Building a better mortar board
For the seniors at the University of Cincinnati, decorating mortar boards for graduation has become a tradition. Our university encourages this by providing opportunities for us to deck out our fancy hats.
Deciding that I was better off avoiding subjecting my fellow classmates to my terrible arts and crafts skills, I instead decided to use my skills as a developer to mount an LED matrix to my head. I found inspiration from Jermey Blum’s write up of doing something similar for his own graduation.
Parts
32 x 32 LED array — $79.95
Raspberry Pi Model B -$25
2 USB port battery backup — $89.99
Total cost $194.94
Assembly
Graduating from a public school means an extremely long ceremony; this made power my first concern. Doing some quick math with the consumption specs for the Raspberry Pi and LED matrix, I knew I’d need at least a 10000mAh backup to last the 4 hour ceremony. I’d also need a unit with two USB ports, one of which must output at 2 Amps to meet the power needs of the LED array.
Using a battery backup also allowed me to purchase a device with a smaller form factor that I was able to duct tape to the shirt underneath my graduation gown during the ceremony.
The LED matrix that I chose unfortunately didn’t come with the ability to be powered over USB, so I first had to strip a USB cable. A standard USB cable contains 4 wires, two of which are used for power. Soldering the provided spade terminals to power wires inside the USB cable resulted in an acceptable power cable for the matrix.
Next, I wired up the the Raspberry Pi to the LED panel, following the instructions from hzellers rpi-rgb-led-matrix repo.
Finally, I mounted the panel and Raspberry Pi to the cap, propped up by cardboard to create a better viewing angle for those behind me.
Custom Animations
While hzeller’s repo comes with a few stock animations, I wanted to add animations that would let me display school spirit. The LED matrix takes animations in the ppm file format. Using Pillow, a fork of the Python Imaging Library, I was able to write a python script that would take a static 32x32 pixel image and apply some basic transformations to create an animated file.
Originally, I intended to take tweets containing the string “#UCGRAD14" from Twitter and dynamically creating ppm files of scrolling text. I was able to code an implementation of this, but unfortunately wasn’t able to use this in production due to wifi constraints.
Finally, I knew I wouldn’t have the luxury of a screen with me when it came time to turning the hat on, so I wrote a bash script that would load hzeller’s repo when the Raspberry Pi was booted and cycle through all the animations it found in a folder I’d placed in the shared directory.
Results
The hat worked perfectly the day of graduation. Unfortunately, the duck tape I used to stick everything to my chest wasn’t strong enough resulting in my having to carry electronics across the stage during the ceremony.
My engineering department was so impressed they asked to film a short video of the project.
Additionally I was tangentially mentioned in an NPR article by someone who attended my graduation.
Going forwards I’m excited to see what cool projects other hackers do during their graduations.
