Traffic Light Simulator — Cnipbotics Projects — Cnipbotics

Traffic Light Simulator

Learning Objectives

Understand the basic principles of traffic signal control
Wire LEDs with current-limiting resistors on a breadboard
Write an Arduino sketch with delay() to sequence LED states
Relate real-world timing constraints to embedded programming

Overview

The Traffic Light Simulator is the classic first Arduino project. You will build a miniature traffic signal that cycles through Green → Yellow → Red using three LEDs and an Arduino Uno. Along the way you'll learn how to protect LEDs with resistors, write a timed sequence in C++, and debug your circuit with a multimeter.

Good to Know

Real traffic lights use programmable logic controllers (PLCs) with much more complex state machines that account for pedestrian crossings, emergency vehicle overrides, and adaptive timing based on traffic density. Your Arduino sketch is a simplified model of this same idea.

Components Required

Component	Quantity	Specification
Arduino Uno R3	1	ATmega328P, 5 V logic
Red LED	1	5 mm, standard
Yellow LED	1	5 mm, standard

Circuit Diagram

Step 1

Wire the LEDs

Connect each LED anode (+) through a 220 Ω resistor to the corresponding Arduino digital pin:

Red LED → Pin 8
Yellow LED → Pin 9
Green LED → Pin 10

Connect all LED cathodes (−) to the breadboard's GND rail, which connects to Arduino's GND pin.

ACTIVITY

Resistor Color Code Challenge

Before wiring, identify each 220 Ω resistor using the color code: Red – Red – Brown – Gold. Use a multimeter in resistance mode to verify the value is between 209 Ω and 231 Ω (5% tolerance band).

Arduino Sketch

Step 2

Write the Code

// Traffic Light Simulator
// Pins
const int RED_PIN    = 8;
const int YELLOW_PIN = 9;
const int GREEN_PIN  = 10;
 
// Timing (milliseconds)
const int GREEN_TIME  = 5000;
const int YELLOW_TIME = 2000;
const int RED_TIME    = 5000;

Good to Know

delay() blocks the entire microcontroller — the Arduino cannot do anything else while waiting. In a production traffic controller, engineers use non-blocking timers (via millis()) so the processor can handle pedestrian buttons and sensor inputs simultaneously.

Testing Your Circuit

Step 3

Upload and Observe

Open Arduino IDE and paste the sketch above.
Select Tools → Board → Arduino Uno and the correct Port.
Click Upload (→ arrow).
Observe the LED sequence: Green (5 s) → Yellow (2 s) → Red (5 s) → repeat.

ACTIVITY

Timing Experiment

Modify GREEN_TIME to 2000 and RED_TIME to 8000. Re-upload and observe how the light cycle changes. Discuss: why do real intersections use longer red phases on main roads?

Troubleshooting

| Symptom | Likely Cause | Fix | |---------|-------------|-----| | LED doesn't light | LED inserted backwards | Flip the LED (longer leg = anode/+) | | All LEDs stay off | Wrong pins in code | Check const int values match wiring | | LED very dim | Resistor too high | Use 220 Ω, not 2.2 kΩ | | Upload fails | Wrong port selected | Tools → Port → select your COM port |

Extension Challenges

ACTIVITY

Pedestrian Button

Add a push button to pin 2. When pressed, extend the RED phase by 5 seconds to simulate a pedestrian crossing request. Use digitalRead() inside the loop.