My graduation cap runs Rust
May 12, 2026
I’ve never graduated before. I mean, from college. So all the cap and gown stuff is new to me.
Fun fact #1: you rent your cap and gown in the US. You have to return them. And they’re expensive, too! I paid $94 just for the privilege of renting mine, which is insane because they probably cost way less than that to manufacture. What if, say, you say you’re fine without a cap and gown? Well, then you can’t walk in the ceremony. So you do need to shell out to rent them. And they don’t give you the option to buy the cap and gown outright.
OK, that’s not such a fun fact. How about:
Fun fact #2: when you graduate, they move your tassel from right to left to signify… something? Why not left to right? What about left-handed people?! Why are graduation ceremonies discriminating against left-handed people?!
Anyway. I was thinking about fun fact #2, and then I thought it might be cool if my cap lit on fire as whoever it is moves my tassel. But the rental agreements clause 98.c.2 probably fobids it, and I don’t think Purdue would like it very much if I set the stage on fire.
Hmm. What if I made a contraption that detects when the tassel is moved away and light up the bottom-side of the cap?
And with that, I got to building this crazy idea. And the end result is beautiful if I do say so myself:
FAQ
What parts did you use?
- One Digispark ATtiny85
- 48 WS2812B LEDs
- Wires stripped from a dead Apple USB-C-to-C cable
- Reed switch and magnet to detect tassel movement (not shown in demo)
- A USB-C Power Delivery trigger board
- Power bank (and USB-C cable)
How long did you spend on this thing?!
Writing the code took about 2 hours, mostly because avr-hal and ws2812-avr do not support the ATtiny85 out of the box, at least not without a couple of tweaks. I had to fork them and dirty-patch a couple of things, including setting the default clock speed to 16 MHz.
It probably would’ve been easier if I didn’t use Rust and just used the Arduino libraries, or if I used a different board. But I was really married to this blog post title idea, and I was pretty sure a ESP32 board would’ve been overkill and wouldn’t have stayed on the cap properly.
The hardware side took the longest, at 3+ hours. If anybody tells you hardware is easy they’re wrong or they’re lying and have never worked on a custom hardware project!
Are you actually going to wear this to your graduation?
Heck no.
I thought about it but decided it looks pretty tacky. It looks like what kids would think of as a gaming PC and what boomers would think of as a seizure.
Speaking of seizure, there really was a missed opportunity…
…missed?
Warning: the following video contains rapid strobing of light. I’ve written this out so people who are reading this with a screen reader know not to watch the video!
Can I see the code?
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