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Arduino UNO

Arduino UNO is based on ATmega328P Microcontroller, an 8-bit AVR Architecture based MCU from ATMEL. Arduino UNO comes in two variants: one consists of a 28-pin DIP Microcontroller while the other consists of 32 lead Quad Flat Package Microcontroller.

Layout


The Type-B USB connector on the left short edge of the board, which is used for powering on the board as well as programming the Microcontroller. There is also a 2.1 mm DC jack to provide external power supply.

Technical Specifications

MCUATmega328P
ArchitectureAVR
Operating Voltage5V
Input Voltage6V – 20V (limit)
7V – 12V (recommended)
Clock Speed16 MHz
Flash Memory32 KB (2 KB of this used by bootloader)
SRAM2 KB
EEPROM1 KB
Digital IO Pins24 (of which 6 can produce PWM)
Analog Input Pins6

Power

There are a couple of ways in which you can power the UNO board. The first and easy way is using the Type-B USB Connector. The next way is to provide an unregulated supply in the range of 6V to 20V to VIN pin of the UNO (Pin number 26).
You can also supply the unregulated supply through the 2.1mm DC Jack, in which case, you can access the supplied voltage through the VIN Pin.

Memory

Strictly speaking, this is specific to the MCU i.e., ATmega328P, used on the Arduino UNO Board. There are three different memories available in ATmega328P. They are:

  • 32 KB of Flash Memory
  • 2 KB of SRAM
  • 1 KB of EEPROM
  • 0.5 KB of the Flash Memory is used by the bootloader code.

Input and Output Pins

Of the 32 pins available on the UNO board, 22 pins are associated with input and output. In that 14 pins (D0 to D13) are true digital IO pins, which can be configured as per you application using pinMode(), digitalWrite() and digitalRead() functions.
All these Digital IO pins are capable of sourcing or sinking 20mA of current (maximum 40mA is allowed). An additional feature of the Digital IO pins is the availability of internal pull-up resistor (which is not connected by default).
The value of the internal pull-up resistor will be in the range of 20KΩ to 50KΩ.
There are also 6 Analog Input Pins (A0 to A5). All the analog input pins provide a 10-bit resolution ADC feature, which can be read using analogRead() function.
An important point about Analog Input pins is that they can be configured as Digital IO pins, if required.
Digital IO pins 3, 5, 6, 9, 10 and 11 are capable of producing 8-bit PWM Signals. You can use analogWrite() function for this.

Communication Interfaces

Arduino UNO supports three different types of communication interfaces. They are:

  • Serial
  • I2C
  • SPI
Perhaps the most common communication interface in the Arduino universe is the Serial Communication. In fact, the Arduino boards (UNO or Nano or Mega) are programmed using the serial communication.
Digital IO pins 0 and 1 are used as Serial RX and TX pins to receive and transmit serial data. These pins are connected to the serial pins of the on-board USB to Serial Converter IC.
Analog Input Pins A4 and A5 have alternative functions. They can be configured as SDA (A4) and SCL (A5) to support I2C or I2C or Two Wire Interface (TWI) communication.
The final communication interface is the SPI. Digital IO Pins 10, 11 12 and 13 can be configured as SPI pins SS, MOSI, MISO and SCK respectively.

Additional features

There is an on-board LED connected to digital IO pin 13. Use this LED to perform Blinky operations. The reference voltage for the internal ADC is by default set to 5V. But using the AREF pin, you can manually set the upper limit of the ADC.
Using the IOREF pin, you can set the reference voltage for Microcontroller operations.
To reset the microcontroller, you can use the on-board RESET button.
Although you can program the Arduino UNO using the USB cable, there is a provision to program the MCU using the In-Circuit Serial Programming (ICSP) interface.
The UART bootloader, which is preloaded in to the ATmega328P microcontroller, enables programming through serial interface. But ICSP doesn’t need any bootloader.
You can program Arduino UNO using ISCP or use the ISCP of Arduino UNO to program other Arduino Boards.
Digital IO Pins 2 and 3 can be configured as External Interrupts Pins INT0 and INT1 respectively. Use attachInterrupt() function to configure the Interrupt for rising edge, falling edge or level change on the pin.

Pinout

Pin Description

For pin description of Arduino UNO, let us assume some basic numbering. Let the numbering begin with the RX Pin (D0). So, RX is Pin 1, TX is Pin 2, D2 is Pin 3 and so on.
On the other side, NC is Pin 19, IOREF is Pin 20 etc. Overall, there are 32 pins on the Arduino UNO Board.

Pin NumberPin NameDescriptionAlternative Functions
1RX/D0Digital IO Pin 0
Serial RX Pin
Generally used as RX
2TX/D1Digital IO Pin 1
Serial TX Pin
Generally used as TX
3D2Digital IO Pin 2
4D3Digital IO Pin 3Timer (OC2B)
5D4Digital IO Pin 4Timer (T0/XCK)
6D5Digital IO Pin 5Timer (OC0B/T1)
7D6Digital IO Pin 6
8D7Digital IO Pin 7
9D8Digital IO Pin 8Timer (CLK0/ICP1)
10D9Digital IO Pin 9Timer (OC1A)
11D10Digital IO Pin 10Timer (OC1B)
12D11Digital IO Pin 11SPI (MOSI) Timer (OC2A)
13D12Digital IO Pin 12SPI (MISO)
14D13Digital IO Pin 13SPI (SCK)
15GNDGround
16AREFAnalog Reference
17SDA/D18Digital IO Pin 18I2C Data Pin
18SCL/D19Digital IO Pin 19I2C Clock Pin
19NCNot Connected
20IOREFVoltage Reference
21RESETReset (Active LOW)
223V3 Power
235V+5V Output from regulator or
+5V regulated Input
24GNDGround
25GNDGround
26VINUnregulated Supply
27A0Analog Input 0Digital IO Pin 14
28A1Analog Input 1Digital IO Pin 15
29A2Analog Input 2Digital IO Pin 16
30A3Analog Input 3Digital IO Pin 17
31A4Analog Input 4Digital IO Pin 18I2C (SDA)
32A5Analog Input 5Digital IO Pin 19I2C (SCL)

Pins of the ICSP Connector

MISOMaster In Slave Out (Input or Output)
5VSupply
SCKClock (from Master to Slave)
MOSIMaster Out Slave In (Input or Output)
RESETReset (Active LOW)
GNDGround


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