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:

Expressive Generator / Strings
Speaker / Violin Body
Keyboard / Fret Board

In the the next picture, you can see the electronic insides. The electronic insides have three major jobs:

Rectifier - Rectify and buffer power from generator
Synthesizer - Synthesize musical instrument sound
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!