Arduino Board Description:
(1) Power USB: Every Arduino board needs a way to be connected to a power source. Arduino board can be powered with the USB cable from computer.
(2) Power (Barrel Jack): Arduino boards can also be powered from the AC mains power supply by connecting it to the Barrel Jack.
Pins (5V, 3.3V, GND, Analog, Digital, PWM, AREF)
(3, 15) GND: There are several GND (Ground) pins on the Arduino, any of which can be used to ground your circuit.
(4) 5V : Supply 5 output volt
(5) 3.3V : Supply 3.3 output volt
(6) Analog Pins : The Arduino UNO board has five analog input pins A0 through A5. These pins can read the signal from an analog sensor (humidity sensor or temperature sensor ) and convert it into a digital value that can be read by the microprocessor.
(7) Digital Pin : The Arduino UNO board has 14 digital I/O pins (0 to 13). These pins can be used for both digital input (like telling if a button is pushed) and digital output (like powering an LED).
(8~) PWM : The tilde (~) next to some of the digital pins (3, 5, 6, 9, 10, and 11 on the UNO) act as normal digital pins, but can also be called Pulse-Width Modulation (PWM).
(9) AREF : Stands for Analog Reference. It is at times used to set an external reference voltage (between 0 and 5 Volts) as the upper limit for the analog input pins.
Reset : (10 & 17)
One can reset Arduino board, i.e., start the program from the beginning. Arduino UNO board can be reset in two ways. First, by using the reset button (10) on the board. Second, connect an external reset button to the Arduino pin labelled RESET (17).
Power LED Indicator : (11)
The LED light up when Arduino is plugged into a power source. It indicate that the board is powered up correctly. If this light does not turn on, then there is something wrong with the connection.
TX RX LEDs : (12)
TX is short for transmit, RX is short for receive. There are two places on the Arduino UNO where TX and RX appear – once by digital pins 0 and 1, and a second time next to the TX and RX indicator LEDs (12). These LEDs blink whenever Arduino is receiving or transmitting data (like when loading a new program onto the board).
Main Controller : (13)
Every Arduino has a controller. It can be assumed as the brain of Arduino board. The main IC (integrated circuit) on the Arduino is slightly different from board to board. The microcontrollers are usually of the ATMEL Company. One must know what IC the board has before loading up a new program from the Arduino IDE. This information is available on the top of the IC.
Voltage Regulator : (14)
It act as an gatekeeper and controls the amount of voltage that let into the Arduino board also stabilize the DC voltages used by the processor and other elements.
ICSP Pin : (15)
Mostly, ICSP is an AVR, a tiny programming header for the Arduino consisting of MOSI, MISO, SCK, RESET, VCC, and GND. It is often referred to as an SPI (Serial Peripheral Interface), which could be considered as an "expansion" of the output. Actually, it slaves the output device to the master of the SPI bus.
Crystal Oscillator : (16)
The crystal oscillator helps Arduino in dealing with time issues. The number printed on top of the Arduino crystal is 16.000H9H. It tells that the frequency is 16,000,000 Hertz or 16 MHz.