Arduino Project

Arduino Ultrasonic Distance Meter with LCD V6

Course Introduction

In this project, an ultrasonic sensor and a set of green, yellow, and red LEDs are used to create a proximity-alert system with the Arduino.

The sensor continuously measures distance and switches between three states: safe, warning, and danger. The green LED indicates a safe distance, the yellow LED blinks with a beep when an object gets closer, and the red LED turns on with a short alarm when the object is too close.

The system updates smoothly by completing each LED–buzzer cycle before changing to the next state.

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 WIFI	1	BUY
2	USB Type-C cable	1	×
3	Breadboard	1	BUY
4	Wires	Several	BUY
5	Ultrasonic Sensor Module	1	BUY
6	Traffic Light LED	1	BUY
7	Buzzer Modudle	1	BUY
8	I2C LCD 1602	1	BUY

Wiring

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Common Connections:

Traffic light LED
R: Connect to 5 on the Arduino.
Y: Connect to 4 on the Arduino.
G: Connect to 3 on the Arduino.
GND: Connect to breadboard’s negative power bus.

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.

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.

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

// Create LCD object (I2C address 0x27)
LiquidCrystal_I2C lcd(0x27, 16, 2);

// Pins
const int buzzerPin = 2;
const int greenPin  = 3;
const int yellowPin = 4;
const int redPin    = 5;
const int trigPin   = 11;
const int echoPin   = 10;

// Distance thresholds (cm)
#define SAFE_DIST     13      // Safe when distance >= 13 cm
#define WARNING_DIST   5      // Warning when distance >= 5 cm

// System states
enum State { SAFE, WARNING, DANGER };

// Current running state
State currentState = SAFE;
// Target state based on distance
State nextState = SAFE;
// Last state for LCD update
State lastState = SAFE;

// Timers for non-blocking control
unsigned long ledTimer  = 0;
unsigned long beepTimer = 0;
unsigned long lcdTimer  = 0;

// Yellow LED status
bool yellowOn = false;

// Read distance from ultrasonic sensor
float getDistance() {
  // Send trigger pulse
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Read echo time
  unsigned long duration = pulseIn(echoPin, HIGH, 30000);

  // If no echo, return a large value
  if (duration == 0) return 999;

  // Convert time to distance (cm)
  return duration / 58.0;
}

// Show distance on LCD
void updateDistanceLine(float dist) {
  lcd.setCursor(0, 0);
  lcd.print("Dist: ");

  if (dist > 99) {
    lcd.print("--.- cm ");
  } else {
    lcd.print(dist, 1);
    lcd.print(" cm   ");
  }
}

// Show system status on LCD
void updateStatusLine(State state) {
  lcd.setCursor(0, 1);
  lcd.print("Status:        ");
  lcd.setCursor(8, 1);

  if (state == SAFE)    lcd.print("SAFE");
  if (state == WARNING) lcd.print("WARNING");
  if (state == DANGER)  lcd.print("DANGER");
}

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

  // Set pin modes
  pinMode(buzzerPin, OUTPUT);
  pinMode(greenPin, OUTPUT);
  pinMode(yellowPin, OUTPUT);
  pinMode(redPin, OUTPUT);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);

  // Stop buzzer at start
  noTone(buzzerPin);

  // Initialize LCD
  lcd.init();
  lcd.backlight();
  lcd.clear();

  // Show initial LCD content
  updateDistanceLine(999);
  updateStatusLine(currentState);
  lastState = currentState;
}

void loop() {
  // Read distance
  float dist = getDistance();
  Serial.println(dist);

  // Decide next state based on distance
  if (dist >= SAFE_DIST)         nextState = SAFE;
  else if (dist >= WARNING_DIST) nextState = WARNING;
  else                           nextState = DANGER;

  unsigned long now = millis();

  // Run state machine
  switch (currentState) {

    case SAFE:
      digitalWrite(greenPin, HIGH);
      digitalWrite(yellowPin, LOW);
      digitalWrite(redPin, LOW);
      noTone(buzzerPin);
      currentState = nextState;
      break;

    case WARNING:
      digitalWrite(greenPin, LOW);
      digitalWrite(redPin, LOW);

      // Blink yellow LED every 500 ms
      if (now - ledTimer >= 500) {
        ledTimer = now;
        yellowOn = !yellowOn;
        digitalWrite(yellowPin, yellowOn);

        // Buzzer follows yellow LED
        if (yellowOn) tone(buzzerPin, 2000);
        else noTone(buzzerPin);

        // Change state only after one blink cycle
        if (currentState != nextState && !yellowOn) {
          currentState = nextState;
        }
      }
      break;

    case DANGER:
      digitalWrite(greenPin, LOW);
      digitalWrite(yellowPin, LOW);
      digitalWrite(redPin, HIGH);

      // Beep every 300 ms
      if (now - beepTimer >= 300) {
        beepTimer = now;
        tone(buzzerPin, 2000, 120);

        // Change state at the end of beep cycle
        if (currentState != nextState) {
          noTone(buzzerPin);
          currentState = nextState;
        }
      }
      break;
  }

  // Update distance on LCD every 250 ms
  if (now - lcdTimer >= 250) {
    lcdTimer = now;
    updateDistanceLine(dist);
  }

  // Update status on LCD only when state changes
  if (currentState != lastState) {
    updateStatusLine(currentState);
    lastState = currentState;
  }
}

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Arduino Project

Arduino Ultrasonic Distance Meter with LCD V6

Course Introduction

Required Components

Wiring

Common Connections:

Writing the Code

Arduino Project

Arduino Ultrasonic Distance Meter with LCD V6

Course Introduction

Required Components

Wiring

Common Connections:

Writing the Code

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