Arduino UNO

Overview
Arduino Uno is a microcontroller board based on 8-bit ATmega328P
microcontroller. Along with ATmega328P, it consists other components such
as crystal oscillator, serial communication, voltage regulator, etc. to support
the microcontroller. Arduino Uno has 14 digital input/output pins (out of
which 6 can be used as PWM outputs), 6 analog input pins, a USB
connection, A Power barrel jack, an ICSP header and a reset button.

The Arduino Uno is an open-source microcontroller board that is based on the

Microchip ATmega328P (for Arduino UNO R3) or Microchip ATmega4809 (for
Arduino UNO WIFI R2) micro-controller by Atmel and was the first USB
powered board developed by Arduino.

Both Atmega328 and ATmega4809 have a built-in bootloader, which makes it

very convenient to flash the board with our code. Like all Arduino boards, we
can program the software running on the board using a language derived from
C and C++. The easiest development environment is the Arduino IDE.

How to use Arduino Board

The 14 digital input/output pins can be used as input or output pins by using
pinMode(), digitalRead() and digitalWrite() functions in arduino programming.
Each pin operate at 5V and can provide or receive a maximum of 40mA
current, and has an internal pull-up resistor of 20-50 KOhms which are
disconnected by default. Out of these 14 pins, some pins have specific
functions as listed below:

 Serial Pins 0 (Rx) and 1 (Tx): Rx and Tx pins are used to receive and
transmit TTL serial data. They are connected with the corresponding
ATmega328P USB to TTL serial chip.
 External Interrupt 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 Pins 3, 5, 6, 9 and 11: These pins provide an 8-bit PWM output by
using analogWrite() function.
 SPI Pins 10 (SS), 11 (MOSI), 12 (MISO) and 13 (SCK): These pins are
used for SPI communication.
 In-built LED Pin 13: This pin is connected with an built-in LED, when pin 13
is HIGH – LED is on and when pin 13 is LOW, its off.

Along with 14 Digital pins, there are 6 analog input pins, each of which
provide 10 bits of resolution, i.e. 1024 different values. They measure from 0
to 5 volts but this limit can be increased by using AREF pin with analog
Reference() function.

 Analog pin 4 (SDA) and pin 5 (SCA) also used for TWI communication using
Wire library.

Arduino Uno has a couple of other pins as explained below:

 AREF: Used to provide reference voltage for analog inputs with

analogReference() function.
 Reset Pin: Making this pin LOW, resets the microcontroller.

Communication
Arduino can be used to communicate with a computer, another Arduino
board or other microcontrollers. The ATmega328P microcontroller provides
UART TTL (5V) serial communication which can be done using digital pin 0
(Rx) and digital pin 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 ATmega16U2 firmware uses the standard USB COM
drivers, and no external driver is needed. However, on Windows, a .inf file is
required. The Arduino software includes a serial monitor which allows simple
textual data to be sent to and from the Arduino board. There are two RX and
TX LEDs on the arduino board which will flash when data is being transmitted
via the USB-to-serial chip and USB connection to the computer (not for serial
communication on pins 0 and 1). A SoftwareSerial library allows for serial
communication on any of the Uno's digital pins. The ATmega328P also
 supports I2C (TWI) and SPI communication. The Arduino software includes a
Wire library to simplify use of the I2C bus.

Pin Description
Pin Pin Name Details
Category
Power Vin, 3.3V, 5V, GND Vin: Input voltage to Arduino when using an external
power source.
5V: Regulated power supply used to power
microcontroller and other components on the board.
3.3V: 3.3V supply generated by on-board voltage
regulator. Maximum current draw is 50mA.
GND: ground pins.
Reset Reset Resets the microcontroller. If this pin is supplied with
5 V, the board will reset automatically
Analog Pins A0 – A5 Used to provide analog input in the range of 0-5V
Input/Output Digital Pins 0 - 13 Can be used as input or output pins.
Pins
Serial 0(Rx), 1(Tx) Used to receive and transmit TTL serial data.
External 2, 3 To trigger an interrupt.
Interrupts
PWM 3, 5, 6, 9, 11 Provides 8-bit PWM output.
SPI 10 (SS), 11 (MOSI), 12 Used for SPI communication.
(MISO) and 13 (SCK)
Inbuilt LED 13 To turn on the inbuilt LED.
TWI A4 (SDA), A5 (SCA) Used for TWI communication.
AREF AREF To provide reference voltage for input voltage.
 Arduino Uno Technical Specifications
Microcontroller ATmega328P – 8 bit AVR family microcontroller
Operating Voltage 5V
Recommended Input Voltage 7-12V
Input Voltage Limits 6-20V
Analog Input Pins 6 (A0 – A5)
Digital I/O Pins 14 (Out of which 6 provide PWM output)
DC Current on I/O Pins 40 mA
DC Current on 3.3V Pin 50 mA
Flash Memory 32 KB (0.5 KB is used for Bootloader)
SRAM 2 KB
EEPROM 1 KB
Frequency (Clock Speed) 16 MHz

 Length:6 mm
 Width:4 mm
 Weight: 25 g

Voltage Regulator-The voltage regulator converts the input voltage to 5V.

The primary use of a voltage regulator is to control the voltage level in
the Arduino board. Even if there are any fluctuations in the input supply
voltage of the regulator, the output voltage remains constant and near 5 volts.

Crystal Oscillator– The Crystal oscillator has a frequency of 16MHz, which

provides the clock signal to the microcontroller. It provides the basic timing
and control to the board.
 RESET Button–It is used to reset the board. It’s recommended to press this
button every time we flash the code to the board.

Barrel Jack – The Barrel jack or DC Power Jack is used to power the Arduino
board using an external power supply. The barrel jack is usually connected to
an adapter. The board can be powered by an adapter that ranges between 5-
20 volts but the manufacturer recommends keeping it between 7-12 volts.

Note: Above 12 volts, the board may overheat and below 7 volts, the voltage
might not be sufficient to power the board.

USB B-port–The USB Interface is used to plug in the USB cable. This port can
be used to power the device from the 5V supply. It allows us to connect the
board to the computer. The program is uploaded to the board serially from the
computer through the USB cable.

Vin–It is the modulated DC supply voltage, which is used to regulate the IC’s
used in the connection. It is also called the primary voltage for IC’s present on
the Arduino board. The Vcc voltage value can be negative or positive to the
GND pin.

SPI stands for Serial Peripheral Interface. It is used by microcontrollers to communicate with
one or more peripheral devices quickly.

 SCK-It stands for Serial Clock. These are the clock pulses, that is used to
synchronize the transfer of data.
 MISO-It stands for Master Input/ Slave Output. This data line in the MISO
pin is used to receive the data from the Slave.
 MOSI-It stands for Master Output/ Slave Input. This line is used for sending
data to the peripherals.
 SS-It stands for Slave Select. This line is used by the master. It acts as the
enable line. When a device’s Slave Select pin value is LOW, it can
communicate with the master. When it’s value HIGH, it ignores the master.
This allows us to have multiple SPI peripheral devices sharing the same
MISO, MOSI, and CLK lines.

Arduino Uno Pinout – Analog Pins:

 The Arduino Uno consists of 6 analog pins, which use ADC (Analog to
Digital converter). These pins can serve as analog inputs but can also
function as digital inputs or digital outputs. These pins accept inputs in
 the form of Analog signals and return values that range between 0 and
1023 (because the Arduino Uno has a 10-bit Analog to Digital
converter or 210 resolution).

 An Analog to digital converter works in three stages: sampling,

quantization, and digitization. Because the Arduino operates on a 0–5
volts range, the step size of the device is
5/1023=0.00488volts or 4.88mV.

 Thus, we can interpret a 4.88 mV input voltage to any of the analog pins
as 1, 9.77 mV as 2, and so on until 5 V as 1023. Anything below 4.88
mV is considered 0 and above 4.99 V as 1023.

Arduino Uno Pinout – Digital Pins:

On the Arduino UNO board, pins 0-13 are digital input/output pins.

The Arduino digital pins can read only two states: when there is a voltage
signal and when there is no signal. This kind of input is usually called digital
(or binary) and these states are referred to as HIGH and LOW or 1 and 0.

LED (13): On the board, there is a built-in LED connected to digital pin 13.
When this pin is HIGH or 1, the LED is switched on, when the pin is LOW or 0,
it’s switched off.

PWM pins:

If you look closely, you will find the ‘~’ symbol on digital pin 3,5,6,9,10, and 11.
These pins have an additional feature called PWM. Hence these pins are
called PWM pins.

PWM stands for “Pulse Width Modulation”. It means, that an analog value is
being modulated on a digital signal. Suppose you want a DC motor to run at a
certain analog voltage between 0 and 5 V. This is not possible because the
Arduino board is MOSFET-based.
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