Radar Guard 2.0

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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 lesson, we will learn how to use the Ultrasonic Sensor Module, Digital Servo Motor, and I2C LCD 1602 with the Arduino Board to create a radar defense system version 2.0.

When the ultrasonic sensor module is running, it emits an audible alarm and flashes the red LED if it detects an obstacle within its sensing range. If no obstacle is detected, indicating a safe state, the green LED stays on.

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 Type-C cable	1
3	Breadboard	1	BUY
4	Wires	Several	BUY
5	1kΩ resistor	4	BUY
6	Ultrasonic Sensor Module	1	BUY
7	LED	4	BUY
8	I2C LCD 1602	1	BUY
9	Digital Servo Motor	1	BUY
10	Passive Buzzer	1	BUY

Wiring

Common Connections:

LED
- Connect the LEDs anode to a 1kΩ resistor then to the 3, 4 on Arduino, and the LEDs cathode to negative power bus on the breadboard.
Digital Servo Motor
- Connect to breadboard’s positive power bus.
- Connect to breadboard’s negative power bus.
- Connect to 12 on the Arduino.
Passive Buzzer
- ＋: Connect to 2 on the Arduino.
- －: 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.
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.

Writing the Code

Note

You can copy this code into Arduino IDE.
To install the library, use the Arduino Library Manager and search for LiquidCrystal I2C and install it.
Don’t forget to select the board(Arduino UNO R4 Minima/WIFI) and the correct port before clicking the Upload button.

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

// Servo and ultrasonic sensor
Servo radarServo;
const int trigPin    = 11;
const int echoPin    = 10;
const int servoPin   = 12;

// LEDs and passive buzzer (controlled by tone()/noTone())
const int redLed     = 3;
const int greenLed   = 4;
const int buzzer     = 2;

// I2C LCD (address 0x27, 16×2 characters)
LiquidCrystal_I2C lcd(0x27, 16, 2);

// Configuration parameters
const int alertDistance        = 30;     // distance threshold for alert (cm)
const unsigned long updateInterval   = 20;     // servo scan interval (ms)
const int triggerThreshold     = 2;      // number of consecutive detections needed
const unsigned long displayDuration     = 500;    // LCD display time (ms)
const unsigned long blinkInterval       = 200;    // LED blink interval (ms)

// Scanning state
int currentAngle     = 0;
int increment        = 1;
unsigned long lastServoUpdate = 0;

// Alert control
bool displayAlarm    = false;  // whether showing text on LCD
bool alarmActive     = false;  // whether in blink alert state
int triggerCount     = 0;
int detectedAngle    = 0;
unsigned long displayStartTime = 0;
unsigned long lastBlinkTime     = 0;
bool blinkState       = false;

void setup() {
  radarServo.attach(servoPin);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(redLed, OUTPUT);
  pinMode(greenLed, OUTPUT);
  // buzzer uses tone()/noTone(), no pinMode needed

  lcd.init();
  lcd.backlight();
  lcd.clear();

  // show idle state
  lcdSetEmpty();
  digitalWrite(greenLed, HIGH);
}

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

  // 1. Smooth scanning & distance measurement
  if (now - lastServoUpdate >= updateInterval) {
    lastServoUpdate = now;
    radarServo.write(currentAngle);

    if (currentAngle % 5 == 0) {
      float d = getDistance();

      // if not already showing or blinking an alert
      if (!displayAlarm && !alarmActive) {
        if (d < alertDistance) triggerCount++;
        else                   triggerCount = 0;

        if (triggerCount >= triggerThreshold) {
          triggerCount = 0;
          detectedAngle = currentAngle;
          startAlarmDisplay();
        }
      }
      // if currently blinking and object is out of range, exit alert
      else if (alarmActive && d >= alertDistance) {
        exitAlarm();
      }
    }

    // update servo angle back and forth between 0°–180°
    currentAngle += increment;
    if (currentAngle >= 180) {
      currentAngle = 180; increment = -1;
    } else if (currentAngle <= 0) {
      currentAngle = 0;   increment = 1;
    }
  }

  // 2. Manage LCD display duration & transition to blinking
  if (displayAlarm) {
    // if display time has passed, switch to blinking state
    if (now - displayStartTime >= displayDuration) {
      displayAlarm = false;
      alarmActive  = true;
      lastBlinkTime = now;
    }
  }
  else if (alarmActive) {
    alarmBlink();
  }
}

// start showing alert text (for displayDuration)
void startAlarmDisplay() {
  displayAlarm     = true;
  alarmActive      = false;
  displayStartTime = millis();

  digitalWrite(greenLed, LOW);
  digitalWrite(redLed, LOW);
  noTone(buzzer);

  lcd.clear();
  // first line: centered "{detectedAngle}°"
  char buf[6];
  sprintf(buf, "%d", detectedAngle);
  int len1 = strlen(buf) + 1;
  int start1 = (16 - len1) / 2;
  lcd.setCursor(start1, 0);
  lcd.print(buf);
  lcd.write(223);

  // second line: centered "Foreign Body"
  const char* msg = "Foreign Body";
  int len2 = strlen(msg);
  int start2 = (16 - len2) / 2;
  lcd.setCursor(start2, 1);
  lcd.print(msg);
}

// non-blocking blink of red LED and buzzer
void alarmBlink() {
  unsigned long now = millis();
  if (now - lastBlinkTime >= blinkInterval) {
    lastBlinkTime = now;
    blinkState = !blinkState;
    digitalWrite(redLed, blinkState);
    if (blinkState) tone(buzzer, 1000);
    else           noTone(buzzer);
  }
}

// exit alert and return to idle state
void exitAlarm() {
  displayAlarm = false;
  alarmActive  = false;
  triggerCount = 0;

  digitalWrite(redLed, LOW);
  noTone(buzzer);
  digitalWrite(greenLed, HIGH);
  lcdSetEmpty();
}

// show idle state on LCD
void lcdSetEmpty() {
  lcd.clear();
  lcd.setCursor(1, 0);
  lcd.print("Area is Empty");
}

// perform ultrasonic distance measurement (cm)
float getDistance() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  long duration = pulseIn(echoPin, HIGH, 30000);
  return duration * 0.034 / 2;
}