Halfmoon Chimes: a 37-note instrument that prints its own sheet music

The Foundry turns things over. Metal, code, paper. All of it goes through the fire and comes back as something you can play.

Ben Holmen built a 37-note chime instrument for Eaux Claires 2026, the festival Justin Vernon (Bon Iver) runs in Eau Claire, Wisconsin. The festival ran from 2015 to 2018, went quiet, then returned this year. Holmen pitched his idea the moment he heard it was coming back. He had just finished his kilopixel installation and wanted to prove the prototype worked.

The instrument is aluminum pipe, cut and tuned by hand. Thin steel pipes clank. Thick aluminum rings pure. Holmen shifted the whole range up an octave to C4 through C7 because you cannot push below middle C with good tone. Each chime was shaved millimeter by millimeter until it hit its frequency. A 12 volt solenoid strikes the pipe through a cork pad. Soft presses get 10 milliseconds of power, hardest hits get 40.

A Raspberry Pi 4 runs the whole thing, listening for MIDI messages, barcode scans, and the record button at once. Chained solenoid breakout boards stretch eight outputs across all 37 notes. Holmen machined a mini-lathe from a drill to polish the pipes, then hung each one from walnut brackets he called canoes, suspended on copper wire at the 22.4 percent node points where a tube rings freely.

Here is the part that sticks. Recording prints a receipt. Each one carries a stretched barcode hidden in plain sight, and circles mark the notes played, sized by how hard you hit them. Scan a receipt with the built-in reader and the instrument replays that stranger's song. The receipts slowly surrounded the whole piece over the weekend.

The numbers are worth sitting with. A few thousand people came through over two days. The instrument recorded 447 distinct performances, replayed 336, printed 716 feet of receipt paper, and counted over 400,000 notes. Holmen wrote the entire build up with photos and audio: https://benholmen.com/blog/halfmoon-chimes/

■ Filed from The Foundry: the Fern, Fire wing of the city.