Analog input technologies for keyboards

Keyboards

Analog input on an input device isn’t anything new. It’s been done time and time again with console controllers’ joysticks and trigger keys, but only recently has it made its way into consumer keyboards. Like the good ol’ console controllers, analog keyboards have so far been primarily made with gaming applications in mind, but there’s more than that to the technology. In this post, I will take a look at different ways of achieving analog input on a keyboard.There’s a few different technologies in existence today, which could and have been used to achieve analog input in keyboards. I will cover the following technologies in more details:

Optical switches
Hall effect switches
Membrane pressure sensitive switches
Capacitive switches

What is analog input?

Analog input is the term given to a gradual adjustment of signal, depending on how far a key is pressed or moved. Thus, an analog keyboard is a keyboard that allows for a gradual adjustment of the signals.Game controllers operate on a similar principle. The further you move the joysticks from their resting position, the stronger the outputted signal is.The most obvious way to take advantage of a gradual signal is in games. Pressing lightly to move your character slowly, and hammering down on the key to sprint is ultimately a very intuitive way to control a character. Same can be said about controlling a car.

Outside of games, the gradual signal can be used for a multitude of purposes. An interesting use case for it could be typing research, or even security purposes. Not only would you need to type your password in correctly, but you would also need to type it at a certain cadence and intensity. If someone ever got your password, they would also need to know your way of typing it in.

Different analog technologies in keyboards

Optical switches / Flaretech

We already wrote about the intricacies of the Flaretech switch, as this is the technology the Wooting One uses. You can read more about the Flaretech switch here.[caption id="attachment_1585" align="aligncenter" width="1000"]

Wooting one with flaretech switches.[/caption]The Flaretech keyboard switch is a simple device. Pushing down on the key lowers a prism which reflects infrared light produced by an emitter on the circuit board back to a sensor on the circuit board. The amount of light reflected back is dependent on how far down the prism is. The amount of light picked up by the sensor can then be translated into a gradual signal.Keep in mind though, that not just any old optical switch can do analog input. The analog input is not only dependent on the switches, but also on the construction and components on the circuit board. Most other optical switches employ a horizontally placed laser beam, which the switch plunger intercepts while at resting position. Pushing down allows the beam to pass through to a sensor, activating the key. This system doesn’t allow a gradual signal.

Hall effect switch (AKA magnets man, how do they work?)

A hall effect switch measures distance with magnets. The switch moves a magnet next to a hall effect sensor, which is a transducer that varies its voltage output by the strength of a magnetic field. Hall effect switches were used to a degree in the early days of computing, most notably in the Space-cadet keyboard of the 1980s.[caption id="attachment_1577" align="alignnone" width="1200"]

The Space-cadet keyboard was developed by Tom Knight to be used on MIT’s LISP machines in the 70's/80’s[/caption]Since there’s a moving magnet, and a transducer that varies its voltage based on the proximity of the magnet, the functionality can be translated into analog input.There has been only a few public attempts of making a hall effect-based keyboard in recent years, one of which is commercially available but unfortunately not analog supported.Ben Heck, a professional hardware hacker created a hall effect-based analog control for his WASD keys:https://www.youtube.com/watch?v=gEwDImE0DU4Hall effect switches were resurrected in the last few years by a joint effort of Massdrop and XMIT, bringing the Massdrop x XMIT hall effect keyboard available to the masses. This keyboard doesn’t support analog input however, the hall effect here is just used to activate switches on an on/off principle.

Pressure sensitive membrane

Good ol’ membrane keyboards can be made force-sensitive too. The idea here is not to measure the key’s travel distance, but rather the force applied when bottoming out the key. This has been done on the ROCCAT Isku+ Force FX keyboard by utilizing a piezoelectric layer.[caption id="attachment_1579" align="alignnone" width="830"]

The ROCCAT Isku+ Force Fx utilizes a piezoelectric composite material under the QWEASD keys to achieve analog input[/caption]A piezoelectric material produces a voltage when squeezed. Measuring this voltage allows for measurement of a gradual signal and thus analog control is achieved.[caption id="attachment_1569" align="alignnone" width="256"]

Basic illustration on how a piezoelectric material works. By Tizeff - Template:Ownnn, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=2961245[/caption]Microsoft produced a prototype keyboard utilizing a piezoresistive system (nearly the same, I’ll spare you the details), a video of which is an interesting watch:https://www.youtube.com/watch?v=80FWh_fQ_ZgThis keyboard was never developed to a consumer level and released to the public.The obvious drawback with these kinds of systems is that a key has to be bottomed out before the analog input goes in effect. In other words, this system has more to do with measuring force rather than distance.

Capacitive switches

There’s only a couple known manufacturers of capacitive keyboard switches, the most recognizable of which is Topre. Topre is the switch hailed as the ultimate typing experience by many enthusiasts. While great for typing, the capacitive properties can also be used to achieve analog input.[caption id="attachment_1571" align="alignnone" width="525"]

A Topre switch's inner workings[/caption]The Topre switch works by a sensor on the circuit board. The conical spring inside the rubber dome compresses, and a capacitive sensing mechanism on the circuit board senses the keypress. This premise could in theory be used for an analog mechanism as the capacitive field grows stronger as the spring is compressed.However, as this system requires a rubber dome to serve as feedback to the user, the utility of analog input is greatly hampered. Rubber domes have a tendency to resist the keypress until a certain point, at which they collapse and the user bottoms out the switch. This would make a half-way signal nearly impossible to achieve consistently.

Final words

And there we have it. Even though analog input isn’t a new technology per se, utilizing it in keyboards is. The analog keyboard industry is only now in its infancy, and only time will tell what kinds of applications of analog input we can see in the future. One thing is for sure though: analog technology will grow in the gaming industry in the coming years.What I really would like to see though, is ground-up support for analog input in applications. Analog in games is fun, but analog in productive work would be awesome. I would love to see analog input taken advantage of in something like video editors or photo manipulation software.