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Arduino Uno R3 Board Overview


Arduino Uno is a microcontroller board based on the ATmega328P. It has 14 pins of digital input or output pin where only 7 of them can be used as a pulse width modulation (PWM) output. There are also 6 analog input pin available for analog purpose.

Arduino Uno is a microcontroller board based on the ATmega328P. It has 14 pins of digital input or output pin where only 7 of them can be used as a pulse width modulation (PWM) output. There are also 6 analog input pin available for analog purpose. The Arduino Uno can be powered via the USB connection or with an external power supply. The power source is selected automatically. Operating voltage of this Arduino Uno is 5V with input voltage ranging from 6-20V as a power source.

The Arduino Uno differs from all preceding boards as it does not use the FTDI USB-to-serial driver chip. Instead, it features the Atmega16U2 (Atmega8U2 up to version R2) programmed as a USB-to-serial converter. 

The Arduino Uno has a number of facilities for communicating with a computer, another Arduino, or other microcontrollers. The ATmega328 provides UART TTL (5V) serial communication, which is available on digital pins 0 (RX) and 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 16U2 firmware uses the standard USB COM drivers, and no external driver is needed.

Arduino Uno R3 (Top view)

Arduino Uno R3 (Bottom view)

The Arduino Uno has a resettable polyfuse that protects your computer's USB ports from shorts and overcurrent. Although most computers provide their own internal protection, the fuse provides an extra layer of protection. If more than 500 mA is applied to the USB port, the fuse will automatically break the connection until the short or overload is removed.

The maximum length and width of the Uno PCB are 2.7 and 2.1 inches respectively, with the USB connector and power jack extending beyond the former dimension. Four screw holes allow the board to be attached to a surface or case. Note that the distance between digital pins 7 and 8 is 160 mil (0.16"), not an even multiple of the 100 mil spacing of the other pins. 


Input and Output Pins of Arduino Uno R3:


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:

  1. 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.
  2. 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.
  3. PWM: 3, 5, 6, 9, 10, and 11. Provide 8-bit PWM output with the analogWrite() function. 
  4. SPI: 10 (SS), 11 (MOSI), 12 (MISO), 13 (SCK). These pins support SPI communication using the SPI library.
  5. LED: 13. There is a built-in LED connected to digital pin 13. When the pin is HIGH value, the LED is on, when the pin is LOW, it's off.


The Uno has 6 analog inputs, labeled A0 through A5, each of which provide 10 bits of resolution (i.e. 1024 different values). By default they measure from ground to 5 volts, though is it possible to change the upper end of their range using the AREF pin and the analogReference() function. Additionally, some pins have specialized functionality:

  1. TWI: A4 or SDA pin and A5 or SCL pin. Support TWI communication using the Wire library.


There are a couple of other pins on the board:

  1. AREF. Reference voltage for the analog inputs. Used with analogReference().
  2. Reset. Bring this line LOW to reset the microcontroller. Typically used to add a reset button to shields which block the one on the board. 



Below is an overview video of Arduino Uno R3.



Overview of Arduino UNO board

Features:
Microcontroller: ATmega328
Operating Voltage: 5V
Input Voltage recommended: 7-12V
Input Voltage limits: 6-20V
Digital I/O Pins: 14 - of which 6 provide PWM output
Analog Input Pins: 6
DC Current per I/O Pin: 40 mA
DC Current for 3.3V Pin: 50 mA
Flash Memory: 32 KB ATmega328 of which 0.5 KB used by bootloader
SRAM: 2 KB - ATmega328
EEPROM: 1 KB (ATmega328)
Clock Speed: 16 MHz


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