Datasheet

EAGLE files: arduino-uno-Rev3-reference-design.zip (NOTE: works with Eagle 6.0 and
newer)
Schematic: arduino-uno-Rev3-schematic.pdf
Note: The Arduino reference design can use an Atmega8, 168, or 328, Current models use an
ATmega328, but an Atmega8 is shown in the schematic for reference. The pin configuration
is identical on all three processors.
The Arduino Uno 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 (wall-wart) or 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 inserted in the Gnd and Vin pin headers 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 be unstable. If using
more than 12V, the voltage regulator may overheat and damage the board. The recommended
range is 7 to 12 volts.
The power pins are as follows:
VIN. The input voltage to the Arduino board when it's 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 - 12V), the USB connector (5V), or the
VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the
regulator, and can damage your board. We don't advise it.
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 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 for working
with the 5V or 3.3V.
The ATmega328 has 32 KB (with 0.5 KB used for the bootloader). It also has 2 KB of SRAM
and 1 KB of EEPROM (which can be read and written with the EEPROM library).
Each of the 14 digital pins on the Uno can be used as an input or output, using pinMode(),
digitalWrite(), and digitalRead() functions. They operate at 5 volts. Each pin can provide or
receive a maximum of 40 mA and has an internal pull-up resistor (disconnected by default)
of 20-50 kOhms. In addition, some pins have specialized functions:
Serial: 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: 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. See the attachInterrupt() function for
details.
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.