Distance Display 4.0

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
Ultimate Sensor Kit	Arduino Uno R4 Minima	BUY
Elite Explorer Kit	Arduino Uno R4 WiFi	BUY
3 in 1 Ultimate Starter Kit	Arduino Uno R4 Minima	BUY
Universal Maker Sensor Kit	×	BUY

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.

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

Wiring

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.

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 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     15     // Green: >=15 cm
#define WARNING_DIST   5     // Yellow: 15~5 cm, Red: <5 cm

// ============================
// System States
// ============================
enum State { SAFE, WARNING, DANGER };
State currentState = SAFE;
State nextState = SAFE;   // We switch to next state only after current cycle ends

// ============================
// Timing Control (millis)
// ============================
unsigned long ledTimer = 0;
unsigned long beepTimer = 0;
bool yellowOn = false;

// ============================
// Read Distance (cm)
// ============================
float getDistance() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);

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

  unsigned long duration = pulseIn(echoPin, HIGH, 30000);
  if (duration == 0) return 999;
  return duration / 58.0;
}

// ============================
// Setup
// ============================
void setup() {
  Serial.begin(9600);

  pinMode(buzzerPin, OUTPUT);
  pinMode(greenPin, OUTPUT);
  pinMode(yellowPin, OUTPUT);
  pinMode(redPin, OUTPUT);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);

  digitalWrite(greenPin, LOW);
  digitalWrite(yellowPin, LOW);
  digitalWrite(redPin, LOW);
  noTone(buzzerPin);
}

// ============================
// Main Loop
// ============================
void loop() {
  float dist = getDistance();
  Serial.println(dist);

  // ===== Decide which state we want to switch to =====
  if (dist >= SAFE_DIST)         nextState = SAFE;
  else if (dist >= WARNING_DIST) nextState = WARNING;
  else                           nextState = DANGER;

  unsigned long now = millis();

  // ===== Execute current state (only switch after cycle completes) =====
  switch (currentState) {

    // ---------------- 🟢 SAFE MODE ----------------
    case SAFE:
      digitalWrite(greenPin, HIGH);
      digitalWrite(yellowPin, LOW);
      digitalWrite(redPin, LOW);
      noTone(buzzerPin);

      // If next state is different, switch immediately (no cycle needed)
      currentState = nextState;
      break;

    // ---------------- 🟡 WARNING MODE ----------------
    case WARNING:
      digitalWrite(greenPin, LOW);
      digitalWrite(redPin, LOW);

      // Complete the 500ms blink + beep cycle before switching
      if (now - ledTimer >= 500) {
        ledTimer = now;
        yellowOn = !yellowOn;
        digitalWrite(yellowPin, yellowOn);

        if (yellowOn) tone(buzzerPin, 2000);
        else noTone(buzzerPin);

        // Switch to next state ONLY after the blink finishes
        if (currentState != nextState && !yellowOn) {
          currentState = nextState;
        }
      }
      break;

    // ---------------- 🔴 DANGER MODE ----------------
    case DANGER:
      digitalWrite(greenPin, LOW);
      digitalWrite(yellowPin, LOW);
      digitalWrite(redPin, HIGH);

      // Complete one beep cycle before switching
      if (now - beepTimer >= 300) {
        beepTimer = now;
        tone(buzzerPin, 2000, 120);  // Short beep (not annoying)

        // Switch to next state at end of cycle
        if (currentState != nextState) {
          noTone(buzzerPin);
          currentState = nextState;
        }
      }
      break;
  }
}