DEF CON 27 is a mere week away, and hackers and infosec experts all around the globe are gearing up for their annual pilgrimage to Las Vegas for the event. While DEF CON is nominally a hacker convention focused on talks and workshops about various computer security topics, it has developed a unique cultural atmosphere over the decades. One of the most popular aspects of that culture is the “badge life,” in which attendees construct elaborate electronic badges for the conference. For this year’s event, Dr.n0psl3d designed a “Frankenbadge” that features working Nixie tubes.
We often see projects that utilize Nixie tubes to display the time on desktop clocks, but it’s rare to see them on anything portable or battery-powered. That’s because Nixie tubes work by passing voltage through cathodes that are shaped like numerals. That takes a lot of voltage — usually somewhere between 170–190V — which is tricky to achieve with a power supply small enough for a badge to be wearable. But Dr.n0psl3d was able to pull it off using a custom power supply built with a 555 timer, IRF740 MOSFET, a couple of transistors, a large capacitor, and some passive components. That boosts the 9V from the battery up to an adjustable 130–230V.
But Dr.n0psl3d still needed to drive those Nixie tubes, and they only had one Soviet K155ID1 BCD-to-decimal decoder IC to do so. Those haven’t been manufactured in a long time, and prices are going up as supply dwindles. To make the most of the one K155ID1 available, Dr.n0psl3d used multiplexing to drive all four Nixie tubes by switching very quickly between them. That’s controlled by a Microchip ATmega32U4, which is the same microcontroller found in the Arduino Leonardo boards.
The final step was to design the badge’s PCB. Dr.n0psl3d decided to go with a Frankenstein’s monster theme, with some of the components carefully placed to resemble the stitching on his head. The PCBs were then fabricated by OSH Park. Unfortunately, some of the parts got held up in customs, so Dr.n0psl3d won’t be able to take badges to DEF CON 27, but the Frankenbadge is still a fantastic work of art.