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
I cut them apart then used the supplied battery case to find the positive wire for each.
Step 2: Wiring Up the Sets
Step 3: Covering the Wires With Paper Plant Tape
Step 4: Hooking Up the Lights
To hook up the lights I used pins 10,11,12,13 on the Arduino. How you hook up each wire of each pair of LEDs doesn't matter - the wires of each are interchangeable. You just have to hook each pair across different pins through the 100 ohm resister. In this case:
a 10 & 11
b 11 & 12
c 12 & 13
d 10 & 12
e 11 & 13
f 10 & 13
You can add more sets by using more pins, but the more you add the less time each light stays on and the dimmer it will get. 12 seemed to be a nice round number and nicely bright.
Step 5: Collecting the Wires Together
So I put them all on a little perfboard and with a female connector to keep the wires managed.
Radio shack sells a four conductor Rainbow Wire that has solid conductors and fits the connector quite well.
The connector was cut from a long strip of female headers I picked up on eBay.
Step 6: Breadboard Layout
Step 7: A Little Software
I made a few arrays that hold each animation frame lighting one LED , two, three.... and so on.