Smart Stop 3.0

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

Course Introduction

In this lesson, you’ll learn how to use an L9110 Motor Driver Module, an Ultrasonic Sensor Module, a buzzer module, a traffic light module and a TT motor with the Arduino UNO R4 to create a Smart Stop 3.0 system.

As the obstacle gets closer to the Ultrasonic Sensor Module, the LCD screen displays the distance to obstacles and the servo speed. When the distance exceeds the predefined safety threshold, the green light switches to a flashing red light as a warning, the TT motor gradually slows down until it comes to a stop.

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 Cable	1
3	Breadboard	1	BUY
4	Wires	Several	BUY
5	L9110 Motor Driver Module	1
6	Ultrasonic Sensor Module	1	BUY
7	TT Motor	1
8	Buzzer Modudle	1	BUY
9	Traffic Light LED	1	BUY

Wiring

Common Connections:

Ultrasonic Sensor Module
- Trig: Connect to 10 on the Arduino.
- Echo: Connect to 11 on the Arduino.
- GND: Connect to breadboard’s negative power bus.
- VCC: Connect to breadboard’s red power bus.
TT Motor
- Connect to MOTOR B on the L9110 Motor Driver Module.
L9110 Motor Driver Module
- GND: Connect to breadboard’s negative power bus.
- VCC: Connect to breadboard’s red power bus.
- B-1B: Connect to 2 on the Arduino.
- B-1A: Connect to 3 on the Arduino.
Buzzer Module
- I/0: Connect to 4 on the Arduino.
- ＋: Connect to breadboard’s red power bus.
- －: Connect to breadboard’s negative power bus.
Traffic light LED
- R: Connect to 5 on the Arduino.
- Y: Connect to 6 on the Arduino.
- G: Connect to 7 on the Arduino.
- GND: 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 WiFi) and the correct port before clicking the Upload button.

// ================= Pin Definitions =================
const int motorPinA = 3;   // L9110 B-1A (PWM speed control)
const int motorPinB = 2;   // L9110 B-1B (direction)

const int trigPin = 10;    // Ultrasonic trigger pin
const int echoPin = 11;    // Ultrasonic echo pin

const int buzzerPin = 4;   // Passive buzzer

const int redPin = 5;      // Traffic light - Red
const int yellowPin = 6;   // Traffic light - Yellow
const int greenPin = 7;    // Traffic light - Green

// ================= Distance Thresholds (cm) =================
const int STOP_DISTANCE = 5;    // Stop when distance < 5 cm
const int SLOW_DISTANCE = 20;   // Slow down when distance < 20 cm

// ================= Motor Parameters =================
const int MIN_MOTOR_PWM = 75;   // Minimum PWM to make motor rotate
const int MAX_MOTOR_PWM = 255;  // Maximum motor speed

// ================= Buzzer Timing =================
unsigned long previousBeepTime = 0;
bool beepState = false;

// ================= Setup =================
void setup() {
  pinMode(motorPinA, OUTPUT);
  pinMode(motorPinB, OUTPUT);

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

  pinMode(buzzerPin, OUTPUT);

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

  // Set motor direction (one direction only)
  digitalWrite(motorPinB, LOW);
}

// ================= Main Loop =================
void loop() {
  int distance = readDistance();        // Get distance in cm
  int speed = calculateSpeed(distance); // Convert distance to motor speed

  controlMotor(speed);                  // Drive the motor
  updateTrafficLight(distance);         // Update traffic lights
  updateBuzzer(distance);               // Control buzzer sound

  delay(50);  // Small delay for stable reading
}

// ================= Read Distance =================
int readDistance() {
  long duration;

  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Read echo pulse, timeout prevents blocking
  duration = pulseIn(echoPin, HIGH, 25000);

  if (duration == 0) {
    return 100;  // No obstacle detected
  }

  return duration / 58;  // Convert to centimeters
}

// ================= Distance to Speed =================
int calculateSpeed(int distance) {
  if (distance < STOP_DISTANCE) {
    return 0;  // Stop motor
  }

  if (distance < SLOW_DISTANCE) {
    // Map distance to valid motor speed range
    return map(distance, STOP_DISTANCE, SLOW_DISTANCE - 1,
              MIN_MOTOR_PWM, MAX_MOTOR_PWM);
  }

  return MAX_MOTOR_PWM;  // Full speed
}

// ================= Motor Control =================
void controlMotor(int speed) {
  analogWrite(motorPinA, speed);   // Set motor speed
  digitalWrite(motorPinB, LOW);    // Fixed direction
}

// ================= Traffic Light Control =================
void updateTrafficLight(int distance) {
  digitalWrite(redPin, LOW);
  digitalWrite(yellowPin, LOW);
  digitalWrite(greenPin, LOW);

  if (distance < STOP_DISTANCE) {
    digitalWrite(redPin, HIGH);        // Stop
  } else if (distance < SLOW_DISTANCE) {
    digitalWrite(yellowPin, HIGH);     // Slow down
  } else {
    digitalWrite(greenPin, HIGH);      // Go
  }
}

// ================= Buzzer Control =================
void updateBuzzer(int distance) {
  unsigned long currentTime = millis();

  if (distance < STOP_DISTANCE) {
    // Fast warning beep
    if (currentTime - previousBeepTime >= 100) {
      previousBeepTime = currentTime;
      beepState = !beepState;
      beepState ? tone(buzzerPin, 2000) : noTone(buzzerPin);
    }
  }
  else if (distance < SLOW_DISTANCE) {
    // Slow warning beep
    if (currentTime - previousBeepTime >= 500) {
      previousBeepTime = currentTime;
      beepState = !beepState;
      beepState ? tone(buzzerPin, 800) : noTone(buzzerPin);
    }
  }
  else {
    noTone(buzzerPin);  // Silent
  }
}