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Basics

Arduino IDE

  • Install Arduino IDE
  • Tools > Manage Libaries
  • ESP8266/Node MCU

  • Preferences > Additional boards manager URLS

Simulators

  • Wokwi (Open-Source)
  • TinkerCad

Code

Skeleton

void setup(){
  // initialization code
}
void loop(){
  // infinitely-looping code
}

Input/Outputs

Function
Configuring A GPIO pin cannot be used for both input and output. You need to specify one. pinMode(<pin_number>, <i/o>); pinMode(3, INPUT);
pinMode(3, OUTPUT);
Outputs Digital digitalWrite(<pin_number>, <state>); digitalWrite(3, HIGH); // or digitalWrite(3, 1);
digitalWrite(3, LOW); // or digitalWrite(3, 0);
Analog analogWrite(<pin_number>, value); analogWrite(3, 25); 
// Code for blinking LED

void setup(){
  pinMode(3, OUTPUT);
}
void loop(){
  digitalWrite(3, HIGH);
  delay(1000); // 1000ms

  digitalWrite(3, LOW);
  delay(1000); // 1000ms
}

// Code for changing LED brightness

void setup(){
  pinMode(3, OUTPUT);
}
void loop(){
  for (int i=0; i<=1023; i++) {
    analogWrite(3, i);
    delay(1000); // 1000ms
  }
}

image-20231216005331149

Serial Monitor

Baudrate \(\equiv\) Bitrate

  • Bitrate is for binary
  • Baudrate is for analog signal
Serial.begin(9600); // ; baudrate // initializes serial monitor

Serial.read() // return ASCII values

int reading_int;
char reading_char;

void setup(){
  Serial.begin(9600);
}
void loop(){
  while (Serial.available()){
    reading_int = Serial.read();
    reading_char = reading_int;

    Serial.println(reading_int);
    Serial.println(reading_char);
  }  
  delay(500);
}

Unique ID for Arduino

Method 1: Automatic (using external library)

#include <ArduinoUniqueID.h> // in the same folder of this note

for(size_t i = 0; i < UniqueIDsize; i++)
  Serial.println(UniqueID[i], HEX);

Method 2: Automatic

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/fcntl.h>
int main(int ac, char **av) {
    int fd, i;
    unsigned char eui[8];
    fd = open("/dev/random", O_RDONLY);
    if (fd < 0) {
        perror("can't open /dev/random");
        exit(1);
    }
    if (read(fd, eui, sizeof(eui)) != sizeof(eui)) {
        fprintf(stderr, "couldn't read %zu bytes\n", sizeof(eui));
        exit(1);
    }
    eui[0] = (eui[0] & ~1) | 2;
    for (i = 0; i < sizeof(eui); ++i) {
        printf("%02X%c", eui[i], i == sizeof(eui)-1 ? '\n' : '-');
    }
    return 0;
}

Method 3: Manual/Custom ID

Get the code from TOOLS > Get Board Info or put a custom one

write_id_to_eeprom.ino

char sID[7] = "AE0001";

// do this only once on an Arduino, 
// write the Serial of the Arduino in the first 6 bytes of the EEPROM

#include <EEPROM.h>

void setup()
{
  Serial.begin(9600);
  for (int i=0; i<6; i++) {
    EEPROM.write(i,sID[i]);
  }
}

void loop() {
  // 
}
read_id_from_eeprom.ino

// reads the Serial of the Arduino from the 
// first 6 bytes of the EEPROM

#include <EEPROM.h>
char sID[7];

void setup()
{
  Serial.begin(9600);
  for (int i=0; i<6; i++) {
    sID[i] = EEPROM.read(i);
  }
  Serial.println(sID);
}

void loop() {
  // 
}

Multi-Tasking

Interrupts

Trigger Meaning in Bits
High 1
Low 0
Rising 0-1
Falling 1-0
Change 0-1 or 1-0 
void my_func() {
  delay_seconds = 1;
  delayMicroseconds(delay_seconds * 1000 * 1000);

  if (digitalRead(buttonPin) == LOW)
  {
    return ;
  }

  led_state = !led_state;
  digitalWrite(ledPin, ledState);
}

void setup(){
  pinMode(buttonPin, INPUT);
  pinMode(ledPin, OUTPUT);

  attachInterrupt(buttonPin, my_func, RISING);
}

void loop() {
  while(WiFi.connected()){

  }
}

millis() instead of delay()

Arduino does not support multi-threading/processing, and hence parallel processing is not possible

millis()
// -> unsigned long
// -> returns number of ms since Arduino powered up/reset

unsigned long prevTime = millis();
unsigned long currentTime;

void setup() {

}

void loop() {
  currentTime = millis();

  if (currentTime - prevTime > 1000) {
    doSomething();

    prevTime = currentTime;
  }
}

Example

#define LED1 13
#define LED2 12
#define LED3 11

#define BTN 4

// set LED states
int LED1_state = LOW;
int brightness = 0;

// previous time for the tasks depending upon time.
unsigned long prevTime_T1 = millis(); 
unsigned long prevTime_T4 = millis(); 

// time intervals for the tasks
long interval_T1 = 1000; // blink every 1 second
long interval_T4 = 5000; // print brightness of LED3 every 5 seconds

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  pinMode(LED1, OUTPUT);
  pinMode(LED2, OUTPUT);
  pinMode(LED3, OUTPUT);
  pinMode(BTN, INPUT_PULLUP);
}

void loop() {
  // put your main code here, to run repeatedly:
  unsigned long currentTime = millis();

  // Task 1 : Blink LED1 (T1)
  if (currentTime - prevTime_T1 > interval_T1) {
    LED1_state = !LED1_state;
    digitalWrite(LED1, LED1_state);

    prevTime_T1 = currentTime;
  }

  // Task 2 : Glow LED2 when BTN is pressed
  if (digitalRead(BTN)) {
    digitalWrite(LED2, LOW);
  } else {
    digitalWrite(LED2, HIGH);
  }

  // Task 3 : Read input from serial monitor (0-255) and then write to LED3
  if (Serial.available()) {
    brightness = Serial.parseInt();
    if (brightness >=0 && brightness <= 255) {
      analogWrite(LED3, brightness);
    }
  }

  // Task 4 : print the brightness of LED3 in the serial monitor after every 5 seconds
  if (currentTime - prevTime_T4 > interval_T4) {
    Serial.print("Brightness (0-255): ");
    Serial.println(brightness);

    prevTime_T4 = currentTime;
  }
}

Code Cloning

How to

Protection

Code Security

main.ino

#include "secrets.h"

void setup(){
  Serial.begin(9600);
  Serial.println(secret_variable);
}

secrets.h

#define secret_variable "Secret";

2025-12-01

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