Classic Mega 2560 R3 with ATmega2560-16AU, ATmega16U2 & USB-B (Arduino-compatible board) angle front

Classic Mega 2560 R3 ATmega16U2/ATmega2560-16AU, USB-B

1-Digit 0.56 inch LED, 7-segments, common-anode (pack 5 pcs) Angle Front


Classic UNO R3 ATmega16U2/ATmega328P-PU, DIP

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Uno R3 is the ideal board for getting started with electronics!

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General information

Uno R3 is the ideal board for getting started with electronics! It can be used in a variety of projects. UNO R3 is based on the ATmega328P with 32KB of FLASH and 2KB of RAM. It has 14 digital input/output pins (6 of which are PWM outputs), 6 analog inputs, a 16MHz crystal, a USB-B socket, a DC power jack, an ICSP 2×3 header, and also a Reset button. UNO R3 comes with the bootloader already pre-installed. For use with the Arduino IDE, please choose «Arduino UNO» in the board selection menu.


The Uno R3 board can be programmed with the Arduino Software (IDE). The Uno R3 comes pre-programmed with a bootloader that allows you to upload new code to it without the use of an external hardware programmer. You can also bypass the bootloader and program the microcontroller through the ICSP (In-Circuit Serial Programming) header using ISP or similar. ATmega16U2 is used for the USB-to-TTL interface.


The Uno R3 can be powered via the USB connection or with an external power supply. The power source is selected automatically. External (non-USB) power can come either from an AC-to-DC adapter or a battery. The adapter can be connected by plugging a 2.1mm center-positive plug into the board’s power jack. Leads from a battery can be connected to the GND and VIN pins of the POWER connector. The board can operate on an external supply of 6 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may become unstable. If using more than 12V, the voltage regulator will likely need additional cooling (a heatsink), otherwise a damage may occur. The recommended input voltage range is 7 to 12 V DC.


The ATmega328 has 32KB of FLASH (with 0.5 KB occupied by the bootloader). It also has 2KB of SRAM and 1KB of EEPROM.

Input and Output (I/O)

Each of the 14 digital pins on the Uno can be used as an input or an output. They operate at 5 volts.
In addition, some pins have specialized functions:

  • Serial: 0 (RX) and 1 (TX).These are 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: 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: 3, 5, 6, 9, 10, and 11. Provide 8-bit PWM output with the analogWrite() function.
  • SPI: 10 (SS), 11 (MOSI), 12 (MISO), 13 (SCK). These pins support SPI communication using the SPI library.
  • LED: 13. 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’s off.
  • TWI: A4 or SDA pin and A5 or SCL pin. Support TWI communication using the Wire library.
  • AREF. Reference voltage for the analog inputs. It is used with analogReference().
  • Reset. Bring this line LOW to reset the microcontroller. Typically used to add a reset button to shields (in case if the on-board reset button is not reachable).

*See also the mapping UNO R3 PinOut diagram


The Uno R3 board has a number of facilities for communicating with a computer, another board, or other microcontrollers. The ATmega328 provides four hardware UARTs for TTL (5V) serial communication. An ATmega16U2 on the board links one of these over USB to a virtual COM port on the computer (Windows machines may need a driver (an .inf file), while MacOS and Linux machines will recognize the board as a COM port automatically). The 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 ATmega16U2 chip and USB connection to the computer (but not for serial communication on pins 0 and 1).

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Microcontroller ATmega328P
Operating Voltage 5V
DC Current for 5V Out 1A
DC Current for 3.3V Out 800mA
DC Current for USB 5V 500mA (limitation)
Digital I/O Pins 14 (of which 6 provide PWM output)
PWM Digital I/O Pins 6
Analog Input Pins 6
DC Current per I/O Pin 20mA
DC Current for 3.3V Pin 50mA
Flash Memory 32KB (ATmega328P) of which 0.5KB used by bootloader
SRAM 2KB (ATmega328P)
EEPROM 1KB (ATmega328P)
Clock Speed 16MHz
Length × Width 68.6mm × 53.4mm
Weigth 30g

Please note: the higher the input voltage is, the higher the load on a voltage regulator will be. Please avoid using high currents if input voltage exceeds 12V.


Dimensional drawing

Dimensional drawing Classic UNO R3 ATmega16U2 with ATmega328P-PU (Arduino-compatible board) Dimensional drawing Classic UNO R3 ATmega16U2 with ATmega328P-PU (Arduino-compatible board)

Input and Output (I/O) diagram

Input and Output (I/O) diagram Classic UNO R3 ATmega16U2 with ATmega328P-PU (Arduino-compatible board) Input and Output (I/O) diagram Classic UNO R3 ATmega16U2 with ATmega328P-PU (Arduino-compatible board)


Schematic of Classic UNO R3 ATmega16U2 with ATmega328P-PU (Arduino-compatible board)