Microcontrollers and Your First Circuit

A microcontroller is a tiny computer on a chip that runs one program and talks to the physical world through its pins: reading sensors and controlling lights, motors and displays. Arduino boards and their programming environment make microcontrollers approachable. For connected (IoT) projects, ESP32 boards add Wi-Fi and Bluetooth and can be programmed with the same Arduino tools.

Common boards

Setup

1. Install the Arduino IDE (version 2.x).
2. Connect the board by USB; select the board and port in the IDE.
3. For ESP32, add Espressif's board package via the Boards Manager.

Your first sketch

const int LED_PIN = 13;           // many boards have an on-board LED here (LED_BUILTIN)

void setup() {
  pinMode(LED_PIN, OUTPUT);
}

void loop() {
  digitalWrite(LED_PIN, HIGH);
  delay(500);
  digitalWrite(LED_PIN, LOW);
  delay(500);
}

setup() runs once; loop() runs forever. Click Upload.

An external LED on a breadboard

Connect: pin → current-limiting resistor (220–330 Ω) → LED long leg (anode); LED short leg (cathode) → GND. Without the resistor, the LED and the pin can be damaged.

Electrical safety basics

• Work with USB or low-voltage supplies while learning; never connect mains (AC) voltage to a breadboard.
• Check board voltage: many boards use 5 V logic, ESP32 and many sensors use 3.3 V and can be damaged by 5 V signals.
• Disconnect power before rewiring.

Exercise

Blink an external LED with a resistor, then make three LEDs blink in a traffic-light sequence.

Check yourself

• What is the difference between setup() and loop()?
• Why does an LED need a resistor?
• Why must you check whether a board uses 3.3 V or 5 V logic?