Barrier Gate 4.0

Note

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Kit purchase

Looking for parts? Check out our all-in-one kits below — packed with components, beginner-friendly guides, and tons of fun.

Name	Includes Arduino board	PURCHASE LINK
Ultimate Sensor Kit	Arduino Uno R4 Minima	BUY
Elite Explorer Kit	Arduino Uno R4 WiFi	BUY
3 in 1 Ultimate Starter Kit	Arduino Uno R4 Minima	BUY
Universal Maker Sensor Kit	×	BUY

Course Introduction

This project uses an ultrasonic sensor, traffic lights, a servo, and a buzzer to create an automatic gate system.

When a car is detected, the lights change, the gate opens, and the buzzer signals. After the car passes, the gate closes and the red light turns back on.

Note

If this is your first time working with an Arduino project, we recommend downloading and reviewing the basic materials first.

Required Components

In this project, we need the following components:

SN	COMPONENT INTRODUCTION	QUANTITY	PURCHASE LINK
1	Arduino UNO R4 Minima/Arduino UNO R4 WIFI	1	BUY
2	USB Type-C cable	1
3	Breadboard	1	BUY
4	Wires	Several	BUY
5	Traffic Light LED	1	BUY
6	Digital Servo Motor	1	BUY
7	Buzzer Modudle	1	BUY
8	Ultrasonic Sensor Module	1	BUY

Wiring

Common Connections:

Traffic light LED
- R: Connect to 7 on the Arduino.
- Y: Connect to 6 on the Arduino.
- G: Connect to 5 on the Arduino.
- GND: Connect to breadboard’s negative power bus.
Digital Servo Motor
- Connect to breadboard’s positive power bus.
- Connect to breadboard’s negative power bus.
- Connect to 3 on the Arduino.
Ultrasonic Sensor Module
- Trig: Connect to 11 on the Arduino.
- Echo: Connect to 10 on the Arduino.
- GND: Connect to breadboard’s negative power bus.
- VCC: Connect to breadboard’s red power bus.
Buzzer Module
- I/0: Connect to 2 on the Arduino.
- ＋: Connect to breadboard’s red power bus.
- －: Connect to breadboard’s negative power bus.

Writing the Code

Note

You can copy this code into Arduino IDE.
Don’t forget to select the board(Arduino UNO R4 Minima/WIFI) and the correct port before clicking the Upload button.

#include <Servo.h>

// Ultrasonic sensor pins
const int trigPin = 11;
const int echoPin = 10;

// Traffic light pins
const int redPin = 7;
const int yellowPin = 6;
const int greenPin = 5;

// Servo and buzzer pins
const int servoPin = 3;
const int buzzerPin = 2;

Servo myServo;

// Play one beep
void beepOnce(int freq, int dur) {
  tone(buzzerPin, freq, dur);
  delay(dur * 1.2);
  noTone(buzzerPin);
}

// Play three short beeps
void beepTriple() {
  for (int i = 0; i < 3; i++) {
    tone(buzzerPin, 1500, 120);
    delay(150);
    noTone(buzzerPin);
    delay(80);
  }
}

// Smoothly open the gate
void openGate() {
  for (int pos = 0; pos <= 90; pos++) {
    myServo.write(pos);
    delay(10);   // smooth speed
  }
}

// Smoothly close the gate
void closeGate() {
  for (int pos = 90; pos >= 0; pos--) {
    myServo.write(pos);
    delay(10);
  }
}

// Read distance once
float getDistance() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  long duration = pulseIn(echoPin, HIGH, 25000); // 25ms timeout
  if (duration == 0) return 999;                 // no echo

  return duration * 0.034 / 2;
}

void setup() {
  Serial.begin(9600);

  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);

  pinMode(redPin, OUTPUT);
  pinMode(yellowPin, OUTPUT);
  pinMode(greenPin, OUTPUT);

  pinMode(buzzerPin, OUTPUT);

  myServo.attach(servoPin);
  myServo.write(0);   // gate starts closed

  digitalWrite(redPin, HIGH); // red ON at start
}

void loop() {

  float distance = getDistance();
  Serial.print("Distance: ");
  Serial.println(distance);

  // Car detected
  if (distance < 10) {

    // Yellow + warning beep
    digitalWrite(redPin, LOW);
    digitalWrite(yellowPin, HIGH);
    digitalWrite(greenPin, LOW);
    beepOnce(1000, 300);

    delay(1000);

    // Green light + open gate
    digitalWrite(yellowPin, LOW);
    digitalWrite(greenPin, HIGH);

    openGate();       // smooth motion (no ultrasonic during movement)
    beepTriple();     // pass signal

    delay(1500);

    // Red light + close gate
    digitalWrite(greenPin, LOW);
    digitalWrite(redPin, HIGH);

    closeGate();      // smooth motion
    beepOnce(800, 200);

    delay(500);
  }

  delay(200);   // small delay between checks
}