#Summarized

Digital Interfaces

Overview

• Arduino UNO has 14 digital pins (labeled 0-13)
• Each pin can function as either input (read) or output (write)
• Digital pins work with binary values only: 0 (LOW) or 1 (HIGH)

Digital Pin Commands

1. Setting Pin Mode

pinMode(pin, MODE);

• pin: Number between 0-13
• MODE: Either INPUT or OUTPUT

Examples:

pinMode(4, INPUT);   // Set pin 4 as input
pinMode(7, OUTPUT);  // Set pin 7 as output

2. Writing to Digital Pins

digitalWrite(pin, value);

• pin: Number between 0-13
• value: Either 0 (LOW ≈ 0V) or 1 (HIGH ≈ 5V)

Examples:

digitalWrite(4, 1);  // Output 5V on pin 4
digitalWrite(7, 0);  // Output 0V on pin 7

3. Reading from Digital Pins

value = digitalRead(pin);

• value: Variable to store the read value (0 or 1)
• pin: Number between 0-13

Examples:

x = digitalRead(4);  // Read state of pin 4 into variable x

Example: LED Blink with Counter

int pin = 8;
int counter = 0;
 
void setup() {
  Serial.begin(9600);
  pinMode(pin, OUTPUT);
  digitalWrite(pin, LOW);
}
 
void loop() {
  counter = counter + 1;
  Serial.print("Blink #");
  Serial.println(counter);
  
  digitalWrite(pin, HIGH);  // Turn LED on
  delay(1000);              // Wait 1 second
  digitalWrite(pin, LOW);   // Turn LED off
  delay(1000);              // Wait 1 second
}

Example: Switch Controlling LED

int pin1 = 7;  // Switch
int pin2 = 8;  // LED
 
void setup() {
  pinMode(pin1, INPUT);
  pinMode(pin2, OUTPUT);
  digitalWrite(pin2, LOW);
}
 
void loop() {
  if (digitalRead(pin1) == 0) {
    digitalWrite(pin2, HIGH);  // Turn LED on when switch pressed
  } else {
    digitalWrite(pin2, LOW);   // Turn LED off when switch not pressed
  }
}

Analog Interfaces

Overview

• Arduino UNO has two types of analog interfaces:
  • Analog Input Pins: A0-A5 (read analog values)
  • PWM Output Pins: 3, 5, 6, 9, 10, 11 (pins with ~ symbol, write analog-like values)

Analog Pin Commands

1. Writing to PWM Pins

analogWrite(pin, value);

• pin: PWM pin number (3, 5, 6, 9, 10, or 11)
• value: Number between 0-255 (0 = 0V, 255 = 5V)
• No need to set pinMode() when using analogWrite()

Examples:

analogWrite(5, 0);    // Output 0V on pin 5
analogWrite(10, 200); // Output ~3.92V on pin 10 (200 × 5 ÷ 255)

2. Reading from Analog Pins

value = analogRead(pin);

• value: Variable to store the read value (0-1023)
• pin: Analog pin (A0-A5)
• Input voltage (0-5V) is mapped to 0-1023 (10-bit resolution)

Examples:

x = analogRead(A0);  // Read voltage at pin A0 into variable x

Example: Variable LED Brightness

int x;
 
void setup() {
}
 
void loop() {
  for (x = 0; x <= 255; x = x + 10) {
    analogWrite(5, x);  // Gradually increase LED brightness
    delay(500);
  }
}

Example: Reading Potentiometer

int x;
 
void setup() {
  Serial.begin(9600);
}
 
void loop() {
  x = analogRead(A0);
  Serial.print("The value of x is ");
  Serial.println(x);
  delay(1000);
}

Sensors and Actuators

Sensors (Input Devices)

• Devices that sense environment (temperature, gas, light, etc.)
• Send data to the microcontroller

Actuators (Output Devices)

• Devices controlled by the microcontroller to perform actions
• Examples: motors, LEDs, buzzers, displays
  

Working with Sensors and Actuators

When using sensors or actuators, you need to know:

1. Circuit connection - how to properly connect to Arduino
2. Example code - how to interface with the device

Buzzer

A buzzer is an actuator used to generate sound/alarm signals.

Circuit Connection

• Connect the positive terminal of the buzzer to a digital pin (pin 4 in the example)
• Connect the negative terminal to GND
• Some buzzers may require a current-limiting resistor (220-330Ω) in series

Example Code

int buzzerPin = 4;
 
void setup() {
  pinMode(buzzerPin, OUTPUT);
}
 
void loop() {
  digitalWrite(buzzerPin, HIGH);  // Turn buzzer on
  delay(2000);                    // Sound for 2 seconds
  digitalWrite(buzzerPin, LOW);   // Turn buzzer off
  delay(2000);                    // Silent for 2 seconds
}

Photoresistor/Light-Dependent Resistor (LDR)

An LDR is a sensor that measures light intensity.

How It Works

• Variable resistor whose resistance changes with light exposure
• Higher light intensity → Lower resistance
• Lower light intensity → Higher resistance

Circuit Connection

• Connect one leg of the LDR to 5V
• Connect the other leg to both:
  • An analog pin (A0 in the example)
  • A pull-down resistor (10kΩ) that connects to GND

Example Code

int LDR_value;
 
void setup() {
  Serial.begin(9600);
}
 
void loop() {
  LDR_value = analogRead(A0);
  Serial.print("The LDR value is ");
  Serial.println(LDR_value);
  delay(2000);
}

Soil Moisture Sensor

Measures moisture content in soil using resistance changes.

How It Works

• Acts as a variable resistor
• Higher moisture → Lower resistance → Lower readings
• Lower moisture → Higher resistance → Higher readings

Circuit Connection

Example Code

int Soil_value;
 
void setup() {
  Serial.begin(9600);
}
 
void loop() {
  Soil_value = analogRead(A0);
  Serial.print("The soil moisture value is ");
  Serial.println(Soil_value);
  delay(2000);
}

Keypad

A matrix keypad for user input. Requires the Keypad.h library.

Library Installation

1. Select: Sketch > Include Library > Manage Libraries...
2. Search for: Keypad
3. Install the library

Circuit Connection

Based on the example code:

• Row pins (4 pins) connect to Arduino pins 9, 8, 7, 6
• Column pins (4 pins) connect to Arduino pins 5, 4, 3, 2

Keypad Layout

1 2 3 A
4 5 6 B
7 8 9 C
* 0 # D

Example Code

#include <Keypad.h>
 
const byte ROWS = 4;
const byte COLS = 4;
 
char layout[ROWS][COLS] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'*', '0', '#', 'D'}
};
 
byte rowPins[ROWS] = {9, 8, 7, 6};
byte colPins[COLS] = {5, 4, 3, 2};
 
Keypad customKeypad = Keypad(makeKeymap(layout), rowPins, colPins, ROWS, COLS);
 
void setup() {
  Serial.begin(9600);
}
 
void loop() {
  char customKey = customKeypad.getKey();
  
  if (customKey) {
    Serial.println(customKey);
  }
}