Hubbry Logo
Arduino UnoArduino UnoMain
Open search
Arduino Uno
Community hub
Arduino Uno
logo
8 pages, 0 posts
0 subscribers
Be the first to start a discussion here.
Be the first to start a discussion here.
Arduino Uno
Arduino Uno
Arduino Uno
View on Wikipedia
from Wikipedia
Arduino Uno
Arduino Uno R3 SMD board with ATmega328P MCU in SMD package
Developerarduino.cc
ManufacturerMany
TypeSingle-board microcontroller[1]
AvailabilityUno R4 webpage
Operating systemNone, with bootloader (default), FreeRTOS
CPU
MemorySRAM
StorageFlash, EEPROM
Websitearduino.cc

The Arduino Uno is a series of open-source microcontroller board based on a diverse range of microcontrollers (MCU). It was initially developed and released by the Arduino company in 2010.[2][3] The microcontroller board is equipped with sets of digital and analog input/output (I/O) pins that may be interfaced to various expansion boards (shields) and other circuits.[1] The board has 14 digital I/O pins (six capable of PWM output), 6 analog I/O pins, and is programmable with the Arduino IDE (Integrated Development Environment), via a type B USB cable.[4] It can be powered by a USB cable or a barrel connector that accepts voltages between 7 and 20 volts, such as a rectangular 9-volt battery. It has the same microcontroller as the Arduino Nano board, and the same headers as the Leonardo board.[5][6] The hardware reference design is distributed under a Creative Commons Attribution Share-Alike 2.5 license and is available on the Arduino website. Layout and production files for some versions of the hardware are also available.

The word "uno" means "one" in Italian and was chosen to mark a major redesign of the Arduino hardware and software.[7] The Uno board was the successor of the Duemilanove release and was the 9th version in a series of USB-based Arduino boards.[8] Version 1.0 of the Arduino IDE for the Arduino Uno board has now evolved to newer releases.[4] The ATmega328 on the board comes preprogrammed with a bootloader that allows uploading new code to it without the use of an external hardware programmer.[3]

While the Uno communicates using the original STK500 protocol,[1] it differs from all preceding boards in that it does not use a FTDI USB-to-UART serial chip. Instead, it uses the Atmega16U2 (Atmega8U2 up to version R2) programmed as a USB-to-serial converter.[9]

History

[edit]
Arduino RS232 serial board - a predecessor with ATmega8 MCU

The Arduino project started at the Interaction Design Institute Ivrea (IDII) in Ivrea, Italy. At that time, the students used a BASIC Stamp microcontroller, at a considerable price. In 2003, Hernando Barragán created the development platform Wiring as a Master's thesis project at IDII, under the supervision of Massimo Banzi and Casey Reas, who are known for work on the Processing language. The project goal was to create simple, low-cost tools for creating digital projects by non-engineers. The Wiring platform consisted of a printed circuit board (PCB) with an ATmega168 microcontroller, an IDE based on Processing, and library functions to easily program the microcontroller.[10] In 2003, Massimo Banzi, with David Mellis, another IDII student, and David Cuartielles, added support for the cheaper ATmega8 microcontroller to Wiring. But instead of continuing the work on Wiring, they forked the project and renamed it Arduino. Early Arduino boards used the FTDI USB-to-UART serial chip and an ATmega168.[10] The Uno differed from all preceding boards by featuring the ATmega328P microcontroller and an ATmega16U2 (Atmega8U2 up to version R2) programmed as a USB-to-serial converter.

In June 2023, Arduino released two new flavors of the Uno; R4 Minima and R4 Wifi. These mark a departure from previous boards as they use Renesas RA4M1 ARM Cortex M4 microcontroller, and the R4 Wifi a Espressif ESP32-S3-MINI co-processor. These versions are form factor, pin and power compatible with version R1 to R3, so should be largely be able to be drop in replacements.[11]

In October 2025, Arduino released the Arduino UNO Q, a board with Linux support and WIFi, featuring a Qualcomm co-processor following their acquisition by Qualcomm. It also has a LED matrix and Bluetooth support.[12][13]

Technical specifications

[edit]

Uno R1 to R3

[edit]
Arduino Uno R3 board with AVR-based ATmega328P MCU in DIP-28 package

Microcontroller (MCU):[14]

  • IC: Microchip ATmega328P (8-bit AVR core)
  • Clock Speed: 16 MHz (on Uno R1 to R3 boards), though IC supports 20 MHz maximum at 5 Volts
  • Flash memory: 32 KB, of which 0.5 KB used by the bootloader
  • SRAM: 2 KB
  • EEPROM: 1 KB
  • USART peripherals: 1 (Arduino software default configures USART as a 8N1 UART)
  • SPI peripherals: 1
  • I²C peripherals: 1
  • Operating Voltage: 5 Volts (on Uno R1 to R3 boards), though IC supports 1.8 to 5.5 Volts (some 3rd-party Uno variations support 3.3V)

Board:

  • Digital I/O Pins: 14
  • PWM Pins: 6 (Pin # 3, 5, 6, 9, 10 and 11)[15]
  • Analog Input Pins: 6
  • DC Current per I/O Pin: 20 mA
  • DC Current for 3.3V Pin: 50 mA
  • Size: 68.6 mm x 53.4 mm
  • Weight: 25 g
  • ICSP Header: Yes
  • Power Sources:
  • USB connector. USB bus specification has a voltage range of 4.75 to 5.25 volts. The official Uno boards have a USB-B connector, but 3rd party boards may have a miniUSB / microUSB / USB-C connector.
  • 5.5mm/2.1mm barrel jack connector. Official Uno boards support 6 to 20 volts, though 7 to 12 volts is recommended. The maximum voltage for 3rd party Uno boards varies between board manufactures because various voltage regulators are used, each having a different maximum input rating. Power into this connector is routed through a series diode before connecting to VIN to protect against accidental reverse voltage situations.
  • VIN pin on shield header. It has a similar voltage range of the barrel jack. Since this pin doesn't have reverse voltage protection, power can be injected or pulled from this pin. When supplying power into VIN pin, an external series diode is required in case barrel jack is used. When board is powered by barrel jack, power can be pulled out of this pin.[16]

Uno R4

[edit]
Arduino Uno R4 WiFi with ARM-based R7FA4M1AB MCU in 64pin SMD package

Two Uno R4 boards are available: Uno R4 Minima and Uno R4 WiFi. The latter has a WiFi coprocessor and LED matrix, but the Minima doesn't.

Common features on both Uno R4 Minima[17] and Uno R4 WiFi[18] boards:

Microcontroller (MCU):[19]

Board:

Additional features only available on the Uno R4 Minima board:[17]

  • SWD programming connector. This is a 10-pin 5x2 1.27mm header for connecting the microcontroller (R7FA4M1AB) to an external SWD (serial wire debug) programming / debugging device.

Additional features only available on the Uno R4 WiFi board:[18]

  • WiFi coprocessor - 240 MHz Espressif ESP32-S3-MINI (IEEE802.11 b/g/n WiFi and Bluetooth 5 LE) and a 6-pin 3x2 2.54mm header for external programming.
  • 12x8 LED matrix - it is driven by 11 GPIO pins using a charlieplexing scheme.
  • Qwiic I²C connector. This 4-pin 1.00mm JST SH connector provides external connection to a 3.3 volt I²C bus. Don't attach 5 volt I²C devices directly to this connector.[20]
  • RTC battery header pin (VRTC). This pin connects an external battery to the RTC (real-time clock) inside the microcontroller (R7FA4M1AB) to keep clock running when board is powered down. Connect this pin to positive side of 1.6 to 3.6 volt battery and negative side of battery to ground header pin (GND), such as a 3 volt lithium coin battery.[19]
  • Remote-Off header pin (OFF). This pin disables the 5 volt buck switching voltage regulator (SL854102) when powered by the barrel jack or VIN header pin. Connect this pin to ground header pin (GND) to disable this voltage regulator.

Uno Q

[edit]

The Arduino Uno Q has a dual processor setup with the Qualcomm Dragonwing serving as the MPU (microprocessor) and the ARM based STM32U585 as the MCU (microcontroller).

Headers

[edit]
Header pinout of the Arduino Uno board

General pin functions

[edit]
  • LED: There is a built-in LED driven by digital pin 13. When the pin is high value, the LED is on, when the pin is low, it is off.
  • VIN: The input voltage to the Arduino/Genuino board when it is using an external power source (as opposed to 5 volts from the USB connection or other regulated power source). You can supply voltage through this pin, or, if supplying voltage via the power jack, access it through this pin.
  • 5V: This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 20V), the USB connector (5V), or the VIN pin of the board (7-20V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage the board.
  • 3V3: A 3.3 volt supply generated by the on-board regulator. Maximum current draw is 50 mA.
  • GND: Ground pins.
  • IOREF: This pin on the Arduino/Genuino board provides the voltage reference with which the microcontroller operates. A properly configured shield can read the IOREF pin voltage and select the appropriate power source, or enable voltage translators on the outputs to work with the 5V or 3.3V.
  • Reset: Typically used to add a reset button to shields that block the one on the board.[9]

Special pin functions

[edit]

Each of the 14 digital pins and 6 analog pins on the Uno can be used as an input or output, under software control (using pinMode(), digitalWrite(), and digitalRead() functions). They operate at 5 volts. Each pin can provide or receive 20 mA as the recommended operating condition and has an internal pull-up resistor (disconnected by default) of 20-50K ohm. A maximum of 40mA must not be exceeded on any I/O pin to avoid permanent damage to the microcontroller. The Uno has 6 analog inputs, labeled A0 through A5; each provides 10 bits of resolution (i.e. 1024 different values). By default, they measure from ground to 5 volts, though it is possible to change the upper end of the range using the AREF pin and the analogReference() function.[9]

In addition, some pins have specialized functions:

  • Serial / UART: pins 0 (RX) and 1 (TX). Used to receive (RX) and transmit (TX) TTL serial data. These pins are connected to the corresponding pins of the ATmega8U2 USB-to-TTL serial chip.
  • External interrupts: pins 2 and 3. These pins can be configured to trigger an interrupt on a low value, a rising or falling edge, or a change in value.
  • PWM (pulse-width modulation): pins 3, 5, 6, 9, 10, and 11. Can provide 8-bit PWM output with the analogWrite() function.
  • SPI (Serial Peripheral Interface): pins 10 (SS), 11 (MOSI), 12 (MISO), and 13 (SCK). These pins support SPI communication using the SPI library.
  • TWI (two-wire interface) / I²C: pin SDA (A4) and pin SCL (A5). Support TWI communication using the Wire library.
  • AREF (analog reference): Reference voltage for the analog inputs.[9]

Communication

[edit]

The Arduino/Genuino Uno has a number of facilities for communicating with a computer, another Arduino/Genuino board, or other microcontrollers. The ATmega328 provides UART TTL (5V) serial communication, which is available on digital pins 0 (RX) and 1 (TX). An ATmega16U2 on the board channels this serial communication over USB and appears as a virtual com port to software on the computer. The 16U2 firmware uses the standard USB COM drivers, and no external driver is needed. However, on Windows, a .inf file is required. Arduino Software (IDE) includes a serial monitor which allows simple textual data to be sent to and from the board. The RX and TX LEDs on the board will flash when data is being transmitted via the USB-to-serial chip and USB connection to the computer (but not for serial communication on pins 0 and 1). A SoftwareSerial library allows serial communication on any of the Uno's digital pins.[9]

Automatic (software) reset

[edit]

Rather than requiring a physical press of the reset button before an upload, the Arduino/Genuino Uno board is designed in a way that allows it to be reset by the software running on a connected computer. One of the hardware flow control lines (DTR) of the ATmega8U2/16U2 is connected to the reset line of the ATmega328 via a 100 nanofarad capacitor. When this line is asserted (taken low), the reset line drops long enough to reset the chip.[9]

This setup has other implications. When the Uno is connected to a computer running Mac OS X or Linux, it resets each time a connection is made to it from software (via USB). For the following half-second or so, the bootloader is running on the Uno. While it is programmed to ignore malformed data (i.e. anything besides an upload of new code), it will intercept the first few bytes of data sent to the board after a connection is opened.[9]

Arduino board comparison

[edit]

The following table compares official Arduino boards, and has a similar layout as a table in the Arduino Nano article. The table is split with a dark bar into two high-level microcontroller groups: 8-bit AVR cores (upper group), and 32-bit ARM Cortex-M cores (lower group). Though 3rd-party boards have similar board names it doesn't automatically mean they are 100% identical to official Arduino boards. 3rd-party boards often have a different voltage regulator / different USB-to-UART chip / different color solder mask, and some have a different USB connector or additional features, too.[21]

Board
Name
& Part# 		Board
Size
Group 		Board
Commun-
ication 		MCU
Part#
& Pins 		MCU
I/O
Voltage 		MCU
Core 		MCU
Clock 		MCU
Flash 		MCU
SRAM 		MCU
EEPROM 		MCU
USART
& UART 		MCU
SPI 		MCU
I²C 		MCU
Other Bus
Peripherals 		MCU Timers
32/24/16/8
/WD/RT/RC 		MCU
ADC
& DAC 		MCU
Engines
Uno R3,[22]
A000066,[9]
Uno R3 SMD,[23]
A000073[24] 		Uno USB-B ATmega328P,[14]
28 pin DIP,
32 pin SMD 		5V
(1.8-5.5V) 		8bit AVR 16 MHz* 32 KB 2 KB 1 KB 1, 0 1 1 None 0, 0, 1, 2,
WD 		10bit,
None 		None
Uno WiFi R2,[25]
ABX00021[26] 		Uno USB-B,
WiFi,
Bluetooth 		ATmega4809,[27]
48 pin 		5V
(1.8-5.5V) 		8bit AVR 16 MHz* 48 KB 6 KB 0.25 KB 4, 0 1 1 None 0, 0, 5, 0,
WD, RT 		10bit,
None 		None
Leonardo,[28]
A000057[29] 		Uno USB-Micro-B ATmega32U4,[30]
44 pin 		5V
(2.7-5.5V) 		8bit AVR 16 MHz 32 KB 2.5 KB 1 KB 1, 0 1 1 USB-FS 0, 0, 2, 1,
WD, 10bit 		10bit,
None 		None
Mega 2560 R3,[31]
A000067[32] 		Mega USB-B ATmega2560,[33]
100 pin 		5V
(4.5-5.5V) 		8bit AVR 16 MHz 256 KB 8 KB 4 KB 4, 0 1 1 None 0, 0, 4, 2,
WD 		10bit,
None 		None
Uno R4 Minima,[17]
ABX00080,[34]
Uno R4 WiFi,[18]
ABX00087,[35] 		Uno USB-C,
WiFi* 		R7FA4M1AB,[19]
64 pin 		5V
(1.6-5.5V) 		32bit ARM
Cortex-M4F
(FPU) 		48 MHz 256 KB
+ bootrom 		32 KB
(ECC)
(parity) 		None
+ 8 KB
data flash 		4, 0 2 2 USB-FS,
CAN-A/B 		2, 0, 8, 0,
WD, RC,
24bit SysTick 		14bit,
12bit 		DMA x4,
CRC, RNG,
Crypto, Touch,
LCD
Zero,[36]
ABX00003[37] 		Uno USB-Micro-B
x2 		ATSAMD21G18,[38]
48 pin 		3.3V
(1.62-3.63V) 		32bit ARM
Cortex-M0+ 		48 MHz 256 KB 32 KB None 6, 0 None None USB-FS,
I²S 		0, 4, 5, 0,
WD, RC,
24bit SysTick 		12bit,
10bit 		DMA x12,
CRC32, Touch
Due,[39]
A000062[40] 		Mega USB-Micro-B
x2 		ATSAM3X8E,[41]
144 pin 		3.3V
(1.62-3.6V) 		32bit ARM
Cortex-M3 		84 MHz 512 KB
+ bootrom 		96 KB None 4, 1 1 2 USB-HS,
CAN-A/B x2,
I²S, SD 		3, 0, 8, 0,
WD, RT, RC,
24bit SysTick 		12bit,
12bit x2 		DMA x8,
RNG
GIGA R1 WiFi,[42]
ABX00063[43] 		Mega USB-C,
USB-A,
WiFi,
Bluetooth 		STM32H747XI,[44]
240 pin 		3.3V
(1.62-3.6V) 		32bit ARM
Cortex-M7F
Cortex-M4F
(dual core)
(FPU) 		480 MHz
(M7F),
240 MHz
(M4F) 		2048 KB
+ bootrom 		1056 KB
(ECC) 		None 4, 5 6 4 USB-HS & FS,
CAN-A/B/FD x2,
I²S x4, SD x2,
S/PDIF x4, CEC,
SWP, QSPI 		2, 0, 18, 0,
WD, RC,
24bit SysTick 		16bit x3,
12bit x2 		DMA x4,
CRC, RNG,
Graphics
Table notes
  • Board Size Group column - Simplified board dimension size grouping: Uno means similar size as Arduino Uno R3 and Duemilanove (predecessor) boards, Mega means similar size as the longer Arduino Mega 2560 R3 and Mega (predecessor) boards. This table has a similar layout as a table in the Arduino Nano article.
  • MCU Part# / Pins column - MCU means microcontroller. All MCU information in this table was sourced from official datasheets in this column. The pin count is useful to determine the quantity of internal MCU features that are available. All MCU hardware features may not be available at the shield header pins because the MCU IC package has more pins than the shield header pins on the Arduino board (*).
  • MCU I/O Voltage column - Microcontrollers on official Arduino boards are powered at a fixed voltage of either 3.3 or 5 volts, though some 3rd party boards have a voltage selection switch. The voltage rating of the microcontroller is stated inside parenthesis, though Arduino boards don't support this full range.
  • MCU Clock column - MHz means 106 Hertz. The ATmega328P MPU and ATmega4809 MCU are rated for a maximum of 20 MHz, but the Uno R3 and Uno WiFi R2 boards both operate at 16 MHz. The following Arduino boards have a 32.768 kHz crystal too: Uno WiFi R2, Zero, Due, GIGA R1 WiFi. The Uno R4 Minima has SMD footprints for a 32.768 kHz crystal and two capacitors, but aren't installed.
  • MCU memory columns - KB means 1024 bytes, MB means 10242 bytes. The R7FA4M1AB MCU (Uno R4 boards) contains data flash memory instead of EEPROM memory.
  • MCU SRAM column - SRAM size doesn't include caches or peripheral buffers. ECC means SRAM has error correction code checking, Parity means SRAM has parity checking.
  • MCU USART/UART column - USARTs are software configurable to be a: UART / SPI / other peripherals (varies across MCUs).
  • MCU Other Bus Peripherals column - For USB bus, "FS" means Full Speed (12 Mbit/s max), "HS" means High Speed (480 Mbit/s max). For CAN bus, "A" means CAN 2.0A, "B" means CAN 2.0B, "FD" means CAN-FD. Some buses require additional external circuitry to operate.
  • MCU Timers column - The numbers in this column are the total number of each timer bit width, for example, the ATmega328P has one 16-bit timer and two 8-bit timers. "WD" means Watchdog timer, "RT" means Real Time Counter/Timer, "RC" means Real Time Clock (sec/min/hr). The 24-bit SysTick timer(s) inside the ARM cores aren't included in the 24-bit total in this column. PWM features are not documented in this table.
[edit]
  • Arduino Leonardo board with ATmega32U4 MCU
    Arduino Leonardo board with ATmega32U4 MCU
  • Arduino Mega with ATmega2560 MCU
    Arduino Mega with ATmega2560 MCU
  • Arduino Due board with ATSAM3X8E MCU
    Arduino Due board with ATSAM3X8E MCU
  • Arduino GIGA R1 WiFi board with STM32H747XI MCU
    Arduino GIGA R1 WiFi board with STM32H747XI MCU

See also

[edit]

References

[edit]

Further reading

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Arduino Uno

View on Grokipedia
from Grokipedia
The Arduino Uno is an open-source board based on the ATmega328P, featuring 14 digital pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz quartz crystal, USB connection, a power jack, an ICSP header, and a reset button. It operates at 5V with a 40 mA maximum current per I/O pin and includes 32 KB of , 2 KB of SRAM, and 1 KB of for program storage and data retention. Designed for ease of use, the board can be powered via USB, a DC barrel jack (7-12V recommended), or a dedicated VIN pin, making it suitable for prototyping interactive projects without requiring advanced or complex wiring. Introduced in 2010 at Maker Faire New York, the Arduino Uno evolved from earlier prototypes like the 2005 Arduino Serial and the 2007 Diecimila, which commemorated the sale of 10,000 units and introduced features such as automatic reset circuitry. Developed by a collaborative team of designers, educators, and artists in , it marked 's transition to a standardized, blue-printed circuit board (PCB) design for better branding and reliability, addressing issues like connector misalignment in initial versions. By 2021, the Uno had surpassed 10 million units sold, establishing it as the most popular board in the Arduino family and a cornerstone for the global maker movement. The board family has continued to evolve, with revisions including the Uno R4 released in 2023 featuring a 32-bit processor and the Uno Q in 2025, following Qualcomm's acquisition of in October 2025. Widely adopted in education, hobbyist projects, and professional prototyping, the Uno enables users to sense environmental inputs via sensors and control outputs like lights, motors, and displays through the , which supports programming in C/C++ with simplified syntax. Its replaceable ATmega328P chip facilitates troubleshooting and experimentation, while compatibility with extensive shields and libraries expands its applications in , IoT, and wearable electronics. The board's and software ecosystem, governed by licensing, has democratized access to embedded systems, fostering innovation among beginners and experts alike.

Introduction and Overview

Purpose and Design Philosophy

The Arduino Uno is a board based on the ATmega328P (in its classic versions), designed to facilitate straightforward interfacing with , actuators, and other electronic components for building interactive projects. This platform emphasizes simplicity and accessibility, enabling users to prototype embedded systems without requiring advanced engineering expertise. By integrating a user-friendly programming environment with hardware that supports rapid iteration, the Uno lowers barriers to entry in electronics design and fosters creativity in applications ranging from simple LED circuits to more complex networks. The Arduino project originated in 2005 at the Interaction Design Institute in , where a team of designers and educators sought to create an affordable tool that would empower non-engineers—such as artists, students, and hobbyists—to engage with digital technologies. This initiative addressed the limitations of existing development boards, which were often expensive, proprietary, and intimidating for beginners, by prioritizing ease of use and community-driven innovation. The project's mission, as articulated by co-founder Massimo Banzi, was to "create a world where there are no barriers to technology and innovation," reflecting a commitment to democratizing and prototyping. At its core, the Uno embodies open-source principles for both hardware and software, with freely available schematics, code, and designs licensed under Creative Commons to encourage global collaboration and customization. It features a standardized form factor that supports modular "shields"—expansion boards that stack onto the base for added functionality—along with USB connectivity that handles both power supply and programming without needing specialized drivers. These elements make the Uno particularly suited to its target audience of hobbyists, students, educators, and developers focused on rapid prototyping in Internet of Things (IoT) and embedded systems applications. Later revisions, such as the UNO R4 Minima and UNO R4 WiFi, build on this foundation with enhanced processing while preserving the original philosophy of accessibility. In October 2025, Qualcomm acquired Arduino, launching the UNO Q while pledging to maintain its open-source principles, though this has raised discussions within the community.

Key Features and Compatibility

The Arduino Uno is equipped with 14 digital input/output (I/O) pins, six of which support (PWM) outputs, and six analog input pins, enabling a wide range of integrations and control applications. It features a USB Type-B connector for direct computer communication and powering, a 2.1 mm barrel jack for external DC power input, and an ICSP (In-Circuit Serial Programming) header for advanced programming options. The board's power system supports input via USB at 5V or an external supply of 7-12V recommended (with a limit of 6-20V), providing regulated 5V and 3.3V outputs for powering peripherals at compatible logic levels. With dimensions of 68.6 mm by 53.4 mm, the Uno adheres to the standard Arduino form factor, ensuring seamless compatibility with thousands of expansion shields, such as Ethernet shields for network connectivity and motor control shields for projects. This design promotes within the , allowing users to stack hardware extensions without custom adapters. On the software side, the Uno integrates fully with the Arduino Integrated Development Environment (IDE) in both versions 1.x and 2.x, utilizing a simplified C/C++-like programming language and supporting extensive libraries for peripherals like sensors and displays. As an open-source platform, its hardware schematics and Eagle design files are publicly available under a Attribution-ShareAlike (CC BY-SA) license, facilitating modifications and community-driven enhancements.

History and Development

Origins and Initial Release

The Arduino project originated in 2005 at the Interaction Design Institute (IDII) in , , founded by Massimo Banzi, David Cuartielles, Tom Igoe, David Mellis, and Gianluca Marino to provide an accessible platform for students in interactive art and design programs. The initiative sought to address the high costs and technical complexities of existing tools like the , which priced around $100 and lacked compatibility with common operating systems such as macOS, thereby lowering barriers to prototyping interactive projects. Preceding the Uno were early boards like the Arduino NG and Diecimila, released between 2005 and 2007, which incorporated influences from the Wiring and projects to create a simplified programming environment based on a variant of C/C++. These iterations built a nascent user community while refining hardware for affordability and ease, with the Diecimila marking a milestone of 10,000 units produced. The Arduino Uno debuted in 2010 as a standardized successor, consolidating the pinout for consistency and replacing the USB-to-serial converter from prior boards with the integrated ATmega8U2 chip to enhance reliability and reduce dependency on external drivers. At its core, the initial Uno featured the ATmega328P 8-bit AVR microcontroller running at 16 MHz, offering 32 KB of (with 0.5 KB for the ), 2 KB of SRAM, and 1 KB of , alongside 14 digital I/O pins (6 supporting PWM) and 6 analog inputs. Key motivations included driving costs below $30 per board—comparable to a casual meal—to democratize electronics prototyping, simplifying programming over tools like AVR Studio through an intuitive (IDE), and promoting open-source collaboration to accelerate innovation. The Uno's debut fueled swift uptake within the emerging maker movement, as its plug-and-play empowered novices to build sensors, actuators, and interactive installations, contributing to rapid growth in the ecosystem, with over 250,000 total Arduino boards sold by late 2011, and the introduction of official starter kits around that time to support educational and hobbyist applications.

Evolution of Revisions (R1 to R3)

The Uno R1, released in 2010, marked the initial production version of the board, featuring the ATmega328P and an ATmega8U2 USB-to-serial converter for communication with computers. This revision utilized a mix of through-hole and surface-mount device (SMD) components, providing a straightforward for while supporting 14 digital I/O pins and 6 analog inputs. The ATmega8U2 occasionally presented driver compatibility challenges across operating systems, prompting early refinements in subsequent iterations. In 2011, the transition to the Uno R2 introduced minor (PCB) adjustments primarily aimed at improving manufacturing efficiency, while retaining the core specifications of the R1, including the ATmega328P and ATmega8U2 converter. Key tweaks included repositioning certain components for better assembly flow and adding a 1kΩ pull-down on the hardware watchdog (HWB) line of the USB chip to facilitate easier entry into device firmware update (DFU) mode for troubleshooting. These changes addressed production bottlenecks without altering functionality, maintaining compatibility with existing shields and software. The Uno R3, launched in 2012, represented a major hardware update that solidified the board's reliability and versatility. It replaced the ATmega8U2 with the ATmega16U2 for native USB communication, eliminating external driver dependencies and resolving prior compatibility issues associated with the ATmega8U2 chip. This revision also added dedicated SDA and SCL pins for I2C interfacing adjacent to the AREF pin, alongside an IOREF pin to indicate the operating voltage (5V or 3.3V) for enhanced shield compatibility. Additionally, the R3 shifted to 100% surface-mount components in its SMD variant, enabling for improved durability and cost reductions through optimized production processes. These iterative refinements culminated in the R3 becoming the de facto standard for the Uno series, fostering a robust ecosystem of compatible shields and extensions. By 2021, over 10 million Uno units had been sold worldwide since the 2010 debut, underscoring its enduring impact on , prototyping, and maker projects.

Hardware Specifications

Microcontroller and Processing

The Arduino Uno's core processing is powered by different across its revisions, each tailored to balance performance, power efficiency, and compatibility with the board's 5V operating environment. In revisions R1 through R3, the primary is the ATmega328P, an 8-bit AVR RISC processor from . This chip employs a , featuring separate program memory (Flash) and data memory (SRAM and ) buses to enable simultaneous instruction fetch and data access, optimizing execution efficiency for embedded tasks. Housed in a 28-pin (DIP), the ATmega328P allows for straightforward socketed replacement on the board, facilitating prototyping and repairs. The ATmega328P operates at a fixed clock speed of 16 MHz, driven by an external , delivering up to 16 million (MIPS) in a single-core execution model. It supports comprehensive handling through 26 vectored interrupts, including external pins (INT0/INT1), overflows, and analog-to-digital conversion completions, enabling real-time responses to events like sensor inputs without polling. Lacking a hardware (FPU), floating-point operations are emulated in software via libraries, which incurs a performance overhead but suffices for most hobbyist and educational applications. Power-wise, the draws from the board's 5V supply, with each I/O pin capable of sourcing or sinking up to 40 mA, though sustained operation near this limit requires thermal management to avoid exceeding the chip's 85°C rating. The Uno R4 revision upgrades to the Renesas RA4M1, a 32-bit ARM Cortex-M4 processor, significantly enhancing computational capabilities while maintaining pin compatibility. This microcontroller includes 256 KB of Flash memory for program storage and 32 KB of SRAM for data, supporting more complex sketches and multitasking. Clocked at 48 MHz, it achieves approximately 60 DMIPS (Dhrystone MIPS) performance, leveraging the Cortex-M4's efficient pipeline for faster execution of algorithms involving digital signal processing. The RA4M1 retains single-core operation but incorporates a built-in single-precision FPU compliant with IEEE 754-2008, accelerating floating-point math natively without software emulation. Interrupt support is robust via the Nested Vectored Interrupt Controller (NVIC), handling up to 82 maskable interrupts for precise timing in real-time applications. Operating at the board's 5V level (with internal regulation to 1.6–5.5 V), its I/O pins are rated for a maximum of 8 mA continuous current to ensure reliability under load. In the Uno Q variant, processing shifts to a hybrid architecture centered on the Qualcomm QRB2210 system-on-chip (SoC), a quad-core ARM Cortex-A53 processor at 2.0 GHz for high-performance computing tasks like AI inference and multimedia. This 64-bit ARMv8-A core provides substantial parallelism, with integrated accelerators for vector processing and no dedicated FPU emulation needed due to hardware support for double-precision floating-point via NEON extensions. Memory includes 786 kB SRAM on the STM32U585 MCU alongside 2 GB external LPDDR4 RAM, enabling Linux-based operations alongside real-time MCU duties handled by an auxiliary STM32U585. Interrupts are managed through the ARM Generic Interrupt Controller (GIC), supporting hundreds of sources for low-latency event handling in demanding scenarios. The SoC operates within the 5V board envelope but uses 1.8 V I/O rails, with per-pin current limited to 20 mA to prevent thermal throttling, as the high clock speeds generate notable heat under full load. This setup integrates seamlessly with the board's USB interface for programming and data transfer.

Memory, Power, and Connectivity

The Arduino Uno's memory architecture varies across revisions, providing sufficient capacity for typical embedded applications. In the original R1 to R3 models, the offers 32 KB of , of which 0.5 KB is reserved for the , alongside 2 KB of SRAM for runtime data and 1 KB of for non-volatile storage that persists through power cycles. The R4 revision significantly expands this with the Renesas RA4M1 , delivering 256 KB of and 32 KB of SRAM, while also providing 8 KB of emulated for enhanced data handling in more complex sketches. The UNO Q variant further augments storage with 16 GB of eMMC for file systems and operating system support, complemented by 2 GB LPDDR4 RAM, enabling Linux-based applications alongside tasks. Power management on the Arduino Uno ensures reliable operation across diverse supply sources, with an onboard converting inputs to a stable 5 V output for the and peripherals. R1-R3 models can draw up to 500 mA from a USB connection, automatically switching to this source when connected, while the barrel jack accepts 7-20 V DC inputs—though 9 V is recommended for optimal performance—with the regulator handling dropout voltages as low as 1.7 V to maintain stability under load; later revisions like the UNO Q support up to 3 A via and 7-24 V on VIN. Low-power modes, including and power-down states on the , reduce consumption to as little as 0.1 mA, facilitating battery-powered projects by minimizing quiescent current. Connectivity on the Uno centers on straightforward interfaces for programming and expansion, starting with a USB 2.0 full-speed port operating at 12 Mbps for and sketch uploads in early revisions. An ICSP header enables via SPI for direct loading or recovery, complemented by a manual reset button to trigger reboots or enter programming mode. The R4 introduces a native connector with built-in HID support, allowing the board to emulate keyboards or mice without additional hardware for USB-based interactions. In the Q model, connectivity expands to include 5 (dual-band) for wireless networking and 5.1 for low-energy device pairing, integrating these alongside the traditional USB and ICSP for versatile IoT deployments. For analog-to-digital conversion, the Uno provides an internal 1.1 V voltage reference on R1-R3 models to improve precision in low-voltage measurements, selectable via software, while the dedicated AREF pin allows connection of an external reference up to 5 V for custom scaling in sensor applications. Later revisions, including R4 and , retain compatibility with these references but benefit from the enhanced microcontroller's higher-resolution ADC capabilities. The board's environmental specifications support robust operation in varied conditions, with an range of -40°C to 85°C across industrial-grade components in revisions from R3 onward, ensuring reliability in automotive or outdoor prototypes without additional thermal management.

Board Layout and Dimensions

The board adheres to a standardized form factor measuring 68.6 in length, 53.4 in width, and approximately 7 in thickness, including components, with a of 25 g. This compact rectangular design includes four mounting holes at the corners, positioned 1.8 from the edges and spaced 58.5 apart lengthwise and 45.7 widthwise, facilitating secure attachment to breadboards, enclosures, or project bases. The pin headers follow a 0.1-inch (2.54 ) spacing standard, ensuring seamless compatibility with solderless breadboards and the stacking of expansion shields via extended male pins. On the top side of the Uno Rev3, the layout prominently features two parallel rows of 0.1-inch pitch pin headers: one for 14 digital I/O pins (including 6 PWM-capable) and power/ground, and another for 6 alongside additional power and ground pins. Centered nearby are the USB Type-B port for and powering, a 2.1 mm x 5.5 mm barrel jack for external DC input, a reset , and built-in LED indicators for power status, TX/RX activity, and digital pin 13 operation. The Rev3 revision introduced dedicated breakout pads adjacent to the analog header for I2C pins (SDA on A4 and SCL on A5), enhancing accessibility without requiring jumper wires. The bottom side of the Rev3 board hosts the core components, including the surface-mount centrally placed, the ATmega16U2 USB-to-serial converter chip near the USB area, a 16 MHz for clock generation, the NCP1117 or similar linear for 5V output, and various SMD resistors, capacitors, and a fuse for power protection. This arrangement optimizes space while maintaining thermal dissipation and shielding for the microcontroller. Subsequent revisions maintain the core form factor for but introduce layout refinements. The Uno R4 series (Minima and variants) retains dimensions of approximately 68.85 mm x 53.34 mm, with the USB port upgraded to Type-C in the same end-position for improved connectivity, though the slimmer profile aids in stacked setups. Key additions include a larger QSPI NOR flash chip (up to 16 MB in ) on the bottom for expanded storage and, on the top of the model, a 12x8 LED matrix display between the headers for on-board visual prototyping. The Renesas RA4M1 and ESP32-S3 module (in ) are positioned on the bottom, similar to prior MCUs, alongside updated SMD passives and a Qwiic connector on the top edge for I2C expansions. The Uno Q variant preserves the UNO form factor at 68.85 x 53.34 but incorporates hybrid layout elements for advanced integration, featuring high-speed edge connectors on the sides for camera modules (via dual MIPI CSI interfaces supporting up to 13 MP sensors) and display/audio peripherals, alongside a port and Qwiic connector on the top. The bottom accommodates the Qualcomm QRB2210 SoC with integrated Adreno GPU (potentially requiring a heatsink for sustained loads) and the STM32U585 real-time MCU, with SMD components clustered for efficient power distribution across 5V, 3.3V, and 1.8V rails. An 8x13 blue LED matrix and four RGB user LEDs are arrayed on the top surface near the headers, promoting visual feedback in AI and projects.

Pinout and Interfaces

Digital and Analog Pins

The Arduino Uno is equipped with 14 digital pins, labeled 0 through 13, that serve as general-purpose I/O (GPIO) for bidirectional signal handling. These pins operate at 5V logic levels and are tolerant to input voltages up to 5V, allowing direct interfacing with 5V sensors and modules. Each pin can source or sink up to 40 mA of current as an absolute maximum rating, though the recommended continuous current is 20 mA per pin to ensure reliable operation and prevent damage to the ATmega328P ; the total current across all pins should not exceed 200 mA. Pins 3, 5, 6, 9, 10, and 11 support (PWM) output at 8-bit resolution, at approximately 980 Hz on pins 5 and 6 and 490 Hz on pins 3, 9, 10, and 11, enabling approximate analog output for applications such as LED dimming or motor speed control. Internal pull-up resistors, ranging from 20 to 50 kΩ, can be enabled on these digital pins via software commands, providing weak pull-up functionality for input configurations without external components. While these pins support for additional functions—such as UART on pins 0 (RX) and 1 (TX)—their primary role is as flexible GPIO for custom digital interfacing. In addition to digital capabilities, the Uno provides 6 analog input pins, designated A0 through A5, which connect to a 10-bit successive analog-to-digital converter (ADC). This ADC samples voltages from 0 to 5V, producing digital values ranging from 0 to 1023 (1024 discrete levels), with a default reference voltage derived from the 5V supply. These analog pins can also function as digital I/O, mapping to digital pins 14 through 19 in software, expanding the total GPIO count when analog input is not required. Subsequent revisions introduce enhancements to these I/O features while maintaining . The Uno R4 variants upgrade the analog inputs to support up to 12-bit resolution (4096 levels) by default, with configurable options extending to 14-bit resolution via , and achieve sampling rates up to 1 MSPS for higher-precision signal acquisition. Digital pins on the R4 operate at 3.3V internal logic levels but remain 5V tolerant, with reduced per-pin current limits of approximately 8 mA recommended to accommodate the Renesas RA4M1 microcontroller's specifications. The Uno Q, released in October 2025 as a hybrid board combining a Qualcomm QRB2210 MPU for Linux-based tasks with an STM32U585 MCU for real-time control, provides 6 analog inputs (A0-A5) using the MCU's 12/14-bit SAR ADC at 3.3 V (not 5 V tolerant), while retaining 3.3V logic levels across its design.

Power and Ground Pins

The Arduino Uno features dedicated power pins for supplying regulated voltages to external components and the board itself. The 5V pin delivers a stable 5V output from the onboard , with a capacity of up to 500 mA when powered via USB, limited by the on the USB line. This pin is intended as an output for powering shields or sensors but should not be used as an input to avoid bypassing and damaging the regulator. The 3.3V pin provides a regulated 3.3V supply via a separate onboard regulator, limited to a maximum current of 50 mA in the Uno Rev3 to prevent overheating. The Vin pin serves as the input for external power supplies, accepting 7-12V recommended (6-20V limit) directly before the 5V regulator, allowing the board to operate independently of USB. The USB power input includes a 500 mA positive temperature coefficient (PTC) resettable fuse for overcurrent protection, while the DC barrel jack and Vin lack reverse polarity protection, requiring careful polarity observance. Ground pins are essential for completing circuits and providing return paths, with multiple GND connections—two on each side of the board—distributed to offer low-impedance paths and reduce electromagnetic interference. These are particularly important for analog circuits, where noise can affect readings. In the Uno Rev3 and later revisions, a dedicated analog ground (AGND) pin is available next to the analog inputs, recommended for connecting analog sensors to minimize digital noise coupling, though it connects internally to the main GND plane. In variants like the Uno R4, the 3.3V output capacity increases to 150 mA due to an improved regulator design. The 2025-released Uno Q introduces a 1.8V rail optimized for low-power sensors and high-speed interfaces, alongside programmable power domains that allow voltage-separated I/O banks (1.8V for processor signals and 3.3V for maker headers) to enhance efficiency and compatibility.

Specialized Headers (I2C, SPI, UART)

The Arduino Uno provides dedicated pins and headers for the I2C (also known as TWI on ), SPI, and UART protocols, facilitating communication with sensors, displays, and other modules in embedded systems. These interfaces are mapped to specific digital pins on the board, with configurations handled via the Arduino Wire, SPI, and Serial libraries, respectively. For I2C communication, the Uno uses pins A4 as SDA (data line) and A5 as SCL (clock line), supporting the standard two-wire open-drain bus . The interface operates in standard mode at 100 kHz or fast mode at up to 400 kHz, with 7-bit addressing for up to 128 devices (extendable to 10-bit for more). External pull-up resistors, typically 4.7 kΩ, are required on both SDA and SCL to ensure proper signal levels, as the lines are pulled low by devices during transmission. The SPI interface employs a full-duplex master-slave architecture with dedicated pins: 11 for MOSI (master out, slave in), 12 for MISO (master in, slave out), 13 for SCK (serial clock), and 10 for SS (slave select). It supports all four SPI modes (0 through 3), configurable via clock polarity and phase, and achieves clock speeds up to 8 MHz in master mode at the board's 16 MHz system clock. Slave mode is also available for bidirectional communication with peripherals like SD cards or displays. UART, implemented as a single asynchronous serial port on the classic Uno, utilizes pin 1 for TX (transmit) and pin 0 for RX (receive), with common baud rates ranging from 9600 to 115200 bps and support for up to 1 Mbps depending on the clock. It employs 8 data bits, no parity, and 1 stop bit by default, but lacks built-in hardware flow control, relying on software for . In the Uno R4 variants, support for multiple UARTs is provided, with the primary on pins 0 (RX) and 1 (TX), and additional UARTs configurable on other pins via software. These protocols are exposed through standard 0.1-inch headers on the board edges, with the 6-pin ICSP (In-Circuit Serial Programming) header providing access to SPI signals (, MOSI, SCK, RESET, VCC, GND) primarily for programming or direct flashing. Starting with the Uno R3 revision, dedicated I2C breakout pads are available near the analog pins for easier shielding integration. The Uno Q (2025 release) extends this with a MIPI CSI connector for interfacing, supporting multi-lane serial data transfer at up to 1.8 V signaling. These headers enable straightforward shield stacking for modular expansions like arrays or communication modules. Voltage levels for these interfaces are 5 V logic on classic Uno boards (Rev3 and earlier), compatible with many legacy components but requiring level shifters for 3.3 V devices. The Uno R4 and Q variants operate at 3.3 V logic levels but remain 5 V tolerant on key input pins, including I2C and SPI, to directly interface with modern low-voltage sensors and modules without additional conversion circuitry.

Programming and Operation

Software Environment and IDE

The Arduino Integrated Development Environment (IDE) serves as the primary software tool for programming the Uno, providing a cross-platform editor compatible with Windows, macOS, and operating systems. It integrates essential functionalities including a code editor with and , a based on the AVR-GCC , an uploader for transferring sketches to the board, and a built-in serial monitor for communication. Additionally, the IDE features a serial plotter for visualizing data and a boards manager that allows users to install support for various Arduino board variants without manual configuration. The programming language used in the Arduino IDE is a simplified of C/C++, tailored for applications through the Arduino API, which includes predefined functions, variables, and structures for hardware interaction. Sketches follow a standard structure with two main functions: setup(), which runs once at startup to initialize pins, , and libraries, and loop(), which executes repeatedly for the core program logic. Core libraries, such as Wire for I2C communication, are pre-compiled and included to simplify peripheral control, enabling users to extend functionality with additional libraries managed directly within the IDE. Installation of the Arduino IDE begins with downloading the latest version from the official Arduino website, available as an installer for Windows (version 10 or later, 64-bit), a drag-and-drop application for macOS (version 10.15 or later), or an AppImage for Linux (64-bit distributions like Ubuntu). After installation, users select "Arduino Uno" from the boards menu in the Tools section; for clones using alternative USB chips, additional drivers such as those for the CH340 (common in third-party boards) or the native ATmega16U2 (in official Uno Rev3) may need manual installation via the operating system's device manager to ensure USB-to-serial recognition. The IDE's boards manager then facilitates adding packages for Uno variants, streamlining setup for diverse hardware. For more complex projects, advanced tools complement the standard IDE, including PlatformIO, an open-source ecosystem that integrates with to offer enhanced features like project templates, library dependency management, , and multi-board compilation support for frameworks. Similarly, extensions for provide autocomplete and debugging capabilities, while avrdude—the command-line AVR underlying the IDE's upload process—allows direct firmware flashing for low-level customization. IDE 2.x extends compatibility to newer variants, incorporating USB stack updates for the Uno R4's Renesas RA4M1 microcontroller and Wi-Fi libraries for the Uno Q's Qualcomm QRB2210 processor, enabling seamless integration of connectivity features like over-the-air updates.

Bootloader and Automatic Reset

The bootloader on the Arduino Uno is a small program pre-installed in the microcontroller's flash memory that facilitates the uploading of user sketches via the USB connection without requiring external programmers. For the Uno Revision 3 (R3) and later, it utilizes Optiboot, a compact bootloader occupying 512 bytes of the ATmega328P's 32 KB flash memory, which leaves more space for user code compared to earlier versions. This bootloader listens for incoming serial data at 115200 baud and, if no valid upload sequence is detected within a timeout period of approximately 1 second (configurable up to 8 seconds in some variants), it automatically jumps to the start of the user sketch in the main program memory. In contrast, the original Uno Revision 1 (R1) employed the larger ATmegaBOOT bootloader, which required 2 KB of flash memory and operated at a slower 19200 baud rate, resulting in longer upload times. To enable seamless integration with the Arduino IDE for programming, the Uno incorporates an automatic reset mechanism triggered by the USB-to-serial converter chip. A 100 nF (0.1 µF) capacitor connects the (DTR) signal line of the ATmega16U2 (or ATmega8U2 in R1) to the microcontroller's RESET pin, converting the DTR signal toggle—initiated when the IDE opens the —into a brief low pulse on the RESET line. This pulse resets the ATmega328P, allowing the to take control and prepare for sketch upload. Additionally, a manual reset option is provided via an onboard switch that momentarily grounds the RESET pin, pulling it low for at least 10 ms to ensure a reliable reset cycle, as recommended for stable operation of the ATmega328P. In later variants, these mechanisms have evolved to leverage native USB capabilities and enhanced security. The Uno R4 series, based on the Renesas RA4M1 , features a ROM-based that supports direct USB Communication Device Class (CDC) for , eliminating the need for a separate USB-serial chip and the associated DTR-based automatic reset. Similarly, the 2025-released Uno Q integrates a Qualcomm Dragonwing QRB2210 alongside an STM32U585 MCU, employing a secure powered by the SDK to verify integrity before execution, which includes hardware root-of-trust features for protected uploads. Common troubleshooting for the reset circuit involves issues like unintended double resets during serial operations, often due to timing mismatches in the DTR or capacitor discharge. This can manifest as the board resetting twice in quick succession when the IDE connects, disrupting uploads; a solution is to temporarily add a larger (e.g., 10 µF) between the RESET pin and ground to filter out spurious s, or in advanced setups, remove or jumper the onboard reset-enabling trace for custom control.

Uploading Sketches and Debugging

The process of uploading sketches to the Arduino Uno involves using the Arduino IDE to compile the user's C/C++ code into a hexadecimal (HEX) file, which is then transferred to the board's flash memory via USB. To begin, the user selects the "Arduino Uno" board from the Tools > Board menu and the appropriate serial port from Tools > Port, ensuring the board is connected to the computer. Compilation is initiated by clicking the verify button (checkmark icon), which checks for syntax errors and reports the sketch size; for the Uno R3, sketches must not exceed approximately 32 KB to fit within the ATmega328P's 32 KB flash memory, leaving room for the bootloader (typically verified as under 30 KB for safe uploads). Once verified, clicking the upload button (right arrow icon) initiates the transfer, during which the board's built-in LEDs indicate progress, and the process completes in 5-10 seconds on average, displaying "Done uploading" upon success. The bootloader plays a brief role in this workflow by automatically handling the incoming HEX file and writing it to flash without requiring manual intervention. Common errors during upload often stem from incorrect board or selection, leading to messages like "No device found on selected ," which can be resolved by restarting the IDE with the board connected or verifying the in the operating system's (e.g., COM ports on Windows). Insufficient USB power, particularly when powering peripherals, may cause timeouts or failures, fixable by connecting an external 7-12V supply to the barrel jack while maintaining USB for . Driver issues, such as unrecognized devices on Windows or permission errors on , are addressed by installing the latest or CH340 drivers from the manufacturer's site or adding the user to relevant groups (e.g., dialout on ). Low USB power scenarios are especially prevalent with long cables or hubs, where switching to a powered hub or direct connection resolves the issue. Debugging on the classic Arduino Uno relies on software-based techniques due to the lack of native hardware debugging support on the ATmega328P AVR . The most common method is using Serial.print() or Serial.println() statements in the sketch to output variable values, execution traces, or status messages to the Serial Monitor in the IDE, opened via Tools > Serial Monitor at 9600 (the default rate); for example, Serial.println("Loop iteration: " + String(counter)); logs a counter variable. To indicate code progress without serial overhead, the built-in LED on pin 13 (defined as LED_BUILTIN) serves as a simple heartbeat or status indicator, toggled with digitalWrite(LED_BUILTIN, HIGH); followed by a delay. For more advanced hardware debugging, external tools like the Atmel-ICE probe connect via the board's ISP header to enable in-circuit programming and basic breakpoints, though is not natively supported—requiring ISP mode instead. Over-the-air (OTA) updates are absent in the classic Uno due to no built-in wireless capability, but conditional compilation using #define directives allows platform-specific code variants, such as #ifdef DEBUG Serial.print("Debug info"); #endif, compiled only when the flag is set. In variants like the Uno R4, built-in debugger support is enhanced through Serial Wire Debug (SWD) pins, allowing connection of a Segger J-Link probe for real-time inspection of registers, memory, and breakpoints directly via the Arduino IDE 2 or Segger software. The Uno Q, released in 2025, supports remote debugging and OTA updates over its dual-band 5 connectivity through integration with Arduino App Lab and cloud services, enabling hybrid MPU-MCU workflows leveraging the QRB2210 processor.

Variants and Comparisons

Uno R4 Specifications and Upgrades

The Uno R4 was released in June 2023 as the fourth major revision of the classic Uno board, introducing significant hardware enhancements while maintaining core compatibility with the . It is available in two variants: the Minima, a cost-effective option without connectivity, and the WiFi, which incorporates an ESP32-S3 for built-in and capabilities. Both variants center around the Renesas RA4M1 , a 32-bit Cortex-M4 operating at 48 MHz, marking a shift from the 8-bit ATmega328P used in prior Uno models. This upgrade provides approximately three times the speed of the Uno R3, enabling more efficient handling of demanding applications such as and signal generation. Key specifications include 256 KB of and 32 KB of SRAM, a substantial increase from the 32 KB flash and 2 KB SRAM of earlier versions, allowing for larger sketches and more complex programs without external . The board features a connector for improved connectivity and charging, replacing the older micro-USB port, while supporting input voltages from 6-24 V via the VIN pin or barrel jack. Analog capabilities are enhanced with a 12-bit (DAC) on pin A0 for precise waveform generation, such as in audio projects, and a 12-bit (ADC) across six input channels, offering higher resolution than the 10-bit ADC of previous Unos. Additionally, the RA4M1 includes support for the Controller Area Network ( protocol on pins D4 and D5, requiring an external for full implementation, which facilitates integration with automotive and industrial systems. New features emphasize expanded functionality and reliability. The board incorporates a high-speed 48 MHz oscillator for stable clocking, a (RTC) with battery backup via a dedicated CR1220 holder for persistent timekeeping even when powered off, and 6 (PWM) pins (D3, D5, D6, D9, D10, D11)—the same as the Uno R3, though the advanced MCU timers enable PWM on additional pins with custom code—for control in motor driving and LED dimming applications. The WiFi variant adds the ESP32-S3 module, programmable separately through exposed headers, enabling IoT projects with 802.11 b/g/n and without compromising the main MCU's performance. Both models also support (HID) functionality over USB, allowing the board to emulate devices like keyboards or mice directly. Backward compatibility is a core design principle, ensuring seamless transition for existing projects. The Uno R4 retains the same physical form factor (68.6 x 53.4 mm) and pinout as prior Uno boards, including 14 digital I/O pins, six analog inputs, and standard headers for I2C, SPI, and UART, making it fully compatible with Uno shields and accessories. It operates at 5 V logic levels to match legacy 5 V-based circuits, with no need for level shifters in most cases, though some AVR-specific libraries may require updates due to the architectural change. These upgrades position the Uno R4 as a more capable platform for advanced prototyping, particularly in areas like audio synthesis and networked sensing, while preserving the accessibility that defines the Uno family.

Uno Q (2025 Release) Features

The Uno Q was announced on October 7, 2025, following the completion of Technologies' acquisition of in November 2025, marking a to integrate advanced edge AI capabilities into the ecosystem. Priced at $44 for the base model, the board represents a shift toward for developers, combining a Linux-capable system-on-chip (SoC) with a dedicated for real-time operations. This release builds on the Uno R4's foundation by introducing hybrid processing for AI-driven applications. At its core, the Uno Q features the Dragonwing QRB2210 SoC, which includes a quad-core processor clocked at up to 2.0 GHz, paired with an 702 GPU operating at 845 MHz for graphics and compute tasks. The SoC also incorporates a dual-core (DSP) for AI acceleration, enabling efficient on-device inference. Complementing this is a low-power from , which handles real-time control functions independently. Memory specifications include 2 GB of LPDDR4 RAM and 16 GB of eMMC storage in the base configuration, with optional upgrades to 4 GB RAM and 32 GB storage available. Key features emphasize edge AI and connectivity, including support for through a MIPI CSI-2 camera interface capable of handling up to 12 MP sensors for tasks like . Wireless options comprise 5 (dual-band 2.4/5 GHz) with an onboard antenna and 5.1 for low-energy applications. The board retains Arduino compatibility via a 40-pin header that exposes GPIO, PWM, and ADC pins, with up to 26 GPIOs available from the STM32U585 for expanded I/O. An optional -based operating system, such as Yocto Linux, allows for running complex applications, while the integrated GPU and NPU support frameworks like TensorFlow Lite for lightweight AI models. Upgrades in the Uno Q focus on blending real-time control with edge AI processing, enabling seamless integration of sensor data and inference without cloud dependency—for instance, deploying models for audio or vision analytics directly on the board. Compatibility with modems is supported through expansion interfaces, though not built-in, allowing for future-proof IoT deployments. Integration with Arduino Cloud provides over-the-air (OTA) updates and remote management, streamlining prototyping workflows. This evolution targets a transition from hobbyist projects to professional IoT and AI prototyping, empowering developers to build sophisticated systems like smart cameras or autonomous devices with the familiarity of the Arduino platform.

Comparison with Other Arduino Boards

The Arduino Uno serves as an entry-level board in the Arduino ecosystem, but its suitability varies compared to other models depending on project requirements such as size, pin availability, and specialized features. Compared to the , the Uno offers a larger form factor (68.6 x 53.4 mm versus the Nano's compact 45 x 18 mm), making it more suitable for prototyping and integration, while both share the same ATmega328P , 16 MHz clock speed, 14 digital pins, and 6 PWM pins; however, the Nano provides 8 analog inputs to the Uno's 6, prioritizing portability for embedded applications. In contrast to the Arduino Mega 2560, which features 54 digital pins (15 PWM) and 16 analog inputs powered by the ATmega2560 with 256 KB , the Uno's simpler design with 14 digital pins (6 PWM) and 6 analog inputs on the ATmega328P (32 KB flash) suits beginner and educational projects, while the Mega excels in complex, multi-sensor setups; the Uno is also more affordable at approximately $28 versus the Mega's $50. The Arduino Leonardo differs from the Uno by using a single ATmega32u4 to handle both sketches and native USB communication, enabling advanced HID functionalities like keyboard or emulation without a separate USB-to-serial chip, whereas the Uno relies on an external chip (ATmega16U2) for USB; both boards share similar dimensions and clock speeds, but the Leonardo offers 20 digital pins (7 PWM) and 12 analog inputs. Within the Uno family, the Rev3 variant provides basic 8-bit performance for introductory tasks, the R4 upgrades to a 32-bit Renesas RA4M1 MCU at 48 MHz for enhanced speed and memory (256 KB flash), and the 2025-released Uno Q introduces AI capabilities via a QRB2210 processor with GPU acceleration, support, and integrated for ; all variants prioritize pin compatibility to ease transitions.
BoardDigital PinsMCU TypeClock SpeedApprox. PricePrimary Use Cases
Uno Rev314 (6 PWM)8-bit AVR16 MHz$28Education, basic prototyping
Nano14 (6 PWM)8-bit AVR16 MHz$26Compact embedded projects
Mega 256054 (15 PWM)8-bit AVR16 MHz$50Complex multi-device systems
Leonardo20 (7 PWM)8-bit AVR16 MHz$25HID devices, USB-native apps
Uno R414 (6 PWM)32-bit 48 MHz$25Performance-intensive tasks
Uno Q14 (6 PWM) + hybrid64-bit Qualcomm + 32-bit Up to 2.0 GHz$44AI and

Applications and Extensions

Common Use Cases

The Arduino Uno serves as a foundational tool in educational environments, particularly for introducing students to programming and through hands-on programs from K-12 to higher education. Simple projects, such as blinking an LED to demonstrate digital output control or reading data from sensors like probes, allow learners to grasp concepts of coding, circuits, and operations in classroom settings. These activities are supported by official kits, including the Arduino Starter Kit, which includes the Uno for and coding projects. In prototyping, the Uno facilitates rapid development of embedded systems, enabling makers to iterate on ideas like setups that monitor environmental conditions using DHT11 sensors for and readings. It is also commonly employed in basic prototypes, where servo motors are controlled for movements in small-scale mechanisms, leveraging the board's PWM pins and extensive ecosystem for quick testing before scaling to custom hardware. This versatility has led to several commercial products originating as Uno prototypes, highlighting its role in efficient design validation. For introductory IoT applications, the Uno connects sensors and actuators to the using add-on shields, such as Ethernet modules for transmission or SD card modules for local logging of sensor readings. These setups support basic remote monitoring systems, where from peripherals like humidity sensors is sent to platforms like Arduino IoT for visualization and alerts. The board's simplicity makes it accessible for developing connected devices without complex networking expertise. The Uno R4 variant extends capabilities into audio synthesis, utilizing its enhanced 12-bit DAC to generate waveforms for monophonic synthesizers and MIDI-controlled sound production via libraries like Mozzi. Meanwhile, the 2025 Uno Q release incorporates a Dragonwing SoC with integrated GPU and image signal processors, enabling tasks such as through camera interfaces for and . Despite these strengths, the Uno has limitations for high-speed or real-time applications, as its single-threaded, polling-based restricts multitasking in scenarios like UAV control or precise timing without supplemental shields or RTOS extensions. Additionally, its power consumption—typically 42-54 mA in active mode—makes it inefficient for prolonged battery operation, often requiring external regulators or low-power modes to extend runtime beyond a few days on standard packs.

Shield Compatibility and Expansion

The Arduino Uno supports expansion through stackable add-on modules known as shields, which are printed circuit boards designed to plug directly into the board's pin headers, providing additional functionality such as connectivity, sensing, or actuation without requiring custom wiring. These shields adhere to the Arduino shield specification, ensuring mechanical and electrical compatibility with the Uno's form factor. For instance, the Proto Shield Rev3 allows users to prototype custom circuits by soldering components or integrating a breadboard directly onto the shield. Similarly, the Sensor Shield V5 simplifies wiring for multiple sensors by breaking out digital, analog, and I2C pins into terminal blocks or headers, enabling easy connections for environmental or motion sensors. Compatibility for the Uno R3 and later revisions relies on the standard 0.1-inch (2.54 mm) pin spacing and power distribution via bridging jumpers, which allow shields to draw power from the Uno's 5V regulator or an external source to avoid overloading the onboard circuitry. The Uno R4 Minima and WiFi variants maintain full with R3-era shields while introducing dedicated passthrough headers for SPI and I2C buses, permitting stacked shields to access these interfaces without signal interruption. The Uno Q, released in 2025, preserves this shield ecosystem compatibility, leveraging its hybrid architecture to support expansion in compute-intensive applications. Among popular shields, the Arduino Motor Shield Rev3 employs dual L298P full-bridge drivers to control DC motors and stepper motors, delivering up to 2A per channel for and tasks. For wireless connectivity, ESP8266-based shields, such as the SparkFun ESP8266 WiFi Shield, enable 802.11 b/g/n networking and TCP/IP stack integration, facilitating IoT projects with minimal code changes. Display options include LCD shields like the Adafruit LCD Shield Kit, which uses an I2C interface to drive a 16x2 character LCD and keypad with just two pins, conserving digital I/O resources. Expansion is constrained by the Uno's power delivery—limited to approximately 500 mA from the 5V regulator—and , making it impractical to stack more than 5-7 shields without external power injection or cooling, as cumulative current draw and buildup can cause or component failure. For non-stackable modules or exceeding these limits, breadboards or jumper wires provide alternative expansion via the Uno's GPIO pins. The Uno Q extends these capabilities by integrating with the ecosystem, supporting AI modules for in through its QRB2210 processor and environment.

References

  1. https://docs.arduino.cc/hardware/uno-rev3
  2. https://blog.arduino.cc/2021/12/09/one-board-to-rule-them-all-history-of-the-arduino-uno/
  3. https://blog.arduino.cc/2023/03/25/arduino-uno-r4/
  4. https://www.qualcomm.com/news/releases/2025/10/qualcomm-to-acquire-arduino-accelerating-developers--access-to-i
  5. https://store-usa.arduino.cc/products/uno-q
  6. https://www.arduino.cc/en/Guide/BoardAnatomy
  7. https://www.arduino.cc/en/about
  8. https://www.arduino.cc/about
  9. https://spectrum.ieee.org/the-making-of-arduino
  10. https://www.qualcomm.com/news/releases/2025/10/qualcomm-to-acquire-arduino-accelerating-developers-access-to-i
  11. https://spectrum.ieee.org/qualcomm-arduino-acquisition-open-source
  12. https://store.arduino.cc/products/arduino-uno-rev3
  13. https://docs.arduino.cc/tutorials/uno-r4-minima/shield-compatibility
  14. https://www.arduino.cc/en/software
  15. https://support.arduino.cc/hc/en-us/articles/4415094490770-Licensing-for-products-based-on-Arduino
  16. https://www.arduino.cc/en/Main/Boards
  17. https://startingelectronics.org/articles/arduino/uno-r3-r2-differences/
  18. https://store-usa.arduino.cc/products/arduino-uno-rev3-smd
  19. https://blog.arduino.cc/2021/11/24/introducing-the-arduino-uno-mini-limited-edition-pre-orders-now-open/
  20. https://docs.arduino.cc/resources/datasheets/Atmel-42735-8-bit-AVR-Microcontroller-ATmega328-328P_Datasheet.pdf
  21. https://store-usa.arduino.cc/products/arduino-uno-rev3
  22. https://docs.arduino.cc/hardware/uno-r4-minima
  23. https://www.renesas.com/en/document/dst/ra4m1-group-datasheet
  24. https://store-usa.arduino.cc/products/uno-r4-minima
  25. https://docs.arduino.cc/hardware/uno-q
  26. https://support.arduino.cc/hc/en-us/articles/9350551575964-What-s-the-difference-between-UNO-R3-and-UNO-R4-boards
  27. https://docs.arduino.cc/resources/datasheets/ABX00162-datasheet.pdf
  28. https://docs.arduino.cc/learn/electronics/power-pins/
  29. https://docs.arduino.cc/learn/programming/memory-guide/
  30. https://docs.arduino.cc/tutorials/uno-r4-minima/cheat-sheet
  31. https://support.arduino.cc/hc/en-us/articles/360018922239-About-the-AREF-pin
  32. https://support.arduino.cc/hc/en-us/articles/360016076980-What-is-the-operating-temperature-range-for-Arduino-boards
  33. https://docs.arduino.cc/resources/datasheets/A000066-datasheet.pdf
  34. https://docs.arduino.cc/hardware/uno-r4-wifi
  35. https://docs.arduino.cc/resources/datasheets/ABX00087-datasheet.pdf
  36. https://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-7810-Automotive-Microcontrollers-ATmega328P_Datasheet.pdf
  37. http://www.righto.com/2009/07/secrets-of-arduino-pwm.html
  38. https://docs.arduino.cc/tutorials/uno-r4-minima/adc-resolution
  39. https://www.st.com/resource/en/datasheet/stm32u585ai.pdf
  40. https://www.arduino.cc/en/uploads/Main/arduino-uno-schematic.pdf
  41. https://docs.arduino.cc/resources/pinouts/A000067-full-pinout.pdf
  42. https://docs.arduino.cc/tutorials/uno-q/power-specification/
  43. https://docs.arduino.cc/learn/communication/wire
  44. https://docs.arduino.cc/learn/communication/spi
  45. https://docs.arduino.cc/learn/communication/uart
  46. https://ww1.microchip.com/downloads/en/DeviceDoc/ATmega48A-PA-88A-PA-168A-PA-328-P-DS-DS40002061A.pdf
  47. https://docs.arduino.cc/software/ide/
  48. https://docs.arduino.cc/software/ide-v2/tutorials/getting-started-ide-v2
  49. https://docs.arduino.cc/learn/starting-guide/getting-started-arduino/
  50. https://docs.arduino.cc/software/ide-v2/tutorials/getting-started/ide-v2-downloading-and-installing
  51. https://docs.arduino.cc/tutorials/generic/DriverInstallation/
  52. https://docs.platformio.org/en/latest/frameworks/arduino.html
  53. https://docs.arduino.cc/tutorials/uno-r4-wifi/r4-wifi-getting-started
  54. https://github.com/Optiboot/optiboot
  55. https://www.arduino.cc/en/Hacking/Bootloader
  56. https://forum.arduino.cc/t/question-on-difference-between-bootloaders/155516
  57. https://www.arduino.cc/en/uploads/Main/Arduino_Uno_Rev3-schematic.pdf
  58. https://www.arduino.cc/product-uno-q
  59. https://forum.arduino.cc/t/arduinoisp-on-uno-requires-10uf-cap-why/102111
  60. https://docs.arduino.cc/learn/starting-guide/the-arduino-software-ide/
  61. https://forum.arduino.cc/t/arduino-uno-sketch-limit-size/28791
  62. https://docs.arduino.cc/learn/starting-guide/troubleshooting-sketches/
  63. https://docs.arduino.cc/learn/microcontrollers/debugging/
  64. https://docs.arduino.cc/software/ide-v2/tutorials/ide-v2-serial-monitor
  65. https://docs.arduino.cc/tutorials/uno-r4-minima/debugger/
  66. https://docs.arduino.cc/resources/datasheets/ABX00080-datasheet.pdf
  67. https://docs.arduino.cc/tutorials/uno-r4-minima/dac
  68. https://blog.arduino.cc/2025/10/07/a-new-chapter-for-arduino-with-qualcomm-uno-q-and-you/
  69. https://www.arduino.cc/qualcomm
  70. https://www.qualcomm.com/developer/hardware/arduino-uno-q
  71. https://www.qualcomm.com/internet-of-things/products/q2-series/qrb2210
  72. https://www.electromaker.io/blog/article/arduino-uno-q-specs-features-and-why-qualcomms-ai-partnership-matters
  73. https://www.qualcomm.com/developer/blog/2025/10/meet-arduino-uno-q-qualcomm-dragonwing-fueled-ai-in-a-blink
  74. https://www.edgeimpulse.com/blog/announcing-support-for-the-arduino-uno-q/
  75. https://www.arduino.cc/en/hardware
  76. https://store.arduino.cc/products/arduino-nano
  77. https://store.arduino.cc/products/arduino-mega-2560-rev3
  78. https://docs.arduino.cc/hardware/leonardo
  79. https://www.arduino.cc/en/Guide/ArduinoLeonardoMicro
  80. https://store.arduino.cc/products/arduino-leonardo-with-headers
  81. https://www.arduino.cc/education
  82. https://www.arduino.cc/education/edu-starter-kit/
  83. https://store.arduino.cc/products/arduino-starter-kit-multi-language
  84. https://www.seeedstudio.com/blog/2025/10/14/20-awesome-arduino-projects-that-you-must-try-2020/
  85. https://predictabledesigns.com/5-successful-products-that-began-as-arduino-prototypes/
  86. https://thinkrobotics.com/blogs/learn/what-is-arduino-in-iot-a-beginner-friendly-guide-to-smart-innovations
  87. https://docs.arduino.cc/cloud/iot-cloud/tutorials/iot-cloud-getting-started
  88. https://www.elektormagazine.com/articles/miniphonic-arduino-based-audio-synthesis-platform-1
  89. https://kastner.ucsd.edu/wp-content/uploads/2021/12/admin/jss22-arte.pdf
  90. https://docs.arduino.cc/learn/electronics/power-consumption/
  91. https://www.the-diy-life.com/how-long-can-an-arduino-run-on-batteries-i-tested-6-of-the-most-common-boards/
  92. https://store-usa.arduino.cc/products/proto-shield-rev3-uno-size
  93. https://www.keyestudio.com/products/free-shipping-keyestudio-sensor-shield-expansion-board-v5-for-arduino-1
  94. https://store-usa.arduino.cc/products/arduino-motor-shield-rev3
  95. https://www.adafruit.com/product/772
  96. https://learn.sparkfun.com/tutorials/arduino-shields/all
Add your contribution
Related Hubs
User Avatar
No comments yet.