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How to Connect and Read Sensors with Arduino (Beginner’s Guide + Example Code)

Introduction

One of the most exciting things about Arduino is connecting sensors—tiny devices that let your project sense light, heat, motion, or distance.

In this guide, we’ll cover:

  • How to wire common sensors to Arduino.
  • How to read sensor values in code.
  • Example code you can copy, paste, and run immediately.

By the end, you’ll be ready to build smarter projects that respond to their environment. 🌱⚡

See The Video Tutorial

  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.

  1. 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.

  1. 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.

  1. 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.

  1. 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.

Tips for Succeeding with Sensors

  • Always connect GND (common mistake for beginners).
  • Check if the sensor is analog (use A0) or digital (use digitalRead / libraries).
  • Use Serial Monitor (Tools → Serial Monitor) to visualize readings.
  • For noisy sensors → add delay(200–1000) to stabilize readings.

FAQs

Q: Can I connect multiple sensors at once?
A: Yes—use multiple pins, or use I2C sensors that share wires.

Q: Why is my sensor not giving correct values?
A: Common causes: wiring issues, missing GND, wrong pin, or missing library.

Q: Do I need resistors with sensors?
A: Sometimes (LDR voltage divider). Many modules already have onboard resistors.

Downloade

Conclusion

With just a few sensors, your Arduino projects go from static circuits to interactive systems that respond to light, motion, distance, or temperature.

Start with one—like the LDR or PIR—get comfortable reading Serial Monitor values, then combine multiple sensors to make projects like:

  • Smart lights 🌃 (LDR + relay).
  • Motion‑activated alarms 🔊 (PIR + buzzer).
  • DIY weather station 🌦 (DHT11 + LCD).

The possibilities are endless once your Arduino starts “sensing the world.”