There are many reasons to want a basic Arduino circuit on a breadboard or PCB. Building the Arduino-compatible circuit on the breadboard or PCB takes up much less space than trying to stuff a standard Arduino board inside your project. Some projects don't always require every pin to be used on the I/O headers, or maybe you won't be using a shield, but you still want the brain of the Arduino at the heart of your project.
Includes
IC, ATmega328P, DIP-28, Optiboot bootloader
Socket, IC, 28-pin, 0.3"
IC, 5V regulator, 7805T
LED, Red, 660nm, T1-3/4 (Replaced 334035)
LED, Green, 565nm, T1-3/4 (693901) or LED, Green, 565nm, T1-3/4, 20mcd (334086)
Resistor, 1/4W, 10K
2 Resistor, 1/4W, 180
2 Capacitor, radial, 10µF, 50V
Crystal, 16 MHz, low-profile
2 Capacitor, ceramic disc, 22pF, 50V
Capacitor, ceramic disc, 0.1µF, 50V
Switch, pushbutton, OFF-(ON)
Header, 6-pin, 1-row, vertical, 0.1"
IC, 3.3V regulator, LM1117T-3.3
2 Capacitor, tantalum, 10µF, 25V