How do you write your own Arduino library?

Creating a custom Arduino library allows you to organize reusable code for sensors, actuators, or algorithms. Here's a step-by-step guide to building your own library from scratch.

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1. Library Folder Structure

A basic Arduino library requires:

text

MyLibrary/
├── MyLibrary.h    (Header file - declarations)
├── MyLibrary.cpp  (Source file - implementations)
├── examples/      (Optional: Example sketches)
│   └── BasicDemo/
│       └── BasicDemo.ino
├── keywords.txt   (Optional: Syntax highlighting)
└── README.md      (Optional: Documentation)

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2. Create the Header File (MyLibrary.h)

This file defines your library's interface.

cpp

// MyLibrary.h
#ifndef MyLibrary_h  // Prevent duplicate inclusion
#define MyLibrary_h

#include "Arduino.h"  // Required for Arduino functions

class MyLibrary {
  public:
    // Constructor (optional)
    MyLibrary(int pin);  

    // Public methods
    void begin();
    int readValue();
    void blink(int times);

  private:
    // Private variables/functions
    int _pin;  
    void _privateHelper();
};

#endif

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3. Implement the Code (MyLibrary.cpp)

This file contains the actual functionality.

cpp

// MyLibrary.cpp
#include "MyLibrary.h"

// Constructor (initialize variables)
MyLibrary::MyLibrary(int pin) {
  _pin = pin;
}

// Initialize the library
void MyLibrary::begin() {
  pinMode(_pin, OUTPUT);
}

// Read a sensor value
int MyLibrary::readValue() {
  return analogRead(_pin);
}

// Blink an LED
void MyLibrary::blink(int times) {
  for (int i=0; i<times; i++) {
    digitalWrite(_pin, HIGH);
    delay(500);
    digitalWrite(_pin, LOW);
    delay(500);
  }
}

// Private function (only accessible within class)
void MyLibrary::_privateHelper() {
  // Internal logic here
}

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4. Add Examples (Optional)

Create an example sketch in examples/BasicDemo/BasicDemo.ino:

cpp

#include <MyLibrary.h>

MyLibrary myLib(13);  // Use pin 13

void setup() {
  myLib.begin();
}

void loop() {
  myLib.blink(3);     // Blink 3 times
  delay(1000);
}

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5. Add Syntax Highlighting (keywords.txt)

To enable Arduino IDE coloring:

text

#######################################
# Syntax coloring for MyLibrary
#######################################

MyLibrary   KEYWORD1
begin       KEYWORD2
readValue   KEYWORD2
blink       KEYWORD2

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6. Install Your Library

1. Manual Installation:

   • Zip the MyLibrary folder.

   • In Arduino IDE: Sketch > Include Library > Add .ZIP Library.

2. Folder Installation:

   • Copy MyLibrary/ to Documents/Arduino/libraries/.

3. Restart the Arduino IDE.

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7. Using Your Library

cpp

#include <MyLibrary.h>  // Your library is now available!

MyLibrary customDevice(8);

void setup() {
  customDevice.begin();
}

void loop() {
  int val = customDevice.readValue();
  customDevice.blink(2);
}

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Best Practices

1. Keep It Modular: Split complex libraries into multiple files.

2. Documentation: Add comments and a README.md.

3. Error Handling: Validate inputs in public methods.

4. Version Control: Use GitHub to share your library.

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Advanced Features

• Support for Multiple Boards: Use #ifdef for platform-specific code.

  cpp

    #ifdef ESP32
      // ESP32-specific code
    #endif
  

• EEPROM Storage: Add methods to save/load settings.

• Interrupts: Handle hardware interrupts within the library.

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Publishing to Arduino Library Manager

1. Follow Arduino's library specification.

2. Submit a pull request to the Arduino Library Registry.

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Now you can create professional Arduino libraries!