| Details | Hackaday.io

<h1>Introduction</h1> <figure><img class="lazy" data-src="https://cdn.hackaday.io/images/4576461667864996570.jpg"></figure> <p><em>Above, the Card Reader (top right) attached to a stock Supercon 2022 Badge (bottom right), next to a stack of attendee-provided programs marked on custom sheets (left). Photo directly after presentation Sunday evening, showing Kenneth's successfully loaded 128-bit counter ("A Candlelit Dinner") still running. Note illuminated scan LEDs, forever awaiting their next program.</em><br></p> <p>The Supercon 2022 Badge Card Reader is a transmissive optical input device designed to facilitate loading hand-marked paper programs onto a stock Supercon 2022 Badge. The Card Reader consists of two arrays of thirteen red LEDs on 0.3" (7.6 mm) centers, harvested from a donor badge, which face each other across a minimal gap set by several layers of cardboard shims and guides. One set of LEDs serve as a single receiver; they are wired in parallel, reverse-biased, and fed into a transimpedance amplifier with 1E6 gain. This useful if somewhat finicky technique can be traced back to Forrest Mims III's various experiments and published circuit diagrams on the subject. The other set of LEDs are Charlieplexed and scanned sequentially, illuminating one bit at a time in rapid succession. All of the LEDs are managed by a Pixelblaze Sensor Expansion Board, chosen for its convenience (as