Project 1: Alarm System

Ultrasonic sensor triggers buzzer when something is too close.

int trigPin = 9, echoPin = 10, buzzer = 8;

void setup() {
    pinMode(trigPin, OUTPUT);
    pinMode(echoPin, INPUT);
    pinMode(buzzer, OUTPUT);
}

void loop() {
    digitalWrite(trigPin, LOW);  delayMicroseconds(2);
    digitalWrite(trigPin, HIGH); delayMicroseconds(10);
    digitalWrite(trigPin, LOW);
    float distance = pulseIn(echoPin, HIGH) * 0.034 / 2;

    if (distance < 20) {       // Less than 20cm
        tone(buzzer, 1000);     // Buzzer ON
    } else {
        noTone(buzzer);         // Buzzer OFF
    }
    delay(100);
}

Project 2: Smart Night Light

LED turns on automatically when it gets dark.

int ldrPin = A0, ledPin = 9;

void setup() {
    pinMode(ledPin, OUTPUT);
    Serial.begin(9600);
}

void loop() {
    int light = analogRead(ldrPin);
    Serial.print("Light: "); Serial.println(light);

    if (light < 300) {              // Dark
        analogWrite(ledPin, 255);    // Full brightness
    } else if (light < 600) {       // Dim
        analogWrite(ledPin, 100);    // Low brightness
    } else {                         // Bright
        analogWrite(ledPin, 0);      // OFF
    }
    delay(200);
}

Project 3: Temperature Monitor with LED Warning

int tempPin = A0;
int greenLED = 11, yellowLED = 10, redLED = 9;

void setup() {
    Serial.begin(9600);
    pinMode(greenLED, OUTPUT);
    pinMode(yellowLED, OUTPUT);
    pinMode(redLED, OUTPUT);
}

void loop() {
    float voltage = analogRead(tempPin) * (5.0 / 1024.0);
    float tempC = (voltage - 0.5) * 100.0;

    // Reset LEDs
    digitalWrite(greenLED, LOW);
    digitalWrite(yellowLED, LOW);
    digitalWrite(redLED, LOW);

    if (tempC < 25) {
        digitalWrite(greenLED, HIGH);   // Cool
    } else if (tempC < 35) {
        digitalWrite(yellowLED, HIGH);  // Warm
    } else {
        digitalWrite(redLED, HIGH);     // Hot!
    }

    Serial.print(tempC); Serial.println(" °C");
    delay(1000);
}

✅ Quick Quiz

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