Hacked Prosthesis Leads To Mind-Controlled Electronic Music

As amazing as prosthetic limbs have become, and as life-changing as they can be for the wearer, they’re still far from perfect. Prosthetic hands, for instance, often lack the precise control needed for fine tasks. That’s a problem for [Bertolt Meyer], an electronic musician with a passion for synthesizers with tiny knobs, a problem he solved by hacking his prosthetic arm to control synthesizers with his mind. (Video, embedded below.)

If that sounds overwrought, it’s not; [Bertolt]’s lower arm prosthesis is electromyographically (EMG) controlled through electrodes placed on the skin of his residual limb. In normal use, he can control the servos inside the hand simply by thinking about moving muscles. After experimenting a bit with an old hand, he discovered that the amplifiers in the prosthesis could produce a proportional control signal based on his inputs, and with a little help from synthesizer manufacturer KOMA Electronik, he came up with a circuit that can replace his hand and generate multiple control voltage channels. Plugged into any of the CV jacks on his Eurorack modular synths, he now has direct mind control of his music.

We have to say this is a pretty slick hack, and hats off to [Bertolt] for being willing to do the experiments and for enlisting the right expertise to get the job done. Interested in the potential for EMG control? Of course there’s a dev board for that, and [Bil Herd]’s EMG signal processing primer should prove helpful as well.

Thanks to [n_B] and [suuppl] for the near-simultaneous tips.

14 thoughts on “Hacked Prosthesis Leads To Mind-Controlled Electronic Music

  1. That is really neat, though I think a few more channels could be really useful.
    Seems to me like there are two ways to do that
    One way to do that is to have one of the sensors ‘rotate’ between channels and the other control the signal for that channel. With a visual rotation and perhaps off center mass for knowing what channel you are on. The other could be to have both sensors driving a channel on the synth and just using the other hand to rotate the shell on the prosthetic and so select which pair to use this time.

    Of course that means you need to define what happens when you rotated from channel 3 to 4. I would assume you want channel 3 to remain as it was but perhaps you want it to fade back to the default position, I’m not a syth lover to know what would be the best behavior, but having played with many mixing desks over the years I’d plump for holding value on exit.

    1. Hmm a third option, related to the first one. Instead of sending a signal to drive the ‘rotation’ of channels (which would allow however many channels you want to wire in) could perhaps use the value of one channel as a selection signal – so no need for feedback as he should know how hard he is signaling well enough to get a few bands x<20% 20%<x<40% style.

    2. Another option is to add a gyroscopic of some sort to measure the orientation of the board and use that as a selector (or an extra control)

      So pointing upwards would mean controlling pitch, down controlling the amplification,…

      Or add an footswitchboard to add additional control switches.

      Making a wireless connection to transfer the signal from your arm to another board that generates the 0-10vsignals does seam like a great idea to me, increasing your personal freedom and safety by not being physically tied to your audiostation.

      I don’t know if there exist something like a wireless midi, but that might be something to look into as well.

    3. Another way of looking at it is that he can now turn two knobs at the same time with the same ‘hand’. Yes, they’re preselected, but it’s an interesting trade-off in flexibility.

      Very cool project no matter how you look at it!

  2. Nice project!

    I would give 2 more ideas:

    – Add a Bluetooth (or Wifi, or any other RF) controller on your arm to read and transmit wirelessly in real time the values of the 2 channels to a “receiver” panel in your mixer, where you could select to where these signals should be routed

    – Add tiny little NFC antennas to each one of the knobs (with PWM NFC tags) where you want to set the level, and add a NFC controller (initiator as it is called) to your arm, which will control the knob you point to with your finger thru a small coil placed at the tip of your finger, in this way you will control the knobs almost in the same way you would do with real fingers

    If you need any help implementing any of these two ideas I am glad to help, I am also located in Germany!

    1. Oooh that NFC idea is really neat. A fair bit of work might be needed to be sure of no crosstalk between nearby knobs. Then all you need is a toggle on the hand itself to toggle the modes.
      Might be better to create an NFC array PCB and jack them in as done above though, don’t bother with making it controllable any other way. That array could then also be used as joystick etc inputs for other adaptive needs.

      1. If the reading antenna is small, then there is almost no chance of crosstalk, and its range will be just ~1cm

        For the reader I would go with ST25R3911B from ST
        And for the tag the ST25DV02K also from ST

        The reader is a bit more complex to interface with, but it is feasible, the tag is piece of cake, just supply VCC and it will output the adjusted PWM level, add simple low-pass you get an analog signal

  3. Man, I’d almost give my left arm to be able to do something like that…

    Though I’d love to see the circuit: from the glimpse in the video it’s not clear how they might be doing the galvanic isolation.

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