Arduino is an open-source hardware and software company, project and user community that designs and manufactures single-board microcontrollers and microcontroller kits for building digital devices.
Arduino UNO is based on the ATmega328P chip. It has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, 1 UART (hardware serial port), a 16 MHz crystal oscillator, a USB connection, a power jack, ICSP header, and a reset button.
The Arduino UNO can be powered via the USB connection or with an external power supply. The power source is selected automatically.