I needed a small arduino for a UAV project, I could of just bought a mini but I wanted to see how small and cheap I could actually build one without requiring etching equipment. The final size of the board got down to 45 x 25 mm although by using a resonator instead of a crystal + two capacitors it may be possible to make it slightly thinner.

The board includes only the bare minimal - just regulated power (both 5v and 3.3v), the Atmel 328, the crystal and four capacitors (two for the power lines and two for the crystal).

On the underside you can see where the tracks have been cut. The power section is a bit of a mess as the first attempt had the regulators mounted vertically but the layout was too tight and had to changed. Even then I still had a problem when I first powered it up because the heat sinks were touching - the sink on the 7805 is grounded but the one on the LD33 is +3.3v.

The first 'shield' I made has the basic extra features - a reset button, a general purpose LED and a serial programming header compatible with the standard FTDI cable or breakout board. This board is not required in normal use and only really needs to be installed during programming.

And the underside - the pin on the right hand side does nothing electrically and is just there to help hold the shield.

The programming shield needs to be at the top of the stack as it only has eight of the stackable headers mounted on it. The main board has a full set of them and so can be anywhere in the stack, not necessarily at the bottom.

The two pins near the power capacitors on the main board are power in - I'm using a standard 9v battery but anything above 7v should work.

I've also built two more shields - one handles the interface to the UAV hardware and the other deals with the I2C bus (both 5v and 3.3v) and SD card via SPI. I'll document these in a future post.

04/Sep/11 - Updated with eagle schematic below - yellow horizontal lines are the copper tracks on the underside of the stripboard, red lines are jumper wires on the top. Notice on the photos the orientation of the 7805 and the LD33.