Arduino Uno

Last updated
Arduino Uno
Arduino Logo.svg
Arduino Uno - R3.jpg
Arduino Uno SMD R3 with ATmega328P MCU
Developerarduino.cc
ManufacturerMany
Type Single-board microcontroller [1]
Availability Uno R3 webpage
Operating system None
CPU Microchip AVR (8-bit)
at 16 MHz
Memory2 KB SRAM
Storage32 KB Flash
1 KB EEPROM

The Arduino Uno is an open-source microcontroller board based on the Microchip ATmega328P microcontroller (MCU) and developed by Arduino.cc and initially released 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.

Contents

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

Arduino RS232 Serial board - a predecessor with an ATmega8 Arduino316.jpg
Arduino RS232 Serial board - a predecessor with an ATmega8

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 cost that was a considerable expense for many students. 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]

Technical specifications

Arduino Uno R3 board with ATmega328P MCU in DIP-28 package Arduino Uno 006.jpg
Arduino Uno R3 board with ATmega328P MCU in DIP-28 package

Uno R1 to R3

  • 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. [14]

Uno R4

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

Common features on both Uno R4 Minima [15] and Uno R4 WiFi [16] boards:

Additional features only available on the Uno R4 Minima board: [15]

Additional features only available on the Uno R4 WiFi board: [16]

Headers

Header pinout of the Arduino Uno board Arduino-uno-pinout.png
Header pinout of the Arduino Uno board

General pin functions

Special pin functions

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:

Communication

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

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

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. [19]

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, [20]
A000066, [9]
Uno R3 SMD, [21]
A000073 [22] 		Uno USB-B ATmega328P, [12]
28 pin DIP,
32 pin SMD 		5V
(1.8-5.5V)		8bit AVR 16 MHz*32 KB2 KB1 KB1, 011None0, 0, 1, 2,
WD		10bit,
None		None
Uno WiFi R2, [23]
ABX00021 [24] 		Uno USB-B,
WiFi,
Bluetooth 		ATmega4809, [25]
48 pin		5V
(1.8-5.5V)		8bit AVR 16 MHz*48 KB6 KB0.25 KB4, 011None0, 0, 5, 0,
WD, RT		10bit,
None		None
Leonardo, [26]
A000057 [27] 		Uno USB-Micro-B ATmega32U4, [28]
44 pin		5V
(2.7-5.5V)		8bit AVR 16 MHz32 KB2.5 KB1 KB1, 011 USB-FS 0, 0, 2, 1,
WD, 10bit		10bit,
None		None
Mega 2560 R3, [29]
A000067 [30] 		Mega USB-B ATmega2560, [31]
100 pin		5V
(4.5-5.5V)		8bit AVR 16 MHz256 KB8 KB4 KB4, 011None0, 0, 4, 2,
WD		10bit,
None		None
Uno R4 Minima, [15]
ABX00080, [32]
Uno R4 WiFi, [16]
ABX00087, [33] 		Uno USB-C,
WiFi*		R7FA4M1AB, [17]
64 pin		5V
(1.6-5.5V)		32bit ARM
Cortex-M4F
(FPU)		48 MHz256 KB
+ bootrom 		32 KB
(ECC)
(parity)		None
+ 8 KB
data flash 		4, 022 USB-FS,
CAN-A/B 		2, 0, 8, 0,
WD, RC,
24bit SysTick		14bit,
12bit		 DMA x4,
CRC, RNG,
Crypto, Touch,
LCD
Zero, [34]
ABX00003 [35] 		Uno USB-Micro-B
x2		ATSAMD21G18, [36]
48 pin		3.3V
(1.62-3.63V)		32bit ARM
Cortex-M0+ 		48 MHz256 KB32 KBNone6, 0NoneNone USB-FS,
I²S 		0, 4, 5, 0,
WD, RC,
24bit SysTick		12bit,
10bit		 DMA x12,
CRC32, Touch
Due, [37]
A000062 [38] 		Mega USB-Micro-B
x2		ATSAM3X8E, [39]
144 pin		3.3V
(1.62-3.6V)		32bit ARM
Cortex-M3 		84 MHz512 KB
+ bootrom 		96 KBNone3, 212 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, [40]
ABX00063 [41] 		Mega USB-C,
USB-A,
WiFi,
Bluetooth 		STM32H747XI, [42]
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)		None4, 564 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
Arduino Leonardo board with ATmega32U4 MCU Arduino Leonardo board (cropped).JPG
Arduino Leonardo board with ATmega32U4 MCU
Arduino Due board with ATSAM3X8E MCU ArduinoDue Front.jpg
Arduino Due board with ATSAM3X8E MCU
Table notes

See also

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References

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  7. ↑ "Previous IDE Releases" . Retrieved 2023-02-08.
  8. ↑ "Arduino Older Boards" . Retrieved 2023-02-08.
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  11. ↑ "Introducing the Arduino UNO R4! - News - SparkFun Electronics". www.sparkfun.com. Retrieved 2023-08-07.
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  16. 1 2 3 "Board; Uno R4 WiFi; Docs". Arduino. Archived from the original on June 27, 2023.
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  35. ↑ "Board; Zero; Store". Arduino.
  36. ↑ "MCU; ATSAMD21G18; Docs". Microchip. Archived from the original on February 1, 2023.
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  41. ↑ "Board; GIGA R1 WiFi; Store". Arduino.
  42. ↑ "MCU; STM32H747XI; Docs". ST. Archived from the original on May 11, 2023.

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