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)

Temperature & Humidity Sensor (DHT22)

3.1 DHT22 Module Specifications

3.2 DHT Library Installation

1. Open Arduino IDE → Sketch → Include Library → Manage Libraries
2. Search for "DHT sensor library" by Adafruit
3. Click Install (also install "Adafruit Unified Sensor" if prompted)

3.3 Basic DHT22 Code — Read Temperature & Humidity

Arduino
// Program: Read Temperature and Humidity from DHT22
// Board: Arduino Uno | Sensor: DHT22 on pin D2

#include <DHT.h>

#define DHTPIN 2       // DHT22 data pin connected to D2
#define DHTTYPE DHT22  // Sensor type: DHT22

DHT dht(DHTPIN, DHTTYPE); // Create DHT object

void setup() {
  Serial.begin(9600);
  dht.begin();  // Initialize DHT sensor
  Serial.println("DHT22 Weather Station Ready!");
  Serial.println("==========================");
}

void loop() {
  delay(2000);  // DHT22 needs 2 sec between readings

  float humidity = dht.readHumidity();
  float tempC = dht.readTemperature();       // Celsius
  float tempF = dht.readTemperature(true);  // Fahrenheit

  // Check if reading failed
  if (isnan(humidity) || isnan(tempC)) {
    Serial.println("ERROR: Failed to read DHT22!");
    return;
  }

  // Calculate heat index
  float heatIndex = dht.computeHeatIndex(tempC, humidity, false);

  Serial.print("Temperature: ");
  Serial.print(tempC);
  Serial.print("°C (");
  Serial.print(tempF);
  Serial.println("°F)");
  Serial.print("Humidity: ");
  Serial.print(humidity);
  Serial.println("%");
  Serial.print("Heat Index: ");
  Serial.print(heatIndex);
  Serial.println("°C");
  Serial.println("---");
}

3.4 Weather Station Project — DHT22 + LCD

Arduino
// Weather Station: DHT22 + 16x2 LCD Display
#include <DHT.h>
#include <LiquidCrystal.h>

#define DHTPIN 2
#define DHTTYPE DHT22

DHT dht(DHTPIN, DHTTYPE);
LiquidCrystal lcd(12, 11, 5, 4, 3, 8); // Changed D2→D8 (D2 used by DHT)

byte degreeChar[8] = {0x06,0x09,0x09,0x06,0x00,0x00,0x00,0x00};

void setup() {
  lcd.begin(16, 2);
  lcd.createChar(0, degreeChar);
  dht.begin();
  lcd.print("Weather Station");
  lcd.setCursor(0, 1);
  lcd.print("Initializing...");
  delay(2000);
}

void loop() {
  float t = dht.readTemperature();
  float h = dht.readHumidity();

  if (isnan(t) || isnan(h)) {
    lcd.clear(); lcd.print("Sensor Error!");
    delay(2000); return;
  }

  lcd.clear();
  lcd.print("Temp: ");
  lcd.print(t, 1);
  lcd.write(byte(0));
  lcd.print("C");
  lcd.setCursor(0, 1);
  lcd.print("Humid: ");
  lcd.print(h, 1);
  lcd.print("%");
  delay(2000);
}

3.5 Worked Examples

Example 1: Temperature alert (buzzer when >35°C)

Arduino
#include <DHT.h>
DHT dht(2, DHT22);
void setup() { dht.begin(); pinMode(8,OUTPUT); Serial.begin(9600); }
void loop() {
  delay(2000);
  float t = dht.readTemperature();
  if(t > 35.0) { tone(8,1000); Serial.println("HOT ALERT!"); }
  else { noTone(8); Serial.print("Temp: "); Serial.println(t); }
}

Example 2: Humidity-based fan control

Arduino
#include <DHT.h>
DHT dht(2, DHT22);
int fanPin = 9;
void setup() { dht.begin(); pinMode(fanPin,OUTPUT); }
void loop() {
  delay(2000);
  float h = dht.readHumidity();
  if(h > 70) digitalWrite(fanPin,HIGH); else digitalWrite(fanPin,LOW);
}

Example 3: Min/Max temperature logger

Arduino
#include <DHT.h>
DHT dht(2, DHT22);
float minT=100, maxT=-100;
void setup() { dht.begin(); Serial.begin(9600); }
void loop() {
  delay(2000);
  float t = dht.readTemperature();
  if(t<minT) minT=t; if(t>maxT) maxT=t;
  Serial.print("Now:"); Serial.print(t);
  Serial.print(" Min:"); Serial.print(minT);
  Serial.print(" Max:"); Serial.println(maxT);
}

Example 4: Comfort index indicator (LED colors)

Arduino
#include <DHT.h>
DHT dht(2, DHT22);
int red=3,green=5,blue=6;
void setup() { dht.begin(); pinMode(red,OUTPUT); pinMode(green,OUTPUT); pinMode(blue,OUTPUT); }
void loop() {
  delay(2000);
  float t = dht.readTemperature();
  if(t<20) { digitalWrite(blue,HIGH); digitalWrite(green,LOW); digitalWrite(red,LOW); } // Cold
  else if(t<30) { digitalWrite(blue,LOW); digitalWrite(green,HIGH); digitalWrite(red,LOW); } // Comfortable
  else { digitalWrite(blue,LOW); digitalWrite(green,LOW); digitalWrite(red,HIGH); } // Hot
}

Example 5: Data logger to Serial (CSV format)

Arduino
#include <DHT.h>
DHT dht(2, DHT22);
unsigned long reading = 0;
void setup() { dht.begin(); Serial.begin(9600); Serial.println("Reading,Temp_C,Humidity_%"); }
void loop() {
  delay(5000); reading++;
  Serial.print(reading); Serial.print(",");
  Serial.print(dht.readTemperature()); Serial.print(",");
  Serial.println(dht.readHumidity());
}

Example 6: Dew point calculation

Arduino
#include <DHT.h>
DHT dht(2, DHT22);
void setup() { dht.begin(); Serial.begin(9600); }
void loop() {
  delay(2000);
  float t=dht.readTemperature(), h=dht.readHumidity();
  float dp = t - ((100-h)/5.0); // Simplified dew point
  Serial.print("Dew Point: "); Serial.print(dp); Serial.println("°C");
}

Example 7: Greenhouse monitor (temp + humidity thresholds)

Arduino
#include <DHT.h>
DHT dht(2, DHT22);
int pumpPin=7, ventPin=8;
void setup() { dht.begin(); pinMode(pumpPin,OUTPUT); pinMode(ventPin,OUTPUT); Serial.begin(9600); }
void loop() {
  delay(2000);
  float t=dht.readTemperature(), h=dht.readHumidity();
  Serial.print("T:"); Serial.print(t); Serial.print(" H:"); Serial.println(h);
  if(h<40) digitalWrite(pumpPin,HIGH); else digitalWrite(pumpPin,LOW); // Irrigate
  if(t>35) digitalWrite(ventPin,HIGH); else digitalWrite(ventPin,LOW); // Ventilate
}

Example 8: Moving average temperature (smoothing)

Arduino
#include <DHT.h>
DHT dht(2, DHT22);
float readings[5]; int idx=0;
void setup() { dht.begin(); Serial.begin(9600); }
void loop() {
  delay(2000);
  readings[idx] = dht.readTemperature();
  idx = (idx+1) % 5;
  float avg = 0;
  for(int i=0;i<5;i++) avg += readings[i];
  avg /= 5;
  Serial.print("Avg Temp: "); Serial.println(avg);
}

Example 9: Heat index warning system

Arduino
#include <DHT.h>
DHT dht(2, DHT22);
void setup() { dht.begin(); Serial.begin(9600); }
void loop() {
  delay(2000);
  float t=dht.readTemperature(), h=dht.readHumidity();
  float hi = dht.computeHeatIndex(t, h, false);
  Serial.print("Heat Index: "); Serial.print(hi);
  if(hi>40) Serial.println(" DANGER!");
  else if(hi>32) Serial.println(" Caution");
  else Serial.println(" Normal");
}

Example 10: Temp + humidity on Serial Plotter

Arduino
#include <DHT.h>
DHT dht(2, DHT22);
void setup() { dht.begin(); Serial.begin(9600); }
void loop() {
  delay(2000);
  Serial.print(dht.readTemperature());
  Serial.print("\t"); // Tab separator for Serial Plotter
  Serial.println(dht.readHumidity());
}

3.6 MCQs — Chapter 3 (20 Questions)

DC Motors with L298N Motor Driver

4.1 L298N Specifications

4.2 H-Bridge Working Principle

Direction Control Truth Table

Connection Table

4.3 Single Motor Control Code

Arduino
// Program: Control single DC motor with L298N
int ENA = 9;   // PWM pin for speed
int IN1 = 8;   // Direction pin 1
int IN2 = 7;   // Direction pin 2

void setup() {
  pinMode(ENA, OUTPUT);
  pinMode(IN1, OUTPUT);
  pinMode(IN2, OUTPUT);
}

void loop() {
  // Forward at full speed
  digitalWrite(IN1, HIGH);
  digitalWrite(IN2, LOW);
  analogWrite(ENA, 255);  // Full speed
  delay(2000);

  // Stop
  digitalWrite(IN1, LOW);
  digitalWrite(IN2, LOW);
  delay(1000);

  // Reverse at half speed
  digitalWrite(IN1, LOW);
  digitalWrite(IN2, HIGH);
  analogWrite(ENA, 128);  // Half speed
  delay(2000);

  // Stop
  digitalWrite(IN1, LOW);
  digitalWrite(IN2, LOW);
  delay(1000);
}

4.4 Robot Car Code (2 Motors)

Arduino
// Robot Car: Forward, Backward, Left, Right
int ENA=9,IN1=8,IN2=7,IN3=6,IN4=5,ENB=3;
int speed = 200;

void setup() {
  int pins[] = {ENA,IN1,IN2,IN3,IN4,ENB};
  for(int i=0;i<6;i++) pinMode(pins[i],OUTPUT);
}

void forward() {
  digitalWrite(IN1,HIGH); digitalWrite(IN2,LOW);
  digitalWrite(IN3,HIGH); digitalWrite(IN4,LOW);
  analogWrite(ENA,speed); analogWrite(ENB,speed);
}
void backward() {
  digitalWrite(IN1,LOW); digitalWrite(IN2,HIGH);
  digitalWrite(IN3,LOW); digitalWrite(IN4,HIGH);
  analogWrite(ENA,speed); analogWrite(ENB,speed);
}
void turnLeft() {
  digitalWrite(IN1,LOW); digitalWrite(IN2,LOW);
  digitalWrite(IN3,HIGH); digitalWrite(IN4,LOW);
  analogWrite(ENB,speed);
}
void turnRight() {
  digitalWrite(IN1,HIGH); digitalWrite(IN2,LOW);
  analogWrite(ENA,speed);
  digitalWrite(IN3,LOW); digitalWrite(IN4,LOW);
}
void stopMotors() {
  digitalWrite(IN1,LOW); digitalWrite(IN2,LOW);
  digitalWrite(IN3,LOW); digitalWrite(IN4,LOW);
}

void loop() {
  forward(); delay(2000);
  stopMotors(); delay(500);
  turnRight(); delay(1000);
  stopMotors(); delay(500);
  backward(); delay(2000);
  stopMotors(); delay(500);
  turnLeft(); delay(1000);
  stopMotors(); delay(500);
}

4.5 Worked Examples

Ex 1: Speed ramp up

Arduino
int ENA=9,IN1=8,IN2=7;
void setup(){pinMode(ENA,OUTPUT);pinMode(IN1,OUTPUT);pinMode(IN2,OUTPUT);}
void loop(){
  digitalWrite(IN1,HIGH);digitalWrite(IN2,LOW);
  for(int s=0;s<=255;s+=5){analogWrite(ENA,s);delay(50);}
  for(int s=255;s>=0;s-=5){analogWrite(ENA,s);delay(50);}
}

Ex 2: Pot-controlled speed

Arduino
int ENA=9,IN1=8,IN2=7;
void setup(){pinMode(ENA,OUTPUT);pinMode(IN1,OUTPUT);pinMode(IN2,OUTPUT);digitalWrite(IN1,HIGH);digitalWrite(IN2,LOW);}
void loop(){analogWrite(ENA,map(analogRead(A0),0,1023,0,255));delay(50);}

Ex 3: Button direction toggle

Arduino
int ENA=9,IN1=8,IN2=7,btn=2;
bool dir=true;
void setup(){pinMode(ENA,OUTPUT);pinMode(IN1,OUTPUT);pinMode(IN2,OUTPUT);pinMode(btn,INPUT_PULLUP);}
void loop(){
  if(digitalRead(btn)==LOW){dir=!dir;delay(300);}
  digitalWrite(IN1,dir?HIGH:LOW);digitalWrite(IN2,dir?LOW:HIGH);
  analogWrite(ENA,200);
}

Ex 4: Serial-controlled motor

Arduino
int ENA=9,IN1=8,IN2=7;
void setup(){Serial.begin(9600);pinMode(ENA,OUTPUT);pinMode(IN1,OUTPUT);pinMode(IN2,OUTPUT);}
void loop(){
  if(Serial.available()){
    char c=Serial.read();
    if(c=='F'){digitalWrite(IN1,HIGH);digitalWrite(IN2,LOW);analogWrite(ENA,200);}
    else if(c=='R'){digitalWrite(IN1,LOW);digitalWrite(IN2,HIGH);analogWrite(ENA,200);}
    else if(c=='S'){digitalWrite(IN1,LOW);digitalWrite(IN2,LOW);}
  }
}

Ex 5–10: Additional motor examples

Arduino
// Ex 5: Obstacle-avoiding robot (ultrasonic + motors)
int trig=10,echo=11,ENA=9,IN1=8,IN2=7,IN3=6,IN4=5,ENB=3;
void setup(){
  pinMode(trig,OUTPUT);pinMode(echo,INPUT);
  int p[]={ENA,IN1,IN2,IN3,IN4,ENB};
  for(int i=0;i<6;i++)pinMode(p[i],OUTPUT);
}
float getDist(){
  digitalWrite(trig,LOW);delayMicroseconds(2);
  digitalWrite(trig,HIGH);delayMicroseconds(10);
  digitalWrite(trig,LOW);
  return(pulseIn(echo,HIGH)*0.034)/2;
}
void loop(){
  float d=getDist();
  if(d>20){
    digitalWrite(IN1,HIGH);digitalWrite(IN2,LOW);
    digitalWrite(IN3,HIGH);digitalWrite(IN4,LOW);
    analogWrite(ENA,180);analogWrite(ENB,180);
  }else{
    digitalWrite(IN1,LOW);digitalWrite(IN2,HIGH);
    digitalWrite(IN3,LOW);digitalWrite(IN4,LOW);
    analogWrite(ENA,150);
    delay(600);
  }
  delay(100);
}

Arduino
// Ex 6: PWM motor speed display on LCD
#include <LiquidCrystal.h>
LiquidCrystal lcd(12,11,5,4,3,2);
int ENA=9,IN1=8,IN2=7;
void setup(){lcd.begin(16,2);pinMode(ENA,OUTPUT);pinMode(IN1,OUTPUT);pinMode(IN2,OUTPUT);digitalWrite(IN1,HIGH);digitalWrite(IN2,LOW);}
void loop(){
  int pot=analogRead(A0);
  int spd=map(pot,0,1023,0,255);
  analogWrite(ENA,spd);
  lcd.clear();lcd.print("Speed: ");lcd.print(spd);
  lcd.setCursor(0,1);lcd.print(map(spd,0,255,0,100));lcd.print("%");
  delay(200);
}

Arduino
// Ex 7: Timed motor sequence
int ENA=9,IN1=8,IN2=7;
void setup(){pinMode(ENA,OUTPUT);pinMode(IN1,OUTPUT);pinMode(IN2,OUTPUT);}
void loop(){
  int speeds[]={50,100,150,200,255};
  digitalWrite(IN1,HIGH);digitalWrite(IN2,LOW);
  for(int i=0;i<5;i++){analogWrite(ENA,speeds[i]);delay(1000);}
  digitalWrite(IN1,LOW);digitalWrite(IN2,LOW);delay(2000);
}

Arduino
// Ex 8: Motor with emergency stop button
int ENA=9,IN1=8,IN2=7,stopBtn=2;
bool running=true;
void setup(){pinMode(ENA,OUTPUT);pinMode(IN1,OUTPUT);pinMode(IN2,OUTPUT);pinMode(stopBtn,INPUT_PULLUP);}
void loop(){
  if(digitalRead(stopBtn)==LOW) running=!running;
  if(running){digitalWrite(IN1,HIGH);digitalWrite(IN2,LOW);analogWrite(ENA,200);}
  else{digitalWrite(IN1,LOW);digitalWrite(IN2,LOW);}
  delay(200);
}

Arduino
// Ex 9: Temperature-controlled fan motor
#include <DHT.h>
DHT dht(2,DHT22);
int ENA=9,IN1=8,IN2=7;
void setup(){dht.begin();pinMode(ENA,OUTPUT);pinMode(IN1,OUTPUT);pinMode(IN2,OUTPUT);digitalWrite(IN1,HIGH);digitalWrite(IN2,LOW);}
void loop(){
  delay(2000);
  float t=dht.readTemperature();
  int spd=constrain(map(t,25,45,0,255),0,255);
  analogWrite(ENA,spd);
}

Arduino
// Ex 10: Dual motor independent control via Serial
int ENA=9,IN1=8,IN2=7,IN3=6,IN4=5,ENB=3;
void setup(){Serial.begin(9600);int p[]={ENA,IN1,IN2,IN3,IN4,ENB};for(int i=0;i<6;i++)pinMode(p[i],OUTPUT);}
void loop(){
  if(Serial.available()){
    char c=Serial.read();
    switch(c){
      case 'W':digitalWrite(IN1,HIGH);digitalWrite(IN2,LOW);digitalWrite(IN3,HIGH);digitalWrite(IN4,LOW);analogWrite(ENA,200);analogWrite(ENB,200);break;
      case 'X':digitalWrite(IN1,LOW);digitalWrite(IN2,LOW);digitalWrite(IN3,LOW);digitalWrite(IN4,LOW);break;
    }
  }
}

4.6 MCQs — Chapter 4 (20 Questions)

LED Displays with MAX7219

5.1 MAX7219 LED Dot Matrix 4-in-1 Display

The MAX7219 4-in-1 dot matrix module combines four 8×8 LED matrices into a single PCB, giving you a 32×8 pixel display. The MAX7219 IC handles all the multiplexing — you just send data over SPI and the chip takes care of driving 64 LEDs per module.

SPI Communication

MAX7219 uses a 3-wire SPI interface:

Cascading Multiple Modules

To chain multiple MAX7219 modules: connect DOUT of the first module to DIN of the next. All modules share the same CLK and CS lines. Data shifts through like a chain — the first data sent ends up on the last module.

Connection Table (Arduino → MAX7219 4-in-1)

5.2 MD_Parola & MD_MAX72XX Libraries

The MD_MAX72XX library provides low-level control of MAX7219 modules. MD_Parola adds high-level text scrolling, animations, and effects on top of it.

5.3 Full Code — Scrolling Text on Dot Matrix

Arduino
// Program: Scrolling text on MAX7219 4-in-1 Dot Matrix
// Board: Arduino Uno
// Libraries: MD_Parola, MD_MAX72XX

#include <MD_Parola.h>
#include <MD_MAX72XX.h>
#include <SPI.h>

// Hardware configuration
#define HARDWARE_TYPE MD_MAX72XX::FC16_HW
#define MAX_DEVICES 4    // 4 modules in the 4-in-1
#define CS_PIN      10

// Create Parola object
MD_Parola myDisplay = MD_Parola(HARDWARE_TYPE, CS_PIN, MAX_DEVICES);

void setup() {
  myDisplay.begin();
  myDisplay.setIntensity(5);        // Brightness 0-15
  myDisplay.displayClear();
  myDisplay.displayScroll(
    "WELCOME TO EDUARTHA IOT LAB",
    PA_CENTER, PA_SCROLL_LEFT,
    100                              // Speed in ms
  );
}

void loop() {
  if (myDisplay.displayAnimate()) {
    myDisplay.displayReset();         // Restart scroll
  }
}

5.4 MAX7219 Digital Tube Display (8-Digit 7-Segment)

The MAX7219 also drives 8-digit 7-segment displays. Each digit has 7 segments (a–g) + decimal point. The MAX7219 multiplexes all 8 digits, and the LedControl library provides easy functions.

LedControl Library Functions

Countdown Timer Code (99 → 00)

Arduino
// Program: Countdown timer on MAX7219 8-digit 7-segment display
#include <LedControl.h>

// LedControl(DIN, CLK, CS, numDevices)
LedControl lc = LedControl(11, 13, 10, 1);

void setup() {
  lc.shutdown(0, false);    // Wake up display
  lc.setIntensity(0, 8);     // Medium brightness
  lc.clearDisplay(0);        // Clear all digits
}

void loop() {
  for (int i = 99; i >= 0; i--) {
    int tens = i / 10;
    int ones = i % 10;
    lc.setDigit(0, 1, tens, false);  // Tens digit
    lc.setDigit(0, 0, ones, false);  // Ones digit
    delay(1000);                      // 1 second interval
  }
}

5.5 Worked Examples

Example 1: Display Static Text "HELLO"

Arduino
#include <MD_Parola.h>
#include <MD_MAX72XX.h>
#include <SPI.h>
#define HARDWARE_TYPE MD_MAX72XX::FC16_HW
#define MAX_DEVICES 4
#define CS_PIN 10
MD_Parola myDisplay = MD_Parola(HARDWARE_TYPE, CS_PIN, MAX_DEVICES);
void setup() {
  myDisplay.begin();
  myDisplay.setIntensity(5);
  myDisplay.setTextAlignment(PA_CENTER);
  myDisplay.print("HELLO");
}
void loop() {}

Example 2: Scrolling Text with Custom Speed

Arduino
#include <MD_Parola.h>
#include <MD_MAX72XX.h>
#include <SPI.h>
#define HARDWARE_TYPE MD_MAX72XX::FC16_HW
MD_Parola myDisplay = MD_Parola(HARDWARE_TYPE, 10, 4);
void setup() {
  myDisplay.begin();
  myDisplay.setIntensity(8);
  myDisplay.displayScroll("FAST SCROLL!", PA_CENTER, PA_SCROLL_LEFT, 50); // 50ms = fast
}
void loop() {
  if (myDisplay.displayAnimate()) myDisplay.displayReset();
}

Example 3: Temperature Reading on 7-Segment

Arduino
#include <LedControl.h>
#include <DHT.h>
LedControl lc = LedControl(11, 13, 10, 1);
DHT dht(2, DHT22);
void setup() {
  lc.shutdown(0, false); lc.setIntensity(0, 8); lc.clearDisplay(0);
  dht.begin();
}
void loop() {
  delay(2000);
  int temp = (int)dht.readTemperature();
  lc.setDigit(0, 3, temp / 10, false);  // Tens
  lc.setDigit(0, 2, temp % 10, true);   // Ones + decimal point
  lc.setChar(0, 1, 'C', false);         // °C symbol
}

Example 4: Dot Matrix Smiley Animation

Arduino
#include <LedControl.h>
LedControl lc = LedControl(11, 13, 10, 1);
byte smiley[8] = {
  0b00111100, 0b01000010, 0b10100101, 0b10000001,
  0b10100101, 0b10011001, 0b01000010, 0b00111100
};
byte sad[8] = {
  0b00111100, 0b01000010, 0b10100101, 0b10000001,
  0b10011001, 0b10100101, 0b01000010, 0b00111100
};
void setup() { lc.shutdown(0,false); lc.setIntensity(0,5); }
void loop() {
  for(int i=0;i<8;i++) lc.setRow(0,i,smiley[i]);
  delay(1000);
  for(int i=0;i<8;i++) lc.setRow(0,i,sad[i]);
  delay(1000);
}

Example 5: Clock Display on 7-Segment (using millis)

Arduino
#include <LedControl.h>
LedControl lc = LedControl(11, 13, 10, 1);
unsigned long prev = 0;
int sec=0, mins=0;
void setup() { lc.shutdown(0,false); lc.setIntensity(0,8); lc.clearDisplay(0); }
void loop() {
  if (millis() - prev >= 1000) {
    prev = millis();
    sec++; if(sec>=60){sec=0;mins++;} if(mins>=60) mins=0;
    lc.setDigit(0,3,mins/10,false);
    lc.setDigit(0,2,mins%10,true);  // Decimal = colon
    lc.setDigit(0,1,sec/10,false);
    lc.setDigit(0,0,sec%10,false);
  }
}

Example 6: Brightness Control via Potentiometer

Arduino
#include <MD_Parola.h>
#include <MD_MAX72XX.h>
#include <SPI.h>
MD_Parola myDisplay = MD_Parola(MD_MAX72XX::FC16_HW, 10, 4);
void setup() {
  myDisplay.begin();
  myDisplay.setTextAlignment(PA_CENTER);
  myDisplay.print("BRIGHT");
}
void loop() {
  int pot = analogRead(A0);
  int brightness = map(pot, 0, 1023, 0, 15);
  myDisplay.setIntensity(brightness);
  delay(100);
}

Example 7: Cycling Multiple Messages

Arduino
#include <MD_Parola.h>
#include <MD_MAX72XX.h>
#include <SPI.h>
MD_Parola P = MD_Parola(MD_MAX72XX::FC16_HW, 10, 4);
const char* msgs[] = {"HELLO", "IoT LAB", "ARDUINO", "MAX7219"};
int idx = 0;
void setup() { P.begin(); P.setIntensity(5); }
void loop() {
  P.setTextAlignment(PA_CENTER);
  P.print(msgs[idx]);
  idx = (idx + 1) % 4;
  delay(2000);
}

Example 8: Visitor Counter on 7-Segment

Arduino
#include <LedControl.h>
LedControl lc = LedControl(11, 13, 10, 1);
int btnPin = 2, count = 0;
void setup() {
  lc.shutdown(0,false); lc.setIntensity(0,8); lc.clearDisplay(0);
  pinMode(btnPin, INPUT_PULLUP);
  showCount();
}
void loop() {
  if (digitalRead(btnPin) == LOW) {
    count++; if(count>9999) count=0;
    showCount();
    delay(300); // Debounce
  }
}
void showCount() {
  lc.setDigit(0,3,count/1000,false);
  lc.setDigit(0,2,(count/100)%10,false);
  lc.setDigit(0,1,(count/10)%10,false);
  lc.setDigit(0,0,count%10,false);
}

Example 9: Scrolling Sensor Data on Dot Matrix

Arduino
#include <MD_Parola.h>
#include <MD_MAX72XX.h>
#include <SPI.h>
MD_Parola P = MD_Parola(MD_MAX72XX::FC16_HW, 10, 4);
char msg[30];
void setup() { P.begin(); P.setIntensity(5); }
void loop() {
  int sensorVal = analogRead(A0);
  sprintf(msg, "Sensor: %d", sensorVal);
  P.displayScroll(msg, PA_LEFT, PA_SCROLL_LEFT, 80);
  while (!P.displayAnimate()) {}
  delay(500);
}

Example 10: Binary Counter on Dot Matrix (Single 8×8)

Arduino
#include <LedControl.h>
LedControl lc = LedControl(11, 13, 10, 1);
void setup() { lc.shutdown(0,false); lc.setIntensity(0,5); lc.clearDisplay(0); }
void loop() {
  for(int i=0; i<256; i++) {
    for(int row=0; row<8; row++)
      lc.setRow(0, row, (i>>row) & 1 ? 0xFF : 0x00);
    delay(200);
  }
}

5.6 MCQs — Chapter 5 (20 Questions)

RFID Module with Arduino (RC522)

6.1 RFID Concept

RFID stands for Radio Frequency Identification. It's a wireless system with two components:

Active vs Passive Tags

RC522 Specifications

6.2 Pin Connections

RC522 Pin Description

Connection Table (Arduino → RC522)

6.3 MFRC522 Library

Install the MFRC522 library by GithubCommunity from Arduino Library Manager.

6.4 Read Card UID — Basic Code

Arduino
// Program: Read RFID card UID using RC522
// Board: Arduino Uno
// Connections: SDA=D10, SCK=D13, MOSI=D11, MISO=D12, RST=D9

#include <SPI.h>
#include <MFRC522.h>

#define SS_PIN  10
#define RST_PIN 9

MFRC522 mfrc522(SS_PIN, RST_PIN);

void setup() {
  Serial.begin(9600);
  SPI.begin();
  mfrc522.PCD_Init();
  Serial.println("Scan your RFID card...");
}

void loop() {
  // Check for new card
  if (!mfrc522.PICC_IsNewCardPresent()) return;
  if (!mfrc522.PICC_ReadCardSerial()) return;

  // Print UID
  Serial.print("Card UID: ");
  for (byte i = 0; i < mfrc522.uid.size; i++) {
    Serial.print(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " ");
    Serial.print(mfrc522.uid.uidByte[i], HEX);
  }
  Serial.println();

  mfrc522.PICC_HaltA();
}

6.5 Access Control Project

Arduino
// Project: RFID Access Control System
// Authorized card → Green LED + Servo opens door
// Unauthorized → Red LED + Buzzer alarm

#include <SPI.h>
#include <MFRC522.h>
#include <Servo.h>

#define SS_PIN  10
#define RST_PIN 9
#define GREEN_LED 6
#define RED_LED   7
#define BUZZER    8
#define SERVO_PIN 3

MFRC522 mfrc522(SS_PIN, RST_PIN);
Servo doorServo;

// Authorized card UID (replace with your card's UID)
byte authorizedUID[4] = {0xA3, 0xB7, 0x2E, 0x1F};

void setup() {
  Serial.begin(9600);
  SPI.begin();
  mfrc522.PCD_Init();
  doorServo.attach(SERVO_PIN);
  doorServo.write(0);  // Door locked
  pinMode(GREEN_LED, OUTPUT);
  pinMode(RED_LED, OUTPUT);
  pinMode(BUZZER, OUTPUT);
  Serial.println("Access Control Ready. Scan card...");
}

void loop() {
  if (!mfrc522.PICC_IsNewCardPresent()) return;
  if (!mfrc522.PICC_ReadCardSerial()) return;

  bool authorized = true;
  for (byte i = 0; i < 4; i++) {
    if (mfrc522.uid.uidByte[i] != authorizedUID[i]) {
      authorized = false;
      break;
    }
  }

  if (authorized) {
    Serial.println("ACCESS GRANTED!");
    digitalWrite(GREEN_LED, HIGH);
    doorServo.write(90);   // Unlock door
    delay(3000);
    doorServo.write(0);    // Lock door
    digitalWrite(GREEN_LED, LOW);
  } else {
    Serial.println("ACCESS DENIED!");
    digitalWrite(RED_LED, HIGH);
    tone(BUZZER, 1000, 1000); // 1kHz beep for 1 second
    delay(2000);
    digitalWrite(RED_LED, LOW);
  }

  mfrc522.PICC_HaltA();
}

6.6 Worked Examples

Example 1: Simple Card Detection

Arduino
#include <SPI.h>
#include <MFRC522.h>
MFRC522 mfrc522(10, 9);
void setup() { Serial.begin(9600); SPI.begin(); mfrc522.PCD_Init(); }
void loop() {
  if (mfrc522.PICC_IsNewCardPresent() && mfrc522.PICC_ReadCardSerial()) {
    Serial.println("Card Detected!");
    mfrc522.PICC_HaltA();
    delay(1000);
  }
}

Example 2: Display UID on LCD

Arduino
#include <SPI.h>
#include <MFRC522.h>
#include <LiquidCrystal.h>
MFRC522 mfrc522(10, 9);
LiquidCrystal lcd(7, 6, 5, 4, 3, 2);
void setup() {
  lcd.begin(16,2); SPI.begin(); mfrc522.PCD_Init();
  lcd.print("Scan Card...");
}
void loop() {
  if (!mfrc522.PICC_IsNewCardPresent() || !mfrc522.PICC_ReadCardSerial()) return;
  lcd.clear(); lcd.print("UID:");
  lcd.setCursor(0,1);
  for(byte i=0;i<mfrc522.uid.size;i++) {
    if(mfrc522.uid.uidByte[i]<0x10) lcd.print("0");
    lcd.print(mfrc522.uid.uidByte[i], HEX);
    lcd.print(" ");
  }
  mfrc522.PICC_HaltA(); delay(2000);
}

Example 3: Multiple Authorized Cards

Arduino
#include <SPI.h>
#include <MFRC522.h>
MFRC522 mfrc522(10, 9);
byte cards[3][4] = {
  {0xA3,0xB7,0x2E,0x1F},  // Card 1 (Rahul)
  {0xD4,0x12,0x8A,0x5C},  // Card 2 (Priya)
  {0x7B,0xE5,0x44,0x91}   // Card 3 (Admin)
};
const char* names[] = {"Rahul", "Priya", "Admin"};
void setup() { Serial.begin(9600); SPI.begin(); mfrc522.PCD_Init(); }
void loop() {
  if(!mfrc522.PICC_IsNewCardPresent() || !mfrc522.PICC_ReadCardSerial()) return;
  for(int c=0;c<3;c++) {
    bool match=true;
    for(byte i=0;i<4;i++) if(mfrc522.uid.uidByte[i]!=cards[c][i]) match=false;
    if(match) { Serial.print("Welcome, "); Serial.println(names[c]); break; }
    if(c==2) Serial.println("Unknown card!");
  }
  mfrc522.PICC_HaltA(); delay(1000);
}

Example 4: Attendance System (Serial Log)

Arduino
#include <SPI.h>
#include <MFRC522.h>
MFRC522 mfrc522(10, 9);
int attendCount = 0;
void setup() {
  Serial.begin(9600); SPI.begin(); mfrc522.PCD_Init();
  Serial.println("Sr.No, UID, Time(ms)");
}
void loop() {
  if(!mfrc522.PICC_IsNewCardPresent() || !mfrc522.PICC_ReadCardSerial()) return;
  attendCount++;
  Serial.print(attendCount); Serial.print(", ");
  for(byte i=0;i<mfrc522.uid.size;i++) {
    Serial.print(mfrc522.uid.uidByte[i], HEX); Serial.print(" ");
  }
  Serial.print(", "); Serial.println(millis());
  mfrc522.PICC_HaltA(); delay(2000);
}

Example 5: RFID LED Toggle

Arduino
#include <SPI.h>
#include <MFRC522.h>
MFRC522 mfrc522(10, 9);
int ledPin = 6;
bool ledState = false;
void setup() { Serial.begin(9600); SPI.begin(); mfrc522.PCD_Init(); pinMode(ledPin,OUTPUT); }
void loop() {
  if(mfrc522.PICC_IsNewCardPresent() && mfrc522.PICC_ReadCardSerial()) {
    ledState = !ledState;
    digitalWrite(ledPin, ledState ? HIGH : LOW);
    Serial.println(ledState ? "LED ON" : "LED OFF");
    mfrc522.PICC_HaltA(); delay(1000);
  }
}

Example 6: RFID Door Lock with Servo

Arduino
#include <SPI.h>
#include <MFRC522.h>
#include <Servo.h>
MFRC522 mfrc522(10, 9);
Servo lockServo;
byte key[4] = {0xA3,0xB7,0x2E,0x1F};
void setup() { Serial.begin(9600); SPI.begin(); mfrc522.PCD_Init(); lockServo.attach(3); lockServo.write(0); }
void loop() {
  if(!mfrc522.PICC_IsNewCardPresent() || !mfrc522.PICC_ReadCardSerial()) return;
  bool ok=true;
  for(byte i=0;i<4;i++) if(mfrc522.uid.uidByte[i]!=key[i]) ok=false;
  if(ok) { Serial.println("Door Unlocked!"); lockServo.write(90); delay(5000); lockServo.write(0); }
  else Serial.println("Wrong Card!");
  mfrc522.PICC_HaltA(); delay(1000);
}

Example 7: Student Record Lookup

Arduino
#include <SPI.h>
#include <MFRC522.h>
MFRC522 mfrc522(10, 9);
byte students[2][4] = {{0xA3,0xB7,0x2E,0x1F},{0xD4,0x12,0x8A,0x5C}};
const char* info[] = {"Rahul|CS|Roll:101", "Priya|ECE|Roll:205"};
void setup() { Serial.begin(9600); SPI.begin(); mfrc522.PCD_Init(); }
void loop() {
  if(!mfrc522.PICC_IsNewCardPresent() || !mfrc522.PICC_ReadCardSerial()) return;
  for(int s=0;s<2;s++) {
    bool m=true;
    for(byte i=0;i<4;i++) if(mfrc522.uid.uidByte[i]!=students[s][i]) m=false;
    if(m) { Serial.print("Student: "); Serial.println(info[s]); break; }
    if(s==1) Serial.println("Student not found!");
  }
  mfrc522.PICC_HaltA(); delay(1000);
}

Example 8: Card Tap Counter

Arduino
#include <SPI.h>
#include <MFRC522.h>
MFRC522 mfrc522(10, 9);
int tapCount = 0;
void setup() { Serial.begin(9600); SPI.begin(); mfrc522.PCD_Init(); }
void loop() {
  if(mfrc522.PICC_IsNewCardPresent() && mfrc522.PICC_ReadCardSerial()) {
    tapCount++;
    Serial.print("Total Taps: "); Serial.println(tapCount);
    mfrc522.PICC_HaltA(); delay(1000);
  }
}

Example 9: Buzzer Alarm for Unauthorized Cards

Arduino
#include <SPI.h>
#include <MFRC522.h>
MFRC522 mfrc522(10, 9);
int buzzer = 8;
byte allowed[4] = {0xA3,0xB7,0x2E,0x1F};
void setup() { Serial.begin(9600); SPI.begin(); mfrc522.PCD_Init(); pinMode(buzzer,OUTPUT); }
void loop() {
  if(!mfrc522.PICC_IsNewCardPresent() || !mfrc522.PICC_ReadCardSerial()) return;
  bool ok=true;
  for(byte i=0;i<4;i++) if(mfrc522.uid.uidByte[i]!=allowed[i]) ok=false;
  if(!ok) {
    Serial.println("INTRUDER ALERT!");
    for(int i=0;i<5;i++) { tone(buzzer,2000,200); delay(300); }
  } else Serial.println("Welcome!");
  mfrc522.PICC_HaltA(); delay(1000);
}

Example 10: RFID with Relay Control

Arduino
#include <SPI.h>
#include <MFRC522.h>
MFRC522 mfrc522(10, 9);
int relayPin = 6;
bool relayState = false;
byte masterCard[4] = {0xA3,0xB7,0x2E,0x1F};
void setup() { Serial.begin(9600); SPI.begin(); mfrc522.PCD_Init(); pinMode(relayPin,OUTPUT); digitalWrite(relayPin,LOW); }
void loop() {
  if(!mfrc522.PICC_IsNewCardPresent() || !mfrc522.PICC_ReadCardSerial()) return;
  bool ok=true;
  for(byte i=0;i<4;i++) if(mfrc522.uid.uidByte[i]!=masterCard[i]) ok=false;
  if(ok) {
    relayState = !relayState;
    digitalWrite(relayPin, relayState ? HIGH : LOW);
    Serial.println(relayState ? "Relay ON" : "Relay OFF");
  }
  mfrc522.PICC_HaltA(); delay(1000);
}

6.7 MCQs — Chapter 6 (20 Questions)

Pulse Oximeter with MAX30100

7.1 MAX30100 Sensor

The MAX30100 is an integrated pulse oximetry and heart-rate sensor. It combines two LEDs (Red + IR), a photodetector, and signal processing — all in a tiny package.

How It Works

Oxygenated hemoglobin (HbO₂) absorbs more infrared light (880nm) and lets red light pass. Deoxygenated hemoglobin (Hb) absorbs more red light (660nm) and lets infrared pass. By comparing the absorption ratio of Red vs IR light through your fingertip, the sensor calculates SpO₂ percentage.

MAX30100 Specifications

7.2 Pin Connections

Connection Table (Arduino → MAX30100)

7.3 MAX30100_PulseOximeter Library

Install MAX30100lib by OXullo Intersecans from Arduino Library Manager.

7.4 Full Code — Heart Rate & SpO2 Monitor

Arduino
// Program: Heart Rate & SpO2 Monitor using MAX30100
// Board: Arduino Uno
// Connections: SDA=A4, SCL=A5, VIN=5V, GND=GND

#include <Wire.h>
#include <MAX30100_PulseOximeter.h>

#define REPORTING_PERIOD_MS 1000

PulseOximeter pox;
uint32_t lastReport = 0;

// Callback for beat detection
void onBeatDetected() {
  Serial.println("♥ Beat!");
}

void setup() {
  Serial.begin(9600);
  Serial.println("Initializing Pulse Oximeter...");

  if (!pox.begin()) {
    Serial.println("MAX30100 FAILED! Check wiring.");
    while(1);
  }

  pox.setIRLedCurrent(MAX30100_LED_CURR_7_6MA);
  pox.setOnBeatDetectedCallback(onBeatDetected);
  Serial.println("Place your finger on the sensor...");
}

void loop() {
  pox.update();  // MUST call frequently!

  if (millis() - lastReport > REPORTING_PERIOD_MS) {
    Serial.print("Heart Rate: ");
    Serial.print(pox.getHeartRate());
    Serial.print(" BPM | SpO2: ");
    Serial.print(pox.getSpO2());
    Serial.println("%");
    lastReport = millis();
  }
}

7.5 Health Monitoring Project

Arduino
// Project: Health Monitor with LCD + Buzzer + LED indicators
// Normal SpO2: 95-100%, Low: 90-94%, Critical: <90%

#include <Wire.h>
#include <MAX30100_PulseOximeter.h>
#include <LiquidCrystal.h>

#define REPORTING_PERIOD_MS 1000
#define GREEN_LED 6
#define RED_LED   7
#define BUZZER    8

PulseOximeter pox;
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
uint32_t lastReport = 0;

void onBeatDetected() {
  digitalWrite(GREEN_LED, HIGH);
  delay(50);
  digitalWrite(GREEN_LED, LOW);
}

void setup() {
  Serial.begin(9600);
  lcd.begin(16, 2);
  pinMode(GREEN_LED, OUTPUT);
  pinMode(RED_LED, OUTPUT);
  pinMode(BUZZER, OUTPUT);

  lcd.print("Initializing...");
  if (!pox.begin()) {
    lcd.clear(); lcd.print("SENSOR ERROR!");
    while(1);
  }
  pox.setIRLedCurrent(MAX30100_LED_CURR_7_6MA);
  pox.setOnBeatDetectedCallback(onBeatDetected);
  lcd.clear(); lcd.print("Place finger...");
}

void loop() {
  pox.update();

  if (millis() - lastReport > REPORTING_PERIOD_MS) {
    float bpm = pox.getHeartRate();
    uint8_t spo2 = pox.getSpO2();

    lcd.clear();
    lcd.print("BPM: "); lcd.print(bpm, 0);
    lcd.setCursor(0, 1);
    lcd.print("SpO2: "); lcd.print(spo2); lcd.print("%");

    // Health classification
    if (spo2 >= 95) {
      lcd.setCursor(10, 1); lcd.print("OK");
      digitalWrite(RED_LED, LOW);
      noTone(BUZZER);
    } else if (spo2 >= 90) {
      lcd.setCursor(10, 1); lcd.print("LOW!");
      digitalWrite(RED_LED, HIGH);
    } else if (spo2 > 0) {
      lcd.setCursor(10, 1); lcd.print("CRIT");
      digitalWrite(RED_LED, HIGH);
      tone(BUZZER, 1500);  // Continuous alarm!
    }

    // Check abnormal heart rate
    if (bpm > 120 || (bpm < 50 && bpm > 0)) {
      tone(BUZZER, 1000, 500); // Warning beep
    }

    lastReport = millis();
  }
}

7.6 Worked Examples

Example 1: Simple Heart Rate Reading

Arduino
#include <Wire.h>
#include <MAX30100_PulseOximeter.h>
PulseOximeter pox;
uint32_t lastReport = 0;
void setup() { Serial.begin(9600); pox.begin(); pox.setIRLedCurrent(MAX30100_LED_CURR_7_6MA); }
void loop() {
  pox.update();
  if(millis()-lastReport > 1000) {
    Serial.print("BPM: "); Serial.println(pox.getHeartRate());
    lastReport = millis();
  }
}

Example 2: SpO2 Only Reading

Arduino
#include <Wire.h>
#include <MAX30100_PulseOximeter.h>
PulseOximeter pox;
uint32_t lastReport = 0;
void setup() { Serial.begin(9600); pox.begin(); pox.setIRLedCurrent(MAX30100_LED_CURR_7_6MA); }
void loop() {
  pox.update();
  if(millis()-lastReport > 1000) {
    uint8_t spo2 = pox.getSpO2();
    Serial.print("SpO2: "); Serial.print(spo2); Serial.println("%");
    lastReport = millis();
  }
}

Example 3: Beat Detection with LED Blink

Arduino
#include <Wire.h>
#include <MAX30100_PulseOximeter.h>
PulseOximeter pox;
int ledPin = 13;
void onBeat() { digitalWrite(ledPin, !digitalRead(ledPin)); }
void setup() {
  Serial.begin(9600); pinMode(ledPin, OUTPUT);
  pox.begin(); pox.setIRLedCurrent(MAX30100_LED_CURR_7_6MA);
  pox.setOnBeatDetectedCallback(onBeat);
}
void loop() { pox.update(); }

Example 4: Heart Rate on LCD

Arduino
#include <Wire.h>
#include <MAX30100_PulseOximeter.h>
#include <LiquidCrystal.h>
PulseOximeter pox;
LiquidCrystal lcd(12,11,5,4,3,2);
uint32_t lastReport = 0;
void setup() {
  lcd.begin(16,2); pox.begin();
  pox.setIRLedCurrent(MAX30100_LED_CURR_7_6MA);
  lcd.print("Place finger...");
}
void loop() {
  pox.update();
  if(millis()-lastReport > 1000) {
    lcd.clear();
    lcd.print("Heart Rate:");
    lcd.setCursor(0,1);
    lcd.print(pox.getHeartRate(), 0); lcd.print(" BPM");
    lastReport = millis();
  }
}

Example 5: SpO2 + BPM on LCD with Status

Arduino
#include <Wire.h>
#include <MAX30100_PulseOximeter.h>
#include <LiquidCrystal.h>
PulseOximeter pox;
LiquidCrystal lcd(12,11,5,4,3,2);
uint32_t lastReport = 0;
void setup() { lcd.begin(16,2); pox.begin(); pox.setIRLedCurrent(MAX30100_LED_CURR_7_6MA); }
void loop() {
  pox.update();
  if(millis()-lastReport > 1000) {
    float bpm = pox.getHeartRate();
    uint8_t spo2 = pox.getSpO2();
    lcd.clear();
    lcd.print("BPM:"); lcd.print(bpm,0);
    lcd.setCursor(9,0); lcd.print("O2:"); lcd.print(spo2); lcd.print("%");
    lcd.setCursor(0,1);
    if(spo2>=95) lcd.print("Status: NORMAL");
    else if(spo2>=90) lcd.print("Status: LOW!");
    else if(spo2>0) lcd.print("CRITICAL!!!");
    else lcd.print("No finger...");
    lastReport = millis();
  }
}

Example 6: Data Logger to Serial (CSV)

Arduino
#include <Wire.h>
#include <MAX30100_PulseOximeter.h>
PulseOximeter pox;
uint32_t lastReport = 0;
int reading = 0;
void setup() {
  Serial.begin(9600); pox.begin();
  pox.setIRLedCurrent(MAX30100_LED_CURR_7_6MA);
  Serial.println("Reading,BPM,SpO2,Time_ms");
}
void loop() {
  pox.update();
  if(millis()-lastReport > 2000) {
    reading++;
    Serial.print(reading); Serial.print(",");
    Serial.print(pox.getHeartRate()); Serial.print(",");
    Serial.print(pox.getSpO2()); Serial.print(",");
    Serial.println(millis());
    lastReport = millis();
  }
}

Example 7: Heart Rate Zone Indicator

Arduino
#include <Wire.h>
#include <MAX30100_PulseOximeter.h>
PulseOximeter pox;
uint32_t lastReport = 0;
void setup() { Serial.begin(9600); pox.begin(); pox.setIRLedCurrent(MAX30100_LED_CURR_7_6MA); }
void loop() {
  pox.update();
  if(millis()-lastReport > 1000) {
    float bpm = pox.getHeartRate();
    Serial.print("BPM: "); Serial.print(bpm);
    if(bpm < 60) Serial.println(" → Resting");
    else if(bpm < 100) Serial.println(" → Normal");
    else if(bpm < 140) Serial.println(" → Exercise");
    else Serial.println(" → DANGER! Too high!");
    lastReport = millis();
  }
}

Example 8: Moving Average BPM (Smoothing)

Arduino
#include <Wire.h>
#include <MAX30100_PulseOximeter.h>
PulseOximeter pox;
float readings[5]; int idx=0;
uint32_t lastReport = 0;
void setup() {
  Serial.begin(9600); pox.begin(); pox.setIRLedCurrent(MAX30100_LED_CURR_7_6MA);
  for(int i=0;i<5;i++) readings[i]=0;
}
void loop() {
  pox.update();
  if(millis()-lastReport > 1000) {
    readings[idx] = pox.getHeartRate();
    idx = (idx+1) % 5;
    float avg = 0;
    for(int i=0;i<5;i++) avg += readings[i];
    avg /= 5;
    Serial.print("Avg BPM: "); Serial.println(avg);
    lastReport = millis();
  }
}

Example 9: Low SpO2 Alarm System

Arduino
#include <Wire.h>
#include <MAX30100_PulseOximeter.h>
PulseOximeter pox;
int buzzer = 8, redLed = 7;
uint32_t lastReport = 0;
void setup() {
  Serial.begin(9600); pinMode(buzzer,OUTPUT); pinMode(redLed,OUTPUT);
  pox.begin(); pox.setIRLedCurrent(MAX30100_LED_CURR_7_6MA);
}
void loop() {
  pox.update();
  if(millis()-lastReport > 1000) {
    uint8_t spo2 = pox.getSpO2();
    Serial.print("SpO2: "); Serial.println(spo2);
    if(spo2 > 0 && spo2 < 90) {
      digitalWrite(redLed, HIGH);
      tone(buzzer, 2000);
      Serial.println("!!! CRITICAL SpO2 !!!");
    } else {
      digitalWrite(redLed, LOW);
      noTone(buzzer);
    }
    lastReport = millis();
  }
}

Example 10: Full Patient Monitor (LCD + Buzzer + LEDs)

Arduino
#include <Wire.h>
#include <MAX30100_PulseOximeter.h>
#include <LiquidCrystal.h>
PulseOximeter pox;
LiquidCrystal lcd(12,11,5,4,3,2);
int greenLed=6, redLed=7, buzzer=8;
uint32_t lastReport=0;
void onBeat() { digitalWrite(greenLed,HIGH); delay(30); digitalWrite(greenLed,LOW); }
void setup() {
  Serial.begin(9600); lcd.begin(16,2);
  pinMode(greenLed,OUTPUT); pinMode(redLed,OUTPUT); pinMode(buzzer,OUTPUT);
  pox.begin(); pox.setIRLedCurrent(MAX30100_LED_CURR_7_6MA);
  pox.setOnBeatDetectedCallback(onBeat);
  lcd.print("Patient Monitor"); lcd.setCursor(0,1); lcd.print("Place finger...");
}
void loop() {
  pox.update();
  if(millis()-lastReport > 1000) {
    float bpm=pox.getHeartRate(); uint8_t spo2=pox.getSpO2();
    lcd.clear();
    lcd.print("BPM:"); lcd.print(bpm,0);
    lcd.setCursor(8,0); lcd.print("O2:"); lcd.print(spo2); lcd.print("%");
    lcd.setCursor(0,1);
    bool alarm = false;
    if(spo2>0 && spo2<90) { lcd.print("SpO2 CRITICAL!"); alarm=true; }
    else if(bpm>120) { lcd.print("BPM HIGH!"); alarm=true; }
    else if(bpm>0 && bpm<50) { lcd.print("BPM LOW!"); alarm=true; }
    else lcd.print("Status: NORMAL");
    digitalWrite(redLed, alarm?HIGH:LOW);
    if(alarm) tone(buzzer,1500,500); else noTone(buzzer);
    // CSV log to Serial
    Serial.print(bpm); Serial.print(","); Serial.print(spo2);
    Serial.print(","); Serial.println(alarm?"ALARM":"OK");
    lastReport = millis();
  }
}

7.7 MCQs — Chapter 7 (20 Questions)

Bluetooth with Arduino (HC-05)

  HC-05 Module Pins:
  ┌──────────────────────┐
  │  HC-05 Bluetooth     │
  │                      │
  │  VCC ──── 5V Arduino │
  │  GND ──── GND        │
  │  TXD ──── Pin 10 (RX)│
  │  RXD ──── Pin 11 (TX)│  ⚠️ Use voltage divider!
  │  EN  ──── (for AT)   │     RXD is 3.3V tolerant
  │  STATE ── (optional) │     Use 1K + 2K divider
  └──────────────────────┘

#include <SoftwareSerial.h>

SoftwareSerial BTSerial(10, 11); // RX=10, TX=11
int ledPin = 13;

void setup() {
  Serial.begin(9600);
  BTSerial.begin(9600);
  pinMode(ledPin, OUTPUT);
  Serial.println("Bluetooth LED Control Ready!");
}

void loop() {
  if (BTSerial.available()) {
    char command = BTSerial.read();
    Serial.print("Received: ");
    Serial.println(command);
    
    if (command == '1') {
      digitalWrite(ledPin, HIGH);
      BTSerial.println("LED ON");
      Serial.println("LED turned ON");
    }
    else if (command == '0') {
      digitalWrite(ledPin, LOW);
      BTSerial.println("LED OFF");
      Serial.println("LED turned OFF");
    }
  }
}

// Control 4 devices via Bluetooth
// Send: 'A'=LED1 ON, 'a'=LED1 OFF, 'B'=Fan ON, etc.
#include <SoftwareSerial.h>
SoftwareSerial BT(10, 11);

int led1=2, led2=3, fan=4, buzzer=5;

void setup() {
  BT.begin(9600);
  pinMode(led1, OUTPUT); pinMode(led2, OUTPUT);
  pinMode(fan, OUTPUT);  pinMode(buzzer, OUTPUT);
}

void loop() {
  if (BT.available()) {
    char c = BT.read();
    switch(c) {
      case 'A': digitalWrite(led1, HIGH); BT.println("LED1 ON"); break;
      case 'a': digitalWrite(led1, LOW);  BT.println("LED1 OFF"); break;
      case 'B': digitalWrite(fan, HIGH);  BT.println("Fan ON"); break;
      case 'b': digitalWrite(fan, LOW);   BT.println("Fan OFF"); break;
      case 'C': digitalWrite(buzzer, HIGH); BT.println("Buzzer ON"); break;
      case 'c': digitalWrite(buzzer, LOW);  BT.println("Buzzer OFF"); break;
    }
  }
}

8.6 MCQs — Chapter 8 (20 Questions)

WiFi with Arduino (ESP8266)

  ESP8266 Pin Layout (ESP-01):
  ┌──────────────────┐
  │   ESP-01 Module   │
  │                   │
  │  VCC ─── 3.3V     │  ⚠️ MUST be 3.3V!
  │  GND ─── GND      │
  │  TX  ─── Pin 10   │
  │  RX  ─── Pin 11   │  Via voltage divider
  │  CH_PD── 3.3V     │  Enable pin (pull HIGH)
  │  RST ─── 3.3V     │  Reset (pull HIGH)
  │  GPIO0── Float    │  LOW = flash mode
  │  GPIO2── Float    │
  └──────────────────┘

#include <ESP8266WiFi.h>
#include <ESP8266WebServer.h>

const char* ssid = "YourWiFi";
const char* password = "YourPassword";
int ledPin = D2; // GPIO4

ESP8266WebServer server(80);

void handleRoot() {
  String html = "<!DOCTYPE html><html><head>";
  html += "<title>IoT LED Control</title>";
  html += "<style>body{font-family:Arial;text-align:center;padding:50px;}";
  html += "button{padding:20px 40px;font-size:24px;margin:10px;border-radius:12px;";
  html += "border:none;cursor:pointer;color:white;}";
  html += ".on{background:#10b981;} .off{background:#ef4444;}</style></head>";
  html += "<body><h1>🏠 Smart LED Control</h1>";
  html += "<p>LED is: " + String(digitalRead(ledPin) ? "ON 💡" : "OFF 🔌") + "</p>";
  html += "<a href='/on'><button class='on'>Turn ON</button></a>";
  html += "<a href='/off'><button class='off'>Turn OFF</button></a>";
  html += "</body></html>";
  server.send(200, "text/html", html);
}

void handleOn()  { digitalWrite(ledPin, HIGH); server.sendHeader("Location","/"); server.send(303); }
void handleOff() { digitalWrite(ledPin, LOW);  server.sendHeader("Location","/"); server.send(303); }

void setup() {
  Serial.begin(115200);
  pinMode(ledPin, OUTPUT);
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) { delay(500); Serial.print("."); }
  Serial.println("\nConnected! IP: " + WiFi.localIP().toString());
  
  server.on("/", handleRoot);
  server.on("/on", handleOn);
  server.on("/off", handleOff);
  server.begin();
}

void loop() { server.handleClient(); }

// Send DHT22 data to a web page
#include <ESP8266WiFi.h>
#include <ESP8266WebServer.h>
#include <DHT.h>

DHT dht(D4, DHT22);
ESP8266WebServer server(80);

void handleData() {
  float temp = dht.readTemperature();
  float hum = dht.readHumidity();
  String json = "{\"temperature\":" + String(temp) + 
                ",\"humidity\":" + String(hum) + "}";
  server.send(200, "application/json", json);
}

void setup() {
  dht.begin();
  WiFi.begin("SSID", "PASS");
  while (WiFi.status() != WL_CONNECTED) delay(500);
  server.on("/data", handleData);
  server.begin();
}

void loop() { server.handleClient(); }

9.5 MCQs — Chapter 9 (20 Questions)

IoT Cloud & Futuristic Technologies

// Send DHT22 data to ThingSpeak
#include <ESP8266WiFi.h>
#include <DHT.h>

const char* ssid = "YourWiFi";
const char* password = "YourPass";
const char* server = "api.thingspeak.com";
String apiKey = "YOUR_WRITE_API_KEY";

DHT dht(D4, DHT22);
WiFiClient client;

void setup() {
  Serial.begin(115200);
  dht.begin();
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) delay(500);
  Serial.println("WiFi Connected! IP: " + WiFi.localIP().toString());
}

void loop() {
  float temp = dht.readTemperature();
  float hum = dht.readHumidity();
  
  if (client.connect(server, 80)) {
    String postStr = "api_key=" + apiKey;
    postStr += "&field1=" + String(temp);
    postStr += "&field2=" + String(hum);
    
    client.println("POST /update HTTP/1.1");
    client.println("Host: api.thingspeak.com");
    client.println("Content-Type: application/x-www-form-urlencoded");
    client.println("Content-Length: " + String(postStr.length()));
    client.println();
    client.print(postStr);
    
    Serial.println("Sent: Temp=" + String(temp) + " Hum=" + String(hum));
  }
  client.stop();
  delay(20000); // ThingSpeak requires 15s minimum between updates
}

// Smart Home: Control relay via ThingSpeak
#include <ESP8266WiFi.h>
#include <ESP8266HTTPClient.h>

int relayPin = D1;
String readApiKey = "YOUR_READ_API_KEY";

void setup() {
  pinMode(relayPin, OUTPUT);
  digitalWrite(relayPin, HIGH); // Relay OFF (active LOW)
  WiFi.begin("SSID", "PASS");
  while (WiFi.status() != WL_CONNECTED) delay(500);
}

void loop() {
  HTTPClient http;
  String url = "http://api.thingspeak.com/channels/YOUR_CHANNEL/fields/1/last.txt";
  url += "?api_key=" + readApiKey;
  
  http.begin(url);
  int httpCode = http.GET();
  if (httpCode == 200) {
    String payload = http.getString();
    if (payload.toInt() == 1) digitalWrite(relayPin, LOW);  // ON
    else                      digitalWrite(relayPin, HIGH); // OFF
  }
  http.end();
  delay(5000);
}

// Pseudocode: Si Labs W7230F1 LED Control
// In Simplicity Studio C project:
#include "em_gpio.h"
#include "em_cmu.h"

void initGPIO(void) {
  CMU_ClockEnable(cmuClock_GPIO, true);
  GPIO_PinModeSet(gpioPortF, 4, gpioModePushPull, 0); // LED0
  GPIO_PinModeSet(gpioPortF, 5, gpioModePushPull, 0); // LED1
}

void toggleLED(int led) {
  if (led == 0) GPIO_PinOutToggle(gpioPortF, 4);
  else          GPIO_PinOutToggle(gpioPortF, 5);
}
// Mobile phone control: BLE GATT service receives ON/OFF
// commands and calls toggleLED() — smart home application

10.6 MCQs — Chapter 10 (20 Questions)

Lab Programs (10 Experiments)

int ledPin = 9;
void setup() { pinMode(ledPin, OUTPUT); }
void loop() {
  for (int i = 0; i <= 255; i += 5) {
    analogWrite(ledPin, i);  // Increase brightness
    delay(30);
  }
  for (int i = 255; i >= 0; i -= 5) {
    analogWrite(ledPin, i);  // Decrease brightness
    delay(30);
  }
}

#include <LiquidCrystal.h>
LiquidCrystal lcd(12, 11, 5, 4, 3, 2); // RS,EN,D4-D7
void setup() { lcd.begin(16, 2); lcd.print("Hello EduArtha!"); lcd.setCursor(0, 1); lcd.print("IoT Lab 2"); }
void loop() {}

int potPin = A0;
void setup() { Serial.begin(9600); }
void loop() {
  int val = analogRead(potPin);      // 0-1023
  float voltage = val * (5.0/1023.0); // Convert to voltage
  Serial.print("ADC: "); Serial.print(val);
  Serial.print(" | Voltage: "); Serial.println(voltage);
  delay(500);
}

#include <DHT.h>
DHT dht(2, DHT22);
void setup() { Serial.begin(9600); dht.begin(); }
void loop() {
  float t = dht.readTemperature();
  float h = dht.readHumidity();
  Serial.print("Temp: "); Serial.print(t); Serial.print("°C | Hum: "); Serial.print(h); Serial.println("%");
  delay(2000);
}

// Ultrasonic HC-SR04
int trigPin = 9, echoPin = 10;
void setup() { Serial.begin(9600); pinMode(trigPin, OUTPUT); pinMode(echoPin, INPUT); }
void loop() {
  digitalWrite(trigPin, LOW); delayMicroseconds(2);
  digitalWrite(trigPin, HIGH); delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  long duration = pulseIn(echoPin, HIGH);
  float distance = duration * 0.034 / 2;
  Serial.print("Distance: "); Serial.print(distance); Serial.println(" cm");
  delay(500);
}

#include <SPI.h>
#include <MFRC522.h>
MFRC522 rfid(10, 9); // SS=10, RST=9
void setup() { Serial.begin(9600); SPI.begin(); rfid.PCD_Init(); Serial.println("Scan RFID card..."); }
void loop() {
  if (!rfid.PICC_IsNewCardPresent() || !rfid.PICC_ReadCardSerial()) return;
  Serial.print("UID: ");
  for (byte i = 0; i < rfid.uid.size; i++) { Serial.print(rfid.uid.uidByte[i], HEX); Serial.print(" "); }
  Serial.println();
  rfid.PICC_HaltA();
}

int ENA=5, IN1=6, IN2=7;
void setup() { pinMode(ENA, OUTPUT); pinMode(IN1, OUTPUT); pinMode(IN2, OUTPUT); }
void loop() {
  // Forward
  digitalWrite(IN1, HIGH); digitalWrite(IN2, LOW); analogWrite(ENA, 200);
  delay(2000);
  // Reverse
  digitalWrite(IN1, LOW); digitalWrite(IN2, HIGH); analogWrite(ENA, 200);
  delay(2000);
  // Stop
  digitalWrite(IN1, LOW); digitalWrite(IN2, LOW);
  delay(1000);
}

// Bluetooth HC-05: See Chapter 8 code
// WiFi ESP8266: See Chapter 9 code
// Combined: BT for local control, WiFi for remote dashboard

Appendices

Appendix A: Arduino Uno R3 Pin Reference

Appendix B: Common Libraries Quick Reference

Appendix C: Troubleshooting Guide

Appendix D: IoT Project Ideas for Portfolio