Creating Text Out of Thin Air

New approach allows smartwatch users to write text in mid-air with their fingers

3 min read
hand writing in the air

One possible text entry scenario for smartwatches: handwriting in the air without rotating the user’s wrist.

Wei Dong et al

This article is part of our exclusive IEEE Journal Watch series in partnership with IEEE Xplore.

Smartwatches are growing in popularity thanks to their compact size and wide-ranging abilities, useful for anything from texting to tracking fitness. Yet the convenience of having a smartwatch close on hand (literally) comes with a caveat—namely, that only one hand can be used to input text on smartwatches.

But, one group of researchers in China are pointing to a novel solution, whereby smartwatch users could simply use their finger to write their texts in mid-air in front of them, with no need of a surface. The researchers developed and tested their proposed approach, called AirText, with several volunteers and describe it in a study published November 23 in IEEE Transactions on Mobile Computing.

While speech-to-text input may seem like an obvious solution to the issue of inputting text into smartwatches, relying on audio input involves a number of problems. For example, speech-to-text approaches are not ideal when users are in environments with a lot of background noise, or when users wish to keep the content of their message private from other people within earshot. At the same time, inputting text with just one hand can be slow and cumbersome.

Wei Dong is a professor at the College of Computer Science at Zhejiang University in China. Dong and his colleagues envisioned AirText as a simpler approach and sought to create the app.

“The goal of AirText is to infer the texts written by the fingertip in the air, using only the [inertial measurement unit (IMU)] readings, for example the accelerometers, gyroscopes, and magnetometer, from the smartwatch on the wrist as input,” explains Dong.

However, a major challenge in developing AirText lay in understanding how the user’s wrist movements correspond with the movement of their fingertips as they spell out letters. “[When you are writing] a character in the air using a fingertip, the movements of the wrist and the fingertip are not necessarily the same,” notes Dong. “In fact, as we show in the study, they are quite different.”

To overcome this issue, Dong and his colleagues used a program called Leap Motion, which is able to track the movement of fingers using infrared sensors. Eight volunteers spelled out more than 25,000 characters using five different kinds of smartwatches, while Leap Motion collected data on their wrist and hand movements. The data was then fed into an AI model to infer the relationship between users’ wrist movements and the characters they are spelling out with their fingertips.

The results show that AirText can be effective for writing text in the air, regardless of the type of smartwatch worn or the unique writing style of the user. The volunteers used AirText to achieve an average typing speed of 8.1 words per minute, and their average word error rate ranged from 3.6 percent to 11.2 percent.

table of letters, the hand-gestures necessary to generate those letters both on a surface and in the air (with both non-rotating wrist and rotating wrist)The trajectories of a smartwatch in the three different scenarios when writing four different characters in the air. We see that the trajectories in the rotating wrist scenario are completely different from the written characters. Wei Dong et al

To speed up the writing process, AirText can try to predict the word that a user is trying to spell, just like current word prediction software programs on smartphones. Users can tilt the watch to the right or left to select a suggested word, or shake their watch to indicate a backspace.

One limitation, however, is that AirText users must do a short pause in between spelling out individual characters. “This approach slows down the input speed,” says Dong, noting that his team is exploring ways to eliminate the need for this pause.

Dong notes that his team is also interested in commercializing AirText at some point in the future. He says, “We will talk to smartwatch manufactures and smartwatch application developers to see how to apply out technologies to their products.”

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The Inner Beauty of Basic Electronics

Open Circuits showcases the surprising complexity of passive components

5 min read
A photo of a high-stability film resistor with the letters "MIS" in yellow.
All photos by Eric Schlaepfer & Windell H. Oskay

Eric Schlaepfer was trying to fix a broken piece of test equipment when he came across the cause of the problem—a troubled tantalum capacitor. The component had somehow shorted out, and he wanted to know why. So he polished it down for a look inside. He never found the source of the short, but he and his collaborator, Windell H. Oskay, discovered something even better: a breathtaking hidden world inside electronics. What followed were hours and hours of polishing, cleaning, and photography that resulted in Open Circuits: The Inner Beauty of Electronic Components (No Starch Press, 2022), an excerpt of which follows. As the authors write, everything about these components is deliberately designed to meet specific technical needs, but that design leads to “accidental beauty: the emergent aesthetics of things you were never expected to see.”

From a book that spans the wide world of electronics, what we at IEEE Spectrum found surprisingly compelling were the insides of things we don’t spend much time thinking about, passive components. Transistors, LEDs, and other semiconductors may be where the action is, but the simple physics of resistors, capacitors, and inductors have their own sort of splendor.

High-Stability Film Resistor

A photo of a high-stability film resistor with the letters "MIS" in yellow.

All photos by Eric Schlaepfer & Windell H. Oskay

This high-stability film resistor, about 4 millimeters in diameter, is made in much the same way as its inexpensive carbon-film cousin, but with exacting precision. A ceramic rod is coated with a fine layer of resistive film (thin metal, metal oxide, or carbon) and then a perfectly uniform helical groove is machined into the film.

Instead of coating the resistor with an epoxy, it’s hermetically sealed in a lustrous little glass envelope. This makes the resistor more robust, ideal for specialized cases such as precision reference instrumentation, where long-term stability of the resistor is critical. The glass envelope provides better isolation against moisture and other environmental changes than standard coatings like epoxy.

15-Turn Trimmer Potentiometer

A photo of a blue chip
A photo of a blue chip on a circuit board.

It takes 15 rotations of an adjustment screw to move a 15-turn trimmer potentiometer from one end of its resistive range to the other. Circuits that need to be adjusted with fine resolution control use this type of trimmer pot instead of the single-turn variety.

The resistive element in this trimmer is a strip of cermet—a composite of ceramic and metal—silk-screened on a white ceramic substrate. Screen-printed metal links each end of the strip to the connecting wires. It’s a flattened, linear version of the horseshoe-shaped resistive element in single-turn trimmers.

Turning the adjustment screw moves a plastic slider along a track. The wiper is a spring finger, a spring-loaded metal contact, attached to the slider. It makes contact between a metal strip and the selected point on the strip of resistive film.

Ceramic Disc Capacitor

A cutaway of a Ceramic Disc Capacitor
A photo of a Ceramic Disc Capacitor

Capacitors are fundamental electronic components that store energy in the form of static electricity. They’re used in countless ways, including for bulk energy storage, to smooth out electronic signals, and as computer memory cells. The simplest capacitor consists of two parallel metal plates with a gap between them, but capacitors can take many forms so long as there are two conductive surfaces, called electrodes, separated by an insulator.

A ceramic disc capacitor is a low-cost capacitor that is frequently found in appliances and toys. Its insulator is a ceramic disc, and its two parallel plates are extremely thin metal coatings that are evaporated or sputtered onto the disc’s outer surfaces. Connecting wires are attached using solder, and the whole assembly is dipped into a porous coating material that dries hard and protects the capacitor from damage.

Film Capacitor

An image of a cut away of a capacitor
A photo of a green capacitor.

Film capacitors are frequently found in high-quality audio equipment, such as headphone amplifiers, record players, graphic equalizers, and radio tuners. Their key feature is that the dielectric material is a plastic film, such as polyester or polypropylene.

The metal electrodes of this film capacitor are vacuum-deposited on the surfaces of long strips of plastic film. After the leads are attached, the films are rolled up and dipped into an epoxy that binds the assembly together. Then the completed assembly is dipped in a tough outer coating and marked with its value.

Other types of film capacitors are made by stacking flat layers of metallized plastic film, rather than rolling up layers of film.

Dipped Tantalum Capacitor

A photo of a cutaway of a Dipped Tantalum Capacitor

At the core of this capacitor is a porous pellet of tantalum metal. The pellet is made from tantalum powder and sintered, or compressed at a high temperature, into a dense, spongelike solid.

Just like a kitchen sponge, the resulting pellet has a high surface area per unit volume. The pellet is then anodized, creating an insulating oxide layer with an equally high surface area. This process packs a lot of capacitance into a compact device, using spongelike geometry rather than the stacked or rolled layers that most other capacitors use.

The device’s positive terminal, or anode, is connected directly to the tantalum metal. The negative terminal, or cathode, is formed by a thin layer of conductive manganese dioxide coating the pellet.

Axial Inductor

An image of a cutaway of a Axial Inductor
A photo of a collection of cut wires

Inductors are fundamental electronic components that store energy in the form of a magnetic field. They’re used, for example, in some types of power supplies to convert between voltages by alternately storing and releasing energy. This energy-efficient design helps maximize the battery life of cellphones and other portable electronics.

Inductors typically consist of a coil of insulated wire wrapped around a core of magnetic material like iron or ferrite, a ceramic filled with iron oxide. Current flowing around the core produces a magnetic field that acts as a sort of flywheel for current, smoothing out changes in the current as it flows through the inductor.

This axial inductor has a number of turns of varnished copper wire wrapped around a ferrite form and soldered to copper leads on its two ends. It has several layers of protection: a clear varnish over the windings, a light-green coating around the solder joints, and a striking green outer coating to protect the whole component and provide a surface for the colorful stripes that indicate its inductance value.

Power Supply Transformer

A photo of a collection of cut wires
A photo of a yellow element on a circuit board.

This transformer has multiple sets of windings and is used in a power supply to create multiple output AC voltages from a single AC input such as a wall outlet.

The small wires nearer the center are “high impedance” turns of magnet wire. These windings carry a higher voltage but a lower current. They’re protected by several layers of tape, a copper-foil electrostatic shield, and more tape.

The outer “low impedance” windings are made with thicker insulated wire and fewer turns. They handle a lower voltage but a higher current.

All of the windings are wrapped around a black plastic bobbin. Two pieces of ferrite ceramic are bonded together to form the magnetic core at the heart of the transformer.

This article appears in the February 2023 print issue.