Arduino Project

Speed Detection 2.0

Course Introduction

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

Using the known distance, the system calculates speed and maps it to a servo angle.

Note

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

1.1 Install Arduino IDE(Important)
1.2 Introduction of Arduino IDE

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

Digital Servo Motor

1

BUY

6

IR Obstacle Avoidance Sensor Module

2

BUY

Wiring

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Common Connections:

Digital Servo Motor
Connect to breadboard’s positive power bus.
Connect to breadboard’s negative power bus.
Connect to 9 on the Arduino.

IR Obstacle Avoidance Sensor Module Front
OUT: Connect to 2 on the Arduino.
GND: Connect to breadboard’s negative power bus.
VCC: Connect to breadboard’s red power bus.

IR Obstacle Avoidance Sensor Module Back
OUT: Connect to 3 on the Arduino.
GND: Connect to breadboard’s negative power bus.
VCC: Connect to breadboard’s red power bus

Writing the Code

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


#include 

#define IR1_PIN 2
#define IR2_PIN 3
#define SERVO_PIN 9

Servo myServo;

unsigned long t1 = 0;
unsigned long t2 = 0;
bool waitingForIR2 = false;

float distance_cm = 10.0; // Distance between IR1 and IR2 in cm
float speed = 0; // Speed in cm/s

void setup() {
  Serial.begin(9600);
  pinMode(IR1_PIN, INPUT);
  pinMode(IR2_PIN, INPUT);

  myServo.attach(SERVO_PIN);

  // Initialize servo to -90° (corresponds to 180° in servo signal)
  myServo.write(180);
  delay(500);
}

void loop() {
  // Detect vehicle passing IR1
  if (digitalRead(IR1_PIN) == LOW && !waitingForIR2) {
    t1 = millis();
    waitingForIR2 = true;
    Serial.println("IR1 triggered");
    delay(50); // Debounce delay
  }

  // Detect vehicle passing IR2
  if (waitingForIR2 && digitalRead(IR2_PIN) == LOW) {
    t2 = millis();
    waitingForIR2 = false;
    Serial.println("IR2 triggered");

    // Calculate speed in cm/s
    float timeTaken = (t2 - t1) / 1000.0;
    if (timeTaken > 0) {
      speed = distance_cm / timeTaken;
      Serial.print("Speed: ");
      Serial.print(speed);
      Serial.println(" cm/s");

      // Map speed to servo angle (-90 to +90), max speed = 60 cm/s
      int angle = map(constrain(speed, 0, 60), 0, 60, -90, 90);
      angle = constrain(angle, -90, 90);

      // Convert -90~90 to servo range 0~180 (-90° → 180, +90° → 0)
      int servoPos = 90 - angle;
      myServo.write(servoPos);

      delay(1000); // Display time

      // Return to -90° (servo signal 180°)
      myServo.write(180);
      delay(500);
    }
  }
}