Arduino UNO Traffic Light Control System Using LED | Beginner Arduino Project with Code

Arduino UNO Traffic Light Control System – Smart LED Signal Project

📅 February 2026 ⏱ ~20 min build 🎓 Beginner level 🔌 3 components

Simulate a real-world road traffic signal using an Arduino UNO and three LEDs. Learn digital output control, the delay() timing function, and sequential automation logic — the perfect first embedded systems project.

5sRed Phase

2sYellow Phase

5sGreen Phase

12sFull Cycle

🔴 Red LED — STOP Pin 1 · HIGH for 5 seconds

🟡 Yellow LED — SLOW DOWN Pin 2 · HIGH for 2 seconds

🟢 Green LED — GO Pin 3 · HIGH for 5 seconds

🧩 Components Required

🖥️

Arduino UNO

ATmega328P · 14 digital I/O pins

🔴

Red LED

5mm standard · 2.0V forward voltage

🟡

Yellow LED

5mm standard · 2.1V forward voltage

🟢

Green LED

5mm standard · 2.1V forward voltage

⚡

3× 220Ω Resistors

Current limiting for each LED

🔗

Jumper Wires

Male-to-male · assorted colors

🔲

Breadboard

Half-size or full — 400/830 tie points

💻

Arduino IDE

v2.x recommended · USB-A to USB-B cable

🔌 Circuit Diagram

arduino_traffic_light_circuit.svg Annotated

📌 Pin Connections

Arduino Pin	LED	Via Resistor	Action	Duration
D1	🔴 Red LED	220Ω → Anode	STOP	5 seconds
D2	🟡 Yellow LED	220Ω → Anode	SLOW DOWN	2 seconds
D3	🟢 Green LED	220Ω → Anode	GO	5 seconds
GND	All LEDs (Cathode)	Common GND rail	Return path	Always

⏱ Signal Timing Chart

One complete 12-second cycle — each bar represents 1 second

GREEN

ON · 5s

–

YELLOW

–

ON · 2s

–

RED

–

ON · 5s

← Cycle repeats continuously via void loop()

📄 diagram.json (Wokwi / Cirkit Designer)

💡 Simulate without hardware: Copy the JSON below and paste it into Wokwi.com or Cirkit Designer to run the traffic light simulation in your browser.

diagram.json

{
  "version": 1,
  "author": "MakeMindz",
  "editor": "wokwi",
  "parts": [
    {
      "type": "wokwi-arduino-uno",
      "id": "uno",
      "top": 0, "left": 0,
      "attrs": {}
    },
    {
      "type": "wokwi-resistor",
      "id": "r-red",
      "top": 80, "left": 260,
      "attrs": { "value": "220" }
    },
    {
      "type": "wokwi-resistor",
      "id": "r-yellow",
      "top": 140, "left": 260,
      "attrs": { "value": "220" }
    },
    {
      "type": "wokwi-resistor",
      "id": "r-green",
      "top": 200, "left": 260,
      "attrs": { "value": "220" }
    },
    {
      "type": "wokwi-led",
      "id": "led-red",
      "top": 60, "left": 380,
      "attrs": { "color": "red" }
    },
    {
      "type": "wokwi-led",
      "id": "led-yellow",
      "top": 120, "left": 380,
      "attrs": { "color": "yellow" }
    },
    {
      "type": "wokwi-led",
      "id": "led-green",
      "top": 180, "left": 380,
      "attrs": { "color": "green" }
    }
  ],
  "connections": [
    [ "uno:1",          "r-red:1",      "red",    [] ],
    [ "r-red:2",        "led-red:A",    "red",    [] ],
    [ "led-red:C",      "uno:GND.1",    "black", [] ],
    [ "uno:2",          "r-yellow:1",   "yellow",[] ],
    [ "r-yellow:2",     "led-yellow:A", "yellow",[] ],
    [ "led-yellow:C",   "uno:GND.1",    "black", [] ],
    [ "uno:3",          "r-green:1",    "green", [] ],
    [ "r-green:2",      "led-green:A",  "green", [] ],
    [ "led-green:C",    "uno:GND.1",    "black", [] ]
  ]
}

📋 Step-by-Step Instructions

1

Gather All Components

Collect your Arduino UNO, 3 LEDs (red, yellow, green), 3 × 220Ω resistors, jumper wires, and a breadboard. Connect the Arduino to your computer via USB-B cable to verify the COM port is recognized in Device Manager / System Information.
2

Place LEDs on the Breadboard

Insert the three LEDs vertically into the breadboard in order: Red at top, Yellow in middle, Green at bottom. Ensure the longer leg (anode, +) and shorter leg (cathode, −) are in separate rows. Leave 2–3 rows of gap between each LED.
⚠️ LED polarity matters — longer leg = anode (+), shorter leg = cathode (−)
3

Add 220Ω Current-Limiting Resistors

Place one 220Ω resistor in series with each LED's anode leg. The resistor connects between the Arduino digital pin wire and the LED anode. This limits current to ~15mA, protecting both the LED and Arduino pin (which can only source 40mA max).
✅ Without resistors, LEDs may burn out within seconds — always use them
4

Wire Arduino Pins to Resistors

Connect jumper wires from Arduino digital pins to each resistor:
• D1 → Red LED resistor
• D2 → Yellow LED resistor
• D3 → Green LED resistor
Use color-coded wires to match each LED for easy debugging.
5

Connect All LED Cathodes to GND

Run the cathode (short leg) of each LED to the negative rail of the breadboard. Then connect the negative breadboard rail to any Arduino GND pin with a black jumper wire. All three LEDs now share a common ground return path.
6

Open Arduino IDE and Enter the Code

Open Arduino IDE 2.x. Create a new sketch, delete the template code, and type (or paste) the traffic light sketch shown below. Verify the greenPin = 3, yellowPin = 2, and redPin = 1 match your physical wiring.
📦 Go to Tools → Board → Arduino UNO · Tools → Port → select your COM port
7

Upload Sketch to Arduino

Click the ✓ (Verify) button to compile. If no errors appear, click → (Upload) to flash the sketch onto the Arduino UNO. The LEDs should immediately begin cycling: Green → Yellow → Red → repeat.
⚠️ If upload fails: check COM port, try pressing Reset on Arduino just before upload starts
8

Observe and Verify the Timing

Use a stopwatch to verify the sequence: Green holds for 5 seconds, Yellow for 2 seconds, Red for 5 seconds, then repeats. Adjust the delay() values in the sketch to customize timing for your project — schools often prefer 3s/1s/3s for faster demos.
✅ Unplug the USB and power via DC barrel jack to run standalone

💻 Arduino Sketch

Arduino C++

/*
 * Arduino UNO Traffic Light Control System
 * MakeMindz.com — Beginner Embedded Systems Tutorial
 *
 * Simulates a real traffic signal using 3 LEDs:
 *   Green LED  → Pin 3 → GO      (5 seconds)
 *   Yellow LED → Pin 2 → SLOW    (2 seconds)
 *   Red LED    → Pin 1 → STOP    (5 seconds)
 *
 * Each LED is connected via a 220Ω current-limiting resistor.
 * Total cycle time: 12 seconds (repeating)
 */

const int greenPin  = 3;   // Green LED → Digital Pin 3
const int yellowPin = 2;   // Yellow LED → Digital Pin 2
const int redPin    = 1;   // Red LED → Digital Pin 1

void setup() {
  // Configure all LED pins as digital outputs
  pinMode(greenPin,  OUTPUT);
  pinMode(yellowPin, OUTPUT);
  pinMode(redPin,    OUTPUT);
}

void loop() {

  // ── Phase 1: GREEN — Vehicles GO ──────────────────
  digitalWrite(greenPin, HIGH);    // Turn green ON
  delay(5000);                       // Hold for 5 seconds
  digitalWrite(greenPin, LOW);     // Turn green OFF

  // ── Phase 2: YELLOW — Vehicles SLOW DOWN ──────────
  digitalWrite(yellowPin, HIGH);   // Turn yellow ON
  delay(2000);                       // Hold for 2 seconds
  digitalWrite(yellowPin, LOW);    // Turn yellow OFF

  // ── Phase 3: RED — Vehicles STOP ──────────────────
  digitalWrite(redPin, HIGH);      // Turn red ON
  delay(5000);                       // Hold for 5 seconds
  digitalWrite(redPin, LOW);       // Turn red OFF

  // Cycle restarts automatically — loop() repeats forever
}

🎮 Try the Simulation

🔬

Wokwi Simulator — Arduino UNO Traffic Light

Paste the diagram.json above + the sketch code into Wokwi to simulate the full traffic signal in your browser — no hardware needed.

→ ⚡

Cirkit Designer — Full Interactive Circuit

Build the complete traffic light circuit with drag-and-drop components, then run a live simulation with real-time LED toggle visualization.

→

✨ Key Features

🟢

Beginner Friendly

Only 3 components beyond the Arduino — ideal as a first project

⏱

Timing Control

Learn delay() for precise millisecond-accurate LED sequencing

🔌

Digital I/O

Demonstrates pinMode() and digitalWrite() fundamentals

🔁

Continuous Loop

Infinite cycling via void loop() — just like real road signals

🏫

Exhibition Ready

Ideal for school science fairs and STEM showcase events

🌆

Expandable

Solid foundation for smart city traffic management upgrades

🚀 Project Upgrades

🔘 Pedestrian Button

Add a push button interrupt — pressing it triggers an extended red phase for crossing

📡 Vehicle Detection

Use HC-SR04 ultrasonic sensor to detect waiting vehicles and adapt green duration

📺 Countdown Display

Add a 7-segment or LCD display showing remaining seconds for each phase

🌐 IoT Monitoring

Add ESP8266 Wi-Fi module to log traffic phases to a web dashboard via MQTT

🚦 Multi-Junction

Scale to 4-way intersection with 12 LEDs and synchronized phase logic

📱 GSM Alerts

Use SIM800L to send SMS alerts if a signal fault is detected (LED off unexpectedly)

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