Wherein The Mechanical Keyboard Community Discovers Motorized Linear Potentiometers

Deep in the bowels of the Digikey and Mouser databases, you’ll find the coolest component ever. Motorized linear potentiometers are a rare, exotic, and just plain neat input device most commonly found on gigantic audio mixing boards and other equipment that costs as much as a car. They’re slider potentiometers with a trick up their sleeve: there’s a motor inside that can set the slider to any position.

The mechanical keyboard community has been pushing the boundaries¬†of input devices for the last few years, and it looks like they just discovered motorized linear pots. [Jack] created a motorized sliding keycap for his keyboard. It’s like a scroll wheel, but for a keyboard. It’s beautiful, functional, and awesome.

The hardware for this build is just about what you would expect. A 60 mm motorized linear pot for the side-mount,¬†or 100 mm mounted to the top of the keyboard, is controlled by an Arduino clone and a small motor driver. That’s just the hardware; the real trick here is the software. So far, [Jack] has implemented a plugin system, configuration software, and force feedback. Now, messing with the timeline in any Adobe product is easy and intuitive. This device also has a ‘not quite vibration’ mode for whenever [Jack] gets a notification on his desktop.

Right now, [Jack] is running a group buy for this in a reddit thread, with the cost somewhere between $55 and $75, depending on how many people want one. This is a really awesome product, and we can’t wait for Corsair to come out with a version sporting innumerable RGB LEDs. Until then, we’ll just have to drool over the video [Jack] posted below.

82 thoughts on “Wherein The Mechanical Keyboard Community Discovers Motorized Linear Potentiometers

  1. A little trivia for you snot-nosed kids out there – we used rotary motorized pots in analog computers.

    This linear one has a lot of potential for pranks, though….

    1. Also the first generation of digital scale weight indicators used motorized pots to implement auto zero tracking, to keep the scale on zero if it drifted a bit as the temperature changed. Including the NCI 5775, which I turned into a Nixie clock linked here awhile back.

    2. “This is not a trivia for anyone who does not have allergy, I REPEAT ONLY ANY ONE WHO HIS SNEAZING TFO CAN READ THIS COMMENT. Everyone else, you’re good.”

      1. Anything that requires manipulating a timeline, (As mentioned in the article – video editing or playback) cross fading between 2 sources or volume control.

        The last one of these is the main commercial use I’ve seen them put to. (I remember a bunch of them on an keyboard that recorded all the modulation sliders and volume controls and sliding back to them on playing back the recording made earlier)

        With more of them – part of a very specialised games controller, lighting controller, graphic EQ settings…

        Bit expensive, though.

        1. What advantages does it have over a rotary encoder? The encoder might be *slightly* more complex to read, but that, to my mind, is more than offset by unlimited scalable travel, and software “repositioning”.

          1. Graphic equalisers etc. – the position of the slider is visual feedback of current setting.

            This explains videos I’ve seen of musicians listening to a “final mix” – multiple takes, FX, etc. on a mixer keyboard, the settings are recorded, then everyone sits back to listen as the final mix is played.

          2. What would be ideal is if there were soft zones on the end say 95% where the motor will try and reset the slider.

            Then those zones can be used for infinite scroll.

            I think the demostrated examples kind of suck

          3. Even better would be a stepper motor with a custom driver, that can based on EMF reading tell how it’s being moved. Steppers once energized will have holding torque, so you can have nice haptic feedback.

          4. @AKA:
            This is a servo drive – normally more costly but better. You do not need to try to evaluate back EMF (depending on speed), you just have a position sensor: the potentiometer. The Servo motor applies the holding torque if it is needed, you even have much less power consumption if no force is applied.

            @Alex Rossie: I think this soft zones can be easily implemented.

        2. This seems a bit like a mechanical answer to Apple’s touch bar in many applications. The timeline and volume apps are things baked into Apple stuff now. The tab manipulation is not that different conceptually something done with Safari and tabs now. Perhaps this slider will evolve more gesture based controls to dog with the app context sensitivity.

    1. It’s good for: because I can.

      More practically, I’d love to see an RGB color selecter out of these. Imagine when you click with the color picking tool in a graphics program that you have three sliders that snap to the appropriate value, so you can then tweak them.

      1. Sorry, as someone who does use a colour picker a lot, that’s just annoying, and useless.
        It’s good for effects sliders in audio/video editing, but rotary encoders are generally much better, it’s easier to move them click by click when you want to make small adjustments.

    2. Anything that allows for more choices than a binary one. Think of color picking, sound mixing, easily picking values – you name it. There are plenty of uses. Having a pile of on/off switches on a board really is not that sophisticated at all.

    3. Have you ever seen the really big audio mixing panels in top-end recording studios? All those levels can be saved and recalled and all the linear volume controls move to the saved positions.

    4. Controlling a drone is one use I can see for this. Especially for ones that you need to program waypoints in for automation and then take manual control of once it gets to those waypoints. Not to mention, you can take control in case of issues along the flight path.

  2. adafruit used to carry them, not sure if they still do, but you can also find motorized linear encoders which are a bit nicer, fairly easy to make yourself with a rotary encoder and a small stepper motor.

    1. But why? Part of the advantage of rotary encoders is that there’s no limit to travel, so you can “reposition” in software, by saying “Ok, this position which is physically indistinguishable from any other position this rotary knob might be in now has a value of 7 instead of 3”

      1. ETA – and if you desperately want linear motion, you can have “caterpillar tracks” that give you an eternal slider (albeit without a knob) that is again software controllable.

  3. !!!!

    See that little red V shaped protoboard on his desk?

    I designed that.

    He must’ve gone to an Iowa state hackathon.

    :D :D :D :D

    This makes me so happy because I didn’t expect to ever see one in use, and lo an behold, on hackaday, here it is.

    :D :D :D :D

    On topic, I’d like to see the slider act like a type writer carriage. It would move to the right as you type and get to the end of the page, and you could slide it left for a carriage return.

  4. Put a keyswitch on it. Metallize the underside of the keycap for capacitance sensing. Replace the spacebar with this. Setup a control system that moves the keycap away whenever a finger touches it.

    Tada! The Unusable Space Bar.

  5. And I thought $25 was high years ago for replacing near 30 of them in a Yamaha organ. They wouldn’t move reliably and the bug turned out to be a little rubber drive belt in the motor chain. The fix was little rubber “o” rings. A few years later all the organ makers went to either a pair of – + buttons or a strip of buttons either lighting up a strip of LED’s to show virtual position.

    Remember that a single preset button calls up everything including where all those sliders are at instantly for your eyes while in the middle of a song.

    1. A great advantage of linear sliders over rotary encoders is that you can have your fingers resting on 8 of them and keep your eyes and ears focussed on what’s happening on stage. You don’t need to look at them to know where the current settings are at.

  6. Way back in the early 90s I went for an interview at Solid State Logic, and saw a huge mixing desk packed with these, controlled either by hand or via a Quantel-style screen interface. Very impressive stuff.

  7. I have two chunks of a parted-out Studer digital console with 4 Penny & Giles motorised faders in each section. I remember when those faders were over $100 each.

    For a timeline control, I prefer a rotary encoder with a nice weighted knob.

  8. With the orientation of the slider, I was thinking heck, at first glance the way it’s moving while typing, I was half expecting that in a word processor when you wanted a new line you would whack it like the old time typewriters :)

  9. This have the potential to be the physical interface for bar elements such as the volume.
    One click on the volume icon and the key moves to imitate the current level of volume so the user can regulate it.

    It would be great to add other physical interfaces such as knobs that also turn themselves to imitate the control in focus they are controlling.

  10. OMG! This is hilarious! I discovered these motorized pots two weeks ago, and found some from an online retailer for $12.50 each. (100mm authentic Bourns, PSM01-081A-103B2). I was searching for Bourns 10-turn pots, and stumbled on these completely by accident. I had no idea they were even a thing. Great minds think alike!

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