My Hat for Graduation

I will be graduating with a degree in Computer Science in about a month and looking at my degree now with the knowledge I have, I think that had I it to do over again I would have gone the Computer Engineering route. Software is entertaining and I really enjoy my work, but it is all so intangible. I really would like to be able to hold the product of one of my efforts in my hand.

To this end I have been playing with circuits a bit and want to make my hat for graduation some sort of electronic display. This fits very well for me since I haven't really cared about making anything especially useful, just something that exists physically and being pretty is a plus.

My original idea was to do a seven segment led (those blocky numbers) and have it counting. This is still what I might end up going with, but it has the disadvantage of not being visible from a wide angle and not being especially pretty. A friend of mine suggested instead that I might try some sort of animated pattern and I ended up with concentric squares which works well with the shape of the hat.

One of my design constraints is I would like to have as little as possible actually on the hat. I would like the batteries and chips to be in my pocket since trying to carry them on my head is just not realistic given the weight.

A single seven segment display works well for this since there are seven wires for the segments and then a common ground. A piece of cat5 has 8 wires in it and I could buy an RJ-45 female jack and put it on the back of the hat and use that to easily connect to the rest of it in my pocket.

When looking at switching to the squares I considered having seven squares (one for each wire). The problem is that assuming the original square is three LEDs on a side and the subsequent squares each add one led to the outside then the number of LEDs in a given square would be:

The total number of LEDs to make a given number of squares then would be:

And for 7 squares, T 7= 224. Which, at ~$.20 per LED is around $45.

So, I decided to make the pattern a little more complex and cut back on the number of squares. The new pattern will "walk" its way out the the edge and then fall back to the center. The truth table for this would be: