02·Board Anatomy: Pins, Power, and USB

Introduction

Before you connect anything, you must be able to read the Arduino Uno R3 board like a map: where the digital pins (D0–D13) and analog pins (A0–A5) are, which pins do PWM (marked with ~), where power comes from (USB, barrel jack, VIN), and which voltages and currents are safe. This lesson takes the Uno apart: the pin headers, the voltage regulator, the built-in LED on pin 13, the ATmega16U2 USB-serial chip, the reset button, AREF, and ICSP. You will learn the hard numbers — a 10-bit ADC (0–1023), a recommended 7–12V on the barrel jack, ~40 mA maximum per pin, ~200 mA for the whole chip — and the classic traps, such as mixing 5V and 3.3V logic levels. We do not touch the IDE, code, or Blink yet — those come in later lessons.