Speed Detection 5.0

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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
Elite Explorer Kit	Arduino Uno R4 WiFi	BUY
3 in 1 Ultimate Starter Kit	Arduino Uno R4 Minima	BUY

Course Introduction

This Arduino project detects speed using IR sensor and Ultrasonic Sensor Module. When an object passes the first sensor, a timer starts; it stops at the second sensor.

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	1	BUY
2	USB Type-C cable	1
3	Breadboard	1	BUY
4	Wires	Several	BUY
5	Ultrasonic Sensor Module	1	BUY
6	IR Obstacle Avoidance Sensor Module	1	BUY
7	I2C LCD 1602	1	BUY
8	Buzzer Modudle	1	BUY

Wiring

Common Connections:

I2C LCD 1602
- SDA: Connect to A4 on the Arduino.
- SCL: Connect to A5 on the Arduino.
- GND: Connect to breadboard’s negative power bus.
- VCC: Connect to breadboard’s red power bus.
Ultrasonic Sensor Module
- Trig: Connect to 4 on the Arduino.
- Echo: Connect to 3 on the Arduino.
- GND: Connect to breadboard’s negative power bus.
- VCC: Connect to breadboard’s red power bus.
IR Obstacle Avoidance Sensor Module
- OUT: Connect to 11 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 10 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.
To install the library, use the Arduino Library Manager and search for LiquidCrystal I2C and install it.
Don’t forget to select the board(Arduino UNO R4 Minima/WIFI) and the correct port before clicking the Upload button.

#include <Wire.h>
#include <LiquidCrystal_I2C.h>

// LCD address is usually 0x27 for a 16x2 I2C LCD.
LiquidCrystal_I2C lcd(0x27, 16, 2);

// Ultrasonic sensor pins
#define TRIG1 4
#define ECHO1 3

// Obstacle sensor OUT pin connects to D11.
#define OBSTACLE_PIN 11

// Buzzer connects to D10.
#define BUZZER_PIN 10

// Distance between the ultrasonic sensor and obstacle sensor, in meters.
float gateDistance = 1.30;

// Speed <= 30 km/h shows "Normal"; speed > 30 km/h shows "Over Speed!".
float speedLimit = 30.0;

// The ultrasonic sensor triggers when an object is closer than this distance.
float triggerDist = 15.0;

// These variables store the current detection state.
bool firstGateTriggered = false;
bool speedCalculated = false;

// t1: time when the ultrasonic sensor is triggered.
// t2: time when the obstacle sensor is triggered.
unsigned long t1 = 0;
unsigned long t2 = 0;

// Measure distance with the ultrasonic sensor and return the value in cm.
float getDistanceCM(int trigPin, int echoPin) {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);

  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // pulseIn measures how long the echo pin stays HIGH.
  long duration = pulseIn(echoPin, HIGH, 30000);

  // If no echo is received, return -1 as invalid data.
  if (duration == 0) {
    return -1;
  }

  // Convert echo time to distance.
  // 0.034 cm/us is the approximate speed of sound.
  return duration * 0.034 / 2;
}

// Reset the system and show the waiting screen.
void resetSystem() {
  firstGateTriggered = false;
  speedCalculated = false;

  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("Speed Detector");
  lcd.setCursor(0, 1);
  lcd.print("Waiting...");
}

// One short beep means the result is normal.
void shortBeep() {
  tone(BUZZER_PIN, 1500);
  delay(120);
  noTone(BUZZER_PIN);
}

// Beep 4 times when the speed is over the limit.
void overSpeedAlert() {
  for (int i = 0; i < 4; i++) {
    tone(BUZZER_PIN, 2000);
    delay(200);

    noTone(BUZZER_PIN);
    delay(200);
  }
}

void setup() {
  pinMode(TRIG1, OUTPUT);
  pinMode(ECHO1, INPUT);

  // Most obstacle sensors use OUT to output HIGH or LOW.
  pinMode(OBSTACLE_PIN, INPUT);

  pinMode(BUZZER_PIN, OUTPUT);

  // Use Serial Monitor to check sensor values during testing.
  Serial.begin(9600);

  lcd.init();
  lcd.backlight();

  resetSystem();
}

void loop() {
  // Read the ultrasonic distance.
  float d1 = getDistanceCM(TRIG1, ECHO1);

  // Most obstacle modules output LOW when an object is detected.
  int obstacleState = digitalRead(OBSTACLE_PIN);

  // Print sensor values for debugging.
  Serial.print("Distance: ");
  Serial.print(d1);
  Serial.print(" cm | Obstacle: ");
  Serial.println(obstacleState);

  // The ultrasonic sensor is the first detection point.
  if (!firstGateTriggered && d1 > 0 && d1 < triggerDist) {
    firstGateTriggered = true;
    t1 = millis();

    lcd.clear();
    lcd.setCursor(0, 0);
    lcd.print("Object detected");
    lcd.setCursor(0, 1);
    lcd.print("Measuring...");
  }

  // If the second sensor is not triggered within 5 seconds, reset the system.
  if (firstGateTriggered && !speedCalculated && millis() - t1 > 5000) {
    lcd.clear();
    lcd.setCursor(0, 0);
    lcd.print("Timeout");
    lcd.setCursor(0, 1);
    lcd.print("Try again");

    delay(1500);
    resetSystem();
  }

  // The obstacle sensor is the second detection point.
  if (firstGateTriggered && !speedCalculated && obstacleState == LOW) {
    t2 = millis();
    speedCalculated = true;

    // Convert the time difference from milliseconds to seconds.
    float deltaT = (t2 - t1) / 1000.0;

    lcd.clear();

    // Ignore very small time differences to avoid false triggers.
    if (deltaT > 0.05) {
      // Speed = distance / time, then convert m/s to km/h.
      float speed = (gateDistance / deltaT) * 3.6;

      lcd.setCursor(0, 0);
      lcd.print("Speed:");
      lcd.print(speed, 1);
      lcd.print("km/h");

      lcd.setCursor(0, 1);

      if (speed > speedLimit) {
        lcd.print("Over Speed!");
        overSpeedAlert();
      } else {
        lcd.print("Normal");
        shortBeep();
      }

      Serial.print("Speed: ");
      Serial.print(speed);
      Serial.println(" km/h");
    } else {
      lcd.setCursor(0, 0);
      lcd.print("Invalid data");
    }

    delay(1500);
    resetSystem();
  }

  delay(50);
}