KEY-ONE_

A viewer of ours lost their right hand below the wrist in an accident and had been using a split keyboard with one half removed, which works but requires constantly moving between keys and a mouse.

The brief was to make a single device where text entry and pointing share the same hand position. There was no budget and no schedule; we did it because it was the most interesting fitting problem we had been offered that year.

The key wells are laid out on a fan whose radius comes from a scan of the actual hand, not from a standard. Three revisions: the first had too much travel at the outer columns, the second put the trackball where the thumb had to leave the home position, the third is the one in use.

Everything is printed except the plate, which is water-jet 1.5 mm aluminium. Printing the shell meant a revision cycle of about eleven hours, which is the only reason three revisions fit inside seventeen days.

One 2-layer board, an RP2040, and a PMW3360 sensor for the trackball. Nothing exotic — the entire difficulty of this project was mechanical fit, and the electronics were deliberately chosen to be boring so they never became the problem.

Delivered after seventeen days and three key-well revisions. Sustained 41 wpm after three weeks of daily use, measured over ten two-minute trials.

It has been in daily use since. The two revisions since delivery were both about the thumb cluster, which is the hardest part of any one-handed layout and the part we would expect to keep revising.