The TinyShield Circle Edge LED board has 21 LEDs mounted around the edge of the board. These LEDs only use six signals from the TinyDuino using a technique called Charlieplexing, which saves the other I/O for other functions for your project.
A basic example Arduino sketch that works with the TinyDuino and TinyShield 16 Edge LED boards is shown below:
A library for Charlieplexing can be found on the Arduino Playground: http://playground.arduino.cc/Code/Charlieplex
The TinyShield Circle Edge LED boards use pin numbers IO4, IO5, IO6, IO7, IO8 and IO9. Fo example, to turn-on the LED D1 (and D1 only), IO5 should be high, IO6 should be low, and all other pins should be set to an input (this prevents other LEDs from turning-on when they aren’t supposed to).
Note: A problem with Charlieplexing is that you obviously can’t turn-on all the LED’s at the same time. To account for this, you can “flash” them (turn them on and off really quick) at a frequency of at least 50Hz (assuming you don’t want to be able to see them flicker on and off).