A 3D-printed test ring on my finger read my letters after a few minutes of practice, because 450 people had already written 52,191 letters in the air with their phones to teach the software. The real ring is due in November.
One Bluetooth chip does all the reading, and types into a phone, a TV or a pair of glasses
A motion sensor smaller than a fingernail rides the index finger and records how it moves a hundred times a second, a sample rate that would embarrass a telephone. A Bluetooth chip with its own AI core reads the letters from that movement alone, no camera, no pen, no surface, and types them into whatever is listening: a phone, a TV, a pair of glasses, on a battery a 200th the size of your phone’s. Our handheld wand, the wandBox, already does this on the chip. For the test ring the reading ran on a laptop.
The ring’s own board is not made until November, so I designed a stand-in to start learning a finger now. Adafruit’s BNO055 motion-sensor board sits in a 3D-printed case: a chassis and a face hold the board, and two M2 screws clamp them to a band. The bands print 15 to a plate, US sizes 6 to 13 by halves, so the same case fits anyone who will wear it, and the band that fits is also their ring size. The whole thing weighs about 7 g on the finger, a little more than a US quarter.
Four wires run back over the hand to a Nordic developer board on the desk, which passes the sensor’s readings to the laptop a hundred times a second. The laptop shows a letter; I hold the space bar down with my other hand, write the letter in the air with my index finger, and let go. Over 3 days I wrote 891 letters on it, with the finger, with the whole hand, and with both. Every test fitted the model on one day and read it on another, so the ring had to know me the next morning, not just the same afternoon.
450 people taught the software with their phones, before there was a ring
450 people on Prolific wrote 52,191 letters in the air for us, with the motion sensors in their own phones, and The Wand’s letter model learned handwriting from them. None of them has worn our ring, and a phone in the hand moves differently from a sensor on a finger.
Starting from what they taught it, the ring needed a few minutes of my writing to read me the next morning. Started from nothing, the same model took far longer and never read me as well. We retrained it on smaller and smaller groups of the testers, and the fewer people it had learned from, the worse it read me before I had written a letter for it: the more people it has learned from, the less each new wearer has to teach it.
What you write with The Wand comes with you, too. The letters I had written with the wandBox taught the ring my hand before I had written one on it.
Writing with the ring is a small movement of one finger
On a ring the hand points and the index finger does the writing, turning at the knuckle with the tip about 85 mm out, while the forearm drifts along the word the way a hand moves along a line on paper. The film performs that rule: the knuckle turns the finger, the wrist stays in line, the forearm moves left to right and never back. The trail it draws is not drawn by hand. Each letter is one of my own casts on the test ring, the one the ring’s model read most surely, and the fingertip’s path comes from the sensor’s own orientation: the finger as a lever 85 mm long, turned the way the sensor turned.
The ring itself is a signet with a face 16 × 13 mm, and the radio, the motion sensor and the chip that reads the letters go inside it.
85 words in 100 right for a new user, 95 once the wand has learned their hand
The Wand gets 85 of a new user’s words right first go, and 95 once it has learned your hand. Those are the wandBox’s numbers, measured on writers it had never seen. The ring’s target is the same 95, after a few minutes of teaching it your finger. So far there is one wearer, me, and the test ring is wired to the bench.
Three numbers, three things about us, three for a dinner party
- 52,191 — letters written in the air for us by 450 people, with their own phones.
- 891 — letters I wrote on the test ring in 3 days.
- 7 g — the test ring on the finger, sensor board included.
- One finger — on a ring only the index finger moves, at the knuckle; the forearm carries it along the word.
- 15 bands — US sizes 6 to 13, on one print plate, so anyone can wear the test ring.
- 95 in 100 — the goal, once the ring has learned your finger.
- The index — the Romans named the forefinger digitus index, the one that points out.
- A few minutes — what a new wearer teaches the ring, because 450 people taught The Wand first.
- 4 wires — what joins the test ring to a developer board while it learns our hands.
Where the numbers come from
450 and 52,191 are the Prolific study; the Air-Writing Atlas has the whole of it. 85 and 95 words in 100 are the wandBox’s, on held-out writers. 891 letters are my three test-ring sessions of 2–4 October. The case’s weight is the design’s (the chassis 1.2 g, the face 0.7 g, a band 2 g, Adafruit’s board 3 g); a US quarter weighs 5.67 g. The 85 mm is the finger length the reconstruction uses, knuckle to tip; an adult index finger runs 70–90 mm.