Electric Eel - Introduction

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Introduction: Electric Eel - Introduction

Below, Arthur is playing the Electric Eel.  It's an electronic music instrument I designed to be like an acoustic instrument..  The things that  slow me down when playing most electronic instruments are having to plug into speakers and find batteries, so this instrument has its speaker and generator built in.  And as a bonus, the sound varies with how hard you play and how you move the generator, because the synthesizer can detect your playing movement and the amplifier gets louder when you player louder!  So let's get started and build one like this lovely Exertion Violin below. 

Step 1: Electric Eels - How to Build Your Own

To explain how it's done, we'll use this prototype Exertion Violin.  From the outside, it has three main components.  These can be thought of as similar to a violin:
  1. Expressive Generator / Strings
  2. Speaker / Violin Body
  3. Keyboard / Fret Board
In the the next picture, you can see the electronic insides.  The electronic insides have three major jobs:
  1. Rectifier - Rectify and buffer power from generator
  2. Synthesizer - Synthesize musical instrument sound
  3. Amplifier - Amplify the sound to be as loud as an acoustic instrument
In the next picture, you can see the beginnings of an instrument body.

Step 2: Electric Eel Electronics

So, the three main electronic modules inside the instrument are:
1. Rectifier / Regular
2. Synthesizer
3. Amplifier

The Rectifier, Regulator and Amplifier can be combined into one board, like below.

The Synthesizer is a separate board. 

Step 3: Speakers and Resonators

There is not much power in the brief strokes used to drive instruments and the same is true with generators. Better bodies, efficient, resonant ones, lead to louder sound and more dynamic instrument playing. It is therefore smart to consider the design of your instrument's body well in advance of building your Electric Eel. Use the pictures in this how-to for inspiration. In general, the instrument body should be more like an acoustic musical instrument.

Step 4: Atlernate Generators

As an alternative to the bowed-stick interface, other generators can be crafted.

For example, the sliding carriage from an old printer makes a good generator because its the right width for moving left and right. 

Also, you can mount wheel hubs on stepper motors and use them in creative ways. For example, try wrapping a cord around a motor shaft like this to make a bowed-string generator.  It's good practice for starting fires!  :)

In the oscilloscope photo below, you can see the each time the carriage slider is wiggled back and forth, kind of like strumming a guitar, it charges the internal capacitor a little bit higher.  Usually you can make about 1-4 Watts or so with this kind of generator and its proportional to your movement, so small movements make quieter sounds inherently, you don't even have to program or build that into the synthesizer!

Step 5: The Instrument Family

This page shows some of the highlights of the Exertion Instrument family.  These were constructed at the MIT Media Lab from the years 2007-2011.

Step 6: Other DIY Electric Eels

Step 7: Jingle Bell Rock

Now that you've built your Electric Eel, practice up on this cool old-fashioned ecumenical holiday song! 



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    These things are great! I love the concept--and the expressive quality, unlike any simple electronic instruments I've ever seen! Please-embed the video--you can add it to the instructable itself.

    One small point--the speaker graph on step 3--I believe that's the speaker impedance graphed to the frequency, not the frequency response itself.

    I.E., it's graph of the input impedance change, not the output frequency. A large hump in the impedance around 100+ hZ is pretty typical (but a freq response like that is not).

    aah thanks! I've been wondering about the details of that stuff. I'd love to ask you more questions about it!

    How can we use that impedance graph to choose the frequency range to run the speaker at its most efficient?

    If it's necessary to know the acoustic structures in which it would be placed, the two most important are the fixed-end cylinder and the exponential horn.

    What other information do we need to combine with this graph to estimate how good it would be at e.g. 200 Hz vs. 400 Hz?

    thank you for helping out!

    Way beyond my skill set, but super cool!

    This is a really cool write up, dude. Now, I find myself wanting to build a sort of electric chromatic hurdy gurdy! Out of curiosity, is that Dr. Zoz Brooks of Prototype This! In the 2nd to last image???

    This is really exciting. Have you tried any wind instruments? I picture computer fans as generators, with tubing from a mouthpiece to direct the airflow across the vanes.

    As a trumpet player, I'd want to use three buttons, but there would need to be a way to indicate the pitch shift that would normally come from the emboucher (lip configuration). Perhaps a multiple-position thumb switch? Hmmm.

    Maybe a Tesla turbine for the generator. https://www.instructables.com/id/Tesla-Turbine/

    I am not into electrical stuff , but wouldn't be appropriate to use a capacitor of some sort here , so to avoid the rigid power/sound relation result (ex: stroke - note) ?

    Heya gabdab-

    You are correct with your suggestion. In fact, the Electric Eels do use capacitors to keep power around as long as possible in between audible output.

    The devil is, as the say, in the details: in much the same way that it took hundreds of years to get the peg-tuning and bridge system to the state that it is in a common guitar, getting the analog circuits designed just right for Electric Eels has been a challenge, too.

    Although I spent years on this project, I had to split that time up among the design of the acoustic, electronic, synthesizer, etc. components. I have presented a reasonable, usable analog circuit design for charging, storing and discharging the generator current through capacitors. However, it is not perfect.

    The flaw is not so much in the storage system as it is in the regulator. As you know, digital circuits only function properly when operated in a specific range, so we have to use regulator circuits. This is especially important in generator circuits such as this one in which the generator output can be quite high relative to maximum operating voltage of the digital circuits.

    Most regulator circuits use up the stored power in the capacitors, even when the digital circuit is not running! This part of the design could certainly be improved and I would love to see it!

    I evaluated a number of regulator circuits and chose a switching regulator based on through-hole parts and minimum external components so that it would be easiest for musicians and people with limited electronics skills to build the instrument. What I would like to see added is some kind of cutoff circuit that disconnects the storage capacitors from the regulator at some voltage level. This was beyond my capabilities in the time given to research and design the instrument.

    Currently, the system I designed stops draining from the capacitors when their voltage reaches about 2.5V. That means when each stroke/note has to charge up to about 3.7V from 2.5V before it can start making sounds. That only takes a few milliseconds (there are graphs of it in my dissertation), but it's like the equivalent of tying a string around a bow to make a guitar - it could be improved to make a finer quality instrument. And doing so would cost more time and money and materials, just like a finer quality instrument.

    Hopefully, the Electric Eel style of instrument-making will be adopted by a larger group of people, including musicians and designers, and someone will figure out how to improve this circuit. I did my best to cover all the bases as evenly as I could and to map out the physics limitations of each area. Just as most music instrument development is a lifelong process, I imagine and hope Electric Eels will continue to be developed throughout our entire lifetimes.

    "the Electric Eel. It's an electronic music instrument I designed to be like an acoustic instrument.. The things that slow me down when playing most electronic instruments are having to plug into speakers and find batteries,"

    Great idea, but a useless one...just play an acoustic instrument

    Acoustic instruments are old-fashioned and don't sound good to me. I want synthetic timbres because I like the sounds of synthesizers.