by Evil Mad Scientist Laboratories
We didn't design this, but we absolutely love it! The Diavolino kit is a low-cost, Arduino-compatible that uses the ATMega328p.
It doesn't have a USB interface, so you'll need an FTDI cable or something similar for programming to use it like an Arduino.
It doesn't have power switching, so you'll have to power it from only one source at a time or implement switching yourself.
It also doesn't have a 3.3 V regulator.
The Diavolino kit includes a Diavolino printed circuit board, a ATMega328P microcontroller preprogrammed with the Arduino bootloader, a 16 MHz crystal oscillator, a 3 mm diffused red LED, a reset button, a wire jumper for optional USB power, a 10 kΩ resistor, a 1Ω resistor, a 0.1 uF ceramic capacitor, and a 6-pin header for FTDI cable.
The Diavolino is a through-hole kit. It requires basic through-hole soldering skills. At a minimum, you'll need a soldering iron, solder, and a diagonal cutters.
It usually takes less than an hour to build, but it may take more or less time depending upon your experience with soldering.
This kit is open source hardware. Evil Mad Science makes the hardware source files like the schematic and the pcb files available. The schematic and pcb files are available on the Diavolino page.