Glowtape Is A Watch You Read By Pulling Tape Out Of It

Every display technology on a DIY watch eventually starts to look familiar — e-ink, OLED, LED matrices, the occasional e-paper panel. Henner Zeller’s Glowtape, spotted at Supercon 2024, isn’t any of those. It tells time by writing onto a physical strip of glow-in-the-dark tape as it’s pulled out of the watch.

What They Built

Glowtape uses a dense UV LED array to charge a roughly two-inch-wide strip of phosphorescent tape as it scrolls past, leaving a glowing afterimage that briefly displays the time, date, or — since the system can write arbitrary patterns — images and longer strings of text as a scrolling banner.

How They Did It

Zeller released the complete source for the project: OpenSCAD files for the 3D-printed housing that the tape and LED array sit inside, plus the C firmware running on an RP2040 that controls the UV array timing to “write” onto the tape as it moves. The tricky part isn’t really the electronics — it’s getting the LED charge timing and tape speed to line up so the glow forms legible characters rather than a smear.

Why It’s Worth Your Time

It’s impractical in basically every sense that matters for a watch — the glow fades within seconds, and you’re trailing a foot of tape off your wrist to read the time — but that’s exactly the kind of “why not” build that belongs on a site about hacker watches instead of commercial ones. Nobody is shipping this as a product; that’s the point.

Go See It

Henner Zeller’s source files are on GitHub, and Hackaday covered the project after spotting it at Supercon 2024.