Derek Woodroffe's Extreme Kits Badge Packs 143 Transistors — As QR Code Blocks
The black of the tiny transistors against the white of the PCB delivers exactly the contrast required for a scannable QR code.
Extreme Electronics' Derek Woodroffe has designed a badge with a difference: its fully-working scannable QR code is made up of 143 transistors, built into a circuit that drives 24 LEDs around the badge's circumference.
"Primarily it needs to serve as a badge for Extreme Kits, the QR code is the most important thing," Woodroffe writes of the thinking behind the project. "But it needs to be fun, different and attractive (probably not that pretty though). Why? As a badge, it needs to be different, to stand out. Everyone does badges with microprocessors and displays. Plus, I thought it would be easy."
Quick-response (QR) codes were invented at Denso Wave in Japan in the mid-'90s, taking inspiration from the black and white patterns that would appear on a Go board during play owing the placing of the white and black counters. Data is encoded as squares within a larger square, with three fiducial targets orienting the pattern — which can be scanned in moments using even a low-resolution camera.
Traditionally, QR codes are printed onto a badge; if you wanted to get posh, you might display one on an ePaper screen instead. Woodroffe's badge, though, has a QR code that's functional in two respects: it's both fully-scannable as a QR code, and its blocks are made up of MOSFET transistors — not as decoration, but as functional components in an 11-stage shift register that powers 24 colorful LEDs around the edge of the badge.
"With further consideration, I thought the [fiducial] targets were a cop-out," Woodroffe says of the QR code's only printed parts. "But no combination of components would allow consistent detection without sharply defined lines. So eventually, I put 12mm tactile push buttons in the center of each target so the target is the actual button. The transistors (and other components) were placed by hand. The population/soldering of the whole PCB took around 2.5 hours."
The project is documented in full, including schematics, on Woodroffe's Extreme Kits website.