Lesson 1 of 7 Basics Beginner ◎ 30 min

Lesson 1: LED Basics & Brightness

Make an LED blink, then turn a knob to fade it from off to full brightness. You will learn how to wire an LED safely and how the UNO can dim a light.

Arduino UNO Sensor & Output Starter Kit - LEDs, Buzzer, Servo, Ultrasonic & LCD

One of 7 projects in the Arduino UNO Sensor & Output Starter Kit - LEDs, Buzzer, Servo, Ultras… — the parts below are from that kit.

// Before you start

Before you start

Time

30 min

Do these first

Start here: Blink uploaded and the L light blinking

New to Arduino? Do Start here first →

On your own

You can do this lesson on your own. For your very first wiring, an adult nearby is a good idea.

Exact parts

Part	How many
UNO R3 + USB cable	1
400-point breadboard	1
Yellow LED	1
220 Ω resistor (red-red-brown)	1
10K potentiometer	1
Male-to-male jumper wires	about 7

Not in the box

Nothing extra - just the kit and your computer.

// How it works

What you build and learn

Which LED leg is + and which is −
Why every LED needs a resistor
digitalWrite(): switching a pin on and off
analogRead() and analogWrite(): reading a knob and dimming a light

An LED only works one way round: current goes in through the long leg (+) and out through the short leg (−). On its own it would take too much current, so a 220 Ω resistor always goes in line with it to protect the LED and the UNO pin.

digitalWrite(3, HIGH) puts 5 volts on pin 3 and the LED lights. LOW turns it off. That is how the 3 blinks at the start work.

The potentiometer is a knob. Its middle pin gives a voltage between 0 and 5V depending on how far you turn it, and analogRead(A0) turns that into a number from 0 to 1023.

The UNO cannot make "half a volt". Instead analogWrite() switches pin 3 on and off very fast (PWM). On for half the time looks half as bright. 0 is off, 255 is full brightness.

New words

Breadboard: A board with hidden metal strips inside. Parts pushed into the same short row of holes are connected to each other.
Rail: The long lines of holes along the edge of the breadboard. We use the red line (+) for 5V and the blue line (−) for GND.
GND: Ground: 0 volts. Every circuit needs a way back to GND.
Resistor: A part that limits current. 220 Ω has the colour bands red-red-brown.
Pin: A numbered connection on the UNO's black header strips, like pin 3 or A0.
PWM: Switching a pin on and off very fast. Pins with a ~ mark can do it, and it makes an LED look dimmer.

// Items used

What this project uses

Every item is in the kit — nothing extra to buy.

UNO R3 UNO R3 Development Board ATmega328P Microcontroller with USB Cable, 5V Logic, 14 Digital I/O, 6 Analog Inputs… UNOR3

In the kit

400 tie-point breadboard 400 Tie Point Solderless Breadboard - Half Size Prototyping Circuit Board with Power Rails, for Arduino & Ele… DIY-238

In the kit

jumper wires Jumper Wire Assorted Pack 120 Pieces - Male-to-Male, Male-to-Female, Female-to-Female 10cm Ribbon Cables for… DIY-212

In the kit

yellow LED 5MM LED R-Y-G DIY-228

In the kit

resistor assortment RESISTOR ASSORTED 220-1K-10K DIY-213

In the kit

10K potentiometer 10K Ohm Rotary Potentiometer PCB Type - 3-Pin Variable Resistor for Arduino Analog Input & DIY Electronics DIY-220

In the kit

Basics HC-SR04 Ultrasonic Distance Sensor Module for Arduino, Raspberry Pi & DIY Robotics Projects, 5V Trigger/Echo… DIY-00043

In the kit

Build this with

Arduino UNO Sensor & Output Starter Kit - LEDs, Buzzer, Servo, Ultrasonic & LCD

All 10 parts in one box, with this project and 6 more to build from them.

AED 85.00 See the kit

Need only these parts? Order them loose · from AED 110.05

Used in this project tick what you still need

UNO R3 UNO R3 Development Board ATmega328P Microcontroller with USB Cable, 5V Logic, 14 Digital I/O, 6 Analog Inputs… UNOR3 · ×1

AED 26.39

In stock

400 tie-point breadboard 400 Tie Point Solderless Breadboard - Half Size Prototyping Circuit Board with Power Rails, for Arduino & Ele… DIY-238 · ×1

AED 11.58

In stock

jumper wires Jumper Wire Assorted Pack 120 Pieces - Male-to-Male, Male-to-Female, Female-to-Female 10cm Ribbon Cables for… DIY-212 · ×1

AED 25.02

In stock

yellow LED 5MM LED R-Y-G DIY-228 · ×1

AED 12.14

In stock

resistor assortment RESISTOR ASSORTED 220-1K-10K DIY-213 · ×1

AED 9.35

In stock

10K potentiometer 10K Ohm Rotary Potentiometer PCB Type - 3-Pin Variable Resistor for Arduino Analog Input & DIY Electronics DIY-220 · ×1

AED 10.26

In stock

Also needed untick if you already have them

Basics HC-SR04 Ultrasonic Distance Sensor Module for Arduino, Raspberry Pi & DIY Robotics Projects, 5V Trigger/Echo… DIY-00043 · ×1

AED 15.31

In stock

Selected parts AED 110.05

One of each part. Packs (resistor assortment, jumper wires) already hold more than a single build needs. Delivery is AED 20, free on orders AED 100+.

// Wiring

Connections

Unplug USB before you change any wire. Pin names are the labels printed on the board.

Lesson 1: LED Basics & Brightness - connection diagram with labelled pins — Connection diagram, drawn from this lesson's pin plan - not a photo of a tested build. Tap to open it full size. The table below says the same thing in words.

Part / pin	Connect to	Note
UNO 5V	+ rail (red line)	Powers the knob
UNO GND	− rail (blue line)	Shared ground for everything
UNO pin 3	220 Ω resistor → yellow LED long leg (+)	Pin 3 has a ~ mark, so it can dim
Yellow LED short leg (−)	− rail (GND)
Potentiometer outer pin	+ rail (5V)	Either outer pin
Potentiometer other outer pin	− rail (GND)
Potentiometer middle pin	UNO A0	On the lower header, by ANALOG IN

// Build it

Step by step

One thing at a time. Tick nothing off until it matches the diagram.

Unplug the USB cable from the computer.Watch out: Always unplug the USB cable before you add, move or remove a wire.
Put the breadboard next to the UNO. Find the red (+) and blue (−) lines along its edge: those are the rails.
Connect a jumper wire from the UNO 5V pin to the + rail, and one from a UNO GND pin to the − rail.
Push the yellow LED into the breadboard so its two legs are in two different rows. Remember which row has the long leg.Watch out: The long leg is +. If the legs have been cut, look for the flat edge on the LED's rim: that side is −.
Push one end of a 220 Ω resistor (red-red-brown) into the long-leg row and the other end into an empty row.Watch out: Every LED needs its resistor. Without it the LED or the UNO pin can be damaged.
Connect a jumper wire from that empty row to UNO pin 3.
Connect a jumper wire from the LED's short-leg row to the − rail.
Push the potentiometer into the breadboard. Wire one outer pin to the + rail, the other outer pin to the − rail and the middle pin to A0.
Check every wire against the diagram and the table, then plug the USB cable back in.Watch out: If anything gets hot or smells, unplug straight away.
Copy the Lesson 1 code below into the Arduino IDE and click Upload (→).
Watch the LED blink 3 times, then turn the knob slowly from one end to the other.

// Code

Sketch for this project

Written for the board in the kit. Copy it into the Arduino IDE; change the pin numbers if you wire it differently.

/*
  DIY KIT - Arduino UNO Sensor & Output Starter Kit
  Lesson 1 of 7: LED Basics & Brightness

  WIRING (unplug the USB cable before you wire)
    Yellow LED long leg (+)  -> 220 ohm resistor -> UNO pin 3
    Yellow LED short leg (-) -> GND
    Potentiometer outer pins -> 5V and GND (either way round)
    Potentiometer middle pin -> UNO pin A0

  WHAT SHOULD HAPPEN
    1. The LED blinks 3 times. That proves the LED is wired the right way.
    2. Then turn the knob: the LED fades from off to fully bright.
*/

const int LED_PIN  = 3;    // the yellow LED. Pin 3 has a ~ mark, so it can dim (PWM)
const int KNOB_PIN = A0;   // the middle pin of the potentiometer
const int BLINK_MS = 300;  // how long each start-up blink lasts, in milliseconds

void setup() {
  pinMode(LED_PIN, OUTPUT);   // pin 3 sends power OUT to the LED
  Serial.begin(9600);         // talk to the computer (Serial Monitor at 9600 baud)
  Serial.println("Lesson 1: LED Basics & Brightness");

  // Part A: blink 3 times so you know the LED works.
  for (int i = 1; i <= 3; i++) {
    digitalWrite(LED_PIN, HIGH);  // HIGH = 5 volts = LED on
    delay(BLINK_MS);              // wait
    digitalWrite(LED_PIN, LOW);   // LOW = 0 volts = LED off
    delay(BLINK_MS);
  }
  Serial.println("Now turn the knob");
}

void loop() {
  // Part B: the knob sets the brightness.
  int knob = analogRead(KNOB_PIN);              // 0 at one end of the turn ... 1023 at the other
  int brightness = map(knob, 0, 1023, 0, 255);  // squeeze 0-1023 into 0-255
  analogWrite(LED_PIN, brightness);             // 0 = off, 128 = half, 255 = full

  // Two numbers the Serial Plotter can draw as lines.
  Serial.print("knob:");
  Serial.print(knob);
  Serial.print(",brightness:");
  Serial.println(brightness);

  delay(100);  // 10 readings a second is plenty
}

ℹCompiler-checked for Arduino UNO (0 warnings) and run in the kit simulator. Pins match the lesson diagram. Not yet bench-tested on the shipped parts.

Upload it

Click Copy (or Download .ino and open the file).
In the Arduino IDE choose File → New Sketch, select everything in it and paste.
Check the bottom of the window says Arduino Uno and your port (Start here, step 5).
Click Upload (the → arrow) and wait for Done uploading.

How the code works

In the code	What it does
const int LED_PIN = 3;	Gives pin 3 a name. If you ever move the LED, you only change this number.
setup()	Runs once when the UNO starts. It makes pin 3 an OUTPUT and blinks the LED 3 times with digitalWrite() and delay().
loop()	Runs again and again: read the knob (analogRead), change 0-1023 into 0-255 (map), set the brightness (analogWrite).
Serial.print(...)	Sends the two numbers to your computer. Open Tools → Serial Monitor or Serial Plotter at 9600 baud to see them.

Change it and see

Change: Change BLINK_MS from 300 to 100, then upload.What happens: The 3 start-up blinks become three times faster.

Change: In map(), swap 0, 255 to 255, 0.What happens: The knob works backwards: turning it "up" now makes the LED dimmer.

// Test it

What you should see or hear

As soon as the upload finishes, the yellow LED blinks 3 times.
Turning the knob fades the LED smoothly from off to full brightness.
In Tools → Serial Monitor (9600 baud) you see lines like knob:512,brightness:127.

If it doesn't work

Problem	What to check
The LED never lights, not even the 3 blinks	Unplug USB. The LED is probably the wrong way round: turn it so the long leg is in the resistor's row. Check the wire goes to pin 3 and the short leg reaches the − rail.
The LED blinks 3 times but the knob does nothing	The LED is fine. Check the potentiometer: middle pin to A0, outer pins to the + and − rails.
The LED is only fully on or fully off	The wire is on a pin without a ~ mark. Move it to pin 3.
The LED is very dim even at full brightness	Check the resistor colours: red-red-brown is 220 Ω. Brown-black-orange is 10 kΩ, which is far too big.
The knob works backwards	Nothing is wrong. Swap the two outer potentiometer wires if you prefer the other way.
The upload fails	See Start here, step 6: "If the upload fails".

Small experiment

Cover the LED with a sheet of paper and turn the knob up slowly. At what knob number (shown in the Serial Monitor) can you first see light through the paper?

Check what you learned

Why does the LED need a resistor?

To limit the current, so the LED and the UNO pin are not damaged.

Which leg of the LED is + (positive)?

The long leg.

What number does analogRead() give at each end of the knob?

0 at one end and 1023 at the other.

Why must the LED be on a pin with a ~ mark to fade?

Only those pins can do PWM, the fast on-off switching that analogWrite() uses to dim the LED.

▶In the simulator: In the simulator the LED and the knob slider behave like the real ones. The simulator does not check which way round the LED is or whether you used a resistor - on the real breadboard both matter.

Stuck?

Most problems are one wire in the wrong hole. Check these first:

Unplug, then compare every wire with the lesson's diagram and table. One pin off is the most common problem.
LEDs: is the long leg on the resistor side?
Is the − rail connected to a UNO GND pin, and the + rail to 5V?
Upload problems: is Tools → Board set to Arduino Uno and Tools → Port to your UNO? (Start here, step 5.)
Read the lesson's "If it doesn't work" table and find the line that matches what you see.

Open the troubleshooting table for this step →

Still stuck? Ask us on WhatsApp. Send this message with a photo of your wiring - it tells us exactly where you are.

Hi DIY KIT, I'm stuck on the Arduino UNO Sensor & Output Starter Kit.
Lesson: __
Step number: __
What should happen: __
What happens instead: __
Error message (copied exactly): __
I'll attach a photo of my wiring.

Message us on WhatsApp

// Keep going