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Arduino Uno R3

Board

ATmega328P-based development board, the most widely used Arduino for getting started.

Specifications

Microcontroller

ATmega328P

Operating voltage

5V

Input voltage (recommended)

7-12V

Digital I/O

14 pins (6 with PWM)

Analog inputs

6 pins

Flash memory

32 KB (0.5 KB bootloader)

SRAM

2 KB

EEPROM

1 KB

Clock speed

16 MHz

Shop prices

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Prices read from the shops' pages on 22 October 2026. Prices and stock may have changed since; check at the shop before you buy.

Projects with this part

• LED BlinkBeginner10 minYour first project: it blinks an LED on the Arduino's pin 13 once a second and writes each change to the Serial Monitor. It teaches you to use a breadboard, an LED and a resistor. The board's own L light is also on pin 13, so it blinks along with the LED. No extra library needed.Open project
• Night Light (LDR)Beginner20 minA night light that turns itself on as the room gets dark. An LDR (light sensor) and a 100 kΩ resistor form a voltage divider; the Arduino reads the light level on pin A0 and, in the dark, dims the LED on pin 9 with PWM. It teaches analog reading, thresholds and PWM. No extra library needed.Open project
• DHT11 Temperature and Humidity MeterBeginner20 minA starter project that measures the room's temperature and humidity with a DHT11 sensor and writes the values to the Arduino IDE's Serial Monitor once a second. Before uploading the code, install the DHTlib library in the Arduino IDE.Open project
• DHT22 Temperature and Humidity MeterBeginner20 minA project that measures humidity and temperature, in both Celsius and Fahrenheit, with a DHT22 sensor and writes them to the Serial Monitor every two seconds. It is more precise than the DHT11 and has a wider measuring range. Before uploading the code, install Adafruit's "DHT sensor library" in the Arduino IDE (and the "Adafruit Unified Sensor" library it asks for).Open project
• HC-SR04 Ultrasonic Distance MeterBeginner20 minA project that measures the distance to the object in front of an HC-SR04 ultrasonic sensor in centimetres and writes it to the Serial Monitor about 10 times a second. The sensor measures how long the echo of its sound wave takes to come back; the code turns that time into centimetres by dividing it by 58. No extra library needed.Open project
• Alcohol Measurement with the MQ-3 SensorBeginner25 minA project that measures alcohol vapour in the air with an MQ-3 gas sensor and writes the analog value and the threshold state to the Serial Monitor every half second. The analog value (0-1023) rises as the alcohol concentration goes up; the Limit value shows whether the threshold set with the trimmer on the board has been crossed. No extra library needed. The sensor's heater gets warm while it runs; on first use, leave the sensor powered for a while (ideally 24 hours), and let it warm up for a few minutes before measuring. The code uses 115200 baud, so pick 115200 in the Serial Monitor too.Open project
• LPG Gas Measurement with the MQ-5 (PPM)Intermediate30 minA project that reads the MQ-5 gas sensor's analog output, turns it into a voltage and the sensor's present resistance (Rs), measures Ro itself in clean air at start-up, and writes an estimated LPG concentration (PPM), worked out with the LPG curve in the MQ-5 datasheet, to the Serial Monitor every two seconds. At start-up it waits 10 seconds for the heater to settle, then calibrates for 5 seconds: the sensor must be in clean air then, with no gas near it. In clean air the Rs/Ro ratio is about 6.5 and the PPM below 1; with gas around, the ratio drops and the PPM rises clearly. The PPM value is an estimate: by its datasheet, a new sensor gives steady readings only after more than 24 hours of heating on first use. No extra library needed.Open project
• Level Measurement with a Water Level SensorBeginner15 minA starter project that reads the water level sensor's analog output and writes the level as Empty, Low, Medium or High to the Serial Monitor once a second. As the sensor's parallel tracks go under water, the resistance drops and the reading rises. The thresholds (100, 400, 450) depend on the water's conductivity and the sensor; watching the raw values first and setting your own thresholds gives better results. Only dip the lower part with the tracks in water; keep the electronics and pins at the top dry. To reduce corrosion, do not leave the sensor powered all the time. No extra library needed.Open project
• Colour Detection with the TCS3200Intermediate30 minA circuit that tells the colour of an object held in front of it. The TCS3200 board measures light through red, green and blue filtered photodiodes and puts out the chosen colour's strength as a square wave; the Arduino times the three colours' pulses with pulseIn, prints them to the Serial Monitor and names the strongest. It teaches choosing a filter with digital pins and timing pulses. No extra library needed.Open project
• Traffic LightBeginner20 minA real traffic light with three LEDs: red, red + yellow, green and yellow light up in the order used in Turkey, and each stage is also written to the Serial Monitor. It teaches driving several outputs in turn, timing with digitalWrite and delay, and gathering a repeated job into its own function. You can change how long each light stays on with the constants in the code. No extra library needed.Open project
• Toggle an LED with a ButtonBeginner20 minTurn a red LED on and off with a button: every press flips the LED, and the press count and the LED's state are written to the Serial Monitor. It teaches reading a button with digitalRead, the Arduino's built-in pull-up resistor (INPUT_PULLUP), catching the moment a button is pressed and waiting out contact bounce (debounce). The button needs no extra resistor, and no extra library is needed.Open project
• LED Brightness with a PotentiometerBeginner20 minSet an LED's brightness by turning a potentiometer's knob: with the knob at one end the LED is off, and it gets brighter as you turn towards the other end. The value read and the brightness given to the LED are also written to the Serial Monitor. It teaches reading an analog input with analogRead, turning one range into another with map, and using PWM with analogWrite. No extra library needed.Open project
• Doorbell with a BuzzerBeginner20 minA doorbell that plays a four-note "ding-dong" on a passive buzzer when you press the button; every ring is also written to the Serial Monitor. It teaches making sound with tone(), keeping notes and their lengths in arrays and playing them with a for loop, gathering a job into its own function, and reading a button with the Arduino's built-in pull-up resistor (INPUT_PULLUP). You can make the tune your own by changing the notes in the code. No extra library needed.Open project
• Servo with a PotentiometerBeginner25 minAs you turn a potentiometer's knob, an SG90 servo motor turns with it: one end of the knob is 0°, the other 180°. The angle the servo stops at is also written to the Serial Monitor. It teaches adding a library (Servo) to a project, turning a value read with analogRead into an angle with map, and sending a motor to the angle you want with servo.write. The Servo library comes with the Arduino IDE, so there is nothing to install.Open project
• Parking SensorIntermediate45 minLike the parking sensor in a car: the HC-SR04 measures the distance to whatever is in front of it, the buzzer starts beeping once something comes within 1 metre and the beeps get faster as it comes closer; below 10 cm the tone is steady. Green, yellow and red LEDs show the far, middle and near zones, and the distance is written to the Serial Monitor. It teaches timing with millis() instead of delay, so measuring, beeping and the lights run without waiting for each other, writing a function that returns a value, splitting into zones with if / else if, and turning the distance into a beep gap with map. No extra library needed.Open project
• LCD ThermometerBeginner30 minA small device that shows temperature and humidity on a 16x2 LCD instead of the Serial Monitor, so it can sit on a desk without a computer. The DHT11 is read every two seconds; the top line of the screen shows the temperature and the bottom line the humidity. It teaches driving a screen over I2C with just two data wires, using two libraries together, and updating a line on the screen without clearing it. Install the "LiquidCrystal I2C" and "DHTlib" libraries from the Library Manager.Open project
• Motion AlarmBeginner25 minA small home alarm that goes off when someone walks in: the HC-SR501 PIR sensor senses the change in the heat a human body gives off, the buzzer plays a two-tone siren and the red LED blinks; every alarm is counted in the Serial Monitor. It teaches reading a sensor's digital output, catching only the moment motion starts, sounding for a set time with millis(), and gathering the job into its own function. No extra library needed.Open project
• OLED Distance MeterIntermediate40 minA meter that shows the distance measured by an HC-SR04 on a 0.96" OLED screen, no computer needed: the distance in large text on top, and below it a bar graph of the last 128 readings scrolling to the right. Move your hand closer and further and watch the graph rise and fall. It teaches driving a screen over I2C, drawing text and lines with Adafruit GFX, keeping readings in a ring buffer, and timing with millis() instead of delay. Install the "Adafruit SSD1306" and "Adafruit GFX" libraries from the Library Manager.Open project
• Smoke and Gas AlarmIntermediate35 minAn alarm that goes off when smoke or a flammable gas (LPG, natural gas, methane) shows up in the kitchen or a room: the MQ-2 sensor's analog output is read, the clean air value is measured at start-up, and once the reading rises well above it the buzzer plays the three-beep pattern (T3) that real smoke alarms use while the red LED flashes with the beeps. The green LED blinks while warming up and stays on once the alarm is armed. It teaches reading an analog sensor against its own clean air value, using two separate thresholds so the alarm does not flicker at the edge, and playing a sound pattern with millis() while still taking readings. No extra library needed. This is a learning project; it does not replace a certified smoke and gas alarm at home.Open project
• Automatic Plant WateringIntermediate50 minA system that waters a potted plant by itself once the soil dries out: the soil moisture sensor measures moisture as a percentage, and when it drops below 30% the Arduino runs the mini submersible pump for 3 seconds through a relay, waits for the water to soak in, measures again and repeats until moisture passes 50%. The pump runs on three AA batteries of its own; the relay keeps that circuit fully apart from the Arduino. If 5 waterings in a row leave the soil dry, the tank counts as empty and the pump is stopped so it never runs dry. It teaches calibrating a sensor into a percentage, switching a separately powered load with a relay, powering a sensor only while it reads to slow its corrosion, and guarding a system against faults. No extra library needed.Open project
• Code Door LockIntermediate50 minA door lock that opens with a code typed on a 4x4 keypad: the LCD says what to do and shows the digits as *, and when the code is right the servo turns the latch and opens the door for 5 seconds while the screen counts down. After 3 wrong codes in a row the keypad is locked for 30 seconds. While the door is open, A changes the code; the new code is typed twice and saved in the Arduino's EEPROM memory, so it is kept even if the power goes. It teaches reading a keypad as a matrix, splitting a program into states (locked, open, waiting, changing the code), listening to keys while timing with millis(), and using memory that lasts. Install "Keypad" and "LiquidCrystal I2C" from the Library Manager; Servo and EEPROM come with the Arduino IDE. This is a learning project; do not use it as a real door's only lock.Open project
• RFID Card Door LockIntermediate60 minA door lock that opens with a card or key fob you have introduced: the RC522 reader reads the card's number, and if it is known the green LED lights up, a short beep sounds and the servo turns the latch and opens the door for 5 seconds; an unknown card lights the red LED and sounds a long beep. The first card you scan becomes the master card: scanning it opens adding mode for 10 seconds, and a new card scanned meanwhile is added, a known one removed. The cards are kept in the Arduino's EEPROM memory, so they are not forgotten when the power goes. It teaches talking to a module over SPI, comparing card numbers, keeping a small list in EEPROM, and letting a mode close by itself. Install "MFRC522" from the Library Manager; Servo and EEPROM come with the Arduino IDE. This is a learning project; do not use it as a real door's only lock.Open project
• Joystick Snake GameIntermediate45 minThe classic snake game on an 8x8 LED screen: you steer the snake with the joystick, and when it eats the blinking food it grows one cell longer, gets a little faster and the buzzer gives a short beep. The screen is small, so the snake leaves one edge and comes back in at the other; when it runs into its own body the game is over, three falling notes play, your score shows on the screen in digits, and pressing the joystick's button starts a new game. It teaches reading an analog joystick and turning it into a direction, keeping a game in arrays (the snake's cells), setting the game's speed with millis(), and driving a MAX7219 LED matrix with a few wires. Install "LedControl" from the Library Manager.Open project
• Kitchen TimerBeginner30 minA kitchen timer for tea, eggs or pasta: you set the time by turning the rotary encoder, and the 4-digit display shows it as minutes:seconds. Press the knob and the countdown starts, with the colon in the middle blinking once a second; press again to pause, once more to carry on where it stopped, and hold it down to go back to the time you set. When the time is up the buzzer beeps three times a second and the display blinks; a press silences it and the same time is ready to run again. It teaches reading a rotary encoder's direction with an interrupt, telling a short press from a long one on a single button, counting down with millis(), and driving a TM1637 display with two wires. Install "TM1637" (Avishay Orpaz) from the Library Manager.Open project
• Weather StationIntermediate40 minA small weather station for a room or a balcony: the BME280 sensor measures temperature, humidity and air pressure, and the Arduino works out the approximate altitude from the pressure. The readings show page by page on a 16x2 LCD; each press of the button turns to the next page, and the values refresh every two seconds. It teaches building an I2C line where two modules share the same two wires (SDA and SCL), working out altitude from pressure, and updating an LCD without flicker. Install "Adafruit BME280 Library" (with the extra libraries it asks for) and "LiquidCrystal I2C" from the Library Manager.Open project
• Digital Spirit LevelIntermediate45 minA project that turns the breadboard itself into a spirit level: the MPU6050's accelerometer measures which way gravity pulls, and the Arduino works out the tilt on two axes in degrees. On the left of the OLED a bubble runs to the high side like in a real spirit level, and on the right the X and Y tilt are written; once both are under half a degree the screen says "LEVEL" and the buzzer gives two short beeps. It teaches using a sensor without a library by reading its registers directly, working out an angle from gravity (atan2), smoothing a jittery reading, and putting two I2C modules on one line. Install "Adafruit SSD1306" and "Adafruit GFX" from the Library Manager.Open project
• Joystick Pan-Tilt Camera HeadBeginner40 minA camera head built from two servos: the bottom servo turns the camera left and right, the top one up and down, and you steer it with a joystick. The further you push the stick the faster the head turns, and it stays where it is when you let go; pressing the joystick sends both servos slowly back to the middle. The servos run from a separate 3 x AA battery holder, with the grounds joined. It teaches turning an analog stick into a speed with a dead zone, moving servos smoothly and within limits with millis(), and powering more than one servo from a supply of their own. The Servo library comes with the Arduino IDE; there is nothing to install.Open project
• Flame-Sensing Fire AlarmBeginner30 minA fire alarm that recognises a flame by the infrared light it gives off: when the flame sensor sees a lighter or a candle flame, the buzzer plays a rising siren and the red and blue LEDs flash in turn like a fire engine's lights. While idle, the blue LED blinks briefly every 2 seconds to show the alarm is on watch. The alarm does not sound until a flame has lasted half a second, so a single spark or glint does not set it off, and it keeps sounding for 3 seconds after the flame is out. It teaches smoothing the on-and-off digital signal of a flickering flame, filtering out short flashes with a time condition, and playing a siren with millis() while reading the sensor. No extra library is needed. This is a learning project; it does not replace an approved smoke detector at home.Open project
• Rain Alert and Automatic WindowBeginner40 minA setup that sounds an alert and closes the window by itself when it starts to rain: when water drops land on the rain sensor's plate, the buzzer plays a ding-dong three times, then a servo slowly closes the window. Some time after the plate dries, the window opens again. The sensor board is powered from one of the Arduino's pins and switched on only while measuring, so the plate does not corrode by electrolysis. It teaches turning an analog reading into a percentage, using two separate thresholds for rain and dry, timing a period (that starts over if the plate gets wet again) and turning a servo slowly, one step at a time. The Servo library comes with the Arduino IDE; there is nothing to install.Open project
• Air Quality IndicatorBeginner30 minAn indicator that shows a room's air like a traffic light: the MQ-135 sensor reacts to pollutants such as smoke, ammonia, benzene and the CO₂ that builds up from breathing; green lights while the air is clean, yellow as it starts to get stale and red when it is bad, and the Serial Monitor tells you to air the room. At start the sensor warms up and the clean-air value is measured; every reading after that is judged against it, and if the air gets even cleaner the value is updated. It teaches reading an analog sensor against its own clean-air value, reducing jitter by averaging several readings and leaving a margin at the thresholds so the LEDs do not flicker at the edge. No extra library is needed. The MQ-135 does not tell gases apart and does not give a calibrated CO₂ reading; it shows roughly how polluted the air is.Open project
• Waterproof Thermometer (Aquarium / Tea)Beginner30 minA thermometer that measures water temperature with a waterproof DS18B20 probe and shows it on a 4-digit display as "24°C". When the temperature leaves the allowed range the buzzer sounds and the display blinks: three fast, high beeps when too hot, a slow, low beep when too cold, so you can tell which by ear alone. It comes set to 23-28 °C for an aquarium; for tea, set the lower limit to 60 °C and it beeps once the tea has cooled enough to drink. It teaches 1-Wire communication and the pull-up resistor, not making the program wait while a reading is taken, and leaving a margin so the alarm does not flicker at the limit. The DallasTemperature and TM1637 libraries are installed from the Library Manager.Open project