The Arduino Nano is an incredibly useful board variant: it's breadboard-friendly, comes with extra analogue pins compared with the traditional Uno design, and compatibles are available at an incredibly low cost. There are times, though, when you need the good old Uno layout - oddly-spaced pin headers and all - and that's something Milen Penev aims to address with his latest creation: an Arduino Uno to Nano adapter board.
Acting as a motherboard of sorts, Milen's open-source printed circuit design is simple: a row of pins in the rough centre of the board accepts the Arduino Nano, while the PCB routes its pins out to female headers on either side - matching the traditional Uno layout. The result: it's possible to use standard Arduino shields with the Nano, though if you want to be able to remove the Nano from the board you'll need extended pins in order to provide enough clearance.
The board also adds a few features missing from the traditional Nano design, including the addition of a voltage regulator which allows for input voltages higher than 5V using the freshly-added DC power jack. A reset switch is also added, as with a shield attached the Nano's own switch becomes inaccessible. In short: it provides pretty much everything you'd expect of an Uno, but driven from a Nano.
While you're unlikely to want to replace your existing Unos with a Nano and adapter board combo, having a few boards built up and ready to go could be handy for any maker with Nanos waiting to be used in upcoming projects. Full details and the Gerber production files are available in Milen's Instructable.
[The] Arduino Nano has also some disadvantages compared with Uno. Extension shields can not be used directly with Arduino Nano; external power supply source different than 5V can not be used - no DC jack presents; for the generating of the internal 3.3V is used the embedded in the Atmega328 voltage regulator, which can not provide currents higher than 100-150 mA; making small experimental projects require the presence of a breadboard. All these problems are solved by the Arduino Nano to Uno conversion board developed by me.