Complete IoT Textbook — 10 Chapters

LCD Interfacing with Arduino Uno

1.1 LCD Pin Details — All 16 Pins Explained

A standard 16×2 LCD module (based on the HD44780 controller) has 16 pins. Understanding each pin is crucial before wiring.

1.2 Interfacing 16×2 LCD with Arduino (4-bit Mode)

In 4-bit mode, we only use pins D4–D7, saving 4 Arduino pins. This is the most common wiring method.

Connection Table

1.3 LiquidCrystal Library Functions

1.4 Arduino Code — Hello World on LCD

Arduino
// Program: Display "Hello World!" on 16x2 LCD
// Board: Arduino Uno
// Connection: 4-bit mode (RS=12, EN=11, D4=5, D5=4, D6=3, D7=2)

#include <LiquidCrystal.h>

// Initialize LCD: LiquidCrystal(RS, EN, D4, D5, D6, D7)
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

void setup() {
  lcd.begin(16, 2);       // Set LCD to 16 columns, 2 rows
  lcd.setCursor(0, 0);    // Move cursor to column 0, row 0
  lcd.print("Hello World!"); // Print on first line
  lcd.setCursor(0, 1);    // Move cursor to second line
  lcd.print("Arduino IoT");  // Print on second line
}

void loop() {
  // Nothing to repeat — static display
}

1.5 Custom Character Display — createChar()

The LCD can store up to 8 custom characters (numbered 0–7). Each character is a 5×8 pixel grid defined by a byte array.

Arduino
// Program: Display custom heart character on LCD
#include <LiquidCrystal.h>

LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

// Define heart character as byte array
byte heart[8] = {
  0b01010,  // Row 0: .#.#.
  0b11111,  // Row 1: #####
  0b11111,  // Row 2: #####
  0b11111,  // Row 3: #####
  0b01110,  // Row 4: .###.
  0b00100,  // Row 5: ..#..
  0b00000,  // Row 6: .....(blank)
  0b00000   // Row 7: .....(blank)
};

void setup() {
  lcd.begin(16, 2);
  lcd.createChar(0, heart);   // Store heart at position 0
  lcd.setCursor(0, 0);
  lcd.print("I ");
  lcd.write(byte(0));        // Display custom character 0 (heart)
  lcd.print(" Arduino!");
}

void loop() {}

1.6 Worked Examples

Example 1: Display Your Name

Arduino
#include <LiquidCrystal.h>
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
void setup() {
  lcd.begin(16, 2);
  lcd.print("Name: Rahul");
  lcd.setCursor(0, 1);
  lcd.print("Roll: 101");
}
void loop() {}

Example 2: Counter 0–99

Arduino
#include <LiquidCrystal.h>
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
void setup() { lcd.begin(16, 2); }
void loop() {
  for (int i = 0; i < 100; i++) {
    lcd.clear();
    lcd.print("Count: ");
    lcd.print(i);
    delay(500);
  }
}

Example 3: Scrolling Marquee

Arduino
#include <LiquidCrystal.h>
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
void setup() {
  lcd.begin(16, 2);
  lcd.print("  Welcome to EduArtha IoT Lab!  ");
}
void loop() {
  lcd.scrollDisplayLeft();  // Shift text left by 1 position
  delay(300);              // Speed of scrolling
}

Example 4: Temperature Display Format

Arduino
#include <LiquidCrystal.h>
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
byte degreeSymbol[8] = {0x06,0x09,0x09,0x06,0x00,0x00,0x00,0x00};
void setup() {
  lcd.begin(16, 2);
  lcd.createChar(0, degreeSymbol);
  lcd.print("Temp: 32");
  lcd.write(byte(0));
  lcd.print("C");
  lcd.setCursor(0, 1);
  lcd.print("Humidity: 65%");
}
void loop() {}

Example 5: Custom Heart + Smiley

Arduino
#include <LiquidCrystal.h>
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
byte heart[8] = {0x00,0x0A,0x1F,0x1F,0x0E,0x04,0x00,0x00};
byte smiley[8] = {0x00,0x0A,0x0A,0x00,0x11,0x0E,0x00,0x00};
void setup() {
  lcd.begin(16, 2);
  lcd.createChar(0, heart);
  lcd.createChar(1, smiley);
  lcd.write(byte(0));
  lcd.print(" I love IoT ");
  lcd.write(byte(1));
}
void loop() {}

Example 6: Blinking Cursor

Arduino
#include <LiquidCrystal.h>
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
void setup() {
  lcd.begin(16, 2);
  lcd.print("Enter PIN:");
  lcd.setCursor(0, 1);
  lcd.blink();  // Show blinking block cursor
}
void loop() {}

Example 7: Two-Line Message

Arduino
#include <LiquidCrystal.h>
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
void setup() {
  lcd.begin(16, 2);
  lcd.setCursor(2, 0);
  lcd.print("Jai Hind!");
  lcd.setCursor(0, 1);
  lcd.print("Bharat Mata Ki");
}
void loop() {}

Example 8: Right-to-Left Scroll

Arduino
#include <LiquidCrystal.h>
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
void setup() {
  lcd.begin(16, 2);
  lcd.setCursor(0, 0);
  lcd.print("Scrolling Right");
}
void loop() {
  lcd.scrollDisplayRight();
  delay(400);
}

Example 9: Display Analog Reading

Arduino
#include <LiquidCrystal.h>
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
void setup() {
  lcd.begin(16, 2);
}
void loop() {
  int val = analogRead(A0);  // Read pot/sensor on A0
  lcd.clear();
  lcd.print("Analog: ");
  lcd.print(val);              // 0-1023
  lcd.setCursor(0, 1);
  lcd.print("Volts: ");
  lcd.print(val * 5.0 / 1023, 2); // Convert to voltage
  delay(500);
}

Example 10: Simple LCD Menu

Arduino
#include <LiquidCrystal.h>
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
int btnPin = 7;
int menu = 0;
void setup() {
  lcd.begin(16, 2);
  pinMode(btnPin, INPUT_PULLUP);
  showMenu();
}
void loop() {
  if (digitalRead(btnPin) == LOW) {
    menu = (menu + 1) % 3;
    showMenu();
    delay(300); // Debounce
  }
}
void showMenu() {
  lcd.clear();
  lcd.print("> Menu Option:");
  lcd.setCursor(0, 1);
  if (menu == 0) lcd.print("1. Read Temp");
  else if (menu == 1) lcd.print("2. Read Light");
  else lcd.print("3. Motor ON");
}

1.7 MCQs — Chapter 1 (20 Questions)

LDR, Ultrasonic & IR Sensor Interfacing

2.1 LDR (Light Dependent Resistor)

An LDR's resistance changes with light: bright light → low resistance (~1kΩ), dark → high resistance (~10MΩ). We use a voltage divider circuit to convert this resistance change into a voltage that Arduino can read via analogRead().

Street Light Automation — Full Code

Arduino
// Program: Automatic Street Light using LDR
// When dark (LDR value < threshold) → LED ON
// When bright (LDR value >= threshold) → LED OFF

int ldrPin = A0;     // LDR connected to analog pin A0
int ledPin = 13;     // LED connected to digital pin 13
int threshold = 500; // Adjust based on your environment

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

void loop() {
  int ldrValue = analogRead(ldrPin);  // Read LDR (0-1023)
  Serial.print("LDR Value: ");
  Serial.println(ldrValue);

  if (ldrValue < threshold) {   // Dark condition
    digitalWrite(ledPin, HIGH); // Turn ON street light
    Serial.println("STATUS: Dark → LED ON");
  } else {                       // Bright condition
    digitalWrite(ledPin, LOW);  // Turn OFF street light
    Serial.println("STATUS: Bright → LED OFF");
  }
  delay(500);
}

2.2 Ultrasonic Sensor (HC-SR04)

The HC-SR04 sends an ultrasonic pulse (40kHz) and measures the time it takes for the echo to return. Distance is calculated using: distance = (time × 0.034) / 2 (speed of sound ≈ 340 m/s).

Distance Measurement — Full Code

Arduino
// Program: Measure distance using HC-SR04 Ultrasonic Sensor
// Formula: distance = (duration * 0.034) / 2

const int trigPin = 9;   // Trigger pin
const int echoPin = 10;  // Echo pin
long duration;
float distance;

void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  Serial.begin(9600);
  Serial.println("HC-SR04 Distance Sensor Ready");
}

void loop() {
  // Step 1: Send 10µs trigger pulse
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Step 2: Measure echo pulse duration
  duration = pulseIn(echoPin, HIGH);

  // Step 3: Calculate distance
  distance = (duration * 0.034) / 2;

  // Step 4: Display result
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");
  delay(500);
}

Parking Sensor with Buzzer

Arduino
// Parking sensor: buzzer beeps faster as object gets closer
const int trigPin = 9;
const int echoPin = 10;
const int buzzerPin = 8;
long duration;
float distance;

void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(buzzerPin, OUTPUT);
  Serial.begin(9600);
}

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

  if (distance < 10) {
    tone(buzzerPin, 1000); // Continuous beep — very close!
  } else if (distance < 30) {
    tone(buzzerPin, 1000, 100); // Short beep
    delay(distance * 10);       // Beep faster when closer
  } else {
    noTone(buzzerPin); // No beep — safe distance
  }
  delay(100);
}

2.3 IR Sensor — Object Detection

An IR sensor module has an IR LED (emitter) and a photodiode (receiver). When an object is close, IR light reflects back and the output goes LOW. It gives a digital output — HIGH (no object) or LOW (object detected).

Arduino
// Program: Object detection using IR Sensor
int irPin = 7;
int ledPin = 13;

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

void loop() {
  int irValue = digitalRead(irPin);
  if (irValue == LOW) {  // Object detected
    digitalWrite(ledPin, HIGH);
    Serial.println("Object Detected!");
  } else {
    digitalWrite(ledPin, LOW);
    Serial.println("No Object");
  }
  delay(200);
}

2.4 Worked Examples

Example 1: LDR with LED brightness (PWM)

Arduino
int ldrPin = A0;
int ledPin = 9; // PWM pin
void setup() { pinMode(ledPin, OUTPUT); }
void loop() {
  int val = analogRead(ldrPin);
  int brightness = map(val, 0, 1023, 255, 0); // Dark=bright LED
  analogWrite(ledPin, brightness);
  delay(100);
}

Example 2: Ultrasonic + LCD display

Arduino
#include <LiquidCrystal.h>
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
const int trig = 9, echo = 10;
void setup() { lcd.begin(16,2); pinMode(trig,OUTPUT); pinMode(echo,INPUT); }
void loop() {
  digitalWrite(trig,LOW); delayMicroseconds(2);
  digitalWrite(trig,HIGH); delayMicroseconds(10);
  digitalWrite(trig,LOW);
  float d = (pulseIn(echo,HIGH) * 0.034) / 2;
  lcd.clear(); lcd.print("Distance:");
  lcd.setCursor(0,1); lcd.print(d); lcd.print(" cm");
  delay(300);
}

Example 3: IR counter (count objects passing)

Arduino
int irPin = 7;
int count = 0;
bool lastState = HIGH;
void setup() { pinMode(irPin,INPUT); Serial.begin(9600); }
void loop() {
  bool curr = digitalRead(irPin);
  if (lastState == HIGH && curr == LOW) {
    count++;
    Serial.print("Count: "); Serial.println(count);
  }
  lastState = curr;
  delay(50);
}

Example 4: Multi-zone parking (3 ultrasonic sensors)

Arduino
int trig[] = {2, 4, 6};
int echo[] = {3, 5, 7};
void setup() {
  Serial.begin(9600);
  for(int i=0;i<3;i++) { pinMode(trig[i],OUTPUT); pinMode(echo[i],INPUT); }
}
float getDistance(int t, int e) {
  digitalWrite(t,LOW); delayMicroseconds(2);
  digitalWrite(t,HIGH); delayMicroseconds(10);
  digitalWrite(t,LOW);
  return (pulseIn(e,HIGH) * 0.034) / 2;
}
void loop() {
  for(int i=0;i<3;i++) {
    float d = getDistance(trig[i],echo[i]);
    Serial.print("Zone "); Serial.print(i+1);
    Serial.print(": "); Serial.print(d);
    Serial.println(d<20 ? " OCCUPIED" : " EMPTY");
  }
  Serial.println("---"); delay(1000);
}

Example 5: LDR night lamp with Serial plotter

Arduino
void setup() { Serial.begin(9600); }
void loop() {
  Serial.println(analogRead(A0)); // Open Serial Plotter to see graph
  delay(100);
}

Example 6: Ultrasonic + RGB LED (distance → color)

Arduino
const int trig=9, echo=10, redPin=3, greenPin=5, bluePin=6;
void setup() {
  pinMode(trig,OUTPUT); pinMode(echo,INPUT);
  pinMode(redPin,OUTPUT); pinMode(greenPin,OUTPUT); pinMode(bluePin,OUTPUT);
}
void loop() {
  digitalWrite(trig,LOW); delayMicroseconds(2);
  digitalWrite(trig,HIGH); delayMicroseconds(10);
  digitalWrite(trig,LOW);
  float d = (pulseIn(echo,HIGH)*0.034)/2;
  if(d<10){analogWrite(redPin,255);analogWrite(greenPin,0);analogWrite(bluePin,0);}
  else if(d<30){analogWrite(redPin,255);analogWrite(greenPin,255);analogWrite(bluePin,0);}
  else{analogWrite(redPin,0);analogWrite(greenPin,255);analogWrite(bluePin,0);}
  delay(200);
}

Example 7: IR-based line follower (2 sensors)

Arduino
int leftIR = 6, rightIR = 7;
int motorL = 9, motorR = 10;
void setup() {
  pinMode(leftIR,INPUT); pinMode(rightIR,INPUT);
  pinMode(motorL,OUTPUT); pinMode(motorR,OUTPUT);
}
void loop() {
  int L = digitalRead(leftIR), R = digitalRead(rightIR);
  if(L==LOW && R==LOW) { analogWrite(motorL,200); analogWrite(motorR,200); } // Forward
  else if(L==LOW) { analogWrite(motorL,0); analogWrite(motorR,200); } // Turn left
  else if(R==LOW) { analogWrite(motorL,200); analogWrite(motorR,0); } // Turn right
  else { analogWrite(motorL,0); analogWrite(motorR,0); } // Stop
}

Example 8: LDR alarm (buzzer when too dark)

Arduino
void setup() { pinMode(8,OUTPUT); }
void loop() {
  if(analogRead(A0) < 200) tone(8,1000); else noTone(8);
  delay(100);
}

Example 9: Ultrasonic water level monitor

Arduino
const int trig=9,echo=10;
const float tankHeight = 30.0; // cm
void setup() { pinMode(trig,OUTPUT); pinMode(echo,INPUT); Serial.begin(9600); }
void loop() {
  digitalWrite(trig,LOW); delayMicroseconds(2);
  digitalWrite(trig,HIGH); delayMicroseconds(10);
  digitalWrite(trig,LOW);
  float d = (pulseIn(echo,HIGH)*0.034)/2;
  float level = tankHeight - d;
  float pct = (level/tankHeight)*100;
  Serial.print("Water Level: "); Serial.print(pct); Serial.println("%");
  delay(1000);
}

Example 10: Combined sensor dashboard (LDR+Ultrasonic+IR on Serial)

Arduino
const int trig=9,echo=10,irPin=7;
void setup() {
  pinMode(trig,OUTPUT);pinMode(echo,INPUT);pinMode(irPin,INPUT);
  Serial.begin(9600);
  Serial.println("=== IoT Sensor Dashboard ===");
}
void loop() {
  int ldr = analogRead(A0);
  digitalWrite(trig,LOW);delayMicroseconds(2);
  digitalWrite(trig,HIGH);delayMicroseconds(10);
  digitalWrite(trig,LOW);
  float dist = (pulseIn(echo,HIGH)*0.034)/2;
  int ir = digitalRead(irPin);
  Serial.print("Light:"); Serial.print(ldr);
  Serial.print(" | Dist:"); Serial.print(dist);
  Serial.print("cm | Object:"); Serial.println(ir==LOW?"YES":"NO");
  delay(500);
}

2.5 MCQs — Chapter 2 (20 Questions)