1. LDR (Light Dependent Resistor)

Function: Measures brightness. Resistance decreases as light increases.
Pins: VCC → 5V, GND → GND, Signal → A0.

Wiring:

• LDR + resistor as voltage divider → middle pin to A0.

Code:

C++

int ldrPin = A0;

int ldrValue = 0;

 

void setup() {

Serial.begin(9600);

}

 

void loop() {

ldrValue = analogRead(ldrPin);

Serial.print(“LDR Value: “);

Serial.println(ldrValue);   // 0 (dark) – 1023 (bright)

delay(500);

}

💡 Dark → Low values; Bright → High values.

2. LM35 (Temperature Sensor)

Function: Analog sensor, outputs 10mV per °C.
Pins: +Vs → 5V, GND → GND, Vout → A0.

Code:

C++

int tempPin = A0;

float tempC;

 

void setup() {

Serial.begin(9600);

}

 

void loop() {

int val = analogRead(tempPin);

tempC = (val / 1023.0) * 5.0 * 100;  // Convert to Celsius

Serial.print(“Temperature: “);

Serial.print(tempC);

Serial.println(” °C”);

delay(1000);

}

🌡 Shows real‑time room temperature.

3. PIR Motion Sensor (HC‑SR501)

Function: Detects movement (infrared heat from humans/animals).
Pins: VCC → 5V, GND → GND, OUT → pin 2.

Code:

C++

int pirPin = 2;

int pirState = 0;

 

void setup() {

pinMode(pirPin, INPUT);

Serial.begin(9600);

}

 

void loop() {

pirState = digitalRead(pirPin);

if (pirState == HIGH) {

Serial.println(“Motion detected!”);

} else {

Serial.println(“No motion.”);

}

delay(500);

}

🕵️ Lights up Serial Monitor when someone walks past.

4. Ultrasonic Distance Sensor (HC‑SR04)

Function: Measures distance using ultrasonic sound waves.
Pins: VCC → 5V, GND → GND, Trig → pin 9, Echo → pin 10.

Code:

C++

const int trigPin = 9;

const int echoPin = 10;

long duration;

int distance;

 

void setup() {

pinMode(trigPin, OUTPUT);

pinMode(echoPin, INPUT);

Serial.begin(9600);

}

 

void loop() {

// Send trigger pulse

digitalWrite(trigPin, LOW);

delayMicroseconds(2);

digitalWrite(trigPin, HIGH);

delayMicroseconds(10);

digitalWrite(trigPin, LOW);

 

// Read echo response

duration = pulseIn(echoPin, HIGH);

distance = duration * 0.034 / 2;  // cm

 

Serial.print(“Distance: “);

Serial.print(distance);

Serial.println(” cm”);

 

delay(500);

}

📏 Prints object distance in centimeters.

5. DHT11 (Temperature & Humidity Sensor)

Function: Reads both temperature + humidity (digital sensor).
Pins: VCC → 5V, GND → GND, Data → pin 7.
Library Needed: DHT.h (install via Arduino IDE Library Manager).

Code:

C++

#include “DHT.h”

#define DHTPIN 7

#define DHTTYPE DHT11

 

DHT dht(DHTPIN, DHTTYPE);

 

void setup() {

Serial.begin(9600);

dht.begin();

}

 

void loop() {

float h = dht.readHumidity();

float t = dht.readTemperature();

 

Serial.print(“Humidity: “);

Serial.print(h);

Serial.print(” %  |  Temp: “);

Serial.print(t);

Serial.println(” °C”);

 

delay(2000);

}

🌦 Easy way to make a basic weather station.