Arduino Uno R3

Interactive Arduino Uno R3 pinout with PWM, I2C, SPI and analog pins, current limits, Arduino IDE and PlatformIO setup, and compile-checked code.

5 V logic

Community draft — report a mistake

MCUATmega328P, 16 MHz, 8-bit AVR

Flash / SRAM32 KB (0.5 KB bootloader) / 2 KB

EEPROM1 KB

Logic level5 V

I/O14 digital (6 PWM), 6 analog in

Typical price₹450–650 (clone), ₹2,000+ (original)

The Uno R3 is the classic 5 V board: an ATmega328P at 16 MHz, a USB-serial chip (an ATmega16U2 on originals, usually a CH340 on Indian clones), a 5 V regulator, and headers that fit almost every shield.

It has no Wi-Fi and only 2 KB of RAM, but it is simple and forgiving — 5 V logic matches most hobby modules, and it is the board the Playground emulates in full.

Power it from USB, or 7–12 V on the barrel jack or VIN. The 5V pin can supply a few hundred mA from USB; the 3.3V pin only about 50 mA.

Interactive pinout

Hover or tap a pin for its functions and traps. Filter to light up every I2C, ADC or boot pin.

Safe for most uses
Works, with a caveat
Avoid unless you know why
Power / control

Mind the current: 20 mA per pin, 200 mA for the whole chip. An LED with a 220 Ω resistor is fine. Relays, motors, buzzers and LED strips need a transistor or a driver module — never drive them straight from a pin.

5 V logic out, 5 V logic expected in. A 3.3 V module (ESP-01, many sensors) can be damaged by the Uno's 5 V outputs. Use a level shifter or a divider, and power 3.3 V parts from the 3.3V pin only if they draw under ~50 mA.

Leave D0 and D1 free. They are the USB serial lines. Anything wired there can block uploads and garble the Serial Monitor.

Set up your computer

Install Arduino IDE 2.x from arduino.cc.
Boards Manager → install Arduino AVR Boards (we compile against avr 1.8.8).
Tools → Board → Arduino Uno, then pick the port that appears when you plug the board in.

Your platformio.ini:

platformio.iniOutput

[env:uno]
platform = atmelavr
board = uno
framework = arduino
monitor_speed = 9600

[env:uno]
platform = atmelavr
board = uno
framework = arduino
monitor_speed = 9600

First program

Verified — core avr 1.8.8, 3 Nov 2026Compile-only

blink-uno.inoArduino C++Open in Playground Flash

// Blink the on-board LED (pin 13) of an Arduino Uno R3 or Nano.
void setup() {
  Serial.begin(9600);
  pinMode(LED_BUILTIN, OUTPUT);
  Serial.println(F("FlashReady: blink started"));
}

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

// Blink the on-board LED (pin 13) of an Arduino Uno R3 or Nano.
void setup() {
  Serial.begin(9600);
  pinMode(LED_BUILTIN, OUTPUT);
  Serial.println(F("FlashReady: blink started"));
}

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

Components with Arduino Uno R3

Common errors

avrdude: stk500_recv(): programmer is not responding

Wrong port, wrong board, or something on D0/D1. Pick the port that appears when you plug in, set Tools → Board → Arduino Uno, unplug wires from D0/D1 and try again. Clones with a CH340 need its driver — see our driver links.

Port greyed out or missing

Charge-only USB cable or missing CH340 driver. Try a known data cable; install the driver from wch-ic.com only.

Sketch too big / low memory warning

The Uno has only 2 KB of RAM. Wrap fixed strings in F("…") so they stay in flash, and avoid the String class in long-running sketches.

Projects for Arduino Uno R3

ECG trace on an OLED for learning (Arduino Uno + AD8232) — not medical

UnoMedium

See the P-QRS-T wave of a real heartbeat — the biology textbook diagram, live.

2 h · Student projects

₹1,550Verified core 1.8

Bluetooth RC car controlled from your phone (Arduino Uno + HC-05)

UnoMedium

Drive a robot car from your phone over Bluetooth.

3 h · Robotics

Interactive pinout

Set up your computer

First program

Components with Arduino Uno R3

Common errors

Projects for Arduino Uno R3

ECG trace on an OLED for learning (Arduino Uno + AD8232) — not medical

Bluetooth RC car controlled from your phone (Arduino Uno + HC-05)

Classroom noise meter with a traffic-light LED bar (Arduino Uno + KY-038)

Classroom voting machine for class elections — an EVM model (Arduino Uno + 16x2 LCD)

Colour sorting machine with two servos (Arduino Uno + TCS34725)

Contactless infrared thermometer (Arduino Uno + MLX90614 + OLED)

Debate and elocution competition timer with warning lights (Arduino Uno)

Digital compass with a needle on an OLED (Arduino Uno + GY-271)

Digital dice on an 8×8 LED matrix (Arduino Uno + MAX7219)

Dual-axis solar tracker with four LDRs and two servos (Arduino Uno)

Fire-fighting robot model that finds and puts out a candle (Arduino Uno + flame sensors)

Fire and smoke alarm with heat-rise detection (Arduino Uno + MQ-2 + DS18B20)

LPG gas leak alarm with SMS alert (Arduino Uno + MQ-6)

GPS tracker that texts its location (Arduino Uno + NEO-6M + SIM800L)

GSM farm motor control by SMS (Arduino Uno + SIM800L)

Digital tachometer with a Hall sensor and magnet (Arduino Uno + A3144 + TM1637)

Inverse-square law of light experiment (Arduino Uno + BH1750 + VL53L0X)

Control a lamp with any TV remote (Arduino Uno)

Joystick-controlled robot arm with three servos (Arduino Uno)

Keypad door lock with a servo latch (Arduino Uno)

Snake game on an 8×8 LED matrix with a joystick (Arduino Uno + MAX7219)

Line follower robot with two IR sensors (Arduino Uno)

Medicine reminder with a “taken” button (Arduino Uno + DS3231 + LCD)

Milk collection weighing scale with price display (Arduino Uno + HX711)

Mini sumo robot for college robo-fests (Arduino Uno + HC-SR04)

Morse code trainer that decodes your keying (Arduino Uno + OLED)

Classroom seismograph with a scrolling OLED trace (Arduino Uno + MPU6050)

Obstacle-avoiding robot with a scanning ultrasonic sensor (Arduino Uno)

Garage parking assistant with a ToF sensor and LED bar (Arduino Uno)

Measure g with a simple pendulum and an IR photogate (Arduino Uno)

Two-gate photogate timer for speed and acceleration (Arduino Uno + IR sensors)

Heart-rate display with a live pulse wave (Arduino Uno + Pulse Sensor + OLED)

Quiz buzzer system for 4 teams with lockout (Arduino Uno + TM1637 + WS2812B)

Automatic railway level-crossing gate model (Arduino Uno + IR sensors + servo)

Rain alarm for drying clothes and grain (Arduino Uno + rain sensor)

Reaction timer game with a 4-digit display (Arduino Uno + TM1637)

RGB mood lamp with WS2812B LEDs and a rotary knob (Arduino Uno)

RS485 Modbus sensor reader for long cable runs (Arduino Uno + MAX485)

Digital clock that keeps time through power cuts (Arduino Uno + DS3231)

Sargam piano with 8 keys and a buzzer (Arduino Uno + TM1637)

Automatic school bell timer with RTC and LCD (Arduino Uno + DS3231)

Shop shutter burglar alarm with SMS and call (Arduino Uno + SIM800L)

Queue token number display for a clinic or shop (Arduino Uno + TM1637)

Simon memory game with colours and tones (Arduino Uno + WS2812B + passive buzzer)

Touch-free smart dustbin (Arduino Uno + HC-SR04 + servo)

Solar water heater display — how many buckets of hot water? (Arduino Uno + DS18B20)

Measure the speed of sound with an ultrasonic sensor (Arduino Uno + HC-SR04)

Cyclone and storm pressure alert from a barometer (Arduino Uno + BMP180)

Overhead tank overflow alarm (Arduino Uno + float switch)

Teach-and-repeat robot arm that remembers 40 poses (Arduino Uno)

Tilt-controlled servo with an MPU-6050 (Arduino Uno)

Backup battery power-cut alarm with SMS (Arduino Uno + INA219 + SIM800L)

Four-way traffic junction model with countdown and pedestrian button (Arduino Uno)

Ultrasonic radar scanner with an OLED radar screen (Arduino Uno)

Automatic wet and dry waste segregator model (Arduino Uno + moisture plate + servo)