Skully

Skully is the greatest possible PCB badge.

Description

Backlit amber leds show a simulated flame pattern, making it look like the skull is on fire from behind, reflecting onto your clothing if worn. An accelerometer ensures the flames always originate at the bottom, no matter how the badge is oriented.

It also monitors the overall acceleration of the badge and will slowly die down the flames over the course of about a minute and go into a very low-power sleep mode if the badge doesn’t look like it’s moving at all and will reactivate if you start moving again.

Skully does not go on a lanyard but rather has a bar pin on the back, so it can be worn as a largish lapel pin in relatively normal social environments. It’s roughly 2.3 x 2.3 inches (about 60 x 60 mm). It is powered by a CR2032 coin cell to keep it light and comfortable to wear.

It is really nice to look at even if when it’s not turned on. The flames look best indoors and/or in low light environments such as a futuristic nightclub.

It’s difficult to fully capture the beauty of this badge in photos/video, it looks much better in person IMO.

The story

I made it initially for the Hackday Superconference in 2018 or so.

I was trying to think of unique ways to use PCB elements to represent something aesthetically appealing. I wondered for a long time about art that would look good as exposed copper. I spent weeks thinking though various ideas.

I stumbled across found some ancient scratchboard art that I realized would look stunning. I was so excited by how cool I thought it would look.

Further thinking about design elements no one had thought of before, I mounted the LEDs on the back, so they shine backwards on you rather than facing forward. This would allow a far more unique, organic effect.

It also allowed the construction to be one-sided, though it was extremely challenging doing the routing. Since the entire front of the board was needed for copper art, I could not use any vias or route tracks through the top side of the board.

I chose an ATmega328p microcontroller since I already knew how to use that through Arduino and the LIS3DH accelerometer, chosen because at the time it seemed to be the most popular accelerometer on the market by far. This was the first time I used a real accelerometer instead of the mechanical vibration spring switch I had used in earlier projects.

I left out the pullups on the I2C lines, because I didn’t understand what they were for. Somehow it still worked.

I tried to think of what pattern the board should display. I settled on a “fire” effect. Flames and skulls go well together.

I got the boards in the mail and I wrote all of the source code in my hotel room the morning before the conference. Fortunately it worked on the first try.

I based the algorithm on Mark Kriegsman’s Fire2012 algorithm. I modified it so that the flames would spread in two directions, along either side of the badge. I used the accelerometer to both activate the effect and determine the tilt angle, so the flames would always start at the bottom and travel upwards, regardless of the badge’s orientation. I added an effect where the sparking rate would decrease until it went out completely, and the device could be put into low power sleep. It produced an extremely natural effect of a fire slowly dying. I could also use the accelerometer to wake the device and restart the animation when it was perturbed again.

I was extremely pleased I was able to get the first prototype working for the conference, where it really impressed people. It was one of the first surface-mount projects I had ever made, and I was extremely nervous about contracting a manufacturer to assemble it.