Arduino Project

Arduino Speed Detector Project with Ultrasonic Sensors V4

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	Ultrasonic Sensor Module	2	BUY

Wiring

2.webp__PID:b11ed384-03e0-41fc-b486-ba515ee04317

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.

Ultrasonic Sensor Module Front
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.

Ultrasonic Sensor Module Back
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.

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 <Servo.h>

// Front ultrasonic sensor
#define TRIG1 4
#define ECHO1 3

// Back ultrasonic sensor
#define TRIG2 11
#define ECHO2 10

// Servo
#define SERVO_PIN 9
Servo myServo;

// ---------------------- Tunable parameters ----------------------
// Distance between two sensors (cm). Change to your real spacing.
const float SENSOR_GAP_CM = 10.0;

// Trigger threshold (cm). Object is considered "detected" when distance < this.
const float DETECT_THRESHOLD_CM = 20.0;

// Speed range for gauge mapping (cm/s). 0..MAX_SPEED maps to -90..+90 degrees.
const float MAX_SPEED_CM_S = 60.0;

// Anti-repeat trigger window (ms)
const unsigned long COOLDOWN_MS = 150;

// Timeout for pulseIn (microseconds). 30000us ~ 5m max, safe for HC-SR04.
const unsigned long PULSE_TIMEOUT_US = 30000;

// How long to show the gauge result (ms)
const unsigned long HOLD_MS = 1000;
// ---------------------------------------------------------------

// State
bool waitingForSecond = false;
unsigned long t1_ms = 0;
unsigned long lastTrigger_ms = 0;

// A small helper to read distance (cm) from an HC-SR04-like sensor.
// Returns: distance in cm; returns -1 if timeout/no reading.
float readDistanceCm(uint8_t trigPin, uint8_t echoPin) {
  // Trigger pulse
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Read echo pulse
  unsigned long duration = pulseIn(echoPin, HIGH, PULSE_TIMEOUT_US);
  if (duration == 0) return -1.0; // timeout

  // Sound speed ~ 0.034 cm/us. Divide by 2 for round trip.
  float distance = (duration * 0.034f) / 2.0f;
  return distance;
}

// Map speed (0..MAX_SPEED_CM_S) to a gauge angle (-90..+90),
// then convert to servo position (0..180).
int speedToServoPos(float speed_cm_s) {
  // Clamp speed
  if (speed_cm_s < 0) speed_cm_s = 0;
  if (speed_cm_s > MAX_SPEED_CM_S) speed_cm_s = MAX_SPEED_CM_S;

  // Linear map to angle -90..+90
  float angle = (speed_cm_s / MAX_SPEED_CM_S) * 180.0f - 90.0f; // -90..+90

  // Convert "gauge angle" to servo write value.
  // Keep same style as original project: servoPos = 90 - angle
  int servoPos = (int)(90.0f - angle);

  // Clamp servo bounds
  if (servoPos < 0) servoPos = 0;
  if (servoPos > 180) servoPos = 180;
  return servoPos;
}

void setup() {
  Serial.begin(115200);

  pinMode(TRIG1, OUTPUT);
  pinMode(ECHO1, INPUT);

  pinMode(TRIG2, OUTPUT);
  pinMode(ECHO2, INPUT);

  myServo.attach(SERVO_PIN);

  // Initialize gauge pointer to left side (like original: 180 corresponds to -90° style)
  myServo.write(180);
  delay(300);

  Serial.println("=== Speed Detection 2.0 (Dual Ultrasonic) ===");
  Serial.print("SENSOR_GAP_CM = "); Serial.println(SENSOR_GAP_CM);
  Serial.print("DETECT_THRESHOLD_CM = "); Serial.println(DETECT_THRESHOLD_CM);
  Serial.print("MAX_SPEED_CM_S = "); Serial.println(MAX_SPEED_CM_S);
}

void loop() {
  unsigned long now = millis();

  // Read both distances
  float dFront = readDistanceCm(TRIG1, ECHO1);
  float dBack  = readDistanceCm(TRIG2, ECHO2);

  // Optional debug (comment out if too noisy)
  // Serial.print("Front: "); Serial.print(dFront); Serial.print(" cm, ");
  // Serial.print("Back: ");  Serial.print(dBack);  Serial.println(" cm");

  // Basic validity
  bool frontDetected = (dFront > 0 && dFront < DETECT_THRESHOLD_CM);
  bool backDetected  = (dBack  > 0 && dBack  < DETECT_THRESHOLD_CM);

  // Cooldown to prevent repeated triggers while object stays in front
  bool cooldownOK = (now - lastTrigger_ms) > COOLDOWN_MS;

  // 1) Front sensor triggers start timing
  if (!waitingForSecond && cooldownOK && frontDetected) {
    t1_ms = now;
    waitingForSecond = true;
    lastTrigger_ms = now;

    Serial.print("[Front] Detected at t1 = ");
    Serial.print(t1_ms);
    Serial.println(" ms");
  }

  // 2) Back sensor triggers stop timing and compute speed
  if (waitingForSecond && cooldownOK && backDetected) {
    unsigned long t2_ms = now;
    waitingForSecond = false;
    lastTrigger_ms = now;

    unsigned long dt_ms = (t2_ms >= t1_ms) ? (t2_ms - t1_ms) : 0;

    Serial.print("[Back ] Detected at t2 = ");
    Serial.print(t2_ms);
    Serial.print(" ms, dt = ");
    Serial.print(dt_ms);
    Serial.println(" ms");

    if (dt_ms > 0) {
      float time_s = dt_ms / 1000.0f;
      float speed_cm_s = SENSOR_GAP_CM / time_s;

      Serial.print("Speed = ");
      Serial.print(speed_cm_s, 2);
      Serial.println(" cm/s");

      int servoPos = speedToServoPos(speed_cm_s);
      Serial.print("ServoPos = ");
      Serial.println(servoPos);

      // Show result on gauge
      myServo.write(servoPos);
      delay(HOLD_MS);

      // Return to start position
      myServo.write(180);
      delay(200);
    } else {
      Serial.println("dt_ms == 0, ignored.");
    }
  }

  // Safety: if front triggered but back never arrives, reset after some time
  if (waitingForSecond && (now - t1_ms) > 5000) {
    waitingForSecond = false;
    Serial.println("Timeout waiting for back sensor. Reset.");
    myServo.write(180);
  }

  delay(10); // small loop delay
}

Recover password

Create my account

Arduino Project

Arduino Speed Detector Project with Ultrasonic Sensors V4

Course Introduction

Required Components

Wiring

Common Connections:

Writing the Code

Arduino Project

Arduino Speed Detector Project with Ultrasonic Sensors V4

Course Introduction

Required Components

Wiring

Common Connections:

Writing the Code

Subscribe to our newsletter