David Lovett's Usagi Electric Vacuum Tube Computer Gets a Custom-Milled Paper Tape Reader
Rather than attempting to reuse some 1970s technology, Lovett's vacuum tube computer build gets its own modern paper tape reader design.
Vintage computing enthusiast David Lovett is building his own vacuum tube computer, inspired by Motorola's classic MC14500 one-bit chip — and has successfully created a working paper-tape reader for loading its software into memory.
"Getting [a device] to read paper tape is a pretty big challenge," Lovett admits. "I'm not just going to buy some generic paper tape reader that was built in the '70s that doesn't really fit with the aesthetic and the theme that I'm going with here, which is trying to build as much myself as possible — so we're going to try and build a paper tape reader from scratch, and that is tough."
Paper tapes, also known as punch-tape, were continuous-feed alternatives to punch-cards — physical paper cards with holes punched through at key points, which could be used to record and reload both data and programs into a computer's memory. Inspired by the programmable looms of Basile Bouchon and colleagues in the 1700s, paper tapes gave way to magnetic tape, then magnetic discs, then optical disks, and to today's solid-state storage devices.
The Usagi Electric Vacuum Tube Computer (UEVTC), a work-in-progress project to build a one-bit machine inspired by Motorola's transistor-based MC14500 industrial control chip in discrete vacuum tube form, needs aesthetically-appropriate storage, though, which is where Lovett's return to paper tape comes in. Machined from aluminum, the reader positions photodiodes over each of the nine holes in the paper tape — eight for each bit of the byte being read and one clock bit — to turn the paper back into data.
The build is documented in full in the video embedded above and on the Usagi Electric YouTube channel; more information on the UEVTC project as a whole is available on GitHub.