Charliplexed Christmas Tree for my Cubby

Last Year I got a set battery operated bulb type Christmas light set at the local home store and put it on a table top Christmas Tree.  Just to make the cubby festive.  Almost all the comments I received  were along the line of  "Don't they Blink?"  

This Year I was bound and determined to make something that would stand out.

An  LED battery operated set of lights cut up and hooked to an Arduino, Charlieplexed style, and a little code to make them bllnk in nice patterns, changed randomly,  filled the bill.  

It took some time to get the random part to work, but I didn't want the pattern to repeat over and over and get boring.

I could have fancied it up hiding all the connections and putting the arduino in an Altoids tin. But I wanted them to see all the wires. Besides, its geekier that way.

Step 1: Finding the Positive Side of the LED

Charliplexing allows N*(N-1)  LEDs to be driven by  N pins. In this case i had 20leds, so using 4 pins to get a of  12 leds  

I cut them apart then used the supplied battery case to find the positive wire for each.