Board Description

1-Power USB

                Arduino Board can be powered by using the cable from your computer. All you need to do is to connect USB cable to USB port.

2-Crystal Oscillator

                    The Crystal Oscillator helps in dealing with the time issues. how does Arduino calculate time? the answer is, by using the Crystal Oscillator. The number printed on the top of the Arduino Crystal is 16.000H9H.  It tells us that the frequency is 16,000,000 Hertz or 16 MHz.

3- Voltage Regulator

                    Function of the voltage regulator is to control voltage and supply the voltage as much as the board needs and stabilize the DC voltage used by the  processor and the other elements.

4-Power(Barrel Jack)

                   Arduino Board can be powered directly from the AC main power supplying by connecting it to the Barrel Jack. 

5,17-Arduino RESET

                    You can reset your Arduino board, i.e., start your program from the beginning. You can reset the UNO board in two ways. First, by using the reset button (17) on the board. Second, you can connect an external reset button to the Arduino pin labelled RESET.

6,7,8,9-Pins(3.3,5, GND, vin)

• 3.3V (6) − Supply 3.3 output volt  
• 5V (7) − Supply 5 output volt  Most of the components used with Arduino board works fine with 3.3 volt and 5 volt.
• GND (8)(Ground) − There are several GND pins on the Arduino, any of which can be used to ground your circuit.   
•  Vin (9) − This pin also can be used to power the Arduino board from  an external power source, like AC mains power supply. 

10-Analog pin

                   The Arduino UNO board has six analog input pins A0 through A5. These pins can read the signal from an analog sensor like the humidity sensor or temperature sensor and convert it into a digital value that can be read by the microprocessor.

11-MicrocontrollerICS 

                    Each Arduino board has its own microcontroller (11). You can assume it as the brain of your board. The main IC (integrated circuit) on the Arduino is slightly different from board to board. The microcontrollers are usually of the ATMEL Company. You must know what IC your board has before loading up a new program from the Arduino IDE. This information is available on the top of the IC. For more details about the IC construction and functions, you can refer to the data sheet.

12-ICSP pin

                    Mostly, ICSP (12) 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, you are slaving the output device to the master of the SPI bus.

13-Power LED indicator

                    This LED should light up when you plug your Arduino into a power source to indicate that your board is powered up correctly. If this light does not turn on, then there is something wrong with the connection.

14-TX and RX LEDs

                    On your board, you will find two labels: TX (transmit) and RX (receive). They appear in two places on the Arduino UNO board. First, at the digital pins 0 and 1, to indicate the pins responsible for serial communication. Second, the TX and RX led (13). The TX led flashes with different speed while sending the serial data. The speed of flashing depends on the baud rate used by the board. RX flashes during the receiving process.

15- Digital I/O

                    The Arduino UNO board has 14 digital I/O pins (15) (of which 6 provide PWM (Pulse Width Modulation) output. These pins can be configured to work as input digital pins to read logic values (0 or 1) or as digital output pins to drive different modules like LEDs, relays, etc. The pins labeled “~” can be used to generate PWM.

16- AREF

                    AREF stands for Analog Reference. It is sometimes, used to set an external reference voltage (between 0 and 5 Volts) as the upper limit for the analog input pins.