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How To Build Exertion Instruments

This version was saved 13 years, 1 month ago View current version     Page history
Saved by Noah Vawter
on January 5, 2010 at 8:01:28 am
 

 

Part 2


 

 

Basic Exertion Instruments are comprised of the following four modules:

 

Generator                                  Amplifier Module                 Synthesizer Module                      Speaker

 

 

 

 

For selecting/buying/scrounging parts, go to this page.

 

 

Keyboard * CPU * Generator Electronics * Speaker * Belt/Gear * Generator

 

 

Keyboard

 

 

 This keyboard is a row of 10 switches.  They can be programmed to do anything, but the standard setup

is a pentatonic or major scale. 

 

These switches were chosen because they have a nice springy action to them, but future keyboards may use

capacitive sensing (like a theremin!) for even faster action.

 

 

 

CPU

 

 

The Electric Eels use a chip similar to the Arduino - the Atmega32 microcontroller.  This one runs faster than the Arduino.  It also has more programmable pins for controls and sensors. 

 

Chip                              Pros                                             Cons               Power Consumption          Price               Features               Environmental Footprint

Atmega32                    mucho I/O                  lots of pins to solder.

Atmega8                         cheap, low current?

ATTiny                             low current? 

DSPIC 33 MHz               Fast, multiplier.

DSPIC 40 MHz               surface mount version of 33 MHz

PSOC                         Reprog. Analog Sections.              Win. only?                    

 

 

 

 

 

What CPUs would you like to use? 

 

Old sound chip?  If you use an old sound chip, you will need some way to send it register messages.  You may use a second, small chip to do this.

 

Example sound chips:

MOS 6581 SID, AY-3-8910, Yamaha YM3812

 

 

 

Voice synthesizer? 

 

 

 

Generator Electronics

 

 

This circuit conditions the instrument's generator output so it can run the CPU and amplifier.  It is an area of constant technical improvement. 

 

Early Generator Electronics

 

In the earliest generations of Exertion Instruments, hand-cranked generators utilized plastic gears to transfer the slow-movement of a handcrank into a fast-spinning DC motor shaft.  Their generator electronics simply regulated the DC output to 5 or less volts in order to protect the CPU.  They used the familiar 7805 regulator.

 

Later Generator Electronics

 

The later generations of exertion instruments, such as the Electric Eels and Kick Drum, used both phases of a stepper motor to drive individual voltage doubler circuits. 

These circuits rectify and smooth the generator's energy with diodes and capacitors.  One output supplied the CPU.  The second output supplied the amplifier.  Switching to this configuration resulted in lower necessary RPMs to supply power to the instruments and reduction in gear train noise.  There were quirks with this design, though.  While it works with a large range of component values, there are certain preferred ranges.  Preferred, in this case, because they lead to either louder sound or longer CPU Execution time.

 

Recommendations

Since the generator drives the instrument by sending current through its coils into a capacitor and the CPU, the internal resistance and inductance of the motor should be matched to the rectifier's capacitance.  This results in a charge curve which can be measured on an oscilloscope. 

 

In general, supplying unnecessarily high voltage to the CPU is not recommended.  If the motor/rectifier combination leads to voltage which is much higher than the CPU's normal operating voltage, try swapping the voltage doubler, for a bridge rectifier with a single output capacitor.

 

Currently Researched Generator Electronics

 

Switching generator - At very low thresholds of movement, the instrument should respond, even if is quietly.  This is analogous to a very lightly plucked string.  With a linear power supply, the minimum movement necessary to make sound is limited by the voltage the generator can provide.

 

Switching generators

 

Possible Future Generator Electronics

 

Self-Interrupting FET/transformer combination -  These oscillators work as low as 27mV with common parts like Junction FETs and a transformer.

 

 

 

 

Speaker

 

 

This speaker was chosen because it was small and cheap.  Since then we've learned that larger speakers are usually more efficient.  This is because larger cone excursions carry the cone beyond its most efficient range of motion.  It's better to have longer magnets than voice coils, which is precisely the architecture of many woofers. 

 

 

Belt/Gear

 

This makes it so that a side-to-side strumming motion, like writing with crayons, spins a rotating generator.

 

 

Generator

 

 

This generator is a backdriven. two-phase stepper motor.  It provides 0-50V to drive the audio amplifier and synthesizer CPU.

When building exertion instruments, the motor/generator is the source of all electrical energy in the instrument.  Its size is roughly proportional to the amount of energy it can put out.  Bigger motors put out more energy.  Smaller motors are less efficient :(

Motors with neodymium magnets are preferred.  The stronger field results in more wattage and louder volume. 

 

 

 

 

Assemblage * Aufbau * Construction * Zusammenbasteln

 

xxxxxx

 

 

x

This is the resonator body with its printed jacket.  These tulips were chosen because they represent life in spring. 

This jacket was printed out on a largish color printer and adhered with F77 aerosol adhesive. 

 

On the body, you can see the keyboard slot in the middle.  It allows the keyboard to be mounted with two large bolts.

 

For this cylindrical body shape, jacket designs are rectangular, with three cutouts:

 

1. A slot in the middle allows the keyboard to be mounted with two large bolts.

2. The opening of the Eel's body is curved, so the contour of the jacket matches it.

3. A mount point holds a strap to the body.  

 

The body was chosen because the cardboard is heavy enough that it will stand up to travel and maybe light rain.  It was also free and recycled.  You could design a much more complex body for it if you like.  This website is hoping to go in that direction :)

 

 

 

 

Here, the six major electrical components

 are ready to mount into the resonator body.

 

 

 

 

 

Everything is in place, now to screw it back together.

 

 

 

Ready to play.  Actually, it was ready to play even while disassembled, just less convenient :)

 

 

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