The SparkFun AVR Stick is a simple data logging device that instantiates itself as an HID keyboard and reports the voltages, along with a ‘timestamp,’ from two pins on an ATtiny85.
The repository is at https://github.com/sparkfun/AVR_Stick where you can find out more details.
I like looking over the schematics for boards like this, in fact I’ll be posting more creative commons designs. Using the files from the repository you can load them into Eagle and look at the schematics and board layout, if you plan on designing your own boards at some point this can be an invaluable learning aid just seeing how professionals layout schematics neatly and how people layout boards and route them.
Avr stick