Arduino Uno R3

Power, Ground & Reset

Pin GND: Ground (0V) pins.

PR1: Reset push button. To restart arduino program.

Pin1 | PC6: External reset pin. Momentary GND (0V) to this pin resets arduino.

PR2: 5V Regulator. (NCP1117ST50T3G)

Pin 5V: 5V, 400 mA on USB or 900mA on Barrel Output Supply.

PR3: 3.3V Regulator. (LP2958)

Pin 3V3: 3.3V, 150 mA Output Supply.

PR4: Barrel 2.1mm Connector (F) for Power (7V - 12V, 0.5 A - 2A) using AC-DC adapter.

Pin Vin: You can supply voltage (7V - 12V) through this pin, or, if supplying voltage via the power jack, access it through this pin. Not USB but power!

PR5: Type B USB Port (F): for Power (5V, 500mA) from PC or Power Bank and Serial Communication from PC.

Microcontrollers & Peripherals

MP1: Main Microcontroller-ATmega328P. The high-performance Microchip picoPower 8-bit AVR RISC-based microcontroller combines 32KB ISP flash memory with read-while-write capabilities, 1024B EEPROM, 2KB SRAM, 23 general purpose I/O lines.

MP2: Crystal Oscillator: 16MHz. Microcontroller's Clock.

MP3: ATmega328P ICSP pins - "In Circuit Serial Programming" pins are used to program the microcontroller directly via SPI Communication Protocol. You need an external AVR Programmer to do so.

MP4: Sub Microcontroller-Atmega16U2 (Atmega8U2 up to version R2) programmed as a USB-to-serial converter.

MP5: ATmega16U2 ICSP pins - "In Circuit Serial Programming" pins are used to program the microcontroller directly via SPI Communication Protocol. You need an external AVR Programmer to do so.

Indicator LEDs

ON LED: Arduino Power LED. Shows Arduino is ON/OFF.

RX LED & TX LED: UART Serial Communication LEDs.

L LED: LED connected to Pin 13 (UNO).

General Purpose Input Output Pins (GPIOs)

Pin A0-A5: 6 Analog Input Pins.

Pin AREF: "Analogue REFerence" Reference voltage for ADCs.

Pin 0 - 13: 14 Digital IO pins of which 6 pins labeled “~” can be used to generate PWM (Pulse Width Modulation).

Pin IOREF: "Input Output REFerence" Logic reference voltage for Shields. 5V for UNO. 3.3V for DUE.