Arduino

Most Arduino boards consist of an Atmel 8-bit AVR microcontroller (ATmega8,[28] ATmega168, ATmega328, ATmega1280, or ATmega2560) with varying amounts of flash memory, pins, and features..
The boards use single or double-row pins or female headers that facilitate connections for programming and incorporation into other circuits. These may connect with add-on modules termed shields. Multiple and possibly stacked shields may be individually addressable via an I²C serial bus. Most boards include a 5 V linear regulator and a 16 MHz crystal oscillator or ceramic resonator.
Arduino microcontrollers are pre-programmed with a bootloader that simplifies the uploading of programs to the on-chip flash memory.
Current Arduino boards are programmed via Universal Serial Bus (USB), implemented using USB-to-serial adapter chips such as the FTDI FT232. Some boards, such as later-model Uno boards, substitute the FTDI chip with a separate AVR chip containing USB-to-serial firmware, which is reprogrammable via its own ICSP header.