The Nano can be powered via the Mini-B USB connection, 7-12V unregulated external power supply (pin 30), or 5V regulated external power supply (pin 27). The power source is automatically selected to the highest voltage source. Input and output: each of the 14 digital pins on the Nano can be applied as an input or output; Some pins have special functions Nano's got the breadboard-ability of the Mini+USB with smaller footprint than either, so users have more breadboard space. It's got a pin layout that works well with the Mini or the Basic Stamp (TX, RX, ATN, GND on one top, power and ground on the other). ATmega328P chips: using Atmega328P-AU MCU, support ISP download, using the same chips ATmega328P and CH340 with the official version Nano V3.0 ATMEGA328P improved version with 3pcs pin headers. No welding needed.