	LED bar graph A6
Arduino pin 8	→	LED bar graph A7
Arduino pin 9	→	LED bar graph A8
Arduino pin 10	→	LED bar graph A9
Arduino pin 11	→	LED bar graph A10
LED bar graph C10	→	Arduino GND

See it

Let's make a running light!

A bright dot zooms along a row of ten lights, like a tiny race car.

You see this on loading bars, volume meters, and fancy car taillights!

The story

The problem

One blinking light is fun, but a moving dot of light is even cooler.

Think of it like

It's like a spotlight at a show — it shines on one kid, then slides to the next.

Meet the parts

Holds all the parts and joins them, like a LEGO baseplate.

Breadboard

Our building board

Loading part…

It thinks and tells each light when to glow.

Arduino

The brain

Loading part…

Ten little lights in a line that you can switch on one by one.

LED bar graph

The row of lights

Loading part…

How it works

Turn them all off

First we turn every light off, so only one light will glow at a time.

digitalWrite(FIRST_PIN + j, LOW);

Light up one

The number i picks which light glows. That glowing light is our racing dot!

digitalWrite(FIRST_PIN + i, HIGH);

Wait, then move on

A short wait lets us see the dot. Then i goes up by one and the dot jumps to the next light.

delay(100);

Then loop back to step 1

Build the circuit

Follow these steps in order. Match the wires to the colors shown.

1
Place Breadboard
Place the Breadboard (bb1) on the breadboard.
Breadboard placed — build like the real world!
Loading part…
2
Place Arduino
Place the Arduino (uno) on the breadboard.
Arduino placed — ready to build!
Loading part…
3
Place LED bar graph
Place the LED bar graph (bar1) on the breadboard.
Row of ten lights placed — now let's wire them up!
Loading part…
4
Connect Arduino pin 2 to LED bar graph (bar1) A1
Arduino pin 2 to segment 1's anode (A1)
Tip: Arduino pin 2 to segment 1's anode (A1)
Light 1 wired!
5
Connect Arduino pin 3 to LED bar graph (bar1) A2
Arduino pin 3 to segment 2's anode (A2)
Tip: Arduino pin 3 to segment 2's anode (A2)
Light 2 wired!
6
Connect Arduino pin 4 to LED bar graph (bar1) A3
Arduino pin 4 to segment 3's anode (A3)
Tip: Arduino pin 4 to segment 3's anode (A3)
Light 3 wired!
7
Connect Arduino pin 5 to LED bar graph (bar1) A4
Arduino pin 5 to segment 4's anode (A4)
Tip: Arduino pin 5 to segment 4's anode (A4)
Light 4 wired!
8
Connect Arduino pin 6 to LED bar graph (bar1) A5
Arduino pin 6 to segment 5's anode (A5)
Tip: Arduino pin 6 to segment 5's anode (A5)
Light 5 wired!
9
Connect Arduino pin 7 to LED bar graph (bar1) A6
Arduino pin 7 to segment 6's anode (A6)
Tip: Arduino pin 7 to segment 6's anode (A6)
Light 6 wired!
10
Connect Arduino pin 8 to LED bar graph (bar1) A7
Arduino pin 8 to segment 7's anode (A7)
Tip: Arduino pin 8 to segment 7's anode (A7)
Light 7 wired!
11
Connect Arduino pin 9 to LED bar graph (bar1) A8
Arduino pin 9 to segment 8's anode (A8)
Tip: Arduino pin 9 to segment 8's anode (A8)
Light 8 wired!
12
Connect Arduino pin 10 to LED bar graph (bar1) A9
Arduino pin 10 to segment 9's anode (A9)
Tip: Arduino pin 10 to segment 9's anode (A9)
Light 9 wired!
13
Connect Arduino pin 11 to LED bar graph (bar1) A10
Arduino pin 11 to segment 10's anode (A10)
Tip: Arduino pin 11 to segment 10's anode (A10)
All ten lights are wired!
14
Connect LED bar graph (bar1) C10 to Arduino GND
One wire from the bar graph's common cathode side to Arduino GND — all segments share this ground inside the part
Tip: One wire from the bar graph's common cathode side to Arduino GND — all segments share this ground inside the part
Circuit complete — the dot can run!

Try it

Press the green Run button — follow the bright dot from one end to the other.
Only one light should glow at a time!

Peek at code

How many lights and where

const int FIRST_PIN = 2;
const int NUM_LEDS = 10;

FIRST_PIN is the first light (pin 2) and NUM_LEDS is how many lights there are (10).

Get all the lights ready

void setup() {
  for (int i = 0; i < NUM_LEDS; i++) {
    pinMode(FIRST_PIN + i, OUTPUT);
  }
}

This loop gets every light pin ready, one after another, so they can all glow.

The chasing dot

void loop() {
  for (int i = 0; i < NUM_LEDS; i++) {
    for (int j = 0; j < NUM_LEDS; j++) {
      digitalWrite(FIRST_PIN + j, LOW);
    }
    digitalWrite(FIRST_PIN + i, HIGH);
    delay(100);
  }
}

First all the lights turn off, then one turns on. Doing this over and over makes the dot race along the row.

Show full sketch (led-chaser.ino)

const int FIRST_PIN = 2;
const int NUM_LEDS = 10;
void setup() {
  for (int i = 0; i < NUM_LEDS; i++) {
    pinMode(FIRST_PIN + i, OUTPUT);
  }
}
void loop() {
  for (int i = 0; i < NUM_LEDS; i++) {
    for (int j = 0; j < NUM_LEDS; j++) {
      digitalWrite(FIRST_PIN + j, LOW);
    }
    digitalWrite(FIRST_PIN + i, HIGH);
    delay(100);
  }
}

Quick quiz

Q1. Which part runs again and again?

A. loop() ✓
B. setup()
C. pinMode only

Why: Yes! loop() runs again and again, forever.

Q2. What does the number i pick in this program?

A. Which light is glowing ✓
B. How bright the row is
C. A random number

Why: Yes! i is the number that picks which light glows right now.

Code lab — try on your own

Make the dot race faster — change delay(100) to delay(50).
Hint: There is only one delay() inside loop().
Add a little note (comment) on the line that lights one light up.
Hint: Type // and your words at the end of the line with + i.

Code walkthrough

A line-by-line tour of the sketch — the same steps as in Robot Gurukul Studio.

Program overview

Big idea

Every Arduino program has a top part, a setup() part that runs once, and a loop() part that runs again and again.

In this project

One light at a time glows and the bright dot runs along a bar of ten lights.

Tip

Read from the top to the bottom. Tap any word or line if you need help!

const int FIRST_PIN = 2;
const int NUM_LEDS = 10;

setup()

Big idea

setup() runs one time when the board turns on.

In this project

It gets all ten light pins (starting at pin 2) ready.

Why here

Things we do only once go inside setup().

void setup() {
  for (int i = 0; i < NUM_LEDS; i++) {
    pinMode(FIRST_PIN + i, OUTPUT);
  }
}

loop()

Big idea

loop() runs again and again, forever.

In this project

This is where the glowing dot moves from one light to the next.

Why here

Things that repeat go inside loop().

void loop() {
  for (int i = 0; i < NUM_LEDS; i++) {
    for (int j = 0; j < NUM_LEDS; j++) {
      digitalWrite(FIRST_PIN + j, LOW);
    }
    digitalWrite(FIRST_PIN + i, HIGH);
    delay(100);
  }
}

Try this: Change the delay number inside loop(), then press Run to make the dot race faster or slower.

pinMode

Big idea

pinMode tells a pin if it will listen or push power out.

In this project

It makes each light pin ready to push power to a light.

Why here

It goes in setup() because we only set it once.

    pinMode(FIRST_PIN + i, OUTPUT);

digitalWrite

Big idea

digitalWrite turns a pin ON or OFF.

In this project

ON lights up one little light, OFF turns it dark.

Why here

It goes in loop() so the lights can keep changing.

      digitalWrite(FIRST_PIN + j, LOW);

delay

Big idea

delay means wait. Nothing else happens while it waits.

In this project

A short wait lets you see the dot before it jumps to the next light.

Why here

Right after we light up a light.

    delay(100);

← 3. Traffic Light 5. Multiple LED Patterns →